JP3685819B2 - Information recording method to hole burning memory using spatial light modulator - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for recording information in a hole burning memory using a spatial light modulator, in which a hologram generated by interference between object light on which information is placed by the spatial light modulator and reference light is recorded as information in the hole burning memory. Is.
[0002]
[Prior art]
Conventionally, photochemical hole burning memory (PHB) has been studied as a bit-by-bit memory such as an optical disk, but with this method, sufficient contrast cannot be obtained, resulting in an increase in memory density. Absent. Therefore, it has been proposed and experimented to record a two-dimensional image (information) as a hologram on the PHB.
[0003]
The light absorption band of the organic molecules in the polymer constituting the PHB extends over a wide band of several terahertz as shown in the graph of FIG. Here, the horizontal axis of the graph indicates the wavelength [λ] of light, and the vertical axis indicates the degree of light absorption. When such a PHB is irradiated with light of a single wavelength, the illustrated holes remain in the absorption band corresponding to that wavelength, and information is recorded. Therefore, if a plurality of recording holes are employed, multiplexed recording can be performed on the PHB, and a wavelength multiplexing memory can be configured. Since PHB requires a very good wavelength purity, laser light must be used for recording. However, in principle, multiplexing of recording is performed if the wavelength width of the laser light is 10 [MHz]. ^Five It will be about. Further, the recorded hole can be read out by a laser beam having a wavelength used for recording the hole. Such an effect of reading and writing information with respect to PHB is currently obtained in an environment where PHB is kept at an extremely low temperature of several degrees K or less.
[0004]
It is also known that by applying a voltage to a polymer and applying an electric field E, different holes can be recorded depending on the difference in the applied electric field E. That is, even if the wavelength of light to be recorded on the PHB is fixed, different information can be recorded by changing the voltage applied to the PHB, that is, the electric field E. When information is recorded in this way, information can be read by applying the same electric field E to the PHB as the electric field E applied during recording.
[0005]
Accordingly, the PHB can be used as a four-dimensional memory of the two-dimensional positions x and y for writing holes, the wavelength λ of light used for writing holes, and the applied electric field E.
[0006]
However, as described above, laser light having a high wavelength purity must be used for information recording on the PHB. Therefore, in order to record a two-dimensional image on the PHB, conventionally, a transmissive film is used to obtain a predetermined wavelength. The incident laser beam was selectively transmitted. Therefore, in the conventional information recording method in which input information is written using this transmissive film, it takes time to create the film and replace the film. For this reason, the precious advantage that wavelength multiplex recording can be easily performed by using PHB has not been utilized at all.
[0007]
As a method for solving this problem, there is an information recording method disclosed in Japanese Patent Laid-Open No. 3-72313 by the present applicant. In this publication, a PHB recording system using a spatial light modulator (SLM) shown in FIG. 10 is used for this information recording, and an SLM is adopted instead of a transmissive film that is inconvenient to handle.
[0008]
An input image 62 illuminated by a lamp 61 is provided on the photocathode 11 side of the spatial light modulation tube 1. Light from the input image 62 is imaged on the photocathode 11 by the lens 63, and electrons corresponding to the input image are emitted. On the other hand, the light source is composed of a wavelength tunable laser light source 7 composed of an Ar laser 71 and a dye laser 72, and the wavelength of the output light is set to a different value every 1 nm. Laser light from the wavelength tunable laser light source 7 is incident on the polarizer 3 through the lens 81, the pinhole 82 and the lens 83, collimated, and incident on the half mirror 84. The laser light reflected by the half mirror 84 passes through the λ / 2 plate 85 and enters the PHB 9 as reference light (REF). The laser light transmitted through the half mirror 84 is reflected by the electro-optic crystal plate 15 of the spatial light modulation tube 1, the optical path is changed by the half mirror 4, and enters the PHB 9 as object light (OBJ) through the analyzer 5. As a result, a hologram obtained by the interference between the object beam and the reference beam is recorded on the PHB 9, and a laser beam image having an intensity distribution corresponding to the input image is recorded on the PHB 9 as information.
