JP2010218621A - Optical pickup device, and optical disk apparatus using the same - Google Patents

Abstract

In order to correct astigmatism, no power or special system is required, and astigmatism is also reflected in the reflected light of an optical disc having a polarization direction different from that of the laser light toward the optical disc as well as the laser beam toward the optical disc. An optical pickup device that can be controlled is provided.
A phase plate having a central portion and a phase modulation portion made of different materials is arranged perpendicularly to a laser beam between a collimator lens and an objective lens, and the laser beam passing through the phase plate is transmitted. Of these, the optical path length is made different between the laser light that passes through the phase modulation section and the laser light that does not pass through, and the tangential direction and radial direction that are generated when the laser light that causes astigmatism passes through the rising mirror 9. Astigmatism is corrected by offsetting the difference in optical path length by the difference in optical path length caused by the phase plate 19.
[Selection] Figure 1

Description

  The present invention relates to an optical pickup device that performs at least one of recording and reproduction of information on an optical disc and an optical disc device using the same.

  There are CD, DVD, and BD (Blu-ray Disc) as optical discs which are one of the application fields of the present invention. From the viewpoint of user convenience, it is required to record and reproduce these three types of optical disks with one optical disk device. In recent years, multilayer discs with higher density than BD have been proposed, and there are optical discs with four or eight recording layers for recording signals. Since the recording layers of such a multilayer disc are separated by an intermediate layer, the thickness from the surface of the optical disc to the recording layer, that is, the thickness of the substrate, varies greatly depending on the recording or reproducing layer. Spherical aberration occurs due to this change in substrate thickness.

  FIG. 21 is a diagram showing a part of an optical system in a conventional optical pickup device. This spherical aberration can be corrected by changing the laser light incident on the objective lens 104 into convergent light or divergent light by moving the collimator lens 100. When the laser light passes through the collimator lens 100, it passes through the rising mirror 101 and is reflected substantially vertically by the rising mirror 102. Thereafter, the light passes through the achromatic diffraction lens 103 and is focused on the optical disk 105 by the objective lens 104. However, astigmatism occurs when the laser light passes through the rising mirror 101.

  The occurrence of this astigmatism is due to the following reason. FIG. 22 is a diagram showing the optical path length of the light passing through the tilted raising mirror 101 for explaining astigmatism, and FIG. 22A shows the optical path length of the light when viewed from the x-axis direction. FIG. 22B is a diagram showing the optical path length of light when viewed from the y-axis direction. As shown in FIGS. 22A and 22B, the optical path length in the yz plane in the flat plate is longer than the optical path length in the xz plane in the flat plate. Astigmatism occurs due to the difference between the optical path length in the yz plane and the optical path length in the xz plane.

  Thus, astigmatism also occurs in the rising mirror 101 of the conventional optical pickup device as shown in FIG. 21 for the same reason. That is, the x axis and the y axis shown in FIG. 22 are the radial direction and the y axis direction are the tangential direction in FIG. 21, and the conventional optical pickup device shown in FIG. However, there is a difference in the optical path length of the laser light between the radial direction and the tangential direction. The radial direction of the optical disc 105 is a radial direction, and the circumferential direction of the optical disc 105 is a tangential direction. Astigmatism occurs due to the difference between the optical path length in the radial direction of the laser light and the optical path length in the tangential direction. In particular, in the optical disc 105 having, for example, eight or more recording layers, the substrate thickness error when recording or reproducing on the optical disc 105 becomes large, and the convergence distance of light is increased by increasing the moving distance of the collimator lens 100. It is necessary to increase the degree. As a result, astigmatism generated in the laser light transmitted through the tilted rising mirror 101 becomes large, and normal recording or reproduction of the multilayered optical disk 105 becomes impossible.

  In order to solve these problems, the following technology has been developed in the conventional pickup device. FIG. 23 is a view showing a part of an optical system in a conventional optical pickup device provided with a rising prism, and FIG. 24 is a liquid crystal for correcting astigmatism in the conventional optical pickup device as shown in FIG. It is a figure which shows an apparatus.

  In the conventional optical pickup device as shown in FIG. 23, the laser light emitted from the light source 110 passes through the beam splitter 111 and is converted into convergent light or divergent light by the movement of the collimator lens 112. Thereafter, the light passes through the astigmatism correction element 113, is reflected by the rising prism 114 toward the quarter-wave plate 115 and the objective lens 116, and enters the optical disk 117. The laser light reflected by the optical disc 117 passes through the objective lens 116 and the quarter wavelength plate 115 and enters the rising prism 114, and is directed toward the astigmatism correction element 113 and the collimator lens 112 by the rising prism 114. It is reflected and enters the beam splitter 111. Since the beam splitter 111 can reflect only the reflected light from the optical disk 117 substantially vertically, the laser light is reflected toward the lens 118 and is collected by the lens 118 onto the signal detection system 119. When the rising prism 114 is used in this manner, astigmatism occurs as in the case where the laser beam for BD passes through the rising mirror. At this time, for example, astigmatism is corrected by controlling the astigmatism correction element 113 configured by a liquid crystal device (see, for example, Patent Document 1).

With regard to this liquid crystal device, a technique is disclosed in which a transparent electrode 210 of a liquid crystal panel is divided into nine pattern electrodes 200 to 208 as shown in FIG. A circular pattern electrode 200 is formed at the center of the incident range 209 of the light beam corresponding to the pupil of the objective lens, and similar pattern electrodes 201 to 208 that are radially divided are formed on the outer periphery thereof. Corresponding to the direction of astigmatism caused by the optical system, the drive pattern and drive voltage applied to the outer peripheral pattern electrodes 201 to 208 are appropriately controlled, and in this state, the light beam is allowed to pass and the difference in refractive index. Astigmatism is corrected by giving a phase difference based on (see, for example, Patent Document 2).
JP 2007-188588 A JP 2000-040249 A

  However, with the above configuration, even if the astigmatism in the polarization direction of the laser light toward the optical disk can be corrected, the astigmatism in the reflected light from the optical disk whose polarization direction has changed to a right angle cannot be corrected. That is, the achromatic diffractive lens 103 shown in FIG. 21 is provided with a wave plate that rotates the polarization direction of the short-wavelength laser light that has passed twice (the forward path and the backward path) by approximately 90 degrees, and the liquid crystal is polarization-dependent. Astigmatism of the reflected light from the optical disk 105 whose polarization direction has changed cannot be controlled. Furthermore, in order to drive the liquid crystal device, power consumption and a system for controlling the liquid crystal device are required.

  Accordingly, the present invention has been made in view of the above problems, and laser light directed to an optical disc without requiring power or a special system when correcting astigmatism caused by a rising mirror or a rising prism or the like. Of course, an object of the present invention is to provide an optical pickup device capable of correcting astigmatism even in the reflected light of an optical disk whose polarization direction is approximately 90 degrees different from the laser light directed to the optical disk.

  The present invention has been made to achieve the above object, and includes a light source that emits laser light, a movable condenser lens that converts the laser light into convergent light or divergent light, and passing through the condenser lens. A rising prism or a rising mirror that converts the optical axis of the laser beam into a substantially vertical direction, and an objective lens that condenses the laser light whose optical axis has been converted by the rising prism or the rising mirror onto an optical disc. A phase plate composed of a central part and a phase modulation part made of materials having different refractive indexes between the condenser lens and the objective lens, and a part of the laser beam having a certain size or more is included in the phase By passing through the phase modulation part of the plate, the optical path length is different between the laser light that passes through the phase modulation part and the laser light that does not pass through the phase modulation part. An optical pickup device and correcting the astigmatism.

  With the above configuration, the present invention enables the phase plate to polarize not only the laser beam toward the optical disc but also the laser beam toward the optical disc without controlling the astigmatism caused by the rising mirror or the rising prism. Since there is no dependency, the laser beam directed to the optical disk has an effect of correcting astigmatism even in the reflected light of the optical disk whose polarization direction is approximately 90 degrees different. In addition, by configuring the phase modulation part and the central part of the phase plate with different materials, it is possible to configure phase plates with various material combinations and shapes, which increases the degree of design freedom, so that the optical path length of the laser light can be increased. Control, thinning of the phase plate, precise correction of astigmatism, etc. are facilitated.

  The invention according to claim 1 of the present invention includes a light source that emits laser light, a movable condensing lens that converts the laser light into convergent light or divergent light, and laser light that has passed through the condensing lens. A rising prism or a rising mirror that converts an optical axis in a substantially vertical direction; and an objective lens that focuses the laser light whose optical axis has been converted by the rising prism or the rising mirror onto an optical disk, and A phase plate composed of a central portion and a phase modulation portion made of materials having different refractive indexes is provided between the optical lens and the objective lens, and a portion of the laser beam having a certain size or more is phase-modulated by the phase plate. Astigmatism caused by the rising prism or the rising mirror by causing the optical path length to be different between the laser light that passes through the phase modulation portion and the laser light that does not pass by passing through the portion. The optical pickup device is characterized by correcting the laser beam toward the optical disc without requiring any power or a special system when controlling astigmatism caused by a rising mirror or a rising prism. Of course, since the phase plate does not have polarization dependency, astigmatism can be corrected even in the reflected light of the optical disk whose polarization direction is approximately 90 degrees different from the laser light toward the optical disk. In addition, by configuring the phase modulation part and the central part of the phase plate with different materials, it is possible to configure phase plates with various material combinations and shapes, which increases the degree of design freedom, so that the optical path length of the laser light can be increased. Control, thinning of the phase plate, precise correction of astigmatism, etc. are facilitated.

  The invention according to claim 2 of the present invention is the optical pickup device according to claim 1, wherein the phase plate is configured by laminating a flat substrate and a binder. Astigmatism can be corrected by configuring the phase modulation part and center part of the phase plate with different materials called materials, and phase plates with various material combinations and shapes can be configured. As the degree increases, it becomes easy to control the optical path length of the laser light, thin the phase plate, and precisely correct astigmatism.

  According to a third aspect of the present invention, in the light according to the second aspect, the phase modulation portion of the phase plate is formed by laminating a binder on opposite sides of a flat substrate. In the pickup device, the phase plate has a simple configuration and can be easily formed, and is easy to design.

  According to a fourth aspect of the present invention, in the optical pickup device according to the second aspect, the central portion of the phase plate is formed by laminating a binder on the central portion of a flat substrate. Thus, the phase plate has a simple configuration and can be easily formed, and is easy to design.

