JP2004085974A - Spatial optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a spatial optical modulator of simple structure, capable of high-speed data conversion, and large in light intensity. <P>SOLUTION: The spatial optical modulator is used for a holographic storage device which records and reproduces interference fringes of light on and from a recording medium and has a plurality of elements which each comprise a lower electrode 14, a piezoelectric layer 10, an upper electrode 12, and a reflecting layer 11 formed one over another on a substrate 15 and arranged in two dimensions while sectioned in the laminating direction and can be controlled independently of one another; and surfaces of reflecting layers 11 reflecting light are formed on the same plane. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a spatial light modulator used in a holographic storage device for recording and reproducing interference fringes of light on a recording medium.
[0002]
[Prior art]
In recent years, the recording density of magnetic recording media, magneto-optical recording media, and thermal phase change media has been dramatically increased with the improvement of information recording technology.
[0003]
However, all of these are bit-by-bit recording methods, and since recording and reproduction must be performed in units of one bit, the data transfer speed is limited, and it may not be possible to meet the demands of the era of high-speed multiplex communication. ing.
[0004]
In response to such progress of the times, volume holographic memories have attracted attention as a recording system having both high recording density and high data transfer speed of the next generation.
[0005]
This volume holographic memory was proposed by Polaroid Heerden in 1963, and several prototypes were made in the 1970s. With the rapid growth of optoelectronics in the 1990's and the availability of high performance light sources, detectors and screens, volume holographic memories were once again actively researched and developed. In addition, error correction and access methods, which have been issues, have advanced, and polymers can be used in addition to crystals.
[0006]
The principle of the volume holographic memory is that a coherent light such as a laser is divided into two lights by a beam splitter or the like and information is superimposed on one light called a signal light, so that a spatial light called SLM (Spatial Light Modulator) is used. The light separated by the modulator is reflected or transmitted to spatially modulate the light, and the other light called reference light is caused to interfere in a recording medium made of a light-sensitive material to record information. When reading information, only the reference light is irradiated at the same angle as when the information to be read is recorded on the recording medium on which the information is recorded, and the information is recorded as two-dimensional information in the same direction as when the signal light was recorded. The information is reproduced. The reproduced image information is captured by a two-dimensional image detector such as a CCD camera or a CMOS camera and is extracted as digital information.
[0007]
The outline of the holographic storage device will be described below with reference to FIG.
[0008]
Here, FIG. 4 is an explanatory diagram showing the outline and recording principle of a holographic storage device using a spatial light modulator.
[0009]
In FIG. 4, an encoder 125 converts digital data to be recorded in the holographic memory 101 as a bright and dark dot pattern image on a plane, rearranges the data into, for example, a data array of 480 bits in length × 640 bits in width and unit page sequence data. Generate This data is sent to a spatial light modulator 115 such as a panel of a transmission type TFT liquid crystal display (LCD).
[0010]
The spatial light modulator 115 has a modulation processing unit of 480 pixels in length × 640 pixels in width corresponding to a unit page, and converts the irradiated light beam into spatial light on according to the unit page sequence data from the encoder 125. Light is modulated to an OFF signal, and the modulated signal beam, that is, the signal light is guided to the Fourier transform lens 116. More specifically, the spatial light modulator 115 passes the signal beam in response to the logical value “1” of the unit page sequence data, which is an electric signal, and shuts off the signal beam in response to the logical value “0”. The electro-optical conversion according to each bit content in the unit page data is achieved, and a modulated signal beam as a signal light of a unit page sequence is generated.
[0011]
The signal light enters the volume holographic memory 101 via the Fourier transform lens 116. In addition to the signal light, the reference light enters the volume holographic memory 101 at an incident angle β from a predetermined reference line orthogonal to the optical axis of the signal light beam. The signal light and the reference light interfere with each other in the holographic memory 101, and the interference fringes are stored in the volume holographic memory 101 as a refractive index grating, that is, a hologram, thereby recording data. In addition, three-dimensional data can be recorded by changing the angle of incidence β and irradiating a reference beam to perform angle multiplex recording of a plurality of two-dimensional plane data.
