JP2009015881A - Hologram recording unit, hologram recording method, optical disk recording unit, and optical disk recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control the possibility of forming hologram without changing the irradiation intensity of a light beam. <P>SOLUTION: The hologram recording/reproducing apparatus 20 can switch on and off an interference of light beams L1A and L1B for irradiating a recording medium 28 by controlling the coherence of the light beam L1 with a coherence controlling section 22, thereby switching on and off the recording of hologram in the recording medium 28 without changing the irradiation state of the light beam L1 by a light source 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hologram recording apparatus, a hologram recording method, an optical disk recording apparatus, and an optical disk recording method, and is suitable for application to, for example, an optical disk apparatus that records a hologram on an optical disk.

  2. Description of the Related Art Conventionally, in an optical disc apparatus, a light beam is irradiated onto an optical disc such as a CD (Compact Disc), a DVD (Digital Versatile Disc), and a Blu-ray Disc (registered trademark, hereinafter referred to as BD) and the reflected light is read. Thus, information that can be reproduced is widely used.

  In such a conventional optical disc apparatus, information is recorded by irradiating the optical disc with a light beam to change the local reflectance of the optical disc.

  For this optical disc, the size of the light spot formed on the optical disc is given by approximately λ / NA (λ: wavelength of the light beam, NA: numerical aperture), and the resolution is also known to be proportional to this value. It has been. For example, Non-Patent Document 1 shows details of a BD that can record data of approximately 26 [GB] on an optical disk having a diameter of 120 [mm].

  By the way, various kinds of information such as various contents such as music contents and video contents, or various data for computers are recorded on the optical disc. In particular, in recent years, the amount of information has increased due to higher definition of video and higher sound quality of music, and an increase in the number of contents to be recorded on one optical disc has been demanded. It is requested.

  In view of this, there has also been proposed a method of increasing the recording capacity of one optical disc by overlapping recording layers in one optical disc (see, for example, Non-Patent Document 2).

  On the other hand, an optical disk apparatus using a hologram has been proposed as a method for recording information on the optical disk (see, for example, Non-Patent Document 3).

  For example, as shown in FIG. 1, the optical disk apparatus 1 condenses a light beam from an optical head 7 once in an optical disk 8 made of a photopolymer whose refractive index changes depending on the intensity of the irradiated light. By using the reflection device 9 provided on the back side (lower side in FIG. 1), the light beam is once again condensed at the same focal position from the opposite direction.

  The optical disc apparatus 1 emits a light beam composed of laser light from a laser 2, modulates the light wave by an acousto-optic modulator 3, and converts it into parallel light by a collimator lens 4. Subsequently, the light beam passes through the polarization beam splitter 5, is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 6, and then enters the optical head 7.

  The optical head 7 is adapted to record and reproduce information. The optical head reflects a light beam by a mirror 7A, condenses it by an objective lens 7B, and is rotated by a spindle motor (not shown). 8 is irradiated.

  At this time, the light beam is once focused inside the optical disc 8, then reflected by the reflecting device 9 disposed on the back side of the optical disc 8, and from the back side of the optical disc 8 to the same focal point inside the optical disc 8. Focused. Incidentally, the reflection device 9 includes a condenser lens 9A, a shutter 9B, a condenser lens 9C, and a reflection mirror 9D.

  As a result, as shown in FIG. 2 (A), a standing wave is generated at the focal position of the light beam, and the light spot size is formed in a shape in which two cones are bonded together on the bottom surfaces. A recording mark RM composed of a small hologram is formed. Thus, the recording mark RM is recorded as information.

  When a plurality of recording marks RM are recorded in the optical disk 8, the optical disk apparatus 1 rotates the optical disk 8 and arranges the recording marks RM along a concentric or spiral track to form one mark recording layer. And by adjusting the focal position of the light beam, each recording mark RM can be recorded so that a plurality of mark recording layers are stacked.

  As a result, the optical disc 8 has a multilayer structure having a plurality of mark recording layers therein. For example, in the optical disc 8, as shown in FIG. 2B, the distance (mark pitch) p1 between the recording marks RM is 1.5 [μm], the distance between tracks (track pitch) p2 is 2 [μm], and the interlayer The distance p3 is 22.5 [μm].

  Further, when reproducing information from the disc 8 on which the recording mark RM is recorded, the optical disc apparatus 1 closes the shutter 9B of the reflection device 9 so that the light beam is not irradiated from the back side of the optical disc 8.

  At this time, the optical disc apparatus 1 irradiates the recording mark RM in the optical disc 8 with the optical beam by the optical head 7 and causes the reproducing light beam generated from the recording mark RM to enter the optical head 7. The reproduction light beam is converted from circularly polarized light to linearly polarized light by the quarter wavelength plate 6 and reflected by the polarizing beam splitter 5. Further, the reproduction light beam is condensed by the condenser lens 10 and irradiated to the photodetector 12 through the pinhole 11.

  At this time, the optical disc apparatus 1 detects the light amount of the reproduction light beam by the photodetector 12 and reproduces information based on the detection result.

  Further, as in the optical disc apparatus 13 shown in FIG. 3 in which parts corresponding to those in FIG. 1 are given the same reference numerals, one light beam emitted from a single light source is used as two recording light beams during the recording process. There has been proposed a technique in which a hologram is formed while being separated into beams and performing position control similar to that of a conventional optical disk device based on the reflected light (see, for example, Patent Document 1).

  In the optical disk device 13, the light beam emitted from the laser diode 14 is converted into parallel light by the collimator lens 4 and separated into two light beams (first light beam and second light beam) by the beam splitter 5A.

  The optical disc device 13 makes the first light beam transmitted through the beam splitter 5A incident on the objective lens 7B via the beam splitters 5B and 5C. The objective lens 7B condenses the first light beam and irradiates it on the first surface 8A side of the optical disc 8.

  At this time, the optical disk apparatus 13 uses the objective lens 7B, the beam splitters 5C and 5B, and the cylindrical part of the first reflected light beam formed by reflecting the first light beam by the interface between the substrate 8C and the dielectric layer 8D in the optical disk 8. Light is received by the photodetector 12B via the lens 18, and a detection signal corresponding to the amount of received light is amplified by the matrix amplifier 19, and a servo control signal is generated based on the amplified detection signal.