  The invention according to claim 5 of the present invention is characterized in that the phase modulation portion of the phase plate is configured by laminating a binder on a thin portion of a base body that is formed thin on opposite sides. 2. The optical pickup device according to 2, wherein the step at the boundary between the thick part and the thin part of the substrate serves as a reference for attaching the binding material, and the positioning of the binding material is facilitated to easily form the phase plate. Can do.

  The invention according to claim 6 of the present invention is the optical pickup device according to claim 2, wherein the central portion of the phase plate is configured by laminating a binder on the thin portion of the base. The step at the boundary between the thick part and the thin part of the substrate serves as a reference for attaching the binding material, so that the positioning of the binding material is facilitated and the phase plate can be easily formed.

  The invention according to claim 7 of the present invention is characterized in that the phase plate binder is formed by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate. In the described optical pickup device, the degree of design freedom increases, and the optical path length of the laser light passing through the phase modulation unit can be easily controlled.

  The invention according to claim 8 of the present invention is such that the refractive index increases or decreases as the binder forming the phase modulation portion of the phase plate approaches a plurality of different refractive index materials toward the end of the phase plate. 6. The optical pickup device according to claim 3, wherein the optical plate is stacked in a direction from a center side of the phase plate to an outer edge portion, and is incident on the phase plate. Since the size of the laser beam diameter changes step by step for each substrate thickness of the plurality of recording surfaces of the optical disk, more precise astigmatism can be achieved by providing a plurality of phase modulation portions with different refractive index materials. Correction can be performed.

  According to a ninth aspect of the present invention, the binder forming the phase modulation portion of the phase plate is configured such that the cross section is stepped and becomes thicker toward the end of the phase plate. 6. The optical pickup device according to claim 3, wherein the diameter of the laser beam incident on the phase plate is stepwise for each substrate thickness of a plurality of recording surfaces of the optical disk. Therefore, the astigmatism can be corrected with higher accuracy by configuring the phase modulation section in a step shape. Further, since the binding material is made of one substance, it is easy to form stepped steps with high accuracy.

  In the invention according to claim 10 of the present invention, the binder forming the phase modulation portion of the phase plate has a plurality of sections such that the cross section is stepped and becomes thicker or thinner toward the end of the phase plate. 6. The optical pickup device according to claim 3, wherein materials having different refractive indexes are laminated in the thickness direction of the phase plate or in the direction from the center side to the outer edge portion. Since the diameter of the laser beam incident on the phase plate changes step by step for each base material thickness of the plurality of recording surfaces of the optical disc, the phase modulation unit is configured in a step shape to provide more accuracy. High astigmatism correction can be performed. Furthermore, since the phase modulation section is formed of a plurality of materials having different refractive indexes, the degree of freedom in design is increased and the optical path length of the laser light passing through the phase modulation section can be easily controlled.

  The invention according to claim 11 of the present invention is such that the phase modulation portion of the phase plate is thicker or thinner as the cross-sections on the opposite sides of the base material are stepped and approach the end of the phase plate. 7. The optical pickup device according to claim 4, wherein the diameter of the laser beam incident on the phase plate is a plurality of recording surfaces of the optical disc. Therefore, astigmatism can be corrected with higher accuracy by configuring the phase modulation section in a step shape.

  The invention according to claim 12 of the present invention is the optical pickup device according to claim 2, wherein the phase plate binder is formed by coating a film on a substrate. The phase plate can be easily formed by a simple process of coating the film, and the thickness of the phase modulation part and the central part can be easily controlled.

  According to a thirteenth aspect of the present invention, in the optical pickup according to the first aspect, the phase plate is formed by connecting a phase modulation section to the outer side surfaces of the central portion on the opposite sides. In this apparatus, the phase plate can be made thin, and the symmetry of the phase plate is maintained, so that warpage and aberration are reduced, and astigmatism can be corrected with high accuracy.

  According to a fourteenth aspect of the present invention, the phase modulation unit of the phase plate is configured such that the refractive index increases or decreases as the plurality of materials having different refractive indexes approach the end of the phase plate. 14. The optical pickup device according to claim 13, wherein the optical pickup device is configured so as to be laminated in the direction from the center side of the plate to the outer edge portion. Since the recording surface changes step by step for each substrate thickness, it is possible to correct astigmatism with higher accuracy by providing a plurality of phase modulators with different refractive index substances, and to make the phase plate thin. At the same time, since the symmetry of the phase plate is maintained, warpage and aberration are reduced, and astigmatism can be corrected with higher accuracy.

  According to a fifteenth aspect of the present invention, in the light according to the thirteenth aspect, the phase modulation section of the phase plate is configured by laminating a plurality of materials having different refractive indexes in the thickness direction. This pickup device increases the degree of freedom in design, makes it easier to control the optical path length of the laser light passing through the phase modulation section, and reduces the thickness of the phase plate while maintaining the symmetry of the phase plate. As a result, the aberration is reduced, and astigmatism can be corrected with higher accuracy.

  The invention according to claim 16 of the present invention is characterized in that the phase modulation portion of the phase plate is configured to be thicker or thinner as the cross section is stepped and closer to the end of the phase plate. 14. The optical pickup device according to claim 13, wherein the diameter of the laser beam incident on the phase plate changes stepwise for each base material thickness of the plurality of recording surfaces of the optical disc. As a result, the astigmatism can be corrected with higher accuracy, and the phase plate can be made thin and the symmetry of the phase plate can be maintained. High astigmatism can be corrected.

  According to a seventeenth aspect of the present invention, the phase modulation portion of the phase plate has a plurality of materials having different refractive indexes so that the cross section is stepped and becomes thicker or thinner as it approaches the end of the phase plate. 14. The optical pickup device according to claim 13, wherein the optical plate is laminated in the thickness direction of the phase plate or in the direction from the center side to the outer edge, and the diameter of the laser light incident on the phase plate Since the size of the optical disk changes step by step for each substrate thickness of the plurality of recording surfaces of the optical disc, it is possible to correct astigmatism with higher accuracy by configuring the phase modulation section in a step shape. Since the thickness of the phase plate is reduced and the symmetry of the phase plate is maintained, warpage and aberration are reduced, and astigmatism can be corrected with higher accuracy. Furthermore, since the phase modulation section is formed of a plurality of materials having different refractive indexes, the degree of freedom in design is increased and the optical path length of the laser light passing through the phase modulation section can be easily controlled.

  According to an eighteenth aspect of the present invention, the optical pickup device according to any one of the first to seventeenth aspects, a rotation driving means for rotating the optical disk, and the optical pickup apparatus with respect to the rotation driving means are arranged on the optical disk. And a tangential direction generated when the laser light emitted from the short wavelength optical unit passes through the rising mirror, and a moving means for moving in the radial direction. Astigmatism can be corrected by canceling out the difference in the optical path length in the radial direction by the difference in optical path length generated when the laser light passes through the phase plate. In addition, since the phase plate does not have polarization dependency unlike the liquid crystal, astigmatism can be corrected not only in the laser beam directed to the optical disc but also in the reflected light of the optical disc having a polarization direction different from that of the laser beam directed toward the optical disc. it can. Therefore, even in a multi-layer optical disc, information can be recorded or reproduced accurately without being redundant. Furthermore, since only a phase plate made of glass or the like is provided, it is inexpensive, and astigmatism can be corrected without power or a special system.

  Embodiments of the present invention will be described below with reference to the drawings.

Example 1
FIG. 1 is a schematic diagram illustrating a configuration of an optical pickup device according to the first embodiment. The radial direction of the optical disk is referred to as a radial direction, and the circumferential direction of the optical disk surface is referred to as a tangential direction. FIG. 2 is a plan view showing an example in which the optical configuration of the optical pickup device shown in FIG. 1 is actually realized. Although the shape and the like are slightly different from each member shown in FIG. 1, the functions are almost the same. is there.

  Reference numeral 1 denotes a short wavelength optical unit that emits a short wavelength laser. The laser light emitted from the short wavelength optical unit 1 has a wavelength of 400 nm to 415 nm, and in the first embodiment, it is configured to emit light of approximately 405 nm. In the first embodiment, a light source unit 1a that emits short-wavelength laser light, a signal detection light-receiving unit 1b that receives laser light reflected from the optical disc 2, and a laser beam emitted from the light source unit 1a. It includes a light receiving portion 1c provided to monitor the amount of light, an optical member 1d, and a holding member (not shown) that holds these constituent members in a predetermined positional relationship. The light source unit 1a is provided with a semiconductor laser element (not shown) containing GaN or the like as a main component. Laser light emitted from the semiconductor laser element is incident on the optical member 1d, and the incident laser light. Is reflected by the optical member 1d and enters the light receiving section 1c for monitoring. Although not shown, a circuit for converting the laser light into an electrical signal by the light receiving unit 1c for monitoring and adjusting the intensity of the laser beam emitted from the light source unit 1a to a desired intensity based on the electrical signal, etc. Is provided. The signal detection light-receiving unit 1b converts the laser light into an electrical signal, and generates an RF signal, a tracking error signal, a focus error signal, and the like from the electrical signal. In the optical member 1d, there is provided a hologram 1e for separating the reflected light from the optical disc 2 so that a focus error signal can be obtained.

  Reference numeral 3 denotes a long wavelength optical unit that emits a long wavelength laser. The laser beam emitted from the long wavelength optical unit 3 has a wavelength of 640 nm to 800 nm, and is configured to emit a single type of laser beam or a plurality of types of laser beams of a plurality of types. . In the first embodiment, a light beam having a wavelength of about 660 nm (red: for example for DVD) and a light beam of about 780 nm (infrared: for example for CD) are emitted. In the first embodiment, a light source unit 3a that emits a long-wavelength laser beam, a signal detection light-receiving unit 3b that receives a laser beam reflected from the optical disc 2, and a laser beam emitted from the light source unit 3a. It includes a light receiving portion 3c provided to monitor the amount of light, an optical member 3d, and a holding member (not shown) that holds these constituent members in a predetermined positional relationship. The light source unit 3a is provided with a semiconductor laser element (not shown). The semiconductor laser element is composed of a monoblock (monolithic structure), and a light flux (red) having a wavelength of about 660 nm from the monoblock element. And a light beam (infrared) of about 780 nm is emitted. In the first embodiment, a monoblock element emits two light beams. However, a single block element may emit two light beams. A plurality of light beams emitted from the semiconductor laser element are incident on the optical member 3d, and a part of the incident laser light is reflected by the optical member 3d and enters the light receiving unit 3c for monitoring. The light detecting unit 3b for signal detection converts the laser light into an electric signal, and generates an RF signal, a tracking error signal, a focus error signal, and the like from the electric signal. The optical member 3d has a hologram 3e that separates the reflected light from the optical disc 2 into a plurality of pieces and generates a focus error signal for CD, and guides the light to a predetermined location of the light receiving unit 3b for signal detection. Is provided.