[0012]
When the recorded data is reproduced from the volume holographic memory 101, only the reference light is applied to the center of the area where the signal light beam and the reference light beam intersect at the same incident angle β as that at the time of recording. Incident on That is, unlike during recording, no signal light is incident. As a result, diffracted light from the interference fringes recorded in the volume holographic memory 101 is guided to a charge coupled device (CCD) 120 of the photodetector through the Fourier transform lens 119.
[0013]
The CCD 120 converts the brightness of the incident light into the intensity of an electric signal, and outputs an analog electric signal having a level corresponding to the luminance of the incident light to a decoder 126 (not shown).
[0014]
The decoder 126 compares this analog signal with a predetermined amplitude value (slice level) and reproduces the corresponding data of "1" and "0".
[0015]
In the holographic memory 101, since recording is performed using a two-dimensional plane data sequence as described above, angle multiplex recording can be performed by changing the incident angle β of the reference light. That is, by changing the incident angle β of the reference light, a plurality of two-dimensional planes, which are recording units, can be defined in the holographic memory 101. As a result, three-dimensional recording becomes possible.
[0016]
In the rewritable volume holographic memory 101 using the photorefractive effect described above, a single crystal of lithium niobate (LiNbO ₃ , LN for short) to which Fe is added is generally used as a recording material, and the recording light is used as the recording light. Uses an Nd: YAG laser as excitation light for a second harmonic generator (SHG), and uses a wavelength selection filter after passing through the SHG to use only a wavelength of 532 nm as the second harmonic.
[0017]
In this conventional recording method (referred to as a conventional single-color recording method), in a region where the interference fringes are bright, the level of Fe ²⁺ corresponds to the interference fringes formed from the signal light as the recording light and the reference light. , Electrons are excited by the conductor, and are finally trapped in Fe ³⁺ levels through a photorefractive process to complete the storage.
[0018]
[Problems to be solved by the invention]
Here, as the spatial light modulator, a transmission type and a reflection type using a liquid crystal shutter have been proposed.
[0019]
In a transmission type spatial light modulator using liquid crystal, since the polarization of light is controlled and modulated through a polarizing plate, the intensity is reduced, the S / N ratio is adversely affected, and the BER (Bit Error Rate) is reduced. There's a problem.
[0020]
In addition, the reflective spatial light modulator has a problem that the structure is complicated and the display speed of the liquid crystal is slow, so that it takes a long time to write.
[0021]
Therefore, an object of the present invention is to provide a spatial light modulator which can perform data conversion at a high speed with a simple structure and has a high light intensity.
[0022]
[Means for Solving the Problems]
In order to solve this problem, a spatial light modulator of the present invention is a spatial light modulator used for a holographic storage device that records and reproduces interference fringes of light on a recording medium, and is formed by lamination on a substrate. A lower electrode, a piezoelectric layer, an upper electrode, and a reflective layer which are partitioned two-dimensionally in a stacking direction and have a plurality of elements which can be controlled independently of each other. In this configuration, the surfaces of the layers are formed on the same plane.
[0023]
In order to solve this problem, a spatial light modulator according to the present invention is a spatial light modulator used for a holographic storage device that records and reproduces interference fringes of light on a recording medium, and is stacked on a substrate. It is composed of a lower electrode, a piezoelectric layer, and an upper electrode / reflection layer which are formed and partitioned in the stacking direction and are two-dimensionally arranged. The surface of the upper electrode / reflection layer is formed on the same plane.
[0024]
Thus, with a simple structure, data conversion can be performed at high speed, the intensity of light is increased, and a spatial light modulator having a good S / N ratio can be obtained.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 of the present invention is a spatial light modulator used for a holographic storage device for recording and reproducing light interference fringes on a recording medium, wherein the spatial light modulator is formed on a substrate and stacked in a stacking direction. It is composed of a lower electrode, a piezoelectric layer, an upper electrode, and a reflective layer that are partitioned and two-dimensionally arranged, and has a plurality of elements that can be controlled independently of each other. The spatial light modulator is formed on the same plane, has a simple structure, can perform data conversion at a high speed, has a high light intensity, and has a good S / N ratio. It has the effect of being obtained.
