JP5231765B2 - Hologram recording / reproducing apparatus, hologram multiplex recording method, and hologram recording medium - Google Patents

Description

  The present invention relates to a hologram recording / reproducing apparatus, a hologram multiplexing recording method, and a hologram recording medium that multiplex-record a plurality of holograms in an arbitrary recording area of a hologram recording medium.

  In recent years, with the rapid development of information technology such as digitalization of information, a style of distributing various content information such as video and audio at high speed at high speed and utilizing them by users has been permeating. On the user side, there are many information utilization forms in which the above distribution data is temporarily stored, for example, on a hard disk or the like, and information to be stored for a long time is stored in another recording medium while being selected and edited. . In order to cope with the explosive increase in the amount of information in such high-quality information and changes in the information utilization style, a system capable of realizing ultra-high-speed recording and reproduction and ultra-large capacity is desired.

  As one promising means that satisfies the above requirements, a hologram optical information recording / reproducing apparatus (also referred to as a hologram recording / reproducing apparatus, a hologram memory, or a holographic memory) using photon mode optical information recording has been proposed. In the hologram recording / reproducing method, signal light and reference light modulated according to data to be recorded are recorded as interference fringes in the hologram recording medium, and readout equivalent to the reference light is performed on the data-recorded hologram recording medium. This is a method of reproducing data recorded on the hologram recording medium by entering light (hereinafter referred to as reproduction reference light, generally using reference light used during recording).

  As a hologram optical information recording system, for example, in a shift multiplex recording type hologram memory optical system proposed by Psaltis et al., Light from a laser light source is expanded by a beam expander and then divided by a half mirror. One of the divided beams passes through the spatial light modulator, is condensed on the hologram recording medium by a Fourier transform lens, and becomes signal light. The other beam becomes reference light that irradiates the same position as the signal light on the hologram recording medium. The hologram recording medium has a form in which, for example, a hologram medium such as a photopolymer is sealed between two glass substrates, and interference fringes formed by signal light and reference light are recorded.

  The spatial light modulator is composed of a two-dimensional array of optical switches such as a liquid crystal panel and a DMD (digital micromirror device), for example, and each optical switch is independently turned on / off in response to an input signal to be recorded. For example, when a spatial light modulator of 1024 cells × 1024 cells is used, 1-Mbit information can be displayed simultaneously. When the signal light passes through the spatial light modulator, 1-Mbit information displayed on the spatial light modulator is converted into a two-dimensional light beam array and recorded as interference fringes on the hologram recording medium. When reproducing the recorded signal, only the reference light is irradiated onto the hologram recording medium, and diffracted light (also referred to as reproduction light) from the hologram is received by a two-dimensional image acquisition means such as a CMOS sensor or a CCD element.

  The above-mentioned hologram optical information recording system is characterized by the fact that the hologram medium is about 1 mm thick and has a thick interference fringe, so-called Bragg grating, so that multiple recording is possible and a large-capacity optical recording system is realized. It is to be done. Multiplex recording is one of the greatest features of hologram recording / reproduction, and the development of multiple recording / reproduction systems is being energetically promoted. For example, in the above-described shift multiplex recording method, since spherical waves are used during hologram recording, the hologram recording area and the next hologram recording area are shifted by an amount that can be selectively reproduced and overlapped. Multiple recording is possible within the range of

  As another example of the multiplex recording system, an angle multiplex system that performs multiplex recording / reproduction in the same area by changing the incident angle of one or both of the reference light and signal light to the hologram recording medium for each hologram to be recorded. In addition, a peritropy multiplexing method in which the incident directions of the reference light and the signal light are rotated with respect to the normal line of the recording medium to perform multiplex recording may be used.

  In the angle multiplexing system described above, the change in the incident angle is realized by mechanical means such as a galvano mirror, or electrical means such as a deflector using an acousto-optic element or an electro-optic element. Further, as a method of removing crosstalk of the multiplex recorded holograms, a plurality of adjacently multiplexed holograms that are reproduced simultaneously are filtered by an opening or the like, and substantially only reproduced light from one hologram is extracted. A polytopic multiplexing scheme characterized by this has been proposed. Also proposed is a method in which a light beam deflection unit and a deflection control unit are configured by a wedge prism and a rotation operation unit for rotating the wedge prism, and angle multiplexing recording and peritropic multiplexing recording are performed in combination. In addition, a method has been proposed in which angle multiplex recording is performed by using a spherical reference wave instead of the reference light incident angle change.

This configuration utilizes the fact that the reference light incident angle felt by each part of the medium slightly changes when the recording position is shifted by slightly rotating the disk-shaped hologram recording medium. When the thickness of the hologram medium is 1 mm, the wavelength selectivity specified by the reproduction signal intensity is 0.014 degrees full width at half maximum. When the reference beam NA is 0.5 and the hologram size is 2 mmφ, multiple holograms are recorded at intervals of about 20 microns. The recording density is 600 Gbit / inch ² and 730 GB is realized in terms of 12 cm disk capacity.

  As another multiplex recording method, for example, by changing the incident angle of the reference light and the phase distribution of the reference light each time one two-dimensional data is hologram-recorded, a plurality of recording methods can be applied to one recording area of the hologram recording medium. Multiple holograms can be recorded. These multiplex recording systems enable data recording at a very high density, and the recording capacity can be dramatically improved compared to conventional optical disks (compact disks: CD, digital versatile disks: DVD, etc.). Has features.

  Further, according to the present system, two-dimensional data displayed on the spatial light modulator can be recorded / reproduced at a time, so that data access can be performed at a very high speed as compared with CD and DVD. The proposal of the hologram recording / reproducing method including the above-described multiplex recording method mainly realizes an improvement in recording capacity due to an increase in multiplicity, and provides a principle and method of multiplex recording on a hologram recording medium.

  In general, multiplex recording of holograms means forming a state having a plurality of holograms in the same area of a hologram recording medium, and is conventionally realized by changing the angle, wavelength, phase code, etc. during recording or reproduction. . The same region is a volume region (a region including an in-plane direction and a thickness direction of the medium) where at least a part of a plurality of holograms overlap. Many of the multiplex recording methods utilize a light diffraction phenomenon under Bragg conditions in order to separate and record and reproduce a plurality of holograms.

  For example, in the case of the angle multiplex recording method, an interference fringe pattern formed by signal light including arbitrary two-dimensional data information and reference light emitted from the same light source as the signal light is recorded as a refractive index distribution. This pattern is a hologram, and diffracted light for a desired hologram can be obtained only when the incident angle of the readout light is substantially the same as the incident angle of the signal light or the reference light on the recording medium during recording.

  Therefore, as a multiplex recording method, it is possible to multiplex-record holograms that can be independently read in the same volume region by changing the incident angle of at least one of the signal light and the reference light with respect to the medium. Here, for example, assuming that the amount of change in angle at which holograms can be separated and reproduced in the same region is (Δθ) and the total amount of change in incident angle of signal light and reference light is θ, θ / (Δθ) holograms are obtained. Can be multiplexed.

  By the way, in a hologram recording material such as a photopolymer, for example, a figure of merit called an M number (hereinafter referred to as M / #) is used. M / # is an amount that is proportional to the square root of the diffraction efficiency (value expressed by the ratio of the diffracted light to the incident light, not a percentage notation, a dimensionless number), and proportional to the refractive index change. The larger the M / #, the greater the total diffraction efficiency. A value obtained by dividing M / # by the square root of the minimum diffraction efficiency required for reproduction is a multiplicity that is possible as material performance.

  Here, the concept of the multiplicity limit by the mechanical restriction or recording method in the hologram recording / reproducing apparatus will be described. FIG. 15 is a schematic diagram for explaining a general angle multiplex recording system. FIG. 15 shows the cross section in the thickness direction of the hologram recording medium and the positional relationship between the signal light and the reference light. In the example of FIG. 15, the signal light 204 maintains a constant incident angle with respect to the hologram recording medium 200, while the first reference light 201, the second reference light 202, and the third reference light 203 are It is assumed that the hologram recording medium 200 is irradiated at different incident angles.

  At this time, for example, a hologram recorded by the signal light 204 and the first reference light 201 can be reproduced by making the readout light incident at substantially the same angular arrangement as the first reference light 201. Note that the above-described notation of “substantially the same angular arrangement” may not completely coincide with the incident angle of the first reference light 201 during recording due to shrinkage of the recording medium, thermal factors during recording / reproduction, and the like. It shows the possibility of happening. Considering these factors, the holograms reproduced by the readout light corresponding to the angles of the first reference light 201, the second reference light 202, and the third reference light 203 can be sufficiently separated. By doing so, it is possible to perform multiplex recording of holograms in substantially the same region of the hologram recording medium 200.

  The above-described angle range that can be separated from other holograms is hereinafter referred to as angle selectivity. As a specific example, for example, if the angle selectivity is 0.01 ° and the reference beam angle range is possible within a range of 60 ° with respect to the normal direction of the recording medium due to mechanical restrictions, for example, 3000 multiplexing Is possible. Therefore, the multiplicity limit that depends substantially on the above-mentioned recording material (determined by M / #) and the multiplicity limit that depends on the angular resolution, wavelength resolution, phase code number, etc. depending on the multiple recording method, It can be said that the possible multiplicity, that is, the recording capacity is determined.

  In addition, a variety of materials such as organic materials such as photopolymers and inorganic materials called photorefractive crystals have been proposed as hologram recording media. From the basic properties of materials such as recording sensitivity, recording capacity, and information retention performance, manufacturing is possible. Various research and development are underway, including methods and costs. Hologram recording / reproducing is generally an information recording / reproducing method using a photon mode of light. Accordingly, the hologram recording medium is a so-called photoconductor in the nature of the recording system, and has sensitivity to light having a wavelength below the visible light region.

  As a general hologram material, for example, in hologram recording using a photopolymer material, a hologram is obtained by utilizing a difference in refractive index between a polymer formed by polymerization of monomers by light irradiation and a material called a matrix material or a binder. A record is made. In addition, when these are used as recording media, they contain substances called reaction inhibitors so that the reaction does not start due to slight unnecessary light (for example, stray light) and dyes for increasing the sensitivity to the light wavelength for recording. It is.

  Therefore, in practice, for example, when a radical polymerizable photopolymer is used, the recording medium is irradiated with light energy including interference pattern information, and then light absorption by the dye, radical generation, polymerization, and diffusion / fixation are performed. Follow the process. It is known that it takes a certain time to complete the formation of interference patterns (hereinafter also referred to as hologram formation) by this series of chemical and structural changes.

  Here, the above-described hologram forming process will be described. FIG. 16 is a conceptual diagram for explaining the hologram forming process. FIG. 16A is a diagram showing a light irradiation process on the hologram recording medium, FIG. 16B is a diagram showing a monomer polymerization process by light irradiation, and FIG. 16C is a relative expression in the recording medium in FIG. 16B. It is a figure which shows the movement and the spreading | diffusion process of the monomer and binder considered as a phenomenon which relaxes a monomer concentration distribution.

  For example, as shown in FIG. 16A, light 105 is irradiated onto a hologram recording medium 101 in which a monomer 102 and a binder 103 are mixed. The refractive index n of the monomer 102 is 1.45, and the refractive index n of the binder 103 is 1.58. In the case of the photopolymerizable hologram recording medium 101, the polymer 104 polymerized by light irradiation in FIG. 16B has a relatively high refractive index n relative to other portions (region where the binder 103 and the monomer 102 are mixed). Become. The refractive index n of the polymer 104 is 1.48.

