JP5170587B2 - Objective optical element of optical pickup device, optical pickup device, and optical information recording / reproducing device - Google Patents

Description

  The present invention relates to an objective optical element, an optical pickup apparatus, and an optical information recording / reproducing apparatus that are used in an optical pickup apparatus that performs recording / reproduction of optical information recording media having different operating wavelengths and different transparent substrate thicknesses using a single objective lens. In particular, light sources that oscillate different wavelengths are used in modularized light sources (two-laser, one-package module), or are used in optical systems that have a short focal length of the objective lens and are sensitive to error factors. The present invention relates to an objective optical element having improved image height coma aberration characteristics when a recording medium is used, an optical pickup apparatus using the objective optical element, and an optical information recording / reproducing apparatus.

Currently, there are many types of optical information recording media, and the standards of these optical information recording media are determined as shown in [Table 1]. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented using E (for example, 2.5 × E-3).

  Here, DVDs and CDs are required for compatibility between optical information recording media having different recording densities. These optical information recording media have different transparent substrate thicknesses as shown in [Table 1]. In order to ensure compatibility, it is necessary to correct the spherical aberration caused by the difference in the thickness of the transparent substrate by some means. Furthermore, since the required numerical aperture is different between DVD and CD, some countermeasures are necessary for this.

  In order to realize an optical pickup device compatible with DVD / CD, an objective lens provided with a diffraction structure has been developed. As such an objective lens, for example, on one surface of the objective lens, different diffractive structures are provided on the inside and outside of the specific height h from the optical axis, and spherical aberration is provided for each transparent substrate thickness in the inner region. In the outer region, the spherical aberration is corrected only with the DVD, and the CD is flared without correcting the spherical aberration. By configuring the objective lens in this manner, it is possible to appropriately form a condensing spot required at the time of recording or reproducing information on each optical information recording medium.

  By the way, by using such a diffractive structure for the objective lens, it is relatively easy to correct spherical aberration when recording or reproducing information on both DVD / CD. However, coma aberration exists in addition to spherical aberration as an optical characteristic deterioration factor that hinders appropriate information recording or reproduction. If the coma aberration is large, when a light beam tilted with respect to the optical axis is incident due to the tilt of the objective lens caused by an assembly error, an appropriate spot is formed on the optical information recording medium. May interfere. However, by using the above-described diffractive structure, both spherical aberrations when using both DVD / CD can be reduced, but regarding coma aberration, there is a problem that both cannot be corrected simultaneously.

  In particular, as a light source for an optical pickup device that achieves DVD / CD compatibility, a so-called two-laser / one-package two semiconductor lasers mounted on one substrate are known as one unit. When recording or reproducing information on both DVD / CD using such a light source, for example, when a light source for DVD is arranged on the optical axis of the objective lens, the light source for CD is In this case, it is desirable to reduce the coma aberration when using the CD as much as possible.

  The present invention has been made in view of the above problems, and an objective optical element for an optical pickup device capable of correcting coma aberration in a well-balanced manner and appropriately recording or reproducing information on different optical information recording media, and An object is to provide an optical pickup device and an optical information recording / reproducing device.

The objective optical element of the optical pickup device according to claim 1 records or reproduces information by irradiating a light beam onto the first optical information recording medium having a transparent substrate thickness t1. The information is recorded or reproduced by irradiating the first light source having the wavelength λ1 and the second optical information recording medium having a transparent substrate thickness t2 (t1 <t2). The second light source having the wavelength λ2 (λ1 <λ2) and the light beams emitted from the first and second light sources are passed through the transparent substrates of the first and second optical information recording media. A focusing optical system including an objective optical element for focusing on the information recording surface, and an objective optical element of an optical pickup device,
The objective optical element has an objective lens that condenses the light flux from the first or second light source, and an optical function surface that gives an optical action to the light flux,
The optical function surface of the objective optical element includes an optical axis and a common area used for recording and / or reproducing information with respect to both the first optical information recording medium and the second optical information recording medium. A dedicated area that is provided outside the shared area (on the side away from the optical axis, hereinafter the same) and is mainly used for recording and / or reproducing information with respect to the first optical information recording medium. ,
In the first optical information recording medium, the objective optical element forms a spot diameter on the first optical information recording medium determined from an effective diameter and a focal length of the objective optical element,
When the first optical information recording medium is used, there is a case where the absolute value of the unsatisfactory sine condition is maximum in the common area,
COMA1 (λ1 rms) is generated when the first optical information recording medium is obliquely incident on the objective optical element at an angle of view of 1 ° when the first optical information recording medium is used, and the angle of view is 1 when the second optical information recording medium is used. If the coma generated when obliquely incident on the objective optical element at ° is COMA2 (λ2rms),
0.5 ≦ COMA1 / COMA2 ≦ 1.0 (1)
It is characterized by satisfying. Regarding the coma aberration, the third-order coma aberration of the wavefront aberration is ΔW3 (λrms) and the fifth-order coma aberration is ΔW5 (λrms) and the seventh-order coma aberration is ΔW7 (λrms) with respect to the light beam from the light source having the wavelength λ. Then, the coma aberration COMA (λrms) is obtained by the following equation.
COMA = {(ΔW3) 2+ (ΔW5) 2+ (ΔW7) 2} 1/2 (1 ′)

