JP2004139021A - Hologram recording apparatus and hologram recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording apparatus which records data on a hologram recording medium without using liquid crystal elements. <P>SOLUTION: The hologram recording apparatus includes a diffraction control element which receives a laser beam emitted from a laser beam source and controls the diffraction of the received laser beam before letting it exit, and a beam condensing element which condenses the diffracted light emitted from the diffraction control element onto the hologram recording medium. The information corresponding to the diffraction condition in the diffraction control element can be recorded on the hologram recording medium by condensing the light controlled in the diffraction condition by the diffraction control element onto the hologram recording medium. <P>COPYRIGHT: (C)2004,JPO

Description

ｓｉｎ（ωｔ＋２πｓ／λ）は入射光に対する位相の変化を表しており、光量変化には関係しない。光量変化はｃｏｓ（２πｓ／λ）に依存しており、リボンがｓだけ降下すると振幅はｃｏｓ（２πｓ／λ）倍に減少する。
【００５５】
光量は振幅の２乗だから、０次回折光の反射率Ｄ（ｓ）は次の式（４）のように表される。

式（４）をグラフとして表したものが図１１である。リボン４２の変位ｓ
が０のとき反射率Ｄ（０）は１で、変位ｓがλ／４のとき反射率Ｄ（λ／４）は０となる。
【００５６】
リボン４２の降下量ｓは印加電圧Ｖに比例し、ｓ＝λ／４のときに０次回折光量は０となる。このため、降下量ｓ＝０〜λ／４を８ビットのディジタル電圧Ｖｄ＝０〜２５５と対応させると、ディジタル電圧Ｖｄは式（５）のように表される。
Ｖｄ＝２５５・（４／λ）・ｓ　　　　　　　　　　　　　　　　…式（５）
【００５７】
以下、ホログラム記録装置３００の制御部９０の動作を説明する。制御部９０は次のように動作する。
Ａ．データ記憶部９１から記憶すべきデータが出力される。
【００５８】
Ｂ．制御量調節部９２により次のような処理が行われる。
（１）データ記憶部９１から出力されたデータを回折制御素子４０を構成する個別回折制御素子４１の個数（画素数、例えば１０８８個）ごとに区切る。
（２）各データが回折制御素子４０のどの個別回折制御素子４１で表示されるかを求める。
（３）個別回折制御素子４１の位置に対応する０次反射光量の補正値を式（２）により算出する。
（４）０次反射光量の補正値に対応するリボン４２の変位量を式（４）により算出する。
（５）その個別回折制御素子４１に印加する電圧（ディジタル値）を式（５）により算出する。
【００５９】
ここで、それぞれの個別回折制御素子４１に対応するデータが”０”、”１”のいずれであるか（「明」状態か、「暗」状態か）に応じて、（３）〜（５）の処理を行うか否かを決めることができる。
即ち、個別回折制御素子４１が「明」状態のときには（３）〜（５）に従いディジタル電圧を補正する。これに対して、個別回折制御素子４１が「暗」状態のときにはディジタル電圧を補正せず一律に所定の値（例えば、ディジタル電圧が８ビットのとき２５５）とする。個別回折制御素子４１が「暗」状態のときには、レーザ光の強度分布がホログラム記録媒体Ｍへの入射光の強度に与える影響が小さいためである。このようにして、制御量調節部９２による計算量を低減することができる。
【００６０】
Ｃ．制御量調節部９２により算出されたディジタル電圧に基づき、回折制御素子制御部９３により回折制御素子４０が駆動される。その結果、信号光が変調され、ホログラム記録媒体Ｍへのデータの記録が行われる。
なお、光学系の動作は第１の実施形態と同様であるので説明を省略する。
【００６１】
図１２は、個別回折制御素子４１が補正制御されたときのリボン４２の変位状態の一例を表す模式図である。Ｙａ、Ｙｂ、Ｙｃが図１０に示した個別回折制御素子４１の位置に対応し、０，１がデータの”０”、”１”に対応する。即ち、（Ｙａ：０）はＹａの位置の個別回折制御素子４１がデータ”０”を表示した場合に対応する。
回折制御素子４０の端から中央に向かうにつれ（Ｙａ→Ｙｂ→Ｙｃ）、データ”０”の表示状態（「明」状態）が本来のリボン４２の変位がない状態（ディジタル電圧：０）から変位がある状態に移り変わることが判る。この結果、回折制御素子４０の端の光強度に対応するように回折制御素子４０から出射される０次回折光の強度分布が均一化される。なお、データ”１”の表示状態は「暗」状態なので、ここではリボン４２の変位量の調節を行わず、一律にディジタル電圧２５５で表される状態としている。
【００６２】
（第３の実施形態の変形例１）
第３の実施形態における制御量調節部９２の動作では、制御量調節部９２により個別回折制御素子４１毎の制御量を毎回算出している。これは、ホログラム記録媒体Ｍへの多重記録を行う場合に角度や位置によって補正量が異なる場合に有用である。
これに対して、補正量の算出を毎回行わないようにすることも可能である。
図１３は制御部９０の変形例たる制御部９０Ａを表すブロック図であり、補正量を記憶しておくことで、その算出を不要としている。これは補正量が決まっている場合に有用である。例えば、ホログラム記録媒体Ｍへの多重記録を行う場合に角度を変えても補正量を変える必要がない場合に用いることができる。
【００６３】
制御部９０Ａは、データ記憶部９１，補正量記憶部９２Ａ，回折制御素子駆動部９３Ａを有する。
補正量記憶部９２Ａは、各個別回折制御素子４１に対応する補正量を記憶する。この補正量は，制御量調節部９２の動作で説明した手法を用い予め算出しておけばよい。
回折制御素子駆動部９３Ａは、補正量記憶部９２Ａに記憶された各個別回折制御素子４１毎の補正量と、データ記憶部９１から出力されたデータの両者に基づき回折制御素子４０を駆動する。この結果、回折制御素子４０から出射される０次回折光の強度分布が均一化される。
【００６４】
なお、補正量記憶部９２Ａに記憶される補正量の組み合わせは単一である必要はない。例えば、１００　回の角度多重でホログラム記録媒体Ｍに記録を行う場合に角度ごとに最適補正量が異なるときにはその１００　種類のパターンを記憶してもよい。
なお、ホログラム記録媒体Ｍへの記録位置を変えても角度に関する１００　種類の補正量がそのまま使える場合には、角度に関する１００　種類のパターンを補正量記憶部９２Ａに記憶しておけば良く、記録位置に対応する補正量を記憶する必要はない。
【００６５】
（第３の実施形態の変形例２）
第３の実施形態では光量分布の補正値を計算する際にガウス関数を使用したが、他の関数を用いることもできる。光学系によっては光量分布がガウス分布からずれることもありえる。それぞれの光学系の光量分布に合わせた補正を行うことができる。他の関数の例として、中心が強く端が弱い類似の関数、たとえば２次関数を挙げることができる。
【００６６】
（第３の実施形態の変形例３）
第３の実施形態は、信号光の制御に一次元型回折制御素子４０を用いているが、これに換えて第２の実施形態で示した二次元型回折制御素子４０Ａを用いることも可能である。
その場合には二次元型回折制御素子４０Ａを構成する個別回折制御素子４１は２つの座標で表すことができる。この座標を（ｙ，　ｕ）とすると式（２）は次の式（１２）で表すことができる。
