WO2017061020A1

WO2017061020A1 - Optical disc recording and reproducing device

Info

Publication number: WO2017061020A1
Application number: PCT/JP2015/078705
Authority: WO
Inventors: 嶋田　堅一; 和良山崎; 健宇津木; 誠保坂
Original assignee: 株式会社日立製作所
Priority date: 2015-10-09
Filing date: 2015-10-09
Publication date: 2017-04-13

Abstract

Although it is effective to lay books to the extent that the beam waists of adjacent holograms overlap each other to achieve high density, the beam waists cannot be made to overlap each other since the signals from the adjacent holograms cannot be separated. The present invention provides a hologram recording and reproducing device that records a hologram including two-dimensional page data information or reproduces the recorded page data information, said hologram recording and reproducing device including: a light source for emitting a light beam; a beam splitter for separating the light beam into reference light and signal light; a phase modulation unit for periodically modulating the phase of the reference light within the plane of the reference light beam; and an angle scanning unit for scanning and changing the incident angle of the phase-modulated reference light relative to the optical information recording medium. The period of phase modulation for the reference light depends on the recording interval of the hologram.

Description

Optical disc recording / reproducing apparatus

The present invention relates to an apparatus for recording or reproducing optical information using holography.

While research on next-generation optical storage technology is underway, hologram recording technology that records digital information using holography is attracting attention. As a method for increasing the recording density of a holographic memory, for example, Patent Document 1 discloses that an amount equal to the beam waist of signal light for writing a hologram separates individual stacks of holograms. All the holograms adjacent to are read out simultaneously, and the adjacent holograms read out are not transmitted to the camera surface by arranging the filter at the beam waist of the reproduced data, or these are not desired. The reproduction can be filtered by an angular filter in the middle plane in an optical system with a limited angular passband. "

Further, Patent Document 2 states that “the reference light deflecting unit 6A is mounted on the angle rotating device 6B, and the angle rotating device 6B rotationally drives the reference light deflecting unit 6A by a minute angle to enable angle multiplex recording. A flat mirror is used as the reference light deflecting means 6A, and a light diffusing layer is formed on the surface by applying an acrylic resin-based light diffusing paint as the reference light phase changing means 20. The light diffusing layer is reflected from the mirror. The wavefront of the reference light is made random, and the position shift selectivity is improved. ”Also,“ the reference light phase changing means 20 is attached to the reference light deflecting means 6A to change the phase of the reference light when deflecting the reference light. The recording density is greatly improved by spatially changing it and increasing the position shift selectivity. "

JP 2004-272268 A JP 2007-305218 A

In order to achieve high density, it is effective to narrow the recording interval between adjacent holograms. Patent Document 1 describes that a spatial filter (polytopic filter) is arranged in the beam waist of the reproduction light and recording is performed at an interval where the beam waists of adjacent holograms do not overlap. However, with this method, if the holograms to be reproduced are reproduced when the holograms are recorded at intervals where the beam waists of adjacent holograms overlap, the polytopic filter cannot block the leakage light of the reproduction light of the adjacent holograms, and Since the hologram reproduction is affected, the recording interval of the hologram cannot be reduced.

In the method shown in Patent Document 2, the phase pattern superimposed on the reference light is random. Even if a known irregular pattern is used, it is difficult to adjust the position so that any device irradiates with the same pattern, and compatibility between devices becomes a problem.

Therefore, an object of the present invention is to provide a technique for improving recording density while maintaining compatibility between apparatuses.

In order to solve the above problems, the present invention uses the configuration described in the claims as an example. For example, in a hologram recording / reproducing apparatus for recording a hologram having two-dimensional page data information or reproducing the recorded page data information, a light source for emitting a light beam, and the light beam as a reference light A beam splitter that separates the reference light into a signal light, a phase modulation unit that periodically modulates the phase of the reference light in a light beam plane of the reference light, and an incident angle of the phase-modulated reference light with respect to the optical information recording medium The hologram recording / reproducing apparatus is characterized in that the period of the phase modulation of the reference light depends on the recording interval of the hologram.

