WO2013008453A1

WO2013008453A1 - Holographic memory recording method and reproduction method, and holographic memory recording device and reproduction device

Info

Publication number: WO2013008453A1
Application number: PCT/JP2012/004455
Authority: WO
Inventors: 岡本　淳; 圭佑瑞慶覧; 高林　正典; 敦史渋川
Original assignee: 国立大学法人北海道大学
Priority date: 2011-07-11
Filing date: 2012-07-10
Publication date: 2013-01-17
Also published as: JPWO2013008453A1; JP5988054B2

Abstract

A hologram (A) generated by a signal beam and a partial reference beam (A), and a hologram (B) generated by an interference beam and a partial reference beam (B) are recorded in a specific location in a holographic memory. The specific location in the holographic memory is simultaneously irradiated with the partial reference beam (A) and the partial reference beam (B), simultaneously generating diffracted light of the hologram (A) and diffracted light of the hologram (B). From the diffracted light of the hologram (A) and the diffracted light of the hologram (B), the phase modulated signal contained in the signal beam is demodulated.

Description

Holographic memory recording method and reproducing method, and holographic memory recording device and reproducing device

The present invention relates to a holographic memory recording method and reproducing method, and a holographic memory recording device and reproducing device.

So far, optical memory has been developed mainly for optical disks of two-dimensional recording system such as CD, DVD and Blu-ray disc. However, the optical memory of the two-dimensional recording system has already reached the diffraction limit, and it is difficult to increase the capacity beyond this. In recent years, therefore, development of an optical memory of a three-dimensional recording system has been actively conducted. If the three-dimensional recording method is adopted, there is a possibility that the recording capacity can be increased 100 to 1000 times or more than that of the two-dimensional recording method. Theoretically, a 100 TB class optical disk memory can be realized.

There are three technologies for increasing the capacity of optical memories: 1) near-field optical recording, 2) two-photon absorption memory, and 3) holographic memory. 1) The near-field light recording method is a recording method using “near-field light” which is light having a wavelength equal to or smaller than the wavelength of light. Near-field optical recording is basically a two-dimensional recording technique, but there is a possibility that high-density recording exceeding the diffraction limit can be realized by using near-field light. 2) The two-photon absorption memory is a three-dimensional recording type optical memory that can access a recording medium three-dimensionally by utilizing the intensity dependency of the nonlinear effect. In contrast to these technologies, 3) a holographic memory can perform three-dimensional recording without multi-layering a recording medium by multiplex recording a hologram generated by interference between signal light and reference light. It is an optical memory that can be used.

All of the optical memories 1) to 3) have achieved a recording capacity of about 500 GB to 1 TB at present. Therefore, from the viewpoint of recording capacity, there is no significant difference between the optical memories 1) to 3). However, from the viewpoint of data transfer speed, among the optical memories 1) to 3), a holographic memory having a spatially two-dimensional massively parallel input / output function has a great advantage. Recently, a spatial light modulator (Spatial Light Modulator; hereinafter abbreviated as “SLM”) having a response time exceeding microseconds has been developed. By applying such a high-speed response SLM to the holographic memory, there is a possibility that a transfer rate exceeding 100 Gbps can be realized.

Holographic memory is expected to be put to practical use as a next-generation optical memory because it can realize both high-density recording and high data transfer rate. The recording capacity of the currently developed holographic memory is about 600 GB to 1 TB / disk (for example, see Non-Patent Document 1). Since the recording capacity of one side of one platter of HDD (3.5 inch, storage capacity 2 TB) is 333 GB, the holographic memory is in terms of recording capacity compared to a magnetic recording medium in practical use. There is an advantage of about 2 to 3 times. The holographic memory is theoretically considered to be able to expand the recording capacity up to 10 to 100 times. Under such circumstances, for the purpose of increasing the recording capacity of the holographic memory, not only the conventional intensity modulation system but also a phase modulation holographic memory has been studied. However, the phase modulation type holographic memory cannot detect the phase modulation signal directly by the photodetector, and therefore has a problem that it must be detected after converting the phase modulation signal into an intensity signal by some method. there were.

The intensity modulation method is the most common modulation method, and many examples have been reported so far (see, for example, Non-Patent Documents 1 to 3). Holography was used from literature (Non-Patent Document 2) that first suggested that information can be recorded using holography to recent literature (Non-Patent Documents 1 and 3) with a view to commercialization. Many of the recording methods use binary (0 and 1) intensity modulation. However, while intensity modulation has the advantage that a system can be constructed with a simple optical system, the difference in exposure intensity between the central and peripheral areas of the laser light irradiation area increases, greatly consuming the dynamic range of the recording medium. Therefore, there is a problem that the recording efficiency is poor. This problem is that in general Fourier transform holograms, the intensity near the center of the Fourier transform image is proportional to the sum of the amplitudes of all pixels, so the difference in exposure intensity between the center of the laser light irradiation area and the peripheral area is small. This occurs because of an increase in size (for example, see Non-Patent Document 4).

As a technique to alleviate the problem of this intensity modulation method, a modulation code that expresses data by dispersing binary information into a plurality of pixels called blocks and coding them, and illuminating only some of the pixels in the block. There is a method of using. By using the modulation code in this way, errors due to inter-pixel crosstalk can be reduced. In addition, by using the modulation code, efficient recording can be performed by reducing the difference in exposure intensity between the central portion and the peripheral portion of the laser light irradiation region and increasing the number of multiple recordings (for example, non-recording). (See Patent Documents 5 and 6). However, when a modulation code is used, the code rate defined by “(number of recording bits per block) / (number of pixels per block)” is less than 1. This means that the recording capacity per block when the modulation code is used is in principle lower than the recording capacity when the modulation code is not used.

In order to expand the recording capacity of the holographic memory, a method of recording a plurality of information per pixel, that is, a code rate exceeding 1 is required. In order to realize a code rate exceeding 1, it is necessary to use a multilevel signal exceeding 0 and 1 binary values. A multi-level signal can be realized by dividing the light intensity into several stages, and thereby the code rate can be dramatically improved. However, in the current direct detection method, due to the accuracy and noise of the detection system, the signal-to-noise ratio of the reproduction light is greatly degraded due to an increase in the multi-value number (see, for example, Non-Patent Document 7).

In the intensity modulation method, the problem that the difference in exposure intensity between the central portion and the peripheral portion of the laser light irradiation area becomes large and consumes a large dynamic range of the recording medium can be solved by the phase modulation method. it can. The phase modulation method is a method of performing modulation using the phase of a light wave, and has recently attracted attention. In the phase modulation method, when the phase of the light wave of a certain pixel is 0, information is expressed by setting the phase of the light wave of another pixel as π. When the number of 0 and π pixels is the same among the pixels included in the two-dimensional page data generated by the spatial light modulator (SLM), the difference in exposure intensity between the center and the periphery of the laser light irradiation area Therefore, useless consumption of the dynamic range of the recording medium can be suppressed. This point greatly contributes to an increase in the number of multiplexed recordings. However, since a photoelectric conversion device such as a CCD has sensitivity only to the intensity of light, phase information cannot be directly detected. Therefore, in order to detect the phase information, the phase must be converted into intensity before light detection is performed. This is a major problem with the phase modulation method.

Several phase detection methods for realizing a phase modulation holographic memory have been proposed so far (see, for example, Non-Patent Documents 4, 8 to 10).

Non-Patent Document 4 proposes an edge-detection method as a phase detection method used for a holographic memory. Non-Patent Document 8 proposes a phase detection method using a birefringent medium. However, these methods have a problem that they are not suitable for detecting a multilevel phase modulation signal, which is an essential element for increasing the capacity of a holographic memory.

Non-Patent Document 9 proposes an optical phase-locked collinear holographic method as a phase modulation type holographic memory specialized for a collinear optical system that is attracting attention as a one-beam recording method. In this method, at the time of reproduction of the holographic memory, the recorded hologram is simultaneously irradiated with interference light having a known phase called phase-locked light in addition to normal collinear reference light on the recorded hologram. This is a method of reading information as intensity information. In this method, since the phase-locked light is transmitted through the recorded hologram, the phase distribution of the phase-locked light is affected by the propagation in the hologram having the phase diffraction grating. This can cause a phase error on the detection surface. Moreover, the hologram recorded by this method must be reproduced by an apparatus having a function of generating phase-locked light. Since the beam diameter of the phase-locked light is different from the beam diameter of the reference light, this type of reproducing apparatus is not compatible with the reproducing apparatus of the intensity modulation type hologram memory.

Non-Patent Document 10 proposes a dual stage holography method. In this method, a spatial quadrature amplitude modulation signal including multilevel phase modulation is optically recorded, and at the time of reproduction, the optically recorded hologram is transferred to the second-stage hologram and reproduced. Also in this method, in order to generate the second stage hologram, reference light (light that interferes with the diffracted light of the first stage hologram) different from the reference light used for reproducing the first stage hologram is required. . However, unlike the optical phase lock method, the reference light necessary for generating the second-stage hologram does not pass through the recorded hologram, and thus is not affected by the phase error caused by propagating through the hologram. On the other hand, similar to the optical phase-lock method, since a reference beam different from the first-stage hologram reproduction is required to generate the second-stage hologram, this type of reproduction apparatus also uses an intensity-modulated hologram. Incompatible with memory playback device.

As described above, the conventional intensity-modulated holographic memory has a large exposure intensity difference between the central portion and the peripheral portion of the laser light irradiation region, and consumes a large dynamic range of the recording medium. There is a problem that the efficiency of multiple recording is poor. In the method using the modulation code, the above problem can be avoided, but there is a problem that the recording capacity is reduced because the code rate per block is lowered. In order to increase the code rate, it is necessary to use a multilevel intensity signal, but an intensity modulation type holographic memory having a large multilevel number has not been realized due to the accuracy and noise of the detection system.

The phase modulation holographic memory can solve these problems. However, the phase modulation type holographic memory has a problem that in order to detect phase information, it is necessary to convert the phase into intensity before performing light detection. In addition, when detecting the intensity signal after conversion, there are problems of accuracy and noise of the detection system as in the case of the intensity modulation type holographic memory. As a result, a phase modulation holographic memory having a large multilevel number has not been realized.

