JP2006277894A - Optical pickup apparatus and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately acquire a desired signal from a plurality of kinds of information recording mediums corresponding to a luminous flux of the same wavelength and having appropriate numerical apertures different from each other. <P>SOLUTION: An aperture switching optical system 57 regulating a beam diameter of a luminous flux made incident in an objective lens according to a numerical aperture suitable for an optical disk 15 and emitting a returned luminous flux via the objective lens while maintaining the beam diameter is fixedly disposed on an optical path between a light source LD and the objective lens 60. Thereby, an optical spot suitable for the optical disk is formed on a recording surface and a needed light receiving quantity at a photo detector PD can be secured. The desired signal can be accurately acquired regardless of the kind of the optical disk. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup device and an optical disc device, and more particularly, an optical pickup device used for at least reproducing data from recording, reproducing and erasing data on an optical disc and an optical disc including the optical pickup device. Relates to the device.

  In recent years, with the advancement of digital technology and the improvement of data compression technology, DVD (digital versatile disc) and the like are used as media for recording information (hereinafter also referred to as “content”) such as music, movies, photos, and computer software. Optical discs have attracted attention, and along with the reduction in price, optical disc apparatuses that use optical discs as information recording media have become widespread.

  In an optical disc apparatus, information is recorded by forming a micro-spot of laser light on a recording surface on which spiral or concentric tracks of an optical disc are formed, and information is reproduced based on reflected light from the recording surface. Is going. This optical disc apparatus is provided with an optical pickup device for irradiating the recording surface of the optical disc with laser light and receiving reflected light from the recording surface.

  Incidentally, the amount of content information tends to increase year by year, and further increase in the recording capacity of the optical disc is expected. Therefore, HD-DVD (High Definition DVD, hereinafter abbreviated as “HD”) and Blu-ray (hereinafter abbreviated as “BD”) standards have been proposed. HD has a disk substrate thickness of 0.6 mm, and an optical disk device compatible with HD uses a light source having a wavelength of 405 nm to form a condensing spot with NA (numerical aperture) of 0.65 by an objective lens. Record, play and erase information. On the other hand, a BD has a disc substrate thickness of 0.1 mm, and an optical disc apparatus corresponding to the BD uses a light source having a wavelength of 405 nm to form a condensed spot having an NA of 0.85 by an objective lens. Record, play and erase. That is, both HD and BD correspond to light having a wavelength of 405 nm, but NAs are different from each other. Therefore, in an optical disc apparatus that can handle both HD and BD, it is necessary to change the NA according to the type of information recording medium.

  Various devices have been proposed for changing the NA by limiting the aperture for one light beam (see, for example, Patent Document 1 and Patent Document 2). However, in the optical head device disclosed in Patent Document 1, aperture restriction is performed using the difference in the wavelength of the light source, so in this configuration, BD and HD that perform recording and reproduction using the same wavelength are used. On the other hand, it is difficult to change the NA. Further, in the information recording / reproducing apparatus disclosed in Patent Document 2, since the opening of the return path changes with respect to the opening of the outbound path, for example, a light beam that is not aperture-limited in the outbound path is aperture-limited in the return path. The S / N ratio of the output signal of the pickup device is significantly reduced.

Japanese Patent No. 0271257 Japanese Patent Laid-Open No. 5-120720

  The present invention has been made under such circumstances, and a first object of the present invention is to accurately obtain a desired signal from a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures. An object of the present invention is to provide an optical pickup device that can be used.

  A second object of the present invention is to provide an optical disc apparatus capable of accurately accessing a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures.

  According to the first aspect of the present invention, there is provided an optical pickup used for performing at least reproduction of information recording, reproduction, and erasure on a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures. An apparatus comprising: a light source; an objective lens that collects a light beam emitted from the light source on a recording surface of an information recording medium; and a fixed arrangement on an optical path between the light source and the objective lens. An aperture adjustment optical system that defines a beam diameter of a light beam incident on the objective lens according to an appropriate numerical aperture for a recording medium, and that outputs a return light beam through the objective lens while maintaining the beam diameter; An optical pickup device comprising: an optical system including: a photodetector that receives a return light beam through the aperture adjustment optical system at a predetermined light receiving position.

  According to this, the beam diameter of the light beam emitted from the light source is regulated by the aperture adjustment optical system according to the numerical aperture appropriate for the information recording medium, and is condensed on the recording surface of the information recording medium by the objective lens. The returning light flux through the objective lens is transmitted through the aperture adjustment optical system while the beam diameter is maintained as it is, and is received by the photodetector. Therefore, an appropriate light spot is formed on the information recording medium on the recording surface, and a necessary amount of light received by the photodetector can be secured. As a result, it is possible to accurately obtain a desired signal from a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures.

  In this case, when the linearly polarized light is emitted from the light source as in the optical pickup device according to claim 2, the aperture adjustment optical system sets the polarization direction of the linearly polarized light emitted from the light source from 0 degree. A variable rotation optical element that is rotated within an angle range of 90 degrees or less and a variable rotation optical element that is disposed on the side opposite to the light source side of the variable rotation optical element and is incident on a region on one side of a dividing line orthogonal to the optical axis A first rotating optical element that rotates the polarization direction of the linearly polarized light by +45 degrees and rotates the polarization direction of the linearly polarized light that has entered the region on the other side of the dividing line by -45 degrees; One of dividing lines orthogonal to the optical axis among a circular first region that is disposed on the opposite side of the variable rotation optical element side and transmits an incident light beam and a donut-shaped region that is in contact with the outer periphery of the first region A second area on the side and Among the doughnut-shaped regions, there are three regions consisting of a third region on the other side of the dividing line, and when the polarization direction of incident linearly polarized light is rotated by +45 degrees, the second region A polarizing optical element that reflects, absorbs or diffracts and reflects, absorbs or diffracts in the three regions when the polarization direction of the incident linearly polarized light is rotated by −45 degrees; and the first rotation of the polarizing optical element; It is arranged on the side opposite to the optical element side, and the polarization direction of the linearly polarized light incident on the region on one side of the dividing line orthogonal to the optical axis is rotated by −45 degrees, and the region on the other side of the dividing line is rotated. A second rotating optical element that rotates the polarization direction of the incident linearly polarized light by +45 degrees.

