JP2007193912A - Light source unit, optical detector unit, optical pickup device, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source unit to be miniaturized without deteriorating light use efficiency. <P>SOLUTION: A hologram element H11 allows light beams from hologram units HU2, HU3 to be transmitted as they are and diffracts a light beam from a hologram unit HU1 toward a +X direction. A hologram element H31 allows the light beam which is from the hologram unit HU2 and passes through the hologram element H11, and the diffracted light beam from the hologram element H11 to be transmitted as they are and diffracts the light beam, which is from the hologram unit HU3 and passes through the hologram element H11, toward the +X direction. Both the hologram elements are arranged side by side in an X-axis direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light source unit, a light detection unit, an optical pickup device, and an optical disk device. More specifically, the present invention relates to a light source unit that emits a plurality of lights, a light detection unit that individually detects a plurality of light beams, and irradiates light onto an optical disk. In addition, the present invention relates to an optical pickup device that receives reflected light from the optical disc, and an optical disc device including the optical pickup device.

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

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

  Incidentally, the amount of content information tends to increase year by year, and further increase in the recording capacity of the optical disc is expected. Therefore, as one of means for increasing the recording capacity of the optical disc, the Blu-ray standard having a higher recording density than that of a commercially available DVD has been proposed. The optical disc conforming to the Blu-ray standard (hereinafter abbreviated as “BD”) has a substrate thickness of 0.1 mm, and the optical disc apparatus corresponding to BD uses a light source having a wavelength of 405 nm and has an NA of the objective lens. A 0.85 focused spot is formed, and information is recorded, reproduced and erased. That is, DVD and BD have different light source wavelengths, substrate thicknesses, and NAs.

  Therefore, it is possible to deal with both DVD and BD, and in an optical disc apparatus having one objective lens, if the characteristics of the objective lens are matched to one medium, an aberration caused by a difference in substrate thickness occurs in the other medium. There is an inconvenience.

  As another means for increasing the recording capacity of an optical disk, a so-called hologram method has recently attracted attention, but the reliability of the recording material and the reproducibility in the optical system are not sufficient, so that it can be put into practical use from a fundamental viewpoint. There is a dangerous opinion. On the other hand, as another promising means, a so-called three-dimensional multilayer system in which a plurality of recording layers of about several tens of layers are superposed has been developed. In this three-dimensional multilayer system, there have been published many examples in which a fluorescent material or a two-photon absorption material is used as a recording material and the transmittance and interlayer crosstalk are improved. However, the recording / reproducing speed is slower than the hologram system. Is the biggest drawback.

  According to the optical element disclosed in Patent Document 1, in order to make the number of recording layers of an optical disk several tens of layers, it is necessary to use different recording materials for each layer. was there.

  According to the apparatus disclosed in Patent Document 2, when a plurality of light sources are arranged on the same plane, wavefront aberration (coma aberration) is generated in the lens system with light from a light source outside the optical axis. There is a disadvantage that it is difficult to obtain a diffraction-limited light spot on the disk surface. Further, since the light from the collimating lens is emitted at a certain angle, the amount of light taken into the objective lens is different for each light source, and there is a disadvantage that the light use efficiency is lowered.

  Furthermore, according to the optical element disclosed in Non-Patent Document 1, the volume hologram has a diffraction efficiency that decreases as the multiple exposure is performed. . If the light source is placed on a plane perpendicular to the optical axis, the light from the collimating lens is emitted at a certain angle. There is a disadvantage that the light spot is lowered or the light spot is asymmetrical.

JP-A-63-1113947 Japanese Patent No. 2998732 Lee, S.M. C. Y. Kawata "Volume holographic device for the theoretical correlation correction and the parallel data access in three-dimensional memory" Fr-PD-15 ISOM2000

  The present invention has been made under such circumstances, and a first object of the present invention is to provide a light source unit and a light detection unit that can be reduced in size without lowering light utilization efficiency.

  A second object of the present invention is to provide an optical pickup device that can be reduced in size without degrading performance.

  A third object of the present invention is to provide an optical disc apparatus that can be miniaturized without lowering the access accuracy to the optical disc.

  According to a first aspect of the present invention, there is provided a light source unit that emits a plurality of lights in a predetermined emission direction, a plurality of light sources; provided corresponding to the plurality of light sources individually, and the plurality of light sources A plurality of volumes that are arranged side by side in the emission direction on the optical path of a plurality of light beams emitted from the light source, diffract light from the corresponding light source, and allow light from light sources other than the corresponding light source to pass through without being diffracted And a hologram element.

  According to this, there are provided a plurality of volume hologram elements that are individually provided corresponding to a plurality of light sources, diffract light from the corresponding light sources, and transmit light from light sources other than the corresponding light sources as they are without being diffracted. Since it is arranged side by side in the emission direction on the optical paths of the plurality of lights emitted from the plurality of light sources, it is possible to reduce the size without reducing the light utilization efficiency.

  From a second aspect, the present invention is a light source unit that emits a plurality of lights in a predetermined emission direction, a plurality of light sources; and at least one light source excluding a preset light source among the plurality of light sources. Are arranged on the optical path of a plurality of light emitted from the plurality of light sources, diffracts light from at least one corresponding light source, and does not diffract light from other light sources as they are. And at least one volume hologram element to be transmitted.

  According to this, it is provided corresponding to at least one light source excluding a preset light source among a plurality of light sources, diffracts light from at least one corresponding light source, and diffracts light from other light sources. Since at least one volume hologram element that is transmitted as it is is arranged on the optical paths of a plurality of lights emitted from a plurality of light sources, it is possible to reduce the size without reducing the light utilization efficiency. Become.

  From a third viewpoint, the present invention is a light detection unit that individually detects a plurality of light beams incident from a predetermined incident direction, and is provided corresponding to each of the plurality of light beams. A plurality of volume hologram elements that are arranged side by side in the incident direction on the optical path, and that diffract corresponding light beams and transmit light beams other than the corresponding light beams as they are without being diffracted; and individually for the plurality of volume hologram elements A plurality of photodetectors provided correspondingly and receiving diffracted light from the corresponding volume hologram elements.

  According to this, the plurality of volume hologram elements that are provided corresponding to the plurality of light beams individually, diffract the corresponding light beams, and transmit the light beams other than the corresponding light beams as they are without being diffracted. Since they are arranged side by side in the incident direction of a plurality of light beams on the road, it is possible to reduce the size without reducing the light utilization efficiency.

  According to a fourth aspect of the present invention, there is provided a light detection unit for individually detecting a plurality of light beams incident from a predetermined incident direction, wherein at least one light beam excluding a preset light beam among the plurality of light beams. And at least one volume hologram element disposed on an optical path of the plurality of light beams, diffracting at least one corresponding light beam, and transmitting the other light beams without being diffracted; And a plurality of photodetectors that individually receive the diffracted light flux and diffracted light from the at least one volume hologram element.

  According to this, at least one luminous flux excluding a preset luminous flux is provided among a plurality of luminous fluxes, and at least one corresponding luminous flux is diffracted, and the other luminous flux is transmitted as it is without being diffracted. Since one volume hologram element is disposed on the optical path of a plurality of light beams, it is possible to reduce the size without reducing the light utilization efficiency.

  From a fifth aspect, the present invention is an optical pickup device that irradiates an optical disk with light and receives reflected light from the optical disk, the light source unit of the present invention; and a plurality of light sources emitted from the light source unit An optical pickup device comprising: an optical system including an objective lens that condenses light on an optical disc; and a photodetector that receives return light from the optical disc.

  According to this, since the light source unit of the present invention is provided, it is possible to reduce the size without degrading the performance.

  According to a sixth aspect of the present invention, there is provided an optical pickup device that irradiates an optical disc with light and receives reflected light from the optical disc, comprising: a plurality of light sources; and a plurality of lights emitted from the plurality of light sources. An optical pickup device comprising: an objective lens that focuses the light on the optical disc; and a light detection unit of the present invention that is disposed on an optical path of the return light from the optical disc via the objective lens and detects the return light. is there.

  According to this, since the light detection unit of the present invention is provided, it is possible to reduce the size without incurring performance degradation.

  From a seventh aspect, the present invention is an optical pickup device that irradiates light to an optical disk and receives reflected light from the optical disk, the light source unit of the present invention; and a plurality of light sources emitted from the light source unit An optical system including an objective lens for condensing light on the optical disc; and a light detection unit of the present invention that is disposed on an optical path of return light from the optical disc via the objective lens and detects the return light; An optical pickup device provided.

  According to this, since the light source unit of the present invention and the light detection unit of the present invention are provided, it is possible to reduce the size without degrading the performance.

  According to an eighth aspect of the present invention, there is provided an optical pickup device for irradiating an optical disc with light and receiving reflected light from the optical disc, comprising: a plurality of light sources; and light emitted from the plurality of light sources, respectively. An objective lens for condensing on the optical disc; provided individually corresponding to the plurality of light sources, arranged side by side on an optical path between the plurality of light sources and the objective lens, and emitted from the corresponding light source and the objective The light directed to the lens and the light emitted from the corresponding light source are diffracted from the optical disk, and the light emitted from the light source other than the corresponding light source toward the objective lens and the light source other than the corresponding light source A plurality of volume hologram elements that allow the light emitted from the optical disk to pass through without being diffracted, and to the plurality of volume hologram elements; Separately it provided corresponding a plurality of photodetectors for receiving the return light diffracted by the corresponding volume hologram element; an optical pickup apparatus comprising a.

  According to this, it is provided corresponding to each of a plurality of light sources individually, diffracts the light emitted from the corresponding light source and directed to the objective lens, and the return light from the optical disk of the light emitted from the corresponding light source, A plurality of volume hologram elements that transmit the light emitted from the light source other than the corresponding light source toward the objective lens and the light emitted from the light source other than the corresponding light source from the optical disk without being diffracted as it is, Since they are arranged side by side on the optical path between the plurality of light sources and the objective lens, it is possible to reduce the size without degrading the performance.

  According to a ninth aspect of the present invention, there is provided an optical pickup device that irradiates an optical disc with light and receives reflected light from the optical disc, comprising: a plurality of light sources; and light emitted from the plurality of light sources, respectively. An objective lens for condensing on the optical disk; provided corresponding to at least one of the plurality of light sources excluding a preset light source, and disposed on an optical path between the plurality of light sources and the objective lens The light emitted from the corresponding at least one light source and directed to the objective lens and the return light from the optical disc of the light emitted from the corresponding at least one light source are each diffracted and emitted from the other light sources and output from the objective. At least the light that goes to the lens and the light that is emitted from the other light source returns from the optical disk without being diffracted. A plurality of volume hologram elements; and a plurality of light beams individually receiving return light through the objective lens of light emitted from the preset light source and return light diffracted by the at least one volume hologram element And an optical detector.

  According to this, it is provided corresponding to at least one light source excluding a preset light source among the plurality of light sources, and is emitted from the corresponding at least one light source and directed to the objective lens, and the corresponding at least one light source. The light emitted from the optical disk is diffracted from the optical disk, and the light emitted from the other light sources and directed to the objective lens and the light emitted from the other light sources from the optical disk are not diffracted. Since at least one volume hologram element that directly transmits light is arranged on the optical path between the plurality of light sources and the objective lens, it is possible to reduce the size without degrading the performance.

  According to a tenth aspect of the present invention, there is provided an optical disc apparatus capable of reproducing at least one of recording, reproduction and erasure of information on an optical disc, the optical pickup device of the present invention; and a photodetector of the optical pickup device. A processing device for reproducing information recorded on the optical disc using an output signal.

  According to this, since the optical pickup device of the present invention is provided, it is possible to reduce the size without lowering the access accuracy to the optical disc.

<< First Embodiment >>
A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a schematic configuration of an optical disc apparatus 20 according to the first embodiment of the present invention.

  An optical disk device 20 shown in FIG. 1 includes a spindle motor 22 for rotating the optical disk 15, an optical pickup device 23, a seek motor 21 for driving the optical pickup device 23 in the seek direction, a laser control circuit 24, An encoder 25, a drive control circuit 26, a reproduction signal processing circuit 28, a buffer RAM 34, a buffer manager 37, an interface 38, a flash memory 39, a CPU 40, a RAM 41, and the like are provided. Note that the arrows in FIG. 1 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block.

  Here, the optical disc 15 is a three-layer disc as an example, and in order from the laser light incident side, a first recording layer (referred to as L1), a second recording layer (referred to as L2), and a third recording layer (referred to as L3). (See FIG. 2). Further, as an example, it is assumed that the optical disk 15 is a DVD-type information recording medium.

  The optical pickup device 23 is an optical pickup device capable of simultaneously irradiating three recording layers of the optical disc 15 with laser light and simultaneously receiving reflected light from the three recording layers.

  As shown in FIG. 2 as an example, the optical pickup device 23 includes three light sources (Ld1, Ld2, Ld3), a collimator lens 52, two hologram elements (H1, H3), a polarization beam splitter 54, λ / 4 plate 55, objective lens 60, condenser lens 58, cylinder lens 73, two half prisms (76a, 76b), three pinholes (75a, 75b, 75c), three light receivers (Pd1, Pd2, Pd3), and a driving system (not shown) for driving the objective lens 60 are provided.

  Each light source emits laser light having a wavelength of 660 nm. Here, the light source Ld2 is disposed on the optical axis of the collimating lens 52, the light source Ld1 is disposed on the + Z side of the light source Ld2, and the light source Ld3 is disposed on the −Z side of the light source Ld2. As an example, it is assumed that P-polarized light is emitted from each light source. The maximum intensity emission direction of the laser light emitted from each light source is the + X direction.

