JP2008021339A - Optical pickup and information device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reproduce or record information signals accurately while reducing the effect of stray light on an information recording medium such as a multi-layered optical disk, for instance. <P>SOLUTION: The optical pickup (100) has (i) a light source to emit a laser beam (101), (ii) optical systems (105, etc.) to guide the laser beam to one of the recording layers, (iii) an optical function element (104) including a phase shifter to partially change the wave phases of the signal light and the stray light, and (iv) a light receiver (PD0) to receive the laser beam at least. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to the technical field of an optical pickup that irradiates a laser beam when recording or reproducing data on an information recording medium such as a DVD, and an information device including the optical pickup.

  For example, an information recording medium such as a multi-layer type optical disc that optically records or reproduces an information signal (data) using a laser beam or the like, such as a two-layer DVD, has been developed. In such a multilayer optical disc, if the distance between the recording layer and the recording layer is wide, the signal from the selected recording layer may deteriorate due to the influence of spherical aberration. It tends to narrow the interval. However, when the interval between the recording layers is reduced, so-called interlayer crosstalk causes the return light from the multilayer type optical disc to receive a desired desired recording layer (hereinafter referred to as “one recording layer” as appropriate). In addition to the component of the reflected light (hereinafter referred to as “signal light” as appropriate), the reflected light (hereinafter referred to as “stray light” as appropriate) generated in other recording layers other than one recording layer. Ingredients are also included at high levels. Therefore, for example, the S / N ratio of a signal component such as a reproduction signal is lowered, and it may be difficult to appropriately perform various controls such as tracking control. Specifically, in general, the beam diameter of the signal light applied to the light receiving element (photodetector) (that is, the stability in the optical path in the optical pickup and the reliability in the control operation of the optical pickup) and the stray light component Is known to be in a trade-off relationship. Specifically, if the optical magnification is increased and the area of the light receiving element to be normalized is reduced, the influence “Noise” of the stray light on the signal level “Signal” is relatively reduced, and the SN ratio (Signal to Noise Ratio) is reduced. ) Can be improved. However, the light beam diameter of the signal light applied to the light receiving element is inevitably small, and when various signals such as tracking error signals are generated in various divided regions constituting the light receiving element, the signal light The positional deviation is detected unnecessarily large as much as the beam diameter of the signal light is reduced. Therefore, it is necessary to control the irradiation position of the signal light with high accuracy by adjusting the mechanical, structural, and positional accuracy of various actuators in the optical pickup highly. That is, there arises a technical problem that the stability in the optical path in the optical pickup and the reliability in the control operation of the optical pickup are lowered.

  Therefore, for example, in the tracking method when recording or reproducing a two-layer Blu-ray disc, the push-pull signal is separated from the signal light by the hologram element, so that the stray light is incident on the light receiving element. Techniques for avoiding this have been proposed. Alternatively, Patent Document 1 describes a technique for separating reflected light from each recording layer with high accuracy by using a difference in optical axis angle of return light from each recording layer of a two-layer optical disc. ing.

JP 2005-228436 A

  However, when the area of the light receiving element is increased as compared with the above, a technical problem that the optical pickup has to be enlarged occurs. Alternatively, in the above-described various methods, for example, it is difficult to appropriately reduce the influence of stray light in correspondence with an optical disc having a smaller interlayer distance than a conventional one such as a BD (Blu-ray Disc). Problems will occur. Alternatively, in the various methods described above, as shown in FIG. 19, stray light (“Stray light” and “Transmitted” in FIG. 19) is received in the light receiving element for receiving the focus error signal (or RF signal). (refer to the overlap with “beam”), and the S / N ratio of the signal component of the return light from the desired recording layer is lowered due to the influence of stray light. .

  The present invention has been made in view of, for example, the conventional problems described above, and reproduces or records data with higher accuracy while reducing the influence of stray light on a recording medium such as a multilayer optical disk. It is an object of the present invention to provide an optical pickup capable of realizing the above and an information device including such an optical pickup.

  In order to solve the above-described problem, the optical pickup according to claim 1 is an optical pickup that performs at least one of data recording and reproduction with respect to a recording medium including a plurality of recording layers, and a light source that emits laser light. And an optical system (for example, an objective lens, an optical path branching element, or a prism) that guides the irradiated laser light to one recording layer of the plurality of recording layers, and the guided laser light is When focused on the one recording layer, (i) a part of signal light generated in the one recording layer, and (ii) stray light generated in another recording layer of the plurality of recording layers. An optical functional element (for example, two phase plates of a predetermined length arranged along the radial direction of the optical disc) including phase change means (or a phase change region) for changing the phase of the wavefront in part, and (iii) Signal light Provided with one or more light receiving means for at least receiving (PD1a / PD1b / PD0), and.

  In order to solve the above-described problem, an information device according to claim 19 irradiates the recording medium with the optical pickup according to any one of claims 1 to 18 and the laser beam. Recording / reproducing means for recording or reproducing data.

  The operation and other advantages of the present invention will become apparent from the embodiments described below.

  Hereinafter, an optical pickup and an information device according to an embodiment of the present invention as the best mode for carrying out the invention will be described in order.

(Embodiment of optical pickup)
An embodiment of the optical pickup according to the present invention is an optical pickup that performs at least one of recording and reproduction of data on a recording medium having a plurality of recording layers, the light source for irradiating laser light, and the irradiated laser An optical system (for example, an objective lens, an optical path branching element, or a prism) that guides light to one recording layer of the plurality of recording layers and the guided laser beam are combined with the one recording layer. When focused, (i) a part of the signal light generated in the one recording layer, and (ii) a wavefront phase in a part of the stray light generated in the other recording layer of the plurality of recording layers. An optical functional element (for example, two phase plates of a predetermined length arranged along the radial direction of the optical disc) including phase changing means (or a phase changing region) to be changed; and (iii) receiving at least the signal light It provided with one or more light receiving means (PD1a / PD1b / PD0), and.

  According to the embodiment of the optical pickup of the present invention, the laser light emitted from the light source is, for example, an objective lens, an optical path branching element (polarizing beam splitter), or an optical system such as a prism, among a plurality of recording layers. To one recording layer and condensed. At the same time, one return light generated in one recording layer is received by the light receiving means. Therefore, the focused laser beam guided to one recording layer can reproduce information pits and marks formed on the one recording layer. Therefore, it is possible to reproduce predetermined information from the recording medium. Alternatively, the focused laser beam can form information pits and marks in one recording layer. Therefore, it is possible to record predetermined information on the recording medium.

  In particular, according to the present embodiment, a part of the signal light generated in one recording layer such as zero-order light or diffracted light transmitted through the phase change means by the phase change means included in the optical functional element, And (ii) the phase of the wavefront in a part of the stray light generated in the other recording layer among the plurality of recording layers is changed. Here, the “wavefront” according to the present invention means a surface connecting points having the same phase in a light wave such as a laser beam. The light receiving means receives at least the signal light transmitted through the optical functional element.

  If the optical functional element does not include the phase change means, for example, the interference pattern caused by the interference between the signal light and the stray light is relatively large in a relatively wide range including the central portion of the beam diameter of the signal light. It occurs at a low spatial frequency and at a relatively high level of light intensity, and the influence of light interference becomes large. Here, the interference pattern according to the present invention means a position distribution in which a portion having a relatively high light intensity and a portion having a relatively low light intensity are generated.

  On the other hand, according to the present embodiment, the phase change means included in the optical functional element changes the phase of the wavefront in a part of the signal light and a part of the stray light transmitted through the phase change means. The

  As a result, in the light receiving means, the irradiated areas overlap, (i) interference between, for example, ± 1st order diffracted signal light and, for example, 0th order stray light, or (ii) 0th order signal light, for example. For example, interference with stray light of ± 1st order diffracted light, or (iii) increasing spatial frequency in interference pattern generated based on interference between 0th order signal light and 0th order stray light, or light intensity By reducing the level of the difference, it is possible to effectively suppress the influence of light interference between signal light and stray light.

  As a result, in the multilayer information recording medium, for example, in the tracking control and the focus control based on the three-beam method, the effect of stray light is effectively reduced, and the light intensity level is maintained higher. It is possible to make the light receiving means receive light and to realize highly accurate tracking control and focus control.

  In one aspect of the optical pickup according to the present invention, the phase change unit includes: (i) a part of the signal light transmitted through the phase change unit, and a phase of a wavefront in a part of the stray light. (Ii) A predetermined phase difference is generated between the other part of the signal light that does not pass through the phase changing unit and the phase of the wavefront in the other part of the stray light.