  The optical disk device 13 is configured to displace the objective lens 7B by driving the actuator 7Ba based on the servo control signal.

  On the other hand, the optical disc device 13 makes the second light beam reflected by the beam splitter 5A incident on the convex lens 7C via the mirrors 15A, 15B, 15C and 15D. The convex lens 7C condenses the second light beam and enters the optical disk 8 from the second surface 8B side of the optical disk 8.

  At this time, in the optical disc apparatus 13, a portion where the first light beam and the second light beam overlap (shown by oblique lines) interferes to form a recording mark RM made of a hologram. Thus, the recording mark RM is recorded as information on the recording layer 8E.

  Further, the optical disc device 13 blocks the second light beam by the shutter 16 installed on the optical path of the second light beam during the reproduction process, and uses the recording mark RM recorded on the optical disc 8 to record the first light beam. The reproduction light beam generated by the reflection is received by the photodetector 12A through the objective lens 7B, the beam splitter 5C, the concave lens 17, the condenser lens 10, and the pinhole plate 11.

  At this time, the optical disk apparatus 1 detects the light amount of the reproduction light beam by the photodetector 12, and reproduces information based on the detection result.

For example, the optical disk device 13 emits the laser diode 14 to emit light corresponding to the code “1” when information is expressed in binary numbers, records the recording mark RM, and turns off the laser diode 14 corresponding to the code “0”. The recording mark RM is not recorded. As a result, the optical disk device 13 can recognize the code “0” or “1” based on the presence or absence of the recording mark RM and can reproduce the original information during reproduction.
Y. Kasami, Y. Kuroda, K. Seo, O. Kawakubo, S. Takagawa, M. Ono, and M. Yamada, Jpn. J. Appl. Phys., 39, 756 (2000) I. Ichimura etal, Technical Digest of ISOM'04, pp52, Oct. 11-15, 2005, Jeju Korea RR McLeod etal., “Microholographic multilayer optical disk data storage,” Appl. Opt., Vol. 44, 2005, pp3197 Japanese Patent No. 3452106

  By the way, in the optical disc apparatus 13, since the position control is performed based on a part of the first reflected light beam, the position control can be appropriately performed when the code to be recorded is “1”, but the code to be recorded is “0”. In this case, the position control cannot be performed because the optical disk 8 is not irradiated with the first light beam.

  In particular, when “0” continues as a code to be recorded, the optical disc apparatus 13 cannot perform position control at all. Therefore, the recording mark RM is inappropriate when the code becomes “1” next time. There was a problem that there was a risk of recording in the position.

  The present invention has been made in consideration of the above points. A hologram recording apparatus and a hologram recording method capable of controlling whether or not to form a hologram without changing the emission intensity of the light beam, and light emitted from the same light source. It is an object of the present invention to propose an optical disc recording apparatus and an optical disc recording method capable of stably performing position control when performing information recording and position control using a beam.

  In order to solve such problems, in the hologram recording apparatus and the hologram recording method of the present invention, the light is emitted from a predetermined light source to a desired recording position in the recording medium whose refractive index changes according to the intensity of the irradiated light. The light beam is separated and condensed from different directions, and the coherency of the light beam emitted from the light source before being separated is controlled to switch whether or not to form a hologram at a desired recording position. did.

  This makes it possible to control whether or not to form a hologram at a desired recording position while a light beam having a predetermined intensity is emitted from the light source.

  In the optical disc recording apparatus and optical disc recording method of the present invention, the position control light beam for position control and the first recording light beam and the second recording light beam for information recording are separated from the light beam emitted from a predetermined light source. And a recording layer that is formed in a substantially disc shape and whose refractive index changes according to the intensity of irradiated light, and a position identification layer provided in the recording section for identifying the position in the recording medium layer. The position control light beam is condensed from the one surface side of the optical disk by the first objective lens, and the focus of the position control light beam is based on the reception result of the reflected light beam reflected by the position identification layer. When the position of the first objective lens is controlled so as to match the desired identification position in the position identification layer, and the focal point of the second light beam is condensed by the second objective lens, The position of the second objective lens is controlled so that the second light beam is focused on the desired recording position where the first light beam is focused by the first objective lens, and the coherence of the light beam emitted from the light source is controlled. By controlling, whether or not to form a hologram at a desired recording position is switched.

  Thereby, it is possible to always irradiate the position control light beam having a constant light quantity to the position identification layer of the optical disc regardless of whether or not the hologram is formed.

  According to the present invention, it is possible to control whether or not a hologram is formed at a desired recording position while a light beam having a predetermined intensity is emitted from a light source, and thus, without changing the emission intensity of the light beam. It is possible to realize a hologram recording apparatus and a hologram recording method that can control whether or not formation is possible.

  Further, according to the present invention, it is possible to always irradiate the position control light beam having a constant light amount to the position identification layer of the optical disc irrespective of whether or not the hologram is formed, and thus the light is emitted from the same light source. An optical disc recording apparatus and an optical disc recording method capable of stably performing position control when performing information recording and position control using a light beam can be realized.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) First Embodiment (1-1) Configuration of Hologram Recording / Reproducing Device In FIG. 4, the hologram recording / reproducing device 20 in the first embodiment interferes with two light beams in the recording medium 28. By doing so, a hologram can be recorded.

  Upon receiving an information recording instruction from an external device (not shown), the hologram recording / reproducing apparatus 20 emits a light beam L1 made of laser light from the light source 21 and makes it incident on the coherence control unit 22. The coherence control unit 22 controls the coherence (details will be described later) of the light beam L1 so as to enter the beam splitter 24 of the light beam irradiation unit 23.

  The beam splitter 24 transmits the light beam L1 at a predetermined light quantity ratio (for example, about 50%) to form the light beam L1A, and makes this incident on the beam splitter 25A. The beam splitter 25 transmits the light beam L1A at a predetermined ratio and enters the recording medium 28.

  The beam splitter 24 reflects the remaining part (for example, about 50%) of the light beam L1 to form the light beam L1B, which is sequentially reflected by the mirrors 26 and 27, thereby recording the recording medium from a direction different from that of the light beam L1A. 28 is incident.