  The collimating lens 52 is disposed on the + X side of each light source, and the light emitted from each light source is substantially parallel light. Here, when the light emitted from the light source Ld1 passes through the collimating lens 52, the light becomes substantially parallel to a direction slightly inclined clockwise with respect to the X-axis direction, and the light emitted from the light source Ld2 The light emitted from the light source Ld3 passes through the collimator lens 52, and the light emitted from the light source Ld3 is substantially parallel to the direction slightly tilted counterclockwise with respect to the X-axis direction. It becomes.

Each of the hologram elements is a so-called volume hologram element, and the light incident surface and the diffracted light exit surface are substantially parallel. The volume hologram element is, for example, the value (Q value) of the parameter Q calculated by the following equation (1) according to “Lightwave Electro-Optics” (Corona) pages 117-132 by Jiro Koyama and Hiroshi Nishihara. Are over 10 hologram elements. Here, λ ₀ is the wavelength of incident light (in the air: 660 nm in this case), T is the thickness of the element, n ₀ is the refractive index of the hologram element substrate, and Λ is the pitch of the pattern grooves (hologram pitch).

Q = 2πλ ₀ T / (n ₀ Λ ² ) (1)

  As is well known, the volume hologram element diffracts only light having a wavelength and an incident angle satisfying a specific diffraction condition (so-called Bragg condition). As an example, as shown in FIG. 3, the first-order diffraction efficiency P (%) when Q = 10 has a peak value when the incident angle satisfies the Bragg condition. Note that α in FIG. 3 is −sin (incident angle) / 2 sin (Bragg angle).

  A photopolymer is an organic polymer recording material, and is often used in a WORM (Write Once Read Many) type hologram memory. Photopolymers have greatly improved their performance over the last few years, and now manufacturers have succeeded in developing materials with excellent optical properties and reduced shrinkage associated with recording at a thickness of several hundreds of micrometers. For example, a low-shrinkage photopolymer composed of 2-chemistry-materials, a low-shrinkage photopolymer polymerized using a cation ring polymerization mechanism, and the like are known. As a result, both high photosensitivity and high volume recording density can be achieved. By using such a photopolymer for the volume hologram element, a highly efficient and highly accurate light beam synthesizing means and light beam separating means can be realized.

  Thermoplastics are also often used for WORM hologram memories. In particular, a thermoplastic doped with a dye can be recorded and reproduced with light of various wavelengths. Manufacturers have succeeded in developing thermoplastics that can be molded several millimeters thick, have excellent optical properties, and reduce shrinkage associated with recording. As a result, both high photosensitivity and high volume recording density can be achieved. Since such a thermoplastic can be a volume hologram element using the material itself as a substrate, it is possible to realize a high-efficiency and high-precision light beam synthesizing device and light beam separating device having a thickness of several millimeters.

Here, as an example, each hologram element is made using a so-called two-beam interference exposure method using a thermoplastic material, and T = 2 mm, n ₀ = 1.5, Λ = 0.7 × λ ₀ / It was n _0. When the respective values are substituted into the above equation (1), Q≈5800, which sufficiently satisfies the conditions of the volume hologram element. In addition, when using the material which cannot be so thick like a photopolymer for the material of each hologram element, it is good to set it as the layer structure which pinched | interposed the material between 2 sheets of glass. At this time, the thickness T of the material layer satisfying Q> 10 is 4 μm or more.

  The hologram element H1 is arranged on the + X side of the collimating lens 52, and is set so that light from the light source Ld1 via the collimating lens 52 satisfies the Bragg condition. Therefore, the light from the light source Ld1 through the collimator lens 52 is diffracted in the + X direction by the hologram element H1. The diffracted light (not shown in FIG. 2) emitted from the hologram element H1 becomes slightly convergent light, and the degree of convergence is determined when the light from the light source Ld2 is condensed on the recording layer L2. Is preliminarily designed by optical parameters so that the light from the light is condensed on the recording layer L1.

  Note that the light from the light source Ld2 and the light from the light source Ld3 via the collimator lens 52 do not satisfy the Bragg condition of the hologram element H1, and pass through the hologram element H1 as it is.

  The hologram element H3 is arranged on the + X side of the hologram element H1, and the light from the light source Ld3 that has passed through the hologram element H1 as it is is set so as to satisfy the Bragg condition. Therefore, the light from the light source Ld3 that has passed through the hologram element H1 as it is is diffracted in the + X direction by the hologram element H3. The diffracted light (not shown in FIG. 2) emitted from the hologram element H3 becomes slightly divergent light, and the degree of divergence is determined when the light from the light source Ld2 is condensed on the recording layer L2. Is preliminarily designed with optical parameters so that the light from the light is condensed on the recording layer L3.

  Note that the diffracted light from the hologram element H1 and the light from the light source Ld2 that has passed through the hologram element H1 as they are do not satisfy the Bragg condition of the hologram element H3, and pass through the hologram element H3 as they are.

  Thus, the hologram element H1 and the hologram element H3 have different Bragg conditions and are arranged side by side in the X-axis direction. Further, the angular magnification (= sin (exit angle) / sin (incident angle)) of each hologram element is smaller than 1. The hologram element H3 may be disposed on the + X side of the collimating lens 52, and the hologram element H1 may be disposed on the + X side of the hologram element H3.

  The polarization beam splitter 54 is disposed on the + X side of the hologram element H3. The polarization beam splitter 54 has a different reflectance depending on the polarization state of incident light. Here, as an example, the polarization beam splitter 54 is set so that the reflectance with respect to the P-polarized light is small and the reflectance with respect to the S-polarized light is large. Therefore, most of the light from each light source via the hologram element H3 can pass through the polarization beam splitter 54.

  The λ / 4 plate 55 is disposed on the + X side of the polarization beam splitter 54 and imparts an optical phase difference of ¼ wavelength to incident light. An objective lens 60 is disposed on the + X side of the quarter wavelength plate 55 and condenses the light that has passed through the quarter wavelength plate 55.

  Here, the light from the light source Ld1 is condensed on the first recording layer L1, the light from the light source Ld2 is condensed on the second recording layer L2, and the light from the light source Ld3 is condensed on the third recording layer L3. The That is, when three light sources emit light simultaneously, a light spot can be simultaneously formed on the three recording layers of the optical disc 15.

  The condensing lens 58 is disposed on the −Z side of the polarizing beam splitter 54 and converts the return light from the optical disk 15 reflected in the −Z direction by the polarizing beam splitter 54 into convergent light.

  The cylinder lens 73 is disposed on the −Z side of the condenser lens 58 and imparts astigmatism to the light from the condenser lens 58.

  The half prism 76a is disposed on the −Z side of the cylinder lens 73, reflects the return light component from the third recording layer L3 included in the light via the cylinder lens 73 in the + X direction, and transmits the remaining light.

  The half prism 76b is arranged on the −Z side of the half prism 76a, reflects the return light component from the second recording layer L2 included in the light transmitted through the half prism 76a in the + X direction, and transmits the rest.

  The pinhole 75a is disposed on the + X side of the half prism 76a, and the light reflected by the half prism 76a is incident thereon. The light that has passed through the pinhole 75a is received by the light receiver Pd3. Therefore, the light received by the light receiver Pd3 is mainly the return light from the third recording layer L3.

  The pinhole 75b is disposed on the + X side of the half prism 76b, and the light reflected by the half prism 76b is incident thereon. The light that has passed through the pinhole 75b is received by the light receiver Pd2. Therefore, the light received by the light receiver Pd2 is mainly the return light from the second recording layer L2.

  The pinhole 75c is disposed on the −Z side of the half prism 76b, and light transmitted through the half prism 76b is incident thereon. The light that has passed through the pinhole 75c is received by the light receiver Pd1. Therefore, the light received by the light receiver Pd1 is mainly the return light from the first recording layer L1.

  The drive system includes a focusing actuator for minutely driving the objective lens 60 in the focus direction that is the optical axis direction of the objective lens 60, and a tracking actuator for minutely driving the objective lens 60 in the tracking direction.

  The operation of the optical pickup device 23 configured as described above will be briefly described.

  The linearly polarized light (here, P-polarized light) emitted from the light source Ld1 is converted into substantially parallel light by the collimator lens 52, then diffracted by the hologram element H1, and transmitted through the hologram element H3 as it is to the polarization beam splitter 54. Incident.

  The linearly polarized light (here P-polarized light) emitted from the light source Ld2 is converted into substantially parallel light by the collimator lens 52, and then passes through the hologram element H1 and the hologram element H3 as they are and enters the polarization beam splitter 54.

  The linearly polarized light (P-polarized light in this case) emitted from the light source Ld3 is converted into substantially parallel light by the collimator lens 52, then passes through the hologram element H1 as it is, is diffracted by the hologram element H3, and enters the polarization beam splitter 54. Incident.

  Most of the light incident on the polarization beam splitter 54 passes through the polarization beam splitter 54 as it is, is circularly polarized by the quarter wavelength plate 55, and is condensed on each recording layer of the optical disk 15 via the objective lens 60. The

  Reflected light from each recording layer of the optical disk 15 becomes circularly polarized light opposite to the outward path, and enters the quarter-wave plate 55 as return light through the objective lens 60, where it is linearly polarized light orthogonal to the outward path ( Here, it is S-polarized light. Then, this return light enters the polarization beam splitter 54.

  The return light reflected in the −Z direction by the polarization beam splitter 54 enters the half prism 76 a via the condenser lens 58 and the cylinder lens 73. The return light component from the third recording layer L3 included in the return light is reflected by the half prism 76a and received by the light receiver Pd3 through the pinhole 75a.

  The return light transmitted through the half prism 76a enters the half prism 76b. The return light component from the second recording layer L2 contained in the return light is reflected by the half prism 76b and received by the light receiver Pd2 through the pinhole 75b.

  The return light transmitted through the half prism 76b is received by the light receiver Pd1 through the pinhole 75c.

  Each pinhole is provided to remove interlayer crosstalk.

  Each light receiver includes a plurality of light receiving elements (or a plurality of light receiving regions) that output signals including wobble signal information, reproduction data information, focus error information, track error information, and the like, as in a normal optical disk device. It consists of Each light receiving element (or each light receiving region) generates a signal corresponding to the amount of received light by photoelectric conversion and outputs the signal to the reproduction signal processing circuit 28.

  Returning to FIG. 1, the reproduction signal processing circuit 28 is based on output signals (a plurality of photoelectric conversion signals) of the respective light receivers of the optical pickup device 23, servo signals (focus error signal, track error signal, etc.), address information. , Synchronization information, and RF signal are acquired.

  The servo signal obtained here is output to the control circuit 26, the address information is output to the CPU 40, and the synchronization signal is output to the encoder 25, the drive control circuit 26, and the like. Further, the reproduction signal processing circuit 28 performs a decoding process and an error detection process on the RF signal. When an error is detected, the reproduction signal processing circuit 28 performs an error correction process, and then plays back the buffer RAM 34 via the buffer manager 37 as reproduction data. To store. The address information included in the reproduction data is output to the CPU 40.

  The drive control circuit 26 generates a drive signal for the drive system based on the servo signal from the reproduction signal processing circuit 28 and outputs the drive signal to the optical pickup device 23. Thereby, tracking control and focus control are performed. The drive control circuit 26 generates a drive signal for driving the seek motor 21 and a drive signal for driving the spindle motor 22 based on an instruction from the CPU 40. The drive signal of each motor is output to the seek motor 21 and the spindle motor 22, respectively.

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

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

  The laser control circuit 24 controls the light emission power of each light source of the optical pickup device 23. For example, at the time of recording, a drive signal for each light source is generated by the laser control circuit 24 based on the write signal, recording conditions, light emission characteristics of each light source and the like.

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

  The flash memory 39 stores various programs described by codes readable by the CPU 40, light emission characteristics of each light source, and the like.

  The CPU 40 controls the operation of each unit in accordance with the program stored in the flash memory 39 and saves data necessary for control in the RAM 41 and the buffer RAM 34.

<Recording process>
Next, a process (recording process) in the optical disc apparatus 20 when there is a user data recording request from the host apparatus 90 will be described with reference to FIG. The flowchart in FIG. 4 corresponds to a series of processing algorithms executed by the CPU 40.

  When a recording request command is received from the host device 90, the start address of the program corresponding to the flowchart of FIG. 4 is set in the program counter of the CPU 40, and the recording process starts.

  In the first step 401, the drive control circuit 26 is instructed to rotate the optical disc 15 at a predetermined linear velocity (or angular velocity), and the reproduction signal processing circuit 28 or the like is notified that the recording request command has been received from the host device 90. Notice. Further, the recording layer to be recorded is specified based on the recording request command, and the specified result is notified to the reproduction signal processing circuit 28, the encoder 25, the laser control circuit 24, and the like. Here, it is assumed that user data is recorded in the first recording layer L1, the second recording layer L2, and the third recording layer L3.

  In the next step 403, user data (recording data) stored in the buffer RAM 34 from the host device 90 is recorded in the first recording layer L1, user data recorded in the second recording layer L2, and Dividing into user data to be recorded in the third recording layer L3.

  In the next step 405, the drive control circuit 26 is instructed to form a light spot near the target position corresponding to the designated address. Thereby, a seek operation is performed. If the seek operation is unnecessary, the process here is skipped.

  In the next step 407, recording is permitted. Thus, user data is recorded on each recording layer of the optical disc 15 via the encoder 25, the laser control circuit 24, and the optical pickup device 23.

  In the next step 409, it is determined whether or not the recording is completed. If it is not completed, the determination here is denied and the determination is made again after a predetermined time has elapsed. If the recording is completed, the determination here is affirmed and the recording process is terminated. Here, since recording on each recording layer is performed almost simultaneously, the recording process can be completed in a single time as compared with the conventional case.

《Reproduction processing》
Next, processing (playback processing) in the optical disc device 20 when a playback request is received from the host device 90 will be described with reference to FIG. The flowchart in FIG. 5 corresponds to a series of processing algorithms executed by the CPU 40.