  In this case, as in the optical pickup device according to claim 3, the second region of the polarizing optical element is formed of a polarizer that quenches linearly polarized light whose polarization direction is rotated by +45 degrees, The third region may be formed of a polarizer that extinguishes linearly polarized light whose polarization direction is rotated by −45 degrees.

  In this case, as in the optical pickup device according to the fourth aspect, each of the polarizers can be inclined with respect to a direction orthogonal to the optical axis.

  3. The optical pickup device according to claim 2, wherein the second region of the polarizing optical element diffracts linearly polarized light whose polarization direction is rotated by +45 degrees as in the optical pickup device according to claim 5. The third region may be formed of a polarization diffraction element that diffracts linearly polarized light whose polarization direction is rotated by −45 degrees.

  In each of the optical pickup devices according to claims 2 to 5, as in the optical pickup device according to claim 6, the plurality of information recording media includes a first information recording medium and an incident surface to a recording surface. And a second information recording medium having a longer distance than the first information recording medium, and a polarization direction of linearly polarized light from the variable rotation optical element with respect to the second information recording medium is the first information recording medium. The polarization direction of the linearly polarized light from the variable rotation optical element with respect to the medium may be a direction rotated by +90 degrees.

  In each of the optical pickup devices according to the second to sixth aspects, as in the optical pickup device according to the seventh aspect, each dividing line of the aperture adjustment optical system extends in a direction corresponding to the tracking direction. It can be.

  In each of the optical pickup devices according to claims 2 to 7, as in the optical pickup device according to claim 8, the first rotating optical element, the polarizing optical element, and the second rotating optical element, Can be integrated.

  In each of the optical pickup devices according to claims 2 to 7, as in the optical pickup device according to claim 9, the optical system further includes a quarter wavelength plate, the first rotating optical element, The polarizing optical element, the second rotating optical element, and the quarter-wave plate can be integrated.

  In this case, as in the optical pickup device according to claim 10, the first rotating optical element, the polarizing optical element, the second rotating optical element, the quarter wavelength plate, and the objective. The lens can be stored in the same housing.

  In each optical pickup device according to any one of claims 1 to 10, as in the optical pickup device according to claim 11, the optical pickup device is disposed between the light source and the aperture adjustment optical system, and is configured to pass through the aperture adjustment optical system. A polarization branching optical element that branches the return light beam to the light receiving position can be further provided.

  According to a twelfth aspect of the present invention, there is provided an optical disc apparatus capable of reproducing at least one of information recording, reproduction and erasure on a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures. And reproducing the information recorded on the information recording medium by using the optical pickup device according to any one of claims 1 to 11; and an output signal of a photodetector constituting the optical pickup device. An optical disk device comprising: a processing device for performing;

  According to this, a desired signal can be accurately acquired from a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures. Since the optical pickup device is provided, it is possible to accurately access a plurality of types of information recording media corresponding to light beams having the same wavelength and having different appropriate numerical apertures.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of an optical disc apparatus 20 according to an embodiment of the present invention.

  An optical disk device 20 shown in FIG. 1 includes a spindle motor 22 for rotating the optical disk 15, an optical pickup device 23, a seek motor 21 for driving the optical pickup device 23 in the sledge direction, a laser control circuit 24, An encoder 25, a motor control circuit 26, a PU drive control circuit 27, a reproduction signal processing circuit 28, a buffer RAM 34, a buffer manager 37, an interface 38, a flash memory 39, a CPU 40, a RAM 41, and the like are provided. Note that the arrows in FIG. 1 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block. In addition, the optical disc apparatus 20 can handle an information recording medium that complies with the HD and BD standards as an example. Therefore, an information recording medium compliant with HD and BD standards is used for the optical disc 15.

  As described above, the distance from the incident surface of the disc to the recording surface, the so-called substrate thickness, is 0.6 mm for HD (see FIG. 2A) and 0.1 mm for BD (FIG. 2B). reference). An appropriate NA (numerical aperture) is 0.65 for HD and 0.85 for BD.

  The optical pickup device 23 is a device for irradiating the recording surface of the optical disc 15 with laser light and receiving reflected light from the recording surface. As shown in FIG. 3 as an example, the optical pickup device 23 includes a light source LD, a coupling lens 52, a polarization beam splitter 54 as a polarization branching optical element, a quarter wavelength plate 55, a beam expander 56, an aperture switching. An optical system 57, a detection lens 58, an objective lens 60, a light receiver PD as a light detector, a drive system (focusing actuator 61 and tracking actuator (not shown)), and the like are provided.

  The light source LD is a semiconductor laser that emits laser light having a wavelength of about 405 nm. Note that the maximum intensity emission direction of the light beam emitted from the light source LD is defined as the + Z direction. Further, as an example, it is assumed that a light beam of linearly polarized light (here, P-polarized light) is emitted from the light source LD. Furthermore, in this embodiment, for the sake of convenience, the angle of the polarization direction (polarization orientation) of linearly polarized light is based on the polarization direction of P-polarized light. Therefore, linearly polarized light having a polarization direction of +90 degrees means S-polarized light.

  The coupling lens 52 is disposed on the + Z side of the light source LD, and the light beam emitted from the light source LD is set as substantially parallel light.

  The polarization beam splitter 54 is disposed on the + Z side of the coupling lens 52, and branches the light beam (return light beam) reflected by the optical disc 15 in the + Y direction. The polarization beam splitter 54 has different reflectance depending on the polarization state of the incident light beam. Here, as an example, the polarization beam splitter 54 is set so that the reflectance with respect to P-polarized light is small and the reflectance with respect to S-polarized light is large. That is, most of the light beam emitted from the light source LD can pass through the polarization beam splitter 54.

  The aperture switching optical system 57 changes the beam diameter of the light beam incident on the objective lens 60 in accordance with an appropriate numerical aperture on the optical disc 15 and maintains the return light beam through the objective lens 60 at the beam diameter of the forward path. Exit. Here, the aperture switching optical system 57 includes a variable optical rotator 57a, two optical rotators (first optical rotator 57b and second optical rotator 57d), a polarization aperture limiting element 57c, and the like.

