JP2010040073A - Optical system for optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system for an optical pickup that improves both temperature characteristics and wavelength characteristics, and that is manufactured more easily. <P>SOLUTION: The optical system for an optical pickup has an objective lens 17 which is made from plastic and which has a numerical aperture of ≥0.85, a coupling lens 14 and a phase correcting element 15 provided between the objective lens 17 and the coupling lens 14, and in the objective lens 17 and the phase correcting element 15, a ring band structure formed with a plurality of ring bands with different sizes of concentric rings is formed in one face, a step is formed between adjacent ring bands of the ring band structure, and the step of the objective lens 17 has a step difference amount which generates such a phase difference that reduces a wavefront aberration caused by an ambient temperature change in a light flux which transmits through the objective lens 17, and a step of the phase correcting element 15 has a step difference amount which generates such a phase difference that reduces a wavefront aberration caused by a change of a wavelength of a laser light emitted from a laser light source 11 in a light flux which transmits through the phase correcting element 15. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical pickup optical system, and more particularly to an optical pickup optical system that suppresses performance deterioration due to temperature change and wavelength change.

  An objective lens used in a conventional optical disc (optical information recording medium) such as a DVD (Digital Versatile Disc) has a numerical aperture (NA) of 0.85 and is used in a BD (Blu-ray Disc). Greater than the numerical aperture. Therefore, aberrations are likely to increase with changes in temperature and wavelength, and the light spot is likely to deteriorate.

In general, the amount of change in the refractive index accompanying the temperature change of the glass material is on the order of 1 × 10 ⁻⁶ (1 / ° C.). On the other hand, the amount of change in the refractive index accompanying the temperature change of the plastic material is on the order of 1 × 10 ⁻⁴ (1 / ° C.). Therefore, the amount of change in the refractive index accompanying the temperature change of the plastic material is 10 to 100 times larger than that of the glass material. Therefore, in general, a glass material having a small refractive index change and a small shape change when the temperature changes is used for the objective lens dedicated to BD.

  However, in general, plastic materials are superior to glass materials in terms of productivity, cost, and weight reduction. Therefore, it is strongly desired to improve the temperature characteristics of a lens formed of a plastic material.

  Further, in the optical pickup optical system, focus position shift and aberration occur due to wavelength variation due to individual differences of laser light sources and wavelength change due to mode hop phenomenon.

Therefore, in Patent Document 1, an annular zone structure is provided on the surface of the coupling lens to reduce the aberration caused by the wavelength change. The annular structure described in Patent Document 1 does not cause a diffraction phenomenon but generates a phase difference.
JP 2004-185746 A

  However, as a result of intensive studies, the inventor of the present application formed an annular structure that reduces aberration based on wavelength shift on the surface of the coupling lens as in the technique described in Patent Document 1, and the temperature on the surface of the objective lens. It has been found that the wavelength characteristics and temperature characteristics of the optical pickup optical system cannot be improved even if an annular structure that reduces aberration due to changes is formed.

  FIG. 15 shows temperature characteristics and wavelength characteristics when an annular structure for correcting wavefront aberration caused by temperature change is formed on the surface of a plastic objective lens. In FIG. 15, the vertical axis represents the wavefront aberration, and the horizontal axis represents the normalized ray height. The normalized ray height is the ray height from the optical axis normalized by the effective diameter of the objective lens. FIG. 15A shows the wavefront aberration that occurs when the temperature of the objective lens rises by 30 ° C. from the design temperature. FIG. 15B shows wavefront aberration that occurs when the wavelength is 1 nm longer than the design wavelength. As shown in FIG. 15A, the objective lens can correct aberrations caused by temperature changes. On the other hand, as shown in FIG. 15B, the objective lens increases aberration caused by wavelength change.

  FIG. 16 shows temperature characteristics and wavelength characteristics when the objective lens of FIG. 15 is combined with a plastic coupling lens having an annular structure that corrects a wavefront aberration caused by a wavelength change. In FIG. 16, the vertical axis indicates wavefront aberration, and the horizontal axis indicates the normalized ray height. FIG. 16A shows wavefront aberration that occurs when the temperature of the objective lens and the coupling lens rises by 30 ° C. from the design temperature. FIG. 16B shows the wavefront aberration that occurs when the wavelength is 1 nm longer than the design wavelength. As shown in FIG. 16B, by combining the coupling lens with the objective lens, it is possible to correct the aberration caused by the wavelength change. However, on the other hand, as shown in FIG. 16A, an objective lens having an annular step for correcting wavefront aberration caused by a temperature change and a coupling lens having an annular step for correcting wavefront aberration caused by a wavelength change. When combined with, the temperature characteristics deteriorate.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an optical pickup optical system that can improve both temperature characteristics and wavelength characteristics and can be manufactured more easily. .

  The pickup optical system according to the present invention is an optical pickup optical system that focuses a light beam from a laser light source onto an optical information recording medium. The pickup optical system according to the present invention includes a plastic objective lens having a numerical aperture of 0.85 or more, a coupling lens for adjusting a divergence angle of a light beam from the laser light source, the objective lens, and the coupling lens. And a phase correction element disposed between the two. In addition, the objective lens and the phase correction element have an annular structure formed of a plurality of annular zones having different concentric sizes on at least one surface, and the annular zones adjacent to the annular structure are formed. A step is formed between them. Further, the step formed on the objective lens has a step amount that causes a phase difference in the light beam transmitted through the objective lens so as to reduce wavefront aberration caused by a change in ambient temperature. In addition, the step formed in the phase correction element has a phase difference that reduces wavefront aberration caused by a change in the wavelength of the laser light emitted from the laser light source in the light beam transmitted through the phase correction element. It has a level difference to be generated.

In the present invention, the annular structure formed on at least one surface of the objective lens generates a phase difference in the light beam transmitted through the objective lens so as to reduce wavefront aberration caused by a change in ambient temperature. Can do. Further, due to the ring zone structure on at least one surface of the phase correction element, the light flux transmitted through the phase correction element has a phase difference that reduces wavefront aberration caused by a change in the wavelength of the laser light emitted from the laser light source. Can be generated. Therefore, the temperature characteristics can be improved by the annular structure formed on the objective lens, and the wavelength characteristics can be improved by the annular structure formed on the phase correction element. In addition, when an annular structure that improves the temperature characteristics is formed on the objective lens and an annular structure that improves the wavelength characteristics is formed on the coupling lens, the temperature characteristics are deteriorated. Both temperature characteristics and wavelength characteristics can be improved without sacrificing.
Further, since the objective lens is made of plastic, it can be manufactured more easily.