As optical holographic memories that can handle multi-level phase modulation signals, optical phase-locked holographic methods and dual-stage holographic methods have been proposed. However, as described above, a hologram recorded by this method must be reproduced by a device having a function of generating interference light (phase-locked light or second reference light). For this reason, the reproducing apparatus of these systems is not compatible with the reproducing apparatus of the intensity modulation type hologram memory.

An object of the present invention is to provide a holographic memory recording method and reproducing method, and a holographic memory recording apparatus and reproducing device capable of precisely reproducing multi-level phase information using one reference beam. That is.

The inventor records the hologram B generated by the interference light and the reference light, in addition to the hologram A generated by the signal light and the reference light, in the same location of the holographic memory. The present invention has been completed by finding out that the problem can be solved and further studying it.

That is, the present invention relates to the following holographic memory recording method.
[1] The signal light including the spatial phase modulation signal or the spatial quadrature amplitude modulation signal and the partial reference light A are irradiated to a specific portion of the holographic memory, and generated by the signal light and the partial reference light A. Recording the hologram A; irradiating the specific portion of the holographic memory with interference light and partial reference light B, and recording the hologram B generated by the interference light and partial reference light B And a holographic memory recording method.
[2] The partial reference light A is a part of the laser light emitted from the laser light source; the partial reference light B is a part of the remaining part of the laser light emitted from the laser light source. [1] A recording method of a holographic memory according to [1].
[3] The holographic memory recording method according to [1] or [2], wherein the hologram A and the hologram B are recorded in the holographic memory by a collinear holography method.

The present invention also relates to a method for reproducing the following holographic memory.
[4] A method for reproducing a holographic memory in which a spatial phase modulation signal or a spatial quadrature amplitude modulation signal is recorded by the holographic memory recording method according to any one of [1] to [3], wherein: The partial reference light A and the partial reference light B are simultaneously irradiated onto a specific portion of the holographic memory, and the diffracted light of the hologram A and the diffracted light of the hologram B that can interfere with the diffracted light of the hologram A And simultaneously demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal using the diffracted light of the hologram A and the diffracted light of the hologram B. .
[5] The spatial phase modulation signal or the spatial quadrature amplitude modulation signal includes binary phase information; and demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal includes diffracted light of the hologram A and The method for reproducing a holographic memory according to [4], comprising: generating an interference fringe from the diffracted light of the hologram B; and detecting an intensity distribution of the interference fringe.
[6] The spatial phase modulation signal or the spatial quadrature amplitude modulation signal includes multi-level phase information; and demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal includes diffracted light of the hologram A and A step of generating a hologram C from the diffracted light of the hologram B, a step of detecting an intensity distribution of the hologram C, and a demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal based on the intensity distribution The method for reproducing a holographic memory according to [4], including the step of:
[7] In the step of simultaneously generating the diffracted light of the hologram A and the diffracted light of the hologram B, the partial reference light while shifting the phase of the partial reference light A or the partial reference light B to the specific location A plurality of combinations of the diffracted light of the hologram A and the diffracted light of the hologram B having different phases of the diffracted light of the hologram A or the hologram B by irradiating A and the partial reference light B simultaneously at a plurality of times In the step of generating and generating the hologram C, a plurality of holograms C having different intensity distributions are generated from the plurality of combinations, and in the step of detecting the intensity distribution of the hologram C, each of the plurality of holograms C is generated. Detecting the intensity distribution of the signal and demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal. , Based on the plurality of intensity distribution, said demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal, a holographic memory reproducing method according to [6].
[8] The interference light includes a plurality of subpixels having different phases with respect to one data pixel of the signal light, and the diffracted light of the hologram B is related to one data pixel of the diffracted light of the hologram A. The hologram C includes a plurality of sub-pixels having different phases, the hologram C includes a plurality of hologram information having different phases, and is included in the hologram C in the step of demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal The method for reproducing a holographic memory according to [6], wherein the spatial phase modulation signal or the spatial quadrature amplitude modulation signal is demodulated based on a plurality of hologram information.
[9] The signal light includes a plurality of subpixels having different phases with respect to one data pixel, and the diffracted light of the hologram A includes a plurality of subpixels having different phases with respect to one data pixel, The hologram C includes a plurality of hologram information having different phases, and in the step of demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal, the space C is based on the plurality of hologram information included in the hologram C. The method for reproducing a holographic memory according to [6], wherein the phase modulation signal or the spatial quadrature amplitude modulation signal is demodulated.
[10] The partial reference light A is a part of the laser light emitted from the laser light source; the partial reference light B is a part of the remaining part of the laser light emitted from the laser light source. [4] The reproduction method of a holographic memory according to any one of [9].
[11] The method for reproducing a holographic memory according to any one of [4] to [10], wherein the hologram A and the hologram B are reproduced from the holographic memory by a collinear holography method.

The present invention also relates to the following holographic memory recording apparatus.
[12] The signal light including the spatial phase modulation signal or the spatial quadrature amplitude modulation signal and the partial reference light A are irradiated to a specific portion of the holographic memory, and generated by the signal light and the partial reference light A. Hologram A recording unit for recording hologram A; Hologram B generated by irradiating interference light and partial reference light B to the specific location of the holographic memory and generating the interference light and partial reference light B A holographic memory recording apparatus, comprising:

The present invention also relates to the following holographic memory reproducing device.
[13] A holographic memory reproducing device in which a spatial phase modulation signal or a spatial quadrature amplitude modulation signal is recorded by the holographic memory recording device according to [12], wherein: A hologram diffracted light generator that simultaneously irradiates the reference light A and the partial reference light B to simultaneously generate the diffracted light of the hologram A and the diffracted light of the hologram B that can interfere with the diffracted light of the hologram A; A holographic memory reproducing apparatus comprising: a demodulator that demodulates the spatial phase modulation signal or the spatial quadrature amplitude modulation signal using the diffracted light of the hologram A and the diffracted light of the hologram B;

According to the present invention, multi-level phase information can be accurately reproduced using a single reference beam. Therefore, according to the present invention, a holographic memory in which a spatial phase modulation signal or a spatial quadrature amplitude modulation signal is recorded can be reproduced with high accuracy.

1A and 1B are schematic diagrams illustrating examples of reference light. 2A and 2B are schematic diagrams showing how a phase modulation signal is recorded in a holographic memory. It is a schematic diagram which shows a mode that the phase modulation signal currently recorded on the holographic memory is reproduced | regenerated. It is a schematic diagram which shows a mode that the phase modulation signal currently recorded on the holographic memory is reproduced | regenerated. 5A and 5B are schematic diagrams showing a conventional reproducing method, and FIG. 5C is a schematic diagram showing a reproducing method according to the present invention. The schematic diagram which shows a mode that it records and reproduces by a collinear holography method. FIG. 7A is a diagram showing a pattern of the spatial light modulator when recording is performed by the collinear holography method, and FIG. 7B is a diagram showing a pattern of the spatial light modulator when reproducing is performed by the collinear holography method. It is a figure which shows the pattern of the spatial light modulator in the case of combining the recording method of this invention, and a collinear holography method. It is a schematic diagram which shows a mode that page data is recorded combining the recording method of this invention, and a collinear holography method. It is a schematic diagram which shows a mode that page data is reproduced | regenerated combining the reproduction | regenerating method of this invention, and a collinear holography method. It is a schematic diagram which shows a mode that page data is recorded combining the recording method of this invention, and 2 light beam interferometry. It is a schematic diagram which shows a mode that page data is reproduced | regenerated combining the reproduction | regenerating method of this invention and the two light beam interferometry. It is a schematic diagram which shows a mode that a phase modulation signal is demodulated in direct detection mode. It is a schematic diagram which shows a mode that a phase modulation signal is demodulated in multi-shot dual stage mode. It is a schematic diagram which shows a mode that a phase modulation signal is demodulated in single shot dual stage mode. 16A and 16B are diagrams showing an example of the phase distribution of signal light and interference light in the single shot / dual stage mode. 17A and 17B are diagrams illustrating an example of the phase distribution of signal light and interference light in the single shot / dual stage mode. FIG. 18A and FIG. 18B are schematic diagrams showing examples of reference light division patterns. 2 is a diagram of a 16-value spatial quadrature amplitude modulation signal (16-SQAM) used in Example 1. FIG. FIG. 20A is a diagram showing phase information of original page data, and FIG. 20B is a diagram showing amplitude information of original page data. FIG. 21A is a diagram showing an intensity pattern of partial reference light A, and FIG. 21B is a diagram showing an intensity pattern of partial reference light B. 22A to 22D are diagrams showing signal intensity distributions of the second-stage hologram (digital hologram) (reproduction in multi-shot / dual-stage mode). FIG. 23A is a diagram showing phase information of demodulated page data, and FIG. 23B is a diagram showing amplitude information of demodulated page data (reproduction in multi-shot dual stage mode). It is a graph which shows the signal point distribution of the demodulated page data (reproduction | regeneration by multi-shot dual stage mode). It is a figure which shows signal intensity distribution of the hologram (digital hologram) of the 2nd step (reproduction | regeneration by a single shot dual stage mode). FIG. 26A is a diagram showing phase information of demodulated page data, and FIG. 26B is a diagram showing amplitude information of demodulated page data (reproduction in single shot / dual stage mode). It is a graph which shows the signal point distribution of the demodulated page data (reproduction by a single shot dual stage mode). 28A is a diagram showing the phase information of the original page data # 1, FIG. 28B is a diagram showing the phase information of the original page data # 2, and FIG. 28C is the phase information of the original page data # 3. It is a figure which shows information (reproduction | regeneration of the multiplex recording signal by multi-shot dual stage mode). FIG. 29A is a diagram illustrating phase information (analog data) of demodulated page data # 1, FIG. 29B is a diagram illustrating phase information (analog data) of demodulated page data # 2, and FIG. It is a figure which shows the phase information (analog data) of the demodulated page data # 3 (reproduction | regeneration of the multiplex recording signal by multi-shot dual stage mode). 30A is a diagram showing phase information (digital data) of demodulated page data # 1, FIG. 30B is a diagram showing phase information (digital data) of demodulated page data # 2, and FIG. It is a figure which shows the phase information (digital data) of demodulated page data # 3 (reproduction | regeneration of the multiplex recording signal by a multi-shot dual stage mode). 31A is a graph showing the signal point distribution of demodulated page data # 1, FIG. 31B is a graph showing the signal point distribution of demodulated page data # 2, and FIG. 31C is demodulated page data # 3. 5 is a graph showing the signal point distribution of (multi-shot / dual stage mode reproduction of multiple recording signals). FIG. 6 is a schematic diagram showing a configuration of a holographic memory recording / reproducing apparatus used in Example 3. It is a figure which shows the pattern of phase modulation SLM at the time of recording the hologram B. FIG. 34A and 34B are diagrams showing patterns of the phase modulation SLM when the hologram A is recorded. FIGS. 35A and 35B are diagrams showing patterns of the phase modulation SLM when the hologram A and the hologram B are reproduced. 36A and 36B are images showing the detected signal page data (reproduction in the direct detection mode). FIG. 37A and FIG. 37B are images showing the results of performing threshold processing on the images shown in FIG. 36A and FIG. 36B, respectively (reproduction in the direct detection mode). 38A is a diagram illustrating phase information of original page data, FIG. 38B is a diagram illustrating an intensity pattern of interference light, and FIGS. 38C to 38E are diagrams illustrating intensity patterns of reference light. 38F is a diagram showing a signal intensity distribution of the second-stage hologram (digital hologram) (reproduction in the direct detection mode). 39A and 39F show the amplitude information and phase information of the original page data # 1, FIG. 39B and FIG. 39G show the amplitude information and phase information of the original page data # 2, and FIG. 39C and FIG. 39D and 39I show the amplitude information and phase information of the original page data # 3. FIGS. 39D and 39I show the amplitude information and phase information of the original page data # 4. FIGS. 39E and 39J show the original page data # 3. 5 shows amplitude information and phase information. 40A shows the phase information of the signal page data # 1, FIG. 40B shows the phase distribution added to the signal light, and FIG. 40C shows the signal page after adding the phase distribution to the phase information of the signal page data # 1. This is phase information of data # 1. 41A shows the phase information of the interference light, and FIG. 41B shows the phase distribution added to the interference light. 42A and 42B are graphs showing signal point distributions of demodulated page data.