[0026]
According to a second aspect of the present invention, there is provided a spatial light modulator used in a holographic storage device for recording and reproducing light interference fringes on a recording medium, wherein the spatial light modulator is formed on a substrate in a laminating direction. The lower electrode, the piezoelectric layer, and the upper electrode / reflection layer, which are partitioned and two-dimensionally arranged, have a plurality of elements that can be controlled independently of each other, and serve as an upper electrode / reflection layer that reflects object light. This is a spatial light modulator whose surfaces are formed on the same plane with each other. It has a simple structure, can perform data conversion at high speed, and has a high light intensity and a good S / N ratio. This has the effect that a modulator can be obtained.
[0027]
The invention according to claim 3 of the present invention is the invention according to claim 1 or 2, wherein the piezoelectric layer is a spatial light modulator that is an oxide film having a perovskite structure, and is excellent in withstand voltage and simple. With the structure, data conversion can be performed at a high speed, and the intensity of light is increased to provide a spatial light modulator having a good S / N ratio.
[0028]
According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the element is a spatial light modulator partitioned in a stacking direction by a photolithography technique. With such a simple structure, data conversion can be performed at a high speed, the intensity of light is increased, and a spatial light modulator having a good S / N ratio can be obtained.
[0029]
According to a fifth aspect of the present invention, there is provided the spatial light modulator according to any one of the first to fourth aspects, wherein the element is a spatial light modulator having a cantilever structure with respect to the substrate. With such a simple structure, data conversion can be performed at a high speed, the intensity of light is increased, and a spatial light modulator having a good S / N ratio can be obtained.
[0030]
The invention according to claim 6 of the present invention is the invention according to any one of claims 1 to 5, wherein the element is a spatial light modulator that spatially modulates the phase or intensity of the reflected light, With a simple structure, data conversion can be performed at high speed, the light intensity is increased, and a spatial light modulator having a good S / N ratio can be obtained.
[0031]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. The embodiment of the present invention is a particularly useful embodiment in which the present invention is implemented, and the present invention is not limited to the embodiment.
[0032]
(Embodiment 1)
FIG. 1 is a perspective view showing a spatial light modulator according to Embodiment 1 of the present invention.
[0033]
The spatial light modulator according to the present embodiment includes a lower electrode 14, a piezoelectric layer 10, an upper electrode 12, and a reflective layer 11 formed on a substrate 15. The lower electrode 14, the piezoelectric layer 10, the upper electrode 12, and the reflective layer 11 are partitioned in the laminating direction by the slits 13 so that the respective elements are formed in a lattice shape, so that they can be controlled independently of each other. The number of elements can be set arbitrarily. For example, in this embodiment, the number of elements is 1024 × 1024 two-dimensionally arranged.
[0034]
Here, the reflection layer 11 is for reflecting object light on the surface of the piezoelectric layer 10. This reflective layer 11 may be used together with the upper electrode 12, or may be formed on the electrode separately from the electrode as in the present embodiment. As the material of the reflective layer 11, it is desirable to select a material that does not cause deterioration such as corrosion due to moisture in the air, such as a thin film of aluminum, gold, platinum, Ti, or an alloy thereof.
[0035]
By arranging the reflection layers 11 so as to be flush with each other, a spatial light modulator can be formed. Note that a circuit for driving the piezoelectric layer 10 can be formed in a matrix below the piezoelectric layer 10.
[0036]
When the lower electrode 14 and the upper electrode 12 are provided in the polarization direction, and a voltage is applied to the piezoelectric layer 10 formed so as to generate a strain, if the polarity corresponds to the polarization direction of the piezoelectric layer 10, the polarity contracts. If it expands. At this time, the magnitude of the displacement of the reflective layer 11 from the same initial plane is designed to be 波長 wavelength, and the displacement distance is determined. In comparison, the light reflected by the displaced reflecting surface of the piezoelectric layer 10 has a phase shifted by 波長 wavelength.
[0037]
After phase conversion, the phase modulation is converted into intensity modulation by passing through a wavelength selection filter that passes only light whose phase has not changed, and this light is used as signal light, and one of the two is split by a beam splitter before conversion. Recording can be performed by using unmodulated light as reference light and causing interference in a photorefractive material.