  The variable optical rotator 57a rotates the polarization direction of the linearly polarized light emitted from the light source LD within an angle range of greater than 0 degrees and less than 90 degrees. As this variable optical rotator 57a, in this embodiment, as shown in FIGS. 4A and 4B as an example, a twisted nematic liquid crystal having positive dielectric anisotropy is interposed between two glass substrates. A so-called liquid crystal element hermetically sealed is used. A transparent electrode made of indium tin oxide (ITO) and an alignment film made of polyimide are formed on each glass substrate, and the alignment film is subjected to an alignment process by rubbing. Here, the thickness of the liquid crystal layer is about 5 mm. Further, the orientation direction of the major axis of the liquid crystal molecules, that is, the rubbing direction, crosses 90 ° between the glass substrate on the incident side and the glass substrate on the emission side, and the liquid crystal layer is continuously twisted and oriented by 90 degrees. An AC voltage is applied to the variable optical rotator 57a through a transparent electrode.

  The variable optical rotator 57a is on the + Z side of the polarization beam splitter 54, and makes the linearly polarized light (P-polarized light in this case) from the light source LD orthogonal to the orientation direction of the liquid crystal molecules on the glass substrate surface adjacent to the deflection surface. Are arranged as follows. Therefore, in a state where an AC voltage sufficiently lower than the threshold is applied (hereinafter also referred to as “off state”), the variable optical rotator 57a emits light by rotating the polarization direction of the incident light beam by 90 ° (FIG. 4A). )reference). On the other hand, in a state where an AC voltage sufficiently higher than the threshold is applied (hereinafter also referred to as “on state”), the twisted orientation of the liquid crystal molecules is eliminated, so that the variable rotator 57a changes the polarization direction of the incident light beam. The light is emitted as it is (see FIG. 4B).

  The variable optical rotator 57a is attached to a fixed portion in the optical pickup device 23 because it is not necessary to follow the axis deviation and inclination of the objective lens 60. The variable optical rotator 57a may simply have a structure in which the half-wave plate is simply rotated in a plane perpendicular to the traveling direction of the light beam.

  The beam expander 56 is disposed on the + Z side of the variable optical rotator 57a, and drives at least one of a concave lens 56a as a negative lens, a convex lens 56b as a positive lens, and the concave lens 56a and the convex lens 56b, and an interval between the two lenses. (Hereinafter also referred to as “lens interval”). When the lens interval changes, the divergence angle of the light beam emitted from the beam expander 56 changes, and the magnitude of the wavefront aberration changes. The lens interval is controlled by a lens interval control signal from the CPU 40.

  The first optical rotator 57 b is disposed on the + Z side of the beam expander 56. As shown in FIG. 5 as an example, the first optical rotator 57b is divided into two regions (b1, b2) by a dividing line b3 extending in the X-axis direction. Here, the −Y side of the dividing line b3 is defined as a region b1, and the + Y side of the dividing line b3 is defined as a region b2. Region b1 rotates the incident light beam by +45 degrees, and region b2 rotates the incident light beam by -45 degrees. When the objective lens 60 is shifted in the tracking direction, the return light beam incident on the first optical rotator 57b is shifted in a direction corresponding to the tracking direction (here, the X-axis direction). That is, the dividing line b3 extends in a direction corresponding to the tracking direction.

  Thus, an optical rotator that rotates the polarization direction by +45 degrees or −45 degrees has, for example, a main axis (fast axis or slow axis) of 22.5 with respect to linearly polarized light incident on a half-wave plate. This can be realized by rotating the angle (or -22.5 degrees). The half-wave plate can be made of a film having an anisotropy in refractive index, a sub-wavelength grating composed of a linear grating shorter than the wavelength of the incident light beam, and a photonic crystal. Further, it can be realized using a twisted nematic liquid crystal element.

  The polarization aperture limiting element 57c is disposed on the + Z side of the first optical rotator 57b. As shown in FIG. 6 as an example, the polarization aperture limiting element 57c has a circular complete transmission region c1 (first region) in the center, and a donut-shaped polarization region adjacent to the outer periphery of the complete transmission region c1. There is. This polarizing region is divided into two regions (c2, c3) by a dividing line c4 extending in the X-axis direction. Here, the −Y side of the dividing line c4 is defined as a region c2 (second region), and the + Y side of the dividing line c4 is defined as a region c3 (third region). The region c2 is formed of a polarizer that extinguishes linearly polarized light with a polarization direction of +45 degrees, and the region c3 is formed of a polarizer that extinguishes linearly polarized light with a polarization direction of −45 degrees. When the objective lens 60 is shifted in the tracking direction, the return light beam incident on the polarization aperture limiting element 57c is shifted in a direction corresponding to the tracking direction (here, the X-axis direction). That is, the dividing line c4 extends in a direction corresponding to the tracking direction.

  The polarizer can be produced by dying a polyvinyl alcohol (PVA) film with iodine or a dye, and then stretching in a uniaxial direction. The polarizer may be made of a sub-wavelength grating composed of a linear grating with a pitch shorter than the wavelength of the incident light beam, and a photonic crystal. In the present embodiment, for the sake of convenience, the case where the polarizing region is transmitted is referred to as “no aperture restriction”, and the case where the light is not transmitted is referred to as “aperture restriction”.

  The second optical rotator 57d is disposed on the + Z side of the polarization aperture limiting element 57c. As illustrated in FIG. 7 as an example, the second optical rotator 57d is divided into two regions (d1, d2) by a dividing line d3 extending in the X-axis direction. Here, the −Y side of the dividing line d3 is defined as a region d1, and the + Y side of the dividing line d3 is defined as a region d2. Region d1 rotates the incident light beam by −45 degrees, and region d2 rotates the incident light beam by +45 degrees. When the objective lens 60 is shifted in the tracking direction, the return light beam incident on the second optical rotator 57d is shifted in a direction corresponding to the tracking direction (here, the X-axis direction). That is, the dividing line d3 extends in a direction corresponding to the tracking direction.

