JP4815595B2 - Multiple hologram transfer apparatus and multiple hologram transfer method - Google Patents

Description

  The present invention relates to an apparatus and a method for transferring multiple holograms from a master medium to a copy medium in a hologram memory which can use, for example, a photorefractive crystal and record / reproduce a hologram in the crystal.

  The hologram memory can record information expressed as a two-dimensional image in multiple layers by applying a technology (holography) that can illuminate an object with a laser beam or other highly coherent light and record a three-dimensional stereoscopic image. This is a storage device. Information reproduction is realized by reading an image with information by applying reference light for reading and writing information to the hologram memory.

  For example, a conventional optical disk recording device such as a CD or a DVD applies a laser to a rotating optical disk and reads / writes data in bit units, while a hologram memory reads / writes thousands of bits at the same time by applying a laser once. Write. That is, the hologram memory is capable of high-speed data transfer as compared with a conventional optical disk recording apparatus.

  The hologram memory can multiplex-record a hologram of a two-dimensional image as information at the same location in the hologram medium. Therefore, the recording density of information can be made extremely high, so that a large capacity can be realized.

  As described above, the hologram memory has high speed derived from a direct recording / reproducing method of two-dimensional data and large capacity derived from multiplex recording at the same location. Has been.

  Thus, for the commercialization of a hologram memory having both a large capacity and a high transfer rate, a ROM (Read Only Memory) creation technique has become an important study subject (see, for example, Non-Patent Document 1). In an example of a conventionally proposed hologram transfer method, the transfer operation is repeated as many times as the number of holograms that are spatially overlapped (the number of multiplexes) when the ROM is created. That is, in this method, it is necessary to overwrite the hologram incoherently (non-interfering).

  On the other hand, it is not easy to transfer the multiplexed hologram in a multiplexed state. For example, in Non-Patent Document 2, only diffracted light corresponding to one hologram is extracted using the selectivity of Bragg diffraction conditions in volume holograms for many multiplex recording methods such as angle multiplexing, shift multiplexing, and phase correlation multiplexing. It is described. When such normal multiplex recording is used, when the hologram is reproduced after coherent (interference) transfer of the multiplex hologram, the Bragg condition is satisfied for all the multiplex holograms, and all holograms from the irradiation area of the reproduction light are satisfied. Are simultaneously read. In other words, if the diffracted light reproduced simultaneously from multiple holograms is transferred as it is (coherent transfer) as it is, when reproducing the copy hologram, unacceptably large crosstalk occurs between adjacent holograms, and the reproduced signal is completely discriminated. It won't stick.

  For this reason, as a method for transferring multiple holograms at once, there has been proposed a method (incoherent batch transfer) for batch transfer without crosstalk by eliminating mutual time coherence of light waves used for recording each hologram. (For example, refer nonpatent literature 3).

  However, in order to change only the temporal coherence at the same wavelength, the optical path length of the reference light corresponding to each hologram must be separated from the coherence length of the laser, resulting in a problem that the optical system becomes complicated. . These incoherent transfers have been compared and examined in detail in Non-Patent Document 4, but it has been shown that the maximum diffraction efficiency obtained after transfer is virtually unchanged by any method. .

  On the other hand, the applicant of the present invention does not use the Bragg condition in the hologram medium, but spatial spread spectrum multiplexing (hereinafter referred to as SSS multiplexing) in which holograms are multiplexed and recorded and selectively reproduced by phase modulation / demodulation of the signal light itself using a random diffuser. The system is proposed (refer nonpatent literatures 5 and 6).

