JP2006243243A - Device and method for hologram recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that a shift multiplex system has high shift selectivity in a direction (along tracks) parallel to an incidence plane of two light waves since Bragg conditions are adapted in the direction, but has less shift selectivity in a direction (across the tracks) perpendicular to the incidence plane of the two light waves than in the direction parallel to the incidence plane of the two light waves, and the reliability decreases as crosstalk noise is easily generated between tracks when the shift pitch between the tracks is made narrow. <P>SOLUTION: The oscillation wavelength of a variable wavelength laser light source 2 is switched according to a track position on a disk 1 to increase shift selectively in the direction crossing tracks and also suppress an effect of crosstalk between adjacent tracks. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hologram recording / reproducing apparatus and a hologram recording method for performing recording and reproduction using hologram technology.

  Development of a hologram recording / reproducing apparatus for recording data using holography is in progress. In the hologram recording / reproducing apparatus, two modulated signal light (data superimposed) and unmodulated reference light are generated from laser light, and these are irradiated to the same location on the hologram recording medium. As a result, the signal light and the reference light interfere on the hologram recording medium, a diffraction grating (hologram) is formed at the irradiation point, and data is recorded on the hologram recording medium.

  By irradiating the recorded hologram recording medium with reference light, diffracted light (reproduced light) is generated from the diffraction grating formed during recording. Since the reproduction light includes data superimposed on the signal light at the time of recording, the recorded signal can be reproduced by receiving this with a light receiving element.

In order to record a large amount of information on the hologram recording medium, a large number of holograms may be formed on the hologram recording medium. In this case, the hologram is not necessarily formed at different locations on the hologram recording medium, and the hologram can also be formed at the same location (or overlapping region) of the hologram recording medium. This is so-called multiplex recording, and an angle multiplex method, a wavelength multiplex method, a rotation multiplex method, a shift multiplex method, and various methods have been proposed.
Also, the collinear method is regarded as important as an optical system that follows the optical system of the current optical disk. Since this system uses a reflective optical system, the current optical disk servo system can be used. Further, since correlation shift multiplexing is used, multiplex recording is possible only by rotating the disk.

  For example, in the angle multiplexing method, the hologram is formed by changing (shifting) the incident angle of the reference light at the same location on the hologram recording medium. By using the same reference light as that used during recording during reproduction, it is possible to obtain reproduction light and data corresponding to each of a plurality of holograms formed at the same location.

  The shift multiplexing method is a method of recording a hologram by shifting (laterally shifting) the light irradiation position on the hologram recording medium at a pitch smaller than the size of the hologram pattern formed on the hologram recording medium. .

  In the collinear method, the signal light pattern is placed in the center and the reference light pattern is placed so as to surround it, so that the signal light and the reference light interfere with each other from all directions to record the hologram. is there.

  Compared to the angle multiplexing method, the shift multiplexing method and the collinear method can multiplex-record a hologram only by rotating a disk-shaped hologram recording medium, so that the optical system can be simplified and is now widely used. Since an optical system similar to that for current optical disk drives such as CD and DVD can be used, it has various advantages such as being able to make full use of existing servo technology.

However, in the shift multiplexing method, if the shift pitch between tracks is increased, crosstalk noise between tracks tends to be generated, and reliability is lowered. From this point, it is difficult to improve the recording density in the shift multiplexing method. This problem is also the same in the collinear method.

  In view of the circumstances as described above, an object of the present invention is to provide a hologram recording / reproducing apparatus and a hologram recording method capable of improving recording density and reliability.

  A hologram recording / reproducing apparatus according to the present invention includes a laser light source that emits laser light, the oscillation wavelength of which can be changed, a light branching element that branches the laser light emitted from the laser light source into signal light and reference light, An optical modulation element that modulates the signal light branched by the branch element, and an optical system that focuses the signal light modulated by the light modulation element and the reference light branched by the optical branch element at substantially the same location of the hologram recording medium; The oscillation wavelength of the laser light source is switched according to the position in the direction perpendicular to the incident plane of the signal light and the reference light on the hologram recording medium, and the light detection element for detecting the reproduction light from the hologram recording medium And a control means.