The recording method of the holographic memory of the present invention (hereinafter also referred to as “recording method of the present invention”) is a method of recording a spatial phase modulation signal or a spatial quadrature amplitude modulation signal in the holographic memory. The holographic memory reproduction method of the present invention (hereinafter also referred to as “reproduction method of the present invention”) reproduces a spatial phase modulation signal or a spatial quadrature amplitude modulation signal recorded in the holographic memory by the recording method of the present invention. It is a method to do. Here, the “spatial phase modulation signal” refers to a signal modulated by spatial phase modulation (SPM). A “spatial quadrature amplitude modulation signal” refers to a signal modulated by spatial quadrature amplitude modulation (SQAM).

“Phase modulation (hereinafter abbreviated as“ PM ”)” is a phase modulation, phase shift modulation (PSM) or phase shift used in the field of communication technology such as wireless communication and optical communication. This is a modulation method by keying (Phase Shift Keying; PSK). The PM transmits information by changing the phase of the carrier wave. In the holographic memory of the present invention, signal light whose phase is changed is recorded in the same manner as PM used in the field of communication technology. However, in the holographic memory, unlike communication that modulates a signal in the time axis direction, the signal is modulated in a two-dimensional spatial axis direction (x, y), and is recorded and reproduced as page data. Therefore, in the present specification, in order to distinguish the modulation method by phase modulation used in the present invention from “phase modulation (PM)” used in the field of communication technology, “spatial phase modulation (SPM)” is used. " SPM includes the concept of phase modulation and multi-level phase modulation used in the optical memory field.

“Quadrature Amplitude Modulation” (hereinafter abbreviated as “QAM”) is used in the field of communication technologies such as wireless communication and optical communication, and is used for amplitude modulation (AM) and phase modulation (Phase Modulation). PM) in combination. QAM can transmit a plurality of information at a time by changing both amplitude and phase elements. In the holographic memory of the present invention, a signal in which both amplitude and phase elements are changed is recorded, similarly to QAM used in the field of communication technology. However, in the holographic memory, unlike communication that modulates a signal in the time axis direction, the signal is modulated in a two-dimensional spatial axis direction (x, y), and is recorded and reproduced as page data. Therefore, in this specification, in order to distinguish the modulation method combining amplitude modulation and phase modulation used in the present invention from “quadrature amplitude modulation (QAM)” used in the field of communication technology, “spatial quadrature amplitude” is used. Modulation (Spatial Quadrature Amplitude Modulation; SQAM) ".

The recording method and the reproducing method of the present invention are characterized by using reference light including two partial reference lights, partial reference light A and partial reference light B. For this reason, the recording method and the reproducing method of the present invention are also referred to as double reference holography. In the reproducing method of the present invention, signal light and interference light are multiplexed and recorded in advance using two partial reference lights, so that interference light (for example, phase-locked light) is not irradiated from the outside during reproduction. The spatial phase modulation signal and the spatial quadrature amplitude modulation signal can be demodulated.

As shown in FIG. 1A, in the recording method and reproducing method of the present invention, one reference light 100 is divided into two parts, a partial reference light A110 and a partial reference light B120. The shapes of the partial reference light A110 and the partial reference light B120 (the shape in the cross section orthogonal to the optical axis of the reference light 100) are not particularly limited as long as they do not overlap each other. Further, the light intensity distribution and the light phase distribution in the partial reference light A110 and the partial reference light B120 are not particularly limited. For example, as shown in FIG. 1B, the partial reference light A110 and the partial reference light B120 may have a binary random intensity distribution.

When recording a phase modulation signal (spatial phase modulation signal or spatial quadrature amplitude modulation signal) in the holographic memory (recording medium), as shown in FIG. 2A, the phase modulation signal 130 ( The signal light 140 including the page data) and the partial reference light A110 are irradiated. Thus, the hologram A generated by the interference between the signal light 130 and the partial reference light A110 is recorded at a specific location of the holographic memory 200.

Further, as shown in FIG. 2B, the same portion of the holographic memory 200 is irradiated with the interference light 150 and the partial reference light B120. Accordingly, the hologram B generated by the interference between the interference light 150 and the partial reference light B120 is recorded at the same location of the holographic memory 200. The interference light 150 does not include information to be recorded. For example, the interference light 150 is light having a uniform light intensity distribution and phase distribution.

The recording order of hologram A and hologram B is not particularly limited. For example, the hologram B may be recorded after the hologram A is recorded. Further, the hologram A may be recorded after the hologram B is recorded.

When reproducing the phase modulation signal 130 recorded in the holographic memory, as shown in FIG. 3, the reference light 100 including the partial reference light A110 and the partial reference light B120 is irradiated to the same portion of the holographic memory 200. To do. Thereby, the diffracted light 160 (signal light 140) of the hologram A and the diffracted light 170 (interference light 150) of the hologram B are generated simultaneously. The diffracted light 170 of the hologram B needs to be light that can interfere with the diffracted light 160 of the hologram A. Therefore, normally, the light source of the partial reference light A110 and the light source of the partial reference light B120 are the same laser light source.

When the phase modulation signal 130 included in the signal light 140 is a binary phase modulation signal, phase information (for example, 0 and π) is included due to interference between the diffracted light 160 of the hologram A and the diffracted light 170 of the hologram B. The diffracted light 160 of the hologram A is converted into diffracted light 180 (interference fringes) including intensity information (for example, 0 and 1) (see FIG. 3). In this case, the phase intensity signal 130 can be demodulated by detecting the intensity distribution of the diffracted light 180 (interference fringes) by the light intensity detector 210 (an imaging device such as a CCD or CMOS).

On the other hand, when the phase modulation signal 130 included in the signal light 140 is a multi-level phase modulation signal, the diffracted light 160 of the hologram A functions as a new signal light as shown in FIG. The light 170 functions as new reference light, so that a second-stage hologram 220 (hologram C) is generated. In this case, the phase modulation signal 130 can be demodulated by performing electronic signal processing (described later) after the light intensity detector detects the intensity distribution of the second stage hologram 220 (hologram C). .

The diffracted light 170 of the hologram B is an interference light used when converting the diffracted light 160 of the hologram A including phase information into a diffracted light 180 (interference fringe) including intensity information, or the diffracted light 160 to 2 of the hologram A. It functions as reference light used when generating the stage hologram 220 (hologram C). Therefore, when recording the hologram B in the holographic memory 200, the holographic memory 200 is irradiated with the interference light 150 having an intensity distribution and a phase distribution capable of realizing these functions.

As shown in FIG. 5A, in the conventional dual-stage reproduction method (see Non-Patent Document 10), the second reference light necessary for multi-level phase detection is supplied from the outside. As described above, when the second reference light is separately supplied from the outside as the reference light that interferes with the signal light, the optical system becomes complicated, so that it may be weak against vibration and air fluctuation.

As shown in FIG. 5B, in the conventional phase-locked reproduction method (see Non-Patent Document 9), phase-locked light necessary for multi-level phase detection is supplied from the outside and transmitted through the holographic memory 200. . As described above, when the light transmitted through the holographic memory 200 is used as the phase-locked light that interferes with the signal light, phase distortion due to transmission through the holographic memory 200 may occur.

On the other hand, in the reproducing method of the present invention, as shown in FIG. 5C, the reference light for generating the second stage hologram (hologram C) necessary for multilevel phase detection is recorded in the holographic memory 200. Is supplied as diffracted light of the hologram B. Therefore, in the reproducing method of the present invention, it is not necessary to supply the reference light for generating the second stage hologram (hologram C) from the outside, and the optical system can be simplified. In addition, since phase distortion does not occur in the reference light (diffracted light of hologram B), the quality of the reference light can be improved.