The coupling lens is preferably made of plastic, and the phase correction element is preferably made of glass.
When the coupling lens is made of plastic, when the ambient temperature changes, the aberration that occurs in the coupling lens due to the change in the ambient temperature can be reduced, and the aberration that occurs in the objective lens due to the change in the ambient temperature can be reduced.
In addition, when the phase correction element is made of glass, since the aberration generated in the phase correction element due to the change in the ambient temperature is small, the temperature characteristics of the optical pickup optical system are not deteriorated.

Further, the annular structure formed in the objective lens is such that the lens thickness of the objective lens decreases as it goes from the optical axis to the outer edge in the radial direction of the objective lens, and further toward the outer edge side, the It is preferable that the objective lens is formed to have a large thickness.
Thereby, the number of annular zones formed on the objective lens can be minimized while maintaining the performance of correcting the aberration caused by the temperature change by the annular zone structure formed on the objective lens.

Further, in the annular structure formed in the phase correction element, the thickness of the phase correction element becomes thicker toward the outer edge from the optical axis in the radial direction of the phase correction element, and further on the outer edge side. It is preferable that the complementary element is formed so that the thickness of the complementary element decreases as it goes.
In general, when correcting the aberration due to the temperature change by the annular structure of the objective lens, if the correction amount by the annular structure of the objective lens is increased, the step amount of the entire annular structure formed in the objective lens increases. . Thereby, the wavefront aberration which arises by a wavelength change will increase by the ring zone structure formed in the objective lens. Here, the thickness of the phase correction element increases toward the outer edge from the optical axis in the radial direction of the phase correction element, and the thickness of the complementary element decreases further toward the outer edge side. In this way, when the annular structure is formed, when the aberration due to the temperature change is corrected by the annular structure of the objective lens, the wavelength characteristic deteriorated by increasing the correction amount by the annular structure of the objective lens is compensated. can do.

Moreover, it is preferable that the said ring zone structure formed in the phase correction element is formed so that the thickness of the said phase correction element becomes thick as it goes to an outer edge from an optical axis in the radial direction of the said phase correction element.
When the correction amount for correcting the aberration due to the temperature change by the annular structure of the objective lens is not large, the thickness of the phase correction element increases from the optical axis toward the outer edge in the radial direction of the phase correction element. By forming the ring structure so that the thickness of the ring is increased, the number of ring zones formed on the phase correction element is minimized while maintaining the performance of correcting the aberration caused by the wavelength change by the ring structure formed on the phase correction element. To the limit.

  According to the present invention, both the temperature characteristic and the wavelength characteristic can be improved, and the production can be facilitated.

Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments.
First, the principle of correction of wavefront aberration and spherical aberration by the annular structure in the present invention will be described.
FIG. 1 shows an example of the objective lens 17 according to the present embodiment. As shown in FIG. 1, at least one surface of the objective lens 17 according to the present embodiment is formed with an annular structure composed of a plurality of annular zones having different concentric sizes. In addition, a similar ring zone structure is formed on at least one surface of the phase correction element 15 according to the present embodiment.
And the level | step difference is formed between the adjacent ring zones of each ring zone structure. Due to this level difference, a phase difference is generated between the light fluxes transmitted through the adjacent annular zones.

FIG. 2A shows an enlarged cross-sectional view of a stepped portion between adjacent annular zones. In FIG. 2A, the right annular zone is lower than the left annular zone in the drawing, and a step having a step amount d is formed between the annular zones. Further, the refractive index of the hatched portion on the lower side of the paper is N1, and the refractive index of the upper portion of the paper is N0. Further, a light flux that passes through the left annular zone is referred to as a light flux A, and a light flux that passes through the right annular zone is referred to as a light flux B. Further, the wavelengths of the light beam A and the light beam B are λ. At this time, the wavefront aberration generated between the light flux A and the light flux B due to the step is expressed by the following formula (1).

  FIG. 2B is a graph showing the relationship between the phase component of the wavefront aberration OPD (AB) and the step amount d. In FIG. 2B, the vertical axis represents the phase component of the wavefront aberration OPD (AB), and the horizontal axis represents the step amount d. Note that the deviation of the phase component of the wavefront aberration OPD (AB) by an integral multiple of the wavelength λ is equivalent to the case where there is no such deviation. Therefore, in FIG. 2B, the phase component of the wavefront aberration OPD (AB) is shown in a range from −0.5λ to 0.5λ. In FIG. 2, the solid line (state 1) indicates the phase component of the wavefront aberration OPD (AB) in the designed state, and the broken line (state 2) indicates that the surrounding environment such as the ambient temperature and the wavelength of the light flux has changed. The phase component of wavefront aberration OPD (AB) in the case is shown.

  As shown in FIG. 2B, the phase component of the wavefront aberration OPD (AB) generated in the design state is different from the wavefront aberration OPD (AB) generated when the surrounding environment changes. . As shown in FIG. 2B, when d = d1, the phase component of the wavefront aberration OPD (AB) in the designed state is 0, whereas the OPD (A The phase component of -B) is δW. In other words, no wavefront aberration is generated in the design state, and the step amount d that generates the wavefront aberration only when the surrounding environment changes is d1. In the present invention, the wavefront aberration is not generated in the design state, and only when the surrounding environment changes, the step amount d that generates the wavefront aberration that cancels the wavefront aberration caused by the change in the surrounding environment is selected. To prevent aberrations from deteriorating due to changes in angle.

FIG. 3 shows wavefront aberration caused by temperature change or wavelength change, and wavefront aberration corrected by the annular structure. In FIG. 3, the vertical axis indicates the wavefront aberration, and the horizontal axis indicates the radial position in the light beam radial direction centered on the optical axis. In FIG. 3, the broken line indicates wavefront aberration caused by temperature change or wavelength change, the thick solid line indicates wavefront aberration corrected by the annular structure, and the thin solid line indicates wavefront aberration generated by the annular structure. Show.
As shown in FIG. 3, spherical aberration caused by temperature change or wavelength change can be reduced by generating stepwise wavefront aberration by the annular structure. Specifically, for example, at each of the radii R1, R2, R3, and R4, a step having a step amount d that generates δW necessary to reduce spherical aberration caused by temperature change or wavelength change. Is formed on the surface of the optical element. In other words, an annular structure having a step amount d that generates a wavefront aberration δW that reduces spherical aberration caused by a temperature change or a wavelength change and that does not generate a wavefront aberration in a designed state is formed on the surface of the optical element. Thus, the temperature characteristic or wavelength characteristic of the optical pickup optical system 1 can be improved.

