JP4165666B2 - Optical pickup device - Google Patents

Description

【０１３１】
で表される。
【０１３２】
実施例１
【０１３３】
【表１】

【０１３４】
この実施例は、対物レンズ１６が樹脂製の場合の例である。この対物レンズ１６の光路図を図１に、その球面収差および正弦条件の収差図を図２に、温度特性を図３に示す。
【０１３５】
温度特性は３０℃変化で波面収差は０．０２８λの変化を生じているに過ぎず、無限共役型の対物レンズに比してかなり温度変化の影響が小さくなっている。
この実施例において
ｘ₂＝−０．０８６０６ Δ₂＝ ０．０４５６９
であり
ｘ₂・（ｎ−１） ／｛Ｆ・（ＮＡ）²｝＝−０．０３１６０
Δ₂・（ｎ−１）³／｛Ｆ・（ＮＡ）⁴｝＝ ０．０１１５６
である。
【０１３６】
実施例２
【０１３７】
【表２】

【０１３８】
この実施例は、実施例１と同様、対物レンズ１６が樹脂製の場合である。この対物レンズ１６の光路図を図４に、その球面収差および正弦条件の収差図を図５に、温度特性を図６に示す。実施例２は実施例１に比べてＭがさらに大きくなるため、効果が大きい。
【０１３９】
この実施例においては、
ｘ₂＝ ０．０１３３７ Δ₂＝ ０．０１８９４
であり
ｘ₂・（ｎ−１） ／｛Ｆ・（ＮＡ）²｝＝ ０．００４０３
Δ₂・（ｎ−１）³／｛Ｆ・（ＮＡ）⁴｝＝ ０．００３９４
である。
【０１４０】
実施例３
【０１４１】
【表３】

【０１４２】
この実施例の対物レンズ１６も樹脂製であり、その光路図を図７に、その球面収差および正弦条件の収差図を図８（ａ），８（ｂ）に、温度特性を図９に示す。
【０１４３】
この実施例においては、
ｘ₂＝−０．０８０７６ Δ₂＝ ０．０５７３４
であり
ｘ₂・（ｎ−１） ／｛Ｆ・（ＮＡ）²｝＝−０．０３０２３
Δ₂・（ｎ−１）³／｛Ｆ・（ＮＡ）⁴｝＝ ０．０１４７９
である。
【０１４４】
実施例４
【０１４５】
【表４】

【０１４６】
この実施例の対物レンズ１６も樹脂製であり、ＮＡ０．７、使用光の波長４５０ｎｍの例である。その光路図を図１０に、その球面収差および正弦条件の収差図を図１１（ａ），１１（ｂ）に、温度特性を図１２に示す。Ｍが０．２倍であると、ＮＡ０．７の樹脂製レンズであっても、温度３０℃の変化に対して波面収差の変化は０．０２８λ程度ですんでおり、また、設計においても初期収差が良好に補正されている。
【０１４７】
この実施例においては、
ｘ₂＝ ０．０５２４８ Δ₂＝ ０．０３９６２
であり
ｘ₂・（ｎ−１） ／｛Ｆ・（ＮＡ）²｝＝ ０．０１１８２
Δ₂・（ｎ−１）³／｛Ｆ・（ＮＡ）⁴｝＝ ０．００４７１
である。
【０１４８】
実施例５
【０１４９】
【表５】

【０１５０】
この実施例の対物レンズ１６はガラス製で、ＮＡ０．７５、波長４５０ｎｍの例であり、ＮＡ０．７５でも初期収差が良好に補正されている。その光路図を図１３に、その球面収差および正弦条件の収差図を図１４（ａ），１４（ｂ）に、温度特性を図１５に示す。
【０１５１】
この実施例においては、
ｘ₂＝ ０．２５１８８ Δ₂＝ ０．００６６０
であり
ｘ₂・（ｎ−１） ／｛Ｆ・（ＮＡ）²｝＝ ０．０６８９２
Δ₂・（ｎ−１）³／｛Ｆ・（ＮＡ）⁴｝＝ ０．００１６２
である。
【０１５２】
実施例６
【０１５３】
【表６】

【０１５４】
この実施例の光学系は、対物レンズ１６は実施例１のものを使用し、カップリングレンズ１３はガラス製の１群２枚レンズと組合せた例である。その光路図を図１６に、温度特性を図１７に示す。
【０１５５】
温度変化による波面収差変化量は実施例１とほぼ同等で、対物レンズによるものである。
【０１５６】
また、カップリングレンズによる収差を補正するため、対物レンズの波面収差ベストの倍率が実施例１の倍率と若干異なっている。
【０１５７】
この実施例においてはＤｃｏ＝９．９０である。
【０１５８】
実施例７
【０１５９】
【表７】

【０１６０】
この実施例の光学系は、対物レンズ１６は樹脂製で、実施例１のものを使用し、カップリングレンズ１３に樹脂製の両面非球面の単レンズを用いた光学系の例である。その光路図を図１８に、その温度特性を図１９に示す。
【０１６１】
温度変化による波面収差変化は実施例１に比べて半分以下とさらに小さくなっている。これは、温度が上昇することにより、各レンズの屈折率が下がり、カップリングレンズによる収束光の角度が小さくなり、対物レンズの横倍率が小さくなる影響（この影響だけの場合、対物レンズの球面収差はアンダー側に動く。）と対物レンズ自身の屈折率が下がることによる影響（この場合、球面収差はオーバー側に動く。）がキャンセルし合っているためである。
【０１６２】
この実施例においてはＤｃｏ＝１０．０である。
【０１６３】
実施例８
【０１６４】
【表８】

【０１６５】
この実施例は対物レンズ１６のみの例で、対物レンズ１６は樹脂製で光源側の面は非球面、像側の面は球面の例である。その光路図を図２０に、その球面収差および正弦条件の収差図を図２１（ａ），２１（ｂ）に、温度特性を図２２に示す。
【０１６６】
この実施例においては、
ｘ₂＝−０．０２９６２２ Δ₂＝ ０．００（球面であるため）であり
ｘ₂・（ｎ−１） ／｛Ｆ・（ＮＡ）²｝＝−０．００９０７
Δ₂・（ｎ−１）³／｛Ｆ・（ＮＡ）⁴｝＝ ０．００
である。
【０１６７】
実施例９
カップリングレンズ
【０１６８】
【表９】

【０１６９】
全光学系
【０１７０】
【表１０】

【０１７１】
実施例９はカップリングレンズ１３が樹脂製で両面非球面の両凸レンズの例であり、その収差図を図２４（ａ），２４（ｂ）に示す。球面収差、正弦条件も十分に満足している。これと組み合わせた対物レンズは実施例１の樹脂製対物レンズであり、全光学系の光路図を図２３に、その温度特性を図２５に示す。
【０１７２】
この実施例において
Ｄｃｏ＝３
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０５５６９
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０１７３】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．０１３λと実施例１の対物レンズ単体のそれより約半分と小さくなっている。これは温度が上昇することにより各レンズの屈折率が下がり、カップリングレンズによる収束光の角度が小さくなり、対物レンズ単体の横倍率が小さくなる影響（この影響だけの場合、対物レンズの球面収差はアンダー側に動く。）と対物レンズ自身の屈折率が下がることによる影響（この場合、球面収差はオーバー側に動く。）が相殺しあっているためである。
【０１７４】
実施例１０
カップリングレンズ
【０１７５】
【表１１】

【０１７６】
全光学系
【０１７７】
【表１２】

【０１７８】
実施例１０はカップリングレンズ１３が樹脂製で両面非球面の両凸レンズの例であり、実施例９と同じ倍率Ｍｃ＝−２．０であるが、焦点距離Ｆｃが若干長いときの実施例で、その収差図を図２７（ａ），２７（ｂ）に示す。球面収差、正弦条件も十分満足している。
【０１７９】
また、全光学系は、このカップリングレンズと実施例１の樹脂製対物レンズを組み合わせたものであり、倍率Ｍ、Ｍｔは実施例７，９と同じ仕様であり、対物レンズとカップリングレンズの間隔Ｄｃｏも実施例７と同じである。その光路図を図２６に、温度特性を図２８に示す。
【０１８０】
この実施例において
Ｄｃｏ＝１０
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０６４２９
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０１８１】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．０１１λと実施例７とほぼ同等、実施例９より若干小さくなっている。これはカップリングレンズの焦点距離Ｆｃが実施例９より長くなり、温度が上昇することによるカップリングレンズによる収束光の角度が小さくなる度合いが実施例９よりも大きくなるためである。
【０１８２】
実施例１１
カップリングレンズ
【０１８３】
【表１３】

【０１８４】
全光学系
【０１８５】
【表１４】

【０１８６】
実施例１１はカップリングレンズが樹脂製で両面非球面、光源側の面が凹面のメニスカスレンズである例であり、実施例９と同じ倍率Ｍｃ＝−２．０であり、その収差図を図３０（ａ），３０（ｂ）に示す。正弦条件は補正過剰となっている。
【０１８７】
また、全光学系は、このカップリングレンズと実施例１の樹脂製対物レンズを組み合わせたものであり、倍率Ｍ、Ｍｔは実施例９と同じ仕様であり、対物レンズとカップリングレンズの間隔Ｄｃｏも実施例９と同じである。その光路図を図２９に、温度特性を図３１に示す。
【０１８８】
この実施例において
Ｄｃｏ＝３
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０５４７６
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０１８９】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．０１６λとほぼ同一仕様の実施例９より若干大きいが、物像間距離は短くなっている。これはカップリングレンズの光源側面が凹面のメニスカスレンズのため、該レンズの主点位置が、両凸カップリングレンズである実施例９に比べて対物レンズよりとなるためである。
【０１９０】
実施例１２
カップリングレンズ
【０１９１】
【表１５】

【０１９２】
全光学系
【０１９３】
【表１６】

【０１９４】
実施例１２はカップリングレンズが樹脂製で両面非球面、光源側の面が凸面のメニスカスレンズである例であり、実施例９と同じ倍率Ｍｃ＝−２．０であり、その収差図を図３３（ａ），３３（ｂ）に示す。正弦条件は補正不足となっている。
【０１９５】
また、全光学系は、このカップリングレンズと実施例１の樹脂製対物レンズを組み合わせたものであり、倍率Ｍ、Ｍｔは実施例９と同じ仕様であり、対物レンズとカップリングレンズの間隔Ｄｃｏも実施例９と同じである。その光路図を図３２に、温度特性を図３４に示す。
【０１９６】
この実施例において
Ｄｃｏ＝３
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０５７０３
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０１９７】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．０１０λとほぼ同一仕様の実施例９より小さい。これはカップリングレンズの光源側面が凸面のメニスカスレンズのため、該レンズの主点位置が、両凸カップリングレンズである実施例９に比べて光源よりとなるためで、このためカップリングレンズの焦点距離Ｆｃが長くなるためである。
【０１９８】
実施例１３
カップリングレンズ
【０１９９】
【表１７】

【０２００】
全光学系
【０２０１】
【表１８】

【０２０２】
実施例１３はカップリングレンズが樹脂製で光源側の面は球面、像側の面は非球面である両凸レンズの例であり、実施例９と同じ倍率Ｍｃ＝−２．０であり、その収差図を図３６（ａ），３６（ｂ）に示す。正弦条件は補正過剰となっている。
【０２０３】
また、全光学系は、このカップリングレンズと実施例１の樹脂製対物レンズを組み合わせたものであり、倍率Ｍ、Ｍｔは実施例９と同じ仕様であり、対物レンズとカップリングレンズの間隔Ｄｃｏも実施例９と同じである。その光路図を図３５に、温度特性を図３７に示す。
【０２０４】
この実施例において
Ｄｃｏ＝３
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０５５１２
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０２０５】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．０１５λとなる。
【０２０６】
実施例１４
カップリングレンズ
【０２０７】
【表１９】

【０２０８】
全光学系
【０２０９】
【表２０】

【０２１０】
実施例１４はカップリングレンズが樹脂製で両面非球面の両凸レンズの例であり、その収差図を図３９（ａ），３９（ｂ）に示す。
【０２１１】
また、全光学系は、このカップリングレンズと実施例１の樹脂製対物レンズを組み合わせたものであり、その光路図を図３８に、温度特性を図４０に示す。
【０２１２】
この実施例において
Ｄｃｏ＝３
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０６６６６
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０２１３】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．００８λと、実施例９よりも小さい。また物像間距離もかなり短くなっている。
【０２１４】
実施例１５
カップリングレンズ
【０２１５】
【表２１】

【０２１６】
全光学系
【０２１７】
【表２２】

【０２１８】
実施例１５はカップリングレンズが樹脂製で両面非球面の両凸レンズの例である。実施例１４と同じ倍率Ｍｃで焦点距離が長い。その収差図を図４２（ａ），４２（ｂ）に示す。
【０２１９】
また、全光学系は、このカップリングレンズと実施例１の樹脂製対物レンズを組み合わせたものであり、倍率Ｍ、Ｍｔは実施例１４と同じ仕様である。その光路図を図４１に、温度特性を図４３に示す。
【０２２０】
この実施例において
Ｄｃｏ＝１０
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０７６９７
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０２２１】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．００６λと、かなり小さくなっている。
【０２２２】
実施例１６
カップリングレンズ
【０２２３】
【表２３】

【０２２４】
全光学系
【０２２５】
【表２４】

【０２２６】
実施例１６はカップリングレンズが樹脂製で両面非球面の両凸レンズの例であり、その収差図を図４５（ａ），４５（ｂ）に示す。
【０２２７】
また、全光学系は、このカップリングレンズと実施例１の樹脂製対物レンズを組み合わせたものであり、その光路図を図４４に、温度特性を図４６に示す。
【０２２８】
この実施例において
Ｄｃｏ＝３
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０４７８３
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０２２９】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．０１６λである。
【０２３０】
実施例１７
カップリングレンズ
【０２３１】
【表２５】

【０２３２】
全光学系
【０２３３】
【表２６】

【０２３４】
実施例１７はカップリングレンズが樹脂製で両面非球面の両凸レンズの例であり、その収差図を図４８（ａ），４８（ｂ）に示す。
【０２３５】
また、全光学系は、このカップリングレンズと実施例２の樹脂製対物レンズを組み合わせたものであり、その光路図を図４７に、温度特性を図４９に示す。
【０２３６】
この実施例において
Ｄｃｏ＝３
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０８７６７
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０２３７】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．０１４λで、対物レンズ単体のそれより若干大きい。これはカップリングレンズのパワーが大きくなり、温度変化によるカップリングレンズ自身の波面収差変化が無視できないくらいの大きさとなるためである。
【０２３８】
実施例１８
カップリングレンズ
【０２３９】
【表２７】

【０２４０】
全光学系
【０２４１】
【表２８】

【０２４２】
実施例１８はカップリングレンズが樹脂製で両面非球面の両凸レンズの例であり、その収差図を図５１（ａ），５１（ｂ）に示す。
【０２４３】
また、全光学系は、このカップリングレンズと実施例３の樹脂製対物レンズを組み合わせたものであり、その光路図を図５０に、温度特性を図５２に示す。
【０２４４】
この実施例において
Ｄｃｏ＝３
Ｍｔ・Ｍ・Ｆｃｐ／Ｆ＝−０．０４７７６
となる。ここで樹脂カップリングレンズは単玉レンズであるのでＦｃ＝Ｆｃｐとなる。
【０２４５】
温度変化による波面収差変化は、基準設計温度より３０℃上昇したとき０．０１７λである。
【０２４６】
以上の実施例９から実施例１８までのカップリングレンズ１３の実施例はすべて樹脂製としたが、光学系の温度特性を除けば、ガラスの場合でも同様の結果が得られる。
【０２４７】
実施例１９
【０２４８】
【表２９】