  More specifically, the control means switches the oscillation wavelength of the laser light source according to the recording position or the reproduction position based on the wavelength information acquired by the wavelength information acquisition means.

  In this invention, the signal light on the hologram recording medium and the reference are switched by switching the oscillation wavelength of the laser light source according to the position in the direction perpendicular to the incident plane of the signal light and the reference light on the hologram recording medium. The shift selectivity in the direction perpendicular to the light incident plane can be increased, and the influence of crosstalk between adjacent tracks can be suppressed.

  The hologram recording / reproducing apparatus of the present invention further comprises wavelength information acquisition means for acquiring wavelength information corresponding to the position recorded in advance on the hologram recording medium, and the control means is acquired by the wavelength information acquisition means. The oscillation wavelength of the laser light source may be switched based on the wavelength information.

  By switching the oscillation wavelength of the laser light source based on the information of the wavelength corresponding to the position recorded in advance on the hologram recording medium, the optimum oscillation wavelength can be switched for each hologram recording medium.

  Furthermore, the hologram recording / reproducing apparatus of the present invention may further include a position correcting unit that corrects the position of the light receiving element during reproduction based on the wavelength information acquired by the wavelength information acquiring unit. Thereby, it is possible to eliminate the positional deviation in the plane direction and the focus direction of the light receiving element due to the angular deviation of the diffracted light caused by changing the wavelength during reproduction.

  The wavelength information pre-recorded on the hologram recording medium may correspond to each position in a direction perpendicular to the incident plane of the signal light and the reference light, but is continuous. By dividing a predetermined number of positions into a plurality of groups as one group and assigning different wavelengths to each common position ranked in this group, the amount of wavelength information recorded on the hologram recording medium can be greatly reduced. And the consumption of memory by wavelength information can be reduced.

  As described above, according to the present invention, it is possible to provide a hologram recording / reproducing apparatus and a hologram recording method capable of improving recording density and reliability.

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

  FIG. 1 is a diagram showing a multiplexing method of a hologram recording / reproducing apparatus according to an embodiment of the present invention. As shown in the figure, in this embodiment, a light irradiation position 3 is arranged at a pitch smaller than the size of the hologram pattern along a track 2 of a disk-shaped hologram recording medium (hereinafter simply referred to as “disk”) 1. In addition to the shift multiplexing method that shifts in step 2, the wavelength multiplexing method that switches the oscillation wavelength of the laser light source according to the track 2 is used in combination. A header information recording area 4 in which header information including wavelength information for each track 2 of the disk 1 is recorded is provided on the innermost circumference of the disk 1, for example.

  In the shift multiplex method, the incident light is treated as a part of a spherical wave by narrowing the reference light with a lens and making it incident on the disk. A hologram is recorded on the disk by interference between the reference light which is a spherical wave and light (signal light) having information. At the time of reproduction, as shown in FIG. 2, diffracted light (reproduced light) 6 from a hologram recorded on the disk 1 is obtained by irradiating only the reference light 5.

  If the irradiation position of the reference light 5 is shifted from the recorded position of the hologram in a direction parallel to the plane of incidence of the two light waves of the reference light and the signal light (direction along the track 2 of the disk 1), Thus, the incident angle of the reference light 5 is equivalent to a change, and diffracted light cannot be obtained even with a shift amount sufficiently smaller than the hologram size. Therefore, by using a spherical wave as the reference light 5, hologram recording can be performed at a very fine pitch, and the number of multiplexing can be increased.

  The direction parallel to the incident plane of the two light waves (the direction along the track 2 of the disk 1) is a direction to which the Bragg condition is applied, and therefore has a very high shift selectivity. The direction perpendicular to the direction (the direction crossing the track 2 of the disk 1) is inferior in shift selectivity to the direction parallel to the incident plane of the two light waves.

