JPWO2007026588A1 - Optical pickup device and hologram recording / reproducing system - Google Patents

Abstract

An optical pickup device for recording or reproducing information on a hologram record carrier, comprising a light source, a central region disposed on the optical axis, and an annular region disposed so as to surround the central region. And a spatial light modulator that spatially separates the passing component of the annular region and generates reference light and signal light and propagates them in the same direction on the same axis, and signal light and reference light arranged on the optical axis Is arranged on the optical axis, an objective lens for condensing the reference light and the signal light at different focal points, an image detecting means for receiving the light returning from the hologram recording layer, The center correction area and the annular surrounding area arranged so as to surround the center correction area, and at least one of the center correction area and the annular surrounding area partially changes the phase of the wavefront of the passing light flux. Including, an aberration correcting device comprising a transmissive liquid crystal device comprising a plurality of transparent electrodes to correct the difference.

Description

  The present invention relates to a record carrier on which information is recorded or reproduced optically, such as an optical disk and an optical card, and more particularly to an optical pickup device for a hologram record carrier having a hologram recording layer capable of recording or reproducing information by irradiation with a light beam. And a hologram recording / reproducing system.

Holograms that can record two-dimensional data at high density are attracting attention for high-density information recording. The feature of this hologram is that the wavefront of light carrying recorded information is recorded as a change in refractive index in volume on a recording medium made of a photosensitive material such as a photorefractive material. By performing multiplex recording on the hologram record carrier, the recording capacity can be dramatically increased. As a structure, a recording medium in which a substrate, an information recording layer, and a reflective layer are formed in this order is known.
For example, conventionally, in an information recording apparatus for recording a hologram by coaxially irradiating a short wavelength object light for writing and a reference light on a thin film recording layer to record a hologram, There is a technique for performing polarization hologram recording by condensing reference light on a recording medium with the same lens (see Japanese Patent Application Publication No. 2002-513981). In such polarization holography recording, two plane wave object beams and reference beams having polarizations orthogonal to each other are converted into right-handed circularly polarized light and left-handed circularly polarized light using a quarter-wave plate, and their interference in the recording medium. Thus, one polarization hologram is recorded. At the time of reproduction, reference light for reading having a longer wavelength than that at the time of recording is used, and reproduction is performed by a separate reproduction optical system. In the reproduction optical system, a special half-wave plate having a central aperture is provided, and reproduction light is obtained from the polarization hologram by irradiation of the central reference light. Since the reproduction light is broadened due to the long wavelength reference light, it passes through the half-wave plate part around the aperture, so the polarization direction is changed and separated by the polarization beam splitter, and the transmitted reproduction light is detected. The Therefore, in the technique of JP-T-2002-513981, it is necessary to switch between the writing and reading wavelength light sources and the optical system at the time of recording and reproduction, and the reflected light does not return from the recording medium at the time of recording. A separate optical system that performs positioning servo control with the medium is required. Further, in the technique disclosed in JP-T-2002-513981, since the reference light is parallel light in the recording medium, shift multiplex recording cannot be performed.
Further, conventionally, the information light is converged and irradiated so as to have the smallest diameter on the boundary surface between the hologram recording layer and the protective layer of the recording medium, and reflected by the reflective layer. At the same time, the recording reference light is reflected by the hologram recording layer and the protective layer. The light is converged so as to have the smallest diameter on the front side of the boundary surface, irradiated with divergent light, and recorded on the hologram recording layer by causing interference (see JP-A-11-311938).
Furthermore, in the recording optical system, the information light is converged on the reflection layer, the recording reference light is defocused on the reflection layer, and the conjugate focal point of the recording reference light is from the boundary surface between the substrate and the information recording layer. There is also a technique of irradiating recording reference light so as to be positioned on the substrate side (see Japanese Patent Laid-Open No. 2004-171611).

In order to record the refractive index as a volume change on the recording medium in the prior art, the diffraction pattern spacing may change due to the shrinkage of the recording medium after recording, which may reduce the diffraction efficiency during reproduction. There is a problem that the reproduction signal includes distortion. Conventional recording media, particularly polymer-based photosensitive materials, have a large rate of change in expansion and contraction due to light irradiation, but no countermeasures have been taken in the prior art.
Furthermore, examples of objective lens configuration in a mode in which recording / reproduction is performed from one side of the recording layer in the prior art, for example, the techniques disclosed in JP-A-11-311938 and JP-A-2004-171611 are shown in FIGS. 1 and 2, respectively. Show.
In any technique, as shown in the drawing, the reference light and the signal light are guided to the objective lens OB so as to be coaxial and overlap each other at the time of recording. The reference light and the signal light after passing through the objective lens OB are set to have different focal lengths.
In FIG. 1A, the signal light is condensed (focal point P) at a position where the reflective layer is to be disposed, and the reference light is condensed (focal point P1) before the focal point P. In FIG. 2A, the signal light is condensed (focal point P) at a position where the reflection layer is to be disposed, and the reference light is condensed (focal point P2) before the focal point P. In any case, the reference light and the signal light collected by the objective lens OB always interfere with each other on the optical axis. Therefore, as shown in FIGS. 1B and 2B, when the reflective layer is arranged at the position of the focal point P of the signal light and the recording medium is arranged between the objective lens and the reflective layer, the reference light and The signal light passes back and forth through the recording medium to perform hologram recording. During reproduction, the reference light passes back and forth through the recording medium, and the reflected reference light returns to the objective lens OB together with the reproduction light.
As shown in FIG. 3, the holograms to be specifically recorded are hologram recording A (reflecting reference light and reflected signal light) and hologram recording B (incident reference light and reflected signal light) in any technique. ), Hologram recording C (reflecting reference light and incident signal light), and hologram recording D (incident reference light and incident signal light). In addition, the hologram to be reproduced is also a hologram record A (read by reflected reference light), hologram record B (read by incident reference light), hologram record C (read by reflected reference light), hologram record D. There are four types (read by the incident reference light).
Therefore, in these conventional techniques, all the light rays (incident light and reflected light of the reference light and incident light and reflected light of the information light) interfere with each other in the recording layer, so that a plurality of holograms are recorded and reproduced. . This is, for example, as described in paragraphs (0096) and (0097) of Japanese Patent Application Laid-Open No. 2004-171611.
In the conventional method, when a hologram is recorded on a hologram record carrier having a reflective surface, four holograms are recorded due to interference of four light fluxes of incident reference light, signal light, reflected reference light, and signal light. The performance of the recording layer was used unnecessarily. Therefore, when reproducing information, the reference light is reflected by the reflection layer of the hologram record carrier, and thus it is necessary to separate it from the reproduced light from the reproduced hologram. For this reason, the read performance of the reproduction signal is degraded.
In the conventional method, since many optical components are required for generating and merging the reference light and the signal light, it is desired to reduce the size of the apparatus.
Thus, the problem to be solved by the present invention is to provide an optical pickup device and hologram recording / reproducing system for hologram recording / reproducing that enable stable recording or reproduction.
An optical pickup device of the present invention is an optical pickup device that records or reproduces information on a hologram record carrier having a hologram recording layer that stores therein an optical interference pattern of reference light and signal light as a diffraction grating.
A light source that generates coherent light;
The coherent light comprises a central region disposed on the optical axis and an annular region disposed so as to surround the central region, and the coherent light passes through the central region and the annular region. A spatial light modulator that spatially separates components to generate reference light and signal light and propagates them in the same direction on the same axis;
An objective lens optical system that is arranged on an optical axis and irradiates the signal light and the reference light to the hologram recording layer on a coaxial axis and collects the reference light and the signal light at different focal points;
An image detecting means for receiving light that is arranged on an optical axis and returns from the hologram recording layer via the objective lens optical system when the reference light is irradiated onto the hologram recording layer;
A central correction region disposed on the optical axis and an annular peripheral region disposed so as to surround the central correction region, wherein at least one of the central correction region and the annular peripheral region partially includes a phase of a wavefront of a passing light beam; And an aberration correction device comprising a transmissive liquid crystal device provided with a plurality of transparent electrodes for correcting wavefront aberration of the passing light flux that is changed in a steadily manner.
The hologram recording / reproducing system of the present invention is a hologram recording / reproducing system that records or reproduces information on a hologram record carrier that stores therein an optical interference pattern of reference light and signal light as a diffraction grating,
Light generating means for generating, from coherent light, reference light and signal light obtained by modulating the coherent light according to recording information;
One of the reference light and the signal light is on the optical axis, the other is annularly formed around the one, spatially separated from each other and propagated coaxially in the same direction, via the objective lens optical system, Interference means for condensing the reference light and the signal light at different focal points on an optical axis and interfering the reference light and the signal light;
A hologram recording carrier having a hologram recording layer located on the focal side near the objective lens optical system among the different focal points;
A reflective layer located on the focal side far from the objective lens optical system among the different focal points;
An image detecting means for receiving light that is arranged on an optical axis and returns from the hologram recording layer via the objective lens optical system when the reference light is irradiated onto the hologram recording layer;
A central correction region disposed on the optical axis and an annular peripheral region disposed so as to surround the central correction region, wherein at least one of the central correction region and the annular peripheral region partially includes a phase of a wavefront of a passing light beam; An aberration correction device comprising a transmissive liquid crystal device including a plurality of transparent electrodes for correcting wavefront aberrations of the passing light flux to be changed in an automatic manner,
And an aberration correction liquid crystal driving circuit for supplying a correction voltage to each of the plurality of transparent electrodes when recording or reproducing information.
According to the above configuration, even when distortion, thickness error, inclination, etc. occur in the hologram record carrier, etc., the transparent electrode in the aberration correction device has a divided shape suitable for correcting according to the aberration. Therefore, the applied correction voltage can give the liquid crystal a change in refractive index corresponding to the divided electrode pattern, so that a phase difference (aberration) suitable for canceling the aberration can be given to the transmitted wavefront. By providing the phase difference, it is possible to reduce the aberration generated in the passing light due to the tilt and thickness error of the hologram record carrier, the refractive index error of the hologram record carrier, and the like. Since appropriate reference light can be obtained regardless of physical errors of the hologram record carrier, hologram recording can be performed satisfactorily. For the tilt of the hologram record carrier disk, an error signal obtained by a tilt sensor provided separately can be used.