In addition, as other documents disclosing the multiple hologram recording, for example, the following non-patent documents 7 to 9 can be cited.
H. Horimai and X. Tan, “Duplication technology for secured read-only holographic versatile disc”, Proc. International Symposium on Optical Memory and Optical Data Storage Topical Meeting, ISOM / ODS2005, no.M-B7, Hawaii, USA, Jul . 2005 L. Solymar, DJ Webb and A. Grunnet-jepsen, “The Physics and Applications of Photorefractive Materials”, Oxford Unversity Press, New York, 1996. S. Piazzolla, BK Jenkins and AR Tanguay, Jr., “Single-step copying process for multiplexed volume holograms”, Opt. Lett., 17, pp. 676-678, 1992. S. Campbell, Y. Zhang, P. Yeh, “Writing and Copying in Volume holographic memories: approaches and analysis”, Opt. Commun., 123, pp. 27-33, 1996 T. Ito and A. Okamoto, “Volume holographic recording using spatial spread-spectrum multiplexing”, Jpn. J. Appl. Phys. 45 Part 1, pp. 1270-1276, 2006 T. Ito and A. Okamoto, “Volume holographic recording using spatial spread-spectrum multiplexing technique”, Proc. ISOM / ODS2005, MP-20, Honolulu, USA, Jul.2005 FH Mok, GW Burr and D. Psaltis, “System metric for holographic memory systems”, Opt. Lett., 21, pp. 896-898, 1996 KM Johnson, M. Armstrong, L. Hesselink and JW Goodman, “Multiple multiple-exposure hologram”, Appl. Opt., 24, pp. 4467-4472, 1985 K. Anderson and K. Curtis, “Polytopic multiplexing”, Opt. Lett., 29, pp.1402-1404, 2004

  In the case of a hologram recorded by the SSS multiplexing method, it is addressed by despreading in the diffuser during reproduction. Therefore, if a transfer system for multiple holograms is established based on SSS multiplexing, each page data can be selected and reproduced without any problem even when multiple diffracted light is written on the copy-side medium, so that coherent transfer is possible. it is conceivable that. Further, in the coherent batch transfer, complication of the optical system due to the coherence adjustment is eliminated as compared with the incoherent type. Furthermore, it is considered that the diffraction efficiency can be greatly enhanced by coherent batch transfer.

  However, the coherent batch transfer using the SSS multiplexing method has not been studied so far.

  The present invention has been made in view of the above problems, and an object thereof is to propose a specific method of coherent batch transfer using the SSS multiplexing method.

  In order to solve the above problems, a multiple hologram transfer apparatus according to the present invention is a multiple hologram transfer apparatus that transfers a multiple hologram recorded in a master hologram memory to a copy hologram memory by a spatial spectrum diffusion multiplexing method. A first reference light source for irradiating the hologram memory with the first reference light to collectively reproduce the recorded multiple holograms; and a second reference light light source for irradiating the copy hologram memory with the second reference light. The copy hologram memory is simultaneously irradiated with the multiple hologram reproduced from the master hologram memory and the second reference light, and the multiple holograms are collectively transferred to the copy hologram memory.

  Moreover, in order to solve the above-mentioned problem, the multiple hologram transfer method according to the present invention is a multiple hologram transfer method for transferring a multiple hologram recorded in a master hologram memory by a spatial spectrum diffusion multiplexing method to a copy hologram memory. Irradiating the master hologram memory with the first reference light to reproduce the recorded multiple holograms at once, irradiating the copy hologram memory with the multiple holograms and the second reference light, It is characterized by collectively transferring multiple holograms reproduced from a master hologram memory.

  According to said structure, the multiple hologram currently recorded on the master hologram memory is recorded by the spatial spread spectrum multiplexing system. In this case, when transferring from the master hologram memory to the copy hologram memory, coherent batch transfer of multiple holograms can be performed while irradiating the first reference light and the second reference light with the same wavelength and the same optical path. Therefore, the transfer operation can be simplified without complicating the optical system as in the conventional incoherent batch transfer.

In the multiplex hologram transfer apparatus, the multiplex hologram is a multiplex of M holograms, and the intensity sum of all signal lights of the multiplex hologram reproduced from the master hologram memory is represented by MI _i , copy hologram memory _Is the intensity I _ref of the second reference light irradiated to the light, and the light intensity ratio between the intensity sum of all the copied signal lights and the intensity I _ref of the second reference light is r = MI _i / I _ref , It is preferable that the emitted light intensity of the first reference light source and the second reference light source is set so that the light intensity ratio r is r = 1.

