JPWO2007138924A1 - Optical pickup device - Google Patents

Abstract

In order to appropriately perform high-precision recording and / or reproduction on an optical information recording medium having a high recording density regardless of changes in the environmental temperature and variations in the wavelength of the light source, the optical pickup device 1 according to the present invention has a wavelength The semiconductor laser oscillator LD1 that emits the first light beam L1 of 380 to 420 nm and the objective lens 15 that is a single lens whose main component is a resin material are included, and the first light beam passes through the objective lens 15. Recording and / or reproduction on the BD 10 by L1, the image-side numerical aperture NA1 of the objective lens 15 is 0.75 to 0.87, and the working distance of the objective lens 15 relative to the BD 10 is 0.3 mm or more. Yes, satisfying a certain relational expression.

Description

  The present invention relates to an optical pickup device that records and / or reproduces optical information, and in particular, uses a blue-violet light source having a wavelength of 380 to 420 nm and an image density of an objective lens is 0.75 to 0.87. The present invention relates to an optical pickup device capable of recording and / or reproducing the above, and can be manufactured at low cost by using a resin as a main component of an objective lens and has excellent optical performance.

  Conventionally, an optical pickup device for recording and / or reproducing information on an optical information recording medium such as a compact disc (CD) or a digital versatile disc (DVD) has been developed. As an optical pickup device for CD, an optical pickup device having a light source wavelength of about 770 to 800 nm and an image side numerical aperture of an objective lens of about 0.42 to 0.52 is used. As an optical pickup device for DVD, an optical pickup device in which the wavelength of a light source is about 630 to 660 nm and the image side numerical aperture of an objective lens is about 0.60 to 0.70 is used.

  In recent years, an optical information recording medium having a further improved recording capacity has been demanded with the increase in the number of pixels of digital images and the spread of terrestrial digital broadcasting, and accordingly, a blue-violet light source (blue-violet laser) of 380 to 420 nm is used. Development of optical pickup devices that have been underway is ongoing.

  Furthermore, in order to improve the recording density, it is necessary to increase the numerical aperture of the objective lens in addition to shortening the wavelength of the light source, and it is used for recording and / or reproduction of a standard optical information recording medium called Blu-Ray Disk. A value in the range of 0.75 to 0.85 is required for the image-side numerical aperture of the objective lens.

  On the other hand, an optical element for an optical pickup device has been developed in which the base material is made of glass and the base material is made of a resin material. In general, a glass material has a higher melting point than a resin material, and when an optical element for an optical pickup device is manufactured using the glass material, the lens molding die is rapidly deteriorated and the manufacturing cost is increased. There was a problem. Therefore, development of an optical element using a resin material is strongly desired in order to reduce manufacturing costs.

  However, the resin material has a problem that the optical performance changes greatly due to the temperature change as compared with the glass material. That is, as an optical element for an optical pickup device, aberration may occur due to a change in the refractive index of the material of the optical element due to a change in temperature, and the accuracy of reading information in an optical information recording medium may be reduced. There is. In particular, a high-precision optical pickup used for high-density recording using the above-described blue-violet light source and a high numerical aperture objective lens, in which the temperature change is not a problem in conventional CD and DVD recording and / or reproduction. In the apparatus, it has been found that this causes a large spherical aberration and causes a problem.

  In order to reduce the above problems, a diffractive structure is formed on the optical surface of the objective lens or other optical element, which is offset by changes in the diffractive action caused by changes in the wavelength of the light source when the temperature changes. Therefore, a technique for reducing the change in the amount of spherical aberration has been proposed (see, for example, Patent Document 1). However, the wavelength change due to the temperature change of the blue-violet light source used for recording and / or reproduction of the above-described high-density recording material is very small, and the refractive index change of the objective lens material cannot be sufficiently reduced.

  Furthermore, when a phase structure is formed on the optical surface of the optical element and there is no temperature change, a step is provided that gives an optical path difference that is an integral multiple of the wavelength. A non-periodic phase structure (hereinafter referred to as “Non-Periodic Phase Structure”) that reduces the amount of spherical aberration caused by temperature change by utilizing the fact that the refractive index of the material changes and the optical path difference given by the step shifts from an integral multiple of the wavelength. A technique for providing a phase structure called “NPS”) has also been proposed (see, for example, Patent Document 2).

On the other hand, when information is recorded and / or reproduced by an optical pickup device, the wavelength of the light source may cause a wavelength jump called a so-called mode hop, or the wavelength of the light source itself may vary, thereby eliminating the wavelength shift. It is difficult. However, if the change in the amount of spherical aberration due to a temperature change is corrected using NPS, the light condensing performance (wavelength characteristics) when the wavelength of the light source is shifted by several nm from the design wavelength is deteriorated compared to when NPS is not applied. There was found. That is, when trying to suppress the aberration change using NPS, the spherical aberration change (temperature characteristic) due to temperature change and the spherical aberration change (wavelength characteristic) due to light source wavelength change have a trade-off relationship, and the above-described high-density recording is performed. It has been difficult to obtain sufficient optical performance as an optical pickup device used for recording and / or reproducing a medium.
JP 2001-28359 A JP 2003-248168 A

By the way, when the numerical aperture of the objective lens for the optical pickup device is increased in order to improve the recording density, the condensing angle is increased and the working distance between the objective lens and the optical information recording medium is shortened. However, in order to record and / or reproduce optical information with high accuracy, it is necessary to drive the objective lens in the optical axis direction or in a direction perpendicular to the optical axis for focusing and tracking of the objective lens. A working distance of 3 mm or more is desired. Further, considering the correction of coma aberration that may occur due to the disc tilt of the optical information recording medium and the correspondence to the bad disc, it is desirable that the relationship of the following formula (1.1) is satisfied.
1.0 <d / f <1.5 (1.1)
In formula (1.1), “d” represents the axial thickness of the objective lens, and “f” represents the focal length of the objective lens.

  When the upper limit of d / f in the above formula (1.1) is 1.5 or more, the objective lens becomes thick and it is difficult to secure a sufficient distance from the optical information recording medium. Although it becomes difficult to correct aberrations and cope with bad disks, when d / f is smaller than 1.5, a sufficient interval between the objective lens and the optical information recording medium can be secured.

  On the other hand, when the lower limit of d / f in the above formula (1.1) is 1.0 or less, the radius of curvature of the optical surface on the light source side of the objective lens must be reduced, and as a result, the objective lens is configured. However, when d / f is larger than 1.0, the change of the spherical aberration amount with respect to the change of the refractive index is small, and the working distance can be sufficiently secured. .

  Furthermore, when manufacturing an objective lens having a large numerical aperture, it is one of the desirable conditions to satisfy the relationship of the following formula (1.2).

55 ° <θ _0.9 <65 ° (1.2)
In equation (1.2), “θ _0.9 ” represents a prospective angle at a position corresponding to 0.9 times the pupil diameter on the optical surface on the light source side of the objective lens.

When the lower limit of θ _{0.9 in} the above formula (1.2) is 55 ° or less, the sensitivity effect on the axial thickness error of the objective lens is large, and it becomes difficult to adjust the spherical aberration control during manufacturing. However, if θ _0.9 is greater than 55 °, it will be difficult to supply lenses with stable performance. However, if θ _0.9 is greater than 55 °, large quantities of optical elements based on resin will be produced using conventional injection molding technology. can do.

On the other hand, when the upper limit of θ _{0.9 in} the above formula (1.2) is 65 ° or more, the sensitivity of surface eccentricity (tilt and shift) at the time of manufacturing the objective lens is large, and the coma at the time of manufacture is large. Adjustment of aberration control becomes difficult, and as a result, it is difficult to supply a lens with stable performance at low cost. However, if θ _0.9 is smaller than 65 °, the resin is made by using conventional injection molding technology. It is possible to produce a large amount of lenses with the main component.

  As described above, in developing an optical pickup device used for recording and / or reproducing optical information of an optical information recording medium having a higher recording density than conventional optical information recording media such as CDs and DVDs, a light source is simply used. It is not enough to shorten the wavelength or increase the numerical aperture of the objective lens. In addition to satisfying the performance required from the viewpoint of working distance and manufacturing as described above, aberration changes due to temperature changes and light source wavelength There is a demand for development of an optical pickup device that reduces aberration changes due to variations in the frequency.

  The present invention has been made in view of the above circumstances, and can accurately perform high-precision recording and / or reproduction on an optical information recording medium having a high recording density regardless of changes in environmental temperature and wavelength variations of the light source. Another object of the present invention is to provide an optical pickup device that can be manufactured at low cost by using a resin material as the main component of the base material of the objective lens.

In order to solve the above problems, the first aspect of the present invention is:
A first light source that emits a first light flux having a wavelength of 380 to 420 nm;
An objective lens composed of a single lens whose main component is a resin material;
An optical pickup device that performs recording and / or reproduction on a first optical information recording medium with the first light flux through the objective lens,
The image-side numerical aperture NA1 of the objective lens is 0.75 to 0.87,
The working distance of the objective lens to the first optical information recording medium is 0.3 mm or more,
It is characterized by satisfying all the relationships of the following formulas (1.1), (2), and (3).
1.0 <d / f <1.5 (1.1)
ΔW _T <0.07λrms (2)
ΔW _N <0.07λrms (3)
In formula (1.1), “d” is the axial thickness of the objective lens, and “f” is the focal length of the objective lens. In equation (2), “ΔW _T ” is the wavefront at the focused spot when the ambient temperature of the objective lens changes by 30 ° C. when recording and / or reproducing is performed on the first optical information recording medium. This represents the amount of change in aberration. In equation (3), “ΔW _N ” is the light concentration when the wavelength of the first light flux changes ± 5 nm from the design wavelength when recording and / or reproduction is performed on the first optical information recording medium. It represents the amount of change in wavefront aberration at the spot.

  According to the optical pickup device of the first aspect of the present invention, even in an optical pickup device having a high numerical aperture using a first light source with a wavelength of 380 to 420 nm, a coma caused by disc tilt can be obtained by sufficiently securing a working distance. Aberration correction and compatibility with bad disks can be taken, the wavefront aberration can be kept within an appropriate range even when the ambient temperature changes by about 30 °, and the wavelength of the first light source is designed. Since the wavefront aberration can be maintained in an appropriate range even when the wavelength is deviated from the wavelength, recording and / or reproduction on the first optical information recording medium can be performed without any problem.