  The recording medium 28 is made of, for example, a photopolymerization type photopolymer, and the monomers are uniformly dispersed therein. When the recording medium 28 is irradiated with light, the monomer is polymerized at the irradiated position (that is, photopolymerized) to become a polymer, and the refractive index changes accordingly. In addition, the refractive index of the recording medium 28 may be further changed by so-called photocrosslinking that causes “crosslinking” between polymers by light irradiation to increase the molecular weight.

  Incidentally, the hologram recording / reproducing apparatus 20 is actually provided with various optical elements such as a collimator lens, an objective lens, and a wave plate in addition to the beam splitter 24 shown in the figure, but it is omitted for convenience of explanation. is doing.

  Incidentally, the coherence control unit 22 includes a diffraction element 22A, a piezoelectric element 22B, and a piezoelectric control circuit 22C, as shown in FIG.

  The diffractive element 22A can diffract the light beam L0 emitted from the laser diode 21A provided in the light source 21 and return it to the laser diode 21A. The diffractive element 22A is arranged such that the distance d1 from the laser diode 21A is an integral multiple of a half wavelength (λ / 2) where the wavelength of the light beam L1 is λ.

  At this time, the coherence control unit 22 returns the light beam L1 into the laser diode 21A, so that the wavelength of the light beam L1 made of laser light is expanded from the spread state as shown in FIG. As shown in FIG. 6B, the distribution state is narrowed.

  That is, the coherence control unit 22 constitutes a so-called external resonator type semiconductor laser together with the light source 21, thereby improving the wavelength accuracy of the light beam L1, that is, the frequency accuracy that is the reciprocal thereof, and The coherence in the beam L1 can be improved (hereinafter, the state of the diffraction element 22A at this time is referred to as a coherent state).

  As a result, the hologram recording / reproducing apparatus 20 can cause the light beams L1A and L1B to interfere with each other in the recording medium 28.

  Here, as schematically shown in FIG. 7A, in the recording medium 28, polymerization of monomers occurs only in a portion where the light intensity is strong in the interference fringes by the light beams L1A and L1B. Will be recorded. As shown in FIG. 7B corresponding to FIG. 7A, this interference fringe acts as a hologram because the refractive index of light changes sharply according to the position. This is because the light reflectance generally increases at the boundary surface where the refractive indexes are greatly different.

  By the way, the diffraction element 22A is attached to a predetermined chassis via the piezoelectric element 22B. The piezoelectric element 22B has a property of slightly changing its thickness when a predetermined voltage is applied by the voltage control circuit 22C. By changing the thickness, the angle of the diffraction element 22A is slightly changed. To change.

  In this case, as shown in FIG. 6A, the coherence of the light beam L1 decreases. As a result, the hologram recording / reproducing apparatus 20 does not interfere the light beams L1A and L1B in the recording medium 28 (hereinafter, the state of the diffraction element 22A at this time is referred to as a non-interference state).

  In this case, as shown in FIG. 8A corresponding to FIG. 7A, in the recording medium 28, polymerization of monomers partially occurs according to the light intensity by the light beams L1A and L1B. However, in this case, as shown in FIG. 8B corresponding to FIG. 8A, the refractive index changes gently, so that the reflectance of light is not increased and the hologram does not function.

  That is, when a predetermined voltage is not applied to the piezoelectric element 22B, the coherence control unit 22 raises the coherence of the light beam L1 by setting the diffraction element 22A to be in a coherent state, thereby causing interference fringes (that is, holograms) in the recording medium 28. ) Can be recorded.

  On the other hand, when a predetermined voltage is applied to the piezoelectric element 22B, the coherence control unit 22 reduces the coherence of the light beam L1 by setting the diffraction element 22A in a non-interference state, thereby causing interference fringes into the recording medium 28. Suppress recording.

  As described above, the hologram recording / reproducing apparatus 20 controls the diffraction element 22A of the coherence control unit 22 to an interference state or a non-interference state, thereby irradiating the recording medium 28 with the light beams L1A and L2A. Can be switched.

  For example, the hologram recording / reproducing apparatus 20 forms a hologram in accordance with the code “1” when the information to be recorded is encoded in a binary number at a desired location on the recording medium 28 and also in accordance with the code “0”. By not forming a hologram, the information to be recorded can be recorded.

  Further, when reproducing the information, the hologram recording / reproducing apparatus 20 blocks the light beam L1B by an optical path blocker (not shown) and irradiates only a desired position with the light beam L1A. Incidentally, the hologram recording / reproducing apparatus 20 does not destroy the existing hologram by the light beam L1A by making the intensity of the light beam L1 emitted from the light source 21 weaker than that at the time of recording when reproducing information.

  At this time, the hologram recording / reproducing apparatus 20 reflects the reproduction light beam L2A generated only from the position where the hologram of the recording medium 28 is formed, by the beam splitter 25 and receives it by the light receiving element 29. As a result, the hologram recording / reproducing apparatus 20 can reproduce the information recorded on the recording medium 28.

(1-2) Operation and Effect In the above configuration, the hologram recording / reproducing apparatus 20 does not apply a predetermined voltage to the piezoelectric element 22B of the coherence control unit 22 and sets the diffraction element 22A in a coherent state. The coherence control unit 22 constitutes an external resonator type semiconductor laser to increase the coherence of the light beam L1, thereby causing the light beams L1A and L1B to interfere with each other in the recording medium 28, thereby causing interference fringes (ie, holograms). To record.

  On the other hand, the hologram recording / reproducing apparatus 20 reduces the coherence of the light beam L1 when a predetermined voltage is applied to the piezoelectric element 22B of the coherence control unit 22 to place the diffraction element 22A in a non-interference state. The recording of interference fringes is suppressed while the recording medium 28 is irradiated with the light beams L1A and L1B.

  Therefore, the hologram recording / reproducing apparatus 20 controls whether or not to apply a predetermined voltage to the piezoelectric element 22B of the coherence control unit 22, thereby changing the light beam L1 emitted from the light source 21 to the recording medium 28 without changing it. Whether or not to record the hologram can be switched while irradiating the light beams L1A and L1B.

  By the way, in a general hologram recording apparatus, it is switched whether or not the light beam L1 is emitted from the light source 21, or whether or not the optical path is blocked by an optical path blocker (not shown) that blocks the light beam L1. Some switch whether or not to record a hologram by switching.