  As a result of intensive studies, the present inventors have found that these problems can be solved by reviewing the objective lens design, in particular, the sine condition unsatisfactory amount design. Further, a sine condition unsatisfactory state of the first optical information recording medium is devised for a shared area of the first optical information recording medium (for example, DVD) and the second optical information recording medium (for example, CD). Thus, a more preferable design of the unsatisfactory sine condition of the first optical information recording medium dedicated area was found. Furthermore, by suppressing the amount of wavefront aberration of coma aberration that occurs when the first and second optical information recording media are used (also referred to as information recording or reproduction), an arrangement error of two lasers and one package module is reduced. The present inventors have found that the occurrence of coma aberration can be suppressed for any optical information recording medium that is strong and always used off-axis. This technique is effective even for an optical pickup device that does not use a two-laser, one-package module light source, and for an objective optical element that has a shorter focal length by attempting to reduce the size.

Here, as shown in FIG. 1, the sine condition is that when a light beam having a height h ₁ from the optical axis is incident on the lens parallel to the optical axis, the emission angle when the light beam is emitted from the lens is U. Sometimes h ₁ / sinU meets a certain value. If this is a constant value regardless of the height from the optical axis h ₁ , the sine condition is satisfied and the lateral magnification of each ray within the effective diameter can be regarded as constant. This sine condition is a calculated value on the axis, but is effective in correcting off-axis lateral magnification error (ie off-axis coma).

However, the present invention has the following problems when the thickness of the protective substrate of the optical information recording medium within the technical field is different. If the sine condition is completely corrected when one (first) optical information recording medium (for example, thickness t1) is used, the (second) optical information recording medium having the other thickness t2 is used. The sine condition has a characteristic that the amount of deviation from a constant value increases and as a result, off-axis coma aberration increases. In this case, when the sine condition unsatisfied amount is defined as SC = h ₁ / sinU−f, the sine condition unsatisfied amount at the light ray height h ₁ within the effective diameter is defined as the first optical information recording medium and the second optical information recording medium. The inventors of the present invention have found that the off-axis coma aberration balance can be achieved when each optical information recording medium is used, as a result of performing the distribution design when the optical information recording medium is used. . More specifically, the above effects can be obtained by satisfying the expression (1).

  On the other hand, if the absolute value of the unsatisfactory sine condition is too large, the following problems occur. Although the required numerical aperture is determined for each optical information recording medium, it is also related to the spot size on the optical information recording medium surface. Here, if the sine condition unsatisfactory amount becomes positive, the objective optical element (an objective lens in the embodiments described later, the same shall apply hereinafter) has a smaller light beam tilt angle. Even if a light beam having the same effective diameter is incident on the surface, the spot diameter formed on the surface of the optical information recording medium cannot be reduced. In order to obtain a desired spot diameter, it is necessary to increase the aperture diameter, and the tracking margin becomes narrow. Therefore, it is preferable to form a spot diameter obtained from the focal length and the effective diameter of the ideal objective optical element on the optical information recording medium surface.

  Here, the “optical functional surface” means a lens surface of the objective optical element through which a light beam from each light source passes. In this specification, it is defined as the range of the lens surface through which the light beam limited by the aperture diameter when the first optical information recording medium is used passes.