  Further, the concentration distribution of the monomer 102 and the binder 103 is generated due to the presence of the polymer 104 formed by polymerization. Accordingly, in FIG. 16C, the migration and diffusion of the monomer 102 and the binder 103 that relieve the above concentration distribution occur, and the peripheral portion where the refractive index n of the portion polymerized by light irradiation is not irradiated with light is finally reached. A refractive index profile that is lower than the above is formed. Conventionally shown hologram recording materials have a limit in shortening the interference pattern formation time, and the interference pattern formation time requires a longer time than the irradiation time of the recording reference light and the signal light.

  In addition, in organic photorefractive materials and ferroelectric liquid crystal materials that are being researched and developed as other hologram recording materials, interference patterns can be obtained by utilizing chemical and / or structural changes caused by irradiation of reference light and signal light. In order to perform formation, that is, hologram recording, there are many materials whose interference pattern formation time is longer than the light irradiation time. Also, depending on the material components employed, for example, the above interference pattern formation process may proceed after the irradiation of the signal light and the reference light for recording the hologram is completed. This is generally called a dark reaction.

  The interference pattern formation time including the presence or absence of a dark reaction or the size of the interference is caused by the distribution ratio of the material components in consideration of the basic performance of the recording medium as a target. Therefore, it is possible to shorten the formation time by material design processes such as increasing the material sensitivity and diffusion speed, but other characteristics of the recording medium capable of multi-recording aiming for large-capacity storage (suppressing the occurrence of shrinkage) To improve the controllability of diffraction efficiency for each hologram, etc.).

As a general knowledge, there is a performance index called recording sensitivity. This is the diffraction efficiency (value expressed by the ratio of the diffracted light to the incident light, not the percentage notation, and the dimensionless number) with respect to the amount of recording energy irradiated per unit area (the unit is expressed in, for example, mJ / cm ² ). Indicated by the value of the square root. The recording sensitivity is considered to be an amount related to the amount of residual monomer (monomer in a non-polymerized state) in a photopolymerizable photopolymer material, for example. That is, the recording medium in an unrecorded state has a high recording sensitivity because there are sufficient residual monomers, and a desired diffraction efficiency can be obtained with a small amount of irradiation energy.

  However, as the multiplex recording progresses, the residual monomer amount decreases, so that the recording sensitivity decreases. In order to compensate for this, a method of securing the same diffraction efficiency by increasing the amount of irradiation energy is taken. This method is shown in Patent Document 1 and Patent Document 2, for example.

  From the above discussion, the recording sensitivity is influenced by the amount of monomer consumption, and is thus determined by integrating the given irradiation energy amount. Therefore, by grasping the irradiation energy amount given to an arbitrary area of the hologram recording medium, it is possible to calculate the current recording sensitivity in that area.

  By the way, hologram recording, particularly hologram recording based on multiple recording, has a concept called recording scheduling. This is known as a technique for making the diffraction efficiency of each of a plurality of multiplex-recorded holograms constant by controlling the amount of recording energy according to the number of times of multiplex recording when there is a change in recording sensitivity of the hologram recording medium. ing.

  For example, in Patent Document 1, in the shift multiplex recording method, the multiplicity of the hologram already recorded on the recording layer is specified by the multiplicity specifying step, and the recording light (= signal light + reference light) is determined by the irradiation condition determining step. There has been proposed a method of irradiating recording light by determining the amount of irradiation energy. The above-mentioned Patent Document 1 discloses a method of controlling the amount of irradiation energy by changing the recording light irradiation time or the recording light power more specifically.

Also, in Patent Document 2, a method for increasing the recording light power in accordance with a decrease in recording sensitivity of the hologram recording medium by making the recording time per data page in the multiplex recording process, that is, the light irradiation time to the hologram recording medium constant. Has been proposed. In the above-mentioned Patent Document 2, a method is also proposed in which the recording time and the recording light power are made constant, and the data information amount per page is reduced in accordance with the reduction in the recording sensitivity of the hologram recording medium. In both Patent Document 1 and Patent Document 2, the object is to prevent an increase in recording time accompanying a decrease in sensitivity of the hologram recording medium, that is, a decrease or fluctuation in data transfer rate.
JP 2005-327393 A JP 2005-189748 A

  However, when the conventional multiplex recording method including the above proposal was used to study hologram multiplex recording / reproduction with respect to a photopolymer which is a general holographic recording medium, the dynamic range decreased, that is, the holographic recording medium Has been observed to be in a state where recording is impossible with a small recording capacity with respect to the recording capacity potential that is expected to be possessed or presented by the medium manufacturer. Therefore, in order to realize high-density and large-capacity recording, which is a major feature of hologram recording / reproduction, there is a problem that it is necessary to prevent such a decrease in dynamic range.

  The present invention has been made to solve the above problem, and can prevent a decrease in the dynamic range of the hologram recording medium without decreasing the average data transfer rate and stabilize the recording sensitivity. It is an object of the present invention to provide a multiplex recording method, a holographic recording medium, and a holographic recording / reproducing apparatus that can perform recording.

  A hologram recording / reproducing apparatus according to an aspect of the present invention provides a hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light. A hologram recording / reproducing apparatus that reproduces the hologram recorded by multiplex recording in a recording area a plurality of times and irradiating the reference light, wherein the plurality of multiplex recordings are performed so that at least a part thereof overlaps in an arbitrary recording area A recording interval time determining unit that determines a recording interval time from light irradiation for recording an arbitrary hologram among the holograms to light irradiation for recording the next hologram, and the recording interval time determining unit A control unit that controls light emitted from the light source according to the recording interval time.

  According to another aspect of the present invention, there is provided a hologram multiplex recording method comprising: a hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light; A hologram multiplex recording method for performing multiplex recording on a plurality of recording areas of a plurality of times, from light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in an arbitrary recording area A recording interval time determining step for determining a recording interval time until light irradiation for recording the next hologram, and light emitted from the light source according to the recording interval time determined in the recording interval time determining step. Control steps to control.

  According to these configurations, light irradiation for recording the next hologram from light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in an arbitrary recording area The recording interval time until is determined, and the light emitted from the light source is controlled according to the determined recording interval time.

  Therefore, a hologram having a desired diffraction efficiency is formed by changing the recording interval time from the light irradiation for recording an arbitrary hologram to the light irradiation for overlapping and recording the next hologram. A decrease in the dynamic range of the hologram recording medium can be prevented without reducing the data transfer rate, and the recording sensitivity can be stabilized.

  In the hologram recording / reproducing apparatus, the recording interval time determination unit determines a recording energy amount for each of the plurality of holograms, and the control unit determines the recording energy determined by the recording interval time determination unit. It is preferable to control the light emitted from the light source according to the amount.

  According to this configuration, the amount of recording energy for each of the plurality of holograms is determined, and light emitted from the light source is controlled in accordance with the determined amount of recording energy. Therefore, by changing not only the recording interval time but also the recording energy amount, the hologram can be recorded with an appropriate recording energy amount.

  In the hologram recording / reproducing apparatus, a reaction rate information acquisition unit that acquires reaction rate information indicating a reaction rate until a hologram having a desired diffraction efficiency with respect to light irradiation is recorded and formed on the hologram recording medium. Further, it is preferable that the recording interval time determination unit determines the recording interval time based on the reaction rate information acquired by the reaction rate information acquisition unit.

  According to this configuration, reaction rate information indicating the reaction rate until a hologram having a desired diffraction efficiency with respect to light irradiation is recorded and formed on the hologram recording medium is acquired, and recording is performed based on the acquired reaction rate information. An interval time is determined.

  Therefore, since the recording interval time is determined based on the reaction speed until a hologram having a desired diffraction efficiency with respect to light irradiation is recorded on the hologram recording medium, the reaction speed specific to the material constituting the hologram recording medium is determined. It is possible to determine the optimum recording interval time according to.

  In the hologram recording / reproducing apparatus, the reaction rate information acquisition unit may acquire reaction rate information indicating a time-series reaction rate from an initial stage to a later stage of multiplex recording on the hologram recording medium. preferable.

  According to this configuration, since the reaction rate information indicating the time-series reaction rate from the initial stage to the later stage of the multiplex recording on the hologram recording medium is acquired, the process for determining the recording interval time can be simplified. Can do.

  The hologram recording / reproducing apparatus may further include a multiplicity information acquisition unit that acquires multiplicity information indicating the number of times the hologram is recorded in an arbitrary recording area of the hologram recording medium, and the recording interval time determination unit includes: Preferably, the recording interval time is determined based on the multiplicity information acquired by the multiplicity information acquisition unit.

  According to this configuration, multiplicity information indicating the number of times a hologram is recorded in an arbitrary recording area of the hologram recording medium is acquired, and a recording interval time is determined based on the acquired multiplicity information. Therefore, as the number of times the hologram is recorded in an arbitrary recording area of the hologram recording medium is increased, the recording interval time is lengthened to prevent the deterioration of M / #, and the average data transfer rate is equal to the conventional one. Or it can be shorter.

  In the hologram recording / reproducing apparatus, the recording interval time determination unit determines a time from the start of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram as a recording interval time. It is preferable to do.

  According to this configuration, the time from the start of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram is determined as the recording interval time. Therefore, by changing the time from the start of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram, a hologram having a desired diffraction efficiency can be formed.

  Further, in the above hologram recording / reproducing apparatus, the recording interval time determination unit determines a time from the end of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram. It is preferable to determine the recording interval time.

  According to this configuration, the time from the end of light irradiation for recording an arbitrary hologram until the start of light irradiation for recording the next hologram is determined as the recording interval time. Therefore, a hologram having a desired diffraction efficiency can be formed by changing the time from the end of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram. Can do.

In the hologram recording / reproducing apparatus, a recording interval time from when the N-th hologram is recorded to when the (N + 1) -th hologram is recorded is t _(N) , When the recording interval time from when the _{(N + 1) th} hologram is recorded to when the (N + 2) th hologram is recorded is t _{(N + 1)} , the recording interval time determination unit is t _(N) ≦ t _{( The} recording interval time is preferably determined so as to satisfy the relationship of ( _{N + 1)} .

According to this configuration, the recording interval time from when the Nth hologram is recorded to when the (N + 1) th hologram is recorded is t _(N) , and the (N + 1) th hologram is recorded. The recording interval time is determined so as to satisfy the relationship t _(N) ≦ t _{(N + 1)} , where t _{(N + 1)} is the recording interval time from when the hologram is recorded until the (N + 2) -th hologram is recorded. Is done. Therefore, for example, by defining only the change rate or change amount of the recording interval time according to the hologram recording medium, the recording interval time can be easily determined.

  In the hologram recording / reproducing apparatus, the hologram recording medium stores in advance identification information for identifying the hologram recording medium, and the identification information and the reaction speed information of the hologram recording medium are stored. A reaction rate information storage unit that stores the association rate information in advance, and the reaction rate information acquisition unit reads the identification information from the hologram recording medium and stores the reaction rate information associated with the read identification information. It is preferable to obtain from the reaction rate information storage unit.

  According to this configuration, the identification information for identifying the hologram recording medium is stored in advance in the hologram recording medium. In the reaction rate information storage unit, identification information and reaction rate information of the hologram recording medium are stored in association with each other in advance. Then, identification information is read from the hologram recording medium, and reaction rate information associated with the read identification information is acquired from the reaction rate information storage unit.

  Accordingly, by storing the reaction rate information associated with the identification information in the hologram recording / reproducing apparatus in advance, it is not necessary to store the reaction rate information in the hologram recording medium, and the reaction rate can be calculated from the identification information of the hologram recording medium. Can be easily identified.