【０２４９】
この実施例は対物レンズのみの例で、対物レンズは樹脂性で対物レンズを構成する面は両面ともに非球面で対物レンズ単体の倍率が＋１／３０倍の例である。この対物レンズの光路図を図５３に、その球面収差および正弦条件の収差図を図５４（ａ），５４（ｂ）に、温度特性を図５５に示す。
【０２５０】
この実施例においては
ｘ₂＝−０．１０７３１ Δ₂＝ ０．０７０６４
であり
ｘ₂・（ｎ−１） ／｛Ｆ・（ＮＡ）²｝＝−０．０４２１
Δ₂・（ｎ−１）³／｛Ｆ・（ＮＡ）⁴｝＝ ０．０１９１０
となる。
【０２５１】
温度変化による波面収差変化は他の実施例に比べて大きいが、同一焦点距離の無限対物レンズよりは小さい。
【０２５２】
この実施例はある程度、無限光学系よりも温度特性をおさえ、光学系全体において光軸方向に垂直な方向の大きさをある程度小さくしたいときに有効である。
【０２５３】
本発明における第２の目的を達成するための光情報媒体の記録再生用光学系の実施例２０から実施例２４について、図５６（ａ），５６（ｂ），図５７，図５８，図５９，図６０，図６１及び図６２に基づいて説明する。
【０２５４】
実施例の説明に入る前に、図５６（ａ），５６（ｂ）を用い、光情報媒体の記録再生用光学系の基本的な構成を説明する図である。
【０２５５】
図５６（ａ）において、１３は正の単レンズよりなるカップリングレンズ、１６は対物レンズ、１７は光情報記録媒体の透明基板、１８は光情報記録媒体の情報記録面である。光源１１より出射した発散光束は対物レンズ１６に近接して配置したカップリングレンズ１３で収束光に変換された後、対物レンズ１６に入射し、透明基板１７を介して情報記録面１８上に集光される。
【０２５６】
図５６（ｂ）は、図５６（ａ）のカップリングレンズ１３を対物レンズ１６から離して配置し、カップリングレンズ１３と対物レンズ１６との間にミラー等の光学素子の配置を可能とした例である。
【０２５７】
図５７は、対物レンズ１６から出射する光束が透明基板を介して記録面に集光した状態を説明する図で、２７は厚み０．６ｍｍの透明基板、２７８は厚み０．６ｍｍの透明基板を有する光情報記録媒体の記録面、２８は厚み１．２ｍｍの透明基板、２８８は厚み１．２ｍｍの透明基板を有する光情報記録媒体の記録面を示し、対物レンズ１６から出射される実線で示した光束は、厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８に集光した状態を、破線で示した光束は、厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光した状態を示している。
【０２５８】
実施例２０
図５８は、本発明に云う可変手段の１例である光軸を中心とした同心の帯状に形成され隣合うレンズ面の屈折力が異なる複数の輪帯状レンズ面を、図５６（ａ）や５６（ｂ）に示した対物レンズ１６の光源側の面に形成した場合の対物レンズ１６の形状、および対物レンズ１６に入射した光束が輪帯状レンズ面により分割されて、厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８に集光した状態（実線で記載）と、厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光した状態（破線で記載）を示している。
【０２５９】
このように２つの集光状態での集光位置を光軸方向に離しているので、１つの透明基板厚みに対応した対物レンズの集光状態で再生を行っている場合に、他の透明基板厚みに対応した集光状態の光は記録面上ではデフォーカス状態となり、再生信号への影響を小さくすることができる。
【０２６０】
この例の場合、複数の輪帯状レンズ面は、最も外側に位置する第１の輪帯状レンズ面３１（このレンズ面は光源からみてドーナツ状である。）と、第１の輪帯状レンズ面３１の内側に隣接した第２の輪帯状レンズ面３２（このレンズ面は光源からみてドーナツ状である。）と、第２の輪帯状レンズ面３２の内側に隣接した第３の輪帯状レンズ面３３（このレンズ面は光源からみてドーナツ状である。）と、第３の輪帯状レンズ面３３の内側に隣接した第４の輪帯状レンズ面３４（このレンズ面は光源からみてドーナツ状である。）と、第４の輪帯状レンズ面３４の内側に隣接した対物レンズの中央に位置する第５の輪帯状レンズ面３５（この輪帯状レンズ面は光軸を含むレンズ面であり、光源からみたレンズ面の形状は円である。）と、の５つの輪帯状レンズ面により構成されている。
【０２６１】
そして、最外周に位置する第１の輪帯状レンズ面３１、第３の輪帯状レンズ面３３および第５の輪帯状レンズ面３５を通過した光束が、厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８に集光し、第２の輪帯状レンズ面３２および第４の輪帯状レンズ面３４を通過した光束が厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光するように構成している。
【０２６２】
これは、厚み０．６ｍｍの透明基板を介して集光する場合は、高密度に対応させるためのスポットを得る必要があるので、最外周の輪帯状レンズ面（この例の場合は第１の輪帯状レンズ面３１）を使用して大ＮＡの対物レンズとしての微小スポットを得、厚み１．２ｍｍの透明基板を介して集光する場合は、最外周に輪帯状レンズ面の内側に隣接する輪帯状レンズ面（この例の場合は第２の輪帯状レンズ面３２）を使用して基板厚みに応じた小さなＮＡの対物レンズとしての微小スポットを得ている。
【０２６３】
また、この例の場合は、高密度に対応させるためのスポットを得るために使用される輪帯状レンズ面として第１の輪帯状レンズ面３１、第３の輪帯状レンズ面３３および第５の輪帯状レンズ面３５の３つの輪帯状レンズ面を使用しているが、これは、最外周に位置する輪帯状レンズ面１つで高密度に対応させるためのスポットを得た場合には、サイドローブの強度が大きくなってノイズの増大を招いてしまい、良好な情報記録や再生に支障をきたす場合があるからである。このようなサイドローブの影響を少なくするため、最外周に位置する輪帯状レンズ面の内側に隣接する、厚み１．２ｍｍの透明基板に対応する輪帯状レンズ面の内側に隣接してさらに厚み０．６ｍｍの透明基板に対応する屈折力を有する第３の輪帯状レンズ面を、その内側に厚み１．２ｍｍの透明基板に対応する第４の輪帯状レンズ面をさらにその内側に厚み０．６ｍｍの透明基板に対応する屈折力を有する第５の輪帯状レンズ面を形成する事により、基板厚み０．６ｍｍ対応時に不要光を出射する第２の輪帯状レンズ面の面積を減少させ、サイドローブを減少させることが出来る。さらにこれを繰り返し、すなわちレンズ面に設ける屈折力の異なる輪帯状レンズ面を外周から一つおきに複数構成することにより、基板厚みの異なる光情報記録媒体の記録再生を行うに適した二つの光スポットを得ることが可能となる。
【０２６４】
しかし、輪帯状レンズ面の数を過度に増やすと、最外周に位置する輪帯状レンズ面よりも内側に位置する各輪帯状レンズ面の幅が小さくなり過ぎ、加工性が悪くなるので、サイドローブを実用上問題ないレベルにまで低減し、なおかつ加工性を良好に保つためには、輪帯状レンズ面の数は最外周に位置する輪帯状レンズ面を含めて３以上１０以下、さらに望ましくは上限を６以下とするすることが好ましい。
【０２６５】
また、同一の透明基板に対応する輪帯状レンズ面を複数設ける場合は、それら複数の各輪帯状レンズ面をそれぞれの輪帯状レンズ面を表す式（例えば、各輪帯状レンズ面を同一形式の非球面の式として表す）に従って光軸まで延長した際に、光軸上におけるレンズ厚みを等しくすることが望ましい。
【０２６６】
これは、レンズ厚みが等しくない場合に、同一の透明基板に対応する各輪帯状レンズ面を通過する光束に光路長差が生じてしまい、光路長差を有する波面が重なりあって干渉が発生し、各輪帯状レンズ面を通過する光束により得られる光の強度が干渉により小さくなってしまうおそれがあるからである。
【０２６７】
このような場合は、隣接する輪帯状レンズ面間に段差３７が生じるが、少なくとも１か所の隣接する輪帯状レンズ面は段差なく（３６）形成することも可能であるので、１か所は隣接する輪帯状レンズ面は段差なく形成することが加工上望ましい。
【０２６８】
なお、同一の透明基板に対応する各輪帯状レンズ面を光軸まで延長した際に、光軸上におけるレンズ厚みが等しくないものとして構成する場合には、光路差長Δと波長λの間にΔ＝ｍλ（ｍは整数）の関係がみたすように構成し、かつｍを−１０から１０までの整数とすることで、多少光源の波長λが変動しても本来の強度の５０％以上の強度を維持することができる。
【０２６９】
なお、図５８の例においては、対物レンズ１６の光源側の面に光軸を中心とした同心の帯状に形成され隣合うレンズ面の屈折力が異なる複数の輪帯状レンズ面を設けているが、この例に限らず、本発明に云う可変手段の１例であるこの複数の輪帯状レンズ面は、対物レンズ１６の像側の面や、カップリングレンズ１３の何れか１面に形成することもできる。また、複数の輪帯状レンズ面を対物レンズ１６およびカップリングレンズ１３を構成するレンズ面の何れか２箇所以上に設けることも可能である。
【０２７０】
実施例２１
図５９は、本発明に云う可変手段の１例であるホログラムを、図５６（ａ），５６（ｂ）に示した対物レンズ１６の光源側の面に形成した場合の対物レンズ１６の形状、および対物レンズ１６に入射した光束がホログラム４１を透過する透過光４３と回折光４４に分けられて、厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８に集光した状態（実線で記載）と、厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光した状態（破線で記載）を示している。
【０２７１】
このように２つの集光状態での集光位置を光軸方向に離しているので、１つの透明基板厚みに対応した対物レンズの集光状態で再生を行っている場合に、他の透明基板厚みに対応した集光状態の光は記録面上ではデフォーカス状態となり、再生信号への影響を小さくすることができる。
【０２７２】
この例の場合は、ホログラムをレンズ面の端部付近には形成せず、厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光するのに必要なＮＡが得られるレンズ面部分にのみホログラムを形成し、ホログラムによる回折光を厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光するように構成し、ホログラム４１を透過した光束およびホログラムが形成されていないレンズ面４２を透過した光束を厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８に集光するようにしている。
【０２７３】
このように構成することで、高密度に対応させるためのビームスポットを得る必要がある厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８への記録および／または再生に必要なＮＡを得ることができ、しかも十分な光量を有するビームスポットを得ることができる。
【０２７４】
なお、図５９の例においては、対物レンズ１６の光源側の面にホログラムを設けているが、この例に限らず、本発明に云う可変手段の１例であるこのホログラムは、対物レンズ１６の像側の面や、カップリングレンズ１３の何れか１面に形成することもできる。また、ホログラムを対物レンズ１６およびカップリングレンズ１３を構成するレンズ面の何れか２箇所以上に設けることも可能である。
【０２７５】
実施例２２
図６０は、本発明に云う可変手段の１例である光軸を中心とした同心の帯状に形成され隣合うレンズ面の屈折力が異なる複数の輪帯状レンズ面を有する光学素子を、図５６（ａ），５６（ｂ）に示した対物レンズ１６とカップリングレンズ１３の間に配置した例で、光学素子５０の周囲部分に形成した第１の輪帯状レンズ面である平行平面板部分５１を透過して対物レンズ１６に入射した光束が、厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８に集光した状態（実線で記載）と、光学素子５０の中央部分に形成した第２の輪帯状レンズ面である凹レンズ部分５２を透過した光束が、厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光した状態（破線で記載）を示している。
【０２７６】
このように２つの集光状態での集光位置を光軸方向に離しているので、１つの透明基板厚みに対応した対物レンズの集光状態で再生を行っている場合に、他の透明基板厚みに対応した集光状態の光は記録面上ではデフォーカス状態となり、再生信号への影響を小さくすることができる。
【０２７７】
この例においても図５８の例に示したと同様、サイドローブの影響を少なくするため、最外周に位置する輪帯状レンズ面（この場合平行平面板）の内側に隣接する、厚み１．２ｍｍの透明基板に対応する輪帯状レンズ面の内側に隣接してさらに厚み０．６ｍｍの透明基板に対応する第３の輪帯状レンズ面（この場合平行平面板）を、その内側に厚み１．２ｍｍの透明基板に対応する第４の輪帯状レンズ面をさらにその内側に厚み０．６ｍｍの透明基板に対応する屈折力を有する第５の輪帯状レンズ面（この場合平行平面板）を形成する事により、基板厚み０．６ｍｍ対応時に不要光を出射する第２の輪帯状レンズ面の面積を減少させ、サイドローブを減少させることが出来る。さらにこれを繰り返し、すなわちレンズ面に設ける屈折力の異なる輪帯状レンズ面を外周から一つおきに複数構成することにより、基板厚みの異なる光情報記録媒体の記録再生を行うに適した二つの光スポットを得ることが可能となる。
【０２７８】
この輪帯状レンズ面の数は最外周に位置する輪帯状レンズ面を含めて２以上１０以下、さらに望ましくは３以上６以下とするすることが好ましい。
【０２７９】
また、同一の透明基板に対応する輪帯状レンズ面を複数設ける場合は、それら複数の各輪帯状レンズ面をそれぞれの輪帯状レンズ面を表す式（例えば、各輪帯状レンズ面を同一形式の非球面の式として表す）に従って光軸まで延長した際に、光軸上におけるレンズ厚みを等しくすることが望ましい。
【０２８０】
実施例２３
また、本発明に云う可変手段の１例であるホログラム素子は、図６０の光学素子５０を平行平面板で構成し、凹レンズ部分５２に替えて、光源側または像側の凹レンズ部分５２に対応する部分にホログラムを形成することで構成することができ、その場合は、ホログラムによる回折光を厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光するように構成し、ホログラム４１を透過した光束およびホログラムが形成されていないレンズ面４２を透過した光束を厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８に集光するようにする。
【０２８１】
この場合も２つの集光状態での集光位置を光軸方向に離しているので、１つの透明基板厚みに対応した対物レンズの集光状態で再生を行っている場合に、他の透明基板厚みに対応した集光状態の光は記録面上ではデフォーカス状態となり、再生信号への影響を小さくすることができる。
【０２８２】
実施例２４
図６１，６２は、図５６（ａ），５６（ｂ）におけるカップリングレンズ１３を光軸方向に移動させることで、厚み０．６ｍｍの透明基板２７を有する光情報記録媒体の記録面２７８に集光した状態（図６１）と、厚み１．２ｍｍの透明基板２８を有する光情報記録媒体の記録面２８８に集光した状態（図６２）に切り換える光情報の光ピックアップ装置の構成を示している。
【０２８３】
図６１において、１１は半導体レーザ等の光源、１２はビームスプリッタ、１３はカップリングレンズ、１４は第２の絞り、１５は第１の絞り、１６は対物レンズ、１７は厚み０．６ｍｍの透明基板、１８は厚み０．６ｍｍの透明基板を有する光情報記録媒体の情報記録面、１９は光検出器、２０はカップリングレンズ１３を保持する枠、２１は枠２０を光軸方向に移動させるためのレンズ移動手段、２２は第２の絞り１４を光路中に挿入するために絞り手段である。
【０２８４】
半導体レーザ等の光源１１から出射した光束はビームスプリッタ１２を通ってカップリングレンズ１３に入射し、収束光束となって絞り１５で所定の光束に制限されて対物レンズ１６に入射する。この対物レンズ１６は、収束光束が入射すると、所定の厚みの透明基板１７を通してほぼ無収差の光スポットを情報記録面１８上に結像する。
【０２８５】
この情報記録面１８で情報ピットによって変調されて反射した光束は、対物レンズ１６、カップリングレンズ１３を介してビームスプリッタ１２に戻り、ここでレーザ光源１１の光路から分離され、光検出器１９へ入射する。この光検出器１９は多分割されたＰＩＮフォトダイオードであり、各素子から入射光束の温度に比例した電流を出力し、この電流を図には示さない検出回路に送り、ここで情報信号、フォーカスエラー信号、トラックエラー信号に基づき、磁気回路とコイル等で構成される２次元アクチュエータで対物レンズ１６を制御し、常に情報トラック上に光スポット位置を合わせる。
【０２８６】
図６２は、カップリングレンズ１３をレンズ移動手段２１より対物レンズ１６から離れた、厚み１．２ｍｍの透明基板の記録または／再生を行う位置に移動し、第２の絞り１４を絞り手段により光路中に挿入した図である。
【０２８７】
この例のように、カップリングレンズを光軸方向に移動するように構成するように構成すれば、厚み０．６ｍｍから１．２ｍｍの透明基板を有する全ての光情報記録媒体について記録および／または再生を行うことが可能となる。また、この例においては、カップリングレンズを光軸方向に移動するようにしているが、カップリングレンズは固定位置として光源を光軸方向に移動する、あるいは、カップリングレンズと光源の両者を光軸方向に移動するようにしても良い。また、カップリングレンズは固定として、カップリングレンズとの光学的距離が異なる２つの光源を用い、この２つの光源を選択的に切りかえて用いるようにしても良い。
【０２８８】
また、図６２の例においては、カップリングレンズ１３から出射する光束は、収束光としているが、厚み１．２ｍｍの透明基板を有する光情報媒体の場合は、発散光または平行光を対物レンズ１６に入射することで、情報の再生が可能な場合は、厚み１．２ｍｍの透明基板を有する光情報記録媒体の場合はにおいては、対物レンズ１６に発散光または平行光を入射するようにしても良い。しかし収束光のほうが望ましことは言うまでもない。
【０２８９】
【発明の効果】
本発明により、各実施例でも見られるように、高ＮＡ化の下で、樹脂製の対物レンズを用いた場合でも、温度変化による波面収差の変化をレンズの許容誤差を確保できる程度に抑えた光学系が得られた。
【０２９０】
その上、今後さらに記録を高密度化される予想に対しても、波長４５０ｎｍまでの使用光の短波長化、ＮＡ０．７５程度までのレンズの高ＮＡ化が可能であることが明らかとなった。
【０２９１】
さらに、本発明によれば、一つの光ピックアップ装置で異なる基板厚を有する光ディスクの記録再生を可能とし、相互に互換性を有し、しかも大ＮＡ化の下で、樹脂製の対物レンズを用いた場合でも、温度変化による波面収差の変化をレンズの許容誤差を確保できる程度に抑えた、構造が簡単でコンパクトな光情報媒体の記録再生用光学系、及び、光情報記録再生用対物レンズが得られた。
【図面の簡単な説明】
【図１】本発明の光情報記録媒体の記録再生用光学系における対物レンズの実施例１の光路図である。
【図２】上記実施例１の対物レンズの球面収差および正弦条件の収差図である。
【図３】上記実施例１の対物レンズの温度特性図である。
【図４】本発明の光情報記録媒体の記録再生用光学系における対物レンズの実施例２の光路図である。
【図５】上記実施例２の対物レンズの球面収差および正弦条件の収差図である。
【図６】上記実施例２の対物レンズの温度特性図である。
【図７】本発明の光情報記録媒体の記録再生用光学系における対物レンズの実施例３の光路図である。
【図８】上記実施例３の対物レンズの球面収差および正弦条件の収差図である。
【図９】上記実施例３の対物レンズの温度特性図である。
【図１０】本発明の光情報記録媒体の記録再生用光学系における対物レンズの実施例４の光路図である。
【図１１】上記実施例４の対物レンズの球面収差および正弦条件の収差図である。
【図１２】上記実施例４の対物レンズの温度特性図である。
【図１３】本発明の光情報記録媒体の記録再生用光学系における対物レンズの実施例５の光路図である。
【図１４】上記実施例５の対物レンズの球面収差および正弦条件の収差図である。
【図１５】上記実施例５の対物レンズの温度特性図である。
【図１６】本発明の光情報記録媒体の記録再生用光学系の実施例６の光路図である。
【図１７】上記実施例６の光学系の温度特性図である。
【図１８】本発明の光情報記録媒体の記録再生用光学系の実施例７の光路図である。
【図１９】上記実施例７の光学系の温度特性図である。
【図２０】本発明の光情報記録媒体の記録再生用光学系における対物レンズの実施例８の光路図である。
【図２１】上記実施例８の対物レンズの球面収差および正弦条件の収差図である。
【図２２】上記実施例８の対物レンズの温度特性図である。
【図２３】本発明の光情報記録媒体の記録再生用光学系における実施例９の光路図である。
【図２４】上記実施例９のカップリングレンズの球面収差および正弦条件の収差図である。
【図２５】上記実施例９の光学系の温度特性図である。
【図２６】本発明の光情報記録媒体の記録再生用光学系における実施例１０の光路図である。
【図２７】上記実施例１０のカップリングレンズの球面収差および正弦条件の収差図である。
【図２８】上記実施例１０の光学系の温度特性図である。
【図２９】本発明の光情報記録媒体の記録再生用光学系における実施例１１の光路図である。
【図３０】上記実施例１１のカップリングレンズの球面収差および正弦条件の収差図である。
【図３１】上記実施例１１の光学系の温度特性図である。
【図３２】本発明の光情報記録媒体の記録再生用光学系における実施例１２の光路図である。
【図３３】上記実施例１２のカップリングレンズの球面収差および正弦条件の収差図である。
【図３４】上記実施例１２の光学系の温度特性図である。
【図３５】本発明の光情報記録媒体の記録再生用光学系における実施例１３の光路図である。
【図３６】上記実施例１３のカップリングレンズの球面収差および正弦条件の収差図である。
【図３７】上記実施例１３の光学系の温度特性図である。
【図３８】本発明の光情報記録媒体の記録再生用光学系の実施例１４の光路図である。
【図３９】上記実施例１４のカップリングレンズの球面収差および正弦条件の収差図である。
【図４０】上記実施例１４の光学系の温度特性図である。
【図４１】本発明の光情報記録媒体の記録再生用光学系の実施例１５の光路図である。
【図４２】上記実施例１５のカップリングレンズの球面収差および正弦条件の収差図である。
【図４３】上記実施例１５の光学系の温度特性図である。
【図４４】本発明の光情報記録媒体の記録再生用光学系における実施例１６の光路図である。
【図４５】上記実施例１６のカップリングレンズの球面収差および正弦条件の収差図である。
【図４６】上記実施例１６の光学系の温度特性図である。
【図４７】本発明の光情報記録媒体の記録再生用光学系の実施例１７の光路図である。
【図４８】上記実施例１７のカップリングレンズの球面収差および正弦条件の収差図である。
【図４９】上記実施例１７の光学系の温度特性図である。
【図５０】本発明の光情報記録媒体の記録再生用光学系における実施例１８の光路図である。
【図５１】上記実施例１８のカップリングレンズの球面収差および正弦条件の収差図である。
【図５２】上記実施例１８の光学系の温度特性図である。
【図５３】本発明の光情報記録媒体の記録再生用光学系の実施例１９の光路図である。
【図５４】上記実施例１９の対物レンズの球面収差および正弦条件の収差図を示す。
【図５５】上記実施例１９の対物レンズの温度特性を示す。
【図５６】本発明の光情報媒体の記録再生用光学系の基本的な構成図である。
【図５７】対物レンズから出射する光束の集光状態を示す図である。
【図５８】本発明の対物レンズの１例を示す図である。
【図５９】本発明の対物レンズの１例を示す図である。
【図６０】本発明の光学素子を使用した例を示す図である。
【図６１】本発明の光情報の光ピックアップ装置の説明図である。
【図６２】本発明の光情報の光ピックアップ装置の説明図である。
【図６３】従来例の説明図である。
【図６４】対物レンズの波面収差の変化を示す図である。
【符号の説明】
１１ レーザ光源（光源）
１２ ビームスプリッタ
１３ カップリングレンズ
１５ 絞り（第１絞り）
１６ 対物レンズ
１７ 透明基板
１８ 情報記録面
１９ 光検出器[0001]
BACKGROUND OF THE INVENTION
  The present invention condenses a light beam from a light source on an optical information recording medium, and records or reproduces optical information.Optical pickup deviceAbout.
[0002]
[Prior art]
As an optical system for recording / reproducing optical information recording media with the accuracy required for conventional CD correspondence (for recording / reproducing in the present invention includes recording, reproducing, and both recording and reproducing). Infinite conjugate type JP-A 57-76512, finite conjugate type JP-A 61-56314 and the like can be seen. Japanese Patent Application Laid-Open No. 6-258573 discloses a technique using a coupling lens in order to prevent the occurrence of aberration due to a temperature change when a resin lens is used.
[0003]
However, in recent years, the recording density of information recording media such as optical disks has been further increased, and accordingly, the NA of optical systems and objective lenses has been increased. In addition to this, requirements for performance such as wavefront aberration (spherical aberration) are becoming more severe.
[0004]
An optical system using a finite conjugate objective lens that forms an image on a recording surface of an optical information medium with a double-sided aspheric objective lens with corrected spherical aberration and sine conditions is well known. In this case, since the refractive power of each surface becomes large, when the numerical aperture NA becomes large,
(1) There is a limit to high NA.
[0005]
(2) A large amount of spherical aberration occurs when focusing is performed by moving the objective lens in the optical axis direction.
[0006]
(3) The occurrence of spherical aberration due to the change in the refractive index of the objective lens is large.
[0007]
There is a problem.
[0008]
When trying to meet such demands for higher NA and higher accuracy, due to changes in the distance between object images due to disc blurring, etc., and when the objective lens is made of resin, due to environmental changes such as temperature changes Wavefront aberration changes due to causes such as a change in refractive index become large. In addition, performance requirements may become stricter, the tolerance for the objective lens becomes stricter than before, and in some cases, the error may not be allowed.
[0009]
In particular, in the case where the objective lens is made of a resin, or in the case of a finite conjugate type, the level of accuracy required for conventional CD correspondence can be dealt with by the method using a coupling lens disclosed in JP-A-6-258573. However, the performance required to cope with the recent increase in recording density cannot be met.
[0010]
In the case of the infinite conjugate type, the change in wavefront aberration due to the change in the distance between the object images is eliminated. However, if the NA is increased to about NA 0.60, the change in the wavefront aberration due to the temperature change can cope with the higher recording density. In the performance required, the tolerance becomes strict.
[0011]
As an example, in the case of an infinite conjugate lens (parallel light is incident from the light source side) made of a resin lens having a focal length F = 3.36 mm and NA 0.6, 0.043λ (λ == 635 nm), the wavefront aberration changes. In fact, even with this change, there is a considerable restriction on the accuracy required for DVDs that are currently announced.
[0012]
On the other hand, it is desired that an optical pickup device equipped with a recording / reproducing optical system corresponding to a DVD that is currently announced can reproduce a compact disc (CD) that has been widely used. FIG. 63 shows an example of an optical pickup device of an optical information medium that can reproduce both DVD and CD. In the figure, a light beam emitted from a light source 1 such as a semiconductor laser enters a collimator lens 3 through a beam splitter 2, becomes a parallel light beam, is limited to a predetermined light beam by a diaphragm 5, and enters an objective lens 6. When a parallel light beam is incident on the objective lens 6, a light beam having almost no aberration is formed on the information recording surface 8 through a transparent substrate 7 having a predetermined thickness.
[0013]
The light beam modulated and reflected by the information pits on the information recording surface 8 returns to the beam splitter 2 through the objective lens 6 and the collimator lens 3, where it is separated from the optical path from the laser light source 1, and to the photodetector 9. Incident. This photodetector 9 is a multi-divided PIN photodiode that outputs a current proportional to the intensity of the incident light beam from each element and sends this current to a detection circuit not shown in the figure, where an information signal, a focus Based on the error signal and the track error signal, the objective lens 6 is controlled by a two-dimensional actuator composed of a magnetic circuit and a coil and the light spot position is always aligned on the information track.
[0014]
In such an optical information medium optical pickup device, a large NA (for example, NA 0.6) is used in order to reduce the light spot collected by the objective lens 6, and therefore, a transparent substrate placed in such a condensed light flux. When the thickness of the lens deviates from a predetermined thickness, large spherical aberration is generated.
[0015]
For example, when the substrate thickness is changed with an objective lens optimized under the conditions of NA 0.6, wavelength 635 nm of laser light emitted from the laser light source, transparent substrate thickness 0.6 mm, and substrate refractive index 1.58, As shown in FIG. 64, the aberration increases by 0.01 λ rms every time the thickness of the 0.01 mm substrate shifts. Accordingly, when the thickness of the transparent substrate is shifted by ± 0.07 mm, an aberration of 0.07 λrms occurs, and the Marshallal limit value (0.07 λrms), which serves as a standard for normal reading, is reached.
[0016]
For this reason, in the example shown in FIG. 63, when the thickness of the transparent substrate 7 is changed from 0.6 mm to 1.2 mm, the objective lens 6 corresponding to the 0.6 mm thickness is replaced with the 1.2 mm corresponding thickness. The objective lens 111 and the diaphragm 10 are switched for reproduction.
[0017]
In addition, as another countermeasure when the thickness of the transparent substrate is changed from 0.6 mm to 1.2 mm, two optical pickup devices for a 0.6 mm substrate and a 1.2 mm substrate are provided. It is also possible to do.
[0018]
[Problems to be solved by the invention]
  A first object of the present invention is to provide an optical system that suppresses changes in wavefront aberration due to temperature changes to such an extent that a lens tolerance can be ensured even when a resin objective lens is used under these high NAs. TheOptical pickup device withI want to get it.
[0019]
  In addition, it is expected that standards with higher recording density will come out in the future, and it is expected that use of light with a wavelength of up to 450 nm will be shortened and that lenses with a NA of up to about 0.75 will be required to have high NA. The When an objective lens with an NA of 0.65 or more is used, it is difficult to maintain the performance of an infinite conjugate glass lens unless the lens axis thickness is increased.Optical pickup device withI want to get it.
[0020]
  The second object of the present invention is to solve the above-mentioned drawbacks, enable recording and / or reproduction of optical disks having different substrate thicknesses with a single optical pickup device, have compatibility with each other, and increase the NA. Even if a resin objective lens is used, the structure is simple and compact with the change of wavefront aberration due to temperature change suppressed to a level that can secure the tolerance of the lens.Optical pickup deviceIs going to get.
[0021]
[Means for Solving the Problems]
  The present inventionofTo achieve the purposeThe configuration of the optical pickup device includes a light source, a condensing optical system for condensing a light beam emitted from the light source onto a recording surface of an optical information recording medium having a transparent substrate, and the optical information recording. A coupling lens having at least one aspherical surface for converting the diverging light from the light source into convergent light. And an objective lens that is movable at least in the optical axis direction, further converges the convergent light and forms an image on the information recording surface of the optical information recording medium, and has a wavefront aberration within the Marshall limit. When the lateral magnification of the objective lens alone in the minimum case is M, the distance between the image side surface of the coupling lens and the light source side surface of the objective lens is Dco, and the focal length of the objective lens is F, The following conditions And satisfying.
[0022]
0 <M <1 (1)
0.1 ≦ Dco / F ≦ 5.0 (2)
[0023]
Preferably
1.0 ≦ Dco / F ≦ 5.0 (3)
More desirably
1.0 ≦ Dco / F ≦ 3.0 (4)
Satisfied.
[0024]
According to another aspect of the present invention, there is provided a configuration of an optical pickup device that condenses a light source and a light beam emitted from the light source on a recording surface of an optical information recording medium having a transparent substrate via the transparent substrate. A condensing optical system, and a photodetector for receiving a light beam reflected by the recording surface of the optical information recording medium, the condensing optical system for converting divergent light from the light source into convergent light A coupling lens having at least one aspherical surface, and an objective lens that is movable at least in the optical axis direction and further converges the convergent light to form an image on the information recording surface of the optical information recording medium. In the case where the wavefront aberration within the Marshall limit is minimum, the following condition is satisfied, where M is the lateral magnification of the objective lens alone and F is the focal length of the objective lens.
0 <M <1 (1)
(1-M) · F ≦ 6.0 mm (11)
[0025]
These objective lenses are preferably made of resin, but may be made of glass.
[0026]
In the condensing optical system, it is desirable that the objective lens is made of a resin, and at least one of the coupling lenses is a resin lens having a positive refractive power. A ball lens is desirable.
[0027]
  The coupling lens is preferably a refractive optical system.
[0028]
According to another aspect of the present invention, there is provided a configuration of an optical pickup device that condenses a light source and a light beam emitted from the light source on a recording surface of an optical information recording medium having a transparent substrate via the transparent substrate. A condensing optical system, and a photodetector for receiving a light beam reflected by the recording surface of the optical information recording medium, the condensing optical system for converting divergent light from the light source into convergent light At least one surface is aspherical, and at least one lens is a coupling lens that is a resin lens having a positive refractive power, and is movable at least in the direction of the optical axis, and further converges the convergent light to provide the optical information. An objective lens that is a resin lens for forming an image on the information recording surface of the recording medium, and M represents the lateral magnification of the objective lens alone when the wavefront aberration within the Marechal limit is minimized. Optical optics Mt lateral magnification of the body, Fcp the focal length of the resin lens in the coupling lens, and the focal length of the objective lens is F, and satisfies the following condition.
0 <M <1 (1)
−0.10 ≦ Mt · M · Fcp / F ≦ −0.04 (12)
[0029]
According to another aspect of the present invention, there is provided a configuration of an optical pickup device that condenses a light source and a light beam emitted from the light source on a recording surface of an optical information recording medium having a transparent substrate via the transparent substrate. A condensing optical system, and a photodetector for receiving a light beam reflected by the recording surface of the optical information recording medium, the condensing optical system for converting divergent light from the light source into convergent light A coupling lens that is a single lens lens made of a resin having at least one aspheric surface, and movable at least in the optical axis direction, further converges the convergent light and forms an image on the information recording surface of the optical information recording medium. Objective lens, and when the wavefront aberration within the Marechal limit is minimized, the lateral magnification of the objective lens alone is M, the lateral magnification of the entire condensing optical system is Mt, and the resin in the coupling lens Wren made Fcp the focal length of the focal length of the objective lens is F, and satisfies the following condition.
0 <M <1 (1)
−0.10 ≦ Mt · M · Fcp / F ≦ −0.04 (12)
[0030]