In the multiplex hologram transfer method, the multiplex hologram is obtained by multiplexing M holograms, and the intensity sum of all the signal lights of the multiplex hologram reproduced from the master hologram memory is represented by MI _i . _Is the intensity I _ref of the second reference light irradiated to the light, and the light intensity ratio between the intensity sum of all the copied signal lights and the intensity I _ref of the second reference light is r = MI _i / I _ref , The light intensity ratio r is preferably set to r = 1.

According to the above configuration, the diffraction efficiency per hologram can be set to the maximum value by setting the light intensity ratio r to r = 1. In addition, the diffraction efficiency per hologram is proportional to 1 / M, and compared to the conventional incoherent batch transfer method (the diffraction efficiency per hologram is proportional to 1 / M ² ), the diffraction efficiency after transfer. Can be improved M times.

  As described above, the multiplex hologram transfer apparatus according to the present invention is a multiplex hologram transfer apparatus for transferring a multiplex hologram recorded in a master hologram memory to a copy hologram memory by a spatial spectrum diffusion multiplex method. The copy hologram memory comprising: a first reference light source that irradiates a first reference light and collectively reproduces recorded multiple holograms; and a second reference light source that irradiates the copy hologram memory with a second reference light. Further, the multiple hologram reproduced from the master hologram memory and the second reference light are simultaneously irradiated, and the multiple holograms are collectively transferred to the copy hologram memory.

  Further, the multiple hologram transfer method according to the present invention is the multiple hologram transfer method for transferring the multiple hologram recorded in the master hologram memory by the spatial spectrum diffusion multiplexing method to the copy hologram memory as described above. Irradiating the memory with the first reference light, reproducing the recorded multiple holograms at once, irradiating the copy hologram memory with the multiple holograms and the second reference light, and supplying the copy hologram memory with the master hologram memory In this configuration, multiple holograms reproduced from the above are collectively transferred.

  Therefore, when performing transfer from the master hologram memory to the copy hologram memory, coherent batch transfer of multiple holograms can be performed while irradiating the first reference light and the second reference light as the same wavelength and the same optical path, The transfer operation can be simplified without complicating the optical system as in the conventional incoherent batch transfer.

  An embodiment of the present invention will be described below with reference to FIGS.

[Configuration of hologram memory device]
FIG. 1 shows a schematic configuration of a hologram memory device according to an embodiment of the present invention. The hologram memory device shown in FIG. 1 adopts a spatial spectrum spread multiplexing (SSS multiplexing) system, a configuration for recording multiple holograms in the master hologram memory 1, and the master hologram memory 1. A configuration for coherent batch transfer of recorded multiple holograms to a hologram memory 2 serving as a copy is described. The hologram memory device includes a first light source 3, a second light source 4, a third light source 5, an SLM 6, a random diffuser 7, and a control unit 8.

  The first light source 3 is a light source for irradiating the SLM 6 with light. The SLM 6 modulates the light from the first light source 3 in accordance with the data to be recorded and uses it as signal light. Further, the random diffuser 7 applies spatial phase modulation to the signal light sent from the SLM 6 and makes it incident on the hologram memory 1 as object light. In the present invention, the means for applying the spatial phase modulation to the signal light is not limited to the random diffuser as described above, but other spatial phase modulation means (for example, a fiber bundle in which fibers are bundled). It is also possible to use.

  The second light source 4 is a light source for irradiating the hologram memory 1 with the first reference light at the time of multiplex hologram recording to the hologram memory 1 and coherent batch transfer from the hologram memory 1 to the hologram memory 2. The reference light incident on the hologram memory 1 from the second light source 4 is controlled by the control unit 8 so as to be coherent with the object light incident on the hologram memory 1 from the first light source 3. The third light source 5 is a light source for irradiating the hologram memory 2 with the second reference light at the time of coherent batch transfer from the hologram memory 1 to the hologram memory 2.