  Therefore, by changing the wavelength when shifting in the direction perpendicular to the plane of incidence of the two light waves, the shift selectivity in the direction perpendicular to the plane of incidence of the two light waves can be improved, and the pitch between tracks can be improved. As well as crosstalk noise between tracks can be suppressed.

  FIG. 3 is a graph showing the results of measuring diffraction efficiency by shifting the reproduction wavelength back and forth around the wavelength used for recording on a certain track.

  As shown in this graph, the diffraction efficiency is 0 at a wavelength shifted by about 0.7 nm from the wavelength (407 nm) used for recording a certain track. Therefore, if the wavelength is further shifted, the influence of diffracted light from tracks other than the track to be reproduced can be suppressed.

  Also, in order to suppress crosstalk between tracks, it is not always necessary to shift the wavelength so that the diffraction efficiency is zero, and various factors such as the degree of crosstalk and the distance between tracks are taken into consideration. Therefore, it is necessary to determine an optimum shift amount of the wavelength.

The range of wavelengths to be shifted is shown by an equation. Assuming that the wavelength used for recording in the transmission hologram is λ ₀ , the incident angle of the reference light is θ, the media thickness is L, and the refractive index of the media is n, the diffracted light initially becomes 0 for each of the transmission hologram and the reflection hologram. The wavelength shift width Δλ until reaching is expressed as follows.

  By shifting the wavelength by this wavelength shift width Δλ, no diffracted light is generated with respect to the hologram written at the same location, and only the desired hologram can be reproduced. However, as the wavelength shift width Δλ increases, the diffracted light from the hologram causes an angle shift, so that it is necessary to make the wavelength shift amount as close to the wavelength shift width Δλ as possible.

Here, if the wavelength shift amount is Δλ, the recorded diffraction grating interval is Λ, and the original read angle (the angle when the Bragg diffraction condition is met) is θ _B , the angle deviation θ of the diffracted light outside the disk θ _outside is as follows.

  In the Fourier optical system, this angular deviation becomes a positional deviation on the real image plane (on the CCD). Therefore, a mechanism that shifts the CCD position according to the reproduction wavelength is used so that this positional deviation can be corrected. Alternatively, a CCD having a margin that can sufficiently detect the image area even if the wavelength is shifted is required.

  Next, the header information will be described.

  In the header information recording area 4 of the disc 1 shown in FIG. 1, information on the wavelength for recording / reproduction for each position (each track) in the radius (R) direction of the disc is described. A different wavelength may be assigned to each track. However, due to restrictions on the variable region of the wavelength tunable light source, a predetermined number of tracks on the disk are grouped into one group, and all tracks are divided into a plurality of groups. A different wavelength may be assigned to each track ranked in (1). For example, as shown in FIG. 4, a continuous track T0 to T5 is a group G1, a next continuous track T6 to T11 is a group G2, and a common track (T0 and T6) ranked in each of the groups G1 and G2. , T10 and T7, T2 and T8, T3 and T9, T4 and T10, and T5 and T11).

  Assuming that the entire wavelength variable region is Δλtotal and the wavelength variable amount between adjacent tracks is Δλ, the number N of tracks in the group is Δλtotal / Δλ. That is, in the example of FIG. 4, the number of tracks in one group is 6, and six types of wavelengths or the same order are commonly assigned to the tracks in each group. As a result, it is possible to know the wavelength for recording / reproducing only by acquiring the information of which track in the group, and there is no need to record the wavelength information of all tracks as header information. Occurs.

  FIG. 5 is a diagram showing a difference in information amount of header information between the case where the tracks of the disk are not grouped (A) and the case where the tracks are grouped (B). As shown in FIG. 5A, in the case of not grouping, for example, if the track position information and the wavelength information are 8 bits, the information amount is (8 bits × number of tracks), whereas FIG. As shown in B), when grouping is performed, the information amount corresponding to (8 bits × number of wavelength divisions in the group) is sufficient, and a significant reduction in the header information amount is expected.

  Next, a more specific embodiment of the hologram recording / reproducing apparatus to which the present invention is applied will be described.

  FIG. 6 is a diagram showing a configuration of an optical system of the shift multiplexing type hologram recording / reproducing apparatus of the present embodiment.