  In such a hologram recording apparatus, when a plurality of holograms are continuously formed based on continuous information, the recording speed (that is, so-called transfer rate) is determined by the modulation frequency in the light source 21, and the transfer rate. In order to increase the frequency, it is necessary to increase the modulation frequency of the light source 21 or the optical path interrupter.

  On the other hand, the hologram recording / reproducing apparatus 20 according to the present invention does not need to increase the modulation frequency of the light source 21, and increases the transfer rate by increasing the response speed of the coherence control unit 22, that is, the operation speed of the piezoelectric element 22B. be able to.

  For this reason, since the hologram recording / reproducing apparatus 20 can exclude the height of the modulation frequency from the selection conditions of the light source 21, for example, the light intensity is high, the light emission efficiency is high, or the coherence is good. A light source that cannot be used in a conventional hologram recording apparatus because of its low frequency can be used as the light source 21.

  According to the above configuration, the hologram recording / reproducing apparatus 20 controls the coherence of the light beam L1 by the coherence control unit 22 so that the light beams L1A and L1B irradiated into the recording medium 28 interfere with each other. Therefore, it is possible to switch whether or not to record a hologram in the recording medium 28 without changing the irradiation state of the light beam L1 from the light source 21.

(2) Second embodiment (2-1) Configuration of optical disc

  In the second embodiment, instead of the recording medium 28 in the first embodiment, information is recorded on the optical disc 100 shown in FIGS. It is made to be played.

  As shown in the external view in FIG. 9A, the optical disc 100 is formed in a substantially disk shape as a whole, and a hole 100H is provided at the center thereof. The hole 100H is used for positioning with respect to the rotating shaft when the optical disc 100 is driven to rotate.

  Further, as shown in the cross-sectional view of FIG. 9B, the optical disc 100 has a recording layer 101 for recording information at the center, and the recording layer 101 is sandwiched from both sides by the substrates 102 and 103. It is configured.

  The substrates 102 and 103 are made of, for example, a material such as polycarbonate or glass, and both of them transmit light incident from one surface to the opposite surface with high transmittance. Further, the substrates 102 and 103 have a certain degree of strength and play a role of protecting the recording layer 101.

  Incidentally, the optical disc 100 has a substantially symmetric structure with the recording layer 101 as the center in the thickness direction, and consideration is given to suppressing the occurrence of warpage, distortion, etc. due to secular change as a whole. In addition, about the surface of the board | substrates 102 and 103, unnecessary reflection may be made to be prevented by anti-reflective coating.

  Similar to the recording medium 28 (FIG. 4), the recording layer 101 is made of a photopolymer whose refractive index changes depending on the intensity of irradiated light, and responds to a blue light beam having a wavelength of 405 [nm]. .

  In practice, the optical disk 100 is configured such that the light beams L1A and L1B are condensed and irradiated by the objective lens 38 during information recording and reproduction (details will be described later).

  Further, the optical disc 100 has a reflection / transmission film 104 as a reflection / transmission layer on the boundary surface between the recording layer 101 and the substrate 102. The reflection / transmission film 104 is made of a dielectric multilayer film or the like, and is configured to reflect a predetermined ratio (for example, about 10%) of the light beam L1B and transmit the remaining (for example, about 90%).

  The reflection / transmission film 104 forms a tracking servo guide groove, and specifically, a spiral track is formed by lands and grooves similar to a general BD-R (Recordable) disk or the like. . This track is given an address consisting of a series of numbers for each predetermined recording unit, and the track on which information is recorded or reproduced can be specified by the address.

  The reflective / transmissive film 104 (that is, the boundary surface between the recording layer 101 and the substrate 102) may be formed with pits or the like instead of the guide grooves, or a combination of guide grooves and pits. What is necessary is just to be able to recognize an address using a beam.

  When a predetermined position control light beam L1C is irradiated from the substrate 102 side, the reflection / transmission film 104 reflects the reflection control film 104 to the substrate 102 side at a predetermined ratio. Hereinafter, the light beam reflected at this time is referred to as a position-controlled reflected light beam L2C.

  For example, in the optical disc apparatus, the position-controlled reflected light beam L2C is focused on a target track (hereinafter referred to as a target track) with the focus FC of the position-controlled reflected light beam L2C collected by the objective lens 38. Therefore, it is assumed that the objective lens 38 is used for position control (that is, focus control and tracking control).

  In practice, when information is recorded on the optical disc 100, as shown in FIG. 5, the position control light beam L1C is condensed by the position-controlled objective lens 38 and focused on the target track of the reflective / transmissive film 104. Is done.

  Further, the light beam L1B sharing the optical axis Lx with the position control light beam L1C and condensed by the objective lens 38 is transmitted through the substrate 102 and the reflective / transmissive film 104, and behind the target track in the recording layer 101 ( That is, it is focused on a position corresponding to the substrate 103 side). At this time, the focal point FB of the light beam L1B is located farther than the focal point FC on the common optical axis Lx with the objective lens 38 as a reference.

  Further, in the optical disc 100, the light beam L1A is condensed by the objective lens 47 from the substrate 103 side, and is condensed at the same focal point FB as the light beam L1B.

  At this time, as in the first embodiment, if the coherence of the light beams L1A and L1B is increased, the optical disc 100 forms a hologram at the position of the focal point FB (hereinafter, this hologram is also referred to as a recording mark RM). If the coherence of the light beams L1A and L1B is reduced, no hologram is formed at the position of the focal point FB.

  Incidentally, the recording mark RM has a diameter RMr of about 1.0 [μm] and a height RMh of about 9.7 [μm].

  Further, the optical disc 100 is designed such that the thickness of the recording layer 101 is sufficiently larger than the height RMh of the recording mark RM. For this reason, the optical disc 100 records a plurality of mark recording layers by recording the recording marks RM while switching the distance from the recording reflective film 104 in the recording layer 101 (hereinafter referred to as depth d). Multi-layer recording in the thickness direction of the optical disc 100 can be performed.

  In this case, the depth d of the recording mark RM is changed by adjusting the depth d of the focal point Fb1 of the blue light beam Lb1 in the recording layer 101 of the optical disc 100. For example, in the optical disc 100, when the thickness of the recording layer 101 is 0.3 [mm], the distance p3 between the mark recording layers is set to about 15 [μm] in consideration of the mutual interference between the recording marks RM. Then, about 20 mark recording layers can be formed in the recording layer 101. The distance p3 may be set to various values other than about 15 [μm] in consideration of the mutual interference between the recording marks RM.