  The quarter-wave plate 55 is disposed on the + Z side of the second optical rotator 57d. The quarter wavelength plate 55 gives an optical phase difference of a quarter wavelength to the incident light flux. The objective lens 60 is disposed on the + Z side of the quarter-wave plate 55, and the light beam that has passed through the quarter-wave plate 55 is condensed on the recording surface.

  The detection lens 58 is arranged on the + Y side of the polarizing beam splitter 54, and the return light beam branched in the + Y direction by the polarizing beam splitter 54 is condensed on the light receiving surface of the light receiving device PD. The light receiver PD includes a plurality of light receiving elements (or light receiving regions) for generating signals (photoelectric conversion signals) used for detecting an RF signal, a wobble signal, a servo signal, and the like in the reproduction signal processing circuit 28. It is configured to include.

  The focusing actuator 61 is an actuator for minutely driving the objective lens 60 in the focus direction that is the optical axis direction of the objective lens 60. Here, for convenience, the optimum position of the objective lens 60 in the focus direction when the optical disc 15 is HD is referred to as “first lens position”, and the optimum position of the objective lens 60 in the focus direction when the optical disc 15 is BD is “first”. 2 lens positions ”. When the objective lens 60 is at the second lens position, the distance between the objective lens 60 and the optical disk 15 is longer than when the objective lens 60 is at the first lens position (see FIGS. 8A and 8B). .

  The tracking actuator (not shown) is an actuator for slightly driving the objective lens 60 in the tracking direction.

  The operation of the optical pickup device 23 configured as described above will be described with reference to FIGS. Here, for convenience, with respect to the optical axis direction, the optical path between the polarization beam splitter 54 and the variable optical rotator 57a is the section A, the optical path between the variable optical rotator 57a and the first optical rotator 57b is the section B, and the first optical rotation. The optical path between the polarizer 57b and the polarization aperture limiting element 57c is the section C, the optical path between the polarization aperture limiting element 57c and the second optical rotator 57d is the section D, the second optical rotator 57d and the quarter wavelength plate 55 An optical path between the quarter wavelength plate 55 and the objective lens 60 is defined as a section F. Further, the −Y side of the optical axis is also referred to as region I, and the + Y side is also referred to as region II. 10 indicates the angle of the polarization direction of linearly polarized light (hereinafter, abbreviated as “angle of linearly polarized light” for convenience). “R” indicates clockwise circularly polarized light, and “L” indicates counterclockwise circularly polarized light.

<< When optical disc 15 is HD >>
In this case, since the appropriate NA is 0.65, aperture restriction is performed. Here, the variable optical rotator 57a is already turned on by the CPU 40, and the lens interval of the beam expander 56 is controlled so that the wavefront aberration on the recording surface (here, HD) of the optical disc 15 is minimized. And The objective lens 60 is assumed to be positioned at the first lens position by a focusing actuator 61.

  The light beam of linearly polarized light (here, P-polarized light) emitted from the light source LD becomes substantially parallel light by the coupling lens 52 and enters the polarization beam splitter 54. Most of this light beam passes through the polarization beam splitter 54 as it is and enters the variable optical rotator 57a. Here, since the variable rotator 57a is in the on state, the light beam incident on the variable rotator 57a is transmitted as it is. That is, in the forward section B, the angle of the linearly polarized light is 0 degree in both the region I and the region II.

  The light beam that has passed through the variable optical rotator 57 a enters the first optical rotator 57 b via the beam expander 56. In the first optical rotator 57b, the light beam incident on the region b1 rotates +45 degrees, and the light beam incident on the region b2 rotates -45 degrees. As a result, in the region I in the forward section C, the angle of linearly polarized light is +45 degrees, and in the region II, the angle of linearly polarized light is −45 degrees.

  The light beam from the first optical rotator 57b is incident on the polarization aperture limiting element 57c. In the polarization aperture limiting element 57c, the light beam incident on the region c2 is extinguished and the light beam incident on the region c3 is extinguished. Accordingly, only the light beam incident on the region c1 is transmitted through the polarization aperture limiting element 57c. That is, the opening is limited here. In the region I of the forward section D, the angle of linearly polarized light remains +45 degrees, and in the region II, the angle of linearly polarized light remains −45 degrees.

  The light beam from the polarization aperture limiting element 57c enters the second optical rotator 57d. In the second optical rotator 57d, the light beam incident on the region d1 rotates -45 degrees, and the light beam incident on the region d2 rotates +45 degrees. As a result, in the forward section E, the angle of linearly polarized light is 0 degrees in both the area I and the area II.

  The light beam from the second optical rotator 57d is given an optical phase difference of ¼ wavelength by the ¼ wavelength plate 55. Thereby, in the forward section F, both the region I and the region II are clockwise circularly polarized light.

  The light beam from the quarter wave plate 55 is condensed as a minute spot on the recording surface of the optical disk 15 through the objective lens 60. Here, a light flux corresponding to an NA of about 0.65 is collected.

  The reflected light from the optical disk 15 becomes circularly polarized light opposite to the outward path (here, counterclockwise), and is returned to the substantially parallel light again by the objective lens 60 as a return light beam, and is a straight line orthogonal to the outward path by the quarter wavelength plate 55. Polarized light (here, S-polarized light) is used. That is, in the section E on the return path, the angle of linearly polarized light is +90 degrees in both the area I and the area II.

  The return light beam from the quarter-wave plate 55 enters the second optical rotator 57d. In the second optical rotator 57d, the light beam incident on the region d1 rotates -45 degrees, and the light beam incident on the region d2 rotates +45 degrees. As a result, the angle of linearly polarized light is +45 degrees in the region I in the section D of the return path, and the angle of linearly polarized light is +135 degrees in the region II. The state where the angle of linearly polarized light is +135 degrees is equivalent to the state where the angle of linearly polarized light is −45 degrees.

  The return light beam from the second optical rotator 57d enters the polarization aperture limiting element 57c. In the polarization aperture limiting element 57c, the light beam incident on the region c2 is extinguished and the light beam incident on the region c3 is extinguished. Accordingly, only the light beam incident on the region c1 is transmitted through the polarization aperture limiting element 57c. That is, the opening is limited here. In the region I of the section C on the return path, the angle of linearly polarized light remains +45 degrees, and in the region II, the angle of linearly polarized light remains +135 degrees.

