JP2005050504A - Optical pickup lens device and optical information recording and reproducing device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein a spot at a focus is deviated in the track direction of an information recording medium, and tracking cannot be performed when a quick light source wavelength change occurs, while an objective lens is shifted in the track direction of the information recording medium for tracking. <P>SOLUTION: By appropriately distributing the amount of color aberration correction of a collimating means and the amount of color aberration correction of an aberration correcting element, the amount of angular change in the emitted light beams of the collimating means with respect to the light wavelength change from the light source and the amount of angular change of the emitted light beams of the aberration correcting element are suppressed and thus, stable tracking is conducted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical pickup lens device, and more specifically, optical information capable of high-density recording such as a DVD (Digital Versatile Disk) device using a light beam with a wavelength of 390 to 420 nm, an optical recording device for a computer, and the like. The present invention relates to a lens device for an optical pickup applied to a recording device. The present invention also relates to an optical information recording / reproducing apparatus including the optical pickup lens device.

  Conventionally, lens devices for optical pickups have been used with a light source wavelength of 650 nm or more and an objective lens element having a numerical aperture of about NA = 0.6, so the amount of spot shift due to axial chromatic aberration or lateral chromatic aberration is a problem. It was a grade that did not become.

  However, in recent years, with the increase in capacity of information recording media, the shortening of the wavelength of light sources and the increase in NA (numerical aperture) of optical information recording apparatuses have been progressing. In such a short wavelength region, since the dispersion of the optical material such as the lens element is very large, the refractive index of the optical material greatly changes due to a slight change in the wavelength of the light beam. Therefore, in recent optical pickup lens devices, it is necessary to consider correction of chromatic aberration.

  In particular, optical information recording devices such as DVD ± RW that are currently popular in DVD recorders and the like record and erase information by using phase change of the medium. The optical power for reading the written information is different. For this reason, in an optical information recording apparatus using a phase transition type medium, it is inevitable in principle that the wavelength of the light beam emitted from the light source changes greatly when switching between recording or erasing and reproduction.

  Therefore, in an optical information recording apparatus using a phase transition type medium, correction of chromatic aberration of an optical pickup lens apparatus is an important issue. This is because, in an optical pickup device using a phase transition type medium, if the chromatic aberration of the lens device is not corrected, there is a possibility that the focus control may not be performed due to a sudden change in focal position due to a change in the wavelength emitted by the light source. .

Conventionally, in order to suppress these chromatic aberrations, as described in Patent Documents 1 to 3, a technique for providing an objective lens element with a chromatic aberration correction function, and a chromatic aberration correction for a collimator lens disposed between the light source and the objective lens element. A technique for providing a function, a technique for canceling the chromatic aberration of the objective lens element by inserting a chromatic aberration correction element in the optical path and overcorrecting the chromatic aberration have been proposed.
Japanese Unexamined Patent Publication No. 64-19316 JP 7-294707 A Japanese Patent Laid-Open No. 11-337818

  However, each conventional configuration for realizing chromatic aberration correction is insufficient in an optical pickup lens device for an information recording medium for high-density recording with a very small spot diameter and a very narrow track width.

  An object of the present invention is to provide an optical pickup lens device capable of stable tracking while having a large chromatic aberration correction function, and an optical information recording / reproducing device using the same.

One of the above objects is achieved by the following optical pickup lens device. Used in an optical pickup device that performs at least one of reading, writing, and erasing information by condensing a light beam having a wavelength range of 390 nm to 420 nm emitted from a light source onto an information recording medium to form a spot. A lens device for optical pickup, which is held in order from the light source side so as to be movable along the direction of the optical axis of the light beam emitted from the light source, and converts the light beam into parallel light or predetermined convergent or divergent light Means, an aberration correction element that transmits the light beam emitted from the collimating means, and an objective that has a numerical aperture of 0.8 or more and focuses the light beam emitted from the aberration correction element on the information recording medium to form a spot. A lens element, and the aberration correction element and the objective lens element are integrally held in a direction perpendicular to the optical axis in order to track the information recording medium. And which satisfies the following conditions.
−0.1 ≦ CAt ≦ 0.1 (1)
−20 ≦ CAf ≦ 20 (2)
−20 ≦ CAm ≦ 0 (3)
−0.25 ≦ θf ≦ 0.25 (4)
−0.75 ≦ θm ≦ 0.75 (5)
However,
CAt: axial chromatic aberration of all optical systems [μm / nm]
CAf: axial chromatic aberration of collimating means [μm / nm]
CAm: On-axis chromatic aberration [μm / nm] of the aberration correction element
θf: Amount of change in angle per unit wavelength of light beam emitted from collimator means [min / nm]
θm: Amount of change in angle per unit wavelength of outgoing light flux of aberration correction element [min / nm]
It is.

