CN101217044B - Phase amplitude conversion method and device adaptable for volume hologram memory - Google Patents

Abstract

The phase-to-amplitude conversion method and device suitable for volume holographic memory are simple and easy to implement, have good correction ability for phase shift error and reference light tilt error, and are based on phase shift interferometry. The technical solution includes the following steps: upload the data page to the spatial light modulator; holographic recording, the object light wave passes through the Fourier transform lens and interferes with the reference wave on the spectrum plane, and the interference fringes are placed on the light-induced light wave on the spectrum plane of the 4-f system. Polymer material recording, forming a volume holographic grating; holographic reading; phase-amplitude conversion, a beam of coherent plane waves is separated from the light source, without going through the optical path of the holographic recording and holographic reading part, it directly reaches the image plane and reproduces the object light wave in the The CCD surface interferes, and the interferogram is collected by the CCD camera, and then the phase of this beam of plane wave is uniformly changed by the phase shift device, and then interferes with the object light wave again to obtain the second interferogram. Through the phase shift recovery algorithm, the original phase information can be calculated from the two interferograms. The invention also provides a device for realizing the phase amplitude conversion method suitable for the volume holographic memory.

Description

A phase-amplitude conversion method and device suitable for volume holographic memory

technical field

The invention relates to a phase-amplitude conversion method and device suitable for a volume holographic memory, which can be used for recovering phase modulation data in a volume holographic memory, and belongs to the field of optical information processing. the

Background technique

According to the type of spatial light modulator (SLM) used in the volume holographic memory, the data input of the volume holographic memory generally adopts two methods: amplitude modulation and phase modulation. Amplitude modulation is to use a transmissive or reflective spatial light modulator to modulate the amplitude of the object light wave, and load input information to the amplitude of the object light wave. Phase modulation is to use a transmissive or reflective spatial light modulator to modulate the phase of the object light wave, and load input information to the phase of the object light wave. the

Traditional volume holographic memory uses amplitude modulation, such as the volume holographic storage system DEMONI and DEMON II developed by IBM, and the HDSS disk storage system developed by Stanford University in 2000. Since the volume holographic memory requires a high storage capacity, a 4-f Fourier transform optical structure is generally used, and the recording is performed on the Fourier spectrum, as shown in Figure 1. The amplitude-modulated object light waves have different intensities, and it is difficult to adjust the intensity of the light waves of the reference light to achieve the best interference effect. What's more serious is that the amplitude-modulated object light wave will produce a very strong central spot on the Fourier spectrum surface of the volume holographic memory. The simulation results and optical experiment results are shown in Figure 2 and Figure 3, respectively. The left figure of attached drawing 2 is the Fourier transform of the object light wave with random amplitude modulation, and the right figure is the Fourier transform of the object light wave with random phase modulation. It can be seen that there is a very strong peak in the center of the left picture, while the right picture is relatively stable. The left figure of accompanying drawing 3 is the optical Fourier transform of the object light wave with random amplitude modulation, and the right figure is the Fourier transform of the optical object light wave with random phase modulation. It is obvious that the center spot of amplitude modulation can be eliminated by phase modulation. This phenomenon is an inherent property of the Fourier transform optical system. The central spot represents the zero-frequency and low-frequency parts of the spatial frequency of the input light wave. This spot does not work for holographic recording and reproduction, and it will consume a lot of dynamic range of the storage material. To overcome this defect, researchers have proposed many countermeasures, such as placing a random phase template on the surface of the spatial light modulator, or placing an optical element on the Fourier spectrum surface to block the central spot. However, these methods not only require additional equipment, but also are not very effective. In contrast, phase modulation has obvious advantages. The phase-modulated object light wave is uniform in intensity, and interfering with the reference wave can achieve a better interferogram. Moreover, after Fourier transform, there is no extremely strong central spot on the spectrum, as shown in Figure 3 . In this way, the dynamic range of the storage material can be effectively utilized, and the storage density of the volume holographic memory can be improved. the