FIG. 4 shows wavefront aberration caused by focus position shift caused by wavelength change and wavefront aberration corrected by the annular structure. In FIG. 4, the vertical axis indicates the wavefront aberration, and the horizontal axis indicates the radial position in the light beam radial direction centered on the optical axis. In FIG. 4, the broken line indicates the wavefront aberration generated by the focus position shift accompanying the wavelength change, the thick solid line indicates the wavefront aberration corrected by the annular structure, and the thin solid line is generated by the annular structure. Wavefront aberration is shown.
As shown in FIG. 4, by generating a stepped wavefront aberration by the annular structure, it is possible to reduce the wavefront aberration generated by the focus position shift accompanying the wavelength change. Specifically, for example, at each of the radii R1, R2, R3, and R4, the step amount d that generates δW necessary to reduce the wavefront aberration caused by the focus position shift accompanying the wavelength change. Is formed on the surface of the optical element. In other words, an annular structure having a step amount d that generates a wavefront aberration δW that reduces wavefront aberration caused by a focus position shift accompanying a wavelength change and that does not generate a wavefront aberration in the design state is formed on the surface of the optical element. By forming, the wavelength characteristic of the optical pickup optical system 1 can be improved.

In the embodiment according to the present invention, as shown in FIG. 3, an annular structure for generating wavefront aberration for reducing spherical aberration caused by temperature change is formed on one surface of the objective lens 17. Further, as shown in FIG. 3, a wavefront aberration that reduces spherical aberration caused by the wavelength change is generated on one surface of the phase correction element 15, and as shown in FIG. An annular structure that reduces the generated wavefront aberration is formed. Thereby, both the temperature characteristic and the wavelength characteristic of the optical pickup optical system 1 can be improved.
As described above, when an annular structure for temperature correction is formed on one surface of the objective lens and an annular structure for wavelength correction is formed on one surface of the coupling lens, the temperature characteristics of the optical pickup optical system are increased. It will deteriorate. However, in the optical pickup optical system 1 according to the present embodiment, the temperature correction ring zone structure is formed on one surface of the objective lens, and the wavelength correction ring zone structure is formed on one surface of the phase correction element. Therefore, both temperature characteristics and wavelength characteristics of the optical pickup optical system 1 can be improved.

  The phase correction element 15 according to the present embodiment is made of glass. Thereby, the wavefront aberration caused by the annular structure formed on the surface of the phase correction element 15 due to the temperature change can be reduced. Therefore, even if an annular structure is formed in the phase correction element 15, deterioration of spherical aberration caused by a temperature change is not promoted. Therefore, the temperature characteristics of the optical pickup optical system 1 are not deteriorated.

Further, the coupling lens 14 according to the present embodiment is made of plastic. Thereby, the spherical aberration which generate | occur | produces in an objective lens with a temperature change can be reduced. Specifically, when the temperature increases, the refractive index of the plastic decreases. Therefore, the refractive power of the objective lens 17 becomes small. Therefore, when the temperature rises, spherical aberration occurs in the plus direction in the objective lens 17 made of plastic. On the other hand, the light beam emitted from the coupling lens 14 becomes a more divergent light beam than before the temperature rise. When the divergent light beam enters the objective lens 17, spherical aberration occurs in the minus direction in the objective lens 17. Therefore, by forming the coupling lens 14 with a plastic having a large refractive index change due to a temperature change, it is possible to cancel the spherical aberration generated by the temperature change in the objective lens 17.
When the coupling lens is made of glass, the amount of change in refractive index due to temperature change is small. Further, when the coupling lens is made of glass, the refractive index may increase as the temperature rises. Therefore, when the coupling lens is made of glass, the amount by which the degree of divergence of the emitted light beam from the coupling lens changes due to temperature change is small. For this reason, when the light beam enters the objective lens, the spherical aberration generated in the objective lens is also reduced. For this reason, when the coupling lens is made of glass, the effect of canceling out spherical aberration caused by a temperature change in the plastic objective lens is reduced.

  Next, the optical pickup optical system 1 according to the present embodiment will be described. FIG. 5 shows an example of the optical pickup optical system 1 according to the embodiment of the present invention. The optical pickup optical system 1 includes a laser light source 11 (laser light source), a beam splitter 12, a quarter wavelength plate 13, a coupling lens 14, a phase correction element 15, an aperture 16, an objective lens 17, a photodetector 18, and the like. ing. In the present embodiment, BD (Blu-ray) is used as the optical disc 19 (optical information recording medium).

  The laser light source 11 includes a blue-violet semiconductor laser that emits a light flux of about 400 nm.

  A beam splitter 12 is provided on the optical path of the laser light (light beam) emitted from the laser light source 11. A quarter-wave plate 13 is provided on the optical path of the laser light emitted from the beam splitter 12. The laser light emitted from the laser light source 11 passes through the beam splitter 12 and the quarter wavelength plate 13 and is converted into circularly polarized light.

  A coupling lens 14 is provided on the optical path of the laser light emitted from the quarter wavelength plate 13. The coupling lens 14 converts the laser light emitted from the quarter-wave plate 13 from divergent light to substantially parallel light. The coupling lens 14 is made of a plastic material.

A phase correction element 15 is provided on the optical path of the laser light emitted from the coupling lens 14. A side view of the phase correction element 15 is shown in FIG. As shown in FIG. 6A, at least one surface of the phase correction element 15 is formed with an annular structure composed of a plurality of annular zones having different sizes with the optical axis of the phase correction element 15 being concentric. Yes.
Further, a step is formed between adjacent annular zones of the annular zone structure. In other words, at least one surface of the phase correction element 15 is divided into a plurality of annular zones having the optical axis of the phase correction element 15 concentric by a plurality of steps. The phase correction element 15 is made of a glass material.

  The amount of the step formed in the phase correction element 15 is such that the phase of the laser beam transmitted in the normal state (when the wavelength of the laser beam is not changed) differs in wavelength units between adjacent annular zones. Is set to That is, the level difference of the level difference formed in the phase correction element 15 is substantially an integer multiple of the wavelength of the laser beam at the normal time. Further, the step formed in the phase correction element 15 is caused by a spherical aberration caused by a change in the wavelength of the laser light emitted from the laser light source 11 in the light beam transmitted through the phase correction element 15 and a change in the wavelength of the laser light. A step amount for generating a phase difference that reduces the wavefront aberration caused by the shift of the focus position due to. Therefore, the phase correction element 15 causes spherical aberration generated due to a change in the wavelength of the laser light and wavefront aberration generated due to a focus position shift accompanying a change in the wavelength of the laser light to the laser light emitted from the coupling lens 14. A phase difference that decreases is emitted.