According to the present invention, the recording density can be improved while maintaining compatibility between apparatuses. Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

Block diagram of hologram recording / reproducing optical system in embodiment at the time of hologram recording Schematic diagram of hologram multiplex recording in an embodiment Schematic showing the recording position of the book in the embodiment Schematic of phase distribution given by phase modulation element in embodiment Schematic of phase distribution given by phase modulation element in embodiment Schematic of phase distribution given by phase modulation element in embodiment Block diagram at the time of hologram reproduction of the hologram recording / reproducing optical system in the embodiment Schematic which shows the relationship of the phase of the reference light and reproduction | regeneration light in an Example Schematic which shows the relationship of the phase of the reference light and reproduction | regeneration light in an Example Schematic diagram of phase distribution of reference light of book to be reproduced in the embodiment Schematic of phase distribution of reference light of adjacent book in embodiment Schematic of phase relationship of reproduction light in the embodiment Schematic of a reproduction image of a reproduction target book in the embodiment Schematic of a reproduction image of an adjacent book in the embodiment Schematic showing the hologram reproduction performance in the example Schematic of phase distribution given by phase modulation element in embodiment Schematic diagram of hologram recording / reproducing apparatus in an embodiment Another schematic diagram of hologram recording / reproducing optical system in the embodiment

First, the configuration of the hologram recording / reproducing apparatus will be described.

FIG. 11 is a block diagram of the hologram recording / reproducing apparatus 10 in the present embodiment. In the hologram recording / reproducing apparatus 10 of this embodiment, the hologram recording medium 30 can be attached and detached. The drive control unit 11, the hologram recording / reproducing optical system 12, the cure optical system 13, the optical system control unit 14, and the access The mechanism 15 includes an access control unit 16, a recording information processing unit 17, a reproduction information processing unit 18, and an input / output unit 19.

The hologram recording / reproducing apparatus 10 is connected to the host library control unit 71 via the input / output unit 20 and receives various commands such as a recording command and a reproduction command and data to be recorded on the hologram recording medium 30 from the library control unit 71. The command execution result and the data reproduced from the hologram recording medium 30 are transmitted to the library control unit 71.

The drive control unit 11 controls the overall operation of the hologram recording / reproducing apparatus 10 and operates the hologram recording / reproducing apparatus 10 in accordance with various received commands. That is, the access mechanism 15 is operated via the access control unit 16 to position the hologram recording medium 30 at a predetermined position, and the data received via the recording information processing unit 17 is encoded and converted into two-dimensional data. The hologram recording / reproducing optical system 12 and the cure optical system 13 are operated via the system control unit 14 to record two-dimensional data on the hologram recording medium 30 as a hologram. In the case of binary recording, the recorded two-dimensional data is composed of a two-dimensional array of white (on pixel) and black (off pixel) pixels.

Further, the hologram recording / reproducing optical system 12 is operated to acquire two-dimensional data recorded as a hologram on the hologram recording medium 30, and the two-dimensional data is decoded via the reproduction information processing unit 18 to reproduce the data.

The access mechanism 15 moves the hologram recording medium 30 so that an arbitrary area of the mounted hologram recording medium 30 is positioned at a predetermined position with respect to the hologram recording / reproducing optical system 12 and the cure optical system 13. In this embodiment, the hologram recording medium 30 has a disk shape, and the access mechanism 15 includes a spindle motor that rotates the hologram recording medium 30 around the central axis of the disk and a slide mechanism that moves the disk in a predetermined radial direction. I have. Further, a hologram recording medium rotation angle detection unit that detects the rotation angle of the hologram recording medium 30 is provided, and a signal corresponding to the rotation angle of the hologram recording medium 30 is output.

The access control unit 16 controls the access mechanism 15 to position the hologram recording medium 30 at a position specified by the drive control unit 11. Based on the output signal of the hologram recording medium rotation angle detector, the spindle motor is driven to control the rotation angle of the hologram recording medium 30, and the slide mechanism is driven to control the radial position of the hologram recording medium 30.

The hologram recording / reproducing optical system 12 includes a laser light source 101 having a highly variable 405 nm band wavelength variable, and irradiates the hologram recording medium 30 with signal light and reference light spatially modulated with two-dimensional data by the spatial light modulator 110. Then, two-dimensional data is recorded by forming a hologram. In addition, the two-dimensional data is detected and reproduced by the two-dimensional light detection element 122 by irradiating the hologram recorded on the hologram recording medium 30 with the reference light from the opposite direction to the time of recording.

The cure optical system 13 performs pre-cure and post-cure by irradiating the hologram recording medium 30 with a light beam having low coherence. Precure is a pre-process of hologram recording processing performed for the purpose of easily exposing a region in which a hologram is recorded by irradiating signal light and reference light in advance. On the other hand, post-cure is a post-process of hologram recording processing performed for the purpose of inactivating the area where the hologram is recorded so that the quality of the hologram recorded by unintentional exposure is not deteriorated.