  Preferably, the aberration correction element is a diffractive lens having a power for deflecting a light beam by diffraction. Preferably, the aberration correction element has a phase step surface including a plurality of annular zones defined by concentric circles centered on the optical axis and a phase step formed at a boundary between the regions.

One of the above objects is achieved by the following optical pickup device. An optical pickup device that performs at least one of reading, writing, and erasing information by condensing a light beam on an information recording medium to form a spot, and radiates a light beam in a wavelength range of 390 nm to 420 nm A collimator that converts the luminous flux into parallel light or a predetermined convergent or divergent light, and a luminous flux emitted from the collimating means, which is held movably along the direction of the optical axis of the luminous flux emitted from the light source. An aberration correction element that transmits the light, and an objective lens element that has a numerical aperture of 0.8 or more and focuses a light beam emitted from the aberration correction element on an information recording medium to form a spot. The lens element is integrally held in a direction perpendicular to the optical axis in order to track the information recording medium, and satisfies the following conditions.
−0.1 ≦ CAt ≦ 0.1 (1)
−20 ≦ CAf ≦ 20 (2)
−20 ≦ CAm ≦ 0 (3)
−0.25 ≦ θf ≦ 0.25 (4)
−0.75 ≦ θm ≦ 0.75 (5)
However,
CAt: axial chromatic aberration of all optical systems [μm / nm]
CAf: axial chromatic aberration of collimating means [μm / nm]
CAm: On-axis chromatic aberration [μm / nm] of the aberration correction element
θf: Amount of change in angle per unit wavelength of light beam emitted from collimator means [min / nm]
θm: Amount of change in angle per unit wavelength of the emitted light beam of the aberration correction element [min / nm]
It is.

  According to the present invention, it is possible to provide an optical pickup lens device capable of stable tracking while having a large chromatic aberration correction function, and an optical information recording / reproducing device using the same.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of an optical pickup lens device according to Embodiment 1 of the present invention. The optical pickup lens device according to Embodiment 1 includes a light source 1, a collimating lens 3 (collimating means), a diffraction lens 4 (aberration correction element), an objective lens 5, and an actuator 7. The light source 1 is composed of a semiconductor laser and emits a light beam 2 having a wavelength in the range of 390 nm to 420 n.

  In FIG. 1, a light beam 2 emitted from a light source 1 made of a semiconductor laser becomes substantially parallel light by a collimating lens 3. Then, the light passes through the diffraction lens 4 and is condensed on the information recording medium 6 by the objective lens 5.

  Here, the diffractive lens 4 is attached to the actuator 7 together with the objective lens 5 in a state where the optical axes thereof are substantially coincident with each other, and can be moved as indicated by arrows A and -A in a direction perpendicular to the optical axis direction. Even when the wavelength changes and the light beam diverges and converges, the deviation of the spot in the track direction is corrected, that is, tracking is performed.

  The collimating lens 3 is formed of an achromatic cemented lens and is movable as indicated by an arrow B in the optical axis direction so that spherical aberration generated in the optical system can be corrected. Thereby, the angle of the light beam incident on the objective lens 5 can be changed, and the spherical aberration caused by the difference in the thickness of the information recording medium 6 or each optical element constituting the optical system can be canceled.

The optical pickup lens device according to Embodiment 1 satisfies the following conditions.
−0.1 ≦ CAt ≦ 0.1 (1)
−20 ≦ CAf ≦ 20 (2)
−20 ≦ CAm ≦ 0 (3)
−0.25 ≦ θf ≦ 0.25 (4)
−0.75 ≦ θm ≦ 0.75 (5)
However,
CAt: axial chromatic aberration of all optical systems [μm / nm]
CAf: axial chromatic aberration of collimating means [μm / nm]
CAm: On-axis chromatic aberration [μm / nm] of the aberration correction element
θf: Amount of change in angle per unit wavelength of light beam emitted from collimator means [min / nm]
θm: Amount of change in angle per unit wavelength of the emitted light beam of the aberration correction element [min / nm]
It is.