  The return light beam from the polarization aperture limiting element 57c is incident on the first optical rotator 57b. In the first optical rotator 57b, the light beam incident on the region b1 rotates +45 degrees, and the light beam incident on the region b2 rotates -45 degrees. Thereby, in the section B of the return path, the angle of the linearly polarized light is +90 degrees in both the area I and the area II.

  The returned light beam from the first optical rotator 57 b enters the variable optical rotator 57 a via the beam expander 56. This return light beam passes through the variable optical rotator 57 a as it is and enters the polarization beam splitter 54. The return light beam reflected in the + Y direction by the polarization beam splitter 54 is received by the light receiver PD via the detection lens 58. In the light receiver PD, photoelectric conversion is performed for each light receiving element (or light receiving region), and each photoelectric conversion signal is output to the reproduction signal processing circuit 28.

<< When the optical disc 15 is a BD >>
In this case, since the appropriate NA is 0.85, aperture restriction is not performed. Here, the variable optical rotator 57a is already turned off by the CPU 40, and the lens interval of the beam expander 56 is controlled so that the wavefront aberration on the recording surface of the optical disc 15 (here, BD) is minimized. And Further, it is assumed that the objective lens 60 is positioned at the second lens position by the focusing actuator 61.

  The light beam of linearly polarized light (here P-polarized light) emitted from the light source LD becomes substantially parallel light by the coupling lens 52 and enters the polarization beam splitter 54. Most of the luminous flux passes through the polarization beam splitter 54 as it is and enters the variable optical rotator 57a. Here, since the variable rotator 57a is in the OFF state, the light beam incident on the variable rotator 57a is emitted with the polarization direction rotated by 90 °. That is, in the forward section B, the angle of the linearly polarized light is +90 degrees in both the region I and the region II.

  The light beam that has passed through the variable optical rotator 57 a enters the first optical rotator 57 b via the beam expander 56. In the first optical rotator 57b, the light beam incident on the region b1 rotates +45 degrees, and the light beam incident on the region b2 rotates -45 degrees. As a result, in the region I in the forward section C, the angle of linearly polarized light is +135 degrees, and in the region II, the angle of linearly polarized light is +45 degrees.

  The light beam from the first optical rotator 57b is incident on the polarization aperture limiting element 57c. In the polarization aperture limiting element 57c, the light beam incident on the region c2 is transmitted and the light beam incident on the region c3 is transmitted. Accordingly, the light beams incident on the region c1, the region c2, and the region c3 are transmitted through the polarization aperture limiting element 57c. That is, the opening is not limited. In the region I of the forward section D, the angle of linearly polarized light remains +135 degrees, and in the region II, the angle of linearly polarized light remains +45 degrees.

  The light beam from the polarization aperture limiting element 57c enters the second optical rotator 57d. In the second optical rotator 57d, the light beam incident on the region d1 rotates -45 degrees, and the light beam incident on the region d2 rotates +45 degrees. As a result, in the forward section E, the angle of linearly polarized light is +90 degrees in both the area I and the area II.

  The light beam from the second optical rotator 57d is given an optical phase difference of ¼ wavelength by the ¼ wavelength plate 55. As a result, in the forward section F, both the region I and the region II are counterclockwise circularly polarized light.

  The light beam from the quarter wave plate 55 is condensed as a minute spot on the recording surface of the optical disk 15 through the objective lens 60. Here, a light flux corresponding to an NA of about 0.85 is collected.

  The reflected light from the optical disk 15 becomes circularly polarized light opposite to the forward path (clockwise in this case), and is returned to the substantially parallel light again by the objective lens 60 as a return light beam, and is a straight line orthogonal to the forward path by the quarter wavelength plate 55. Polarized light (here, P-polarized light) is used. That is, in the section E on the return path, the angle of linearly polarized light is 0 degrees in both the area I and the area II.

  The return light beam from the quarter-wave plate 55 enters the second optical rotator 57d. In the second optical rotator 57d, the light beam incident on the region d1 rotates -45 degrees, and the light beam incident on the region d2 rotates +45 degrees. Thereby, in the area I of the section D of the return path, the angle of the linearly polarized light is −45 degrees, and in the area II, the angle of the linearly polarized light is +45 degrees.

  The return light beam from the second optical rotator 57d enters the polarization aperture limiting element 57c. In the polarization aperture limiting element 57c, the light beam incident on the region c2 is transmitted, and the light beam incident on the region c3 is transmitted. Accordingly, the light beams incident on the region c1, the region c2, and the region c3 are transmitted through the polarization aperture limiting element 57c. That is, the opening is not limited. In the area I of the section C on the return path, the angle of linearly polarized light remains −45 degrees, and in the area II, the angle of linearly polarized light remains +45 degrees.

  The return light beam from the polarization aperture limiting element 57c is incident on the first optical rotator 57b. In the first optical rotator 57b, the light beam incident on the region b1 rotates +45 degrees, and the light beam incident on the region b2 rotates -45 degrees. As a result, in the section B on the return path, the angle of the linearly polarized light becomes 0 degrees in both the area I and the area II.

  The returned light beam from the first optical rotator 57 b enters the variable optical rotator 57 a via the beam expander 56. This return light beam is emitted by the variable optical rotator 57a with the polarization direction rotated by 90 °. That is, in the section A on the return path, the angle of the linearly polarized light is +90 degrees in both the area I and the area II.

  The return light beam from the variable optical rotator 57 a enters the polarization beam splitter 54. The return light beam reflected in the + Y direction by the polarization beam splitter 54 is received by the light receiver PD via the detection lens 58. In the light receiver PD, photoelectric conversion is performed for each light receiving element (or light receiving region), and each photoelectric conversion signal is output to the reproduction signal processing circuit 28.

  As described above, the polarization direction of the light beam incident on the polarization beam splitter 54 on the forward path and the polarization direction of the light beam incident on the polarization beam splitter 54 on the return path are different from each other by 90 degrees regardless of whether or not the aperture is limited. Further, when the opening is not restricted on the forward path, the opening is not restricted on the return path. Therefore, the light utilization efficiency does not decrease regardless of whether the optical disk 15 is HD or BD.