The optical system control unit 14 controls each device mounted on the hologram recording / reproducing optical system 12 and the cure optical system 13. In order to multiplex and record the hologram at a predetermined position on the hologram recording medium 30, the laser light source 101 of the hologram recording / reproducing optical system 12 is driven to emit light with a predetermined light amount, and each actuator is driven to record the recording mode. The reproduction mode is switched, and the incident angle of the reference light applied to the hologram recording medium 30 is controlled. Further, the light source mounted on the cure optical system 13 is driven so that the hologram recording medium 30 is irradiated with energy suitable for pre-cure and post-cure.

The recording information processing unit 17 converts the data received from the host library control unit 71 into two-dimensional data to be displayed on the spatial light modulator 110. After the received data is divided into a plurality of data strings, parity addition for CRC (Cyclic Redundancy Check), scramble processing, and error correction code addition are performed. This data string is converted into two-dimensional data for sub-pages, a plurality of sub-pages are collected to form two-dimensional data for one page, and a marker serving as a reference in image position detection and image distortion correction at the time of reproduction is set. In addition, it is transferred to the spatial light modulator 110.

The reproduction information processing unit 18 reproduces data from the image detected by the two-dimensional light detection element 122. The image position is detected based on the received marker of the image data to correct the distortion of the image, binarization processing is performed, the marker is removed, and two-dimensional data for one page is acquired. The data is converted into a plurality of data strings for each subpage, and error correction processing, descrambling, and CRC are performed to obtain data.

FIG. 1 is a block diagram of the hologram recording / reproducing optical system 12 in this embodiment, and shows a state during hologram recording. A highly coherent light beam emitted from the laser light source 101 that can be adjusted to a predetermined wavelength in the 405 nm band is transmitted through the collimator lens 102 to be converted into a parallel light beam, reflected by the polarizing element 135, and guided to the shutter unit 130.

In the recording mode, the shutter unit 130 functions as a shutter that switches between transmission and blocking of an incident light beam. The light beam that has passed through the shutter unit 130 is directed to the half-wave plate 104. The half-wave plate 104 is mounted on an actuator and is configured to be rotatable around the optical axis. By rotating the half-wave plate 104 at a predetermined angle, the incident light beam has a predetermined light amount ratio between the P-polarized component and the S-polarized component. Then, the light is separated into P-polarized light and S-polarized light by the subsequent polarizing element 105.

The P-polarized light beam that has passed through the polarizing element 105 is used as signal light, and the diameter of the light beam is expanded by the beam expander 106, and then transmitted through the phase mask 107, the relay lens 108, and the polarizing element 109 to enter the spatial light modulator 110. . The signal light is spatially modulated by reflecting the spatial light modulator 110 displaying predetermined two-dimensional data, and the polarization direction of the light passing through the predetermined pixel of the spatial light modulator 110 is converted to S-polarized light. .

The signal light on which the two-dimensional data is superimposed is reflected by the polarizing element 109, transmitted through the relay lens 111 and the spatial filter 112, and condensed on the hologram recording medium 30 by the objective lens 113.

On the other hand, the S-polarized light beam reflected from the polarizing element 105 is used as reference light, converted into a predetermined polarization direction by the half-wave plate 114, reflected by the total reflection mirror 115 and the total reflection mirror 116, and the phase modulation element 120. Irradiate. The phase pattern of the reference light is modulated into a phase pattern described later by the phase modulation element 120, passes through the relay lens 119, reflects the galvano mirror 117, and irradiates the hologram recording medium 30 through the scanner lens 118.

The galvanometer mirror 117 is configured such that the reflection angle can be changed by an actuator, and by controlling the reflection angle of the galvanometer mirror 117, the incident angle of the reference light applied to the hologram recording medium 30 is set to a predetermined angle. The signal light 150 and the reference light 160 are irradiated so as to overlap each other in the hologram recording medium 30, a hologram is formed on the hologram recording medium 30 by interference, and two-dimensional data (page) superimposed on the signal light is recorded. Here, the polarization directions of the signal light and the reference light at the time of recording are both configured to be incident on the medium as S-polarized light in order to increase the degree of modulation of interference.

Hereinafter, in holograms recorded in the same area with different reference beam angles, holograms corresponding to each reference beam angle are called pages, and a set of pages angle-multiplexed in the same area is called a book. .

Note that the position of the phase modulation element 120 is not limited to the illustrated arrangement, but the phase distribution superimposed on the phase modulation element 120 needs to be arranged at a position where it is projected onto the hologram recording medium 30. As a projection method, it is effective to arrange the optical element so that the light modulated by the phase modulation element 120 passes through, for example, a 4f lens system.