  In the hologram recording / reproducing apparatus, the identification information is preferably recorded on the hologram recording medium. According to this configuration, identification information can be read from the inside or the surface of the hologram recording medium.

  In the hologram recording / reproducing apparatus, the identification information is preferably recorded in a cartridge that stores the hologram recording medium. According to this configuration, the identification information can be read from the inside or the surface of the cartridge that stores the hologram recording medium.

  In the hologram recording / reproducing apparatus, the identification information is preferably recorded in a memory arranged in a cartridge that stores the hologram recording medium. According to this configuration, the identification information can be read from the memory arranged on the surface or inside of the cartridge that stores the hologram recording medium.

  In the hologram recording / reproducing apparatus, the identification information is preferably recorded in a memory arranged in the hologram recording medium. According to this configuration, the identification information can be read from the memory arranged on the surface or inside of the hologram recording medium.

  In the hologram recording / reproducing apparatus, the hologram recording medium stores identification information for identifying the hologram recording medium in advance, and the identification information and a hologram are recorded in an arbitrary recording area of the hologram recording medium. The recording interval time information storage unit stores the recording interval time information representing the recording interval time in association with the hologram recording medium in advance, and the recording interval time determination unit includes: The identification information is read from the hologram recording medium, the recording interval time information associated with the read identification information is acquired from the recording interval time information storage unit, and based on the acquired recording interval time information Determine the recording interval time Door is preferable.

  According to this configuration, the identification information for identifying the hologram recording medium is stored in advance in the hologram recording medium. The recording interval time information storage unit includes identification information and recording interval time information that represents the recording interval time on the hologram recording medium, which differs depending on the number of times the hologram is recorded in an arbitrary recording area of the hologram recording medium. It is stored in advance in association with each other. Then, the identification information is read from the hologram recording medium, the recording interval time information associated with the read identification information is acquired from the recording interval time information storage unit, and based on the acquired recording interval time information The recording interval time is determined.

  Therefore, by storing the recording interval time information in the hologram recording / reproducing apparatus in advance, the recording interval time can be easily specified from the identification information of the hologram recording medium.

  Further, in the hologram recording / reproducing apparatus, the recording area of the hologram recording medium is divided into a plurality of areas for recording a plurality of holograms, and each of the divided areas is multiplied by the number of times the holograms are overlapped and recorded. It is preferable that the hologram is recorded for each block by dividing the block into a plurality of corresponding logical blocks and mixing the block having a short recording interval time and the block having a long recording interval time.

  According to this configuration, the recording area of the hologram recording medium is divided into a plurality of areas for recording a plurality of holograms, and each of the divided areas is a logical plurality according to the number of times of multiplex recording. Divided into blocks. Then, a hologram is recorded for each block by mixing a block having a short recording interval time and a block having a long recording interval time.

  For example, when recording holograms in an arbitrary recording area, a certain time interval is required from recording one hologram to recording the next hologram in the same area. At this time, for example, in a hologram recording medium in which the reaction speed gradually decreases from the initial stage to the latter stage of multiplex recording, the data transfer rate in the latter stage of multiplex recording becomes very slow, and finally the recording of the recording area is performed. It takes a very long time to reach capacity. Therefore, a hologram is recorded by mixing a block having a short recording interval time and a block having a long recording interval time, instead of recording the hologram continuously in a block having a short recording interval time or a block having a long recording interval time. As a result, the average hologram recording speed can be kept substantially constant, and the data transfer rate can be kept constant.

  In the hologram recording / reproducing apparatus, the hologram in the first block with the smallest number of times of multiplexing in the first area of the plurality of areas is recorded, and then the first area adjacent to the first area is recorded. The hologram in the second block with the smallest number of multiplexing in the second area is recorded, and then the hologram in the third block with the smallest number of multiplexing is next to the first block in the first area. Preferably it is recorded.

  According to this configuration, first, the hologram in the first block with the smallest number of multiplexing in the first area of the plurality of areas is recorded. Subsequently, the hologram in the second block with the smallest number of multiplexing in the second area adjacent to the first area is recorded. Thereafter, the hologram in the third block with the smallest number of multiplexing is recorded next to the first block in the first area.

  Therefore, blocks having different recording interval times can be mixed, the average hologram recording speed can be kept substantially constant, and the data transfer rate can be made constant.

  In the above hologram recording / reproducing apparatus, it is preferable that a plurality of holograms are continuously recorded in the block along the recording direction for recording the hologram, and the plurality of consecutive holograms are recorded a plurality of times. .

  According to this configuration, a plurality of holograms are continuously recorded in the block along the recording direction in which the hologram is recorded, and the plurality of consecutive holograms are recorded by being overlapped a plurality of times. It is possible to record in order from a hologram with a small number of times.

  In the hologram recording / reproducing apparatus, the recording interval time of each hologram in the block is preferably the same. According to this configuration, since the recording interval time of each hologram in the block is the same, there is no need to change the recording interval time each time a hologram in the same block is recorded, and the process for determining the recording interval time Time can be shortened.

  A hologram recording medium according to another aspect of the present invention is a hologram recording medium that includes a recording layer and records information by irradiating the recording layer with reference light and signal light to form a hologram. In the hologram recording medium, reaction speed information on the reaction speed of the material constituting the recording layer when a hologram having a desired diffraction efficiency for light irradiation is formed on the recording layer, or in an arbitrary recording area Recording interval time information from light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part overlaps is recorded in advance. .

  According to this configuration, the hologram recording medium includes reaction rate information on the reaction rate of the material constituting the recording layer when a hologram having a desired diffraction efficiency with respect to light irradiation is formed on the recording layer, or any arbitrary Recording interval time information from light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in a recording area to light irradiation for recording the next hologram is recorded in advance. Has been.

  Therefore, since the reaction speed information or the recording interval time information is read from the hologram recording medium, it is possible to determine the optimum recording interval time according to the reaction speed unique to the material constituting the hologram recording medium using the reaction speed information. The recording interval time can be easily determined using the recording interval time information.

  In the above-mentioned hologram recording medium, it is preferable that the reaction speed information or the recording interval time information is recorded inside or on the surface of the hologram recording medium. According to this configuration, reaction speed information or recording interval time information can be read from the inside or the surface of the hologram recording medium.

  The hologram recording medium preferably further comprises a cartridge, and the reaction speed information or the recording interval time information is recorded on the surface or inside of the cartridge. According to this configuration, the reaction rate information or the recording interval time information can be read from the inside or the surface of the cartridge.

  The hologram recording medium further includes a cartridge and a memory disposed on or in the surface of the cartridge, or on the surface or in the hologram recording medium, and the reaction speed information or the recording interval time information is Preferably, it is recorded in the memory.

  According to this configuration, the reaction rate information or the recording interval time information can be read from the memory arranged on the surface or inside of the cartridge or the surface or inside of the hologram recording medium.

  According to the present invention, a hologram having a desired diffraction efficiency is formed by changing the recording interval time from the light irradiation for recording an arbitrary hologram to the light irradiation for overlapping and recording the next hologram. Therefore, it is possible to prevent a decrease in the dynamic range of the hologram recording medium without reducing the average data transfer rate, and it is possible to stabilize the recording sensitivity.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: It is not the thing of the character which limits the technical scope of this invention.

(Embodiment 1)
First, the hologram multiplex recording method according to Embodiment 1 of the present invention will be described in terms of preventing the dynamic range of the hologram recording medium from being lowered.

  FIG. 1 is a diagram schematically showing a hologram multiplex recording method according to Embodiment 1, FIG. 1A is a diagram schematically showing the relationship between the number of multiplexed holograms and the amount of recording energy, and FIG. FIG. 1C is a diagram schematically illustrating an example of a concept of hologram multiplex recording scheduling in Embodiment 1, and FIG. 1C is a diagram schematically illustrating another example of the concept of hologram multiplex recording scheduling in Embodiment 1.

  FIG. 2 is a diagram schematically showing a hologram multiplex recording method proposed in the above-described prior art as an example of a general multiplex recording method. FIG. 2A shows the multiplex number of holograms and the recording energy amount. 2B is a diagram schematically showing the concept of hologram multiplex recording scheduling in the prior art, and FIG. 2C is another example of the concept of hologram multiplex recording scheduling in the prior art. FIG.

  1A and 2A, the horizontal axis indicates the number of multiplexed holograms, and the vertical axis indicates the amount of recording energy to be irradiated (= irradiation light intensity × time). 1B, FIG. 1C, FIG. 2B, and FIG. 2C, the horizontal axis indicates time, and the vertical axis indicates recording light power that is the sum of signal light and reference light power necessary for recording.

  As recording scheduling in the conventional hologram multiplex recording method, as shown in FIG. 1A and FIG. 2A, a change in recording energy amount according to the number of multiplexes has been proposed. It is controlled by power (= reference light intensity + signal light intensity) or irradiation time. At this time, as shown in FIGS. 2B and 2C, light irradiation for recording the next hologram on at least a part of the same region after the irradiation of recording light necessary for recording an arbitrary hologram is completed. Usually, the time until the start of the recording (hereinafter referred to as recording interval time) is constant.

  On the other hand, as shown in FIGS. 1B and 1C, the point of the present invention is that, in addition to the change in the recording energy amount at the time of hologram recording in multiple recording, the recording interval time is set to the reaction speed of the hologram medium (desired by light irradiation). The time until a hologram having a diffraction efficiency of (2) is recorded and formed is positively changed. More specifically, the interval is increased as the multiplicity increases by a certain level or more (that is, in the later stage of multiple recording compared to the initial stage of multiple recording).

  The inventors conducted a multiple recording experiment of a simple grating hologram by two-beam interference in order to measure M / # which is the material performance of the hologram recording medium. As specific experimental parameters, HMC-050-G-12-D-400 (thickness 400 microns) manufactured by Aprilis was used as a hologram recording medium, and multiple recording was performed with the optical system arrangement shown in FIG. . FIG. 3 is a diagram schematically showing an optical system arrangement of the hologram recording apparatus used in the experiment.

  The hologram recording apparatus shown in FIG. 3 includes a laser light source 1, a polarization beam splitter (hereinafter referred to as PBS) 2, a mirror 3a, 3b, and a hologram recording medium 4 for branching the laser light from the laser light source 1 into two beams. A rotating stage 5 and a shutter 8 for rotation are provided. Although this configuration is a two-beam interference system that does not include modulated signal data, for convenience, light reflected by the mirror 3a is referred to as signal light 6, and light reflected by the mirror 3b is referred to as reference light 7.

  With the above configuration, laser light emitted from the laser light source 1 is first converted into parallel light having a diameter of 5 mm by a magnifying optical system, a spatial filter, and a collimating lens (all not shown). Thereafter, it is branched into two parallel beams by the PBS 2 to become signal light 6 and reference light 7 respectively. In addition, since the beam is branched by polarization in the PBS 2, the polarization direction of the branched beam is orthogonal. Accordingly, a half-wave plate 41 is inserted in the path of the reference light 7 in order to align the polarization directions of the two beams.

  The signal light 6 is reflected by the mirror 3a and the reference light 7 is reflected by the mirror 3b, and is irradiated on the same area of the hologram recording medium 4. At this time, interference fringes formed spatially by the signal light 6 and the reference light 7 are recorded as holograms in the irradiation area of the hologram recording medium 4. The recording energy amount for recording the hologram is controlled by the opening time of the shutter 8 and the emission power of the laser light source 1. Further, angle multiplex recording can be realized by making the angle formed by the signal light 6 and the reference light 7 constant and rotating the hologram recording medium 4 by the rotary stage 5.

