JP2004139023A - Hologram recording device, hologram recording method, and hologram record medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording device which reduces the noise component generated from a spatial light modulator of a phase modulation type and can improve the reliability of data, a hologram recording method, and a hologram recording medium. <P>SOLUTION: In recording the information corresponding to the diffraction state in a diffraction control element to the hologram recording medium, a prescribed diffracted light component is shut off from the diffracted light emitted from the diffraction control element by condensing the light controlled in the diffraction state in the diffraction control element to the hologram recording medium. Consequently, the noise component in recording the information can be reduced. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hologram recording device that records data on a hologram recording medium, a hologram recording method, and a hologram recording medium.
[0002]
[Prior art]
A hologram recording device for recording data on a hologram recording medium has been developed.
In a hologram recording device, a signal light modulated by a spatial light modulator and a non-modulated reference light are superimposed on a hologram recording medium, and an interference pattern is recorded.
There are two types of modulation methods in this spatial light modulator, a light-dark type and a phase modulation type. In the light-dark type spatial light modulator, modulation is performed by controlling the amount of transmission or reflection of light, and for example, a liquid crystal display element can be used.
On the other hand, in a phase modulation type spatial light modulator, the phase of light is partially changed to generate an intensity distribution of light by causing interference. For example, a GLV (Grating Light Valve) manufactured by Silicon Light Machine Co., Ltd. ) Is available. In the phase modulation type, for example, a state in which only the 0th-order diffracted light is generated from the spatial light modulator and a state in which the 0th-order diffracted light is not generated and only the ± 1st-order diffracted light is generated are “1” and “0”, respectively. And digital data can be recorded on the hologram recording medium.
The GLV technology is disclosed in Patent Document 1.
[0003]
[Patent Document 1]
U.S. Pat.
[0004]
[Problems to be solved by the invention]
However, as a result of our research, it was found that not only the 0th-order diffracted light and ± 1st-order diffracted light but also various diffracted lights are generated from the phase modulation type spatial light modulator. Such various types of diffracted light become noise when recording data on the hologram recording medium, and may cause an error when decoding data.
In view of the above, an object of the present invention is to provide a hologram recording device, a hologram recording method, and a hologram recording medium that can reduce noise components generated from a phase modulation type spatial light modulator and improve data reliability. .
[0005]
[Means for Solving the Problems]
A. In view of the above, a hologram recording apparatus according to the present invention includes a laser light source that emits laser light, and a diffraction control element that receives laser light emitted from the laser light source, controls the diffraction of the incident laser light, and emits the laser light. A diffracted light component blocking element that blocks a predetermined diffracted light component from the diffracted light emitted from the diffraction control element; and a condensing device that condenses a diffracted light component that is not blocked by the diffracted light component blocking element on a hologram recording medium. And an element.
By condensing the light whose diffraction state is controlled by the diffraction control element on the hologram recording medium, information corresponding to the diffraction state of the diffraction control element can be recorded on the hologram recording medium. Here, by blocking a predetermined diffracted light component from the diffracted light emitted from the diffraction control element by the diffracted light component blocking element, it is possible to reduce a noise component at the time of recording information.
As an example of the diffracted light component blocking element, a member having an opening can be cited. A predetermined diffracted light component can be easily blocked.
It should be noted that the hologram recording device may have a built-in hologram recording medium, or the hologram recording medium may be replaceable. When the hologram recording medium is replaceable, it is preferable to have a stage for holding the hologram recording medium.
[0006]
(1) The diffraction control element may include a plurality of individual diffraction control elements for controlling the diffraction of the incident laser light independently of each other.
Information corresponding to the number of individual diffraction control elements can be recorded on the hologram recording medium, and higher-density recording can be performed.
At this time, a one-dimensional (linear) or two-dimensional (planar) array can be considered as an array of the individual diffraction control elements. When a member having an opening is used as the diffracted light component blocking element, the shape of the opening is preferably a slit or a pinhole corresponding to this arrangement.
1) The diffracted light component blocking element may block the third or higher order diffracted light in absolute value by the individual diffraction control element.
By doing so, a noise component at the time of recording information can be reduced, and data reproducibility can be maintained in a good state.
[0007]
2) The individual diffraction control element may include first and second phase control elements for controlling a phase difference between light beams emitted from the individual diffraction control elements.
By controlling the phase difference between the emitted lights emitted from the first and second phase control elements, the diffraction state of the light obtained by combining the emitted lights can be controlled. For example, the state of diffraction of light can be controlled by adjusting the relative displacement between the first and second phase control elements. However, one of the first and second phase control elements may be fixed and the other may be movable, and the state of diffraction of light may be controlled by the amount of displacement on the movable side.
Note that a third or more phase control element may be added.
[0008]
Here, since the first and second phase control elements are often small to some extent (about the wavelength of light or smaller than that), the light emitted from each of them is controlled by the first and second phase control elements. Usually, the diffracted light is diffracted.
At this time, it is preferable that the diffracted light component blocking element blocks the first-order or higher-order diffracted light in absolute value by each of the first and second phase control elements.
By doing so, a noise component at the time of recording information can be reduced, and data reproducibility can be maintained in a good state.
[0009]
Each of the first and second phase control elements can take various shapes, but can have, for example, a substantially ribbon shape.
This shape is easy to create and drive. For example, when the ribbon is made of a conductive and elastic material (for example, a metal material), the ribbon is displaced by an electrostatic force based on a voltage applied to the ribbon, and the original state (shape) is formed by the elasticity of the ribbon. Can be restored. This makes it possible to operate the first and second phase control elements, and hence the individual diffraction control element, at a high speed (for example, about 1 μsec).