FIG. 2 is a schematic diagram of hologram recording. FIG. 2A shows a state where multiple recording of holograms is performed. By sequentially irradiating the reference light with different incident angles 200A, 200B, and 200C of the reference light, a plurality of pages are angled in the same recording area. Multiplex recording. Note that an aggregate of a plurality of pages recorded in the same recording area as a book is a book, and the direction in which the incident angle of the reference light with respect to the recording medium is changed when a predetermined book is recorded is the angle scanning direction.

FIG. 2B shows the recording positions of a plurality of books. After the book 300, which is an aggregate of a plurality of pages recorded in a predetermined recording area, is recorded, as shown in FIG. In the same manner, a plurality of pages are similarly recorded by angle multiplexing and newly recorded as book 300A, book 300B,..., Book 300E. In this embodiment, the interval between adjacent books is A, and recording is performed so that a plurality of books are spread.

The arrangement of the book shown in FIG. 2B is such that the waist portions 400 of the adjacent books do not overlap each other, but this embodiment is not limited to this, and in order to achieve higher density. , It is possible to record the book closely packed so that the waist of adjacent books overlap.

Therefore, in this embodiment, when reproducing the recorded hologram, in order to remove the occurrence of leakage light (hereinafter referred to as crosstalk) of light reproduced from the adjacent book with overlapping waist portions, the phase modulation element 120 uses the reference light. A predetermined phase distribution is periodically superimposed on.

FIG. 3 shows a schematic diagram of the phase distribution given to the reference light by the phase modulation element 120 in this embodiment. For example, as shown in FIG. 3A, the phase modulation element 120 is arranged at intervals of a period A in a predetermined direction (x-axis in the figure) in a plane perpendicular to the optical axis (in the xy plane in the figure). It plays the role of periodically giving the phase difference π. In this embodiment, the x axis in FIG. 3 corresponds to the angle scanning direction of the reference light.

By generating such a phase distribution, the phase distribution is superimposed on the reference light transmitted through the phase modulation element 120, and an area having a phase difference of zero with respect to a predetermined phase as a reference in the light beam plane of the reference light A region of phase difference π is generated. Therefore, this embodiment can be applied not only to the binary amplitude recording but also to the phase multi-level recording technique being studied for the purpose of further increasing the capacity.

The period of the phase distribution of the reference light projected on the surface of the hologram recording medium 30 is determined by the incident angle of the reference light 160 with respect to the hologram recording medium and the optical magnification of the scanner lens 118, etc., and the period is shown in FIG. As defined in FIG. The phase modulation element 120 is not limited to the stepped phase distribution.

FIG. 4 is a configuration example of the phase modulation element 120 that superimposes a phase distribution that adds a phase difference π in a sine wave shape. Even in the case of a sine wave shape, an area having a phase difference of zero and an area having a phase difference of π can be generated with respect to a predetermined phase. Therefore, the cancellation effect of the reproduction light amplitude, which is a feature of this embodiment described later, is expected. Is done. Since the sinusoidal phase distribution does not have a high-frequency component wavefront compared to the stepped phase distribution, unnecessary angular components and intensity distributions of the reference light generated in the process in which the reference light propagates through the hologram recording medium 30 are obtained. The occurrence of high-frequency fluctuations can be suppressed, and the playback quality is improved.

FIG. 5 is a block diagram of the hologram recording / reproducing optical system 12 in this embodiment, and shows a state during hologram reproduction. The light beam emitted from the laser light source 101 is transmitted through the collimator lens 102 and reflected by the polarizing element 135. The light beam that has passed through the shutter unit 130 is directed to the half-wave plate 104, converted into a light beam in which the P-polarized component and the S-polarized component have a predetermined light amount ratio, and is incident on the polarizing element 105. The S-polarized light beam reflected by the polarizing element 105 is converted to P-polarized light by the half-wave plate 114, reflected by the total reflection mirror 115 and the total reflection mirror 116, and applied to the phase modulation element 120.

The phase pattern of the reference light is modulated by the phase modulation element 120 into a phase pattern as shown in FIG. Thereafter, the reference light passes through the relay lens 119, reflects off the galvanometer mirror 117, and irradiates the hologram recording medium 30 via the scanner lens 118. The reference light transmitted through the hologram recording medium 30 is reflected at a predetermined reflection angle by the angle-adjustable galvanometer mirror 121 having a wavelength plate function, and is incident again on the hologram recording medium 30 as S-polarized reproduction reference light. By reproducing with S-polarized light, the coupling efficiency based on the coupled wave theory can be increased, and the reproduction light intensity is improved. Also, since the reflectance is generally higher for S-polarized light than for P-polarized light, reproduction with S-polarized light allows the surface reflected light of the reference light in the hologram recording medium 30 to be incident on the two-dimensional light detection element. Can be reduced.