  The shutter 8 opening time, opening timing, rotation angle of the rotary stage 5, and rotation timing are controlled by a computer (not shown). In this examination, first, M / # was compared using the recording energy amount that can be changed according to the recording light intensity and the recording time as parameters. The recording interval time at this time was a constant value (for example, 5 seconds), and the rotation stage 5 (that is, the hologram recording medium 4) was rotated in increments of 2 degrees to perform 31-multiplex angle multiplex recording.

  FIG. 4 is a graph showing the result of the multiple recording experiment when the amount of hologram recording energy is changed. In FIG. 4, the horizontal axis represents the accumulated recording energy amount, and the vertical axis represents the value obtained by integrating the square roots of the diffraction efficiencies of each of the multiple recorded holograms. The saturation arrival point on the vertical axis is M / #. Further, the conditions A, B, and C in FIG. 4 are such that the recording energy amount of the hologram is such that the recording energy amount of the hologram satisfies the relationship of condition A <condition B <condition C with respect to different areas in the same hologram recording medium. This is the result when multiple recording is performed by changing the recording energy amount by changing the intensity and irradiation time.

More specifically, the irradiation light power density used for recording is made constant at about 23 mW / cm ² , and the recording energy amount in Condition A, Condition B, and Condition C is Condition A: Condition B: Condition C = 1: 2. 4, that is, the irradiation time was scheduled so that the intensity (diffraction efficiency) of the hologram would be Condition A: Condition B: Condition C = 1: 4: 16. At this time, the investigation was performed based on the recording energy amount at which the diffraction efficiency of one hologram under condition A was 0.01. However, the recording energy amount at the 31st multiple is the above-mentioned irradiation time constraint (recording energy amount ratio is condition A: condition B: condition so that the integrated recording energy amount until 31 holograms are recorded becomes substantially the same. C = 1: 2: 4).

  From the graph shown in FIG. 4, the inventors have found that M / # is improved as the amount of recording energy per hologram is smaller, that is, as the diffraction efficiency per hologram is smaller. While paying attention to the above results and proceeding with further discussion, in addition to the change in the recording sensitivity known in the past, the reaction speed of the hologram recording medium (diffraction efficiency from the start of hologram recording by light irradiation increases with the progress of multiple recording). It was assumed that the speed until the desired value was reached. That is, the inventors have assumed that the hologram formation speed (= reaction speed) in hologram recording is related to the recording energy amount and / or the recording interval to be irradiated.

In order to confirm this assumption experimentally, the inventors investigated the dependency of M / # on the recording interval in the multiplex recording. The angle multiplex recording of 31 holograms was performed under the same recording energy amount. More specifically, the exposure energy corresponding to the multiplicity was calculated from the recording sensitivity characteristics of the hologram recording medium, and the recording energy density was controlled by the irradiation time with the recording power density kept constant at about 23 mW / cm ² . At this time, the recording characteristics in the case of 1 sec, 2 sec, 5 sec and 10 sec were compared using the recording interval time as a parameter.

  FIG. 5 is a graph showing the result of the multiple recording experiment when the recording interval time is changed. In FIG. 5, the horizontal axis represents the accumulated recording energy amount in 31 multiplexed holograms, and the vertical axis represents the sum of the square roots of the diffraction efficiency of each of the multiple recorded holograms. The saturation arrival point on the vertical axis is M / #.

  As is apparent from the graph shown in FIG. 5, it was discovered that M / # improves as the recording interval time increases. This indicates that the so-called dark reaction, in which the interference pattern formation process proceeds after the irradiation of the signal light and the reference light for recording the hologram, is greatly affected. The magnitude of the dark reaction and the time until the dark reaction ends (reaction time or reaction rate) depend on the amount of residual monomer and the amount of excited reaction initiator (radical), that is, the amount of accumulated recording energy. It is thought that there is.

  That is, in the initial stage of multiple recording, there are many monomers capable of polymerization reaction or migration diffusion when following the reaction process as shown in FIG. Unpolymerized monomers have low viscosity and can easily move through the recording medium. Therefore, in the initial stage of multiple recording, the refractive index profile formation rate (= reaction rate) including the dark reaction is fast, and the reaction time is short. Conversely, as the multiplicity of multiplex recording increases, the amount of monomer and the density of the monomer decrease, so that the polymerization reaction due to the proximity of the monomer hardly proceeds.

In addition, since the molecules polymerized by the polymerization reaction are fixed in the recording medium, the apparent viscosity increases, so that the movement / diffusion rate of the monomer necessary for forming the refractive index distribution is substantially reduced. Accordingly, the reaction speed becomes slow and the reaction time becomes long in the latter stage of multiple recording. Therefore, in the graph of FIG. 5, there is almost no difference in the slope of the graph in the initial stage of multiplex recording with a small cumulative recording energy amount, for example, in the region where the cumulative recording energy amount is 50 mJ / cm ² or less in FIG. It can be read that the difference in diffraction efficiency of holograms after the middle stage of recording determines the superiority or inferiority of recording characteristics, that is, the magnitude of M / #.

  Here, the relationship between the recording interval time, M / #, and recording sensitivity will be described in more detail. For example, if light irradiation for recording an arbitrary hologram A is performed and light irradiation for recording another hologram B is performed during the dark reaction, a monomer in the middle of forming the interference fringe pattern of the hologram A is newly added. It is trapped by radicals excited by and cannot contribute to the formation of the interference fringe pattern of hologram A. Thereby, in order to obtain a desired diffraction efficiency for the hologram A, an excessive amount of recording energy is given assuming a diffraction efficiency smaller than the diffraction efficiency finally obtained when the dark reaction is completed. There is a need.

  As a result, unnecessary radical excitation and monomer consumption occur, and the recording capacity inherent in the hologram recording medium is wasted (consumed in a form not used for information recording). Even if the monomer consumption does not contribute to the formation of the interference fringe pattern, the amount of residual monomer is reduced, so that the recording sensitivity is lowered as the multiple recording proceeds as described above.

  On the other hand, for example, if the recording energy amount and the recording interval time are scheduled so that the diffraction efficiency when the dark reaction proceeds sufficiently becomes a desired value by taking a sufficiently large recording interval time, the irradiation becomes smaller. The same diffraction efficiency can be obtained with energy. In addition, since monomer consumption can be reduced, it is possible to suppress a decrease in recording sensitivity. In addition, for example, the basic characteristics of hologram recording materials are clarified by manufacturers who develop and manufacture materials, so that the reaction speed inherent to the materials can be grasped. Scheduling including dark reaction characteristics such as sex can be easily performed.

  However, when the recording interval time is increased and the above-mentioned M / # is improved, the data transfer rate is greatly reduced, which causes a problem of an increase in recording time on the hologram recording system. . On the other hand, the present invention changes the recording interval time in accordance with the change in the reaction speed of the hologram recording medium in addition to the change in the recording energy amount. In the materials examined by the inventors, there are roughly the following two stages.

  Multiple recording initial stage: Since the recording sensitivity is high, the amount of recording energy for forming a hologram having an arbitrary diffraction efficiency can be reduced. At this time, the amount of residual monomer is abundant, but the dark reaction is also small. Accordingly, the time from the recording light irradiation to the hologram formation (reaction time) is short and the reaction speed is large.

  Late stage of multiple recording: Since the recording sensitivity is decreasing, the amount of recording energy for forming a hologram having an arbitrary diffraction efficiency increases. Since the amount of residual monomer decreases, the amount of recording energy required for obtaining diffraction efficiency is also large, so that the time constant for the dark reaction to proceed becomes longer, the reaction time becomes longer, and the reaction rate becomes smaller.

As described above, the inventors have found that in an arbitrary recording area, the reaction speed is high at the beginning of multiplex recording, and the reaction speed decreases as the multiplicity increases. Specifically, in the 31-multiplex recording described above, for example, the first is to form a hologram having a diffraction efficiency of 0.01 (= diffracted light power / reference light power) under the condition that the irradiation light power density is 20 mW / cm ^2. It took about 1 second from the end of recording light irradiation to the hologram No. 10 and about 5 seconds for the 10th hologram and about 30 to 35 seconds for the 20th and subsequent holograms. In other words, when recording scheduling is performed at a fixed recording interval time (for example, 5 seconds), the recording interval time is longer than necessary from the beginning to the middle of the multiple recording, and the hologram is formed from the middle to the latter of the multiple recording. This means that the necessary recording interval time could not be secured.

  It should be noted that the relationship between the multiplicity and the reaction rate shown in the present embodiment can be understood as an integrated recording energy amount and a reaction rate when more generalized. That is, the reaction speed of the recording area during multiplex recording is not essentially dependent on the multiplicity, but the amount of residual monomer existing in any recording area of the hologram recording medium or photopolymerization. It depends on the amount of dye that triggers the reaction (= accumulated recording energy amount).

  In order to confirm that the capacity (M / #) of the recording medium can be improved without lowering the data transfer rate, which is the effect of the present invention, based on the examination results and considerations as described above, the total multiplexing including the recording interval time is performed. When the recording time is constant and the recording interval time is changed according to the reaction rate (when the recording interval time at the initial stage of multiplex recording is shortened and the recording interval time at the latter stage of multiplex recording is increased), all the recording interval times are The case of equalization was compared. The result is shown in FIG.

  FIG. 6A is a graph showing the recording characteristics when the condition of the recording interval time is changed, and FIG. 6B is a graph schematically showing the relationship between the multiplicity of the hologram and the recording interval time. In FIG. 6A, the horizontal axis represents the accumulated recording energy amount, and the vertical axis represents the value obtained by integrating the square roots of the diffraction efficiencies of the multiple recorded holograms. The saturation arrival point on the vertical axis is M / #. In FIG. 6B, the horizontal axis represents the number of multiplexed holograms, and the vertical axis represents the recording interval time. As a hologram recording condition, multiplex recording of a very weak hologram (that is, a recording energy amount is small) having a diffraction efficiency of about 0.05 was performed assuming that the effect of controlling the recording interval time appears more remarkably.

Under the conditions A, B and C shown in FIG. 6A, 35 holograms were recorded by angle multiplexing using the recording interval time as a parameter. Irradiation energy scheduling is the same for all three conditions. As shown in FIGS. 6A and 6B, in condition A, the recording interval time is constant (5 sec). Condition B is that the recording interval time from the multiplexing number 1 to 19 (where the integrated recording energy amount is about 35 mJ / cm ² ) is 1 sec, and the recording interval time from the multiplexing number 20 to 35 is 10 sec. The recording interval time was changed. The condition C is that the recording interval time from the multiplexing number 1 to 9 (where the integrated recording energy amount is about 7 mJ / cm ² ) is 1 sec, and the multiplexing number 10 to 28 (the integrated recording energy amount is about 90 mJ / cm 2). ² ), the recording interval time from 5 to 35 was set to 10 sec, and the recording interval time was changed in three stages. At this time, in each of the condition A, the condition B, and the condition C, the time until the multiplex recording of 35 holograms is completed can be substantially constant at around 175 sec.

  As can be seen from the graph of FIG. 6A, the M / # is improved in the condition B and the condition C in which the recording interval time is changed stepwise compared to the condition A in which the recording interval time is a constant value. I understand. Further, in the initial stage of multiple recording, that is, in the stage where the accumulated recording energy amount is small, between the case where the recording interval time is 1 sec (condition B and condition C) and the case where the recording interval time is 5 sec (condition A). There is no significant difference. As described above, the amount of residual monomer in the hologram recording medium is abundant. However, since the dark reaction is dependent on the recording energy amount, the dark reaction is small. Therefore, from recording light irradiation to hologram formation. This shows that the reaction time is short.