  Reference numeral 4 denotes a beam shaping lens through which light emitted from the short wavelength optical unit 1 and reflected light from the optical disk 2 pass. The beam shaping lens 4 increases the utilization efficiency of light emitted from the short wavelength laser, astigmatism of the short wavelength laser light, and astigmatism generated in the optical path from the short wavelength optical unit 1 to the optical disc 2. It is provided for the purpose of canceling. Further, convex portions 4a and concave portions 4b are respectively provided at both ends of the beam shaping lens 4, and the light emitted from the short wavelength optical unit 1 is first incident on the convex portions 4a and emitted from the concave portions 4b. The shaping lens 4 is arranged.

  Reference numeral 5 denotes an optical component, and the optical component 5 is arranged at the tip of the beam shaping lens 4 on the optical path and arranged on the concave portion 4b side of the beam shaping lens 4. That is, the laser light emitted from the short wavelength optical unit 1 is incident on the optical component 5 through the beam shaping lens 4 and guided to the optical disc 2, and the laser light reflected from the optical disc 2 is reflected on the optical component 5 and beam shaping. The light enters the short wavelength optical unit 1 through the lens 4 in order. The optical component 5 is provided with a hologram or the like, and the laser beam reflected from the optical disc 2 is separated into a predetermined light beam so as to mainly generate a tracking error signal.

  Reference numeral 6 denotes a relay lens through which a long-wavelength laser beam emitted from the long-wavelength optical unit 3 passes. The relay lens 6 is made of a transparent member such as resin or glass. The relay lens 6 is provided to efficiently guide the light emitted from the long wavelength optical unit 3 to the rear member.

  A beam splitter 7 is an optical member. In the beam splitter 7, at least two transparent members 7b and 7c are joined and provided, and an inclined surface 7a provided with one wavelength selection film is provided between the transparent members 7b and 7c. A wavelength selection film is directly formed on the inclined surface 7a of the transparent member 7c into which the laser light emitted from the short wavelength optical unit 1 enters, and resin or resin is applied to the inclined surface 7a of the transparent member 7c on which the wavelength selection film is formed. The transparent member 7b is joined via a joining material such as glass.

  A collimator lens 8 is movably held. The laser light is converted from divergent light into parallel light by passing through the collimator lens 8. The collimator lens 8 is attached to a slider 8b, and the slider 8b is movably attached to a pair of support members 8a provided substantially in parallel. A lead screw 8c provided with a helical groove is provided so as to be substantially parallel to the support member 8a, and a protrusion entering the groove of the lead screw 8c is provided at the end of the slider 8b. A gear group 8d is coupled to the lead screw 8c, and a driving member 8e composed of a stepping motor is coupled to the gear group 8d. The driving force of the driving member 8e is transmitted to the lead screw 8c through the gear group 8d, and the lead screw 8c is rotated by the driving force, and as a result, the slider 8b moves along the supporting member 8a. Thus, by adopting a configuration in which the collimator lens 8 is brought close to or away from the beam splitter 7, the spherical aberration can be easily adjusted. In the first embodiment, the collimator lens 8 is moved by the driving member 8e as a configuration for correcting the spherical aberration of the short-wavelength laser light. However, the collimator lens 8 may be moved by other configurations. However, the spherical aberration of the short-wavelength laser light may be adjusted using other means.

  Reference numeral 9 denotes a rising mirror, and the rising mirror 9 is provided with a quarter wavelength member 9a that acts on a short wavelength laser beam. As the quarter-wave member 9a, a quarter-wave plate that rotates the polarization direction of the laser beam that has passed twice (in the forward path and the return path) by approximately 90 degrees is preferably used. A wavelength selection film 9b is provided on the surface of the rising mirror 9 on which the light emitted from the optical units 1 and 3 is incident, so that the long wavelength laser light emitted from the long wavelength optical unit 3 is almost reflected. And has a function of transmitting almost all of the short-wavelength laser light emitted from the short-wavelength optical unit 1.

  Reference numeral 10 denotes an objective lens for a long wavelength laser. The objective lens 10 focuses the laser beam reflected from the rising mirror 9 on the optical disk 2. In the first embodiment, the objective lens 10 is used.

  Reference numeral 11 denotes an optical component provided between the objective lens 10 and the raising mirror 9. The optical component 11 is compatible with the optical disc 2 of DVD (light having a wavelength of approximately 660 nm) and CD (light having a wavelength of approximately 780 nm). As described above, an aperture filter for realizing a necessary numerical aperture, a polarization hologram that reacts to a laser beam having a wavelength of about 660 nm, and a quarter wavelength member (preferably a quarter wavelength plate) are provided. Yes. The optical component 11 includes a dielectric multilayer film, a diffraction grating aperture means, and the like. A polarization hologram applies deflection to light of approximately 660 nm (separates light having a wavelength of approximately 660 nm into light for tracking error signals and focus error signals).

  Reference numeral 12 denotes a rising mirror that almost reflects short-wavelength laser light. The rising mirror 12 is provided with a reflective film.

  Reference numeral 13 denotes an objective lens, and the objective lens 13 condenses the laser light reflected from the raising mirror 12 on the optical disk 2. In the first embodiment, the objective lens 13 is used. However, the objective lens 13 may be composed of another light collecting member such as a hologram. The objective lens 13 is made of glass or resin, but when the objective lens 13 is made of resin, it is preferably made of a short-wavelength light resin (a resin that does not deteriorate or hardly deteriorate due to a short wavelength). Composed.

  Reference numeral 14 denotes an achromatic diffraction lens provided between the objective lens 13 and the raising mirror 12, and the achromatic diffraction lens 14 has a function of correcting chromatic aberration. The achromatic diffractive lens 14 is provided with a quarter wavelength member that acts on short wavelength light. As this quarter-wave member, a quarter-wave plate that rotates the polarization direction of light that has passed twice (the forward path and the return path) by approximately 90 degrees is preferably used. The achromatic diffractive lens 14 is provided so as to cancel out and reduce chromatic aberration generated in each optical component through which a short wavelength laser beam passes.

  Reference numeral 15 denotes a base, to which the above-described members are attached so as to be fixed or movable. The base 15 has a short wavelength optical unit 1 that emits and receives short wavelength laser light, a long wavelength optical unit 3 that emits and receives long wavelength laser light, and a lens holding unit on which the objective lenses 10 and 13 are mounted. The lens holder 16 is attached to the shafts 23 and 24 so as to be movable. The base 15 is made of a metal such as zinc, zinc alloy, aluminum, aluminum alloy, magnesium, magnesium alloy, or a metal alloy material, and is preferably made using a die casting method or the like from the viewpoint of mass production.

  Reference numeral 17 denotes a suspension holder. The suspension holder 17 is attached to the base 15 by various joining methods. The lens holder 16 and the suspension holder 17 are coupled via a plurality of suspensions 18, and the lens holder 16 is a base. The base 15 is supported so as to be movable within a predetermined range. The objective lens 10 and 13, the optical component 11, the achromatic diffraction lens 14 (see FIG. 1), and the like are attached to the lens holder 16. The optical component 11 and the achromatic diffraction lens 14 also move. Reference numeral 19 denotes a phase plate provided with a phase modulation unit on the opposite sides, and corrects astigmatism. The phase plate 19 includes a base body 20 and a binder 21 and will be described in detail later. Reference numerals 23 and 24 denote shafts that enable the base 15 to move in the radial direction. Reference numeral 25 denotes a spindle motor on which the optical disk 2 is placed.

  Next, the phase plate 19 that is a feature of the present invention will be described in detail.

  FIG. 3A is a plan view of a phase plate in which the phase modulation unit in the first embodiment is formed by laminating a binder on two sides opposite to each other in the tangential direction of a flat substrate, and FIG. FIG. 4 is a side view of the phase plate shown in FIG. FIG. 4 is a plan view of a phase plate formed by laminating a binder on two sides opposite to each other in the radial direction of a flat substrate in the phase modulation unit in the first embodiment. FIG. 5A is a plan view of a phase plate in which the central portion in the first embodiment is configured by laminating a binder on the central portion of a flat substrate, and FIG. 5B is a phase plate shown in FIG. 5A. FIG. FIG. 6A is a plan view of a phase plate formed by laminating a binder on a thin portion of a substrate in which the opposite sides of the phase modulation portion in Example 1 are formed thin, and FIG. 6B is a diagram. It is a side view of the phase plate shown to 6 (a). 7A is a plan view of a phase plate formed by laminating a binder on the thin portion of the base body in the central portion in Example 1, and FIG. 7B is a side view of the phase plate shown in FIG. 7A. FIG. FIG. 8A is a plan view of a phase plate formed by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate, and FIG. FIG. 9 is a side view of the phase plate shown in FIG. FIG. 9A is a plan view of a phase plate formed by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate at the center of the phase plate in the first embodiment, and FIG. It is a side view of the phase plate shown to 9 (a). FIG. 10A shows the center of the phase plate so that the refractive index increases or decreases as the binder forming the phase modulation portion in the first embodiment approaches the end of the phase plate with a plurality of different refractive index materials. FIG. 10B is a side view of the phase plate shown in FIG. 10A, and FIG. 10B is a plan view of the phase plate formed by laminating in the direction from the side toward the outer edge. FIG. 11A is a plan view of a phase plate in which the binder forming the phase modulation unit in the first embodiment is configured such that the cross section is stepped and becomes thicker or thinner toward the end of the phase plate. 11 (b) is a side view of the phase plate shown in FIG. 11 (a) in the case where the binder is formed so as to become thicker as it approaches the end of the flat substrate, and FIG. 11 (c) is opposed to each other. FIG. 12 is a side view of the phase plate shown in FIG. 11A in a case where a base material having two sides formed thin is laminated with a binder that becomes thinner toward the end. FIG. 12 (a) shows the phase modulation unit in the first embodiment having a plurality of different refractive indexes in the thickness direction of the phase plate so that the cross section of the phase modulation unit is stepped and becomes thicker or thinner toward the end of the phase plate. Or it is a top view of the phase plate comprised by laminating | stacking from the center side to the direction of an external shape edge part, FIG.12 (b) is a phase plate so that it may become thick, so that the phase modulation part approaches the edge part of a flat base | substrate. FIG. 12A is a side view of the phase plate shown in FIG. 12A in the case where the layers are laminated in the thickness direction, and FIG. 12C shows the phase modulation portion at the end of the substrate formed with two opposing sides thinly formed. FIG. 13 is a side view of the phase plate shown in FIG. 12A in the case of being laminated in the direction from the center side of the phase plate toward the outer edge so as to become thinner as it gets closer. In FIG. 13A, a binder is laminated on the central portion of the base body in the first embodiment to form a central portion, and the phase modulation portion has a step-like cross section on the opposite side of the substrate and approaches the end portion of the phase plate. FIG. 13B is a plan view of a phase plate composed of portions that are formed so as to be thicker or thinner. FIG. 13B is a diagram illustrating a state in which a binder is laminated on a flat substrate and a phase modulation unit is brought close to an end portion as a central portion. FIG. 13A is a side view of the phase plate shown in FIG. 13A when laminated on a flat substrate that is configured to be thin, and FIG. 13C is a central portion obtained by laminating a binder on the thin portion of the substrate. FIG. 14 is a side view of the phase plate shown in FIG. 13A when the cross-sections on opposite sides of the base are stepped and become thicker toward the end of the phase plate.