  When CAt, which is the longitudinal chromatic aberration of the entire optical system, is smaller than −0.1 [μm / nm] or larger than 0.1 [μm / nm], it is stable because the amount of spot movement in the optical axis direction due to wavelength variation is large. It is difficult to perform recording / reproduction, which is not preferable.

  Further, when the axial chromatic aberration CAf of the collimating means is smaller than −20 [μm / nm], when the axial chromatic aberration CAm of the aberration correcting element is 0, the spot deviation amount exceeds 10 nm, which is not preferable. When the axial chromatic aberration CAf of the collimating means is larger than 20 [μm / nm], it is difficult to satisfy the condition (1) with the aberration correcting element, which is not preferable.

  Further, when the longitudinal chromatic aberration CAm of the aberration correction element is smaller than −20 [μm / nm], it is not preferable because the above equation (1) cannot be satisfied even if the collimating means is in a state of insufficient chromatic aberration. If the axial chromatic aberration CAm of the aberration correction element is larger than 0, it is not preferable because the chromatic aberration of the objective lens element cannot be corrected.

  Further, when the angle change amount θf per unit wavelength of the emitted light beam of the collimator means is smaller than −0.25 [min / nm] or larger than 0.25 [min / nm], the chromatic aberration of the aberration correcting element is 0. Even so, the amount of spot deviation exceeds 10 nm, which is not preferable.

  Further, when the angle change amount θm per unit wavelength of the emitted light beam of the aberration correction element is smaller than −0.75 [min / nm] or larger than 0.75 [min / nm], the magnification of the optical system, Since the numerical aperture NA of the objective lens element changes greatly, it is not preferable in terms of the configuration of the optical pickup device.

  FIG. 6 is a schematic configuration diagram of an optical pickup device to which the optical pickup lens device according to the first embodiment of the present invention is applied. In FIG. 6, the same components as those in FIG. 1 are denoted by the same reference numerals. In FIG. 6, a light beam emitted from a light source 1 made of a semiconductor laser passes through a beam splitter 8 and becomes substantially parallel light by a collimating lens 3 made of a collimating lens. Then, the light passes through the diffractive lens 4, which is a diffractive lens, and is focused on the information recording surface 6 a of the information recording medium 6 by the objective lens 5. The focused spot focused on the information recording surface 6a is reflected by pits having different reflectivities formed on the information recording surface 6a, and the reflected laser light passes through the objective lens 5, the diffraction lens 4, and the collimating lens 3. Then, the light is reflected by the beam splitter 8, refracted by the detection lens 9, and condensed on the light receiving element 10. A change in the amount of light modulated by the information recording surface 6a is detected by an electric signal from the light receiving element 10, and data recorded on the information recording medium 6 is read.

  Here, both the diffractive lens 4 and the objective lens 5 are attached to the actuator 7 and can move in the directions of arrows A and -A, that is, in the direction orthogonal to the optical axis direction, and the collimating lens 3 is indicated by the arrow B. Thus, it is configured to be movable in the optical axis direction.

  In the first embodiment, the collimating lens is a laminated lens. However, the collimating lens may be a diffractive lens having a color correction function or a single lens having no color correction function. In addition, although the aberration correction element is a diffractive lens, it may be a cemented lens having a chromatic aberration correction function. However, since the diffractive lens can be molded from resin, it is light in weight, and is advantageous for being attached to the actuator and moved together with the objective lens.

   In addition, although the aberration correction element, that is, the diffractive lens and the objective lens are configured separately, an integral type having a diffractive structure on at least one surface of the objective lens may be used.

  As described above, according to the optical pickup lens device according to the first embodiment, the objective lens is separated from the optical axis for tracking by appropriately allocating the chromatic aberration correction amounts of the collimator means and the aberration correction element. Even when the wavelength of the light source changes abruptly during shifting, it is possible to minimize spot deviation not only in the axial direction but also in the disk track direction. Therefore, the optical pickup lens device according to Embodiment 1 can suppress the risk of off-track. That is, the optical pickup lens device according to Embodiment 1 corrects a large axial chromatic aberration generated in the objective lens due to a short wavelength region and a high numerical aperture NA, and suppresses a spot deviation amount that is a chromatic aberration of magnification. be able to.

(Embodiment 2)
Hereinafter, the optical pickup lens device according to the second embodiment will be described. Since the optical pickup device according to the second embodiment has the same schematic configuration as that of the optical pickup device according to the first embodiment, only different parts will be described.