A diaphragm 16 is provided on the optical path of the laser light emitted from the phase correction element 15. An objective lens 17 is provided on the optical path of the laser beam that has passed through the diaphragm 16.
The objective lens 17 has a function of condensing incident light on the information recording surface of the optical disc (BD) 19 to near the diffraction limit. The objective lens 17 further has a function of guiding the laser beam reflected by the information recording surface of the optical disc 19 to the photodetector 18.
A side view of the objective lens 17 is shown in FIG. As shown in FIG. 6 (b), at least one surface of the objective lens 17 is formed with an annular structure composed of a plurality of annular zones having different sizes with the optical axis of the objective lens 17 being concentric.
Further, a step is formed between adjacent annular zones of the annular zone structure. In other words, at least one surface of the objective lens 17 is divided into a plurality of annular zones having the optical axis of the objective lens 17 concentric by a plurality of steps. The objective lens 17 is made of a plastic material.

  The step amounts of the plurality of steps formed on the objective lens 17 are set such that the phase of the laser beam transmitted in the normal time (when the ambient temperature is not changed) is different in wavelength units between adjacent annular regions. Is set. That is, the level difference of the level difference formed on the objective lens 17 is substantially an integer multiple of the wavelength of the laser beam at the normal time. The plurality of steps formed on the objective lens 17 have a step amount that causes a phase difference in the light beam transmitted through the objective lens 17 to reduce wavefront aberration caused by a change in ambient temperature. Accordingly, the objective lens 17 emits a laser beam that has passed through the diaphragm 16 with a phase difference that reduces spherical aberration caused by a change in ambient temperature.

  At the time of focus servo and tracking servo, the objective lens 17 is operated by an actuator (not shown).

  Next, the behavior until the laser beam emitted from the laser light source 11 is reflected by the information recording surface of the optical disc 19 and detected by the photodetector 18 will be described. The laser light emitted from the laser light source 11 passes through the beam splitter 12 and the quarter wavelength plate 13 and enters the coupling lens 14.

  The coupling lens 14 converts the laser light emitted from the laser light source 11 from divergent light to substantially parallel light.

  The laser light that has passed through the coupling lens 14 is incident on the phase correction element 15. Here, in the present embodiment, when the wavelength of the laser beam changes, the plurality of steps provided in the phase correction element 15 causes the laser beam to reduce the aberration caused by the change in the wavelength of the laser beam. Correct the phase.

  Next, the laser light transmitted through the phase correction element 15 passes through the diaphragm 16 and then enters the objective lens 17. Here, in the present embodiment, when the ambient temperature changes, the plurality of steps provided in the objective lens 17 adjust the phase of the laser beam so as to reduce the aberration caused by the ambient temperature change. to correct. Then, the objective lens 17 focuses the corrected laser beam on the information recording surface of the optical disc 19 to near the diffraction limit. The laser beam reflected by the information recording surface of the optical disk 19 enters the photodetector 18 through the objective lens 17 and is detected. The photodetector 18 detects the laser beam, performs photoelectric conversion, and outputs an output signal. Based on the output signal of the photodetector 18, a focus error signal, a track error signal, a reproduction signal, and the like are generated. Further, recording and / or reproduction of the optical disk 19 is performed using the focus error signal, track error signal, reproduction signal, and the like.

  Next, the phase correction element 15 according to the embodiment of the present invention will be described in detail. In the present embodiment, the plurality of steps described above are provided on the surface of the phase correction element 15 on the optical disc 19 side. The step amounts of the plurality of steps are set so that the phase of the laser beam transmitted in normal time (when the wavelength of the laser beam is not changed) is different between adjacent annular zones in wavelength units. Further, the level difference of the phase correction element 15 has a level difference that causes a phase difference in the laser beam so as to reduce the aberration caused by the change in the wavelength of the laser beam when the wavelength of the laser beam changes.

  That is, when the laser beam is incident on the phase correction element 15 at normal times, the phases of the laser beams transmitted through the respective annular zones differ from each other by an integral multiple of the wavelength. Therefore, at the normal time, no phase difference occurs in the laser light transmitted through different annular zones. Therefore, the laser light incident on the phase correction element 15 is emitted with the same phase. Therefore, in the normal state, the aberration of the laser light emitted from the phase correction element 15 is substantially the same as the aberration of the laser light emitted from the phase correction element in which no step is formed.

  On the other hand, when the wavelength of the laser light changes and the laser light having the changed wavelength enters the phase correction element 15, the difference in phase of the laser light transmitted through each annular zone does not become an integral multiple of the wavelength. Therefore, when the wavelength is changed, a phase difference is generated in the laser light transmitted through different annular regions. In the present invention, the phase difference is sized so as to reduce the aberration caused by the change in the wavelength of the laser beam. For this reason, when the wavelength of the laser beam changes, the aberration of the laser beam focused by the objective lens increases conventionally. In the present invention, however, the laser beam transmitted through each annular zone of the phase correction element 15 Due to this phase difference, an increase in aberration associated with a change in the wavelength of the laser light is suppressed. Then, the laser light emitted from the objective lens 17 is well focused on the information recording surface of the optical disk 19.

  Next, the objective lens 17 according to the embodiment of the present invention will be described in detail. In the present embodiment, the plurality of steps described above are provided on the surface of the objective lens 17 on the laser light source 11 side. The step amounts of the plurality of steps are set so that the phase of the laser beam transmitted in the normal state (when the ambient temperature is not changed) is different in wavelength units from each other adjacent annular regions. Further, the step of the objective lens 17 has a step amount that causes a phase difference in the laser beam so as to reduce aberration caused by the change in the ambient temperature when the ambient temperature changes.

  That is, when the laser light is normally incident on the objective lens 17, the phases of the laser light transmitted through each annular zone are different from each other by an integral multiple of the wavelength. Therefore, at the normal time, no phase difference occurs in the laser light transmitted through different annular zones. Therefore, the laser light incident on the objective lens 17 is emitted with the same phase. Therefore, in the normal state, the aberration of the laser beam emitted from the objective lens 17 is substantially the same as the aberration of the laser beam emitted from the objective lens in which no step is formed.