  According to this aspect, based on a predetermined phase difference, in the light receiving unit, the irradiated areas overlap, for example, interference between ± 1st order diffracted signal light and 0th order stray light, or 0th order light, for example. It is possible to increase the spatial frequency in the interference pattern generated based on the interference between the signal light of the light and the stray light of, for example, ± 1st order diffracted light, or to reduce the level of the light intensity difference. Therefore, it is possible to effectively suppress the influence of interference between signal light and stray light.

  The aspect related to the predetermined phase difference described above may be configured such that the predetermined phase difference is defined based on a quarter to a half of the wavelength of the laser beam.

  If comprised in this way, the phase of a wave front in a part of signal light and a part of stray light which permeate | transmitted the said phase change means will be changed more appropriately by the phase change means which produces a predetermined phase difference. It is possible.

  In another aspect of the embodiment of the optical pickup of the present invention, the phase change unit includes a medium having one optical refractive index (“n”).

  According to this aspect, the phase of the wavefront in the part of the signal light and the part of the stray light transmitted through the phase change unit by the phase change unit including the medium having one optical refractive index (“n”). Can be changed appropriately.

  In the aspect related to the predetermined phase difference described above, the portion of the optical functional element that does not include the phase change unit may include a medium having another optical refractive index (“n ′”). .

  According to this configuration, a part of the signal light and one of the stray light transmitted through the phase change unit by the phase change unit further including a medium having another optical refractive index (“n ′”). It is possible to appropriately change the phase of the wave front in the section.

  In another aspect of the embodiment of the optical pickup of the present invention, in the optical functional element, at least two of the phase change units are formed along a reference direction, and the laser light is diffracted in the reference direction. It is defined based on the radial direction of the recording medium (direction for receiving a push-pull signal: Rad direction) corresponding to the position irradiated with the 0th-order light and the diffracted light.

  According to this aspect, the phase change means formed along the reference direction appropriately changes the phase of the wavefront in the part of the signal light and the part of the stray light transmitted through the phase change means. Is possible.

  According to another aspect of the embodiment of the optical pickup of the present invention, in the optical functional element, at least two of the phases correspond to positions where the laser light is diffracted and zero-order light and the position where the diffracted light is irradiated. The changing means is formed along a reference direction, and the at least two phase changing means are arranged so as to be symmetrical with respect to a tangential direction orthogonal to the reference direction.

  According to this aspect, the phase change means arranged so as to be line symmetric with respect to the tangential direction as the axis changes the phase of the wavefront in the part of the signal light and the part of the stray light transmitted through the phase change means. It is possible to change appropriately.

  According to another aspect of the embodiment of the optical pickup of the present invention, in the optical functional element, at least two of the phases correspond to positions where the laser light is diffracted and zero-order light and the position where the diffracted light is irradiated. The changing means is formed along a reference direction, and the at least two phase changing means are arranged so as to be symmetric with respect to the reference direction and a tangential direction orthogonal to the reference direction.

  According to this aspect, the part of the signal light and the part of the stray light transmitted through the phase changing unit by the phase changing unit arranged to be symmetrical with respect to the reference direction and the tangential direction as an axis. It is possible to appropriately change the phase of the wavefront at.

  According to another aspect of the embodiment of the optical pickup of the present invention, the size, shape, and arrangement of one or a plurality of the phase change units are determined by the size of the laser beam irradiated on the optical functional element ( (Light beam diameter) and shape.

  According to this aspect, a part of the signal light and a part of the stray light transmitted through the phase change means by the phase change means defined based on the size (light beam diameter) and shape of the laser light. It is possible to appropriately change the phase of the wavefront at.

  In another aspect of the embodiment of the optical pickup of the present invention, the size, shape, and arrangement of one or a plurality of the phase change means are the signal light received by the light receiving means, the stray light, and the like. It is defined based on the shape and size of the interference pattern generated by the interference of the light waves.

  According to this aspect, the phase of the wave front in the part of the signal light and the part of the stray light transmitted through the phase changing unit by the phase changing unit defined based on the shape and size of the interference pattern. Can be changed appropriately.

  In another aspect of the embodiment of the optical pickup of the present invention, the size, shape, and arrangement in one or a plurality of the phase change means are defined based on the interlayer distance between the plurality of recording layers.

  According to this aspect, the phase of the wavefront in the part of the signal light and the part of the stray light transmitted through the phase change unit by the phase change unit defined based on the interlayer distance of the plurality of recording layers, It can be changed appropriately.

  In another aspect of the embodiment of the optical pickup of the present invention, the size, shape, and arrangement of one or a plurality of the phase change means correspond to the plurality of recording layers, respectively. It is prescribed based on.

  According to this aspect, a part of the signal light and one of the stray light transmitted through the phase change means by the phase change means defined based on the plurality of condensing positions respectively corresponding to the plurality of recording layers. It is possible to appropriately change the phase of the wavefront in the unit while corresponding to a plurality of condensing positions.

  In another aspect of the embodiment of the optical pickup of the present invention, the optical functional element includes (i) a first substrate, (ii) a second substrate, (iii) the first substrate, and the second substrate. And (iv) an electrode that changes the voltage applied to the anisotropic medium in accordance with the size, shape, and arrangement of the phase change means. Has been.

  According to this aspect, the phase of the wave front in the part of the signal light and the part of the stray light transmitted through the anisotropic medium is appropriately changed by the anisotropic medium constituting the phase changing means. Is possible.

  Another aspect of the embodiment of the optical pickup of the present invention further includes diffraction means (diffraction grating) for diffracting the irradiated laser light into zero-order light and diffracted light (± first-order diffracted light), The optical system guides the diffracted zero-order light and the diffracted light to the one recording layer, and the optical functional element includes a part of the zero-order light and a part of the diffracted light. The phase of the wavefront is changed, and the light receiving means receives at least the diffracted light.

  According to this aspect, the phase change means included in the optical functional element transmits part of the signal light and stray light included in the diffracted zero-order light and diffracted light transmitted through the phase change means. The wavefront phase in some is changed. In particular, the 0th-order stray light and the diffracted signal light have substantially the same light intensity level. Therefore, the wavefront phase is changed, so that the light receiving means that receives the diffracted light interferes with the stray light. Can be suppressed more significantly.

  As a result, in the light receiving means, the irradiated regions overlap, for example, interference between the signal light of ± 1st order diffracted light and the stray light of 0th order light, for example, or the signal light of 0th order light and, for example, ± 1st order diffracted light By effectively increasing the spatial frequency in the interference pattern generated based on interference with stray light and reducing the level of light intensity difference, the effect of interference between signal light and stray light is effectively suppressed. Is possible.

  The aspect related to the optical functional element described above further includes optical path branching means for guiding the zero-order light and the diffracted light from the one recording layer to the light receiving means, and the optical functional element includes (i It may be arranged such that it is disposed on the optical path from the recording medium to the optical path branching means, or (ii) on the optical path from the optical path branching means to the light receiving means.

  With this configuration, (i) the optical functional element and (ii-1) the optical path from the recording medium to the optical path branching means, or (ii-2) the optical path from the optical path branching means to the light receiving means. Based on the relative positional relationship, the phase of the wavefront in part of the signal light and part of the stray light can be appropriately changed after passing through the optical functional element.

  The aspect related to the optical functional element described above may be configured such that the order of the diffracted light is ± 1st order.

  According to this aspect, the wavefront of the part of the signal light and the part of the stray light included in the 0th-order light and the ± 1st-order diffracted light transmitted through the optical functional element by the optical functional element. The phase is changed.

  According to another aspect of the embodiment of the optical pickup of the present invention, as the light receiving means, a first light receiving means and a second light receiving means for receiving the diffracted light of the laser light, and a zero order light of the laser light. The third light receiving means for receiving light is provided.

  According to this aspect, in the tracking control based on the three-beam method in the multilayer information recording medium, the light receiving means can be used in a state where the influence of stray light is effectively reduced and the light intensity level is maintained higher. It is possible to realize high-precision tracking control.

  According to another aspect of the embodiment of the optical pickup of the present invention, the laser light is guided to a recording track included in the one recording layer based on zeroth-order light and diffracted light in the laser light. Control means (tracking control or focus control) for controlling the optical system is further provided.