The second aspect of the present invention is:
A first light source that emits a first light flux having a wavelength of 380 to 420 nm;
An objective lens composed of a single lens whose main component is a resin material;
An optical pickup device that performs recording and / or reproduction on a first optical information recording medium with the first light flux through the objective lens,
The image-side numerical aperture NA1 of the objective lens is 0.75 to 0.87,
The working distance of the objective lens to the first optical information recording medium is 0.3 mm or more,
It is characterized by satisfying all the relationships of the following formulas (1.2), (2), and (3).

55 ° <θ _0.9 <65 ° (1.2)
ΔW _T <0.07λrms (2)
ΔW _N <0.07λrms (3)
In equation (1.2), “θ _0.9 ” is an expected angle at a position corresponding to 0.9 times the pupil diameter on the light source side optical surface of the objective lens. In equation (2), “ΔW _T ” is the wavefront at the focused spot when the ambient temperature of the objective lens changes by 30 ° C. when recording and / or reproducing is performed on the first optical information recording medium. This represents the amount of change in aberration. In equation (3), “ΔW _N ” is the light concentration when the wavelength of the first light flux changes ± 5 nm from the design wavelength when recording and / or reproduction is performed on the first optical information recording medium. It represents the amount of change in wavefront aberration at the spot.

  According to the optical pickup device of the second aspect of the present invention, even an optical pickup device having a high numerical aperture using a first light source having a wavelength of 380 to 420 nm can be easily molded using a conventional injection molding technique. The wavefront aberration can be maintained in an appropriate range even when the environmental temperature changes by about 30 °, and the wavefront aberration can be maintained even when the wavelength of the first light source deviates from the design wavelength. Can be maintained in an appropriate range, and recording and / or reproduction on the first optical information recording medium can be performed without any problem.

  In the optical pickup devices of the first and second embodiments, it is preferable that the objective lens is made of an organic-inorganic composite material in which inorganic particles are dispersed in a resin material.

  In the optical pickup devices of the first and second embodiments, it is preferable that a phase structure is provided on at least one optical surface of the objective lens.

  The phase structure is a so-called NPS, and the phase structure itself cancels out the change in the spherical aberration component caused by the change in the refractive index of the base material of the objective lens due to the change in the ambient temperature of the objective lens. It is preferable to have.

  The phase structure may be a diffractive structure.

  The diffractive structure is a spherical aberration component generated when the refractive index of the base material of the objective lens changes due to a change in the ambient temperature of the objective lens when recording or reproducing is performed on the first optical information recording medium. It is preferable to have an action of canceling out the change by the change of the spherical aberration component generated by the change of the wavelength of the first light beam due to the change of the ambient temperature of the first light source.

  The phase structure preferably has a plurality of annular structures concentric with the optical axis of the objective lens.

In the optical pickup devices of the first and second embodiments,
A second light source that emits a second light flux having a wavelength of 630 to 660 nm;
A third light source that emits a third light flux having a wavelength of 770 to 800 nm,
Recording and / or reproduction on the second optical information recording medium with the second light flux through the objective lens,
It is preferable that recording and / or reproduction is performed on the third optical information recording medium with the third light flux through the objective lens.

  When recording and / or reproducing on the second optical information recording medium, the image-side numerical aperture NA2 of the objective lens is 0.60 to 0.70, and recording and / or recording on the third optical information recording medium is performed. In the case of performing reproduction, it is preferable that the image side numerical aperture NA3 of the objective lens is 0.42 to 0.52 in terms of corresponding to the standard of optical information recording media such as CD and DVD that are widely used at present. .

  Further, when recording and / or reproducing with respect to a plurality of optical information recording media with the same optical pickup device, it is necessary to reduce the spherical aberration due to the difference in the thickness of the protective substrate of the optical information recording medium. When each of the first to third optical information recording media has a transparent protective substrate, the objective lens has at least one of the first to third optical information recording media on the at least one optical surface. It is preferable to have a phase structure that corrects spherical aberration due to the difference in thickness of the transparent protective substrate of the third optical information recording medium.

  According to the present invention, high-precision recording and / or reproduction can be appropriately performed on an optical information recording medium having a high recording density regardless of a change in environmental temperature or a variation in wavelength of a light source, and By using a resin material as the main component, an optical pickup device that can be manufactured at low cost can be obtained.

It is a figure which shows schematic structure of an optical pick-up apparatus. It is sectional drawing which shows an example of the phase structure of an objective lens. It is sectional drawing which shows an example of the phase structure of an objective lens. It is sectional drawing which shows an example of the phase structure of an objective lens. It is sectional drawing which shows an example of the phase structure of an objective lens. It is sectional drawing which shows an example of the phase structure of an objective lens. It is sectional drawing which shows an example of the phase structure of an objective lens. The numerical aperture of the objective lens is 0.45, a graph illustrating focal length 2.5 mm, dn / dt in the case of the entrance pupil diameter Fai2.35Mm, the relationship between the refractive index n and the wave front aberration change amount [Delta] W _T. The numerical aperture of the objective lens is 0.65, a graph illustrating focal length 2.5 mm, dn / dt in the case of the entrance pupil diameter Fai3.35Mm, the relationship between the refractive index n and the wave front aberration change amount [Delta] W _T. The numerical aperture of the objective lens is 0.85, the focal length 1.7645mm, dn / dt in the case of the entrance pupil diameter Fai3.00Mm, graph showing the relationship between the refractive index n and the wave front aberration change amount [Delta] W _T. It is a graph which shows the relationship between the addition amount of the inorganic particle with respect to resin, dn / dt, and the refractive index n. 6 is a schematic diagram showing a cross section of an objective lens shown in Example 2. FIG. 6 is a schematic diagram showing a cross section of an objective lens shown in Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 15 Objective lens 10 BD (1st optical information recording medium)
20 DVD (second optical information recording medium)
30 CD (third optical information recording medium)
LD1 Semiconductor laser oscillator (first light source)
LD2 Semiconductor laser oscillator (second light source)
LD3 Semiconductor laser oscillator (third light source)
L1 1st light beam L2 2nd light beam L3 3rd light beam

  The best mode for carrying out the present invention will be described below with reference to the drawings. However, although various technically preferable limitations for carrying out the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

In this embodiment, first, (A) an optical pickup device and (B) an objective lens applied to the optical pickup device according to the present invention will be described, and then (C) characteristics of the optical pickup device will be described. explain.
(A) Optical Pickup Device Hereinafter, preferred embodiments of the optical pickup device according to the present invention will be described.

  As shown in FIG. 1, the optical pickup device 1 includes three types of semiconductor laser oscillators LD1, LD2, and LD3 as light sources. A semiconductor laser oscillator LD1 as a first light source emits a light beam having a specific wavelength in a wavelength of 380 to 420 nm, for example, a wavelength of 405 nm or 407 nm, as a first light beam L1 for a BD (Blu-Ray Disc) 10. Yes. The semiconductor laser oscillator LD2 as the second light source emits a light beam having a specific wavelength in a wavelength of 630 to 660 nm as the second light beam L2 for the DVD 20. The semiconductor laser oscillator LD3 as the third light source emits a light beam having a specific wavelength in the range of 770 to 800 nm as the third light beam L3 for the CD30.

  Here, an optical pickup device corresponding to three types of optical information recording media of BD10, DVD20, and CD30 will be described as a preferred form, but the present invention is applicable to two types of optical information recording media even when dedicated to BD. An optical pickup device may be used.

  In the optical axis direction of the blue-violet light emitted from the semiconductor laser oscillator LD1, a shave SH1, a splitter BS1, a collimator CL, splitters BS4 and BS5, and an objective lens 15 are sequentially arranged from the lower side to the upper side in FIG. ing. At a position facing the objective lens 15, a BD 10 as a first optical information recording medium, a DVD 20 as a second optical information recording medium, and a CD 30 as a third optical information recording medium are arranged. Yes. A cylindrical lens L11, a concave lens L12, and a photodetector PD1 are sequentially disposed on the right side of the splitter BS1 in FIG.

  In the optical axis direction of the red light emitted from the semiconductor laser oscillator LD2, splitters BS2 and BS4 are sequentially arranged from the left to the right in FIG. A cylindrical lens L21, a concave lens L22, and a photodetector PD2 are sequentially disposed below the splitter BS2 in FIG.

  In the optical axis direction of the light emitted from the semiconductor laser oscillator LD3, splitters BS3 and BS5 are sequentially arranged from the right to the left in FIG. A cylindrical lens L31, a concave lens L32, and a photodetector PD3 are sequentially disposed below the splitter BS3 in FIG.

  The objective lens 15 is disposed opposite to the BD10, DVD20, or CD30 as the first to third optical information recording media, and the light emitted from each of the semiconductor laser oscillators LD1, LD2, LD3 is BD10, DVD20, or It concentrates on CD30. The BD 10, the DVD 20, and the CD 30 have recording surfaces 10a, 20a, and 30a, respectively, and the surfaces of the recording surfaces 10a, 20a, and 30a are covered with a transparent protective substrate.

  The objective lens 15 includes the two-dimensional actuator 2, and the objective lens 15 is movable in the vertical direction and the horizontal direction by the operation of the two-dimensional actuator 2. In the optical pickup device 1, the working distance of the objective lens 15 with respect to each of the transparent protective substrates BD10, DVD20 and CD30 is set to 0.3 mm or more.

  Next, the operation of the optical pickup device 1 will be described.

  Since the optical pickup device 1 in the present embodiment performs different operations depending on the types of the first to third optical information recording media, details of operation modes for the BD 10, the DVD 20, and the CD 30 will be described below.

First, the operation of the optical pickup device 1 with respect to the BD 10 will be described.
At the time of recording and / or reproducing information on the BD 10, the semiconductor laser oscillator LD1 emits the first light beam L1. As shown in FIG. 1, the first light beam L1 passes through the shave SH1 and is shaped, passes through the splitter BS1, and is converted into parallel light by the collimator CL, and then the splitters BS4 and BS5, the objective lens 15 and the BD10. A condensing spot is formed on the recording surface 10a of the BD 10 through the transparent protective substrate.

  The first light beam L1 that forms the condensed spot is modulated by the information pits on the recording surface 10a of the BD 10 and reflected by the recording surface 10a. The reflected first light beam L1 passes through the transparent protective substrate of the BD 10, the objective lens 15, the splitter BS5, the splitter BS4, and the collimator CL, and is reflected by the splitter BS1 and then passes through the cylindrical lens L11, resulting in astigmatism. Given. Thereafter, the first light beam L1 passes through the concave lens L12 and is received by the photodetector PD1.