Further, in the latter half of the multiplex recording, the diffraction efficiency for each hologram decreases under the condition A, and the inclination of the graph gradually decreases. The diffraction efficiency of the last hologram is about 0.005, whereas the condition B And in the condition C, the diffraction efficiency for each hologram is reduced only to 0.035. This is because the sample used in this study gives sufficient recording interval time according to the reaction time and reaction speed in the multiplex recording where the integrated recording energy amount is about 90 mJ / cm ^2. This means that sufficient efficiency can be secured.

  Thus, M / # was improved by performing recording scheduling according to the reaction speed of the hologram recording medium. That is, by controlling the recording interval time according to the reaction speed which is the point of the present invention, for example, by shortening the recording interval time in the initial stage of multiple recording, and by increasing the recording interval time in the latter stage of multiple recording, In addition to preventing the deterioration of M / #, it is possible to further reduce the average data transfer rate to be equal to or shorter than the conventional one.

  As described so far, the inventors, as recording scheduling in holographic multiplex recording, each recording energy amount for a plurality of holograms and from the start of light irradiation for recording any of the plurality of holograms It was proposed to change the time (recording interval time) until the start of light irradiation for recording the next hologram. In particular, as a method of changing the recording interval time, in addition to the irradiation time change in the scheduling of the recording energy amount (= recording light intensity × irradiation time) used for recording a hologram that has been conventionally used, a new hologram recording medium We proposed to schedule the hologram recording interval including the recording interval time according to the reaction speed, and realized large capacity recording without losing the high data transfer rate which is a major feature of hologram recording. .

  In this embodiment, the recording interval time has been described as an example in which the degree of progress of multiple recording is changed to two stages of the initial stage and the latter stage, or three stages of the initial stage, the middle stage, and the latter stage. This change is not limited to this. For example, the same effect can be obtained even if the recording interval time changes in conjunction with the increase in multiplicity.

For example, scheduling may be performed so that the recording interval time always increases from the initial stage to the latter stage of multiple recording. That is, the time from when the Nth hologram is recorded to when the (N + 1) th hologram is recorded among the plurality of holograms to be multiplexed is t _(N) , and the (N + 1) th hologram is When the time from recording to the recording of the (N + 2) th hologram is t _{(N + 1)} , the time can be determined so as to satisfy the relationship of t _(N) ≤t _{(N + 1).} By defining only the change rate or change amount of the recording interval time according to the hologram recording medium, it is possible to easily construct a hologram recording system.

  As a result, as shown in the present embodiment, it is possible to prevent M / # deterioration due to recording scheduling without reducing the data transfer rate, and to effectively use the recording capacity potential inherent in the hologram recording medium. This makes it possible to realize high-capacity and high-speed hologram recording.

  In this embodiment, the time from when the Nth hologram is recorded until the (N + 1) th hologram is recorded is (N + 1) from the start of light irradiation for recording the Nth hologram. This represents the time until the start of light irradiation for recording the first hologram, but the present invention is not particularly limited to this. It may be the time from the end of light irradiation for recording the Nth hologram to the start of light irradiation for recording the (N + 1) th hologram.

  In this study, multiple recording was performed using the above-mentioned photopolymer manufactured by Aprilis. However, as an actual hologram recording system, it is assumed that a hologram recording / reproducing system is constructed using various recording materials. Even in such a case, the same effect can be expected to be obtained by using a plurality of stepwise recording interval time changes as described above depending on the material characteristics of the hologram recording medium.

  In the present embodiment, as described above, the material whose reaction speed becomes slower from the initial stage of the multiple recording to the later stage has been described, but in addition to the change in the recording energy amount which is the point of the present invention. The concept of multiple recording scheduling that changes the recording interval time according to the reaction speed is not limited to this. For example, the material can be designed so that the reaction speed increases from the initial stage to the late stage of multiple recording by controlling sensitivity characteristics and reaction speed by material development. In such a case, for example, scheduling may be performed so that the recording interval time decreases stepwise or continuously (every time the multiplicity increases) from the initial stage to the late stage of multiple recording.

  Further, in this embodiment, for the sake of simplicity, the study result by two-beam interference has been described as an example, but the same applies to two-dimensional data hologram recording using signal light having two-dimensional data information and reference light. An effect is obtained. In this embodiment, the angle multiplexing method has been described as an example of the multiplexing method. However, the present invention is not limited to this, and wavelength multiplexing, phase code multiplexing, peritropic multiplexing, The present invention can be applied to various hologram recording multiplexing methods such as topic multiplexing.

  Further, in this embodiment, 31 multiplex hologram recording has been described in the study of angle multiplex recording. However, the present invention is not limited to this, and the recording energy amount and recording are determined according to the characteristics and thickness of the hologram recording medium. By appropriately scheduling the interval time, it is possible to record and reproduce holograms having a desired diffraction efficiency by several hundred to several thousand multiplexing.

(Embodiment 2)
As a second embodiment of the present invention, a hologram multiplex recording method in which recording scheduling is actually performed and multiplex recording of holograms is performed will be clarified. FIG. 7 is a diagram showing a configuration of a hologram recording / reproducing apparatus for realizing the hologram multiplex recording method described in the first embodiment of the present invention. 7 includes a laser light source 9, a shutter 10, mirrors 11 and 16, a magnifying optical system 12, half-wave plates 13 and 15, a polarizing beam splitter (hereinafter abbreviated as PBS) 14, and a liquid crystal panel. 17, an input signal control unit 18, a condenser lens 19, a reproduction optical system 23, a two-dimensional light receiving element array 24, a reproduction signal acquisition unit 25, and a control unit 100.

  The laser light source 9 emits laser light. The shutter 10 is opened and closed to change the time for which the laser light emitted from the laser light source 9 is applied to the hologram recording medium 22. The mirror 11 reflects the laser light emitted from the laser light source 9 toward the magnifying optical system 12. The magnifying optical system 12 converts the laser light into parallel light having a desired beam diameter. The half-wave plate 13 changes the polarization direction of the laser light.

  The PBS 14 transmits a part of the laser light and reflects the other part to split the laser light into two. The half-wave plate 15 changes the polarization direction of the laser light reflected by the PBS 14. The mirror 16 reflects the laser light whose polarization direction has been changed by the half-wave plate 15 toward the hologram recording medium 22. The laser light reflected by the mirror 16 becomes the reference light 20.

  The liquid crystal panel 17 is an example of a spatial light modulator, displays a desired two-dimensional pattern, and modulates laser light transmitted by the PBS 14 into signal light 21 having two-dimensional data. The input signal control unit 18 controls the liquid crystal panel 17 based on the two-dimensional data information to be displayed. The condensing lens 19 condenses the signal light 21 that has passed through the liquid crystal panel 17 onto the hologram recording medium 22.

  The reproduction optical system 23 turns the reproduction light into a substantially parallel light beam. The two-dimensional light receiving element array 24 receives reproduction light. The reproduction signal acquisition unit 25 takes in the data acquired by the two-dimensional light receiving element array 24 as a reproduction signal.

  The control unit 100 determines a recording interval time from the start of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram, and opens and closes the shutter 10 based on the determined recording interval time. Control and change the recording interval time during which the laser beam is irradiated. The configuration of the control unit 100 will be described later with reference to FIG.

  The laser light emitted from the laser light source 9 is incident on the magnifying optical system 12 through the mirror 11 and becomes parallel light having a desired beam diameter. This parallel light is split into two beams by the PBS 14. At this time, the intensity ratio of the branched beam can be adjusted by controlling the polarization state of the beam incident on the PBS 14 by the half-wave plate 13. The beam on the path from the PBS 14 to the mirror 16 is polarized and converted by passing through the half-wave plate 15 to become reference light 20 having the same polarization state as that of the beam from the PBS 14 to the liquid crystal panel 17. 22 desired recording areas are irradiated.

  On the other hand, the beam directed from the PBS 14 toward the liquid crystal panel 17 passes through the liquid crystal panel 17 on which a desired two-dimensional pattern is displayed by the input signal control unit 18 to become signal light 21 having two-dimensional data. The signal light 21 is condensed by the condensing lens 19 and irradiated to the same area as the irradiation area of the reference light 20 of the hologram recording medium 22. In this way, interference fringes between the reference light 20 and the signal light 21 overlapped on the hologram recording medium 22 are recorded as a hologram.

  The amount of recording energy to be irradiated is controlled by the opening time of the shutter 10 and the output light power of the laser light source 9. Also, the control unit 100 calculates a recording interval time from the start of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram, for example, a shutter for multiplex recording of the next hologram Ten opening start operations are controlled in time.

  Further, when reproducing the hologram recorded on the hologram recording medium 22, only the reference light 20 is obtained by, for example, a method of controlling the half-wave plate 13 to eliminate the light beam that passes through the PBS 14 and goes to the liquid crystal panel 17. The hologram recording area is irradiated. The reproduction light diffracted by the hologram is incident on the two-dimensional light receiving element array 24 through the reproduction optical system 23. The two-dimensional light receiving element array 24 converts the incident reproduction light into two-dimensional image data and outputs it to the reproduction signal acquisition unit 25. The reproduction signal acquisition unit 25 takes in the two-dimensional image data output by the two-dimensional light receiving element array 24 and reproduces the two-dimensional data information.

  Next, a specific configuration of the control unit 100 shown in FIG. 7 will be described. FIG. 8 is a diagram showing a specific configuration of the control unit shown in FIG. The control unit 100 shown in FIG. 8 includes a scheduling unit 26, a recording interval time control unit 27, a multiplicity information acquisition unit 28, a reaction rate information acquisition unit 29, a recording interval time storage unit 30, and a recording control unit 31.

  The multiplicity information acquisition unit 28 acquires multiplicity information indicating the multiplicity in the recording area in which the hologram is recorded. Specifically, the multiplicity information is recorded on the hologram recording medium, and the reference light is irradiated onto the area where the multiplicity information is recorded, so that the multidimensional information is obtained by the two-dimensional light receiving element array 24 and the reproduction signal acquisition unit 25. Severity information is read, and the read multiplicity information is output to the multiplicity information acquisition unit 28.

  The reaction rate information acquisition unit 29 acquires reaction rate information indicating a reaction rate at which a hologram having a desired diffraction efficiency with respect to light irradiation is recorded and formed on the hologram recording medium. Specifically, the reaction speed information is recorded on the hologram recording medium, and the reaction is performed by the two-dimensional light receiving element array 24 and the reproduction signal acquisition unit 25 by irradiating the area where the reaction speed information is recorded with the reference light. The speed information is read, and the read reaction speed information is output to the reaction speed information acquisition unit 29.

  The recording interval time storage unit 30 stores the recording interval time associated with the reaction speed of the hologram recording medium and the multiplicity in the recording area where the hologram is recorded. The storage interval in the present embodiment represents the time from the start of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram.

  The scheduling unit 26 determines a recording interval time from the start of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram. Specifically, the scheduling unit 26 sets the recording interval time associated with the multiplicity information acquired by the multiplicity information acquisition unit 28 and the reaction rate information acquired by the reaction rate information acquisition unit 29 as the recording interval. The recording interval time is determined by reading from the time storage unit 30. The recording interval time control unit 27 controls the opening and closing of the shutter 10 based on the recording interval time determined by the scheduling unit 26, and changes the time during which the laser beam is irradiated.