[0009]
[Problems to be solved by the invention]
However, when a hologram is recorded on the PHB by such a method, there is a considerable non-uniformity especially in the SLM that produces object light, which is not preferable because of non-uniformity (shading) of the image. The cause of this non-uniformity is the processing accuracy (polishing accuracy) when the electro-optic crystal, which is the light modulation material of the SLM, is processed into a parallel plate, and the refractive index distribution of the electro-optic crystal material itself. This is due to the uniformity and errors of the optical system constituting the apparatus. For example, 55 ° cut LiNbO _Three Is used for the electro-optic crystal and this LiNbO _Three Is processed as shown in the cross-sectional view of FIG. 11, and a height difference of Δd = 1.3 μm is generated between the central portion and the peripheral portion of the crystal plate. When readout laser light or reference laser light having a wavelength of 632.8 nm reciprocates with respect to such an electro-optic crystal plate, a difference of π radians occurs in the phase of the light between the peripheral portion and the central portion of the crystal plate, and after passing through the polarizing plate In the light intensity distribution, the central part is bright and the peripheral part is dark.
[0010]
Similar problems occur in SLMs that use liquid crystals instead of electro-optic crystal plates. In this case, the cause of the non-uniformity in the image is due to the non-uniformity between the two glass substrates into which the liquid crystal is injected, that is, the non-uniform cell thickness.
[0011]
When a hologram is recorded on the PHB with such a non-uniform optical phase distribution or light intensity distribution, it is clear that the reproduced image includes the same non-uniformity.
[0012]
The present invention has been made to solve such a problem, and an object of the present invention is to provide an optical recording method that can compensate for non-uniformity of a hologram image and can read and write to a multiple hologram memory in real time. To do.
[0013]
[Means for Solving the Problems]
In the present invention, information is placed on object light using an SLM, a hologram generated by interference between the object light and reference light is recorded on the PHB as information, and the information recorded on the PHB is read using light having a predetermined wavelength. In the information recording method to the PHB using the SLM, the wavelength (λ) -electric field (E) plane shown in FIG. 1A is considered and information is read from and written to the PHB according to the following steps.
[0014]
(1) Electric field E on PHB ₁ In the state where information is not on the object light, the wavelength λ ₀ The first hologram is recorded on the PHB using the reference beam.
[0015]
(2) Electric field E on PHB ₂ In the state where information is on the object light, the wavelength λ ₀ The second hologram is recorded on the PHB using the reference beam.
[0016]
▲ 3 ▼ About (E ₁ + E ₂ ) / 2 electric field E ₀ Is applied to the PHB, the wavelength λ ₀ Wavelength λ that creates holes in the wavelength region adjacent to ₁ Or wavelength λ ₂ The information recorded in the PHB is read using the reading light of.
[0017]
Further, considering the λ-E plane shown in FIG. 1B, information is read from and written to the PHB according to the following steps.
[0018]
(1) Electric field E on PHB ₀ In the state where information is not on the object light, the wavelength λ ₁ The first hologram is recorded on the PHB using the reference light.
[0019]
(2) Electric field E on PHB ₀ In the state where information is on the object light, the wavelength λ ₂ The second hologram is recorded on the PHB using the reference light.
[0020]
(3) Electric field E ₀ Electric field E that generates holes in the electric field area adjacent to ₁ Or electric field E ₂ Is applied to the PHB, about (λ ₁ + Λ ₂ ) / 2 wavelength λ ₀ The information recorded in the PHB is read using the reading light of.
[0021]
In step (1) or step (2), the phase of the object light is shifted by π, and the first or second hologram is recorded on the PHB.