  The phase plate 19 is disposed between the collimator lens 8 and the objective lens 13 substantially perpendicular to the laser beam. In order to avoid the influence of stray light, the phase plate 19 may be disposed with an inclination of about 4 degrees with respect to the laser light. The phase plate 19 is composed of a phase modulation portion 19a and a central portion 19b constituted by a flat base 20 and a binder 21, and examples of the material include optical glass such as BK7, white plate glass, silica, and a transparent resin material. The substrate 20 and the bonding material 21 are bonded by an optical adhesive or the like. By configuring the phase modulation portion 19a and the central portion 19b of the phase plate 19 with the base body 20 and the binding material 21 made of different materials, the phase plate 19 having various combinations and shapes of materials can be configured. Therefore, it becomes easy to control the optical path length of the laser light, make the phase plate 19 thinner, and accurately correct astigmatism.

  As described above, the recording layer of the optical disk 2 having the multilayer structure has a large change in the substrate thickness depending on each recording layer, and spherical aberration occurs due to the change. In order to correct this spherical aberration, the collimator lens 8 is moved to change the laser light into convergent light or divergent light. In the case where the substrate thickness is reduced, the laser light is increased by moving the collimator lens 8. Further, in the conventional optical pickup device, the influence of astigmatism increases as the substrate thickness of the recording layer decreases. That is, as the substrate thickness of the recording layer decreases, the diameter of the laser beam increases and the influence of astigmatism increases.

  In the optical pickup device according to the first embodiment, a part of the laser beam having a diameter of a certain diameter or more so as to increase the influence of astigmatism passes through the phase modulation unit 19a. The phase modulation unit 19a has a function of changing the optical path length of the laser light passing through the phase modulation unit 19a out of the laser light passing through the phase plate 19 with respect to the laser light not passing through the phase modulation unit 19a. Have. When the laser light passes through the phase plate 19, the optical path length of the laser light in one direction of the tangential direction or the radial direction changes, so that a difference in optical path length occurs between the tangential direction and the radial direction. Therefore, the difference between the optical path lengths in the tangential direction and the radial direction generated when the laser light causing astigmatism passes through the rising mirror 9 passes through the phase modulator 19a when passing through the phase plate 19. It can be canceled by the difference in the optical path length in one direction of the tangential direction or radial direction generated between the laser beam that passes and the laser beam that does not pass.

  In the phase plate 19 shown in FIGS. 3A and 3B, the phase modulation unit 19 a is configured by laminating a binder 21 on two sides facing each other with respect to the tangential direction of the flat substrate 20. . At this time, the central portion 19b is a portion of the base body 20 only. The phase plate 19 shown in FIG. 4 is configured by laminating a binder 21 on two sides opposite to each other in the radial direction of the flat substrate 20 in the phase modulation unit 19a. Also in this case, like the phase plate 19 of FIG.

  As shown in FIG. 3A, the width X of the phase modulation unit 19a in the first embodiment is such that the maximum optical disk base material thickness through which part of the laser light passes through the phase modulation unit 19a is 0.07 mm. When the substrate thickness is 0.07 mm or more, the laser beam does not pass through the phase modulation unit 19a. That is, the laser beam when the substrate thickness shown in FIG. 3A is 0.1 mm is smaller in diameter than the laser beam when the substrate thickness is 0.07 mm and passes only through the central portion 19b. On the other hand, the laser beam when the substrate thickness is 0.05 mm has a larger diameter than the laser beam when the substrate thickness is 0.07 mm, and a part of the laser beam passes through the phase modulator 19a. Therefore, the magnitude of astigmatism in the recording layer with the base material thickness of the optical disc 2 larger than 0.07 mm is the same as that of the conventional optical pickup device, and the astigmatism in the recording layer with the base material thickness smaller than 0.07 mm. The influence of can be suppressed. Note that the maximum substrate thickness of the optical disk 2 through which a part of the laser light passes through the phase modulation unit 19a may be appropriately changed to a value other than 0.07 mm, such as 0.06 mm or 0.08 mm.

The refractive index of the binder 21 n, and the refractive index of air 1, the thickness of the coupling member 21 and d _1, the optical path length when the laser light passing through the phase modulating unit 19a passes through the bonding material 21 is d ₁ n, and the optical path length of the laser light passing through only the air amount of the thickness of the binder 21 without passing through the phase modulating unit 19a is a d _1, the laser beam and the central portion which has passed through the phase modulating unit 19a A difference of d ₁ (n−1) occurs in the optical path length of the laser light that has passed through 19b. Therefore, the difference between the optical path lengths in the tangential direction and the radial direction, which are generated when the laser beam causing astigmatism passes through the rising mirror 9, is represented by the tanger generated by the laser beam passing through the phase plate 19. It can be canceled out by the difference d ₁ (n−1) in the optical path length in one direction of the radial direction or the radial direction. Incidentally, a wavelength of light lambda, when the phase difference to be given to the laser light passing through the phase modulating unit 19a and delta, the thickness d ₁ of the coupling member 21 is given by Δλ / (n-1). Δλ represents a difference in optical path length to be given to the laser light passing through the phase modulator 19a.

  The same applies to the phase plate 19 shown in FIG. 4, and the phase modulator 19a may be provided on two sides opposite to the tangential direction of the base 20 as shown in FIG. Alternatively, they may be provided on two sides opposite to each other in the radial direction. However, if provided on two opposite sides with respect to the tangential direction, the area of the laser light passing through the phase modulation unit 19a does not change even when the laser light moves in the radial direction by tracking control or the like, so astigmatism. Can be corrected without any problem.

  As described above, the phase modulation portion 19a is formed by laminating the binding material 21 on the two opposite sides of the flat base 20, so that the central portion 19b becomes a portion where the binding material 21 of the base 20 is not laminated, and the phase plate 19 has a simple configuration and can be easily formed, and is easy to design.

  The phase plate 19 shown in FIGS. 5A and 5B is configured by laminating a binder 21 on a central portion of a flat base 20 at a central portion 19b. At this time, the phase modulation section 19a is composed only of the base body 20.

N the refractive index of the binder 21 of the phase plate 19, the refractive index of air 1, the thickness of the coupling member 21 when the d _2, the optical path length when the laser beam passing through the central portion 19b passes through the bonding material 21 Is d ₂ n, and since the optical path length of the laser light that has passed through the phase modulation part 19a and passed through the air by the thickness of the binder 21 is d ₂ , the phase of the laser light that has passed through the central part 19b and the phase A difference of d ₂ (n−1) occurs in the optical path length of the laser light that has passed through the modulation unit 19a. Therefore, the difference between the optical path lengths in the tangential direction and the radial direction, which are generated when the laser beam causing astigmatism passes through the rising mirror 9, is represented by the tanger generated by the laser beam passing through the phase plate 19. It can be canceled by the difference d ₂ (n−1) in the optical path length in one direction of the radial direction or the radial direction. Incidentally, a wavelength of light lambda, when the phase difference to be given to the laser beam passing through the central portion 19b and delta, the thickness d ₂ of the coupling member 21 is given by Δλ / (n-1). Δλ represents a difference in optical path length to be given to the laser light passing through the phase modulator 19a.

  The phase modulation unit 19a may be provided on two sides opposite to the tangential direction of the base 20 or on two sides opposite to each other in the radial direction.

  Thus, by forming the central portion 19b by laminating the binder 21 on the central portion of the flat base 20, the phase modulation portion 19a becomes a portion of only the base 20, and the phase plate 19 has a simple configuration and is easily formed. It is easy to design.

  The phase plate 19 shown in FIGS. 6 (a) and 6 (b) is configured by laminating a binder 21 on a thin portion of a base body 20 in which the opposite sides of the phase modulation portion 19a are formed thin. At this time, the central portion 19 b is a thick portion of the base body 20.

When the refractive index of the coupling material 21 of the phase plate 19 is n ₁ , the refractive index of the substrate 20 is n ₂ , and the thickness of the coupling material 21 is d ₃ , the laser light that passes through the phase modulation unit 19 a passes through the coupling material 21. The optical path length at this time is d ₃ n ₁ , and the optical path length when the laser light passing through only the base body 20 that is the central portion 19 b passes through the base body 20 by the thickness of the binder 21 is d ₃ n ₂ . Therefore, a difference of d ₃ (n ₁ −n ₂ ) is generated between the optical path lengths of the laser light that has passed through the phase modulation unit 19a and the laser light that has passed through only the central portion 19b. Therefore, the difference between the optical path lengths in the tangential direction and the radial direction, which are generated when the laser beam causing astigmatism passes through the rising mirror 9, is represented by the tanger generated by the laser beam passing through the phase plate 19. It can be canceled by the optical path length difference d ₃ (n ₁ −n ₂ ) in one direction of the radial direction or radial direction. If the wavelength of the light is λ and the phase difference to be given to the laser light passing through the phase modulator 19a is Δ, the thickness d ₃ of the binder 21 is given by Δλ / (n ₁ −n ₂ ).

  In this way, by laminating the binder 21 on the thin portion of the base 20 in which the opposite sides of the phase modulation portion 19a are thinly formed, the central portion 19b becomes the thick portion of the base 20, and the thickness of the base 20 is increased. The level difference between the thick part and the thin part becomes the attachment reference of the binding material 21, so that the positioning of the binding material 21 becomes easy and the phase plate 19 can be easily formed.

  In the phase plate 19 shown in FIGS. 7A and 7B, the central portion 19 b is configured by laminating the binder 21 on the thin portion of the base 20. At this time, the phase modulation portion 19 a is a thick portion of the base body 20.