（式中、ｍ１は黒レベルの平均光量を、ｍ２は白レベルの平均光量を、σ１は黒レベルの標準偏差を、σ２は白レベルの標準偏差を、それぞれ示す。）
次に、取得された画像のＳＮＲ又はエラーレートが制御回路３７のメモリにあらかじめ記録されている所定値を超えるか否かで、最適補正値探索を行う（ステップＳ２７）。取得値が所定値未満であれば継続してステップＳ２４に戻り、取得値が所定値を超えれば探索終了として、次へ移行し、参照光収差補正値を決定する（ステップＳ２８）。
次に、参照光収差補正値に基づき参照光領域で収差補正を行いつつ、レーザ光の出力を上昇させて参照光のみをホログラム記録担体に照射してホログラム再生を開始する（ステップＳ２９）。
次に、情報データの再生継続又は終了を判別して（ステップＳ３０）、継続であればステップＳ２２へ戻り、再生終了であれば終了する。
ここでは特にホログラム記録担体特有の収縮や屈折率の変化による収差をホログラム記録担体の記録状態に応じて補正するので、種々のホログラム記録担体の再生に有効である。また、ホログラム記録担体の収縮などによってホログラムの読み取り品位が低下する場合には参照光の波面制御が効果的と思われるがそれを実施した場合にサーボビームまでもその作用を受けると不具合が生じることが予想される。そのためにサーボビームには液晶の収差補正効果が作用しないようにすることは効果がある。
以上のように、収差補正液晶パネルＬＣＰの透明電極はホログラム記録担体などに歪みや厚みの誤差、傾きなどが生じた場合にその収差に応じた補正を行うのに適した分割になっているので、参照光の収差補正を行うことができる。
このように、先行技術ではホログラム記録用の参照光は平行光束であるが、本実施形態では、特定の対物レンズモジュールにより信号光及び参照光をそれら焦点位置を異ならすように発散又は収束光とするとともに、収差補正液晶パネルなどの特定の収差補正装置を用いて記録時と再生時に行う偏光状態の切り替える構成としている。また、この対物レンズモジュールにおいては対物レンズとの組み合わせる特定光学素子により、記録再生のレーザ波長とは異なる波長を用いるサーボビームにおいて、ホログラム記録担体のサーボガイド層上で収差無く集光するように設定されている。さらに、従来技術では記録再生で光学系を変更する必要があったが、本実施形態では収差補正液晶パネルに印加する電圧をコントロールすることで同一の効果を得ることができる。
また従来技術では参照光が平行光であるため、シフト多重記録が不可能であり記録容量が少なかった。しかしながら本実施形態では参照光ＲＢを収束光にしてシフト多重可能にしたことで高品位な再生信号を得ることができる。このことは、記録後にホログラム記録層の収縮や屈折率変化などによって記録時の参照光の波面と再生時の参照光の波面が異なってしまう場合などに特に有効である。また、サーボビームＳＶＢの波長において光学素子と対物レンズの組み合わせによって収差が除去されているので、サーボ信号の再生が良好に行える。
さらに、サーボビームの合成光路を検出系の４ｆ系内に配置することで省スペース化を実現でき、集光系中に合成プリズムを配置できるのでプリズムなどの有効径を小さくすることができる。
＜他のピックアップ変形例＞
図４０に他のピックアップの構成を示す。
このピックアップは、図３４に示すピックアップにおけるミラーＭＲ、１／４波長板１／４λ及び４ｆレンズｆｃを取り除き、これらの位置に、透過型の空間光変調器ＳＬＭに代えて、反射型の偏光空間光変調器ＰＳＬＭを配置して、ホログラム記録再生用レーザ光源ＬＤ１からの光束を偏光ビームスプリッタＰＢＳを経て偏光空間光変調器ＰＳＬＭへ入射してその反射光を用いる以外、上記ピックアップ２３と同一である。よって、記録再生動作も上記ピックアップ２３と同様に行われる。
偏光空間光変調器ＰＳＬＭは、図４１に示すように、光軸近傍で光軸を含む中央領域Ａとその周囲の光軸を含まない空間光変調領域Ｂとに分割されているいわゆるＬＣＯＳ（Ｌｉｑｕｉｄ Ｃｒｙｓｔａｌ Ｏｎ Ｓｉｌｉｃｏｎ）装置である。反射される光束に９０度回転する偏光の変調が与えられ、偏光空間光変調器ＰＳＬＭが光束を反射した時点で光束は空間光変調領域Ｂの空間変調された信号光ＳＢと中央領域Ａの空間変調されない参照光ＲＢに同軸上にて分離される。
偏光空間光変調器ＰＳＬＭは、マトリクス状に分割された複数の画素電極を有する液晶パネルなどで電気的に入射光の一部を画素毎に偏光する機能を有する。この偏光空間光変調器ＰＳＬＭは空間光変調器駆動回路２６に接続され、これからの記録すべきページデータに基づいた分布を有するように光束偏光を変調して、環状断面の信号光ＳＢを生成する。また、偏光空間光変調器ＰＳＬＭは入射及び反射で同一偏光を維持することもできるので、空間光変調領域Ｂのみで変調状態を維持したまま反射状態とする制御を行えば、偏光ビームスプリッタＰＢＳとの組み合わせでシャッタとして機能して、中央領域Ａの空間変調されない参照光のみを対物レンズモジュールＯＢＭへ供給できる。1 to 3 are schematic partial sectional views showing a hologram record carrier for explaining conventional hologram recording.
FIG. 4 is a configuration diagram showing an outline of a pickup of a hologram apparatus for recording / reproducing information on the hologram record carrier according to the embodiment of the present invention.
FIG. 5 is a front view seen from the optical axis of the spatial light modulator of the pickup according to the embodiment of the present invention.
FIG. 6 is a front view seen from the optical axis of a spatial light modulator of a pickup according to another embodiment of the present invention.
FIG. 7 is a schematic cross-sectional view showing the objective lens module of the pickup according to the embodiment of the present invention.
FIG. 8 is a schematic cross-sectional view showing a hologram record carrier and an objective lens module for explaining hologram recording according to an embodiment of the present invention.
FIG. 9 is a schematic partial sectional view showing a hologram record carrier for explaining hologram recording of an embodiment according to the present invention.
FIG. 10 is a schematic sectional view showing a hologram record carrier and an objective lens for explaining hologram reproduction according to an embodiment of the present invention.
FIG. 11 is a schematic sectional view showing a hologram record carrier and an objective lens module for explaining hologram recording of another embodiment according to the present invention.
FIG. 12 is a schematic partial sectional view showing a hologram record carrier for explaining hologram recording of another embodiment according to the present invention.
FIG. 13 is a schematic sectional view showing an objective lens module of a pickup according to another embodiment of the present invention.
14 and 15 are schematic sectional views showing a bifocal lens of an objective lens of a pickup according to another embodiment of the present invention.
FIG. 16 is a schematic cross-sectional view showing an objective lens module of a pickup according to another embodiment of the present invention.
FIG. 17 is a schematic sectional view showing a hologram record carrier and an objective lens module for explaining hologram recording of another embodiment according to the present invention.
FIG. 18 is a schematic partial sectional view showing a hologram record carrier for explaining hologram recording of another embodiment according to the present invention.
FIG. 19 is a schematic sectional view showing a hologram record carrier and an objective lens for explaining hologram reproduction according to another embodiment of the present invention.
FIG. 20 is a schematic sectional view showing a hologram record carrier and objective lens module for explaining hologram recording of another embodiment according to the present invention.
FIG. 21 is a schematic partial sectional view showing a hologram record carrier for explaining hologram recording of another embodiment according to the present invention.
FIG. 22 is a schematic sectional view showing an objective lens module of a pickup according to another embodiment of the present invention.
23 and 24 are schematic cross-sectional views showing a bifocal lens of an objective lens of a pickup according to another embodiment of the present invention.
FIG. 25 is a perspective view of an aberration correction liquid crystal panel of the aberration correction apparatus for a pickup according to the embodiment of the present invention.
FIG. 26 is a perspective view of an aberration correction liquid crystal panel of an aberration correction apparatus for a pickup according to another embodiment of the present invention.
27 is a partial cross-sectional view taken along line XX in FIG.
FIG. 28 is a partially cutaway perspective view of an aberration correction apparatus for a pickup according to another embodiment of the present invention.
FIG. 29 is a schematic partial sectional view showing a hologram record carrier according to an embodiment of the present invention.
FIG. 30 is a front view as seen from the optical axis of the spatial light modulator of the pickup according to another embodiment of the present invention.
FIG. 31 is a partial cross-sectional view taken along line XX in FIG. 26 for explaining the polarization state.
FIG. 32 is a configuration diagram showing an outline of a pickup of a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention.
FIG. 33 is a block diagram showing a schematic configuration of the hologram apparatus according to the embodiment of the present invention.
FIG. 34 is a block diagram showing an outline of a pickup of a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention.
FIG. 35 and FIG. 36 are schematic cross-sectional views showing a hologram record carrier and an objective lens module in a pickup of a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention.
FIG. 37 is a flowchart showing a recording method in a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention.
38 and 39 are flowcharts showing a reproducing method in a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention.
FIG. 40 is a configuration diagram showing an outline of a pickup of a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention.
FIG. 41 is a front view seen from the optical axis of the polarization spatial light modulator of the pickup according to another embodiment of the present invention.
Detailed Description of the Invention
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 4 shows a schematic configuration of a pickup 23 for recording or reproducing the hologram record carrier 2.
The pickup 23 includes a hologram light source LD for recording and reproduction, a collimator lens CL, a transmissive spatial light modulator SLM, a polarization beam splitter PBS, an imaging lens ML, an image sensor IS, and a drive system (not shown). , A transmissive aberration correction liquid crystal panel LCP, and an objective lens module OBM. The objective lens module OBM and the like are disposed on the optical axis of the light beam from the laser light source LD in the housing (not shown). The wavelength of the laser light source LD is a wavelength at which a light-transmitting photosensitive material capable of preserving the optical interference pattern of the hologram record carrier 2 reacts. The collimator lens CL converts coherent light diverging from the laser light source LD into parallel light.
<Spatial light modulator>
FIG. 5 is a front view of the spatial light modulator SLM irradiated within the parallel light beam diameter as seen from the optical axis. The spatial light modulator SLM is divided in the vicinity of the optical axis into a central region LCCR including the optical axis and an annular region LCPR not including the surrounding optical axis. The central region LCCR is made of a through-opening or a transparent material, and the light beam passing therethrough is not modulated. The transmissive annular region LCPR has a function of electrically shielding a part of incident light for each pixel in a liquid crystal panel with an analyzer having a plurality of pixel electrodes divided in a matrix, or transmitting all light. It has a function to make a modulation state. As shown in FIG. 4, the annular region LCPR modulates the parallel light from the collimator lens CL according to the recording information. That is, when the light passes through the spatial light modulator SLM, the light beam is concentrically separated into the spatially modulated signal light SB and the non-spatial modulated reference light RB.
This spatial light modulator SLM is connected to the spatial light modulator drive circuit 26 and has a light flux so as to have a distribution based on page data to be recorded (information pattern of two-dimensional data such as bright and dark dot patterns on a plane). Is modulated and transmitted to generate a signal light SB.
Further, as shown in FIG. 6, the entire spatial light modulator SLM is used as a transmissive matrix liquid crystal display device, and the control circuit 26 controls an annular region LCPR for displaying a predetermined pattern of page data to be recorded and a central region therein. It can also be configured to display the unmodulated light transmission region of the LCCR. The central region LCCR can also be used as a phase-modulated light transmission region, and phase-modulated reference light may be generated.
As described above, the spatial light modulator SLM includes the central region LCCR arranged on the optical axis of the coherent light and the annular region LCPR arranged so as to surround the central region LCCR. The passing component and the passing component of the annular region are spatially separated to generate reference light and signal light, which are propagated coaxially. The central region LCCR and the annular region LCPR generate reference light and signal light. However, the central region LCCR can generate signal light and the annular region LCPR can generate reference light.
As an example of the spatial light modulator, a reflection type liquid crystal panel or DMD can be used in addition to the transmission type. In the reflection type spatial light modulator, as in the transmission type, the central region LCCR and its surrounding optical axes are used. And an annular region LCPR that does not contain the light, and its action separates the light flux in the central region and the annular region.
