JP4239696B2 - Optical memory device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical memory device using a hologram medium.
[0002]
[Prior art]
Holographic recording, in which information is recorded on a recording medium using holography, is generally performed by superimposing signal light having image information and reference light inside the recording medium, and forming interference fringes generated at that time. Is done by writing to At the time of reproducing the recorded information, the image information is reproduced by diffraction by interference fringes by irradiating the recording medium with reference light.
[0003]
In this holographic recording, volume holography, particularly digital volume holography, has been developed for ultra-high density optical recording. Volume holography is a method of writing interference fringes in three dimensions by actively utilizing the thickness direction of the recording medium. Increasing the thickness increases the diffraction efficiency and increases the storage capacity using multiple recording. It is intended.
[0004]
Digital volume holography is a computer-oriented holographic recording method that uses a recording medium and a recording method similar to those of volume holography, but restricts image information to be recorded to a binarized digital pattern. In this digital volume holography, for example, image information such as an analog picture is once digitized, developed into two-dimensional digital pattern information, and recorded as image information. At the time of reproduction, the digital pattern information is read and decoded so that the original image information is restored and displayed. As a result, even if the S / N ratio (signal to noise ratio) is somewhat poor at the time of reproduction, the original information is reproduced very faithfully by performing differential detection or encoding binary data and performing error correction. It becomes possible.
[0005]
However, in the conventional recording and reproducing method of digital volume holography, the contrast of the two-dimensional pattern of the reproduction light is lower than the contrast of the two-dimensional pattern of the information light at the time of recording, and noise is superimposed on the reproduction light. There is a problem that the S / N ratio is lowered and the accuracy of information reproduction is lowered.
[0006]
In order to solve this problem (Patent Document 1), at least a part of the light beam emitted from the light source is spatially modulated by the spatial modulation means, and two light beams having complementary patterns are obtained. An optical information recording apparatus is disclosed that generates and irradiates an information recording layer with these two light beams by a recording optical system and records information on the information recording layer by an interference pattern due to interference between the two light beams. Yes. According to this optical information recording apparatus, when reproducing information, two reproduced lights having mutually complementary patterns can be obtained. Therefore, accurate information reproduction is performed by differential detection using the two complementary reproduced lights. Is supposed to be possible.
[0007]
[Patent Document 1]
JP-A-10-302293 (paragraph numbers 0009 to 0078)
[0008]
[Problems to be solved by the invention]
However, in an optical memory device using a two-dimensional spatial light modulator described in (Patent Document 1), a light beam having at least the same area as that of the spatial light modulator is required. That is, in such a conventional optical memory device, the thickness of the device is governed by the size of one side of the spatial light modulator. Technology development is underway for miniaturization of the two-dimensional spatial light modulator itself, but if the area of the spatial light modulator is the same, as the number of pixels increases, Since the light utilization efficiency deteriorates, there is a limit to downsizing.
[0009]
An object of the present invention is to realize a reduction in thickness of an optical memory device that enables high-precision recording / reproduction using spatial modulation means.
[0010]
[Means for Solving the Problems]
In order to solve this problem, the present invention records information by irradiating a hologram medium with signal light and reference light, and reproduces information by irradiating the hologram medium on which information is recorded with reference light. In the optical memory device, the laser light source that emits the signal light and the reference light, the optical waveguide that widens the light beam emitted from the laser light source, and the light beam widened by the optical waveguide is deflected toward the hologram medium. And a grating that condenses the light, a spatial light modulation element that modulates the light beam that has passed through the grating, a two-part rotator that converts the deflection direction of the light beam that has passed through the spatial light modulation element and irradiates the hologram medium, and a hologram An image sensor that converts a reproduced image from a medium into an electric signal, the grating is formed on a surface of the optical waveguide, and a base of the optical waveguide is formed. An optical memory apparatus characterized in that a said spatial light modulator on top.
