JP2008103016A - Optical pickup device and optical information recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device and an optical information recording and reproducing device performing recording and/or reproducing of information for an optical disk though it is compact and at low cost. <P>SOLUTION: Since an optical pickup device PU1 can omit a polarization beam splitter and a λ/4 wavelength plate used in conventional technology, the device can shorten largely distance between a semiconductor laser LD and an optical disk DSC, then a compact and low cost optical pickup device can be provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup apparatus and an optical information recording / reproducing apparatus, and more particularly to an optical pickup apparatus and an optical information recording / reproducing apparatus suitable for recording and / or reproducing information on a high-density optical disc.

In an optical pickup device that records and / or reproduces an optical disk, it is common to split the optical path of a light beam reflected on the optical disk with respect to the optical path of the light beam emitted from the light source and enter the light detector. In addition, a combination of a λ / 4 wavelength plate and a polarizing beam splitter is used (see Patent Document 1).
JP 2002-197712 A

  However, the optical pickup device is required to be further reduced in size and cost, and there is a demand for reducing the number of parts as much as possible. In particular, since the polarization beam splitter requires a certain dimension in the optical axis direction, the optical path length tends to be increased by installing it. On the other hand, if the polarizing beam splitter can be omitted from the optical pickup device, a λ / 4 wavelength plate is not required, which can contribute to downsizing and cost reduction of the optical pickup device. However, since the current technology cannot be used as both a light source and a photodetector, in order to omit the λ / 4 wavelength plate and the polarization beam splitter, some technology for branching the optical path is required instead. It becomes.

  The present invention has been made in view of the problems of the prior art, and provides a pickup apparatus and an optical information recording / reproducing apparatus capable of recording and / or reproducing information with respect to an optical disc while being compact and low in cost. For the purpose.

The optical pickup device according to claim 1, a light source for emitting a light beam, an objective optical element for condensing the light beam on an information recording surface of a first optical disk having a protective substrate having a thickness t1, and the first optical device. A light detector that receives the light beam reflected on the information recording surface of the optical disc, and the objective optical element transmits the light beam from the light source to the information recording surface of the first optical disc via the protective substrate. An optical pickup device capable of recording and / or reproducing information by collecting light,
The light source and the photodetector are disposed outside the optical axis of the objective optical element,
The light source and the photodetector are arranged on the same plane orthogonal to the optical axis of the objective optical element so as to be point-symmetric about the optical axis.

  According to the present invention, since the light source and the photodetector are disposed outside the optical axis of the objective optical element, the incident direction of the principal ray of the light beam incident on the information recording surface of the first optical disc; Since the reflection direction of the principal ray of the light beam reflected from the information recording surface is different, the light source and the photodetector can be arranged at different positions in a plane orthogonal to the optical axis, thereby eliminating the polarization beam splitter and the like. Thus, a compact optical pickup device can be provided. The light source and the light detector may be integrated into one package. Note that “outside the optical axis of the objective optical element” means a position where the optical axis of the objective optical element does not pass when the optical axis of the objective optical element is bent by a rising mirror or the like. .

  According to a second aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the light beam reflected by the information recording surface of the first optical disc is the incident surface of the optical element on which the light beam emitted from the light source is first incident. Therefore, it is not necessary to provide a polarizing beam splitter or the like that bends the optical path, and a compact optical pickup device can be provided.

According to a third aspect of the present invention, there is provided the optical pickup device according to the first or second aspect, wherein the objective optical element has a protective substrate having a thickness t2 (t1 <t2) for the light beam from the light source. By focusing on the information recording surface of the optical disc, it is possible to record and / or reproduce information.
A polarization plane switching element that selectively switches the polarization direction of the light beam to the first polarization direction or the second polarization direction, and a first amount of aberration when the light beam in the first polarization direction passes. An aberration correction element that generates a second amount of aberration different from the first amount when the light flux in the second polarization direction passes,
When recording and / or reproducing information with respect to the first optical disc, a light beam emitted from the light source is directed to the first polarization direction after passing through the polarization plane switching element, and further the aberration correction element. Is supposed to pass through
When recording and / or reproducing information with respect to the second optical disk, the light beam emitted from the light source is directed to the second polarization direction after passing through the polarization plane switching element, and further the aberration correction element. It is characterized by passing through.