According to another aspect of the present invention, there is provided a configuration of an optical pickup device that condenses a light source and a light beam emitted from the light source on a recording surface of an optical information recording medium having a transparent substrate via the transparent substrate. A condensing optical system, and a photodetector for receiving a light beam reflected by the recording surface of the optical information recording medium, the condensing optical system for converting divergent light from the light source into convergent light A coupling lens having at least one aspherical surface; and an objective lens that is movable at least in the optical axis direction and further converges the convergent light to form an image on the information recording surface of the optical information recording medium. M is the lateral magnification of the objective lens alone, Mt is the lateral magnification of the entire condensing optical system, and NA is the numerical aperture on the image side of the objective lens. Then, the following conditions Characterized by foot.
0 <M <1 (1)
0.06 ≦ | Mt | · NA ≦ 0.21 (13)
[0031]
  ReAs a live optical system
    0.06 ≦ | Mt | · NA ≦ 0.12 (14)
  As a recording optical system
    0.12 ≦ | Mt | · NA ≦ 0.21 (15)
It is desirable to satisfy
[0032]
Desirably, the lateral magnification of the objective lens alone is
0.05 ≦ M <1 (1 ′)
The objective lens desirably satisfies the following conditions.
0.48 ≦ NA (7)
Where NA is the numerical aperture on the image side of the objective lens
[0033]
It is desirable that the objective lens satisfies the following.
0.05 ≦ M ≦ 0.23 (5)
NA · (1-M) ≦ 0.65 (6)
But in general,
0.05 ≦ M ≦ 0.125 (8)
It is desirable that
0.65 ≦ NA ≦ 0.8 (9)
If
0.125 ≦ M ≦ 0.23 (10)
It is desirable that
[0034]
  And the objective lens is
    −0.25 ≦ F · (n−1) / r₂≦ 0.7 (17)
However,
n:Objective lensRefractive index of the material forming the
F: Focal length of objective lens
r₂:Objective lensVertex radius of curvature of the image side surface
    −0.045 ≦ x₂・ (N-1) / {F ・ (NA)²} ≦ 0.1 (18)
However,
n: Refractive index of the material forming the objective lens
F: Focal length of objective lens
NA: Numerical aperture on the image side of the objective lens
x₂:Objective lensThe difference in the optical axis direction between the outermost effective diameter of the axial ray on the image-side surface (the position on the image-side surface where the peripheral ray of NA is incident) and the apex of the surface increases as the distance from the optical axis increases. The direction of displacement to the image side is positive
    −0.005 ≦ Δ₂・ (N-1)³/ {F ・ (NA)⁴} ≦ 0.018 (19)
However,
n: Refractive index of the material forming the objective lens
F: Focal length of objective lens
NA: Numerical aperture on the image side of the objective lens
Δ₂:Objective lensAn aspherical surface and the apex radius of curvature r of the surface on the image side surface at the outermost effective diameter of the axial ray (the position on the image side surface on which the peripheral ray of NA is incident)₂The difference in the optical axis direction from the reference spherical surface with
It is desirable to satisfy all or some of these conditions.
[0035]
  ThisThese objective lenses are preferably made of resin, but may be made of glass.
[0036]
  MosquitoA pulling lens is a coupling lens that is placed between an objective lens that forms an image on an optical information recording medium within the marginal limit and the light source when diverging light beams emitted from the light source. Is converted into a convergent beam, and the following conditions are satisfied, and at least one lens is an aspherical lens.Is desirable.
[0037]
      −7.0 ≦ Mc ≦ −0.5 (20)
      0.06 ≦ NAo ≦ 0.21 (21)
Here, Mc: lateral magnification with respect to the light source side on the image side of the coupling lens
NAo: numerical aperture on the light source side
And the objective lens combined with this coupling lens is
      0 <M <1 (1)
Preferably
      0.05 ≦ M <1 (1 ′)
      0.3 ≦ NA (16)
Satisfy the conditions. The coupling lens may be composed of a single lens having both aspheric surfaces.
[0038]
These coupling lenses may be made of glass or resin.
[0039]
When this coupling lens is a single lens, it can be a meniscus lens having convex surfaces on both sides and a convex surface on the light source side, or a meniscus lens having a concave surface on the light source side.
[0040]
Next, the operation of the optical system of the present invention will be described. By providing a means for changing the divergence of the divergent light from the light source as a coupling means between the light source and the objective lens, the refractive power shared by the objective lens can be reduced. In particular, by providing the coupling means with a function of converting divergent light from the light source into convergent light, the refractive power shared by the objective lens when the NA is large can be optimized.
[0041]
The numerical aperture converted to infinite light incidence for a finite conjugate objective lens having a lateral magnification M and a numerical aperture NA (hereinafter referred to as converted NA) NA∞ is
NA∞ = (1-M) · NA (22)
Can be expressed as As the converted NA increases, the influence of environmental changes such as lens design, difficulty in maintaining performance, and temperature characteristics increases. At this time, when the lateral magnification M of the objective lens is in the range of the conditional expression (1), that is, the convergent light is incident on the objective lens, the converted NA can be reduced. Further, the influence of a change in refractive index and the like can be reduced.
[0042]
If the upper limit of conditional expression (1) is exceeded, the coupling means must have a power higher than that of the conventional objective lens, and it becomes difficult to manufacture the coupling means.
[0043]
In addition, the objective lens itself has a wavefront aberration that is minimized when the lateral magnification M is within the range of the conditional expression (1 ') and is within the Marechal limit, so that the optical axis of the coupling means and the light of the objective lens can be reduced. Deterioration of aberration when the axis is decentered is reduced, and the optical information recording / reproducing optical system is desirable.
[0044]
As such a coupling means, a lens, a mirror, a transmission type diffraction element, a reflection type diffraction element, etc. can be considered.
[0045]
By making the objective lens movable at least in the optical axis direction, the movable part can be reduced in weight, and focusing on the recording surface of the optical information medium can be performed with a small amount of movement.
[0046]
In addition, as NA increases, the occurrence of spherical aberration due to changes in the distance between object images due to disc blurring and the like, as well as temperature changes, etc. increases. To cope with this, not only the objective lens but also the light source and coupling means are included. Similarly to the objective lens, focusing can be performed by moving each independently or integrally with the objective lens.
[0047]
In conditional expression (2) for the distance between the coupling means normalized by the focal length of the objective lens and the objective lens, if the upper limit is exceeded, the size in the direction perpendicular to the optical axis of the coupling means will increase, and if the lower limit is exceeded, Even in the case of a movable mechanism in which the objective lens and the coupling element move integrally, a problem arises in realization due to mechanical interference or the like.
[0048]
If the lower limit of conditional expression (3) is exceeded, if only the objective lens is attached to the movable mechanism, the coupling element may cause mechanical interference with the movable mechanism around the objective lens. Furthermore, by making it within the upper limit of conditional expression (4), the distance from the light source to the optical information recording medium can be shortened within the determined specifications such as magnification.
[0049]
INDUSTRIAL APPLICABILITY The optical system of the present invention can be advantageously used when a spot having diffraction limited performance is imaged on the recording surface of an optical information recording medium when the NA is large and the wavelength of the used light is short, and NA of 0.48 or more Optimal optical system for the case.
[0050]
At that time, it is desirable that the lateral magnification M of the objective lens alone satisfies the conditional expression (5). If the upper limit is exceeded, the size in the direction perpendicular to the optical axis of the coupling means becomes larger, and if the lower limit is exceeded, the lateral magnification M is high. The error in the case of NA, particularly the spherical aberration due to the refractive index error of the objective lens, becomes large.
[0051]
If the upper limit of conditional expression (6) is exceeded, the thickness of the objective lens increases, and therefore the entire optical system needs to be enlarged in order to ensure the required working distance.
[0052]
Exceeding the upper limit of conditional expression (8) causes a large amount of spherical aberration when focusing is performed by moving the objective lens in the direction of the optical axis when there is a change in the distance between object images due to blurring of the optical information medium. Become. If the lower limit is exceeded, the amount of generation of spherical aberration based on the error when the NA is high, particularly the refractive error of the objective lens, becomes large.
[0053]
In particular, the resin material has a large change in refractive index due to temperature change. In the case of resin, the temperature change is ΔT, the refractive index change due to the temperature change is Δn,
Δn / ΔT = α (23)
In this case, α is almost constant and a negative value in the same material from 0 ° C. to around 60 ° C.
[0054]
The wavefront aberration (spherical aberration) change ΔWT with respect to the refractive index change Δn is proportional to the fourth power of the converted NA, and is also proportional to the focal lengths F and Δn. That is,
ΔWT = β · (NA∞)^Four・ F ・ Δn (24)
It becomes. Here, β is a proportional coefficient.
[0055]
Substituting Equation (22) and Equation (23) into Equation (24),
ΔWT = β · {NA · (1-M)}^Four・ F ・ α ・ ΔT (25)
From equation (25), it can be seen that by making M positive, the effect of temperature change becomes smaller corresponding to the fourth power of M.
[0056]
Therefore, by satisfying the conditional expression (8) and satisfying the conditional expression (6), a recording / reproducing optical system for a compact optical information recording medium is realized by a lightweight and low-cost resinous objective lens. it can.
[0057]
In order to realize an unprecedented high NA as an objective lens for recording / reproducing of an optical information recording medium as in the conditional expression (9), it is desirable to satisfy the conditional expression (10). If the upper limit is exceeded, the size in the direction perpendicular to the optical axis of the coupling means will increase, and if the lower limit is exceeded, the thickness of the objective lens will increase, and therefore an optical system will be required to ensure the required working distance. The whole thing needs to be enlarged. Moreover, weight reduction and cost reduction can be realized by using a resin lens under these conditions.
[0058]
If the upper limit of conditional expression (11) is exceeded, the objective lens becomes large and the entire optical system becomes large.
[0059]
Various means can be considered as the coupling means, but the reflection system is vulnerable to manufacturing errors, the diffraction means has a problem of diffraction efficiency, and the power of the light source needs to be increased. It is desirable to use a coupling lens that is a refractive optical system as a recording / reproducing optical system of an optical information recording medium.
[0060]
By making the coupling lens one or more spherical lens systems, the coupling lens can be manufactured by the same manufacturing method as a conventional collimator.
[0061]
However, since the coupling lens has a function of making divergent light emitted from the light source into convergent light, its refractive power is larger than that of a conventional collimator, and when trying to capture more light from the light source. The NA on the light source side is increased. Therefore, the number of lenses to be used increases only with the spherical system. For this reason, it is desirable to correct spherical aberration by introducing at least one aspheric surface.
[0062]
When the objective lens is made of resin, the change of the spherical aberration due to the change of the refractive index with respect to the temperature change of the refractive index can be reduced by the optical system of the present invention, but at least one of the positive lenses constituting the coupling lens has a positive refractive power. By making the lens made of resin, it is possible to further correct the spherical aberration change of the entire optical system due to the refractive index change with respect to the temperature change.
[0063]
This is because when the temperature increases by ΔT (0 <ΔT), the refractive index change Δnc of the coupling lens becomes negative (Δnc <0). For this reason, the refractive power of the coupling lens becomes small, and the light flux emitted from the coupling lens has a smaller convergence than before the temperature rise. For this reason, the lateral magnification M of the objective lens itself changes in a decreasing direction (ΔM <0).
[0064]
When ΔM changes in the negative direction with respect to the magnification M at which the wavefront aberration of the objective lens is minimized, the spherical aberration moves to the under side. Further, the refractive index change Δn of the objective lens itself becomes Δn <0 because the refractive index decreases as the temperature rises, and at this time, the spherical aberration moves to the over side.
[0065]
For this reason, the influence on the spherical aberration due to the change in the lateral magnification of the objective lens due to the change in the refractive index of the coupling lens and the influence on the change in the refractive index of the objective lens itself are offset. By using a resin lens, it is possible to further reduce the influence of temperature changes.
[0066]
Further, the correction effect is greater in the configuration of the conventional collimator and resin single objective lens than in the case where at least one of the collimator lenses is made of resin having a positive refractive power. This is because even if the NA on the light source side is the same as that of the collimator, the coupling lens has a negative magnification, so the converted NA of the coupling lens increases, and the absolute value of the magnification change ΔM of the objective lens itself increases. Because.
[0067]
In this case, since the coupling lens has a large NA on the light source side and has a negative magnification, it is desirable to use an aspherical surface as described above.
[0068]
Further, by using a single lens aspheric lens made of resin as the coupling lens, it is possible to obtain inexpensive and necessary performance. From the imaging magnification of the coupling lens, it is desirable that at least the surface on the objective lens side is an aspherical surface.
[0069]
Further, when the lateral magnification Mc of the coupling lens is further increased, both surfaces need to be aspherical in order to satisfactorily correct spherical aberration. This can be applied to a known finite conjugate objective lens design and production technique.
[0070]
When the upper limit of conditional expression (12) is exceeded, the magnification change of the objective lens alone due to the resin coupling lens accompanying the temperature change becomes small, and the effect of canceling the change in the refractive index of the objective lens becomes small.
[0071]
In addition, if the lower limit is exceeded, the magnification change of the objective lens alone due to the resin coupling lens due to the temperature change becomes small, but the wavefront aberration change due to the refractive index change caused by the resin coupling lens cannot be ignored any more, and the canceling effect is effective. In some cases, the change in wavefront aberration due to the temperature characteristics of the entire optical system becomes larger than when the coupling lens is made of glass.
[0072]
| Mt | · NA in the conditional expression (13) substantially corresponds to the numerical aperture NAo on the light source side of the optical system. If the lower limit of conditional expression (13) is exceeded, a sufficient amount of light cannot be obtained. When the upper limit is exceeded, the influence of laser astigmatism increases, and the influence of unevenness in light quantity also increases.
[0073]
If the upper limit of conditional expression (14) is exceeded, a concave lens or the like is required for the detection system with respect to the reproducing optical system, resulting in an increase in cost.
[0074]
Considering the recording optical system, a sufficient amount of light cannot be obtained if the lower limit of conditional expression (15) is exceeded.
[0075]
Next, the operation of the objective lens of the present invention will be described. By making convergent light incident on the objective lens and satisfying conditional expression (1), the NA can be increased without increasing the lens thickness, and the influence of a change in refractive index and the like is also reduced. This is because the converted NA becomes small by setting 0 <M (incident convergent light) as shown in the above equation (22).
[0076]
When NA is 0.3 or more, by making the convergent light incident side aspherical, spherical aberration can be corrected while maintaining a sine condition, and wavefront aberration can be within the Marshall limit.
[0077]
Moreover, since the objective lens can maintain its performance independently by making the wavefront aberration within the Marshallal limit by the incidence of convergent light within the range of the conditional expression (1) of the lateral magnification M of the objective lens itself, the divergent light from the light source can be maintained. Can be easily combined with the means for making the light into convergent light, and the error sensitivity of the arrangement including the eccentricity can be reduced.
[0078]
The objective lens corrects aberrations with respect to the imaginary light source, and by making the wavefront aberration within the Marechal limit, it becomes easy to combine with means for making the diverging light from the light source into convergent light, and has a wide range of applications. It becomes. Although the imaginary light source is virtual, it is practically equivalent to the fact that the incident light beam is condensed at one point by the diffraction limited spot.
[0079]
Spherical aberration and sine conditions can be corrected by using a single objective lens and aspheric surfaces on both sides. Therefore, the occurrence of aberration can be reduced even when tracking is performed by moving the objective lens in a direction perpendicular to the optical axis, for example, as in the objective lens of a recording / reproducing optical system of an optical information recording medium.
[0080]
If the refractive power of the image side surface of the objective lens composed of a single lens exceeds the upper limit of conditional expression (17) and becomes negative and strong, negative spherical aberration is greatly generated on the surface on the convergent light incident side, and the convergence is increased. The amount of aspherical surface on the light incident side becomes large, resulting in a lens that is difficult to manufacture. When the refractive power of the image side surface of an objective lens composed of a single lens exceeding the lower limit is positive and strong, negative spherical aberration on the image side surface increases, and the amount of aspherical surface on the convergent light incident side increases. This results in a lens that is difficult to manufacture.
[0081]
When the upper limit of the conditional expression (18) is exceeded, in order to correct the spherical aberration and the sine condition, the image side surface is made aspherical, and the aspherical amount of both surfaces becomes large, making it difficult to manufacture. It becomes a lens. Similarly, in order to correct spherical aberration and sinusoidal conditions when the lower limit is exceeded, the surface on the image side becomes aspherical, and the amount of aspherical surface increases on both sides, making the lens difficult to manufacture. End up.
[0082]
When the upper limit of conditional expression (19) is exceeded, the sine condition is overcorrected, and when the lower limit is exceeded, the sine condition is undercorrected.
[0083]
When using an objective lens whose aberration is corrected with respect to such a convergent light beam as an objective lens of an optical information recording medium recording / reproducing optical system, a coupling means for converting the divergent light beam from the light source into a convergent light beam is required. It becomes. In that case, in an optical system having a large NA of 0.48 or more and a short wavelength of used light, it is preferable that the lateral magnification M of the objective lens alone satisfies the conditional expression (5). If the upper limit is exceeded, the size in the direction perpendicular to the optical axis of the coupling means will increase, and if the lower limit is exceeded, errors in the case of a high NA, particularly the occurrence of spherical aberration due to the refractive index error of the objective lens will increase. .
[0084]
If the upper limit of conditional expression (6) is exceeded, the thickness of the objective lens increases, and thus the entire optical system needs to be enlarged in order to ensure the required working distance.
[0085]
Further, if the upper limit of conditional expression (11) is exceeded, the objective lens becomes large and the entire optical system becomes large.
[0086]
Further, when focusing by moving the objective lens in the optical axis direction, it is desirable that the lateral magnification M of the objective lens alone satisfies the conditional expression (8). If the upper limit is exceeded, the amount of spherical aberration generated when focusing is performed by moving the objective lens in the optical axis direction is large. If the lower limit is exceeded, errors in the case of a high NA, particularly spherical aberration due to the refractive power error of the objective lens, are large.
[0087]
The resin material has a large change in refractive index with temperature. Therefore, when the conditional expression (8) is satisfied and the conditional expression (6) is satisfied, a lightweight and inexpensive objective lens necessary for a recording / reproducing optical system of a compact optical information recording medium is obtained. If the upper limit of conditional expression (6) is exceeded, the thickness of the objective lens increases, and therefore the entire optical system needs to be enlarged in order to ensure the required working distance.
[0088]
When realizing an unprecedented high NA as a recording / reproducing objective lens for an optical information recording medium that satisfies the conditional expression (16), it is desirable to satisfy the conditional expression (10). If the upper limit is exceeded, the size in the direction perpendicular to the optical axis of the coupling means will increase, and if the lower limit is exceeded, the thickness of the objective lens will increase, and therefore an optical system will be required to ensure the required working distance. The whole thing needs to be enlarged.
[0089]
Moreover, weight reduction and cost reduction can be realized by using a resin lens under these conditions.
[0090]
It has been described above that the refractive power of the objective lens can be reduced by using the objective lens that forms the image on the optical information recording medium within the Marechal limit while the wavefront aberration is minimized when the convergent light is incident. In order to realize an optical system using such an objective lens, a coupling lens having a positive refractive power that uses divergent light emitted from a light source as predetermined convergent light may be used.