[0022]
[Action]
When the information recorded on the PHB in step (3) is read, the first and second hologram images recorded on the PHB in steps (1) and (2) are read out superimposed. That is, the wavefronts of the light waves of the first and second hologram images are read simultaneously, and the read images are strengthened or weakened by the phase difference of the read light waves. That is, when the wavefront (phase) of the light wave of each of the first and second hologram images recorded on the PHB is 0 (equal), the recorded images are read out with emphasis on each other, and the PHB readout output is The brightest. Further, when the phase difference of the light wave is π, the recorded images are read out with weakening each other, and the PHB read output becomes the darkest. Further, when the phase difference between the light waves of the first and second hologram images is an intermediate value such as π / 4 or π / 2, the readout output is an intermediate level between the brightest output and the darkest output. Read out as intensity output. Accordingly, the phase differences between the background noises recorded in the first hologram in which the object light is not recorded and the second hologram in which the object light is recorded are equal. Therefore, the first and second holograms are By reading out simultaneously, the background of the synthetic hologram obtained by superimposing these holograms is brightest. When the phase of the object light is shifted by π and the first or second hologram is recorded on the PHB, the phase difference between the background noises recorded on the first hologram and the second hologram is π Therefore, when the holograms are read out simultaneously, the background of the synthesized hologram is read out the darkest.
[0023]
【Example】
FIG. 2 shows a PHB recording system used in a method for recording information on a PHB using an SLM according to an embodiment of the present invention.
[0024]
The photochemical hole burning memory (PHB) 31 is a polyvinyl butyran (PYB) film doped with chlorin (2,3-dihydroporphyrin) and has a thickness of about 90 μm. This film is in direct contact with the liquid helium in the cryostat (cooler) 32, and its temperature is maintained at 1.7 to 4.2K. This film constituting the PHB 31 is fixed by being sandwiched between glass plates coated with a transparent conductive film. By supplying a voltage to the transparent conductive film from a voltage-variable power source 33, 10% of the film is formed. ^Five An electric field of about V / cm can be applied.
[0025]
Ar for recording / reproducing light source ⁺ A tunable laser light source (not shown) composed of a laser and a dye laser is used. A wavelength of 610 to 670 nm is used as the wavelength of the output laser light. Similarly, the light from the dye laser is magnified by an objective lens (not shown), becomes parallel light by a collimator lens (not shown), and enters the half mirror 34. The laser beam that has passed through the half mirror 34 is applied to the PHB 31 as reference light or recording / reading light. Further, the laser beam reflected by the half mirror 34 is further converted in optical path by the half mirror 35 to become information readout light, and enters the readout side (modulation material side) of the spatial light modulator (SLM) 37 via the phase shifter 36. To do. On the other hand, the input image 38 illuminated by the lamp light source also enters the writing side (address material side) of the SLM 37 through the lens 39. Accordingly, the information readout light whose optical path has been converted by the half mirror 35 overlaps the input image 38 while reciprocating the modulation material, and object light phase-modulated by the input information is generated. If necessary, the phase of the object light is shifted by the phase shifter 36 and enters the PHB 31.
[0026]
The object light incident on the PHB 31 interferes with the reference light transmitted through the half mirror 34 on the PHB 31. Due to this interference, an interference fringe of about 2 μm is formed, and the input information on the object light is recorded in the PHB 31 as a hologram. This record is 500 μW / cm ² It is performed with power of rank. Further, the reading of the recorded image is 1/10 of the recording power. ^Four It is done with the power of.
[0027]
The SLM 37 is used as means for placing information on object light, and its detailed structure is shown in FIG. In this SLM 37, a parallel alignment nematic liquid crystal 37a is used as a modulation material. The liquid crystal molecules of the parallel alignment nematic liquid crystal 37a are aligned parallel to the plane and are sandwiched between the alignment layers 37b and c. A dielectric mirror 37d that reflects incident information read light is provided on the alignment layer 37b side. A photoconductor 37e made of amorphous silicon (a-Si) is provided in contact with the dielectric mirror 37d. The photoconductor 37e is used as an addressing material that reacts to writing light. Further, transparent conductive films (ITO) 37f, g are provided on the outer sides of the photoconductor 37e and the alignment layer 37c, and glass face plates 37h, i are provided on the outer sides of the transparent conductive films 37f, g. It has been. A predetermined voltage is applied from the power supply 40 to the transparent conductive films 37 f and g.
