JP3984055B2 - Write-once hologram memory - Google Patents

Description

【００３５】
となればよい。Ｕm'n'は、空間光変調器４５の第m'行、第n'列の画素に対応する光電磁場であり、スカラー複素表示されている。ｉは虚数単位、ｋは光の波数、Ｌｍ，Ｌｎはホログラム画像Ｉｍの画素ピッチ、Ｄm'，Ｄn'は空間光変調器４１，４５の画素ピッチ、ｌは空間光変調器４５と結像面４４との距離である。また、Ｃ，ｓk，ｓyは実定数である。
【００３６】
このとき、空間光変調器４１に入力する振幅Ｔm'n'は、
【００３７】
【数２】

【００３８】
となる。また、空間光変調器４５では、
【００３９】
【数３】

【００４０】
だけ位相を進めれば良い。なお、位相θm'n'は、上式を２πで割ったときの剰余でもよい。
【００４１】
図６に示した第３の実施形態にかかる高速データ光生成装置において、空間光変調器４１と凸レンズ４２，４３とを省略することもできる。すなわち、光波の振幅変調は行わず、位相のみを変調する。このために理想的な光波の合成はできないが、振幅変調よりも位相変調の方が光波面生成への寄与が大きく、多少のノイズを除いて、十分なホログラム像を生成することができる。この構成によれば、第２の実施形態と同様に、レンズ系を必要としない安価な装置により、ライトワンスホログラムメモリに書込みと読み出しを行うことができる。
【００４２】
本実施形態によれば、複雑なレンズ群を必要としない装置により、ライトワンスホログラムメモリに書き込みを行うことができ、かつ、複雑なレンズ群を必要とせず読み出しも行うことができる。
【００４３】
【発明の効果】
以上説明したように、本発明によれば、情報を書き込むコア層に導波光として導入したゲート光と、情報が重畳され平面型光導波路の界面から導入したデータ光とにより、情報を書き込むコア層に、２光子吸収によるホトクロミック現象を生じさせ、導波光の散乱要因を形成することにより、１度だけ前記情報の書込を行うので、プログラム可能な読み出し専用のホログラムメモリが可能となる。
【００４４】
また、本発明によれば、複雑なレンズ群を必要としないことから、ライトワンスホログラムメモリに対する情報の書込や読み出しが容易になり、プログラム済みライトワンスホログラムメモリの生産効率が向上するとともに、読み出し専用装置の小型化を図ることが可能となる。
【図面の簡単な説明】
【図１】本発明の一実施形態にかかるライトワンスホログラムメモリを示した構造図である。
【図２】本発明の一実施形態にかかるライトワンスホログラムメモリに情報を書き込む方法を説明するための図である。
【図３】ライトワンスホログラムメモリに書き込む情報からデータ光を生成する手順を示したフローチャートである。
【図４】本発明の第１の実施形態にかかる高速データ光生成装置の光学系を示した構成図である。
【図５】本発明の第２の実施形態にかかる高速データ光生成装置の光学系を示した構成図である。
【図６】本発明の第３の実施形態にかかる高速データ光生成装置の光学系を示した構成図である。
【符号の説明】
１０ ライトワンスホログラムメモリ
１１ａ，１２ａ，１３ａ，１４ａ，１５ クラッド層
１１ｂ，１２ｂ，１３ｂ，１４ｂ コア層
１６ 基板
２０ 再生照明光光源
３１ シリンドリカルレンズ
３２ ビームスプリッタ
３３ ゲート光光源
４０ 高速データ光生成装置
４１，４５ 空間光変調器
４２，４３ 凸レンズ
４４ 結像面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a write-once hologram memory, and more particularly to a write-once hologram memory that is a programmable read-only hologram memory.
[0002]
[Prior art]
Conventionally, magnetic cards and IC cards are known as card-type information recording media. A magnetic card records information on a magnetic tape attached to the card, and can be easily manufactured and mass-produced, but has a drawback that it has a small storage capacity and is easily counterfeited. An IC card records information on an IC chip built in the card, and has a drawback that it has a large storage capacity and is difficult to forge, but the bit unit price is expensive.
[0003]
Therefore, a hologram memory has been devised that has a larger storage capacity than an IC card, is difficult to forge, and has a low bit unit price. For example, Japanese Patent Laid-Open No. 9-101735 discloses a hologram memory in which optical waveguides are laminated in multiple layers. However, in order to write information in such a hologram memory or to read out stored information, a writing device and a reproducing device having a complicated optical system are necessary.
[0004]
Japanese Laid-Open Patent Publication No. 11-345419 describes a read-only multiplex hologram information recording medium in which single mode planar optical waveguides are stacked in multiple layers. This information recording medium is provided with a periodic scattering factor having a period substantially equal to the period of the waveguide mode of the single mode planar optical waveguide. When guided light is introduced into an arbitrary optical waveguide, a hologram is formed by diffracted light diffracted out of the waveguide due to periodic scattering factors. In this way, it is described that a reproducing apparatus having a complicated optical system is not required for reading information. This information recording medium is described as having a storage capacity of about 130 GB, having a size of a business card and 100 layers of planar optical waveguides laminated.
[0005]
[Problems to be solved by the invention]
However, the read-only multiplex hologram memory is a read-only memory and has a problem that it cannot be written. For example, as described in Japanese Patent Laid-Open No. 2001-83865, a hologram master is created for each layer of a planar optical waveguide. By using a device called a stamper, a planar optical waveguide is created for each layer from the hologram master, and this is laminated to create a hologram memory. According to this method, a large number of hologram memories in which the same information is written can be produced by the stamper. That is, small-variety mass production is possible. However, it is not suitable for high-mix low-volume production in which a wide variety of information is written in a hologram memory.
[0006]