<Objective lens optical system>
The objective lens module OBM of FIG. 4 belongs to an objective lens optical system that irradiates signal light and reference light toward the hologram recording carrier 2 on the same axis and collects the reference light RB and the signal light SB at different focal points.
FIG. 7 is a schematic cross-sectional view of an example of the objective lens module OBM. The objective lens module OBM is a convex lens optical element CVX in which a convex lens having a diameter smaller than that of the objective lens OB and a convex lens having a diameter smaller than that of the objective lens OB is fixed by a hollow holder (not shown) and the like. Consists of. The convex lens optical element CVX includes a central region CR (convex lens) including the optical axis and an annular region PR (transmission parallel plate) around the central region CR (convex lens). As shown in FIG. 8A, the objective lens module OBM collects the light passing through the central region CR at the near focal point nP on the near side and condensing the light passing through the annular region PR at the far focal point fP far away. Let The short-distance focal point nP is the combined focal point of the objective lens OB and the convex lens optical element CVX, and the long-distance focal point fP is the focal point of the objective lens OB.
At the time of hologram recording, as shown in FIG. 8A, the reference light RB and the signal light SB around the optical axis from the spatial light modulator SLM are respectively coaxially and spatially separated from each other in the objective state. Guided to the lens module OBM. The spatial light modulator spatially separates the reference light RB from the central region CR on the optical axis and the signal light SB having an annular cross section to the annular region PR around the reference light RB and propagates them coaxially. . The objective lens module OBM refracts the reference light RB and the signal light SB in the central region CR and the annular region PR, respectively. Therefore, the reference light RB and the signal light SB are spatially separated even after passing through the objective lens, the reference light RB is condensed on the short-distance focal point nP close to the objective lens OB, and the signal light SB is far away from the short-distance focal point. Since the light is focused on the focal point, interference occurs farther than the short-distance focal point nP.
As shown in FIG. 8B, the reflective layer 5 is disposed at the position of the short-distance focal point nP of the reference light RB, and the hologram recording layer 7 is disposed between the objective lens module OBM and the reflective layer 5 as a recording medium. The signal light SB having an annular cross section is reflected by the reflection layer 5 and collected at a symmetrical position of the far-distance focal point fP, and the reference light RB is reflected by the reflection layer 5 before (the short-distance focal point nP). Therefore, the signal light SB reflected and converged in the opposite propagation directions and the reference light RB interfere with each other in the annular region near the optical axis. If a hologram record carrier having a hologram recording layer located between the near focus nP and the far focus fP is used, since the reference light RB and the signal light SB are spherical waves that propagate in directions opposite to each other, Since the angle can be made relatively large, an optical interference pattern that can reduce the multiplexing interval is recorded as the hologram HG. Therefore, the hologram recording layer 7 needs to have a film thickness that is sufficient for the reflected signal light and the reference light to intersect and interfere to generate an optical interference pattern.
As shown in FIG. 9, the holograms to be specifically recorded are hologram recording A (reflected and diverged reference light and reflected and converged signal light), hologram record B (incident and converged reference light reflected and reflected). 2 types of convergent signal light). There are also two types of holograms to be reproduced: hologram recording A (read out with reflected reference light) and hologram recording B (read out with incident reference light).
Therefore, in the hologram reproduction system for reproducing information from such a hologram record carrier, as shown in FIG. 10, only the reference light RB is supplied to the central region CR of the objective lens module OBM, and the reference light RB is supplied to the short-distance focus nP (reflection). When the hologram HG of the hologram recording layer is transmitted while being converged on the layer 5), normal reproduction light and phase conjugate wave reproduction light can be generated from the hologram HG. By the objective lens OB which is also a part of the detection means, the reproduction light and the phase conjugate wave can be guided to the photodetector.
In another hologram recording / reproducing system, the reflective layer 5 is not disposed at the position of the short-distance focal point nP of the reference light RB, but as shown in FIG. 11, the reflective layer is disposed at the position of the long-distance focal point fP of the signal light SB. 5 is arranged, and the hologram recording carrier 2 is arranged so that the hologram recording layer 7 is between the objective lens module OBM and the reflection layer 5. The signal light SB having an annular cross section is focused and reflected by the reflection layer 5, and the reference light RB is reflected by the reflection layer 5 while being condensed and diverged before the reflection layer 5 (short-distance focal point nP). In this case, in the reflection layer 5, the reference light RB is in focus and the signal light SB is in focus. Therefore, if the hologram recording layer 7 is arranged away from the reflective layer 5 so that only the reflected reference light RB and the signal light SB intersect, the signal light SB and the reference light in the opposite propagation directions are arranged. The RB component interferes with the annular region near the optical axis. As shown in FIG. 12, the holograms to be recorded specifically are hologram recording A (reflected and diverging reference light and reflected and diverging signal light), hologram recording C (reflected and diverging reference light and incident light). 2 types of convergent signal light). There are also two types of holograms to be reproduced. In the hologram reproducing system in this case, only the reference light RB is supplied to the central region CR of the objective lens module OBM, and the reference light RB is irradiated to the reflection layer 5 in the same defocused state as at the time of recording. If the hologram HG is transmitted, normal reproduction light and phase conjugate wave reproduction light can be generated from the hologram HG in the same optical path.
Note that an objective lens module OBM of another modified example has a transmission type diffractive optical element DOE having a convex lens function on the optical axis coaxially in front of the objective lens OB, as shown in FIG. 13, instead of the convex lens optical element. It can also be configured by arranging. As shown in FIG. 14, the objective lens OB and the transmissive diffractive optical element DOE having a convex lens function can be integrated. By constructing the objective lens module OBM as a bifocal lens OB2 having a convex lens function or a Fresnel lens surface coaxially formed on the refracting surface (central region CR), the reference light RB and the signal light SB are formed. The focal lengths can be different from each other. Further, as shown in FIG. 15, the convex lens portion CVX is integrated with the objective lens, a step is formed at the boundary between the central region CR and the annular region PR, and the objective lens module OBM is configured as a bifocal lens OB2 of an aspherical lens having different curvatures. May be. Further, a modification of the bifocal lens is one in which an annular diffraction grating is provided in the central region CR and a convex lens portion is left around it, but conversely, an annular diffraction grating is provided in the annular region PR and a convex lens portion is provided in the central region. You may leave.
In the above embodiment, the mode in which the signal light around the reference light is irradiated so as to be in a defocused state on the reflection layer is used when the focus of the signal light is farther from the objective lens than the focus of the reference light. However, such a defocused state can be achieved even when the focus of the signal light is in front of the focus of the reference light. For example, FIG. 16 shows a configuration example of an objective lens optical system according to another embodiment.
The objective lens module OBM of FIG. 16 is a concave lens in which a convex lens is fixed by a hollow holder (not shown) and the like, and a concave lens whose diameter is smaller than that of the objective lens OB. It consists of an optical element CCV. The concave lens optical element CCV includes a central region CR (concave lens) including the optical axis and a surrounding annular region PR (transmission parallel plate). As shown in FIG. 17A, the objective lens module OBM collects the light passing through the central region CR at the far focal point fP at the far end and condensing the light passing through the annular region PR at the near focal point nP at the front. Let The far focus fP is a combined focus of the objective lens OB and the concave lens optical element CCV, and the short focus nP is a focus of the objective lens OB.
At the time of hologram recording, first, the coherent reference light RB around the optical axis is modulated by the spatial light modulator or the like coaxial with the objective lens module OBM, and the reference light RB is modulated around it according to the recording information. The signal light SB obtained in this way is generated. As shown in FIG. 17A, the reference light RB and the signal light SB are guided to the objective lens module OBM while being coaxial and spatially separated from each other. The objective lens module OBM refracts the reference light RB and the signal light SB in the central region CR and the annular region PR, respectively. Therefore, the reference light RB and the signal light SB are spatially separated even after passing through the objective lens, the signal light SB is condensed on the short-distance focal point nP close to the objective lens OB, and the reference light RB is far away from the short-distance focal point. Focused at the focal point.
At the time of hologram recording, first, a coherent reference beam RB and a signal beam SB obtained by modulating the reference beam RB according to the recording information are generated.
Then, the reference light RB and the signal light SB are guided to the objective lens module OBM so as to be coaxially spaced apart from each other. That is, as shown in FIG. 17A, the reference light RB is spatially separated and coaxially separated from each other into the central region CR on the optical axis and the signal light SB into the annular region PR around the reference light RB. Propagate. Even after passing through the objective lens, the reference light RB and the signal light SB are spatially separated, the signal light SB is collected at the short-distance focal point nP near the objective lens module OBM, and the reference light RB is far-distance focal point farther than the short-distance focal point Focused on fP.
As shown in FIG. 17B, the reflective layer 5 is disposed at the position of the long-distance focal point fP of the reference light RB, and the hologram recording layer 7 is disposed between the objective lens module OBM and the reflective layer 5. The signal light SB having an annular cross section is reflected by the reflection layer 5 while being condensed and diverged before the reflection layer 5 (short-distance focal point nP), and the reference light RB is focused and reflected by the reflection layer 5. Therefore, since the signal light SB having the annular cross section is condensed before the reflection layer 5, the signal light SB is defocused by the reflection layer 5, and the reflected signal light SB does not intersect with the reference light RB and does not interfere. Since the intersection angle between the incident signal light SB and the reference light RB can be made relatively large, the multiplexing interval can be reduced.
As shown in FIG. 18, the holograms that are specifically recorded are hologram recording C (reflected and divergent reference light and incident convergent signal light), hologram record D (incident convergent reference light and incident convergent signal light). ). Also, the same two types of holograms are reproduced.
Therefore, in the hologram reproducing system for reproducing information from the hologram record carrier, as shown in FIG. 19, only the reference light RB is supplied to the central region CR of the objective lens module OBM, and the reference light RB is supplied to the reflection layer 5 (long distance). When the hologram HG of the hologram recording layer is transmitted while being converged to the focal point fP), renormal reproduction light and phase conjugate wave reproduction light can be generated from the hologram HG. The objective lens module OBM which is also a part of the detection means can guide the reproduction light and the phase conjugate wave to the photodetector.
In another hologram recording / reproducing system, the reflective layer 5 is disposed at the position of the long-distance focal point fP of the reference light RB, and the hologram recording layer 7 is not disposed between the objective lens module OBM and the reflective layer 5. As shown in FIG. 20, the reflection layer 5 is arranged at the position of the short-distance focal point nP of the signal light SB passing through the annular region PR, and the hologram recording carrier 2 has the hologram recording layer 7 between the objective lens module OBM and the reflection layer 5. Arrange as shown. The signal light SB having an annular cross section is focused and reflected by the reflective layer 5, and the reference light RB is reflected by the reflective layer 5 and collected at a symmetrical position of the long-distance focal point fP. In this case, in the reflection layer 5, the reference light RB is in focus and the signal light SB is in focus. As shown in FIG. 21, there are two types of holograms specifically recorded: hologram recording B (incident reference light and reflected signal light) and hologram recording C (incident reference light and incident signal light). . There are also two types of holograms to be reproduced. In the hologram reproducing system in this case, only the reference light RB is supplied to the central region CR of the objective lens module OBM, and the reference light RB is irradiated to the reflection layer 5 in the same defocused state as at the time of recording. If the hologram HG is transmitted, normal reproduction light and phase conjugate wave reproduction light can be generated from the hologram HG in the same optical path.