  Also, the meaning of “mainly” in “mainly used for recording and / or reproducing information on the first optical information recording medium” will be described. The light beam that passes through the dedicated area when the first optical information recording medium is used is imaged on the optical information recording medium surface when the objective lens is focused. Here, the light beam passing through the dedicated area when the second optical information recording medium is used flares on the surface of the second optical information recording medium at a position away from the spot light when the objective lens is focused and defocused. It becomes light. Here, the word “mainly” is used for the following two reasons. First, as a first reason, when attention is paid to a signal detection sensor normally provided in an optical pickup device, the flare light may be incident into the sensor opening depending on the sensor opening size. In this case, the defocus control of the objective lens is performed practically including flare light. In a broad sense, even when the second optical information recording medium is used, the influence of the light flux passing through this dedicated area is affected. It may be received in actual use. The second reason is that, in terms of wave optics, it is possible to increase the peak intensity of the Airy disc of spot light by controlling the phase difference between flare light and spot light on the optical information recording medium. There is. For these reasons, the term “mainly” is used in the present invention to avoid unnecessary limitations.

  Furthermore, the “objective optical element” may be an optical surface of the objective lens provided with the optical function surface. In addition to the objective lens, an optical element provided with the optical function surface is separately provided. It may be provided.

The objective optical element of the optical pickup device according to claim 2 is a height from the optical axis of the light beam that passes through the outermost peripheral portion of the effective diameter of the objective optical element when the first optical information recording medium is used. Where hmax is the sine condition dissatisfaction amount SC1 of the outermost peripheral ray,
│SC1 (hmax) │ ≦ 0.010mm (4)
If satisfied, the objective optical element satisfying the spot diameter on the first optical information recording medium determined from the effective diameter and the focal length of the objective optical element can be provided in the first optical information recording medium.

The objective optical element of the optical pickup device according to claim 3, when an infinite object distance light beam having a height of h from the optical axis is emitted from the objective optical element, is formed by the light beam after emission and the optical axis. When the angle is represented by U and the unsatisfactory sine condition is defined as SC (h) = h / sinU−f (f is the focal length of the objective optical element when using each information recording medium), the first When the optical information recording medium is used, the minimum value of the unsatisfactory sine condition in the common area is SC1Dmin, and the minimum value of the unsatisfactory sine condition in the dedicated area is SC1Smin (see FIG. 8A).
1.2 · SC1Dmin ≤ SC1Smin (5)
It is characterized by being.

  FIG. 2 shows the height from the optical axis on the horizontal axis (x), the sine condition unsatisfied amount when using the second optical information recording medium (for example, CD) on the vertical axis (y), and the common area and It is a figure which shows the example which calculated | required the curve f2 which shows the said sine condition dissatisfaction amount in the said exclusive area | region. Here, the curve f2 is always negative, and the negative value increases as the distance from the optical axis increases. In addition, when the straight line d1 having the differential value as the slope is drawn at the first height x1 (meaning that the tangent is drawn to the curve f2 at the first height x1), the first height x1 On the side farther from the optical axis, the curve f2 has a region R1 existing on the positive side of the straight line (tangent line) d1. Note that there is another region existing on the negative side of the straight line d1 between x1 and the region R1. According to such characteristics, it is possible to obtain the same effect as that of the invention according to claim 1 that it is possible to balance off-axis coma aberration when each optical information recording medium is used.

  When a straight line (the tangent line drawn on the curve f2 at the fourth height x4) with the differential value is drawn at the fourth height x4, the side closer to the optical axis than the first height x1. The curve f2 has a region R4 existing on the positive side of the straight line (tangent line) d4.

  FIG. 3 shows the height from the optical axis on the horizontal axis (x), the sine condition unsatisfactory amount when using the first optical information recording medium (for example, DVD) on the vertical axis (y), and the common area and It is a figure which shows the example which calculated | required the curve f1 which shows the said sine condition dissatisfaction amount in the said exclusive area | region. Here, at a certain height x2, when a straight line d2 having the differential value as an inclination is drawn (meaning drawing a tangent to the curve f1 at a certain height x2), it is farther from the optical axis than the certain height x2. On the side, the curve f1 has a region R2 existing on the positive side of the straight line (tangent line) d2. In addition, it has another area | region which exists in the negative side from the straight line d2 between x2 and area | region R2. If it has such a characteristic, the effect similar to the invention of Claim 5 can be acquired.

