JP2006092671A - Optical pickup device and drive unit for optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device and a drive unit for optical disk which can appropriately perform information recording and/or information reproduction to different high-density disks using luminous flux of short wavelengths. <P>SOLUTION: Since a mechanism for varying magnification changes an incident angle of the 1st luminous flux over an objective optical system OL, compensation of spherical aberration can be performed by making a divergent luminous flux incident to the objective optical system OL in relation to an HD which generates spherical aberration for example, if a parallel light flux is made incident to the objective optical system OL. Difference in numerical aperture when using a BD and using the HD can be dealt with by selecting an appropriate aperture according to the optical information recording medium to be used by using an aperture limit mechanism. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup apparatus and an optical disc drive apparatus capable of recording and / or reproducing information interchangeably with different types of optical information recording media.

  In recent years, along with the practical use of short-wavelength red semiconductor lasers, high-density optical discs (optical discs) that have the same size and capacity as CDs (compact discs), which are conventional optical discs (also called optical information recording media). A DVD (digital versatile disk), which is also called an information recording medium, has been developed and commercialized, but a higher density next-generation optical disk has also been developed. In such a condensing optical system of an optical pickup device using a next-generation optical disk as a medium, an information recording surface is provided via an objective optical system in order to increase the recording signal density or to reproduce the high-density recording signal. It is required to reduce the diameter of the spot condensed on the top. For that purpose, it is necessary to shorten the wavelength of the laser as the light source. A blue-violet semiconductor laser having a wavelength of about 400 nm is expected to be put to practical use as a short wavelength laser light source.

    As an example, in an optical disc (for example, HD DVD: hereinafter referred to as HD) for recording / reproducing information with a numerical aperture NA of 0.67, a light source wavelength of 405 nm, and a protective layer thickness of 0.6 mm, DVD (NA 0.6, light source wavelength) Information of 15 to 20 GB per side can be recorded on an optical disk having a diameter of 12 cm and the same size as 650 nm and a storage capacity of 4 and 7 GB. An optical disc that records and reproduces information with specifications of a numerical aperture NA of 0.85, a light source wavelength of 405 nm, and a protective layer thickness of 0.1 mm (for example, abbreviated as Blu-ray Disc: BD) Thus, it is possible to record information of 20 to 30 GB per side. In this specification, optical disks that record and / or reproduce information using a blue-violet semiconductor laser having a wavelength of about 400 nm are collectively referred to as “high-density optical disks”.

By the way, it can not be said that the value as a product of the optical pickup device is sufficient just by being able to appropriately record / reproduce information on only one type of high-density optical disk. At present, the standards for two types of high-density optical discs have been established, and it is clear that software with information recorded on both high-density optical discs is commercially available. This is because even if information can be recorded / reproduced only with respect to the optical disk, it cannot be said that the usability is sufficient.
JP 2001-195769 A JP-A-11-96585

  However, when information is recorded and / or reproduced so as to be compatible with BD and HD, the thicknesses of the two protective layers are different from each other and the light source wavelengths are the same.

  As an objective optical system capable of recording and / or reproducing information interchangeably with optical discs having different protective layer thicknesses and light source wavelengths, an objective optical system using a diffraction action is disclosed in Patent Document 1. The technique of Patent Document 1 is a technique for correcting spherical aberration caused by the thickness of the protective layer by utilizing the wavelength dependency of spherical aberration generated by the diffractive structure. However, the light source wavelengths of BD and HD are the same. Therefore, the spherical aberration due to the thickness of the protective layer cannot be corrected using the diffractive action.

  On the other hand, as an objective optical system capable of recording and / or reproducing information interchangeably with optical discs having different protective layer thicknesses and the same light source wavelength, an annular zone having a minute step is formed in the optical surface. An objective optical system is disclosed in Patent Document 2. The technique of Patent Document 2 is a technique for correcting spherical aberration caused by the protective layer thickness by utilizing the fact that the condensing position of the light beam passing through the annular zone depends on the protective layer thickness. Since BD and HD having a high numerical aperture have a large amount of spherical aberration due to the difference in the thickness of the protective layer, such technology cannot correct spherical aberration to the extent that it can withstand actual use.

  In addition, when information is recorded and / or reproduced so as to be compatible with BD and HD, the numerical apertures are different from each other. A technique that is generally known as a technique for controlling the numerical aperture of the objective optical system in accordance with the light source wavelength (disclosed in Patent Document 1), or a transmission technique that utilizes the wavelength dependency of diffraction action. This is because the technology using the wavelength selective filter having the wavelength dependency of the rate cannot be used for BD and HD having the same light source wavelength.

  The present invention takes the above-mentioned problems into consideration, and an optical pickup device and an optical disc drive capable of appropriately recording and / or reproducing information with respect to different high-density discs using a short wavelength light beam An object is to provide an apparatus.

The optical pickup device according to claim 1 has a first optical information recording medium having a protective layer having a thickness t1 and a thickness t2 (4 <t2 / t1 <8) by the first light flux having the first wavelength λ1. A first light source unit capable of emitting the first light flux to record and / or reproduce information on each information recording surface of a second optical information recording medium having a protective layer; and the information recording surface An optical pickup device having one first photodetector having a first photodetector for detecting a reflected light beam from
A coupling optical system for converting and emitting a divergence angle of the first light beam emitted from the first light source unit;
A function of condensing the first light flux emitted from the first light source unit to form a condensing spot on each information recording surface of the first optical information recording medium and the second optical information recording medium; And the wavefront aberration of the focused spot when the parallel luminous flux of the first luminous flux is condensed at the first numerical aperture NA1 on the information recording surface of the first optical information recording medium is 0.07λ1 rms or less, When the collimated light beam of the first light beam is condensed on the information recording surface of the second optical information recording medium with the second numerical aperture NA2 (NA2 <NA1), the wavefront aberration of the condensed spot is 0.5λ1 rms or more. An objective optical system that is less than or equal to 5λ1 rms;
A magnification changing optical system disposed in an optical path between the first light source unit and the objective optical system, and changing an incident angle of the first light flux with respect to the objective optical system, thereby magnifying the objective optical system; A variable magnification mechanism,
An aperture limiting mechanism that is arranged in an optical path between the zooming mechanism and the objective optical system and can change the numerical aperture of the objective optical system,
When recording and / or reproducing information with respect to the first optical information recording medium, the magnification changing mechanism is configured so that the magnification m of the objective optical system satisfies −0.03 ≦ m ≦ 0.03. The first light flux is made incident on the objective optical system, and the aperture limiting mechanism forms an aperture so that the numerical aperture of the objective optical system becomes the first numerical aperture NA1.
When recording and / or reproducing information with respect to the second optical information recording medium, the zoom mechanism is arranged so that the magnification of the objective optical system satisfies −0.15 ≦ m ≦ −0.04. The first light flux is made incident on the objective optical system, and the aperture limiting mechanism forms an aperture so that the numerical aperture of the objective optical system becomes the second numerical aperture NA2.

  The objective optical system used in common can suppress spherical aberration to a low level (less than 0.07λ1 rms) when a parallel light beam is incident on the first optical information recording medium. Is a characteristic that causes spherical aberration (1.0λ1 rms to 1.8λ1 rms) when a parallel light beam is incident. According to the optical pickup device of the present invention, since the zoom mechanism changes the incident angle of the first light beam with respect to the objective optical system, for example, when a parallel light beam is incident on the objective optical system, the spherical aberration is generated. For the second optical information recording medium, spherical aberration can be corrected by making a divergent light beam incident on the objective optical system. Further, the difference in numerical aperture between when the first optical information recording medium is used and when the second optical information recording medium is used is appropriate depending on the optical information recording medium to be used by using the aperture limiting mechanism. This can be done by selecting an opening.

  According to a second aspect of the present invention, there is provided the optical pickup device according to the first aspect of the invention, wherein the optical pickup device performs the objective recording when recording and / or reproducing information on the second optical information recording medium. The optical system further includes a coma aberration correcting mechanism having a function of correcting coma generated when the optical system is tracking driven.