Further, another modified example of the bifocal objective lens module OBM is an objective lens module in which a transmissive diffractive optical element DOE having a concave lens function at the center is disposed immediately before the objective lens OB as shown in FIG. By doing so, the focal lengths of the reference light RB and the signal light SB can be made different from each other. Further, as shown in FIG. 23, the objective lens OB and the transmissive diffractive optical element DOE are integrated (having a Fresnel lens surface having a concave lens action or a diffraction grating DOE formed coaxially in the central region CR of the refractive surface). By using the bifocal lens OB2, the focal lengths of the reference light RB and the signal light SB can be made different from each other. Further, instead of the lens-integrated diffraction grating, as shown in FIG. 24, the concave lens portion CCV is integrated and a step is provided at the boundary between the central region CR and the annular region PR, and the bifocal lens OB2 of an aspherical lens having different curvatures. The objective lens module OBM may be configured as follows.
According to the configuration in which the reference light and the signal light are propagated and irradiated so that the other is separated and surrounded by a coaxial axis, the overlap of the reference light and the signal light can be limited to some extent at the time of incidence.
Further, in the embodiment shown in FIGS. 8 and 17, the reference light focused on the reflective layer can be used as a light beam for servo error detection. Further, in the embodiment shown in FIGS. 11 and 20, the reference light is generated in the center and the signal light is generated in the outer annular region, but this is modified to generate the signal light in the central region and the reference light in the outer annular region. Can be used as the light beam for servo error detection.
According to the embodiment and the modification described above, during hologram recording, the interfering signal light and reference light are limited, so that no extra hologram is recorded or reproduced. Further, since the reference light RB and the signal light SB are spherical waves propagating in directions opposite to each other, their crossing angle can be made relatively large, so that shift multiplexing is possible and the multiplexing interval can be reduced.
<Image detection means>
The polarization beam splitter PBS, the imaging lens ML, and the image sensor IS arranged on the optical axis in FIG. 4 return from the hologram recording carrier 2 through the objective lens module OBM when the reference light is irradiated onto the hologram recording layer. It functions as image detection means for receiving light. The image sensor IS is a photoelectric conversion element composed of an array such as a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor device).
<Aberration correction LCD panel>
The transmission type aberration correction liquid crystal panel LCP of FIG. 4 includes a central correction region PLCCR disposed on the optical axis and an annular peripheral region PLCPR disposed so as to surround the center correction region PLCCR, and at least one of them is a passing light beam. This is a transmissive liquid crystal device including a plurality of transparent electrodes that partially correct the wavefront phase of the light beam and correct the wavefront aberration of the passing light beam.
FIG. 25 shows an aberration correction liquid crystal panel LCP composed of a transmissive liquid crystal device. The aberration correction liquid crystal panel LCP is connected to the aberration correction liquid crystal driving circuit LCPD, and includes an annular peripheral region PLCPR and a central correction region PLCCR therein.
As shown in FIGS. 25 and 26, in the aberration-correcting liquid crystal panel LCP, a fluid transparent liquid crystal composition 11 is sandwiched between two glass substrates 12a and 12b, and the periphery of the substrate is sealed. have. On the inner surfaces of both glass substrates 12a and 12b, the transparent electrode layers (13ai, 13a) and (13b) for applying a voltage to the liquid crystal made of indium tin oxide and the direction (alignment) of the axis of liquid crystal molecules in the vicinity are defined. The alignment films 14a and 14b to be stacked are sequentially stacked. In the aberration correction liquid crystal panel LCP, the orientation of the liquid crystal changes according to the potential difference generated in the liquid crystal, and the refractive index changes according to the voltage, thereby changing the phase of the wavefront passing through the liquid crystal, thereby It is intended to cancel the aberration of the passing light.
The central correction region PLCCR through which only the reference light is transmitted has an electrode division shape corresponding to the aberration generated in the reference light. The electrode division shape of the central correction region PLCCR can take a spherical aberration correction pattern, a coma aberration correction pattern, an astigmatism correction pattern, and the like, which will be described later, and are configured in a composite manner. You can also. For example, at least one of the opposing electrode layers of the central correction region PLCCR is divided into a plurality of transparent electrodes as a phase adjustment unit, and a voltage corresponding to the distribution shape of the aberration generated in the reference light is applied to each of the plurality of transparent electrodes. By adopting the configuration to apply, the aberration of the reference light transmitted through the aberration correction liquid crystal panel LCP can be corrected. In FIG. 26, the transparent electrode 13b is a common electrode, but the transparent electrode 13a in the annular peripheral region PLCPR and a plurality of transparent electrodes 13ai (i = 1, 2, 3,...) In the central correction region PLCC therein. The correction voltage is applied independently by the aberration correction liquid crystal drive circuit LCPD.
FIG. 27 is a plan view of an electrode pattern schematically showing an example of the structure of the central correction region PLCCR of the aberration correction liquid crystal panel LCP for correcting spherical aberration. As shown in FIG. 27 (a), the central correction region PLCCR is partitioned by a gap and electrically connected to the distribution of spherical aberration generated in the hologram record carrier 2 within the effective diameter of the incident reference light beam. It includes a plurality of concentric (annular) separated transparent electrodes 13a1, 13a2, 13a3, 13a4, 13a5, 13a6, 13a7. The width of each of the transparent electrodes 13a1-13a7 can be varied in order to change the phase of the wavefront corresponding to the distribution of spherical aberration, but may be configured equally. FIG. 27 shows a case where the central correction region PLCCR has seven transparent electrodes, but the number of electrodes may be two or more. When the correction voltage Vi (i = 1, 2, 3, 4, 5, 6, 7) is applied to the transparent electrodes 13a1 to 13a7 via the lead lines, the liquid crystal layer 11 according to the electric field generated by the correction voltage Vi. The refractive index alignment of the liquid crystal molecules in each part changes. As a result, the wavefront of the light passing through the liquid crystal layer 11 changes in phase due to the birefringence of the liquid crystal layer 11. That is, the wavefront of the reference light passing through can be controlled by the correction voltage Vi applied to the liquid crystal layer 11.
As shown in FIG. 27B, the voltage waveform of the correction voltage Vi from the reference voltage applied to the transparent electrodes 13a1-13a7 on the diameter of the central correction region PLCCR is shown. By applying a correction voltage corresponding to the distribution shape of the spherical aberration to be corrected to the electrode pattern, it is possible to cancel the spherical aberration caused by the uneven thickness of the light transmission protective layer of the hologram record carrier. Correction is performed so that the aberration is suppressed.
Therefore, when the recording layer contracts due to hologram recording or when the refractive index changes, it is considered that axially symmetric aberration occurs, and in that case, spherical aberration and defocus aberration occur. In such a case, the aberration correction of the reference light is realized by applying a spherical aberration correction amount stored in advance as a correction voltage to the aberration correction liquid crystal panel LCP, and a reference having the same wavefront as that during recording. Since it can be reproduced with light, a good reproduction signal can be obtained.
FIG. 28 is a plan view schematically showing an example of the structure of the central correction region PLCCR of the aberration correction liquid crystal panel LCP for correcting the coma aberration. FIG. 28A shows a transparent electrode pattern for correcting coma aberration in the central correction region PLCCR. Four divided transparent electrodes 13a11, 13a12, 13a13, 13a14 for changing the phase of the wavefront are partitioned by a gap and electrically separated within the effective diameter of the reference light beam incident on the central correction region PLCCR. Is arranged. A set of the transparent electrodes 13a11, 13a12 and the transparent electrodes 13a13, 13a14 is arranged symmetrically with respect to the diameter of the central correction region PLCCR. That is, in the coma aberration correcting transparent electrode pattern, the central correction region PLCCR is arranged as inner and outer regions divided by a gap including the straight line symmetrical to the diameter perpendicular to the optical axis. A correction voltage corresponding to the coma aberration to be corrected by the drive circuit is supplied.
When a positive voltage is applied to the divided transparent electrode with respect to the reference voltage, a potential difference is generated between the transparent electrode 13b and the orientation of the liquid crystal therebetween changes according to the potential difference and the refractive index changes. The phase of the wavefront of the reference light component passing through the transparent electrode is advanced. Conversely, when a negative voltage with respect to the reference voltage is applied to the divided transparent electrode, the phase of the wavefront of the reference light component passing through the transparent electrode is delayed. Therefore, by applying a correction voltage having a voltage waveform corresponding to the distribution shape of coma aberration to be corrected to the transparent electrodes 13a11 and 13a12 and the transparent electrodes 13a13 and 13a14 arranged symmetrically, as shown in FIG. The central correction area PLCCR is corrected so that the coma aberration generated when the hologram record carrier is tilted with respect to the optical axis can be canceled and the coma aberration is suppressed.
Therefore, when the recording layer is tilted with respect to the light beam by hologram recording, the aberration of the reference light can be corrected based on the quality of the reproduction signal. The quality of the reproduced signal is evaluated based on the SNR or error rate of the reproduced image, and the correction voltage is determined so as to obtain the best result. By applying the correction voltage to the aberration correction liquid crystal panel LCP, the aberration correction of the reference light is realized, and reproduction can be performed with the reference light having the same wavefront as that during recording, so that a good reproduction signal can be obtained.
Further, the aberration-correcting liquid crystal panel LCP is connected to the annular peripheral region PLCPR and the central correction region PLCCR in the same optically polarized light transmission state at the time of hologram recording by the connected aberration-correcting liquid crystal driving circuit LCPD. It can be controlled to have different polarization action states in the region.
The aberration correction liquid crystal panel LCP, for example, rotates the polarization plane of the signal light that passes through the annular area and the reference light that passes through the central area inside thereof, and changes the rotation angle from the time of hologram recording to the time of reproduction. It can be controlled by the correction liquid crystal driving circuit LCPD. The aberration correction liquid crystal driving circuit LCPD and the aberration correction liquid crystal panel LCP are systems capable of rotating the polarization directions of the annular region light beam portion and the central region light beam portion inside the light beam emitted from the laser light source by a predetermined angle, for example, 90 degrees.
A liquid crystal is a substance exhibiting an intermediate phase between a solid and a liquid in which the molecule is elongated and the position and the direction of its axis are both regular and irregular. In general, in a natural state (non-application electric field), a plurality of liquid crystal molecules are arranged with gentle regularity in the major axis direction. When liquid crystal molecules are brought into contact with an alignment film in which a plurality of micro grooves in a certain direction are cut by rubbing or the like, there is a property that the molecular axes of the liquid crystal molecules change the alignment along the grooves. Therefore, in a TN (Twisted Nematic) type liquid crystal, if the liquid crystal is filled between two alignment films arranged in parallel at a predetermined interval so that the direction of each minute groove is 90 degrees, the liquid crystal molecules The alignment film is twisted gradually from one alignment film to the other alignment film so as to rotate 90 degrees (helical array). When light passes through the liquid crystal from one alignment film to the other alignment film in a state where the liquid crystal molecules are aligned in a twisted manner, the light is transmitted along the gap where the liquid crystal molecules are arranged. For example, linearly polarized light parallel to the liquid crystal molecular axis near one alignment film becomes linearly polarized light parallel to the liquid crystal molecular axis near the other alignment film, and its vibration plane (polarization plane) is twisted by 90 degrees and transmitted. (Off state when no voltage is applied).