  On the other hand, when the ambient temperature changes and the laser light whose wavelength has changed enters the objective lens 17, the difference in phase of the laser light transmitted through each annular zone region does not become an integral multiple of the wavelength. Therefore, when the wavelength is changed, a phase difference is generated in the laser light transmitted through different annular regions. In the present invention, the phase difference is sized so as to reduce aberrations caused by changes in ambient temperature. For this reason, when the ambient temperature changes, the aberration of the laser beam condensed by the objective lens increases conventionally. However, in the present invention, the phase difference of the laser beam transmitted through each annular region of the objective lens 17 is increased. Thus, an increase in aberration associated with a change in ambient temperature is suppressed. Then, the laser light emitted from the objective lens 17 is well focused on the information recording surface of the optical disk 19.

  In addition, as shown in FIG. 6B, the annular structure formed in the objective lens 17 has a lens thickness that decreases from the optical axis toward the outer edge in the radial direction of the objective lens 17, and Further, the lens thickness of the objective lens is increased toward the outer edge side. In other words, the annular zone structure of the objective lens 17 is formed such that the shape of the entrance surface of the objective lens 17 is convex at the central portion of the objective lens 17 and concave at the outer edge portion outside the central portion. Has been. Thereby, the number of ring zones formed on the objective lens 17 can be minimized while maintaining the performance of correcting the aberration caused by the temperature change by the ring zone structure formed on the objective lens 17.

Further, as shown in FIG. 6A, in the annular structure formed in the phase correction element 15, the thickness of the phase correction element 15 increases from the optical axis toward the outer edge in the radial direction of the phase correction element 15. In addition, the thickness of the phase correction element 15 is made thinner toward the outer edge side. In other words, the ring zone of the phase correction element 15 is such that the shape of the exit surface of the phase correction element 15 is concave at the central portion of the phase correction element 15 and convex at the outer edge portion outside the central portion. A structure is formed.
In general, when the aberration due to the temperature change is corrected by the annular structure of the objective lens 17, if the correction amount by the annular structure of the objective lens 17 is increased, the step amount of the entire annular structure formed in the objective lens 17 is increased. Will increase. As a result, the wavefront aberration caused by the wavelength change is increased by the annular structure formed in the objective lens 17. Here, the thickness of the phase correction element 15 increases toward the outer edge from the optical axis in the radial direction of the phase correction element 15, and the thickness of the phase complementary element 15 increases further toward the outer edge side. When the annular structure is formed so as to be thin, when the aberration due to the temperature change is corrected by the annular structure of the objective lens 17, the correction amount by the annular structure of the objective lens 17 is increased. The deteriorated wavelength characteristic can be compensated.

As shown in FIG. 6C, in the annular structure formed in the phase correction element 15, the thickness of the phase correction element 15 increases from the optical axis toward the outer edge in the radial direction of the phase correction element 15. It may be formed as follows. In other words, the annular structure of the phase correction element 15 may be formed so that the shape of the emission surface of the phase correction element 15 is concave.
When the correction amount for correcting the aberration due to the temperature change by the annular structure of the objective lens 17 is not large, the phase correction element 15 is phase-corrected from the optical axis toward the outer edge in the radial direction of the phase correction element 15. By forming the annular structure so that the thickness of the element 15 is increased, it is formed in the phase correction element 15 while maintaining the performance of correcting the aberration caused by the wavelength change by the annular structure formed in the phase correction element 15. The number of ring zones to be played can be minimized.

According to the optical pickup optical system 1 according to the present embodiment configured as described above, the annular temperature formed on at least one surface of the objective lens 17 causes the luminous flux transmitted through the objective lens 17 to be changed to the ambient temperature. It is possible to generate a phase difference that reduces the wavefront aberration that occurs due to the change in. Further, the wavefront aberration generated by the change in the wavelength of the laser beam emitted from the laser light source 11 in the light beam transmitted through the phase correction element 15 is reduced by the annular structure on at least one surface of the phase correction element 15. A phase difference can be generated. Therefore, the temperature characteristics can be improved by the annular structure formed in the objective lens 17, and the wavelength characteristics can be improved by the annular structure formed in the phase correction element 15. Further, when an annular structure that improves the temperature characteristics is formed on the objective lens 17 and an annular structure that improves the wavelength characteristics is formed on the coupling lens 14, the temperature characteristics deteriorate. Both temperature characteristics and wavelength characteristics can be improved without sacrificing characteristics.
Further, since the objective lens 17 is made of plastic, it can be manufactured more easily.

The coupling lens 14 is made of plastic, and the phase correction element 15 is made of glass.
When the coupling lens 14 is made of plastic, when the ambient temperature changes, the aberration generated in the coupling lens 14 due to the change in the ambient temperature reduces the aberration generated in the objective lens 17 due to the change in the ambient temperature. Can do.
If the phase correction element 15 is made of glass, the aberration generated in the phase correction element 15 due to a change in the ambient temperature is small, so that the temperature characteristics of the optical pickup optical system 1 are not deteriorated.

Further, the annular structure formed in the objective lens 17 is such that the lens thickness of the objective lens 17 becomes thinner as it goes from the optical axis to the outer edge in the radial direction of the objective lens 17, and further as it goes further toward the outer edge side. 17 is formed so that the lens thickness is increased.
Thereby, the number of ring zones formed on the objective lens 17 can be minimized while maintaining the performance of correcting the aberration caused by the temperature change by the ring zone structure formed on the objective lens 17.

Furthermore, in the annular structure formed in the phase correction element 15, the thickness of the phase correction element 15 increases toward the outer edge from the optical axis in the radial direction of the phase correction element 15, and further toward the outer edge side. Accordingly, the thickness of the complementary element 15 is preferably reduced.
In general, when the aberration due to the temperature change is corrected by the annular structure of the objective lens 17, if the correction amount by the annular structure of the objective lens 17 is increased, the step amount of the entire annular structure formed in the objective lens 17 is increased. Will increase. As a result, the wavefront aberration caused by the wavelength change is increased by the annular structure formed in the objective lens 17. Here, the thickness of the phase correction element 15 increases toward the outer edge from the optical axis in the radial direction of the phase correction element 15, and the thickness of the phase complementary element 15 increases further toward the outer edge side. When the annular structure is formed so as to be thin, when the aberration due to the temperature change is corrected by the annular structure of the objective lens 17, the correction amount by the annular structure of the objective lens 17 is increased. The deteriorated wavelength characteristic can be compensated.