[0091]
Next, the operation of the coupling lens of the present invention will be described. From the magnification Mt of the optical system and the magnification M of the objective lens, the magnification Mc of the coupling lens is
Mc = Mt / M
However, it is desirable that the wavefront aberration is minimized by the coupling lens alone at the magnification Mc at this time and is within the marginal limit. Thereby, the deterioration of the aberration when the objective lens is decentered with respect to the optical axis can be reduced.
[0092]
The magnification Mc of the coupling lens is preferably within the range of conditional expression (20). If the upper limit is exceeded, the burden on the refractive power of the coupling lens will increase, the effect of error sensitivity, etc. will increase, and the requirements for mounting and manufacturing accuracy will become stricter than conventional collimator lenses, and the coupling lens will be more difficult than the objective lens. The size perpendicular to the optical axis must be increased.
[0093]
If the lower limit is exceeded, the burden of the refractive power of the objective lens increases, and there is no significant difference in effect from the infinite conjugate objective lens using a collimator.
[0094]
Further, it is desirable to satisfy the conditional expression (21) for the numerical aperture NAo on the light source side. If the lower limit is exceeded, a sufficient amount of light cannot be obtained. When the upper limit is exceeded, the influence of laser astigmatism increases, and the influence of unevenness in light quantity also increases.
[0095]
At this time, if the objective lens satisfies the conditional expression (1), the image-side numerical aperture NA can be increased without increasing the lens thickness. If NA exceeds the lower limit of the conditional expression (16), a known method such as a collimator and an objective lens for parallel light incidence is sufficient without using such a coupling lens and an objective lens for incident convergent light. The performance can be maintained, and even in the case of a resin lens, the performance change due to the temperature change can be sufficiently reduced.
[0096]
By making the coupling lens one or more spherical lens systems, the coupling lens can be manufactured by the same manufacturing method as a conventional collimator.
[0097]
However, since the coupling lens has a function of making divergent light emitted from the light source into convergent light, its refractive power is larger than that of a conventional collimator, and when trying to capture more light from the light source. The NA on the light source side is increased. Therefore, the number of lenses to be used increases only with the spherical system. For this reason, it is desirable to correct spherical aberration by introducing at least one aspheric surface.
[0098]
When the objective lens is made of glass, the performance change due to temperature change can be reduced by making the coupling lens also made of glass, which is particularly useful for use in a high NA lens with NA of 0.65 or more.
[0099]
By making both surfaces of the coupling lens convex, the moldability is improved and the shape is easy to manufacture. Further, the shape satisfies the sine condition.
[0100]
By making the coupling lens a meniscus lens having a convex surface on the light source side, particularly when the coupling lens is made of resin, the distance Dco between the coupling lens and the objective lens, the magnification M of the objective lens, and the magnification of the entire optical system With the same specification of Mt, the effect of changing the magnification of the objective lens alone due to temperature change can be increased compared to other shapes, and the degree of cancellation with respect to performance change due to refractive index change of the objective lens itself is increased.
[0101]
In addition, when the coupling lens is a meniscus lens having a concave surface on the light source side, the main point is that the distance Dco between the coupling lens and the objective lens, the magnification M of the objective lens, and the magnification Mt of the entire optical system are the same. Due to the positional relationship, the overall length of the optical system can be shortened compared to other shapes.
[0102]
A first configuration for achieving the second object of the present invention includes a coupling lens that converts a light beam from a light source into convergent light, and a transparent substrate that further converges convergent light from the coupling lens. In order to enable recording and / or reproduction of information on at least two types of information recording media having an objective lens that condenses on the recording surface of the information recording medium via the transparent substrate and transparent substrates having different thicknesses, A recording / reproducing optical system for an optical information medium, comprising: variable means for varying a condensing state by the objective lens in accordance with a thickness of a transparent substrate of the at least two types of information recording medium. It is a thing.
[0103]
According to a second configuration, in the first configuration, the variable means is formed in a concentric band centered on the optical axis and formed on at least one of the lens surfaces constituting the coupling lens and the objective lens. In this configuration, a plurality of annular lens surfaces having different refractive powers of adjacent lens surfaces are used, and the light beam emitted from the objective lens is condensed in at least two kinds of condensing states. Preferably, in the first configuration, the variable means is formed on at least one surface of the objective lens and is formed in a concentric band shape with the optical axis as the center, and a plurality of rings having different refractive powers of adjacent lens surfaces. Consists of a band-shaped lens surface, the objective lens is configured to condense incident convergent light in at least two kinds of condensing states. In the first configuration, the variable means is formed in at least one surface of the coupling lens, is formed in a concentric strip shape centered on the optical axis, and has a plurality of annular zones having different refractive powers of adjacent lens surfaces. The objective lens is configured to condense at least two kinds of convergent lights having different convergence degrees emitted from the coupling lens in at least two kinds of condensed states. Also good. According to a third configuration, in the first configuration, the variable unit is configured by a hologram formed on at least one lens surface of the coupling lens and the objective lens, and the hologram Corresponding to the transmitted light and diffracted light, the light beam emitted from the objective lens is condensed in at least two kinds of condensing states.
[0104]
Preferably, the hologram is formed on at least one lens surface of the objective lens. In the third configuration, the hologram may be formed on at least one lens surface of the coupling lens.
[0105]
According to a fourth configuration, in the first configuration, the variable unit includes a hologram element provided in an optical path of the light source and the objective lens, and transmits and diffracts transmitted light and diffraction transmitted through the hologram element. Corresponding to the light, the objective lens is configured to condense incident convergent light in at least two kinds of condensing states. Further, a fifth configuration is the first configuration according to the first configuration, wherein the variable means is formed in a concentric band centering on an optical axis provided in an optical path of the light source and the objective lens, and has a refractive power between adjacent lens surfaces. Are constituted by optical elements having a plurality of annular zone lens surfaces.
[0106]
In the sixth configuration, the variable means is composed of a coupling lens, or a light source, or means for moving the coupling lens and the light source on the optical axis according to the thickness of the transparent substrate. Recording information on at least two types of information recording media having transparent substrates with different thicknesses, with the condensed state being at least two types of condensed states according to the thickness of different transparent substrates of at least two types of information recording media Alternatively, the recording / reproducing optical system of the optical information medium is characterized by performing reproduction.
[0107]
In the seventh configuration, the variable means is configured by means for switching a plurality of light sources in accordance with the thickness of the transparent substrate of the optical information recording medium.
[0108]
Further, in the above configuration, the objective lens is configured so that the lateral magnification at which the wavefront aberration satisfies the Marechal limit and becomes the minimum is positive. Further, in the case where one surface of the objective lens is constituted by an annular lens surface, or in the configuration in which a hologram is formed on one surface, the objective lens has a wavefront aberration satisfying the Marshall limit for each of the at least two kinds of condensing states. In addition, the minimum lateral magnification is positive.
[0109]
The optical pickup device of the present invention includes at least a light source, a condensing optical system for condensing a light beam emitted from the light source on a recording surface of an information recording medium having a transparent substrate, and the information recording medium. An optical pickup device for an optical information medium comprising a photodetector that receives a light beam reflected by the recording surface and outputs an electrical signal corresponding to the amount of light, wherein the condensing optical system is one of the optical information An optical pickup device for an optical information medium, which is an optical system for recording / reproducing the medium, is provided.
[0110]
In the optical information recording / reproducing optical system of the present invention described in the first configuration, the condensing state by the objective lens is changed to at least two kinds of condensing states according to the thickness of the transparent substrate of at least two kinds of information recording media. The optical recording and reproducing optical system of one optical information medium is provided with a coupling lens that converts the light flux from the light source into convergent light so that the convergent light is incident on the objective lens. When recording and / or reproducing information to / from at least two types of information recording media having different values, the refractive power shared by the objective lens can be reduced, and a resin objective lens is used as the objective lens In addition, a change in wavefront aberration due to a temperature change can be suppressed to such an extent that a lens tolerance can be secured.
[0111]
In the optical information recording / reproducing optical system of the present invention described in the second configuration, the variable means is at least one of the lens surfaces constituting the coupling lens and the objective lens, or at least the objective lens. Since it is composed of one or a plurality of annular lens surfaces formed on at least one surface of the coupling lens and formed in concentric belts around the optical axis and having different refractive powers of adjacent lens surfaces, the optical element In the case of recording and / or reproducing information on at least two types of information recording media having different thicknesses without increasing the number of objectives, there is no special lens moving mechanism or the like that has been conventionally used. At least corresponding to the thickness of two types of transparent substrates of at least two types of information recording media having different thicknesses within the movement range of the lens focus adjustment mechanism. It is possible to obtain various kinds of condensing states, record and / or reproduce information on at least two kinds of information recording media having different thicknesses, and at least two kinds of light fluxes on a plurality of annular lens surfaces. Therefore, it is possible to reduce useless light flux that cannot be used for recording and / or reproducing information on at least two types of information recording media. Can be used effectively.
[0112]
In the optical information recording / reproducing optical system of the present invention described in the third configuration, the variable means may be at least one of the lens surfaces constituting the coupling lens and the objective lens, or the objective. Since the hologram is formed on at least one lens surface of the lens or at least one lens surface of the coupling lens, the number of optical elements can be increased without increasing the number of optical elements and at least two types of information recording media having different thicknesses. When recording and / or reproducing the above information, at least two types of information having different thicknesses within the movement range of the focus adjustment mechanism of the objective lens conventionally used without providing a special lens movement mechanism or the like At least two kinds of light condensing states corresponding to the thicknesses of two kinds of transparent substrates of the recording medium can be obtained, and the thicknesses are different. Without even can perform recording and / or reproducing information into two types of information recording medium, it is possible to obtain a small beam spot of impact of further sidelobes.
[0113]
In the recording / reproducing optical system of the optical information medium of the present invention described in the fourth configuration, the variable means is configured by a hologram element provided in the optical path from the light source to the objective lens, so that at least two of different thicknesses are used. When recording and / or reproducing information to / from various types of information recording media, the thickness of the object can be adjusted within the range of movement of the focus adjustment mechanism of the objective lens conventionally used without providing a special lens movement mechanism. It is possible to obtain at least two kinds of light condensing states corresponding to the thicknesses of two kinds of transparent substrates of at least two kinds of different information recording media, and record information on at least two kinds of information recording media having different thicknesses and / or Reproduction can be performed, and a beam spot less influenced by side lobes can be obtained.
[0114]
In the optical information recording / reproducing optical system of the present invention described in the fifth configuration, the variable means is formed in a concentric band centered on the optical axis provided in the optical path from the light source to the objective lens. Since it is composed of a plurality of annular lens surfaces having different refractive powers of adjacent lens surfaces, a special lens moving mechanism or the like is used when recording and / or reproducing information on at least two types of information recording media having different thicknesses. And at least two types of light condensing states corresponding to the thickness of the transparent substrate of at least two types of information recording media having different thicknesses are obtained within the range of movement of the focus adjustment mechanism of the objective lens conventionally used. It is possible to record and / or reproduce information on at least two kinds of information recording media having different thicknesses, and at least two kinds of light fluxes are formed on a plurality of annular lens surfaces. Therefore, it is possible to reduce useless light flux that cannot be used for recording and / or reproducing information on at least two types of information recording media. Can be used effectively.
[0115]
In the optical information recording / reproducing optical system of the present invention described in the sixth configuration, the variable means can be a coupling lens or a light source or a coupling lens and a light source with an optical axis according to the thickness of the transparent substrate. In the ninth configuration, the variable means is configured by means for switching a plurality of light sources in accordance with the thickness of the transparent substrate of the optical information recording medium, so that the light is emitted from the coupling lens. It is possible to select at least two types of convergence of the light beam including convergent light, and set the condensing state of the objective lens to at least two types of condensing states according to the thickness of different transparent substrates of at least two types of information recording media. Thus, information is recorded and / or reproduced on at least two types of information recording media having transparent substrates having different thicknesses. An optical system for recording / reproducing the medium can record and / or reproduce information on at least two types of information recording media having different thicknesses, and can reduce the refractive power shared by the objective lens. Even when a resin objective lens is used, it is possible to suppress changes in wavefront aberration due to temperature changes to such an extent that the tolerance of the lens can be ensured. Further, there is little light loss and at least two types of information with different thicknesses. The amount of light at the time of recording and / or reproducing information on the recording medium can also be set to an optimum amount, and a beam spot that is less affected by side lobes can be obtained.
[0116]
In the case where convergent light and parallel light, or convergent light and divergent light are selected as the two types of convergence to be selected, the convergent light is used in the direction in which the NA of the exit side surface of the objective lens becomes larger.
[0117]
In the optical information medium recording / reproducing optical system of the present invention described above, the objective lens has a positive lateral magnification at which the wavefront aberration satisfies the Marshallal limit and is minimum. Even if the NA on the image side (optical information recording medium side) of the lens is set to a large NA, the refractive power shared by the objective lens can be reduced, and even when a resin objective lens is used as the objective lens, it also depends on the temperature change. It becomes possible to suppress the change of the wavefront aberration to such an extent that the tolerance of the lens can be ensured.
[0118]
Further, the optical system for recording / reproducing on the optical information medium of the present invention in which an annular lens surface or hologram is formed on one surface of the objective lens, the wavefront aberration of each of the at least two kinds of condensing states is limited to the Marshall limit. Since the minimum lateral magnification that satisfies the above is assumed to be positive, the refractive power shared by the objective lens is reduced even when the NA on the image side (optical information recording medium side) of the objective lens in use is a large NA. Even when a resin objective lens is used as the objective lens, the change in wavefront aberration due to the temperature change can be suppressed to such an extent that a tolerance of the lens can be ensured.
[0119]
An optical pickup device for an optical information medium according to the present invention can record and / or reproduce information on at least two types of information recording media having different thicknesses with a recording / reproducing optical system for one optical information medium, The refractive power shared by the objective lens can be reduced, and even when a resin objective lens is used as the objective lens, it is possible to suppress changes in wavefront aberration due to temperature changes to such an extent that a lens tolerance can be secured. Thus, a compact and highly reliable optical pickup device can be obtained.
[0120]
【Example】
Examples 1 to 19 for achieving the first object will be described below. In each example, assuming that a recording / reproducing optical system of a high-density optical information recording medium having a transparent substrate is used, the numerical aperture NA is 0.6 or more. Moreover, all the thickness of the transparent substrate 17 is 0.6 mm.
[0121]
Examples 1 to 5 and Example 8 Furthermore, Example 19 shows only the objective lens 16, and Examples 6 and 7 are examples of the optical system using the objective lens 16 of Example 1 and the coupling lens 13. Indicates. Examples 9 to 18 show a single lens coupling lens 13 and an optical system in which the coupling lens 13 and the objective lens 16 are combined. At this time, the objective lens of Example 1 is used in Examples 9 to 16, the objective lens of Example 2 is used in Example 17, and the objective lens of Example 3 is used in Example 18.
[0122]
The symbols in the table indicate the focal length of the objective lens 16 as F (mm), the radius of curvature of the i-th surface in order from the light source side 11, ri, and on the optical axis between the i-th surface and the i + 1-th surface. Di, the refractive index at the light source wavelength of the medium between the i-th surface and the (i + 1) -th surface is ni, the lateral magnification of the objective lens 16 is M, and the image-side numerical aperture is NA. The wavelength is represented by λ.
[0123]
In Examples 6 and 7, Ft is the focal length of the entire optical system, Mt is the lateral magnification of the entire optical system, T is the distance to the light source 11 when viewed from the first surface, and the light traveling direction is positive. U represents the distance between the object images, and Examples 1 to 5 and Example 8 are negative values because the incident light is a convergent light beam in the example of only the objective lens 16.
[0124]
In Examples 6 and 7 and Examples 9 to 18, Ft is the focal length of the entire optical system, Mt is the lateral magnification of the entire optical system, U is the distance between object images of the optical system, and T is the coupling lens 13. This represents the distance to the light source when viewed from the first surface.
[0125]
Further, in the coupling lens 13 alone of Examples 9 to 18, Fc is the focal length of the single lens coupling lens, Mc is the lateral magnification of the coupling lens alone, and Uc is the coupling lens alone in the arrangement at that time. The object image distance, NAo, represents the numerical aperture on the light source side.
[0126]
Regarding the temperature characteristics, when the objective lens or the coupling lens is made of resin, when the temperature increases by 1 ° C., −12 × 10^-FiveIt is assumed to change. Further, when the objective lens or the coupling lens is made of glass, when the temperature increases by 1 ° C., 39 × 10^-7It is assumed to change.
[0127]
The temperature characteristic is evaluated by the wavefront aberration rms value. For this wavefront aberration, the rms value is calculated by ray tracing by a known method. The Marechal limit means that the wavefront aberration rms value is 0.07λ. Further, the wavefront aberration can be measured using an interferometer capable of numerical analysis.
[0128]
It should be noted that the influence of the linear expansion of the material due to the temperature change on the wavefront aberration is considerably smaller than the influence of the change in the refractive index, and is not calculated here.
[0129]
The aspherical shape of the lens surface should be a conic coefficient, Ai aspherical coefficient, and Pi (4 ≦ Pi) aspherical in an orthogonal coordinate system with the vertex of the surface as the origin and the optical axis direction as the X axis. When it is a number
[0130]
[Expression 1]