In reproduction of a holographic memory, in a conventional phase-locked reproduction method (see Non-Patent Document 9) and a conventional dual-stage reproduction method (see Non-Patent Document 10), reference light and interference light (phase-locked light or Two light beams (second reference light) are required. Moreover, since these two beams must interfere with each other, they need to be emitted from the same light source. For this reason, the reproducing device of the intensity modulation type holographic memory can reproduce the hologram by one reference light, whereas the reproducing device of the phase modulation type holographic memory increases the number of light beams for reproduction. The configuration becomes complicated, and precise adjustment of the optical system is also required. This means that the conventional intensity modulation type holographic memory reproducing apparatus cannot reproduce the holographic memory in which the phase modulation signal is recorded.

On the other hand, in the reproducing method of the present invention, only reference light for reproducing the first-stage hologram (hologram A and hologram B) is required. In the reproducing method of the present invention, the configuration of the holographic memory reproducing apparatus is greatly simplified, and the light source and the optical system at the time of reproduction have high compatibility with the reproducing apparatus of the conventional intensity modulation type holographic memory.

Further, when the recording medium is a movable medium such as an optical disk, the conventional phase-locked reproducing method and the conventional dual-stage reproducing method, when the recording medium moves or rotates, the diffracted light from the recording medium ( There is a possibility that the wavefront component of the signal light will change over time. For this reason, it is very difficult to always match the wavefront of the signal light with the wavefront of the interference light (phase-locked light or second reference light).

On the other hand, in the reproducing method of the present invention, in addition to the hologram A generated by the signal light and the partial reference light A, the hologram B generated by the interference light and the partial reference light B is recorded on the same recording medium. Phase detection is performed by interference between diffracted lights obtained by reproducing simultaneously. Therefore, in the reproducing method of the present invention, the signal light and the interference light are reproduced as diffracted light from the same recording medium. Therefore, even if the recording medium is a movable medium such as an optical disk, the relative relationship between the signal light and the interference light is The positional relationship is always constant, and stable and highly accurate signal reproduction is possible.

The recording method and reproducing method of the present invention can realize not only an increase in storage capacity due to a multi-level phase modulation signal but also an increase in storage capacity due to multiple recording. In the description so far, the case where one signal light is recorded for one interference light has been described. However, in the recording method of the present invention, a plurality of signal lights are multiplexed and recorded for one interference light. You can also.

For example, by using the partial reference light B120 shown in FIG. 1B, the hologram B generated by the interference light 150 and the partial reference light B120 is recorded in a specific location of the holographic memory 200 (see FIG. 2B). Next, the first signal page data 130-1 is recorded in the same location of the holographic memory 200 using the first partial reference light A110-1 shown in FIG. 1B (see FIG. 2A). 1B is used as the second partial reference light A110-2 to change the second signal reference data 130-2 to the same location in the holographic memory 200. Record (see FIG. 2A). 1B is used as the third partial reference light A110-3 to change the third signal page data 130-3 to the same location in the holographic memory 200. (See FIG. 2A).

At this time, the following four holograms are recorded in the holographic memory 200.
a) Hologram generated by the interference light 150 and the partial reference light B120 (hologram B)
b) Hologram (hologram A) generated by the first signal page data 130-1 and the first partial reference beam A110-1
c) Hologram generated by second signal page data 130-2 and second partial reference light A110-2 (hologram A)
d) Hologram (hologram A) generated by the third signal page data 130-3 and the third partial reference light A110-3

During reproduction, the first signal page data 130-1 is demodulated by irradiating the holographic memory 200 with the reference light 100 including the first partial reference light A110-1 and the partial reference light B120. Similarly, by irradiating the holographic memory 200 with the reference light 100 including the second partial reference light A110-2 and the partial reference light B120, the second signal page data 130-2 is demodulated. By irradiating the holographic memory 200 with the reference light 100 including the third partial reference light A110-3 and the partial reference light B120, the third signal page data 130-3 is demodulated.

The upper limit of the number of signal page data 130 that can be recorded in the same location of the holographic memory 200 depends on the number of patterns that the partial reference light A110 can take. The number of patterns that the partial reference light A110 can take can be a very large value. As described above, in the recording method of the present invention, it is possible to multiplex-record a plurality of signal page data (signal light) with respect to one interference light, and the holograms a) to d) described above are formed into one hologram unit. Can be treated as By combining this hologram unit with a conventional angle multiplexing method, shift multiplexing method, wavelength multiplexing method, etc., the storage capacity can be dramatically improved.

In the above description, the recording method and reproducing method of the holographic memory have been described without any particular limitation. In the following description, a recording method and a reproducing method for a holographic memory when realizing the recording method and the reproducing method of the present invention while ensuring high compatibility with collinear holography will be described.

As a hologram recording method, a two-beam interference method using light of different angles for signal light and reference light is widely known. However, this method has a problem in consistency with the optical disc technology. As a method for solving this problem, as shown in FIG. 6, the signal light and the reference light are arranged on the same optical axis, and the central portion of the spatial light modulator (SLM) is used to generate the hologram signal light. There is a collinear holography method in which the outer periphery is used to generate a reference light pattern (Hideyoshi Horimai, Xiaodi Tan and Jun Li, Col "Collinear Holography", Appl. Opt., Vol.44, pp.2575-2579.). As shown in FIG. 6, during recording and reproduction, laser light 310 (signal light and / or reference light) passes through the SLM 320, the half mirror 330, and the objective lens 340, and irradiates the recording medium 350 (for example, an optical disk). Is done. At the time of reproduction, the diffracted light extracted from the recording medium 350 is reflected by the half mirror 330 and reaches the image sensor 360. Although FIG. 6 shows an optical arrangement of a reflection hologram, an optical arrangement of a transmission hologram may be used.

FIG. 7 shows an example of a spatial light modulator (SLM) pattern when recording and reproduction are performed by the collinear holography method. At the time of recording, as shown in FIG. 7A, page data separated into a central portion and an outer peripheral portion are used, the central portion is used for forming signal light, and the outer peripheral portion is used for forming reference light. The light emitted from the central portion (signal light) and the light emitted from the outer peripheral portion (reference light) are condensed and irradiated onto a recording medium (for example, an optical disc) with one objective lens, and the interference pattern of both is recorded. At the time of reproduction, as shown in FIG. 7B, only the light (reference light) emitted from the outer peripheral portion is condensed and irradiated onto the recording medium, and the recording data is extracted from the recording medium as diffracted light. In the collinear holography method, multiple recording can be performed by slightly shifting the position of the light spot spatially (shift multiplexing).

As shown in FIG. 8, the recording method and the reproducing method of the present invention have high compatibility with the collinear holography method by dividing the ring of reference light in the collinear holography method into an outer region and an inner region. Can be made. In the example shown in FIG. 8, the region outside the outer peripheral portion is used for forming the partial reference light A110, and the region inside the outer peripheral portion is used for forming the partial reference light B120. The central region is used to form the signal light 140 or the interference light 150.

At the time of recording, as shown in FIG. 9, first, signal light 140 having information of page data to be recorded is generated by the SLM 320 in the central area, and the partial reference light A110 is generated in the outer area of the outer periphery. Generated by the SLM 320. Then, the hologram A generated by the signal light 140 and the partial reference light A110 is recorded in the holographic memory 200 (recording medium 350). At this time, the region inside the outer peripheral portion (the region where the partial reference light B120 is generated) is set in a state in which the laser light 310 is not transmitted by turning off the pixels of the SLM 320.

Next, as shown in FIG. 9, in the central region, the SLM 320 generates the interference light 150 having the reference light information necessary for generating the second hologram at the time of reproduction, and the inner region of the outer peripheral portion. The partial reference beam B120 is generated by the SLM 320. Then, the hologram B generated by the interference light 150 and the partial reference light B120 is recorded in the holographic memory 200 (recording medium 350). At this time, the region outside the outer periphery is turned off by turning off the pixels of the SLM 320. The phase distribution and intensity distribution of the interference light 150 differ depending on the operation mode described later. For example, data having the same phase and the same intensity for all data pixels is given to the SLM 320, and the output light is used as the interference light 150.

In FIGS. 8 and 9, no pattern is drawn in the region of the partial reference light A110 and the region of the partial reference light B120, but actually, the reference light data having a different phase or intensity for each pixel. Provided by SLM 320. The SLM 320 used here is an element that can spatially modulate the phase and / or intensity of light.

During reproduction, the holographic memory 200 is irradiated with the reference light 100 including both the partial reference light A110 and the partial reference light B120, as shown in FIG. Thereby, the diffracted light of hologram A and the diffracted light of hologram B are generated simultaneously. Then, the diffracted light of the hologram A functions as new signal light, and the diffracted light of the hologram B functions as new reference light, whereby the second-stage hologram 220 is generated on the surface of the image sensor 360. Thereafter, the phase modulation signal included in the page data can be demodulated by electronic signal processing. Since the reproduction method of the present invention can reproduce data only by irradiating the reference light (partial reference light A110 and partial reference light B120) used at the time of recording, it is completely compatible with an intensity modulation type collinear holography method reproduction apparatus. Have sex.

Note that the recording method and reproducing method of the present invention can be applied not only to the collinear holography method but also to various holography methods. For example, the recording method and reproducing method of the present invention can be applied to the two-beam interference method. In the following description, a recording method and a reproducing method of the holographic memory when the recording method and the reproducing method of the present invention are realized by the two-beam interference method will be described.

At the time of recording, as shown in FIG. 11, first, the signal light 140 or the interference light 150 is generated by the first SLM 320 (SLM1), and the partial reference light A110 or the partial reference light is generated by the second SLM 320 (SLM2). B120 is generated. The hologram A generated by the signal light 140 and the partial reference light A110 and the hologram B generated by the interference light 150 and the partial reference light B120 are recorded in the holographic memory 200.

In the example shown in FIG. 11, the second SLM 320 (SLM2) is divided into a partial reference light A110 region (left half) and a partial reference light B120 region (right half). In the second SLM 320 (SLM 2), a black region indicates that light is not transmitted, and other regions (regions with a pattern) transmit light while providing a phase pattern or an intensity pattern. It shows that you are letting. In the second SLM 320 (SLM2), no pattern is drawn in the area of the partial reference light A110 and the area of the partial reference light B120, but actually, the reference light data having a different phase or intensity for each pixel is obtained. 2 SLM320 (SLM2).