  FIG. 9 is a cross-sectional view of an objective optical element (for example, an objective lens) exaggeratingly showing a step and a diffraction ring zone formed on the optical function surface on the optical information recording medium side. As shown in FIG. 9, a stepped portion T2 is provided adjacent to the shared castle and the dedicated region, substantially parallel to the optical axis and facing outward with respect to the optical axis. By providing such a stepped portion T2, as described in relation to the invention according to claim 1, it is possible to balance off-axis coma aberration when each optical information recording medium is used. When a diffraction structure D is provided in at least one of the shared region and the dedicated region (in this example, the light source side), the step amount (d1) of the step portion (T1, T2) as shown in FIG. , D2) is determined by the position of the mother aspherical surface and the level difference of the diffraction structure provided on the mother aspherical surface.

The optical pickup device according to claim 4 is a first light source having a wavelength λ1 for recording or reproducing information by irradiating a light beam onto a first optical information recording medium having a transparent substrate thickness t1. And a second wavelength λ2 (λ1 <λ2) at which information is recorded or reproduced by irradiating the second optical information recording medium having a thickness t2 (t1 <t2) with a light beam. And an objective optical element that condenses the light beams emitted from the first and second light sources onto the information recording surface via the transparent substrates of the first and second optical information recording media. An optical pickup device having a condensing optical system,
The objective optical element has an objective lens that condenses the light flux from the first or second light source, and an optical function surface that gives an optical action to the light flux,
The optical function surface of the objective optical element includes an optical axis and a common area used for recording and / or reproducing information with respect to both the first optical information recording medium and the second optical information recording medium. A dedicated area provided outside the shared area and mainly used for recording and / or reproducing information with respect to the first optical information recording medium,
In the first optical information recording medium, the objective optical element forms a spot diameter on the first optical information recording medium determined from an effective diameter and a focal length of the objective optical element,
When the first optical information recording medium is used, there is a case where the absolute value of the unsatisfactory sine condition is maximum in the common area,
COMA1 (λ1 rms) is generated when the first optical information recording medium is obliquely incident on the objective optical element at an angle of view of 1 ° when the first optical information recording medium is used, and the angle of view is 1 when the second optical information recording medium is used. If the coma generated when obliquely incident on the objective optical element at ° is COMA2 (λ2rms),
0.5 ≦ COMA1 / COMA2 ≦ 1.0 (1)
Thus, the same effect as that of the first aspect of the invention can be achieved.

  The “diffractive structure” used in the present specification refers to a portion provided with a relief on the surface of the objective lens so as to condense or diverge a light beam by diffraction. As the shape of the relief, for example, the surface of the objective lens is formed as a substantially concentric annular zone centered on the optical axis, and each annular zone is shaped like a sawtooth if the cross section is viewed in a plane including the optical axis. Is known, but includes such a shape, and such a shape is particularly referred to as a “diffraction ring zone”.

  In this specification, the objective lens is, in a narrow sense, a light collecting action that is arranged to face the optical information recording medium at the position closest to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. In a broad sense, it refers to a lens group that can be operated at least in the optical axis direction by an actuator together with the lens. Here, the lens group refers to at least one lens (for example, two lenses). Therefore, in this specification, the numerical aperture NA on the optical information recording medium side (image side) of the objective lens refers to the numerical aperture NA of the lens surface closest to the optical information recording medium side of the objective lens. . Further, in this specification, the required numerical aperture NA is the numerical aperture specified by the standard of each optical information recording medium, or the information of the information depending on the wavelength of the light source used for each optical information recording medium. The numerical aperture of an objective lens having a diffraction limited performance capable of obtaining a spot diameter necessary for recording or reproduction is shown.

  In this specification, the second optical information recording medium refers to various optical discs such as CD-R, CD-RW, CD-Video, CD-ROM, etc., and the first optical information recording medium. The term “DVD-ROM”, “DVD-RAM”, “DVD-R”, “DVD-RW”, and “DVD-Video” refers to various DVD optical disks. Further, in this specification, the thickness t of the transparent substrate includes t = 0.

  According to the present invention, an objective optical element for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device that can correct coma aberration in a well-balanced manner and can appropriately record or reproduce information on different optical information recording media. Can be provided.