When the refractive index of the base 20 of the phase plate 19 is n ₁ , the refractive index of the binder 21 is n ₂ , and the thickness of the binder 21 is d ₄ , the laser light passing through the central portion 19 b passes through the binder 21. The optical path length of d ₄ n ₂ is d ₄ n ₂ , and the optical path length when the laser beam passing through the phase modulation unit 19 a passes through the substrate 20 by the thickness of the binder 21 is d ₄ n _1. A difference of d ₄ (n ₁ −n ₂ ) is generated between the optical path lengths of the laser light passing through 19a and the laser light passing through the central portion 19b. Therefore, the difference between the optical path lengths in the tangential direction and the radial direction, which are generated when the laser beam causing astigmatism passes through the rising mirror 9, is represented by the tanger generated by the laser beam passing through the phase plate 19. It can be canceled by the optical path length difference d ₄ (n ₁ −n ₂ ) in one direction of the radial direction or the radial direction. Incidentally, a wavelength of light lambda, when the phase difference to be given between the laser beam passing through the laser beam and the central portion 19b which passes only the phase modulation unit 19a and delta, the thickness d ₄ of the coupling member 21 is [Delta] [lambda] / It is given by (n ₁ −n ₂ ).

  In this way, by forming the central portion 19b by laminating the binder 21 on the thin portion of the base 20, the phase modulation portion 19a becomes the thick portion of the base 20, and the step between the thick portion and the thin portion of the base 20 is combined. As a reference for attaching the material 21, positioning of the binding material 21 is facilitated, and the phase plate 19 can be easily formed.

  Next, various forms of the phase modulation unit 19a and the center unit 19b will be described.

  In the phase plate 19 shown in FIGS. 8A and 8B, the coupling material 21 of the phase modulation unit 19 a is configured by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate 19. . The phase plate 19 shown in FIG. 8B is constructed by laminating a phase modulating portion 19a on two opposite sides of a flat substrate 20 with a binder 21 laminated in the thickness direction of the phase plate 19. The bonding material 21 may be laminated on the thin portion of the base body 20 that is formed so that the facing side is thin.

  Further, the phase plate 19 shown in FIGS. 9A and 9B is formed by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate 19 with the binder 21 in the central portion 19b. Yes. The phase plate 19 shown in FIG. 9B is constructed by laminating a central portion 19b with a central portion of a flat base 20 and a binder 21 laminated in the thickness direction of the phase plate 19. A binder may be laminated on the central portion of the base body 20 having a thin portion. In the first embodiment, the binder 21 is laminated in three layers. However, the binder 21 may be appropriately changed depending on the optical path length difference desired to be given between the laser light passing through the phase modulation unit 19a and the laser light not passing through.

  Like the phase plate 19 shown in FIGS. 8 and 9, the coupling material 21 is formed by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate 19. It becomes easy to control the optical path length of the laser light passing through the portion 19a or the central portion 19b.

  The phase plate 19 shown in FIG. 10A and FIG. 10B is formed by combining the binders 21a to 21c forming the phase modulation portion 19a on the flat base 20 with a plurality of materials having different refractive indexes. The refractive index increases or decreases as the distance from the center of the phase plate 19 increases and decreases in the direction from the center of the phase plate 19 toward the outer edge. Of course, such a binding material 21 may be laminated on the thin portion of the base body 20 where the opposing sides are thin.

  In FIG. 10 (a), the binders 21a to 21c forming the phase modulation part 19a are the same as the substrate thickness of the maximum optical disk 2 through which a part of the laser light passes through the binder 21a, and a part of the laser light. Is configured such that the base material thickness of the maximum optical disk 2 that passes through the binding material 21b is 0.07 mm, and the base material thickness of the maximum optical disk 2 through which part of the laser light passes through the binding material 21c is 0.05 mm. ing.

  As described above, the phase plate 19 is made of the binders 21a to 21c that form the phase modulation portion 19a on the flat substrate 20, and the refractive index increases or decreases as the materials having a plurality of different refractive indexes approach the end of the phase plate 19. By stacking in the direction from the center side of the phase plate 19 to the outer shape end portion, the refractive index of the phase modulation unit 19a can be increased or decreased stepwise, so that astigmatism with higher accuracy can be achieved. Can be corrected. Further, in such a configuration, the height of the phase modulation unit 19a can be unified, and the thickness can be reduced. Further, as shown in FIG. 10, the diameter of the laser beam incident on the phase plate 19 changes for each base material thickness of the plurality of recording surfaces of the optical disc 2, and as shown in FIG. The binding materials 21a to 21c may be provided according to the size of the laser beam to be used. In addition, when the phase modulation part 19a is comprised with the coupling material which consists of a several material of different refractive index, the correction | amendment of astigmatism with higher precision can be performed by increasing the number of coupling materials 21a-21c.

  11A to 11C, the coupling members 21a to 21c forming the phase modulation unit 19a are stepped in cross section and become thicker or thinner as they approach the end of the phase plate 19. It is configured as follows. The phase plate 19 shown in FIG. 11B is configured by laminating the binders 21a to 21c that become thicker toward the end of the flat substrate 20, and the phase plate 19 shown in FIG. The binders 21a to 21c that are thinner as they approach the end of the base body 20 having the two opposing sides thinner are stacked. As described above, the binders 21a to 21c may become thicker or thinner as they approach the end of the phase plate 19, and the base body 20 is thin even on two sides that are opposed to each other. What you did is fine.

  In FIG. 11A, the binders 21a to 21c are such that the maximum thickness of the optical disk 2 through which a part of the laser light passes through the binder 21a is 0.1 mm, and a part of the laser light passes through the binder 21b. The maximum substrate thickness of the optical disc 2 is 0.07 mm, and the maximum substrate thickness of the optical disc 2 through which a part of the laser light passes through the binder 21c is 0.05 mm.

  By configuring the phase plate 19 in this way, it is possible to correct astigmatism with higher accuracy. In particular, since the diameter of the laser beam incident on the phase plate 19 varies with the thickness of the base material on the plurality of recording surfaces of the optical disc 2, the size of the laser beam used as shown in FIG. It is good to provide the binding materials 21a-21c according to the thickness. Moreover, since the binding materials 21a to 21c are made of one material, it is possible to easily form stepped steps with high accuracy.

  12A to 12C, the coupling members 21a to 21c forming the phase modulation part 19a are stepped in cross section and become thicker or thinner as they approach the end of the phase plate 19. In this way, a plurality of materials having different refractive indexes are laminated in the thickness direction of the phase plate 19 or in the direction from the center to the outer edge. The phase plate 19 shown in FIG. 12B is configured by laminating the binders 21a to 21c that become thicker toward the end of the flat substrate 20 in the phase modulation part 19a. The phase plate 19 shown is formed by laminating the binders 21a to 21c that become thinner as they approach the end of the base body 20 in which two opposite sides of the phase modulation part 19a are formed thinner. As described above, the phase modulation portion 19a may become thicker or thinner as it approaches the end of the phase plate 19, and the base 20 is formed with two opposing sides thin even if it is flat. Things can be used. Further, a plurality of materials having different refractive indexes constituting the binding materials 21a to 21c may be laminated in the thickness direction of the phase plate 19, or may be laminated in a direction in which the outer shape is enlarged from the center side.

  In FIG. 12 (a), the binders 21a to 21c are such that the maximum thickness of the optical disk 2 through which a part of the laser light passes through the binder 21a is 0.1 mm, and a part of the laser light passes through the binder 21b. The maximum substrate thickness of the optical disc 2 is 0.07 mm, and the maximum substrate thickness of the optical disc 2 through which a part of the laser light passes through the binder 21c is 0.05 mm.

  By configuring the phase plate 19 in this way, the size of the diameter of the laser light incident on the phase plate 19 changes stepwise for each base material thickness of the plurality of recording surfaces of the optical disc 2. By configuring in a staircase pattern, it is possible to correct astigmatism with higher accuracy. Further, since the binder 21 is formed of a plurality of materials having different refractive indexes, the degree of freedom in design is increased, and the optical path length of the laser light passing through the phase modulation unit 19a can be easily controlled.

  The phase plate 19 shown in FIGS. 13A to 13C has a central portion 19b formed by laminating a binder 21 at the central portion of the base 20, and the phase modulator 19a has a stepped cross section on the opposite side of the base 20. It is comprised by the level | step differences 20a-20c which become thick or thin as it approaches the edge part of the phase plate 19 in shape. The phase plate 19 shown in FIG. 13B is formed with steps 20a to 20c that become thinner as it approaches the end, and the phase plate 19 shown in FIG. Such steps 20a to 20c are stacked. As described above, the steps 20a to 20c may become thicker or thinner as the end of the phase plate 19 is approached, and the base 20 has a thick central portion where the central portion 19b is laminated. Or thinly formed.

  In FIG. 13A, the binders 21a to 21c are such that the maximum thickness of the optical disk 2 through which a part of the laser light passes through the binder 21a is 0.1 mm, and a part of the laser light passes through the binder 21b. The maximum substrate thickness of the optical disc 2 is 0.07 mm, and the maximum substrate thickness of the optical disc 2 through which a part of the laser light passes through the binder 21c is 0.05 mm.

  By configuring the phase plate 19 in this manner, the diameter of the laser light incident on the phase plate 19 changes stepwise for each base material thickness of the plurality of recording surfaces of the optical disc 2, so that the end of the base 20 Astigmatism can be corrected with higher accuracy by forming the steps 20a to 20c in the portion and forming a stepped shape.

  The shape of the phase plate 19 shown in FIGS. 3 to 13 is a substantially square shape, but may be other shapes such as a polygon or a circle. Further, the phase plate 19 shown in FIGS. 4 to 13 is also provided with two phase modulation portions 19a on two opposite sides because the phase plate 19 has a square shape like the phase plate 19 shown in FIG. When the phase plate 19 has another shape such as a polygonal shape or a circular shape, the phase modulation portion 19a may be provided in a portion facing each other in the tangential direction or the radial direction.

  Next, the optical system of the optical pickup device in the first embodiment will be described in detail. FIG. 14 is a diagram illustrating a part of the optical system according to the first embodiment, and FIG. 14A illustrates a part of the optical system when the phase plate is provided between the collimator lens and the rising mirror. FIG. 14B shows a part of the optical system when the phase plate is provided between two rising mirrors, and FIG. 14C shows the phase plate between the rising mirror and the objective lens. It is a figure showing a part of optical system at the time of being provided.

  As shown in FIGS. 14A to 14C, the laser light emitted from the short wavelength optical unit passes through the collimator lens 8 to be converted from divergent light into substantially parallel laser light. The degree of convergence and divergence of the laser beam is controlled by moving the laser beam.