  When a diffractive lens is used as an aberration correction element, the number of annular zones required to obtain a sufficient chromatic aberration correction effect increases when used for a light beam having a wavelength in a short wavelength region such as a reference wavelength of 420 nm or less. The interval between the annular zones is reduced. This is because the amount of chromatic aberration to be corrected increases as the wavelength dependence of the refractive index of the lens material increases in the short wavelength region.

  In a diffractive lens, when the number of annular zones increases and the interval between the annular zones decreases, manufacturing becomes very difficult. First, when the number of annular zones increases and the interval between the annular zones decreases, it is difficult to process an injection mold corresponding to such a fine shape. Even if the mold can be processed, it is difficult to sufficiently transfer the fine mold shape due to the viscosity of the resin.

  Therefore, the lens device for an optical pickup according to the second embodiment forms a phase step in addition to the correction of the aberration due to the diffracted light of the diffractive lens, and also performs the correction of the aberration due to the phase step.

  FIG. 7 is a schematic configuration diagram illustrating a lens device used in the optical pickup device according to the second embodiment. The aberration correction element 22 is a lens that includes a diffraction surface S1 and a phase step surface S3 in this order from the light source side, and is made of resin. The objective lens 23 includes a light source side refractive surface S4 and an information recording medium side refractive surface S5.

  The diffractive surface S1 functions as a positive power optical surface that generates and converges diffracted light from incident light incident on the surface. The diffraction surface S1 has a diffraction efficiency set so that the light amount of the + 1st order diffracted light is maximized. Further, the phase step surface S3 functions as an optical surface having a negative power with respect to the diffracted light, and has a power whose absolute value is equal to the positive power of the diffraction surface S1. As a result, the aberration correction element 22 is non-powered with respect to the reference wavelength light beam, and emits the parallel light beam when the parallel light beam is incident.

  FIG. 8 is a schematic diagram illustrating the structure of the phase step surface of the aberration correction element of the lens device used in the optical pickup device according to the second embodiment. The phase step surface S3 includes a plurality of annular zones defined by concentric circles with the optical axis of the light beam as the center, and phase steps formed at boundaries between the regions. In FIG. 8, the center including the optical axis is defined as region 1, and the radius of region 1 is defined as H1. Hereinafter, the ring-shaped regions formed from the optical axis toward the periphery are referred to as region 2, region 3... Region n in order from the optical axis side. The outer diameter of the region 2 is H2, the outer diameter of the region 3 is H3, and the outer diameter of the region n is Hn. Further, the size of the step between the region 1 and the region 2 along the optical axis is A1, and the size of the step between the region 2 and the region 3 along the optical axis is A2. Let An be the size in the direction along the optical axis of the step between the region n-1 and the region n.

The aberration correction element 22 used in the lens device according to Embodiment 2 has five annular regions. The boundary portion between the regions is configured such that the size in the direction along the optical axis is increased by an integral multiple of λ ₀ / (n ₀ −1) (here, q). Here, λ ₀ is a reference wavelength of the semiconductor laser 26 incident on the lens device, and n ₀ is a refractive index of the resin material of the aberration correction element 22 with respect to light having the wavelength λ ₀ .

  The value of q is equal to the phase of 2π radians of the reference wavelength of the semiconductor laser 26. As a result, the phase difference between two different light beams that pass through the phase step surface S3 is an integral multiple of 2π, and the phase step surface S3 does not change the spherical aberration of the transmitted light beam. The objective lens 23 is corrected for aberration with respect to the reference wavelength, and forms a good spot on the information recording surface 29a of the information recording medium 29 when a light beam having the reference wavelength is incident.

On the other hand, let us consider a case where the wavelength at which the semiconductor laser 26 oscillates changes by several nm from the reference wavelength due to individual variations among elements, temperature changes, and the like. Here, the oscillation wavelength of the semiconductor laser 26 deviated from the reference wavelength is λ1, and the refractive index of the resin material with respect to the wavelength λ1 is n ₁ . At this time, the phase difference between two different light fluxes transmitted through the phase step surface S3 is expressed by 2πqλ ₀ (n ₁ −1) / ((n ₀ −1) λ ₁ ). Since this value deviates from an integer multiple of 2π with respect to a wavelength that has changed by several nm from the reference wavelength, the light beam transmitted through the phase step surface S3 generates spherical aberration.