  The control unit 8 comprehensively controls the operation of the hologram memory device. Specifically, the control unit 8 controls the operations of the first light source 3, the second light source 4, the third light source 5, the SLM 6, and the random diffuser 7. The following hologram recording / transfer processing is performed under the control of the control unit 8.

  In the above description, the first light source 3 and the second light source 4 are described as separate light sources. However, actually, the laser light emitted from the first light source 3 and the second light source 4 is different. Hologram recording is not possible without interference. For this reason, the first light source 3 and the second light source 4 are configured to separate light emitted from a single light source into two lights using a beam splitter, a mirror, and the like, and to function as each light source. .

[Recording operation of multiple holograms to master hologram memory]
In the above hologram memory device, a recording operation of multiple holograms with respect to the hologram memory 1 will be described with reference to FIG.

  When recording multiple holograms in the hologram memory 1 serving as a master, as shown in FIG. 2, the light emitted from the first light source 3 is modulated by the SLM 6 in accordance with the data to be recorded to obtain signal light. . For example, when M-layer holograms are multiplexed and recorded, this signal light becomes signal light for M pages.

  The signal light is spatially modulated by the random diffuser 7 and then applied to the hologram memory 1. At this time, the first reference light emitted from the second light source 4 is simultaneously applied to the hologram memory 1. In the SSS multiplexing system, the phase of the first reference light is not changed, and the random diffuser 7 on the signal light side is slightly displaced to change the spatial phase modulated into the signal light for each hologram of each page.

  In the recording operation described above, the object light that has passed through the random diffuser 7 enters the hologram memory 1 together with the first reference light. Data in the object light is recorded as a hologram (refractive index grating) H induced according to the interference fringes of these two light waves. At this time, exposure scheduling for making the diffraction efficiency uniform is performed as in the case of other multiple recording.

[Coherent batch transfer of multiple holograms from master hologram memory to copy hologram]
The coherent batch transfer operation from the hologram memory 1 to the hologram memory 2 in the hologram memory device will be described with reference to FIG.

  In the coherent batch transfer operation, the first reference light emitted from the second light source 4 is applied to the hologram memory 1 as a master. Thereby, the recorded holographic holograms are collectively reproduced from the hologram memory 1, and this reproduced light (that is, the reproduced multiplex hologram) is irradiated to the hologram memory 2 serving as a copy. At this time, the hologram memory 2 is simultaneously irradiated with the second reference light emitted from the third light source 5.

  As described above, in the hologram memory 2, the reproduction light from the hologram memory 1 and the second reference light from the third light source 5 are simultaneously irradiated, so that the multiplexed hologram recorded in the hologram memory 1 is coherent. Batch transfer. In such batch transfer, it is not necessary to consider an exposure schedule when creating a copy.

  In the coherent batch transfer, since the reference light can be irradiated with the same wavelength and the same optical path, the problem that the optical system becomes complicated as in the conventional incoherent batch transfer can be avoided.

[Playback operation]
Next, the data reproduction operation for the hologram memory in which the multiple holograms are recorded will be described with reference to FIG.

  When data is reproduced from the hologram memory, the readout light is applied to the hologram memory 1 in which multiple holograms are recorded, and the excitation light is incident on the phase conjugate mirror 9. The reading light is incident on the hologram memory 1 from the same direction as the reference light used at the time of recording. The readout light is diffracted by the hologram H in the hologram memory 1, and the diffracted light enters the phase conjugate mirror 9.

  In the phase conjugate mirror 9, only when the diffracted light intensity is greater than the intensity threshold determined by the excitation light intensity, the mutual phase conjugation occurs through the mutual excitation type phase conjugation phenomenon caused by the incidence of the diffracted light and the excitation light. A hologram that generates light is generated. As a result, feedback light that is a phase conjugate of the diffracted light is generated, and automatically enters the phase matching condition of the hologram H recorded in the hologram memory 1.