  Thereafter, such an operation is repeatedly performed, and an operation for recording information on the BD 10 and an operation for reproducing information recorded on the BD 10 are performed.

  Next, the operation of the optical pickup device 1 for the DVD 20 will be described.

  At the time of recording and / or reproducing information on the DVD 20, the semiconductor laser oscillator LD2 emits the second light beam L2. As shown in FIG. 1, the second light beam L2 passes through the splitter BS2 and is reflected by the splitter BS4. The reflected second light beam L2 passes through the splitter BS5, the objective lens 15, and the transparent protective substrate of the DVD 20, and forms a condensed spot on the recording surface 20a of the DVD 20.

  The second light beam L2 that forms the condensed spot is modulated by the information pits on the recording surface 20a of the DVD 20 and reflected by the recording surface 20a. The reflected second light beam L2 is transmitted through the transparent protective substrate of the DVD 20, the objective lens 15 and the splitter BS5, reflected by the splitters BS4 and BS2, and then transmitted through the cylindrical lens L21 to give astigmatism. Thereafter, the second light beam L2 passes through the concave lens L22 and is received by the photodetector PD2.

  Thereafter, such an operation is repeatedly performed, and an operation for recording information on the DVD 20 and an operation for reproducing information recorded on the DVD 20 are performed.

  Finally, the operation of the optical pickup device 1 for the CD 30 will be described.

  At the time of recording and / or reproducing information on the CD 30, the third light beam L3 is emitted from the semiconductor laser oscillator LD3. As shown in FIG. 1, the third light beam L3 passes through the splitter BS3 and is reflected by the splitter BS5. The reflected third light beam L3 passes through the objective lens 15 and the transparent protective substrate of the CD 30, and forms a condensed spot on the recording surface 30a of the CD 30.

  The third light beam L3 forming the focused spot is modulated by the information pits on the recording surface 30a of the CD 30, and reflected by the recording surface 30a. The reflected third light beam L3 is transmitted through the transparent protective substrate of CD 30 and the objective lens 15, reflected by the splitters BS5 and BS3, and then transmitted through the cylindrical lens L31 to give astigmatism. Thereafter, the third light beam L3 passes through the concave lens L32 and is received by the photodetector PD3.

  Thereafter, such an operation is repeatedly performed, and an operation for recording information on the CD 30 and an operation for reproducing information recorded on the CD 30 are performed.

  The optical pickup device 1 detects a change in light amount due to a change in the shape or position of a spot in each of the photodetectors PD1, PD2, and PD3 at the time of recording and / or reproducing information on the BD 10, DVD 20 or CD 30. Focus detection and track detection are performed. In such an optical pickup device 1, the two-dimensional actuator 2 transmits the light from the semiconductor laser oscillators LD1, LD2, and LD3 to the BD10, DVD20, or CD30 based on the detection results of the photodetectors PD1, PD2, and PD3. The objective lens 15 is moved so as to form an image on the recording surfaces 10a, 20a, and 30a, and the light from the semiconductor laser oscillators LD1, LD2, and LD3 is formed on predetermined tracks on the recording surfaces 10a, 20a, and 30a. The objective lens 15 is moved.

Further, in the optical pickup device 1, when recording and / or reproduction is performed on the BD 10 with the first light beam L1, the image-side numerical aperture NA1 of the objective lens 15 is 0.75 to 0.87, and the second When recording and / or reproducing on the DVD 20 with the light beam L2, the image-side numerical aperture NA2 of the objective lens 15 is 0.60 to 0.70, and recording and / or reproduction on the CD 30 with the third light beam L3. When performing the above, the image-side numerical aperture NA3 of the objective lens 15 is 0.42 to 0.52.
(B) Objective lens (B.1) Characteristics of objective lens The objective lens 15 is composed of a single lens whose main component is a resin material (see below), and has a phase structure on at least one optical surface. Have. The “phase structure” is a general term for a structure having a step in the optical axis direction and adding an optical path difference (phase difference) to the incident light flux (first to third light fluxes L1 to L3). The shape of the phase structure is not particularly limited, but the phase structure is preferably an annular structure divided by a plurality of concentric steps with the optical axis as the center. The optical path difference added to the incident light flux may be an integer multiple of the wavelength of the incident light flux or a non-integer multiple of the wavelength of the incident light flux.

  In the objective lens 15, the above-described phase structure is configured to change the spherical aberration component generated due to the change in the refractive index of the base material of the objective lens 15 when the ambient temperature of the objective lens 15 changes. Due to self-cancelling action or due to the difference in the thickness of the transparent protective substrate of at least two of the first to third optical information recording media among BD10, DVD20 and CD30 as the first to third optical information recording media The spherical aberration is corrected.

  In the objective lens 15, the phase structure may be a diffractive structure. In this case, when performing recording or reproduction on the BD 10 as the first optical information recording medium, the diffractive structure changes the refractive index of the base material of the objective lens 15 when the ambient temperature of the objective lens 15 changes. Therefore, the spherical aberration component change caused by the change of the spherical aberration component generated by the change of the wavelength of the first light beam L1 due to the change of the ambient temperature of the semiconductor laser oscillator LD1 is canceled. ing.

  The phase structure of the objective lens 15 can take various cross-sectional shapes, and application examples (cross-sectional structures) thereof are shown in FIGS.

  Each phase structure will be briefly described. The phase structure in FIG. 2 has a sawtooth shape, and the phase structure in FIG. 3 has a step shape in which all the steps are in the same direction. The structure has a stepped shape in which the direction of the step is opposite in the middle, and the phase structure of FIG. 5 is arranged in a concentric pattern with a stepped cross-sectional shape and has a predetermined number of level faces (in FIG. 5). For each number of (5 level planes), the level is shifted by a height corresponding to the number of level planes (4 levels in FIG. 5).

  The phase structure of FIG. 2 shows the case where the directions of the saw blades are the same, and the phase structure of FIG. 5 shows the case where the directions of the patterns whose cross-sectional shapes are stepped are the same. As shown in FIG. 6 and FIG. 7, it has a phase inversion part PR, and sawtooth or pattern directions are inverted from each other on the side closer to the optical axis and the side farther from the phase inversion part PR. There may be.

2 to 7 show examples in which each phase structure is formed on a plane, but each phase structure may be formed on a spherical surface or an aspherical surface. Further, in FIG. 5 and FIG. 7, the predetermined number of level faces is 5, but the present invention is not limited to this.
(B.2) Objective lens composition and manufacturing method There are no particular limitations on the base material constituting the objective lens 15 as long as the main component is a resin material. It is necessary to appropriately select a resin material or to adjust the characteristics of the resin material so as to satisfy the expressions (2) and (3). In order to adjust the characteristics of the resin material, it is one of preferred modes to use an organic-inorganic composite material in which inorganic particles are dispersed in the main resin material as the base material of the objective lens.
(B.2.1) Resin Material The resin material to be selected is not particularly limited as long as it is a transparent resin material generally used as an optical material. However, the workability as an optical element (objective lens 15) is not limited. In consideration, it is preferably an acrylic resin, a cyclic olefin resin, a polycarbonate resin, a polyester resin, a polyether resin, a polyamide resin, or a polyimide resin, and particularly preferably a cyclic olefin resin, for example, JP-A-2003-73559. And the like. Preferred compounds are shown in Table 1.

In the resin material, the water absorption is preferably 0.2% by mass or less. Examples of the resin having a water absorption of 0.2% by mass or less include polyolefin resin (for example, polyethylene, polypropylene, etc.), fluororesin (for example, polytetrafluoroethylene, Teflon (registered trademark) AF (manufactured by DuPont), Top (made by Asahi Glass Co., Ltd.), cyclic olefin resin (for example, ZEONEX (manufactured by Nippon Zeon), Arton (manufactured by JSR), Apel (manufactured by Mitsui Chemicals), TOPAS (manufactured by Polyplastics), etc.), Styrenic resins, polycarbonates and the like are suitable, but not limited to these. It is also preferable to use other resins compatible with these resins. When two or more kinds of resins are used, the water absorption rate is considered to be approximately equal to the average value of the water absorption rates of the individual resins, and the average water absorption rate only needs to be 0.2% or less.
(B.2.2) Types and characteristics of inorganic particles, production methods, etc. [types of inorganic particles, etc.]
When inorganic particles are added to the resin material, the particle size of the inorganic particles that can be used needs to be sufficiently smaller than the working wavelength of 380 to 420 nm, but the volume average dispersed particle size is 30 nm or less. It is preferably 1 to 30 nm, more preferably 1 to 10 nm or less. If the volume average dispersed particle diameter is 1 nm or more, the dispersibility of the inorganic particles can be ensured and desired performance can be obtained. If the volume average dispersed particle diameter is 30 nm or less, the obtained organic inorganic Good transparency of the composite material can be obtained, and a light transmittance of 70% or more can be achieved. The volume average dispersed particle size here refers to the diameter when inorganic particles in a dispersed state are converted into spheres having the same volume.

  The shape of the inorganic particles is not particularly limited, but spherical fine particles are preferably used from the viewpoint of fluidity. Further, the particle size distribution is not particularly limited, but those having a relatively narrow distribution are preferably used rather than those having a wide distribution from the viewpoint of stability. Some of these inorganic particles may be present as amorphous.

  Examples of the inorganic particles include oxide fine particles. More specifically, as the oxide fine particles, for example, silicon oxide, titanium oxide, zinc oxide, aluminum oxide, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, Yttrium oxide, lanthanum oxide, cerium oxide, indium oxide, tin oxide, lead oxide, multiple oxides composed of these oxides such as lithium niobate, potassium niobate, lithium tantalate, etc., or phosphate, sulfuric acid Examples thereof include salts.