[0028]
When the input image 38 is illuminated with external light and focused on the photoconductor 37e by the lens 39, the electrical resistance of the a-Si in the portion where the light hits is lowered and applied between the transparent conductive films 37f and 37g. The applied voltage is applied to the parallel-aligned nematic liquid crystal 37a through the photoconductor 37e having a reduced electric resistance. The liquid crystal molecules of the parallel-aligned nematic liquid crystal 37a are aligned parallel to the plane as described above, but tilt when a voltage is applied. The information readout light has a plane of polarization e parallel to the liquid crystal molecules, and the refractive index of the nematic liquid crystal 37a where the liquid crystal molecules are tilted changes due to voltage application, so the phase of the readout light reflected by the dielectric mirror 37d is , And is modulated corresponding to the input image 38. That is, input information that is two-dimensionally phase-modulated is placed on the object light.
[0029]
The phase of the object light is uniformly shifted by π as necessary by the phase shifter 36. FIG. 4 shows the detailed structure of the phase shifter 36. The phase shifter 36 is made of the same parallel alignment nematic liquid crystal 36a as the SLM, and alignment layers 36b and c are provided on both sides of the parallel alignment nematic liquid crystal 36a. Further, transparent conductive films 36d, e are provided on both outer sides of the alignment layers 36b, c, and glass face plates 36f, g are provided on both outer sides of the transparent conductive films 36d, e. A predetermined voltage is applied from the power supply 41 to each transparent conductive film 36d, e as required. When this voltage is applied between the transparent conductive films 36d and 36e, the refractive index of the parallel-aligned nematic liquid crystal 36a changes uniformly as in the above-described SLM, and the phase of the object light passing through the liquid crystal 36a is uniform. Is shifted by π.
[0030]
A method for recording information on the PHB using the SLM according to the present embodiment using the apparatus configured as described above will be described in detail below with reference to FIG.
[0031]
Assume that the object light before the input image is written to the PHB 31, that is, the object light with no input image and no information, has non-uniform phase as shown in FIG. This nonuniformity of the phase of the object light is caused by the nonuniformity of the thickness of the parallel alignment nematic liquid crystal 37a constituting the SLM 37 and the error of the optical system constituting the apparatus. In FIG. 6A, the non-uniformity of the phase is depicted so as to change binaryly between a phase 0 portion and a phase π portion for convenience of explanation. The phase change to the portion of phase π changes gently like a sine wave, for example. The object light shown in FIG. 6A is shown in FIG. ₀ , E ₁ The first hologram is recorded on the PHB 31 together with the reference light. That is, the electric field E is supplied from the power source 33 to the PHB 31. ₁ Wavelength λ ₀ The first hologram image is recorded on the PHB 31 using the reference light. This object light corresponds to the background (background noise).
[0032]
Next, when the input image having the shape shown in FIG. 5D is written into the SLM 37 so as to π-modulate the phase of the readout light, the object light shown in FIG. 5B is obtained. The phase π corresponding to the input image is added to the background phase at each image position, and the object light has the illustrated phase change. This object light on which the input image is carried as information is shown in FIG. ₀ , E ₂ The second hologram is recorded on the PHB 31 together with the reference light. That is, the voltage supplied from the power source 33 to the PHB 31 is the electric field E. ₂ The same wavelength λ as above ₀ The second hologram image is recorded on the PHB 31 using the reference light.
[0033]
Next, the image recorded on the PHB 31 in this way is read using the collimated laser beam that has passed through the half mirror 34 as readout light. At this time, the information reading light of the SLM 37 is closed by a shutter (not shown). This read condition is shown in FIG. ₁ , E ₀ ) Or (λ ₂ , E ₀ ). That is, the voltage applied from the power source 33 to the PHB 31 is the electric field E. ₀ (= (E ₁ + E ₂ ) / 2), the wavelength λ ₁ Or λ ₂ The information recorded in the PHB 31 is read using the reading light. Where the wavelength λ ₁ , Λ ₂ Is the wavelength λ ₀ This is a wavelength that generates holes in the wavelength region adjacent to. For example, λ ₀ Is 633 nm, λ ₁ = 633-5 GHz, λ ₂ = 633 + 5 GHz. 5 GHz is about 6.5 × 10 ^-3 Corresponds to nm. In addition, the electric field E ₀ Is 0, E ₁ = -2KV / cm, E ₂ = +2 KV / cm. FIG. 5C shows an image obtained by this readout, and a clear image from which background noise has been removed is obtained. The background noise is removed as follows.