  According to this aspect, in the multi-layered information recording medium, the influence of stray light is effectively reduced, and the light receiving means is made to receive light in a state where the light intensity level is maintained at a higher level. Control and tracking control can be realized.

(Embodiment of information equipment)
An embodiment of the information device of the present invention includes the above-described embodiment of the optical pickup of the present invention and a recording / reproducing unit that records or reproduces the data by irradiating the recording medium with the laser beam. Prepare.

  According to the embodiment of the information apparatus of the present invention, data is recorded on the recording medium while receiving the same benefits as those of the above-described embodiment of the optical pickup of the present invention, or the recording medium It is possible to reproduce the data recorded in

  These effects and other advantages of the present invention will become more apparent from the embodiments described below.

  As described above, according to the embodiment of the optical pickup of the present invention, the light source, the optical system, the optical functional element, and the light receiving means are provided. Therefore, in a multilayer information recording medium, for example, in tracking control or focus control, the influence of stray light is effectively reduced, and the light intensity is maintained at a higher level. Accurate tracking control and focus control can be realized.

  Alternatively, according to the embodiment of the information apparatus of the present invention, the light source, the optical system, the optical functional element, the light receiving means, and the recording / reproducing means are provided. Therefore, in a multilayer information recording medium, for example, in tracking control or focus control, the influence of stray light is effectively reduced, and the light intensity is maintained at a higher level. Accurate tracking control and focus control can be realized.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(1) Embodiment of Information Recording / Reproducing Apparatus First, the configuration and operation of an embodiment of the information recording apparatus of the present invention will be described in detail with reference to FIG. In particular, the present embodiment is an example in which the information recording apparatus according to the present invention is applied to an information recording / reproducing apparatus for an optical disc.

(1-1) Basic Configuration First, the basic configuration of the information recording / reproducing apparatus 300 and the host computer 400 in the embodiment of the information recording apparatus of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the basic configuration of an information recording / reproducing apparatus and a host computer according to an embodiment of the information recording apparatus of the present invention. The information recording / reproducing apparatus 300 has a function of recording record data on the optical disc 10 and a function of reproducing the record data recorded on the optical disc 10.

  The internal configuration of the information recording / reproducing apparatus 300 will be described with reference to FIG. The information recording / reproducing apparatus 300 is an apparatus that records information on the optical disc 10 and reads information recorded on the optical disc 10 under the control of a CPU (Central Processing Unit) 314 for driving.

  The information recording / reproducing apparatus 300 includes an optical disc 10, an optical pickup 100, a signal recording / reproducing unit 302, an address detecting unit 303, a CPU (drive control unit) 314, a spindle motor 306, a memory 307, a data input / output control unit 308, and a bus 309. It is configured with.

  The host computer 400 includes a CPU (host control means) 401, a memory 402, operation control means 403, operation buttons 404, a display panel 405, data input / output control means 406, and a bus 407.

  In particular, the information recording / reproducing apparatus 300 may be configured to be communicable with an external network by housing the host computer 400 equipped with communication means such as a modem in the same housing. Alternatively, for example, the CPU (host control means) 401 of the host computer 400 having communication means such as i-link directly connects the information recording / reproducing apparatus 300 via the data input / output control means 308 and the bus 309. You may comprise so that it can communicate with an external network by controlling.

  The optical pickup 100 performs recording / reproduction with respect to the optical disc 10 and includes a semiconductor laser device and a lens. More specifically, the optical pickup 100 irradiates the optical disc 10 with a light beam such as a laser beam at a first power as a read light during reproduction and modulates it with a second power as a write light at the time of recording. Irradiate.

  The signal recording / reproducing means 302 records or reproduces the optical disc 10 by controlling the optical pickup 100 and the spindle motor 306. More specifically, the signal recording / reproducing unit 302 includes, for example, a laser diode driver (LD driver) and a head amplifier. The laser diode driver drives a semiconductor laser (not shown) provided in the optical pickup 100. The head amplifier amplifies the output signal of the optical pickup 100, that is, the reflected light of the light beam, and outputs the amplified signal. More specifically, during the OPC (Optimum Power Control) process, the signal recording / playback unit 302 determines the optimum laser power by the OPC pattern recording and playback process together with a timing generator (not shown) under the control of the CPU 314. A semiconductor laser (not shown) provided in the optical pickup 100 is driven so that it can be performed. In particular, the signal recording / reproducing means 302 constitutes an example of the “recording / reproducing means” according to the present invention together with the optical pickup 100.

  The address detection unit 303 detects an address (address information) on the optical disc 10 from a reproduction signal output from the signal recording / reproducing unit 302, for example, including a preformat address signal.

  A CPU (drive control means) 314 controls the entire information recording / reproducing apparatus 300 by giving instructions to various control means via the bus 309. Note that software or firmware for operating the CPU 314 is stored in the memory 307. In particular, the CPU 314 constitutes an example of a “control unit” according to the present invention.

  The spindle motor 306 rotates and stops the optical disc 10 and operates when accessing the optical disc. More specifically, the spindle motor 306 is configured to rotate and stop the optical disc 10 at a predetermined speed while receiving spindle servo from a servo unit (not shown) or the like.

  The memory 307 is used in general data processing and OPC processing in the information recording / reproducing apparatus 300, such as a buffer area for recording / reproducing data and an area used as an intermediate buffer for conversion to data usable by the signal recording / reproducing means 302. . The memory 307 stores a program for operating as the recorder device, that is, a ROM area in which firmware is stored, a buffer for temporarily storing recording / playback data, variables necessary for the operation of the firmware program, and the like. It consists of a RAM area and the like.

  The data input / output control means 308 controls external data input / output with respect to the information recording / reproducing apparatus 300, and stores and retrieves data in / from the data buffer on the memory 307. A drive control command issued from the information recording / reproducing apparatus 300 and an external host computer 400 (hereinafter referred to as a host as appropriate) connected to the information recording / reproducing apparatus 300 via an interface such as SCSI or ATAPI is sent to the data input / output control means 308. Via the CPU 314. Similarly, recording / reproduction data is transmitted / received to / from the host computer 400 via the data input / output control means 308.

  In the host computer 400, the CPU (host control means) 401, the memory 402, the data input / output control means 406, and the bus 407 are generally the same as the corresponding components in the information recording / reproducing apparatus 300.

  The operation control unit 403 receives and displays an operation instruction with respect to the host computer 400, and transmits an instruction by the operation button 404 such as recording or reproduction to the CPU 401. The CPU 401 transmits a control command (command) to the information recording / reproducing apparatus 300 via the data input / output means 406 based on the instruction information from the operation control means 403 to control the entire information recording / reproducing apparatus 300. You may comprise as follows. Similarly, the CPU 401 can transmit a command requesting the information recording / reproducing apparatus 300 to transmit the operation state to the host. Thus, since the operation state of the information recording / reproducing apparatus 300 such as recording or reproduction can be grasped, the CPU 401 displays the operation state of the information recording / reproducing apparatus 300 on the display panel 405 such as a fluorescent tube or LCD via the operation control means 403. Can be output.

  One specific example in which the information recording / reproducing apparatus 300 and the host computer 400 described above are used in combination is a household device such as a recorder device that records and reproduces video. This recorder device is a device that records a video signal from a broadcast receiving tuner or an external connection terminal on a disk and outputs a video signal reproduced from the disk to an external display device such as a television. An operation as a recorder device is performed by causing the CPU 401 to execute a program stored in the memory 402. In another specific example, the information recording / reproducing apparatus 300 is a disk drive (hereinafter referred to as a drive as appropriate), and the host computer 400 is a personal computer or a workstation. A host computer such as a personal computer and a drive are connected via data input / output control means 308 (406) such as SCSI and ATAPI, and an application such as writing software installed in the host computer controls the disk drive.

(1-2) Optical pickup
Next, a more detailed configuration of the optical pickup 100 provided in the information recording / reproducing apparatus 300 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram conceptually showing a more detailed structure of the optical pickup 100 provided in the information recording / reproducing apparatus 300 according to the present embodiment.