  The spherical aberration that occurs on the phase step surface S3 is how the radius of each region formed on the phase step surface S3 is set with respect to the effective diameter of the optical system, and how the surface shape of each region is set. It is possible to adjust depending on the situation. Therefore, when the wavelength of the light beam oscillated by the semiconductor laser 26 deviates from the reference wavelength by several nm, the tendency of the spherical aberration generated on the diffractive surface S1 and the spherical aberration generated on the phase step surface S3 is in the same direction, and the objective It can be designed to be in the opposite direction to the spherical aberration generated by the lens 23. By designing in this way, a large number of ring zones in the periphery of the diffractive surface S1 are not formed and the width of the ring zones is not reduced as in the case where spherical aberration is generated only by the diffractive surface S1. A large aberration can be generated by the aberration correction element 22 alone. By canceling the spherical aberration between the aberration correction element 22 and the objective lens 23, the substantial image point position on the optical axis can be corrected, and as a result, the axial chromatic aberration can be corrected.

  By the way, even if both surfaces of the aberration correction element 22 are diffractive surfaces, large spherical aberration can be generated without forming a large number of zonal zones of the diffractive surfaces and without reducing the width of the zonal zones. Is possible. However, it is not preferable to use both surfaces as diffractive surfaces, because the loss of light amount used for spot formation on the optical information recording surface out of the light beam transmitted through the aberration correction element becomes large. Therefore, as in the lens apparatus according to the embodiment, it is preferable that one of the aberration correction elements 22 is a diffractive surface and the other is a phase step surface.

  Further, the size of the step between the regions formed on the phase step surface S3 in the direction along the optical axis causes a phase difference of an integral multiple of 2π radians between the light beams having the reference wavelengths that pass through the different regions. However, the integer value can be appropriately set according to the required characteristics. For example, when a phase difference that matches 2π radians is given, the amount of phase difference that occurs when the phase shifts several nm from the reference wavelength is reduced from 2π. Therefore, in order to increase the aberration correction amount, the phase difference must be increased by deepening the step.

  On the contrary, if the depth of the phase step becomes deeper, the extra high-order spherical aberration increases and the overall aberration deteriorates. Therefore, if only the third-order spherical aberration is to be corrected, the depth of the phase step is It is desirable to set the amount corresponding to the necessary minimum phase difference 2π.

  The aberration correction element 22 described in the second embodiment is a lens element in which the diffractive surface S1 and the phase step surface S3 are integrally formed. However, the present invention is not limited to this. For example, a combination of a lens element having only a diffractive surface and a lens element having only a phase step surface may be used. However, in consideration of molding and assembly adjustment at the time of manufacturing and inter-surface reflection occurring at the boundary surface, it is desirable that the aberration correction element 22 be configured by a single lens element formed integrally.

  In addition, it is desirable that the width of each region of the aberration correction element 22 in the direction orthogonal to the optical axis becomes smaller as the distance from the optical axis increases. When the objective lens is composed of a single lens element and used at a high NA such as NA 0.8, the amount of spherical aberration that occurs when it deviates from the reference wavelength by several nanometers increases rapidly as the distance from the optical axis increases. Has increasing properties. In order to correct this characteristic, it is necessary to increase the amount of spherical aberration generated in the aberration correction element 22 as it goes to the periphery. Therefore, since it is necessary to provide a large number of phase steps toward the periphery, it is preferable that the width of each region in the direction orthogonal to the optical axis is narrowed toward the periphery.

  In addition, when the optical surface of each region is connected by a phase step, the phase step surface is an aspheric surface defined by a different aspheric definition formula, even if it is an aspheric surface defined by a single aspheric definition formula. Or either. However, it is preferable to use an aspherical surface defined by different aspherical defining equations. The aberration correction element in which each region is configured with a different aspheric surface that is optimal for each region has a spherical aberration at the reference wavelength compared to the aberration correction element in which each region is defined by one aspheric definition formula. This is because the aberration correction element can be corrected alone.

  That is, the aberration correction element in which each region is defined by one aspheric definition formula has different thicknesses in the optical axis direction in each region, so that spherical aberration or a power component is generated even at the reference wavelength. In contrast, an aberration correction element in which each region is configured with a different aspheric surface that is optimal for each region can be designed without generating spherical aberration and power components for each region. The characteristics of the lens device can be further improved.

  The aberration correction element 22 adjusts the spherical aberration generated in the aberration correction element by appropriately designing the diffractive surface S1 or the phase step surface S3, and can be used in an optical system other than the objective lens (for example, It is possible to correct axial chromatic aberration caused by a collimating lens 24 or a protective layer provided on the information recording surface 29).