  The recording control unit 31 controls the recording light power of the laser light source 9 and controls the angle of the reference light applied to the hologram recording medium by moving the mirror 16 to record the hologram on the hologram recording medium.

  In the present embodiment, the scheduling unit 26 corresponds to an example of a recording interval time determining unit, the recording interval time control unit 27 corresponds to an example of a control unit, and the reaction rate information acquiring unit 29 is a reaction rate information acquiring unit. The multiplicity information acquisition unit 28 corresponds to an example of the multiplicity information acquisition unit.

  The scheduling unit 26 in the present embodiment determines the time from the start of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram as a recording interval time. The invention is not particularly limited to this. The scheduling unit 26 may determine, as the recording interval time, the time from the end of light irradiation for recording an arbitrary hologram until the start of light irradiation for recording the next hologram. Further, the scheduling unit 26 may determine the time from the end of light irradiation for recording an arbitrary hologram to the end of light irradiation for recording the next hologram as a recording interval time.

  FIG. 9 is a flowchart showing the flow of control when performing multiplex recording in the hologram recording / reproducing apparatus shown in FIGS.

  As shown in FIG. 9, first, before starting the hologram recording, multiplicity information in an arbitrary recording area of the hologram recording medium 22 and reaction speed information of the hologram recording medium 22 are acquired. First, in step S <b> 1, the reaction rate information acquisition unit 29 acquires reaction rate information indicating a reaction rate at which a hologram having a desired diffraction efficiency with respect to light irradiation is recorded and formed on the hologram recording medium 22. The hologram recording medium 22 is provided with an area X in which reaction speed information is recorded in an area different from the data recording area. In the area X, the two-dimensional light receiving element array 24 and the reproduction are performed in the same manner as the hologram reproduction. Reaction rate information can be obtained by the signal acquisition unit 25.

  Next, in step S2, the multiplicity information acquisition unit 28 acquires multiplicity information representing the multiplicity of the hologram in an arbitrary recording area. The multiplicity information of the hologram recording medium 22 is recorded in advance on the hologram recording medium 22, for example, and can be obtained by the same method as the acquisition of the reaction rate information. That is, for example, the hologram recording medium 22 is provided with a region Y in which multiplicity information is recorded in a region different from the data recording region, and in the region Y, a two-dimensional light receiving element array is formed in the same manner as the hologram reproduction. 24 and the reproduced signal acquisition unit 25 can obtain multiplicity information.

  By feeding back the multiplicity information and the reaction rate information obtained in this way to the scheduling unit 26, calculation of recording scheduling including the recording energy amount and the recording interval time is executed.

  That is, in step S <b> 3, the scheduling unit 26 determines the recording interval time based on the multiplicity information acquired by the multiplicity information acquisition unit 28 and the reaction rate information acquired by the reaction rate information acquisition unit 29. Specifically, the scheduling unit 26 reads the recording interval time associated with the multiplicity information and the reaction rate information from the recording interval time storage unit 30 to determine the recording interval time.

  Based on this scheduling data, the recording interval time control unit 27 electrically controls the opening operation of the shutter 10, for example, and hologram multiplex recording is performed in the same recording area according to the desired scheduling.

  That is, in step S4, the recording interval time control unit 27 opens the shutter 10 and records a hologram. Next, in step S5, the recording interval time control unit 27 determines whether or not the recording of all data to be recorded is completed and the recording of the hologram is finished. Here, when it is determined not to end the hologram recording (NO in step S5), in step S6, the recording interval time control unit 27 determines whether or not to record the hologram in the same recording area. If it is determined not to record the hologram in the same recording area (NO in step S6), in step S7, the recording interval time control unit 27 determines whether the other recording area of the movement destination is a recording area in which the hologram is recorded. Judge whether or not. If it is determined that the other recording area of the movement destination is not the recording area where the hologram is recorded (NO in step S7), the process returns to step S2, and another recording area is recorded to record the hologram in another recording area. Multiplicity information in the recording area is acquired.

  On the other hand, when it is determined that the hologram is recorded in the same recording area (YES in step S6), or when it is determined that the other recording area of the movement destination is the recording area where the hologram is recorded (YES in step S7). In step S8, the recording control unit 31 changes the angle at which the reference light enters the hologram recording medium 22.

  Next, in step S9, the recording interval time control unit 27 determines whether or not the recording interval time determined by the scheduling unit 26 has elapsed. If it is determined that the recording interval time has not elapsed (NO in step S9), the determination in step S9 is repeated until the recording interval time elapses.

  The scheduling unit 26 determines not only the hologram recording interval time but also the positional information on the hologram recording medium in the recording area in which the hologram is recorded and the irradiation start time of the laser beam for recording the hologram. These pieces of information are stored in the RAM. Therefore, the recording interval time control unit 27 can determine whether or not to record the hologram in the same recording area based on the position information, and the recording area in which the other recording area of the movement destination has recorded the hologram. It can be determined whether or not. The recording interval time control unit 27 can determine whether the recording interval time has elapsed based on the irradiation start time and the current time.

  On the other hand, if it is determined that the recording interval time has elapsed (YES in step S9), the recording interval time control unit 27 closes the shutter 10 to finish recording the hologram, and returns to the process of step S3. Then, the recording interval time control unit 27 determines the recording interval time in order to record the next hologram. In the present embodiment, the recording position, the irradiation start time, and the recording interval time are determined every time one hologram is recorded, but the present invention is not particularly limited to this. After determining the recording position, irradiation start time, and recording interval time of a plurality of holograms, the plurality of holograms may be recorded in order according to the determined recording position, irradiation start time, and recording interval time. In this case, when the recording interval time of a plurality of holograms is determined in step 3 and it is determined that the recording interval time has passed in step S9, the process returns to step S4 and the next hologram is recorded.

  When it is determined in step S5 that the hologram recording is to be ended (YES in step S5), in step S10, the recording control unit 31 updates the multiplicity information. In other words, the recording control unit 31 changes the multiplicity information of the recording area that has been multiplex-recorded when recording data this time.

  In addition, as shown in FIG. 9, in a situation (time zone) in which multiple recording in the same recording area is restricted as a recording interval time, movement to another recording area and hologram recording, or reference light angle in the recording area Preparation operations for the next multiple recording such as adjustment may be performed, and the recording scheduling and control operation including the recording interval time control to the recording area restricts the multiple recording to the recording area within the recording interval time. It does not interfere with any operation of the device other than.

  In this embodiment, the recording energy amount is constant and only the recording interval time is changed. However, the present invention is not particularly limited to this, and the recording energy amount may be changed. That is, the scheduling unit 26 determines the recording interval time and the recording energy amounts for the plurality of holograms. In this case, the control unit 100 of the hologram recording / reproducing apparatus further includes a recording energy amount storage unit that stores the recording energy amount associated with the reaction speed of the hologram recording medium and the multiplicity in the recording area where the hologram is recorded. Specifically, the scheduling unit 26 determines the recording energy amount associated with the multiplicity information acquired by the multiplicity information acquisition unit 28 and the reaction rate information acquired by the reaction rate information acquisition unit 29 as the recording energy. The recording energy amount is determined by reading from the amount storage unit. The recording interval time control unit 27 controls the light emitted from the laser light source 9 according to the recording energy amount determined by the scheduling unit 26.

  In the present embodiment, the case where the reaction speed information of the hologram recording medium 22 is recorded on the hologram recording medium 22 has been described. However, the present invention is not limited to this, for example, a hologram recording medium The reaction rate information 22 may be held in the hologram recording / reproducing apparatus as known information.

  FIG. 10 is a block diagram showing a schematic configuration of a hologram recording / reproducing apparatus in a modification of the present embodiment. The control unit 100 shown in FIG. 10 includes a scheduling unit 26, a recording interval time control unit 27, a multiplicity information acquisition unit 28, a reaction rate information acquisition unit 29, a recording interval time storage unit 30, a recording control unit 31, and an identification information acquisition unit. 32 and reaction rate information storage unit 33. The description of the same configuration as that of the control unit 100 of the hologram recording / reproducing apparatus shown in FIG. 8 is omitted.

  The identification information acquisition unit 32 acquires identification information for identifying the hologram recording medium. Specifically, the identification information is recorded in a predetermined area of the hologram recording medium. By irradiating the area where the identification information is recorded with the reference light, the two-dimensional light receiving element array 24 and the reproduction signal acquisition unit 25 The identification information is read, and the read identification information is output to the identification information acquisition unit 32.

  The reaction rate information storage unit 33 stores identification information and reaction rate information in association with each other. The reaction rate information acquisition unit 29 reads the reaction rate information associated with the identification information acquired by the identification information acquisition unit 32 from the reaction rate information storage unit 33 and acquires the reaction rate information. In the present embodiment, the reaction rate information storage unit 33 corresponds to an example of a reaction rate information storage unit.

  Thereby, for example, only the identification information of the simple hologram recording medium may be recorded and held in the inside or the surface of the hologram recording medium 22, and the manufacturing cost of the hologram recording medium can be reduced and the manufacturing throughput can be improved. it can.

  The reaction speed information, multiplicity information, recording interval time information and identification information of the hologram recording medium may be recorded on the surface of the cartridge storing the hologram recording medium, and the reaction speed information, multiplicity information, recording A memory or the like in which interval time information and identification information are stored may be attached to the surface of the hologram recording medium, the surface of the cartridge, or the inside thereof.

  FIG. 11A is a diagram illustrating an appearance of a hologram recording medium stored in a cartridge, and FIG. 11B is a diagram illustrating an appearance of a hologram recording medium having a memory on the surface. In FIG. 11A, a hologram recording medium 111 is stored in a cartridge 112, and the cartridge 112 includes a memory 113 and an openable / closable shutter 114 on the surface thereof.

  For example, in the memory 113, reaction speed information of the hologram recording medium 111 or identification information that can identify the type of the hologram recording medium 111 is recorded. The information recorded in the memory 113 may be information that can be acquired electrically or optically. For example, by an optical system including a reading light source provided in the hologram recording / reproducing apparatus, It can be obtained optically.

  Further, the memory 113 may be arranged in the cartridge 112 or at an arbitrary place on the surface of the hologram recording medium 111 accommodated in the cartridge 112. For example, the information reading provided in the hologram information recording apparatus is possible. It can be appropriately arranged according to the optical system or mechanism for use.

  Furthermore, as shown in FIG. 11B, the memory 113 may be arranged at an arbitrary location on the surface of the hologram recording medium 111. In the example of FIG. 11B, the memory 113 is affixed to the clamp area 121 in the inner peripheral portion of the hologram recording medium 111. In addition, reaction speed information, multiplicity information, and identification information may be recorded in a BCA (burst cutting area) region of the hologram recording medium 111, and these information may be recorded by a bar code or the like.

  Note that the response speed information of the hologram recording medium described above may be a time-series response speed from the initial stage to the late stage of multiple recording. In this case, for example, the scheduling calculation process is simplified. Therefore, there is an advantage that multiplex recording on a plurality of types of hologram recording media having different reaction speeds can be easily realized.

  In the present embodiment, the recording interval time storage unit 30 stores the recording interval time associated with the reaction speed of the hologram recording medium and the multiplicity in the recording area for recording the hologram. The recording interval time storage unit 30 differs depending on the identification information for identifying the hologram recording medium and the number of times the hologram is recorded in an arbitrary recording area of the hologram recording medium. Recording interval time information representing the recording interval time optimum for the medium may be stored in association with each other in advance.

