JP2007293130A - Hologram recording apparatus and hologram recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a recording apparatus small in size/lightweight/inexpensive and to achieve high density recording in a recording medium. <P>SOLUTION: The light exiting from a light source 1 is partially reflected as reference light by an optical element 3 toward a hologram recording medium 4 while the rest of the light is transmitted. The light transmitted through the optical element is modulated according to recording signals by a spatial optical modulator 2 disposed on an opposite face of the optical element to the light source side; and the modulated light is reflected as signal light and transmitted through the optical element to exit toward the hologram recording medium. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hologram recording apparatus and a hologram recording method using holography technology.

  In the current optical recording represented by CD and DVD, recording is performed in a plane on a recording medium every 1 bit. The recording density by this method is limited by the diffraction limit of light, that is, how much light can be reduced. On the other hand, in optical recording using the holographic technique, page data composed of a plurality of bits is recorded on a three-dimensional volume hologram layer. In addition, since each page data can exist while overlapping, multiple recording is possible. For this reason, in optical recording using a hologram, recording with dramatically high density and large capacity is possible compared with the conventional recording method for each 1 bit. In addition, in the conventional method, only 1 bit can be transferred at a time, whereas in the hologram method, data for one page consisting of a plurality of bits can be read and written at a time, so that the data transfer speed is greatly improved. For this reason, optical recording technology using holograms has been vigorously researched and developed for practical use in various places.

  In holographic recording, signal light having page data and reference light having the same wavelength are irradiated onto a recording medium, and interference fringes formed from both lights are recorded on the medium as signal information. Since the interference fringes are used as recording information, the positional relationship between the signal light, the reference light, and the medium during recording is not allowed to deviate in the order of the wavelength of the light due to causes such as vibration. It was one of the major factors hindering practical use.

  In order to overcome the weakness against vibration, a method has been proposed in which signal light and reference light are arranged coaxially so that the positional relationship does not shift with respect to vibration. An example of a recording system using this technique is shown in FIG. In FIG. 4, LD is a semiconductor laser as a light source, L1, L2 and L3 are convex lenses, M1 and M2 are mirrors, PBS (Polarizing Beam Splitter) 1, PBS2 is a polarizing beam splitter, and SLM (Spatial Light Modulator) is spatial light modulation. , G is an optical rotation plate, and H is a hologram medium.

  A recording method using this system will be described. The light generated from the semiconductor laser LD passes through the convex lens L1 and becomes parallel light, and is divided into two directions by the polarization beam splitter PBS1. One of the light passes through the spatial light modulator SLM. At this time, digital information for one page to be recorded is input as an electrical signal to the spatial light modulator SLM, and the light passing through the spatial light modulator SLM is a two-dimensional light-dark pattern corresponding to the input signal. Is converted as signal light. Then, after being reflected by the mirror M1, it passes through the polarization beam splitter PBS2.

  On the other hand, the other light divided by the polarization beam splitter PBSl acts as reference light, is reflected by the mirror M2, passes through the convex lens L2, is reflected by the polarization beam splitter PBS2, and is combined with the signal light. . The convex lens L2 is inserted for the purpose of shifting the focal positions of the signal light and the reference light with respect to the light traveling direction. At this time, the combined signal light and reference light do not interfere with each other because the polarization plane is shifted by 90 ° by the action of the polarization beam splitter PBS2. The synthesized light passes through the optical rotation plate G and the convex lens L3, reaches the hologram medium H, and is reflected by the reflection layer provided on the back surface of the hologram medium H. At this time, the optical rotation plate G is divided into, for example, an upper half and a lower half, and the polarization plane is rotated 45 ° to the right when the light passes through the upper half and 45 ° to the left when the light passes through the lower half. Yes. By doing so, inside the hologram medium H, the incident reference light and the signal light reflected by the back surface of the hologram H cause selective interference to perform holographic recording.

  Next, a method for reproducing a signal recorded on the hologram medium H will be described. For reproduction, the hologram medium H is irradiated under the same conditions as when recording only the reference light used for recording. Since the interference fringes corresponding to the recording signal are recorded on the hologram medium H, the same diffracted light as the recording light can be obtained by irradiating the reference light. The optical rotation plate G is operated in the same manner as when recording, and the interference light is guided to the detector so that the reference light and the obtained diffracted light do not interfere with each other. Although the detector is not shown in the figure, the same signal as the recording signal is reproduced by converting it into an electrical signal using a CCD array, an image sensor, or the like.