[0038]
Since the switching speed of the piezoelectric layer 10 is higher than that of the liquid crystal, the data transfer speed does not decrease.
[0039]
Further, according to the present embodiment, since a reflective spatial light modulator can be relatively easily configured, a small spatial light modulator having a simple structure can be obtained.
[0040]
(Embodiment 2)
FIG. 2 is a perspective view showing a spatial light modulator according to Embodiment 2 of the present invention.
[0041]
The spatial light modulator according to the present embodiment includes a lower electrode 17, a piezoelectric layer 18, and an upper electrode / reflection layer 19 which are sequentially formed on a substrate 16. The lower electrode 17, the piezoelectric layer 18, and the upper electrode / reflection layer 19 are separated in a lattice shape to form respective elements, and can be controlled independently of each other. A controller 20 for controlling the operation of these elements is provided around these elements.
[0042]
In the spatial light modulator of the present embodiment, a thin film piezo is used as a thin film piezoelectric material constituting the piezoelectric layer 18.
[0043]
Here, the thin film piezo will be described.
[0044]
2. Description of the Related Art Conventionally, as an actuator that performs a mechanical operation when an electric signal is applied, a piezoelectric actuator including two electrodes and a piezoelectric body provided between these electrodes has been known. 2. Description of the Related Art Piezoelectric actuators convert electrical energy into mechanical energy by utilizing the piezoelectric effect of a piezoelectric body, and are used in a wide range of applications such as actuators such as a head of an ink jet recording apparatus.
[0045]
By the way, in recent years, along with the miniaturization of the ink jet head and the like, the miniaturization of the piezoelectric actuator itself has been desired, and for that purpose, the thinning of the piezoelectric body has been desired. However, simply reducing the thickness of the piezoelectric film without changing the properties of the film itself tends to cause dielectric breakdown. Therefore, there is a certain limit in reducing the thickness of the piezoelectric film from the viewpoint of ensuring the withstand voltage.
[0046]
Therefore, in order to further reduce the size of the piezoelectric actuator, and further reduce the size of the inkjet head and the inkjet recording apparatus using the piezoelectric actuator, a piezoelectric film having characteristics different from those of the related art and having excellent withstand voltage is required. It is said. For example, an oxide film having a perovskite structure including Pb, Zr, and Ti (hereinafter, referred to as “PZT”) is formed of a piezoelectric film having a thickness of 1 μm to 10 μm and a relative dielectric constant of 150 to 500. Things have been suggested.
[0047]
As the substrate 16 on which the piezoelectric layer 18 using a thin film piezoelectric material is formed, single crystal silicon can be used. The lower electrode 17 is formed of a material such as a silicide used as an electrode such as an aluminum thin film or an LSI by using a vacuum thin film forming technique such as vacuum deposition or sputtering. Then, a piezoelectric film 18 of PZT or the like is formed on the lower electrode 17 by sputtering. Further thereon, an upper electrode / reflection layer 19 serving both as an upper electrode and a reflection surface is formed of an aluminum film.
[0048]
Thereafter, the lower electrode layer 17 and the piezoelectric layer 18 are patterned into a predetermined shape by a photolithography technique, and are formed by separating elements by reactive etching. Further, the control unit 20 is formed on the substrate 16, and the array of the piezoelectric layers 18 is displaced in a two-dimensional pattern using the encoded information. The two-dimensional array can function as a spatial light modulator by reflecting the signal light and modulating the phase as in the first embodiment.
[0049]
The advantage of forming the piezoelectric layer 18 from a thin-film piezoelectric material is that the film thickness can be controlled with high precision because it is formed with a thin film, and thus the displacement control of the formed piezoelectric layer 18 can be performed with high precision. Further, since the pattern can be formed with high precision and high density by the photolithography technology, a large aperture ratio can be obtained, the light reflection efficiency can be improved, and the light can be brightened. As a result, the light intensity can be increased and the S / N ratio can be increased. This is because it has a good effect on the ratio and the BER is improved.
[0050]
(Embodiment 3)
FIG. 3 is a perspective view showing a spatial light modulator according to Embodiment 3 of the present invention.