[0010]
(2) The light-collecting element may be constituted by a plurality of lenses.
For example, by letting outgoing light emitted from the diffraction control element pass through two lenses, Fourier transform is performed twice, and the diffraction spectrum of the diffraction control element can be used for recording on the hologram recording medium.
[0011]
(3) a hologram recording device that divides a laser beam emitted from the laser light source into first and second beams, and that divides the first beam into the diffraction control element; A second condensing element for condensing the second light emitted from the element at a position on the hologram recording medium where the laser light emitted from the condensing element is condensed. Good.
The laser light emitted from the laser light source is divided into a reference light that does not pass through the diffraction control element and a signal light that passes through the diffraction control element, and both are condensed on the hologram recording medium, so that they are referred to on the hologram recording medium. Interference fringes between light and signal light can be recorded.
Note that a half mirror is an example of the light splitting element.
[0012]
Here, the hologram recording device is based on a light shielding element for shielding the first light emitted from the light splitting element, and a laser beam converged on the hologram recording medium by the second condensing element. A light receiving element for receiving light emitted from the hologram recording medium.
By blocking the signal light emitted from the light splitting element from reaching the hologram recording medium and allowing only the reference light to reach the hologram recording medium, a signal corresponding to the data recorded from the hologram recording medium is obtained. Generate light. The recorded data can be reproduced by reading the generated signal light with the light receiving element. This light receiving element preferably corresponds to the diffraction control element that generated the original signal. For example, when the diffraction control element is constituted by individual diffraction control elements arranged one-dimensionally or two-dimensionally, it is preferable that the diffraction control element is constituted by individual light-receiving elements arranged correspondingly.
[0013]
B. The hologram recording method according to the present invention includes a diffraction control step of controlling the diffraction of a laser beam by a diffraction control element and emitting the laser beam; and a diffracted light beam that blocks a predetermined diffracted light component from the diffracted light emitted in the diffraction control step. The method further comprises: a component blocking step; and a focusing step of focusing a diffracted light component that is not blocked by the diffracted light component blocking step on a hologram recording medium.
By condensing the light whose diffraction state is controlled by the diffraction control element on the hologram recording medium, information corresponding to the diffraction state of the diffraction control element can be recorded on the hologram recording medium. Here, by blocking a predetermined diffracted light component from the diffracted light emitted from the diffraction control element by the diffracted light component blocking element, it is possible to reduce a noise component at the time of recording information.
[0014]
Here, the diffraction control element may include a plurality of individual diffraction control elements that independently control the diffraction of the incident laser light.
Information corresponding to the number of individual diffraction control elements can be recorded on the hologram recording medium, and higher-density recording can be performed.
At this time, a one-dimensional (linear) or two-dimensional (planar) array can be considered as an array of the individual diffraction control elements.
[0015]
1) The diffracted light component blocking element may block the third or higher order diffracted light in absolute value by the individual diffraction control element.
By doing so, a noise component at the time of recording information can be reduced, and data reproducibility can be maintained in a good state. In addition, as an example of the diffracted light to be cut off, there is a third-order diffracted light in a case where the individual diffraction control elements sequentially indicate 0101...
[0016]
2) The individual diffraction control element may include first and second phase control elements for controlling a phase difference between light beams emitted from the individual diffraction control elements.
By controlling the phase difference between the emitted lights emitted from the first and second phase control elements, the diffraction state of the light obtained by combining the emitted lights can be controlled. In this case, a third or more phase control element may be added.
[0017]
Here, since the first and second phase control elements are often small to some extent (about the wavelength of light or smaller than that), the light emitted from each of them is controlled by the first and second phase control elements. Usually, the diffracted light is diffracted.
At this time, it is preferable that the diffracted light component blocking element blocks the first-order or higher-order diffracted light in absolute value by each of the first and second phase control elements.
By doing so, a noise component at the time of recording information can be reduced, and data reproducibility can be maintained in a good state.
[0018]
C. In the hologram recording medium according to the present invention, data is recorded by using a diffracted light obtained by blocking a predetermined diffracted light component in the diffracted light emitted from the diffraction control element that controls and emits the diffraction of the laser light. Features.
By blocking a predetermined diffracted light component from the diffracted light emitted from the diffraction control element, a noise component at the time of recording information on the hologram recording medium can be reduced.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(1st Embodiment)
FIG. 1 is a schematic diagram illustrating a hologram recording device 100 according to the first embodiment of the present invention. FIG. 2 is a schematic diagram showing a state in which the hologram recording device 100 is viewed from the X-axis direction in FIG.
As shown in FIGS. 1 and 2, the hologram recording apparatus 100 includes a laser light source 10, a one-dimensional beam expander 20, a half mirror 30, a one-dimensional diffraction control element 40, a slit element 50, a one-dimensional light receiving element 60, It is composed of a cylindrical lens 71 and convex lenses 81 to 85, and records and reproduces information on the hologram recording medium M.
[0020]
(Internal Configuration of One-Dimensional Diffraction Control Element 40)
First, the one-dimensional diffraction control element 40 will be described.
FIG. 3 is a top view illustrating a state in which the one-dimensional diffraction control element 40 is viewed from above. 4 and 5 are a side view and a front view, respectively, showing the one-dimensional diffraction control element 40 as viewed from the side and the front. 4A and 4B show two states (OFF, ON) of the individual diffraction control element 41, respectively. FIG. 5 schematically illustrates the operation state of the ribbon 42.
The one-dimensional diffraction control element 40 is configured by arranging a plurality of individual diffraction control elements 41 in the Y direction. The individual diffraction control elements 41 diffract incident light and emit it as diffracted light, and can control the state of diffraction independently of each other.