The reproduction reference light is diffracted by the hologram recorded on the hologram recording medium 30, passes through the objective lens 113, the relay lens 111, the spatial filter 112, and the polarization element 109 as reproduction light and enters the two-dimensional light detection element 122. The two-dimensional light detection element 122 outputs a signal corresponding to the light intensity of the reproduction light incident on each cell. The galvano mirror 117 and the galvano mirror 121 are set to angles corresponding to the respective pages, and a predetermined page of a predetermined book is reproduced.

Note that the phase of the reproduction light corresponds to the phase of the reference light during reproduction. FIG. 6 shows the relationship between the phase of the reference light and the reproduction light. FIG. 6A shows the case where no phase is added to the complex amplitude R of the reference light 160, and FIG. A case where a phase π is added to the complex amplitude R of the reference beam 160 is shown. The phase of the reproduction light corresponds to the phase of the reference light at the time of reproduction, and the complex amplitude of the reproduction light is shown in FIG. 6B with respect to the complex amplitude P of the reproduction light shown in FIG. Thus, phase π is added. Therefore, for example, if reference light having a predetermined phase and a reference light having a phase difference of π can be simultaneously irradiated to the reference light, it is considered that two reproduction lights having a phase difference of π are generated.

In the synthesis of two reproduction lights having a phase difference of π, the amplitudes cancel each other because P + P · exp (jπ) = 0, and the reproduction light disappears. The present embodiment provides a technique for suppressing crosstalk due to reproduction light from an adjacent book by actively utilizing this phenomenon.

In this embodiment, the adjacent book shown in FIG. 2B is used to suppress the light amount of the reproduction light from the adjacent book without reducing the light amount of the reproduction light from the target book to be reproduced (reproduction target book). The period B of the phase distribution of the phase modulation element 120 is set so that the relationship between the interval A of FIG. 3 and the period C of the phase distribution of the reference light shown in FIG. To do.
(Formula 1) C = 4 × A
Assuming that the optical magnification of the

relay lenses

118 and 119 is 1.0, the relationship between the period B shown in FIG. 3A and the period C shown in FIG. It changes as shown in (Formula 2) according to θ.
(Formula 2) B = C × cos θ
Therefore, it is desirable that the period B of the phase distribution of the phase modulation element 120 can be dynamically controlled according to the incident angle θ. For example, dynamic control becomes possible by using a spatial light modulator or the like using liquid crystal as the phase modulation element 120. Although detailed description is omitted because it is described in, for example, Japanese Patent Application Laid-Open No. 2014-203500, for example, by using a wedge prism instead of the galvanometer mirror 117, the beam diameter of the reference light is changed according to the incident angle θ. Therefore, the relationship between the period B and the period C can be made independent of the incident angle θ by appropriately setting the apex angle of the wedge prism. The phase distribution can be a fixed pattern.

Here, the effect when the hologram is recorded and reproduced using the phase modulation element 120 shown in FIG. The manner in which crosstalk due to reproduction light from the adjacent book recorded next to the reproduction target book is suppressed when reproducing the recorded hologram will be described with reference to FIGS. FIG. 7 shows the relationship between the phase distribution of the reference light and the phase of the reproduction light at the time of recording and reproduction of the reproduction target book and the adjacent book. FIG. 8 shows the calculation result of the reproduced image of the hologram in this example.

FIG. 7A shows the phase distribution of the reference light during recording and reproduction of the reproduction target book, and the phase difference during recording and reproduction. As described above, in this embodiment, the phase distribution of the reference light when recording a hologram is such that, for example, a phase difference π is periodically added with a period C in the plane of the hologram recording medium 30 as shown in FIG. It is a phase pattern.

Also at the time of reproduction, the reference light to which the phase difference π is periodically added with the period C is irradiated in the plane of the hologram recording medium 30 as shown in the middle part of FIG. Therefore, as shown in the lower part of FIG. 7A, the difference in the phase of the reference light applied to the reproduction target book during recording and during reproduction is zero.

As described in FIG. 6, the phase of the reproduction light corresponds to the phase of the reference light at the time of reproduction. Therefore, when the phase difference between the reference light during recording and reproduction is 0, that is, when the phase of the reference light during recording and reproduction is the same, the reproduction light from the reproduction target book is not canceled and a sufficient amount of light is obtained. It is detected and reproduced by the two-dimensional photodetecting element 122 while keeping it. FIG. 8A shows the calculation result of the reproduction image of the reproduction target book, and shows that the light amount of the reproduction image of the reproduction target book is sufficiently detected.