  If a divergent light beam is incident on the objective optical system when the second optical information recording medium is used, coma aberration may increase during tracking. Therefore, the coma aberration correcting mechanism is provided to correct the coma aberration, thereby forming an appropriate condensing spot.

  According to a third aspect of the present invention, there is provided the optical pickup device according to the second aspect, wherein the coma aberration correcting mechanism is configured to shift the optical element in a direction perpendicular to the optical axis or to rotate about a rotation axis perpendicular to the optical axis. It has an actuator for driving, and the optical element is shifted or rotated by the actuator following the tracking driving of the objective optical system.

  According to a fourth aspect of the present invention, in the optical pickup device according to the third aspect, the optical element has at least one aspherical surface.

  According to a fifth aspect of the present invention, in the optical pickup device according to the second aspect, the coma aberration correcting mechanism rotates the objective optical element of the objective optical system around a rotation axis perpendicular to the optical axis. And the objective optical element is rotated by the actuator following the tracking drive of the objective optical system.

  According to a sixth aspect of the present invention, in the optical pickup device according to the fifth aspect, the actuator for rotationally driving the objective optical system further has a function of driving the objective optical system for tracking and focusing. It is a shaft actuator

  According to a seventh aspect of the present invention, in the invention of the second aspect, the coma aberration correction mechanism includes at least one electrode panel that is divided asymmetrically with respect to the optical axis, and a sandwiched between the electrode panels. And a power supply unit for supplying a voltage to the electrode panel, and the power supply unit supplies a voltage to the electrode panel following the tracking drive of the objective optical system. And

  According to an eighth aspect of the present invention, in the invention according to the seventh aspect, the objective optical system performs tracking driving integrally with the coma aberration correcting mechanism.

  According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects, the zooming mechanism includes an actuator for shifting and driving an optical element having refractive power in the optical axis direction. The incident angle of the first light beam with respect to the objective optical system is changed by driving the optical element with the actuator in accordance with the thickness of the protective layer of the optical information recording medium for recording and / or reproducing information. It is characterized by being changed.

  According to a tenth aspect of the present invention, in the invention according to any one of the first to eighth aspects, the zooming mechanism is configured to insert and remove the optical element having refractive power from the optical path of the first light flux. According to the thickness of a protective layer of an optical information recording medium that has an actuator and records and / or reproduces information, the optical element is inserted into and removed from the optical path of the first light beam by the actuator. The incident angle of the first light beam with respect to the system is changed.

  An optical pickup device according to an eleventh aspect is the optical pickup device according to the tenth aspect, wherein the optical element is a convex lens, and information is recorded and / or reproduced on the first optical information recording medium. When the optical element is inserted into the optical path of the first light flux by the actuator and information is recorded and / or reproduced from the second optical information recording medium, the optical element is It is characterized by being desorbed from the optical path of the first light beam.

  According to a twelfth aspect of the present invention, in the optical pickup device according to the tenth aspect, the optical element is a concave lens, and information is recorded and / or reproduced on the first optical information recording medium. When the optical element is detached from the optical path of the first light beam by the actuator and information is recorded and / or reproduced from the second optical information recording medium, the optical element is moved by the actuator. It is inserted into the optical path of the first light flux.

  According to a thirteenth aspect of the present invention, in the invention according to any one of the first to twelfth aspects, the first optical information recording medium and / or the second optical information recording medium has a plurality of information recording surfaces. The variable magnification mechanism includes the first optical information recording medium and / or the second light in response to the objective optical system performing a focus jump between information recording surfaces. An incident angle of the first light beam with respect to the objective optical system is changed based on a distance from a light beam incident surface of the information recording medium to the information recording surface.

  An optical pickup device according to a fourteenth aspect is the invention according to any one of the first to thirteenth aspects, wherein the objective optical system has at least one optical element made of resin, and the zooming mechanism includes the objective A change in spherical aberration on the information recording surface due to a temperature change is corrected by changing the incident angle of the first light flux with respect to the optical system.

  An optical pickup device according to a fifteenth aspect is the invention according to any one of the first to fourteenth aspects, wherein the opening limiting mechanism includes a first opening corresponding to the first numerical aperture NA1 and the second opening. The first optical information recording medium, comprising: a plate member formed with a second opening corresponding to several NA2; and an actuator for driving the plate member to shift or rotate about a predetermined rotation axis. When recording and / or reproducing information, the plate member is driven to shift or rotate so that the center of the first opening coincides with the optical axis of the objective optical system. When recording and / or reproducing information with respect to the second optical information recording medium, the plate member is driven to shift so that the center of the second opening coincides with the optical axis of the objective optical system. Or it is characterized by being driven to rotate .

  In an optical pickup device according to a sixteenth aspect, in the invention according to any one of the first to fourteenth aspects, the opening limiting mechanism includes a plurality of wing members and an actuator for driving the plurality of wing members. And having the actuator change the size of the opening formed from the plurality of wing members in accordance with the thickness of the protective layer of the optical information recording medium for recording and / or reproducing information. To do.

  An optical pickup device according to a seventeenth aspect is the invention according to any one of the first to fourteenth aspects, wherein the opening limiting mechanism is a liquid crystal shutter.

  According to an eighteenth aspect of the present invention, there is provided the optical pickup device according to the seventeenth aspect of the present invention, wherein the opening limiting mechanism is divided into a central region including at least one of the optical axes and a peripheral region surrounding the central region. An electrode panel, a power source for supplying a voltage to the electrode panel, and polarization of a light beam that is sandwiched between the electrode panels and that passes through the peripheral region among the first light beam that is incident on the objective optical system It has a liquid crystal panel as a polarization plane rotating mechanism for rotating a surface by a predetermined amount based on the amount of voltage applied to the electrode panel by the power supply unit.

  An optical pickup device according to a nineteenth aspect is characterized in that, in the invention according to the eighteenth aspect, a quarter wavelength plate is provided in an optical path between the aperture limiting mechanism and the objective optical system.

  An optical pickup device according to a twentieth aspect is characterized in that, in the invention according to the eighteenth or nineteenth aspect, the central region is a region corresponding to the second numerical aperture NA2.

  An optical pickup device according to a twenty-first aspect is the invention according to any one of the first to twentieth aspects, wherein the optical pickup device has a second wavelength λ2 (1.5 <λ2 / λ1 <1.7). It further includes an outgoing second light source unit capable of two luminous fluxes and a second photodetector for detecting a reflected luminous flux of the second luminous flux, and the thickness t3 (4 <t3 / t1 < 8) Information can be recorded and / or reproduced with respect to the third optical disk having the protective layer, and the objective optical system corrects spherical aberration caused by the difference between the thickness t1 and the thickness t2. Therefore, it is possible to provide an optical pickup device capable of recording and / or reproducing information so as to be compatible with a DVD or the like.

  An optical pickup device according to a twenty-second aspect is the invention according to any one of the first to twenty-first aspects, wherein the optical pickup device has a third wavelength λ3 (1.8 <λ3 / λ1 <2.1). A third light detector for detecting the reflected light beam of the third light beam, and a thickness t4 (10 <t4 / t1 < 14) Information can be recorded and / or reproduced with respect to the third optical disc having the protective layer, and the objective optical system corrects spherical aberration caused by the difference between the thickness t1 and the thickness t4. Therefore, it is possible to provide an optical pickup device capable of recording and / or reproducing information so as to be compatible with a CD or the like.

  According to a twenty-third aspect of the present invention, there is provided an optical disc drive device including the optical pickup device according to any one of the first to twenty-second aspects.