  In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a blue-violet semiconductor laser, Laser light sources with wavelengths of 400 to 420 nm, such as blue SHG lasers that perform wavelength conversion of infrared semiconductor lasers using harmonics, are being put into practical use. When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used (HD DVD, hereinafter referred to as HD), it is 15 to 15 cm for an optical disk having a diameter of 12 cm. When 20 GB of information can be recorded and the NA of the objective lens is increased to 0.85 (Blu-ray Disc, hereinafter referred to as BD), 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm. Is possible. Hereinafter, in this specification, an optical disk and a magneto-optical disk using a blue-violet laser light source are collectively referred to as a “high density optical disk”.

  Here, although the BD and HD use the same blue-violet laser light, the thickness of the protective substrate is different (BD is about 0.1 mm, HD is about 0.6 mm). When the system is used, for example, if the design is such that the spherical aberration when using BD is optimally suppressed, spherical aberration that cannot be ignored when using HD will occur. Therefore, according to the present invention, for example, when using a BD, a first polarization direction is given to the light beam emitted from the light source by the polarization plane switching element, and a first amount (zero is set by the aberration correction element). On the other hand, when the HD is used, the second polarization direction is given to the light beam emitted from the light source by the polarization plane switching element, and the aberration correction element further applies the first amount. By generating an aberration of a second amount different from (including zero, but if the first amount is zero, the second amount will not be zero), the first aberration amount and the second Spherical aberration due to the difference in the thickness of the protective substrate can be corrected despite the use of the light source of the same wavelength by utilizing the difference from the aberration amount, and high light utilization efficiency for any optical disk Can record and / or reproduce information appropriately. That. In addition, even when the numerical aperture NA is different, for example, only the light beam in the second polarization direction can be flared with the light beam having the required numerical aperture or more through the aberration correction element, so that a diaphragm effect can be provided. When such an aberration correction element that depends on the polarization direction is used in an optical pickup device that separates the reflected light from the optical disk by a polarization beam splitter and a λ / 4 wavelength plate as in the prior art and enters the photodetector, that is, polarization If a λ / 4 wavelength plate is arranged behind the dependent aberration correction element, the polarization direction is rotated by 90 degrees when the reflected light from the optical disk passes through the wavelength plate again, and the light incident on the photodetector Therefore, an excessive first aberration or second aberration occurs.

Examples of the polarization plane switching element include the following.
(1) TN (twisted nematic) type liquid crystal When a light beam polarized in a direction parallel to the paper surface (first polarization direction) is incident on the TN type liquid crystal, no voltage is applied to the liquid crystal. As shown in (a), the incident light flux is emitted with the polarization direction changed by 90 degrees by the TN liquid crystal and the polarization direction changed to the direction perpendicular to the paper surface (second polarization direction). On the other hand, when a voltage is applied to the liquid crystal, as shown in FIG. 1B, the incident light beam is not changed in polarization direction by the TN type liquid crystal and is parallel to the paper surface (first polarization direction). ) To pass through.
(2) λ / 2 plate When using the BD, the polarization direction can be changed by 90 degrees by rotating 45 degrees around the optical axis from the state of using the HD.

  As an example of the aberration correction element, there is a “polarization diffraction element” that can selectively diffract the light beam depending on the polarization direction of the light beam and vary the amount of aberration to be given. When the second optical disk is used, the light beam passing outside the predetermined numerical aperture is flare, and when the first optical disk is used, the light beam passing outside the predetermined numerical aperture is also on the information recording surface. It is preferable to provide aberration so that light can be condensed. In addition, it is preferable that the aberration correction element corrects spherical aberration that occurs based on a difference in thickness between the protective substrates of the first optical disc and the second optical disc. For example, when using the first optical disk, the light beam emitted from the aberration correction element enters the objective lens as parallel light, and when using the second optical disk, the light beam emitted from the aberration correction element is divergent. You may make it inject into an objective lens as light.

  Specific examples of the polarization diffraction element include a polarization hologram element in which an isotropic medium and a birefringence medium are combined in a diffractive manner. The polarization hologram element has a partial cross-sectional shape in the direction perpendicular to the optical axis shown in FIG. In FIG. 2, the polarization hologram element includes an isotropic medium H2, a birefringent medium H3, and a pair of glass plates H1 and H1 arranged so as to sandwich them. As shown in FIG. 2, the birefringent medium H3 has a diffractive structure in which a cross section in the traveling direction of incident light is formed in a sawtooth shape, and a large number of concentric circles are formed from the center to the circumference. Yes. The specific shape is not limited to that shown in the figure. Other sawtooth shapes may be used, and the slope of the sawtooth may be stepped. The isotropic medium H2 has a complementary shape to the birefringent medium H3, and is in close contact with the surface of the birefringent medium formed in a sawtooth shape. The isotropic medium H2 is a substance having a refractive index n with respect to incident light, and the birefringent medium H3 has a refractive index n when the polarization plane of the incident light is in a predetermined direction, and the polarization plane of the incident light. When orthogonal to a predetermined direction, it has a characteristic of a refractive index n ′. That is, when the light beam that has passed through the polarization plane switching element enters the polarization hologram element in a predetermined polarization state, the polarization hologram bare hand generates diffracted light that maximizes the diffraction efficiency at a predetermined diffraction order other than zero. It has become.