However, the input method of phase modulation will bring inconvenience in the process of data holographic reading. CCD or CMOS detectors can only detect intensity, not phase directly. For this, a phase-to-amplitude conversion is necessary for detection. The existing phase-amplitude conversion methods mainly include: real-time interferometry; double exposure interferometry; coaxial interferometry. The real-time interferometry means that the object light wave and the reference light are irradiated simultaneously during the reading process, and the reference light irradiates the recording material to reproduce the recorded object light wave, while the object light wave passes through the blank spatial light modulator without loading any information. After the object light wave passes through the recording material, it interferes with the reproduced object light wave to achieve the conversion from phase to amplitude. This method requires sophisticated optical instruments and high reset accuracy because the two light waves pass through different optical paths. The double exposure method is to record phase modulated information and a blank page at the same position of the recording material. Two beams of object light waves can be reproduced with one beam of reference waves, thereby performing phase-amplitude conversion. The disadvantage of this method is obvious. Since an additional blank page is stored for phase-amplitude conversion, the dynamic range of the material will be consumed by half, and the storage density of the volume holographic memory will be reduced accordingly. The coaxial interferometry cleverly uses the central spot on the spectrum surface as a reference light, which interferes with the reproduced object light wave to achieve the purpose of phase-amplitude conversion. However, this method requires a strong central light spot as a reference light, which deviates from the requirement of eliminating the central light spot on the spectral surface to increase the density of the volume holographic memory. In addition, these methods have a common problem: the light beam used for phase-amplitude conversion all passes through the recording material, which consumes the recording material to a certain extent. Strictly speaking, these phase-to-amplitude conversion methods are not suitable for volume holographic memory. the

Contents of the invention

The object of the present invention is to provide a phase-amplitude conversion method and device for volume holographic memory based on phase-shift interferometry. In view of the structure of the reference light passing through the recording material in the previous method, the present invention introduces the third light wave that does not pass through the recording material as the reference wave. In order to avoid precise optical path adjustment, a phase-shifting interferometry is introduced, and from the recorded multiple interferograms The original phase information is extracted, and the reference wave phase shift error and reference wave tilt error can be corrected. Although this method requires phase-amplitude conversion during the data reading process, this process only performs phase-amplitude conversion during the holographic reproduction process, which does not affect the recording process and improves the storage density of the system. the

The technical solution of the present invention is: a phase-to-amplitude conversion method suitable for volume holographic memory, which is characterized in that it includes the following steps:

In the first step, the data page is uploaded to the spatial light modulator. Compared with the amplitude adjustment, the phase modulation has the advantages of eliminating the central spot, uniform spectral surface, and easy to increase the density of the volume holographic memory, so the phase modulation of the object light wave is carried out by using the phase spatial light modulator. the

The second step is holographic recording. The object light wave interferes with the reference wave on the spectral plane through the front Fourier transform lens, and the interference fringes are recorded by the photopolymer material placed on the spectral plane of the 4-f system to form a volume holographic grating. the

The third step is holographic reading. During the input and reading process, we use the shutter to block the object light wave, and only use the reference wave to irradiate the recording material to reproduce the phase-modulated object light wave, and then pass through the post-Fourier transform lens to reach the image plane of the 4-f system. A CCD camera is placed on the image plane for data reading. Since the data input process uses phase modulation, the directly acquired image discards phase information and has uniform intensity. the

The fourth step is phase-amplitude conversion. A beam of coherent plane waves is separated from the light source, without going through the optical path of holographic recording and holographic reading, directly reaching the image plane and interfering with the reproduced object light wave on the surface of the CCD. The interferogram is collected by a CCD camera to obtain the first interferogram. Then the phase of this beam of plane wave is uniformly changed by the phase shifting device, and interferes with the object light wave again to obtain the second interferogram. the