  When the phase plate 19 is provided between the collimator lens 8 and the rising mirror 9 as shown in FIG. 14A, the laser light that has passed through the collimator lens 8 is incident on the phase plate 19 and part of the laser. The optical path length in the tangential direction of light changes, and the laser light enters the rising mirror 9. The short-wavelength laser light is almost transmitted through the rising mirror 9, and at that time, a difference occurs in the optical path length between the tangential direction and the radial direction. However, the difference between the optical path lengths in the tangential direction and the radial direction, which are generated when the laser light passes through the rising mirror 9, and the difference in optical path lengths in the tangential direction, which is generated when the laser light passes through the phase plate 19. Can be offset by Thereafter, the light is reflected by the rising mirror 12, passes through the achromatic diffraction lens 14, and enters the objective lens 13.

  As shown in FIG. 14B, when the phase plate 19 is provided between the two raising mirrors 9 and 12, the laser beam that has passed through the collimator lens 8 is incident on the raising mirror 9 as it is. To do. The short-wavelength laser light is almost transmitted through the rising mirror 9, and at that time, a difference occurs in the optical path length between the tangential direction and the radial direction. Thereafter, the laser light enters the phase plate 19 and the optical path length in the tangential direction of a part of the laser light changes. Therefore, the difference between the optical path lengths in the tangential direction and the radial direction generated when the laser light passes through the rising mirror 9 is the difference between the optical path lengths in the tangential direction generated when the laser light passes through the phase plate 19. Can be offset by Thereafter, the light is reflected by the rising mirror 12, passes through the achromatic diffraction lens 14, and enters the objective lens 13.

  When the phase plate 19 is provided between the raising mirror 12 and the objective lens 13 as shown in FIG. 14C, the laser light that has passed through the collimator lens 8 is incident on the raising mirror 9 as it is. The short-wavelength laser light is almost transmitted through the rising mirror 9, and at that time, a difference occurs in the optical path length between the tangential direction and the radial direction. Thereafter, the laser beam is reflected by the rising mirror 12 and before or after passing through the achromatic lens 14, the laser beam is incident on the phase plate 19, and the optical path length in the tangential direction of a part of the laser beam is changed. Therefore, the difference between the optical path lengths in the tangential direction and the radial direction generated when the laser light passes through the rising mirror 9 is the difference between the optical path lengths in the tangential direction generated when the laser light passes through the phase plate 19. Can be offset by Thereafter, the laser light enters the objective lens 13.

  However, since the phase modulation unit 19a according to the first embodiment corrects astigmatism by using the fact that the diameter of the laser beam varies depending on the thickness of the base material, the phase modulation unit 19a has a phase in a portion where the variation in the diameter of the laser beam is significant. Astigmatism can be corrected with higher accuracy by arranging the plate 19. The change in the diameter of the laser beam due to the change in the substrate thickness is more remarkable at a position further away from the objective lens 13. Therefore, if the phase plate 19 is disposed between the collimator lens 8 and the objective lens 13, preferably between the collimator lens 8 and the rising mirror 9 as shown in FIG. Correction is possible.

Further, in the case of the position of the phase plate 19 as shown in FIGS. 14B and 14C, since the long wavelength laser beam does not pass through the phase plate 19, the phase modulation unit 19a of the phase plate 19 is The determination may be made in consideration of only the short wavelength laser beam. In the case of the position of the phase plate 19 as shown in FIG. 14A, the long wavelength laser light passes through the phase plate 19. If the size of the long wavelength laser light is set so as not to pass through the phase modulation section 19a of the phase plate 19, the long wavelength laser light is not affected by the phase modulation section 19a. Or even if it is a case where a long wavelength laser beam is the magnitude | size which passes the phase modulation part 19a, the thickness of the phase modulation part 19a should just be made into the integral multiple of the wavelength of a long wavelength laser beam. That is, assuming that the wavelength of the long wavelength light is λ ₂ , the refractive index of the phase plate 19 at the wavelength λ ₂ is n ₄ , and an arbitrary integer is m, the thickness d of the phase modulation unit 19 a is mλ ₂ / (n ₄ − 1). In this way, the long wavelength laser light is not affected by the phase modulator 19a, and the short wavelength laser light is corrected for astigmatism.

  If the recording layer of the optical disk 2 is made multilayer, the change in the substrate thickness increases, so that the spherical aberration increases. In order to correct this spherical aberration, the collimator lens 8 is moved in the conventional optical pickup device to further change the degree of convergence and divergence of the laser light. As a result, the influence of astigmatism increased. However, in the optical pickup device according to the first embodiment, the phase plate 19 is disposed between the collimator lens 8 and the objective lens 13, and the phase modulators 19 a are provided on two opposite sides of the phase plate 19. Therefore, the diameter of the laser beam increases when recording or reproducing on the recording layer having a small substrate thickness, but the area of the laser beam that changes the optical path length through the phase modulation section 19a also increases. Therefore, the difference between the optical path lengths in the tangential direction and the radial direction generated when the laser beam passes through the rising mirror 9, and the laser beam that passes through the phase modulator 19 a when the laser beam passes through the phase plate 19. Astigmatism can be corrected by canceling out the difference in optical path length generated between the laser beam and the laser beam that does not pass.

  Further, since the phase plate 19 has no polarization dependency, astigmatism can be controlled not only in the laser beam directed toward the optical disc 2 but also in the reflected light of the optical disc 2 having a polarization direction different from that of the laser beam directed toward the optical disc 2. it can. Further, the optical pickup apparatus of the first embodiment is inexpensive because it only includes the phase plate 19 made of glass or the like, and does not require power or a special system to correct astigmatism. Further, since the degree of freedom of design is increased by configuring the phase modulation portion 19a and the central portion 19b of the phase plate 19 with different materials, the control of the optical path length of the laser light, the thinning of the phase plate 19, and the precision of astigmatism are achieved. Correction is easy.

(Example 2)
In the second embodiment, the configuration of the phase plate 19 described in the first embodiment is changed. Instead of the binder 21 shown in FIGS. Thus, the phase plate 19 is formed.

The phase plate 19 of the second embodiment has a flat substrate made of optical glass such as BK7, white plate glass, silica, or a transparent resin material, TA ₂ O ₅ , Nb ₂ O ₃ , Al ₂ O ₃ , SiO _2. The phase modulation part 19a or the center part 19b is formed by coating an optical thin film such as. As a method of coating the optical thin film, a sputtering method, a vapor deposition method, or the like can be considered. The optical thin film is adhered by being dried once.

  Instead of the binder 21 forming the phase modulation part 19a of the phase plate 19 shown in FIGS. 3 and 4, the phase modulation part 19a can be configured by coating a film on the opposite side of the flat substrate 20. .

  Instead of the binding material 21 forming the central portion 19b of the phase plate 19 shown in FIGS. 5 and 13B, the central portion 19b can be configured by coating a film on the central portion of the flat substrate 20.

  Instead of the binding material 21 forming the phase modulation part 19a of the phase plate 19 shown in FIG. 6, the phase modulation part 19a is configured by coating the thin part of the base 20 formed thin on the opposite side with a film. Can do.

  Instead of the binding material 21 forming the central portion 19b of the phase plate 19 shown in FIG. 7 and FIG. 13 (c), the thin portion of the base 20 having a thin central portion is coated with a film to form the central portion 19b. can do.

  In the phase plate 19 shown in FIGS. 8 to 12, a plurality of films having different refractive indexes may be stacked and coated to replace the binder 21, and the films may be stacked and coated stepwise. In the case of replacing the binder 21, the film can be easily laminated.

  By configuring the phase plate 19 in this way, the phase plate 19 can be easily formed by a simple process of coating the base 20 with a film, and the phase modulation unit 19a or the center formed by coating the film The thickness of the part 19b can also be easily controlled.

Example 3
In the third embodiment, the configuration of the phase plate 19 described in the first embodiment is changed.

  FIG. 15A is a plan view of a phase plate configured by connecting a phase modulation unit to the outer surface on the opposite side of the central part in the third embodiment, and FIG. 15B is a plan view of FIG. It is a side view of a phase plate. FIG. 16A shows the phase modulation unit according to the third embodiment from the center side of the phase plate so that the refractive index increases or decreases as the material approaches the end of the phase plate. FIG. 16 (b) is a side view of the phase plate shown in FIG. 16 (a). FIG. 17A is a plan view of a phase plate formed by laminating a plurality of materials having different refractive indexes in the thickness direction in the phase modulation unit in the third embodiment, and FIG. 17B is a plan view of FIG. It is a side view of the phase plate shown. FIG. 18A is a plan view of a phase plate in which the phase modulation unit in the third embodiment is configured such that the cross section is stepped and becomes thicker or thinner toward the end of the phase plate, and FIG. FIG. 18A is a side view of the phase plate shown in FIG. 18A when the phase modulation unit is configured to become thinner toward the end of the phase plate. FIG. 18C shows the phase modulation unit at the end of the phase plate. It is a side view of the phase plate shown to Fig.18 (a) at the time of comprising so that it may become thick as it approaches. FIG. 19A shows the phase modulation section in the third embodiment in which the cross section of the phase modulation section has a stepped shape, and a plurality of materials having different refractive indexes are made thicker or thinner toward the end of the phase plate. Alternatively, FIG. 19B is a plan view of a phase plate configured by laminating in the direction from the center side to the outer edge, and FIG. 19B shows the phase plate so that the phase modulation unit becomes thinner as it approaches the opposite end of the phase plate. FIG. 19A is a side view of the phase plate shown in FIG. 19A in the case of being laminated in the direction from the center side to the outer edge, and FIG. 19C shows that the phase modulation unit becomes thicker as it approaches the end of the phase plate. FIG. 20 is a side view of the phase plate shown in FIG. 19A when the phase plate is configured so as to be laminated in the thickness direction.

  The phase plate 19 shown in FIGS. 15 (a) and 15 (b) is configured by connecting a phase modulation portion 19a to the outer surface on the opposite side of the central portion 19b.

When the refractive index of the phase modulation part 19a of the phase plate 19 is n ₁ , the refractive index of the center part 19b is n ₂ , and the thickness of the phase plate 19 is d ₅ , the optical path length of the laser light when passing through the phase modulation part 19a Is d ₅ n ₁ , and the optical path length of the laser light that has passed through the central portion 19 b is d ₅ n ₂ , so that the optical path lengths of the laser light that has passed through the phase modulating portion 19 a and the laser light that has passed through the central portion 19 b are Produces a difference of d ₅ (n ₁ −n ₂ ). Therefore, the difference between the optical path lengths in the tangential direction and the radial direction, which are generated when the laser beam causing astigmatism passes through the rising mirror 9, is represented by the tanger generated by the laser beam passing through the phase plate 19. It can be canceled by the optical path length difference d ₅ (n ₁ −n ₂ ) in one direction of the radial direction or the radial direction. Note that the thickness d ₅ of the phase plate 19 is given by Δλ / (n ₁ −n ₂ ), where λ is the wavelength of the light and Δ is the phase difference to be given to the laser light passing through the phase modulator 19a.