Ｃ（ｙ，ｕ）＝｛ｅｘｐ［−２・（ｙｍａｘ／σ）^２］・　ｅｘｐ［−２・（ｕｍａｘ／σ）^２］｝／｛ｅｘｐ［−２・（ｙ／σ）^２］　＊　ｅｘｐ［−２・（ｕ／σ）^２］｝　　　　…式（１２）
ここでは、ｕの最大値（二次元型回折制御素子４０Ａのｕ方向の端）をｕｍａｘとしている。
なお、式（３）〜（５）は二次元型回折制御素子４０Ａを用いた場合でもそのまま用いることができる。
この変形例３の光学系は図８に示した第２の実施形態と同様であり、二次元型回折制御素子４０Ａの制御は式（２）に換えて式（１２）を用いることが異なるのみである。他の点では第２、第３の実施形態と本質的に変わるわけではないので詳細な説明を省略する。
【００６７】
（第３の実施形態の変形例４）
第３の実施形態での光量均一化の考え方は、一次元型回折制御素子４０に換えて液晶等の光変調素子として用いる場合にも適用できる。液晶の場合も画素に印加する電圧により透過光量または反射光量を調整できるからである。
図１４は、第３の実施形態の変形例４に係るホログラム記録装置４００を表す模式図である。
本図に示すようにホログラム記録装置４００は、レーザ光源１０、二次元型ビームエキスパンダ４２０，ハーフミラー３０，空間変調素子４４０，ミラー４５０，二次元型受光素子４６０、凸レンズ８３〜８５、制御部４９０から構成され、ホログラム記録媒体Ｍへの情報の記録および再生を行う。
【００６８】
二次元型ビームエキスパンダ４２０は、凹レンズ４２１と凸レンズ４２２を組み合わせて構成され、入射したレーザ光のビーム径を二次元方向に拡大する光学素子である。
空間変調素子４４０は、縦横２次元方向に画素を有し、入射したレーザ光を２次元的に変調する光学素子であり、例えば、液晶表示素子を用いることができる。
ミラー４５０は空間変調素子４４０を通過したレーザ光を反射しその方向を変える光学素子である。
【００６９】
制御部４９０は、データ記憶部９１，制御量調節部４９２，空間変調器駆動部４９３から構成される。
データ記憶部９１はホログラム記録媒体Ｍに記録するデータを記憶する記憶部である。
制御量調節部４９２は、それぞれの個別回折制御素子４１の位置に応じて空間変調素子４４０の画素の制御量を調節する。この結果、ホログラム記録媒体Ｍに到達する信号光の光量の均一性の向上が図られる。
空間変調素子駆動部４９３は制御量調節部４９２で調節された制御量に基づき空間変調素子４４０を駆動する。
制御量調節部４９２による画素の制御量の補正は既述の式（１２）を利用することができる。制御対象が二次元型回折制御素子４０Ａと空間変調素子４４０とで異なるものの、ホログラム記録媒体Ｍに到達する信号光の光量の均一性の向上を図らんとすることは変わらない。このため、制御対象の相違によるものを除き制御内容の本質は変形例３と同様となる。
【００７０】
ホログラム記録装置４００では、レーザ光源２０から出射されたレーザ光のビーム径が二次元型ビームエキスパンダ４２０で拡大されてハーフミラー３０で信号光と参照光に分離される。参照光は凸レンズ８４でホログラム記録媒体Ｍに集光される。信号光は空間変調素子４４０で変調されミラー４５０で反射され、凸レンズ８３でホログラム記録媒体Ｍに集光される。ホログラム記録媒体Ｍでの信号光の強度分布が均一化されるように制御部４９０による制御が行われる。
【００７１】
（第３の実施形態の特徴）
第３の実施形態には以下のような特徴がある。
（１）必要以上の強度の信号光をホログラム記録媒体Ｍに照射することが防止できる。このため、ホログラム記録媒体Ｍへの多重記録の際の他重度を理論値に近づけることができる。
【００７２】
（２）”明”状態の個別回折制御素子４１から出射される０次回折光がほぼ同一の強度となるので、再生時の”明”状態の明るさは受光素子６０の各画素の位置によらず同一となる。このため、受光素子６０の最適光量に再生光を設定できる。
本実施形態で示したような光量の調節を行わない場合には、再生光は受光素子６０の中心付近の”明”状態で明るく、端付近の”暗”状態では暗い。このため、例えば、受光素子６０の端付近で最適光量となる再生光を照射すると、受光素子６０の中心付近では光量過多（オーバーパワー）となる可能性がある。
【００７３】
（その他の実施形態）
本発明の実施形態は上記の実施形態に限られず拡張、変更可能であり、拡張、変更した実施形態も本発明の技術的範囲に含まれる。
例えば、一次元型回折制御素子あるいは二次元型回折制御素子に換えて、回折状態を制御可能な回折格子一般を用いることができる。個別回折制御素子４１がそれぞれ有するリボンは６つに限らずもっと多数、あるいはより少ない個数でも差し支えない。但し、このリボンの個数は偶数とし、一本おきに上下に駆動されることが望ましい。
回折格子として、リボンから回折される回折光それぞれに位相差を付与する位相差方式以外の種々の回折格子を用いることができる。
また、既述のように、回折制御素子を構成するリボンそれぞれを位相可変素子（位相変調素子）と考えられることから、位相可変素子を組み合わせて回折格子を構成することができる。即ち、一次元型回折制御素子あるいは二次元型回折制御素子に換えて、一次元あるいは二次元の位相変調素子一般を用いてホログラム記録装置を構成できる。
【００７４】
【発明の効果】
以上説明したように、本発明によれば液晶素子を用いることなく、ホログラム記録媒体へのデータの記録を行うホログラム記録装置およびホログラム記録方法を提供できる。
【図面の簡単な説明】
【図１】本発明の第１の実施形態に係るホログラム記録装置を表す模式図である。
【図２】図１のＸ軸方向からホログラム記録装置を見た状態を表す模式図である。
【図３】図１に示す一次元型回折制御素子を上面から見た状態を表す上面図である。
【図４】図１に示す一次元型回折制御素子を側面から見た状態を表す上面図である。
【図５】図１に示す一次元型回折制御素子を正面から見た状態を表す正面図である。
【図６】一次元型回折制御素子からの１次回折光がスリット素子により遮断されている状態を表した模式図である。
【図７】ホログラム記録装置を用いてホログラム記録媒体からのデータの再生を行っている状態を表す模式図である。
【図８】本発明の第２の実施形態に係るホログラム記録装置を表す模式図である。
【図９】本発明の第３の実施形態に係るホログラム記録装置を表す模式図である。
【図１０】個別回折制御素子に入射するレーザ光の強度分布を個別回折制御素子の位置と対応して表したグラフである。
【図１１】リボンの変位と個別回折制御素子からの０次回折光の反射率の関係を表すグラフである。
【図１２】個別回折制御素子が補正制御されたときのリボンの変位状態の一例を表す模式図である。
【図１３】第３の実施形態の変形例１に係る制御部を表すブロック図である。
【図１４】第３の実施形態の変形例４に係るホログラム記録装置を表す模式図である。
【図１５】従来のホログラム記録装置を表す模式図である。
【図１６】ホログラム記録媒体からデータを再生している状態を表す模式図である。
【符号の説明】
１００　ホログラム記録装置
１０　レーザ光源
２０　一次元型ビームエキスパンダ
２１　平凹レンズ
２２　シリンドリカルレンズ
３０　ハーフミラー
４０　一次元型回折制御素子
４１　個別回折制御素子
４２　リボン
４３　絶縁膜
４４　対向電極
４５　基板
５０　スリット素子
５１　スリット
６０　一次元型受光素子
７１　シリンドリカルレンズ
８１〜８５　凸レンズ
Ｍ　ホログラム記録媒体[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hologram recording device and a hologram recording method for recording data on a hologram recording medium.
[0002]
[Prior art]
A hologram recording device for recording data on a hologram recording medium has been developed.