  The light beam emitted from the light source passes through a TN type liquid crystal, which is a polarization plane switching element, for example, so that the polarization plane is 90 degrees different between when recording and reproducing BD and when recording and reproducing HD. If the polarization plane of the light beam when recording / reproducing BD is a predetermined direction, the divergence angle is changed because it passes through the polarization hologram element and is the same as passing through a homogeneous parallel plane medium. However, since it is incident on the objective lens as it is, appropriate information can be recorded and / or reproduced with respect to a BD having a protective layer of 0.1 mm.

  On the other hand, when recording / reproducing HD, the light beam passes through a medium having a refractive index n and n ′ in the polarization hologram element, so that the diffraction effect of the positive lens is produced in the diffractive structure of the boundary surface, and the divergence angle or Since the spherical aberration is changed and incident on the objective lens, even when the same objective lens is used, the spherical aberration is corrected and appropriate information is recorded and / or reproduced for the HD having a protective layer of 0.6 mm. Can be done.

  Further, when HD is used, the polarizing hologram element can have a diaphragm function by flaring so that the light beam outside the effective diameter does not contribute to spot imaging by the selective diffraction action of the polarization hologram. At this time, it is preferable that the polarization hologram element generates diffracted light that is diffracted at a diffraction efficiency of 85% or more for at least one incident light with respect to incident light having a predetermined wavelength whose polarization planes are orthogonal to each other.

  A preferable range of the light source wavelength is 350 to 440 nm. A preferred example of the first optical disc is BD, and a preferred example of the second optical disc is HD. Therefore, a preferable range of the thickness t1 in the protective substrate of the first optical disc is 0.0750 ≦ t1 (mm) ≦ 0.1125, and a preferable range of the thickness t2 in the protective substrate of the second optical disc is 0.5 ≦ t2 (mm) ≦ 0.7.

  According to a fourth aspect of the present invention, there is provided the optical pickup device according to any one of the first to third aspects, wherein a central ray of the light beam emitted from the light source and irradiated on the optical disc is a straight line in the radial direction of the optical disc and the optical disc. The light source and the photodetector are arranged so as to be included in a plane including the normal line of the optical disc. In the optical pickup device, when the disc tilt has a larger influence on the reading accuracy than the tracking displacement, it is preferable to arrange the light source LD and the photodetector PD in the positional relationship shown by the white circles in FIG.

  According to a fifth aspect of the present invention, in the optical pickup device according to the first to third aspects, a central ray of the light beam emitted from the light source and irradiated onto the optical disc is a straight line perpendicular to the radial direction of the optical disc. The light source and the photodetector are arranged so as to be included in a plane including the normal line of the optical disc. In the optical pickup device, when the tracking displacement has a larger influence on the reading accuracy than the disc tilt, it is preferable to arrange the light source LD and the photodetector PD in the positional relationship shown by the black circles in FIG.

  An optical information recording / reproducing apparatus according to a sixth aspect uses the optical pickup apparatus according to any one of the first to fifth aspects.

  According to the present invention, it is possible to provide a pickup apparatus and an optical information recording / reproducing apparatus capable of recording and / or reproducing information with respect to an optical disc while being compact and low in cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a diagram schematically showing a configuration of the optical pickup device PU1 of the present embodiment that can appropriately record / reproduce information with respect to the optical disc DSC (which may be any of BD, HD, DVD, and CD). . Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. In the present embodiment, the semiconductor laser LD and the photodetector PD mounted on a plane orthogonal to the optical axis of the objective lens are disposed outside the optical axis of the objective lens OBJ, and the center position thereof is light. Equidistant from the axis. The semiconductor laser LD and the photodetector PD are arranged symmetrically with respect to each other about the optical axis of the objective lens OBJ.

  A light beam emitted from a semiconductor laser LD serving as a light source is converted into a parallel light beam by a collimator CL, which is an optical element that is incident first, and then passes through a stop (not shown). The light enters the optical disc DSC at a tilted predetermined incident angle and is condensed on the information recording surface via the protective substrate, thereby forming a condensing spot.