On the other hand, when a voltage is applied between the opposing transparent electrodes sandwiching the liquid crystal, the liquid crystal molecules are aligned along the electric field with the axis changing from the direction along the alignment film to the vertical direction. Since the liquid crystal molecules stand upright from the alignment film and the alignment of the liquid crystal molecules changes, for example, as shown in FIG. 26, the polarization plane (parallel to the paper surface) of the linearly polarized transmitted light is transmitted as it is without being rotated. (On state with the same voltage applied).
In order to obtain a liquid crystal panel having a plurality of functions as described above, an alignment film is set so that liquid crystal molecules are aligned in parallel in the region used for aberration correction, while TN alignment is used in the region used for polarization action. The alignment film is set so that For example, in the alignment films 14a and 14b facing each other in the aberration-correcting liquid crystal panel LCP shown in FIG. 26, one alignment film 14b is uniformly rubbed in a fixed direction (shown by a broken-line bidirectional arrow in FIG. 25) In the other alignment film 14a, the annular peripheral region PLCPR is separated from the central correction region PLCCR, and in the annular peripheral region PLCPR, the direction is 90 degrees with respect to the rubbing direction of the alignment film 14b (in FIG. In the central correction region PLCCR, the rubbing is performed in parallel with the rubbing direction of the alignment film 14b (indicated by a solid double-directional arrow in FIG. 25). In this way, the liquid crystal molecules can be aligned in parallel in the central correction region PLCCR used for aberration correction, while the TN alignment can be set in the annular peripheral region PLCPR used for polarization action.
<Hologram record carrier>
An example of the hologram record carrier 2 of FIG. 4 is shown in FIG. The hologram record carrier 2 includes a reflection layer 5, a separation layer 6, a hologram recording layer 7, and a protective layer 8 laminated on the substrate 3 in the film thickness direction.
The hologram recording layer 7 stores therein an optical interference pattern by the recording coherent reference light RB and the signal light SB as a diffraction grating (hologram). For the hologram recording layer 7, for example, a light-transmitting photosensitive material capable of storing an optical interference pattern such as a photopolymer, a light anisotropic material, a photorefractive material, a hole burning material, or a photochromic material is used.
The substrate 3 supporting each film is made of, for example, glass, plastic such as polycarbonate, amorphous polyolefin, polyimide, PET, PEN, or PES, or an ultraviolet curable acrylic resin.
The separation layer 6 and the protective layer 8 are made of a light transmissive material, and have functions of flattening the laminated structure and protecting the hologram recording layer and the like.
If the substrate 3 is a disc, the track can be formed spirally or concentrically on it with respect to the center of the circular substrate, or in the form of a plurality of split spiral arcs. In addition, when the board | substrate 3 is card shape, a track | truck may be formed in parallel on the board | substrate. Further, even in the case of the rectangular card substrate 3, the track may be formed in a spiral shape, a spiral arc shape or a concentric shape on the center of gravity of the substrate, for example.
<Recording and playback operation>
The recording / reproducing operation of the present embodiment shown in FIG. 4 will be described.
In the recording operation, as shown in FIG. 4A, the laser light from the laser light source LD polarized in parallel to the paper surface is converted into a parallel light beam by the collimator lens CL, and then passes through the spatial light modulator SLM. Are divided into a light beam including the optical axis and an annular cross-section light beam surrounding the light beam, and a light beam including the optical axis is generated as the reference light RB and an annular cross-sectional light beam as the signal light SB. The reference light RB and the signal light SB are coaxially passed through the polarization beam splitter PBS and the aberration correction liquid crystal panel LCP, and are collected on the hologram record carrier 2 by the objective lens module OBM. At the time of hologram recording, the region through which only the reference light RB of the aberration correction liquid crystal panel LCP passes (center correction region PLCCR) and the region through which only the signal light SB passes (annular peripheral region PLCPR) are turned on, and the signal light SB is referred to. The polarization state of the light RB is set to be the same (parallel to the paper surface). Therefore, it is recorded on the hologram recording layer 7 of the hologram record carrier 2 by the interference between the signal light SB and the reference light RB. Here, all of the central correction region PLCCR and the annular peripheral region PLCPR are set to the on state and the aberration correction of the reference light may be performed, but may not be performed. It is considered that the influence of the aberration is small when the recording medium is irradiated.
In the reproduction operation, as shown in FIG. 4B, only a light beam including the optical axis (reference light RB) is generated by the spatial light modulator SLM from a light beam having a polarization direction parallel to the paper surface, and the reference light RB is polarized. When the light is condensed on the hologram record carrier 2 through the beam splitter PBS and the aberration correction liquid crystal panel LCP via the objective lens module OBM, the reproduction light having the polarization parallel to the paper surface is reconstructed. At the time of reproduction, a correction voltage corresponding to the distribution shape of the aberration generated in the reference light is applied to the plurality of divided transparent electrodes of the phase adjustment unit of the aberration correction liquid crystal panel LCP, and the central correction region PLCCR is turned on to The polarization state of the light passing through the PLCPR and the light passing through the central correction region PLCCR is set to be different by about 90 °. The reproduction light reproduced by the reference light RB is a light beam that diverges and converges with the signal light at the time of recording and has a polarization direction parallel to the paper surface. Due to the polarization action by the liquid crystal panel LCP, the polarization direction becomes perpendicular to the paper surface. On the other hand, the reference light RB is reflected by the reflection layer 5 while being parallel to the paper surface, and is not subjected to the polarization action at the aberration correcting liquid crystal panel LCP. Therefore, since the polarization direction of the reference light RB reflected by the reflective layer 5 and the reproduction light to be reproduced differs during reproduction, it can be separated by the polarization beam splitter PBS, and the reference light RB is received on the detector that receives the reproduction light. Since it does not enter, reproduction SN improves.
The aberration correction liquid crystal panel LCP makes the polarized light perpendicular to the paper surface (the polarization direction of the transmitted light beam is rotated by 90 degrees by the aberration correction liquid crystal panel LCP), and the component reflected by the polarization beam splitter PBS enters the image sensor IS. The image sensor IS sends an output corresponding to the image formed with the reproduction light to a reproduction signal detection processing circuit (not shown), and performs processing to reproduce the page data.
Thus, in the pickup used for hologram recording, the hologram recording light beam is divided into a light beam including the optical axis in the vicinity of the optical axis (reference light) and an annular cross-section light beam (signal light) surrounding it. And an objective lens optical system (lens group) having different focal lengths for the reference light and an aberration correction liquid crystal panel LCP disposed between the spatial light modulator SLM and the objective lens OB. The aberration correction liquid crystal panel LCP has a central correction region PLCCR and an annular peripheral region PLCPR, and the divided shapes thereof are a light beam including an optical axis to be transmitted (reference light) and an annular cross-section light beam (signal light) surrounding it. It substantially matches the cross-sectional shape.
<Modification>
In the above-described aberration correction liquid crystal panel LCP, the divided transparent electrode of the central correction region PLCCR is used for reference light to be corrected for wavefront aberration depending on the voltage application state, and the light beam transmitted through the annular peripheral region PLCPR is used for signal light. Although described, as a modification, the configuration of the aberration-correcting liquid crystal panel LCP and the spatial light modulator SLM does not propagate the reference light on the optical axis and the signal light around it, but conversely transmits the signal light. It is also possible to generate and propagate reference light around the optical axis. In this case, as shown in FIG. 30, the entire spatial light modulator SLM is used as a transmissive matrix liquid crystal display device, and the control circuit 26 has a central region LCCR for displaying a predetermined pattern of page data to be recorded and a ring around it. It can also be configured to display an unmodulated light transmission region of the region LCPR. The non-modulated light transmission region of the annular region LCPR can be formed from a transparent material. Further, as shown in FIG. 31, a spherical aberration correcting transparent electrode pattern, a coma aberration correcting transparent electrode pattern 13ai, etc. are formed for passing the reference light in the annular peripheral region PLCPR of the aberration correcting liquid crystal panel LCP, and the central correcting region PLCCR. The transparent electrode pattern 13aa is formed for signal light passage. That is, the configuration shown in FIG. 26 can be the same as that of the central correction region PLCCR and the annular peripheral region PLCPR except that the transparent electrode patterns are replaced.
Also in this modified example, the aberration correction liquid crystal panel LCP is used so that the polarization states of the signal light SB and the reference light RB are the same in the hologram recording layer 7 during hologram recording and differ from each other by approximately 90 ° during reproduction. You can also Therefore, the aberration-correcting liquid crystal panel LCP has the same polarized light-transmitting state in both areas at the time of hologram recording by the aberration-correcting liquid crystal driving circuit LCPD, or the central correction area PLCCR of the aberration-correcting liquid crystal panel LCP is in the off state at the time of reproduction, for example. In the annular peripheral region PLCPR, the wavefront aberration correction voltage is applied and turned on so that both regions can have different polarization action states. In this case, as shown in FIG. 32A, the parallel light beam that has passed through the spatial light modulator SLM is divided and generated into the signal light SB (light beam including the optical axis) and the reference light beam RB of the annular cross-section light beam that surrounds it. Further, the reference light RB of the annular cross section light beam is subjected to wavefront aberration and passes through the polarization beam splitter PBS and the aberration correction liquid crystal panel LCP. The recording operation (FIG. 32 (a)) and the reproducing operation (FIG. 32 (b)) are the same as the above example except that the reference light and the signal light have different propagation positions inside and outside. Even in this modification, the configuration of the objective lens module OBM as shown in FIGS. 8 to 24 can be applied.
According to the above embodiment, since the reference light RB reflected at the time of reproduction is separated or does not form an image, the reference light RB does not reach the image sensor IS, so that only the reproduction light from the hologram necessary for signal reproduction is obtained. Can receive light. As a result, the reproduction SN is improved and stable reproduction can be performed.
Servo control is not shown, but using a servo optical system including an objective lens that provides a track on the reflective layer 5 and condenses the reference light RB as a spot on the track and guides the reflected light to a photodetector, for example. This is possible by driving the objective lens optical system with an actuator in accordance with the detected servo error signal. That is, the reference light RB light beam irradiated from the objective lens is used so as to be in focus when the reflective layer 5 is positioned at the position of the beam waist.
<Hologram device>
As another embodiment, a hologram apparatus will be described as a hologram recording / reproducing system of the present invention for recording and reproducing information on a disc-shaped hologram record carrier.
FIG. 33 is a block diagram of an example of a hologram apparatus.
The hologram apparatus includes a spindle motor 22 that rotates a disk of the hologram record carrier 2 on a turntable, a pickup 23 that reads a signal from the hologram record carrier 2 by a light beam, and a pickup drive unit that holds the pickup and moves it in the radial direction (x direction). 24, a light source drive circuit 25, a spatial light modulator drive circuit 26, a reproduction light signal detection circuit 27, a servo signal processing circuit 28, a focus servo circuit 29, an xy direction moving servo circuit 30, and a pickup drive unit 24 connected to the pickup position. A pickup position detection circuit 31 that detects a signal, a slider servo circuit 32 that is connected to the pickup drive unit 24 and supplies a predetermined signal thereto, a rotation number detection unit 33 that is connected to the spindle motor 22 and detects a rotation number signal of the spindle motor, Connected to the rotation speed detector Is provided with a hologram recording rotational position detecting circuit 34 for generating a rotational position signal of the carrier 2, the aberration correcting liquid crystal drive circuit LCPD and the spindle servo circuit 35 supplies a predetermined signal connected to the spindle motor 22.