FIG. 15 shows a conventional hologram recording device 500. The beam diameter of the laser light L emitted from the laser light source 110 is enlarged by the beam expander 120 and split by the half mirror 130 into the reference light L00 and the signal light L01. The signal light L01 is projected onto the hologram recording medium M after passing through the liquid crystal element 140 having a plurality of pixels while the reference light L00 remains as it is. Interference fringes formed by interference between the reference light L00 and the signal light L01 are recorded on the hologram recording medium M.
Here, desired data can be recorded on the hologram recording medium M by setting the transmission and shielding patterns of each pixel of the liquid crystal element 130.
When the hologram recording medium M on which data is recorded is irradiated only with the reference light L00, the reference light L00 is diffracted by interference fringes in the hologram recording medium M. As a result, diffracted light corresponding to the pattern displayed on the liquid crystal element is generated at the time of recording, and the recorded data can be reproduced by receiving the diffracted light by the image pickup device 180 such as a CCD (see FIG. 16). .
In addition, in a volume multiplexed hologram having unevenness in a page, a technique for removing a signal reading error due to unevenness is disclosed (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-9-197947
[0004]
[Problems to be solved by the invention]
However, the reaction speed of the liquid crystal element is not always fast, and it usually takes about several tens of milliseconds to switch the display. Therefore, it takes time to record data on the hologram recording medium.
In view of the above, an object of the present invention is to provide a hologram recording apparatus and a hologram recording method for recording data on a hologram recording medium without using a liquid crystal element.
[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. And a condensing element that condenses the diffracted light emitted from the diffraction control element onto 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, the hologram recording device may incorporate a hologram recording medium, or the hologram recording medium may be exchangeable. When the hologram recording medium is replaceable, it is preferable to have a stage for holding the hologram recording medium.
[0006]
(1) The hologram recording apparatus further includes a diffracted light component extraction element that is located between the diffraction control element and the light condensing element and that extracts a predetermined order diffracted light component from the diffracted light emitted from the diffraction control element. Is also good.
By extracting a diffracted light component of a predetermined order from the diffracted light by the diffracted light component extracting element, the intensity of the diffracted light can be changed, and the data can be recorded on the hologram recording medium as light intensity.
As an example of the diffracted light component extraction element, a combination of a convex lens and a slit can be considered. With this combination, it is possible to easily extract only the zero-order diffracted light by removing the first-order or higher-order diffracted light components.
[0007]
(2) The diffraction control element may include a plurality of individual diffraction control elements for controlling 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.
[0008]
1) 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.
[0009]
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.
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 plurality of individual diffraction control elements may control the diffraction of the laser beam according to the arrangement of each individual diffraction control element.