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

  In this specification, an optical disk (also referred to as an optical information recording medium) that uses a blue-violet semiconductor laser or a blue-violet SHG laser as a light source for recording / reproducing information is generally referred to as a “high-density optical disk”, and NA0 In addition to a standard optical disc (for example, BD) in which information is recorded / reproduced by an objective optical system of .85 and the thickness of the protective layer is about 0.1 mm, an objective optical system of NA 0.65 to 0.67 Information recording / reproducing is performed, and a standard optical disc (for example, HD) having a protective layer thickness of about 0.6 mm is also included. In addition to an optical disc having such a protective layer on its information recording surface, an optical disc having a protective film with a thickness of several to several tens of nanometers on the information recording surface, the thickness of the protective layer or protective film It also includes an optical disc with 0. In this specification, the high-density optical disk includes a magneto-optical disk that uses a blue-violet semiconductor laser or a blue-violet SHG laser as a light source for recording / reproducing information.

  Furthermore, in this specification, DVD is a generic term for DVD series optical disks such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. Is a general term for CD-series optical disks such as CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like. The recording density is highest in the high-density optical disc, and then decreases in the order of DVD and CD.

  ADVANTAGE OF THE INVENTION According to this invention, the optical pick-up apparatus and the drive device for optical discs which can perform recording and / or reproduction | regeneration of information appropriately with respect to a different high-density disc using a short wavelength light beam can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the optical pickup device according to the first embodiment will be described with reference to FIG. The optical pickup device PU1 according to the present embodiment can be incorporated in an optical disk drive device.

  FIG. 1 is a diagram schematically showing a configuration of an optical pickup apparatus PU1 capable of appropriately recording / reproducing information for both high-density optical discs BD and HD. The optical specifications of the BD are the wavelength λ1 = 405 nm, the thickness t1 = 0.1 mm of the protective layer PL1, and the first numerical aperture NA1 = 0.85. The optical specifications of the HD are the wavelength λ1 = 405 nm, the protective layer The thickness t2 of PL2 is 0.6 mm, the second numerical aperture NA2 is 0.67, and the focal length f of the objective optical system is 2.2 mm. However, the combination of the wavelength, the thickness of the protective layer, and the numerical aperture is not limited to this.

  The optical pickup device PU1 is a blue-violet semiconductor laser LD (first light source unit) that emits a 405 nm blue-violet laser beam (first beam) when recording / reproducing information to / from the BD and HD. And an optical detector PD (first photodetector) for HD, an objective optical system OL having a function of condensing an incident laser beam on the information recording surface RL1 of BD or the information recording surface RL2 of HD, and a triaxial actuator AC1, a single-axis actuator AC2, a negative lens L1 disposed in a common optical path through which the first light flux passes in common, and capable of shifting in the optical axis direction from the single-axis actuator AC2, and a positive lens L2 Astigmatism is added to the reflected beam from the beam expander EXP, the polarization beam splitter PS, the quarter wave plate QWP, and the information recording surface RL1, which is a variable magnification optical system. To sensor lens SEN for the liquid crystal shutters LQS, it is constructed from the collimator CL (coupling optical system). As a light source, a blue-violet SHG laser can be used in addition to the above-described blue-violet semiconductor laser LD.

  The magnification of the objective optical system OL at the time of BD recording / reproduction is zero, and the magnification at the time of HD recording / reproduction is -1 / 14.75.

  The zoom mechanism used in the present embodiment optimizes the distance between the negative lens L1 and the positive lens L2 by the single-axis actuator AC2 so that a parallel light beam is emitted during BD recording / reproduction. On the other hand, the interval between the negative lens L1 and the positive lens L2 is optimized by the uniaxial actuator AC2 so that the divergent light beam is emitted during HD recording / reproducing so as to be narrower than the interval during BD recording / reproducing. Yes. The optical pickup device PU1 determines a type (BD or HD) of an optical information recording medium (also referred to as an optical disc) accommodated in a disc tray (not shown), and has a control means for moving the negative lens L1 to an optimal position. Have.

  This zooming mechanism also supports BDs capable of multilayer recording. More specifically, in order to access information recording layers of different depths in the same BD, spherical aberration that occurs during a so-called focus jump that displaces the objective optical system OL in the optical axis direction is positive with the negative lens L1. Correction can be made by optimizing the distance between the lenses L2 with a single-axis actuator (that is, changing the magnification of the objective optical system OL). Note that the amount of movement of the negative lens L1 during the focus jump is smaller than the amount of movement during HD recording / reproduction. Of course, it is also possible to adopt a configuration corresponding to an HD capable of multilayer recording by using such a zoom mechanism. The optical pickup device PU1 has a layer discriminating unit for discriminating which layer (L0, L1, L1,...) Is the information recording layer on which the objective optical system OL is focused.

Next, the operation of the optical pickup device PU1 will be described together with the operation principle of the liquid crystal shutter LQS. Here, a method of performing aperture restriction by the liquid crystal shutter LQS using the technique disclosed in Patent Document 3 will be described. FIG. 5A is a schematic perspective view for explaining the twist alignment state of the liquid crystal molecules of the liquid crystal shutter LQS, and FIG. 5B is a schematic plan view of FIG. FIG. 6A shows a pattern of the transparent electrode 2a on the upper side of the liquid crystal shutter LQS. Transparent electrodes 2a of the upper is divided into an outer peripheral pattern 2a ₂ surrounding the periphery central circular pattern 2a ₁ and. A region surrounded by the circular pattern 2a ₁ is a region corresponding to the second numerical aperture NA2. When a voltage is uniformly applied to each of the upper and lower transparent electrodes 2a and 2b of the liquid crystal shutter LQS shown in FIG. 5 and the value is varied, the received voltage of the laser beam in the photodetector PD is measured. 7 having a characteristic curve.
Japanese Patent Laid-Open No. 10-20263

  As is apparent from FIG. 7, the received light amount is almost zero when the voltage is 2.0 V or less, and the received light amount is 90 to 100% when the voltage is 3.5 V or more. Therefore, it is possible to control the amount of received light by changing the voltage applied to the transparent electrode of the liquid crystal shutter LQS.

First, at the time of BD recording / reproducing operation, a BD selection signal is given as a disk selection signal _SSEL to the liquid crystal shutter control circuit CNT (FIG. 1).

  When the BD selection signal is given, the liquid crystal shutter control circuit CNT drops the entire surface of the lower transparent electrode 2b (FIG. 6B) of the liquid crystal shutter LQS to the ground (earth potential) and the upper transparent electrode 2a ( For example, a voltage of 3.5 V is applied to the entire surface of FIG.

  When this voltage of 3.5 V is applied, all the liquid crystal molecules M in the liquid crystal shutter LQS are in a substantially vertical alignment state by the electric field, and the entire surface of the liquid crystal shutter LQS acts as a mere transparent plate, and the polarization action by the twist. Is almost gone. That is, the divergent light beam emitted from the blue-violet semiconductor laser LD passes through the polarization beam splitter PS and is converted into a parallel light beam by the collimator CL, as shown by the solid line in FIG. 1, and the beam expander EXP Passes and enters the liquid crystal shutter LQS. At this time, the laser beam composed of linearly polarized light passes through the polarization plane without rotating and reaches the quarter-wave plate QWP.

  Since the polarization plane P of the linearly polarized laser beam incident on the quarter-wave plate QWP intersects the crystal axis Pc of the quarter-wave plate QWP at an angle of 45 °, the linearly polarized laser beam is changed from circularly polarized light to circularly polarized light. Then, the beam diameter is regulated by a diaphragm (not shown), and after entering the objective optical system OL in the state of parallel light, it becomes a spot formed on the information recording surface RL1 through the protective layer PL1 of the BD. The objective optical system OL is driven for tracking and focusing by a three-axis actuator AC1.

  The reflected laser beam modulated by the information pits on the information recording surface RL1 passes through the objective optical system OL again and enters the quarter-wave plate QWP again, and is changed from circularly polarized light to linearly polarized light.