[0011]
As a result, since the light beam emitted from the laser light source is expanded by the optical waveguide and enters the spatial light modulation element, a light beam having a cross-sectional area larger than the area of the spatial light modulation element can be easily obtained. Thinning is possible.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, information is recorded by irradiating a hologram medium with signal light and reference light, and information is recorded by irradiating the hologram medium on which information is recorded with reference light. In a reproducing optical memory device, a laser light source that emits the signal light and the reference light, an optical waveguide that widens a light beam emitted from the laser light source, and a light beam that is widened by the optical waveguide is deflected toward the hologram medium And a grating that collects light, a spatial light modulation element that modulates the light beam that has passed through the grating, a two-part rotator that converts the deflection direction of the light beam that has passed through the spatial light modulation element and irradiates the hologram medium, An image pickup device for converting a reproduced image from a hologram medium into an electric signal, the grating is formed on the surface of the optical waveguide, and the optical waveguide substrate Wherein an optical memory apparatus characterized in that a spatial light modulator, the light beam emitted from the laser light source enters is enlarged by the optical waveguide in the spatial light modulator, larger than the area of the spatial light modulator to A light beam having a cross-sectional area can be easily obtained, and the optical memory device can be thinned.
[0013]
In addition, the optical waveguide substrate and the spatial light modulation element are integrally formed, so that the device can be thinned and the position between each component can be shifted due to the impact from the outside. Less and improves reliability.
[0014]
In addition, it is characterized by the fact that a grating is formed on the surface of the optical waveguide, so that the thickness of the device can be reduced, and the light receiving parts can be arranged with high precision by the process technology. A high optical memory device can be realized.
[0015]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
(Embodiment 1)
FIG. 1 is a schematic configuration diagram showing a pickup section of an optical memory device according to Embodiment 1 of the present invention.
[0017]
In FIG. 1, reference numeral 1 denotes a laser light source serving as an energy source for recording / reproducing on a hologram recording medium, 2 denotes a waveguide substrate, and 3 denotes an optical waveguide formed on the waveguide substrate 2 (hereinafter also referred to as a waveguide for short). 4) is a grating formed on the waveguide surface, and 5 is a transmissive spatial light modulator provided on the waveguide substrate 2.
[0018]
An optical system using such a waveguide was originally studied for an optical disk. The basic configuration and operating principle of the waveguide pickup according to the present invention are almost the same as those of the waveguide pickup for optical discs. Therefore, the detailed description will be given to previously published materials and the like, and an example of the waveguide pickup for optical discs in FIG. An outline will be described with reference to an explanatory diagram.
[0019]
In FIG. 2, 20 is an optical disk, 21 is a laser light source, 22 is a waveguide substrate comprising a waveguide layer, a buffer layer, and a Si substrate layer, and 23 is a condensing grating for converging light guided to the waveguide onto the optical disk 20. , 24 is a beam splitter for generating a control signal for causing the position of the pickup to follow the movement of the optical disc 20, and 25 is a light receiving element for converting the light deflected by the beam splitter into an electric signal.
[0020]
The light oscillated from the laser light source 21 becomes light that widens while traveling in the waveguide layer in the waveguide substrate 22, and is condensed on the recording surface of the optical disk 20 by the condensing grating 23. A part of the light reflected by the optical disk 20 is returned to the waveguide layer by the condensing grating 23, and the part of the light is further guided to the light receiving element 25 by the beam splitter 24. A relative position signal with respect to the optical disc 20 is obtained from the signal photoelectrically converted by the light receiving element 25, and the position of the optical pickup is controlled.
[0021]
Such a waveguide pickup can be obtained by forming a condensing grating 23 and a waveguide on a light receiving element substrate using a semiconductor process. The waveguide is formed by sandwiching a high refractive index thin film with a low refractive index thin film. This high refractive index film is called a waveguide layer, and the low refractive index film is called a cladding layer. As described above, when a plane wave is incident on the grating 23 formed on the waveguide layer at an angle θ, a certain condition among the laser wavelength, the incident angle, the focusing grating period, the refractive index of each layer, and the like can be satisfied. For example, part of the incident light is converted into guided light, and the remaining part becomes transmitted light.
[0022]
Although the waveguide pickup has the above-described function, what is particularly useful in this embodiment is a light beam widening function performed in the waveguide. Widening of a light beam in a general optical system is performed by a beam expander configured by a spherical or aspheric lens. For this reason, a three-dimensional space occupied by the widened light flux is required, which has been a factor that hinders the thinning of the pickup and, consequently, the thinning of the entire optical memory device.