FIG. 7B shows the phase distribution of the reference light when recording the adjacent book, the phase distribution of the reference light irradiated to the adjacent book when reproducing the reproduction target book, and the difference between these phases. When recording an adjacent book, as shown in the upper part of FIG. 7B, the reference light irradiation position is adjusted at the recording position of the adjacent book, and the reference light on which the phase distribution is superimposed is applied. .

When the reproduction target book is reproduced, the irradiation position is controlled so as to irradiate the reference light to a position suitable for reproduction of the reproduction target book, that is, a position where the reproduction target book is recorded. As shown in the middle row, the adjacent book is irradiated with the reference light that is displaced by the recording interval A.

That is, as shown in the lower part of FIG. 7B, there is a difference between the phase pattern of the reference light when recording the adjacent book and the phase pattern of the reference light irradiated to the adjacent book when reproducing the reproduction target book. Further, in this embodiment, the adjacent book interval A and the phase period C are set so as to satisfy the relationship of (Equation 1), so that the phase difference between the region where the phase difference between recording and reproduction is zero and the phase difference is π. Are generated at approximately the same rate.

FIG. 7C shows an example of the relationship between the phase of the reproduction light from the region where the phase difference between recording and reproduction is zero and the phase of the reproduction light from the region where the phase difference is π. As described above, since the phase of the reproduction light corresponds to the phase of the reference light at the time of reproduction, as shown in FIG. 7C, the reproduction light is reproduced in the region where the phase difference is zero and the phase difference is π. The reproduced lights that are reproduced cancel each other, and as a result, the amount of reproduced light from the adjacent book can be suppressed.

FIG. 8B shows a calculation result of a reproduction image of reproduction light from a predetermined page in the adjacent book. Although both the reproduction target book and the adjacent book are recorded with the reference light having the same incident angle, the light quantity of the reproduction light from the adjacent book is sufficiently suppressed by the configuration of the above-described embodiment.

From the viewpoint of the reproduction book, the phase pattern at the time of recording the reference light and the phase pattern at the time of reproduction are the same, so that the reproduction is possible without being suppressed like the reproduction light from the adjacent book. In this way, it is possible to suppress crosstalk due to reproduction light from an adjacent book while allowing reproduction from the reproduction target book.

Note that it is conceivable that the irradiation area of the reference light 160 in the surface of the hologram recording medium 30 changes according to the incident angle of the reference light with respect to the hologram recording medium 30. For example, when the relationship of (Equation 1) is satisfied in the state of a predetermined incident angle, there is a possibility that the relationship of (Equation 1) may not be satisfied if reference light having an incident angle different from that is used. In order to suppress crosstalk at any incident angle of the reference light, the irradiation area of the reference light projected onto the hologram recording medium 30 does not depend on the incident angle of the reference light and needs to be substantially equal. As a means for making the irradiation region substantially constant regardless of the incident angle of the reference light, for example, there is a method using a wedge prism instead of the galvanometer mirror 117, and in this application, by combining with such a method, Crosstalk can be suppressed regardless of the incident angle of the reference light.

FIG. 9 shows the result of calculating the quality of the hologram reproduction image with respect to the interval A between adjacent books. The horizontal axis indicates the adjacent book interval A, and the vertical axis indicates the quality of the hologram reproduction image. The quality of the hologram reproduction image shown on the vertical axis uses SNR (Signal to Noise ratio) defined by (Equation 1), and in (Equation 1), μ _on and μ _off are two-dimensional pages superimposed on signal light. The average value of the intensity distribution of the on pixel and the off pixel in the data is shown, and σ _on and σ _off show the standard deviation of the intensity distribution of the on pixel and the off pixel.

In the case where the reference light is not phase-modulated by the phase modulation element 120 as in the prior art, as the interval A between adjacent books is reduced, the crosstalk due to the reproduction light from the adjacent books increases and the reproduction quality deteriorates. On the other hand, when the reference light is phase-modulated by the phase modulation element 120 as in this embodiment, crosstalk due to the reproduction light from the adjacent book is suppressed, and the reproduction quality of the hologram reproduction image is reduced even if the interval A between the adjacent books is reduced. It is possible to record holograms at high density while maintaining the above.

Based on the calculation result of FIG. 9, when the SNR threshold is set to, for example, 3.0 dB or more, the interval A between adjacent books is about 350 μm when phase modulation is not performed, but is narrowed to about 220 μm when phase modulation is performed. be able to.