It is a figure for demonstrating a sine condition. It is a figure for demonstrating the sine condition unsatisfactory amount at the time of use of the 2nd optical information recording medium. It is a figure for demonstrating the sine condition dissatisfaction amount at the time of 1st optical information recording medium use. 1 is a schematic configuration diagram of an optical information recording / reproducing apparatus or an optical pickup apparatus (including a two-laser / one-package module type light source) according to the present embodiment. FIG. 3 is a diagram showing spherical aberration diagrams (indicated by longitudinal spherical aberration amounts) applied to the objective lens of Example 1 for DVD (a) and CD (b), respectively. It is a figure which shows the sine condition unsatisfactory amount concerning the objective lens of Example 1 about DVD (a) and CD (b), respectively. FIG. 7 is a diagram illustrating spherical aberration diagrams (indicated by longitudinal spherical aberration amounts) according to the objective lens of Example 2 for DVD (a) and CD (b), respectively. It is a figure which shows the sine condition unsatisfactory amount concerning the objective lens of Example 2 about DVD (a) and CD (b), respectively. It is sectional drawing of the objective lens which exaggerated and showed the level | step difference and diffraction ring zone which are formed on the optical function surface by the side of an optical information recording medium. It is a figure which shows the example of the level | step difference amount (d1, d2) of the level | step-difference part (T1, T2) in an optical function surface. It is a figure which shows the sine condition dissatisfaction amount concerning the objective lens of the reference example 1 about DVD. It is a figure which shows the sine condition unsatisfactory amount concerning the objective lens of the reference example 1 about CD. It is a figure which shows the spherical aberration figure (it shows by the amount of longitudinal spherical aberration) concerning the objective lens of the reference example 1 about DVD. It is a figure which shows the spherical aberration figure (it shows with the amount of longitudinal spherical aberration) concerning the objective lens of the reference example 1 about CD. It is a figure which shows the sine condition unsatisfactory amount concerning the objective lens of the reference example 2 about DVD. It is a figure which shows the sine condition unsatisfactory amount concerning the objective lens of the reference example 2 about CD. It is a figure which shows the spherical aberration figure (it shows by the amount of longitudinal spherical aberration) concerning the objective lens of the reference example 2 about DVD. It is a figure which shows the spherical aberration figure (it shows with the amount of longitudinal spherical aberration) concerning the objective lens of the reference example 2 about CD.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 4 is a schematic configuration diagram of an optical information recording / reproducing apparatus or an optical pickup apparatus (including a two-laser / one-package module type light source) according to the present embodiment. In FIG. 4, a first semiconductor laser 111 as a first light source and a second semiconductor laser 112 as a second light source are mounted on the same substrate surface orthogonal to the optical axis and configured as one unit. Yes. A beam emitted from the first semiconductor laser 111 (wavelength λ1 = 610 nm to 670 nm) is transmitted through the beam splitter 120 which is an optical multiplexing unit, further narrowed by the diaphragm 17, and transparent by the objective lens 16 of the first optical disk 20. The light is condensed on the information recording surface 22 through the substrate 21.

  Then, the light beam modulated and reflected by the information bit on the information recording surface 22 passes through the objective lens 16 and the diaphragm 17 again, enters the beam splitter 120, is reflected there, and is given astigmatism by the cylindrical lens 180. Then, the light is incident on the photodetector 30 through the concave lens 50, and a read signal of information recorded on the first optical disc 20 is obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 30. Based on this detection, the two-dimensional actuator (not shown) moves the objective lens 16 so that the light beam from the first semiconductor laser 111 forms an image on the recording surface 22 of the first optical disc 20, and the semiconductor laser 111. The objective lens 16 is moved so that the light beam from the light beam is imaged on a predetermined track.

  A beam emitted from the second semiconductor laser 112 (wavelength λ1 = 740 nm to 870 nm) is transmitted through the beam splitter 120 which is an optical multiplexing unit, and further passes through the diaphragm 17 and the objective lens 16 to form a transparent substrate of the second optical disk 20. The light is condensed on the information recording surface 22 via 21.

  Then, the light beam modulated and reflected by the information pits on the information recording surface 22 is reflected again by the objective lens 16, the diaphragm 17 and the beam splitter 120, is given astigmatism by the cylindrical lens 180, and passes through the concave lens 50. The light incident on the detector 30 is used to obtain a read signal of information recorded on the second optical disc 20 using the output signal.

  Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 30 is detected to detect focus and track, and a two-dimensional actuator (not shown) is used to focus and track the object. The lens 16 is moved.

  Although FIG. 4 shows an optical pickup device in which a divergent light beam is incident on the objective lens, the following embodiment shows an example in which a parallel light beam is incident on the objective lens when each of the DVD and CD is used. Therefore, the surface interval between the 0th surface and the 1st surface is ∞. It is assumed that a collimating lens exists between each of the semiconductor lasers 111 and 112 and the beam splitter 120.