During reproduction, the holographic memory 200 is irradiated with the reference light 100 including both the partial reference light A110 and the partial reference light B120, as shown in FIG. Thereby, the diffracted light of hologram A and the diffracted light of hologram B are generated simultaneously. Then, the diffracted light of the hologram A functions as new signal light, and the diffracted light of the hologram B functions as new reference light, whereby the second-stage hologram 220 is generated on the surface of the image sensor 360. Thereafter, the phase modulation signal included in the page data can be demodulated by electronic signal processing.

In the reproduction method of the present invention, three modes for demodulating the phase modulation signal will be described.

1) Direct detection mode (see Fig. 13)
When the recorded page data is a binary phase modulation signal, the phase modulation signal can be demodulated in the direct detection mode. The interference light has the same intensity and the same phase for all data pixels. During reproduction, the diffracted light of the hologram A (binary phase modulation signal) and the diffracted light of the hologram B (interference light) interfere with each other and are converted into light (interference fringes) including binary intensity information. The image sensor detects the intensity distribution in the interference fringes. Since the detected intensity distribution (for example, 0 and 1) directly corresponds to the binary phase modulation signal (for example, 0 and π) recorded in the data page, the demodulation of the binary phase modulation signal is completed. .

2) Multi-shot dual stage mode (see Fig. 14)
In order to increase the capacity of the holographic memory, it is necessary to record a multilevel phase modulation signal or a spatial quadrature amplitude modulation signal.

When demodulating a multi-level phase modulation signal or spatial quadrature amplitude modulation signal in the multi-shot dual stage mode, the diffracted light (interference light) of hologram B is used as a new reference light, and the diffracted light of hologram A generated simultaneously is newly added. Second stage hologram (digital hologram) is generated as a simple signal light (Ichirou Yamaguchi and Tong Zhang, "Phase-shifting digital holography", Optics Letters, Vol.22, No.16, pp.1268-1270 (1997 )). At this time, the first stage hologram (hologram A and hologram B) is reproduced while shifting the phase of the partial reference light A or the partial reference light B, and a plurality of (at least three) digital holograms having different phases are generated. To do. Thereby, the information of the page data included in the diffracted light of the hologram A can be demodulated.

FIG. 14 is a conceptual diagram when four digital holograms are generated by shifting the phase of the partial reference light B. The signal processing for demodulation is the same as that for holographic diversity and phase shift interferometry (AtsushiAOkamoto, kaKeisuke Kunori, Masanori Takabayashi, Akihisa Tomita and Kunihiro Sato, “Holographic diversity interferometry for optical storage”, Optics storage , Vol.19, No.14, pp.13436-13444 (2011); P. Hariharan, "Optical Holography", Cambridge University Press, pp.291-310 (1996)). The “holographic diversity interferometry” is used for generating a second-stage hologram and demodulating a phase modulation signal in a dual-stage holographic method (see Non-Patent Document 10).

The phase change of interference light as a _n, when the distribution of the signal intensity detected by the second-stage hologram (digital holograms) and V _{n (x,} y), the original signal phase phi (x, y) and the amplitude A (x, y) is obtained as follows.

Thereby, the phase φ (x, y) and the amplitude A (x, y) of the original signal can be estimated. Here, when generating four digital holograms, n = 1, 2, 3, and 4.

3) Single-shot / dual-stage mode (see Fig. 15)
In the multi-shot dual stage mode, it is necessary to perform reproduction a plurality of times while shifting the phase of the partial reference light B in order to detect a multi-level phase modulation signal. In order to improve this point, as shown in FIG. 15, interference light having a finer phase distribution than the data pixel is recorded in the holographic memory using a high-definition SLM. The diffracted light (interference light) of hologram B thus obtained is used as a new reference light, and the diffracted light of hologram A generated at the same time is used as a new signal light to generate a second-stage hologram (digital hologram). As a result, a plurality of phase-shifted digital hologram information can be detected by one reference light irradiation (single shot).

For example, as shown in FIG. 15, modulation is performed so that four data pixels (subpixels) of interference light are included in one data pixel of signal light. The phase of the interference light takes four values of 0, π / 2, π, and 3π / 2 in one data pixel of the signal light. In this case, it is possible to detect the digital hologram information for four sheets shifted in phase by one detection. In the signal processing for demodulation, instead of the digital hologram information for four images obtained in time series in the multi-shot mode, the digital hologram information for four images obtained simultaneously in the single-shot mode may be used (multi-shot). Equivalent to mode).

In the single shot / dual stage mode, the phase distribution may be given not to the interference light but to the signal light or both the signal light and the interference light. FIG. 16 is a diagram showing the phase distribution of the signal light and the interference light when giving the phase distribution to the interference light (the same contents as FIG. 15). FIG. 16A shows one data pixel of signal light, and FIG. 16B shows the phase distribution of four sub-pixels of interference light. In this aspect, four subpixels of interference light correspond to one data pixel of signal light, and the phases of the four subpixels are different from each other.

FIG. 17 is a diagram showing the phase distribution of the signal light and the interference light when the phase distribution is given only to the signal light or to both the signal light and the interference light. FIG. 17A shows one data pixel of signal light, and FIG. 17B shows a phase distribution of one data pixel of interference light. In this aspect, one data pixel of signal light is divided into four subpixels, and four subpixels of interference light correspond to each of the four subpixels of signal light.

In the example shown in FIG. 17, the phase values applied to the four subpixels of the signal light are α1, α2, α3, and α4, respectively. Further, the phase values of the subpixels of the interference light corresponding to the subpixels of the signal light are β1, β2, β3, and β4. At this time,
β1-α1 = 0 (A1)
β2-α2 = π / 2 (or -3π / 2) (A2)
β3-α3 = π (or -π) (A3)
β4-α4 = 3π / 2 (or -π / 2) (A4)
By selecting the values of α1 to α4 and β1 to β4 so as to satisfy the conditions, the digital hologram information for the four phase-shifted images can be detected by one detection as in the embodiment shown in FIG. Can do. For example, when the phase of the interference light is made constant, one data pixel of the signal light is divided into four subpixels, and 0, 3π / 2, π, and π / 2 are added to the phase φ of the signal light.
β1 = β2 = β3 = β4 = 0
α1 = 0, α2 = 3π / 2, α3 = π, α4 = π / 2
It becomes. Further, a phase distribution satisfying the above formulas (A1) to (A4) is added to both the sub-pixels of the signal light and the interference light, and the phase combination of each sub-pixel of the interference light is different for each data pixel of the signal light By setting the value, it can be avoided that the spectrum of the interference light is concentrated at a specific position of the recording medium, and as a result, an improvement in performance can be expected (see Example 5).

In the above description of the collinear holography method, the reference light pattern outside the outer peripheral part is used for recording signal light (partial reference light A), and the reference light pattern inside the outer peripheral part is used for recording interference light (partial reference). For the light B), the division pattern of the reference light is not limited to this. For example, as shown in FIG. 18A, the outer region may be used for the partial reference light B120, and the outer region may be used for the partial reference light A110. Further, as shown in FIG. 18B, the outer peripheral region may be divided in the circumferential direction.

In the recording method of the present invention, since interference light is recorded in addition to signal light, consumption of the dynamic range of the recording medium becomes a problem. However, this problem can be easily solved by making a plurality of signal lights (page data) correspond to one interference light.

For example, as shown in FIGS. 9 and 11, one interference light is multiplexed and recorded together with n signal page data. In this case, first, interference light (phantom) and partial reference light B (ref0) are generated by the SLM 320, and the hologram B is recorded on the recording medium 350. Next, signal light (sig 1) including page data # 1 and first partial reference light A (ref 1) are generated by the SLM, and the first hologram A is recorded on the recording medium 350. Next, signal light (sig 2) including page data # 2 and second partial reference light A (ref 2) are generated by the SLM, and the second hologram A is recorded on the recording medium 350. Here, the partial reference light A (ref1) used when recording the first signal light (sig1) and the partial reference light A (ref2) used when recording the second signal light (sig2) are: Use patterns with different phases or intensity distributions. Thereby, multiple recording of the first signal light (sig1) and the second signal light (sig2) can be realized. Similarly, signal light (sig3 to sign) including page data # 3 to #n can be multiplexed and recorded on the recording medium 350 by changing the pattern (ref3 to refn) of the partial reference light A.

At the time of reproduction, as shown in FIGS. 10 and 12, when it is desired to reproduce page data # 1, partial reference light B (ref0) used for recording interference light and signal light including page data # 1 are used. The reference light 100 including the first partial reference light A (ref1) used at the time of recording is generated by the SLM 320, and irradiated to the recording medium 350. Thereby, interference light (phantom; diffracted light of hologram B) and signal light (sig1; diffracted light of first hologram A) are generated simultaneously. Similarly, when it is desired to reproduce the page data # 2, reference light including partial reference light B (ref0) and second partial reference light A (ref2) is generated by the SLM 320 and applied to the recording medium 350. Thereby, interference light (phantom; diffracted light of hologram B) and signal light (sig2; diffracted light of second hologram A) are generated simultaneously.

As described above, a plurality of page data can be recorded and reproduced by one interference light by multiplex recording a plurality of page data while changing the pattern of the partial reference light A with respect to one interference light. It becomes. As a result, the problem of consumption of the dynamic range due to the recording and reproduction of interference light can be greatly reduced, and the storage capacity can be greatly increased.

Furthermore, in the recording method and reproducing method of the present invention, a plurality of holograms obtained by associating a plurality of signal lights (page data) with one interference light can be handled as one hologram unit. By combining this hologram unit with a multiplex recording method such as a conventional angle multiplex method, shift multiplex method, or wavelength multiplex method, a dramatic improvement in storage capacity can be realized.

Note that the recording method and reproducing method of the present invention can also be applied to optical memories other than holographic memories. For example, signal light including phase information is recorded in the optical memory A, and interference light is recorded in the optical memory B. Thereafter, two reproduction lights obtained by simultaneously reproducing the optical memory A and the optical memory B are caused to interfere with each other. By doing so, the phase information can be converted into intensity information, and the phase information recorded in the optical memory A can be demodulated by the intensity detector.