  The reflected laser beam returned to the linearly polarized light has its polarization plane rotated by 90 ° from the original linear polarization plane, and has a polarization wave in a direction parallel to the polarization plane P of the polarization beam splitter PS. It has become. The reflected laser beam consisting of linearly polarized light rotated by 90 ° passes through the liquid crystal shutter LQS acting as a transparent plate as it is, and reaches the polarizing beam splitter PS. As described above, since the polarization plane of the reflected laser beam is rotated in the direction orthogonal to the polarization plane P of the polarization beam splitter PS, it is reflected in the orthogonal direction by the polarization plane of the polarization beam splitter PS and passes through the sensor lens SEN. And received by the photodetector PD. And the information recorded on BD can be read using the output signal of photodetector PD.

  In this way, at the time of BD recording / reproduction, the entire surface of the liquid crystal shutter LQS acts as a mere transparent plate, so that all of the reflected laser light beam from the BD enters the photodetector PD. For this reason, the entire surface of the lens is used for the objective optical system OL during BD reproduction. Therefore, if the aperture of the diaphragm (not shown) at this time is set to a value suitable for BD recording / reproduction, for example, NA1 = 0.85, recording / reproduction can be efficiently performed on BD. It can be done.

At the time of HD recording / reproduction, the HD selection signal is given to the liquid crystal shutter control circuit CNT (see FIG. 1) as the disk selection signal _SSEL .

When this HD selection signal is given, the liquid crystal shutter control circuit CNT drops the entire surface of the transparent electrode 2b below the liquid crystal shutter LQS (see FIG. 6B) to the ground (earth potential). On the other hand, for the upper transparent electrode 2a (see FIG. 6A), for example, a voltage of 3.5V is applied to the central circular pattern 2a ₁ and the outer peripheral pattern 2a ₂ surrounding the circular pattern. Drop to ground (earth potential).

The central circular pattern 2a ₁ portion to which a voltage of 3.5 V is applied functions as a simple transparent plate by the same action as in the BD recording / reproducing operation described above. Accordingly, all of the reflected light passing through the central circular pattern 2a ₁ portion passes through the polarization beam splitter PS and enters the photodetector PD as in the case of the BD.

On the other hand, since the outer circumferential pattern 2a ₂ surrounding the circular pattern is dropped to ground (earth potential), it does not act any of the electric field to the liquid crystal molecules in this portion. Therefore, the liquid crystal molecules in the peripheral pattern 2a ₂ portion remain in the twist alignment state. For this reason, the polarization plane of the laser beam B that has passed through the outer peripheral pattern 2a ₂ is rotated along the twisted liquid crystal molecules M and is incident on the quarter-wave plate QWP.

The divergent light beam emitted from the blue-violet semiconductor laser LD passes through the polarization beam splitter PS, is converted into a parallel light beam by the collimator CL, and passes through the beam expander EXP as shown by the ray path in FIG. Is incident on the liquid crystal shutter LQS. The laser beam incident on the quarter-wave plate QWP through the outer peripheral pattern 2a ₂ has the direction of the polarization plane and the crystal axis Pc of the quarter-wave plate QWP substantially the same, so that the quarter. After passing through the quarter-wave plate QWP with almost no action of the wave plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and is incident on the objective optical system OL in the state of diverging light, and from there, the HD protective layer It becomes a spot formed on the information recording surface RL2 via PL2. The objective optical system OL is rotationally driven (strictly, pendulum driven) in addition to tracking driving and focusing driving by the three-axis actuator AC1. This pendulum drive is performed along the radial direction of the optical disc following the tracking drive of the objective optical system OL. The coma aberration generated by the pendulum drive (tilt drive of the objective optical system OL) and the coma aberration generated by the tracking drive are offset. The optical pickup device PU1 has a control means for detecting the tracking amount and the direction of the objective optical system OL and determining the pendulum drive amount and the pendulum direction of the objective optical system OL according to the result. Such a control means and the triaxial actuator AC1 constitute a coma aberration correcting mechanism. Instead of the objective optical system OL, an optical element having an aspherical optical surface may be driven to shift in the direction perpendicular to the optical axis by an actuator, or may be rotationally driven around a rotation axis perpendicular to the optical axis.

  The reflected laser beam modulated by the information pits on the information recording surface RL2 passes through the objective optical system OL again and enters the quarter-wave plate QWP.

The reflected light incident on the quarter-wave plate QWP passes through the quarter-wave plate QWP as linearly polarized light without being affected by the quarter-wave plate QWP again, and enters the liquid crystal shutter LQS. The reflected light composed of the linearly polarized wave is rotated along the twist of the liquid crystal molecules M while passing through the liquid crystal shutter LQS, and is almost the same as the polarization plane P of the original laser beam when exiting the liquid crystal shutter LQS. The same polarization direction. Therefore, the laser beam reflected by HD through the outer peripheral pattern 2a ₂ portion of the liquid crystal shutter LQS passes through the polarization beam splitter PS as it is and does not enter the photodetector PD. Therefore, information recorded on the HD can be read using the output signal of the photodetector PD that receives only the reflected laser beam passing through the circular pattern 2a ₁ part.

As described above, at the time of HD recording / reproduction, only the central circular pattern 2a ₁ portion of the transparent electrode 2a on the upper side of the liquid crystal shutter LQS is made to act as a transparent plate, so that only the reflected laser light beam passing through the circular pattern 2a ₁ portion. Can be incident on the photodetector PD.

This is equivalent to the case where the laser beam that passes through the outer periphery of the lens is cut out of the laser beam that passes through the objective optical system OL. That is, the same effect as that obtained when the aperture is restricted is obtained. Therefore, if the shape of the circular pattern 2a ₁ is set so that the apparent numerical aperture NA at this time is a value suitable for HD reproduction, for example, NA2 = 0.67, the optical pickup for BD is used. Using the device, the HD can be used interchangeably.

  In addition, although the HD has a shorter wavelength than the DVD, the protective layer thickness is 0.6 mm as it is, so that coma aberration is greatly generated due to surface wobbling of the optical disk (bad disk). Measures against this are essential for an optical pickup device. The coma due to the surface shake of the optical disk is also canceled by the pendulum drive (tilt) of the objective optical system OL by the triaxial actuator. The optical pickup device PU1 has a control means for detecting the HD disc surface shake amount and controlling the pendulum drive of the objective optical system OL.

  As another coma aberration correcting mechanism, although not shown, at least one of the electrode panels divided asymmetrically with respect to the optical axis, a liquid crystal panel sandwiched between the electrode panels, and the electrode panel And a power supply unit for supplying a voltage to the electrode panel, and the power supply unit supplies a voltage to the electrode panel following the tracking drive of the objective optical system OL. As a method of correcting coma aberration using a liquid crystal panel, for example, the technique disclosed in Patent Document 3 described above can be used.

Example 1
The first embodiment is an optical system including an objective optical system OL and a beam expander EXP suitable for the optical pickup device PU1 shown in FIG. Table 1 shows lens data of Example 1. FIG. 2 is a diagram showing the arrangement in the optical axis direction of the objective optical system OL and the beam expander EXP when using BD, and FIG. 3 is the arrangement in the optical axis direction of the objective optical system OL and the beam expander EXP when using HD. FIG. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E−3).

The optical surface of the objective optical system OL of the present embodiment is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into the following aspherical expression. ing.
[Aspherical expression]
z = (y ² / R) / [1 + √ {1- (K + 1) (y / R) ² }] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ + A ₁₂ y ¹² + A ₁₄ y ¹⁴ + A ₁₆ y ¹⁶ + A ₁₈ y ¹⁸ + A ₂₀ y ²⁰
However,
z: Aspherical shape (distance in the direction along the optical axis from the apex of the aspherical surface)
y: Distance from optical axis R: Radius of curvature Κ: Conic coefficient A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ , A ₁₆ , A ₁₈ , A ₂₀ : Aspheric coefficient

  FIG. 4 shows a graph comparing spherical aberrations with and without tilt correction of the objective optical system OL when the objective optical system OL is shifted (corresponding to tracking drive of the objective optical system OL). Table 2 shows the numerical data. It can be seen that when a divergent light beam is incident on the objective optical system OL, spherical aberration caused by the optical axis shift (shift) of the OL of the objective optical system can be corrected by tilt.