[0021]
The individual diffraction control element 41 includes six ribbons 42, an insulating film 43 facing the ribbons 42, and a counter electrode 44, and is configured on a substrate 45. Three of the six ribbons 42 are driven up and down every other ribbon. By applying a voltage between the ribbon 42 and the counter electrode 44, an electrostatic force is generated during this time, and the ribbon 42 is attracted to the counter electrode 44 (ON state: FIGS. 4B and 5B). reference). When the voltage applied between the ribbon 42 and the counter electrode 44 is removed, the ribbon 42 returns to its original state by the elastic force of the ribbon 42 (OFF state: see FIGS. 4A and 5A). ).
For example, the ribbon 42 can have a width of several μm, a length of about 100 μm, and a distance d of several hundred nm. At this time, the operation time of the ribbon 42 can be about 1 μs.
[0022]
Hereinafter, the basic concept of the diffracted light generated from the individual diffraction control element 41 of the one-dimensional diffraction control element 40 will be described. This concept is based on the idea that the intensity of the diffracted light other than the 0th and 1st order diffracted light from the ribbon 42 is weak and can be ignored.
As will be described later, various kinds of diffracted light are generated from the one-dimensional diffraction control element 40, and their existence cannot be ignored. However, the following describes how the one-dimensional diffraction control element 40 records data on the hologram recording medium M. It is still fundamental. The details of the diffracted light generated from the one-dimensional diffraction control element 40 will be described later.
[0023]
Consider a case where a laser beam is vertically incident on the one-dimensional diffraction control element 40 (individual diffraction control element 41). As shown in FIG. 5A, when the six ribbons 42 of the individual diffraction control element 41 are on the same plane (OFF state), the laser light is reflected vertically as it is, and only the zero-order diffracted light is generated. On the other hand, as shown in FIG. 5B, if every other ribbon 42 is lowered (ON state), the first-order diffracted light is generated in addition to the vertically reflected zero-order diffracted light.
At this time, the ratio between the 0th-order diffracted light and the 1st-order diffracted light from the one-dimensional diffraction control element 40 is determined by the distance d between the ribbon 42 that has dropped and the ribbon 42 that has not dropped, and the distance d is λ / 4 (λ: laser light). ), Only the first-order diffracted light is emitted. That is, the 0th-order diffracted light from the ribbon 42 that has descended and the 0th-order diffracted light from the ribbon 42 that has not descended cancel each other out to have an intensity of 0, and only the first-order diffracted light remains.
[0024]
The diffracted light in the ON state of the individual diffraction control element 41 is a mixed light of the diffracted lights from the ribbon 42 that has fallen and the ribbon 42 that has not fallen, each having a half-wave phase shifted from each other. That is, each of the ribbons 42 can be considered as a phase variable element that can change the phase of the diffracted light diffracted from each ribbon by its displacement.
[0025]
As described above, each of the individual diffraction control elements 41 constituting the one-dimensional diffraction control element 40 independently takes two diffraction states (OFF: only the 0th-order diffracted light, ON: only the 1st-order diffracted light), whereby the number of pixels is increased. Data of the number of bits for (the number of individual diffraction control elements 41) can be expressed. For example, by arranging 1088 individual diffraction control elements 41, 1088-bit data can be expressed.
[0026]
The operation of the one-dimensional diffraction control element 40 (individual diffraction control element 41) in the case where the laser light is directly incident has been described. However, this operation principle is also applied to the case where the laser light is obliquely incident on the one-dimensional diffraction control element 40. Basically the same. However, since the optical path length difference is shorter at oblique incidence than at direct incidence, only the first-order diffracted light is emitted when the distance d is approximately (λ / 4) / cos θ (θ is a one-dimensional diffraction control element). Incident angle of laser light with respect to 40).
[0027]
(Other components)
Hereinafter, components other than the one-dimensional diffraction control element 40 will be described.
The laser light source 10 is a light source that emits laser light.
The one-dimensional beam expander 20 is configured by combining a plano-concave lens 21 having a semi-elliptic cylindrical recess and a cylindrical lens 22 having an elliptic cylindrical shape, and enlarges the beam diameter of incident light in the one-dimensional direction (Y direction). Optical element. By passing through the one-dimensional beam expander 20, the beam shape of the laser light emitted from the laser light source 10 is converted from a substantially circular shape to a substantially elliptical shape. This conversion is performed to irradiate the entire individual diffraction control element 41 arranged in the Y direction of the one-dimensional diffraction control element 40 with a light beam, as shown in FIG.
The half mirror 30 is an optical element that splits incident light into two lights.
The cylindrical lens 71 is an optical element for condensing the incident light beam in the X direction. This focusing is performed to make the laser light correspond to the size of the one-dimensional diffraction control element 40 in the X direction.
The convex lens 81 is an optical element for forming a diffraction spectrum of the diffracted light emitted from the one-dimensional diffraction control element 40.
[0028]
The slit element 50 is disposed near the focal point of the convex lens 81 and is an optical element for removing a predetermined diffracted light component from the diffracted light emitted from the one-dimensional diffraction control element 40, and functions as a diffracted light component blocking element. . A slit 51 (opening) is formed in the slit element 50 so that a predetermined diffracted light component does not pass through the slit 51.
For example, as shown in FIG. 6, the 0th-order diffracted light L0 passes through the slit 51, but the 1st-order diffracted light L1 (including both the positive and negative first-order diffracted lights L + 1 and L-1) cannot pass through the slit 51, and the slit element Shielded by 50. This is because the first-order diffracted light L1 is emitted at an angle ± α with respect to the 0th-order diffracted light L1 (the sign of the angle α corresponds to the sign of the first-order diffracted light (+1 or −1).