[0131]
It is represented by
[0132]
Example 1
[0133]
[Table 1]

[0134]
In this embodiment, the objective lens 16 is made of resin. An optical path diagram of the objective lens 16 is shown in FIG. 1, its spherical aberration and sine aberration diagram are shown in FIG. 2, and temperature characteristics are shown in FIG.
[0135]
The temperature characteristic changes by 30 ° C. and the wavefront aberration only changes by 0.028λ, and the influence of the temperature change is considerably smaller than that of the infinite conjugate objective lens.
In this example
x₂= −0.08606 Δ₂= 0.04569
And
x₂・ (N-1) / {F ・ (NA)²} = − 0.03160
Δ₂・ (N-1)^Three/ {F ・ (NA)^Four} = 0.01156
It is.
[0136]
Example 2
[0137]
[Table 2]

[0138]
In this embodiment, as in the first embodiment, the objective lens 16 is made of resin. An optical path diagram of the objective lens 16 is shown in FIG. 4, its spherical aberration and sinusoidal aberration diagram is shown in FIG. 5, and temperature characteristics are shown in FIG. In the second embodiment, M is further increased compared to the first embodiment, so that the effect is great.
[0139]
In this example,
x₂= 0.01337 Δ₂= 0.01894
And
x₂・ (N-1) / {F ・ (NA)²} = 0.00403
Δ₂・ (N-1)^Three/ {F ・ (NA)^Four} = 0.00394
It is.
[0140]
Example 3
[0141]
[Table 3]