The present invention has been made in view of such problems, and an object of the present invention is to provide a write-once hologram memory that is a so-called programmable read-only hologram memory that can be written only once. It is in.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a multi-layered planar optical waveguide having a core layer formed of a recording material that generates a photochromic phenomenon by two-photon absorption. A write-once hologram memory, wherein the information is written by the gate light introduced as guided light into the core layer for writing information and the data light introduced from the interface of the planar optical waveguide with the information superimposed thereon In addition, the photochromic phenomenon due to the two-photon absorption is generated, and the information is written only once by forming the scattering factor of the guided light, and is introduced into the core layer where the information is written as the guided light. The reproduction illumination light is diffracted out of the planar optical waveguide due to the scattering factor to form a hologram image obtained by two-dimensionally encoding the information. Data beam, wherein the laser beam modulated based on the amplitude distribution and phase distribution determined so as to form a holographic image, characterized in that it is introduced from the interface of the planar optical waveguide.
[0008]
The invention according to claim 2 is characterized in that the recording material according to claim 1 is composed of a diarylethene molecule.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0012]
FIG. 1 shows the structure of a write-once hologram memory according to an embodiment of the present invention. The write-once hologram memory 10 has a structure in which a clad layer 11a, a core layer 11b, a clad layer 12a, a core layer 12b, a clad layer 13a, and a core layer 13b are sequentially laminated on a substrate 16 from the bottom. A clad layer 15 is provided. In each core layer, a scattering factor, that is, a hologram having a period substantially equal to the period of the waveguide mode of the optical waveguide is formed. The scattering factor modulates the refractive index of the core layer, thereby superimposing information in advance.
[0013]
With such a configuration, the reproduction illumination light IL is introduced from the reproduction illumination light source 20 into an arbitrary core layer, that is, the core layer 13b in FIG. The reproduction illumination light IL propagates as guided light in the in-plane direction of the core layer 13b, is scattered by the hologram, and is emitted from the surface of the write-once hologram memory 10 as diffracted light DL. A hologram image Im is formed on the image plane by the diffracted light DL.
[0014]
For example, as in the multilayer waveguide read-only memory card described in Japanese Patent Application Laid-Open No. 11-337756, information can be read out by capturing a hologram image Im with a two-dimensional photodetector such as a CCD. In this way, by directly detecting the hologram image Im with the two-dimensional photodetector, a special lens group for reading information becomes unnecessary.
[0015]
For the core layers 11b to 14b, diarylethene-based materials that generate a photochromic phenomenon by two-photon absorption were used. A photochemical reaction absorbs energy in units of photons, and usually generates a one-photon reaction in which one photon is absorbed by a compound. On the other hand, the two-photon absorption material has a non-linear absorption characteristic with respect to the light intensity, and generates a two-photon reaction when irradiated with light having a very strong intensity. The photochromic phenomenon refers to a phenomenon in which the absorption spectrum of a crystal, molecule, complex, or the like reversibly changes upon irradiation with light. A diarylethene-based material usually has absorption in a wavelength region of 450 nm or less, causes a two-photon reaction with light having a wavelength of 760 nm, and also absorbs in the vicinity of 500 to 600 nm. The diarylethene-based material is described as a three-dimensional recording material using a photochromic phenomenon by Irie et al., For example, on page 3987 of Japanese Applied Physics Vol. 35 (1993). A method for forming a hologram on the core layers 11b to 14b using such a material will be described below.
[0016]
FIG. 2 shows a method for writing information to the write-once hologram memory according to one embodiment of the present invention. In order to write information into the write-once hologram memory 10, the gate light GL and the data light WL are required. The gate light GL enters from the gate light source 33 through the beam splitter 32 and the cylindrical lens 31 as waveguide light of the core layer for writing information. The data light WL is output from the high-speed data light generation device 40, introduced from the interface of the write-once hologram memory 10, and passes through each core layer of the write-once hologram memory 10.