[0029]
In the above description, it is described that the light emitted from the one-dimensional diffraction control element 40 is limited to the zero-order and first-order diffracted lights from the ribbon 42.
However, as described above, the one-dimensional diffraction control element 40 emits not only zero-order and first-order diffracted lights but also various diffracted lights. Thus, the slit element 50 blocks not only the first-order diffracted light from the ribbon 42 but also the entire diffracted light that causes noise during recording on the hologram recording medium M. The details will be described later.
[0030]
The convex lens 82 is an optical element for converting light emitted from the slit element 50 into substantially parallel light.
The convex lens 83 is an optical element for collecting substantially parallel light emitted from the convex lens 82 on the hologram recording medium M.
Here, the reason why the convex lenses 82 and 83 and the two lenses are used is to record the diffraction spectrum itself of the diffracted light from which the first-order diffracted light has been removed by the slit 51 on the hologram recording medium M.
If only one of the convex lenses 82, 83 is used, the diffracted light is Fourier-transformed only once, and what is recorded on the hologram recording medium M is a real image of the one-dimensional diffraction control element 40. . In this real image, since the first-order diffraction component is removed from the diffracted light by the slit element 50, the pixels (FIG. 5A) where the positions of the ribbons 42 are aligned are clear, and the ribbons 42 move up and down every other line. Pixels (FIG. 5B) are dark. In the present embodiment, by using the convex lenses 82 and 83, the diffraction spectrum itself of the diffracted light is recorded on the hologram recording medium M.
The recording of data on the hologram recording medium M can be performed using either the diffraction spectrum itself from the one-dimensional diffraction control element 40 or its real image.
[0031]
The convex lens 84 is an optical element for condensing light emitted from the half mirror 30 in the negative X direction on the hologram recording medium M. The light emitted from the convex lens 84 is applied to the same portion of the hologram recording medium M as the light emitted from the convex lens 83 to form interference fringes (light and dark).
[0032]
The hologram recording medium M is a recording medium that records interference fringes caused by light emitted from the convex lenses 83 and 84 as a change in refractive index. By changing the refractive index of the hologram recording medium M in accordance with the exposure amount, interference fringes generated by interference between the reference light and the signal light can be recorded on the hologram recording medium M as a change in the refractive index.
As a constituent material of the hologram recording medium M, any material can be used regardless of whether it is an organic material or an inorganic material, as long as the material changes its refractive index according to the intensity of light. As the inorganic material, for example, lithium niobate (LiNbO) ₃ ), A photorefractive material whose refractive index changes according to the amount of exposure due to the electro-optic effect can be used.
As the organic material, for example, a photopolymerizable photopolymer can be used. In the photopolymerizable photopolymer, in its initial state, monomers are uniformly dispersed in the matrix polymer. When this is irradiated with light, the monomer polymerizes in the exposed area. Then, as it is polymerized, the refractive index at that location changes.
[0033]
The convex lens 85 is an optical element for converging the reproduction light when reproducing the recording from the hologram recording medium M to the one-dimensional light receiving element 60.
The one-dimensional light receiving element 60 includes a plurality of light receiving elements arranged in the Y direction, receives the reproduction light emitted from the convex lens 85, and outputs a signal corresponding to the intensity of the received light. In the one-dimensional light receiving element 60, the light receiving elements are one-dimensionally arranged in the Y direction corresponding to the individual diffraction control elements 41 of the one-dimensional diffraction control element 40.
Here, the number of light receiving elements of the one-dimensional diffraction control element 40 is larger than the number of diffraction control elements 41 of the one-dimensional diffraction control element 40, and a plurality of light receiving elements correspond to one individual diffraction control element 41. Is preferred.
Instead of the one-dimensional light receiving element 60, a light receiving element in which a plurality of light receiving elements are arranged two-dimensionally (in a plane) can be used.
[0034]
(Details of Diffracted Light Emitted from One-Dimensional Diffraction Control Element 40)
Here, the details of the diffracted light emitted from the one-dimensional diffraction controller 40 will be considered.
Until now, it has been described that only the zero-order and first-order diffracted lights from the ribbon 42 are emitted from the one-dimensional diffraction control element 40, and that the diffracted lights of other components can be ignored.
However, as a result of our research, it has been found that various kinds of diffracted light are generated from the one-dimensional diffraction control element 40, and the existence of these lights cannot necessarily be ignored. That is, various types of diffracted light generated from the one-dimensional diffraction control element 40 may be a cause of noise when data is recorded on the hologram recording medium M.
[0035]
FIGS. 7 and 8 are schematic diagrams schematically showing diffracted light generated from the one-dimensional diffraction control element 40 in which the individual diffraction control elements 41 are in the ON state (on / off repetition pattern) every other one. is there. FIG. 7 shows a state where the diffracted light generated from the one-dimensional diffraction control element 40 is viewed from the side surface of the one-dimensional diffraction control element 40. FIG. 8 shows a state in which the diffracted light generated from the one-dimensional diffraction control element 40 is projected on a screen through a convex lens (Fourier image of the diffraction pattern). It corresponds to the state you saw.
[0036]
As shown in FIGS. 7 and 8, the diffracted light from the one-dimensional diffraction control element 40 having the repeating pattern of ON and OFF includes the diffracted light (L00, L ± 01, L ± 02, L ± 03,...) And diffracted light (L ± 11, L ± 12,..., L ± 15, L ± 21,..., L ± 25, L ± 31,...) From the individual diffraction control element 41. included.