  By the way, in digital holographic recording, page data composed of “1” and “0” is a portion through which light does not pass according to “1” and “0” by a spatial light modulator (SLM) or the like. Is converted into a signal light comprising: On the other hand, the reference light is applied to the hologram medium H as uniform light having no distribution according to the signal. At this time, in the hologram medium H, interference fringes are formed only on the part where the signal light passes, and only the reference light is irradiated on the other part, and the hologram medium H is exposed to the reference light. This causes the S / N to deteriorate during reproduction. In order to prevent this, medium characteristics and a recording / reproducing optical system that are not sensitized by only the reference light are required, and a margin in system design is reduced.

  In the conventional digital holographic recording, it is necessary to separate light emitted from a common light source into signal light and reference light by arranging optical components such as a beam splitter and a mirror. For this reason, the loss of the effective light quantity for recording is large. Introducing such a large number of optical components leads to a complicated and large recording / reproducing optical system.

Therefore, in order to solve such a problem, the following Patent Document 1 discloses that the light from the light source 1 is applied to the recording signal by the spatial light modulator (SLM) 2 as shown in FIGS. A plurality of diffracted lights having different orders are generated from the modulated light by the diffraction grating 5 so that one order of diffracted light acts as signal light, and the other orders of diffracted light act as reference light, A method of recording on the hologram recording medium 4 has been proposed. The diffraction grating 5 is formed in a floating block (not shown) for positioning with the hologram recording medium 4, and the floating block is positioned with respect to the hologram recording medium 4 by a floating slider (not shown). FIG. 6B shows the process of reproducing the hologram recording medium 4.
JP 2005-128473 A (Abstract, FIG. 3, Paragraph 0019)

  However, in the above conventional example, since the diffraction grating 5 is provided on the flying slider, it is difficult to manufacture a flying slider having an appropriate flying height. Further, since it is necessary to keep the flying height of the surface of the hologram recording medium 4 and the flying slider constant, it is necessary to strictly manage defects and protrusions on the surface of the hologram recording medium 4. In addition, attention must be paid to the problem of adsorption between the hologram recording medium 4 and the flying slider, which makes it difficult to reduce the size, weight, and cost of the recording apparatus.

  Further, as shown in FIGS. 6A and 6B, since the diffracted light of the recording light is used as the reference light, the diffracted light is generated when the pixel of the spatial light modulator is “dark”. Therefore, there is also a drawback that the recording light and the reference light are not overlapped, and the recording density is lowered and it is difficult to achieve high density recording.

  The present invention has been made in view of the above-described problems of the conventional example, and an object thereof is to provide a hologram recording apparatus and a hologram recording method that can be reduced in size, weight, and cost and can be recorded at high density. .

In order to achieve the above object, the hologram recording apparatus of the present invention
A hologram recording apparatus for recording information on a hologram recording medium,
A light source;
A part of the light emitted from the light source is reflected as reference light toward the hologram recording medium, and the first surface on which the remainder of the light is incident on the inside and the light incident on the inside are emitted to the outside. An optical element having a second surface;
A spatial light modulator having a reflecting surface that transmits the light emitted from the second surface through the second surface and the first surface and reflects it as signal light toward the hologram recording medium;
It is characterized by having.

In order to achieve the above object, the hologram recording method of the present invention provides
A hologram recording method for recording information on a hologram recording medium,
Emit light from the light source,
The light emitted from the light source is reflected by the optical element as a reference light toward the hologram recording medium, and the remainder is incident on the optical element.
The light incident on the inside of the optical element is modulated by a spatial light modulator and reflected as signal light toward the hologram recording medium.

  With this configuration and method, in the hologram recording medium, a plurality of diffracted lights are not irradiated only on a portion where light corresponding to a recording signal has arrived and recorded as interference fringes. Therefore, it is possible to ensure a high density recording.

  According to the present invention, it is not necessary to dispose light emitted from a common light source into signal light and reference light by arranging optical components such as a beam splitter and a mirror. The cost can be increased, and the loss of light amount for recording is small, and the efficiency is high. Further, since the diffracted light is not used as the reference light as in Patent Document 1, high-density recording can be achieved, and the diffraction grating need not be removed during reproduction.