[0142]
The objective lens 16 of this embodiment is also made of resin, its optical path diagram is shown in FIG. 7, its spherical aberration and sinusoidal aberration diagrams are shown in FIGS. 8 (a) and 8 (b), and temperature characteristics are shown in FIG. .
[0143]
In this example,
x₂= −0.08076 Δ₂= 0.05734
And
x₂・ (N-1) / {F ・ (NA)²} = − 0.03023
Δ₂・ (N-1)^Three/ {F ・ (NA)^Four} = 0.01479
It is.
[0144]
Example 4
[0145]
[Table 4]

[0146]
The objective lens 16 of this embodiment is also made of resin, and has an NA of 0.7 and a wavelength of used light of 450 nm. The optical path diagram is shown in FIG. 10, the spherical aberration and sinusoidal aberration diagrams are shown in FIGS. 11 (a) and 11 (b), and the temperature characteristics are shown in FIG. When M is 0.2 times, even with a resin lens with a NA of 0.7, the change in wavefront aberration is about 0.028λ with respect to a change in temperature of 30 ° C. Is corrected well.
[0147]
In this example,
x₂= 0.05248 Δ₂= 0.03962
And
x₂・ (N-1) / {F ・ (NA)²} = 0.01182
Δ₂・ (N-1)^Three/ {F ・ (NA)^Four} = 0.00471
It is.
[0148]
Example 5
[0149]
[Table 5]

[0150]
The objective lens 16 of this embodiment is made of glass and has an NA of 0.75 and a wavelength of 450 nm. The initial aberration is well corrected even with an NA of 0.75. The optical path diagram is shown in FIG. 13, the spherical aberration and sinusoidal aberration diagrams are shown in FIGS. 14 (a) and 14 (b), and the temperature characteristics are shown in FIG.
[0151]
In this example,
x₂= 0.25188 Δ₂= 0.00660
And
x₂・ (N-1) / {F ・ (NA)²} = 0.06992
Δ₂・ (N-1)^Three/ {F ・ (NA)^Four} = 0.00162
It is.
[0152]
Example 6
[0153]
[Table 6]

[0154]
In the optical system of this embodiment, the objective lens 16 is the same as that of the first embodiment, and the coupling lens 13 is an example in which the objective lens 16 is combined with a one-group two-lens lens made of glass. The optical path diagram is shown in FIG. 16, and the temperature characteristics are shown in FIG.
[0155]
The amount of change in wavefront aberration due to temperature change is almost the same as in Example 1, and is due to the objective lens.
[0156]
Further, in order to correct the aberration caused by the coupling lens, the magnification of the wavefront aberration best of the objective lens is slightly different from the magnification of the first embodiment.
[0157]
In this example, Dco = 9.90.
[0158]
Example 7
[0159]
[Table 7]

[0160]
The optical system of this example is an example of an optical system in which the objective lens 16 is made of resin, the one of Example 1 is used, and the coupling lens 13 is a single-sided aspheric lens made of resin. The optical path diagram is shown in FIG. 18, and its temperature characteristics are shown in FIG.
[0161]
The change in wavefront aberration due to the temperature change is even smaller than half that of the first embodiment. This is because when the temperature rises, the refractive index of each lens decreases, the angle of convergent light by the coupling lens decreases, and the lateral magnification of the objective lens decreases (if this effect alone, the spherical surface of the objective lens This is because the influence of the lowering of the refractive index of the objective lens itself (in this case, the spherical aberration moves to the over side) cancels each other.
[0162]
In this embodiment, Dco = 10.0.
[0163]
Example 8
[0164]
[Table 8]

[0165]
In this embodiment, only the objective lens 16 is used, and the objective lens 16 is made of resin, the light source side surface is aspherical, and the image side surface is spherical. The optical path diagram is shown in FIG. 20, the spherical aberration and sinusoidal aberration diagrams are shown in FIGS. 21 (a) and 21 (b), and the temperature characteristics are shown in FIG.
[0166]
In this example,
x₂= -0.029622 Δ₂= 0.00 (because it is a spherical surface)
x₂・ (N-1) / {F ・ (NA)²} = − 0.00907
Δ₂・ (N-1)^Three/ {F ・ (NA)^Four} = 0.00
It is.
[0167]
Example 9
Coupling lens
[0168]
[Table 9]

[0169]
All optical system
[0170]
[Table 10]

[0171]
Example 9 is an example of a biconvex lens in which the coupling lens 13 is made of resin and has a double-sided aspheric surface, and aberration diagrams thereof are shown in FIGS. 24 (a) and 24 (b). Spherical aberration and sine conditions are also fully satisfied. The objective lens combined with this is the resin objective lens of Example 1. FIG. 23 shows the optical path diagram of the entire optical system, and FIG. 25 shows the temperature characteristics thereof.
[0172]
In this example
Dco = 3
Mt · M · Fcp / F = −0.05569
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0173]
The change in wavefront aberration due to the temperature change is 0.013λ when the temperature rises by 30 ° C. from the reference design temperature, which is about half that of the objective lens alone in Example 1. This is because the refractive index of each lens decreases as the temperature rises, the angle of convergent light from the coupling lens decreases, and the lateral magnification of the objective lens alone decreases (if this effect alone, spherical aberration of the objective lens) This is because the effect of lowering the refractive index of the objective lens itself (in this case, the spherical aberration moves to the over side) cancels out.
[0174]
Example 10
Coupling lens
[0175]
[Table 11]

[0176]
All optical system
[0177]
[Table 12]

[0178]
Example 10 is an example of a biconvex lens in which the coupling lens 13 is made of resin and has a double-sided aspheric surface. The magnification Mc is equal to −2.0 as in Example 9, but the focal length Fc is slightly longer. The aberration diagrams are shown in FIGS. 27 (a) and 27 (b). Spherical aberration and sine conditions are fully satisfied.
[0179]
The entire optical system is a combination of this coupling lens and the resin objective lens of Example 1. The magnifications M and Mt have the same specifications as in Examples 7 and 9, and the objective lens and the coupling lens have the same specifications. The interval Dco is also the same as in the seventh embodiment. The optical path diagram is shown in FIG. 26, and the temperature characteristics are shown in FIG.
[0180]
In this example
Dco = 10
Mt · M · Fcp / F = −0.06429
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0181]
The change in wavefront aberration due to the temperature change is 0.011λ, which is substantially the same as that in Example 7 and slightly smaller than that in Example 9, when 30 ° C. is raised from the reference design temperature. This is because the focal length Fc of the coupling lens is longer than that of the ninth embodiment, and the degree to which the angle of convergent light by the coupling lens is reduced due to the temperature rise is greater than that of the ninth embodiment.
[0182]
Example 11
Coupling lens
[0183]
[Table 13]

[0184]
All optical system
[0185]
[Table 14]

[0186]
Example 11 is an example in which the coupling lens is made of resin, a double-sided aspheric surface, and the light source side surface is a concave meniscus lens, and has the same magnification Mc = −2.0 as Example 9, and its aberration diagram is shown in FIG. 30 (a) and 30 (b). The sine condition is overcorrected.
[0187]
The entire optical system is a combination of this coupling lens and the resin objective lens of Example 1. The magnifications M and Mt have the same specifications as in Example 9, and the distance Dco between the objective lens and the coupling lens is Dco. Is the same as in Example 9. The optical path diagram is shown in FIG. 29, and the temperature characteristics are shown in FIG.
[0188]
In this example
Dco = 3
Mt · M · Fcp / F = −0.05476
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0189]
The change in wavefront aberration due to the temperature change is slightly larger than that of Example 9 having substantially the same specification as 0.016λ when the temperature rises by 30 ° C. from the reference design temperature, but the distance between the object images is short. This is because the light source side surface of the coupling lens is a concave meniscus lens, and the principal point position of the lens is the objective lens as compared with Example 9 which is a biconvex coupling lens.
[0190]
Example 12
Coupling lens
[0191]
[Table 15]

[0192]
All optical system
[0193]
[Table 16]

[0194]
Example 12 is an example in which the coupling lens is made of resin, a double-sided aspheric surface, and the light source side surface is a convex meniscus lens, and has the same magnification Mc = −2.0 as Example 9, and its aberration diagram is shown in FIG. 33 (a) and 33 (b). The sine condition is undercorrected.
[0195]
The entire optical system is a combination of this coupling lens and the resin objective lens of Example 1. The magnifications M and Mt have the same specifications as in Example 9, and the distance Dco between the objective lens and the coupling lens is Dco. Is the same as in Example 9. The optical path diagram is shown in FIG. 32, and the temperature characteristics are shown in FIG.
[0196]
In this example
Dco = 3
Mt · M · Fcp / F = −0.05703
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0197]
The change in wavefront aberration due to the temperature change is smaller than that of Example 9 having substantially the same specifications as 0.010λ when the temperature rises by 30 ° C. from the reference design temperature. This is because the coupling lens is a meniscus lens having a convex light source side surface, and the principal point position of the lens is a light source as compared with Example 9 which is a biconvex coupling lens. This is because the focal length Fc becomes long.
[0198]
Example 13
Coupling lens
[0199]
[Table 17]

[0200]
All optical system
[0201]
[Table 18]

[0202]
Example 13 is an example of a biconvex lens in which the coupling lens is made of resin, the light source side surface is a spherical surface, and the image side surface is an aspherical surface, and has the same magnification Mc = −2.0 as in Example 9, Aberration diagrams are shown in FIGS. 36 (a) and 36 (b). The sine condition is overcorrected.
[0203]
The entire optical system is a combination of this coupling lens and the resin objective lens of Example 1. The magnifications M and Mt have the same specifications as in Example 9, and the distance Dco between the objective lens and the coupling lens is Dco. Is the same as in Example 9. The optical path diagram is shown in FIG. 35, and the temperature characteristics are shown in FIG.
[0204]
In this example
Dco = 3
Mt · M · Fcp / F = −0.05512
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0205]
The wavefront aberration change due to the temperature change is 0.015λ when the temperature rises by 30 ° C. from the reference design temperature.
[0206]
Example 14
Coupling lens
[0207]
[Table 19]

[0208]
All optical system
[0209]
[Table 20]

[0210]
Example 14 is an example of a biconvex lens in which the coupling lens is made of resin and has a double-sided aspheric surface, and aberration diagrams thereof are shown in FIGS.
[0211]
Further, the entire optical system is a combination of this coupling lens and the resin objective lens of Example 1. The optical path diagram is shown in FIG. 38 and the temperature characteristics are shown in FIG.
[0212]
In this example
Dco = 3
Mt · M · Fcp / F = −0.06666
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0213]
The wavefront aberration change due to the temperature change is 0.008λ when the temperature rises by 30 ° C. from the reference design temperature, which is smaller than that of the ninth embodiment. In addition, the distance between object images is considerably shortened.
[0214]
Example 15
Coupling lens
[0215]
[Table 21]

[0216]
All optical system
[0217]
[Table 22]

[0218]
Example 15 is an example of a biconvex lens in which the coupling lens is made of resin and has a double-sided aspheric surface. The focal length is long at the same magnification Mc as in Example 14. The aberration diagrams are shown in FIGS. 42 (a) and 42 (b).
[0219]
Further, the entire optical system is a combination of this coupling lens and the resin objective lens of Example 1, and the magnifications M and Mt have the same specifications as in Example 14. The optical path diagram is shown in FIG. 41 and the temperature characteristics are shown in FIG.
[0220]
In this example
Dco = 10
Mt · M · Fcp / F = −0.07697
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0221]
The wavefront aberration change due to the temperature change is considerably small at 0.006λ when the temperature rises by 30 ° C. from the reference design temperature.
[0222]
Example 16
Coupling lens
[0223]
[Table 23]

[0224]
All optical system
[0225]
[Table 24]

[0226]
Example 16 is an example of a biconvex lens in which the coupling lens is made of resin and has a double-sided aspheric surface, and aberration diagrams thereof are shown in FIGS. 45 (a) and 45 (b).
[0227]
Further, the entire optical system is a combination of this coupling lens and the resin objective lens of Example 1. The optical path diagram is shown in FIG. 44 and the temperature characteristics are shown in FIG.
[0228]
In this example
Dco = 3
Mt · M · Fcp / F = −0.04783
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0229]
The change in wavefront aberration due to the temperature change is 0.016λ when the temperature rises by 30 ° C. from the reference design temperature.
[0230]
Example 17
Coupling lens
[0231]
[Table 25]

[0232]
All optical system
[0233]
[Table 26]

[0234]
Example 17 is an example of a biconvex lens in which the coupling lens is made of resin and has a double-sided aspheric surface, and aberration diagrams thereof are shown in FIGS.
[0235]
Further, the entire optical system is a combination of this coupling lens and the resin objective lens of Example 2. The optical path diagram is shown in FIG. 47 and the temperature characteristics are shown in FIG.
[0236]
In this example
Dco = 3
Mt · M · Fcp / F = −0.08767
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0237]
The change in wavefront aberration due to temperature change is 0.014λ when the temperature rises by 30 ° C. from the reference design temperature, which is slightly larger than that of the objective lens alone. This is because the power of the coupling lens is increased, and the change of the wavefront aberration of the coupling lens itself due to the temperature change cannot be ignored.
[0238]
Example 18
Coupling lens
[0239]
[Table 27]

[0240]
All optical system
[0241]
[Table 28]