  The light beam modulated by the information pits on the information recording surface and reflected at a predetermined emission angle inclined with respect to the optical axis of the objective lens OBJ is transmitted again through the objective lens OBJ, a diaphragm (not shown), and a collimator CL, and the semiconductor laser. Since the light beam of the LD is emitted from the collimator incident surface on which it is incident toward the photodetector PD and further incident on the light receiving surface of the photodetector PD, the output signal is used to read the information recorded on the optical disk DSC. A signal is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, an actuator (not shown) moves the objective lens OBJ so as to form an image of the light beam from the semiconductor laser LD on the information recording surface of the optical disk DSC.

  According to the present embodiment, the optical pickup device PU1 can omit the polarizing beam splitter and the λ / 4 wavelength plate used in the prior art, so that the distance between the semiconductor laser LD and the optical disc DSC can be greatly reduced. A compact and low-cost optical pickup device can be provided. Note that the collimator may be omitted, the light beam from the semiconductor laser LD may be directly incident on the objective lens OBJ, and the reflected light from the information recording surface emitted from the objective lens OBJ may be directly incident on the photodetector PD.

  FIG. 5 is a diagram schematically showing a configuration of the optical pickup device PU2 of the present embodiment that can appropriately record / reproduce information with respect to the optical discs DSC1, DSC2 (here, BD, HD). Such an optical pickup device PU2 can be mounted on an optical information recording / reproducing device. Also in the present embodiment, the semiconductor laser LD and the photodetector PD mounted on a plane orthogonal to the optical axis of the objective lens are arranged outside the optical axis of the objective lens OBJ, and the center position thereof is It is equidistant from the optical axis. The semiconductor laser LD and the photodetector PD are arranged symmetrically with respect to each other about the optical axis of the objective lens OBJ. In the present embodiment, a TN liquid crystal TN as a polarization plane switching element and a polarization diffraction element HOE as an aberration correction element are arranged between the collimator CL and the objective lens OBJ. Since the configurations of the TN liquid crystal TN and the polarization diffraction element HOE have been described above, description thereof will be omitted.

  When recording / reproducing information with respect to the first optical disc DSC1, a predetermined voltage is applied to the TN type liquid crystal TN. In FIG. 5A, a light beam emitted from a semiconductor laser LD (here, wavelength λ1 = 405 nm) has a first polarization direction and is converted into a parallel light beam by a collimator CL, and then a TN type liquid crystal. Although it is incident on the TN, the polarization direction does not change as described with reference to FIG. Therefore, the light beam emitted from the TN liquid crystal TN with the first polarization direction functions as a parallel plate (the first aberration amount = 0) with the polarization diffraction element HOE, and therefore the numerical aperture NA is 0. The light is incident on the 85 objective lens OBJ and is incident on the information recording surface through a protective layer (thickness t1 = 0.1 mm) of the first optical disc DSC1 at a predetermined incident angle inclined with respect to the optical axis. The light is condensed and a condensing spot is formed here.

  Then, the light beam modulated by the information pits on the information recording surface and reflected at a predetermined emission angle inclined with respect to the optical axis of the objective lens OBJ again passes through the objective lens OBJ, the polarization diffraction element HOE, the TN liquid crystal TN, and the collimator CL. Since it is transmitted and emitted from the collimator incident surface on which the light beam of the semiconductor laser LD is incident toward the photodetector PD and further incident on the light receiving surface of the photodetector PD, the output signal is used to enter the first optical disc DSC1. A read signal of the recorded information is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, an actuator (not shown) moves the objective lens OBJ so that the light beam from the semiconductor laser LD is imaged on the information recording surface of the first optical disk DSC1.

  Next, when recording / reproducing information with respect to the second optical disk DSC2, a predetermined voltage is not applied to the TN liquid crystal TN. In FIG. 5B, the light beam emitted from the semiconductor laser LD has the first polarization direction, and is converted into a parallel light beam by the collimator CL and then enters the TN liquid crystal TN. As described in a), the polarization direction is a second polarization direction that differs by 90 degrees. Therefore, the light beam that has exited the TN liquid crystal TN in the state of the second polarization direction and entered the polarization diffraction element HOE has an effective diameter because the polarization diffraction element HOE exhibits a diffraction effect (second aberration amount ≠ 0). The light beam that passes outside (here, the portion larger than NA 0.65) becomes flare light by the diffraction action, and the light beam within the effective diameter (here, the portion of NA 0.65 or less) becomes the divergent light by the diffraction action. A divergent light beam enters the objective lens OBJ, and the information recording surface of the second optical disc DSC2 through a protective layer (thickness t2 = 0.6 mm) at a predetermined incident angle inclined with respect to the optical axis. And a condensed spot is formed here.