[0051]
The spatial light modulator of the present embodiment includes a lower electrode 25, a piezoelectric layer 23, and an upper electrode / reflection layer 26 which are sequentially formed on a substrate 24. The lower electrode 17, the piezoelectric layer 18, and the upper electrode / reflection layer 19 are separated from each other in a lattice shape to form the respective elements, and are formed in a lattice shape so that they can be controlled independently of each other. A controller 28 for controlling the operation of these elements is provided around these elements.
[0052]
In the spatial light modulator of the present embodiment, the element has a cantilever (cantilever) structure.
[0053]
As the substrate 24 on which the piezoelectric layer 23 using the thin film piezoelectric material is formed, single crystal silicon is used as in the second embodiment. First, the substrate 24 is thermally oxidized to form SiO ₂ having a desired thickness, and a lower electrode layer 25 made of, for example, Ti / Pt is formed thereon. Then, a PZT film, that is, a piezoelectric layer 18 is formed as desired by a sputtering method, and an upper electrode 26 is formed thereover from, for example, aluminum.
[0054]
Thereafter, the elements are separated by photolithography, and a resist is formed in a beam shape. Then, after etching the aluminum with a wet etchant, the resist was stripped off to form a beam.
[0055]
In order to form a cantilever structure from the substrate 24, the back side of the silicon wafer as the substrate 24 was protected by an oxide film. Thereafter, etching was performed up to the lower electrode 25 of the cantilever by reactive ion etching (Reactive Ion Ething). Next, the substrate 24 was anisotropically etched at 90 ° C. in a 13 wt% aqueous solution of TMAH (tetramethylammonium hydroxide) to form a cantilever beam.
[0056]
Each element, which is a cantilever array formed in this manner, is controlled by the control unit 28 and displaced in a two-dimensional pattern using the encoded information. Then, by reflecting the signal light to the two-dimensional cantilever array and modulating the reflection direction, it is possible to function as an intensity modulation type spatial light modulator.
[0057]
【The invention's effect】
As described above, according to the present invention, data conversion can be performed at a high speed with a simple structure, the light intensity is increased, and an effective spatial light modulator having a good S / N ratio can be obtained. The effect is obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a spatial light modulator according to a first embodiment of the present invention; FIG. 2 is a perspective view showing a spatial light modulator according to a second embodiment of the present invention; FIG. FIG. 4 is a perspective view showing a spatial light modulator according to No. 3; FIG. 4 is an explanatory diagram showing an outline of a holographic storage device using the spatial light modulator and a recording principle;
Reference Signs List 10 piezoelectric layer 11 reflective layer 12 upper electrode 14 lower electrode 15 substrate 16 substrate 17 lower electrode 18 piezoelectric layer 19 upper electrode / reflective layer 20 control unit 23 piezoelectric layer 24 substrate 25 lower electrode 26 upper electrode / reflective layer 28 control unit

Claims (6)

A spatial light modulator used for a holographic storage device for recording and reproducing interference fringes of light on a recording medium,
A lower electrode, a piezoelectric layer, an upper electrode, and a reflective layer, which are formed two-dimensionally while being formed on the substrate and partitioned in the stacking direction, and having a plurality of elements which can be independently controlled,
A spatial light modulator, wherein the surfaces of the reflection layers that reflect object light are formed on the same plane. A spatial light modulator used for a holographic storage device for recording and reproducing interference fringes of light on a recording medium,
A lower electrode, a piezoelectric layer and an upper electrode / reflection layer, which are formed two-dimensionally on the substrate and partitioned in the laminating direction and are arranged in a two-dimensional manner, having a plurality of elements which can be controlled independently of each other;
The spatial light modulator, wherein the surfaces of the upper electrode and the reflection layer that reflect the object light are formed on the same plane. 3. The spatial light modulator according to claim 1, wherein the piezoelectric layer is an oxide film having a perovskite structure. 4. The spatial light modulator according to claim 1, wherein the element is partitioned in a stacking direction by a photolithography technique. 5. The spatial light modulator according to claim 1, wherein the element has a cantilever structure with respect to the substrate. The spatial light modulator according to claim 1, wherein the element spatially modulates a phase or an intensity of the reflected light.

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