  In addition, when information is reproduced, the optical disc 100 is positioned so that the position control light beam L1C is focused on the target track of the reflective / transmissive film 104 by the objective lens 38, as in the case of recording the information. It is made to be controlled.

  In this case, the optical disc 100 is configured such that the focal point FA of the light beam L1A transmitted through the substrate 103 via the objective lens 47 interlocked with the objective lens 38 is focused on the target mark position PS in the recording layer 101.

  Here, when the recording mark RM is recorded at the target mark position PS, the recording mark RM exhibits a property as a hologram. Therefore, the reproduction light beam L2A is generated from the target mark position PS of the recording layer 101.

  This reproduction light beam L2A has the same optical characteristics as the light beam L1B irradiated during recording, and proceeds in the same direction as the light beam L1B, that is, while diverging from the recording layer 101 to the substrate 103 side. become.

  On the other hand, when the recording mark RM is not recorded at the target mark position PS, the target mark position PS of the recording layer 101 does not exhibit a property as a hologram. Therefore, the reproduction light beam L2A is not generated from the target mark position PS.

  As described above, when recorded information is reproduced, the optical disc 100 focuses the recording beam RM at the target mark position PS by focusing the focal point FA of the light beam L1A on the target mark position PS in the recording layer 101. Whether or not to generate the reproduction light beam L2A is changed according to the presence or absence of.

(2-2) Configuration of Optical Disc Device As shown in FIG. 10 in which the same reference numerals are assigned to corresponding parts to FIG. 4, the optical disc device 30 in the second embodiment is partially similar to the hologram recording / reproducing device 20. As a whole, information is recorded on the optical disc 100 using a hologram, and information is reproduced from the optical disc 100.

  As in the first embodiment, the light source 21 emits a light beam L1 made of divergent light from the internal laser diode 21A (FIG. 5) and makes it incident on the collimator lens 31. The collimator lens 31 converts the light beam L1 from divergent light to parallel light, and makes this incident on the coherence control unit 22.

  As in the first embodiment, the coherence control unit 22 forms an external resonator type semiconductor laser with the laser diode 51 of the light source 21, and applies a voltage to be applied to the piezoelectric element 22B (FIG. 5). The coherence of the light beam L1 is controlled by controlling the voltage control circuit 22C, and then the polarization direction of the light beam L1 is adjusted by the half-wave plate 32 and is incident on the polarization beam splitter 33.

  The polarization beam splitter 33 reflects a part of the light beam L1 according to the polarization direction of the light beam L1 to form a position control light beam L1C, which is sequentially reflected by the mirror 34 and the polarization beam splitter 35, and further reflected by the beam splitter 36. The portion is reflected and is incident on the quarter-wave plate 37.

  The quarter-wave plate 37 converts the position control light beam L1C from linearly polarized light to circularly polarized light and makes it incident on the objective lens 38. The objective lens 38 irradiates the reflection / transmission film 104 of the optical disc 100 with the position control light beam L1C.

  At this time, a part of the position control light beam L1C is reflected by the reflection / transmission film 104 to become the position control reflection light beam L2C, and is incident on the objective lens 38 again. At this time, the rotational direction of the circularly polarized light of the position-controlled reflected light beam L2C is reversed by reflection on the reflection / transmission film 104.

  Thereafter, the position-controlled reflected light beam L2C is converted into linearly polarized light by the quarter wavelength plate 37 and is incident on the beam splitter 36. At this time, the position-controlled reflected light beam L2C is converted into linearly polarized light that is orthogonal to the position-controlled light beam L1C because the turning direction of the circularly polarized light is the opposite direction of the original position-controlled light beam L1C.

  A part of the position-controlled reflected light beam L2C is reflected by the beam splitter 36 and is incident on the polarization beam splitter 35. The polarization beam splitter 35 is transmitted through the polarization beam splitter 35 according to the polarization direction, and is collected by the condenser lens 39 and servoed. The signal detector 40 is irradiated.

  The servo signal detection unit 40 receives the position control reflected light beam L2C with a photodetector (not shown) or the like, and based on the light reception result, the servo signal detection unit 40 in the focus direction between the focal point FC of the position control light beam L1C and the target track. A focus error signal representing the amount of deviation and a tracking error signal representing the amount of deviation in the tracking direction are generated.

  Based on the focus error signal and tracking error signal, the optical disc apparatus 30 moves the objective lens 36 in the focus direction (that is, the direction in which the objective lens 36 is brought close to or away from the optical disc 100) and the tracking direction (that is, toward the inner or outer peripheral side of the optical disc). Direction) (hereinafter referred to as servo control).

  As a result, the optical disc apparatus 30 can cause the focal point FC of the position control light beam L1C to follow the desired track of the optical disc 100.

  Incidentally, the polarization direction of the light beam L1T transmitted through the polarization beam splitter 33 is again incident on the adjustment polarization beam splitter 42 by the half-wave plate 41. The polarization beam splitter 42 transmits the light beam L1T at a predetermined light amount ratio (for example, about 50%) according to the polarization direction of the light beam L1T to make the light beam L1A, and makes this incident on the polarization beam splitter 43.

  The polarization beam splitter 43 transmits the light beam L1A according to the polarization direction and makes it incident on the relay lens 44. The relay lens 44 is a combination of a movable lens 44A movable along the optical axis of the light beam L1A and a fixed lens 44B. The light beam L1A is once converged by the movable lens 44A and then diverged again. After changing the divergence angle by the fixed lens 44B, the light enters the quarter wavelength plate 45.

  The quarter-wave plate 45 converts the light beam L1A from linearly polarized light to circularly polarized light and makes it incident on the objective lens 46. The objective lens 46 condenses the light beam L <b> 1 </ b> A and positions the focal point FA in the recording layer 101 of the optical disc 100.

  On the other hand, the polarization beam splitter 42 reflects the light beam L1T with a predetermined light amount ratio (for example, about 50%) according to the polarization direction of the light beam L1T, and makes the light beam L1B incident on the mirror 51. The light beam L1B is reflected by the mirror 51, is sequentially reflected by the mirrors 53 and 54 via the shutter 52, and is incident on the relay lens 55.