  Further, in the forward path, the light beam incident on the objective lens 60 (the light beam in the section F) has the same polarization state in the region I and the polarization state in the region II, regardless of whether there is an aperture restriction. A good and good light spot can be formed on the recording surface.

  Returning to FIG. 1, the reproduction signal processing circuit 28 includes an I / V amplifier 28a, a servo signal detection circuit 28b, a wobble signal detection circuit 28c, an RF signal detection circuit 28d, and a decoder 28e.

  The I / V amplifier 28a converts each output signal of the light receiver PD into a voltage signal and amplifies it with a predetermined gain.

  The servo signal detection circuit 28b detects servo signals such as a focus error signal and a track error signal based on the output signal of the I / V amplifier 28a. The servo signal detected here is output to the PU drive control circuit 27.

  The wobble signal detection circuit 28c detects a wobble signal based on the output signal of the I / V amplifier 28a. The detected wobble signal is output to the decoder 28e.

  The RF signal detection circuit 28d detects an RF signal based on the output signal of the I / V amplifier 28a. The RF signal detected here is output to the decoder 28e.

  The decoder 28e extracts address information, a synchronization signal, optical disc vendor information, strategy information, and the like from the wobble signal. The extracted address information, vendor information, and strategy information are output to the CPU 40, and the synchronization signal is output to the encoder 25, the motor control circuit 26, and the like. The decoder 28e performs a decoding process and an error detection process on the RF signal. When an error is detected, the decoder 28e performs an error correction process, and then stores the reproduced data in the buffer RAM 34 via the buffer manager 37. To do.

  The PU drive control circuit 27 includes a variable optical rotator control circuit 27a, an aberration correction circuit 27b, an ACT control circuit 27c, and the like.

  The variable optical rotator control circuit 27a turns the variable optical rotator 57a off or on according to an instruction from the CPU 40. In the present embodiment, the optical disk 15 is turned on when it is HD, and is turned off when it is BD.

  The aberration correction circuit 27 b generates a driving signal for the lens driving device 56 c constituting the beam expander 56 in accordance with the lens interval control signal from the CPU 40, and outputs the driving signal to the optical pickup device 23. The CPU 40 outputs a lens interval control signal set in advance according to the type of the optical disk 15.

  The ACT control circuit 27 c generates a drive signal for the focusing actuator 61 for correcting the focus shift based on the focus error signal, and outputs the drive signal to the optical pickup device 23. Further, the ACT control circuit 27 c generates a drive signal for the tracking actuator (not shown) for correcting the track deviation based on the track error signal, and outputs the drive signal to the optical pickup device 23.

  The motor control circuit 26 drives and controls the spindle motor 22 and the seek motor 21 based on instructions from the CPU 40.

  The buffer RAM 34 temporarily stores data to be recorded on the optical disc 15 (recording data), data reproduced from the optical disc 15 (reproduction data), and the like. Data input / output to / from the buffer RAM 34 is managed by the buffer manager 37.

  The encoder 25 takes out the recording data stored in the buffer RAM 34 through the buffer manager 37 based on an instruction from the CPU 40, modulates the data, adds an error correction code, etc., and writes a signal to the optical disc 15. Is generated. The write signal generated here is output to the laser control circuit 24.

  The laser control circuit 24 controls the power of laser light emitted from the light source LD. For example, at the time of recording, a drive signal for the light source LD is generated by the laser control circuit 24 based on the write signal, recording conditions, light emission characteristics of the light source LD, and the like.

  The interface 38 is a bidirectional communication interface with a host device (for example, a personal computer) 90, and is a standard interface such as ATAPI (AT Attachment Packet Interface), SCSI (Small Computer System Interface), and USB (Universal Serial Bus). It is compliant.

  The flash memory 39 stores various programs written in codes readable by the CPU 40, lens interval control signals for each type of optical disc, recording conditions, light emission characteristics of the light source LD, and the like.

  The CPU 40 controls the operation of each unit according to a program stored in the flash memory 39 and saves data necessary for control in the RAM 41.

  Whether the optical disc 15 is HD or BD is determined based on disc information recorded at a predetermined position of the optical disc when the optical disc 15 is set in the optical disc apparatus 20. Then, the determination result is notified to the reproduction signal processing circuit 28, the PU drive control circuit 27, and the like. Further, the CPU 40 sets the lens interval of the variable optical rotator 57a and the beam expander 56 to an appropriate state according to the type of the optical disk 15.

《Playback processing》
When the CPU 40 receives the playback request command from the host device 90, the CPU 40 instructs the motor control circuit 26 to rotate the optical disc 15 at a predetermined linear velocity (or angular velocity), and also indicates that the playback request command has been received from the host device 90. To the reproduction signal processing circuit 28.

  When the CPU 40 confirms that the optical disk 15 is rotating at a predetermined linear velocity (or angular velocity), the CPU 40 instructs the motor control circuit 26 to form a light spot near the target position corresponding to the designated address. To do. Thereby, a seek operation is performed.

  When the seek operation is completed, the CPU 40 permits reproduction. Thereby, the reproduction signal processing circuit 28 performs reproduction processing.

  When the reproduction of the designated data is completed, the CPU 40 ends the process for the reproduction request command.

  As is clear from the above description, in the optical pickup device 23 according to the present embodiment, the aperture switching optical system 57 constitutes an aperture adjustment optical system. The variable rotator 57a is a variable rotation optical element, the first optical rotator 57b is a first rotation optical element, the polarization aperture limiting element 57c is a polarization optical element, and the second optical rotator 57d is a second rotation optical element. Is configured.

  Further, in the optical disc apparatus 20 according to the present embodiment, a processing apparatus is configured by the reproduction signal processing circuit 28, the CPU 40, and a program executed by the CPU 40. It should be noted that at least a part of the processing according to the program by the CPU 40 may be configured by hardware, or all may be configured by hardware.

