Optically controlled spatial light modulator was demonstrated as application of photorefractive polymeric material. Since photorefractive composite based on carbazole-substituted polysiloxane matrix (PSX-Cz) has an advantages of stability in phase separation, compared to poly(N-vinyl carbazole) based composite, we can dope almost all kinds of chromophore with the PSX-Cz to prepare a photorefractive composite. Here a chromophore 2-[3-[(<i>E</i>)-2-(piperidino)-1-ethenyl]-5,5-dimethyl-2-cyclohexenyliden] malononitrile (P-IP-DC), with large dipole moment and large polarizability anisotropy was adopted into a photorefractive sample, which showed a high diffraction efficiency of 85 % at an external field of 28 V/μm. Using this photorefractive composite, incoherent image imposed in Xe-lamp light was converted into coherent image in He-Ne laser light by the optically controlled spatial light modulator.
We proposed a method for measuring the magnitude of the space-charge field of the polymeric photorefractive materials. In the case of polymeric photorefractive material with low glass transition temperature, optically anisotropic chromophores are known to be reoriented under space-charge field. Simply by adding a pair of crossed polarizers unit to a conventional degenerated four wave mixing setup, we could measure the birefringence of the photorefractive materials induced by a newly formed space-charge field. Since the birefringence of a given material is governed by the applied electric field, the space-charge field can be determined from the variation of birefringence using the oriented gas model. We investigated the dependence of the grating formation on temperature in photorefractive polymeric composite, especially the index contrast of the grating. The diffraction efficiency of the photorefractive polymeric composite decreased with increasing the temperature, and it could be explained with the magnitude of space-charge field and the electro-optic behavior at various temperatures.
The polymeric photorefractive composite was prepared from the mixture of carbazole-substituted polysiloxane as a photoconducting medium, 2, 4, 7-trinitro-9-fluorenone as a photo-sensitizer, and 2-(3-((<i>E</i>)-2-(dibutylamino)-1-ethenyl)-5,5-dimethyl-2-cyclohexenyliden) malononitrile as an optically nonlinear chromophore. This polymeric composite with the thickness of 100 μm exhibited the high diffraction efficiency of 92% at the applied electric field of 30V/μm, which corresponds the refractive index modulation (<i>Δn</i>) of 3 x 10<sup>-3</sup>. The applications of this polymeric composite to pattern recognition are demonstrated. Character and fingerprint recognitions based on joint-transform optical correlation are successfully demonstrated.