Further, the annular structure formed in the phase correction element 15 may be formed such that the thickness of the phase correction element 15 increases in the radial direction of the phase correction element 15 from the optical axis toward the outer edge.
When the correction amount for correcting the aberration due to the temperature change by the annular structure of the objective lens 17 is not large, the phase correction element 15 is phase-corrected from the optical axis toward the outer edge in the radial direction of the phase correction element 15. By forming the annular structure so that the thickness of the element 15 is increased, it is formed in the phase correction element 15 while maintaining the performance of correcting the aberration caused by the wavelength change by the annular structure formed in the phase correction element 15. The number of ring zones to be played can be minimized.

[Example 1]
Next, Example 1 according to the present invention will be described. The table shown in FIG. 7 shows design data of the pickup optical system 1 according to the first example. In the table shown in FIG. 7, surface numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 are the emission surface of the laser light source 11, the incident surface of the coupling 14, and the coupling lens 14, respectively. Exit surface, the entrance surface of the phase correction element 15, the exit surface of the phase correction element 15, the stop surface of the diaphragm 16, the entrance surface of the objective lens 17, the exit surface of the objective lens 17, the surface of the protective layer of the optical disc 19, This is the information recording surface. FIG. 7 shows the curvature radius R of each surface, the inter-surface distance to the next surface, material, refractive index (design conditions), and remarks.

  The optical pickup optical system 1 according to the example 1 has a design wavelength of 405 nm and a design temperature of 25 ° C. The focal length of the objective lens 17 is 1.41 mm, the numerical aperture of the objective lens 17 is 0.85, and the incident light beam diameter of the objective lens 17 is 2.4 mm. The focal length of the coupling lens 14 is 15.51 mm.

  In the optical pickup optical system 1 according to the example 1, as shown in FIG. 7, the coupling lens 14 is formed of plastic. The incident surface of the coupling lens 14 has a single aspherical shape with a radius of curvature R of 8.0745 mm. Further, the radius of curvature R of the exit surface of the coupling lens 14 is infinite and is substantially flat.

  Further, in the optical pickup optical system 1 according to Example 1, as shown in FIG. 7, the phase correction element 15 is formed of glass. Further, the incident surface of the phase correction element 15 is substantially flat. In addition, an annular structure is formed on the exit surface of the phase correction element 15.

  Further, in the optical pickup optical system 1 according to Example 1, as shown in FIG. 7, the objective lens 17 is formed of plastic. Further, the incident surface of the objective lens 17 has an aspherical shape in which an annular structure is formed. The exit surface of the phase correction element 15 has a single aspherical shape with a radius of curvature R of −1.4515 mm.

数式（２）において、ｈは、光軸からの光線の高さ、Ｚ_ｊは、高さｈにおける非球面を光軸まで仮想的に延長したときの光軸との交点と接平面からの距離（サグ量）、Ｃは、非球面の光軸上での曲率、Ｋは、コーニック係数、Ａ４、Ａ６、Ａ８、Ａ１０、Ａ１２、Ａ１４、Ａ１６は、それぞれ、４次から１６次までの非球面係数である。なお、Ｃ＝１／Ｒ、（Ｒは曲率半径）である。
そして、数式（２）と図８に示す係数の値とにより、実施例１にかかるカップリングレンズ１４の入射面の面形状が規定される。 The table shown in FIG. 8 shows the aspheric coefficient, curvature, etc. of the coupling lens 14. The coefficients shown in FIG. 8 are used in Equation (2) described later. Therefore, the surface shape of the incident surface of the coupling lens 14 according to the first embodiment is defined by the coefficient and the mathematical formula (2) shown in FIG.

In Equation (2), h is the height of the light beam from the optical axis, Z _j is the distance from the intersection point with the optical axis when the aspherical surface at height h is virtually extended to the optical axis, and the tangent plane. (Sag amount), C is the curvature of the aspherical surface on the optical axis, K is the conic coefficient, and A4, A6, A8, A10, A12, A14, and A16 are the aspherical surfaces from the 4th order to the 16th order, respectively. It is a coefficient. Note that C = 1 / R, where R is a radius of curvature.
The surface shape of the incident surface of the coupling lens 14 according to the first embodiment is defined by the mathematical formula (2) and the coefficient values shown in FIG.

The table shown in FIG. 9 shows the annular zone position and the level difference of the annular zone formed on the incident surface of the objective lens 17. The inner ring zone position is a position in the radial direction of the inner edge of each ring zone region. The outer ring zone position is a position in the radial direction of the outer edge of each ring zone region. Further, each annular zone position is a position from the optical axis in the radial direction.
In addition, the table shown in FIG. 10 shows the aspheric coefficient, curvature, etc. of the objective lens 17.
As shown in FIGS. 9 and 10, a plurality of annular zones are formed on the incident surface of the objective lens 17, and each annular zone has a different aspherical shape. The aspheric shape of each annular zone is defined by the aspherical coefficient, curvature, conic coefficient, and equation (2) of each annular zone shown in FIG.
The exit surface of the objective lens 17 has a single aspherical shape. The aspherical shape of the exit surface of the objective lens 17 is defined by the aspherical coefficient, curvature, conic coefficient, and equation (2) of the exit surface shown in FIG.

  Further, in the annular structure formed on the entrance surface of the objective lens 17, the step amount increases from the first annular zone (annular zone No. 1) to the seventh annular zone (annular zone No. 7). After the level difference is maximized in the belt, it decreases from the seventh ring zone to the sixteenth ring zone (ring zone No. 16). In the present embodiment, a step having a positive step amount is formed in the direction from the laser light source 11 toward the optical disk 19, and a step having a negative step amount is formed in the direction from the optical disk 19 toward the laser light source 11. Therefore, an annular zone structure is formed on the incident surface of the objective lens 17 so that the shape of the incident surface of the objective lens 17 is a convex shape at the central portion of the objective lens 17 and a concave shape at the outer edge portion outside the central portion. Is formed. Thereby, the number of ring zones formed on the objective lens 17 can be minimized while maintaining the performance of correcting the aberration caused by the temperature change by the ring zone structure formed on the objective lens 17.

The table shown in FIG. 11 shows the zone position and the step amount of the zone structure formed on the exit surface of the phase correction element 15.
As shown in FIG. 11, in the annular structure formed on the emission surface of the phase correction element 15, there is a step amount from the first annular zone (annular zone No. 1) to the thirteenth annular zone (annular zone No. 13). After the increase, the step amount in the thirteenth annular zone becomes maximum, and the step amount decreases from the thirteenth annular zone to the seventeenth annular zone (annular zone No. 17). In other words, the exit surface of the phase correction element 15 has a concave shape at the central portion of the phase correction element 15 and a convex shape at the outer edge portion outside the central portion. An annular structure is formed on the surface.