The recording device of the holographic memory of the present invention records a spatial phase modulation signal or a spatial quadrature amplitude modulation signal in the holographic memory by the recording method of the present invention. The recording device of the holographic memory of the present invention has a hologram A recording unit and a hologram B recording unit. The hologram A recording unit is generated by the signal light and the partial reference light A by irradiating a specific portion of the holographic memory with the signal light including the spatial phase modulation signal or the spatial quadrature amplitude modulation signal and the partial reference light A. Hologram A is recorded. The hologram B recording unit records the hologram B generated by the interference light and the partial reference light B by irradiating the same position of the holographic memory with the interference light and the partial reference light B. As shown in Example 3 described later, the hologram A recording unit and the hologram B recording unit may be realized by the same optical system.

The reproducing apparatus for a holographic memory according to the present invention reproduces a spatial phase modulation signal or a spatial quadrature amplitude modulation signal recorded in the holographic memory by the reproducing method according to the present invention. The reproducing device for a holographic memory according to the present invention includes a hologram diffracted light generation unit and a demodulation unit. The hologram diffracted light generation unit simultaneously irradiates a specific portion of the holographic memory with the partial reference light A and the partial reference light B, thereby diffracting the hologram A and the hologram B that can interfere with the diffracted light of the hologram A. It produces light at the same time. The demodulation unit demodulates the spatial phase modulation signal or the spatial quadrature amplitude modulation signal using the diffracted light of the hologram A and the diffracted light of the hologram B. As shown in Example 3 to be described later, the hologram diffracted light generation unit may be realized by one optical system.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[Example 1]
Example 1 shows the results of simulation of recording and reproduction of a 16-value spatial quadrature amplitude modulation signal (16-SQAM) using the recording method and reproducing method of the holographic memory of the present invention.

では Arranging more than 8 phase states just by arranging signal points on a circle makes the signal waveforms similar to each other, and it is not preferable to pack many signal states by phase modulation alone. Therefore, a spatial quadrature amplitude modulation (SQAM) is a modulation system that gives more signal states by adding amplitude modulation to phase modulation.

When the in-phase component of the signal to be modulated is I and the quadrature component is Q, these signals can be expressed as follows.

Here, when the angular frequency of the light wave is ω, the time is t, the wave number is k, and the spatial variable is r, from the addition theorem of the trigonometric function,

It is expressed. That is, modulating the in-phase component I and the quadrature component Q of the signal is equivalent to modulating the amplitude A and the phase φ of the light wave. From the above, the fact that recording and reproduction of spatial quadrature amplitude modulation signals is possible means that it is possible to record and reproduce multilevel phase modulation signals, multilevel amplitude modulation signals, and various modulation signals combining these. Means.

FIG. 19 shows a diagram of the 16-value spatial quadrature amplitude modulation signal (16-SQAM) used in this example. The horizontal axis in the figure is called “real axis” or “I axis”, and the vertical axis is called “imaginary axis” or “Q axis”. These correspond to the variables I and Q in equation (3). The points plotted on the diagram are called “signal points”. A set of modulation codes is represented by a plurality of signal points. Further, the complex plane represented by this diagram shows the amplitude and phase of the signal with the “0” point on both axes as the center. The distance from the “0” point represents the amplitude, and the angle with respect to the “0” point represents the phase. Therefore, although the symbols are located at the same distance from the center but are located at different angles with respect to the center, the symbols have the same signal waveform amplitude but different phases.

In this example, simulation was performed when a 16-value spatial quadrature amplitude modulation signal (16-SQAM) was recorded and reproduced using the recording method and the reproducing method of the present invention. The numerical analysis tool used was FFT-BPM (Junya Tanaka, Atsushi Okamoto and Motoki Kitano, "Development of Image-Based Simulation for Holographic Data Storage System by Fast Fourier Transform Beam-Propagation Method". , Japanese Journal of Applied Physics, Vol.48, No.3 (Issue 2), pp.03A028 (1-5).). Table 1 shows the parameters used for the numerical analysis.

The signal page data (spatial quadrature amplitude modulation signal) used for recording is shown in FIG. As shown in FIG. 20, the size of the signal page data is 32 × 32 pixels. Each pixel of the signal page data has both values of the phase information φ (x, y) shown in FIG. 20A and the amplitude information A (x, y) shown in FIG. 20B. That is, one signal page data is expressed by combining the phase information φ (x, y) shown in FIG. 20A and the amplitude information A (x, y) shown in FIG. 20B. The phase information shown in FIG. 20A is drawn in gray scale for visualization.

FIG. 21 shows the intensity pattern of the reference light used for recording and reproduction. FIG. 21A shows an intensity pattern of the partial reference light A, which is located outside the outer peripheral portion. FIG. 21B shows an intensity pattern of the partial reference light B, which is located inside the outer peripheral portion (see FIG. 8).

In this simulation, a standard photopolymer was assumed as a recording medium, and signal page data (signal light) and interference light were multiplexed and recorded. The recorded holograms (hologram A and hologram B) were irradiated with reference light (partial reference light A and partial reference light B) to generate diffracted light of hologram A and diffracted light of hologram B.

(Demodulation by multi-shot dual stage mode)
In the multi-shot dual stage mode (see FIG. 14), the phase of the partial reference light B is sequentially changed to 0, π / 2, π, 3π / 2 by the SLM during reproduction, and the phase of the diffracted light of the hologram B is 0. , Π / 2, π, and 3π / 2 were sequentially changed to obtain four second-stage holograms (digital holograms). The signal intensity distribution obtained by photoelectric conversion of these four digital holograms is shown in FIG. 22A is a digital hologram when the phase of the partial reference light B is 0, FIG. 22B is a digital hologram when the phase of the partial reference light B is π / 2, and FIG. 22C is a partial reference light B. FIG. 22D is a digital hologram when the phase of the partial reference light B is 3π / 2.

FIG. 23 shows the page data demodulated from the four signal intensity distributions using the above formulas (1) and (2). FIG. 23A shows phase information of demodulated page data, and FIG. 23B shows amplitude information of demodulated page data (see comparison with FIG. 20).

FIG. 24 is a graph showing the signal point distribution of demodulated page data. From this graph, it can be seen that the 16-value spatial quadrature amplitude modulation signal (16-SQAM) is clearly separated.

The number of errors that occurred in this simulation was two. Since the number of symbols of page data is 1024 (32 × 32), the symbol error rate is 1.95 × 10 ⁻³ . This is a practically sufficient performance considering the error correction capability (1 × 10 ⁻² ) in the current holographic memory.

(Demodulation by single shot / dual stage mode)
In the single shot dual stage mode (see FIG. 15), the phase of the interference light is changed by the SLM during recording, so that four different phases (0, π / 2, π, 3π / One second-stage hologram (digital hologram) having 2) was obtained. FIG. 25 shows a signal intensity distribution obtained by photoelectric conversion of this digital hologram. The signal area (square portion at the center) shown in FIG. 25 is twice as fine as that of FIG.

FIG. 26 shows the page data demodulated from the signal intensity distribution using the above equations (1) and (2). FIG. 26A shows phase information of demodulated page data, and FIG. 26B shows amplitude information of demodulated page data (see comparison with FIG. 20).

FIG. 27 is a graph showing the signal point distribution of demodulated page data. From this graph, it can be seen that the 16-value spatial quadrature amplitude modulation signal (16-SQAM) is clearly separated.

The number of errors that occurred in this simulation was three. As described above, since the number of symbols in the page data is 1024, the symbol error rate is 2.93 × 10 ⁻³ . This is a practically sufficient performance considering the error correction capability (1 × 10 ⁻² ) in the current holographic memory.

[Example 2]
In Example 2, in the recording method and the reproducing method of the holographic memory of the present invention, operation verification was performed when a plurality of signal page data was recorded in a multiplexed manner with respect to one interference light.

In this example, a simulation was performed when a 4-level spatial phase modulation signal (4-SPM) was recorded and reproduced. As the numerical analysis tool, the same FFT-BPM (Fast Fourier Transform Beam Propagation Method) as in Example 1 was used. The parameters used for the numerical analysis are the same as in Example 1 (see Table 1).

FIG. 28 shows three signal page data (four-level phase modulation signal) used for recording. 28A shows the phase information φ (x, y) of the signal page data # 1, FIG. 28B shows the phase information φ (x, y) of the signal page data # 2, and FIG. 28C shows the signal page data # 1. 3 shows phase information φ (x, y). The phase of each pixel is one of four values of 0, π / 2, π, and 3π / 2. As shown in FIG. 28, the size of the signal page data is 32 × 32 pixels. The phase information shown in FIG. 28 is drawn in gray scale for visualization.

In this simulation, assuming that a standard photopolymer was used as a recording medium, three signal page data were multiplexed and recorded for one interference light. The recorded holograms (hologram A and hologram B) were irradiated with reference light (partial reference light A and partial reference light B) to generate diffracted light of hologram A and diffracted light of hologram B.

(Demodulation by multi-shot dual stage mode)
FIG. 29 shows page data (analog data) demodulated using the above equations (1) and (2) from four second-stage holograms obtained using the multi-shot dual-stage mode (see FIG. 14). Shown in 29A shows phase information of demodulated signal page data # 1, FIG. 29B shows phase information of demodulated signal page data # 2, and FIG. 29C shows phase information of demodulated signal page data # 3. ing.

29. Since the signal page data in FIG. 29 is an analog value immediately after the calculation, the signal page data is converted into digital data having a phase 4 value by threshold processing. The converted page data (digital data) is shown in FIG. 30A shows phase information of demodulated signal page data # 1, FIG. 30B shows phase information of demodulated signal page data # 2, and FIG. 30C shows phase information of demodulated signal page data # 3. (See comparison with FIG. 28).

FIG. 31 is a graph showing the signal point distribution of each demodulated page data. 31A shows the signal point distribution of the signal page data # 1, FIG. 31B shows the signal point distribution of the signal page data # 2, and FIG. 31C shows the signal point distribution of the signal page data # 3. From these graphs, it can be seen that the quaternary spatial phase modulation signal (4-SPM) is clearly separated.