  When the reproduction request command is received from the host device 90, the start address of the program corresponding to the flowchart of FIG. 5 is set in the program counter of the CPU 40, and the reproduction process is started.

  In the first step 501, the drive control circuit 26 is instructed to rotate the optical disc 15 at a predetermined linear velocity (or angular velocity), and the reproduction signal processing circuit 28 or the like is notified that a reproduction request command has been received from the host device 90. Notice. Further, the recording layer to be reproduced is identified based on the reproduction request command, and the identification result is notified to the reproduction signal processing circuit 28, the laser control circuit 24, and the like. Here, it is assumed that data is reproduced from the first recording layer L1, the second recording layer L2, and the third recording layer L3.

  In the next step 503, the drive control circuit 26 is instructed to form a light spot in the vicinity of the target position corresponding to the designated address. Thereby, a seek operation is performed. If the seek operation is unnecessary, the process here is skipped.

  In the next step 505, reproduction is permitted. Thereby, the data recorded on each recording layer of the optical disc 15 is reproduced via the optical pickup device 23 and the reproduction signal processing circuit 28, respectively.

  In the next step 507, it is determined whether or not the reproduction is completed. If it is not completed, the determination here is denied and the determination is made again after a predetermined time has elapsed. If the reproduction has been completed, the determination here is affirmed and the routine proceeds to step 509.

  In this step 509, the reproduction data from the first recording layer L1, the reproduction data from the second recording layer L2, and the reproduction data from the third recording layer L3 are connected and transferred to the host device 90. Then, the reproduction process ends. Here, since the reproduction from each recording layer is performed almost simultaneously, the reproduction process can be completed in a single time as compared with the conventional case.

  As is apparent from the above description, in the optical disc device 20 according to the first embodiment, the processing device is realized by the reproduction signal processing circuit 28, the CPU 40, and the program executed by the CPU 40. Note that at least a part of the processing device realized by the processing according to the program by the CPU 40 may be realized by hardware, or all may be realized by hardware.

  In the optical pickup device 23 according to the first embodiment, a light source unit is realized by three light sources (Ld1, Ld2, Ld3) and two hologram elements (H1, H3).

  As described above, according to the optical pickup device 23 according to the first embodiment, the three light sources (Ld1, Ld2, Ld3) and the light from the light source Ld1 are diffracted in the + X direction, and the light sources Ld2 and Ld3 are diffracted. Light from the light source Ld2 that diffracts light from the light source Ld3 that has passed through the hologram element H1 as it is, diffracted light in the + X direction, and has passed through the hologram element H1 as it is, and the hologram element And a hologram element H3 that transmits the diffracted light from H1 as it is. The hologram element H1 and the hologram element H3 are both volume hologram elements in which the light incident surface and the diffracted light exit surface are substantially parallel, and include three light sources (Ld1, Ld2, Ld3), the objective lens 60, and the like. Are arranged side by side on the optical path between. Thereby, it is possible to reduce the size of the illumination system without reducing the light utilization efficiency, and as a result, it is possible to reduce the size without causing a decrease in performance.

  Further, according to the optical disc device 20 according to the first embodiment, since the optical pickup device 23 according to the first embodiment is provided, the access accuracy with respect to the optical disc having a plurality of recording layers is not lowered. It is possible to reduce the size.

  Further, according to the optical disc device 20 according to the first embodiment, recording on the first recording layer L1, recording on the second recording layer L2, and recording on the third recording layer L3 can be performed almost simultaneously. Therefore, it is possible to perform the recording process on the optical disc quickly.

  In addition, according to the optical disc apparatus 20 according to the first embodiment, reproduction from the first recording layer L1, reproduction from the second recording layer L2, and reproduction from the third recording layer L3 can be performed almost simultaneously. Therefore, it is possible to quickly perform playback processing from the optical disc.

  In the first embodiment, recording and reproduction can be performed almost simultaneously. For example, information can be reproduced from the second recording layer L2 while recording information on the first recording layer L1.

  Further, in the first embodiment, as shown in FIG. 6 as an example, instead of the half prism 76a and the half prism 76b, the return between the polarization beam splitter 54 and the condenser lens 58 is performed. Two hologram elements (R3, R1) may be arranged on the optical path of light. The hologram element R3 and the hologram element R1 have different Bragg conditions, and both are volume hologram elements in which the light incident surface and the diffracted light exit surface are substantially parallel.

  The hologram element R3 is disposed on the −Z side of the polarization beam splitter 54, and the return light component from the third recording layer L3 included in the return light reflected in the −Z direction by the polarization beam splitter 54 satisfies the Bragg condition. It is set to be satisfied. Therefore, the return light component from the third recording layer L3 included in the return light is diffracted by the hologram element R3. The diffracted light (not shown in FIG. 6) emitted from the hologram element R3 is slightly inclined with respect to the optical axis of the condenser lens 58. Further, the hologram element R3 has a function of correcting aberration caused by the difference between the position of the second recording layer L2 and the position of the third recording layer L3 with respect to the objective lens 60. The return light component from the first recording layer L1 and the return light component from the second recording layer L2 included in the return light reflected in the −Z direction by the polarization beam splitter 54 satisfy the Bragg condition of the hologram element R3. Without passing through the hologram element R3.

  The hologram element R1 is disposed on the −Z side of the hologram element R3, and is set so that the return light component from the first recording layer L1 included in the return light transmitted through the hologram element R3 as it is satisfies the Bragg condition. ing. Therefore, the return light component from the first recording layer L1 included in the return light is diffracted by the hologram element R1. Diffracted light (not shown in FIG. 6) emitted from the hologram element R 1 is slightly inclined with respect to the optical axis of the condenser lens 58. Further, the hologram element R1 has a function of correcting aberration caused by the difference between the position of the second recording layer L2 and the position of the first recording layer L1 with respect to the objective lens 60. The return light component from the second recording layer L2 included in the diffracted light from the hologram element R3 and the return light transmitted through the hologram element R3 as it is does not satisfy the Bragg condition of the hologram element R1, and the hologram element R1 is left as it is. To Penetrate.

  Thereby, each light receiver can be arrange | positioned on the same surface, and a normal focus signal can be generated with a small detection spot. That is, the light receiver Pd3 is disposed on the −X side of the light receiver Pd2, and the light receiver Pd1 is disposed on the + X side of the light receiver Pd2.

  In this case, a light detection unit is realized by two hologram elements (R3, R1) and three light receivers (Pd1, Pd2, Pd3). And each said pinhole is unnecessary. In this case, the hologram element R1 may be disposed on the −Z side of the polarization beam splitter 54, and the hologram element R3 may be disposed on the −Z side of the hologram element R1.

  As a result, the detection system can be reduced in size without lowering the light utilization efficiency, and as a result, the optical pickup device can be reduced in size without causing further deterioration in performance.

  Moreover, although the said 1st Embodiment demonstrated the case where there were three light sources, it is not limited to this.

  In the first embodiment, the case where the recording layer of the optical disc 15 has three layers has been described. However, the present invention is not limited to this.

  In the first embodiment, high-order spherical aberration may be added to the information light used when creating each hologram element. Thereby, it is also possible to completely correct the spherical aberration. Moreover, you may add the aberration resulting from the shift of the objective lens 60 at the time of tracking control to the said information light. In this case, a hologram element to which the aberration correction action described above is added may be further provided corresponding to the light source Ld2.

<< Second Embodiment >>
The second embodiment is characterized in that a hologram unit is used in place of each light source in the first embodiment described above. The configuration of the optical disk device excluding the optical pickup device is the same as that of the first embodiment. Accordingly, the following description will be focused on the differences from the first embodiment, and the same reference numerals will be used for the same or equivalent components as in the first embodiment, and the description thereof will be simplified or omitted. Shall.

  As shown in FIG. 7, the optical pickup device 23 according to the second embodiment includes three hologram units (HU1, HU2, HU3), a collimator lens 52, two hologram elements (H11, H31), A λ / 4 plate 55, an objective lens 60, a drive system (not shown) for driving the objective lens 60, and the like are provided. Each hologram unit is a hologram unit having the same characteristics.

  As an example, the hologram unit HU2 includes a light source k2 that emits laser light having a wavelength of 660 nm, a light receiver m2, and a polarization hologram n2, and is arranged on the optical axis of the collimating lens 52, as shown in FIG. Has been. It is assumed that P-polarized light is emitted from the light source k2. The polarization hologram n2 is arranged on the + X side of the light source k2, and is set so that the reflectance with respect to the P-polarized light is small and the reflectance with respect to the S-polarized light is large. The light receiver m2 is disposed in the vicinity of the light source k2, and receives the return light deflected by the polarization hologram n2. Therefore, the light emitted from the light source k2 enters the collimating lens 52 via the polarization hologram n2.

  As an example, as shown in FIG. 8B, the hologram unit HU1 includes a light source k1, a light receiver m1, and a polarization hologram n1 that emit laser light having a wavelength of 660 nm, and is disposed on the + Z side of the hologram unit HU2. ing. It is assumed that P-polarized light is emitted from the light source k1. The polarization hologram n1 is arranged on the + X side of the light source k1, and is set so that the reflectance with respect to the P-polarized light is small and the reflectance with respect to the S-polarized light is large. The light receiver m1 is disposed near the light source k1 and receives the return light deflected by the polarization hologram n1. Accordingly, the light emitted from the light source k1 enters the collimating lens 52 through the polarization hologram n1.

  As an example, as shown in FIG. 8C, the hologram unit HU3 includes a light source k3 that emits laser light having a wavelength of 660 nm, a light receiver m3, and a polarization hologram n3, and is arranged on the −Z side of the hologram unit HU2. Has been. It is assumed that P-polarized light is emitted from the light source k3. The polarization hologram n3 is disposed on the + X side of the light source k3, and is set so that the reflectance with respect to the P-polarized light is small and the reflectance with respect to the S-polarized light is large. The light receiver m3 is disposed near the light source k3 and receives the return light deflected by the polarization hologram n3. Therefore, the light emitted from the light source k3 enters the collimating lens 52 through the polarization hologram n3.

  The hologram element H11 and the hologram element H31 are volume hologram elements in which the Bragg conditions are different from each other, and both the light incident surface and the diffracted light exit surface are substantially parallel. In addition, the angular magnification of each hologram element is smaller than 1. Each hologram element is made by using a so-called two-beam interference exposure method using a thermoplastic or photopolymer as a material.

  The hologram element H11 is disposed on the + X side of the collimating lens 52, and is set so that light from the hologram unit HU1 via the collimating lens 52 satisfies the Bragg condition. Accordingly, the hologram element H11 diffracts the light from the hologram unit HU1 via the collimating lens 52. The diffracted light (not shown in FIG. 7) emitted from the hologram element H11 becomes slightly convergent light slightly inclined with respect to the optical axis of the objective lens 60. The degree of convergence is determined from the hologram unit HU2. The optical parameters are designed in advance so that the light from the hologram unit HU1 is collected on the recording layer L1 when the light is collected on the recording layer L2.

  Further, the hologram element H11 has a function of correcting aberration caused by the difference between the position of the second recording layer L2 and the position of the first recording layer L1 with respect to the objective lens 60. Note that the light from the hologram unit HU2 and the light from the hologram unit HU3 via the collimator lens 52 do not satisfy the Bragg condition of the hologram element H11 and pass through the hologram element H11 as it is.

  The hologram element H31 is arranged on the + X side of the hologram element H11, and the light from the hologram unit HU3 that has passed through the hologram element H11 as it is is set so as to satisfy the Bragg condition. Accordingly, the hologram element H31 diffracts the light from the hologram unit HU3 that has passed through the hologram element H11 as it is. The diffracted light emitted from the hologram element H31 (not shown in FIG. 7) becomes slightly divergent light slightly inclined with respect to the optical axis of the objective lens 60. The degree of divergence is from the hologram unit HU2. The optical parameters are designed in advance so that the light from the hologram unit HU3 is condensed on the recording layer L3 when the light is condensed on the recording layer L2.

  Further, the hologram element H31 has a function of correcting aberration caused by the difference between the position of the second recording layer L2 and the position of the third recording layer L3 with respect to the objective lens 60. Note that the diffracted light from the hologram element H11 and the light from the hologram unit HU2 that has passed through the hologram element H11 as they are do not satisfy the Bragg condition of the hologram element H31, and pass through the hologram element H31 as they are.

  The λ / 4 plate 55 is disposed on the + X side of the hologram element H31, and the objective lens 60 is disposed on the + X side of the quarter-wave plate 55.

  The operation of the optical pickup device 23 according to the second embodiment configured as described above will be briefly described.

  Light of linearly polarized light (here P-polarized light) emitted from the light source k1 enters the collimating lens 52 via the polarization hologram n1, is diffracted by the hologram element H11, passes through the hologram element H31 as it is, and has a quarter wavelength. Incident on the plate 55. Then, the light is converted into circularly polarized light by the quarter-wave plate 55 and condensed on the recording layer L 1 of the optical disk 15 through the objective lens 60.

  Light of linearly polarized light (here, P-polarized light) emitted from the light source k2 enters the collimating lens 52 through the polarization hologram n2, passes through the hologram element H11 and the hologram element H31 as it is, and enters the quarter wavelength plate 55. Incident. Then, the light is converted into circularly polarized light by the quarter-wave plate 55 and condensed on the recording layer L 2 of the optical disk 15 through the objective lens 60.

  The linearly polarized light (here, P-polarized light) emitted from the light source k3 enters the collimating lens 52 through the polarization hologram n3, passes through the hologram element H11 as it is, is diffracted by the hologram element H31, and is ¼ wavelength. Incident on the plate 55. Then, the light is converted into circularly polarized light by the quarter-wave plate 55 and condensed on the recording layer L 3 of the optical disk 15 through the objective lens 60.