  As described above, according to the optical pickup device 23 according to the present embodiment, the linearly polarized light emitted from the light source LD is incident on the optical disc 15 by the aperture switching optical system 57 according to the appropriate numerical aperture. The beam diameter of the light beam is defined and is focused on the recording surface of the optical disk 15 by the objective lens 60. The returning light flux through the objective lens 60 is transmitted through the aperture switching optical system 57 while maintaining the beam diameter, and is received by the light receiver PD. Accordingly, an appropriate light spot is formed on the optical disc 15 on the recording surface, and the required amount of light received by the light receiver PD can be secured. As a result, it is possible to accurately obtain a desired signal from a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures.

  Further, according to the present embodiment, since the dividing lines in the first optical rotator 57b, the polarization aperture limiting element 57c, and the second optical rotator 57d coincide with the direction corresponding to the tracking direction, the objective lens 60 is in the tracking direction. When shifted, it is possible to suppress a decrease in the amount of light received by the light receiver PD.

  In addition, according to the optical disk device 20 according to the present embodiment, a signal with a high S / N ratio is output from the optical pickup device 23 regardless of whether the optical disk 15 is HD or BD. However, access can be performed with high accuracy. Therefore, it is possible to accurately access a plurality of types of information recording media corresponding to light beams having the same wavelength and having different appropriate NAs.

  In the above embodiment, as shown in FIG. 11 as an example, the first optical rotator 57b, the polarization aperture limiting element 57c, and the second optical rotator 57d may be integrated. Thereby, the position of each dividing line can be adjusted with high accuracy on the same optical axis. And assembly work can be simplified. Further, the time required for adjustment can be shortened.

  Further, for example, the polarization aperture limiting element 57c may be held by a glass member, and an optical rotator may be formed on the surface of the glass member with a subwavelength grating or a photonic crystal. Thereby, the optical pickup device 23 can be thinned.

  Moreover, in the said embodiment, as FIG. 12 shows as an example, even if the 1st optical rotator 57b, the polarization aperture limiting element 57c, the 2nd optical rotator 57d, and the quarter wavelength plate 55 are integrated. good. As a result, the optical pickup device 23 can be further reduced in thickness.

  Moreover, in the said embodiment, as FIG.13 and FIG.14 shows, the 1st optical rotator 57b, the polarization aperture limiting element 57c, the 2nd optical rotator 57d, the quarter wavelength plate 55, and the objective lens 60 are shown. And may be driven in conjunction with each other. That is, the first optical rotator 57b, the polarization aperture limiting element 57c, the second optical rotator 57d, the quarter-wave plate 55, and the objective lens 60 may be arranged in one casing. Thereby, even if the objective lens 60 is shifted in the tracking direction, the incident position of the outgoing light beam and the incident position of the returning light beam in the first optical rotator 57b, the polarization aperture limiting element 57c, and the second optical rotator 57d are mutually different. Will be equal.

  In the above embodiment, the polarization aperture limiting element 57c may be tilted as shown in FIG. Thereby, it is possible to suppress the stray light reflected by the polarization aperture limiting element 57c from entering the light receiver PD. In this case, it is preferable to incline the polarization aperture limiting element 57c so that the incident angle of the light beam is 1 degree or more.

In the above embodiment, as shown in FIG. 16, the polarization region of the polarization aperture limiting element 57c may be formed using a polarization diffraction element. In this case, the polarizing region is formed in a birefringent medium with an annular shape in a plan view and a saw-tooth shaped groove in a sectional view. As a birefringent medium, as shown in FIG. 17 as an example, a medium having different refractive indexes between n _// and n _⊥ is used. Specific examples include photocurable liquid crystal (PP-LC), holographic polymer dispersed liquid crystal (HPDLC), organic stretched film (PET), and lithium niobate. FIG. 18 is a schematic diagram for linearly polarized light having a polarization direction of +45 degrees, and FIG. 19 is a schematic diagram for linearly polarized light having a polarization direction of −45 degrees. The upper side (+ Z side) is filled with an isotropic refractive index medium, and the lower side (−Z side) is filled with an anisotropic refractive index medium, with a sawtooth-shaped unevenness as a boundary. . In the region c2, the refractive index is different with respect to the linearly polarized light of +45 degrees, with the sawtooth-shaped unevenness as a boundary. On the other hand, in the region c3, the refractive index is different with respect to the linearly polarized light of −45 degrees, with the sawtooth-shaped unevenness as a boundary. As a result, linearly polarized light having an azimuth angle of +45 degrees is diffracted in the area c2, and linearly polarized light having an azimuth angle of −45 degrees is diffracted in the area c3.

  In the above embodiment, the optical disk apparatus capable of recording and reproducing information has been described. However, the present invention is not limited to this, and any optical disk apparatus capable of reproducing at least information among recording, reproducing and erasing of information may be used. .

  In the above embodiment, the case where the optical pickup device includes one semiconductor laser has been described. However, the present invention is not limited thereto, and for example, a plurality of semiconductor lasers that emit light beams having different wavelengths may be included. In this case, for example, at least one of a semiconductor laser that emits a light beam with a wavelength of about 660 nm and a semiconductor laser that emits a light beam with a wavelength of about 780 nm may be further provided.

  As described above, according to the optical pickup device of the present invention, it is suitable for accurately obtaining a desired signal from a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures. . The optical disc apparatus of the present invention is suitable for accurately accessing a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures.