  Next, an optical pickup device according to a second embodiment will be described. The optical pickup device PU2 according to the present embodiment can be incorporated in an optical disk drive device.

  FIGS. 8A and 8B are diagrams schematically showing a configuration of an optical pickup apparatus PU2 capable of appropriately recording / reproducing information on any of the high-density optical disc BD, HD, DVD, and CD. It is. The optical specifications of the BD are the focal length f1 = 2.200 mm of the objective optical system, the wavelength λ1 = 405 nm, the thickness t1 = 0.1 mm of the protective layer PL1, the first numerical aperture NA1 = 0.85, The optical specifications are the focal length f1 of the objective optical system = 2.200 mm, the wavelength λ1 = 405 nm, the thickness t2 of the protective layer PL2 = 0.6 mm, and the second numerical aperture NA2 = 0.67. The specifications are the focal length f2 = 2.335 mm of the objective optical system, the wavelength λ2 = 655 nm, the thickness t3 = 0.6 mm of the protective layer PL3, the third numerical aperture NA3 = 0.65, and the optical specification of the CD is The focal length f3 of the objective optical system = 2.540 mm, the wavelength λ3 = 785 nm, the thickness t4 of the protective layer PL4 = 1.2 mm, and the fourth numerical aperture NA4 = 0.51. However, the combination of the wavelength, the thickness of the protective layer, and the numerical aperture is not limited to this.

  The optical pickup device PU2 is a blue-violet semiconductor laser LD (first light source unit) that emits a 405 nm blue-violet laser beam (first beam) when recording / reproducing information to / from the BD and HD, and a DVD. A second light emitting point EP1 (second light source part) that emits a 655 nm laser beam (second beam) and records / reproduces information to / from a CD. A second light emitting point EP2 (third light source unit) that emits a 785 nm laser beam (third beam) and a first light receiving unit DS1 that receives a reflected beam from the information recording surface RL2 of the DVD. (Second photodetector), a second light receiving unit DS2 (third photodetector) that receives a reflected light beam from the information recording surface RL3 of the CD, and a laser module LM, BD, and a prism PS, and For HD The detector PD, the objective optical system OL having a function of condensing the incident laser beam on the information recording surfaces RL1, RL2, RL3, and RL4, the three-axis actuator AC1, the one-axis actuator AC2, and the first to third beams are common. And a variable power optical system that includes a negative lens L1 that is arranged in a common optical path that passes through the optical axis and that can be shifted in the optical axis direction by a single-axis actuator AC2, and a positive lens L2 that can be inserted into and removed from the optical axis. Sensors for adding astigmatism to reflected light beams from the beam expander EXP, the first polarizing beam splitter PS1, the second polarizing beam splitter PS2, the quarter wavelength plate QWP, and the information recording surfaces RL1 and RL2, which are systems A lens SEN, a first collimator COL1 (cup) that is disposed in a dedicated optical path through which only the first light beam passes and converts the first light beam into a parallel light beam Ring optical system), and a second collimator COL2 Metropolitan which converts the second light flux and the third light flux into a parallel light beam. In addition to the blue-violet semiconductor laser LD1 described above, a blue-violet SHG laser can also be used as a light source for BD. The objective optical system OL is composed of an aberration correction element and a glass lens for BD, and is coaxially fixed via a lens frame.

  The objective optical system OL has a BD recording / reproducing magnification of zero, an HD recording / reproducing magnification of −1 / 14.75, a DVD recording / reproducing magnification of zero, and a CD recording. / The magnification during playback is zero.

  As shown in FIG. 14A, the zooming mechanism used in the present embodiment is an interval between the negative lens L1 and the positive lens L2 arranged in the optical axis direction so as to emit a parallel light beam, as shown in FIG. Is optimized by the single-axis actuator AC2. On the other hand, at the time of HD recording / reproduction, as shown in FIG. 14B, the positive lens L2 is detached from the optical axis (the state indicated by the dotted line in FIG. 1), and the divergent light beam corresponding to the magnification of the objective optical system OL is obtained. So that the negative lens L1 is positioned by the uniaxial actuator AC2.

  Further, the interval between the negative lens L1 and the positive lens L2 arranged in the optical axis direction is wider than that at the time of BD recording / reproduction so that the positive lens L2 is inserted into the optical axis at the time of DVD recording / reproduction and a parallel light beam is emitted. In this way, the single-axis actuator AC2 is optimized. The interval between the negative lens L1 and the positive lens L2 aligned in the optical axis direction is wider than that at the time of BD recording / reproduction so that the positive lens L2 is inserted into the optical axis during CD recording / reproduction and a parallel light beam is emitted. Thus, optimization is performed by the single-axis actuator AC2. The optical pickup device PU2 determines the type (BD, HD, DVD, CD) of an optical information recording medium (also referred to as an optical disc) accommodated in a disc tray (not shown), and inserts and removes the positive lens L2 and a negative lens. Control means for moving L1 to the optimum position is provided.

  This zooming mechanism also supports BDs capable of multilayer recording. More specifically, in order to access information recording layers of different depths in the same BD, spherical aberration that occurs during a so-called focus jump that displaces the objective optical system OL in the optical axis direction is positive with the negative lens L1. Correction can be made by optimizing the distance between the lenses L2 by the single-axis actuator AC2 (that is, changing the magnification of the objective optical system OL). Note that the amount of movement of the negative lens L1 during the focus jump is smaller than the amount of movement during HD recording / reproduction. Of course, it is also possible to adopt a configuration corresponding to an HD capable of multilayer recording by using such a zoom mechanism. In this case, since the positive lens L2 is detached from the optical axis, only the negative lens L1 is moved. The optical pickup device PU2 has a layer discriminating unit for discriminating which layer (L0, L1, L1,...) Is the information recording layer on which the objective optical system OL is focused.

  As shown in FIG. 15 (B) when viewed in the optical axis direction, the aperture limiting mechanism in the present embodiment has a first opening A1 corresponding to the first numerical aperture NA1 and a second numerical aperture corresponding to the second numerical aperture NA2. The plate member STO in which the two openings A2 are formed is configured to shift-drive in the direction orthogonal to the optical axis depending on whether it is BD or HD. When recording and / or reproducing information on the BD, the plate member STO is driven to shift so that the center of the first opening A1 and the optical axis X of the objective optical system OL coincide with each other. When recording and / or reproducing information, the plate member STO is driven to shift so that the center of the second opening A2 coincides with the optical axis X of the objective optical system OL. Accordingly, the optical pickup device PU2 discriminates the type (BD / HD) of the disc put in the disc tray, and disc discriminating for inserting / removing the plate member STO (shift driving or rotational driving) by an actuator (not shown). Have means. The aperture limitation for DVD and CD is automatically performed by an aperture limitation function (for example, a phase structure formed on an optical surface described later) provided in the objective optical system OL itself.

  As another aperture limiting mechanism, as shown in FIG. 15A as viewed in the optical axis direction, the first aperture A1 corresponding to the first numerical aperture NA1 and the second aperture corresponding to the second numerical aperture NA2. A configuration in which the plate member STO formed with the portion A2 is rotationally driven around an axis O parallel to the optical axis X using an actuator (not shown) can also be used. When recording and / or reproducing information on the BD, the plate member STO is rotated so that the center of the first opening A1 and the optical axis X of the objective optical system OL coincide with each other. When recording and / or reproducing information, the plate member STO is rotationally driven so that the center of the second opening A2 coincides with the optical axis X of the objective optical system OL.

  Furthermore, as another opening limiting mechanism, for example, as shown in FIG. 13, seven wing members SP are pivotally arranged around the optical axis O, and the wing members SP are moved by an actuator (not shown). The numerical aperture NA is set by changing the diameter of the opening formed from the wing member SP by being rotationally driven according to the thickness of the BD or HD protective layer for recording and / or reproducing information. You can also.