  Therefore, if each light source emits light at the same time, a light spot can be simultaneously formed on each recording layer. However, unlike the above-described first embodiment, the positions of the light spots in the Z-axis direction are different from each other. That is, the respective light spots have different distances from the rotation center of the optical disk 15.

  The reflected light from the optical disk 15 is circularly polarized in the opposite direction to the outward path, and enters the quarter-wave plate 55 as return light through the objective lens 60, where it is linearly polarized light (here, S-polarized light) orthogonal to the forward path. ). Then, the return light enters the hologram element H31, and the return light component from the third recording layer L3 included in the return light is diffracted. This diffracted light is slightly inclined with respect to the optical axis of the collimating lens 52.

  The return light that has passed through the hologram element H31 enters the hologram element H11, and the return light component from the first recording layer L1 included in the return light is diffracted. This diffracted light is slightly inclined with respect to the optical axis of the collimating lens 52.

  The return light that has passed through the hologram element H11 enters the collimating lens 52.

  The return light component (light diffracted by the hologram element H31) from the third recording layer L3 included in the return light incident on the collimator lens 52 is emitted from the collimator lens 52 toward the hologram unit HU3 and passes through the polarization hologram n3. Via the light receiver m3.

  The return light component (the light diffracted by the hologram element H11) included in the return light incident on the collimator lens 52 is emitted from the collimator lens 52 toward the hologram unit HU1, and passes through the polarization hologram n1. Through the light receiver m1.

  The return light component from the second recording layer L2 included in the return light incident on the collimator lens 52 (light that has passed through each hologram element as it is) is emitted from the collimator lens 52 toward the hologram unit HU2, and passes through the polarization hologram n2. Via the light receiver m2.

  Each light receiver is configured in the same manner as in the first embodiment described above, and outputs a signal corresponding to the amount of received light to the reproduction signal processing circuit 28.

  As described above, according to the optical pickup device 23 according to the second embodiment, the three light sources (k1, k2, k3) and the light from the light source k1 are diffracted in the direction toward the objective lens 60. The hologram element H11 that diffracts the return light of the light emitted from the light source k1 through the objective lens 60 in the direction toward the light receiver m1, and the light from the light source k3 in the direction toward the objective lens 60 and the light source a hologram element H31 that diffracts the return light of the light emitted from k3 through the objective lens 60 in a direction toward the light receiver m3. Each hologram element has an incident surface of light and emission of diffracted light. The volume hologram elements are substantially parallel to the surface, and are arranged side by side in the X-axis direction. Thereby, further miniaturization of the optical pickup device and the optical disk device can be promoted as compared with the first embodiment described above.

  By the way, in the second embodiment, if each light spot is formed at a position where the distances from the rotation center of the optical disk 15 are equal to each other, the return light component from the first recording layer L1, the second recording layer. The return light component from L2 and the return light component from the third recording layer L3 are almost equal in incident angle in the vicinity of the optical axis of each volume hologram element. For example, in the hologram element H31, the third recording layer L3 In addition to the return light component from, the return light component from the first recording layer L1 and a part of the return light component from the second recording layer L2 are also diffracted. However, in the second embodiment, since the light spots formed on each recording layer have different distances from the rotation center of the optical disc 15, the first recording layer in the vicinity of the optical axis in each hologram element. The incident angle of the return light component from L1, the incident angle of the return light component from the second recording layer L2, and the incident angle of the return light component from the third recording layer L3 can be made different from each other. Therefore, only the return light component from the third recording layer L3 can be diffracted by the hologram element H31, and only the return light component from the first recording layer L1 can be diffracted by the hologram element H11. That is, the return light separation characteristics of each hologram element are improved.

  In the second embodiment, when it is necessary to correct the aberration of light from the hologram unit HU2, the two hologram elements (H11, H31) are used as an example as shown in FIG. Three hologram elements (H13, H23, H33) corresponding to each of the three hologram units (HU1, HU2, HU3) may be used. In this case, in order to separate the light from the corresponding hologram unit into the zero-order light and the first-order diffracted light in all the hologram elements, for example, the maximum intensity emission direction of the light emitted from each light source is set as the objective. It is inclined with respect to the optical axis of the lens 60.

  The three hologram elements (H13, H23, H33) have different Bragg conditions, and are all volume hologram elements in which the light incident surface and the diffracted light exit surface are substantially parallel.

  The hologram element H13 is disposed on the + X side of the collimating lens 52, and is set so that light from the hologram unit HU1 via the collimating lens 52 satisfies the Bragg condition. Accordingly, the hologram element H13 diffracts the light from the hologram unit HU1 via the collimating lens 52. The diffracted light (not shown in FIG. 9) emitted from the hologram element H13 becomes slightly convergent light slightly inclined with respect to the optical axis of the objective lens 60, and the degree of convergence is from the hologram unit HU2. The optical parameters are designed in advance so that the light from the hologram unit HU13 is condensed on the recording layer L1 when the light is condensed on the recording layer L2.

  In addition, the hologram element H13 has a function of correcting aberration caused by the difference between the position of the second recording layer L2 and the position of the first recording layer L1 with respect to the objective lens 60. Note that the light from the hologram unit HU2 and the light from the hologram unit HU3 via the collimator lens 52 do not satisfy the Bragg condition of the hologram element H13 and pass through the hologram element H13 as they are.

  The hologram element H23 is disposed on the + X side of the hologram element H13, and is set so that light from the hologram unit HU2 that has passed through the hologram element H13 as it is satisfies the Bragg condition. Accordingly, the hologram element H23 diffracts the light from the hologram unit HU2 that has passed through the hologram element H13 as it is. The diffracted light emitted from the hologram element H23 becomes light substantially parallel to the optical axis of the objective lens 60. That is, the angular magnification of the hologram element H23 is zero.

  Note that the diffracted light from the hologram element H13 and the light from the hologram unit HU3 that has passed through the hologram element H13 as they are do not satisfy the Bragg condition of the hologram element H23, and pass through the hologram element H23 as they are.

  The hologram element H33 is arranged on the + X side of the hologram element H23, and the light from the hologram unit HU3 that has passed through the hologram element H23 as it is is set so as to satisfy the Bragg condition. Accordingly, the hologram element H33 diffracts the light from the hologram unit HU3 that has passed through the hologram element H23 as it is. The diffracted light (not shown in FIG. 9) emitted from the hologram element H33 is slightly diverging light slightly inclined with respect to the optical axis of the objective lens 60. The degree of divergence is from the hologram unit HU2. The optical parameters are designed in advance so that the light from the hologram unit HU3 is condensed on the recording layer L3 when the light is condensed on the recording layer L2.

  Further, the hologram element H33 has a function of correcting aberration caused by the difference between the position of the second recording layer L2 and the position of the third recording layer L3 with respect to the objective lens 60. Note that the diffracted light from the hologram element H13 and the diffracted light from the hologram element H23 do not satisfy the Bragg condition of the hologram element H33, and pass through the hologram element H33 as they are.

  In the second embodiment, the number of light sources is not limited to three. Further, the recording layer of the optical disc 15 is not limited to three layers.

<< Third Embodiment >>
The third embodiment is characterized in that a plurality of light spots can be simultaneously formed on the same recording layer, unlike the first and second embodiments described above. The configuration of the optical disk apparatus excluding the optical pickup apparatus is almost the same as that of the first embodiment except for the data processing and signal processing. Accordingly, the following description will be focused on the differences from the first embodiment, and the same reference numerals will be used for the same or equivalent components as in the first embodiment, and the description thereof will be simplified or omitted. Shall. Here, as an example, the optical disk 15 is assumed to be a DVD-type optical disk having one recording layer.

  As shown in FIG. 10 as an example, the optical pickup device 23 according to the third embodiment includes three light sources (Ld1, Ld2, Ld3), a collimator lens 52, and two hologram elements (H12, H32). , Polarization beam splitter 54, λ / 4 plate 55, objective lens 60, condenser lens 58, cylinder lens 73, three light receivers (Pd 1, Pd 2, Pd 3), and objective lens 60 (not shown) for driving the objective lens 60. It has a drive system.

  Each light source emits laser light having a wavelength of 660 nm. Here, the light source Ld2 is disposed on the optical axis of the collimating lens 52, the light source Ld1 is disposed on the + Z side of the light source Ld2, and the light source Ld3 is disposed on the −Z side of the light source Ld2. As an example, it is assumed that P-polarized light is emitted from each light source. The maximum intensity emission direction of the laser light emitted from each light source is the + X direction.

  The collimating lens 52 is disposed on the + X side of each light source, and makes light from each light source substantially parallel light. Here, when the light emitted from the light source Ld1 passes through the collimating lens 52, as shown in FIG. 11A as an example, the light is inclined in the direction inclined by θa1 (+ θa1) clockwise with respect to the X-axis direction. When the light emitted from the light source Ld2 is transmitted through the collimator lens 52, the light becomes substantially parallel to the X-axis direction and is emitted from the light source Ld3 as shown in FIG. 11B as an example. When the light passes through the collimating lens 52, for example, as shown in FIG. 11C, the light becomes substantially parallel to a direction inclined by θc1 (−θc1) counterclockwise with respect to the X-axis direction. Shall. In the present specification, the clockwise inclination is +, and the counterclockwise inclination is-.

  The hologram element H12 and the hologram element H32 have different Bragg conditions, and both are volume hologram elements in which the light incident surface and the diffracted light exit surface are substantially parallel.

  The hologram element H12 is disposed on the + X side of the collimating lens 52, and the hologram element H32 is disposed on the + X side of the hologram element H12.

  Each hologram element is made by using a so-called two-beam interference exposure method using a thermoplastic or photopolymer as a material. For example, as shown in FIG. 12A as an example, the reference light Lr is applied to the hologram element Hm on which the hologram pattern has not yet been formed from the upper left side of the hologram element Hm (direction inclined by + θa1 with respect to the horizontal direction). Is incident on the left side of the hologram element Hm (a direction inclined by −θa2 with respect to the horizontal direction) to form a hologram pattern inside the hologram element Hm. H12 is created. Here, the same aberration as the aberration due to the fact that the light source Ld1 is arranged on the + Z side with respect to the optical axis of the collimating lens 52 is given to the reference light Lr, and the information light Li is made non-aberrated. That is, the hologram element H12 can correct aberration due to the light source Ld1 being disposed on the + Z side with respect to the optical axis of the collimating lens 52.

  As an example, as shown in FIG. 12B, a hologram element Hm on which a hologram pattern has not yet been formed is referenced from the lower left side of the hologram element Hm (a direction inclined by −θc1 with respect to the horizontal direction). The hologram element is formed by entering the light Lr and entering the information light Li from the upper left side of the hologram element Hm (the direction inclined by + θc2 with respect to the horizontal direction) to form a hologram pattern inside the hologram element Hm. H32 is created. Here, the same aberration as the aberration caused by the light source Ld3 being arranged on the −Z side with respect to the optical axis of the collimating lens 52 is given to the reference light Lr, and the information light Li is made free of aberration. That is, the hologram element H32 can correct aberration due to the light source Ld3 being arranged on the −Z side with respect to the optical axis of the collimating lens 52.

  The light from the light source Ld1 through the collimator lens 52 is diffracted by the hologram element H12 in order to satisfy the Bragg condition of the hologram element H12. As an example, the hologram element H12 emits diffracted light in a direction inclined by −θa2 with respect to the X-axis direction, as shown in FIG.

  Further, the light from the light source Ld2 and the light from the light source Ld3 via the collimator lens 52 do not satisfy the Bragg condition of the hologram element H12 and pass through the hologram element H12 as they are.

  The light from the light source Ld3 that has passed through the hologram element H12 as it is is diffracted by the hologram element H32 in order to satisfy the Bragg condition of the hologram element H32. As an example, the hologram element H32 emits diffracted light in a direction inclined by + θc2 with respect to the X-axis direction, as shown in FIG. 13B.

  In addition, the diffracted light from the light source Ld2 that has passed through the hologram element H12 and from the hologram element H12 do not satisfy the Bragg condition of the hologram element H32, and pass through the hologram element H32 as it is.

  The hologram element H32 may be disposed on the + X side of the collimating lens 52, and the hologram element H12 may be disposed on the + X side of the hologram element H32.

  Further, in order to make the intensity distribution of the diffracted light from the hologram elements equal or have an axial object, the intensity distribution of the information light may be corrected. As an example, as shown in FIG. 14A, when the volume hologram element H12 is created with the reference light Lr and the information light Li having a normal Gaussian intensity distribution with the center axis shifted, the refractive index change on the upper side of the paper becomes large. Therefore, as an example, as shown in FIG. 14B, the intensity distribution of the diffracted light becomes a biased Gaussian distribution, and the shape of the light spot formed on the optical disk may be deformed to deteriorate the signal characteristics. Therefore, as shown in FIG. 15 (A) as an example, when the volume hologram element H12 is created with information light Li having a peak intensity on the lower side of the paper, as shown in FIG. 15 (B) as an example, Axisymmetric diffracted light having a normal Gaussian intensity distribution can be obtained. As an example, as shown in FIG. 16A, when the volume hologram element H12 is made of information light Li in which the intensity at the beam end is larger than the intensity at the center of the beam, an example is shown in FIG. As a result, diffracted light having a high intensity at the beam end can be obtained. Therefore, the edge intensity (RIM intensity) of the diffracted light can be adjusted by adjusting the intensity distribution of the information light Li. This corresponds to a normal beam shaping action.

  Here, the diffracted light emitted from each hologram element has an intensity distribution that is axially symmetric with respect to the optical axis of the hologram element. Each hologram element is set so that the full width at half maximum of the intensity distribution of the diffracted light to be emitted is larger than the full width at half maximum of the intensity distribution of the incident light.

  Returning to FIG. 10, the polarization beam splitter 54 is disposed on the + X side of the hologram element H32, and the λ / 4 plate 55, the objective lens 60, the condenser lens 58, and the cylinder lens 73 are all the first embodiment described above. Arranged in the same way as the form.