  FIG. 12 is a block diagram showing a schematic configuration of a hologram recording / reproducing apparatus in another modification of the present embodiment. The control unit 100 illustrated in FIG. 12 includes a scheduling unit 26, a recording interval time control unit 27, a multiplicity information acquisition unit 28, a recording interval time storage unit 30, a recording control unit 31, and an identification information acquisition unit 32. The description of the same configuration as that of the control unit 100 of the hologram recording / reproducing apparatus shown in FIGS. 8 and 10 is omitted.

  The recording interval time storage unit 30 differs depending on the identification information for identifying the hologram recording medium and the number of times the hologram is recorded in an arbitrary recording area of the hologram recording medium, and the optimum recording interval time for the hologram recording medium. The recording interval time information to be represented is stored in advance in association with each other. Specifically, the recording interval time storage unit 30 includes the hologram recording medium with identification information for identifying the hologram recording medium and multiplicity information indicating the number of times the hologram is recorded in an arbitrary recording area of the hologram recording medium. Recording interval time information indicating the optimum recording interval time is stored in advance in association with each other. In the present embodiment, the recording interval time storage unit 30 corresponds to an example of a recording interval time information storage unit.

  The scheduling unit 26 acquires the recording interval time information associated with the identification information acquired by the identification information acquisition unit 32 from the recording interval time storage unit 30, and based on the acquired recording interval time information, the recording interval time To decide. Specifically, the scheduling unit 26 records the recording interval time information associated with the identification information acquired by the identification information acquisition unit 32 and the multiplicity information acquired by the multiplicity information acquisition unit 28 as the recording interval time. Acquired from the storage unit 30 to determine the recording interval time.

  Thereby, for example, only the identification information of the simple hologram recording medium may be recorded and held in the inside or the surface of the hologram recording medium 22, and the manufacturing cost of the hologram recording medium can be reduced and the manufacturing throughput can be improved. it can.

  In the present embodiment, the recording interval time storage unit 30 stores the recording interval time associated with the reaction speed of the hologram recording medium and the multiplicity in the recording area for recording the hologram. Is not particularly limited to this, and recording interval time information in which the recording interval time is associated with the reaction speed of the hologram recording medium and the multiplicity in the recording area in which the hologram is recorded is recorded on the hologram recording medium. Recording interval time information may be acquired from the medium.

  FIG. 13 is a block diagram showing a schematic configuration of a hologram recording / reproducing apparatus in still another modification of the present embodiment. The control unit 100 shown in FIG. 13 includes a scheduling unit 26, a recording interval time control unit 27, a multiplicity information acquisition unit 28, a reaction rate information acquisition unit 29, a recording control unit 31, and a recording interval time information acquisition unit 34. The description of the same configuration as that of the control unit 100 of the hologram recording / reproducing apparatus shown in FIG. 8 is omitted.

  The recording interval time information acquisition unit 34 acquires recording interval time information in which the recording interval time is associated with the reaction speed of the hologram recording medium and the multiplicity in the recording area where the hologram is recorded from the hologram recording medium. Specifically, the recording interval time information is recorded on the hologram recording medium, and the two-dimensional light receiving element array 24 and the reproduction signal acquisition unit 25 are irradiated by irradiating the reference light to the area where the recording interval time information is recorded. Thus, the recording interval time information is read out, and the read out recording interval time information is output to the recording interval time information acquisition unit 34.

  The scheduling unit 26 refers to the recording interval time information acquired by the recording interval time information acquisition unit 34, the multiplicity information acquired by the multiplicity information acquisition unit 28, and the reaction acquired by the reaction rate information acquisition unit 29. The recording interval time associated with the speed information is determined.

  The recording interval time information is not only recorded inside the hologram recording medium as described above, but also the surface of the hologram recording medium, the surface or inside of the cartridge, or the memory provided in the hologram recording medium or cartridge. May be recorded.

  Thereby, it is not necessary to store reaction speed information, multiplicity information, and recording interval time information in advance in the hologram recording / reproducing apparatus, and the configuration of the hologram recording / reproducing apparatus can be simplified.

(Embodiment 3)
In the first embodiment and the second embodiment described above, the hologram recording / reproducing apparatus and the hologram multiplex recording method capable of improving the M / # without reducing the recording data transfer rate have been described. Here, an example of a hologram multiplex recording method to which these are applied will be described as a third embodiment of the present invention.

  In hologram multiplex recording, it is useful to keep the data transfer rate of information to be recorded constant. As a characteristic unique to the hologram recording material, there is a change in recording sensitivity due to a change in reaction speed. Therefore, it is difficult to perform multiple recording under the same recording conditions (recording energy amount = irradiation light power × irradiation time). In addition, since there is a change in the hologram formation speed with an increase in the number of multiplexed recordings as shown in the first embodiment, for example, when enormous multiplicity of several hundreds of multiplexing to several thousand multiplexing is assumed, multiplexing is performed. It is expected that the time required for hologram recording in the initial stage of recording and the time required for hologram recording in the latter stage will differ by several orders of magnitude.

  Thereby, for example, a very high data transfer rate (for example, about several tens of gigabits) is obtained in the initial stage of the above-described multiplex recording, but the data transfer rate is several orders of magnitude lower (for example, Several megabps). Such a data transfer rate that changes by an order of magnitude is not easy to use as a hologram recording / reproducing apparatus, and causes a decrease in the stability of the hologram recording / reproducing apparatus, and is difficult to configure as a system. Even if a high-performance and high-speed data transfer function, such as an information processing semiconductor device or wide channel for high-speed data transfer, is used to support the high data transfer rate that is characteristic of hologram recording and reproduction There are only a few recording steps required, and the cost performance is poor.

  Therefore, the present inventors have made an average recording method of information on a hologram recording medium by a method of accumulating multiplicity in an arbitrary recording area, which is a combination of a recording interval time change at the time of multiplex recording, a recording area, and a recording order. The present inventors have found a configuration capable of making the hologram recording speed almost constant.

  FIG. 14 is a conceptual diagram schematically showing the multiplicity of holograms recorded in each recording area and the recording interval time when recording the hologram in any adjacent recording area of the hologram recording medium. Note that each recording area is physically or logically divided. The horizontal axis represents the recording position on the hologram recording medium, and the vertical axis represents the number of times the holograms are superposed (multiplicity). As the multiplicity increases, the recording interval time increases, and as the multiplicity decreases, the recording interval time decreases.

  FIG. 14 shows a hologram having a large area recording area by combining the recording interval time control and the recording order (multiplicity accumulation method) across the recording position and recording area in the hologram recording medium according to the third embodiment. 1 shows a configuration in which an average recording speed (= recording information transfer rate) can be made constant in a recording medium.

  The hologram recording medium is divided into a plurality of areas in which a recording area records a predetermined number of holograms. In FIG. 14, for the sake of simplicity, a plurality of areas A, B, C, D, and E are continuously divided in the horizontal axis direction, and the areas A, B, C, D, and E do not overlap each other. The four holographic recording areas HR. Further, the vertical axis in FIG. 14 schematically shows the multiplicity of multiplex recording of holograms performed in the micro hologram recording region HR. Further, as shown in FIG. 14, the recording interval time is controlled so as to accompany the increase in multiplicity, that is, the change in the reaction speed of the hologram recording medium as shown in the first embodiment.

  For example, in each of the recording areas A to E, a plurality of logical blocks (indicated by dotted lines in FIG. 14) A1 to A5, B1 to B4, C1 to C3, D1 to D2, for each multiplicity. Divide into E1. At this time, the multiplicity may be different for each block. The multiplicity blocks A1 to A5, B1 to B4, C1 to C3, D1 to D2, and E1 in the areas A, B, C, D, and E are assumed to have different recording interval times. In such a hologram recording medium, the recording interval time is lengthened as the number of multiplicity blocks increases.

  The recording interval time between each hologram recording in the multiplicity block may be changed. However, for the sake of simplicity, the recording interval time is constant in each multiplicity block in this embodiment. In this way, since the recording interval time of each hologram in the multiplicity power block is the same, it is not necessary to change the recording interval time each time a hologram in the same multiplicity block is recorded, and the recording interval time is determined. The processing time can be shortened.

  The multiplicity blocks A1, B1, C1, D1, and E1 record four adjacent holograms four times, and the multiplicity blocks A2, B2, C2, and D2 superimpose four adjacent holograms three times. The multiplicity blocks A3, B3, and C3 record four adjacent holograms twice, and the multiplicity blocks A4, A5, and B4 record four adjacent holograms only once. .

  In such a configuration, hologram recording is continuously performed across a plurality of recording areas. At this time, by performing multiplex recording while mixing a multiplicity block having a short recording interval time and a multiplicity block having a long recording interval time existing between arbitrary recording areas, the average hologram recording speed is substantially reduced. It becomes possible to keep constant, and the data transfer rate can be made constant.

  Specifically, first, a hologram is recorded in the multiplicity block A1, and then a hologram is recorded in the multiplicity block B1. Then, after recording the hologram in the multiplicity block A2, the hologram is recorded in the multiplicity block C1. Thereafter, holograms are recorded in the order of multiplicity blocks B2, A3, D1, C2, B3, A4, E1, D2, C3, B4, and A5. In this way, a hologram is recorded by mixing a block with a low multiplicity and a block with a high multiplicity.

  As indicated by an arrow Y1, a plurality of adjacent holograms are continuously recorded in each block, and then a plurality of adjacent holograms are continuously recorded again. This operation is performed by the multiplicity of each block. It is performed as many times as necessary. In this way, a plurality of holograms are continuously recorded along the recording direction in which holograms are recorded in the multiplicity power block, and a plurality of successive holograms are recorded by being overlapped a plurality of times. It is possible to record in order from a hologram with a small number of times.

  Advantages of using the hologram multiplex recording method of Embodiment 3 include the following. For example, when recording holograms in an arbitrary recording area, as described above, a certain time interval is required from recording a certain hologram to recording the next hologram in the same area. At this time, for example, in a hologram recording medium in which the reaction speed gradually decreases from the initial stage to the latter stage of multiplex recording, the data transfer rate in the latter stage of multiplex recording becomes very slow, and finally the recording of the recording area is performed. It takes a very long time to reach capacity. This is the same even when the recording areas are changed and the multiplicity is accumulated in order so that the multiplicity between the recording areas is substantially constant in a plurality of arbitrary recording areas.

  On the other hand, in the hologram multiplex recording method shown in the third embodiment, there is a correlation between the multiplicity block (essentially according to the reaction speed of the recording medium) and the recording interval time in an arbitrary recording area. Thus, the recording interval time is changed and the recording area and the recording order are controlled. According to this, for example, when the multiplicity in an arbitrary recording area has increased, that is, when a long recording interval time must be ensured until the next multiplex recording, the recording existing in the other recording area It is possible to maintain the data transfer rate of the entire system by recording a plurality of holograms in a multiplicity block having a short interval time.

  First, the hologram in the multiplicity power block A1 having the smallest average number of times of multiplexing in the area A among the plurality of areas A to E is recorded. Subsequently, the hologram in the multiplicity block B1 with the smallest average number of times of multiplexing in the region B adjacent to the region A is recorded. After that, the hologram in the multiplicity block A2 having the smallest average multiplexing number next to the multiplicity block A1 in the area A is recorded. Therefore, multiplicity blocks having different recording interval times can be mixed, the average hologram recording speed can be kept substantially constant, and the data transfer rate can be made constant.

  The hologram recording / reproducing apparatus, the hologram multiplex recording method, and the hologram recording medium according to the present invention can prevent the dynamic range of the hologram recording medium from being lowered without lowering the average data transfer rate, and can stabilize the recording sensitivity. A hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light can be multiplexed and recorded multiple times in an arbitrary recording area of the hologram recording medium, It is useful as a hologram recording / reproducing apparatus, a hologram multiplex recording method, and a hologram recording medium for reproducing a hologram recorded by irradiating with reference light.

