JP2005181709A - Optical recording method using organic photorefractive material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a time period from starting light irradiation on a material to completing optical recording (response time) in an organic photorefractive material. <P>SOLUTION: In conducting optical recording by making write light irradiate the organic photorefractive material and varying a refractive index of the material, the optical recording method is characterized by setting a storage modulus of the material to 1×10<SP>5</SP>to 1×10<SP>7</SP>Pa on the time of write light irradiation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical recording method using a photorefractive material. According to the present invention, it is possible to shorten the response time when writing light is irradiated.

  A photorefractive material is a material whose refractive index changes upon light irradiation. That is, when a photorefractive material is irradiated with light, electrons and holes (hereinafter referred to as carriers) are generated, and a spatial electric field is generated by the movement of the carriers. Then, the refractive index in the material changes corresponding to this spatial electric field, and refractive index modulation becomes possible. When this photorefractive material is irradiated with interference light, light is absorbed only in the bright part of the interference light and not in the dark part, so that a diffraction grating whose refractive index changes periodically is formed in the material.

  Further, the period of refractive index modulation induced by the photorefractive material deviates from the period of light / dark intensity modulation of interference light. Therefore, when the material is irradiated with two coherent beams, energy transfer occurs between the beams, and a transmitted beam having an intensity ratio different from that of the irradiated beam is obtained. Since photorefractive materials have such properties, they are expected to be applied to hologram recording elements, optical multiplexers / demultiplexers, beam amplifiers, image correlation processing, associative memory elements, and the like.

Conventionally known photorefractive materials include inorganic photorefractive materials using lithium niobate and the like, but their use is limited because sample preparation and molding are difficult. On the other hand, photorefractive materials using organic compounds are expected to be used in various applications due to their easy processability and functional modification (WE Moerner and SM
Silence, Chemistry Review, 94, 127-155, 1994).

W. E. Moerner and S. M. Silence, Chemistry Review, 94, 127-155, 1994

  The present inventors have studied various organic photorefractive materials so far and have obtained photorefractive materials exhibiting excellent processability and optical properties. However, shortening of the response time of the organic photorefractive material, that is, the time from the start of light irradiation to the material to the completion of optical recording is not sufficient, and an improvement in recording efficiency is desired.

In the present invention, when performing optical recording by irradiating an organic photorefractive material with writing light and changing the refractive index of the material, the storage elastic modulus of the material at the time of writing light irradiation is set to 1 × 10 ⁵ to 1 × 10 ^7. The present invention provides an optical recording method characterized by using Pa. In the optical recording method of the present invention, the temperature of the organic photorefractive material at the time of writing light irradiation is preferably 10 to 50 ° C. According to the method of the present invention, the response time when writing light is irradiated can be shortened.

Detailed description of the invention

  Next, the optical recording method of the present invention will be described in more detail. Examples of the photorefractive material to which the recording method of the present invention can be applied include various organic photorefractive materials. Typical recording materials include (A) an electric field responsive optical functional compound, (B) a sensitizer, and (C). The thing containing an organic polymer compound and (D) plasticizer is mentioned. An outline of the photorefractive material will be described.

(A) Electric field responsive optical functional compound The electric field responsive optical functional compound forms a charge transfer complex together with the sensitizer. Examples of such compounds include N- (4-nitrophenyl) -L-prolinol (NPP) (formula 1), [[4- (hexahydro-1H-azepin-1-yl) phenyl] methylene] propanediene. Nitrile (7DCST) (formula 2), 4- (N-ethyl- (5-hydroxyheptyl) aminodicyanostyrene (HHAS) (formula 3), etc. Formulation of an electric field response optical functional compound in an organic photorefractive material The amount is usually preferably 0.01 to 50% by weight in consideration of compatibility with other components.

(B) Sensitizer A sensitizer that easily forms a charge transfer complex with the electric field response optical functional compound is used. For example, 2,4,7-trinitro-9-fluorenone (TNF) (formula 4) is used. The blending amount of the sensitizer is 0.01 to 25% by weight in the organic photorefractive material.

(C) Organic polymer compound As a typical photorefractive material, an organic polymer compound in which the above components are uniformly mixed and dispersed is used. Examples of the organic polymer compound include acrylic acid esters such as polymethyl methacrylate (PMMA), poly t-butyl methacrylate (PtBuMA), and polypropyl methacrylate (PPMA), poly (vinyl butyral) (PVB), and poly (acetic acid). Vinyl) (PVAc), polycarbonate (PC) and the like, and particularly when transparency and heat resistance are required, polyimides, polyether ketones and polyether sulfones are used. These organic polymer compounds are preferably 10 to 50% by weight based on the total composition.

(D) Plasticizer It is preferable to add a plasticizer to the photorefractive material used in the recording method of the present invention to improve compatibility. Examples of such a plasticizer include 2- (1,2-cyclohexanedicarboximido) ethyl propionate (AX22) (formula 5), 2- (1,2-cyclohexanedicarboximido) ethyl butyrate ( AX23) (Formula 6), 2- (1,2-cyclohexanedicarboximido) ethyl benzoate (AXPH) (Formula 7), 2- (1,2-cyclohexanedicarboximide) ethyl acrylate (AX14) (Formula 8) , 2- (phthalimido) ethyl propionate (AX24) (formula 9) and the like. The blending amount of the plasticizer is preferably 50% by weight or less with respect to the total composition.