  As shown in FIG. 2, the optical pickup 100 includes a semiconductor laser 101, a diffraction grating 102, a condenser lens 103, an optical functional element 104, an optical path branching element 105, a reflection mirror 106, and a quarter wavelength plate. 107, a condensing lens 108, a condensing lens 109, an astigmatism generation lens 110, a light receiving unit PD0, a light receiving unit PD1a, and a light receiving unit PD1b. Accordingly, the laser beam LB is emitted from the semiconductor laser 101 in the following order, and is received by the light receiving unit PD0 and the like through each element. That is, when the laser beam LB emitted from the semiconductor laser 101 is guided to one recording layer of the optical disc as a so-called outgoing path on the optical path, the diffraction grating 102, the condensing lens 103, the optical functional element 104, It is guided to one recording layer through the optical path branching element 105, the reflection mirror 106, the quarter wavelength plate 107, and the condenser lens 108. On the other hand, as a so-called return path on the optical path, the laser beam LB reflected on one recording layer is a condensing lens 108, a quarter-wave plate 107, a reflecting mirror 106, an optical path branching element 105, a condensing lens 109, and a non-condensing lens 109. The light is received by the light receiving unit PD0 through the point aberration generating lens 110.

  In particular, the display of the diffracted light generated in the diffraction grating 102 is omitted from the diffraction grating 102 on the optical path between the condenser lenses 108. In general, the display of diffracted light is also omitted on the optical path between the condenser lens 108 and the astigmatism generation lens 110.

  The condensing lenses 103, 108 and 109, the optical path branching element 105, the reflection mirror 106, the quarter wavelength plate 107, and the astigmatism generation lens 110 constitute a specific example of the optical system according to the present invention. . In addition, the light receiving units PD0, PD1a, and PD1b constitute a specific example of the light receiving unit according to the present invention.

  The semiconductor laser 101 emits a laser beam LB with an elliptical light emission pattern that spreads in the vertical direction as compared with the horizontal direction, for example.

  The diffraction grating 102 diffracts laser light emitted from the semiconductor laser 101 into 0th order light, + 1st order diffracted light, and −1st order diffracted light.

  The condensing lens 103 makes the incident laser beam LB substantially parallel and makes it incident on the optical path branching element 105.

  The optical functional element 104 includes a part of signal light generated in one recording layer such as 0th-order light and diffracted light that has passed through the phase change means included in the optical functional element, and (ii) a plurality of recordings The phase of the wavefront in a part of the stray light generated in the other recording layer among the layers is changed. Details of the optical functional element 104 will be described later. Further, the optical functional element 104 may be configured to be disposed at a position close to the optical path branching element 105 on the optical path from the optical path branching element 105 to the light receiving unit described later. As a result, it is necessary to cope with a change in the size of the light beam of the laser light on the optical path, but the phase change means included in the optical functional element can be realized by a low-cost phase plate.

  The optical path branching element 105 is an optical element such as a beam splitter that branches the optical path based on the polarization direction. Specifically, the laser beam LB whose polarization direction is one direction is transmitted with little or no light loss, and is incident from the optical disc side, and the laser beam whose polarization direction is the other direction. The light LB is reflected with little or no light loss. The reflected light reflected by the optical path branching element 105 is received by the light receiving parts PD0, PD1a, and PD1b via the condenser lens 109 and the astigmatism generation lens 110.

  The reflection mirror reflects the laser beam LB with little or no loss of light quantity.

  The quarter-wave plate 107 can convert linearly polarized laser light into circularly polarized light or convert circularly polarized laser light into linearly polarized light by giving a 90-degree phase difference to the laser light. It is.

  The condensing lens 108 condenses the incident laser beam LB and irradiates the recording surface of the optical disc 10. Specifically, the condensing lens 108 is configured to include an actuator unit, for example, and has a drive mechanism for changing the arrangement position of the condensing lens 108. More specifically, the actuator unit can focus on one recording layer and another recording layer of the optical disc by moving the position of the objective lens 108 in the focus direction.

  The condensing lens 109 condenses the reflected light reflected by the optical path branching element 105.

  The light receiving unit PD0 receives the 0th order light, the light receiving unit PD1a receives the + 1st order diffracted light, and the light receiving unit PD1b receives the −1st order diffracted light.

(2) Light interference between signal light and stray light
Next, with reference to FIG. 3, the interference of light between signal light and stray light in a general optical pickup will be described. FIG. 3 is a schematic diagram conceptually showing light interference between signal light and stray light in a general optical pickup. In FIG. 3, the light intensity is lighter (whiter) as the light intensity is higher, and the light intensity is darker (black) as the light intensity is lower.

  As shown in FIG. 3, for example, in the case of an optical disc having a plurality of recording layers, when the recording or reproducing process is performed on the recording layer on the back side (the other recording layer in FIG. 2 described above), 0 In the region including the light receiving unit PD0 that receives the next light, the light receiving unit PD1a that receives the + 1st order light, and the light receiving unit PD1b that receives the −1st order light, the stray light of the 0th order light is defocused (blurred). Irradiated. In particular, the focal position of the 0th-order stray light is on the optical axis on the rear side of the light receiving part PD as seen from the side irradiated with the laser light.

  Alternatively, in an optical disc having a plurality of recording layers, when a recording or reproducing process is performed on the recording layer on the front side (one recording layer in FIG. 2 described above), a light receiving unit PD0 that receives zero-order light. In the region including the light receiving unit PD1a that receives the + 1st order light and the light receiving unit PD1b that receives the −1st order light, the stray light of the 0th order light is defocused (blurred) and irradiated. In particular, the focal position of the 0th-order stray light is on the optical axis on the front side of the light receiving part PD as seen from the side irradiated with the laser light.

  Therefore, the distribution of the light intensity of the laser light received on the light receiving surface of the light receiving unit shown in FIG. 3 is the case where there is no light interference due to stray light (see the thin (white) part in FIG. 10 described later). In the case where there is interference of light due to stray light, the level of light intensity varies finely within the light flux due to the interference pattern (in enlarged views 1 and 2 in FIG. 3). (See the black and white stripes). The main object of the present invention is to reduce the influence of stray light and maintain the quality (quality) of signal light at a high level. Here, the interference pattern according to the present embodiment refers to a portion having a relatively high light intensity generated based on an optical phase condition in which signal light and stray light interfere with each other, and a light intensity relatively It means the position distribution with the low level part.

  In particular, when a condensing lens such as an objective lens moves (shifts) in the Rad direction of the optical disk, it becomes asymmetric in the direction of receiving laser light for outputting a push-pull signal, corresponding to the amount of lens shift. The noise level affected by light interference will fluctuate.

  More specifically, the phase condition in which the signal light and the stray light interfere can be defined based on the interlayer thickness of the multilayer optical disk, and the thickness of the recording layer between which the light intensity increases or decreases. The difference is about a quarter of the wavelength of the laser beam (about “0.1 (μm)”) or less, and with this accuracy, it is generally impossible to control the interlayer thickness of a multilayer optical disc. It is supposed to be. Incidentally, the multilayer type optical disc permits to maintain an error of the interlayer thickness of ± 2 μm according to the standard.

(3) One specific example of optical functional element
Next, a specific example of the optical functional element according to the present embodiment will be described with reference to FIGS.

(3-1) Physical shape of optical functional element and optical principle
First, with reference to FIG. 4, the physical shape and optical principle of the optical functional element that changes the phase of the wavefront of the laser light according to the present embodiment will be described. FIG. 4 is a side view (FIG. 4 (a)), a plan view (FIG. 4 (b)), and a perspective view schematically showing the physical shape of the optical functional element according to the present embodiment. It is a figure (FIG.4 (c)). FIG. 5 is a plan view schematically showing the physical shape of the optical functional element according to the present embodiment.

  For convenience of explanation, the magnitude of the wavefront phase in the laser light according to the present embodiment is based on the wavelength such as the magnitude of the phase of the wavefront corresponding to one half or one quarter of the wavelength. It is expressed by the value.

  As shown in FIG. 4A to FIG. 4C and FIG. 5, the optical functional element that changes the phase of the wavefront of the laser light according to the present embodiment is a part of the irradiated laser light. In order to change the phase of the wave front at, two phase changing means are arranged along the Tan direction and arranged so as to be symmetrical about the Rad direction passing through the center of the optical functional element. Both have a glass substrate. Here, the “Rad direction” according to the present embodiment is a specific example of the reference direction according to the present invention, and means a radial direction of the optical disc (that is, a direction for receiving a push-pull signal). The Rad direction substantially coincides with the direction in which the objective lens moves during tracking control, the so-called lens shift direction. The “Tan direction” according to the present embodiment is a specific example of the tangential direction according to the present invention, and means the tangential direction of the optical disc (that is, the direction orthogonal to the Rad direction).