[0017]
FIG. 2 also shows a reproduction illumination light source 20 that outputs reproduction illumination light IL for reading information. The wavelength is 633 nm. On the other hand, the read-only device need only include the reproduction illumination light source 20, and for example, by applying a waveguide type optical head described in Japanese Patent Application Laid-Open No. 2001-66621, a smaller read-only device can be used. An apparatus can be realized.
[0018]
FIG. 3 is a flowchart showing a procedure for generating data light from information written in the write-once hologram memory. Information to be written in the write-once hologram memory 10 is generated as one-dimensional digital data (S301), and an error correction code is added (S302). The digital data is two-dimensionally encoded for each core layer and expressed as a light-dark distribution on a two-dimensional surface (S303). Further, a servo signal serving as a synchronization signal at the time of reading is added (S304), and the write-once hologram memory 10 becomes a hologram image Im to be diffracted.
[0019]
Next, wavefront calculation for obtaining the light intensity distribution in the waveguide from the hologram image Im is performed (S305). Wavefront calculation refers to obtaining the amplitude distribution and phase distribution of the electric field of light. Data light WL on which information to be written to the write-once hologram memory is superimposed is generated by modulating the plane wave laser beam based on the obtained amplitude distribution and phase distribution (S306). Details of the high-speed data light generation device 40 will be described later with reference to FIG.
[0020]
The gate light GL and the data light WL are lights having the same wavelength, and the diarylethene-based material forming the core layer has a wavelength of 760 nm that causes two-photon absorption. The gate light GL is plane light with a constant intensity, and the data light WL is light modulated so as to generate the hologram image Im. Therefore, the gate light GL and the data light WL are combined to generate a predetermined light. Two-photon absorption occurs only in the region having the light intensity, and the absorption spectrum of the core layer changes. In this way, in the core layer into which the gate light GL is introduced, a periodic scattering factor, that is, a hologram is formed only in a predetermined region through which the data light WL is transmitted.
[0021]
The write-once hologram memory described above applies a two-photon writing technique. However, since a diarylethene material is used as a recording medium, information can be erased by irradiating erasing light. Therefore, the hologram memory described above can also be used as a rewritable hologram memory.
[0022]
FIG. 4 shows an optical system of the high-speed data light generating device according to the first embodiment of the present invention. As the optical system of the high-speed data light generation device 40, for example, an optical system described in Japanese Patent Laid-Open No. 2001-83865 can be applied. The optical system of the high-speed data light generating device 40 includes a spatial light modulator 41 and convex lenses 42 and 43. In this configuration, if the focal distance between the convex lens 42 and the convex lens 43 is f, the distance between the spatial light modulator 41 and the convex lens 42 is f, and the distance between the convex lens 42 and the convex lens 43 is 2f. The spatial light modulator has minute rectangular pixels arranged in a matrix, and can individually electrically control the light transmittance (or reflectance) of each rectangular pixel. The spatial light modulator is also used as a main part of a projector apparatus which is a kind of large-area computer display.
[0023]
With such a configuration, when the plane wave laser beam RL is incident on the spatial light modulator 41 on which the hologram image Im is displayed, light including image information is output. The output light passes through the two convex lenses 42 and 43 in order, and then forms an image in a plane separated from the convex lens 43 by the distance f, and the image displayed on the spatial light modulator 41 is reproduced. This plane is referred to as an imaging plane 44. As shown in FIG. 4, the write-once hologram memory 10 is placed between the imaging surface 44 and the convex lens 43, and information is recorded by the above-described method using the light emitted from the convex lens 43 as the data light WL.
[0024]