[0242]
Example 18 is an example of a biconvex lens in which the coupling lens is made of resin and has a double-sided aspheric surface, and aberration diagrams thereof are shown in FIGS. 51 (a) and 51 (b).
[0243]
Further, the entire optical system is a combination of this coupling lens and the resin objective lens of Example 3. The optical path diagram is shown in FIG. 50, and the temperature characteristics are shown in FIG.
[0244]
In this example
Dco = 3
Mt · M · Fcp / F = −0.04776
It becomes. Here, since the resin coupling lens is a single lens, Fc = Fcp.
[0245]
The wavefront aberration change due to the temperature change is 0.017λ when the temperature rises by 30 ° C. from the reference design temperature.
[0246]
Although all the examples of the coupling lens 13 from Example 9 to Example 18 are made of resin, the same result can be obtained even in the case of glass except for the temperature characteristics of the optical system.
[0247]
Example 19
[0248]
[Table 29]

[0249]
In this example, only the objective lens is used, and the objective lens is made of resin, and both surfaces of the objective lens are aspherical surfaces, and the magnification of the objective lens alone is +1/30. The optical path diagram of this objective lens is shown in FIG. 53, the spherical aberration and sinusoidal aberration diagrams are shown in FIGS. 54 (a) and 54 (b), and the temperature characteristics are shown in FIG.
[0250]
In this example
x₂= −0.100731 Δ₂= 0.07064
And
x₂・ (N-1) / {F ・ (NA)²} =-0.0421
Δ₂・ (N-1)^Three/ {F ・ (NA)^Four} = 0.01910
It becomes.
[0251]
Although the change in wavefront aberration due to temperature change is larger than in other embodiments, it is smaller than that of an infinite objective lens having the same focal length.
[0252]
This embodiment is effective when the temperature characteristic is suppressed to some extent than the infinite optical system and the size in the direction perpendicular to the optical axis direction is to be reduced to some extent in the entire optical system.
[0253]
FIGS. 56 (a), 56 (b), FIG. 57, FIG. 58, and FIG. 59 for Examples 20 to 24 of the optical information recording / reproducing optical system for achieving the second object of the present invention. 60, 61 and 62 will be described.
[0254]
FIG. 56 is a diagram for explaining the basic configuration of an optical information recording / reproducing optical system using FIGS. 56 (a) and 56 (b) before describing the embodiment.
[0255]
In FIG. 56A, 13 is a coupling lens made of a single positive lens, 16 is an objective lens, 17 is a transparent substrate of the optical information recording medium, and 18 is an information recording surface of the optical information recording medium. The divergent light beam emitted from the light source 11 is converted into convergent light by the coupling lens 13 disposed close to the objective lens 16, then enters the objective lens 16, and is collected on the information recording surface 18 through the transparent substrate 17. Lighted.
[0256]
In FIG. 56 (b), the coupling lens 13 of FIG. 56 (a) is arranged away from the objective lens 16, and an optical element such as a mirror can be arranged between the coupling lens 13 and the objective lens 16. It is an example.
[0257]
FIG. 57 is a diagram for explaining a state where the light beam emitted from the objective lens 16 is condensed on the recording surface via the transparent substrate. 27 is a transparent substrate having a thickness of 0.6 mm, and 278 is a transparent substrate having a thickness of 0.6 mm. A recording surface of the optical information recording medium, 28 is a transparent substrate having a thickness of 1.2 mm, 288 is a recording surface of the optical information recording medium having a transparent substrate having a thickness of 1.2 mm, and is indicated by a solid line emitted from the objective lens 16. The light beam indicated by a broken line indicates a state where the light beam is condensed on the recording surface 278 of the optical information recording medium having the transparent substrate 27 having a thickness of 0.6 mm, and the optical information recording medium having the transparent substrate 28 having a thickness of 1.2 mm. The state where the light is condensed on the recording surface 288 is shown.
[0258]
Example 20
FIG. 58 shows a plurality of annular lens surfaces that are formed as concentric belts around the optical axis as an example of variable means according to the present invention and have different refractive powers of adjacent lens surfaces. The shape of the objective lens 16 when it is formed on the light source side surface of the objective lens 16 shown in FIG. 56 (b) and the light beam incident on the objective lens 16 are divided by the annular lens surface to be transparent with a thickness of 0.6 mm. A state of focusing on the recording surface 278 of the optical information recording medium having the substrate 27 (shown by a solid line) and a state of focusing on the recording surface 288 of the optical information recording medium having a transparent substrate 28 having a thickness of 1.2 mm (shown by a broken line). Description).
[0259]
Since the condensing positions in the two condensing states are separated in the optical axis direction in this way, when reproduction is performed in the condensing state of the objective lens corresponding to one transparent substrate thickness, the other transparent substrate The condensed light corresponding to the thickness is defocused on the recording surface, and the influence on the reproduction signal can be reduced.
[0260]
In the case of this example, the plurality of annular zone lens surfaces are the outermost first annular zone lens surface 31 (this lens surface is donut-like when viewed from the light source) and the first annular zone lens surface 31. A second annular lens surface 32 adjacent to the inner side of the lens (this lens surface is donut-shaped when viewed from the light source) and a third annular lens surface 33 adjacent to the inner side of the second annular lens surface 32. (This lens surface has a donut shape when viewed from the light source.) And a fourth annular lens surface 34 adjacent to the inside of the third annular lens surface 33 (this lens surface has a donut shape when viewed from the light source. ) And a fifth annular lens surface 35 located in the center of the objective lens adjacent to the inside of the fourth annular lens surface 34 (this annular lens surface is a lens surface including an optical axis, as viewed from the light source) The shape of the lens surface is a circle.) It is constituted by the annular lens surface.
[0261]
The light beam that has passed through the first annular lens surface 31, the third annular lens surface 33, and the fifth annular lens surface 35 located on the outermost periphery has a transparent substrate 27 with a thickness of 0.6 mm. Recording of an optical information recording medium having a transparent substrate 28 having a thickness of 1.2 mm, a light beam that is condensed on the recording surface 278 of the information recording medium and passes through the second annular lens surface 32 and the fourth annular lens surface 34 The light is condensed on the surface 288.
[0262]
This is because when collecting light through a transparent substrate having a thickness of 0.6 mm, it is necessary to obtain spots for high density, so the outermost ring-shaped lens surface (the first lens in this example is the first When a minute spot as an objective lens having a large NA is obtained using the annular lens surface 31) and condensed through a transparent substrate having a thickness of 1.2 mm, the outermost periphery is adjacent to the inner side of the annular lens surface. A minute spot as an objective lens having a small NA corresponding to the thickness of the substrate is obtained by using the annular lens surface (in this example, the second annular lens surface 32).
[0263]
In the case of this example, the first annular lens surface 31, the third annular lens surface 33, and the fifth wheel are used as the annular lens surfaces used to obtain spots for high density. Three ring-shaped lens surfaces of the band-shaped lens surface 35 are used. This is because, when a spot for corresponding to a high density is obtained with one ring-shaped lens surface located on the outermost periphery, side lobes are used. This is because the intensity of noise increases and causes an increase in noise, which may hinder good information recording and reproduction. In order to reduce the influence of such side lobes, a thickness of 0 is further provided adjacent to the inner side of the annular lens surface corresponding to the transparent substrate having a thickness of 1.2 mm adjacent to the inner side of the annular lens surface located on the outermost periphery. A third annular lens surface having a refractive power corresponding to a 6 mm transparent substrate and a fourth annular lens surface corresponding to a transparent substrate having a thickness of 1.2 mm on the inner side and a thickness of 0.6 mm on the inner side thereof. By forming a fifth annular lens surface having a refractive power corresponding to the transparent substrate, the area of the second annular lens surface that emits unnecessary light when the substrate thickness is 0.6 mm is reduced, and the side lobe is reduced. Can be reduced. Furthermore, by repeating this, that is, by forming a plurality of ring-shaped lens surfaces having different refractive powers provided on the lens surface from the outer periphery, two light beams suitable for recording / reproducing optical information recording media having different substrate thicknesses. A spot can be obtained.
[0264]
However, if the number of ring-shaped lens surfaces is excessively increased, the width of each ring-shaped lens surface located on the inner side of the ring-shaped lens surface located on the outermost circumference becomes too small, and the workability deteriorates. Is reduced to a level where there is no problem in practical use, and the workability is kept good, the number of ring-shaped lens surfaces is 3 or more and 10 or less including the ring-shaped lens surfaces located on the outermost periphery, and more preferably the upper limit. Is preferably 6 or less.
[0265]
In addition, when a plurality of annular lens surfaces corresponding to the same transparent substrate are provided, each of the plurality of annular lens surfaces is represented by an expression that represents each annular lens surface (for example, each annular lens surface is a non-uniform type lens). It is desirable that the lens thickness on the optical axis be equal when extended to the optical axis according to (expressed as a spherical equation).
[0266]
This is because when the lens thicknesses are not equal, an optical path length difference occurs in the light beams passing through the respective annular lens surfaces corresponding to the same transparent substrate, and wavefronts having optical path length differences overlap to generate interference. This is because the intensity of light obtained by the light flux passing through each annular lens surface may be reduced by interference.
[0267]
In such a case, a step 37 occurs between the adjacent annular lens surfaces, but at least one adjacent annular lens surface can be formed without a step (36). It is desirable for processing that the adjacent annular lens surfaces are formed without any step.
[0268]
When each annular lens surface corresponding to the same transparent substrate is extended to the optical axis, when the lens thickness on the optical axis is not equal, it is between the optical path difference length Δ and the wavelength λ. By configuring so that the relationship Δ = mλ (m is an integer) is satisfied, and m is an integer from −10 to 10, even if the wavelength λ of the light source slightly fluctuates, it is 50% or more of the original intensity. The strength can be maintained.
[0269]
In the example of FIG. 58, a plurality of annular lens surfaces that are formed in concentric belts around the optical axis and have different refractive powers of adjacent lens surfaces are provided on the light source side surface of the objective lens 16. In addition to this example, the plurality of annular lens surfaces, which are an example of the variable means according to the present invention, are formed on any one of the image side surface of the objective lens 16 and the coupling lens 13. You can also. It is also possible to provide a plurality of annular lens surfaces at any two or more of the lens surfaces constituting the objective lens 16 and the coupling lens 13.
[0270]
Example 21
FIG. 59 shows the shape of the objective lens 16 when a hologram as an example of the variable means according to the present invention is formed on the light source side surface of the objective lens 16 shown in FIGS. 56 (a) and 56 (b). In addition, the light beam incident on the objective lens 16 is divided into transmitted light 43 and diffracted light 44 transmitted through the hologram 41, and is condensed on the recording surface 278 of the optical information recording medium having the transparent substrate 27 having a thickness of 0.6 mm (see FIG. And a state of focusing on the recording surface 288 of the optical information recording medium having the transparent substrate 28 having a thickness of 1.2 mm (shown by a broken line).
[0271]
Since the condensing positions in the two condensing states are separated in the optical axis direction in this way, when reproduction is performed in the condensing state of the objective lens corresponding to one transparent substrate thickness, the other transparent substrate The condensed light corresponding to the thickness is defocused on the recording surface, and the influence on the reproduction signal can be reduced.
[0272]
In the case of this example, the NA necessary for focusing on the recording surface 288 of the optical information recording medium having the transparent substrate 28 having a thickness of 1.2 mm is obtained without forming the hologram near the end of the lens surface. A hologram is formed only on the lens surface portion, and the diffracted light by the hologram is configured to be condensed on the recording surface 288 of the optical information recording medium having the transparent substrate 28 having a thickness of 1.2 mm. The light beam that has passed through the lens surface 42 on which no light is formed is condensed on the recording surface 278 of the optical information recording medium having the transparent substrate 27 having a thickness of 0.6 mm.
[0273]
With such a configuration, it is necessary for recording and / or reproduction on the recording surface 278 of the optical information recording medium having the transparent substrate 27 having a thickness of 0.6 mm, which needs to obtain a beam spot for corresponding to high density. NA can be obtained, and a beam spot having a sufficient amount of light can be obtained.
[0274]
In the example of FIG. 59, a hologram is provided on the surface of the objective lens 16 on the light source side. However, the hologram is not limited to this example, and is an example of variable means according to the present invention. It can also be formed on any one of the image side surface and the coupling lens 13. It is also possible to provide holograms at any two or more positions on the lens surfaces constituting the objective lens 16 and the coupling lens 13.
[0275]
Example 22
FIG. 60 shows an example of a variable means according to the present invention, which is an optical element having a plurality of annular lens surfaces formed in concentric belts around the optical axis and having different refractive powers of adjacent lens surfaces. In the example shown between (a) and 56 (b) and disposed between the objective lens 16 and the coupling lens 13, a plane-parallel plate portion 51 which is a first annular lens surface formed in the peripheral portion of the optical element 50. The light beam that has passed through the objective lens 16 and is focused on the recording surface 278 of the optical information recording medium having the transparent substrate 27 having a thickness of 0.6 mm (shown by a solid line) and the central portion of the optical element 50 A state in which the light beam transmitted through the concave lens portion 52 which is the formed second annular lens surface is condensed on the recording surface 288 of the optical information recording medium having the transparent substrate 28 having a thickness of 1.2 mm (shown by a broken line) is shown. ing.
[0276]
Since the condensing positions in the two condensing states are separated in the optical axis direction in this way, when reproduction is performed in the condensing state of the objective lens corresponding to one transparent substrate thickness, the other transparent substrate The condensed light corresponding to the thickness is defocused on the recording surface, and the influence on the reproduction signal can be reduced.
[0277]
In this example as well, as shown in the example of FIG. 58, in order to reduce the influence of side lobes, a transparent film having a thickness of 1.2 mm adjacent to the inner side of the annular lens surface (in this case, a plane parallel plate) located at the outermost periphery. A third annular lens surface (in this case, a parallel flat plate) corresponding to a transparent substrate having a thickness of 0.6 mm is adjacent to the inner side of the annular lens surface corresponding to the substrate, and a transparent material having a thickness of 1.2 mm is provided on the inner side. By forming a fourth annular lens surface corresponding to the substrate and a fifth annular lens surface having a refractive power corresponding to the transparent substrate having a thickness of 0.6 mm (in this case, a plane parallel plate) on the inner side thereof, When the substrate thickness is 0.6 mm, the area of the second annular lens surface that emits unnecessary light can be reduced, and side lobes can be reduced. Furthermore, by repeating this, that is, by forming a plurality of ring-shaped lens surfaces having different refractive powers provided on the lens surface from the outer periphery, two light beams suitable for recording / reproducing optical information recording media having different substrate thicknesses. A spot can be obtained.
[0278]
The number of the annular lens surfaces is preferably 2 or more and 10 or less, more preferably 3 or more and 6 or less, including the annular lens surface located on the outermost periphery.
[0279]
In addition, when a plurality of annular lens surfaces corresponding to the same transparent substrate are provided, each of the plurality of annular lens surfaces is represented by an expression that represents each annular lens surface (for example, each annular lens surface is a non-uniform type lens). It is desirable that the lens thickness on the optical axis be equal when extended to the optical axis according to (expressed as a spherical equation).
[0280]
Example 23
In addition, the hologram element as an example of the variable means according to the present invention includes the optical element 50 shown in FIG. 60 as a parallel plane plate, and corresponds to the concave lens portion 52 on the light source side or the image side instead of the concave lens portion 52. It can be configured by forming a hologram in the part, in which case, the diffracted light by the hologram is configured to be condensed on the recording surface 288 of the optical information recording medium having the transparent substrate 28 having a thickness of 1.2 mm, The light beam transmitted through the hologram 41 and the light beam transmitted through the lens surface 42 where no hologram is formed are condensed on the recording surface 278 of the optical information recording medium having the transparent substrate 27 having a thickness of 0.6 mm.
[0281]
Also in this case, since the condensing positions in the two condensing states are separated in the optical axis direction, when reproduction is performed in the condensing state of the objective lens corresponding to one transparent substrate thickness, another transparent substrate is used. The condensed light corresponding to the thickness is defocused on the recording surface, and the influence on the reproduction signal can be reduced.
[0282]
Example 24
61 and 62 show the recording surface 278 of the optical information recording medium having the transparent substrate 27 having a thickness of 0.6 mm by moving the coupling lens 13 in FIGS. 56 (a) and 56 (b) in the optical axis direction. FIG. 61 shows a configuration of an optical information pickup apparatus for switching optical information between a condensed state (FIG. 61) and a condensed state (FIG. 62) on a recording surface 288 of an optical information recording medium having a transparent substrate 28 having a thickness of 1.2 mm. Yes.
[0283]
In FIG. 61, 11 is a light source such as a semiconductor laser, 12 is a beam splitter, 13 is a coupling lens, 14 is a second diaphragm, 15 is a first diaphragm, 16 is an objective lens, and 17 is transparent with a thickness of 0.6 mm. Substrate, 18 is an information recording surface of an optical information recording medium having a transparent substrate having a thickness of 0.6 mm, 19 is a photodetector, 20 is a frame for holding the coupling lens 13, and 21 is for moving the frame 20 in the optical axis direction. A lens moving means 22 is a diaphragm means for inserting the second diaphragm 14 into the optical path.
[0284]
A light beam emitted from a light source 11 such as a semiconductor laser enters a coupling lens 13 through a beam splitter 12, becomes a convergent light beam, is limited to a predetermined light beam by a diaphragm 15, and enters an objective lens 16. When the convergent light beam is incident, the objective lens 16 forms an almost aberration-free light spot on the information recording surface 18 through the transparent substrate 17 having a predetermined thickness.
[0285]
The light beam modulated and reflected by the information pits on the information recording surface 18 returns to the beam splitter 12 via the objective lens 16 and the coupling lens 13, where it is separated from the optical path of the laser light source 11 and then to the photodetector 19. Incident. This photodetector 19 is a multi-divided PIN photodiode that outputs a current proportional to the temperature of the incident light beam from each element and sends this current to a detection circuit not shown in the figure. Based on the error signal and the track error signal, the objective lens 16 is controlled by a two-dimensional actuator including a magnetic circuit and a coil, and the light spot position is always aligned on the information track.
[0286]
In FIG. 62, the coupling lens 13 is moved to a position where recording or reproduction of a transparent substrate having a thickness of 1.2 mm, which is away from the objective lens 16 by the lens moving means 21, and the second diaphragm 14 is moved by the diaphragm means. It is the figure inserted in.
[0287]
If the coupling lens is configured to move in the direction of the optical axis as in this example, recording and / or recording on all optical information recording media having a transparent substrate with a thickness of 0.6 mm to 1.2 mm is possible. Playback can be performed. In this example, the coupling lens is moved in the optical axis direction. However, the coupling lens is moved to the optical axis direction at a fixed position, or both the coupling lens and the light source are illuminated. You may make it move to an axial direction. In addition, the coupling lens may be fixed, and two light sources having different optical distances from the coupling lens may be used, and the two light sources may be selectively switched.
[0288]
In the example of FIG. 62, the light beam emitted from the coupling lens 13 is converged light. However, in the case of an optical information medium having a transparent substrate having a thickness of 1.2 mm, divergent light or parallel light is used as the objective lens 16. In the case of an optical information recording medium having a transparent substrate with a thickness of 1.2 mm, divergent light or parallel light may be incident on the objective lens 16 when information can be reproduced by being incident on the objective lens 16. good. However, it goes without saying that convergent light is more desirable.
[0289]
【The invention's effect】
According to the present invention, as seen in each example, even when a resin objective lens is used under a high NA, the change in wavefront aberration due to a temperature change is suppressed to such an extent that a lens tolerance can be secured. An optical system was obtained.
[0290]
In addition, it has become clear that it is possible to shorten the wavelength of the light used up to a wavelength of 450 nm and to increase the NA of the lens up to about NA 0.75, even in anticipation of higher recording density in the future. .
[0291]
Furthermore, according to the present invention, it is possible to record / reproduce optical disks having different substrate thicknesses with a single optical pickup device, to be compatible with each other, and to use a resin objective lens with a large NA. Even if the optical information recording / reproducing optical system of the optical information medium and the optical information recording / reproducing objective lens have a simple structure and a compact structure that suppresses the change of the wavefront aberration due to the temperature change to such an extent that the tolerance of the lens can be secured Obtained.
[Brief description of the drawings]
FIG. 1 is an optical path diagram of Example 1 of an objective lens in a recording / reproducing optical system of an optical information recording medium of the present invention.
FIG. 2 is a diagram illustrating spherical aberration and sine condition aberrations of the objective lens according to Example 1 described above.
FIG. 3 is a temperature characteristic diagram of the objective lens of Example 1 described above.
FIG. 4 is an optical path diagram of Example 2 of an objective lens in the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 5 is a diagram illustrating spherical aberration and sine condition aberrations of the objective lens according to Example 2 described above.
6 is a temperature characteristic diagram of the objective lens of Example 2. FIG.
FIG. 7 is an optical path diagram of an objective lens of Example 3 in the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 8 is a diagram illustrating spherical aberration and sine aberration of the objective lens according to Example 3 described above.
FIG. 9 is a temperature characteristic diagram of the objective lens of Example 3 described above.
FIG. 10 is an optical path diagram of an objective lens of Example 4 in the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 11 is a diagram illustrating spherical aberration and sine condition aberrations of the objective lens according to Example 4 described above.
12 is a temperature characteristic diagram of the objective lens of Example 4. FIG.
FIG. 13 is an optical path diagram of Example 5 of an objective lens in the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 14 is a diagram illustrating spherical aberration and sine aberration of the objective lens according to Example 5 described above.
15 is a temperature characteristic diagram of the objective lens according to Example 5. FIG.
FIG. 16 is an optical path diagram of Example 6 of the recording / reproducing optical system of the optical information recording medium of the present invention.
17 is a temperature characteristic diagram of the optical system of Example 6. FIG.
FIG. 18 is an optical path diagram of Example 7 of the recording / reproducing optical system of the optical information recording medium of the present invention.
19 is a temperature characteristic diagram of the optical system of Example 7. FIG.
20 is an optical path diagram of an objective lens in Example 8 of the optical system for recording / reproducing optical information recording media according to the present invention. FIG.
FIG. 21 is a diagram illustrating spherical aberration and sine condition of the objective lens according to Example 8 described above.
FIG. 22 is a temperature characteristic diagram of the objective lens according to Example 8 described above.
FIG. 23 is an optical path diagram of Example 9 in the recording / reproducing optical system of the optical information recording medium of the present invention.
24 is a diagram illustrating spherical aberration and sine aberration of the coupling lens of Example 9. FIG.
25 is a temperature characteristic diagram of the optical system of Example 9. FIG.
FIG. 26 is an optical path diagram of Example 10 in the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 27 is a diagram illustrating spherical aberration and sine condition of the coupling lens of Example 10 described above.
28 is a temperature characteristic diagram of the optical system of Example 10. FIG.
FIG. 29 is an optical path diagram of Example 11 in the recording / reproducing optical system of the optical information recording medium of the present invention.
30 is a diagram illustrating spherical aberration and sine condition aberration of the coupling lens of Example 11. FIG.
31 is a temperature characteristic diagram of the optical system according to Example 11; FIG.
FIG. 32 is an optical path diagram of Example 12 in the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 33 is a diagram illustrating spherical aberration and sine condition of the coupling lens of Example 12 described above.
34 is a temperature characteristic diagram of the optical system of Example 12. FIG.
FIG. 35 is an optical path diagram of Example 13 in the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 36 is a diagram illustrating spherical aberration and sine condition of the coupling lens of Example 13;
FIG. 37 is a temperature characteristic diagram of the optical system of Example 13.
FIG. 38 is an optical path diagram of Example 14 of the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 39 is a diagram illustrating spherical aberration and sine condition of the coupling lens of Example 14;
40 is a temperature characteristic diagram of the optical system of Example 14. FIG.
FIG. 41 is an optical path diagram of Example 15 of the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 42 is a diagram illustrating spherical aberration and sine condition of the coupling lens of Example 15 above.
43 is a temperature characteristic diagram of the optical system of Example 15. FIG.
FIG. 44 is an optical path diagram of Example 16 in the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 45 is a diagram illustrating spherical aberration and sine condition of the coupling lens of Example 16;
46 is a temperature characteristic diagram of the optical system of Example 16. FIG.
FIG. 47 is an optical path diagram of Example 17 of the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 48 is a diagram illustrating spherical aberration and sine condition of the coupling lens of Example 17 described above.
49 is a temperature characteristic diagram of the optical system of Example 17. FIG.
50 is an optical path diagram of Example 18 in the recording / reproducing optical system of the optical information recording medium of the present invention. FIG.
51 is a spherical aberration diagram of the coupling lens of Example 18 and aberration diagrams under a sine condition. FIG.
52 is a temperature characteristic diagram of the optical system according to Example 18; FIG.
FIG. 53 is an optical path diagram of Example 19 of the recording / reproducing optical system of the optical information recording medium of the present invention.
FIG. 54 shows aberration diagrams of the spherical aberration and sine condition of the objective lens of Example 19 described above.
FIG. 55 shows the temperature characteristic of the objective lens of Example 19 described above.
FIG. 56 is a basic configuration diagram of an optical information recording / reproducing optical system according to the present invention.
FIG. 57 is a diagram showing a condensing state of a light beam emitted from an objective lens.
FIG. 58 is a diagram showing an example of an objective lens according to the present invention.
FIG. 59 is a diagram showing an example of an objective lens according to the present invention.
FIG. 60 is a diagram showing an example using the optical element of the present invention.
FIG. 61 is an explanatory diagram of an optical pickup device for optical information according to the present invention.
FIG. 62 is an explanatory diagram of an optical pickup device for optical information according to the present invention.
FIG. 63 is an explanatory diagram of a conventional example.
FIG. 64 is a diagram showing a change in wavefront aberration of the objective lens.
[Explanation of symbols]
11 Laser light source
12 Beam splitter
13 Coupling lens
15 Aperture (first aperture)
16 Objective lens
17 Transparent substrate
18 Information recording surface
19 Photodetector