Examples suitable for the above-described embodiment will be described below.
Both surfaces of the objective lens are aspherical surfaces represented by [Equation 1]. Here, Z is an axis in the optical axis direction, h is a height from the optical axis, r is a paraxial radius of curvature, κ is a conical coefficient, and A _2i is an aspheric coefficient.

  The local curvature R (h) used in this specification is defined by [Equation 2].

  Furthermore, a diffractive structure is integrally formed on the light source side aspheric surface of the objective lens. This diffractive structure is expressed by [Equation 3] where the unit is mm by the optical path difference function Φ with respect to the blazed wavelength λB. This second order coefficient represents the paraxial power of the diffraction part. Further, spherical aberration can be controlled by a coefficient other than the second order, for example, a fourth order or sixth order coefficient. Controllable here means that the spherical aberration of the refracting part is added to the diffractive part with the opposite spherical aberration to correct the spherical aberration, or the spherical aberration of the diffractive part is manipulated to obtain the total spherical aberration. It means to make the amount of flare. In this case, the spherical aberration at the time of temperature change can also be considered as the total of the temperature change of the spherical aberration of the refracted part and the spherical aberration change of the diffractive part.

Example 1
In this embodiment, two optical functional surfaces are formed on the light source side surface of the objective lens as the objective optical element. The optical functional surface including the optical axis is formed with an inner optical functional surface (common area) in which spherical aberration is corrected when using DVD and CD, and the outer optical functional surface is corrected with spherical aberration when using DVD and When the CD is used in the best focus state, a dedicated area is formed in which the light beam that has passed through the optical function surface becomes flare light on the surface of the optical information recording medium. Table 2 shows lens data of the objective lens according to the present example.

  Since the objective lens of the present embodiment is designed as described above, the main spot diameter required on the optical information recording medium surface can be obtained even if the aperture diameter is the same for DVD and CD. Regarding the CD off-axis coma aberration value, since the order of the distance between the flare light formed in the main spot light and the dedicated area is about 10 times the spot diameter, the evaluation is performed for the light flux only in the common area.

In this way, it is impossible in principle to make both sine condition dissatisfaction amounts at the time of transparent substrate thickness zero, and the design should balance off-axis coma aberration of each DVD / CD. Was made. As shown in FIG. 6, focusing on the CD sine condition unsatisfactory amount design, in the common area, the sine condition unsatisfactory amount itself is generally larger than the reference example indicated by the dotted line, but the curve design itself is. And off-axis coma aberration was made relatively small. In this embodiment, the unsatisfactory amount of the sine condition in the DVD is not aimed at zero, but the resulting DVD off-axis coma aberration can be suppressed to a level that is not practically problematic. In FIG. 6, h, h1, h2, and hmax correspond to the symbols used in the claims. Further, values defined in the claims are as follows in the embodiment.
SC1max 0.006mm
SC2max 0.024mm
SC1 (hmax) 0.007mm
SC1 (h ₀ ) 0.004mm
SC1 (h _0/2) -0.006mm
SC2 (h ₀ ) -0.024mm
SC2 (h _0/2) -0.012mm

(Example 2)
In this embodiment, two optical functional surfaces are formed on both the light source side and the optical information recording medium side of the objective lens as the objective optical element. The optical functional surface including the optical axis is formed with an inner optical functional surface (common area) in which spherical aberration is corrected when using DVD and CD, and the outer optical functional surface is corrected with spherical aberration when using DVD and When the CD is used in the best focus state, a dedicated area is formed in which the light beam that has passed through the optical function surface becomes flare light on the surface of the optical information recording medium. Further, a step as shown in FIG. 9 is provided between the shared area and the dedicated area. Table 3 shows lens data of the objective lens according to the present example.

  7 and 8 show a spherical aberration diagram and a sine condition unsatisfactory diagram for Example 2, respectively. The unit of the horizontal axis is mm.