In addition, fine particles having a semiconductor crystal composition can be preferably used as the inorganic particles. Although there is no restriction | limiting in particular in the said semiconductor crystal composition, What does not produce absorption, light emission, fluorescence, etc. in the wavelength range used as an optical element (objective lens 15) is desirable. Specific examples of the composition include, for example, a simple substance of Group 14 element of the periodic table such as carbon, silicon, germanium and tin, a simple substance of Group 15 element of the periodic table such as phosphorus (black phosphorus), and a periodicity of selenium, tellurium and the like. Table 16 group element simple substance, compound consisting of a plurality of periodic table group 14 elements such as silicon carbide (SiC), tin (IV) (SnO ₂ ), tin sulfide (II, IV) (Sn (II) Sn (IV) S ₃ ), tin sulfide (IV) (SnS ₂ ), tin (II) sulfide (SnS), tin (II) selenide (SnSe), tin telluride (II) (SnTe), lead sulfide (II) ) (PbS), lead selenide (II) (PbSe), lead telluride (II) (PbTe) periodic table group 14 element and periodic table group 16 element compound, boron nitride (BN), phosphorus Boron bromide (BP), boron arsenide (BAs), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb) , Indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), etc. group 13 element and periodic table group 15 element (or III-V group) Compound semiconductor), aluminum sulfide (Al ₂ S ₃ ), aluminum selenide (Al ₂ Se ₃ ), gallium sulfide (Ga ₂ S ₃ ), gallium selenide (Ga ₂ Se ₃ ), gallium telluride (Ga ₂ Te ₃₎ ), Indium oxide (In ₂ O ₃ ), indium sulfide (In ₂ S) ₃ ), a compound of a periodic table group 13 element and a periodic table group 16 element such as indium selenide (In ₂ Se ₃ ), indium telluride (In ₂ Te ₃ ), thallium chloride (I) (TlCl), Compounds of Group 13 elements of the periodic table and Group 17 elements of the periodic table such as thallium bromide (I) (TlBr), thallium iodide (I) (TlI), zinc oxide (ZnO), zinc sulfide (ZnS), Zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium oxide (CdO), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenide ( HgSe), mercury telluride (HgTe) and other compounds of Group 12 elements of the periodic table and Group 16 elements of the periodic table (or II to VI compound semiconductors), arsenic sulfide (II) I) (As ₂ S ₃ ), arsenic selenide (III) (As ₂ Se ₃ ), arsenic telluride (III) (As ₂ Te ₃ ), antimony sulfide (III) (Sb ₂ S ₃ ), antimony selenide (III) (Sb ₂ Se ₃ ), antimony telluride (III) (Sb ₂ Te ₃ ), bismuth sulfide (III) (Bi ₂ S ₃ ), bismuth selenide (III) (Bi ₂ Se ₃ ), telluride Compound of periodic table group 15 element and periodic table group 16 element such as bismuth (III) (Bi ₂ Te ₃ ), copper oxide (I) (Cu ₂ O), copper selenide (Cu ₂ Se) ) And other compounds of Group 11 elements of the periodic table and Group 16 elements of the periodic table, copper chloride (I) (CuCl), copper bromide (I) (CuBr), copper iodide (I) (CuI), chloride Silver (AgCl), silver bromide (AgBr), etc. Compound of periodic table group 11 element and periodic table group 17 element, compound of periodic table group 10 element such as nickel oxide (II) (NiO) and periodic table group 16 element, cobalt oxide (II) ( Compounds of Group 9 elements of the periodic table and Group 16 elements of the periodic table such as CoO) and cobalt sulfide (II) (CoS), triiron tetroxide (Fe ₃ O ₄ ), iron (II) sulfide (FeS), etc. Compound of Group 8 element of Periodic Table and Group 16 element of Periodic Table, Compound of Group 7 Element of Periodic Table such as Manganese (II) (MnO) and Group 16 Element of Periodic Table, Molybdenum Sulfide (IV) (MoS ₂ ), tungsten oxide (IV) (WO ₂ ) and other periodic table group 6 elements and periodic table group 16 elements, vanadium oxide (II) (VO), vanadium oxide (IV) (VO 2) , peripheral, such as a tantalum oxide _{(V) (Ta 2 O 5} ) Table Compounds of the group 5 element and the Periodic Table Group 16 element, a titanium oxide _{(TiO 2, Ti 2 O 5} , Ti 2 O 3, Ti5O9 , etc.) Group 4 of the periodic table element and Periodic Table Group 16 element such as , Compounds of periodic table group 2 elements such as magnesium sulfide (MgS), magnesium selenide (MgSe), and periodic table group 16 elements, cadmium (II) oxide (Chromium (III) (CdCr ₂ O ₄ ) , Cadmium selenide (II) chromium (III) (CdCr ₂ Se ₄ ), copper (II) sulfide (III) (CuCr ₂ S ₄ ), mercury (II) selenide (III) (HgCr ₂ Se ₄ ) And chalcogen spinels such as barium titanate (BaTiO ₃ ).

In addition, G. Schmid et al .; Adv. Mater. 4, 494 (1991) (BN) 75 (BF2) 15F15 and D.C. Fenske et al .; Angew. Chem. Int. Ed. Engl. 29, page 1452 (1990), a semiconductor cluster having a fixed structure such as Cu ₁₄₆ Se ₇₃ (triethylphosphine) 22 reported in the same manner is also exemplified.

As these inorganic particles, one kind of inorganic particles may be used, or a plurality of kinds of inorganic particles may be used in combination. It is also possible to use inorganic particles having a composite composition. The plurality of types of inorganic particles may be any of a mixed type, a core-shell (laminated) type, a compound type, and a composite type (a type in which another inorganic particle is present in one base material inorganic particle). When two or more kinds of inorganic particles are used, the composition of the inorganic particles is preferably a substantially uniform composition. The uniformity of the composition is usually determined by a composition analysis by TEM or the like. However, in the case of a uniform composition, light scattering due to the composition distribution inside the particles does not occur, which is preferable because of high transparency and uniform refractive index. .
[Refractive index of inorganic particles]
The refractive index of the resin material used as the optical element (objective lens 15) is often a refractive index nd25 measured using helium d-line (25 ° C.) as a light source and is in the vicinity of 1.5 to 1.7. The refractive index of the particles is also preferably adjusted so that nd25 is 1.5 to 1.7. Specific examples of preferable inorganic particles include silicon oxide, aluminum oxide, zirconium oxide, and composite composition particles, which are appropriately selected depending on the resin material used and the characteristics required for the optical element (objective lens 15). For example, the refractive index is measured by an Abbe refractometer or the like according to ASTM D542 standard, and values described in various documents can be used. Also, the inorganic particles are dispersed in various solvents with adjusted refractive indexes, the absorbance of the dispersion is measured, and the refractive index of the solvent that minimizes the value is measured, thereby confirming the refractive index of the inorganic particles. it can.
[Filling rate of inorganic particles]
The volume ratio of the inorganic particles contained in the final organic-inorganic composite material is 1 to 70% by volume, preferably 10 to 50% by volume. When the content of the inorganic particles of the organic-inorganic composite material is 1% by volume or less, desired physical property improvement may not be obtained. Moreover, when content of the inorganic particle of an organic inorganic composite material is 70 volume% or more, it may become a problem in economical efficiency, moldability, and permeability.
[Method for producing inorganic particles]
The method for producing the inorganic particles is not particularly limited, and any known method can be used. In general, inorganic particles can be produced by a pyrolysis method (a method in which raw materials are thermally decomposed to obtain fine particles. A spray drying method, a flame spray method, a plasma method, a gas phase reaction method, a freeze drying method, a heated kerosene method. , Heating petroleum method), precipitation method (coprecipitation method), hydrolysis method (salt aqueous solution method, alkoxide method, sol-gel method), hydrothermal method (precipitation method, crystallization method, hydrothermal decomposition method, hydrothermal oxidation method) Etc.

  As a specific production method, oxide fine particles can be obtained by using a metal halide or an alkoxy metal as a raw material and hydrolyzing in a reaction system containing water. At this time, a method of using an organic acid, an organic amine or the like in combination is also used for stabilizing the fine particles. More detailed methods include titanium dioxide fine particles in Journal of Chemical Engineering of Japan Vol. 31, No. 1, pp. 21-28 (1998), and Journal of Physical Chemistry, Vol. 100, pp. 468-471 (1996). ) Zinc sulfide fine particles. According to these methods, titanium oxide having a volume average dispersed particle diameter of 5 nm is added with a suitable surface modifier when hydrolyzed in a suitable solvent using titanium tetraisopropoxide or titanium tetrachloride as a raw material. Can be easily manufactured.

In addition, zinc sulfide having a volume average dispersed particle size of 40 nm can be produced by adding a surface modifier when dimethylzinc or zinc chloride is used as a raw material and sulfurized with hydrogen sulfide or sodium sulfide. The method for surface modification is not particularly limited, and any known method can be used. For example, there is a method of modifying the surface of the fine particles by hydrolysis under conditions where water is present. In this method, a catalyst such as an acid or an alkali is preferably used, and it is generally considered that a hydroxyl group on the surface of fine particles and a hydroxyl group generated by hydrolysis of a surface modifier dehydrate to form a bond [ Surface modifier]
Affinity with the resin material can be improved by performing an appropriate surface treatment on the inorganic particles. Examples of the surface modifier to be applied include silane coupling agents, aluminate coupling agents, titanate coupling agents, amino acid dispersants, and various silicone oils.

  These are appropriately selected in consideration of the properties of the inorganic particles used and the affinity with the resin material used in obtaining the inorganic particle-dispersed resin material. Two or more surface treatments may be performed simultaneously or at different times.

  There are various methods for performing the surface treatment of the inorganic particles, and the surface treatment may be performed in advance before mixing with the resin material. Examples thereof include a wet heating method, a wet filtration method, and a method (integral blend method) performed at the time of mixing with a thermoplastic resin.

  Specific examples of the silane coupling agent include vinylsilazane trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, trimethylalkoxysilane, dimethyldialkoxysilane, methyltrialkoxysilane, hexamethyldisilazane, and the like. Hexamethyldisilazane or the like is preferably used to cover the surface of the particles widely.