That is,
(1) The optical system is simple and the number of parts constituting the apparatus can be greatly reduced.
(2) There is little loss of light generated from the light source.
(3) Strong against vibration during recording and reproduction.
(4) The design margin for scheduling in recording / reproducing system design, particularly recording can be increased.
(5) Since the flying slider need not be designed and manufactured, the apparatus can be reduced in size, weight, and cost.
(6) It is not necessary to spend a great deal of man-hour for managing the surface shape of the recording medium.
(7) Since there is no gap between the flying slider and the recording medium, the interference fringe area is increased, and the recording sensitivity is improved.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a basic configuration of a hologram recording apparatus according to the present invention. FIG. 2 is a schematic diagram when recording is actually performed using the hologram recording apparatus. FIGS. 3 (a) and 3 (b) are diagrams. It is explanatory drawing which shows the hologram recording process and reproduction | regeneration process which concern on this invention, respectively. Details of each part will be described below.

  The light source 1 shown in FIG. 1 generates light necessary for recording and reproduction, and is preferably a laser light source capable of generating light of a specific wavelength. As the type of laser, a semiconductor laser (LD: laser diode), a gas laser, or a pulsed laser represented by a YAG laser or a Ti sapphire laser can be used, but an LD is used from the viewpoint of downsizing the apparatus. desirable.

  The optical element 3 is provided with a spatial light modulator (SLM) 2 on the surface opposite to the surface on the light source 1 side, and reflects a part of the light emitted from the light source 1 on the surface on the incident side as reference light. The light is incident on the hologram recording medium 4 and the remaining light is transmitted and incident on the SLM 2. Further, the optical element 3 transmits the signal light reflected from the SLM 2 and makes it incident on the hologram recording medium 4. As the optical element 3, a prism or a half mirror can be used, but a function of diffusing the phase of light may be provided in order to efficiently form interference fringes. Here, the reference light and signal light regions generated in the recording region of the hologram recording medium 4 are designed to have a shape dimension and an optical design of the reflective layer and the transmissive layer so as to overlap spatially.

  The SLM 2 is provided in close contact with the surface of the optical element 3 opposite to the surface on the light source 1 side, and is used for modulating light with a recording signal input as an electric signal. When one page of digital information to be recorded on the SLM 2 is input as an electrical signal, the light reflected from the SLM 2 is converted into a signal light having a two-dimensional light / dark pattern corresponding to the input signal. The SLM 2 is roughly classified into a transmission type using a liquid crystal element or the like and a reflection type (DMD) using a micromirror or the like. In this apparatus, a reflection type is used.

  The above are the minimum necessary parts for configuring the present apparatus. In order to collimate the light from the light source 1 as necessary, the collimating lens L1 is connected to the light source 1 and the optical element 3 as shown in FIG. Insert between. If necessary, a condenser lens L2 is inserted between the optical element 3 and the hologram recording medium 4 as shown in FIG. The condensing lens L2 may be any lens having a function of condensing the recording light beam so as to have a desired beam diameter at the position of the hologram recording medium 4, such as a convex lens, a Fresnel lens, a hologram lens, or a reflective concave mirror. Can be used.

  The condenser lens L2 also plays an important role when performing multiple recording. That is, by using the condensing lens L2, the recording light beam at the position of the hologram recording medium 4 becomes non-parallel light, and the recording can be multiplexed. Multiple recording cannot be performed if the recording light beam at the position of the hologram recording medium 4 is parallel light. That is, after recording certain page data, when the next page data is recorded by shifting the position of the hologram recording medium 4 within a range equal to or less than the spot diameter, the portion overlapped with the previous page is the same interference condition in the case of parallel light. This makes it impossible to separate pages during playback. If this is non-parallel light, the interference conditions of the overlapped portions are different, so that individual interference fringes are formed, which can be separated during reproduction.

  Further, lenses and mirrors may be inserted as appropriate for the purpose of adjusting the optical path in the hologram recording apparatus, and a shutter may be inserted for the purpose of turning light on and off. In the above description, the configuration necessary for recording is shown. However, elements having both recording and reproduction functions including an image sensor such as a CCD array and a C-MOS sensor may be used. Good.

  The hologram recording medium 4 used for recording / reproduction using the hologram recording apparatus is provided with at least a material that can be recorded as interference fringes when light of the same wavelength is irradiated from two directions to cause interference. Specific materials include materials such as a photopolymer system, a photorefractive crystal system, and a chalcogenite glass system. As types of interference fringes, there are an amplitude modulation type composed of a light and dark distribution and a phase modulation type composed of a change in refractive index.