The hologram apparatus has a control circuit 37. The control circuit 37 is a light source drive circuit 25, a spatial light modulator drive circuit 26, a reproduction light signal detection circuit 27, a servo signal processing circuit 28, a focus servo circuit 29, and an xy direction movement. The servo circuit 30, the pickup position detection circuit 31, the slider servo circuit 32, the rotation speed detection unit 33, the rotation position detection circuit 34, the aberration correction liquid crystal drive circuit LCPD and the spindle servo circuit 35 are connected. Based on signals from these circuits, the control circuit 37 performs focus servo control relating to the pickup, x and y direction movement servo control, reproduction position (positions in the x and y directions), and the like via these drive circuits. The control circuit 37 is composed of a microcomputer equipped with various memories and controls the entire apparatus. Various control operations are performed according to the operation input by the user from the operation unit (not shown) and the current operation state of the apparatus. It is connected to a display unit (not shown) that generates a control signal and displays an operation status and the like to the user.
The light source drive circuit 25 connected to the hologram recording / reproducing laser light source LD1 adjusts the output of the laser light source LD1 so that the intensity of both emitted light beams is strong during hologram recording and weak during reproduction.
The control circuit 37 executes processing such as encoding of data to be recorded on the hologram input from the outside, and supplies a predetermined signal to the spatial light modulator drive circuit 26 to control the hologram recording sequence. The control circuit 37 restores the data recorded on the hologram record carrier by performing demodulation and error correction processing based on the read signal from the reproduction light signal detection circuit 27 connected to the image sensor IS. Further, the control circuit 37 reproduces the information data by performing a decoding process on the restored data, and outputs this as reproduced information data. The control circuit 37 includes an aberration correction unit 40, and determines the aberration of the reference light based on the signal received from the reproduction light signal detection circuit 27 and / or according to a predetermined processing procedure. Furthermore, the control circuit 37 determines each correction voltage Vi of the phase adjustment unit (transparent electrode) of the aberration correction liquid crystal panel LCP based on the aberration of the reference light. The control circuit 37 supplies each control signal representing the correction voltage Vi to the aberration correction liquid crystal drive circuit LCPD for driving the aberration correction liquid crystal panel LCP. The aberration correction liquid crystal drive circuit LCPD generates a drive voltage (correction voltage) to be applied to the aberration correction liquid crystal panel LCP according to the control signal, and supplies the drive voltage to the aberration correction liquid crystal panel LCP.
Furthermore, the control circuit 37 controls to form holograms at predetermined intervals so that the holograms to be recorded can be recorded at predetermined intervals (multiple intervals).
In the servo signal processing circuit 28, a focusing drive signal is generated from the focus error signal, and this is supplied to the focus servo circuit 29 via the control circuit 37. The focus servo circuit 29 drives the focusing portion of the objective lens driving unit 36 (see FIG. 35) mounted on the pickup 23 in accordance with the drive signal, and the focusing portion is the focal point of the light spot irradiated on the hologram record carrier. Operates to adjust position.
Further, in the servo signal processing circuit 28, x and y direction movement drive signals are generated and supplied to the xy direction movement servo circuit 30. The xy direction movement servo circuit 30 drives the objective lens drive unit 36 (see FIG. 35) mounted on the pickup 23 in accordance with the x and y direction movement drive signals. Therefore, the objective lens is driven by an amount corresponding to the drive current by the drive signals in the x, y, and z directions, and the position of the light spot irradiated on the hologram record carrier is displaced. As a result, the hologram formation time can be ensured by keeping the relative position of the light spot relative to the moving hologram record carrier at the time of recording.
The control circuit 37 generates a slider drive signal based on the position signal from the operation unit or pickup position detection circuit 31 and the x-direction movement error signal from the servo signal processing circuit 28, and supplies this to the slider servo circuit 32. The slider servo circuit 32 moves the pickup 23 in the radial direction of the disk via the pickup drive unit 24 in accordance with the drive current generated by the slider drive signal.
The rotation speed detection unit 33 detects a frequency signal indicating the current rotation frequency of the spindle motor 22 that rotates the hologram record carrier 2 on a turntable, generates a rotation speed signal corresponding to the spindle rotation speed, and generates a rotation position. This is supplied to the detection circuit 34. The rotational position detection circuit 34 generates a rotational position signal and supplies it to the control circuit 37. The control circuit 37 generates a spindle drive signal, supplies it to the spindle servo circuit 35, controls the spindle motor 22, and rotationally drives the hologram record carrier 2.
<Optical pickup>
FIG. 34 shows a schematic configuration of the pickup 23.
The pickup 23 includes a hologram recording optical system, a hologram reproduction optical system, and a servo control system. These systems are arranged in a housing (not shown) except for the objective lens module OBM and its drive system. Hologram recording / reproducing laser light source LD1, collimator lens CL1, spatial light modulator SLM, polarization beam splitter PBS, 4f lenses fd and fe and image sensor IS are arranged on a straight line, mirror MR, quarter wavelength plate 1 / 4λ. The 4f lens fc, the polarization beam splitter PBS, the aberration correction liquid crystal panel LCP, and the objective lens module OBM are arranged on a straight line, and these linearly arranged components are arranged orthogonally by the polarization beam splitter PBS.
<Hologram recording optical system>
The hologram recording optical system includes a hologram recording / reproducing laser light source LD1, a collimator lens CL1, a transmissive spatial light modulator SLM, a polarization beam splitter PBS, an aberration correction liquid crystal panel LCP, a 4f lens fc, a mirror MR, and a quarter wavelength plate. 1 / 4λ, as well as the objective lens module OBM.
The light emitted from the laser light source LD1 is converted into parallel light by the collimator lens CL1, and this is sequentially incident on the spatial light modulator SLM and the polarization beam splitter PBS. The polarization direction of the parallel light is a direction perpendicular to the paper surface. The spatial light modulator SLM that displays the page data to be recorded in the central region uses the light beam transmitted through the central region including the optical axis as the unmodulated reference light RB, and the surrounding annular light beam as the signal light SB. The polarization beam splitter PBS is arranged so that both the incident spatially separated reference light RB and signal light SB are reflected by the polarizing film (S-polarized light) and enter the 4f lens fc. The 4f lens fc is a lens for forming an image at the focal position (focal length fob on the optical axis) of the objective lens OB. Since it is difficult to dispose the spatial light modulator SLM at the focal position of the objective lens OB, the distance from the spatial light modulator SLM to the 4f lens fc is the focal length of the 4f lens fc. The 4f lens fc passes through the quarter-wave plate 1 / 4λ and is converted into circularly polarized light, and then is reflected by the mirror MR and incident on the quarter-wave plate 1 / 4λ again. Has been placed. As a result, the reference light RB and the signal light SB from the ¼ wavelength plate ¼λ have the polarization directions parallel to the paper surface and enter the polarization beam splitter PBS again, but the polarization directions are horizontal to the paper surface (P Polarized light) and transmitted through the polarizing beam splitter PBS. The reference light RB and the signal light SB are imaged again at the focal position of the 4f lens fc, which is equivalent to the presence of the spatial light modulator SLM at this imaging position. The aberration correction liquid crystal panel LCP is disposed at this focal position, and the focal position of the objective lens OB of the objective lens module OBM is matched. The aberration correction liquid crystal panel LCP has a TN type orientation direction of the aberration correction liquid crystal panel LCP.
As shown in FIG. 35, in the objective lens module OBM, the concave lens optical element CCV is arranged so that the concave lens action acts only on the reference light RB, and the reference objective lens OB is combined with the action of the objective lens OB. It is set so that the focal point is farther than the focal point of OB and the signal light SB is focused on the focal point of the objective lens OB without receiving the lens action. The relative position of the objective lens module OBM with respect to the hologram record carrier 2 is controlled so that the focal point of the objective lens OB of the signal light SB is located on the wavelength selective reflection layer 5 of the hologram record carrier 2.
<Hologram reproduction optical system>
As shown in FIG. 34, the hologram reproducing optical system includes a hologram recording / reproducing laser light source LD1, a collimator lens CL1, a spatial light modulator SLM, a polarization beam splitter PBS, an aberration correction liquid crystal panel LCP, an objective lens module OBM, and a 4f lens fc. , Fd and fe, mirror MR, ¼ wavelength plate ¼λ, and image sensor IS. In this optical system, the optical components other than the 4f lenses fd and fe and the image sensor IS are the same as those in the hologram recording optical system.
As shown in FIG. 34, the 4f lens fd of the hologram reproducing optical system is arranged at a position where the focal point coincides with the focal position of the objective lens OB via the polarization beam splitter PBS. Further, a 4f lens fe having a focal length similar to that of the 4f lens fd is disposed at a position on the optical axis at a distance twice the focal point from the 4f lens fd, and these constitute a so-called 4f system optical system. Since it is difficult to dispose the image sensor IS at the focal position of the objective lens OB on which a reproduction image by the reproduction light from the hologram record carrier 2 is formed, the light receiving surface of the image sensor IS that receives the reproduction light is 4f. It is arranged so as to be positioned at the focal point of the lens fe, and a reproduced image is formed on the light receiving surface of the image sensor IS to obtain a reproduced signal. By reproducing this, the recorded signal can be reproduced.
<Hologram record carrier>
As shown in FIG. 35, the hologram record carrier 2 includes a protective layer 8, a hologram recording layer 7, a separation layer 6, a wavelength selective reflection layer 5, a second separation layer 4, and a servo guide layer as viewed from the reference light incident side. 9 and a substrate 3 onto which addresses and track structures are transferred. The wavelength selective reflection layer 5 is made of a dielectric laminate that transmits the servo beam SVB and reflects only the reflection wavelength band including the wavelengths of the reference light and the signal light. Servo grooves or pits are formed on the servo guide layer 9 as servo marks T such as a plurality of tracks extending without being separated from each other. The pitch Px (so-called track pitch) of the servo marks T of the servo guide layer 9 is set as a predetermined distance determined from the multiplicity of the hologram HG recorded above the spot of the signal light and the reference light. The width of the servo mark T is appropriately set according to the output of the photodetector that receives the reflected light from the light spot of the servo beam SVB, for example, a push-pull signal. Positioning (focus servo, xy direction servo) on the hologram record carrier 2 for performing hologram recording / reproduction by following the servo beam SVB on the servo mark T of the servo guide layer 9 of the hologram record carrier 2 shown in FIG. Do. A tracking servo or the like can be performed by reproducing a guide track signal such as a focus servo or a pre-recorded group or pit.
<Servo control system>
The servo control system is for servo-controlling (moving in the xyz direction) the position of the objective lens module OBM with respect to the hologram record carrier 2, and as shown in FIG. 34, the second laser light source LD2 that emits the servo beam SVB, the adjustment lens CL2 , Half mirror MR, dichroic prism DP, polarizing beam splitter PBS, objective lens module OBM, coupling lens AS, and photodetector PD.