  The light receiver Pd <b> 2 is arranged on the −Z side of the cylinder lens 73 and on the optical axis of the cylinder lens 73. The light receiver Pd1 is disposed on the −X side of the light receiver Pd2, and the light receiver Pd3 is disposed on the + X side of the light receiver Pd2.

  The operation of the optical pickup device 23 according to the third embodiment configured as described above will be briefly described.

  Light of linearly polarized light (here, P-polarized light) emitted from the light source Ld1 is incident on the hologram element H12 via the collimator lens 52, is diffracted by the hologram element H12, passes through the hologram element H32 as it is, and is polarized by the polarization beam splitter 54. Is incident on. The linearly polarized light (here, P-polarized light) emitted from the light source Ld2 enters the hologram element H12 via the collimator lens 52, passes through the hologram element H12 and the hologram element H32 as they are, and enters the polarization beam splitter 54. . The linearly polarized light (here P-polarized light) emitted from the light source Ld3 enters the hologram element H12 through the collimator lens 52, passes through the hologram element H12 as it is, is diffracted by the hologram element H32, and is polarized by the polarization beam splitter 54. Is incident on.

  Most of the light incident on the polarization beam splitter 54 passes through the polarization beam splitter 54 as it is, is circularly polarized by the quarter wavelength plate 55, and is condensed on the recording layer of the optical disk 15 via the objective lens 60. .

  Here, the light from the light source Ld2 is condensed at a position t2 intersecting the optical axis of the objective lens 60, and the light from the light source Ld1 is condensed at a position t1 on the + Z side of the position t2, and from the light source Ld3. Is condensed at a position t3 on the −Z side of the position t2. That is, the light emitted from each light source is condensed at different positions on the recording layer of the optical disc 15.

  The reflected light from the optical disk 15 is circularly polarized in the opposite direction to the outward path, and enters the quarter-wave plate 55 as return light through the objective lens 60, where it is linearly polarized light (here, S-polarized light) orthogonal to the forward path. ). Then, this return light enters the polarization beam splitter 54.

  The return light reflected in the −Z direction by the polarization beam splitter 54 is received by each light receiver via the condenser lens 58 and the cylinder lens 73. Here, the return light from the position t1 is received by the light receiver Pd1, the return light from the position t2 is received by the light receiver Pd2, and the return light from the position t3 is received by the light receiver Pd3.

  By the way, the distance D of each light spot formed on the recording layer of the optical disc 15 is the distance dp in the Z-axis direction of each light source and the angular magnification m (= sin (emission angle) / sin (incidence angle)) of the hologram element. This depends on the focal length fc of the collimating lens 52 and the focal length fo of the objective lens 60. That is, there is a relationship of the following expression (1).

  m = (D / dp) × (fc / fo) (1)

  Therefore, for example, when dp = 6 mm, fc = 24 mm, and fo = 4 mm, D = 0.01 mm can be achieved by setting m = 0.01. Here, since sin (incident angle) = D / fc = 0.25, sin (exit angle) = sin (incident angle) × 0.01 = 0.0025.

  In this case, for example, the light receiver Pd2 may be a four-divided light receiving element, and the track error signal detection by the astigmatism method and the focus error signal detection by the push-pull method may be performed based on the output signal of the light receiver Pd2. .

  As is clear from the above description, in the optical pickup device 23 according to the third embodiment, the light source unit is composed of three light sources (Ld1, Ld2, Ld3) and two hologram elements (H12, H32). It has been realized.

  As described above, according to the optical pickup device 23 according to the third embodiment, the light from the three light sources (Ld1, Ld2, Ld3) and the light source Ld1 is diffracted, and the light from the light sources Ld2 and Ld3 is diffracted. The light is diffracted by the hologram element H12 that passes through the hologram element H12 without being diffracted, and the light from the light source Ld3 that is transmitted through the hologram element H12 as it is, and is diffracted by the light from the light source Ld2 that is transmitted through the hologram element H12 The hologram element H32 that transmits all the light as it is without being diffracted, and each hologram element is a volume hologram element in which the light incident surface and the diffracted light exit surface are substantially parallel, They are arranged side by side in the X-axis direction. Thereby, it is possible to reduce the size of the illumination system without reducing the light utilization efficiency, and as a result, it is possible to reduce the size without causing a decrease in performance.

  Further, according to the optical disc apparatus according to the third embodiment, since the optical pickup device 23 according to the third embodiment is provided, it is possible to reduce the size without reducing the access accuracy to the optical disc. It becomes.

  In addition, according to the optical disc apparatus of the third embodiment, recording on a plurality of tracks can be performed almost simultaneously, so that recording processing on the optical disc can be performed quickly.

  In addition, according to the optical disc apparatus according to the third embodiment, reproduction from a plurality of tracks can be performed almost simultaneously, so that it is possible to perform reproduction processing on the optical disc quickly.

  In the third embodiment, recording and reproduction can be performed almost simultaneously. For example, information can be reproduced from another track while recording information on one track.

  Note that the third embodiment is not limited to the case where there are three light sources.

  In the third embodiment, as shown in FIG. 17 as an example, instead of the condenser lens 58 and the cylinder lens 73, three hologram elements (R32, R22, R12) are used as the polarization beam splitter. You may arrange | position on the optical path between 54 and each said light receiver. The hologram element R32, the hologram element R22, and the hologram element R12 have different Bragg conditions, and are all volume hologram elements in which the light incident surface and the diffracted light exit surface are substantially parallel.

  The hologram element R32 is disposed on the −Z side of the polarization beam splitter 54, diffracts the return light component from the position t3 included in the return light reflected in the −Z direction by the polarization beam splitter 54, and outputs the light from the light receiver Pd3. It is set to condense on the light receiving surface. The hologram element R32 imparts astigmatism to the diffracted light.

  Note that the return light component from the position t1 and the return light component from the position t2 included in the return light reflected in the −Z direction by the polarization beam splitter 54 do not satisfy the Bragg condition of the hologram element R32, and the hologram element R32 Is transmitted as it is.

  The hologram element R22 is arranged on the −Z side of the hologram element R32, diffracts the return light component from the position t2 included in the return light that has passed through the hologram element R32 as it is, and condenses it on the light receiving surface of the light receiver Pd2. Is set to The hologram element R22 gives astigmatism to the diffracted light.

  Note that light other than the return light component from the position t2 included in the return light that has passed through the hologram element R32 as it is does not satisfy the Bragg condition of the hologram element R22 and passes through the hologram element R22 as it is.

  The hologram element R12 is arranged on the −Z side of the hologram element R22, diffracts the return light component from the position t1 included in the return light that has passed through the hologram element R22 as it is, and condenses it on the light receiving surface of the light receiver Pd1. Is set to The hologram element R12 gives astigmatism to the diffracted light.

  The light other than the return light component from the position t1 included in the return light that has passed through the hologram element R22 as it is does not satisfy the Bragg condition of the hologram element R12 and passes through the hologram element R12 as it is.

  That is, the three hologram elements (R32, R22, R12) have a lens function that changes the divergence of the emitted light with respect to the incident light.

  As a result, the detection system can be reduced in size without lowering the light utilization efficiency, and as a result, the optical pickup device can be reduced in size without causing further deterioration in performance.

  The optical pickup device 23 according to the third embodiment may be configured using a hologram unit. In this case, a hologram element that diffracts both the light emitted from the corresponding hologram unit and the return light received by the corresponding hologram unit is used.

<< Fourth Embodiment >>
The fourth embodiment differs from the first to third embodiments described above in that an optical disc conforming to the DVD standard (hereinafter abbreviated as “DVD”) and an optical disc conforming to the Blu-ray standard (hereinafter “BD”). It is characterized in that it can cope with any of the above. The configuration of the optical disk apparatus excluding the optical pickup apparatus is almost the same as that of the first embodiment except for the data processing and signal processing. Accordingly, the following description will be focused on the differences from the first embodiment, and the same reference numerals will be used for the same or equivalent components as in the first embodiment, and the description thereof will be simplified or omitted. Shall. Here, it is assumed that the optical disk 15 is either a DVD or a BD, and when it is necessary to distinguish between them, the DVD is the optical disk 15d and the BD is the optical disk 15b.

  As shown in FIG. 18, the optical pickup device 23 according to the fourth embodiment includes two light sources (Lb and Ld), a hologram element Hd, a collimator lens 52, a polarizing beam splitter 54, and a λ for wavelength. / 4 plate 55, aperture wavelength filter 57, objective lens 60, condenser lens 58, cylinder lens 73, dichroic prism 76, two light receivers (Pd, Pb), and not shown for driving the objective lens 60. It has a drive system. Note that the objective lens 60 is optimized for BD.

  The light source Lb is used when the optical disc is a BD, and emits a laser beam having a wavelength of 405 nm. The maximum intensity emission direction of the laser light emitted from the light source Lb is the + X direction. The light source Lb is disposed at a position where the light emitting point coincides with the focal point of the collimating lens 52. The light source Ld is used when the optical disc is a DVD and emits laser light having a wavelength of 660 nm. The light source Ld is arranged in the vicinity of the light source Lb so that the light emitted from the light source Ld satisfies the Bragg condition of the hologram element Hd. Note that P-polarized light is emitted from the light source Lb and the light source Ld.

  The hologram element Hd is a volume hologram element in which the light incident surface and the diffracted light exit surface are substantially parallel, and is disposed on the optical path between each light source and the collimator lens 52. The light emitted from the light source Lb does not satisfy the Bragg condition of the hologram element Hd and passes through the hologram element Hd as it is. On the other hand, the light emitted from the light source Ld is diffracted by the hologram element Hd in order to satisfy the Bragg condition of the hologram element Hd. Then, diffracted light is emitted from the hologram element Hd in the + X direction. The hologram element Hd is set so that the diffracted light becomes a divergent light equivalent to the light emitted from the virtual light emitting point S1 located on the + X side of the focal point of the collimating lens 52. As an example, as shown in FIG. 19A, such a hologram element Hd makes the reference light Lr incident on the hologram element Hm on which the hologram pattern has not yet been formed from the same position as the light source Ld, and the virtual light emission. The information light Li is made incident from the point S1 and formed by forming a hologram pattern inside the hologram element Hm. The virtual light emitting point S1 is determined in consideration of the substrate thickness and wavelength difference between BD and DVD. That is, as an example, the diffracted light becomes divergent light in which aberrations due to differences in substrate thickness and wavelength between BD and DVD are corrected, as shown in FIG. 19B. Further, the angular magnification of the hologram element Hd is smaller than 1. The hologram element Hd is made by using a so-called two-beam interference exposure method using a thermoplastic or photopolymer as a material.

  The collimating lens 52, the polarizing beam splitter 54, the λ / 4 plate 55, the objective lens 60, the condenser lens 58, and the cylinder lens 73 are all arranged in the same manner as in the first embodiment.

  The aperture wavelength filter 57 is disposed on the optical path between the λ / 4 plate 55 and the objective lens 60, and is designed so that the aperture diameter varies depending on the wavelength. Here, the aperture of the light from the light source Lb is limited so that the numerical aperture (NA) of the objective lens 60 becomes 0.85, and the light from the light source Ld has a numerical aperture (NA) of the objective lens 60 of 0.65. The opening is limited to be The aperture wavelength filter 57 is servo-driven integrally with the objective lens 60.

  The dichroic prism 76 is disposed on the −Z side of the cylinder lens 73. Return light when the optical disk is DVD is reflected in the + X direction by the dichroic prism 76, and return light when the optical disk is BD passes through the dichroic prism 76 as it is. A light receiver Pd is disposed on the + X side of the dichroic prism 76 and receives the return light reflected by the dichroic prism 76. The light receiver Pb is disposed on the −Z side of the dichroic prism 76 and receives the return light transmitted through the dichroic prism 76.

  The operation of the optical pickup device 23 according to the fourth embodiment configured as described above will be briefly described.

<< When the optical disc is a BD >>
The linearly polarized light (here, P-polarized light) emitted from the light source Lb passes through the hologram element Hd as it is, and enters the polarization beam splitter 54 as substantially parallel light by the collimator lens 52. Most of the light from the collimating lens 52 is transmitted through the polarization beam splitter 54 as it is, is circularly polarized by the quarter wavelength plate 55, is restricted by the aperture wavelength filter 57, and is recorded on the optical disk 15 b via the objective lens 60. Focused on the layer.

  The reflected light from the optical disk 15b becomes circularly polarized light opposite to the outward path, and enters the quarter-wave plate 55 as return light through the objective lens 60 and the aperture wavelength filter 57, where the linearly polarized light is orthogonal to the outward path. (Here, S-polarized light). Then, this return light enters the polarization beam splitter 54.

  The return light reflected in the −Z direction by the polarization beam splitter 54 enters the dichroic prism 76 via the condenser lens 58 and the cylinder lens 73, passes through the dichroic prism 76 as it is, and is received by the light receiver Pb. .

<When the optical disc is a DVD>
Light of linearly polarized light (here, P-polarized light) emitted from the light source Ld enters the hologram element Hd, is diffracted in the + X direction by the hologram element Hd, and becomes slightly divergent light by the collimator lens 52. The polarization beam splitter 54 Is incident on. Most of the diffracted light passes through the polarization beam splitter 54 as it is, is circularly polarized by the quarter-wave plate 55, is aperture-limited by the aperture wavelength filter 57, and is condensed on the recording layer of the optical disc 15d via the objective lens 60. Is done.

  The reflected light from the optical disk 15d becomes circularly polarized light opposite to the outward path, and enters the quarter-wave plate 55 as return light through the objective lens 60 and the aperture wavelength filter 57, where the linearly polarized light is orthogonal to the outward path. (Here, S-polarized light). Then, this return light enters the polarization beam splitter 54.