  The relay lens 55 is configured in the same manner as the relay lens 44, and a movable lens 55A movable along the optical axis of the light beam L1B and a fixed lens 55B are combined. For this reason, the relay lens 55 once converges the light beam L1B by the movable lens 55A, diverges it again, changes the divergence angle by the fixed lens 55B, and makes it incident on the beam splitter 36.

  The beam splitter 36 transmits the light beam L1B at a predetermined ratio, converts it from linearly polarized light to circularly polarized light by the quarter wavelength plate, and condenses it by the objective lens 38. At this time, since the light beam L1B is incident on the objective lens 38 as diverging light, unlike the position control light beam L1C, the light beam L1B is condensed in the recording layer 101, not in the reflection / transmission film 104.

  Here, the objective lens 46 is controlled in conjunction with the objective lens 38 so that the focal point FA of the light beam L1A can coincide with the focal point FB of the light beam L1B.

  At this time, the coherence control unit 22 controls the voltage applied to the piezoelectric element 22B to switch the diffraction element 22A to a coherent state or a non-interfering state, thereby showing the recording layer 101 of the optical disc 100 as shown in FIG. The hologram is formed as described above, or the hologram is not formed as shown in FIG.

  In other words, the optical disk device 30 controls the coherence of the light beam L1 by the coherence control unit 22, thereby changing the hologram with respect to the target mark position PS without changing the light amount of the light beam L1 emitted from the light source 21. It is possible to switch whether or not to form the recording mark RM.

  Accordingly, the optical disc device 30 can keep the light quantity of the position control light beam L1C constant regardless of whether or not the recording mark RM made of hologram is formed with respect to the target mark position PS. The servo signal detector 40 can receive the position control reflected light beam L2C based on the position control light beam L1C.

  As a result, the optical disc apparatus 30 can always perform stable servo control during information recording.

  Further, when reproducing information from the optical disc 100, the optical disc apparatus 30 irradiates the optical disc 100 with a position control light beam L1C to control the positions of the objective lenses 38 and 46, and shuts off the light beam L1B with the shutter 52. The target beam position PS in the recording layer 101 is irradiated with the light beam L1A.

  Here, when the recording mark RM is recorded at the target mark position PS, a part of the light beam L1A is reflected by the action of the recording mark RM as a hologram to become a reproduction light beam L2A, and the optical path of the light beam L1A is changed. The light travels in the opposite direction and enters the polarization beam splitter 43 via the objective lens 46, the quarter-wave plate 45 and the relay lens 44.

  At this time, the reproduction light beam L2A has a polarization direction different from that of the light beam L1A. Therefore, the reproduction light beam L2A is reflected by the polarization beam splitter 43, condensed by the condenser lens 48, and applied to the reproduction signal detection unit 49.

  The reproduction signal detection unit 49 detects the reproduction light beam L2A with a photodetector (not shown), and a hologram is formed as a recording mark RM at the target mark position PS in the recording layer 101 of the optical disc 100 by detecting the reproduction light beam L2A. That is, the code “1” is recorded as information, and a reproduction signal corresponding to this is supplied to a predetermined signal processing unit (not shown).

  On the other hand, when the recording mark RM is not recorded at the target mark position PS, the reproduction light beam L2A is not generated, and the reproduction light beam L2A is not detected by the reproduction signal detection unit 49. At this time, the reproduction signal detection unit 49 recognizes that the hologram as the recording mark RM is not recorded at the target mark position PS in the recording layer 101 of the optical disc 100, that is, the code “0” is recorded as information. Then, a reproduction signal corresponding to this is supplied to a predetermined signal processing unit (not shown).

  Thus, the optical disk device 30 can reproduce the information recorded as a hologram on the optical disk 100.

  By the way, the relay lens 44 can change the divergence angle of the blue light beam Lb1 emitted from the fixed lens 44B by moving the movable lens 44A by an actuator (not shown).

  Accordingly, the divergence angle when the light beam L1A is incident on the objective lens 46 changes, so the distance from the objective lens 46 to the focal point FA changes. In practice, the optical disc apparatus 30 is designed so that the distance of the movable lens 44A from a predetermined reference position and the distance of the focal point FA (that is, the depth d) from the reflection / transmission film 104 are proportional.

  For this reason, the optical disc apparatus 30 can adjust the depth d of the focal point FA in the light beam L1A by controlling the position of the movable lens 44A.

  Further, since the optical disk device 30 has the relay lens 55 configured similarly to the relay lens 44, the depth d of the focal point FB in the light beam L1B can be adjusted by controlling the position of the movable lens 55A. ing.

  In practice, the optical disk device 30 can change the depth d arbitrarily while matching the focal point FA of the light beam L1A and the focal point FB of the light beam L1B by interlocking the movable lenses 44A and 55A. ing. As a result, the optical disc apparatus 30 can realize multi-layer recording / reproduction in which a recording mark RM made of a hologram is formed at different depths d in the recording layer 101 of the optical disc 100 and reproduced.

(2-3) Operation and Effect In the above configuration, the optical disk device 30 according to the second embodiment is similar to the hologram recording / reproducing device 20 according to the first embodiment, and the piezoelectric element 22B of the coherence control unit 22 is used. When the diffraction element 22A is brought into a coherent state without applying a predetermined voltage, the coherence control unit 22 increases the coherence of the light beam L1 so that the light beam L1A and the light beam L1A in the recording layer 101 of the optical disc 100 Recording mark RM (that is, hologram) is recorded by causing L1B to interfere.

  On the other hand, when a predetermined voltage is applied to the piezoelectric element 22B of the coherence control unit 22 to place the diffraction element 22A in a non-interference state, the optical disc device 30 reduces the coherence of the light beam L1 to thereby reduce the recording layer. The recording of interference fringes is suppressed while irradiating the light beams L1A and L1B to 101.

  Accordingly, the optical disk device 30 controls whether or not to apply a predetermined voltage to the piezoelectric element 22B of the coherence control unit 22 as in the first embodiment, thereby generating the light beam L1 emitted from the light source 21. Whether or not to record the hologram can be switched while irradiating the recording layer 101 of the optical disc 100 with the light beams L1A and L1B without being changed.