The number of errors that occurred in this simulation was one in total for the three signal page data. Since the number of symbols of page data is 3072 (32 × 32 × 3), the symbol error rate is 3.26 × 10 ⁻⁴ . This is a practically sufficient performance considering the error correction capability (1 × 10 ⁻² ) in the current holographic memory.

[Example 3]
Example 3 shows the result of actually recording and reproducing a binary spatial phase modulation signal (2-SPM) using the recording method and reproducing method of the holographic memory of the present invention.

FIG. 32 is a schematic diagram showing the configuration of the holographic memory recording / reproducing apparatus used in the experiment. This holographic memory recording / reproducing apparatus records and reproduces holograms (hologram A and hologram B) by a collinear holography method. The binary spatial phase modulation signal was detected in the direct detection mode (see FIG. 13).

As shown in FIG. 32, the holographic memory recording / reproducing apparatus includes a laser light source (Laser), a beam expanding optical system (BE), a half-wave plate (HWP), a polarizer (Pol.), And a random phase plate (RPM). , Intensity modulation spatial light modulator (SLM (Intensity)), first lens (LensＬ1), mirror (Mirror), second lens (Lens 2), beam splitter (BS), phase modulation spatial light modulator ( SLM (Phase)), third lens (Lens3), fourth lens (Lens 4), fifth lens (Lens 5), sixth lens (Lens 6), ND filter (NDF), seventh It has a lens (Lens 7) and a CCD camera (CCD). This holographic memory recording / reproducing apparatus performs recording and reproduction by installing a recording medium (Media) between the fifth lens (Lens 5) and the sixth lens (Lens 6). As a recording medium, a photopolymer generally used for hologram recording was used.

32, the light emitted from the laser light source is enlarged to an appropriate size by a beam expanding optical system (BE), and the polarization direction is adjusted by a half-wave plate (HWP). The random phase plate (RPM) has an effect of preventing the light intensity from being concentrated at the center of the hologram by giving a random phase to the light.

The intensity modulation SLM is composed of an SLM body and two polarizers arranged on both sides thereof. The intensity modulation SLM is used for switching between the partial reference light A and the partial reference light B and for switching the irradiation of the signal light. That is, when recording the hologram B, the intensity modulation SLM transmits the partial reference light B and the interference light (signal light having the same intensity and the same phase in the entire region). When recording the hologram A, the intensity modulation SLM transmits the partial reference light A and the signal light. On the other hand, when reproducing the hologram A and the hologram B, the intensity modulation SLM transmits the partial reference light A and the partial reference light B, but does not transmit the signal light. The light transmitted through the intensity modulation SLM is subjected to predetermined phase modulation in the phase modulation SLM.

FIG. 33 is a diagram showing a pattern of the phase modulation SLM when the hologram B is recorded. As shown in FIG. 33, the partial reference light B is located at the outer peripheral portion, and the interference light is located at the central portion. The partial reference light B and the interference light have the same phase throughout the entire area.

FIG. 34 is a diagram showing a pattern of the phase modulation SLM when the hologram A is recorded. In this experiment, two signal page data (16 × 16) were multiplexed and recorded. FIG. 34A is a diagram showing a pattern of phase modulation SLM when recording the signal page data # 1, and FIG. 34B is a diagram showing a pattern of phase modulation SLM when recording the signal page data # 2. As shown in FIG. 34, the partial reference light A is located at the outer peripheral portion, and the signal light is located at the central portion. The partial reference light A and the partial reference light B are both located on the outer peripheral portion, but do not overlap each other (see FIG. 33 and FIG. 34 for comparison). The phase pattern of the partial reference light A when recording the signal page data # 1 and the phase pattern of the partial reference light A when recording the signal page data # 2 are different from each other (see FIGS. 34A and 34B). Comparison). The phase information shown in FIG. 34 is drawn in gray scale for visualization. The binary phase is white = 0 and black = π.

Hologram B was recorded by irradiating the photopolymer (recording medium) with interference light and partial reference light B (see FIG. 33) generated by the phase modulation SLM. Next, the signal light including the signal page data # 1 generated by the phase modulation SLM and the partial reference light A (see FIG. 34A) for recording the signal page data # 1 are irradiated on the photopolymer to thereby generate the signal page data. # 1 hologram A was recorded. Next, the signal light including the signal page data # 2 generated by the phase modulation SLM and the partial reference light A (see FIG. 34B) for recording the signal page data # 2 are irradiated to the photopolymer to thereby generate the signal page data. # 2 hologram A was recorded.

FIG. 35 is a diagram showing a pattern of the phase modulation SLM when the hologram A and the hologram B are reproduced. FIG. 35A is a diagram showing a pattern of phase modulation SLM when reproducing signal page data # 1, and FIG. 35B is a diagram showing a pattern of phase modulation SLM when reproducing signal page data # 2. As shown in FIG. 35, the reference light includes partial reference light A and partial reference light B.

The reference light (see FIG. 35) generated by the phase modulation SLM was irradiated to the photopolymer to reproduce the hologram A and the hologram B, and the intensity distribution of the signal page data was detected by the CCD camera (direct detection mode).

FIG. 36 is an image showing the signal intensity distribution detected by the CCD camera. 36A is an image showing the signal intensity distribution of the signal page data # 1, and FIG. 36B is an image showing the signal intensity distribution of the signal page data # 2.

FIG. 37 shows an image (reproduction page data) obtained by performing binary threshold processing on the image shown in FIG. 36 and converting the image into binary digital data. FIG. 37A shows reproduction page data of signal page data # 1, and FIG. 36B shows reproduction page data of signal page data # 2.

Note that the pattern shown in FIGS. 36 and 37 is a horizontally reversed image of the pattern shown in FIG. As shown in FIG. 32, the signal pattern emitted from the phase modulation spatial light modulator (SLM (Phase)) is reflected by the beam splitter (BS) and then detected by the CCD camera (CCD). Because.

The number of errors that occurred in this experiment was two in total for the two signal page data. Since the number of symbols of the signal page data is 512 (16 × 16 × 2), the symbol error rate is 4 × 10 ⁻³ . This is a practically sufficient performance considering the error correction capability (1 × 10 ⁻² ) in the current holographic memory.

[Example 4]
Example 4 shows the result of a simulation of recording and reproduction of a binary spatial phase modulation signal (2-SPM) using the recording method and reproducing method of the present invention. In the present embodiment, the binary spatial phase modulation signal (2-SPM) is recorded and reproduced not by the collinear holography method but by the two-beam interference method. As the numerical analysis tool, the same FFT-BPM (Fast Fourier Transform Beam Propagation Method) as in Example 1 was used. The parameters used for the numerical analysis are the same as in Example 1 (see Table 1).

The signal page data (binary spatial phase modulation signal) used for recording is shown in FIG. 38A, and the phase pattern of the interference light is shown in FIG. 38B. The phase information shown in FIGS. 38A and 38B is drawn in gray scale for visualization. As shown in FIG. 38A, the size of the signal page data is 32 × 32 pixels. Each pixel of the signal page data has binary phase information φ (x, y) of 0 (shown in black) or π (shown in white). The intensity of each pixel of the signal page data is constant. Further, as shown in FIG. 38B, the interference light is a plane wave of 32 × 32 pixels (phase and intensity are spatially constant).

38C shows the intensity pattern of the partial reference light A, FIG. 38D shows the intensity pattern of the partial reference light B, and FIG. 38E shows the intensity pattern of the reference light (partial reference light A and partial reference light B). As shown in FIG. 38E, the partial reference light A and the partial reference light B do not overlap each other. The intensity distribution of partial reference light A and partial reference light B is expressed as follows: flat cosine-squared window function (Shun-Der Wu and Elias N. Glytsis, "Finite-number-of-periods holographic gratings with finite-width incident beams: analysis using The “finite-difference” frequency-domain “method”, “J. Opt. Soc. Am. A,” Vol.19, No.10, pp.2018-2029 (2002)).

In this simulation, a standard photopolymer was assumed as a recording medium, and signal page data (signal light) and interference light were multiplexed and recorded by the two-beam interference method (see FIG. 11). The recorded holograms (hologram A and hologram B) are irradiated with reference light (partial reference light A and partial reference light B) to generate diffracted light of hologram A and diffracted light of hologram B, and these diffracted lights. The intensity distribution of interference fringes generated by the above was detected (see FIG. 12). In this embodiment, since the recorded page data is a binary phase modulation signal, the phase modulation signal can be demodulated in the direct detection mode. FIG. 38F shows page data (reproduced page data) reproduced as an intensity modulation signal.

From these results, it can be seen that signal page data can be recorded and reproduced by the recording method and reproducing method of the present invention even if the two-beam interference method is used.

[Example 5]
Example 5 shows the results of simulation of recording and reproduction of a 38-value spatial quadrature amplitude modulation signal (38-SQAM) using the recording method and reproducing method of the present invention. In this example, recording and reproduction of a 38-value spatial quadrature amplitude modulation signal (38-SQAM) was performed by a collinear holography method. As the numerical analysis tool, the same FFT-BPM (Fast Fourier Transform Beam Propagation Method) as in Example 1 was used. The parameters used for the numerical analysis are the same as in Example 1 (see Table 1).

FIG. 39 shows five signal page data (38-value spatial quadrature amplitude modulation signals) used for recording. 39A shows the amplitude information A (x, y) of the signal page data # 1, FIG. 39B shows the amplitude information A (x, y) of the signal page data # 2, and FIG. 39C shows the signal page data # 1. 3 shows amplitude information A (x, y) of FIG. 3, FIG. 39D shows amplitude information A (x, y) of signal page data # 4, and FIG. 39E shows amplitude information A (x, y) of signal page data # 5. y). 39F shows the phase information φ (x, y) of the signal page data # 1, FIG. 39G shows the phase information φ (x, y) of the signal page data # 2, and FIG. 39H shows the signal page The phase information φ (x, y) of data # 3 is shown, FIG. 39I shows the phase information φ (x, y) of signal page data # 4, and FIG. 39J shows the phase information φ (x of signal page data # 5 x, y). In these figures, a square area at the center is a pattern of signal page data (signal light), and an annular area at the periphery is a pattern of partial reference light A. The size of the signal page data is 32 × 32 pixels. The phase information shown in FIGS. 39F-J is drawn in gray scale for visualization.