  In the SSS multiplexing system according to the present invention, “phase conjugate reproduction” is essential for the reproduction operation. However, the above description illustrates the case where a “mutual excitation type” phase conjugator is used. The reproduction operation in this system is not limited to this, and can be applied to other phase conjugate reproduction.

In addition, there are roughly the following two methods to perform phase conjugate reproduction.
(1) A method of recording a hologram with a plane reference beam and reproducing it by irradiating a plane readout beam facing it (this method is used in this example).
(2) A method of recording a hologram with reference light having an arbitrary wavefront other than a plane, inputting the reference light to the phase conjugator, and then reproducing the hologram using the light wave returned from the phase conjugate mirror.

  Furthermore, although the phase conjugator (that is, the phase conjugate mirror 9) used in the above description is an active device to which excitation light is input from the outside, it is not necessarily such an active device. There is no need, and it is also possible to use a passive type called “self-excited phase conjugator” that does not require external pumping light.

  The feedback light transmitted through the hologram H in the hologram memory 1 is a phase conjugate of the object light and is output as output light through the beam splitter 3. Although this output light is a multiplex hologram, an arbitrary hologram can be selectively extracted from the multiplex hologram by the random diffuser 7 and restored. That is, by adjusting the position of the random diffuser 7, only one hologram at the same position as at the time of recording is selectively extracted, and reproduction is performed by detecting this hologram with the photodetector 10.

  FIG. 5 shows a configuration of a hologram memory device having a function of recording a multiplexed hologram in the hologram memory and a function of reproducing the multiplexed hologram recorded in the hologram memory. The hologram memory device shown in FIG. 5 includes a first light source 3, a second light source 4, a fourth light source 11, an SLM 6, a random diffuser 7, a control unit 8, a phase conjugate mirror 9, a photodetector 10, and a beam splatter 12. ing.

  In the hologram memory device configured as described above, the second light source 4 that irradiates the reference light during recording can also be used as the light source that irradiates the readout light to the hologram memory 1 during reproduction. A beam splitter 12 is disposed between the SLM 6 and the random diffuser 7. The beam splitter 12 has a function of causing the signal light emitted from the SLM 6 to enter the random diffuser 7 during recording and causing the output light emitted from the random diffuser 7 to enter the photodetector during reproduction. The fourth light source 11 is a light source for irradiating the phase conjugate mirror 9 with the excitation light described above.

In the above description, the reproducing operation with respect to the hologram memory 1 as a master has been described, but the reproducing operation can be performed in the same manner with respect to the hologram memory 2 as a copy if it is arranged at the same position as the master. When the reproducing function is added to the hologram apparatus having the configuration shown in FIG. 1, the configuration shown in FIG. 6 is used. In this case, the hologram memory 1 serving as the master has the same thickness as the hologram memory 1. It is also possible to reproduce the program memory 2 as a copy by placing a dummy medium having a refractive index. As yet another method, there is also a method of first recording multiple recordings on the master medium (hologram memory 1 in the above example) on the back side, and then transferring them collectively to the copy medium (hologram memory 2 in the above example) by phase conjugate reproduction. Conceivable.

[Diffraction efficiency enhancement effect]
Normally, the refractive index modulation of a hologram after multiple recording is the sum (incoherent sum) of interference fringe intensity patterns of signal light and reference light corresponding to each page. When the dynamic range when one hologram is recorded is Δn ₀ , when M holograms are multiplexed, the dynamic range assigned to one hologram is Δn ₀ / M, so that the diffraction efficiency is 1 / It decreases in proportion to M ² (see Non-Patent Document 7). The same applies to incoherent transfer.