  In the figure, reference numeral 11 denotes a disk as a hologram recording medium. The disk 1 has an antireflection film (not shown), a plastic substrate 12 as one protective layer, a recording layer 13, a track groove / address groove 14 and a plastic substrate as the other protective layer from the light incident side. 15.

  The recording layer 13 records interference fringes due to signal light and reference light as changes in refractive index (or transmittance). The recording layer 13 can be used regardless of whether it is an organic material or an inorganic material as long as the refractive index (or transmittance) is changed according to the intensity of light. As the inorganic material, for example, a photorefractive material whose refractive index changes according to the exposure amount by an electro-optic effect such as lithium niobate (LiNbO3) can be used. As the organic material, for example, a photopolymerization type photopolymer can be used. In the photopolymerization type photopolymer, in the initial state, the monomers are uniformly dispersed in the matrix polymer. When this is irradiated with light, the monomer is polymerized at the exposed portion. Further, as the polymer is polymerized, the monomer diffuses and moves from the surroundings, and the concentration of the monomer changes depending on the location, so that the refractive index (or transmittance) changes. Based on this principle, interference fringes generated by interference between the reference light and the signal light are recorded on the recording layer 13 as changes in refractive index (or transmittance).

  The track groove / address groove 14 is provided for servo control such as tracking and focusing on the disk 1 and reading of address information. On the disk 1, track grooves and address grooves 14 are formed along the tracks. The address information is modulated to the value of the group frequency.

  Reference numeral 100 denotes an optical unit of the hologram recording / reproducing apparatus. The optical unit 100 includes a tunable laser light source 21, a collimator lens 22, an isolator 23, a half-wave plate 24, a mechanical shutter 25, a polarizing beam splitter 26, a wave plate 27, a polarizing beam splitter 28, and a half wavelength. A plate 29, a polarizing beam splitter 30, a half-wave plate 31, a relay lens 32, a pinhole 33, a dichroic mirror 34, an objective lens 35, a servo drive unit 36, a half-wave plate 37 for reference light, Reference light pinhole 38, galvanometer mirror 39, lens 40, reflective liquid crystal 41, magnification adjustment lens 42, CCD (Charge Coupled Device) 43, servo light source 44, collimating lens 45, grating 46, beam splitter 47, Condensing lens 48, cylindrical lens 49 And a light receiving element 50.

  The wavelength tunable laser light source 21 is a laser light source capable of changing the wavelength of the emitted light. As the laser element, for example, an LD with a wavelength of 405 nm or an Nd-YAG laser with a wavelength of 532 nm can be used.

  The collimating lens 22 is an optical element that converts laser light emitted from the wavelength tunable laser light source 21 into parallel light.

  The isolator 23 is an optical element for preventing return light.

  The half-wave plate 24 is an optical element that adjusts the ratio of p-polarized light and s-polarized light.

  The mechanical shutter 25 is a means for opening and closing the light emitted from the wavelength tunable laser light source 21.

  The polarization beam splitter 26 is an optical element that splits the light that has passed through the mechanical shutter 25 into a p-wave signal light line 51 and an s-wave reference light line 52.

  The wave plate 27 is an optical element that adjusts the intensity of light.

  The polarization beam splitter 28 is an optical element that enters only the p-polarized component of the light that has passed through the wave plate 27 into the reflective liquid crystal 41 as a spatial light modulator and reflects the return light from the reflective liquid crystal 41.

  The half-wave plate 29 is an optical element for returning the light reflected by the polarization beam splitter 28 to p-polarized light.

  The polarization beam splitter 30 is an optical element that reflects the light (reproduced light) that is transmitted from the half-wave plate 29 and reflected from the disk 1 and returned from the half-wave plate 31. .

  The half-wave plate 31 passes the light incident from the polarization beam splitter 30 at the time of recording as it is, and rotates the polarization direction of the return light from the hologram recording medium 1 at the time of reproduction by 90 degrees to change from p-polarized light to s-polarized light. It is an element.