  Specifically, as shown in FIG. 4 (b) and FIG. 4 (c) and FIG. 5, the two phase change means are each a rectangular parallelepiped that is relatively long in the Rad direction. When the radius of the laser beam irradiated to the optical functional element is normalized with the reference length “1.0”, the length in the Rad direction is approximately “1.0”, and the length in the Tan direction. Is generally “0.3” to “0.4”. In this way, since the phase change means has a relatively long shape in the Rad direction, when the objective lens is moved during tracking control, even when the objective lens is shifted, so-called lens shift is performed. Corresponding to the movement of the center position of the laser light beam caused by the movement, it is possible to accurately change the phase of a part of the wavefront of the laser light.

(3-1-1) Optical principle of optical functional element
Next, the optical principle of the optical functional element according to the present embodiment will be described with reference to FIGS. FIG. 6 is a schematic diagram (FIG. 6A) schematically showing the optical principle of the optical functional element according to the present embodiment. FIG. 6A shows a laser transmitted through the optical functional element according to the present embodiment. It is the schematic diagram (FIG.6 (b)) which showed the wavefront of light typically, and the schematic diagram (FIG.6 (c)) which showed the wavefront of the laser beam based on a comparative example typically. FIG. 7 is another schematic diagram schematically showing the optical principle of the optical functional element according to the present embodiment. A specific example of the phase changing means according to this embodiment is a phase plate.

  As shown in FIG. 6A, the phase changing means according to the present embodiment includes (i) the phase of the wavefront in a part of the laser light transmitted through the phase changing means, and (ii) the phase changing means. It is possible to cause a predetermined phase difference with respect to the phase of the wavefront in the other part of the laser beam that does not transmit. Specifically, when the phase change unit according to the present embodiment generates a phase difference “λ / 2” that is a half of the wavelength “λ” of the laser light with respect to a part of the laser light, The refractive index “n” of the medium constituting the phase change means and the thickness “d” of the phase change means are configured to satisfy the following expression (1).

(N−1) × d = λ / 2 (1)
However, the refractive index of air is “1”.

  More specifically, the phase plate, which is a specific example of the phase changing means according to the present embodiment, can be formed at a low cost by the same technique as a general grating. That is, the phase plate can easily define a pattern (that is, size, shape, and arrangement) for forming a plurality of phase plates by etching or the like on the surface of the glass substrate. The phase change means is formed by etching the position corresponding to the phase change means as a recess, or leaving the position corresponding to the phase change means as a protrusion. Good.

  Therefore, as shown in FIG. 6B, the optical functional element in which the phase changing means according to the present embodiment is formed has a phase compared to the wavefront of the laser beam shown in FIG. A predetermined phase difference such as “λ / 2” is generated between the phase of the wavefront in a part of the laser light transmitted through the changing means and the phase of the wavefront in the other part of the laser light not transmitted through the phase changing means. Is possible.

  As shown in FIG. 7, when the optical functional element has a medium with a refractive index “na”, for example, in the portion where the other part of the laser light that does not pass through the phase change means passes, The phase change means generates a phase difference “λ / 2” that is a half of the wavelength “λ” of the laser light with respect to a part of the laser light. The refractive index “n” and the thickness “d” of the phase change means may be configured to satisfy the following expression (2).

(N−na) × d = λ / 2 (2)
Specifically, for example, a phase difference may be created with a medium having a refractive index “na” such as a predetermined sheet, and the medium may be integrated with a glass substrate in a sandwich shape. The phase change means using this sheet is expensive, but the property of changing the polarization state, the so-called polarization anisotropy function is added to the phase change means, or it is integrated with the quarter-wave plate and combined. Thus, the function of polarization anisotropy may be added to the phase changing means, and the phase changing means may be enhanced. The functions of the phase change means may be selected individually and specifically based on the arrangement in the optical path of the optical pickup.

(3-2) Improvement of signal intensity level by optical functional element
Next, with reference to FIGS. 8 to 11, the improvement in the signal intensity level of the received push-pull signal caused by the optical functional element according to the present embodiment will be described qualitatively and quantitatively. FIG. 8 is a schematic diagram (FIG. 8A) schematically showing an interference pattern formed on the light receiving means according to the present embodiment, and the optical functional element according to the present embodiment. FIG. 8B is a graph quantitatively showing transitions with interlayer distance as a variable in the signal intensity level of the output push-pull error signal (FIG. 8B). FIG. 9 is a schematic diagram (FIG. 9A) schematically showing an interference pattern formed in the light receiving unit according to the comparative example, and the signal strength of the output push-pull error signal according to the comparative example. It is the graph (Drawing 9 (b)) which showed quantitatively the transition which made interlayer distance a variable in a level. FIG. 10 is a schematic diagram schematically showing an interference pattern formed on the light receiving means according to a general example. FIG. 11 is a schematic diagram schematically showing an optical principle of outputting a push-pull error signal according to a general example.

  The vertical axis in FIGS. 8B and 9B indicates the value of “SPP / SUM” corresponding to the signal strength level of the push-pull signal. Here, “SUM (Summary)” according to the present embodiment is the sum of the amounts of light received by the light receiving means having the light receiving area divided into two when performing tracking control based on the push-pull signal. Indicates the level. In addition, “SPP (Sub Push Pull)” according to the present embodiment refers to a light receiving region divided into two parts included in the light receiving means when performing tracking control based on the above-described push pull signal. The level of the difference between the received light amounts is shown. In addition, the five curves in FIGS. 8B and 9B indicate that the above lens shift magnitudes are “20%”, “10%”, “0%”, “−” in order from the top. 10% "and" -20% "respectively. Here, the “lens shift magnitude” according to the present embodiment is defined by the following equation (2a).

Lens shift size (%) =
(Lens travel / Lens effective diameter) x 100 (2a)
The quantitative results shown in FIGS. 8B and 9B are based on simulations, but can be calculated theoretically, empirically, and experimentally. It should be noted that this simulation was performed on a multi-layered optical disk, ie, a so-called mirror disk, in which no recording pits exist.

  As shown in FIG. 8A, according to the study by the inventors of the present application, qualitatively, the light intensity is relatively high based on the laser light transmitted through the optical functional element according to the present embodiment. Are formed on the light receiving means (see a small amount of white portions in FIG. 8A and a large amount of white portions in FIG. 9A described later). In other words, the spatial frequency in the central portion of the laser light is relatively increased in substantially the same manner as the position distribution of the light intensity of the laser light with little or no influence of the stray light shown in FIG. An interference pattern with a reduced level of light intensity difference is formed on the light receiving means. In this way, in the light receiving means, the irradiated regions overlap, for example, interference between ± 1st order diffracted signal light and, for example, 0th order stray light, or 0th order signal light, for example, ± 1 next time. By increasing the spatial frequency in the interference pattern generated based on interference with the folded stray light or reducing the level of the light intensity difference, the effect of interference between the signal light and the stray light can be effectively reduced. It is possible to suppress. Therefore, as shown in FIG. 8B, based on the laser light transmitted through the optical functional element according to the present embodiment, the interlayer distance at the signal intensity level of the output push-pull error signal is quantitatively determined. It is possible to significantly reduce the degree of transition using as a variable. Specifically, as shown in the uppermost curve in FIG. 8B, even if the interlayer distance changes from “25.0 (μm)” to “25.2 (μm)”, The signal strength level of the output push-pull error signal has a relatively small transition centered at about “0.1”. In particular, the amplitude of the signal strength level of the push-pull error signal corresponding to this uppermost curve is “0.03744”, which passes through the optical functional element shown in FIG. The degree of transition is remarkably reduced by about “1/3” times compared to the amplitude “0.1207” of the signal intensity level of the output push-pull error signal based on the laser light that is not I understand that. In addition, as a result of the comparison of the signal strength levels of the push-pull error signals corresponding to the other four curves shown in FIG. 8B and FIG. It can be seen that the degree of transition with the interlayer distance as a variable at the signal intensity level of the output push-pull error signal is remarkably reduced based on the laser light transmitted through the optical functional element.

  If the light receiving means is irradiated with laser light that does not pass through the optical functional element, as shown in FIG. 9A, qualitatively, there are many interference patterns in which the light intensity is relatively high. (Refer to a small amount of white portions in FIG. 8A and a large amount of white portions in FIG. 9A described later) on the light receiving means. In other words, an interference pattern in which the spatial frequency is relatively low and the level of the light intensity difference is increased is formed on the light receiving means. Therefore, as shown in FIG. 9B, the degree of transition using the interlayer distance as a variable in the signal intensity level of the output push-pull error signal based on the laser light that does not pass through the optical functional element is significant. Thus, the influence of interference between the signal light and the stray light becomes large.