The diffracted light from the ribbon 42 is divided into 0th-order diffracted light L00, 1st-order diffracted light L ± 01, 2nd-order diffracted light L ± 02, 3rd-order diffracted light L ± 03,. In addition to the diffracted light from the ribbon 42, the diffracted light from the individual diffraction control element 41 is added to the diffracted light (L00, L ± 01, L ± 02, L ± 03,...) From the ribbon 42.
The diffracted light from the individual diffraction control element 41 is divided into a first primary diffracted light L ± 11, a first secondary diffracted light L ± 12, a first tertiary diffracted light L ± 13,. The light is divided into a folded light L ± 21, a second second-order diffracted light L ± 22, and a second third-order diffracted light L ± 23. The diffracted light from the individual diffraction control element 41 that matches the diffracted light (L ± 01, L ± 02, L ± 03,...) From the ribbon 42 is the first, second, and third sixth-order diffracted light L ± 16, L ± 26, and L ± 36.
Among these diffracted lights, the 0th-order diffracted light L00 and the 1st-order diffracted light L ± 01 by the ribbon 42 correspond to the 0th-order diffracted light L0 and the 1st-order diffracted light L ± 1, respectively.
[0037]
As can be seen from the above, the interval of the diffracted light from the individual diffraction control element 41 is smaller than the interval of the diffracted light from the ribbon 42. Further, the diffracted light from the individual diffraction control element 41 coincides with the diffracted light from the ribbon 42 every sixth time.
This is because the interval between the diffracted lights (the interval between the emission angles) corresponds to the grating interval of the diffraction grating. That is, the larger the grating interval of the diffraction grating, the smaller the interval between the diffracted lights. Since the width of the ribbon 42 is smaller than the width of the individual diffraction control element 41, the interval of the diffracted light by the ribbon 42 is larger than the interval of the diffracted light by the individual diffraction control element 41. Further, since the six ribbons 42 correspond to one individual diffraction control element 41, the sixth of the diffracted light from the individual diffraction control element 41 overlaps with the diffracted light from the ribbon 42.
[0038]
As described above, the one-dimensional diffraction control element 40 displays a repetitive pattern in which the individual diffraction control elements 41 are alternately turned on and off, whereby the diffracted light (individual diffraction control) using the individual diffraction control elements 41 as a diffraction grating is provided. (Diffraction light from the element 41). On the other hand, when all the individual diffraction control elements 41 are turned ON, only the diffracted light from the ribbon 42 is observed (L00, L ± 01, L ± 02, L ± 03,...) The diffracted light from the individual diffraction control element 41 is practically negligible.
[0039]
When every two individual diffraction control elements 41 are turned ON / OFF (when a pattern in which (ON, ON, OFF, OFF) is repeated) is displayed, compared to a case in which (ON, OFF) is repeated. The grid spacing is doubled. Therefore, the interval between the diffracted lights is halved, and the twelfth (12th-order diffracted light) of the diffracted light from the individual diffraction control element 41 overlaps with the diffracted light from the ribbon 42.
The above is the case where the individual diffraction control elements 41 are set to ON / OFF every third and fourth elements ((ON, ON, ON, OFF, OFF, OFF), (ON, ON, ON, ON, OFF, The same applies to the case of displaying a pattern that repeats OFF, OFF, and OFF), and the diffracted light from the individual diffraction control element 41 appears according to the pattern repetition period.
[0040]
FIG. 9 is a graph showing the light intensity distribution of the diffracted light from the one-dimensional diffraction control element 40 when the light does not pass through the slit element 50. The horizontal axis represents the relative distance (position), and the vertical axis represents the light intensity (White Level) at each position. The distribution of light intensity is measured by receiving only the signal light by the one-dimensional light receiving element similar to the one-dimensional light receiving element 60. The graph in FIG. 9 corresponds to a result obtained by converting the Fourier image shown in FIG. 8 to a real image. In the one-dimensional diffraction control element 40 shown in FIG. 9, the individual diffraction control element 41 represents a pattern in which “1, 0” is repeated (“ON, OFF” is repeated).
As shown in FIG. 9, it can be seen that when there is no slit element 50, the diffracted light generated from the one-dimensional diffraction control element 40 contains much noise (particularly high-frequency noise).
[0041]
The slit element 50 blocks out of the diffracted light generated from the one-dimensional type light receiving element 60, the diffracted light serving as noise. That is, the slit 51 of the slit element 50 has an appropriate width in the Y direction around the 0th-order diffracted light L00 so as to block the diffracted light that becomes noise.
[0042]
FIG. 10 is a schematic diagram showing a correspondence relationship between the slit element 50 and the diffracted light when the diffracted light (L ± 01, L ± 02,...) From the ribbon 42 of the first or higher order in absolute value is shielded. Here, the slit 51 allows the diffracted lights L00, L ± 11 to L ± 15 to pass therethrough and shields the other diffracted lights L ± 01, L ± 21 to L ± 25, L ± 03, and the like.
FIG. 11 shows the correspondence between the slit element 50 and the diffracted light when the diffracted light (L ± 13, L ± 14,...) From the individual diffraction control element 41 of the third order or higher in absolute value is shielded. It is a schematic diagram. Here, the slit 51 allows the diffracted lights L00, L ± 11 to L ± 12 to pass, and the other diffracted lights L ± 13 to L ± 15, L ± 01, L ± 21 to L ± 25, L ± 03, and the like. Shielding.