  The return light reflected in the −Z direction by the polarization beam splitter 54 enters the dichroic prism 76 via the condenser lens 58 and the cylinder lens 73, is reflected by the dichroic prism 76, and is received by the light receiver Pd.

  Here, when the optical disk is a DVD, light incident on the objective lens 60 becomes divergent light, and aberrations due to differences in substrate thickness and wavelength from the BD are corrected. Note that when the hologram element Hd is formed, higher-order spherical aberration and aberration due to the cyst of the objective lens during tracking control may be further added. Specifically, a high-order spherical aberration or coma aberration is added to the information light Li using an aspheric lens, a liquid crystal element, or the like to form a hologram pattern inside the hologram element Hm. The hologram element created using such information light generates the information light at the time of creation when irradiated with the reference light. Therefore, when this hologram element is used, not only the difference in substrate thickness and wavelength from the BD, but also tracking control The aberration caused by the cyst of the objective lens at the time can also be corrected. Further, when the optical disc is a BD, a hologram element having a function of correcting aberration caused by the cyst of the objective lens at the time of tracking control may be further provided.

  As is clear from the above description, in the optical pickup device 23 according to the fourth embodiment, the light source unit is realized by the two light sources (Lb, Ld) and the hologram element Hd.

  As described above, according to the optical pickup device 23 of the fourth embodiment, the two light sources (Lb, Ld), the volume hologram element in which the light incident surface and the diffracted light exit surface are substantially parallel. The light source Lb transmits the light as it is, and the hologram element Hd diffracts the light from the light source Ld in the + X direction. Thereby, it is possible to reduce the size of the illumination system without reducing the light utilization efficiency, and as a result, it is possible to reduce the size without causing a decrease in performance.

  In addition, according to the optical disc device according to the fourth embodiment, since the optical pickup device 23 according to the fourth embodiment is provided, the access accuracy for a plurality of types of optical discs having different substrate thicknesses is not reduced. It is possible to reduce the size.

  In the fourth embodiment, as shown in FIG. 20 as an example, a hologram element Rd may be used instead of the dichroic prism 76. This hologram element Rd is a volume hologram in which the light incident surface and the diffracted light exit surface are substantially parallel, and transmits the return light when the optical disc is BD as it is, and diffracts the return light when the optical disc is DVD. . The light receiver Pd is disposed in the vicinity of the condensing position of the diffracted light. Further, the hologram element Rd also has a function of correcting aberration caused by the difference in substrate thickness. In this case, a light detection unit is realized by the two light receivers (Pb, Pd) and the hologram element Rd.

  As a result, the detection system can be reduced in size without lowering the light utilization efficiency, and as a result, the optical pickup device can be reduced in size without causing further deterioration in performance.

  By the way, the objective lens 60 is a lens designed for BD having a substrate thickness of 0.1 mm and a light source wavelength of 405 nm. When a DVD having a substrate thickness of 0.6 mm and a light source wavelength of 660 nm is used, the difference between the substrate thickness and the wavelength is as follows. Aberration due to. For this reason, if the light receiver Pd is arranged on the same substrate as the light receiver Pb, if the hologram element Rd does not have an aberration correction function, there is a problem that the focus error signal has an offset or sensitivity decrease when the optical disk is a DVD. appear. That is, the return light from the optical disk 15b is incident on the condenser lens 58 in a substantially parallel light state, whereas the return light from the optical disk 15d is incident on the condenser lens 58 in a convergent light state. Pd has to be arranged in front (+ Z side) of the light receiver Pb, which is inconvenient in terms of space. Here, since the hologram element Rd generates diffracted light in which the aberration of the convergent light is corrected, a normal focus error signal can be obtained even if the light receiver Pd and the light receiver Pb are arranged on the same plane. Furthermore, size reduction and simplification can be achieved.

  The optical pickup device 23 according to the fourth embodiment may be configured using a hologram unit. In this case, a hologram element that diffracts both the light emitted from the corresponding hologram unit and the return light received by the corresponding hologram unit is used.

<< Fifth Embodiment >>
Unlike the first to fourth embodiments described above, the fifth embodiment can be applied to any of optical discs (hereinafter abbreviated as “CD”) conforming to the CD standard, the DVD, and the BD. It is characterized by a certain point. The configuration of the optical disk apparatus excluding the optical pickup apparatus is almost the same as that of the first embodiment except for the data processing and signal processing parts. Accordingly, the following description will be focused on the differences from the first embodiment, and the same reference numerals will be used for the same or equivalent components as in the first embodiment, and the description thereof will be simplified or omitted. Shall. Here, the optical disk 15 is assumed to be any one of CD, DVD, and BD. When it is necessary to distinguish each of them, the DVD is the optical disk 15d, the BD is the optical disk 15b, and the CD is the optical disk 15c. And

  As shown in FIG. 21 as an example, the optical pickup device 23 according to the fifth embodiment includes three light sources (Lb, Ld, Lc), three hologram elements (Hb1, Hd1, Hc1), and polarization. Beam splitter 54, λ / 4 plate 55 for three wavelengths, diffractive optical element 56, aperture wavelength filter 57, objective lens 60, condenser lens 58, cylinder lens 73, two dichroic prisms (76c, 76d), three Light receiving devices (Pb, Pd, Pc), a driving system (not shown) for driving the objective lens 60, and the like.

  The light source Ld is used when the optical disc is a DVD and emits laser light having a wavelength of 660 nm. The light source Ld is disposed on the optical axis of the polarization beam splitter 54.

  The light source Lb is used when the optical disc is a BD, and emits a laser beam having a wavelength of 405 nm. The light source Lb is disposed on the + Z side of the light source Ld.

  The light source Lc is used when the optical disk is a CD, and emits laser light having a wavelength of 780 nm. The light source Lc is disposed on the −Z side of the light source Ld.

  In addition, light emitted from each light source is assumed to be P-polarized light.

  Each hologram element is a volume hologram element in which the light incident surface and the diffracted light exit surface are substantially parallel. In addition, the angular magnification of each hologram element is smaller than 1. Each hologram element is made by using a so-called two-beam interference exposure method using a thermoplastic or photopolymer as a material.

  The hologram element Hb1 is disposed on the + X side of each light source, and is set so that the light emitted from the light source Lb satisfies the Bragg condition. Therefore, the light emitted from the light source Lb is diffracted by the hologram element Hb1. This diffracted light is emitted substantially parallel to the optical axis of the objective lens 60. On the other hand, the light emitted from the light source Ld and the light source Lc does not satisfy the Bragg condition of the hologram element Hb1, and passes through the hologram element Hb1 as it is.

  The hologram element Hd1 is arranged on the + X side of the hologram element Hb1, and is set so that light from the light source Ld that has passed through the hologram element Hb1 as it is satisfies the Bragg condition. Accordingly, the light from the light source Ld that has passed through the hologram element Hb1 as it is is diffracted by the hologram element Hd1. This diffracted light is emitted substantially parallel to the optical axis of the objective lens 60. On the other hand, the diffracted light from the hologram element Hb1 and the light from the light source Lc that has passed through the hologram element Hb1 do not satisfy the Bragg condition of the hologram element Hd1, and pass through the hologram element Hd1 as it is.

  The hologram element Hc1 is arranged on the + X side of the hologram element Hd1, and the light from the light source Lc that has passed through the hologram element Hd1 as it is is set so as to satisfy the Bragg condition. Accordingly, the light from the light source Lc that has passed through the hologram element Hd1 as it is is diffracted by the hologram element Hc1. This diffracted light is emitted substantially parallel to the optical axis of the objective lens 60. On the other hand, the diffracted light from the hologram element Hb1 and the diffracted light from the hologram element Hd1 do not satisfy the Bragg condition of the hologram element Hc1, and pass through the hologram element Hc1 as it is.

  That is, each hologram element has a lens function that changes the divergence of the emitted light with respect to the incident light. Thereby, a collimating lens becomes unnecessary. Such a hologram element can be created by making the information light used when creating the hologram element parallel light. The arrangement order of the hologram elements is not limited to this.

  The polarization beam splitter 54 is disposed on the + X side of the hologram element Hc1, and the λ / 4 plate 55, the objective lens 60, the condenser lens 58, and the cylinder lens 73 are all the same as those in the first embodiment described above. Is arranged.

  Further, it is assumed that the objective lens 60 is optimized for the DVD. Therefore, at the time of creating the hologram pattern, the hologram element Hb1 is added with an aberration for correcting the aberration due to the difference in the substrate thickness of the BD and the DVD, and the hologram element Hc1 is caused by the difference in the substrate thickness of the CD and the DVD. Aberration for correcting the resulting aberration is added.

  The diffractive optical element 56 is disposed on the + X side of the λ / 4 plate 55 and performs aberration correction corresponding to each wavelength. The aperture wavelength filter 57 is disposed on the + X side of the diffractive optical element 56 and performs aperture limitation corresponding to each wavelength. Both the diffractive optical element 56 and the aperture wavelength filter 57 are servo-driven integrally with the objective lens 60.

  The dichroic prism 76c is disposed on the −Z side of the cylinder lens 73, and reflects return light in the + X direction when the optical disk is a CD. A light receiver Pc is disposed on the + X side of the dichroic prism 76c, and receives the return light reflected by the dichroic prism 76c. The dichroic prism 76c transmits the return light as it is when the optical disc is a BD or a DVD.

  The dichroic prism 76d is arranged on the −Z side of the dichroic prism 76c, and reflects the return light transmitted through the dichroic prism 76c as it is in the + X direction when the optical disc is a DVD. A light receiver Pd is disposed on the + X side of the dichroic prism 76d, and receives the return light reflected by the dichroic prism 76d. The dichroic prism 76d transmits the return light as it is when the optical disk is a BD. The light receiver Pb is disposed on the −Z side of the dichroic prism 76d, and receives the return light transmitted through the dichroic prism 76d.

  The operation of the optical pickup device 23 according to the fifth embodiment configured as described above will be briefly described.

<< When the optical disc is a BD >>
Light of linearly polarized light (here P-polarized light) emitted from the light source Lb is incident on the hologram element Hb1, diffracted by the hologram element Hb1, and becomes substantially parallel light and passes through the hologram element Hd1 and the hologram element Hc1 as they are. The light enters the polarization beam splitter 54. Most of the diffracted light passes through the polarization beam splitter 54 as it is, is converted into circularly polarized light by the quarter-wave plate 55, the aberration correction suitable for BD is performed by the diffractive optical element 56, and suitable for BD by the aperture wavelength filter 57. The aperture is limited, and the light is condensed on the recording layer of the optical disk 15b through the objective lens 60.

  The reflected light from the optical disk 15 b becomes circularly polarized light opposite to the outward path, and enters the diffractive optical element 56 through the objective lens 60 and the aperture wavelength filter 57 as return light. The return light that has become substantially parallel light by the diffractive optical element 56 is incident on the quarter-wave plate 55 and is converted into linearly polarized light (here, S-polarized light) orthogonal to the forward path. Then, this return light enters the polarization beam splitter 54.

  The return light reflected in the −Z direction by the polarization beam splitter 54 enters the dichroic prism 76c through the condenser lens 58 and the cylinder lens 73, passes through the dichroic prism 76c as it is, and enters the dichroic prism 76d. The light passes through the prism 76d as it is and is received by the light receiver Pb.

<When the optical disc is a DVD>
The linearly polarized light (here, P-polarized light) emitted from the light source Ld is transmitted through the hologram element Hb1 and incident on the hologram element Hd1, diffracted by the hologram element Hd1, and becomes substantially parallel light, leaving the hologram element Hc1 as it is. The light passes through and enters the polarization beam splitter 54. Most of the diffracted light is transmitted as it is through the polarizing beam splitter 54, is circularly polarized by the quarter wavelength plate 55, is transmitted through the diffractive optical element 56 as it is, and the aperture wavelength filter 57 is subjected to aperture restriction suitable for DVD, The light is condensed on the recording layer of the optical disk 15d through the objective lens 60.

  The reflected light from the optical disk 15d becomes circularly polarized light in the opposite direction to the outward path, and enters the diffractive optical element 56 through the objective lens 60 and the aperture wavelength filter 57 as return light. The return light that has become substantially parallel light by the diffractive optical element 56 is incident on the quarter-wave plate 55 and is converted into linearly polarized light (here, S-polarized light) orthogonal to the forward path. Then, this return light enters the polarization beam splitter 54.

  The return light reflected in the −Z direction by the polarization beam splitter 54 enters the dichroic prism 76c through the condenser lens 58 and the cylinder lens 73, passes through the dichroic prism 76c as it is, and enters the dichroic prism 76d. The light is reflected by the prism 76d and received by the light receiver Pd.

<When the optical disc is a CD>
Light of linearly polarized light (here P-polarized light) emitted from the light source Lc passes through the hologram element Hb1 and the hologram element Hd1, enters the hologram element Hc1, is diffracted by the hologram element Hc1, and is polarized as substantially parallel light. The light enters the beam splitter 54. Most of the diffracted light passes through the polarization beam splitter 54 as it is, is converted into circularly polarized light by the quarter-wave plate 55, the aberration correction suitable for CD is performed by the diffractive optical element 56, and suitable for CD by the aperture wavelength filter 57 The aperture is limited, and the light is condensed on the recording layer of the optical disc 15 c via the objective lens 60.

  The reflected light from the optical disk 15 c becomes circularly polarized light in the direction opposite to the outward path, and enters the diffractive optical element 56 through the objective lens 60 and the aperture wavelength filter 57 as return light. The return light that has become substantially parallel light by the diffractive optical element 56 is incident on the quarter-wave plate 55 and is converted into linearly polarized light (here, S-polarized light) orthogonal to the forward path. Then, this return light enters the polarization beam splitter 54.

  The return light reflected in the −Z direction by the polarization beam splitter 54 enters the dichroic prism 76c via the condenser lens 58 and the cylinder lens 73, is reflected by the dichroic prism 76c, and is received by the light receiver Pc.