Silicone oil-based treatment agents include straight silicone oil such as dimethyl silicone oil, methylphenyl silicone oil, and methylhydrogen silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil, carbinol-modified silicone oil, and methacryl-modified silicone. Oil, mercapto modified silicone oil, phenol modified silicone oil, one-end reactive modified silicone oil, heterogeneous functional group modified silicone oil, polyether modified silicone oil, methylstyryl modified silicone oil, alkyl modified silicone oil, higher fatty acid ester modified silicone oil , Hydrophilic specially modified silicone oil, higher alkoxy modified silicone oil, higher fat It can be used containing modified silicone oil, a modified silicone oil such as fluorine-modified silicone oil. These treatment agents may be appropriately diluted with hexane, toluene, methanol, ethanol, acetone water or the like.
[Amount of coupling agent added]
The amount of the coupling agent added is relatively large because the inorganic particles used are nano-sized and have a large specific surface area. The specific amount is about 5 to 100 parts by weight with respect to 100 parts by weight of the inorganic particles, and the expected surface treatment effect cannot be obtained, and the particles are aggregated, and the voids are generated in the resin material. Increase in linear expansion coefficient or decrease in light transmittance is a problem, so 5 parts by weight or more is desirable with respect to 100 parts by weight of inorganic particles, and it is inorganic due to an increase in cost and a problem of solubilization with a resin material to be used. It is desirable to keep it to 100 parts by weight or less with respect to 100 parts by weight of the particles.
(B.2.3) Manufacturing method of organic / inorganic composite material When preparing an organic / inorganic composite material using inorganic particles and a resin material, an organic / inorganic material in which inorganic particles and a resin material are premixed in advance at a predetermined mixing ratio. It is desirable to make a composite material. Advantages include prevention of powder scattering, operational convenience, and improvement in dispersibility. However, wet-mixing is desirable in order to suppress damage to the resin material in the production of the organic-inorganic composite material. The liquid or solution comes into contact with the surface of the inorganic particles that are usually mixed, the surface wets, the solid surface disappears, and there is a newly formed interface between the solid and the liquid or solution, and there is a dissolved resin material that covers the entire interface. It is desirable to mix in this state. However, the amount of liquid or solution specifically used is appropriately selected depending on the inorganic particles and resin material used.
[Wet mixing method]
In wet mixing of resin materials and inorganic particles, known methods such as tumbler mixer, super mixer, Henschel mixer, screw blender, ribbon blender can be applied, but super mixer with large mixing torque and less influence of residue is particularly suitable. Used for.

  Here, the blending amount of the inorganic particles with respect to the resin material is preferably 25 to 300 parts by volume. If it is smaller than 25 parts by volume, the effect of the added inorganic particles is not sufficiently exhibited. On the other hand, when the volume is larger than 300 parts by volume, the resin material as a binder is insufficient, a uniform composition cannot be obtained, the adhesion between the interface between the inorganic particles and the resin material becomes insufficient, and voids are generated. When an organic-inorganic composite material containing voids is produced in this way, resin deterioration due to oxygen contained in the voids occurs, or moisture due to air in the voids exists in the resin composition as bubbles. Since the transmittance decreases, the optical element (objective lens 15) becomes a defect.

In addition, the solvent used for the wet mixing preferably has a volatile residue such as a solvent of 2% or less of the total volume from the viewpoint of adverse effects on the final organic-inorganic composite material and economy. Moreover, the influence of the residual solvent on the final product can be suppressed by drying and removing the solvent during the production of the organic-inorganic composite material.
[Solvent type]
When the resin material and the inorganic particles are wet-mixed by the above method, they can be mixed uniformly by using a solvent.

  Any solvent may be used as long as it dissolves the above-mentioned composition. For example, aromatic hydrocarbons such as benzene, toluene and xylene, ketones such as acetone, methyl ethyl ketone, cyclohexanone and heptanone, ethyl acetate, acetic acid-t- Esters such as butyl, acetic acid-n-butyl, acetic acid-n-hexyl, halogenated hydrocarbons such as 1,2-dichloroethane, chloroform, chlorobenzene, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, Ethers such as diethylene glycol diethyl ether, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolide , It may be mentioned aprotic polar solvents such as sulfolane. Moreover, these solvents can be used individually or in mixture of 2 or more types.

  Regarding the boiling point of the solvent used at atmospheric pressure, it is preferably 30 to 200 ° C, more preferably 50 to 150 ° C. When the boiling point is lower than 30 ° C., it is dangerous in handling. On the other hand, if the boiling point is higher than 150 ° C., it is difficult to remove the solvent, and the final product is adversely affected by the residue of decomposition products and heating.

The amount of the solvent used at the time of producing the organic-inorganic composite material is not particularly limited as long as the resin material is in a range that dissolves, but 500 to 2000 parts by weight of the solvent is preferable with respect to 100 parts by weight of the resin material. When the amount of the solvent is less than 500 parts by weight, the resin material is not completely dissolved and the composition of the organic-inorganic composite material may become nonuniform. Moreover, when it is 2000 parts by weight or more, productivity decreases and sufficient torque cannot be obtained during wet mixing, and the composition of the produced organic-inorganic composite material may become non-uniform.
(B.2.4) Production of optical element (objective lens 15) using an organic-inorganic composite material As a method for producing an optical element (objective lens 15) using the organic-inorganic composite material, an organic-inorganic composite material is mixed. The mixture is preferably molded. In mixing the organic-inorganic composite material, in order to obtain a composition in which inorganic particles are highly dispersed, a method of applying a shearing force with a melt kneader while mixing the organic-inorganic composite material is preferably used.

The mixing with the resin material is preferably carried out in an atmosphere substituted with Ar, N ₂ or the like, not in the air, in order to prevent functional deterioration due to oxidation.

Specific kneaders include KRC kneader (manufactured by Kurimoto Iron Works); polylab system (manufactured by HAAKE); nanoplast mill (manufactured by Toyo Seiki Seisakusho); Nauter Mixer Bus Co. Kneader (manufactured by Buss) ); TEM type extruder (manufactured by Toshiba Machine Co., Ltd.); TEX twin-screw kneader (manufactured by Nippon Steel Works); PCM kneader (manufactured by Ikegai Iron Works Co., Ltd.); ); Needex (manufactured by Mitsui Mining); MS pressure kneader, nider ruder (manufactured by Moriyama Seisakusho); Banbury mixer (manufactured by Kobe Steel).
[Degree of mixing]
When the degree of mixing of the organic-inorganic composite material is insufficient, there is a concern that it may affect optical properties such as refractive index, Abbe number, and light transmittance, and a resin such as thermoplasticity and melt moldability. Sufficient mixing is desirable because it may adversely affect workability. It is important to select the method for the degree of mixing in consideration of the characteristics of the resin material and inorganic particles used.
[Additive]
Additives such as antioxidants, neutralizing agents, lubricants and antistatic agents that are commonly used can be blended with the organic-inorganic composite material as necessary. As the additive, various kinds of additives may be used alone or in combination. Such additives include plasticizers, antioxidants, light stabilizers, whitening agents, heat stabilizers, colorants, impact resistance improvers, extenders, antistatic agents, mold release agents, foaming agents, processing aids. There are substances such as. Various additives that can be incorporated into the composition are generally used and are known to those skilled in the art. Specific examples of such additives are described in R.A. Gachter and H.C. Muller, Plastics Additives Handbook, 4th edition, 1993. Moreover, the range can be used suitably in the range which does not impair the effect as described in invention.

  In the present invention, by adding the above-mentioned additives to the organic-inorganic composite material, it is possible to have a dispersion effect of inorganic particles during the production of the organic-inorganic composite material and a binder function. These additives are appropriately used as long as they are compatible with each material used. In addition, the additive may be added at any timing including when the organic-inorganic composite material is produced.

Specific examples of main ones among the additives will be given below, but are not limited thereto.
[Plasticizer]
The plasticizer is not particularly limited, however, phosphate ester plasticizer, phthalate ester plasticizer, trimellitic ester plasticizer, pyromellitic acid plasticizer, glycolate plasticizer, citrate ester A plasticizer, a polyester plasticizer, etc. can be mentioned.

  Examples of the phosphate plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, and the like.

  Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl benzyl phthalate, diphenyl phthalate, and dicyclohexyl phthalate.

  Examples of trimellitic acid plasticizers include tributyl trimellitate, triphenyl trimellitate, triethyl trimellitate, and the like.

  Examples of the pyromellitic acid ester plasticizer include tetrabutyl pyromellitate, tetraphenyl pyromellitate, and tetraethyl pyromellitate.

  Examples of the glycolate plasticizer include triacetin, tributyrin, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, and the like.

Examples of the citrate plasticizer include triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, acetyl tri-n- (2-ethylhexyl) citrate and the like. Can be mentioned.
[Antioxidant]
Examples of the antioxidant include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, etc. Among them, phenolic antioxidants, particularly alkyl-substituted phenolic antioxidants are preferable. By blending these antioxidants, coloring and strength reduction of the objective lens 15 due to oxidation deterioration during molding can be prevented without lowering transparency, heat resistance and the like. These antioxidants can be used alone or in combination of two or more, and the blending amount thereof is appropriately selected within a range not impairing the object of the present invention.

  A conventionally well-known thing can be used as a phenolic antioxidant, for example, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 , 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like, and JP-A Nos. 63-179953 and 1-168643. Acrylate compounds described in Japanese Patent Publication No. 1; octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,2'-methylene-bis (4-methyl-6-tert-butylphenol) ), 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, pentaerythrityl-tetrakis [3- (3,5-di- -Butyl-4-hydroxyphenyl) propionate], thiodiethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 1,3,5-trimethyl-2,4,6- Alkyl-substituted phenols such as tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene and triethylene glycol bis (3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate) Compound; 6- (4-hydroxy-3,5-di-t-butylanilino) -2,4-bisoctylthio-1,3,5-triazine, 4-bisoctylthio-1,3,5-triazine, Triazine group-containing phenols such as 2-octylthio-4,6-bis- (3,5-di-t-butyl-4-oxyanilino) -1,3,5-triazine Lumpur-based compounds; and the like.

  The phosphorus antioxidant is not particularly limited as long as it is usually used in the general resin industry. For example, triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonylphenyl) Phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, tris- (2,6-dimethylphenyl) phosphite, 10- (3,5-di- monophosphite compounds such as t-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; 4,4′-butylidene-bis (3-methyl-) 6-t-butylphenyl-di-tridecyl phosphite), 4,4'-isopropylidene-bis (phenyl) Sulfonyl - di - alkyl (C12-C15) phosphite), and the like diphosphite compounds such as. Among these, monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.