When the reproduction illumination light IL is introduced into the write-once hologram memory 10 on which information is recorded in this way and hologram reproduction is performed, diffracted light that forms an image on the imaging plane 44 is generated. Therefore, the recorded information can be read by aligning the light detection surface of the two-dimensional photodetector with the imaging surface 44.
[0025]
Since recording is performed using the high-speed data light generator shown in FIG. 4 in this way, information can be directly read out only by a two-dimensional photodetector, so that a lens group for reading out information is not necessary. Thus, an inexpensive information reading device can be realized.
[0026]
In the high-speed data light generator, the convex lenses 42 and 43 constitute an imaging optical system that reproduces an image displayed on the spatial light modulator 41 on the imaging surface 44. This imaging optical system is one of the simplest, but there are many known imaging optical systems having similar functions as represented by commercially available cameras. It is not limited to the type of optical system.
[0027]
FIG. 5 shows an optical system of a high-speed data light generating apparatus according to the second embodiment of the present invention. The optical system of the high-speed data light generating apparatus according to this embodiment is also described in Japanese Patent Laid-Open No. 2001-83865. The optical system of the high-speed data light generation device 40 is composed of only the spatial light modulator 41. The spatial light modulator 41 is fixed at a position corresponding to the image plane 44 shown in FIG.
[0028]
With such a configuration, when the plane wave laser beam RL is incident on the spatial light modulator 41, light including image information is output as in the first embodiment. Incident. At the same time, the gate light GL is incident and information is recorded. In the second embodiment, the light including the image information travels in the opposite direction to the first embodiment. It enters the write-once hologram memory 10. Even when the hologram is formed by such a method, the position of the spatial light modulator 41, that is, the position shown in FIG. 4 is obtained when the hologram is reproduced by introducing the reproduction illumination light IL as in the first embodiment. Diffracted light that forms an image on the image plane 44 is generated. By aligning the light detection surface of the two-dimensional photodetector with the position of the spatial light modulator 41, the recorded information can be read out.
[0029]
According to the second embodiment, not only the information reading apparatus but also the recording apparatus does not require the imaging optical system used in the first embodiment, and an inexpensive apparatus can be realized.
[0030]
FIG. 6 shows an optical system of a high-speed data light generating apparatus according to the third embodiment of the present invention. The high-speed data light generation apparatus according to the third embodiment has a second spatial light modulator 45 in the optical system in the first embodiment shown in FIG. The spatial light modulator 41 is an element that modulates the light intensity in a plane by individually controlling the light transmittance of the rectangular pixels, but the spatial light modulator 45 replaces the transmittance with the light. It is composed of pixels whose phase can be electrically controlled.
[0031]
The electromagnetic field distribution of the light whose intensity is modulated by the spatial light modulator 41 is reproduced at the position of the spatial light modulator 45 by the imaging optical system composed of the convex lenses 42 and 43. By applying phase modulation in the spatial light modulator 45, an optical wave subjected to intensity modulation and phase modulation is obtained as an output of the spatial light modulator 45. This means that light having an arbitrary wavefront can be generated, and can be used effectively as the data light WL.
[0032]
An apparatus for creating amplitude information input to the spatial light modulator 41 and phase information input to the spatial light modulator 45 is, for example, a reproduction-only laminated waveguide hologram described in Japanese Patent Application Laid-Open No. 2000-321964. A memory data creation device can be applied.
[0033]
The amplitude information and phase information can also be obtained by calculation as follows. When the hologram image Im is represented by Imn and the intensity of the pixels constituting the image, the electromagnetic field of light immediately after passing through the spatial light modulator 45 is, for example,
[0034]
[Expression 1]