The second laser light source LD2 has a wavelength (servo beam SVB) different from the wavelength of the recording / reproducing laser. The servo beam SVB is light having a wavelength insensitive to the hologram recording layer 7 other than the sensitive wavelength bands of the signal light and the reference light.
The servo control system is coupled to the hologram reproducing optical system by a dichroic prism DP disposed between the 4f lenses fc and fe in the 4f system optical system. That is, the second laser light source LD2, the adjusting lens CL2, and the like so that the servo beam SVB from the second laser light source LD2 is reflected by the half mirror MR, reflected by the dichroic prism DP, and combined with the light beam of the reproducing optical system. The half mirror MR and the dichroic prism DP are arranged. The adjustment lens CL2 is set so that the servo beam SVB becomes parallel light before the objective lens module OBM by being combined with the detection system 4f lens 4fd.
As shown in FIG. 35, in the objective lens module OBM, the diameter (da) of the servo beam SVB is set to be equal to or smaller than the diameter (db) of the light beam of the reference light RB. Therefore, the relationship between the outer diameter (dc) and inner diameter (dd) of the signal light SB and these diameters is dc>dd> db ≧ da. Here, when the structure serving as a recording guide such as recording interval (multiple interval) and track pitch is wider (larger) than those of a normal optical disc, the aberration of the servo beam SVB and the beam diameter of the servo beam SVB are reduced. Lowering the numerical aperture NA does not significantly affect reading.
As shown in FIG. 34, since the polarization direction of the servo beam SVB is set to be perpendicular to the paper surface, the servo beam SVB is incident on the objective lens module OBM without being affected by the aberration correction liquid crystal panel LCP.
As shown in FIG. 35, in the objective lens module OBM, in combination with the concave lens optical element CCV and the objective lens OB, the servo beam SVB is condensed farther than the wavelength selective reflection layer 5 of the hologram record carrier 2, that is, wavelength selection is performed. It is set together with the hologram record carrier 2 so as to be focused on the servo guide layer 9 which has passed through the reflective reflecting layer 5 and formed the servo mark T. Here, the concave lens optical element CCV is set so that the servo beam SVB is focused on the servo guide layer 9 without aberration at the wavelength in combination with the objective lens OB.
The servo beam SVB passes through the wavelength selective reflection layer 5, reaches the servo guide layer 9, and is reflected by the servo guide layer 9.
The reflected light of the servo beam SVB reflected by the servo guide layer 9 and returning through the objective lens module OBM reaches the half mirror MR through the same optical path from the polarization beam splitter PBS to the dichroic prism DP as indicated by 34. Then, the light enters the photodetector PD through the servo signal generation optical system.
In the photodetector PD, a focus servo signal can be obtained by an astigmatism method using, for example, a cylindrical lens, and a push-pull tracking error signal can be obtained by reading a servo mark T formed on the servo guide layer 9. You can also get It is also possible to read an address signal formed by a pit row or the like.
In this way, the servo control condenses the servo beam SVB as a light spot on the track on the servo guide layer 9 through the objective lens module OBM, and guides the reflected light to the photodetector PD, where it is detected. The objective lens module OBM is driven by the actuator of the objective lens driving unit 36 in accordance with the received signal.
As shown in FIG. 35, since the wavelength selective reflection layer 5 is on the objective lens OB side (light irradiation side) with respect to the servo guide layer 9, the signal light and the reference light are reflected. Since the diffracted light of the signal light and the reference light by the (servo mark T) is not generated, the influence of the diffracted light is reduced, and the hologram reproduction with good SN can be performed.
<Recording and playback operation>
The light emitted from the laser light source LD1 is converted into parallel light by the collimator lens CL1, and this is sequentially incident on the spatial light modulator SLM and the polarization beam splitter PBS. At the time of recording, the parallel light which is divided by the spatial light modulator SLM which displays the page data to be recorded in the annular area and is unmodulated in the central area and becomes the reference light RB and the signal light SB is reflected by the polarization beam splitter PBS, respectively. The light is reflected by the quarter-wave plate ¼λ and the mirror MR, and returns to the polarizing beam splitter PBS and is transmitted therethrough. The transmitted reference light RB and signal light SB enter the aberration correction liquid crystal panel LCP.
At the time of recording, the same voltage is applied to the transparent electrodes in the central correction area PLCCR and the annular peripheral area PLCP of the aberration correction liquid crystal panel LCP shown in FIG. Therefore, no polarization action occurs in the aberration-correcting liquid crystal panel LCP, the transmitted signal light SB and reference light RB do not receive the polarization action, and their polarization directions (parallel to the paper surface) do not change.
The signal light SB and the reference light RB transmitted through the aberration correction liquid crystal panel LCP enter the objective lens module OBM with the same polarization direction. Since the signal light SB is not affected by the concave lens optical element CCV, it is condensed at the focal point of the original objective lens OB, and the reference light RB is condensed further away from the focal point due to the concave lens action.
Since the wavelength selective reflection layer 5 of the hologram record carrier 2 is set so as to reflect the light beam having the wavelength of the recording / reproducing laser, the signal light SB is condensed and reflected on the wavelength selective reflection layer 5. . On the other hand, the reference light RB is reflected by the wavelength selective reflection layer 5 in a defocused state. A region where the signal light SB and the incident reference light RB overlap is generated, and interference between the reference light RB and the signal light SB occurs in this region. By placing the hologram recording layer 7 in this region (the region on the objective lens side from the focal point of the signal light SB and where the incident reference light RB and the signal light SB overlap), the hologram recording layer 7 has a hologram. Is recorded.
At the time of reproduction, as shown in FIG. 36, the light emitted from the laser light source LD1 is shielded by the annular region of the spatial light modulator SLM, and only the light beam including the optical axis is transmitted without modulation in the central region, thereby generating the reference light RB. The reference light RB is made to reach the central correction area PLCCR of the aberration correction liquid crystal panel LCP by following the same optical path as that during recording. Here, a correction voltage corresponding to the distribution shape of the aberration generated in the reference light is applied to the plurality of divided transparent electrodes of the phase adjustment unit of the aberration correction liquid crystal panel LCP, and the annular peripheral region PLCPR is turned off (no voltage is applied). The central correction area PLCC is left in the ON state. Since the reference light RB is incident on the hologram recording layer 7 with the polarization direction being parallel to the paper surface, the reproduced light to be reproduced is the same divergent and convergent light beam as the signal light at the time of recording and has a polarization direction parallel to the paper surface. Therefore, the reproduction light is transmitted through the annular peripheral region PLCPR of the aberration correction liquid crystal panel LCP, so that it receives a polarization action and the polarization direction becomes perpendicular to the paper surface. On the other hand, the reference light RB is reflected by the wavelength-selective reflection layer 5 while being parallel to the paper surface, but has no polarization action in the liquid crystal, and therefore the polarization direction differs from that of the reproduction light. Therefore, since the polarization of the reproduction light is changed, it is reflected by the polarization beam splitter PBS because it is perpendicular to the paper surface, but the signal light SB is transmitted therethrough. The separated reproduction light forms an image on the light receiving surface of the image sensor IS through the 4f lenses fd and fe of the detection system to obtain a reproduction image, and the image sensor IS outputs a reproduction signal.
<Hologram recording and playback method>
In the present embodiment of FIG. 34, a hologram recording / reproducing method will be described.
When the aberration correction amount determined at the time of hologram recording and the polarization of the reproduction light is changed, hologram recording is performed according to the flowchart shown in FIG.
First, after the hologram record carrier is loaded in the apparatus, the focus / tracking (zx direction) servo and the spindle servo are operated, and the focal point of the objective lens acquires predetermined servo mark position information of the hologram record carrier (step) S1) The pickup is moved to the recording area so as to match the position (step S2).
Next, the position servo (y direction) is operated to bring the light beam and the recording layer 7 into a relatively stationary state (step S3).
Next, when irradiating the hologram recording carrier with the reference light and the signal light, the correction voltage for correcting the reference light aberration is not applied (step S4), and the central correction region PLCCR and the annular peripheral region of the aberration correction liquid crystal panel LCP are applied. The same voltage is applied to the PLCP transparent electrode to turn it on (step S5). Then, a predetermined amount of information data to be recorded is supplied to the spatial light modulator, the output of the laser light is increased, the signal light and the reference light are irradiated onto the hologram record carrier, and hologram recording is started (step S6). .
Next, it is determined whether or not the recording of the information data is continued (step S7). If the recording is continued, the process returns to step S2, and if the recording is finished, the process ends.
When the aberration correction amount determined at the time of hologram reproduction is changed and the polarization of the reproduction light is changed, the reproduction of the hologram is performed according to the flowchart shown in FIG.
First, after the hologram record carrier is loaded in the apparatus, the focus / tracking (zx direction) servo and the spindle servo are operated, and the focal point of the objective lens acquires predetermined servo mark position information of the hologram record carrier (step) S11) The pickup is moved to the reproduction area so as to match the position (step S12).
Next, the position servo (y direction) is operated to make the light beam and the recording layer 7 relatively stationary (step S13).
Next, when irradiating the hologram record carrier with only the reference light, a correction voltage for correcting the reference light aberration is applied to correct the aberration in the reference light region (step S14). At the same time, the central correction region PLCCR of the aberration correction liquid crystal panel LCP is turned on and the annular peripheral region PLCP (signal light region) is turned off (step S15), so that the reproduction light can be separated by polarization. In this aberration correction of the reference light, the state change due to the non-recording / recording of the recording layer 7 is recorded in advance in the memory of the control circuit 37, and the aberration correction unit 40 sets the aberration correction amount corresponding thereto according to the aberration correction liquid crystal drive circuit LCPD. Thus, the aberration correction liquid crystal panel LCP corrects the aberration of the reference light. Here, in particular, problems peculiar to the hologram record carrier, for example, aberration due to shrinkage of the hologram record carrier and changes in the refractive index are corrected. Therefore, it is effective when an amount by which the refractive index of the recording layer changes after recording due to the characteristics of the recording layer of the hologram record carrier is expected in advance.
Next, the output of the laser beam is raised and only the reference light is irradiated onto the hologram record carrier to start hologram reproduction (step S16).
Next, it is determined whether or not the reproduction of the information data is continued (step S17). If the reproduction is continued, the process returns to step S12, and if the reproduction is finished, the process ends.
In the process shown in FIGS. 37 and 38, if it is not necessary to change the polarization of the reproduction light, the steps of steps S5 and S15 may be omitted and all the aberration-correcting liquid crystal panels LCP may be kept on.
When the aberration correction amount is determined by the quality of the reproduction signal at the time of reproducing the program, the hologram is reproduced according to the flowchart shown in FIG.
First, steps S21 to S23 are executed in the same manner as the recording process shown in FIG.
Next, hologram reproduction is started by irradiating the hologram record carrier with only the low-power laser beam reference light (step S24).
Next, the correction voltage for correcting the reference light aberration is applied, and the aberration correction is performed in the reference light region (step S25).