  In addition, although the aberration correction element 22 is set to + 1st order as the designed diffraction order, in general, any of ± mth order (m: integer) may be used. In the lens device of the embodiment, the objective lens 2 has been described as being composed of a single lens, but may be composed of a plurality of assembled lenses.

  Further, in the lens device of the second embodiment, the parallel light beam is incident on the aberration correction element 22, but it may be a non-parallel light beam. Further, in the lens device of Embodiment 2, the space between the aberration correction element 22 and the objective lens 23 is a parallel light beam, but may be a non-parallel light beam. The aberration correction element 22 has a diffractive surface disposed on the light source side and a phase step surface disposed on the information recording medium side. Conversely, a phase step surface is disposed on the light source side and diffracted on the information recording medium side. A surface may be arranged.

  As described above, the aberration correction element according to the second embodiment does not generate spherical aberration with respect to a light beam with a reference wavelength, but can generate spherical aberration with respect to a light beam with a wavelength that deviates from the reference wavelength. it can. This spherical aberration is combined with the spherical aberration of the diffractive surface to generate the desired large spherical aberration without forming a large number of ring zones on the diffractive surface and without reducing the width of the ring zones. Can be made. In addition, the aberration correction element according to the embodiment can be manufactured from resin and can be easily manufactured.

  Next, a numerical example embodying the optical pickup lens device according to the first embodiment will be described together with a comparative example. Example 1 and the comparative example differ only in the design values of the collimating lens 3 and the diffractive lens 4. In both Example 1 and Comparative Example, the axial chromatic aberration in the entire optical system is equal to 0.09 μm / nm, but the axial chromatic aberration and the emission angle change amount of the collimating lens 3 are different from those of the diffraction lens 4. The amount of spot deviation differs greatly.

  Specific numerical configurations of the collimating lens 3, the diffraction lens 4, and the objective lens 5 of Example 1 are shown in Table 1, and similarly, the numerical configuration of the comparative example is shown in Table 2. In each, the design wavelength is centered at 410 nm. In Example 1 and the comparative example, a parallel beam is incident on the diffraction lens 4 and the diameter of the parallel beam on the exit side is 2.21 mm. The surface numbers 1 to 4 are the collimating lens 3, the surface numbers 5 to 8 are the diffraction lens 4, the surface numbers 9 and 10 are the objective lens 5, and the surface numbers 11 and 12 are the protective layers of the information recording medium 6. . Where r is the radius of curvature of each lens surface (where the information recording medium is the protective layer surface), d is the lens thickness, nλ is the refractive index of each lens at the wavelength λnm, and ν is the Abbe number of each lens. The phase grating formed on the diffractive surface is expressed by the ultra-high refractive index method (for the ultra-high refractive index method, William C. Sweet: Describing holographic optical elements as lenses: Journal of Optical Society of America, Vol. 67 , No. 6, June 1977).

但し、各符号の意味は、以下の通りである。
Ｘ：光軸からの高さがｈの非球面上の点の非球面頂点の接平面からの距離
ｈ：光軸からの高さ
Ｃｊ：対物レンズの第ｊ面の非球面頂点の曲率（Ｃｊ＝１／Ｒｊ）
Ｋｊ：対物レンズの第ｊ面の円錐定数
Ａｊ，ｎ：対物レンズの第ｊ面のｎ次の非球面係数
但し、ｊ＝１３，１４ The aspheric shape is given by the following (Equation 1).

However, the meaning of each code is as follows.
X: distance from the tangent plane of the aspherical vertex of the point on the aspherical surface having a height from the optical axis h: height from the optical axis Cj: curvature of the aspherical vertex of the jth surface of the objective lens (Cj = 1 / Rj)
Kj: conical constant of the jth surface of the objective lens Aj, n: nth-order aspheric coefficient of the jth surface of the objective lens, where j = 13,14

  The aberrations of the collimating lens 3 of Example 1 are shown in FIG. 2A shows the spherical aberration SA, and FIG. 2B shows the amount of violation of the sine condition SC. FIG. 3 shows aberrations of the diffractive lens 4 that is the aberration correction element of Example 1. 3A shows the spherical aberration SA, and FIG. 3B shows the amount of violation of the sine condition SC.

  As shown in FIG. 2A, the spherical aberration SA of the collimating lens 3 is corrected almost satisfactorily. Further, as shown in FIG. 2B, the sine condition SC is also substantially corrected.