Next, an example of a procedure for recording on the hologram recording medium 4 using the hologram recording apparatus will be described with reference to FIGS. 2 and 3A.
Process 1: The relative position between the hologram recording medium 4 and the beam of recording light is moved to a predetermined position to be recorded. The moving means includes a method of mounting the hologram recording medium 4 on an XY stage and moving the hologram recording medium 4 to a predetermined (x, y) coordinate, a method of rotating the hologram recording medium 4 by mounting it on a rotating part coaxial with the motor, A method of moving the beam of recording light to a predetermined location on the hologram recording medium 4 and a method of moving them in combination are used.
Process 2: An electric signal for one page to be recorded in the SLM 2 is input. Note that the process 1 and the process 2 may be performed simultaneously or in the reverse order.

  Process 3: The emitted light emitted from the light source 1 is incident on the collimator lens L1, collimated, partially reflected on the surface of the optical element 3, and incident on the hologram recording medium 4 via the condenser lens L2. On the other hand, the remainder of the parallel light transmitted through the optical element 3 without being reflected by the surface of the optical element 3 is incident on the SLM 2, and an electrical signal for one page to be recorded is optically modulated by the SLM 2 and reflected by the SLM 2. The recording light is incident on the hologram recording medium 4 through the optical element 3. The irradiation time is determined in consideration of the sensitivity, dynamic range, recording light power, and recording multiplicity of the hologram recording medium 4. Through this process 3, the output light from the SLM 2 is converted into a recording light beam in which bright portions and dark portions are distributed according to the recording signal (for example, the bright portion is “1” and the dark portion is “0”). It reaches the hologram recording medium 4 through the lens L2.

  As described above, the process 1 to the process 3 are repeated to record on the hologram recording medium 4. At this time, if the recording light beam at the position of the hologram recording medium 4 is non-parallel light by the action of the condensing lens L2, the recording spot is exceeded for the reason described in paragraph 0023 when moving to the next recording position in the process 1. It is possible to wrap. As a result, multiple recording becomes possible.

Next, an example of a procedure for reproducing the signal recorded by the above procedure will be described.
Process 11: The relative position between the hologram recording medium 4 and the beam of recording light is moved to the same position as when recording. The moving means includes a method of mounting the hologram recording medium 4 on an XY stage and moving the hologram recording medium 4 to a predetermined (x, y) coordinate, a method of moving a recording light beam to a predetermined location of the hologram recording medium 4, and A method of moving these in combination is used.
Process 12: The hologram recording medium 4 is irradiated with the scattered light emitted from the light source 1 under the same conditions as when recording. However, at this time, the SLM 2 used in the recording process shown in FIG. At this time, a value convenient for reproduction can be selected as the power of the irradiated light. Since the hologram recording medium 4 in the reproducing process shown in FIG. 3B has already formed interference fringes corresponding to the recording light, the interference fringes are formed in the light passing through the hologram recording medium 4 in this process 12. Diffracted light is generated only at the portion where the light is applied. That is, the diffracted light obtained here is light reproduced as the same pattern as the recording light in the recording process shown in FIG. By detecting this with an image sensor such as a CCD or C-MOS sensor, it is reproduced as the same electrical signal as the recording signal.
As described above, the recorded signals are sequentially reproduced by repeating steps 11 and 12.

1 is a basic configuration diagram showing a hologram recording apparatus according to the present invention. It is a block diagram which shows one Embodiment of the hologram recording apparatus which concerns on this invention. It is explanatory drawing which shows the hologram recording process and reproduction | regeneration process of the hologram recording apparatus which concerns on this invention. It is a block diagram which shows the conventional hologram recording device. It is a block diagram which shows the other conventional hologram recording medium and hologram recording apparatus. It is explanatory drawing which shows the hologram recording process and reproduction | regeneration process of the hologram recording apparatus in FIG.

Explanation of symbols

1 Light Source 2 Spatial Light Modulator (SLM)
3 Optical element 4 Hologram recording medium L1 Collimating lens L2 Condensing lens

Claims (2)

A hologram recording apparatus for recording information on a hologram recording medium,
A light source;
A part of the light emitted from the light source is reflected as reference light toward the hologram recording medium, and the first surface on which the remainder of the light is incident on the inside and the light incident on the inside are emitted to the outside. An optical element having a second surface;
A spatial light modulator having a reflecting surface that transmits the light emitted from the second surface through the second surface and the first surface and reflects it as signal light toward the hologram recording medium;
A hologram recording apparatus provided. A hologram recording method for recording information on a hologram recording medium,
Emit light from the light source,
The light emitted from the light source is reflected by the optical element as a reference light toward the hologram recording medium, and the remainder is incident on the optical element.
A hologram recording method in which light incident inside the optical element is modulated by a spatial light modulator and reflected as signal light toward the hologram recording medium.

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