When the laser light incident on the diffraction control element has an intensity distribution, by controlling the diffraction of the laser light according to the arrangement of each individual diffraction control element, the intensity distribution of the diffracted light can be made uniform.
[0011]
Here, the hologram recording device, a calculation unit that calculates the control state of each individual diffraction control element, and a control unit that controls the plurality of individual diffraction control elements based on the calculation result in the calculation unit, It may be further provided.
The control state is calculated according to the state of the hologram recording device, and the plurality of individual diffraction control elements can be appropriately controlled.
[0012]
Further, the hologram recording device, a storage unit that stores a table representing each corresponding individual diffraction control element and control state, based on the table stored in the storage unit, the plurality of individual diffraction control elements, And a control unit for controlling.
A plurality of individual diffraction control elements can be controlled based on the table.
[0013]
The plurality of individual diffraction control elements may have first and second diffraction states, and the first diffraction state may be controlled according to the arrangement of each individual diffraction control element.
For example, when the individual diffraction control element is in the “dark” state, it is less affected by the intensity distribution of the laser beam than in the “bright” state, so that the calculation amount can be reduced.
[0014]
(3) 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.
[0015]
(4) a hologram recording device that divides the laser light emitted from the laser light source into first and second lights, and that splits the first light 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.
[0016]
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 formed of one-dimensional or two-dimensionally arranged individual diffraction control elements, it is preferable that the diffraction control element is formed of individual light-receiving elements arranged correspondingly.
[0017]
B. A hologram recording method according to the present invention includes a diffraction control step of controlling the diffraction of an incident laser beam by a diffraction control element to emit the laser beam, and a collecting step of condensing the diffracted light emitted in the diffraction control step onto a hologram recording medium. And a light step.
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.
[0018]
(1) The hologram recording method further includes a diffracted light component extraction step of extracting a diffracted light component of a predetermined order from the diffracted light emitted in the diffraction control step, between the diffraction control step and the focusing step. You may.
By extracting a diffracted light component of a predetermined order from the diffracted light, the intensity of the diffracted light is changed, and data can be recorded on the hologram recording medium as light intensity.
[0019]
(2) The diffraction control element may include a plurality of individual diffraction control elements for controlling 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.
[0020]
Here, in the diffraction control step, the plurality of individual diffraction control elements may control the diffraction of the laser beam according to the arrangement of each individual diffraction control element.
When the laser light incident on the diffraction control element has an intensity distribution, by controlling the diffraction of the laser light according to the arrangement of each individual diffraction control element, the intensity distribution of the diffracted light can be made uniform.
[0021]
1) The hologram recording method further includes a calculation step of calculating a control state of each individual diffraction control element, and the plurality of individual diffraction control elements in the diffraction control step based on a calculation result in the calculation step. May be performed.
A plurality of individual diffraction control elements can be controlled by appropriately calculating the control state.
[0022]
2) The plurality of individual diffraction control elements may be controlled in the diffraction control step on the basis of a table representing each individual diffraction control element and a control state in a corresponding manner.
A plurality of individual diffraction control elements can be controlled based on the table.
[0023]
3) The plurality of individual diffraction control elements may be in first and second diffraction states, and the first diffraction state may be controlled according to the arrangement of each individual diffraction control element.
For example, when the individual diffraction control element is in the “dark” state, it is less affected by the intensity distribution of the laser beam than in the “bright” state, so that the calculation amount can be reduced.
[0024]
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.
[0025]
(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 where the one-dimensional diffraction control element 40 is viewed from above. FIGS. 4 and 5 are a side view and a front view, respectively, showing a state where the one-dimensional diffraction control element 40 is 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.
[0026]
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.
[0027]
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. Since the intensity of the second-order or higher order diffracted light is small, it is ignored.
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 1st-order diffracted light remains (as described above, 2nd order). Components beyond the following are ignored).
[0028]
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.
[0029]
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 first-order diffracted light), whereby the number of pixels can be 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.
[0030]
The operation of the one-dimensional diffraction control element 40 (individual diffraction control element 41) when the laser light is directly incident has been described above. The principle of this operation is that the laser light is obliquely incident on the one-dimensional diffraction control element 40. The case is basically the same. However, since the difference in optical path length is shorter in oblique incidence than in direct incidence, only the first-order diffracted light is emitted when the interval d is approximately (λ / 4) / cos θ (θ is a one-dimensional diffraction control element). Incident angle of laser light with respect to 40).
[0031]
(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 expands a beam diameter of incident light in a 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 elements 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.
[0032]
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.
The slit element 50 is disposed near the focal point of the convex lens 81 and removes the first-order or higher-order diffracted light component of the diffracted light emitted from the one-dimensional diffraction control element 40 (in other words, extracts the zero-order diffracted light component). ). The slit element 50 has a slit 51 (opening) formed in the Y direction. The slits 51 extending along the Y direction correspond to the arrangement direction of the individual diffraction control elements 41. 6, the first-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, as shown in FIG. Shielded by element 50. This is because the first-order diffracted light L1 is emitted at an angle ± θ with respect to the 0th-order diffracted light L1 (the sign of the angle θ corresponds to the sign of the first-order diffracted light (+1 or −1).
[0033]
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 and 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 by using either the diffraction spectrum itself from the one-dimensional diffraction control element 40 or its real image.
[0034]
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).
[0035]
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. 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 the polymer is formed, the refractive index of the portion changes.
As described above, by changing the refractive index of the hologram recording medium M according to the amount of exposure, 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.
[0036]
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 83, 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.
However, 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.
[0037]
(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 has its beam diameter expanded in the Y direction by the one-dimensional beam expander 20, and is then divided into two lights (reference light and signal light) by the half mirror 30.
The reference light passes through the convex lens 84 and is collected on the hologram recording medium M.
[0038]
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: only the 0th-order diffracted light, ON: only the first-order diffracted light), so that the individual diffraction control elements 40 as a whole can individually diffract. Data of the number of bits corresponding to the number of the control elements 41 (for example, 1088 bits when the number of the individual diffraction control elements 41 is 1088) can be expressed.