Next, in order to evaluate the quality of the reproduction signal based on the aberration correction amount, the SNR or error rate of the reproduced image is acquired (step S26). For example, the page data recorded on the recording layer 7 is represented by a white level where “1” is a pixel which transmits the incident light of the spatial light modulator SLM, and a black level where “0” is a pixel which blocks the incident light. Since it is recorded as representing, the SNR of the reproduced image is calculated by the following equation.

(In the formula, m1 represents the average light amount at the black level, m2 represents the average light amount at the white level, σ1 represents the standard deviation of the black level, and σ2 represents the standard deviation of the white level.)
Next, an optimum correction value search is performed based on whether the SNR or error rate of the acquired image exceeds a predetermined value recorded in advance in the memory of the control circuit 37 (step S27). If the acquired value is less than the predetermined value, the process returns to step S24. If the acquired value exceeds the predetermined value, the search ends, and the process proceeds to the next to determine a reference light aberration correction value (step S28).
Next, while performing aberration correction in the reference light region based on the reference light aberration correction value, the output of the laser light is increased and only the reference light is irradiated onto the hologram record carrier to start hologram reproduction (step S29).
Next, it is determined whether or not the reproduction of the information data is continued (step S30). If the reproduction is continued, the process returns to step S22, and if the reproduction is finished, the process ends.
Here, since the aberration due to the shrinkage and the change in refractive index peculiar to the hologram record carrier is corrected according to the recording state of the hologram record carrier, it is effective for reproducing various hologram record carriers. In addition, when the hologram reading quality deteriorates due to the shrinkage of the hologram record carrier, etc., the wavefront control of the reference light seems to be effective. Is expected. Therefore, it is effective to prevent the aberration correction effect of the liquid crystal from acting on the servo beam.
As described above, the transparent electrode of the aberration-correcting liquid crystal panel LCP has a division suitable for correcting according to the aberration when distortion, thickness error, inclination, etc. occur in the hologram record carrier or the like. Thus, aberration correction of the reference light can be performed.
As described above, in the prior art, the reference light for holographic recording is a parallel light beam, but in this embodiment, the signal light and the reference light are diverged or convergent light so that their focal positions are different by a specific objective lens module. In addition, the polarization state is switched between recording and reproduction using a specific aberration correction device such as an aberration correction liquid crystal panel. Also, in this objective lens module, a specific optical element combined with the objective lens is set so that a servo beam using a wavelength different from the recording / reproducing laser wavelength is condensed without aberration on the servo guide layer of the hologram record carrier. Has been. Furthermore, in the prior art, it was necessary to change the optical system for recording and reproduction, but in the present embodiment, the same effect can be obtained by controlling the voltage applied to the aberration correction liquid crystal panel.
In the prior art, since the reference light is parallel light, shift multiplex recording is impossible and the recording capacity is small. However, in the present embodiment, a high-quality reproduction signal can be obtained by making the reference beam RB the convergent beam and enabling shift multiplexing. This is particularly effective when the wavefront of the reference light during recording differs from the wavefront of the reference light during reproduction due to shrinkage of the hologram recording layer or change in refractive index after recording. Further, since the aberration is removed by the combination of the optical element and the objective lens at the wavelength of the servo beam SVB, the servo signal can be reproduced satisfactorily.
Furthermore, space can be saved by arranging the combined optical path of the servo beam in the detection system 4f system, and the effective diameter of the prism and the like can be reduced because the combining prism can be arranged in the condensing system.
<Other pickup variations>
FIG. 40 shows another pickup configuration.
This pickup removes the mirror MR, the quarter wave plate 1 / 4λ, and the 4f lens fc in the pickup shown in FIG. 34, and instead of the transmissive spatial light modulator SLM, a reflective polarization space is provided at these positions. The optical modulator PSLM is arranged, and the light beam from the hologram recording / reproducing laser light source LD1 is incident on the polarization spatial light modulator PSLM through the polarization beam splitter PBS and the reflected light is used. . Therefore, the recording / reproducing operation is performed in the same manner as the pickup 23.
As shown in FIG. 41, the polarization spatial light modulator PSLM is a so-called LCOS (Liquid) divided into a central region A including the optical axis and a spatial light modulating region B not including the optical axis in the vicinity of the optical axis. Crystal On Silicon) device. When the reflected light beam is modulated by polarized light that rotates by 90 degrees, and the polarization spatial light modulator PSLM reflects the light beam, the light beam is spatially modulated in the spatial light modulation region B and in the space of the central region A. The reference beam RB which is not modulated is separated on the same axis.
The polarization spatial light modulator PSLM has a function of electrically polarizing a part of incident light for each pixel in a liquid crystal panel having a plurality of pixel electrodes divided in a matrix. This polarization spatial light modulator PSLM is connected to the spatial light modulator drive circuit 26, and modulates the light beam polarization so as to have a distribution based on the page data to be recorded from now, and generates the signal light SB having an annular cross section. . In addition, since the polarization spatial light modulator PSLM can maintain the same polarization by incidence and reflection, if the reflection state is maintained while maintaining the modulation state only in the spatial light modulation region B, the polarization beam splitter PBS and Thus, only the reference light that is not spatially modulated in the central area A can be supplied to the objective lens module OBM.

Claims (20)

An optical pickup device that records or reproduces information on a hologram record carrier having a hologram recording layer that stores therein an optical interference pattern of reference light and signal light as a diffraction grating,
A light source that generates coherent light;
The coherent light comprises a central region disposed on the optical axis and an annular region disposed so as to surround the central region, and the coherent light passes through the central region and the annular region. A spatial light modulator that spatially separates components to generate reference light and signal light and propagates them in the same direction on the same axis;
An objective lens optical system that is arranged on an optical axis and irradiates the signal light and the reference light to the hologram recording layer on a coaxial axis and collects the reference light and the signal light at different focal points;
An image detecting means for receiving light that is arranged on an optical axis and returns from the hologram recording layer via the objective lens optical system when the reference light is irradiated onto the hologram recording layer;
A central correction region disposed on the optical axis and an annular peripheral region disposed so as to surround the central correction region, wherein at least one of the central correction region and the annular peripheral region partially includes a phase of a wavefront of a passing light beam; An aberration correction device comprising a transmissive liquid crystal device including a plurality of transparent electrodes for correcting wavefront aberrations of the passing light flux to be changed in an automatic manner,
An optical pickup device comprising:   2. The optical pickup device according to claim 1, wherein the spatial light modulator is made of a transmissive matrix liquid crystal display device, and the central region is made of a through opening or a transparent material.   2. The spatial light modulator comprises a transmissive matrix liquid crystal display device, the central region also comprises a transmissive matrix liquid crystal display device, and the central region is in a translucent state during recording. Optical pickup device.   4. The optical pickup according to claim 2, wherein the central correction area is formed of the transmissive liquid crystal device, and corrects wavefront aberration of the passing light beam at least during recording and during reproduction. apparatus.   5. The optical pickup device according to claim 4, wherein the wavefront aberration of the passing light beam is corrected only during reproduction.   2. The optical pickup device according to claim 1, wherein the spatial light modulator is made of a transmissive matrix liquid crystal display device, and the annular region is made of a through opening or a transparent material.   2. The spatial light modulator comprises a transmissive matrix liquid crystal display device, the annular region also comprises a transmissive matrix liquid crystal display device, and the annular region is in a light-transmitting state during recording. Optical pickup device.   8. The optical pickup according to claim 6, wherein the annular peripheral region is formed of the transmissive liquid crystal device, and corrects wavefront aberration of the passing light beam at least during recording and during reproduction. apparatus.   9. The optical pickup device according to claim 8, wherein the wavefront aberration of the passing light beam is corrected only during reproduction.   The optical pickup device according to claim 1, wherein the aberration correction device makes rotation angles of polarization planes of passing components of the central correction region and the annular peripheral region different from each other.   The objective lens optical system is a bifocal lens having a convex or concave lens, a Fresnel lens surface having a convex or concave lens function, or a diffraction grating formed integrally with a condenser lens and coaxially on a refractive surface thereof. The optical pickup device according to claim 1.   The objective lens optical system is a transmissive optical element having a condenser lens and a convex or concave lens arranged coaxially with the condenser lens, or a Fresnel lens surface having a convex or concave lens action or a diffraction grating. The optical pickup device according to claim 1.   The optical pickup device according to claim 1, wherein the plurality of transparent electrodes are arranged in a concentric pattern centered on the optical axis.   The plurality of transparent electrodes are arranged in a pattern of inner and outer regions that are symmetrical with respect to a straight line perpendicular to the optical axis and divided by a gap including the straight line. The optical pick-up apparatus in any one. A hologram recording / reproducing system for recording or reproducing information to / from a hologram record carrier that stores therein an optical interference pattern of reference light and signal light as a diffraction grating,
Light generating means for generating, from coherent light, reference light and signal light obtained by modulating the coherent light according to recording information;
One of the reference light and the signal light is on the optical axis, the other is annularly formed around the one, spatially separated from each other and propagated coaxially in the same direction, via the objective lens optical system, Interference means for condensing the reference light and the signal light at different focal points on an optical axis and interfering the reference light and the signal light;
A hologram recording carrier having a hologram recording layer located on the focal side near the objective lens optical system among the different focal points;
A reflective layer located on the focal side far from the objective lens optical system among the different focal points;
An image detecting means for receiving light that is arranged on an optical axis and returns from the hologram recording layer via the objective lens optical system when the reference light is irradiated onto the hologram recording layer;
A central correction region disposed on the optical axis and an annular peripheral region disposed so as to surround the central correction region, wherein at least one of the central correction region and the annular peripheral region partially includes a phase of a wavefront of a passing light beam; An aberration correction device comprising a transmissive liquid crystal device including a plurality of transparent electrodes for correcting wavefront aberrations of the passing light flux to be changed in an automatic manner,
A hologram recording / reproducing system, comprising: an aberration correction liquid crystal driving circuit that supplies a correction voltage to each of the plurality of transparent electrodes when information is recorded or reproduced.   The hologram recording layer has a film thickness sufficient to generate a diffraction grating by causing one of the reference light and the signal light to be in a defocused state on the reflective layer and reflected to intersect and interfere with the other. 16. The hologram recording / reproducing system according to claim 15, further comprising:   The hologram recording / reproducing system according to any one of claims 15 to 16, wherein the hologram record carrier is formed as an integrated body in which a separation layer is laminated between the hologram recording layer and the reflective layer.   The aberration correction device has a function of making the rotation angles of the polarization planes different at the time of recording or reproducing information, and the aberration correction liquid crystal driving circuit is configured to have the central correction region and the annular shape with respect to the aberration correction device. 18. The hologram recording / reproducing system according to claim 15, wherein control is performed to make the rotation angles of the polarization planes of the passing components in the surrounding area different from each other.   The plurality of transparent electrodes are arranged in a concentric pattern with the optical axis as a center, and the aberration correction liquid crystal driving circuit supplies a correction voltage corresponding to a spherical aberration to be corrected. The hologram recording / reproducing system according to claim 18.   The plurality of transparent electrodes are arranged in a pattern of inner and outer regions that are symmetric with respect to a straight line perpendicular to the optical axis and divided by a gap including the straight line, and the aberration correction liquid crystal drive circuit includes a frame to be corrected. The hologram recording / reproducing system according to claim 15, wherein a correction voltage corresponding to the aberration is supplied.

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