  As another opening limiting mechanism, as in the first embodiment, at least one of the electrode panels divided into a central region including the optical axis and a peripheral region surrounding the central region, and the electrode A power source for supplying a voltage to the panel; and the peripheral portion based on the amount of voltage applied to the electrode panel by the power source in the first light flux sandwiched between the electrode panels and incident on the objective optical system OL A configuration having a liquid crystal panel as a polarization plane rotation mechanism for rotating the polarization plane of the light beam passing through the region by a predetermined amount can also be used.

  As shown schematically in FIGS. 9 to 11, the objective optical system OL in the present embodiment is joined to the resin-made first aberration correction lens SL <b> 1 and the resin-made second aberration correction lens SL <b> 2 for aberration correction. A glass objective lens OBL whose aspherical shape is designed so that the spherical aberration is minimized with respect to the lens group CSL, the first wavelength λ1, and the thickness t1 of the protective layer PL1 of the BD is a lens frame B. (See FIG. 8 (A)). Specifically, the first aberration correction lens SL1 and the second aberration correction lens SL2 are fitted and fixed to one end of the cylindrical lens frame B, and the objective lens OBL is fitted and fixed to the other end. These are integrated in a coaxial manner along the optical axis.

  The first aberration correction lens SL1 has an Abbe number νd1 = 55.0 at the d line and a refractive index nd1 = 1.5600000 at the d line, and the second aberration correction lens SL2 has an Abbe number νd2 = 23 at the d line. 0.0, refractive index nd2 at the d-line = 1.650000.

  The first phase structure PSA1 is formed on the optical surface on the light source side of the first aberration correction lens SL1, and the second phase structure PSA2 is formed on the optical surface on the optical disk side of the second aberration correction lens SL2. Yes.

  The first phase structure PSA1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shape including the optical axis is stepped are arranged on concentric circles. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Shifted structure).

  Each step Δ1 of the staircase structure is set to a height that satisfies Δ1 = 2 · λ1 / (n1-1) = 1.403 μm. Here, n1 is the refractive index of the first aberration correction lens SL1 at the wavelength λ1 (λ1 = 405 nm in the present embodiment).

  Since the optical path difference added to the first light flux by the step Δ1 is 2 × λ1, the first light flux is transmitted as it is without being affected by the first phase structure PSA1.

  Further, since the optical path difference added to the third light flux by the step Δ1 is 1 × λ3 (λ3 = 785 nm in the present embodiment), the third light flux is also transmitted as it is without being affected by the first phase structure PSA1. To do.

  On the other hand, the optical path difference added to the second light flux by the step Δ1 is 1.19 × λ2≈1.20 × λ2 (λ2 = 655 nm in this embodiment), and passes through the level surfaces before and after the step Δ1. The phase difference between the two light beams (the phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase) is 2π × 0.20. Since one sawtooth is divided into five, the phase difference of the second light flux is exactly 5 × 2π × 0.20 = 2π for one sawtooth, and first-order diffracted light is generated.

  In this way, the first phase structure PSA1 corrects spherical aberration due to the difference between the BD protective layer thickness and the DVD protective layer thickness by selectively diffracting only the second light flux.

  The diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PSA1 is 100%, the diffraction efficiency of the first-order diffracted light of the second light beam is 87.2%, and the zero-order of the third light beam. The diffraction efficiency of the folded light (transmitted light) is 99.0%, and a high diffraction efficiency is obtained for any light flux.

  The second phase structure PSA2 diffracts the third light beam without diffracting the first light beam and the second light beam, and has a structure in which patterns having a stepped cross section including the optical axis are arranged concentrically. Thus, for each predetermined number of level surfaces (four level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces corresponding to the number of level surfaces (in this embodiment, three levels). Shifted structure).

  Each step Δ2 of the staircase structure is set to a height that satisfies Δ2 = 7 · λ1 / (n1-1) = 4.031 μm. Here, n1 is the refractive index of the second aberration correction lens at the wavelength λ1.

  Since the optical path difference added to the first light flux by the step Δ2 is 7 × λ1, the first light flux is transmitted as it is without being affected by the second phase structure PSA2.

  Further, since the optical path difference added to the second light flux by the step Δ2 is 3.95 × λ2≈4 × λ2, the second light flux is also transmitted as it is without being affected by the second phase structure PSA2.

  On the other hand, the optical path difference N2 added to the third light beam by the step Δ2 is 3.25 × λ3, and the phase difference of the third light beam passing through the level surface before and after the step Δ2 (2π which is optically equiphase) The phase difference obtained by subtracting the integral multiple of is 2π × 0.25. Since one sawtooth is divided into four, the phase difference of the third light flux is exactly 4 × 2π × 0.25 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the second phase structure PSA2 corrects spherical aberration due to the difference between the BD protective layer thickness and the CD protective layer thickness by selectively diffracting only the third light flux.

  Note that the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated by the second phase structure PSA1 is 100%, the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light beam is 88.8%, and the third The diffraction efficiency of the first-order diffracted light of the light beam is 81.0%, and high diffraction efficiency is obtained for any light beam.

  As described above, the first phase structure PS1 allows the BD and the DVD to be compatible with each other, so that high transmittance can be secured for both the blue-violet laser beam and the red laser beam. Furthermore, by using the second phase structure PSA2 to achieve mutual compatibility between BD and CD, it is possible to ensure high transmittance for both the blue-violet laser beam and the infrared laser beam.

  In addition, since the first phase structure PSA1 is formed only within the third numerical aperture NA3 of the DVD, the light beam that passes through the area outside the third numerical aperture NA3 becomes a flare component on the information recording surface RL3 of the DVD. In this configuration, the opening restriction on the DVD is automatically performed.

  Further, since the second phase structure PSA2 is formed only within the fourth numerical aperture NA4 of the CD, the light beam passing through the area outside the fourth numerical aperture NA4 becomes a flare component on the information recording surface RL4 of the CD. In this configuration, the opening restriction on the CD is automatically performed.

  In the optical pickup device PU2, when information is recorded / reproduced with respect to the BD, the divergent light beam emitted from the blue-violet semiconductor laser LD1 is depicted as having its light path drawn by a solid line in FIG. After being reflected by the first polarizing beam splitter PS1, it is converted into a parallel light beam by the first collimator COL1, passes through the second polarizing beam splitter PS2, is expanded in diameter by the beam expander EXP, and passes through the quarter-wave plate QWP. Then, the beam diameter is regulated by the first opening A1, and after entering the objective optical system OL in the state of parallel light, it becomes a spot formed on the information recording surface RL1 from there through the protective layer PL1 of the BD. . The objective optical system OL is driven for tracking and focusing by a three-axis actuator AC1.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective optical system OL, the quarter wave plate QWP, the beam expander EXP, and the second polarizing beam splitter PS2, and then converged by the first collimator COL1. After passing through the first polarization beam splitter PS1, astigmatism is added by the sensor lens SEN and converges on the light receiving surface of the photodetector PD. And the information recorded on BD can be read using the output signal of photodetector PD.

  When information is recorded / reproduced with respect to the HD in the optical pickup device PU2, the divergent light beam emitted from the blue-violet semiconductor laser LD1 is drawn as a ray path by a wavy line in FIG. 8A. After being reflected by the first polarization beam splitter PS1, it is converted into a parallel beam by the first collimator COL1, passes through the second polarization beam splitter PS2, is converted into a divergent beam by the negative lens L1, and is a quarter wavelength plate QWP. , The light beam diameter is regulated by the second opening A2, and after entering the objective optical system OL in a divergent light state, a spot formed on the information recording surface RL2 from there through the HD protective layer PL2 It becomes. The objective optical system OL is rotationally driven (strictly, pendulum driven) in addition to tracking driving and focusing driving by the three-axis actuator AC1. This pendulum drive is performed along the radial direction of HD following the tracking drive of the objective optical system OL. The coma aberration generated by the pendulum drive (tilt drive of the objective optical system OL) and the coma aberration generated by the tracking drive are offset. The optical pickup device PU2 has a control means for detecting the tracking amount and the direction of the objective optical system OL and determining the pendulum drive amount and the pendulum direction of the objective optical system OL according to the result. Such a control means and the triaxial actuator AC1 constitute a coma aberration correcting mechanism. Instead of the objective optical system OL, an optical element having an aspherical optical surface may be driven to shift in the direction perpendicular to the optical axis by an actuator, or may be rotationally driven around a rotation axis perpendicular to the optical axis.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical system OL, the quarter wavelength plate QWP, the negative lens L1, and the second polarizing beam splitter PS2, and then converged by the first collimator COL1. After passing through the first polarization beam splitter PS1, astigmatism is added by the sensor lens SEN and converges on the light receiving surface of the photodetector PD. And the information recorded on HD can be read using the output signal of photodetector PD.