[0039]
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 two intensities (bright and dark) corresponding to the two diffraction states (OFF and ON) are obtained. Take. That is, ON and OFF of the individual diffraction control element 41 can be made to correspond to bits 1 and 0.
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.
[0040]
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, by exposing the hologram recording medium M once using the one-dimensional diffraction control element 40, 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. . That is, assuming that the number of the individual diffraction control elements 41 is ON and OFF and the number of times of exposure is m, the hologram recording medium M can record nm data.
[0041]
In the above, by the convex lens 81 and the slit element 50, the diffracted light diffracted by the one-dimensional diffraction control element 40 is converted into light (dark or bright). This corresponds to the fact that the light receiving element (for example, a CCD) constituting the one-dimensional light receiving element 60 can detect the intensity of light but does not have the ability to detect the phase of light.
What is incident on the one-dimensional light receiving element 60 at the time of reproduction of recording to be described later is light corresponding to signal light incident on the hologram recording medium M at the time of recording. By passing the signal light through the convex lens 81 and the slit element 50, the light is converted into light and dark and recorded on the hologram recording medium M to correspond to the characteristics of the one-dimensional light receiving element 60.
However, the convex lens 81 and the slit element 50 can be dispensed with by using a light receiving element constituting the one-dimensional light receiving element 60 capable of detecting a phase difference.
[0042]
When data is recorded using the one-dimensional diffraction control element 40, the time required for data recording is calculated.
As described above, the reaction time of the individual diffraction control element 41 is, for example, 1 μsec. Assuming that the number of pixels (the number of individual diffraction control elements 41) is about 1000, one pixel (individual diffraction control element 41) represents one bit of light and dark, and one bit is 1 nsec (= 1 μsec / 1000).
On the other hand, in a liquid crystal element, when the reaction time is generally several tens of milliseconds, even if the number of pixels is 1000 * 1000, several tens of nsec (= several 10 ms / (1000 × 1000)).
As described above, the one-dimensional diffraction control element 40 is one digit faster than the liquid crystal element as the two-dimensional intensity modulation element.
As described above, by using the one-dimensional diffraction control element 40, the recording speed on the hologram recording medium M can be improved.
By using a two-dimensional diffraction control element 40A, which will be described later, instead of the one-dimensional diffraction control element 40, the recording time per bit is 1 psec (= 1 μsec / (1000 * 1000), Four orders of magnitude faster than liquid crystal elements.
[0043]
B. Reproduction of data from hologram recording medium M
FIG. 7 is a schematic diagram illustrating a state in which data is reproduced from the hologram recording medium M using the hologram recording device 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 85 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.
[0044]
(Second embodiment)
FIG. 8 is a schematic diagram illustrating a hologram recording device 200 according to the second embodiment of the present invention.
As shown in FIG. 8, 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.
[0045]
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 pinhole 51A (a minute opening) is formed in the pinhole element 50A. In addition, a two-dimensional light receiving element 60A is provided instead of the one-dimensional light receiving element 60.
[0046]
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.
[0047]
(Third embodiment)
In the first and second embodiments, if each of the individual diffraction control elements 41 constituting the one-dimensional diffraction control element 40 or the two-dimensional diffraction control element 40A is controlled to two states in which binary values can be identified. It is enough. For example, a state where the amount of signal reaching the hologram recording medium M is large (hereinafter, the state of the individual diffraction control element 41 at this time is referred to as a “bright” state) and a state where it is small (hereinafter, the state of the individual diffraction control element 41 at this time) Are referred to as “dark” state) by the individual diffraction control element 41.
Incidentally, the amount of laser light incident on the one-dimensional diffraction control element 40 or the two-dimensional diffraction control element 40A often has a certain distribution. The laser light beam has, for example, a Gaussian distribution in which the light amount is large near the center of the beam and small at the end of the beam. In this case, a distribution also occurs in the amount of laser light reaching the hologram recording medium M, and it is desirable to make the amount of light reached uniform.
[0048]
There is a greater need to equalize the amount of light reaching when the individual diffraction control element 41 is in the “bright” state than in the “dark” state. In the individual diffraction control element 41 in the "dark" state, the distribution of the light amount of the laser beam does not matter much because the amount of light reaching the hologram recording medium M itself is small. However, in the individual diffraction control element 41 in the “bright” state, the amount of light reaching the hologram recording medium M reflects the distribution of the amount of laser light. The amount of light reaching the hologram recording medium M is large at a position corresponding to the vicinity of the center of the diffraction control element 40 and is small at an end of the diffraction control element 40. For this reason, when the light amount required for recording on the hologram recording medium M is emitted near the end of the diffraction control element 40, an excessively large light amount is emitted near the center of the diffraction control element 40.
[0049]
The recording density of the hologram recording medium M can be increased by multiplex recording at the same location. However, the portion recorded with the irradiation amount more than necessary consumes the recording material of the hologram recording medium M, and the number of times of multiplex recording can be reduced, and the recording density is reduced.
In order to prevent this, in the present embodiment, the amount of movement of the ribbon 42 of the individual diffraction control element 41 is changed in accordance with the position, thereby adjusting the light amount ratio of the 0th-order diffracted light and ± 1st-order diffracted light.
[0050]
FIG. 9 is a schematic diagram illustrating a hologram recording device 300 according to the third embodiment of the present invention. As shown in the figure, the hologram recording apparatus 300 controls the one-dimensional diffraction control element 40 by a control section 90 having a data storage section 91, a control amount adjustment section 92, and a diffraction control element driving section 93. Note that the optical elements are the same as in the first embodiment, and a description thereof will be omitted.
The data storage unit 91 is a storage unit that stores data to be recorded on the hologram recording medium M.
The control amount adjusting section 92 adjusts the control amount of the individual diffraction control element 41 according to the position of each individual diffraction control element 41. As a result, the uniformity of the light amount of the signal light reaching the hologram recording medium M is improved.
The diffraction control element driving section 93 drives the one-dimensional diffraction control element 40 based on the control amount adjusted by the control amount adjusting section 92.