  In this manner, the phase plate 19 is configured by connecting the phase modulation portion 19a to the opposite outer surface of the central portion 19b, whereby the phase plate 19 can be thinned and the symmetry of the phase plate 19 is maintained. Therefore, warpage and aberration are reduced, and astigmatism can be corrected with high accuracy.

  In the phase plate 19 shown in FIGS. 16 (a) and 16 (b), the refractive index increases or decreases as the phase modulators 19 c to 19 e are made of a plurality of materials having different refractive indexes closer to the end of the phase plate 19. In this manner, the phase plate 19 is laminated in the direction from the center side to the outer edge portion. In FIG. 16A, the phase modulators 19c to 19e are such that the maximum thickness of the optical disk 2 through which a part of the laser light passes through the phase modulator 19c is 0.1 mm, and a part of the laser light is the phase modulator. The base material thickness of the maximum optical disk 2 that passes through 19d is 0.07 mm, and the base material thickness of the maximum optical disk 2 through which a part of the laser light passes through the phase modulation unit 19e is 0.05 mm. .

  As described above, the phase modulation unit 19c to the phase modulation unit 19c to increase or decrease the refractive index as the phase plate 19 approaches the end of the phase plate 19 with a plurality of materials having different refractive indexes on the opposite outer surfaces of the central portion 19b. By providing 19e, the thickness of the phase plate 19 and the symmetry of the phase plate 19 are maintained, and warpage and aberration are reduced, so that the astigmatism correction accuracy can be improved. Further, astigmatism can be corrected more precisely by arranging the phase modulators 19c to 19e such that a plurality of materials having different refractive indexes are arranged so that the refractive index becomes larger or smaller as they approach the end of the phase plate 19. It becomes possible. Since the diameter of the laser beam incident on the phase plate 19 changes for each substrate thickness of the plurality of recording surfaces of the optical disc 2, the size of the laser beam to be used is shown in FIG. It is preferable to provide phase modulators 19c to 19e according to the above. Astigmatism can be corrected with higher accuracy by increasing the number of phase modulation portions 19c to 19e made of materials having different refractive indexes.

  In the phase plate 19 shown in FIGS. 17A and 17B, the phase modulation unit 19a is configured by laminating a plurality of materials having different refractive indexes in the thickness direction. In the third embodiment, the phase modulation unit 19a is laminated in three layers. However, the phase modulation unit 19a may be appropriately changed according to the optical path length difference desired to be given between the laser beam that passes through the phase modulation unit 19a and the laser beam that does not pass through.

  As described above, the phase modulation unit 19a is configured by laminating a plurality of materials having different refractive indexes in the thickness direction on the outer surface on the opposite side of the central portion 19b, thereby reducing the thickness of the phase plate 19 and the phase plate. Since 19 symmetries are maintained and warping and aberrations are reduced, the astigmatism correction accuracy can be improved. Furthermore, by configuring the phase modulation unit 19a by laminating a plurality of materials having different refractive indexes in the thickness direction, the degree of freedom in design increases, and the optical path length of the laser light passing through the phase modulation unit 19a can be easily controlled. Become.

  The phase plate 19 shown in FIGS. 18A to 18C is configured such that the phase modulation units 19c to 19e are stepped in cross section and become thicker or thinner as they approach the end of the phase plate 19. That is, the phase plate 19 shown in FIG. 18B is configured such that the phase modulation units 19c to 19e become thinner toward the end of the phase plate 19, and the phase plate 19 shown in FIG. The phase modulators 19c to 19e are configured to have a stepped cross section and become thicker as they approach the end of the phase plate 19.

  In FIG. 18A, the phase modulators 19c to 19e are such that the maximum thickness of the base material of the optical disk 2 through which part of the laser light passes through the phase modulator 19c is 0.1 mm, and part of the laser light is the phase modulator. The base material thickness of the maximum optical disk 2 that passes through 19d is 0.07 mm, and the base material thickness of the maximum optical disk 2 through which part of the laser light passes through the phase modulation unit 19e is 0.05 mm. .

  As described above, the phase modulators 19c to 19e have a stepped cross section and become thicker or thinner toward the end of the phase plate 19, so that the diameter of the laser beam incident on the phase plate 19 is large. Changes stepwise for each base material thickness of the plurality of recording surfaces of the optical disc 2, and the astigmatism can be corrected with higher accuracy by configuring the phase modulation sections 19 c to 19 e in a step shape. Furthermore, since the phase plate 19 is made thin and the symmetry of the phase plate 19 is maintained, warpage and aberration are reduced, and astigmatism can be corrected with higher accuracy.

  The phase plate 19 shown in FIGS. 19A to 19C has a plurality of different refractive indexes so that the phase modulators 19c to 19e are stepped in cross section and become thicker or thinner toward the end of the phase plate 19. These materials are laminated in the thickness direction of the phase plate 19 or in the direction from the center to the outer edge. That is, in the phase plate 19 shown in FIG. 19B, the phase modulators 19c to 19e are thinned toward the end of the phase plate 19 from the center side of the phase plate 19 so as to approach the end of the phase plate 19 facing each other. The phase plate 19 shown in FIG. 19C is laminated in the thickness direction of the phase plate 19 so that the phase modulation units 19c to 19e become thicker as they approach the end of the phase plate 19. Configured. As described above, the phase modulation portions 19 c to 19 e may be thicker or thinner as they approach the end of the phase plate 19, and a plurality of materials having different refractive indexes may be in the thickness direction of the phase plate 19. Alternatively, the outer shape may be stacked in the direction of increasing from the center side.

  In FIG. 19A, the phase modulators 19c to 19e are such that the maximum thickness of the base material of the optical disk 2 through which part of the laser light passes through the phase modulator 19c is 0.1 mm, and part of the laser light is the phase modulator. The base material thickness of the maximum optical disk 2 that passes through 19d is 0.07 mm, and the base material thickness of the maximum optical disk 2 through which part of the laser light passes through the phase modulation unit 19e is 0.05 mm. .

  As described above, a plurality of materials having different refractive indexes are arranged in the thickness direction of the phase plate 19 or on the center side so that the phase modulation units 19c to 19e are stepped in cross section and become thicker or thinner toward the end of the phase plate 19. By laminating in the direction from the outer edge to the outer edge, the diameter of the laser beam incident on the phase plate 19 changes stepwise for each base material thickness of the plurality of recording surfaces of the optical disc 2. By configuring the modulators 19c to 19e in a step shape, it is possible to correct astigmatism with higher accuracy, and at the same time, the phase plate 19 is thinned and the symmetry of the phase plate 19 is maintained. As a result, the aberration is reduced and astigmatism can be corrected with higher accuracy. Furthermore, since the phase modulators 19c to 19e are made of a plurality of materials having different refractive indexes, the degree of freedom in design is increased and the optical path length of the laser light passing through the phase modulators 19c to 19e can be easily controlled.

Example 4
In the fourth embodiment, an optical disk device using the optical pickup device described in the first, second, and third embodiments will be described.

  FIG. 20 is a perspective view showing an optical disk device using the optical pickup device described in the first, second, and third embodiments in the fourth embodiment. In the optical disc apparatus 301 shown in FIG. 20, reference numeral 302 denotes a cover, the cover 302 includes an upper cover 302a and a lower cover 302b, and the cover 302 has a bag-like configuration with an opening 302c at one end. A tray 303 is held on the cover 302 so as to be insertable / removable in the X direction shown in FIG. 20, and the tray 303 is made of a lightweight material such as a resin material. The tray 303 is provided with a bezel 304 at the front portion, and the bezel 304 closes the opening 302 c when the tray 303 is stored in the cover 302. An eject button is exposed on the bezel 304. By pressing this eject button, the tray 303 slightly protrudes from the cover 302 in the X direction shown in FIG. On the other hand, it can be taken in and out in the X direction.

  The optical pickup device 305 described in the first embodiment, the second embodiment, and the third embodiment is attached to the tray 303. The optical pickup device 305 is provided with a spindle motor 25 that rotationally drives the optical disc 2, and further, a base 15 that moves toward and away from the spindle motor 25 is movably provided. A lens holder 16 is attached to the base 15 so as to be elastically movable with respect to the base 15. Objective lenses 10 and 13 are attached to the lens holder 16. In the base 15, a base cover 15 f made of a metal plate is attached to a surface facing the information recording surface of the optical disc mounted on the spindle motor 25, and a flexible substrate attached to the base 15 At least a part of the components such as the lens holder 16 is covered. Thereby, it is possible to prevent parts attached to the base 15 from coming into contact with the optical disc 2, and conversely, these parts can be protected from dust, electrical noise, and the like.

  Reference numerals 306 and 307 denote rails that are held by the lower cover 302 b and are engaged with both sides of the tray 303. The rails 306 and 307 are configured to be slidable within a predetermined range in the X direction in which the tray 303 is inserted and removed with respect to the lower cover 302b and the tray 303.

  By mounting the optical pickup device 305 according to the first, second, and third embodiments of the present invention on the optical disk device shown in FIG. 20, the laser light emitted from the short wavelength optical unit 1 rises and raises the mirror 9. Astigmatism can be corrected by offsetting the difference between the optical path lengths in the tangential direction and the radial direction caused by passing through the difference in the optical path lengths caused by passing the laser light through the phase plate 19. In addition, since the phase plate 19 does not have polarization dependency unlike the liquid crystal, astigmatism is corrected not only in the laser beam toward the optical disc but also in the reflected light of the optical disc having a polarization direction different from that of the laser beam toward the optical disc. Can do. Therefore, even in a multi-layer optical disc, information can be recorded or reproduced accurately without being redundant. Furthermore, the optical disk apparatus of the fourth embodiment is inexpensive because it only includes the phase plate 19 made of glass or the like, and can correct astigmatism without power or a special system.

  The optical pickup apparatus and optical disk apparatus of the present invention corrects astigmatism generated when recording or reproducing on the recording surface of a multi-layer optical disk without any power or special system, and accurately records or reproduces information. It can be applied to portable electronic devices such as notebook personal computers and electronic devices such as stationary personal computers.