Through the phase shift recovery algorithm, we can calculate the original phase information of the object light wave from the two interferograms. This phase shift recovery algorithm is simple and easy to implement, and has a good correction ability for phase shift errors and reference light tilt errors. Very suitable for volume holographic memory. the

The specific actions are as follows:

Assuming that the two collected interferograms are I ₁ I ₂ , they are expressed as:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; A</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; A</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; a</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>$

Where AA _r is the amplitude of the object light wave and the reference wave, a(x, y) is the phase of the object light wave, b is the phase of the reference wave, and c is the phase shift. From the two formulas,

$\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; AAA</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span>$

in, $4{\mathrm{AAA}}_r\sin \frac{c}{2}=\sqrt{{(I_1-I_2)}^2+{\mathrm{the\; tan}}^2\frac{c}{2}{(I_1+I_2-2A^2-2A_r^2)}^2}.$

For the case where the phase shift amount c in the above formula is π, special treatment is required:

$\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; A</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; .</span>$

a(x, y) is the result of the phase-to-amplitude conversion, that is, the stored data page. the

In the actual use of the volume holographic memory, a pre-processing step and a post-processing step are also included. Preprocessing step: encode the original data to be stored to form a two-dimensional data page, and the combination or distribution of pixels on the data page appears in a series of fixed patterns. Like amplitude modulation, the original data is encoded in order to ensure less crosstalk in holographic storage and obtain a reproduced hologram with a high signal-to-noise ratio. The principle of encoding is to impose certain restrictions on the combination or distribution of pixels on the page, that is, only certain fixed patterns are allowed to appear, and other patterns are prohibited from appearing. For example, if there is another 1 pixel in a 1-pixel four-neighborhood, it will easily form interference, so this mode is prohibited; similarly, more than one 1-pixel is prohibited in a 1-pixel eight-neighborhood. the

Post-processing step: binarization processing, converting the grayscale image obtained by the phase shift recovery algorithm into a binary image. the

The device for realizing the above-mentioned phase-amplitude conversion method suitable for volume holographic memory is characterized in that it is composed of a laser, a beam filtering and collimating device, a polarizing beam splitting prism, a beam splitting prism, a mirror, front and rear Fourier transform lenses of a 4-f system, and a reference optical path focusing It is composed of optical lens, diaphragm, phase shift generating device, photopolymer material disc, reflective phase spatial light modulator, CCD detector and computer. The monochromatic linearly polarized plane wave emitted by the laser passes through the beam filtering and collimating device After being collimated by the pinhole filter collimating lens of the microscopic objective lens, a beam of light is refracted by the first polarization beam splitter as a phase-amplitude conversion beam, and the transmitted beam is then divided into an object light wave and a reference light wave by the second polarization beam splitter prism. The object light wave is irradiated to the reflective phase-type spatial light modulator through the third polarization beam-splitting prism, the phase-modulated object light wave is focused to the surface of the photopolymer material disc through the front Fourier transform lens, and the reference wave passes through the diaphragm and passes through the mirror and The reference optical path condenser lens irradiates the surface of the photopolymer material disc and interferes with the object light wave, and the interference light field is recorded by the photopolymer material. When holographic reading is performed, the object light wave is turned off, only the reference light wave is turned on, and the reference light wave is irradiated To the surface of the photopolymer material disc, the reproduced light wave of the diffraction treatment passes through the rear Fourier transform lens and reaches the surface of the CCD detector. , a beam splitting prism, reaching the surface of the CCD detector and reappearing object light waves to realize phase-amplitude conversion, and the CCD detector is connected to a computer for controlling input and output and interferogram processing. the

The present invention will be further described below in conjunction with the accompanying drawings and embodiments. the

Description of drawings

Fig. 1 is a simple schematic diagram of a volume holographic memory in the prior art;

Fig. 2 is the simulation experiment comparison chart of amplitude modulation and phase modulation;

Figure 3 is a comparison diagram of optical experiments of amplitude modulation and phase modulation;