[0051]
Hereinafter, details of adjustment of the control amount of the individual diffraction control element 41 by the control amount adjusting unit 92 will be described. This adjustment is based on the following formula, and digital value data “0” (corresponding to “bright” state) and “1” (corresponding to “dark” state) sent to the individual diffraction control element 41 are multi-valued (for example, The conversion is performed by converting into an 8-bit (256 value) digital voltage.
Here, for the sake of simplicity, a description will be given assuming that the laser beam is incident on the individual diffraction control element 41 almost perpendicularly. When the incidence of the laser beam on the individual diffraction control element 41 is not vertical, it is necessary to adjust the descending amount of the ribbon 42 as compared with the case where the incidence is vertical, but the basic idea is the same. Specifically, assuming that the incident angle of the laser beam on the individual diffraction control element 41 is α, in Expressions (2) and (3) described below, λ may be replaced with λ / COS (α).
[0052]
FIG. 10 is a graph showing the intensity distribution I (y) of the laser beam incident on the individual diffraction control element 41 corresponding to the position y of the individual diffraction control element 41 on the one-dimensional diffraction control element 40. Here, FIG. 10A shows the arrangement of the individual diffraction control elements 41, and FIG. 10B shows the intensity distribution I (y) of the laser beam.
Assuming that the center of the Y-axis in the length direction of the one-dimensional diffraction control element 40 is 0, the light intensity I (y) can be expressed by the following Gaussian function.
I (y) = I ₀ Exp [-2 · (y / σ) ² ] Equation (1)
Where I ₀ : Light intensity I (0) at y = 0, σ: standard deviation.
The light intensity I (σ) when y = σ is the light intensity I when the center y = 0. ₀ 1 / e ² To decline. Note that the value of the standard deviation σ differs depending on the optical system.
[0053]
Both ends of the one-dimensional diffraction control element 40 are set to y = ± ymax. In order to adjust the light quantity at an arbitrary y to the light quantity at both ends, C (y) expressed by the following equation (2) may be added. Equation (2) is the ratio of the values of y = ymax and y = y in equation (1).
C (y) = exp [-2 · (ymax / σ) ² ] / Exp [-2 · (y / σ) ² ] Equation (2)
[0054]
Next, the relationship between the displacement s of the ribbon 42 and the reflectance D (s) of the 0th-order diffracted light from the individual diffraction control element 41 will be described.
As described above, three of the six ribbons 42 of the individual diffraction control element 41 are fixed, and the remaining three drop down according to the applied electric field. The amplitude of the zero-order diffracted light emitted from the fixed ribbon 42 is defined as sin (ωt). Then, the amplitude of the 0th-order diffracted light emitted from the ribbon 42 lowered by s can be expressed as sin (ωt + 4πs / λ). The amplitude f (s) of the 0th-order diffracted light as the entire individual diffraction control element 41 (one pixel) is the sum of these, and can be expressed as in the following equation (3).

sin (ωt + 2πs / λ) indicates a change in the phase with respect to the incident light, and is not related to the change in the light amount. The light quantity change depends on cos (2πs / λ), and when the ribbon drops by s, the amplitude decreases by cos (2πs / λ).
[0055]
Since the amount of light is the square of the amplitude, the reflectance D (s) of the 0th-order diffracted light is represented by the following equation (4).

FIG. 11 shows Expression (4) as a graph. Displacement s of ribbon 42
Is 0, the reflectance D (0) is 1, and when the displacement s is λ / 4, the reflectance D (λ / 4) is 0.
[0056]
The amount of drop s of the ribbon 42 is proportional to the applied voltage V. When s = λ / 4, the zero-order diffracted light amount becomes zero. For this reason, when the amount of drop s = 0 to λ / 4 is made to correspond to the 8-bit digital voltage Vd = 0 to 255, the digital voltage Vd is expressed as in equation (5).
Vd = 255 · (4 / λ) · s Equation (5)
[0057]
Hereinafter, the operation of the control unit 90 of the hologram recording device 300 will be described. The control unit 90 operates as follows.
A. Data to be stored is output from the data storage unit 91.
[0058]
B. The following processing is performed by the control amount adjusting unit 92.
(1) The data output from the data storage unit 91 is divided for each number (the number of pixels, for example, 1088) of the individual diffraction control elements 41 constituting the diffraction control element 40.
(2) Determine which individual diffraction control element 41 of the diffraction control element 40 displays each data.
(3) The correction value of the 0th-order reflected light amount corresponding to the position of the individual diffraction control element 41 is calculated by Expression (2).
(4) The displacement amount of the ribbon 42 corresponding to the correction value of the 0th-order reflected light amount is calculated by Expression (4).
(5) The voltage (digital value) applied to the individual diffraction control element 41 is calculated by equation (5).
[0059]
Here, depending on whether the data corresponding to each individual diffraction control element 41 is “0” or “1” (“bright” state or “dark” state), (3) to (5) ) Can be determined.
That is, when the individual diffraction control element 41 is in the "bright" state, the digital voltage is corrected according to (3) to (5). On the other hand, when the individual diffraction control element 41 is in the "dark" state, the digital voltage is not corrected and is uniformly set to a predetermined value (for example, 255 when the digital voltage is 8 bits). This is because when the individual diffraction control element 41 is in the “dark” state, the intensity distribution of the laser light has little effect on the intensity of the light incident on the hologram recording medium M. Thus, the amount of calculation by the control amount adjusting unit 92 can be reduced.
[0060]
C. The diffraction control element 40 is driven by the diffraction control element control section 93 based on the digital voltage calculated by the control amount adjustment section 92. As a result, the signal light is modulated, and data is recorded on the hologram recording medium M.
The operation of the optical system is the same as in the first embodiment, and a description thereof will not be repeated.
[0061]
FIG. 12 is a schematic diagram illustrating an example of a displacement state of the ribbon 42 when the individual diffraction control element 41 is subjected to correction control. Ya, Yb, and Yc correspond to the positions of the individual diffraction control element 41 shown in FIG. 10, and 0 and 1 correspond to data “0” and “1”. That is, (Ya: 0) corresponds to the case where the individual diffraction control element 41 at the position of Ya displays data “0”.