Schematic which shows the structure of the optical pick-up apparatus in Example 1 of this invention. The top view which shows the example which actualized the optical structure of the optical pick-up apparatus in Example 1 of this invention. FIG. 3A is a plan view of a phase plate formed by laminating a binder on two sides opposite to each other in the tangential direction of a flat substrate, FIG. Side view of phase plate shown in a) The top view of the phase plate which laminated | stacked the binder on the 2 sides which mutually oppose with respect to the radial direction of a flat base | substrate for the phase modulation part in Example 1 of this invention. (A) The top view of the phase plate which laminated | stacked the binder in the center part of the flat base | substrate in Example 1 of this invention, (b) The side view of the phase plate shown to Fig.5 (a) (A) A plan view of a phase plate formed by laminating a binder on a thin portion of a base formed with a thin side on the opposite side of the phase modulation portion, (b) a side view of the phase plate shown in FIG. (A) A plan view of a phase plate formed by laminating a binder on a thin portion of a base at the center, (b) a side view of the phase plate shown in FIG. FIG. 8A is a plan view of a phase plate formed by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate, and FIG. Side view of phase plate shown in FIG. 9A is a plan view of a phase plate formed by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate in the center portion of the phase plate in Example 1 of the present invention, and FIG. Side view of phase plate shown in (A) In the first embodiment of the present invention, the binder that forms the phase modulation section is arranged on the center side of the phase plate so that the refractive index increases or decreases as the material approaches the end of the phase plate. FIG. 10B is a plan view of the phase plate formed by stacking in the direction from the outer edge to the outer edge, and FIG. 10B is a side view of the phase plate shown in FIG. (A) A plan view of a phase plate configured such that the phase modulation portion in Embodiment 1 of the present invention has a stepped cross section and becomes thicker or thinner as it approaches the end of the phase plate; (b) a flat substrate; FIG. 11A is a side view of the phase plate shown in FIG. 11A in a case where the binder is formed so as to become thicker as it approaches the end, and FIG. Side view of the phase plate shown in FIG. 11 (a) in a case where the binders that are thinned toward each other are laminated. (A) A plurality of materials having different refractive indexes are used in the thickness direction of the phase plate or the thickness of the phase modulation unit in the first embodiment of the present invention is increased or decreased as the cross section of the phase modulation unit approaches the end of the phase plate. Plan view of phase plate constructed by laminating in the direction from the center side toward the outer edge, (b) Laminating the phase modulation part in the thickness direction of the phase plate so that the thickness becomes closer to the end of the flat substrate. 12A is a side view of the phase plate shown in FIG. 12A, and FIG. 12C is a phase plate so that the phase modulation unit becomes thinner as it approaches the end of the base that is formed with two sides opposite to each other. 12A is a side view of the phase plate shown in FIG. 12A in the case of being laminated in the direction from the center side to the outer edge. (A) A binder is laminated on the central portion of the base body in Example 1 of the present invention, and the cross section on the opposite side of the base material is stepped as the central portion, and the meat becomes closer to the end of the phase plate. A plan view of a phase plate composed of a portion formed to be thick or thin, (b) a configuration in which a binder is laminated on a flat substrate and the phase modulation portion becomes thinner as it approaches the end portion as a central portion. FIG. 13A is a side view of the phase plate shown in FIG. 13A when laminated on the flat substrate, and FIG. 13C is a stepwise cross section of the opposite side of the substrate as a central portion by laminating a binder on the thin portion of the substrate. FIG. 13A is a side view of the phase plate shown in FIG. 13A when it is configured to become thicker as it approaches the end of the phase plate. (A) The figure showing a part of optical system in case the phase plate in Example 1 of this invention is provided between a collimator lens and a raising mirror, (b) The phase plate in Example 1 of this invention is 2 The figure showing a part of optical system at the time of providing between two raising mirrors, (c) Optical system at the time of providing the phase plate in Example 1 of this invention between a raising mirror and an objective lens A diagram showing a part of (A) The top view of the phase plate comprised by connecting the phase modulation | alteration part to the outer side of the center side in the Example 3 of this invention which opposes, (b) The side surface of the phase plate shown to Fig.15 (a) Figure (A) The outer edge of the phase modulation unit according to the third embodiment of the present invention from the center side of the phase plate so that the refractive index increases or decreases as the material approaches the end of the phase plate. FIG. 16B is a plan view of the phase plate formed by laminating in the direction of FIG. (A) A plan view of a phase plate formed by laminating a plurality of materials having different refractive indexes in the thickness direction, and (b) a side view of the phase plate shown in FIG. (A) The top view of the phase plate which comprised the phase modulation part in Example 3 of this invention so that it might become thick or thin, so that the cross section is stepped and it approaches the edge part of a phase plate, (b) The phase modulation part A side view of the phase plate shown in FIG. 18 (a) when configured to be thinner as it approaches the end of the phase plate, and (c) the thickness of the phase modulator becomes closer to the end of the phase plate. Side view of the phase plate shown in FIG. (A) A plurality of materials with different refractive indexes are used in the thickness direction of the phase plate or the thickness of the phase modulation unit in the third embodiment of the present invention is increased or decreased as the cross section of the phase modulation unit approaches the end of the phase plate. A plan view of a phase plate formed by stacking in the direction from the center side to the outer edge, (b) the outer shape from the center side of the phase plate so that the phase modulation part becomes thinner as it approaches the end of the opposite phase plate. FIG. 19A is a side view of the phase plate shown in FIG. 19A in the case of being laminated in the direction of the end, and (c) the thickness of the phase plate so that the phase modulation unit becomes thicker as it approaches the end of the phase plate. Side view of the phase plate shown in FIG. The perspective view which shows the optical disk apparatus using the optical pick-up apparatus demonstrated in Example 1, Example 2, Example 3 in Example 4 of this invention. The figure which shows a part of optical system in the conventional optical pick-up apparatus (A) The figure which shows the optical path length of the light when seeing the light which passes through the tilting raising mirror explaining astigmatism from the x-axis direction, (b) The tilting raising mirror explaining astigmatism The figure which shows the optical path length of the light when the passing light is seen from the y-axis direction The figure which shows a part of optical system in the conventional optical pick-up apparatus which provided the raising prism The figure which shows the liquid crystal device which performs astigmatism in the conventional optical pick-up apparatus shown by FIG.

DESCRIPTION OF SYMBOLS 1 Short wavelength optical unit 3 Long wavelength optical unit 7 Beam splitter 8 Collimator lens 8a Support member 8c Lead screw 8d Gear group 8e Drive member 9,12 Raising mirror 10,13 Objective lens 19 Phase plate 19a, 19c, 19d, 19e Phase Modulating portion 19b Central portion 20 Base 20a, 20b, 20c Step 21, 21a, 21b, 21c Binder 301 Optical disc device 302 Cover 303 Tray 304 Bezel 305 Optical pickup device

Claims (18)

A light source that emits laser light;
A movable condensing lens that converts the laser light into convergent or divergent light;
A rising prism or a rising mirror that converts the optical axis of the laser light that has passed through the condenser lens into a substantially vertical direction;
An objective lens for condensing the laser beam whose optical axis has been converted by the rising prism or the rising mirror onto an optical disc;
A phase plate composed of a center part and a phase modulation part made of materials having different refractive indexes is provided between the condenser lens and the objective lens, and a part of the laser beam having a size larger than a certain level is placed on the phase plate. Astigmatism caused by the rising prism or the rising mirror is corrected by making the optical path length different between the laser light that passes through the phase modulation part and the laser light that does not pass through the phase modulation part. An optical pickup device. The optical pickup device according to claim 1, wherein the phase plate is configured by laminating a flat substrate and a binder. 3. The optical pickup device according to claim 2, wherein the phase modulation portion of the phase plate is configured by laminating a binder on opposite sides of a flat substrate. 3. The optical pickup device according to claim 2, wherein a central portion of the phase plate is configured by laminating a binder on a central portion of a flat base. 3. The optical pickup device according to claim 2, wherein the phase modulation portion of the phase plate is configured by laminating a binder on a thin portion of a base body that is formed so that opposite sides are thin. 3. The optical pickup device according to claim 2, wherein a central portion of the phase plate is configured by laminating a binder on a thin portion of the base. 3. The optical pickup device according to claim 2, wherein the phase plate coupling material is formed by laminating a plurality of materials having different refractive indexes in the thickness direction of the phase plate. The binding material forming the phase modulation portion of the phase plate is configured such that a plurality of materials having different refractive indexes approach the edge of the phase plate so that the refractive index increases or decreases from the center side of the phase plate. The optical pickup device according to claim 3, wherein the optical pickup device is laminated in a direction of a portion. 6. The coupling material forming the phase modulation portion of the phase plate is configured such that the cross section is stepped and becomes thicker or thinner as it approaches the end of the phase plate. Optical pickup device. The thickness of the phase plate is made of a plurality of materials having different refractive indexes so that the binder forming the phase modulation portion of the phase plate has a stepped cross section and becomes thicker or thinner toward the end of the phase plate. 6. The optical pickup device according to claim 3, wherein the optical pickup device is laminated in a direction or a direction from a center side to a direction of an outer edge. The phase modulation portion of the phase plate is configured by a portion formed such that a cross section on the opposite side of the base material is stepped and becomes thicker or thinner toward the end of the phase plate. Item 7. The optical pickup device according to Item 4 or 6. 3. The optical pickup device according to claim 2, wherein the phase plate binder is formed by coating a film on a substrate. The optical pickup device according to claim 1, wherein the phase plate is configured by connecting a phase modulation unit to an outer surface on the opposite side of the central portion. The phase modulation part of the phase plate is laminated in the direction from the center side of the phase plate to the outer edge so that the refractive index increases or decreases as the material approaches the end of the phase plate. The optical pickup device according to claim 13, which is configured as described above. The optical pickup device according to claim 13, wherein the phase modulation unit of the phase plate is configured by laminating a plurality of materials having different refractive indexes in the thickness direction. The optical pickup device according to claim 13, wherein the phase modulation unit of the phase plate is configured to have a stepped cross section and become thicker or thinner as it approaches the end of the phase plate. The phase modulation part of the phase plate is formed of a plurality of materials having different refractive indexes from the thickness direction or the center side of the phase plate so that the cross section of the phase modulation part is stepped and becomes thicker or thinner toward the end of the phase plate. The optical pickup device according to claim 13, wherein the optical pickup device is configured to be laminated in a direction of an outer edge portion. An optical pickup device according to any one of claims 1 to 17,
Rotation driving means for rotating the optical disc;
An optical disc apparatus comprising: moving means for moving the optical pickup device in a radial direction of the optical disc with respect to the rotation driving means.

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