[0023]
In this embodiment, in order to obtain a light beam having a cross section larger than the area of the spatial light modulator 5 as described above, the waveguide 3 having a two-dimensional configuration shown in FIG. 1 and the grating 4 having a lens function are used. If there is. The details of the information recording of the optical memory device by the hologram are described in documents such as Patent Document 1 and are omitted here. However, the spatial light modulator 5 is inserted into the light beam that is being condensed by the grating 4. The required function can be achieved. Needless to say, FIG. 1 also includes a relative position detection mechanism for a recording medium (not shown). Therefore, the entire optical memory device can be reduced in thickness.
[0024]
(Embodiment 2)
FIG. 3 is an exploded view of the pickup unit of the optical memory device according to the second embodiment of the present invention. In FIG. 3, the reference numerals 1 to 5 are the same as those in FIG. Reference numeral 6 denotes an image pickup element that converts a reproduction image from a recording medium into an electrical signal during reproduction, and 7 denotes a two-part rotator that performs a function of changing the polarization direction of a light beam necessary for recording and reproduction described later. Reference numeral 8 denotes a flexible pattern for electrically connecting the spatial light modulator 5 and the image sensor 6 to an information processing circuit (not shown).
[0025]
A light receiving element (not shown) and other circuits are formed on the waveguide substrate 2 in a process before forming the waveguide layer. The state in which these are assembled together is shown in FIG. 1, but since the exchange of signals with the outside is performed through the flexible flexible pattern 8, the focusing direction and tracking direction by a pickup support mechanism (not shown) are constant. Does not interfere with the movement of the direction. The pickup support mechanism basically restrains the direction other than the focusing direction and the tracking direction, but means for correcting the tilt of the pickup with respect to the recording medium may be provided as necessary.
[0026]
The optical configuration of the pickup according to the present invention will be briefly described with reference to FIG. FIG. 4 is a diagram for explaining the optical configuration of the pickup unit of the optical memory device according to the second embodiment of the present invention. In FIG. 4, the reference numerals 1 to 7 are the same as those in FIG.
[0027]
The light transmitted from the laser light source 1 to the waveguide substrate 2 is widened there, deflected upward by the grating 4, and converged on the reflection film 13 in the disk substrate 10. A spatial light modulation element 5 is provided in the optical path in the middle of convergence, and information to be recorded is modulated by the spatial light modulation element 5 in one of light contrast, phase, and polarization direction.
[0028]
However, here, only one portion polarized by the next two-divided optical rotator 7 is modulated, and the other portion is controlled so as not to modulate light / dark / phase / polarized light. Then, by the two-part rotator 7, the light beam is divided into two parts having different polarization directions, such as an A-polarized part 11 and a B-polarized part 12. Here, it is assumed that the polarization plane of the A polarization portion 11 and the polarization plane of the B polarization portion 12 are perpendicular to each other.
[0029]
The A-polarized portion 11 and the B-polarized portion 12 are reflected by a reflective film 13 having a polarizing property, but this reflected film 13 rotates 90 ° with respect to the reflected light, so that the reflected A-polarized portion 11 has a plane of polarization. By rotating 90 °, the same polarization plane as that of the B polarization portion 12 is obtained. That is, interference occurs in the region where the A-polarized portion 11 and the B-polarized portion 12 intersect after reflection. Since this is the same for the B-polarized portion 12, the modulated light beam portion generates the same interference pattern twice before and after reflection. Eventually, the information recorded at the intersecting portion in the recording layer 14 is the same in the two areas before and after reflection.
[0030]
When reproducing the recording, both the A-polarized portion 11 and the B-polarized portion 12 are incident on the medium without being modulated to reproduce the recorded hologram. Reproduced light from the recording layer 14 travels in the opposite direction in the same direction as the forward direction and returns to the grating 4. However, as described above, a part of the light passes through the waveguide substrate 2 and reaches the image sensor 6. Is converted into an electrical signal. When modulation is performed using polarized light, a polarizing filter film is provided between the grating 4 and the incident surface of the image sensor 6 in order to be recognized as bright and dark information by the image sensor 6.