As the diffraction control element 40 moves from the end toward the center (Ya → Yb → Yc), the display state of the data “0” (the “bright” state) changes from the state where the original ribbon 42 is not displaced (digital voltage: 0). It turns out that there is a certain state. As a result, the intensity distribution of the zero-order diffracted light emitted from the diffraction control element 40 is made uniform so as to correspond to the light intensity at the end of the diffraction control element 40. Since the display state of the data “1” is “dark”, the displacement of the ribbon 42 is not adjusted here, and the state is uniformly represented by the digital voltage 255.
[0062]
(Modification 1 of Third Embodiment)
In the operation of the control amount adjusting section 92 in the third embodiment, the control amount for each individual diffraction control element 41 is calculated by the control amount adjusting section 92 every time. This is useful when performing multiplex recording on the hologram recording medium M and when the correction amount differs depending on the angle or position.
On the other hand, it is also possible not to calculate the correction amount every time.
FIG. 13 is a block diagram showing a control unit 90A which is a modification of the control unit 90. By storing the correction amount, the calculation is unnecessary. This is useful when the correction amount is fixed. For example, it can be used when it is not necessary to change the correction amount even if the angle is changed when performing multiplex recording on the hologram recording medium M.
[0063]
The control unit 90A includes a data storage unit 91, a correction amount storage unit 92A, and a diffraction control element driving unit 93A.
The correction amount storage unit 92A stores a correction amount corresponding to each individual diffraction control element 41. This correction amount may be calculated in advance using the method described in the operation of the control amount adjustment unit 92.
The diffraction control element driving unit 93A drives the diffraction control element 40 based on both the correction amount for each individual diffraction control element 41 stored in the correction amount storage unit 92A and the data output from the data storage unit 91. As a result, the intensity distribution of the zero-order diffracted light emitted from the diffraction control element 40 is made uniform.
[0064]
The combination of correction amounts stored in the correction amount storage unit 92A does not need to be a single combination. For example, when recording is performed on the hologram recording medium M by 100 times of angle multiplexing and the optimal correction amount differs for each angle, the 100 types of patterns may be stored.
If 100 kinds of correction amounts relating to the angle can be used as they are even when the recording position on the hologram recording medium M is changed, 100 patterns relating to the angle may be stored in the correction amount storage unit 92A. Does not need to be stored.
[0065]
(Modification 2 of Third Embodiment)
In the third embodiment, the Gaussian function is used when calculating the correction value of the light amount distribution, but another function may be used. Depending on the optical system, the light quantity distribution may deviate from the Gaussian distribution. Correction according to the light amount distribution of each optical system can be performed. Examples of other functions include similar functions with strong centers and weak edges, such as quadratic functions.
[0066]
(Modification 3 of Third Embodiment)
In the third embodiment, the one-dimensional diffraction control element 40 is used for controlling the signal light. However, the two-dimensional diffraction control element 40A shown in the second embodiment can be used instead. is there.
In that case, the individual diffraction control element 41 constituting the two-dimensional diffraction control element 40A can be represented by two coordinates. If these coordinates are (y, u), equation (2) can be expressed by the following equation (12).
C (y, u) = ｛exp [−2 · (ymax / σ) ² ] Exp [-2 · (ummax / σ) ² ]｝ / ｛Exp [-2 · (y / σ) ² ] * Exp [-2 · (u / σ) ² ]｝… Equation (12)
Here, the maximum value of u (the end in the u direction of the two-dimensional diffraction control element 40A) is umax.
Expressions (3) to (5) can be used as they are even when the two-dimensional diffraction control element 40A is used.
The optical system of Modification 3 is the same as that of the second embodiment shown in FIG. 8, and the control of the two-dimensional diffraction control element 40A is different from that of Expression (12) in that Expression (2) is used. It is. In other respects, it is not essentially different from the second and third embodiments, and a detailed description thereof will be omitted.
[0067]
(Modification 4 of Third Embodiment)
The concept of uniform light intensity in the third embodiment can be applied to a case where the light modulation element such as a liquid crystal is used instead of the one-dimensional diffraction control element 40. This is because in the case of liquid crystal, the amount of transmitted light or the amount of reflected light can be adjusted by the voltage applied to the pixel.
FIG. 14 is a schematic diagram illustrating a hologram recording device 400 according to Modification 4 of the third embodiment.
As shown in the figure, the hologram recording device 400 includes a laser light source 10, a two-dimensional beam expander 420, a half mirror 30, a spatial modulation element 440, a mirror 450, a two-dimensional light receiving element 460, convex lenses 83 to 85, and a control unit. 490 for recording and reproducing information on the hologram recording medium M.
[0068]
The two-dimensional beam expander 420 is an optical element configured by combining a concave lens 421 and a convex lens 422 and expanding the beam diameter of incident laser light in a two-dimensional direction.
The spatial modulation element 440 is an optical element having pixels in two dimensions in the vertical and horizontal directions and two-dimensionally modulating the incident laser light. For example, a liquid crystal display element can be used.
The mirror 450 is an optical element that reflects the laser light that has passed through the spatial modulation element 440 and changes its direction.
[0069]
The control unit 490 includes a data storage unit 91, a control amount adjustment unit 492, and a spatial modulator driving unit 493.
The data storage unit 91 is a storage unit that stores data to be recorded on the hologram recording medium M.
The control amount adjustment unit 492 adjusts the control amount of the pixel of the spatial modulation element 440 according to the position of each individual diffraction control element 41. As a result, the uniformity of the light amount of the signal light reaching the hologram recording medium M is improved.
The spatial modulation element driving section 493 drives the spatial modulation element 440 based on the control amount adjusted by the control amount adjusting section 492.