  The relay lens 32 is an optical element for propagating the signal light that has passed through the half-wave plate 31 to the pinhole 33.

  The pinhole 33 is an optical element for cutting the high-order diffracted light from the liquid crystal by reducing the beam diameter of the signal light.

  The dichroic mirror 34 is an optical element for making light used for recording and reproduction (laser light from the wavelength-tunable laser light source 21) and light used for servo (laser light from the servo light source 44) the same optical path. The dichroic mirror 34 transmits the recording / reproducing light from the wavelength tunable laser light source 21 and responds to the servo from the servo light source 44 in response to the wavelength of the laser light being different between the wavelength tunable laser light source 21 and the servo light source 44. Reflects light.

  The objective lens 35 is an optical element for condensing signal light and servo light at a predetermined layer position of the disk 1.

  The servo drive unit 36 is a drive mechanism for performing tracking control and focus control by driving the objective lens 35 in the biaxial direction by a tracking error signal and a focus error signal from the light receiving element 50. Coils 36A and 36B for driving the objective lens 35 in the axial direction.

  The mirror 39 is a mirror for modulating the incident angle of the reference light to the disk 1.

  The lens 40 is an optical element that collects the reference light from the galvanometer mirror 39 and enters the predetermined layer position of the disk 1.

  The reflective liquid crystal 41 is a spatial light modulator that modulates signal light spatially (in this case, two-dimensionally) and superimposes data. As the spatial light modulator, besides a reflective liquid crystal, a DMD (Digital Micro Mirror) or a transmissive liquid crystal element which is a transmissive element can be used.

  The magnification adjusting lens 42 is an optical element for adjusting the magnification of the reproduction light that is incident after being reflected by the polarization beam splitter 30.

  The CCD 43 is a light receiving element for inputting an image of reproduction light. This light receiving element may be a CMOS.

  The servo light source 44 is a light source for performing servo control such as tracking servo and focus servo, and emits laser light having a wavelength different from that of the wavelength tunable laser light source 21.

  The collimator lens 45 is an optical element that converts the laser light emitted from the servo light source 44 into parallel light.

  The grating 46 is an optical element for dividing the laser light emitted from the collimating lens 45 into three beams, and is composed of two elements. Laser light is divided for servo control.

  The beam splitter 47 is an optical element that transmits the laser light emitted from the grating 46 and reflects the return light that is reflected from the disk 1 and returned.

  The condensing lens 48 is an optical element for condensing the return light from the beam splitter 47 onto the light receiving element 50.

  The cylindrical lens 49 is an optical element for converting the beam shape of the laser light emitted from the condensing lens 48 from a circle to an ellipse.

  The light receiving element 50 is an element, such as a CCD, for receiving return light and outputting a tracking error signal for tracking servo control and a focus error signal for focus servo control.

  The disk 1 is rotated by a spindle motor (not shown). Since the disc 1 moves, recording / reproduction on the disc 1 is performed along tracks formed in the moving direction.

  Next, the operation of this hologram recording / reproducing apparatus will be described.

  The light emitted from the wavelength tunable laser light source 21 becomes parallel light by the collimator lens 22 and passes through an isolator 23 to prevent return light. Thereafter, the ratio of the p-polarized light and the s-polarized light is adjusted by the half-wave plate 24, and the light is split into the p-wave signal light line 51 and the s-wave reference light line 52 by the polarization beam splitter 26.

  The intensity of the signal light is adjusted by the wave plate 27, and only the p-polarized component is incident on the reflective liquid crystal 41 as the spatial light modulator through the polarization beam splitter 28. The light modulated by the reflective liquid crystal 41 is reflected by the polarization beam splitter 28 because the polarization is rotated by 90 °. The light reflected from the polarization beam splitter 28 is returned to p-polarized light again by the half-wave plate 29, passes through the polarization beam splitter 30, and enters the half-wave plate 31. The half-wave plate 31 has a rotation angle that does not change the polarization direction, and transmits the incident p-polarized light as it is. Thereafter, the signal light is propagated through the relay lens 32. At this time, high-order diffracted light from the liquid crystal is cut by the pinhole 33.