[0034]
That is, the readout light wavelength and the applied electric field are (λ ₁ , E ₀ ) Or (λ ₂ , E ₀ ), When the information recorded in the PHB 31 is read, the reference light wavelength and the applied electric field are (λ ₀ , E ₁ ) And the first hologram image recorded on the PHB 31 and (λ ₀ , E ₂ ), The second hologram image recorded on the PHB 31 is superimposed and read. In other words, the wavefronts of the light waves of the first and second hologram images recorded on the PHB 31 are read simultaneously, and the read images are strengthened or weakened with each other depending on the phase difference of the read light waves. That is, when the phase difference between the light waves of the first and second hologram images recorded on the PHB 31 is 0, that is, when the phases of the overlapping light waves are 0, 0, or when the phases of the overlapping light waves are Images recorded at π and π are read out with mutual emphasis by interference. For this reason, the output read from the PHB 31 is brightest in the background portion indicated by the white area in FIG. Further, the images recorded when the phase difference of the light wave is π, that is, where the phases of the overlapping light waves are 0 and π, are read out with each other weakened, and the output read from the PHB 31 is as shown in FIG. The signal portion shown in the shaded area in (c) is the darkest.
[0035]
In addition, although the phase of each light wave is drawn in binary, as described above, the phase actually changes in a sine wave shape. Since this phase change is the same for each background of the object light shown in FIG. 5A and the object light shown in FIG. 5B, the phase difference between the overlapping light waves is 0, and the light is read out most brightly. Here, when the phase difference of each light wave is an intermediate value such as π / 4 or π / 2, the readout output is read out as an output having an intermediate level intensity between the brightest output and the darkest output.
[0036]
Accordingly, between the backgrounds recorded in the first hologram image shown in FIG. 5A where the object light is not recorded and the second hologram image shown in FIG. 5B where the object light is recorded. Since the phase differences are equal as described above, the background of the composite hologram image shown in FIG. 5C obtained by superimposing these holograms by simultaneously reading the first and second hologram images is Brightest.
[0037]
When it is necessary to shift the phase of the signal portion uniformly by π, information recording is performed as follows. In other words, a predetermined voltage is supplied from the power source 41 to the phase shifter 36, and the phase of the object light on which the input information reflected from the SLM 37 does not ride is uniformly shifted by π. The object light is shown in FIG. It becomes a phase change. That is, the phase change is in a state opposite to that shown in FIG. First, the object light has a reference light wavelength and an applied electric field of (λ ₀ , E ₁ ) On the PHB 31 under the same conditions as described above. Next, the object light carrying the same input information as described above shown in FIG. 5D is the same as that shown in FIG. 5B as shown in FIG. ₀ , E ₂ ) Is recorded as a second hologram image on the PHB 31 under the same conditions as described above. Next, the same as above (λ ₁ , E ₀ ) Or (λ ₂ , E ₀ When the information recorded on the PHB 31 is read out under the condition (1), an image shown in FIG. 5 (g) is obtained. In this image, the phase of the background of the first hologram image shown in FIG. 5E and the background phase of the second hologram image shown in FIG. Since there is a difference, when the holograms are read out simultaneously, the image of the background area of the composite hologram becomes the darkest as shown by the hatched area in FIG. Further, since each phase of the light wave in the input image portion is equal to 0, 0 or π, π, the readout output of the input image portion is the brightest as shown in FIG. For this reason, the reproduced image shown in FIG.
The output is an inverted version of the reproduced image shown in (c).
[0038]
As a result, the input information shown in FIG. 5D placed on the object light has the brightest portion in the reproduced image of FIG. 5C as the background and the darkest portion in the reproduced image of FIG. 5G. The background is clearly read. That is, the thickness of the parallel-aligned nematic liquid crystal 37a forming the SLM 37 is non-uniform, and there is an error in the optical system, and background noise that causes image non-uniformity is caused by the first and second holograms. Even in an image, in a synthetic hologram obtained by superimposing these holograms, each background noise compensates for each other to form the brightest or darkest uniform background. As a result, in the reproduced image of FIG. 5C or FIG. 5G read out as a synthetic hologram, input information is restored faithfully and clearly to a uniform background.