(Recording method)
In recording, the storage elastic modulus of the photorefractive material at the time of writing light irradiation is adjusted to 1 × 10 ⁵ to 1 × 10 ⁷ Pa. The storage elastic modulus may be adjusted by an appropriate method. For example, the storage elastic modulus may be adjusted by heating the material to 10 to 50 ° C. by providing a heater on the photorefractive material stage during light irradiation. For example, a helium neon laser may be used as the writing light source.

Next, the present invention will be described in more detail with reference to examples and comparative examples. In the following, “parts” means parts by weight.
(Production of photorefractive material)
The photorefractive material used for carrying out the recording method of the present invention was prepared as follows. That is, the following components were mixed and dissolved in tetrahydrofuran. Subsequently, the obtained solution was filtered through a polytetrafluoroethylene membrane to remove impurities such as dust, and then tetrahydrofuran was completely removed to obtain a photorefractive material.
Component content <br/> Electric field response optical functional compound:
N- (4-nitrophenyl) -L-prolinol (NPP) (Formula 1) 20 parts Sensitizer: 2,4,7-Trinitro-9-fluorenone (TNF) (Formula 4) 5 parts Plasticizer: 2 -(1,2-cyclohexanedicarboximide)
Ethyl propionate (AX22) (Formula 5) 20 parts Polymer resin: 35 parts of polymethyl methacrylate

(Measurement of storage modulus)
The storage elastic modulus is measured by forming an organic photorefractive material into a disk-like sample (diameter 7 mm, thickness 1 mm), and using a dynamic viscoelasticity evaluation apparatus (manufactured by Rheometric Scientific F.E. The measurement was performed at a measurement frequency of 6.28 Hz using an elasticity measurement system expansion type (ARES).
In addition, the storage elastic modulus of the organic photorefractive material was adjusted by setting the material on a stage equipped with a heater and adjusting the material temperature when irradiating the writing light.

(Evaluation)
Diffraction efficiency Diffraction efficiency indicates the ratio of the intensity of transmitted light and diffracted light when a light beam is incident on a diffraction grating formed by the photorefractive effect. The diffraction efficiency was determined by degenerate four-wave mixing, using a 10 mW helium-neon laser as a light source, p-polarization writing, and s-polarization reading. At this time, the writing light was incident at ± 10 ° with respect to the normal line of the sample plane. After measurement for an arbitrary time, the point at which the diffracted light intensity was maximum was determined, and the diffraction efficiency (%) was determined from the ratio with the transmitted light intensity at this time by the following equation.
Diffraction efficiency = {diffracted light intensity / (diffracted light intensity + transmitted light intensity)} × 100

Response time The response time was measured from the start of writing light irradiation until the diffraction efficiency was saturated and the optical recording was completed.

[Examples 1-4 and Comparative Examples 1-2]
The photorefractive material prepared as described above was sandwiched between two glass plates together with spacers (glass beads) to obtain a film-like characteristic evaluation sample (film thickness 100 μm). Next, this sample was placed on a stage with a heater and irradiated with writing light (light source: helium neon laser) to form a diffraction grating. The sample temperature at the time of irradiation was set as shown in Table 1, the storage elastic modulus of the sample was changed, and irradiation of writing light was performed. The diffraction efficiency and response time obtained at this time are shown in Table 1.

表１に示すように、書込み光照射時のフォトリフラクティブ材料の貯蔵弾性率が１×１０^５〜１×１０^７Ｐａの範囲にある実施例１〜４では、貯蔵弾性率がこれを超える比較例１に比べて応答時間が大きく短縮される。また、貯蔵弾性率が所定の範囲より低い比較例２では書込み光照射を１時間行っても回折格子は形成されなかった。

As shown in Table 1, in Examples 1 to 4 in which the storage elastic modulus of the photorefractive material at the time of writing light irradiation is in the range of 1 × 10 ⁵ to 1 × 10 ⁷ Pa, the storage elastic modulus exceeds this value. Compared with 1, the response time is greatly shortened. Further, in Comparative Example 2 where the storage elastic modulus was lower than the predetermined range, no diffraction grating was formed even when writing light irradiation was performed for 1 hour.

[Industrial use]
In the optical recording method of the present invention, the time from the start of light irradiation to the organic photorefractive material until the completion of optical recording (response time) is shortened, the hologram recording element, optical multiplexer / demultiplexer, beam amplifier, image correlation processing, Application to associative memory elements is expected.

Claims (2)

In performing optical recording by irradiating an organic photorefractive material with writing light and changing the refractive index of the material, the storage elastic modulus of the material at the time of writing light irradiation is set to 1 × 10 ⁵ to 1 × 10 ⁷ Pa. An optical recording method characterized by the above. The optical recording method according to claim 1, wherein the temperature of the organic photorefractive material at the time of writing light irradiation is 10 to 50 ° C.