  Subsequently, the signal light passes through the dichroic mirror 34. The light that has passed through the dichroic mirror 34 is collected by the objective lens 35 and enters the disk 1.

  On the other hand, the reference light separated by the polarizing beam splitter 26 is returned to p-polarized light by the half-wave plate 37, the beam diameter is adjusted by the pinhole 38, and the angle is modulated by the galvanometer mirror 39. The light is condensed by 40 and is incident on the same portion of the disk 1 so as to interfere with the signal light. As a result, interference fringes are formed on the disk 1. At this time, information spatially modulated by the reflective liquid crystal 40 is recorded on the disk 1 as a hologram.

  The light is opened and closed during recording by opening and closing the mechanical shutter 25. However, the mechanical shutter 25 may be switched by opening / closing the reflective liquid crystal 41 instead of opening and closing. Alternatively, it may be performed by turning on and off the emitted light of the wavelength tunable laser light source 21. When recording by shift multiplexing, the disk 1 is shifted (rotated) by an amount smaller than the hologram size, and then the signal light and reference light are irradiated onto the disk 1.

  When the multiplex recording on one track of the disk 1 is completed and the recording shifts to the next track, the wavelength of the light emitted from the wavelength tunable laser light source 21 is switched to the wavelength specified by the header information, and the next Move to track recording.

  At the time of reproduction, only the pattern corresponding to the reference light is displayed on the reflective liquid crystal 41 and only the reference light component is incident on the disk 1. Thereby, diffracted light (reproduced light) is generated from the hologram recorded on the disk 1. The reproduction light follows an optical path opposite to that of the signal light, passes through the objective lens 35, passes through the dichroic mirror 34, and passes through the relay lens 32. The noise is cut by the pinhole 33 on the way through the relay lens 32. After that, since the wavelength plate 31 is set so that the polarization direction is rotated by 90 degrees, the reproduction light becomes s-polarized light by the half-wave plate 31 and is reflected by the polarization beam splitter 30 to be a magnification adjusting lens 42. The magnification is adjusted at, and the CCD 43 converts the magnification into an electrical signal corresponding to the spatial two-dimensional data in the reflective liquid crystal 41. The output from the CCD 43 is binarized by a signal processing unit (not shown) and converted to time-series binarized data.

  On the other hand, the light emitted from the servo light source 44 is converted into parallel light by the collimating lens 45, and is divided into three beams by the grating 46. The laser light emitted from the grating 46 passes through the beam splitter 47, the polarization beam splitter 48, and the half mirror 49, reaches the dichroic mirror 34, and is placed on the same optical path as the recording / reproducing light by the dichroic mirror 34. And is incident on the disk 1 by the objective lens 35.

  The servo light reflected from the disk 1 returns to the dichroic mirror 34 through the objective lens 35, is reflected here, and returns to the beam splitter 47. The return servo light is reflected by the beam splitter 47 and enters the condensing lens 48, where it is condensed, and then the beam shape is converted from a circular shape to an elliptic shape by the cylindrical lens 49 and received by the light receiving element 50. Is done. From the light receiving element 50, a tracking error signal for tracking servo control, a focus error signal for focus servo control, and the like are output for the return light.

  Next, the configuration of the control system of the hologram recording / reproducing apparatus of this embodiment will be described.

  FIG. 7 is a diagram showing an electrical configuration of the hologram recording / reproducing apparatus.

  As shown in the figure, this hologram recording / reproducing apparatus is used for a tracking and focusing servo based on the output of a spindle motor 60 for driving the disk 1, a spindle motor control unit 61 for controlling the spindle motor 60, and the light receiving element 50. Servo control unit 63 that performs arithmetic processing, servo mechanical control unit 64 that controls servo drive unit 36 based on a control signal from servo control unit 63, reproduction signal processing unit 65 that processes a reproduction signal of CCD 43, and opening and closing of mechanical shutter 25 A shutter control unit 66 for controlling the reflection type liquid crystal 41, an SLM control unit 67 for controlling the reflective liquid crystal 41, a CCD stage control unit 68 for controlling the position of the CCD 43 in the plane direction and the focus direction, and an oscillation for controlling the oscillation wavelength of the wavelength tunable laser light source 21. Wavelength control unit 69 and this holographic And a control computer 70 for generally controlling the recording and reproducing apparatus.