By the way, the phase distribution of the phase modulation element 120 is assumed to have a periodicity of a phase difference π on a predetermined axis, but the present invention is not limited to a single axis. For example, as shown in FIG. A pattern having a periodicity of phase difference π may be used. By using such a pattern, according to the same principle as described above, the waist portion of the book to be recorded on the hologram recording medium 30 can be arranged so as to overlap in two axes, and further higher density can be realized. it can. The phase distribution pattern is not limited to a rectangular shape, and may be a sine wave shape as in FIG.

As described above, according to the configuration of the present embodiment, by adding a phase difference to the reference light at a period depending on the recording interval, even if the recording interval of the hologram is narrowed, the adjacent book can be reproduced while being reproduced from the reproduction target book. Crosstalk due to reproduction light from the can be suppressed.

In addition, since the phase distribution of the phase modulation element 120 is periodic, even when the recording apparatus and the reproducing apparatus are different, the control of the irradiation position of the reference light becomes easy, and compatibility between apparatuses can be maintained. In addition, it is possible to easily manufacture the element, to suppress phase mismatch in device compatibility, and to maintain the stability of reproduction quality.

Further, when the phase pattern superimposed on the reference light is random, the density can be increased by narrowing the interval between adjacent recording areas to about several tens of μm. On the other hand, if the irradiation position of the reference light during reproduction is shifted by about several μm. In some cases, the hologram reproduction image cannot be detected, and the tolerance for reproduction position control becomes severe. On the other hand, as in this embodiment, the tolerance of reproduction position control tolerance is maintained by making the phase distribution superimposed on the reference light periodic and making the phase of the phase distribution dependent on the recording interval of the hologram. Is also possible.

In this embodiment, the phase difference is set to π. However, if the phase difference is not 0, the amount of reproduction light from the adjacent book can be reduced, and a value other than π may be used.

FIG. 12 is a diagram showing another configuration of the pickup 11 in the present embodiment. In order to avoid duplication of explanation, the difference from FIG. 1 will be described. The difference is that the signal light 1206 and the reference light 1212 enter the hologram recording medium 1 through the same objective lens 1210.

In FIG. 12, the light beam emitted from the light source 1201 passes through the collimating lens 1202 and enters the shutter 1203. When the shutter 1203 is open, after the light beam passes through the shutter 1203, the optical element 1204 composed of, for example, a half-wave plate or the like, adjusts the light quantity ratio of p-polarized light and s-polarized light to a desired ratio. After the polarization direction is controlled, the light enters the PBS prism 1205.

The light beam transmitted through the PBS prism 1205 enters the spatial light modulator 1208 via the PBS prism 1207. The signal light 1206 to which information is added by the spatial light modulator 1208 is reflected by the PBS prism 1207 and propagates through an angle filter 1209 that passes only a light beam having a predetermined incident angle. Thereafter, the signal light beam is focused on the hologram recording medium 1 by the objective lens 510.

On the other hand, the light beam reflected from the PBS prism 1205 functions as reference light 1212, is set to a predetermined polarization direction according to recording or reproduction by the polarization direction conversion element 1219, is then reflected by the mirror 1213, and is reflected by the phase modulation element 120. Irradiate. The phase pattern of the reference light is modulated into the phase pattern shown in FIG. 3 or 4 or 10 by the phase modulation element 120, passes through the relay lens 1222, and enters the lens 1215 via the mirror 1214. The lens 1215 plays a role of condensing the reference light 1212 on the back focus surface of the objective lens 1210, and the reference light once condensed on the back focus surface of the objective lens 1210 becomes parallel light again by the objective lens 1210. Is incident on the hologram recording medium 1.

Here, the objective lens 1210 or the optical block 1221 can be driven, for example, in the direction indicated by reference numeral 1220. By shifting the position of the objective lens 1210 or the optical block 1221 along the driving direction 1220, the objective lens 1210 and the objective lens can be driven. Since the relative positional relationship of the condensing points on the back focus surface 1210 changes, the incident angle of the reference light incident on the hologram recording medium 1 can be set to a desired angle. Instead of driving the objective lens 1210 or the optical block 1221, the incident angle of the reference light may be set to a desired angle by driving the mirror 1214 with an actuator.

In this way, by causing the signal light and the reference light to enter the hologram recording medium 1 so as to overlap each other, an interference fringe pattern is formed in the recording medium, and information is recorded by writing this pattern on the recording medium. . Further, by shifting the position of the objective lens 1210 or the optical block 1221 along the driving direction 1220, the incident angle of the reference light incident on the hologram recording medium 1 can be changed, so that recording by angle multiplexing is possible.