  In the case where an annular structure for temperature correction is formed on the objective lens 17, if the wavelength of the laser light changes, the annular structure formed on the objective lens 17 in addition to the wavefront aberration that occurs due to a focus position shift accompanying the wavelength change. Also causes wavefront aberrations. Therefore, if an annular structure for temperature correction is formed on the objective lens 17, the wavefront aberration will increase. Then, the shape of the emission surface of the phase correction element 15 is formed on the emission surface of the phase correction element 15 such that the shape is concave at the center portion of the phase correction element 15 and is convex at the outer edge portion outside the center portion. By the formed annular zone structure, it is possible to correct the wavefront aberration increased by forming the annular zone structure for temperature correction in the objective lens 17.

  When the temperature correction ring zone structure is not formed in the objective lens 17, the wavefront aberration caused by the change in the wavelength of the laser light is only the wavefront aberration caused by the focus position shift. Further, when the temperature correction range by the annular structure formed on the objective lens 17 is relatively narrow, even if the wavelength of the laser light changes, the wavefront aberration generated by the annular structure is relatively small. Therefore, the wavefront aberration generated by the focus position shift is more dominant than the wavefront aberration generated by the ring zone structure. In this case, the ring zone structure may be formed so that the step amount is simply increased or decreased from the first ring zone to the outermost ring zone.

  Moreover, although the surface shape of each annular zone formed in the phase correction element 15 according to the first embodiment is a plane, the scope of the present invention is not limited to this. For example, the surface shape of each annular zone formed in the phase correction element 15 according to the present invention may be a spherical surface or an aspherical surface. By making the surface shape of each annular zone formed in the phase correction element 15 spherical or aspherical, the wavefront aberration of the light beam transmitted through each annular zone can be controlled with higher accuracy.

  FIG. 12 shows wavefront aberrations that occur in the optical pickup optical system 1 in the designed state. In FIG. 12, the vertical axis represents the wavefront aberration, and the horizontal axis represents the normalized ray height. The normalized ray height is the ray height from the optical axis normalized by the effective diameter of the objective lens 17. As shown in FIG. 12, the TOTAL wavefront aberration value generated in the design state is 0.0093 λrms. Therefore, it is smaller than the Marechal reference value 0.07λrms which is an evaluation index of the amount of wavefront aberration of the optical pickup optical system. That is, the wavefront aberration value generated in the optical pickup optical system 1 according to the first example in the designed state is a good value.

  FIG. 13 shows the wavefront aberration that occurs when the wavelength of the laser light source 11 changes from the design wavelength of 405 nm to +1 nm due to the mode hop phenomenon. In FIG. 13, the vertical axis represents the wavefront aberration, and the horizontal axis represents the normalized ray height. FIG. 13A shows the wavefront aberration when the phase correction element 15 according to the first embodiment is used. FIG. 13B shows wavefront aberration when a phase correction element having no annular structure is used instead of the phase correction element 15 according to the first embodiment. The wavefront aberration shown in FIG. 13 is the wavefront aberration at the focus position of the design wavelength, and includes the wavefront aberration accompanying the focus position shift.

  The TOTAL wavefront aberration value of the wavefront aberration shown in FIG. 13A is 0.0122 λrms, and the TOTAL wavefront aberration value of the wavefront aberration shown in FIG. 13B is 0.1055 λrms. Of the TOTAL wavefront aberration values of the wavefront aberration shown in FIG. 13 (a), the amount of spherical aberration generated by forming the temperature correction ring zone structure on the objective lens 17 is −0.0021λrms, and FIG. Of the TOTAL wavefront aberration values of the wavefront aberration shown in (b), the amount of spherical aberration generated by forming a temperature-correcting annular zone on the objective lens 17 is 0.0492 λrms. Therefore, by using the phase correction element 15 in which the annular zone structure is formed, the spherical aberration that occurs when the wavelength of the laser light is changed by forming the annular zone structure for temperature correction in the objective lens 17, and Both wavefront aberrations caused by focus position shifts associated with changes in the wavelength of the laser light are well corrected.

  Further, when the phase correction element 15 according to the first example is used, the amount of focus position deviation caused by the change of the wavelength of the laser light from the design wavelength of 405 nm to +1 nm is 0.015 μm / nm. On the other hand, when a phase correction element that does not have an annular structure is used instead of the phase correction element 15 according to the first embodiment, the amount of focus position deviation that occurs when the wavelength of the laser light changes from the design wavelength of 405 nm to +1 nm is 0.283 μm / nm. Therefore, by using the phase correction element 15 according to the first embodiment, the focus position shift caused by the wavelength change is also improved. The focus position here is a focus position where the amount of wavefront aberration is minimized, and is different from the paraxial focus position.

Further, the paraxial chromatic aberration in FIGS. 13A and 13B is calculated to be about 0.223 μm / nm, which is almost the same. Therefore, the annular structure formed in the phase correction element 15 does not have a paraxial chromatic aberration correction effect. That is, the annular structure formed in the phase correction element 15 is not a diffractive structure.
In addition, when the wavelength of the laser beam changes from the design wavelength 405 nm to +1 nm, the refractive index change amount Δn / Δλ of the plastic used for the coupling lens 14 and the objective lens 17 is −1.54 × 10 ⁻⁴ , and the phase The refractive index change Δn / Δλ of the glass used for the correction element 15 is −3.40 × 10 ⁻⁶ , and the refractive index change Δn / Δλ of the plastic used for the protective layer of the optical disc 19 is −4.14 ×. 10 ^-4 .