[0043]
FIG. 12 is a graph showing the light intensity distribution of the diffracted light from the one-dimensional diffraction control element 40 when passing through the slit element 50 shown in FIG. The distribution of light intensity is measured by receiving only the signal light by the one-dimensional light receiving element similar to the one-dimensional light receiving element 60. Note that in the one-dimensional individual diffraction control element 40 of FIG. 11, the individual diffraction control element 41 shows a pattern that repeats “1, 0” (repeates “ON, OFF”), as in FIG.
It can be seen that the waveform shown in FIG. 11 is closer to the desired signal to be reproduced as compared to FIG.
[0044]
The narrower the width of the slit 51, the more the diffracted light passing through the slit 51 is limited, and only the diffracted light L00 passes. At first glance, it seems that the narrower the width of the slit 51 is, the more the diffracted light that becomes noise is reduced and the signal-to-noise ratio of the recording on the hologram recording medium M is improved.
However, as a result of our experiments, it has been found that if the width of the slit 51 is made too narrow, the reproducibility of the signal may be rather lowered.
[0045]
We assume that the individual diffraction control element 41 of the one-dimensional individual diffraction control element 40 repeats one of “110” and “001” (one of “ON, ON, OFF”, “OFF, OFF, ON” The effect of the width of the slit 51 on the reproducibility of the signal when the pattern was repeated was verified. This is the shortest repeated pattern in which the appearance ratio of “1” and “0” is not 1 to 1, and the diffracted light L ± 19 overlaps the diffracted light L0 ± 1.
As the width of the slit 51 at this time, (1) when all the diffracted lights pass (the width is infinite: there is no slit element 50), (2) only the diffracted lights L00, L ± 11 and L ± 12 pass. In this case, (3) three cases where only the diffracted lights L00 and L ± 11 are passed were set, and the reproducibility of signals was compared.
[0046]
FIGS. 13 to 15 are graphs showing the light intensity distributions of the diffracted light from the one-dimensional diffraction control element 40 in the settings (1) to (3), respectively. As in FIGS. 9 and 12, the one-dimensional light receiving element similar to the one-dimensional light receiving element 60 receives only the signal light to measure the light intensity distribution.
From FIG. 13, as in FIG. 9, it can be seen that when the light does not pass through the slit element 50 (setting (1)), the diffracted light generated from the one-dimensional diffraction control element 40 contains much noise.
On the other hand, the waveform shown in FIG. 14 is closer to the desired signal to be reproduced as compared with FIG. 13 (the ratio of 1 to 0 is 2: 1, and the original signal is stored). There).
However, in the waveform shown in FIG. 15, the ratio of 1 to 0 is 1: 1 as compared with FIG. 14, and it can be seen that the original signal is lost.
[0047]
As described above, if the width of the slit 51 is made too narrow, the reproducibility of the signal may be rather lowered.
When three consecutive individual diffraction elements 41 (pixels) repeat "110" or "001", the repetition is reflected in the pattern of the diffracted light emitted from the one-dimensional diffraction element 40. This is because the interval (period) at which the repetition is performed corresponds to the interval between the diffraction gratings. As a result, the diffracted light as a signal includes the second-order diffracted light L ± 12 from the individual diffraction element 41 as a component. Since this pattern can appear in data for recording and reproduction, it is preferable that the slit 51 allows the secondary diffracted light L ± 12 to pass through.
[0048]
Note that the second-order diffracted light L ± 12 in this pattern (a pattern that repeats either “110” or “001”) is not the same as the diffracted light L ± 12 shown in FIG. This is because the interval of the diffracted light changes depending on the repetition period of the pattern (the grating interval of the diffraction grating). The position of the diffracted light L ± 12 in this pattern is located between the diffracted light L ± 11 and L ± 12 in the “10” repeating pattern shown in FIG. If this position is formally represented by a decimal point, it becomes L ± 1, 1.33 (first 1.33 order diffracted light).
[0049]
(Operation of hologram recording apparatus 100)
A. Recording of data on the hologram recording medium M (see FIGS. 1 and 2)
The laser light emitted from the laser light source 10 is divided into two lights (reference light and signal light) by the half mirror 30 after the beam diameter is expanded in the Y direction by the one-dimensional beam expander 20.
The reference light passes through the convex lens 84 and is collected on the hologram recording medium M.
[0050]
The signal light is converged in the X direction by the cylindrical lens 71 and enters the one-dimensional diffraction control element 40. As described above, the individual diffraction control elements 41 independently take two diffraction states (OFF: “1”, ON: “0”), so that the individual diffraction control elements 40 as a whole in the one-dimensional diffraction control element 40. 41 bits of data (for example, 1088 bits when the number of individual diffraction control elements 41 is 1088) can be expressed.
[0051]
The diffracted light diffracted by the one-dimensional diffraction control element 40 is converged by the convex lens 81 and passes through the slit element 50, so that extra diffracted light is shielded and noise is reduced. As a result, the two diffraction states (OFF, ON) of the individual diffraction control element 41 are separated from each other, and the display pattern of the one-dimensional diffraction control element 40 is accurately reflected on the signal light (the signal-to-noise ratio). Improvement).
The diffracted light whose diffraction state has been converted into intensity is condensed on the hologram recording medium M via the convex lenses 82 and 83. At this time, since the reference light and the signal light are condensed on substantially the same portion of the hologram recording medium M, an interference fringe is formed on the hologram recording medium M, and the refractive index of the hologram recording medium M is corresponding to the interference fringe. Change. At this time, since the signal-to-noise ratio of the signal light is improved, the signal recorded on the hologram recording medium M also has an improved signal-to-noise ratio.