  In addition, although the HD has a shorter wavelength than the DVD, the protective layer thickness is 0.6 mm as it is, so that coma aberration is greatly generated due to surface wobbling of the optical disk (bad disk). Measures against this are essential for an optical pickup device. The coma due to the surface deflection of the optical disk is also canceled by the pendulum drive of the objective optical system OL by the triaxial actuator AC1. The optical pickup device PU2 has control means for detecting the amount of HD disc surface deflection and controlling the pendulum drive of the objective optical system OL.

  Further, when recording / reproducing information with respect to the DVD in the optical pickup device PU2, the light is emitted from the first light emitting point EP1 as shown by the dotted line in FIG. 8B. The divergent light beam is reflected by the prism PS and then converted into a parallel light beam by the second collimator COL2. After that, after being reflected by the second polarizing beam splitter PS2 and expanded by the beam expander EXP, it passes through the quarter-wave plate QWP, enters the objective optical system OL in the state of parallel light, and from there the DVD It becomes a spot formed on the information recording surface RL3 via the protective layer PL3. The objective optical system OL performs focusing and tracking by a three-axis actuator AC1 disposed around the objective optical system OL.

  The reflected light beam modulated by the information pits on the information recording surface RL3 is again transmitted through the objective optical system OL, the quarter-wave plate QWP, and the beam expander EXP, and then reflected by the second polarization beam splitter PS2 to be reflected by the second collimator COL2. Is converted into a convergent luminous flux. Thereafter, the light is reflected twice in the prism and then converges on the first light receiving part DS1. Then, information recorded on the DVD can be read using the output signal of the first light receiving unit DS1.

  In addition, when information is recorded / reproduced with respect to the CD in the optical pickup device PU2, the light is emitted from the second light emitting point EP2 as shown by the two-dot chain line in FIG. 8B. The divergent light beam is reflected by the prism PS and then converted into a parallel light beam by the second collimator COL2. After that, after being reflected by the second polarizing beam splitter PS2 and expanded by the beam expander EXP, the light passes through the quarter-wave plate QWP, enters the objective optical system OL in the state of parallel light, and then enters the CD. It becomes a spot formed on the information recording surface RL4 through the protective layer PL4. The objective optical system OL performs focusing and tracking by a three-axis actuator AC1 disposed around the objective optical system OL.

  The reflected light flux modulated by the information pits on the information recording surface RL4 is transmitted again through the objective optical system OL, the quarter wavelength plate QWP, and the beam expander EXP, and then reflected by the second polarization beam splitter PS2, and is reflected by the first collimator COL2. Converted to convergent luminous flux. Thereafter, the light is reflected twice in the prism and then converges on the second light receiving unit DS2. The information recorded on the CD can be read using the output signal of the second light receiving unit DS2.

(Example 2)
The second embodiment is an optical system including an objective optical system OL and a beam expander EXP suitable for the optical pickup device shown in FIGS. 8 (A) and 8 (B). Table 3 shows lens data of Example 2. In this embodiment, the optical path difference added to the incident light beam by the first phase structure PSA1 and the second phase structure PSA2 is represented by the following optical path difference function φ (mm).
[Optical path difference function]
φ = λ / λ _B × dor × (B ₂ y ² + B ₄ y ⁴ + B ₆ y ⁶ + B ₈ y ⁸ + B ₁₀ y ¹⁰ )
However,
φ: optical path difference function λ: wavelength of the light beam incident on the diffractive structure λ _B : manufacturing wavelength dor: diffraction order of diffracted light used for recording / reproducing with respect to the optical disk y: distance from the optical axis B ₂ , B ₄ , B ₆ , B ₈ , B ₁₀ : Diffraction surface coefficients

It is a figure which shows schematically the structure of 1st optical pick-up apparatus PU1. It is a figure which shows arrangement | positioning of the optical axis direction of the objective optical system OL at the time of BD use and the beam expander EXP. It is a figure which shows arrangement | positioning of the optical axis direction of the objective optical system OL and the beam expander EXP at the time of HD use. It is the graph which compared the spherical aberration by the presence or absence of tilt correction when the objective optical system OL is shifted. It is a model perspective view (A) for demonstrating the twist orientation state of a liquid crystal molecule, and is a schematic plan view (B). The example of the shape of the electrode pattern formed in the upper and lower transparent electrodes of a liquid crystal panel is shown, (A) is a top view which shows an example of the pattern formed in the upper transparent electrode, (B) is the lower transparent electrode It is a top view which shows an example of this pattern. It is a figure which shows the light reception characteristic of the detector with respect to the applied voltage of a liquid crystal panel. It is a figure which shows roughly the structure of 2nd optical pick-up apparatus PU1, and has shown the optical path at the time of BD use and HD use. It is a figure which shows roughly the structure of 2nd optical pick-up apparatus PU1, and has shown the optical path at the time of DVD use and CD use. It is a figure which shows arrangement | positioning of the optical axis direction of the objective optical system OL at the time of BD use and the beam expander EXP. It is a figure which shows arrangement | positioning of the optical axis direction of the objective optical system OL and the beam expander EXP at the time of HD use. It is a figure which shows arrangement | positioning of the optical axis direction of the objective optical system OL at the time of DVD use and the beam expander EXP. It is a figure which shows arrangement | positioning of the optical axis direction of the objective optical system OL at the time of CD use, and the beam expander EXP. It is a figure which shows the example of the opening restriction | limiting mechanism using a wing | blade member. It is the schematic which shows insertion / removal of the positive lens of a beam expander. It is a figure which shows the example of the opening restriction | limiting mechanism using a board member.

Explanation of symbols

AC1 3 axis actuator AC2 1 axis actuator B Mirror frame CL Collimator CNT Liquid crystal shutter control circuit COL1 1st collimator COL2 2nd collimator DS1 1st light receiving part DS2 1st light receiving part EP1 1st light emission point EP2 1st light emission point EXP Beam expander L1 Negative lens L2 Positive lens LD Blue-violet semiconductor laser LD1 Blue-violet semiconductor laser LM Laser module LQS Liquid crystal shutter OBL Objective lens OL Objective optical system PD Photodetector PS Prism PS Polarizing beam splitter PU1 Optical pickup device PU2 Optical pickup device QWP 1/4 Wave plate SEN Sensor lens STO Plate member

Claims (23)