  At this time, the optical disc device 30 can keep the light amount of the position control light beam L1C constant regardless of whether or not the recording mark RM made of a hologram is formed with respect to the target mark position PS. An error signal and a tracking error signal can be obtained constantly, and stable servo control can always be performed during information recording.

  That is, the optical disk device 30 is servo-controlled by modulating a light beam for position control, which can occur in a conventional optical disk device that modulates a light beam emitted from a light source according to information to be recorded, for example. Can be eliminated in principle.

  Further, in the above-described conventional optical disc apparatus, in order to prevent the light beam from being emitted and servo control becoming unstable when the code “0” continues for a predetermined number or more, the upper limit continuous number of codes “0” (so-called run number) is prevented. In this case, the number of codes increases and the transfer rate decreases as a result.

  On the other hand, in the optical disc apparatus 30 of the present invention, it is not necessary to perform code modulation processing at least from the viewpoint of servo control, and since the track is formed independently on the reflective / transmissive film 104 in the optical disc 100, the track is lost. Since the possibility is extremely low, it is possible to record an unmodulated code as it is.

  When performing unmodulated recording in this way, the optical disk device 30 of the present invention modulates 8-bit data to 16 bits by, for example, 8/16 modulation of DVD, or 3 bits of 2-bit data by 1-7 PP of BD. Compared with the case of modulation into bits, the transfer rate can be significantly improved.

  The optical disk device 30 can exclude the height of the modulation frequency from the selection conditions of the light source 21 as in the case of the hologram recording / reproducing device 20 in the first embodiment, and a light source more suitable for forming a hologram. You can choose.

  According to the above configuration, the optical disc apparatus 30 irradiates the light beam L1 emitted from the light source 21 and the recording layer 101 of the optical disc 100 by controlling the coherence of the light beam L1 by the coherence control unit 22. Since it is possible to switch whether or not to record a hologram without changing the light amounts of the light beams L1A and L1B, stable servo control can be performed using the position control light beam L1C with a stable light amount.

(3) Other Embodiments In the above-described embodiment, the coherence control unit 22 is configured by the diffraction element 22A, the piezoelectric element 22B, and the piezoelectric control circuit 22C, and the light beam L1 is combined with the light source 21. Although the case where the coherence is controlled has been described, the present invention is not limited to this. For example, a predetermined prism is used instead of the diffraction element 22A, and an electric signal such as a solenoid is driven instead of the piezoelectric element 22B. The coherence control unit 22 may be configured by other various means such as using a means for converting to force. In short, whether the light beam L1 is returned to the laser diode 21A (FIG. 5) of the light source 21 or not. It is only necessary to control whether to increase or decrease the coherence of the light beam L1 by controlling the above.

  In the above-described embodiment, the light source 21 and the coherence controller 22 constitute an external resonator type semiconductor laser, and the coherence of the light beam L1 is controlled according to the voltage applied to the piezoelectric element 22B. Although the case of doing so has been described, the present invention is not limited to this, and the coherence of the light beam L1 may be controlled by other various means.

  For example, as shown in FIG. 11, an injection-locked semiconductor laser including a laser diode 61 and a coherence control unit 62 may be configured. Although the laser diode 61 has a relatively high emission intensity, for example, it has low coherence as shown in FIG. 6A, and a single unit cannot form a good hologram. On the other hand, the laser diode 62A, as shown in FIG. 6B, has good coherence, but has a low emission intensity and cannot form a good hologram alone.

  However, the coherence control unit 62 can emit a light beam having high coherence and high intensity by making the light beam having high coherence emitted from the laser diode 62A incident on the laser diode 61. it can.

  In this case, similarly to the diffraction element 22A (FIG. 5), by changing the position of the mirror 62B with a piezoelectric element (not shown) or the like and controlling the coherence, the same as in the first and second embodiments. Coherence can be controlled.

  Furthermore, in the above-described first embodiment, the present invention is applied to the hologram recording / reproducing apparatus 20 that records and reproduces holograms on the recording medium 28, and in the second embodiment, the optical disc 100 is applied. Although the case where the present invention is applied to the optical disk apparatus 30 that records and reproduces holograms has been described, the present invention is not limited thereto, and for example, a hologram recording apparatus that performs only hologram recording or a hologram for the optical disk 100 The present invention may be applied to an optical disc recording apparatus that performs only the recording.

  Furthermore, in the above-described second embodiment, the case where multilayer recording is performed by changing the depth d of the target mark position PS by the relay lenses 44 and 55 has been described, but the present invention is not limited to this. Instead, for example, instead of the relay lenses 44 and 55, a fixed lens or the like may be provided to fix the depth d of the target mark position PS and perform single layer recording.

  Further, in the second embodiment described above, as shown in FIGS. 9A and 9B, the recording layer 101 is sandwiched between the substrates 102 and 103 from both sides, and the boundary between the recording layer 101 and the substrate 102 is obtained. Although the case where the hologram is recorded on the optical disc 100 having the reflection / transmission film 104 on the surface has been described, the present invention is not limited to this. For example, the substrate 103 is omitted, or the reflection / transmission film 104 is provided in the recording layer 101. A hologram may be recorded on an optical disk having other various configurations such as being provided.

  As an optical disk suitable for the present invention, the reflection / transmission film 104 on which a track or the like for specifying the target mark position PS is formed and the recording layer 101 that actually forms a hologram as the recording mark RM are separated. It ’s fine.

  Further, in the embodiment described above, hologram recording / reproduction as a hologram recording apparatus is performed by the light source 21 as the light source, the light beam irradiation unit 23 as the irradiation unit, and the coherence control unit 22 as the coherence control unit. Although the case where the apparatus 20 is configured has been described, the present invention is not limited to this, and a hologram recording apparatus may be configured by a light source having various other circuit configurations, an irradiation means, and a coherence control means. good.

  Furthermore, in the above-described embodiment, the light source 21 as the light source, the polarization beam splitters 33 and 42 as the separation unit, the objective lens 36 as the first objective lens, and the objective lens 46 as the second objective lens, The case where the optical signal device 30 as the optical disk recording device is configured by the servo signal detection unit 40 as the light receiving unit and the lens position control unit and the coherence control unit 22 as the coherence control unit has been described. The optical disc recording is not limited to this, but includes a light source having various configurations, a separation unit, a first objective lens, a second objective lens, a light receiving unit, a lens position control unit, and a coherence control unit. You may make it comprise an apparatus.