Examples of the sulfur-based antioxidant include dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3-thiodiprote. Pionate, pentaerythritol-tetrakis- (β-lauryl-thio-propionate), 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane, etc. Can be mentioned.
[Light stabilizer]
Examples of the light-resistant stabilizer include benzophenone-based light-resistant stabilizer, benzotriazole-based light-resistant stabilizer, hindered amine-based light-resistant stabilizer, etc. In the present invention, from the viewpoint of transparency of the objective lens 15, coloring resistance, etc. It is preferable to use a hindered amine light resistance stabilizer. Among the hindered amine light-resistant stabilizers (hereinafter referred to as HALS), those having a Mn in terms of polystyrene measured by GPC using tetrahydrofuran (THF) as a solvent are preferably 1,000 to 10,000. What is -5,000 is more preferable, and what is 2,800-3,800 is especially preferable. When Mn is too small, when HALS is blended by heat-melting and kneading into a block copolymer, a predetermined amount cannot be blended due to volatilization, and foaming or silver streak occurs during heat-melt molding such as injection molding. Stability is reduced. Further, when the objective lens 15 is used for a long time with the lamp turned on, a volatile component is generated as a gas from the objective lens 15. Conversely, if Mn is too large, the dispersibility in the block copolymer is lowered, the transparency of the lens is lowered, and the effect of improving light resistance is reduced. Therefore, in the present invention, the objective lens 15 excellent in processing stability, low gas generation property, and transparency can be obtained by setting the HALS Mn in the above range.

  Specific examples of such HALS include N, N ′, N ″, N ′ ″-tetrakis- [4,6-bis- {butyl- (N-methyl-2,2,6,6-tetramethylpiperidine. -4-yl) amino} -triazin-2-yl] -4,7-diazadecane-1,10-diamine, dibutylamine and 1,3,5-triazine and N, N'-bis (2,2,6 , 6-tetramethyl-4-piperidyl) butylamine, poly [{(1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} { (2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}], bis (2,2,6,6 -Tetramethyl-4-piperidyl) sebacate, 1,6- A polycondensation product of xylenediamine-N, N′-bis (2,2,6,6-tetramethyl-4-piperidyl) and morpholine-2,4,6-trichloro-1,3,5-triazine, Poly [(6-morpholino-s-triazine-2,4-diyl) (2,2,6,6, -tetramethyl-4-piperidyl) imino] -hexamethylene [(2,2,6,6-tetra High molecular weight HALS in which a plurality of piperidine rings are bonded via a triazine skeleton, such as methyl-4-piperidyl) imino; dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol and 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10 of a mixed ester of tetra oxa spiro [5,5] undecane, piperidine ring linked to a high molecular weight HALS, and the like via an ester bond.

Among these, polycondensates of dibutylamine, 1,3,5-triazine and N, N′-bis (2,2,6,6-tetramethyl-4-piperidyl) butylamine, poly [{(1, 1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2 , 2,6,6-tetramethyl-4-piperidyl) imino}], a polymer of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and the like. 5,000 to 5,000 are preferred.
[Molding method]
The molding method of the optical element (objective lens 15) using the organic-inorganic composite material is not particularly limited, but a molded product having excellent characteristics such as low birefringence, mechanical strength, and dimensional accuracy. In order to obtain, melt molding is preferred. Examples of the melt molding method include commercially available press molding, commercially available extrusion molding, and commercially available injection molding, and injection molding is preferred from the viewpoints of moldability and productivity.

The molding conditions are appropriately selected depending on the purpose of use or the molding method. For example, the resin composition in injection molding (in the case of an organic-inorganic composite material alone or a mixture of an organic-inorganic composite material and an additive) is used. The temperature imparts appropriate fluidity to the organic-inorganic composite material during molding to prevent sink marks and distortion of the molded product, prevents the occurrence of silver streak due to thermal decomposition of the resin material in the organic-inorganic composite material, From the viewpoint of effectively preventing yellowing of the molded product, a range of 150 ° C to 400 ° C is preferable, a range of 200 ° C to 350 ° C is more preferable, and a range of 200 ° C to 330 ° C is particularly preferable.
(C) Characteristics of Optical Pickup Device The optical pickup device 1 satisfies all the combinations of the following formulas (1.1), (2), and (3) as the characteristics, or the following formula (1.2), All the combinations of the combinations (2) and (3) are satisfied, or all the relationships of the following formulas (1.1), (1.2), (2), and (3) are satisfied.

1.0 <d / f <1.5 (1.1)
55 ° <θ _0.9 <65 ° (1.2)
ΔW _T <0.07λrms (2)
ΔW _N <0.07λrms (3)
In formula (1.1), “d” is the axial thickness of the objective lens 15, and “f” is the focal length of the objective lens 15.
In equation (1.2), “θ _0.9 ” is an expected angle at a position corresponding to 0.9 times the pupil diameter on the optical surface of the objective lens 15 on the light source side.

In Expression (2), “ΔW _T ” represents the amount of change in wavefront aberration at the focused spot when the ambient temperature of the objective lens 15 changes by 30 ° C. when recording and / or reproduction is performed on the BD 10. .

In Expression (3), “ΔW _N ” represents a change in wavefront aberration at the focused spot when the wavelength of the first light beam L1 changes ± 5 nm from the design wavelength when recording and / or reproducing is performed on the BD 10. Represents an amount.

  In the optical pickup device 1 according to the present invention, the relations of the above formulas (1.1), (1,2) are as described in the section “Problems to be solved by the invention”. Satisfying the relationship of the above formulas (2) and (3) under the relationship is a remarkable characteristic.

  The technical basis for the relationship between the above formulas (2) and (3) is shown below.

  As described above, when a resin material is used as the base material of the objective lens 15 of the optical pickup device 1, when the ambient temperature of the objective lens 15 changes, the refractive index of the resin material changes and the amount of spherical aberration changes. Are known. Therefore, even if the objective lens 15 is designed to be free of aberrations at a specific temperature, a wavefront aberration occurs in the focused spot due to a change in the amount of spherical aberration due to a temperature change.

In the optical pickup device 1 according to the present invention, in order to satisfactorily record and / or reproduce the BD 10 as the first optical information recording medium, a change in wavefront aberration when the ambient temperature of the objective lens 15 changes by 30 ° C. The quantity ΔW _T needs to satisfy ΔW _T <0.07λrms. Variation [Delta] W _T of the wave front aberration is not less than 0.07Ramudarms, since the change amount of the wavefront aberration when the ambient temperature is changed 30 ° C. of the objective lens 15 exceeds the allowable value of the Marechal, are aplanatic at a reference temperature Even in the optical pickup device 1, there is a possibility that a problem occurs in recording and / or reproduction of optical information due to a temperature change. On the other hand, the change amount [Delta] W _T of wavefront aberration, when 0.07λrms smaller, because the amount of wavefront aberration generated by the refractive index change of the material of the objective lens 15 due to the temperature change does not exceed the allowable value of the Marechal, temperature change Even if this occurs, optical information can be recorded and / or reproduced favorably.

The change of the wavefront aberration due to the temperature change is mainly caused by the change of the spherical aberration of the objective lens 15 due to the change of the refractive index of the base material of the objective lens 15. It has been found that the change amount of the wavefront aberration due to the temperature change is related not only to the change amount of the refractive index (dn / dt) due to the temperature change of the base material of the objective lens 15 but also to the refractive index of the base material of the objective lens 15 itself. It was. A further study results, and at the same specifications, in different objective lens of material properties, the change amount [Delta] W _T of the wavefront aberration when the ambient temperature of the objective lens 15 is changed 30 ° C., the base material of the objective lens 15 It was found that the refractive index change amount dn / dt (/ ° C.) due to temperature change and the following expression (4), which is a function of the refractive index N _O of the base material of the objective lens 15.

ΔW _T = k · f (dn / dt) / (N _O ^m ) (4)
In equation (4), “k” and “m” are coefficients determined by the image-side numerical aperture NA of the objective lens 15, the shape of the objective lens 15, etc., and “f” represents the focal length of the objective lens 15.

That is, the change amount [Delta] W _T of the wave front aberration due to the temperature change, the dn / dt is the change amount of the refractive index due to the temperature change of the substrate of the objective lens 15, divided by m square of the refractive index of the base material of the objective lens 15 It is proportional to the value.

For example, in an objective lens having a birefringent surface in which no phase structure such as a diffractive structure is provided on the optical surface, the image-side numerical aperture NA3 of the objective lens 15 is 0.42 to 0.52 (see FIG. 8). result of examining the amount of change [Delta] W _T of the wave front aberration due to the temperature change for the 8 is about 0.45) CD30 at focused spots optical pickup device 1, the amount of change [Delta] W _T is (dn / dt) / (N The result is proportional to _O ⁶ ).

Further, as shown in FIG. 9, the temperature at the condensing spot of the optical pickup device 1 for DVD 20 in which the image-side numerical aperture NA2 of the objective lens 15 is 0.60 to 0.70 (about 0.65 in FIG. 9). variation [Delta] W _T of the wave front aberration due to the change was obtained results that is proportional to ^{_{(dn / dt) / (N}} O 6.7).

Furthermore, as shown in FIG. 10, the temperature change at the condensing spot of the pickup device 1 for the BD 10 in which the image-side numerical aperture NA1 of the objective lens 15 is 0.75 to 0.87 (about 0.85 in FIG. 10). As a result, the change amount ΔW _T of the wavefront aberration due to is proportional to (dn / dt) / (N _O ⁹ ).

Therefore, in order to suppress the variation [Delta] W _T of the wave front aberration of the light converging spot due to temperature changes, not only suppress the change in the refractive index of the substrate of the objective lens 15 due to the temperature change, refraction of the substrate of the objective lens 15 It turned out that the rate also needs to be considered.

To suppress the variation [Delta] W _T of the wave front aberration due to the temperature change, as a method of controlling the refractive index variation dn / dt and the refractive index N _O due to temperature change of the substrate of the objective lens 15, the base material of the objective lens 15 The easiest method is to select a resin material as appropriate. That is, selecting a material having a small dn / dt, selecting a material having a high refractive index, or selecting a material satisfying both characteristics.

However, in the conventional resin materials used for the optical elements for the optical pickup device as listed above, in the optical pickup device in which the image side numerical aperture NA of the objective lens is 0.75 to 0.87, the light is condensed. the variation [Delta] W _T of the wave front aberration of the spot, could not be made smaller than 0.07Ramudarms.