A first optical information recording medium having a protective layer with a thickness t1 and a second optical information recording medium having a protective layer with a thickness t2 (4 <t2 / t1 <8) by the first light flux with the first wavelength λ1. In order to record and / or reproduce information on each information recording surface, a first light source unit capable of emitting the first light beam and a first light detection for detecting a reflected light beam from the information recording surface And an optical pickup device having one first photodetector having a detector,
A coupling optical system for converting and emitting a divergence angle of the first light beam emitted from the first light source unit;
A function of condensing the first light flux emitted from the first light source unit to form a condensing spot on each information recording surface of the first optical information recording medium and the second optical information recording medium; And the wavefront aberration of the focused spot when the parallel luminous flux of the first luminous flux is condensed at the first numerical aperture NA1 on the information recording surface of the first optical information recording medium is 0.07λ1 rms or less, When the collimated light beam of the first light beam is condensed on the information recording surface of the second optical information recording medium with the second numerical aperture NA2 (NA2 <NA1), the wavefront aberration of the condensed spot is 0.5λ1 rms or more. An objective optical system that is less than or equal to 5λ1 rms;
A magnification changing optical system disposed in an optical path between the first light source unit and the objective optical system, and changing an incident angle of the first light flux with respect to the objective optical system, thereby magnifying the objective optical system; A variable magnification mechanism,
An aperture limiting mechanism that is arranged in an optical path between the zooming mechanism and the objective optical system and can change the numerical aperture of the objective optical system,
When recording and / or reproducing information with respect to the first optical information recording medium, the magnification changing mechanism is configured so that the magnification m of the objective optical system satisfies −0.03 ≦ m ≦ 0.03. The first light flux is made incident on the objective optical system, and the aperture limiting mechanism forms an aperture so that the numerical aperture of the objective optical system becomes the first numerical aperture NA1.
When recording and / or reproducing information with respect to the second optical information recording medium, the zoom mechanism is arranged so that the magnification of the objective optical system satisfies −0.15 ≦ m ≦ −0.04. An optical pickup characterized in that a first light beam is incident on the objective optical system, and the aperture limiting mechanism forms an aperture so that the numerical aperture of the objective optical system becomes the second numerical aperture NA2. apparatus.   The optical pickup device has a function of correcting coma aberration generated when the objective optical system is tracking-driven when information is recorded and / or reproduced on the second optical information recording medium. The optical pickup device according to claim 1, further comprising a correction mechanism.   The coma aberration correction mechanism has an actuator for driving the optical element to shift in the direction perpendicular to the optical axis, or to rotate about the rotation axis perpendicular to the optical axis, and follows the tracking drive of the objective optical system. The optical pickup device according to claim 2, wherein the optical element is driven to shift or rotate by the actuator.   The optical pickup device according to claim 3, wherein the optical element has at least one aspheric surface.   The coma aberration correcting mechanism has an actuator for rotating the objective optical element of the objective optical system around a rotation axis perpendicular to the optical axis, and follows the tracking drive of the objective optical system to follow the objective optical system. The optical pickup device according to claim 2, wherein an element is rotationally driven by the actuator.   6. The optical pickup device according to claim 5, wherein the actuator for rotationally driving the objective optical system is a three-axis actuator having functions of further driving the objective optical system for tracking driving and focusing.   The coma aberration correcting mechanism includes two electrode panels at least one of which is asymmetrically divided with respect to the optical axis, a liquid crystal panel sandwiched between the electrode panels, and a power supply unit for supplying a voltage to the electrode panels. The optical pickup device according to claim 2, wherein a voltage is supplied to the electrode panel by the power supply unit following the tracking drive of the objective optical system.   The optical pickup device according to claim 7, wherein the objective optical system performs tracking driving integrally with the coma aberration correcting mechanism.   The zoom mechanism has an actuator for shifting and driving an optical element having refractive power in the optical axis direction, and according to the thickness of the protective layer of the optical information recording medium for recording and / or reproducing information, 9. The optical pickup device according to claim 1, wherein an incident angle of the first light beam with respect to the objective optical system is changed by driving the optical element to be shifted by the actuator. 10.   The zoom mechanism includes an actuator for inserting and removing an optical element having refractive power from the optical path of the first light flux, and has a thickness of a protective layer of an optical information recording medium for recording and / or reproducing information. Accordingly, the incident angle of the first light beam with respect to the objective optical system is changed by inserting and removing the optical element from the optical path of the first light beam by the actuator. The optical pickup device according to one item.   The optical element is a convex lens, and when recording and / or reproducing information on the first optical information recording medium, the optical element is inserted into the optical path of the first light flux by the actuator, 11. When recording and / or reproducing information with respect to a second optical information recording medium, the optical element is detached from the optical path of the first light flux by the actuator. Optical pickup device.   The optical element is a concave lens, and when recording and / or reproducing information on the first optical information recording medium, the optical element is detached from the optical path of the first light flux by the actuator, The optical element is inserted into the optical path of the first light flux by the actuator when recording and / or reproducing information on the second optical information recording medium. Optical pickup device.   The first optical information recording medium and / or the second optical information recording medium is a multilayer optical information recording medium having a plurality of information recording surfaces, and the zooming mechanism is configured such that the objective optical system has an information recording surface. The first optical information recording medium and / or the second optical information recording medium based on a distance from a light beam incident surface to the information recording surface of the first optical information recording medium. The optical pickup device according to claim 1, wherein an incident angle of the light beam is changed.   The objective optical system has at least one optical element made of resin, and the zooming mechanism changes the incident angle of the first light flux with respect to the objective optical system, thereby changing the information recording surface according to the temperature change. 14. The optical pickup device according to claim 1, wherein a change in spherical aberration is corrected.   The opening limiting mechanism includes a plate member in which a first opening corresponding to the first numerical aperture NA1 and a second opening corresponding to the second numerical aperture NA2 are formed, and the plate member is driven to shift. Or having an actuator for rotationally driving about a predetermined rotation axis, and recording and / or reproducing information on the first optical information recording medium, the center of the first opening and the In the case where information is recorded and / or reproduced on the second optical information recording medium by shifting or rotating the plate member so that the optical axis of the objective optical system coincides with the second optical information recording medium, The optical pickup device according to any one of claims 1 to 14, wherein the plate member is shift-driven or rotationally driven so that the center of the opening coincides with the optical axis of the objective optical system. .   The opening restriction mechanism has a plurality of wing members and an actuator for driving the plurality of wing members, and according to the thickness of the protective layer of the optical information recording medium for recording and / or reproducing information The optical pickup device according to any one of claims 1 to 14, wherein a size of an opening formed by the plurality of wing members is changed by the actuator.   The optical pickup device according to claim 1, wherein the opening restriction mechanism is a liquid crystal shutter.   The aperture limiting mechanism includes two electrode panels divided into a central region including at least one optical axis and a peripheral region surrounding the central region, a power supply unit for supplying a voltage to the electrode panel, Of the first light flux that is sandwiched between the electrode panels and is incident on the objective optical system, the polarization plane of the light flux that passes through the peripheral region is determined based on the amount of voltage applied to the electrode panel by the power supply unit. The optical pickup device according to claim 17, further comprising a liquid crystal panel as a polarization plane rotation mechanism for rotating the fixed amount.   19. The optical pickup device according to claim 18, further comprising a quarter-wave plate in an optical path between the aperture limiting mechanism and the objective optical system.   The optical pickup device according to claim 18 or 19, wherein the central region is a region corresponding to the second numerical aperture NA2.   The optical pickup device includes an outgoing second light source unit capable of generating a second light beam having a second wavelength λ2 (1.5 <λ2 / λ1 <1.7), and a second light beam that detects a reflected light beam of the second light beam. An optical detector, and recording and / or reproducing information with respect to a third optical disc having a protective layer having a thickness t3 (4 <t3 / t1 <8) by the second light flux; 21. The objective optical system according to any one of claims 1 to 20, wherein the objective optical system has a first phase structure for correcting spherical aberration due to a difference between the thickness t1 and the thickness t2. The objective optical system described.   The optical pickup device includes an outgoing third light source unit capable of generating a third light beam having a third wavelength λ3 (1.8 <λ3 / λ1 <2.1), and a third light beam that detects a reflected light beam of the third light beam. An optical detector, and recording and / or reproducing information with respect to a third optical disc having a protective layer having a thickness t4 (10 <t4 / t1 <14) by the third light flux; The objective optical system has a second phase structure for correcting a spherical aberration caused by a difference between the thickness t1 and the thickness t4, according to any one of claims 1 to 21. The objective optical system described. 23. A drive device for an optical disk, wherein the optical pickup device according to any one of claims 1 to 22 is mounted.

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