On the other hand, in the case of coherent transfer as described above, the diffraction efficiency does not always follow the 1 / M ² rule. In this coherent batch transfer, if the signal light intensity per hologram in a multiplexed hologram reproduced from the master medium is I _i , the sum of the intensities of all the signal lights to be copied (signal lights of M holograms) Is MI _i . Further, in the coherent collective transfer, then the intensity I _ref of the second reference light applied to the copy medium, the ratio of r = MI between the intensity I _ref of the intensity sum of all of the signal light to be copied and the second reference light _{If i} / I _ref , the amplitude A _i diffracted from one hologram recorded in the master is

It is expressed. Here, φ _i is a phase corresponding to the signal light of amplitude A _i , and the phase φ _i modulated at the time of master recording has a spatial distribution orthogonal to each other. At this time, the dynamic range of the entire media after coherent transfer is

Can be written. A _i and A _j are the amplitude of the signal light, A _ref and I _ref are the amplitude and intensity of the reference light during transfer, and c.c. Represents a complex conjugate. That is, the amplitude sum (coherent sum) of multiple diffracted light is recorded as a hologram. The amplitude A _out of the multiple diffracted light reproduced by irradiating the reference hologram having the amplitude A _ref to the multiple hologram of the above formula (2) is:

It is. Here, the diffraction component Σ (A _i A _j ^* ) · A _ref of the reference light from the hologram (first term) written by the signal lights of the above formula (2) is speckle noise in the case of a thin hologram However, this noise was assumed to be negligible for thick holograms. When the cross-correlation of exp (φ _i ) is sufficiently low, multiplying the multiple diffracted light A _out by exp (−φ _k ) and back-diffusing results in a signal corresponding to the k-th hologram among the M holograms The light component A _{out k} can be selectively reproduced. Here, A _{out k} is expressed by the following equation (4).

  Therefore, the diffraction efficiency η per multiple hologram after coherent batch transfer is

It becomes. In the above formula (5), when the light intensity ratio at the time of copying is r = M, it is almost the same as the diffraction efficiency of incoherent recording, but when r = 1, the diffraction efficiency per hologram is maximized ( It can be seen that this diffraction efficiency is proportional to 1 / M (see FIG. 8). That is, the diffraction efficiency after coherent transfer is improved up to M times compared to the case of incoherent transfer.

[Multiple hologram batch transfer experiment]
Using the optical system shown in FIG. 9, the effect of enhancing the diffraction efficiency by coherent batch transfer was verified. First, only the shutters S1 and S4 were opened, the ground glass (Diffuser) was shifted by 50 [μm], and SSS multiple recording was performed on the master medium PRC1 (master photorefractive LiNbO ₃ crystal).

Here, if a strong (high diffraction efficiency) hologram is written on the master medium PRC1, the quality of the output image at the time of reproduction is deteriorated due to the scattering at the PRC1 due to the noise hologram. Multiple recordings were made. Light wave incidence conditions at the time of creating the master are: signal light power: 38 [μW], reference light 1 power: 650 [μW], beam diameter of reference light 1: 3 [mm], intersection angle of signal light and reference light: 55 [Degree], and the erase time constant of the Fe-doped LiNbO ₃ used was extremely slower than the recording time constant. Therefore, a special exposure schedule was not performed, and irradiation was performed 90 [s] each.

  Next, the shutter S1 was closed, only the shutters S2 and S4 were opened, and all the holograms were transferred from the master medium PRC1 to the copy medium PRC2. At the time of transfer, PRC 1 is irradiated with reference light 1: 7.2 [mW], adjusted to multiple diffracted light incident on PRC 2: 50 [μW], reference light 2: 260 [μW], and transfer exposure time is 330. [S].

After the copy hologram recording was completed, the shutters S2 and S4 were closed, and 260 [μW] readout light was irradiated for about 0.1 second each for phase conjugate reproduction, and the output light was measured. In order to avoid loss due to scattering, it is desirable to incoherently erase the master hologram of crystal 1 after transfer. However, since the erase time constant of the LiNbO ₃ crystal was slow this time, reproduction was performed without erasing the master hologram. .

  The measurement results are shown in Table 1 below. Further, measurement examples and output image examples when M = 5 are shown in FIGS. 10 and 11, respectively. From the results of Table 1, it can be seen that even when the number of multiplexing M increases, the total output light does not decrease, and the output light power per hologram is 1 / M. The measurement example in FIG. 10 is a measurement result of the output power after coherent batch transfer, and the horizontal axis indicates the elapsed time from the start of measurement. In this measurement example, the small intensity peak shown on the rightmost side in the figure represents a crosstalk component.