  The aberration of the collimating lens 3 of the comparative example is shown in FIG. As shown in FIG. 4A, the spherical aberration SA of the collimating lens 3 is corrected almost satisfactorily. Similarly, as shown in FIG. 4B, the sine condition SC is also corrected well. The aberrations of the diffractive lens 4 of the comparative example are shown in FIG. As shown in FIG. 5 (a), the spherical aberration SA of the diffractive lens 4 is corrected almost satisfactorily, and the sine condition SC is also corrected well as shown in FIG. 5 (b).

Table 3 shows the focal length, effective diameter, axial chromatic aberration, and axial chromatic aberration in the entire optical system of each of the collimating lens 3, the diffractive lens 4, and the objective lens 5 for each of Example 1 and Comparative Example.

Table 4 shows the amount of change in the emission angle per light source unit wavelength of the collimating lens 3 and the diffractive lens 4 for each of Example 1 and Comparative Example. θ1 is the luminous flux output angle of each of the collimating lens 3 and the diffractive lens 4 per 1 nm of the light source wavelength change when the objective lens 5 and the diffractive lens 4 of Example 1 are integrally shifted by 150 μm in the track direction of the information recording medium 6. Indicates the amount of change. θ2 is the luminous flux output angle change amount as in the comparative example.

Further, Table 5 shows the amount of spot deviation in the focal track direction per light source wavelength unit change for each of Example 1 and Comparative Example. D1 indicates the spot position deviation amount in the track direction of the information recording medium 6 at the focal point per 1 nm of light source wavelength change when the objective lens 5 and the diffractive lens 4 are integrally shifted by 150 μm in the disk track direction in the first embodiment. D2 indicates the amount of spot position deviation in the comparative example.

  In Example 1, the collimating lens 3 is sufficiently corrected for chromatic aberration, and the chromatic aberration correction amount of the diffractive lens 4 is large and the chromatic aberration is overcorrected. On the other hand, in the comparative example, the collimating lens 3 is large and the chromatic aberration is overcorrected, and the chromatic aberration correction amount of the diffractive lens 4 is smaller than that of the first embodiment. Therefore, as shown in Table 4, it can be seen that the degree of divergence / convergence of the emitted light beams of the collimating lens 3 and the diffractive lens 4 increases in proportion to the chromatic aberration. As shown in Table 5, the spot deviation amount in the disc track direction varies greatly depending on the distribution of the chromatic aberration correction amount even in the optical pickup device having the same chromatic aberration in all optical systems. In Example 1, the spot deviation hardly occurs at 0.0 nm per wavelength of 1 nm. Therefore, stable recording and reproduction can be performed. In the comparative example, the spot moves steeply at 17.5 nm per wavelength of 1 nm, and there is a sufficient risk of off-track.

  It is desirable that the collimating lens 3 is sufficiently color-corrected. If the color correction is not sufficiently performed, the substantially parallel light emitted from the collimating lens 3 diverges and converges with respect to the wavelength change. is there. This angle change amount affects the spot deviation amount when the objective lens 5 is shifted.

  At present, it is considered that the amount of spot deviation in the disc track direction that can be stably tracked when the wavelength changes by 1 nm with respect to the shift amount of the objective lens 5 of 150 μm is less than 10 nm.

  When the color correction state is insufficient or the color correction is insufficient, the amount of change in the emitted light beam angle per unit wavelength change of the light source becomes large. That is, when the wavelength of the light source changes, the angle of divergence and convergence of the emitted light beam increases, and even if the diffractive lens 4 and the objective lens 5 that are aberration correction elements are always shifted in a coaxial state, the movable part is Since light is incident from the outside, the amount of movement of the spot in the track direction at the focal point increases.

  According to the first embodiment, it is possible to correct large axial chromatic aberration with respect to a steep wavelength variation of the light source in a short wavelength region. Further, even when the wavelength variation occurs in a state where the optical axis is shifted in the track direction of the information recording medium for the objective lens to track, the movement amount of the spot in the track direction of the information recording medium at the focal point is suppressed. It becomes possible. That is, it has a large axial chromatic aberration correction amount and a large magnification chromatic aberration correction amount. On the other hand, the comparative chromatic aberration correction amount is small while the comparative example has the same axial chromatic aberration correction amount.

  The present invention relates to writing / reproducing of information recording media such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD + R, DVD-RW, DVD + RW, HD-DVD, Blu-Ray Disk, etc. Applicable to optical information recording / reproducing apparatus for performing erasure, especially writing of information recording medium for high-density recording using a light beam having a wavelength of 420 nm or less such as HD-DVD / Blu-Ray Disk as a next generation DVD Suitable for an optical information recording / reproducing apparatus that performs reproduction / erasure.