The control computer 70 has a memory 70a for storing wavelength information, which is header information read from the header information recording area 4 shown in FIG. 1 of the disc 1, and an arithmetic processing unit 70b.
The arithmetic processing unit 70b performs control to switch the oscillation wavelength of the wavelength tunable laser light source 21 through the oscillation wavelength control unit 69 based on the wavelength information stored in the memory 70a and the information of the track to be recorded or reproduced. The arithmetic processing unit 70b also stores the wavelength stored in the memory 70a so as to correct the positional deviation in the planar direction and the focus direction of the CCD 43 caused by the angular deviation of the diffracted light caused by changing the wavelength during reproduction. Based on the information, the position of the CCD 43 is controlled through the CCD stage control unit 68. Specifically, this control calculates in advance the amount of deviation of the output image of the CCD 43 for each wavelength and the position correction amount of the CCD 43 so that it becomes 0, and the position correction amount of the CCD 43 is stored in the memory 70a as wavelength information. It is stored by associating and reading the position correction amount of the CCD 43 corresponding to the wavelength information from the memory 70a and supplying it to the CCD stage control unit 68 as a control amount. Further, the arithmetic processing unit 70b supplies a shift amount determined for multiple recording to the spindle motor control unit 61 to control the disk 1 to rotate by the shift amount, or through the shutter control unit 66. Control is performed to open and close the mechanical shutter 25 in accordance with the determined recording scheduling.

  Next, wavelength switching control in the hologram recording / reproducing apparatus will be described.

  FIG. 8 is a flowchart showing the flow of wavelength switching control during recording / reproduction.

  First, the arithmetic processing unit 70a of the control computer 70 performs control to reproduce the header information from the header information recording area 4 shown in FIG. 1 of the disc 1, and the reproduced header information is stored in the memory 70a of the control computer 70. Store (step S1).

  The arithmetic processing unit 70a acquires position information of a track to be recorded or reproduced from now on (step S2), and acquires wavelength information corresponding to the track with reference to header information stored in the memory 70a (step S3). ).

  Next, the arithmetic processing unit 70a outputs a control signal to the oscillation wavelength control unit 69 so as to oscillate the wavelength tunable laser light source 21 at the wavelength acquired from the header information (step S4). Thereby, the oscillation wavelength of the wavelength tunable laser light source 21 is set to a wavelength determined for the track, and hologram recording or reproduction is performed at this wavelength.

  When the multiplex recording or reproduction on one track of the disk 1 is completed and the recording or reproduction is shifted to the next track, the wavelength of the light emitted from the wavelength tunable laser light source 21 is obtained from the header information in the same manner as described above. Switch to the wavelength and move to recording or playback of the next track.

  According to the hologram recording / reproducing apparatus of the present embodiment described above, the shift selectivity in the direction across the track can be improved by switching the oscillation wavelength of the wavelength tunable laser light source 21 in accordance with the track position on the disk 1. In addition, the influence of crosstalk between adjacent tracks can be suppressed.

  Further, by switching the oscillation wavelength of the tunable laser light source 21 based on the wavelength information recorded in advance as the header information of the disk 11, the optimum oscillation wavelength can be switched for each disk 1.

  Furthermore, according to the hologram recording / reproducing apparatus of the present embodiment, by correcting the position of the CCD 43 based on the wavelength information stored in the memory 70a, the angular deviation of the diffracted light is caused by changing the wavelength during reproduction. It is possible to eliminate the positional deviation in the plane direction and the focus direction of the CCD 43 caused by the above.

  The embodiment in which the present invention is applied to the shift multiplexing system has been described above, but the present invention is also effective when applied to the collinear system.