Fig. 4 is the optical path diagram of the phase-amplitude conversion device in the volume holographic memory of the present invention;

Fig. 5 is the input phase information code diagram;

The image of Figure 6 Example 1;

Image of Example 2 in Figure 7. the

Explanation of symbols: 400 is a laser; 401 is a beam filtering and collimating device; 402, 403, 404 are polarization beam splitters; 405 is a beam splitter; 406, 407, 408, 409 are mirrors; 410 is the front of the 4-f system Fourier transform lens; 411 is the post-Fourier transform lens of the 4-f system; 412 is the reference light path condenser lens; 413, 414 are apertures; 415 is a phase shift generating device; 416 is a photopolymer material disc; 417 is a reflection 418 is a CCD detector; 419 is a computer for controlling input and output and interferogram processing. the

Detailed ways

The specific implementation process of the phase-amplitude conversion method and device in the volume holographic memory will be further described in detail below in combination with two specific embodiments and accompanying drawings. the

Example 1:

This embodiment is an example of performing phase-amplitude conversion when an uncoded binary image is input to a volume holographic memory. The input image is, for example, a black and white grid as shown in Fig. 5, and the grid size is 16 pixels, that is, 211.2 microns. the

In this embodiment, the process of phase-amplitude conversion is as follows:

1. The input image is uploaded to the phase-type spatial light modulator. The spatial light modulator used is a reflective ferroelectric liquid crystal spatial light modulator from Displaytech Corporation of the United States, the model is Model LDP-0983-HS1LightCaster, the resolution is 1280×768 pixels, the pixel size is 13.2 microns, and the filling ratio is 90%. This spatial light modulator is originally amplitude modulation. When we rotate it 22.5 degrees along the optical axis relative to the incident polarizer, binary phase modulation can be realized, that is, the output phases are 0 and π. the

2. Holographic recording. Turn on the object light wave and the reference light, let the two interfere on the Fourier spectrum surface of the volume holographic memory, and record it by the photopolymer material disc. The model used in this example is the cationic ring-opening polymer material of HMD-120-G-1206-D-400 from DCE Aprilis in the United States. Thickness 400 microns. the

3. Holographic reading. The object wave is turned off, and only the reference wave is turned on to irradiate the storage material. The reproduced object light wave passes through the post-Fourier transform lens of the volume holographic memory and propagates to the image plane. the

4. Collect the first interferogram. The coherent plane wave (hereinafter referred to as converted wave) drawn from the light source directly propagates to the image plane and interferes with the reproduced object light wave. The CCD camera placed on the image plane collects the first interferogram (shown in Figure 6.a ). the

5. Collect the second interferogram. The phase of the converted wave is changed by the phase shifting device, and interferes with the reproduced object light wave again, and the CCD camera collects the second interferogram (shown in Figure 6.b). the

6. Subtract the first interferogram from the second interferogram, divide by the amplitude of the object light wave and the reference wave, and the sine value of half the phase shift, and then find the arc sine plus the initial phase of the reference wave and the phase shift. Half, that is, the phase diagram of the object light wave is obtained, as shown in Figure 6.c. the

7. Binary processing. Due to the inevitable system noise of the volume holographic memory, the calculated phase map of the object light wave is not perfect. In addition, since the interferogram collected by the CCD has 256 gray levels, the obtained phase image also has 256 gray levels. The noise on the phase map can be eliminated by median filtering, and the binary map can be obtained by thresholding, as shown in Figure 6.d. Since the 4-f optical conversion system structure is used in the volume holographic memory, the obtained phase map of the image plane is the phase of the input plane. the

Example 2:

This embodiment is an example of performing phase-amplitude conversion when an uncoded binary image is input to a volume holographic memory. The input image is, for example, the black and white grid in Figure 6, and the grid size is 8 pixels, that is, 105.6 microns. the

In this embodiment, the process of phase-amplitude conversion is as follows:

1. The input image is uploaded to the phase-type spatial light modulator. As in the previous example, the white squares on the input map are modulated to phase π, and the black squares are modulated to phase 0. the

2. Holographic recording. Turn on the object light wave and the reference light, let the two interfere on the Fourier spectrum surface of the volume holographic memory, and record it by the photopolymer material disc. the

3. Holographic reading. The object wave is turned off, and only the reference wave is turned on to irradiate the storage material. The reproduced object light wave passes through the post-Fourier transform lens of the volume holographic memory and propagates to the image plane. the

4. Collect the first interferogram. The converted wave directly propagates to the image plane and interferes with the reproduced object light wave, and the first interferogram is collected by the CCD camera placed on the image plane (shown in Figure 7.a). the

5. Collect the second interferogram. The phase of the converted wave is changed by the phase shifting device, and interferes with the reproduced object light wave again, and the CCD camera collects the second interferogram (shown in Figure 7.b). the

6. Subtract the first interferogram from the second interferogram, divide by the amplitude of the object light wave and the reference wave, and the sine value of half the phase shift, and then find the arc sine plus the initial phase of the reference wave and the phase shift. Half, that is, the phase diagram of the object light wave is obtained, as shown in Figure 7.c. the

7. Binary processing. The noise on the phase map can be eliminated by median filtering, and the binary map can be obtained by thresholding, as shown in Figure 7.d. Since the 4-f optical conversion system structure is used in the volume holographic memory, the obtained phase map of the image plane is the phase of the input plane. the

Embodiment 3: as shown in Figure 4, 400 is a laser; 401 is a beam filtering and collimating device; 402, 403, 404 are polarization beam splitters; 405 is a beam splitter; 406, 407, 408, 409 are reflectors; 411 is the post-Fourier transform lens of the 4-f system; 412 is the reference light path condenser lens; 413, 414 are the diaphragm; 415 is the phase shift generating device; 416 is the photopolymerization 417 is a reflective phase-type spatial light modulator; 418 is a CCD detector; 419 is a computer for controlling input and output and interferogram processing. the

The monochromatic linearly polarized plane wave emitted by the laser (400) is collimated by the microscopic objective pinhole (401) filtering collimating lens (401), and then refracted by the polarization beam splitter (402) into a beam as a phase-amplitude conversion beam. The transmitted light beam is divided into an object light wave and a reference light wave by a polarization beam splitter (403). A FFT lens (410) is focused onto the surface of the photopolymer material disc (416). The reference wave passes through the diaphragm (413), is reflected by the mirrors (408) and (409), passes through the lens (412) and irradiates the surface of the photopolymer material disc (416) to interfere with the object light wave, and the interference light field is photopolymerized material records. When holographic reading, the object light wave is turned off, and only the reference light wave is turned on. The reference light wave is irradiated on the surface of the photopolymer material disc (416), and the diffraction-processed reproduced light wave passes through the post-Fourier transform lens (411) and reaches the surface of the CCD detector (418). At the same time, the converted light beam reaches the surface of the CCD detector (418) and reproduces the object light wave through the reflector (406), diaphragm (414), phase shift generating device (415), reflector (407) and dichroic prism (405), realizing phase-to-amplitude conversion. The CCD detector is connected to a computer (419) for controlling input and output and interferogram processing. the

Although the present invention provides two embodiments, they are not intended to limit the present invention. Any person skilled in the art can obtain similar results without departing from the scope of the present invention. The protection scope of the present invention shall be determined by the scope defined by the appended claims. the

Claims (4)