  As is clear from the above description, in the optical pickup device 23 according to the fifth embodiment, the light source includes three light sources (Lb, Ld, Lc) and three hologram elements (Hb1, Hd1, Hc1). Unit is realized.

  As described above, according to the optical pickup device 23 according to the fifth embodiment, the three light sources (Lb, Ld, Lc) and the light from the light source Lb are diffracted in the + X direction, and the light source Ld and the light source The light from Lc is transmitted through the hologram element Hb1 as it is without being diffracted, and the light from the light source Lc that is diffracted in the + X direction from the light source Ld that is transmitted through the hologram element Hb1 as it is and is transmitted as it is through the hologram element Hb1 The light diffracted by the hologram element Hb1 is transmitted through the hologram element Hd1 without being diffracted, and the light from the light source Lc that is transmitted through the hologram element Hd1 is diffracted in the + X direction and diffracted by the hologram element Hb1. Both the light and the light diffracted by the hologram element Hd1 are transmitted as they are without being diffracted. Have, each hologram element are both substantially parallel to the volume hologram element and the exit surface of the incident surface and the diffracted light of the light, they are arranged in the X-axis direction. Thereby, it is possible to reduce the size of the illumination system without reducing the light utilization efficiency, and as a result, it is possible to reduce the size without causing a decrease in performance.

  In addition, according to the optical disc device according to the fifth embodiment, since the optical pickup device 23 according to the fifth embodiment is provided, the access accuracy for a plurality of types of optical discs having different substrate thicknesses is not reduced. It is possible to reduce the size.

  In the fifth embodiment, as shown in FIG. 22 as an example, three hologram elements are used instead of the condenser lens 58, the cylindrical lens 73, the dichroic prism 76c, and the dichroic prism 76d. (Rc1, Rd1, Rb1) may be used. All of these three hologram elements (Rc1, Rd1, Rb1) are volume hologram elements having different Bragg conditions and having a light incident surface and a diffracted light exit surface substantially parallel to each other.

  The hologram element Rc1 is arranged on the −Z side of the polarization beam splitter 54, and is set so that the return light when the optical disk is a CD satisfies the Bragg condition. Therefore, the return light when the optical disk is a CD is diffracted by the hologram element Rc1 and collected at a predetermined position. This hologram element Rc1 corrects aberrations caused by the difference in substrate thickness between CD and DVD and gives astigmatism to the emitted diffracted light. Note that the return light when the optical disc is a BD or DVD does not satisfy the Bragg condition of the hologram element Rc1, and passes through the hologram element Rc1 as it is.

  The hologram element Rd1 is arranged on the −Z side of the hologram element Rc1, and is set so that the return light when the optical disk is a DVD satisfies the Bragg condition. Therefore, the return light when the optical disk is a DVD is diffracted by the hologram element Rd1 and condensed at a predetermined position. This hologram element Rd1 gives astigmatism to the emitted diffracted light. Note that the return light when the optical disc is BD and the return light diffracted by the hologram element Rc1 do not satisfy the Bragg condition of the hologram element Rd1, and pass through the hologram element Rd1 as they are.

  The hologram element Rb1 is arranged on the −Z side of the hologram element Rd1, and is set so that the return light when the optical disk is BD satisfies the Bragg condition. Therefore, the return light when the optical disc is BD is diffracted by the hologram element Rb1 and collected at a predetermined position. This hologram element Rb1 corrects the aberration caused by the difference in substrate thickness between BD and DVD, and gives astigmatism to the emitted diffracted light. Note that the return light diffracted by the hologram element Rc1 and the return light diffracted by the hologram element Rd1 do not satisfy the Bragg condition of the hologram element Rb1, and pass through the hologram element Rb1 as they are.

  That is, each of the three hologram elements (Rc1, Rd1, Rb1) has a lens function equivalent to the condensing lens 58 and a lens function equivalent to the cylindrical lens 73. The order of arrangement of the three hologram elements (Rc1, Rd1, Rb1) is not limited to this.

  In this case, the light receiver Pc is disposed in the vicinity of the condensing position of the diffracted light from the hologram element Rc1, and the light receiver Pd is disposed in the vicinity of the condensing position of the diffracted light from the hologram element Rd1, The light receiver Pb is disposed in the vicinity of the condensing position of the diffracted light from the hologram element Rb1. That is, each light receiver can be arranged on the same plane.

  In this case, a light detection unit is realized by three light receivers (Pd, Pb, Pc) and three hologram elements (Rc1, Rd1, Rb1).

  As a result, the detection system can be reduced in size without lowering the light utilization efficiency, and as a result, the optical pickup device can be reduced in size without causing further deterioration in performance.

<< Sixth Embodiment >>
The sixth embodiment is characterized in that a hologram unit is used instead of each light source in the fifth embodiment. Accordingly, the following description will focus on the differences from the fifth embodiment, and the same reference numerals will be used for the same or equivalent components as in the fifth embodiment, and the description thereof will be simplified or omitted. Shall.

  As shown in FIG. 23 as an example, the optical pickup device 23 according to the sixth embodiment includes three hologram units (HUb, HUd, HUc), two hologram elements (Hb2, Hc2), and a collimating lens. 52, a λ / 4 plate 55 for three wavelengths, a diffractive optical element 56, an aperture wavelength filter 57, an objective lens 60, a drive system (not shown) for driving the objective lens 60, and the like.

  The hologram unit HUd is used when the optical disk is a DVD. As shown in FIG. 24A, for example, the hologram unit HUd includes a light source d1, a light receiver d2, and a polarization hologram d3 that emit laser light having a wavelength of 660 nm. It is arranged on the optical axis of the collimating lens 52. P-polarized light is emitted from the light source d1. The polarization hologram d3 is disposed on the + X side of the light source d1, and is set so that the reflectance with respect to the P-polarized light is small and the reflectance with respect to the S-polarized light is large. The light receiver d2 is disposed in the vicinity of the light source d1, and receives the return light deflected by the polarization hologram d3. Accordingly, the light emitted from the light source d1 enters the collimating lens 52 via the polarization hologram d3.

  The hologram unit HUb is used when the optical disk is a BD. As shown in FIG. 24B, for example, the hologram unit HUb includes a light source b1, a light receiver b2, and a polarization hologram b3 that emit laser light having a wavelength of 405 nm. It is arranged on the + Z side of the hologram unit HUd. P-polarized light is emitted from the light source b1. The polarization hologram b3 is arranged on the + X side of the light source b1, and is set so that the reflectance with respect to the P-polarized light is small and the reflectance with respect to the S-polarized light is large. The light receiver b2 is disposed in the vicinity of the light source b1, and receives the return light deflected by the polarization hologram b3. Therefore, the light emitted from the light source b1 enters the collimating lens 52 via the polarization hologram b3.

  The hologram unit HUc is used when the optical disk is a CD. As shown in FIG. 24C, for example, the hologram unit HUc includes a light source c1, a light receiver c2, and a polarization hologram c3 that emit laser light having a wavelength of 780 nm. It is arranged on the −Z side of the hologram unit HUd. P-polarized light is emitted from the light source c1. The polarization hologram c3 is arranged on the + X side of the light source c1, and is set so that the reflectance with respect to the P-polarized light is small and the reflectance with respect to the S-polarized light is large. The light receiver c2 is disposed near the light source c1 and receives the return light deflected by the polarization hologram c3. Accordingly, the light emitted from the light source c1 enters the collimating lens 52 via the polarization hologram c3.

  The hologram element Hb2 and the hologram element Hc2 are volume hologram elements in which the Bragg conditions are different from each other, and both the light incident surface and the diffracted light exit surface are substantially parallel. In addition, the angular magnification of each hologram element is smaller than 1. Each hologram element is made by using a so-called two-beam interference exposure method using a thermoplastic or photopolymer as a material.

  The hologram element Hb2 is disposed on the + X side of the collimating lens 52, and is set so that light from the hologram unit HUb via the collimating lens 52 satisfies the Bragg condition. Therefore, the light from the hologram unit HUb via the collimator lens 52 is diffracted in the + X direction by the hologram element Hb2. Note that the light from the hologram unit HUd and the light from the hologram unit HUc via the collimator lens 52 do not satisfy the Bragg condition of the hologram element Hb2 and pass through as they are.

  The hologram element Hc2 is arranged on the + X side of the hologram element Hb2, and the light from the hologram unit HUc that has passed through the hologram element Hb2 as it is is set so as to satisfy the Bragg condition. Therefore, the light from the hologram unit HUc that has passed through the hologram element Hb2 as it is is diffracted in the + X direction by the hologram element Hc2. The light from the hologram unit HUd that has passed through the hologram element Hb2 and the diffracted light from the hologram element Hb2 do not satisfy the Bragg condition of the hologram element Hc2, and are transmitted as they are.

  Further, it is assumed that the objective lens 60 is optimized for the DVD. Therefore, the hologram element Hb2 is added with an aberration for correcting an aberration caused by a difference in substrate thickness between BD and DVD at the time of creating a hologram pattern. The hologram element Hc2 is added with an aberration for correcting aberration caused by the difference in substrate thickness between the CD and the DVD at the time of creating the hologram pattern.

  The λ / 4 plate 55 is disposed on the + X side of the hologram element Hc2. The diffractive optical element 56, the aperture wavelength filter 57, and the objective lens 60 are all arranged in the same manner as in the fifth embodiment described above.

  The operation of the optical pickup device 23 according to the sixth embodiment configured as described above will be briefly described.

<< When the optical disc is a BD >>
The linearly polarized light emitted from the light source b1 enters the collimator lens 52 via the polarization hologram b3, enters the hologram element Hb2 as substantially parallel light, is diffracted by the hologram element Hb2, and passes through the hologram element Hc2. The quarter-wave plate 55 makes circularly polarized light, the diffractive optical element 56 corrects aberrations suitable for BD, the aperture wavelength filter 57 limits aperture suitable for BD, and recording on the optical disk 15b via the objective lens 60 is performed. Focused on the layer.

  The reflected light from the optical disk 15 b becomes circularly polarized light opposite to the outward path, and enters the diffractive optical element 56 through the objective lens 60 and the aperture wavelength filter 57 as return light. The return light that has become substantially parallel light by the diffractive optical element 56 enters the quarter-wave plate 55, where it is linearly polarized light orthogonal to the forward path. The return light passes through the hologram element Hc2 as it is, is diffracted by the hologram element Hb2, enters the polarization hologram b3 through the collimator lens 52, is deflected by the polarization hologram b3, and is received by the light receiver b2.

<When the optical disc is a DVD>
The linearly polarized light emitted from the light source d1 enters the collimating lens 52 through the polarization hologram d3, passes through the hologram element Hb2 and the hologram element Hc2 as they are substantially parallel light, and is circularly polarized by the quarter wavelength plate 55. Then, the light passes through the diffractive optical element 56 as it is, is subjected to aperture restriction suitable for DVD by the aperture wavelength filter 57, and is condensed on the recording layer of the optical disc 15d via the objective lens 60.

  The reflected light from the optical disk 15d becomes circularly polarized light in the opposite direction to the outward path, and enters the diffractive optical element 56 through the objective lens 60 and the aperture wavelength filter 57 as return light. The return light that has become substantially parallel light by the diffractive optical element 56 enters the quarter-wave plate 55, where it is linearly polarized light orthogonal to the forward path. The return light passes through the hologram element Hc2 and the hologram element Hb2 as they are, enters the polarization hologram d3 through the collimator lens 52, is deflected by the polarization hologram d3, and is received by the light receiver d2.

<When the optical disc is a CD>
The linearly polarized light emitted from the light source c1 enters the collimating lens 52 via the polarization hologram c3, passes through the hologram element Hb2 as substantially parallel light, enters the hologram element Hc2, and is diffracted by the hologram element Hc2. The quarter-wave plate 55 makes the circularly polarized light, the diffractive optical element 56 corrects the aberration suitable for the CD, the aperture wavelength filter 57 limits the aperture suitable for the CD, and the recording on the optical disk 15c through the objective lens 60 is performed. Focused on the layer.

  The reflected light from the optical disk 15 c becomes circularly polarized light in the direction opposite to the outward path, and enters the diffractive optical element 56 through the objective lens 60 and the aperture wavelength filter 57 as return light. The return light that has become substantially parallel light by the diffractive optical element 56 enters the quarter-wave plate 55, where it is linearly polarized light orthogonal to the forward path. The return light is diffracted by the hologram element Hc2, passes through the hologram element Hb2 as it is, enters the polarization hologram c3 through the collimator lens 52, is deflected by the polarization hologram c3, and is received by the light receiver c2.

  As described above, according to the optical pickup device 23 according to the sixth embodiment, the light from the three light sources (b1, d1, c1) and the light source b1 is diffracted in the + X direction and from the light source b1. The hologram element Hb2 that diffracts the return light of the emitted light through the objective lens 60 and the return light of the light emitted from the light source c1 through the objective lens 60 while diffracting the light from the light source c1 in the + X direction. Each hologram element is a volume hologram element in which the light incident surface and the diffracted light exit surface are substantially parallel, and are arranged side by side in the X-axis direction. . Thereby, further downsizing of the optical pickup device can be promoted as compared with the fifth embodiment described above.

  Also, according to the optical disc device according to the sixth embodiment, since the optical pickup device 23 according to the sixth embodiment is provided, the access accuracy for a plurality of types of optical discs having different substrate thicknesses is not reduced. It is possible to reduce the size.

  As described above, the light source unit of the present invention is suitable for downsizing without reducing the light utilization efficiency. In addition, the light detection unit of the present invention is suitable for downsizing without reducing light utilization efficiency. Moreover, the optical pickup device of the present invention is suitable for downsizing without causing performance degradation. Also, the optical disk device of the present invention is suitable for downsizing without lowering the access accuracy to the optical disk.