[0052]
As described above, the refractive index distribution of the hologram recording medium M is formed corresponding to the binary state of each individual diffraction control element 41 of the one-dimensional diffraction control element 40, and data can be recorded on the hologram recording medium M. It becomes. For example, when the number of the individual diffraction control elements 41 is 1088, the hologram recording medium M is exposed once using the one-dimensional diffraction control element 40, so that 1088-bit data is recorded.
By exposing the hologram recording medium M a plurality of times while shifting the condensing positions of the reference light and the signal light, data having a bit number that is a multiple of the number of the individual diffraction control elements 41 can be recorded on the hologram recording medium M. .
[0053]
B. Reproduction of data from hologram recording medium M
FIG. 16 is a schematic diagram illustrating a state in which data is reproduced from the hologram recording medium M using the hologram recording apparatus 100.
In order to reproduce data from the hologram recording medium M, of the two lights (reference light and signal light) emitted from the laser light source 10 and divided by the half mirror 30, the signal light is blocked by the shielding plate 90, Only the reference light passes through the convex lens 84 and is focused on the hologram recording medium M. In order to prevent the light reflected from the shielding plate 90 from being mixed into the reference light and causing noise, for example, it is preferable that the shielding plate 90 is slightly inclined with respect to the incident light. Further, if a normal mirror is used instead of the half mirror 30, the shielding plate 90 becomes unnecessary.
The reference light incident on the hologram recording medium M is diffracted by the refractive index distribution in the hologram recording medium M to generate a signal light. The generated signal light is emitted from the extension of the traveling direction of the recording signal light, on which the signal light has entered during recording on the hologram recording medium M. The reproduced signal light is converged by the convex lens 85 and is incident on the one-dimensional light receiving element 60. Data recorded in the hologram recording medium M can be reproduced as the intensity of light received by each of the one-dimensional light receiving elements 60. At this time, since the recording in the hologram recording medium M is performed with a good signal-to-noise ratio, the signal-to-noise ratio of the generated signal is also good, and the reproducibility of data is improved.
[0054]
(Second embodiment)
FIG. 17 is a schematic diagram illustrating a hologram recording device 200 according to the second embodiment of the present invention.
As shown in FIG. 17, the hologram recording apparatus 200 includes a laser light source 10, a two-dimensional beam expander 20A, a half mirror 30, a two-dimensional diffraction control element 40A, a pinhole element 50A, a two-dimensional light receiving element 60A, and a convex lens. The hologram recording medium M is composed of a convex lens 71A and convex lenses 81-85.
Basically, a two-dimensional diffraction control element 40A is used instead of the one-dimensional diffraction control element 40 of the hologram recording device 100. The two-dimensional diffraction control element 40A has the individual diffraction control elements 41 described above arranged in two directions (in a plane). As a result, the amount of information that can be recorded at one time increases, and the recording speed per bit on the hologram recording medium M can be further improved as described above.
[0055]
With the use of the two-dimensional diffraction control element 40A, the two-dimensional beam expander 20A combining the ordinary concave lens 21A and the convex lens 22A in place of the one-dimensional beam expander 20 is replaced with the slit element 50. The pinhole element 50A is provided with a convex lens 71A instead of the cylindrical lens 71. A substantially circular slit 51A (a minute opening) is formed in the pinhole element 50A. Further, a two-dimensional light receiving element 60 </ b> A is arranged instead of the one-dimensional light receiving element 60.
[0056]
The change to the two-dimensional beam expander 20A and the convex lens 71A is performed so that the laser is irradiated to all the pixels of the two-dimensional light receiving element 60A. The change to the pinhole element 50A corresponds to the fact that the diffraction direction of the diffracted light from the two-dimensional diffraction control element 40A becomes two-dimensional. The two-dimensional light receiving element 60A corresponds to the two-dimensional diffraction control element 40A.
The basic operation of the hologram recording device 200 is not essentially different from that of the hologram recording device 100, and thus the description is omitted.
[0057]
(Other embodiments)
The embodiment of the present invention is not limited to the above embodiment, and can be extended and changed, and the expanded and changed embodiment is also included in the technical scope of the present invention.
For example, a general diffraction grating capable of controlling the diffraction state can be used instead of the one-dimensional diffraction control element or the two-dimensional diffraction control element. The number of ribbons included in each of the individual diffraction control elements 41 is not limited to six, but may be larger or smaller. At this time, the light diffracted by the individual diffraction control element 41 coincides with the light diffracted by the ribbon 42 not every sixth even if the individual diffraction control elements 41 are turned on every other one.
As the diffraction grating, various types of diffraction gratings other than the phase difference method for giving a phase difference to each of the diffracted lights diffracted from the ribbon can be used.
Further, as described above, since each ribbon constituting the diffraction control element is considered as a phase variable element (phase modulation element), a diffraction grating can be configured by combining the phase variable elements. That is, a hologram recording apparatus can be configured using a general one-dimensional or two-dimensional phase modulation element instead of the one-dimensional diffraction control element or the two-dimensional diffraction control element.
[0058]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a hologram recording device, a hologram recording method, and a hologram recording medium that can reduce noise components generated from a phase modulation type spatial light modulator and improve data reliability.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a hologram recording device according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a state in which the hologram recording device is viewed from the X-axis direction in FIG.
FIG. 3 is a top view illustrating the one-dimensional diffraction control element illustrated in FIG. 1 as viewed from above.
FIG. 4 is a top view illustrating a state of the one-dimensional diffraction control element illustrated in FIG. 1 when viewed from a side.
FIG. 5 is a front view showing the one-dimensional diffraction control element shown in FIG. 1 as viewed from the front.
FIG. 6 is a schematic diagram illustrating a state where first-order diffracted light from a one-dimensional diffraction control element is blocked by a slit element.