1 is a block diagram showing a configuration of an optical disc device according to an embodiment of the present invention. 2A is a diagram for explaining the recording surface position of HD, and FIG. 2B is a diagram for explaining the recording surface position of BD. It is a figure for demonstrating the optical pick-up apparatus in FIG. 4A and 4B are diagrams for explaining the variable optical rotator in FIG. It is a figure for demonstrating the 1st optical rotator in FIG. It is a figure for demonstrating the polarization aperture limiting element in FIG. It is a figure for demonstrating the 2nd optical rotator in FIG. FIG. 8A and FIG. 8B are diagrams for explaining the position of the objective lens. FIG. 4 is a diagram (No. 1) for explaining the operation of the aperture switching optical system in FIG. 3; FIG. 4 is a diagram (No. 2) for explaining the operation of the aperture switching optical system in FIG. 3; It is a figure for demonstrating the modification 1 of the aperture switching optical system in FIG. It is a figure for demonstrating the modification 2 of the aperture switching optical system in FIG. It is a figure for demonstrating the modification 3 of the aperture switching optical system in FIG. It is a figure for demonstrating the modification 4 of the aperture switching optical system in FIG. It is a figure for demonstrating another example of arrangement | positioning of the polarization aperture limiting element in FIG. It is a figure for demonstrating the modification of the polarization aperture limiting element in FIG. It is a figure for demonstrating the medium of the polarization area of the polarization aperture limiting element in FIG. It is FIG. (1) for demonstrating the cross section of the polarization region of the polarization aperture limiting element in FIG. FIG. 17 is a diagram (No. 2) for explaining a cross section of the polarization region of the polarization aperture limiting element in FIG. 16;

Explanation of symbols

DESCRIPTION OF SYMBOLS 15 ... Optical disk (information recording medium), 20 ... Optical disk apparatus, 23 ... Optical pick-up apparatus, 28 ... Reproduction signal processing circuit (part of processing apparatus), 40 ... CPU (part of processing apparatus), 54 ... Polarization beam splitter (Polarization splitting optical element), 55... Quarter-wave plate, 57... Aperture switching optical system (aperture adjustment optical system), 57 a... Variable optical rotator (variable rotating optical element), 57 b. Rotating optical element), 57c ... Polarization aperture limiting element (polarizing optical element), 57d ... Second optical rotator (second rotating optical element), 60 ... Objective lens, LD ... Light source, PD ... Light receiver (photodetector) .

Claims (12)

An optical pickup device used for performing at least reproduction of information recording, reproduction, and erasure with respect to a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures,
With a light source;
An objective lens for condensing the light beam emitted from the light source on the recording surface of the information recording medium, and a fixed numerical aperture on the optical path between the light source and the objective lens, and having an appropriate numerical aperture for the information recording medium And an aperture adjustment optical system that regulates the beam diameter of the light beam incident on the objective lens and emits the return light beam through the objective lens while maintaining the beam diameter;
An optical pickup device comprising: a photodetector for receiving a return light beam through the aperture adjustment optical system at a predetermined light receiving position; Linearly polarized light is emitted from the light source,
The aperture adjustment optical system is
A variable rotation optical element that rotates the polarization direction of linearly polarized light emitted from the light source within an angle range of greater than 0 degrees and less than 90 degrees;
The variable rotation optical element is disposed on the side opposite to the light source side, and the polarization direction of linearly polarized light incident on a region on one side of the dividing line orthogonal to the optical axis is rotated +45 degrees, and the other of the dividing lines A first rotating optical element that rotates the polarization direction of the linearly polarized light incident on the side region;
The first rotating optical element is disposed on the opposite side to the variable rotating optical element side, and transmits light out of a circular first area that transmits an incident light beam and a donut-shaped area that is in contact with the outer periphery of the first area. Polarized light of incident linearly polarized light having three regions including a second region on one side of a dividing line orthogonal to the axis and a third region on the other side of the dividing line among the donut-shaped regions When the direction is rotated to +45 degrees, it is reflected, absorbed or diffracted by the second area, and when the polarization direction of incident linearly polarized light is rotated to -45 degrees, it is reflected, absorbed or diffracted by the three areas. A polarizing optical element;
The polarization optical element is disposed on the opposite side of the first rotating optical element side, and the polarization direction of linearly polarized light incident on a region on one side of the dividing line orthogonal to the optical axis is rotated by −45 degrees. The optical pickup device according to claim 1, further comprising: a second rotating optical element that rotates a polarization direction of linearly polarized light incident on a region on the other side of the dividing line by +45 degrees.   The second region of the polarizing optical element is formed of a polarizer that quenches linearly polarized light whose polarization direction is rotated by +45 degrees, and the third region has a polarization direction rotated by -45 degrees. 3. The optical pickup device according to claim 2, wherein the optical pickup device is formed of a polarizer that extinguishes the linearly polarized light that is present.   The optical pickup device according to claim 3, wherein each of the polarizers is inclined with respect to a direction orthogonal to the optical axis.   The second region of the polarizing optical element is formed of a polarization diffractive element that diffracts linearly polarized light whose polarization direction is rotated by +45 degrees, and the third region is rotated by −45 degrees. The optical pickup device according to claim 2, wherein the optical pickup device is formed of a polarization diffraction element that diffracts linearly polarized light. The plurality of information recording media includes a first information recording medium and a second information recording medium having a distance from the incident surface to the recording surface longer than that of the first information recording medium,
The polarization direction of the linearly polarized light from the variable rotation optical element with respect to the second information recording medium is a direction obtained by rotating the polarization direction of the linearly polarized light from the variable rotation optical element with respect to the first information recording medium by +90 degrees. The optical pickup device according to any one of claims 2 to 5, wherein   The optical pickup device according to claim 2, wherein each dividing line of the aperture adjustment optical system extends in a direction corresponding to a tracking direction.   The optical pickup according to claim 2, wherein the first rotating optical element, the polarizing optical element, and the second rotating optical element are integrated. apparatus. The optical system further includes a quarter wave plate,
The said 1st rotation optical element, the said polarization optical element, the said 2nd rotation optical element, and the said 1/4 wavelength plate are integrated, The any one of Claims 2-7 characterized by the above-mentioned. An optical pickup device according to claim 1.   The first rotating optical element, the polarizing optical element, the second rotating optical element, the quarter-wave plate, and the objective lens are housed in the same casing. The optical pickup device according to claim 9.   11. The polarization branching optical element that is disposed between the light source and the aperture adjustment optical system and branches a return light beam through the aperture adjustment optical system to the light receiving position. The optical pick-up apparatus as described in any one. An optical disc apparatus capable of reproducing at least one of recording, reproducing and erasing of information with respect to a plurality of types of information recording media corresponding to light beams having the same wavelength and having different numerical apertures,
An optical pickup device according to any one of claims 1 to 11;
And a processing device for reproducing information recorded on an information recording medium using an output signal of a photodetector constituting the optical pickup device.