[0035]
If it becomes. Um'n 'is a photoelectric magnetic field corresponding to the pixel in the m'th row and the n'th column of the spatial light modulator 45, and is scalar complex displayed. i is the imaginary unit, k is the wave number of light, Lm and Ln are the pixel pitch of the hologram image Im, Dm ′ and Dn ′ are the pixel pitches of the spatial light modulators 41 and 45, and l is the spatial light modulator 45 and the image plane. 44. C, sk, and sy are real constants.
[0036]
At this time, the amplitude Tm′n ′ input to the spatial light modulator 41 is
[0037]
[Expression 2]

[0038]
It becomes. In the spatial light modulator 45,
[0039]
[Equation 3]

[0040]
Just advance the phase. The phase θm′n ′ may be a remainder when the above equation is divided by 2π.
[0041]
In the high-speed data light generating apparatus according to the third embodiment shown in FIG. 6, the spatial light modulator 41 and the convex lenses 42 and 43 can be omitted. That is, only the phase is modulated without amplitude modulation of the light wave. For this reason, ideal light waves cannot be synthesized, but phase modulation contributes more to light wave front generation than amplitude modulation, and a sufficient hologram image can be generated without some noise. According to this configuration, as in the second embodiment, writing to and reading from the write-once hologram memory can be performed by an inexpensive device that does not require a lens system.
[0042]
According to this embodiment, writing to the write-once hologram memory can be performed by an apparatus that does not require a complicated lens group, and reading can be performed without requiring a complicated lens group.
[0043]
【The invention's effect】
As described above, according to the present invention, the core layer for writing information by the gate light introduced as guided light into the core layer for writing information and the data light introduced from the interface of the planar optical waveguide with the information superimposed thereon. In addition, the information is written only once by generating a photochromic phenomenon due to two-photon absorption and forming a scattering factor of guided light, so that a programmable read-only hologram memory becomes possible.
[0044]
In addition, according to the present invention, since a complicated lens group is not required, information can be easily written to and read from the write-once hologram memory, the production efficiency of the programmed write-once hologram memory can be improved, and the read-out can be performed. The dedicated device can be downsized.
[Brief description of the drawings]
FIG. 1 is a structural diagram showing a write-once hologram memory according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining a method of writing information to a write-once hologram memory according to an embodiment of the present invention.
FIG. 3 is a flowchart showing a procedure for generating data light from information written in a write-once hologram memory.
FIG. 4 is a configuration diagram showing an optical system of the high-speed data light generating device according to the first embodiment of the present invention.
FIG. 5 is a configuration diagram showing an optical system of a high-speed data light generating device according to a second embodiment of the present invention.
FIG. 6 is a configuration diagram showing an optical system of a high-speed data light generating device according to a third embodiment of the present invention.
[Explanation of symbols]
10 Write-once hologram memory 11a, 12a, 13a, 14a, 15 Cladding layer 11b, 12b, 13b, 14b Core layer 16 Substrate 20 Reproduction illumination light source 31 Cylindrical lens 32 Beam splitter 33 Gate light source 40 High-speed data light generation device 41 45 Spatial light modulators 42 and 43 Convex lens 44 Imaging surface

Claims (2)

A write-once hologram memory in which a planar optical waveguide having a core layer formed of a recording material that generates a photochromic phenomenon by two-photon absorption is laminated in multiple layers,
Photochromic phenomenon due to two-photon absorption in the core layer for writing information by gate light introduced as guided light into the core layer for writing information and data light introduced from the interface of the planar optical waveguide with the information superimposed thereon And the information is written only once by forming a scattering factor of guided light ,
The reproduction illumination light introduced as guided light is diffracted out of the planar optical waveguide by the scattering factor into the core layer in which the information is written, and a hologram image obtained by two-dimensionally encoding the information is formed. And
The write-once hologram , wherein the data light is introduced from an interface of the planar optical waveguide as laser light modulated based on an amplitude distribution and a phase distribution obtained so as to form the hologram image memory.   2. The write-once hologram memory according to claim 1, wherein the recording material is made of a diarylethene molecule.

Images