FIG. 12 shows a comparison of normalized diffraction efficiency after normal SSS multiplexing and coherent batch transfer. In ordinary SSS multiplex recording, the diffraction efficiency is only slightly higher than 1 / M ² , but the diffraction efficiency after coherent batch transfer almost completely matches the 1 / M curve. Can be confirmed to be greatly improved.

  The hologram memory device according to the present invention can be used as an information recording / reproducing device which is required to record a large amount of data and to perform a high data recording speed and a high data reading speed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, showing an embodiment of the present invention, is a block diagram showing a main configuration of a hologram memory device. It is a figure which shows the recording operation in the said hologram memory apparatus. It is a figure which shows the transfer operation in the said hologram memory apparatus. It is a figure which shows the reproduction | regeneration operation | movement in the said hologram memory apparatus.

FIG.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, showing an embodiment of the present invention, is a block diagram showing a main configuration of a hologram memory device. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, showing an embodiment of the present invention, is a block diagram showing a main configuration of a hologram memory device. It is a graph which shows the relationship between light intensity ratio and diffraction efficiency. It is a graph which shows the relationship between a hologram multiplexing number and diffraction efficiency. It is a figure which shows the optical system used in the multiple hologram batch transfer experiment. It is a graph which shows the example of a measurement when M = 5 in the above-mentioned multiple hologram batch transfer experiment. It is a figure which shows the example of the output image in the said multiple hologram batch transfer experiment. It is a graph which shows the comparison of the normalized diffraction efficiency after SSS multiplexing and coherent batch transfer.

Explanation of symbols

1 Hologram memory (master hologram memory)
2 Hologram memory (copy hologram memory)
3 First light source 4 Second light source (first reference light source)
5 Third light source (second reference light source)
6 SLM
7 Random Diffuser 8 Control Unit 9 Phase Conjugate Mirror 10 Photodetector 11 Fourth Light Source 12 Beam Splitter

Claims (3)

In a multiple hologram transfer apparatus for transferring a multiple hologram recorded in a master hologram memory by a spatial spread spectrum multiplexing method to a copy hologram memory,
A first reference light source that irradiates the master hologram memory with the first reference light and reproduces the recorded multiple holograms at once;
A second reference light source for irradiating the copy hologram memory with a second reference light capable of causing interference with the first reference light;
The multiple hologram reproduced from the master hologram memory and the second reference light are simultaneously irradiated to the copy hologram memory, and the multiple holograms are collectively transferred to the copy hologram memory,
The multiplex hologram is obtained by multiplexing M holograms,
The intensity sum of all the signal lights of the multiplexed hologram reproduced from the master hologram memory is MI _i , and the intensity I _ref of the second reference light irradiated to the copy hologram memory, When the light intensity ratio with the intensity I _ref of the two reference lights is r = MI _i / I _ref
The multiple hologram transfer device, wherein the emitted light intensity of the first reference light source and the second reference light source is set so that the light intensity ratio r is r = 1 . In a multiple hologram transfer method for transferring a multiple hologram recorded in a master hologram memory by a spatial spread spectrum multiplexing method to a copy hologram memory,
Irradiating the master hologram memory with the first reference light to reproduce the recorded multiple holograms at once,
A multiplex hologram transfer method comprising: irradiating the copy hologram memory with the multiplex hologram and second reference light and collectively transferring the multiplex holograms reproduced from the master hologram memory to the copy hologram memory. The multiplex hologram is obtained by multiplexing M holograms,
The intensity sum of all the signal lights of the multiplexed hologram reproduced from the master hologram memory is MI _i , and the intensity I _ref of the second reference light irradiated to the copy hologram memory, When the light intensity ratio with the intensity I _ref of the two reference lights is r = MI _i / I _ref
3. The multiple hologram transfer method according to claim 2 , wherein the light intensity ratio r is set to r = 1.