1. A phase-to-amplitude conversion method suitable for volume holographic memory, characterized in that it comprises the following steps: --- Upload the data page to the phase spatial light modulator; ---Holographic recording, the object light wave passes through the front Fourier transform lens and interferes with the reference wave on the spectral plane, and the interference fringes are recorded by the photopolymer material placed on the spectral plane of the 4-f system to form a volume holographic grating; ---Holographic reading, during the input and reading process, use the shutter to block the object light wave, and only use the reference wave to irradiate the recording material to reproduce the phase modulated object light wave, and then pass through the post-Fourier transform lens to reach the image plane of the 4-f system; a The CCD camera is placed on the image plane for data reading; ---Phase-amplitude conversion, a coherent plane wave is separated from the light source, directly reaches the image plane and interferes with the reproduced object light wave on the CCD surface, and the interferogram is collected by the CCD camera to obtain the first interferogram; then through the phase shift device Change the phase of this plane wave evenly, and interfere with the object light wave again to obtain the second interferogram; ---Through the phase shift recovery algorithm, the original phase information of the object light wave is calculated from the two interferograms. The specific calculation formula is, assuming that the two collected interferograms are I ₁ I ₂ , the two are expressed as: ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; AAA</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>$ ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; AAA</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>$ Where AA _r is the amplitude of the object light wave and the reference wave, a(x, y) is the phase of the object light wave, b is the phase of the reference wave, and c is the phase shift. From the two formulas, $\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; AAA</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span>$ in, $4{\mathrm{AAA}}_r\sin \frac{c}{2}=\sqrt{{(I_1-I_2)}^2+{\mathrm{the\; tan}}^2\frac{c}{2}{(I_1+I_2-2A^2-2A_r^2)}^2,}$ In the above formula, the phase shift c≠π, for the case of c=π, special treatment is required: $\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; AAA</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; ;</span>$ a(x, y) is the result of the phase-to-amplitude conversion, that is, the stored data page. 2. The phase-to-amplitude conversion method suitable for volume holographic memory according to claim 1, characterized in that it also includes the following steps: a preprocessing step, encoding the original data to be stored to form a two-dimensional data page, and the data page on the data page Pixel combinations or distributions occur in a series of fixed patterns. 3. The phase-to-amplitude conversion method suitable for volume holographic memory according to claim 1 or 2, characterized in that it also includes the following steps: binarization processing, converting the grayscale image obtained by the phase shift recovery algorithm into binary picture. 4. The device for implementing the phase-amplitude conversion method suitable for volume holographic memory according to the above claims is characterized by a laser, a beam filtering and collimating device, a first polarization beam splitter, a second polarization beam splitter, and a third polarization beam splitter. Dichroic prism, dichroic prism, first reflector, second reflector, third reflector, fourth reflector, front and rear Fourier transform lens of 4-f system, reference light path condenser lens, first diaphragm, second light It consists of a diaphragm, a phase shift generating device, a photopolymer material disc, a reflective phase spatial light modulator, a CCD detector and a computer. The monochromatic linearly polarized plane wave emitted by the laser passes through the microscopic objective lens of the beam filtering and collimating device. After being collimated by the pinhole filter collimating lens, a beam of light is refracted by the first polarization beam splitter as a phase-amplitude conversion beam, and the transmitted beam is divided into object light wave and reference light wave by the second polarization beam splitter prism, and the object light wave passes through the second polarization beam splitter prism. The three-polarization beamsplitter prism irradiates the reflective phase-type spatial light modulator, the phase-modulated object light wave is focused to the surface of the photopolymer material disc through the front Fourier transform lens, and the reference wave passes through the first aperture and passes through the first reflector, The second reflection mirror and the reference optical path condenser lens irradiate the surface of the photopolymer material disc and interfere with the object light wave, the interference light field is recorded by the photopolymer material, when holographic reading is performed, the object light wave is turned off, and the reference light wave is irradiated to the surface of the photopolymer material disc, the diffracted reproduced object light wave reaches the surface of the CCD detector through the rear Fourier transform lens, and at the same time, the converted light beam passes through the third reflector, the second aperture, and the phase shift generating device , the fourth reflector, and the splitter prism reach the surface of the CCD detector and reproduce the object light wave to realize the phase-amplitude conversion. The CCD detector is connected to a computer for controlling input and output and interferogram processing.

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