In this simulation, a standard photopolymer was assumed as a recording medium, and five signal page data were recorded on one interference light. At this time, as shown in FIG. 17, for the signal light and the interference light, one data pixel was divided into four subpixels, and a phase distribution was added to both the signal light and the interference light. The recorded holograms (hologram A and hologram B) are irradiated with reference light (partial reference light A and partial reference light B) to generate diffracted light of hologram A and diffracted light of hologram B. The phase modulation signal was demodulated by the stage mode.

In the example shown in FIG. 17, the phase values applied to the four subpixels of the signal light are α1, α2, α3, and α4, respectively. In addition, the phase values of the four sub-pixels of the interference light are β1, β2, β3, and β4. At this time,
β1-α1 = 0 (A1)
β2-α2 = π / 2 (or -3π / 2) (A2)
β3-α3 = π (or -π) (A3)
β4-α4 = 3π / 2 (or -π / 2) (A4)
The values of α1 to α4 and β1 to β4 were selected so as to satisfy the above. At this time, α1, α2, α3, and α4 have different phase values. Β1, β2, β3, and β4 are also phase values different from each other.

FIG. 40A shows the phase information (32 × 32 pixels) of the signal page data # 1 (the same as FIG. 39F). FIG. 40B shows a phase distribution (64 × 64 pixels) added to the signal light. 40C shows the phase information (64 × 64 pixels) of the signal page data # 1 after adding the phase distribution shown in FIG. 40B to the phase information of the signal page data # 1 shown in FIG. 40A. As shown in these drawings, signal page data (see FIG. 40B) obtained by adding a phase distribution (see FIG. 40B) satisfying the above equations (A1) to (A4) to the original signal page data (see FIG. 40A). 40C) was generated by SLM and recorded on a recording medium.

FIG. 41A shows phase information (32 × 32 pixels) of interference light. FIG. 41B is a phase distribution (64 × 64 pixels) added to the interference light. In FIG. 41A, the annular region in the peripheral portion shows the phase distribution of the partial reference light B. As shown in these figures, interference light obtained by adding a phase distribution (see FIG. 41B) satisfying the above equations (A1) to (A4) to interference light (see FIG. 41A) is generated by the SLM. And recorded on a recording medium. In this way, by combining the phase combination of each sub-pixel of the interference light with a different value for each data pixel of the signal light, it is avoided that the spectrum of the signal light and the interference light is concentrated at a specific position on the recording medium. As a result, a reduction in errors can be expected.

FIG. 42 is a graph showing the signal point distribution of demodulated page data. FIG. 42A shows the result of demodulating the phase modulation signal in the single shot dual stage mode by adding the phase distribution only to the interference light without adding the phase distribution to the signal light (in the above formulas (A1) to (A4)). Α1 = α2 = α3 = α4 = 0, β1 = 0, β2 = π / 2, β3 = π, β4 = 3π / 2). On the other hand, in FIG. 42B, the phase modulation signal is demodulated by the single shot dual stage mode by adding the phase distribution to both the signal light and the interference light and changing the combination of the phases of each sub pixel of the interference light for each data pixel. (The method shown in FIGS. 40 and 41). From these graphs, it can be seen that the 38-value spatial quadrature amplitude modulation signal (38-SQAM) is clearly separated in any demodulation method.

When the phase distribution was added to only the interference light and demodulated in the single shot / dual stage mode (see FIG. 42A), the symbol error rate was 0.8%. On the other hand, when the phase distribution is added to both the signal light and the interference light, and the phase combination of each sub-pixel of the interference light is changed for each data pixel and demodulated in the single shot / dual stage mode (see FIG. 42B), The symbol error rate was 0.5%.

From these results, when demodulating in the single shot / dual stage mode, the phase distribution satisfying the above equations (A1) to (A4) is added to both the signal light and the interference light, and the subpixels of the interference light are captured. It can be seen that the accuracy of demodulation can be improved by changing the combination of possible phases for each data pixel.

This application claims priority based on Japanese Patent Application No. 2011-152585 filed on July 11, 2011. The contents described in the application specification and the drawings are all incorporated herein by reference.

The holographic memory of the present invention is not only used for consumer AV, but also for archival use in broadcasting and medical fields (data can be stored for a long period of time), optical disc systems such as data centers (power consumption is 1/6 that of HDDs) This is useful in various applications.

100 Reference light 110 Partial reference light A
120 Partial reference beam B
130 Phase modulation signal (signal page data)
140 signal light 150 interference light 160 diffracted light of hologram A 170 diffracted light of hologram B 180 diffracted light including intensity information 200 holographic memory (recording medium)
210 Light intensity detector 220 Second stage hologram (Hologram C)
310 Laser light 320 Spatial light modulator 330 Half mirror 340 Objective lens 350 Recording medium 360 Image sensor

Claims

A specific portion of the holographic memory is irradiated with signal light including a spatial phase modulation signal or spatial quadrature amplitude modulation signal and the partial reference light A, and a hologram A generated by the signal light and the partial reference light A is generated. Recording step;
Irradiating the specific portion of the holographic memory with interference light and partial reference light B, and recording the hologram B generated by the interference light and partial reference light B;
A holographic memory recording method comprising:
The partial reference light A is a part of the laser light emitted from the laser light source,
The partial reference light B is a part of the remaining part of the laser light emitted from the laser light source.
The holographic memory recording method according to claim 1.
The holographic memory recording method according to claim 1, wherein the hologram A and the hologram B are recorded in the holographic memory by a collinear holography method.
A method for reproducing a holographic memory in which a spatial phase modulation signal or a spatial quadrature amplitude modulation signal is recorded by the holographic memory recording method according to claim 1,
The partial reference light A and the partial reference light B are simultaneously irradiated onto a specific portion of the holographic memory, and the diffracted light of the hologram A and the diffracted light of the hologram B that can interfere with the diffracted light of the hologram A And simultaneously generating and
Demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal using the diffracted light of the hologram A and the diffracted light of the hologram B;
A method for reproducing a holographic memory, comprising:
The spatial phase modulation signal or the spatial quadrature amplitude modulation signal includes binary phase information;
Demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal comprises:
Generating interference fringes from the diffracted light of the hologram A and the diffracted light of the hologram B;
Detecting an intensity distribution of the interference fringes,
The method for reproducing a holographic memory according to claim 4.
The spatial phase modulation signal or the spatial quadrature amplitude modulation signal includes multi-level phase information,
Demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal comprises:
Generating a hologram C from the diffracted light of the hologram A and the diffracted light of the hologram B;
Detecting the intensity distribution of the hologram C;
Demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal based on the intensity distribution;
The method for reproducing a holographic memory according to claim 4.
In the step of simultaneously generating the diffracted light of the hologram A and the diffracted light of the hologram B, the partial reference light A and the partial reference light A and the partial reference light A are shifted to the specific location while shifting the phase of the partial reference light A or the partial reference light B. By simultaneously irradiating the partial reference light B a plurality of times, a plurality of combinations of the diffracted light of the hologram A and the diffracted light of the hologram B with different phases of the diffracted light of the hologram A or the hologram B are generated,
In the step of generating the hologram C, a plurality of holograms C having different intensity distributions are generated from the plurality of combinations,
In the step of detecting the intensity distribution of the hologram C, the intensity distribution of each of the plurality of holograms C is detected,
In the step of demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal, the spatial phase modulation signal or the spatial quadrature amplitude modulation signal is demodulated based on the plurality of intensity distributions.
The method for reproducing a holographic memory according to claim 6.
The interference light includes a plurality of subpixels having different phases with respect to one data pixel of the signal light,
The diffracted light of the hologram B includes a plurality of subpixels having different phases with respect to one data pixel of the diffracted light of the hologram A,
The hologram C includes a plurality of hologram information having different phases from each other,
In the step of demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal, the spatial phase modulation signal or the spatial quadrature amplitude modulation signal is demodulated based on a plurality of pieces of hologram information included in the hologram C.
The method for reproducing a holographic memory according to claim 6.
The signal light includes a plurality of subpixels having different phases with respect to one data pixel,
The diffracted light of the hologram A includes a plurality of subpixels having different phases with respect to one data pixel,
The hologram C includes a plurality of hologram information having different phases from each other,
In the step of demodulating the spatial phase modulation signal or the spatial quadrature amplitude modulation signal, the spatial phase modulation signal or the spatial quadrature amplitude modulation signal is demodulated based on a plurality of pieces of hologram information included in the hologram C.
The method for reproducing a holographic memory according to claim 6.
The partial reference light A is a part of the laser light emitted from the laser light source,
The partial reference light B is a part of the remaining part of the laser light emitted from the laser light source.
The method for reproducing a holographic memory according to claim 4.
The method for reproducing a holographic memory according to claim 4, wherein the hologram A and the hologram B are reproduced from the holographic memory by a collinear holography method.
A specific portion of the holographic memory is irradiated with signal light including a spatial phase modulation signal or spatial quadrature amplitude modulation signal and the partial reference light A, and a hologram A generated by the signal light and the partial reference light A is generated. A hologram A recording section for recording;
A hologram B recording unit that records the hologram B generated by the interference light and the partial reference light B by irradiating the specific portion of the holographic memory with the interference light and the partial reference light B;
A holographic memory recording device.
A reproducing apparatus for a holographic memory in which a spatial phase modulation signal or a spatial quadrature amplitude modulation signal is recorded by the holographic memory recording apparatus according to claim 12,
The partial reference light A and the partial reference light B are simultaneously irradiated onto a specific portion of the holographic memory, and the diffracted light of the hologram A and the diffracted light of the hologram B that can interfere with the diffracted light of the hologram A And a hologram diffracted light generator that simultaneously generates
A demodulator that demodulates the spatial phase modulation signal or the spatial quadrature amplitude modulation signal using the diffracted light of the hologram A and the diffracted light of the hologram B;
A holographic memory reproducing device.