FIG. 14 shows wavefront aberrations that occur in the optical pickup optical system 1 when the operating temperature of the optical pickup optical system 1 changes by + 30 ° C. from the design temperature. In FIG. 14, the vertical axis indicates the wavefront aberration, and the horizontal axis indicates the normalized ray height. FIG. 14A shows the wavefront aberration when the phase correction element 15 according to the first embodiment is used. FIG. 14B shows the wavefront aberration when a plastic phase correction element is used instead of the phase correction element 15 according to the first embodiment.
The TOTAL wavefront aberration value of the wavefront aberration shown in FIG. 14A is 0.0143 λrms, and the TOTAL wavefront aberration value of the wavefront aberration shown in FIG. 14B is 0.0887 λrms. Therefore, by using the phase correction element 15 made of glass, wavefront aberration generated in the phase correction element 15 due to temperature change can be reduced. When the temperature changes by + 1 ° C., the refractive index change amount Δn / ΔT of the plastic used for the coupling lens 14 and the objective lens 17 and the phase correction element in FIG. 14B is −1.00 × 10 ^−4. The refractive index change Δn / ΔT of the glass used for the phase correction element 15 is −3.50 × 10 ⁻⁶ , and the refractive index change Δn / ΔT of the plastic used for the protective layer of the optical disc 19 is − It is 1.00 × 10 ⁻⁴ .

Further, in the optical pickup optical system 1 according to the first embodiment, when a glass coupling lens is used instead of the plastic coupling lens 14, the wavefront aberration caused by the temperature changing by + 30 ° C. from the design temperature. The TOTAL wavefront aberration value is 0.0239 λrms. On the other hand, as shown in FIG. 14B, when the plastic coupling lens 14 is used, the TOTAL wavefront aberration value of the wavefront aberration generated when the temperature changes by + 30 ° C. from the design temperature is 0.0143 λrms. Therefore, if a glass coupling lens is used instead of the plastic coupling lens 14, the temperature characteristics are deteriorated. That is, it is preferable to use the plastic coupling lens 14 to correct aberrations caused by temperature changes. When the temperature changes by + 1 ° C., the refractive index change amount Δn / ΔT of the glass used for the coupling lens is −1.00 × 10 ⁻⁶ .

It is a perspective view which shows an example of the objective lens concerning this embodiment. FIG. 2B is an enlarged sectional view of a step portion between adjacent annular zones (FIG. 2A), and a graph showing a relationship between the phase component of the wavefront aberration OPD (AB) and the step amount d (FIG. 2B). is there. It is a graph which shows the wavefront aberration which arises by a temperature change or a wavelength change, and the wavefront aberration corrected by the ring zone structure. It is a graph which shows the wavefront aberration which generate | occur | produces by the focus position shift | offset | difference which arises by a wavelength change, and the wavefront aberration corrected by the annular structure. It is a figure which shows an example of the optical pick-up optical system 1 concerning this embodiment. A side view showing an example of the phase correction element according to the present embodiment (FIG. 6A), a side view showing the objective lens according to the present embodiment (FIG. 6C), and the phase correction element according to the present embodiment. It is a side view (Drawing 6 (c)) showing an example. 3 is a table showing design data of a pickup optical system according to Example 1; 4 is a table showing aspherical coefficients, curvatures, and the like of the coupling lens according to Example 1; 3 is a table showing an annular position and a step amount on an incident surface of an objective lens according to Example 1; 3 is a table showing an aspherical coefficient, a curvature, and the like of the objective lens according to Example 1; It is a table | surface which shows the ring zone position and level | step difference amount of a ring zone structure formed in the output surface of the phase correction element concerning Example 1. FIG. It is a graph which shows the wavefront aberration which generate | occur | produces with an optical pick-up optical system in a design state. When the phase correction element according to Example 1 is used, a graph (FIG. 13A) showing a wavefront aberration that occurs when the wavelength changes by +1 nm from the design wavelength, and a phase correction element that does not have an annular structure. FIG. 13B is a graph showing wavefront aberration that occurs when the wavelength is changed by +1 nm from the design wavelength when used (FIG. 13B). When the phase correction element according to Example 1 is used, a graph (FIG. 14A) showing wavefront aberration that occurs when the temperature changes by + 30 ° C. from the design temperature, when a plastic phase correction element is used FIG. 14B is a graph (FIG. 14B) showing wavefront aberration that occurs when the temperature changes by + 30 ° C. from the design temperature. A graph (FIG. 15 (a)) showing the temperature characteristics of a plastic objective lens having an annular structure that corrects a wavefront aberration caused by a temperature change, and a plastic having an annular structure that corrects a wavefront aberration caused by the temperature change It is a graph (FIG.15 (b)) which shows the wavelength characteristic of manufactured objective lenses. Temperature characteristics when a plastic objective lens with an annular structure that corrects wavefront aberration caused by temperature changes is combined with a plastic coupling lens with an annular structure that corrects wavefront aberrations caused by wavelength changes (FIG. 16A), a plastic objective lens formed with a ring structure for correcting a wavefront aberration caused by a wavelength change on a plastic objective lens formed with a ring structure for correcting a wavefront aberration caused by a temperature change. It is a graph (FIG.16 (b)) which shows the wavelength characteristic at the time of combining the coupling lens of.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up optical system 11 Laser light source 14 Coupling lens 15 Phase correction element 17 Objective lens 19 Optical disk (optical information recording medium)

Claims (5)

An optical pickup optical system for condensing a light beam from a laser light source on an optical information recording medium,
A plastic objective lens having a numerical aperture of 0.85 or more;
A coupling lens for adjusting the divergence angle of the light beam from the laser light source;
A phase correction element disposed between the objective lens and the coupling lens;
Have
The objective lens and the phase correction element have an annular structure formed of a plurality of annular zones having different concentric sizes on at least one surface,
A step is formed between the annular zones adjacent to each other,
The step formed on the objective lens has a step amount that generates a phase difference that reduces wavefront aberration caused by a change in ambient temperature in the light beam transmitted through the objective lens,
The step formed in the phase correction element generates a phase difference that reduces wavefront aberration caused by a change in the wavelength of the laser light emitted from the laser light source in the light beam transmitted through the phase correction element. An optical pickup optical system having a step amount.   The optical pickup optical system according to claim 1, wherein the coupling lens is made of plastic, and the phase correction element is made of glass.   In the annular structure formed on the objective lens, the lens thickness of the objective lens becomes thinner as it goes from the optical axis to the outer edge in the radial direction of the objective lens, and further, the objective lens becomes closer to the outer edge side. The optical pickup optical system according to claim 1, wherein the lens is formed to have a thick lens thickness.   The annular structure formed in the phase correction element has a thickness that increases as it goes from the optical axis to the outer edge in the radial direction of the phase correction element, and further toward the outer edge, The optical pickup optical system according to any one of claims 1 to 3, wherein the position complementary element is formed to have a small thickness.   The ring zone structure formed in the phase correction element is formed such that the thickness of the phase correction element increases in the radial direction of the phase correction element from the optical axis toward the outer edge. The optical pickup optical system according to any one of the above.

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