[0039]
In the description of the above embodiment, the case where the object light shown in FIG. 5A in which no input information is present is phase-shifted uniformly by π using the phase shifter 36 has been described. Alternatively, the object light shown in FIG. 5B may be phase shifted uniformly by π using the phase shifter 36. Also in this case, the same image as that shown in FIG. 5G is obtained as the image obtained by synthesizing the first and second hologram images, and the same effect as in the above embodiment is achieved.
[0040]
In the description of the above embodiment, the recording of each hologram image on the PHB 31 is performed by changing the wavelength of the reference light to λ. ₀ The electric field applied to the PHB 31 is E ₁ , E ₂ In addition, reading from the PHB 31 changes the electric field to E ₀ And the wavelength of the readout light is λ ₁ Or λ ₂ However, the input information may be recorded in the PHB 31 under the following conditions. That is, the recording of each hologram image on the PHB 31 is performed by applying an electric field applied to the PHB 31 as shown in FIG. ₀ And the wavelength of the reference light is λ ₁ Or λ ₂ And change. That is, the first hologram image is (λ ₁ , E ₀ ) On the PHB 31 and the second hologram image is (λ ₂ , E ₀ ) On the PHB 31 under the conditions of Further, reading from the PHB 31 sets the wavelength of the reading light to λ ₀ The electric field applied to the PHB 31 is E ₁ Or E ₂ Do as. Where the electric field E ₁ , E ₂ Is the electric field E ₀ Is an electric field that generates holes in the electric field region adjacent to ₀ Is approximately (λ ₁ + Λ ₂ ) / 2. Even under such conditions, the first and second hologram images recorded on the PHB 31 under the above conditions are read out under the above conditions, so that each background noise compensates for each other so that the brightest or darkest uniform background can be obtained. It is formed. Therefore, the input image is clearly read out with this uniform background as in the case of the above embodiment, and the same effect as in the above embodiment can be obtained.
[0041]
The principle of the information recording method on the PHB according to the present embodiment is shown in the following document.
[0042]
APPLIED OPTICS / Vol.29, No.29 / 10 October 1990, `` Spectral hole burning and molecular computing '', 4329-4331
That is, even in this document, different electric fields E ₁ , E ₂ Is applied to the PHB and the respective electric field E ₁ , E ₂ In FIG. 1, the first and second holograms are recorded on the PHB. The recorded hologram is read out by PHB (E ₁ + E ₂ ) / 2 is applied using light having a wavelength of λ1 or λ2 while an electric field of / 2 is applied. The information recording method to PHB shown in this document is based on the same principle as the method according to this embodiment. A feature of the present embodiment is that this information recording principle is used, fixed noise generated in a recorded image due to phase distortion caused by a device such as an SLM or an optical system is removed, and recorded information is reproduced clearly.
[0043]
Further, in the description of the above embodiment, the case where the SLM 37 is configured using a parallel alignment nematic liquid crystal has been described, but the MSLM shown in FIG. 6 may be used instead of the LC-SLM using this liquid crystal. In this MSLM, a photocathode is used as an address material, and an electro-optic crystal is used as a light modulation material.
[0044]
That is, the writing light for supplying input information is incident on the photocathode 51. Photoelectric conversion is performed on the photocathode 51 where the write light is incident, and electrons are emitted from the photocathode 51 corresponding to the input image. The emitted electrons are guided to the micro channel plate (MCP) 53 by the accelerating / focusing electrode 52 and are multiplied by the electrons in the MCP 53. The multiplied electrons charge the electro-optic crystal surface according to the distribution of incident electrons. For this reason, an electric field corresponding to the input image is applied to the electro-optic crystal 55a. The electro-optic crystal 55a is LiNbO. _Three A dielectric mirror 55b is provided on the writing light side, and a transparent electrode 55c is provided on the reading light side. In the electro-optic crystal 55a, the refractive index of the portion to which an electric field is applied changes, so that information readout light having a polarization plane parallel to the crystal axis is phase-modulated by the electro-optic crystal 55a. Therefore, the input information is put on the object light reflected by the dielectric mirror 55b by this phase modulation.