FIG. 7 is a schematic diagram illustrating a state in which diffracted light from the one-dimensional diffraction control element is viewed from a side surface of the one-dimensional diffraction control element.
FIG. 8 is a schematic diagram illustrating a state in which diffracted light from the one-dimensional diffraction control element is viewed from the front of the one-dimensional diffraction control element.
FIG. 9 is a graph showing an example of a light intensity distribution of diffracted light from a one-dimensional diffraction control element when the light does not pass through a slit element.
FIG. 10 is a schematic diagram illustrating a correspondence relationship between a slit element and a diffracted light when diffracted light from a ribbon of first order or higher in absolute value is shielded.
FIG. 11 is a schematic diagram illustrating a correspondence relationship between a slit element and a diffracted light when diffracted light from an individual diffraction control element having a third order or higher in absolute value is shielded.
12 is a graph showing an example of a light intensity distribution of diffracted light from a one-dimensional diffraction control element when the light passes through the slit element shown in FIG.
FIG. 13 is a graph illustrating an example of a light intensity distribution of diffracted light from a one-dimensional diffraction control element when the light is not passed through a slit element.
14 is a graph showing an example of the light intensity distribution of the diffracted light from the one-dimensional diffraction control element when the light passes through the slit element shown in FIG.
FIG. 15 is a graph showing an example of a light intensity distribution of diffracted light from a one-dimensional diffraction control element when the light passes through a slit element having a smaller slit width than the slit element shown in FIG.
FIG. 16 is a schematic diagram showing a state in which data is reproduced from a hologram recording medium using a hologram recording device.
FIG. 17 is a schematic diagram illustrating a hologram recording device according to a second embodiment of the present invention.
[Explanation of symbols]
100 Hologram recording device
10 Laser light source
20 One-dimensional beam expander
21 Plano-concave lens
22 Cylindrical lens
30 half mirror
40 One-dimensional diffraction control element
41 Individual diffraction control element
42 Ribbon
43 insulating film
44 Counter electrode
45 substrate
50 slit element
51 slit
60 One-dimensional light receiving element
71 cylindrical lens
81-85 convex lens
M hologram recording medium

Claims (18)

A laser light source for emitting laser light,
A diffraction control element that receives laser light emitted from the laser light source, controls diffraction of the incident laser light, and emits the laser light.
A diffracted light component blocking element that blocks a predetermined diffracted light component from the diffracted light emitted from the diffraction control element,
A condensing element that condenses a diffracted light component that is not blocked by the diffracted light component blocking element on a hologram recording medium,
A hologram recording device comprising: 2. The hologram recording apparatus according to claim 1, wherein the diffraction control element includes a plurality of individual diffraction control elements for controlling diffraction of the incident laser light independently of each other. 3. The hologram recording apparatus according to claim 2, wherein the diffracted light component blocking element blocks the third or higher order diffracted light in absolute value by the individual diffraction control element. 3. The hologram recording apparatus according to claim 2, wherein the individual diffraction control elements have first and second phase control elements for controlling a phase difference between light emitted from the individual diffraction control elements. The hologram recording apparatus according to claim 4, wherein the light emitted from each of the first and second phase control elements is a diffracted light diffracted by the first and second phase control elements. 6. The hologram recording apparatus according to claim 5, wherein the diffracted light component blocking element blocks first-order or higher-order diffracted light in absolute value by each of the first and second phase control elements. 6. The hologram recording apparatus according to claim 5, wherein each of the first and second phase control elements has a substantially ribbon shape. 8. The hologram recording apparatus according to claim 7, wherein at least one of the first and second phase control elements is displaced by electrostatic force. 2. The hologram recording device according to claim 1, wherein the light-collecting element includes a plurality of lenses. A light splitting element that splits laser light emitted from the laser light source into first and second lights, and causes the first light to enter the diffraction control element;
A second light-collecting element that focuses the second light emitted from the light splitting element on a portion of the hologram recording medium where the laser light emitted from the light-collecting element is collected,
The hologram recording device according to claim 1, further comprising: A light shielding element for shielding the first light emitted from the light splitting element;
A light-receiving element that receives light emitted from the hologram recording medium based on the laser light converged on the hologram recording medium by the second light-collecting element;
The hologram recording apparatus according to claim 10, further comprising: By a diffraction control element, a diffraction control step of controlling and emitting the diffraction of the laser beam,
A diffracted light component blocking step of blocking a predetermined diffracted light component from the diffracted light emitted in the diffraction control step,
A focusing step of focusing a diffracted light component that is not blocked in the diffracted light component blocking step on a hologram recording medium,
A hologram recording method, comprising: 13. The hologram recording method according to claim 12, wherein the diffraction control element has a plurality of individual diffraction control elements for controlling diffraction of the incident laser light independently of each other. 14. The hologram recording method according to claim 13, wherein the diffracted light component blocking element blocks third or higher order diffracted light in absolute value by the individual diffraction control element. 14. The hologram recording method according to claim 13, wherein the individual diffraction control elements have first and second phase control elements for controlling a phase difference between light emitted from the individual diffraction control elements. The hologram recording method according to claim 15, wherein the light emitted from each of the first and second phase control elements is a diffracted light diffracted by the first and second phase control elements. 17. The hologram recording apparatus according to claim 16, wherein the diffracted light component blocking element blocks first-order or higher-order diffracted light in absolute value by each of the first and second phase control elements. A hologram recording medium, wherein data is recorded by using a diffracted light obtained by blocking a predetermined diffracted light component in a diffracted light emitted from a diffraction control element that controls the diffraction of a laser beam to emit the laser light.

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