The correction of the pixel control amount by the control amount adjustment unit 492 can use the above-described equation (12). Although the control target is different between the two-dimensional diffraction control element 40A and the spatial modulation element 440, the improvement of the uniformity of the light quantity of the signal light reaching the hologram recording medium M remains unchanged. Therefore, the essence of the control contents is the same as that of the third modification except for the difference due to the difference in the control target.
[0070]
In the hologram recording device 400, the beam diameter of the laser light emitted from the laser light source 20 is enlarged by the two-dimensional beam expander 420, and separated by the half mirror 30 into signal light and reference light. The reference light is focused on the hologram recording medium M by the convex lens 84. The signal light is modulated by the spatial modulation element 440, reflected by the mirror 450, and focused on the hologram recording medium M by the convex lens 83. Control by the control unit 490 is performed so that the intensity distribution of the signal light on the hologram recording medium M is made uniform.
[0071]
(Features of the third embodiment)
The third embodiment has the following features.
(1) Irradiation of the hologram recording medium M with signal light having an intensity higher than necessary can be prevented. For this reason, the other weight at the time of multiplex recording on the hologram recording medium M can be made closer to the theoretical value.
[0072]
(2) Since the 0th-order diffracted light emitted from the individual diffraction control element 41 in the “bright” state has substantially the same intensity, the brightness in the “bright” state during reproduction depends on the position of each pixel of the light receiving element 60. The same. Therefore, the reproduction light can be set to the optimum light amount of the light receiving element 60.
When the light amount adjustment is not performed as shown in the present embodiment, the reproduction light is bright in the “bright” state near the center of the light receiving element 60 and dark in the “dark” state near the end. Therefore, for example, when the reproduction light having the optimum light amount is irradiated near the end of the light receiving element 60, the light amount may be excessive (over power) near the center of the light receiving element 60.
[0073]
(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, instead of a one-dimensional diffraction control element or a two-dimensional diffraction control element, a general diffraction grating capable of controlling a diffraction state can be used. 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. However, it is desirable that the number of the ribbons be an even number and that the ribbons be driven up and down every other ribbon.
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 by 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.
[0074]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a hologram recording apparatus and a hologram recording method for recording data on a hologram recording medium without using a liquid crystal element.
[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 a state in which the one-dimensional diffraction control element illustrated in FIG. 1 is 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 showing 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 data is reproduced from a hologram recording medium using a hologram recording device.
FIG. 8 is a schematic diagram illustrating a hologram recording device according to a second embodiment of the present invention.
FIG. 9 is a schematic diagram illustrating a hologram recording device according to a third embodiment of the present invention.
FIG. 10 is a graph showing an intensity distribution of a laser beam incident on an individual diffraction control element in correspondence with a position of the individual diffraction control element.
FIG. 11 is a graph showing the relationship between the displacement of the ribbon and the reflectance of the zero-order diffracted light from the individual diffraction control element.
FIG. 12 is a schematic diagram illustrating an example of a displacement state of a ribbon when an individual diffraction control element is subjected to correction control.
FIG. 13 is a block diagram illustrating a control unit according to a first modification of the third embodiment.
FIG. 14 is a schematic diagram illustrating a hologram recording device according to Modification 4 of the third embodiment.
FIG. 15 is a schematic diagram showing a conventional hologram recording device.
FIG. 16 is a schematic diagram illustrating a state where data is being reproduced from a hologram recording medium.
[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 (21)

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 light-collecting element that focuses the diffracted light emitted from the diffraction control element on a hologram recording medium,
A hologram recording device comprising: 2. The device according to claim 1, further comprising a diffracted light component extracting element between the diffractive control element and the light condensing element, for extracting a diffracted light component of a predetermined order from the diffracted light emitted from the diffraction control element. Hologram recording device. 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. 4. The hologram recording apparatus according to claim 3, 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 each of the first and second phase control elements has a substantially ribbon shape. 7. The hologram recording apparatus according to claim 6, wherein at least one of the first and second phase control elements is displaced by an electrostatic force. 4. The hologram recording apparatus according to claim 3, wherein the plurality of individual diffraction control elements control the diffraction of the laser beam according to the arrangement of each individual diffraction control element. The hologram recording device,
A calculating unit for calculating a control state of each individual diffraction control element,
A control unit that controls the plurality of individual diffraction control elements based on a calculation result in the calculation unit,
9. The hologram recording apparatus according to claim 8, further comprising: The hologram recording device,
A storage unit that stores a table that represents each individual diffraction control element and control state,
Based on the table stored in the storage unit, a control unit that controls the plurality of individual diffraction control elements,
9. The hologram recording apparatus according to claim 8, further comprising: 9. The hologram recording according to claim 8, wherein the plurality of individual diffraction control elements take first and second diffraction states, and control the first diffraction state according to the arrangement of each individual diffraction control element. apparatus. 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;
14. The hologram recording apparatus according to claim 13, further comprising: By a diffraction control element, a diffraction control step of controlling the diffraction of the incident laser light to emit the laser light,
A focusing step of focusing the diffracted light emitted in the diffraction control step on a hologram recording medium,
A hologram recording method, comprising: 16. The method according to claim 15, further comprising a step of extracting a diffracted light component of a predetermined order from the diffracted light emitted in the diffraction control step, between the diffraction control step and the focusing step. The hologram recording method according to the above. 16. The hologram recording method according to claim 15, 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. 18. The hologram recording method according to claim 17, wherein in the diffraction control step, the plurality of individual diffraction control elements control the diffraction of the laser beam according to the arrangement of each individual diffraction control element. The hologram recording method further includes a calculating step of calculating a control state of each individual diffraction control element,
Based on the calculation result in the calculation step, control of the plurality of individual diffraction control elements in the diffraction control step is performed.
The hologram recording method according to claim 18, wherein: Based on a table representing each of the individual diffraction control elements and the control state, control of the plurality of individual diffraction control elements in the diffraction control step is performed.
The hologram recording method according to claim 18, wherein: 19. The hologram recording according to claim 18, wherein the plurality of individual diffraction control elements take first and second diffraction states, and the first diffraction state is controlled according to the arrangement of each individual diffraction control element. Method.

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