[0045]
Such an MSLM may be used in place of the SLM 37 of the above embodiment, and even if the MSLM is used to configure an apparatus and the information recording method according to the above embodiment is applied, the same effects as in the above embodiment can be obtained. Is done.
[0046]
In the above embodiment, the phase of the object light is shifted using the phase shifter 36 using the parallel alignment nematic liquid crystal, but a phase shifter using the electro-optic crystal shown in FIG. 7 may be used. This phase shifter is similar to the MSLM shown in FIG. _Three The electro-optic crystal 61 is composed of transparent electrodes 62 a and 62 b on both sides of the electro-optic crystal 61. When a predetermined voltage is applied from the power source 63 to the transparent electrode 62, an electric field is applied to the electro-optic crystal 61, and the refractive index of the electro-optic crystal 61 changes uniformly. Therefore, the phase of the incident light is uniformly shifted by π due to the change in the optical refractive index.
[0047]
A phase shifter using such an electro-optic crystal may be used instead of the phase shifter 36 of the above-described embodiment. In the apparatus configuration using this phase shifter, the information recording method according to the above-described embodiment may be used. The same effect as the embodiment is achieved.
[0048]
In addition, the LC-SLM according to the above-described embodiment and the above-described MSLM are optical address type SLMs in which an image of the outside world is directly written in object light. However, an image is presented on a display device such as a CRT. It can also be used as an electrical address type by writing to an optical address type SLM.
[0049]
FIG. 8 shows an EBSLM as an example of an electric address type SLM. A video signal that is a time-series electric signal is input to the EBSLM as an input image. The electron gun 71 charges the electro-optic crystal 73a corresponding to the input image in accordance with the video signal, and applies an electric field corresponding to the input image to the electro-optic crystal 73a. The electro-optic crystal 73a is LiNbO. _Three A dielectric mirror 73b is provided on the writing side, and a transparent electrode 73c is provided on the reading light side. The polarization plane of the information readout light is parallel to the crystal axis of the electro-optic crystal 73a. The electro-optic crystal 73a changes the refractive index according to the applied electric field, so that phase modulation is applied to the readout light, and the object light The input information is put on.
[0050]
Even when such an EBSLM is used in place of the LC-SLM 37 of the above embodiment and the information recording method according to the above embodiment is applied to this apparatus, the same effects as in the above embodiment can be obtained. .
[0051]
【The invention's effect】
As described above, according to the present invention, when the information recorded in the PHB is read, the first and second hologram images recorded in the PHB are read out superimposed. That is, the wavefronts of the light waves of the first and second hologram images are read simultaneously, and the read images are strengthened or weakened by the phase difference of the read light waves. That is, where the phase differences of the light waves of the first and second hologram images recorded on the PHB are equal, the recorded images are read out with emphasis on each other, and the PHB readout output is brightest. Further, when the phase difference of the light wave is π, the recorded images are read out with weakening each other, and the PHB read output becomes the darkest. Further, when the phase difference between the light waves of the first and second hologram images is an intermediate value such as π / 4 or π / 2, the readout output is an intermediate level between the brightest output and the darkest output. Read out as intensity output. Accordingly, the phase differences between the background noises recorded in the first hologram in which the object light is not recorded and the second hologram in which the object light is recorded are equal. Therefore, the first and second holograms are By reading out simultaneously, the background of the synthetic hologram obtained by superimposing these holograms is brightest. In addition, when the phase of the object beam or the reference beam is shifted by π and the first or second hologram is recorded on the PHB, the phase difference between the background noises recorded on the first hologram and the second hologram Since π becomes π, the background of the synthesized hologram is read out most darkly by reading out the holograms simultaneously.