  As shown in FIG. 9, in the collinear method, the pattern of the reference light 72 is arranged so as to surround the signal light 71, so that the signal light 71 and the reference light 72 interfere from all directions to generate a hologram. Recording is performed on the disk 1 which is a hologram recording medium. In this collinear method, by providing a speckle pattern to the reference beam 72, steep selectivity in all directions can be obtained. However, as the number of recording tracks increases, there is a risk that crosstalk will occur between tracks due to the coincidence of speckle patterns. Therefore, even in the collinear method, it is possible to suppress crosstalk by performing recording / reproduction by changing the wavelength for each track.

It is a figure which shows the multiplexing system of the hologram recording / reproducing apparatus concerning embodiment of this invention. It is a figure which shows a shift multiplexing system. It is a graph which shows the result of having measured the diffraction efficiency by shifting the wavelength for reproduction back and forth centering on the wavelength used for recording of a certain track. It is a figure which shows the allocation method of the wavelength to each track | truck. It is a figure which shows the difference in the information content of the header information when not grouping each track and when grouping. It is a figure which shows the structure of the optical system of the hologram recording / reproducing apparatus of the shift multiplexing system of this embodiment. It is a figure which shows the electrical structure of the hologram recording / reproducing apparatus of FIG. It is a flowchart which shows the flow of wavelength switching control at the time of recording and reproduction | regeneration with the hologram recording / reproducing apparatus of FIG. It is a figure for demonstrating the collinear system which can apply this invention.

Explanation of symbols

1 Hologram recording medium (disc)
2 tracks 4 header information recording area 21 tunable laser light source 25 mechanical shutter 41 reflective liquid crystal 43 CCD
61 Spindle motor control unit 66 Shutter control unit 67 SLM control unit 68 CCD stage control unit 69 Oscillation wavelength control unit 70 Control computer 70a Memory 70b Arithmetic processing unit 100 Optical unit

Claims (8)

A laser light source that emits laser light and that can change the oscillation wavelength;
A light branching element for branching the laser light emitted from the laser light source into signal light and reference light;
An optical modulation element that modulates the signal light branched by the optical branching element;
An optical system for condensing the signal light modulated by the light modulation element and the reference light branched by the light branching element at substantially the same location of the hologram recording medium;
A light detecting element for detecting reproduction light from the hologram recording medium;
Control means for switching an oscillation wavelength of the laser light source in accordance with a position in a direction perpendicular to an incident plane of the signal light and the reference light on the hologram recording medium. Playback device. Wavelength information acquisition means for acquiring information on the wavelength corresponding to the position, which is recorded in advance on the hologram recording medium,
2. The hologram recording / reproducing apparatus according to claim 1, wherein the control unit switches the oscillation wavelength of the laser light source based on the wavelength information acquired by the wavelength information acquisition unit.   2. The hologram recording / reproducing apparatus according to claim 1, wherein the control unit switches the oscillation wavelength of the laser light source in accordance with a recording position based on wavelength information acquired by the wavelength information acquisition unit.   2. The hologram recording / reproducing apparatus according to claim 1, wherein the control unit switches the oscillation wavelength of the laser light source in accordance with a reproduction position based on the wavelength information acquired by the wavelength information acquisition unit.   2. The hologram recording / reproducing apparatus according to claim 1, further comprising a position correcting unit that corrects a position of the light receiving element during reproduction based on wavelength information acquired by the wavelength information acquiring unit.   The wavelength information pre-recorded on the hologram recording medium is information corresponding to each position in a direction perpendicular to the incidence plane of the signal light and the reference light on a one-to-one basis. The hologram recording / reproducing apparatus according to claim 1.   Each position in the direction perpendicular to the plane of incidence of the signal light and the reference light is divided into a plurality of groups with a predetermined number of consecutive positions as one group, and common positions ranked in this group 2. The hologram recording / reproducing apparatus according to claim 1, wherein a different wavelength is assigned to each.   A hologram recording method, wherein the wavelengths of the signal light and the reference light are switched according to the position in the direction perpendicular to the incident plane of the signal light and the reference light on the hologram recording medium.

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