When reproducing the recorded information, the reference light is incident on the hologram recording medium 1 as described above, and the light beam transmitted through the hologram recording medium 1 is reflected by the galvanometer mirror 1216, so that the reproduction reference light is reflected. Generate. The reproduction light reproduced by the reproduction reference light propagates through the objective lens 1210 and the angle filter 1209. Thereafter, the reproduction light passes through the PBS prism 1207 and enters the photodetector 1218, and the recorded signal can be reproduced.

The optical system shown in FIG. 12 has an advantage that it can be reduced in size as compared with the optical system configuration shown in FIG. 1 by making the signal light and the reference light incident on the same objective lens.

In addition, this invention is not limited to the above-mentioned Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

In addition, each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files that realize each function can be stored in a memory, a hard disk, a recording device such as an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

Also, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

DESCRIPTION OF SYMBOLS 10 ... Hologram recording / reproducing apparatus, 11 ... Drive control part, 12 ... Hologram recording / reproducing optical system,
DESCRIPTION OF SYMBOLS 13 ... Cure optical system, 14 ... Optical system control part, 15 ... Access mechanism, 16 ... Access control part,
17 ... Recording information processing unit, 18 ... Reproduction information processing unit, 19 ... Input / output unit,
30 ... Hologram recording medium, 71 ... Library controller, 101 ... Laser light source,
102 ... collimating lens, 104 ... half-wave plate, 130 ... shutter part,
135: Polarizing element, 150: Signal light, 160: Reference light, 300: Book

Claims

In a hologram recording / reproducing apparatus for recording a hologram having two-dimensional page data information or reproducing the recorded page data information,
A light source that emits a light beam;
A beam splitter for separating the light beam into reference light and signal light;
A phase modulation unit that periodically modulates the phase of the reference light in the light beam plane of the reference light;
An angle scanning unit that scans and changes an incident angle of the phase-modulated reference light with respect to the optical information recording medium;
With
The hologram recording / reproducing apparatus, wherein the phase modulation period of the reference light depends on a hologram recording interval.
The hologram recording / reproducing apparatus according to claim 1,
The hologram recording / reproducing apparatus, wherein the phase modulation unit periodically modulates the difference in the amount of phase addition to the reference light to be π within the light beam plane of the reference light.
The hologram recording / reproducing apparatus according to claim 1,
The hologram recording / reproducing apparatus, wherein the phase modulation unit modulates a phase in a sine wave shape or a rectangular shape in a light beam plane of the reference light.
The hologram recording / reproducing apparatus according to claim 1,
The hologram recording / reproducing apparatus, wherein the phase modulation period of the reference light that has been phase-modulated and applied to the optical information recording medium is approximately four times the hologram recording interval.
The hologram recording / reproducing apparatus according to claim 1,
The hologram recording / reproducing apparatus, wherein the phase modulation unit periodically modulates the phase of the reference light in the scanning direction of the reference light in the light beam plane of the reference light.
The hologram recording / reproducing apparatus according to claim 1,
The phase modulation unit periodically modulates the phase of the reference light in at least one of two directions, ie, a scanning direction of the reference light and a direction perpendicular to the scanning direction, in the light beam plane of the reference light. Hologram recording / reproducing apparatus characterized by the above.
In a hologram recording / reproducing method for recording a hologram having two-dimensional page data information or reproducing the recorded page data information,
Firing a light beam;
A light separation step of separating the light beam into reference light and signal light;
A phase modulation step of periodically modulating the phase of the reference light in the light beam plane of the reference light;
An angle scanning step of scanning and changing an incident angle of the phase-modulated reference light with respect to the optical information recording medium;
With
A hologram recording / reproducing method, wherein the phase modulation period of the reference light depends on a hologram recording interval.
The hologram recording / reproducing method according to claim 7,
In the phase modulation step, the hologram recording / reproducing method is characterized in that modulation is periodically performed so that a difference in phase addition amount to the reference light becomes π in a light beam plane of the reference light.
The hologram recording / reproducing method according to claim 7,
In the phase modulation step, a phase is modulated in a sinusoidal shape or a rectangular shape in a light beam plane of the reference light, and the hologram recording / reproducing method is characterized in that:
The hologram recording / reproducing method according to claim 7,
The hologram recording / reproducing method, wherein the phase modulation period of the reference light that is phase-modulated and applied to the optical information recording medium is approximately four times the hologram recording interval.
The hologram recording / reproducing method according to claim 7,
In the phase modulation step, the phase of the reference light is periodically modulated in the scanning direction of the reference light in the light beam plane of the reference light.
The hologram recording / reproducing method according to claim 7,
In the phase modulation step, the phase of the reference light is periodically modulated in at least one of two directions, ie, a scanning direction of the reference light and a direction perpendicular to the scanning direction, in the light beam plane of the reference light. A method for recording and reproducing holograms.