Claims (24)

In an optical pickup device for recording and / or reproducing information on an optical information recording medium,
A light source;
A condensing optical system for condensing the light beam emitted from the light source onto the recording surface of an optical information recording medium having a transparent substrate via the transparent substrate;
A photodetector for receiving the light beam reflected by the recording surface of the optical information recording medium,
The condensing optical system is
A coupling lens having at least one aspherical surface for converting divergent light from the light source into convergent light;
An objective lens that is movable at least in the optical axis direction, further converges the convergent light and forms an image on the information recording surface of the optical information recording medium,
When the wavefront aberration within the Marechal limit is minimized, the lateral magnification of the objective lens alone is M , the distance between the image side surface of the coupling lens and the light source side surface of the objective lens is Dco, and the objective lens An optical pickup device satisfying the following conditions , where F is the focal length :
0 <M <1
0.1 ≦ Dco / F ≦ 5.0 The optical pickup device according to claim 1, wherein the following condition is satisfied.
1.0 ≦ Dco / F ≦ 5.0 The optical pickup device according to claim 2, wherein the following condition is satisfied.
1.0 ≦ Dco / F ≦ 3.0 In an optical pickup device for recording and / or reproducing information on an optical information recording medium,
A light source;
A condensing optical system for condensing the light beam emitted from the light source onto the recording surface of an optical information recording medium having a transparent substrate via the transparent substrate;
A photodetector for receiving the light beam reflected by the recording surface of the optical information recording medium,
The condensing optical system is
A coupling lens having at least one aspherical surface for converting divergent light from the light source into convergent light;
An objective lens that is movable at least in the optical axis direction, further converges the convergent light and forms an image on the information recording surface of the optical information recording medium,
An optical pickup device satisfying the following condition , where M is the lateral magnification of the objective lens alone and F is the focal length of the objective lens when the wavefront aberration within the Marechal limit is minimum .
0 <M <1
(1-M) · F ≦ 6.0mm Wherein is made objective lens is a resin, and the coupling lens is also at least one optical pickup according to claim 1, any one of 4, which is a resin lens having a positive refractive power Equipment . The optical pickup device according to any one of claims 1 to 5, characterized in that the coupling lens is a plastic single lens. In an optical pickup device for recording and / or reproducing information on an optical information recording medium,
A light source;
A condensing optical system for condensing the light beam emitted from the light source onto the recording surface of an optical information recording medium having a transparent substrate via the transparent substrate;
A photodetector for receiving the light beam reflected by the recording surface of the optical information recording medium,
The condensing optical system is
And at least one surface for converting diverging light from the light source into convergent light is an aspherical surface, and at least one coupling lens is a resin lens having a positive refractive power;
An objective lens that is movable in at least the optical axis direction and is a resin lens for further focusing the convergent light and forming an image on the information recording surface of the optical information recording medium,
When the wavefront aberration within the Marechal limit is minimum, the lateral magnification of the objective lens alone is M, the lateral magnification of the whole condensing optical system is Mt, the focal length of the resin lens in the coupling lens is Fcp, An optical pickup device satisfying the following condition , where F is the focal length of the objective lens .
0 <M <1
−0.10 ≦ Mt · M · Fcp / F ≦ −0.04 In an optical pickup device for recording and / or reproducing information on an optical information recording medium,
A light source;
A condensing optical system for condensing the light beam emitted from the light source onto the recording surface of an optical information recording medium having a transparent substrate via the transparent substrate;
A photodetector for receiving the light beam reflected by the recording surface of the optical information recording medium,
The condensing optical system is
A coupling lens which is a single lens made of a resin having at least one aspherical surface for converting divergent light from the light source into convergent light;
  An objective lens that is movable at least in the optical axis direction, further converges the convergent light and forms an image on the information recording surface of the optical information recording medium,
  When the wavefront aberration within the Marechal limit is minimized, the lateral magnification of the objective lens alone is M, the lateral magnification of the entire focusing optical system is Mt, the focal length of the resin lens in the coupling lens is Fcp, An optical pickup device satisfying the following condition, where F is the focal length of the objective lens.
0 <M <1
−0.10 ≦ Mt · M · Fcp / F ≦ −0.04 In an optical pickup device for recording and / or reproducing information on an optical information recording medium,
A light source;
A condensing optical system for condensing the light beam emitted from the light source onto the recording surface of an optical information recording medium having a transparent substrate via the transparent substrate;
A photodetector for receiving the light beam reflected by the recording surface of the optical information recording medium,
The condensing optical system is
A coupling lens having at least one aspherical surface for converting divergent light from the light source into convergent light;
An objective lens that is movable at least in the optical axis direction, further converges the convergent light and forms an image on the information recording surface of the optical information recording medium,
The lateral magnification of the objective lens only in the case where the wavefront aberration in Marechal within the limits is minimized M, Mt lateral magnification of the entire condensing optical system, the numerical aperture on the image side of the objective lens when the NA, the following An optical pickup device satisfying the following conditions:
0 <M <1
0.06 ≦ | Mt | · NA ≦ 0.21 The optical pickup device according to claim 9 , wherein the following condition is satisfied.
0.06 ≦ | Mt | · NA ≦ 0.12 The optical pickup device according to claim 9 , wherein the following condition is satisfied.
0.12 ≦ | Mt | · NA ≦ 0.21 The optical pickup device according to any one of claims 1 to 11, the optical pickup device characterized by lateral magnification M of a single said objective lens within the following range.
0.05 ≦ M <1 The optical pickup device according to any one of claims 1 to 12, characterized in that the following condition is satisfied.
0.48 ≦ NA
However,
NA: Numerical aperture on the image side of the objective lens The optical pickup device according to claim 13 , wherein the following condition is satisfied.
0.05 ≦ M ≦ 0.23
NA · (1-M) ≦ 0.65 The optical pickup device according to claim 14 , wherein the following condition is satisfied.
0.05 ≦ M ≦ 0.125 The optical pickup device according to claim 13 , wherein the objective lens is made of resin and satisfies the following conditions.
NA · (1-M) ≦ 0.65 The optical pickup device according to claim 16 , wherein the following condition is satisfied.
0.65 ≦ NA ≦ 0.8
0.125 ≦ M ≦ 0.23 18. The optical pickup device according to claim 1 , further comprising variable means for varying a convergence state of the convergent light by the objective lens according to a thickness of a transparent substrate of the optical information recording medium. An optical pickup device characterized by that. 19. The optical pickup device according to claim 18 , wherein the variable means is a hologram formed on at least one surface of the coupling lens or the objective lens. 19. The optical pickup device according to claim 18 , wherein the variable means is means for moving the coupling lens on the optical axis in accordance with the thickness of the transparent substrate of the optical information recording medium. 19. The optical pickup device according to claim 18 , wherein the variable means is means for switching a plurality of light sources in accordance with a thickness of a transparent substrate of the optical information recording medium. The optical pickup device according to any one of claims 1 to 21 , wherein the following condition is satisfied.
−0.25 ≦ F · (n−1) / r ₂ ≦ 0.7
However,
n: refractive index of the material forming the objective lens F: focal length of the objective lens r _2: curvature at the vertex of the image side surface of the objective lens radius The optical pickup device according to any one of claims 1 to 22 , wherein the following condition is satisfied.
−0.045 ≦ x ₂ · (n−1) / {F · (NA) ² } ≦ 0.1
However,
n: Refractive index of the material forming the objective lens
F: Focal length of the objective lens NA: Numerical aperture x ₂ on the image side of the objective lens : Nearest effective diameter of the axial ray on the image side surface of the objective lens (on the image side surface on which the peripheral ray of NA is incident) ) And the apex of the surface, the direction of displacement toward the image side as the distance from the optical axis is positive. The optical pickup device according to any one of claims 1 to 23 , wherein the following condition is satisfied.
−0.005 ≦ Δ ₂ · (n−1) ³ / {F · (NA) ⁴ } ≦ 0.018
However,
n: Refractive index of the material forming the objective lens
F: Focal length of objective lens
NA: numerical aperture Δ ₂ on the image side of the objective lens : an aspherical surface at the outermost periphery of the effective diameter of the axial ray on the image side surface of the objective lens (the position on the image side surface where the peripheral ray of NA is incident) the difference in the optical axis direction between the reference spherical surface having a radius of curvature at the top r ₂ of said surface, and a direction displaced toward the image side farther from the optical axis and the positive

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