  On the other hand, based on the laser beam transmitted through the optical functional element according to the present embodiment, qualitatively, the interference pattern in which the spatial frequency is relatively increased and the level of the light intensity difference is reduced. Is formed on the light receiving means. Therefore, it is possible to effectively suppress the influence of interference between signal light and stray light. As a result, in multi-layer information recording media, for example, tracking control and focus control based on the three-beam method, it is possible to effectively reduce the influence of stray light and maintain the light intensity level higher. It is possible to realize high-precision tracking control and focus control by causing the means to receive light.

  More specifically, as shown in the upper part of FIG. 11, when laser light is irradiated on the groove track (G1 or G2) or land track (L1) of the recording or reproducing surface of the optical disk, In the light receiving area 1 and the light receiving area 2, a push-pull error signal is output based on the difference between the received light amounts. Specifically, laser light including 0th-order light and ± 1st-order diffracted light is moved on the groove track (G1), land track (L1), and groove track (G2) in the radial direction of the optical disk. When the zero-order light is in the groove track (G1), the signal components corresponding to the -1st order diffracted light and the + 1st order diffracted light among the 0th order light shown in the middle part of FIG. Since they are substantially equal, the push-pull error signal whose radial position corresponds to the groove track G1 is substantially zero as shown in the lower part of FIG. On the other hand, when the 0th order light is in the middle of the groove track (G1) and the land track (L1), the -1st order diffracted light and the + 1st order diffracted light among the 0th order light shown in the middle of FIG. The signal component corresponding to one of them becomes the maximum, and the signal component corresponding to either one becomes the minimum. Therefore, as shown in the lower part of FIG. The push-pull error signal corresponding to the intermediate position between G1) and the land track (L1) is the minimum value. In this way, a push-pull error signal is generally output.

(3-3) Examination of functions and effects of optical functional elements
Next, with reference to FIG.12 and FIG.13, the effect | action and effect of the optical function element based on a present Example are demonstrated. FIG. 12 is a schematic diagram schematically showing the interference pattern formed on the light receiving means according to the present embodiment, paying attention to the spatial frequency. FIG. 13 is a diagram illustrating the correlation between the spatial frequency in the interference pattern formed on the light receiving means and the level of the amount of light received by the two light receiving regions due to the optical functional element according to the present embodiment. It is the schematic diagram shown.

  As shown in FIG. 12, according to the study by the present inventor, the spatial frequency is relatively enhanced qualitatively based on the laser light transmitted through the optical functional element according to the present embodiment. An interference pattern with a reduced level of light intensity difference is formed on the light receiving means. Specifically, as shown in the lower and middle stages of FIG. 13, when the spatial frequency of the laser light received in one region of the light receiving means is relatively high, based on a minute change in the interlayer distance. Thus, it is possible to reduce the influence of the brightness of the laser light applied to the light receiving means, that is, the degree of change in the amount of laser light applied to the light receiving means to a relatively small level. In other words, the level of light interference can be made relatively small.

  If an interference pattern having a relatively low spatial frequency is formed on the light receiving means, the spatial frequency of the laser light received in one region of the light receiving means is relatively high as shown in the upper part of FIG. If it is low, the influence of the brightness of the laser light applied to the light receiving means, that is, the degree of change in the amount of laser light applied to the light receiving means is relatively large based on a minute change in the interlayer distance. It becomes a level. In other words, the level of light interference becomes a relatively large level.

  On the other hand, based on the laser beam transmitted through the optical functional element according to the present embodiment, qualitatively, the interference pattern in which the spatial frequency is relatively increased and the level of the light intensity difference is reduced. Is formed on the light receiving means. Accordingly, the level of light interference can be made relatively small. As a result, in multi-layer information recording media, for example, tracking control and focus control based on the three-beam method, it is possible to effectively reduce the influence of stray light and maintain the light intensity level higher. It is possible to realize high-precision tracking control and focus control by causing the means to receive light.

  In addition, the optical functional element according to the present embodiment is configured by an anisotropic medium described later, so that various optical disks or optical pickups based on an applied voltage applied to the anisotropic medium. It is possible to control the phase difference of the wave front so as to be optimal in response to the appropriate characteristics.

  In addition, the optical functional element according to the present embodiment is based on the arrangement of the optical functional element having polarization anisotropy, and the wavefront in the return path without giving a phase difference of the wavefront in the forward path on the optical path of the optical pickup. It is possible to give a phase difference of. As a result, the occurrence of various aberrations can be appropriately suppressed, the quality of the laser light can be improved, and the optical performance in recording or reproduction of the optical pickup can be improved.

(4) Other specific examples of optical functional elements
Next, another specific example of the optical functional element according to the present embodiment will be described with reference to FIGS.

(4-1) Optical principle in an optical functional element constituted by an anisotropic medium
Next, with reference to FIG. 14, the optical principle in the optical functional element constituted by the anisotropic medium according to the present embodiment will be described. FIG. 14 is a schematic diagram (FIG. 14A) schematically showing the refractive index in the anisotropic medium constituting the optical functional element according to the present embodiment, and according to the present embodiment. It is the schematic diagram (FIG.14 (b)) which showed the optical principle of the optical function element typically.

  As shown in FIG. 14B, between the laser beam that has passed through one region of the optical functional element constituted by the anisotropic medium and the laser beam that has passed through the other region, according to this embodiment. In addition, a phase difference can be generated. Specifically, this phase difference is the difference between the optical path length of the laser beam that passes through one region of the optical functional element and the optical path length of the laser beam that passes through the other region. It can be expressed by equation (3).

(Phase difference) = (nz × d) − (nx × d) (3)
However, the refractive index of the anisotropic medium is “nx”, “ny”, and “nz” in the x-axis direction, the y-axis direction, and the z-axis direction, respectively, as shown in FIG. Further, the distance between the first substrate and the second substrate, in which the anisotropic medium is enclosed, is “d”. In addition, as shown in FIG. 14B, an anisotropic medium is applied between the first substrate and the second substrate by applying a predetermined voltage in one region of the optical functional element. The z-axis direction is enclosed so that it is parallel to the polarization direction of the laser beam. On the other hand, in another region of the optical functional element, when a predetermined voltage is applied, the x-axis direction of the anisotropic medium is changed between the polarization direction of the laser light between the first substrate and the second substrate. Enclosed in parallel.

  As a result, the phase of the wavefront in the laser light transmitted through one region of the optical functional element constituted by the anisotropic medium and the phase of the wavefront in the laser light transmitted through the other region without transmitting through the one region It is possible to cause a predetermined phase difference.

  In particular, as described above, as the phase change means included in the optical functional element, for each position, the inclination of the anisotropic medium is based on a plurality of condensing positions respectively corresponding to a plurality of recording layers. The applied voltage may be changed. Specifically, the optical pickup can realize a plurality of types of voltage patterns when applied to an anisotropic medium, and uses one type of voltage pattern corresponding to the recording layer to be condensed. You may do it.

(4-2) Optical Functional Element Defined Based on Size and Shape of Irradiated Laser Light Next, referring to FIG. 15, the size of the irradiated laser light according to the present example. The physical shape of the optical functional element defined on the basis of the shape and the interference pattern formed on the light receiving means corresponding to the phase changing means included in the optical functional element will be described. FIG. 15 is a plan view schematically showing the physical shape of the optical functional element having one phase change means according to this embodiment, and the light reception corresponding to the one phase change means. FIG. 15A is a plan view schematically showing the interference pattern formed on the means, and the physical shape of the optical functional element having other phase change means according to the present embodiment. FIG. 15B is a plan view schematically showing an interference pattern formed on the light receiving means, corresponding to the other phase change means (FIG. 15B).

  As shown in FIGS. 15A and 15B, the size and positional relationship of the two phase change means described above are the size and shape of the laser light irradiated on the light receiving means. Or may be defined based on the size and shape of the interference pattern formed on the light receiving means. Specifically, as shown in FIG. 15B, when the laser beam irradiated onto the light receiving unit is relatively large, the length of the phase changing unit in the Rad direction is set to, for example, “2”. .0 ”or the like, and the length in the Tan direction may be increased from“ 0.4 ”to“ 0.5 ”or the like. Therefore, it corresponds to optical design such as laser light protruding from the light receiving means due to lens shift, and also supports various signal characteristics such as RF signal and focus error signal in addition to push-pull error signal However, according to the present embodiment, a predetermined phase difference is set between the phase of the wavefront in a part of the laser light transmitted through the phase change unit and the phase of the wavefront in the other part of the laser light not transmitted through the phase change unit. Can be generated.