[0031]
Since the optical system including the optical waveguide and the spatial light modulation element, the image sensor, and other optical systems that are indispensable for the optical memory device using the hologram medium are integrally configured, the pickup can be made thin and small. Thinning of the device can be realized. Furthermore, by integrating, the position between each component is less likely to shift due to the impact from the outside, and the reliability is improved.
[0032]
(Embodiment 3)
FIG. 5 is a diagram for explaining the optical configuration of the pickup section of the optical memory device according to the third embodiment of the present invention. Since all reference numerals in FIG. 5 are the same as those in FIG. 4, the description thereof is omitted here. As described above, such a waveguide pickup can be obtained by forming a grating and a waveguide on a light receiving element substrate using a semiconductor process.
[0033]
In FIG. 5, the image pickup device 6 is formed on the waveguide substrate 2 by a semiconductor process before forming the waveguide 3 together with other light receiving elements (not shown). As described above, since the waveguide 3, the light receiving element, the grating 4, and the imaging element 6 are formed on the same waveguide substrate 2, the number of parts of the pickup can be reduced and the thickness can be reduced, and more specific to the semiconductor process. The high relative position accuracy can reduce the assembly accuracy of other parts, thereby reducing the production cost.
[0034]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
[0035]
According to the first aspect of the present invention, an optical memory that records information by irradiating a hologram medium with signal light and reference light and reproduces information by irradiating the hologram medium on which information is recorded with reference light. In the apparatus, a laser light source that emits the signal light and the reference light, an optical waveguide that widens a light beam emitted from the laser light source, and a light beam that is widened by the optical waveguide is deflected toward the hologram medium and collected. A grating that emits light, a spatial light modulator that modulates a light beam that has passed through the grating, a two-part rotator that converts the deflection direction of the light beam that has passed through the spatial light modulator and irradiates the hologram medium, and a hologram medium An image sensor that converts the reproduced image into an electric signal, and the grating is formed on the surface of the optical waveguide, and on the substrate of the optical waveguide. By providing the serial spatial light modulator, the light beam emitted from the laser light source enters is enlarged by the optical waveguide in the spatial light modulator, a light beam having a larger cross-sectional area than the area of the spatial light modulator easily Thus, the optical memory device can be thinned.
[0036]
In addition, since the optical waveguide substrate and the spatial light modulator are integrated, the thickness of the device can be reduced, and the position of each component is less likely to be shifted by the influence of external impacts, etc. Improves.
[0037]
In addition, since the grating is formed on the surface of the optical waveguide , the device can be thinned, and the light receiving parts can be arranged with high precision by the process technology. Can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a pickup section of an optical memory device according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram of an example of a waveguide pickup for an optical disk. FIG. 4 is an exploded view of the pickup unit of the device. FIG. 4 is a diagram for explaining the optical configuration of the pickup unit of the optical memory device according to the second embodiment of the present invention. Diagram explaining optical configuration 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1 Laser light source 2 Waveguide board | substrate 3 Waveguide 4 Grating 5 Spatial light modulation element 6 Image pick-up element 7 Divided optical rotator 8 Flexible pattern 10 Disk substrate 11 A polarization part 12 B polarization part 13 Reflective film 14 Recording layer 20 Optical disk 21 Laser light source 22 Waveguide substrate 23 Condensing grating 24 Beam splitter 25 Light receiving element

Claims (1)

In an optical memory device that records information by irradiating a hologram medium with signal light and reference light, and reproduces information by irradiating the hologram medium on which information is recorded with the reference light, the signal light and the reference A laser light source that emits light, an optical waveguide that widens the light beam emitted from the laser light source, a grating that deflects and condenses the light beam widened by the optical waveguide toward the hologram medium, and transmits the grating A spatial light modulation element that modulates the luminous flux, a two-part rotator that changes the deflection direction of the luminous flux that has passed through the spatial light modulation element and irradiates the hologram medium, and a reproduced image from the hologram medium is converted into an electrical signal. an imaging device, wherein with the grating is formed on the surface of the optical waveguide, provided with the spatial light modulator on a substrate of the optical waveguide this Optical memory device according to claim.

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