For example, when an optical pickup device using a resin material (polyolefin resin: ZEONEX 340R manufactured by Nippon Zeon Co., Ltd.), which has been conventionally used as a material for an optical element for an optical pickup device, as a material for an objective lens, a relatively small numerical aperture is produced. in the optical pickup device for use and DVD CD, the change amount [Delta] W _T of the wave front aberration of the light converging spot due to a temperature change becomes less 0.07Ramudarms, problems did not occur. However, in the optical pickup device for BD of the image-side numerical aperture NA of the objective lens is 0.75 to .87, the focusing spot of the wave front aberration change amount [Delta] W _T of approximately 0.1λrms next due to temperature changes, Marechal Therefore, it has been found that recording and / or reproducing optical information may be hindered. Among conventional optical materials, some polycarbonate resins have a relatively high refractive index, but polycarbonate resins tend to have high birefringence, and are used as materials for optical elements for high-precision optical pickup devices. Was not suitable.

  As a material having a high refractive index and low birefringence, a polycarbonate resin having a fluorene derivative as a basic skeleton described in JP-A-6-25398 and JP-A-2007-57916 is preferably used as a material for the optical element of the present invention. Can be used. Specific examples include polycarbonate resins composed of structural units represented by the following general formulas (1) and (2).

(In the general formula (1), R ₁ , R ₂ , R ₃ and R ₄ each independently represents a hydrogen atom, an alkyl group, an alkoxy group, a cycloalkyl group, a cycloalkoxyl group, an aryl group or an aryloxy group. A represents an alkylene group, a cycloalkylene group or an arylene group, n, m, o and p each represents an integer of 1 to 4, and q and r each represents an integer of 0 to 5)

(In the general formula (2), B represents an alkylene group, a cycloalkylene group or an arylene group.)
As a method of adjusting the dn / dt and the refractive index N _O of the resin material is dispersed the resin material, (in the case of the optical element for the optical pickup device, the wavelength of the light source) using a wavelength sufficiently small inorganic particles than A method of making it possible is considered. According to International Publication No. WO 04/113963, it is described that dn / dt can be controlled by dispersing inorganic particles in a resin material as a base material to obtain an organic-inorganic composite material. Further, by using fine particles sufficiently smaller than the wavelength used, light scattering can be suppressed, and the characteristics of the substrate can be controlled without impairing the transmittance as an optical element. Similarly, the refractive index of the substrate can be controlled by adding inorganic particles. However, in the prior art, it has not been recognized that the wave front aberration change due to the temperature change at the focal spot of the optical pickup device related to the value of dn / dt and the refractive index N _O of the base material of the objective lens, the Even when the organic-inorganic composite material described in the above document is used as a base material for an objective lens, in an optical pickup device for high-density recording in which the image-side numerical aperture NA of the objective lens is 0.75 to 0.87, the temperature the variation [Delta] W _T of the wavefront aberration in the focused spot due to the change can not be sufficiently suppressed.

Hereinafter, the addition of inorganic particles to the substrate is a resin material, a description will be given of a specific method of controlling the change amount [Delta] W _T of the wavefront aberration in the focused spot due to temperature changes.

According to the data of the optical pickup device 1 shown in FIG. 10, the change amount [Delta] W _T of the wavefront aberration image side numerical aperture NA1 is at a high density recording optical pickup device 1 of from 0.75 to 0.87 of the objective lens 15 It can be seen that (dn / dt) / (N _O ⁹ ) needs to be about −1.50 × 10 ⁻⁶ or more in order to make it 0.07λrms or less. (Dn / dt) / in the case where TiO ₂ , ZnO, Al ₂ O ₃ , AlPO ₄ , and SiO ₂ are added as inorganic particles to the above-described resin material for an optical pickup element (ZEONEX 340R manufactured by Nippon Zeon). The relationship between (N _O ⁹ ) and the volume fraction of inorganic particles is shown in FIG.

11 As is clear, that is adjusted to the desired (dn / dt) / (N O 9) by adjusting the amount of the inorganic particles, to control the amount of change [Delta] W _T of the wavefront aberration as a result it can. Inorganic particles to be added, (dn / dt) / a (N O ^₉₎ as the desired value, if the change amount [Delta] W _T of the wavefront aberration within the scope of the present invention as a result, there is no particular limitation. When inorganic particles having a low refractive index are used, it is necessary to add the inorganic particles at a high ratio in the organic-inorganic composite material in order to obtain a desired value of (dn / dt) / (N _O ⁹ ). As a result, the viscosity increases and the molding difficulty may increase.

On the other hand, when the refractive index of the inorganic particles is very high as compared with the resin material used as the base material, the amount required to make (dn / dt) / (N _O ⁹ ) a desired value is relatively small. However, there is a case where light scattering is likely to occur due to a large difference in refractive index with the resin material serving as the base material. Therefore, it is desirable that the fine particles to be added are appropriately selected in consideration of the performance required as an optical element. Moreover, you may obtain desired performance by using a some inorganic particle together.

In the optical pickup apparatus in the present invention, the change amount [Delta] W _T of the wavefront aberration in the focused spot due to a temperature change is preferably greater than 0.02Ramudarms.

As described above, the change amount [Delta] W _T of the wavefront aberration in the present invention, the _{(dn / dt) / (N} O 9) can be controlled by controlling the but variation [Delta] W _T of the wavefront aberration 0 When it is desired to make it less than .02λrms, it is necessary to set (dn / dt) / (N _O ⁹ ) to −5.00 × 10 ⁻⁷ or more as shown in FIG.

At this time, when a fine particle having a relatively high refractive index is added and (dn / dt) / (N _O ⁹ ) is set to −5.00 × 10 ⁻⁷ or more, the refractive index of the objective lens 15 becomes too high. When the objective lens 15 has a meniscus shape and the optical surface on the BD 10 side has a concave shape, it is difficult to keep a distance from the BD 10 and it is difficult to secure a working distance necessary for focusing and tracking. There is. Further, when inorganic particles having a relatively low refractive index are added and (dn / dt) / (N 2 _O ⁹ ) is set to −5.00 × 10 ⁻⁷ or more, it is necessary to add the inorganic particles at a high mixing ratio. In some cases, the transmittance may be reduced.

As described above, in the present invention, the change amount ΔW _T of the wavefront aberration at the focused spot due to the temperature change is preferably 0.02λrms <ΔW _T <0.07λrms.

In addition to controlling the (dn / dt) / (N _O ⁹ ) by mixing inorganic particles into the resin material as the base material, the wavefront aberration change amount ΔW _T is controlled in addition to the method for controlling the wavefront aberration. as a method of controlling the change amount [Delta] W _T aberration, by providing the phase structure on an optical surface of the objective lens 15 as described in the background art and FIGS. 2-7, etc. described above, generated by the objective lens 15 by a temperature change There is a method for suppressing the occurrence of spherical aberration.

However, as in the optical pickup device 1 of the present invention, a light source (semiconductor laser oscillator LD1) having a wavelength of 380 to 420 nm is used, and high-density recording and image-side numerical aperture NA1 of the objective lens 15 are 0.75 to 0.87. the / or when adopting an optical pickup apparatus for reproduction, or can not be sufficiently reduced the variation [Delta] W _T of the wavefront aberration, even when the reduced variation [Delta] W _T of the wavefront aberration, a wavelength characteristic deteriorates, the light source wavelength of Since the change amount ΔW _N of the wavefront aberration at the focused spot when deviating from the design wavelength exceeds 0.07 λrms, the configuration of the present invention cannot be achieved only by the phase structure. Furthermore, only using the high refractive index material, and may not be sufficiently reduced [Delta] W _T, even when adjusted by dispersing fine particles (dn / dt) / (N O 9), by adding a particulate It may be difficult to suppress a decrease in transmittance.

Therefore, as the base material, to select a high refractive index material, on which or with organic inorganic composite material obtained by adding inorganic particles to the resin material, the control of the variation [Delta] W _T of the wavefront aberration by providing a phase structure It is a preferable configuration to take a part of the above. According to such a configuration, the only selection and adjustment of the material, reducing the amount of change [Delta] W _T of the wavefront aberration by when it is not possible to sufficiently reduce the change amount [Delta] W _T of the wavefront aberration becomes a part of the function in the phase structure can do. Further, since the phase structure is that only becomes a part of the function, reduced deterioration of the wavelength characteristics in comparison with the case of correcting in all the variation [Delta] W _T of the wave front aberration phase structure, the wavelength of the light source is deviated from the design wavelength In this case, the change amount ΔW _N of the wavefront aberration at the focused spot can be suppressed to 0.07λrms or less. Further, it is possible to reduce the amount of the inorganic particles by responsible for some functions for the variation [Delta] W _T reduce the wavefront aberration in the phase structure, the molding of optical elements by lowering the viscosity and vulnerability as a result Can be easily.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

As Examples 1, 2, and 3 and Comparative Examples 1 and 2, an optical pickup device for Blu-ray Disk having a substrate thickness of 0.875 mm was designed. The specification and lens data of the objective lens in each optical pickup device are shown. In the following, a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E−3).
[Example 1]
The specifications of the optical pickup device of Example 1 are shown in Table 2 below.

  In Table 2, “di” represents an interval from the i-th surface to the (i + 1) -th surface.

  For the entrance surface (optical surface on the light source side, second surface) and exit surface (optical surface on the optical disc side, third surface) of the objective lens, the coefficients shown in Table 3 below are substituted into the following equation (1). It is formed into an aspherical surface that is axisymmetric about the optical axis, which is defined by the above formula.

Here, “x” is an axis in the optical axis direction (the light traveling direction is positive), “κ” is a conic coefficient, “A _2i ” is an aspheric coefficient, and “h” is a direction perpendicular to the optical axis. Represents the height.

As the base material of the objective lens used in the optical pickup device of Example 1, cycloolefin resin (APEL manufactured by Mitsui Chemicals), which is a resin suitably used for an optical element for a conventional optical pickup device, is used as Al ₂ O _3. By using an organic-inorganic composite material in which (dn / dt) / n ⁹ (n is the refractive index of the base material) is adjusted to −1.31 × 10 ⁻⁶ An objective lens having an aspheric refracting surface without a phase structure was obtained.

The properties of the objective lens substrate are shown in Table 4 below.
However, in Table 4 below, “nd”, “n _{410 nm} ” and “n _{405 nm} ” represent the refractive indexes of the base materials at the d-line (587.6 nm), 410 nm and 405 nm, respectively.

[Example 2]
The specifications of the optical pickup device of Example 2 are shown in Table 5 below.

  For the incident surface (light source side optical surface, second to tenth surfaces) and output surface (optical surface on the optical disk side, eleventh surface) of the objective lens, the coefficients shown in Table 6 below are substituted for Equation (1). It is formed into an aspherical surface that is axisymmetric about the optical axis, which is defined by the above formula.