(4-3) Optical Functional Element Having Phase Change Means with Various Shapes Next, with reference to FIGS. 16 and 17, an optical functional element having phase changes means with various shapes according to the present embodiment. Will be described.

(4-3-1) Optical Functional Element Having Four Phase Change Means First, referring to FIG. 16, the physical shape of the optical functional element having four phase change means according to the present embodiment, The interference pattern formed on the light receiving means corresponding to the phase changing means and the improvement of the signal intensity level of the output push-pull error signal caused by this optical functional element will be described. FIG. 16 is a plan view schematically showing the physical shape of the optical functional element having four phase change means according to the present embodiment (FIG. 16A). Corresponding plan view schematically showing the interference pattern formed on the light receiving means (FIG. 16B), at the signal strength level of the output push-pull error signal caused by this optical functional element FIG. 16 is a graph (FIG. 16C) that quantitatively shows the transition with the interlayer distance as a variable.

  As shown in FIG. 16A, the optical functional element according to the present embodiment is arranged along the Tan direction and is symmetrical with respect to the Rad direction passing through the center of the optical functional element. Are provided with four phase changing means. Even if this arrangement is not completely line symmetric, the degree of reduction in the level of light intensity difference in the interference pattern does not suddenly decrease. An interference pattern with a reduced level is formed. Corresponding to this optical functional element, as shown in FIG. 16B, qualitatively, an interference pattern in which the spatial frequency is relatively increased and the level of the light intensity difference is reduced is received. Formed on the means. In particular, this interference pattern has a shape with little or no symmetry or regularity in optical geometry.

  Accordingly, as shown in FIG. 16C, the push-pull error signal output quantitatively based on the laser light transmitted through the optical functional element having the four phase change means according to the present embodiment. It is possible to significantly reduce the degree of transition with the interlayer distance as a variable at the signal intensity level. Specifically, as shown in the uppermost curve in FIG. 16C, even if the interlayer distance changes from “25.0 (μm)” to “25.2 (μm)”, The signal strength level of the output push-pull error signal has a relatively small transition centered at about “0.1”. In particular, the amplitude of the signal intensity level of the push-pull error signal corresponding to this uppermost curve is “0.04541”, and the laser does not transmit through the optical functional element shown in FIG. 9B described above. Based on the light, the degree of transition is remarkably reduced to about “1/3” times the amplitude “0.1207” of the signal strength level of the output push-pull error signal. I understand. In addition, as a result of the comparison of the signal strength levels of the push-pull error signals corresponding to the other four curves shown in FIG. 16C and FIG. It can be seen that the degree of transition with the interlayer distance as a variable at the signal intensity level of the output push-pull error signal is remarkably reduced based on the laser light transmitted through the optical functional element.

(4-3-2) Optical functional element having nine phase change means Next, referring to FIG. 17, the physical shape of the optical functional element having nine phase change means according to the present embodiment, 9 The interference pattern formed on the light receiving means corresponding to the two phase changing means and the improvement of the signal intensity level of the output push-pull error signal caused by this optical functional element will be described. FIG. 17 is a plan view schematically showing the physical shape of the optical functional element having nine phase change means according to this embodiment (FIG. 17A). The corresponding plan view schematically showing the interference pattern formed on the light receiving means (FIG. 17B), at the signal strength level of the output push-pull error signal caused by this optical functional element FIG. 17 is a graph (FIG. 17C) that quantitatively shows the transition with the interlayer distance as a variable.

  As shown in FIG. 17A, the optical functional element according to the present embodiment is line symmetric with respect to the Rad direction passing through the center of the optical functional element, and has a Tan direction passing through the center of the optical functional element. There are nine phase change means arranged so as to be line-symmetric with respect to the axis (so-called block shape). Even if this arrangement is not completely line symmetric, the degree of reduction in the level of light intensity difference in the interference pattern does not suddenly decrease. An interference pattern having a reduced level is formed. Corresponding to this optical functional element, as shown in FIG. 17B, qualitatively, the spatial frequency is relatively increased, the light intensity difference level is significantly reduced, and the central portion An interference pattern in which the level of the light intensity itself is reduced is formed on the light receiving means. In particular, in this embodiment, nine or more phase change means may be formed irregularly and randomly.

  Therefore, as shown in FIG. 17 (c), based on the laser beam that has passed through the optical functional element having nine phase change means according to the present embodiment, the output push-pull error signal is quantitatively determined. It is possible to significantly reduce the degree of transition with the interlayer distance as a variable at the signal intensity level. Specifically, as shown in the uppermost curve in FIG. 17C, even if the interlayer distance changes from “25.0 (μm)” to “25.2 (μm)”, The signal strength level of the output push-pull error signal has a relatively small transition centered at about “0.1”. In particular, the amplitude of the signal intensity level of the push-pull error signal corresponding to this uppermost curve is “0.02017”, and the laser does not transmit through the optical functional element shown in FIG. 9B described above. Based on light, the degree of transition is remarkably reduced to about “1/6” times the amplitude “0.1207” of the signal strength level of the output push-pull error signal. I understand. In addition, as a result of the comparison of the signal strength levels of the push-pull error signals corresponding to the other four curves shown in FIG. 17C and FIG. It can be seen that the degree of transition with the interlayer distance as a variable at the signal intensity level of the output push-pull error signal is remarkably reduced based on the laser light transmitted through the optical functional element.

  In particular, the number, size, shape, and arrangement of the phase change means included in the optical functional element as described above are respectively defined based on a plurality of condensing positions respectively corresponding to a plurality of recording layers. You may be made to do. Specifically, the optical pickup may include a plurality of types of optical functional elements, and use one type of optical functional elements corresponding to the recording layer to be condensed.

(5) Arrangement of optical functional elements
Next, with reference to FIG. 18, the optical arrangement of the optical functional element according to the present embodiment will be described. FIG. 18 is a block diagram conceptually showing the more detailed structure of the optical pickup 100 provided in the information recording / reproducing apparatus 300 in the example.

  As shown in FIG. 18, the optical functional element 104 a according to the present embodiment may be arranged at a position close to the reflection mirror 106 in the outward path where the laser beam is irradiated. In particular, this optical functional element is integrated with a quarter wavelength plate so that the polarization direction is not changed when the laser beam is first transmitted from the semiconductor laser side, and the laser beam is transmitted from the optical disc side. Further, it may have a property of changing the polarization direction (so-called polarization anisotropy). As a result, it is possible to define an optical functional element that is not affected by a change in the size of the laser beam on the optical path.

  Alternatively, as shown in FIG. 18, the optical functional element 104 b according to the present embodiment is located at a position where the condensing lens (objective lens) 108 is close to the condensing lens (objective lens) 108 in the outward path where the laser light is irradiated. The lens (objective lens) 108 may be integrated with the lens (objective lens) 108. In particular, this optical functional element is integrated with a quarter-wave plate so that the laser beam does not change the polarization direction when the laser beam is first transmitted from the semiconductor laser side, and the laser beam is transmitted from the optical disc side. Further, it may have a property of changing the polarization direction (so-called polarization anisotropy). As a result, it is possible to define an optical functional element that is not affected by a change in the position of the light beam on the optical path in the lens shift of the condenser lens. In addition, the optical functional element according to the present embodiment is based on the arrangement of the optical functional element having polarization anisotropy, and the wavefront in the return path without giving a phase difference of the wavefront in the forward path on the optical path of the optical pickup. It is possible to give a phase difference of. As a result, the occurrence of various aberrations can be appropriately suppressed, the quality of the laser light can be improved, and the optical performance in recording or reproduction of the optical pickup can be improved.

  The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit or idea of the invention that can be read from the claims and the entire specification, and an optical pickup and information accompanying such a change. Equipment is also within the scope of the present invention.