FIG. 1A schematically shows the relationship between the number of multiplexed holograms and the amount of recording energy, and FIG. 1B schematically shows an example of the concept of hologram multiplex recording scheduling in the first embodiment. FIG. 1C is a diagram schematically showing another example of the concept of hologram multiplex recording scheduling in the first embodiment. FIG. 2 (A) is a diagram schematically showing the relationship between the number of multiplexed holograms and the recording energy amount, and FIG. 2 (B) is a diagram schematically showing the concept of hologram multiplex recording scheduling in the prior art. FIG. 2C is a diagram schematically showing another example of the concept of hologram multiplex recording scheduling in the prior art. It is a figure which shows typically the optical system arrangement | positioning of the hologram recording apparatus used for experiment. It is a graph which shows the multiple recording experiment result when changing the amount of hologram recording energy. It is a graph which shows the multiple recording experiment result when recording interval time is changed. FIG. 6A is a graph showing the recording characteristics when the conditions of the recording interval time are changed, and FIG. 6B is a graph schematically showing the relationship between the hologram multiplicity and the recording interval time. is there. FIG. 6 is a diagram showing a configuration of a hologram recording / reproducing apparatus in a second embodiment. It is a figure which shows the specific structure of the control part shown in FIG. FIG. 9 is a flowchart showing a control flow when performing multiplex recording in the hologram recording / reproducing apparatus shown in FIGS. 7 and 8. FIG. It is a block diagram which shows schematic structure of the hologram recording / reproducing apparatus in the modification of this Embodiment. FIG. 11A is a diagram illustrating an appearance of a hologram recording medium stored in a cartridge, and FIG. 11B is a diagram illustrating an appearance of a hologram recording medium having a memory on the surface. It is a block diagram which shows schematic structure of the hologram recording / reproducing apparatus in another modification of this Embodiment. It is a block diagram which shows schematic structure of the hologram recording / reproducing apparatus in another modification of this Embodiment. It is the conceptual diagram which showed typically the multiplicity of the hologram recorded on each recording area, and the recording interval time at the time of recording a hologram in arbitrary adjacent recording areas of a hologram recording medium. It is the schematic for demonstrating a general angle multiplexing recording system. FIG. 16A is a diagram illustrating a light irradiation process on the hologram recording medium, FIG. 16B is a diagram illustrating a monomer polymerization process by light irradiation, and FIG. 16C is a diagram illustrating FIG. It is a figure which shows the movement and the spreading | diffusion process of the monomer and binder considered as a phenomenon which relaxes the relative monomer concentration distribution expressed in the recording medium in (B).

Explanation of symbols

DESCRIPTION OF SYMBOLS 9 Laser light source 10 Shutter 11, 16 Mirror 12 Magnification optical system 13, 15 1/2 wavelength plate 14 Polarization beam splitter 17 Liquid crystal panel 18 Input signal control part 19 Condensing lens 20 Reference light 21 Signal light 22 Hologram recording medium 23 Reproduction optics System 24 Two-dimensional light receiving element array 25 Playback signal acquisition unit 26 Scheduling unit 27 Recording interval time control unit 28 Multiplicity information acquisition unit 29 Reaction rate information acquisition unit 30 Recording interval time storage unit 31 Recording control unit 32 Identification information acquisition unit 33 Reaction Speed information storage unit 34 Recording interval time information acquisition unit 100 Control unit

Claims (16)

A hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light is multiplexed and recorded in an arbitrary recording area of the hologram recording medium a plurality of times, and the reference light is A hologram recording / reproducing apparatus for reproducing the hologram recorded by irradiation,
A reaction rate information acquisition unit for acquiring reaction rate information indicating a reaction rate until a hologram having a desired diffraction efficiency for light irradiation is recorded and formed on the hologram recording medium;
Based on the reaction rate information acquired by the reaction rate information acquisition unit, light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in an arbitrary recording area A recording interval time determining unit for determining a recording interval time from light irradiation for recording the next hologram to,
A control unit that controls light emitted from the light source according to the recording interval time determined by the recording interval time determination unit;
The hologram recording / reproducing apparatus, wherein the reaction speed information acquisition unit acquires time-series reaction speed information from an initial stage to a late stage of multiplex recording on the hologram recording medium. The recording interval time determination unit determines the respective recording energy amounts for the plurality of holograms,
2. The hologram recording / reproducing apparatus according to claim 1, wherein the control unit controls light emitted from the light source in accordance with the recording energy amount determined by the recording interval time determination unit. A multiplicity information acquisition unit for acquiring multiplicity information indicating the number of times a hologram is recorded in an arbitrary recording area of the hologram recording medium;
The hologram recording / reproducing apparatus according to claim 1, wherein the recording interval time determining unit determines the recording interval time based on the multiplicity information acquired by the multiplicity information acquiring unit.   The recording interval time determination unit determines, as a recording interval time, a time from a light irradiation start for recording an arbitrary hologram to a light irradiation start for recording the next hologram. 4. The hologram recording / reproducing apparatus according to any one of 3).   The recording interval time determining unit determines, as the recording interval time, a time from the end of light irradiation for recording an arbitrary hologram to the start of light irradiation for recording the next hologram. The hologram recording / reproducing apparatus according to claim 1. A hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light is multiplexed and recorded in an arbitrary recording area of the hologram recording medium a plurality of times, and the reference light is A hologram recording / reproducing apparatus for reproducing the hologram recorded by irradiation,
The recording interval time from light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in an arbitrary recording area is determined from light irradiation for recording the next hologram A recording interval time determination unit to perform,
A control unit that controls light emitted from the light source according to the recording interval time determined by the recording interval time determination unit;
Of the plurality of holograms, the recording interval time from when the Nth hologram is recorded until the (N + 1) th hologram is recorded is t _(N) , and the (N + 1) th hologram is recorded. When the recording interval time from when (N + 2) th to the recording of the (N + 2) th hologram is t _{(N + 1)} , the recording interval time determination unit performs the recording so as to satisfy the relationship of t _(N) ≦ t _{(N + 1)} A hologram recording / reproducing apparatus for determining an interval time. The hologram recording medium stores in advance identification information for identifying the hologram recording medium,
A reaction rate information storage unit that stores the identification information and the reaction rate information of the hologram recording medium in association with each other;
The reaction rate information acquisition unit reads the identification information from the hologram recording medium, and acquires the reaction rate information associated with the read identification information from the reaction rate information storage unit. Item 3. The hologram recording / reproducing apparatus according to Item 1 or 2.   8. The hologram recording / reproducing apparatus according to claim 7, wherein the identification information is recorded on the hologram recording medium. A hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light is multiplexed and recorded in an arbitrary recording area of the hologram recording medium a plurality of times, and the reference light is A hologram recording / reproducing apparatus for reproducing the hologram recorded by irradiation,
A reaction rate information acquisition unit for acquiring reaction rate information indicating a reaction rate until a hologram having a desired diffraction efficiency for light irradiation is recorded and formed on the hologram recording medium;
Based on the reaction rate information acquired by the reaction rate information acquisition unit, light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in an arbitrary recording area A recording interval time determining unit for determining a recording interval time from light irradiation for recording the next hologram to,
A control unit that controls light emitted from the light source according to the recording interval time determined by the recording interval time determination unit;
The hologram recording medium stores in advance identification information for identifying the hologram recording medium,
A reaction rate information storage unit that stores the identification information and the reaction rate information of the hologram recording medium in association with each other;
The reaction rate information acquisition unit reads the identification information from the hologram recording medium, acquires the reaction rate information associated with the read identification information from the reaction rate information storage unit,
The hologram recording / reproducing apparatus, wherein the identification information is recorded in a cartridge that stores the hologram recording medium. A hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light is multiplexed and recorded in an arbitrary recording area of the hologram recording medium a plurality of times, and the reference light is A hologram recording / reproducing apparatus for reproducing the hologram recorded by irradiation,
A reaction rate information acquisition unit for acquiring reaction rate information indicating a reaction rate until a hologram having a desired diffraction efficiency for light irradiation is recorded and formed on the hologram recording medium;
Based on the reaction rate information acquired by the reaction rate information acquisition unit, light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in an arbitrary recording area A recording interval time determining unit for determining a recording interval time from light irradiation for recording the next hologram to,
A control unit that controls light emitted from the light source according to the recording interval time determined by the recording interval time determination unit;
The hologram recording medium stores in advance identification information for identifying the hologram recording medium,
A reaction rate information storage unit that stores the identification information and the reaction rate information of the hologram recording medium in association with each other;
The reaction rate information acquisition unit reads the identification information from the hologram recording medium, acquires the reaction rate information associated with the read identification information from the reaction rate information storage unit,
The hologram recording / reproducing apparatus, wherein the identification information is recorded in a memory arranged in a cartridge for storing the hologram recording medium.   8. The hologram recording / reproducing apparatus according to claim 7, wherein the identification information is recorded in a memory arranged on the hologram recording medium. A hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light is multiplexed and recorded in an arbitrary recording area of the hologram recording medium a plurality of times, and the reference light is A hologram recording / reproducing apparatus for reproducing the hologram recorded by irradiation,
The recording interval time from light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in an arbitrary recording area is determined from light irradiation for recording the next hologram A recording interval time determination unit to perform,
A control unit that controls light emitted from the light source according to the recording interval time determined by the recording interval time determination unit;
The recording area of the hologram recording medium is divided into a plurality of areas for recording a plurality of holograms, and each of the divided areas is divided into a plurality of logical blocks according to the number of multiplexing times the hologram is recorded in an overlapping manner. A hologram recording / reproducing apparatus, wherein a hologram is recorded for each block by mixing the block having a short recording interval time and the block having a long recording interval time.   The hologram in the first block with the smallest number of multiplexing in the first area of the plurality of areas is recorded, and then the number of multiplexing in the second area adjacent to the first area is the smallest. The hologram in the second block is recorded, and subsequently, the hologram in the third block with the smallest number of multiplexing is recorded next to the first block in the first area. 12. The hologram recording / reproducing apparatus according to 12.   14. The hologram according to claim 12, wherein a plurality of holograms are continuously recorded in the block along a recording direction in which the hologram is recorded, and the plurality of continuous holograms are recorded a plurality of times. Recording / playback device.   The hologram recording / reproducing apparatus according to claim 12, wherein the recording interval times of the holograms in the block are the same. A hologram multiplex recording method in which a hologram formed by a signal light including arbitrary two-dimensional data information and a reference light emitted from the same light source as the signal light is multiplexed and recorded a plurality of times in an arbitrary recording area of a hologram recording medium There,
A reaction rate information obtaining step for obtaining reaction rate information indicating a reaction rate until a hologram having a desired diffraction efficiency for light irradiation is recorded and formed on the hologram recording medium;
Based on the reaction rate information acquired in the reaction rate information acquisition step, light irradiation for recording an arbitrary hologram among a plurality of holograms that are multiplexed and recorded so that at least a part thereof overlaps in an arbitrary recording area A recording interval time determining step for determining a recording interval time from light irradiation for recording the next hologram to,
Controlling the light emitted from the light source according to the recording interval time determined in the recording interval time determining step,
The holographic multiplex recording method characterized in that the reaction rate information acquiring step acquires kinetic rate information indicating a chronological response rate from an initial stage to a later stage of multiplex recording on the hologram recording medium.

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