[0052]
For this reason, the information carried on the object light is clearly read out on this brightest or darkest background. That is, the non-uniformity of the refractive index distribution of the electro-optic crystal plate forming the SLM, the processing accuracy of the electro-optic crystal plate is poor, or the optical system has an error, causing the non-uniformity of the image. Even if the first and second holograms contain background noise, the synthesized hologram obtained by superimposing these holograms compensates for each other to form a uniform background. The As a result, in the reproduced image read out as a synthetic hologram, the input information is restored faithfully and clearly to a uniform background. In other words, by using the phase information of the object light using the SLM, the phase distortion caused by the optical system or device is removed, and a promising system as a two-dimensional optical system can be constructed. Furthermore, since two-dimensional information can be recorded at a speed close to real time, the function as a PHB multiple memory can be used effectively. Therefore, the conventional image non-uniformity problem is solved, high-density information recording can be easily performed, and the advantages of wavelength-multiplexed recording by PHB can be fully exhibited.
[Brief description of the drawings]
FIG. 1 is a graph for explaining the present invention.
FIG. 2 is a diagram illustrating a configuration of an apparatus used for a method of recording information on a PHB using an SLM according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing details of the SLM shown in FIG. 2;
4 is a cross-sectional view showing details of the phase shifter shown in FIG. 2;
FIG. 5 is a diagram for explaining the principle of the information recording method according to the embodiment.
6 is a diagram showing another first example of the SLM shown in FIG. 2. FIG.
7 is a diagram showing another example of the phase shifter shown in FIG. 2; FIG.
FIG. 8 is a diagram showing another second example of the SLM shown in FIG. 2;
FIG. 9 is a graph showing a wavelength band in which information is recorded in a PHB.
FIG. 10 is a diagram showing a configuration of an apparatus used in a method for recording information on a PHB using a conventional SLM.
FIG. 11 is a cross-sectional view showing an electro-optic crystal used in an SLM.
[Explanation of symbols]
31 ... Photochemical hole burning memory (PHB), 32 ... Cryostat, 33, 40, 41 ... Power source, 34, 35 ... Half mirror, 36 ... Phase shifter, 37 ... Spatial light modulator (SLM), 38 ... Input image, 39 …lens.

Claims (3)

A spatial light modulator is used to place information on the object light, and a hologram generated by the interference between the object light and the reference light is recorded as information in the hole burning memory, and the information recorded in the hole burning memory is read at a predetermined wavelength. In a method for recording information in a hole burning memory using a spatial light modulator that reads using light,
A first step of recording a first hologram in the hole burning memory using the reference light having a wavelength of λ _{0 in} a state where information is not carried on the object light by applying an electric field E ₁ to the hole burning memory; A second step of recording a second hologram in the hole burning memory using the reference light of wavelength λ _{0 in} a state where information is carried on the object light by applying an electric field E ₂ to the hole burning memory; With the electric field E ₀ having a value of (E ₁ + E ₂ ) / 2 applied to the hole burning memory, the readout light having the wavelength λ ₁ or the wavelength λ ₂ that generates holes in the wavelength region adjacent to the wavelength λ ₀ And a third step of reading the information recorded in the hole burning memory, and a method for recording information in the hole burning memory using a spatial light modulator . A spatial light modulator is used to place information on the object light, and a hologram generated by the interference between the object light and the reference light is recorded as information in the hole burning memory, and the information recorded in the hole burning memory is read at a predetermined wavelength. In a method for recording information in a hole burning memory using a spatial light modulator that reads using light,
A first step of recording a first hologram in the hole burning memory using the reference light having a wavelength of λ _{1 in} a state in which an electric field E ₀ is applied to the hole burning memory and no information is on the object light; A second step of recording a second hologram in the hole burning memory using the reference light having a wavelength λ _{2 in} a state where the electric field E ₀ is applied to the hole burning memory and information is carried on the object light; The readout light having a wavelength λ ₀ having a value of about (λ ₁ + λ ₂ ) / 2 in a state where an electric field E ₁ or an electric field E ₂ generating holes in the electric field region adjacent to the electric field E ₀ is applied to the hole burning memory. And a third step of reading out information recorded in the hole burning memory using a spatial light modulator, and storing information in the hole burning memory using a spatial light modulator Method. The first or second hologram is recorded in the hole burning memory by shifting the phase of the object light by π in the first step or the second step. 3. A method for recording information in a hole burning memory using the spatial light modulator described in 2.

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