1 is a basic schematic configuration diagram of an optical pickup device according to Embodiment 1 of the present invention. The figure which shows the aberration of the collimating lens of Example 1 in Embodiment 1 of this invention The figure which shows the aberration of the diffraction lens of Example 1 in Embodiment 1 of this invention The figure which shows the aberration of the collimating lens of a comparative example The figure which shows the aberration of the diffraction lens of a comparative example 1 is a schematic configuration diagram of an optical pickup device according to Embodiment 1 of the present invention. Schematic configuration diagram showing a lens device used in the optical pickup device according to Embodiment 2 of the present invention. Schematic diagram showing the structure of the phase step surface of the aberration correction element of the lens device used in the optical pickup device according to Embodiment 2 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Light beam 3 Collimate lens 4 Diffraction lens 5 Objective lens 6 Information recording medium 7 Actuator 8 Beam splitter 9 Detection lens 10 Light receiving element 21 Lens apparatus 22 Aberration correction element 23 Objective lens 29 Information recording medium

Claims (4)

Used in an optical pickup device that performs at least one of reading, writing, and erasing information by condensing a light beam having a wavelength range of 390 nm to 420 nm emitted from a light source onto an information recording medium to form a spot. An optical pickup lens device, in order from the light source side,
Collimating means that is held movably along the direction of the optical axis of the light beam emitted from the light source, and converts the light beam into parallel light or predetermined convergent or divergent light;
An aberration correction element that transmits a light beam emitted from the collimating means;
An objective lens element that has a numerical aperture of 0.8 or more, and collects a light beam emitted from the aberration correction element on the information recording medium to form a spot;
The aberration correction element and the objective lens element are integrally held in a direction perpendicular to the optical axis in order to perform tracking of the information recording medium,
Lens device for optical pickup that satisfies the following conditions:
−0.1 ≦ CAt ≦ 0.1 (1)
−20 ≦ CAf ≦ 20 (2)
−20 ≦ CAm ≦ 0 (3)
−0.25 ≦ θf ≦ 0.25 (4)
−0.75 ≦ θm ≦ 0.75 (5)
However,
CAt: axial chromatic aberration of all optical systems [μm / nm]
CAf: axial chromatic aberration of collimating means [μm / nm]
CAm: On-axis chromatic aberration [μm / nm] of the aberration correction element
θf: Amount of change in angle per unit wavelength of light beam emitted from collimator means [min / nm]
θm: Amount of change in angle per unit wavelength of outgoing light flux of aberration correction element [min / nm]
It is.   The lens apparatus for an optical pickup according to claim 1, wherein the aberration correction element is a diffractive lens having a power for deflecting a light beam by diffraction provided separately from the objective lens element.   The aberration correction element is an element provided separately from the objective lens element, and a plurality of annular zones defined by concentric circles centered on the optical axis, and a boundary portion between the zones The lens device for an optical pickup according to claim 1, having a phase step surface including a phase step to be formed. An optical pickup device that performs at least one of reading, writing, and erasing information by focusing a light beam on an information recording medium to form a spot,
A light source that emits a light flux in a wavelength range of 390 nm to 420 nm;
Collimating means that is held movably along the direction of the optical axis of the light beam emitted from the light source, and converts the light beam into parallel light or predetermined convergent or divergent light;
An aberration correction element that transmits a light beam emitted from the collimating means;
An objective lens element that has a numerical aperture of 0.8 or more, and collects a light beam emitted from the aberration correction element on the information recording medium to form a spot;
The aberration correction element and the objective lens element are integrally held in a direction perpendicular to the optical axis in order to perform tracking of the information recording medium,
An optical pickup device that satisfies the following conditions:
−0.1 ≦ CAt ≦ 0.1 (1)
−20 ≦ CAf ≦ 20 (2)
−20 ≦ CAm ≦ 0 (3)
−0.25 ≦ θf ≦ 0.25 (4)
−0.75 ≦ θm ≦ 0.75 (5)
However,
CAt: axial chromatic aberration of all optical systems [μm / nm]
CAf: axial chromatic aberration of collimating means [μm / nm]
CAm: On-axis chromatic aberration [μm / nm] of the aberration correction element
θf: Amount of change in angle per unit wavelength of light beam emitted from collimator means [min / nm]
θm: Amount of change in angle per unit wavelength of the emitted light beam of the aberration correction element [min / nm]
It is.

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