In this example, an objective lens design that improves CD off-axis coma while suppressing deterioration of DVD off-axis coma was performed. In the present embodiment, the unsatisfactory amount of the sine condition shown in FIG. As a result, the coma aberration (COMA1) when using a DVD when a parallel light beam is incident at an angle of view of 1 ° was 0.006λ1 rms, and the coma aberration (COMA2) when using a CD was 0.008λ2 rms. The values defined in the claims are as follows in the embodiment.
SC1max 0.012mm
SC2max 0.015mm
SC1 (hmax) -0.001mm
SC1 (h ₀ ) 0.012mm
SC1 (h _0/2) -0.001mm
SC2 (h ₀ ) -0.014mm
SC2 (h _0/2) -0.006mm
SC1 _Dmin -0.002mm
SC1 _Smin -0.001mm
SC1 _out (h ₀ ) -0.001mm
d1 0.001mm
d2 0.002mm
h _CDNA 1.589mm

( Reference Example 1 )
In Reference Example 1 , two optical functional surfaces are formed on both the light source side and the optical information recording medium side of an objective lens as an objective optical element. The optical functional surface including the optical axis is formed with an inner optical functional surface (common area) in which spherical aberration is corrected when each of the DVD (light source wavelength 655 nm) and CD (light source wavelength 785 nm) is used. Is formed with a dedicated area in which the spherical aberration is corrected when the DVD is used and the light beam that has passed through the optical function surface becomes flare light on the surface of the optical information recording medium when the CD is used in the best focus state. Table 4 shows lens data of the objective lens according to the first reference example .

11 and 12 are diagrams showing the unsatisfactory sine condition when using DVD and CD for Reference Example 1. FIG. 13 and 14 show spherical aberration diagrams of Reference Example 1 when using DVD and CD. The unit of the horizontal axis is mm.

In the first reference example , an infinite luminous flux is incident on the objective lens when the DVD is used, and a divergent finite luminous flux is incident when the CD is used. The imaging magnification of the objective lens when using the DVD is infinite, and the imaging magnification of the objective lens when using the CD is m = −1 / 15.3. The values defined in the claims are as follows in the first reference example .
SC1max 0.005
SC2max 0.053
SC1 (hmax) -0.001
SC1 (h ₀ ) 0.001
SC1 (h _0/2) -0.004
SC2 (h ₀ ) −0.053
SC2 (h _0/2) -0.014

( Reference Example 2 )
In Reference Example 2 , two optical functional surfaces are formed on both the light source side and the optical information recording medium side of an objective lens as an objective optical element. The optical functional surface including the optical axis is formed with an inner optical functional surface (common area) in which spherical aberration is corrected when each of the DVD (light source wavelength 660 nm) and CD (light source wavelength 788 nm) is used. Is formed with a dedicated area in which the spherical aberration is corrected when the DVD is used and the light beam that has passed through the optical function surface becomes flare light on the surface of the optical information recording medium when the CD is used in the best focus state. Table 5 shows lens data of the objective lens according to the second reference example .

15 and 16 are diagrams showing the unsatisfactory sine condition when using DVD and CD for Reference Example 2. FIG. 17 and 18 show spherical aberration diagrams of Reference Example 2 when using DVD and CD. The unit of the horizontal axis is mm.

In Reference Example 2 , an infinite luminous flux is incident on the objective lens when using a DVD, and a divergent finite luminous flux is incident when using a CD. The imaging magnification of the objective lens when using the DVD is infinite, and the imaging magnification of the objective lens when using the CD is m = −1 / 13.2. The values defined in the claims are as follows in the present Reference Example 2 .
SC1max 0.016
SC2max 0.080
SC1 (hmax) 0.001
SC1 (h ₀ ) −0.003
SC1 (h _0/2) -0.011
SC2 (h ₀ ) −0.080
SC2 (h _0/2) -0.026

  The present invention is not limited to the above embodiment. The surface on the light source side of the objective lens has a diffractive structure. However, the present invention is not limited to this, and the sine condition unsatisfactory amount of the DVD may be set as in the embodiment. Further, although the two-laser one-package module light source is used, the present invention can also be applied to a discrete optical pickup device that is not modularized. Furthermore, although the optical surface of the objective lens on the optical information recording medium side is composed of the same aspherical surface, the present invention is not limited to this. This surface may also be provided with two optical function surfaces to perform the spherical aberration design and the sine condition unsatisfactory design for each of the dedicated area shared areas.

  The sine condition dissatisfaction amount in the design of the objective lens has been described above. On the other hand, since a production error occurs when an actual objective lens is produced, for example, when a surface shift of the objective lens occurs, a coma aberration component is also generated for an axial light beam. Even in this case, it goes without saying that a design that satisfies the requirements of the present invention is preferable in terms of a balance design of off-axis coma aberration between DVD and CD. The diffraction design order is designed to use the first-order diffracted light as the diffraction order for the DVD, CD, the dedicated area, and the shared area, but is not limited thereto. Higher diffraction orders may be used, or / and a DVD and CD may be designed to use different order diffraction orders.