  As the base material of the objective lens used in the optical pickup device of Example 2, the organic-inorganic composite material similar to Example 1 (see Table 4) is used, and the second to tenth surfaces (the optical surface on the light source side of the objective lens). The phase structure shown in Table 7 below was provided.

  However, “inner peripheral radius” represents the distance from the optical axis of the inner (light source side) step portion of each phase structure, and “outer radius” represents the distance from the optical axis of the inner step portion of the adjacent outer phase structure. Represents. The “ring zone depth” represents the depth in the optical axis direction of the outer stepped portion of each phase structure.

FIG. 12 is a schematic diagram illustrating a cross section of the objective lens according to the second embodiment. As shown in FIG. 12, the second to tenth surfaces shown in Table 5 above, which are light source side optical surfaces, correspond to the first to ninth annular zones shown in Table 7 above, respectively. That is, of the second to tenth surfaces facing the light source side, the second surface corresponds to the first annular zone, the third surface corresponds to the second annular zone, and the fourth surface corresponds to the third annular zone. In the same manner, the tenth surface is formed. The eleventh surface is the surface on the optical disc side. O is the optical axis.
[Example 3]
The specifications of the optical pickup device of Example 3 are shown in Table 8 below.

  In Table 8, “di” represents an interval from the i-th surface to the (i + 1) -th surface.

  For the entrance surface (light source side optical surface, second surface) and exit surface (optical surface on the optical disk side, third surface) of the objective lens, the coefficients shown in Table 9 below were substituted for the above equation (1). It is formed into an aspherical surface that is axisymmetric about the optical axis, as defined by the mathematical formula. The second surface is provided with a diffractive structure, and the optical path difference function is expressed by the following equation (2).

A polycarbonate resin having a fluorene structure was used as the base material of the objective lens used in the optical pickup device of Example 3. The characteristics of the base material of the objective lens are shown in Table 10 below. However, in Table 4 below, “nd”, “n _{410 nm} ” and “n _{405 nm} ” represent the refractive indexes of the base materials at the d-line (587.6 nm), 410 nm and 405 nm, respectively.

[Comparative Example 1]
The specifications of the optical pickup device of Comparative Example 1 are shown in Table 11 below.

  In Table 11, “di” represents the displacement from the i-th surface to the (i + 1) -th surface.

  The entrance surface (light source side optical surface, second surface) and exit surface (optical surface on the optical disk side, third surface) of the objective lens are mathematical formulas obtained by substituting the coefficients shown in Table 12 below into the above formula (1). It is formed in an aspherical surface that is symmetric about the optical axis.

As the base material of the objective lens used in the optical pickup device of Comparative Example 1, cycloolefin resin (APEL manufactured by Mitsui Chemicals) was used, and (dn / dt) / n ⁹ (n is the refractive index of the base material) is − It was 2.92 × 10 ⁻⁶ . An objective lens having an aspherical refracting surface that is not provided with a phase structure on both sides was used.

  The characteristics of the objective lens substrate are shown in Table 13 below.

In Table 10 below, “nd”, “n _{410 nm} ”, and “n _{405 nm} ” represent the refractive indexes of the base materials at the d-line (587.6 nm), 410 nm, and 405 nm, respectively.

[Comparative Example 2]
The specifications of the optical pickup device of Comparative Example 2 are shown in Table 14 below.

  The incident surface (light source side optical surface, second to twelfth surfaces) and exit surface (optical surface on the optical disk side, thirteenth surface) of the objective lens are coefficients shown in Table 15 below with respect to the above equation (1). It is formed into an aspherical surface that is symmetric with respect to the optical axis, and is defined by a mathematical formula that substitutes.

  As the base material of the objective lens used in the optical pickup device of Comparative Example 2, the same cycloolefin-based resin (see Table 13) as in Comparative Example 1 was used, and the second to twelfth surfaces (optical on the light source side of the objective lens) The surface structure shown in Table 16 below was provided.

  However, “inner peripheral radius” represents the distance from the optical axis of the inner (light source side) step portion of each phase structure, and “outer radius” represents the distance from the optical axis of the inner step portion of the adjacent outer phase structure. Represents. The “ring zone depth” represents the depth in the optical axis direction of the outer stepped portion of each phase structure.

FIG. 13 is a schematic diagram showing a cross section of the objective lens shown in Comparative Example 2. As shown in FIG. 13, the second to twelfth surfaces shown in Table 15 that are the light source side optical surfaces correspond to the first to eleventh annular zones shown in Table 16 above, respectively. That is, among the second to twelfth surfaces facing the light source side, the second surface corresponds to the first annular zone, the third surface corresponds to the second annular zone, and the fourth surface corresponds to the third annular zone. In the same manner, the twelfth surface is formed. The thirteenth surface is the surface on the optical disc side. O is the optical axis.
[Results and discussion]
When recording / reproducing is performed with the optical pickup devices of Examples 1, 2, and 3 and Comparative Examples 1 and 2, the wavefront aberration (λrms) generated at the design temperature and the design wavelength, and the ambient temperature of the objective lens are the design wavelength 30. The values obtained by simulation for wavefront aberration (λrms) that occurs when the temperature rises by 5 ° C. and wavefront aberration (λrms) that occurs when the design wavelength becomes 5 nm larger than the design wavelength are shown in the following table as A, B, and C, respectively. 17 shows.

  As shown in Table 17 above, an optical pickup device was obtained in which the occurrence of wavefront aberration at the time of temperature increase and wavelength change was 0.07λrms or less, which is a Marechal tolerance. According to the present invention, in addition to satisfying the specifications required for an optical pickup device having a high recording density, a large numerical aperture, and a short-wavelength light source, even when a temperature change or a wavelength change occurs, a reading failure, etc. It is possible to provide an optical pickup device that does not cause this problem.

Claims (11)

A first light source that emits a first light flux having a wavelength of 380 to 420 nm;
An objective lens composed of a single lens whose main component is a resin material;
An optical pickup device that performs recording and / or reproduction on a first optical information recording medium with the first light flux through the objective lens,
The image-side numerical aperture NA1 of the objective lens is 0.75 to 0.87,
The working distance of the objective lens to the first optical information recording medium is 0.3 mm or more,
An optical pickup device characterized by satisfying all the relationships of the following formulas (1.1), (2), and (3).
1.0 <d / f <1.5 (1.1)
ΔW _T <0.07λrms (2)
ΔW _N <0.07λrms (3)
(In formula (1.1), “d” is the axial thickness of the objective lens, and “f” is the focal length of the objective lens. In formula (2), “ΔW _T ” This represents the amount of change in wavefront aberration at the focused spot when the ambient temperature of the objective lens is changed by 30 ° C. when recording and / or reproducing is performed on one optical information recording medium. “ΔW _N ” is the amount of change in wavefront aberration at the focused spot when the wavelength of the first light flux changes ± 5 nm from the design wavelength when recording and / or reproducing is performed on the first optical information recording medium. Represents.) A first light source that emits a first light flux having a wavelength of 380 to 420 nm;
An objective lens composed of a single lens whose main component is a resin material;
An optical pickup device that performs recording and / or reproduction on a first optical information recording medium with the first light flux through the objective lens,
The image-side numerical aperture NA1 of the objective lens is 0.75 to 0.87,
The working distance of the objective lens to the first optical information recording medium is 0.3 mm or more,
An optical pickup device characterized by satisfying all the relationships of the following formulas (1.2), (2), and (3).
55 ° <θ _0.9 <65 ° (1.2)
ΔW _T <0.07λrms (2)
ΔW _N <0.07λrms (3)
(In Expression (1.2), “θ _0.9 ” is an expected angle of a position corresponding to 0.9 times the pupil diameter on the optical surface on the light source side of the objective lens. In Expression (2), “ “ΔW _T ” represents the amount of change in wavefront aberration at the focused spot when the ambient temperature of the objective lens changes by 30 ° C. when recording and / or reproducing is performed on the first optical information recording medium. In equation (3), “ΔW _N ” is the light concentration when the wavelength of the first light flux changes ± 5 nm from the design wavelength when recording and / or reproduction is performed on the first optical information recording medium. (Represents the amount of change in wavefront aberration at the spot.) In the optical pickup device according to claim 1 or 2,
An optical pickup device, wherein the objective lens is composed of an organic-inorganic composite material in which inorganic particles are dispersed in a resin material. The optical pickup device according to any one of claims 1 to 3, wherein:
An optical pickup device, wherein a phase structure is provided on at least one optical surface of the objective lens. In the optical pickup device according to claim 4,
The phase structure has a function of canceling a change in spherical aberration component caused by a change in refractive index of a base material of the objective lens due to a change in ambient temperature of the objective lens, by the phase structure itself. An optical pickup device. In the optical pickup device according to claim 4,
An optical pickup device, wherein the phase structure is a diffractive structure. In the optical pickup device according to claim 6,
The diffractive structure is a spherical aberration component generated when the refractive index of the base material of the objective lens changes due to a change in the ambient temperature of the objective lens when recording or reproducing is performed on the first optical information recording medium. The optical pickup device has a function of canceling the change by a change of a spherical aberration component generated by a change of a wavelength of the first light beam due to a change of an ambient temperature of the first light source. In the optical pickup device according to any one of claims 4 to 7,
The optical pickup device, wherein the phase structure has a plurality of annular zones concentric with the optical axis of the objective lens. In the optical pickup device according to any one of claims 1 to 8,
A second light source that emits a second light flux having a wavelength of 630 to 660 nm;
A third light source that emits a third light flux having a wavelength of 770 to 800 nm,
Recording and / or reproduction on the second optical information recording medium with the second light flux through the objective lens,
An optical pickup device that performs recording and / or reproduction on a third optical information recording medium with the third light flux through the objective lens. In the optical pickup device according to claim 9,
When recording and / or reproducing on the second optical information recording medium, the image-side numerical aperture NA2 of the objective lens is 0.60 to 0.70,
When recording and / or reproducing on the third optical information recording medium, the optical pickup device has an image-side numerical aperture NA3 of the objective lens of 0.42 to 0.52. In the optical pickup device according to claim 9 or 10,
Each of the first to third optical information recording media has a transparent protective substrate,
The objective lens has, on at least one optical surface, a spherical surface caused by a difference in thickness of the transparent protective substrate of at least two of the first to third optical information recording media among the first to third optical information recording media. An optical pickup device having a phase structure for correcting aberration.