1 is a block diagram showing a configuration of an optical disc device according to a first embodiment of the present invention. It is a figure for demonstrating the optical pick-up apparatus in FIG. It is a figure for demonstrating a volume hologram. 3 is a flowchart for explaining processing in the optical disc apparatus in FIG. 1 when a recording request is received from a host apparatus. 3 is a flowchart for explaining processing in the optical disc apparatus in FIG. 1 when a reproduction request is received from a host device. It is a figure for demonstrating the modification of the optical pick-up apparatus of FIG. It is a figure for demonstrating the optical pick-up apparatus which concerns on the 2nd Embodiment of this invention. FIGS. 8A to 8C are diagrams for explaining the hologram unit in FIG. It is a figure for demonstrating the modification of the optical pick-up apparatus of FIG. It is a figure for demonstrating the optical pick-up apparatus which concerns on the 3rd Embodiment of this invention. FIGS. 11A to 11C are diagrams for explaining light emitted from each hologram unit in FIG. FIGS. 12A and 12B are diagrams for explaining a method of creating each hologram element in FIG. 13A and 13B are diagrams for explaining the operation of each hologram element in FIG. FIGS. 14A and 14B are views (No. 1) for explaining the relationship between the intensity distribution of information light and the intensity distribution of diffracted light, respectively. FIGS. 15A and 15B are diagrams (No. 2) for explaining the relationship between the intensity distribution of information light and the intensity distribution of diffracted light, respectively. FIGS. 16A and 16B are views (No. 3) for explaining the relationship between the intensity distribution of information light and the intensity distribution of diffracted light, respectively. It is a figure for demonstrating the modification of the optical pick-up apparatus of FIG. It is a figure for demonstrating the optical pick-up apparatus which concerns on the 4th Embodiment of this invention. FIG. 19A is a diagram for explaining a method of creating the hologram element in FIG. 18, and FIG. 19B is a diagram for explaining the operation of the hologram element in FIG. It is a figure for demonstrating the modification of the optical pick-up apparatus of FIG. It is a figure for demonstrating the optical pick-up apparatus which concerns on the 5th Embodiment of this invention. It is a figure for demonstrating the modification of the optical pick-up apparatus of FIG. It is a figure for demonstrating the optical pick-up apparatus which concerns on the 6th Embodiment of this invention. 24A to 24C are diagrams for explaining the hologram unit in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 15 ... Optical disk, 20 ... Optical disk apparatus, 23 ... Optical pick-up apparatus, 28 ... Reproduction signal processing circuit (a part of processing apparatus), 40 ... CPU (a part of processing apparatus), 60 ... Objective lens, H1, H3, H11 , H12, H13, H23, H31, H32, H33, Hb1, Hb2, Hc1, Hc2, Hd, Hd1 ... Hologram element (volume hologram element), R1, R3, R12, R32, Rb1, Rc1, Rd, Rd1 ... Hologram Element (volume hologram element), k1, k2, k3, b1, c1, d1 ... light source, Ld1, Ld2, Ld3, Lb, Lc, Ld ... light source, b2, c2, d2, m1, m2, m3, Pd1, Pd2 , Pd3, Pb, Pc, Pd... Light receiver (photodetector).

Claims (42)

A light source unit that emits a plurality of lights in a predetermined emission direction,
With multiple light sources;
Provided individually corresponding to the plurality of light sources, arranged side by side in the emission direction on the optical paths of the plurality of lights emitted from the plurality of light sources, diffracts light from the corresponding light sources, and corresponding light sources And a plurality of volume hologram elements that allow light from a light source other than the above to pass through without being diffracted. A light source unit that emits a plurality of lights in a predetermined emission direction,
With multiple light sources;
Among the plurality of light sources, provided corresponding to at least one light source excluding a preset light source, arranged on an optical path of a plurality of lights emitted from the plurality of light sources, and from at least one corresponding light source A light source unit comprising: at least one volume hologram element that diffracts light and allows light from other light sources to pass through without being diffracted. The at least one light source is a plurality of light sources;
The light source unit according to claim 2, wherein the at least one volume hologram element is a plurality of volume hologram elements arranged side by side in the emission direction.   The diffracted light emitted from the volume hologram element has an intensity distribution that is axisymmetric with respect to the optical axis of the volume hologram element, and the full width at half maximum of the intensity distribution is larger than the full width at half maximum of the intensity distribution of incident light. The light source unit according to claim 1, wherein the light source unit is a light source unit.   The light source unit according to any one of claims 1 to 4, wherein the volume hologram element further has a lens function of changing a divergence degree.   The light source unit according to claim 1, wherein a material of the volume hologram element is any one of a photopolymer and a thermoplastic.   The light source unit according to claim 1, wherein the volume hologram element is created using a two-beam interference exposure method.   8. The light source unit according to claim 1, wherein the volume hologram element has a sin (an exit angle of diffracted light) / sin (an incident angle of light) smaller than 1. 8. A light detection unit that individually detects a plurality of light beams incident from a predetermined incident direction,
Provided individually corresponding to the plurality of light fluxes, arranged side by side in the incident direction on the optical path of the plurality of light fluxes, diffracts the corresponding light fluxes, and transmits the light beams other than the corresponding light beams as they are without being diffracted. A plurality of volume hologram elements to be caused;
A plurality of photodetectors provided individually corresponding to the plurality of volume hologram elements and receiving diffracted light from the corresponding volume hologram elements. A light detection unit that individually detects a plurality of light beams incident from a predetermined incident direction,
Among the plurality of light beams, provided corresponding to at least one light beam excluding a preset light beam, disposed on the optical path of the plurality of light beams, diffracting at least one corresponding light beam, and diffracting the other light beams At least one volume hologram element that passes through without being transmitted;
A plurality of photodetectors individually receiving the preset light beam and diffracted light from the at least one volume hologram element; The at least one light flux is a plurality of light fluxes;
The light detection unit according to claim 10, wherein the at least one volume hologram element is a plurality of volume hologram elements arranged side by side in the incident direction.   The light detection unit according to claim 9, wherein the volume hologram element further has a lens function of changing a divergence degree.   The photodetection unit according to claim 9, wherein the volume hologram element further gives astigmatism to diffracted light emitted from the volume hologram element.   The light detection unit according to claim 9, wherein a material of the volume hologram element is one of a photopolymer and a thermoplastic.   The light detection unit according to claim 9, wherein the volume hologram element is formed using a two-beam interference exposure method. An optical pickup device for irradiating an optical disc with light and receiving reflected light from the optical disc,
A light source unit according to any one of claims 1 to 8;
An optical system including an objective lens for condensing a plurality of lights emitted from the light source unit onto an optical disc;
A photodetector for receiving return light from the optical disc; An optical pickup device for irradiating an optical disc with light and receiving reflected light from the optical disc,
With multiple light sources;
An objective lens for condensing a plurality of lights emitted from the plurality of light sources on an optical disc, respectively;
An optical pickup device comprising: the light detection unit according to claim 9, which is disposed on an optical path of return light from the optical disc via the objective lens and detects the return light. An optical pickup device for irradiating an optical disc with light and receiving reflected light from the optical disc,
A light source unit according to any one of claims 1 to 8;
An optical system including an objective lens for condensing a plurality of lights emitted from the light source unit onto an optical disc;
An optical pickup device comprising: the light detection unit according to claim 9, which is disposed on an optical path of return light from the optical disc via the objective lens and detects the return light. As the optical disc, it is possible to support a plurality of types of optical discs having different substrate thicknesses,
19. The optical pickup device according to claim 16, wherein the plurality of lights emitted from the light source unit are light individually corresponding to the plurality of types of optical disks.   The optical pickup device according to claim 19, wherein the volume hologram element of the light source unit further corrects an aberration caused by the difference in thickness of the substrate. As the optical disc, it is possible to correspond to a multilayer disc having a plurality of recording layers,
19. The optical pickup device according to claim 16, wherein the plurality of lights emitted from the light source unit are light individually corresponding to the plurality of recording layers.   The optical pickup device according to claim 21, wherein the positions of the light spots respectively formed on the plurality of recording layers are different in distance from the rotation center of the optical disc.   23. The optical pickup device according to claim 21, wherein the volume hologram element of the light source unit further corrects an aberration caused by a difference in position of the recording layer with respect to the objective lens.   19. The optical pickup device according to claim 16, wherein the plurality of lights emitted from the light source unit are light individually corresponding to different tracks of the optical disc. A collimating lens is disposed on an optical path between the plurality of light sources of the light source unit and the volume hologram element;
The incident angle of light and the exit angle of diffracted light in the volume hologram element of the light source unit are:
The distance Dd in the direction perpendicular to the optical axis of each light emitting point in the plurality of light sources, the focal length fc of the collimating lens, the focal length fo of the objective lens, and the plurality of light sources formed on the recording surface of the optical disc Using the distance Ds between the plurality of light spots in the direction perpendicular to the optical axis, sin (emitted angle of diffracted light) / sin (incident angle of light beam) = (Ds / Dd) · (fc / fo) The optical pickup device according to claim 24, wherein the following relationship is satisfied: As the optical disc, it is possible to support a plurality of types of optical discs having different substrate thicknesses,
The optical pickup device according to claim 17 or 18, wherein the light detection unit individually detects each return light from the plurality of types of optical disks.   27. The optical pickup device according to claim 26, wherein the volume hologram of the light detection unit further corrects an aberration caused by the difference in the substrate thickness. As the optical disc, it is possible to correspond to a multilayer disc having a plurality of recording layers,
The optical pickup device according to claim 17, wherein the light detection unit individually detects each return light from the plurality of recording layers.   29. The optical pickup device according to claim 28, wherein the volume hologram of the light detection unit further corrects an aberration caused by a difference in position of the recording layer with respect to the objective lens. The plurality of lights traveling toward the objective lens are light individually corresponding to different tracks of the optical disc,
The optical pickup device according to claim 17 or 18, wherein the light detection unit individually detects each return light from the different tracks. An optical pickup device for irradiating an optical disc with light and receiving reflected light from the optical disc,
With multiple light sources;
An objective lens for condensing the light emitted from the plurality of light sources on an optical disc;
Light individually provided corresponding to the plurality of light sources, arranged side by side on an optical path between the plurality of light sources and the objective lens, and emitted from the corresponding light source toward the objective lens, and the corresponding light source The return light of the light emitted from the optical disc is diffracted, emitted from a light source other than the corresponding light source and directed to the objective lens, and light emitted from the light source other than the corresponding light source from the optical disc. A plurality of volume hologram elements that pass through all of the return light without being diffracted;
And a plurality of photodetectors provided individually corresponding to the plurality of volume hologram elements and receiving return light diffracted by the corresponding volume hologram elements. An optical pickup device for irradiating an optical disc with light and receiving reflected light from the optical disc,
With multiple light sources;
An objective lens for condensing the light emitted from the plurality of light sources on an optical disc;
Among the plurality of light sources, provided corresponding to at least one light source excluding a preset light source, disposed on an optical path between the plurality of light sources and the objective lens, and emitted from the corresponding at least one light source The light directed toward the objective lens and the return light from the optical disc of the light emitted from the corresponding at least one light source are each diffracted, the light emitted from the other light sources and directed toward the objective lens, and the other light sources At least one volume hologram element that transmits all the light emitted from the optical disc as it is without being diffracted;
A plurality of photodetectors individually receiving return light of the light emitted from the preset light source through the objective lens and return light diffracted by the at least one volume hologram element; Optical pickup device. The at least one light source is a plurality of light sources;
The optical pickup device according to claim 32, wherein the at least one volume hologram element is a plurality of volume hologram elements arranged side by side on an optical path between the plurality of light sources and the objective lens. .   The optical pickup device according to any one of claims 31 to 33, wherein the volume hologram element has sin (an exit angle of diffracted light) / sin (an incident angle of light) smaller than 1. As the optical disc, it is possible to support a plurality of types of optical discs having different substrate thicknesses,
The optical pickup device according to any one of claims 31 to 34, wherein light respectively emitted from the plurality of light sources is light individually corresponding to the plurality of types of optical disks.   36. The optical pickup device according to claim 35, wherein the volume hologram element further corrects an aberration caused by the difference in thickness of the substrate. As the optical disc, it is possible to correspond to a multilayer disc having a plurality of recording layers,
The optical pickup device according to any one of claims 31 to 34, wherein light respectively emitted from the plurality of light sources is light individually corresponding to the plurality of recording layers.   38. The optical pickup device according to claim 37, wherein the positions of the light spots respectively formed on the plurality of recording layers are different from each other in the distance from the rotation center of the optical disc.   The optical pickup device according to claim 37 or 38, wherein the volume hologram element further corrects an aberration caused by a difference in position of the recording layer with respect to the objective lens.   The optical pickup device according to any one of claims 31 to 34, wherein light emitted from the plurality of light sources is light individually corresponding to different tracks of the optical disc. A collimating lens is disposed on an optical path between the plurality of light sources and the volume hologram element;
The incident angle of light and the exit angle of diffracted light in the volume hologram element are as follows:
The distance Dd in the direction perpendicular to the optical axis of each light emitting point in the plurality of light sources, the focal length fc of the collimating lens, the focal length fo of the objective lens, and the plurality of light sources formed on the recording surface of the optical disc Using the distance Ds between the plurality of light spots in the direction perpendicular to the optical axis, sin (emitted angle of diffracted light) / sin (incident angle of light beam) = (Ds / Dd) · (fc / fo) 41. The optical pickup device according to claim 40, wherein the relationship is satisfied. An optical disk apparatus capable of reproducing at least one of recording, reproduction and erasure of information on an optical disk,
An optical pickup device according to any one of claims 16 to 41;
And a processing device for reproducing information recorded on the optical disc using an output signal of a photodetector of the optical pickup device.

Images