  Then, the light beam modulated by the information pits on the information recording surface and reflected at a predetermined emission angle inclined with respect to the optical axis of the objective lens OBJ again passes through the objective lens OBJ, the polarization diffraction element HOE, the TN liquid crystal TN, and the collimator CL. Since it is transmitted and emitted from the collimator incident surface on which the light beam of the semiconductor laser LD is incident toward the photodetector PD, and further incident on the light receiving surface of the photodetector PD, the output signal is used to enter the second optical disc DSC2. A read signal of the recorded information is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, an actuator (not shown) moves the objective lens OBJ so that the light beam from the semiconductor laser LD is imaged on the information recording surface of the second optical disc DSC2.

  According to the present embodiment, the TN type liquid crystal TN is simply turned on and off. For example, even when the same bluish-violet laser beam is used, information is appropriately applied to BD and HD having different protective substrate thicknesses and numerical apertures. Can be recorded / reproduced.

  In the above embodiment, the direction of the straight line connecting the laser light source LD and the photodetector PD may be matched or substantially coincides with the diameter direction of the optical disk to be used, or the diameter direction of the optical disk to be used. And may be orthogonal or substantially orthogonal.

It is a schematic sectional drawing which shows the structure of TN (twisted nematic) type liquid crystal. It is a schematic sectional drawing which shows the structure of a polarization hologram element. It is a figure which shows the positional relationship of laser light source LD and photodetector PD with respect to the optical disk. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment which can record / reproduce information appropriately with respect to the optical disk DSC. 1 is a diagram schematically showing a configuration of an optical pickup device PU2 of the present embodiment that can appropriately record / reproduce information to / from optical discs DSC1, DSC2. FIG.

Explanation of symbols

CL collimator DSC optical disc DSC1 first optical disc DSC2 second optical disc H1 glass plate H2 isotropic medium H3 birefringent medium HOE polarization diffraction element LD laser light source LD semiconductor laser OBJ objective lens PD photodetector PU1 optical pickup device PU2 optical pickup Device TN TN type liquid crystal

Claims (6)

A light source that emits a light beam, an objective optical element that focuses the light beam on an information recording surface of a first optical disk having a protective substrate having a thickness t1, and a light beam reflected on the information recording surface of the first optical disk And the objective optical element focuses the light beam from the light source on the information recording surface of the first optical disc through the protective substrate, thereby recording and / or recording information. Or an optical pickup device capable of reproducing,
The light source and the photodetector are disposed outside the optical axis of the objective optical element,
The optical pickup device, wherein the light source and the photodetector are arranged so as to be point-symmetric about the optical axis on the same plane orthogonal to the optical axis of the objective optical element.   2. The light beam reflected by the information recording surface of the first optical disc is emitted toward the photodetector from the incident surface of the optical element on which the light beam emitted from the light source is first incident. The optical pickup device described in 1. The objective optical element records and / or reproduces information by condensing a light beam from the light source on an information recording surface of a second optical disc having a protective substrate having a thickness t2 (t1 <t2). Is possible,
A polarization plane switching element that selectively switches a polarization direction of the light beam to a first polarization direction or a second polarization direction; and a first amount of aberration is generated when the light beam of the first polarization direction passes. An aberration correction element that generates a second amount of aberration different from the first amount when the light flux in the second polarization direction passes,
When recording and / or reproducing information with respect to the first optical disc, a light beam emitted from the light source is directed to the first polarization direction after passing through the polarization plane switching element, and further the aberration correction element. Is supposed to pass through
When recording and / or reproducing information with respect to the second optical disk, the light beam emitted from the light source is directed to the second polarization direction after passing through the polarization plane switching element, and further the aberration correction element. The optical pickup device according to claim 1, wherein the optical pickup device passes through the optical pickup.   The light source and the photodetector are arranged so that a central ray of the light beam emitted from the light source and irradiated onto the optical disc is included in a plane including a straight line in the radial direction of the optical disc and a normal line of the optical disc. 4. The optical pickup device according to claim 1, wherein the optical pickup device is disposed.   The light source and the light detection are such that a central ray of the light beam emitted from the light source and irradiated on the optical disc is included in a plane including a straight line orthogonal to the radial direction of the optical disc and a normal line of the optical disc. 4. An optical pickup device according to claim 1, wherein a device is disposed.   6. An optical information recording / reproducing apparatus using the optical pickup device according to claim 1.

Images