111 First Semiconductor Laser 112 Second Semiconductor Laser 16 Objective Lens 17 Aperture 20 Optical Information Recording Medium (DVD or CD)
30 photodetectors

Claims (4)

A first light source having a wavelength λ1 for recording or reproducing information by irradiating a light beam onto a first optical information recording medium having a transparent substrate thickness t1, and a transparent substrate having a thickness t2 (t1 A second light source having a wavelength λ2 (λ1 <λ2) for recording or reproducing information by irradiating the second optical information recording medium with <t2) with a light beam, and the first and second And a condensing optical system including an objective optical element that condenses the light beam emitted from the light source on the information recording surface via the transparent substrates of the first and second optical information recording media. Objective optical element,
The objective optical element has an objective lens that condenses the light flux from the first or second light source, and an optical function surface that gives an optical action to the light flux,
The optical function surface of the objective optical element includes an optical axis and a common area used for recording and / or reproducing information with respect to both the first optical information recording medium and the second optical information recording medium. A dedicated area provided outside the shared area and mainly used for recording and / or reproducing information with respect to the first optical information recording medium,
In the first optical information recording medium, the objective optical element forms a spot diameter on the first optical information recording medium determined from an effective diameter and a focal length of the objective optical element,
When the first optical information recording medium is used, a case where the absolute value of the unsatisfactory sine condition is maximum exists in the shared area,
COMA1 (λ1 rms) is generated when the first optical information recording medium is obliquely incident on the objective optical element at an angle of view of 1 ° when the first optical information recording medium is used, and the angle of view is 1 when the second optical information recording medium is used. If the coma generated when obliquely incident on the objective optical element at ° is COMA2 (λ2rms),
0.5 ≦ COMA1 / COMA2 ≦ 1.0 (1)
An objective optical element of an optical pickup device, characterized in that: When using the first optical information recording medium, if the height from the optical axis of the light beam passing through the outermost peripheral portion of the effective diameter of the objective optical element is hmax, the sine condition unsatisfactory amount of the outermost light beam SC1 is
│SC1 (hmax) │ ≦ 0.010mm (4)
The objective optical element of the optical pickup device according to claim 1, wherein: When an infinite object distance ray having a height h from the optical axis is emitted from the objective optical element, the angle formed by the ray and the optical axis after emission is represented by U, and the unsatisfactory sine condition is SC (h ) = H / sinU−f (f is the focal length of the objective optical element when each information recording medium is used), the sine in the common area when the first optical information recording medium is used. If the minimum value of the unsatisfied condition is SC1Dmin and the minimum value of the unsatisfactory sine condition in the dedicated area is SC1Smin,
1.2 · SC1Dmin ≤ SC1Smin (5)
The objective optical element of the optical pickup device according to claim 1 , wherein the objective optical element is an optical element. A first light source having a wavelength λ1 for recording or reproducing information by irradiating a light beam onto a first optical information recording medium having a transparent substrate thickness t1, and a transparent substrate having a thickness t2 (t1 A second light source having a wavelength λ2 (λ1 <λ2) for recording or reproducing information by irradiating the second optical information recording medium with <t2) with a light beam, and the first and second And a condensing optical system including an objective optical element that condenses the light beam emitted from the light source on the information recording surface via the transparent substrates of the first and second optical information recording media. Because
The objective optical element has an objective lens that condenses the light flux from the first or second light source, and an optical function surface that gives an optical action to the light flux,
The optical function surface of the objective optical element includes an optical axis and a common area used for recording and / or reproducing information with respect to both the first optical information recording medium and the second optical information recording medium. A dedicated area provided outside the shared area and mainly used for recording and / or reproducing information with respect to the first optical information recording medium,
In the first optical information recording medium, the objective optical element forms a spot diameter on the first optical information recording medium determined from an effective diameter and a focal length of the objective optical element,
When the first optical information recording medium is used, there is a case where the absolute value of the unsatisfactory sine condition is maximum in the common area,
COMA1 (λ1 rms) is generated when the first optical information recording medium is obliquely incident on the objective optical element at an angle of view of 1 ° when the first optical information recording medium is used, and the angle of view is 1 when the second optical information recording medium is used. If the coma generated when obliquely incident on the objective optical element at ° is COMA2 (λ2rms),
0.5 ≦ COMA1 / COMA2 ≦ 1.0 (1)
An optical pickup device satisfying the requirements.