It is the block diagram which showed the basic composition of the information recording / reproducing apparatus which concerns on the Example of the information recording device of this invention, and a host computer. 2 is a block diagram conceptually showing a more detailed structure of an optical pickup 100 provided in the information recording / reproducing apparatus 300 in the example. FIG. It is a schematic diagram conceptually showing light interference between signal light and stray light in a general optical pickup. A side view (FIG. 4 (a)), a plan view (FIG. 4 (b)), and a schematic perspective view (FIG. 4 (c)) schematically showing the physical shape of the optical functional element according to the present embodiment. ). It is the top view which showed typically the physical shape of the optical functional element which concerns on a present Example. Schematic diagram schematically showing the optical principle of the optical functional element according to the present embodiment (FIG. 6A), and schematically showing the wavefront of the laser light transmitted through the optical functional element according to the present embodiment. It is the schematic diagram shown (FIG.6 (b)), and the schematic diagram (FIG.6 (c)) which showed the wave front of the laser beam based on a comparative example typically. It is the other schematic diagram which showed typically the optical principle of the optical function element based on a present Example. The schematic diagram (FIG. 8A) schematically showing the interference pattern formed in the light receiving means according to the present embodiment, and the output push-pull caused by the optical functional element according to the present embodiment It is the graph (Drawing 8 (b)) which showed quantitatively the transition which made the distance between layers in the signal intensity level of an error signal a variable. A schematic diagram (FIG. 9A) schematically showing an interference pattern formed on the light receiving means according to the comparative example, and an interlayer at the signal strength level of the output push-pull error signal according to the comparative example It is the graph (Drawing 9 (b)) which showed the transition which used distance as a variable quantitatively. It is the schematic diagram which showed typically the interference pattern formed in the light-receiving means based on a general example. It is the schematic diagram which showed the optical principle based on a general example that the push pull error signal is output schematically. It is the schematic diagram which showed schematically the interference pattern formed on the light-receiving means based on a present Example paying attention to a spatial frequency. The correlation between the spatial frequency in the interference pattern formed on the light receiving means and the level of the amount of light received by the two light receiving regions due to the optical functional element according to the present embodiment is schematically shown. It is a schematic diagram. The schematic diagram (FIG. 14A) schematically showing the refractive index in the anisotropic medium constituting the optical functional element according to the present embodiment, and the optical function element according to the present embodiment. It is the schematic diagram (FIG.14 (b)) which showed the principle schematically. The top view which showed typically the physical shape of the optical functional element which has one phase change means based on a present Example, and the interference formed on the light-receiving means corresponding to one phase change means A plan view schematically showing a pattern (FIG. 15A), and a plan view schematically showing a physical shape of an optical functional element having other phase change means according to the present embodiment; and FIG. 15 is a plan view (FIG. 15B) schematically showing an interference pattern formed on the light receiving means, corresponding to another phase changing means. FIG. 16A is a plan view schematically showing the physical shape of an optical functional element having four phase change means according to the present embodiment. On the light receiving means corresponding to the four phase change means. FIG. 16B is a plan view schematically showing the interference pattern formed on the substrate, and the interlayer distance at the signal strength level of the output push-pull error signal caused by this optical functional element is used as a variable. It is the graph (FIG.16 (c)) which showed the transition quantitatively. FIG. 17A is a plan view schematically showing the physical shape of an optical functional element having nine phase change means according to the present embodiment, on the light receiving means corresponding to the nine phase change means. FIG. 17B is a plan view schematically showing the interference pattern formed on the substrate, and the interlayer distance at the signal intensity level of the output push-pull error signal caused by this optical functional element is used as a variable. It is the graph (FIG.17 (c)) which showed the transition quantitatively. 2 is a block diagram conceptually showing a more detailed structure of an optical pickup 100 provided in the information recording / reproducing apparatus 300 in the example. FIG. It is the top view which showed the relative positional relationship of the light-receiving part which concerns on a comparative example, and a light beam diameter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical disk 100 Optical pick-up 101 Semiconductor laser 102 Diffraction grating 103 etc. Condensing lens 104 (104a) Optical functional element 105 Optical path branching element 106 Reflecting mirror 107 1/4 wavelength plate 110 Astigmatism generation lens PD0 etc. Light receiving part 300 Information recording / reproduction Apparatus 302: Signal recording / reproducing means

Claims (19)

An optical pickup that performs at least one of data recording and reproduction on a recording medium having a plurality of recording layers,
A light source that emits laser light;
An optical system for guiding the irradiated laser light to one of the plurality of recording layers;
When the guided laser beam is focused on the one recording layer, (i) a part of the signal light generated in the one recording layer, and (ii) another of the plurality of recording layers An optical functional element including phase change means for changing the phase of the wavefront in a part of the stray light generated in the recording layer;
(Iii) one or more light receiving means for receiving at least the signal light;
An optical pickup comprising:   The phase change means includes (i) a part of the signal light transmitted through the phase change means and a phase of a wavefront in a part of the stray light, and (ii) the signal light not transmitted through the phase change means. 2. The optical pickup according to claim 1, wherein a predetermined phase difference is generated between the other part and the phase of the wavefront in the other part of the stray light.   3. The optical pickup according to claim 2, wherein the predetermined phase difference is defined based on a quarter to a half of the wavelength of the laser light.   4. The optical pickup according to claim 1, wherein the phase change unit includes a medium having one optical refractive index. 5.   The optical pickup according to claim 4, wherein a portion of the optical functional element that does not include the phase change unit includes a medium having another optical refractive index. In the optical functional element, at least two of the phase change means are formed along a reference direction,
The reference direction is defined on the basis of a tangential direction of the recording medium corresponding to a position where the diffracted light is irradiated with zero-order light diffracted by the laser light. 5. The optical pickup according to claim 1. In the optical functional element, at least two phase change means are formed along the reference direction corresponding to the position where the laser light is diffracted and the zero-order light and the diffracted light are irradiated.
The optical pickup according to claim 1, wherein at least two of the phase change units are arranged to be line-symmetric with respect to a radial direction orthogonal to the reference direction as an axis. . In the optical functional element, at least two phase change means are formed along the reference direction corresponding to the position where the laser light is diffracted and the zero-order light and the diffracted light are irradiated.
The at least two phase change means are arranged so as to be line symmetric with respect to the reference direction and a radial direction orthogonal to the reference direction as an axis. The optical pickup according to the item.   The size, shape, and arrangement of one or a plurality of the phase change means are defined based on the size and shape of the laser beam irradiated on the optical functional element. Item 9. The optical pickup according to any one of Items 1 to 8.   The size, shape, and arrangement of one or a plurality of the phase change means are the shape and magnitude of an interference pattern generated by the interference of light waves between the signal light received by the light receiving means and the stray light. The optical pickup according to claim 1, wherein the optical pickup is defined based on the length of the optical pickup.   11. The size, shape, and arrangement in one or a plurality of the phase change means are defined based on an interlayer distance between the plurality of recording layers. The optical pickup described in 1.   2. The size, shape, and arrangement of one or a plurality of the phase change means are defined based on a plurality of condensing positions respectively corresponding to the plurality of recording layers. The optical pickup according to any one of 11.   The optical functional element includes (i) a first substrate, (ii) a second substrate, (iii) an anisotropic medium enclosed between the first substrate and the second substrate, iv) It is constituted by an electrode for changing a voltage applied to the anisotropic medium in accordance with the size, shape and arrangement of the phase changing means. The optical pickup according to any one of the above. A diffracting means for diffracting the irradiated laser light into zero-order light and diffracted light;
The optical system guides the diffracted zero-order light and the diffracted light to the one recording layer,
The optical functional element changes a phase of a wavefront in a part of the zero-order light and a part of the diffracted light,
The optical pickup according to claim 1, wherein the light receiving unit receives at least the diffracted light. An optical path branching unit for guiding the zero-order light from the one recording layer and the diffracted light to the light receiving unit;
The optical functional element is arranged (i) on an optical path from the recording medium to the optical path branching means, or (ii) on an optical path from the optical path branching means to the light receiving means. The optical pickup according to claim 14.   16. The optical pickup according to claim 14, wherein the order of the diffracted light is ± 1st order.   The first light receiving means and the second light receiving means for receiving the diffracted light of the laser light, and the third light receiving means for receiving the 0th order light of the laser light as the light receiving means. Item 17. The optical pickup according to any one of Items 1 to 16.   The apparatus further comprises control means for controlling the optical system so as to guide the laser light to a recording track included in the one recording layer based on zeroth-order light and diffracted light in the laser light. The optical pickup according to claim 1. An optical pickup according to any one of claims 1 to 18, and
An information apparatus comprising: a recording / reproducing unit that records or reproduces the data by irradiating the recording medium with the laser beam.