  The present invention can also be used when video, music, or various data is recorded on an optical disc by a hologram.

It is a basic diagram (1) which shows the structure of the conventional standing wave recording-type optical disk apparatus. It is an approximate line figure used for explanation of formation of a hologram. It is a basic diagram (2) which shows the structure of the conventional standing wave recording-type optical disk apparatus. It is a basic diagram which shows the structure of the hologram recording / reproducing apparatus by 1st Embodiment. It is a basic diagram which shows the structure of a coherence control part. It is a basic diagram which shows the frequency control of a laser beam. It is a basic diagram which shows the mode of formation of a hologram. It is a basic diagram which shows the mode of non-formation of a hologram. It is a basic diagram which shows the structure of an optical disk. It is a basic diagram which shows the structure of the optical disk apparatus by 2nd Embodiment. It is a basic diagram which shows the structure of the coherence control part by other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Hologram recording / reproducing apparatus, 21 ... Light source, 21A, 61 ... Laser diode, 22, 62 ... Coherence control part, 22A ... Diffraction element, 22B ... Piezoelectric element, 22C ... Voltage control circuit , 23... Light beam irradiation unit, 24, 25... Beam splitter, 26, 27... Mirror, 28... Recording medium, 29. ... Polarizing beam splitter, 36 ... Beam splitter, 38, 46 ... Objective lens, 40 ... Servo signal detector, 44, 55 ... Relay lens, 49 ... Playback signal detector, 100 ... Optical disc, 101 ... ... Recording layer, 104 ... Reflective / transmissive film, L1 ... Light beam, L1C ... Position control light beam, FA, FB, FC ... Focus, PS ... Target mark position, RM ... Record mark

Claims (10)

A light source that emits a light beam;
Irradiating means for separating the light beam and condensing it from different directions with respect to a desired recording position in the recording medium whose refractive index changes according to the intensity of the irradiated light;
Coherence control means for switching whether or not to form a hologram at the desired recording position by controlling the coherence of the light beam emitted from the light source and supplying it to the irradiation means. A hologram recording apparatus characterized by the above. The coherence control means is
The hologram recording apparatus according to claim 1, wherein the coherence is controlled by limiting the light beam emitted from the light source to only a frequency component within a predetermined range. The light source is a laser light source,
The coherence control means is
A reflective diffraction element that diffracts the light beam emitted from the light source back to the light source or reflects in a direction other than the light source;
An optical path changing means for changing an optical path of the light beam between the light source and the reflective diffraction element;
3. The hologram recording according to claim 2, further comprising resonator length control means for controlling a resonator length of a resonator composed of the light source and the reflection diffraction element by changing the optical path. apparatus The optical path changing means is a piezoelectric element,
The hologram recording apparatus according to claim 3, wherein the optical path control unit controls the resonator length by controlling a voltage applied to the piezoelectric element. The light source is a laser light source,
The coherence control means is
A reflective diffraction element that diffracts the light beam emitted from the light source or reflects the light beam in a direction other than the light source;
A mirror for returning the light diffracted by the reflection diffraction element to the reflection diffraction element;
An optical path changing means for changing an optical path of the light beam between the light source and the mirror;
The hologram recording apparatus according to claim 2, further comprising: a resonator length control unit configured to control a resonator length of a resonator including the light source and the mirror by changing the optical path. The light source is a high-power laser light source that outputs a first light beam having a large output level and low coherence,
The coherence control means is
The second light beam having a high coherence and a low output level compared to the first light beam is emitted from a predetermined high coherence laser light source and is incident on the high power laser light source. The hologram recording apparatus according to claim 1, wherein injection locking is performed to emit the light beam having a large output level and high coherence. Detecting means for irradiating a part of the light beam to a position identifying unit provided in the recording medium for identifying a position in the recording medium and detecting the reflected light;
2. The condensing position control means for controlling the condensing position of a part of the light beam with respect to the recording medium to be the desired location based on the detection result. Hologram recording device. An irradiation step of separating a light beam emitted from a predetermined light source and collecting the light beams from different directions with respect to a desired recording position in a recording medium whose refractive index changes according to the intensity of the irradiated light;
A coherency control step of switching whether or not to form a hologram at the desired recording position by controlling the coherence of the light beam emitted from the light source and before being separated. Hologram recording method. A light source that emits a light beam;
A separation unit for separating the light beam from the position control light beam for position control and the first recording light beam and the second recording light beam for information recording;
A recording layer that is formed in a substantially disc shape and whose refractive index changes according to the intensity of irradiated light, and a position identification layer that is provided in association with the recording layer in order to identify the position in the recording layer, A first objective lens that focuses the position control light beam and the first recording light beam on different locations from one side of the optical disc having
A second objective lens for condensing the second recording light beam from the other surface side of the optical disc at a focal position of the first light beam;
A light receiving unit that receives a reflected light beam formed by the position control light beam being reflected by the position identification layer;
Based on the reception result of the reflected light beam, the positions of the first objective lens and the second objective lens are controlled so that the position control light beam is focused on a desired position in the position identification layer, and the first recording light is controlled. A lens position control unit for focusing the beam and the second recording light beam on a desired recording position;
An optical disk recording apparatus comprising: a coherence control unit that switches whether or not to form a hologram at the desired recording position by controlling coherence of the light beam emitted from the light source. . A separation step of separating a light beam emitted from a predetermined light source into a position control light beam for position control and a first recording light beam and a second recording light beam for information recording;
An optical disc formed in a substantially disc shape and having a recording layer whose refractive index changes according to the intensity of irradiated light and a position identification layer provided in the recording section for identifying the position in the recording medium layer The position control light beam is condensed from one surface side by the first objective lens, and the position control light beam is reflected on the basis of the reception result of the reflected light beam reflected by the position identification layer. The position of the first objective lens is controlled so as to adjust the focal point to the desired identification position in the position identification layer, and when the focal point of the second light beam is condensed by the second objective lens, A lens position control step for controlling the position of the second objective lens so that the second light beam is focused at a desired recording position where the first light beam is focused;
An optical disc recording method comprising: a coherence control step for switching whether or not to form a hologram at the desired recording position by controlling coherence of the light beam emitted from the light source. .