Photorefractive materials can form "instant" holograms without time-consuming development steps. Their potential applications include image processing, optical data storage, and correction of image distortion, but the cost of crystal growth and preparation has been a primary impediment to commercial application. Polymers, on the other hand, are low in cost and readily fabricated in a variety of forms. Photorefractive polymers were constructed with performance that matched or exceeded the performance of available photorefractive crystals. The largest observed two-beam energy coupling gain coefficient for the polymers was 56 per centimeter.

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We report the photoconductive properties and photorefractive grating response time of a polymer mixture composed of 40-wt. % dissolved diethylamino-benzaldehyde diphenyl hydrazone (DEH) and the non-cross-linking epoxy polymer Bisphenol A 4,4'-nitroaminostilbene. The films have improved photoconductive sensitivities as high as 2.1 x 10-1o cm/(W fi) at a wavelength of 650 nm with a corresponding reduction of the grating response time constant to 0.11 ± 0.02 s at an intensity of 1 W/cm 2 . The nitro-aminostilbene chromophore is deduced to be the source of photogenerated charge carriers on the basis of a comparison of the wavelength dependence of the photoconductivity and absorption coefficient. Degradation of the photoconductivity and the dark conductivity as well as of the photorefractive speed with sample age is attributed to precipitation of the DEH; this explanation is supported by x-ray diffraction observations of crystal growth in the polymer.

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The polymer Bisphenol A 4,4'-nitroaminostilbene mixed with 40 wt. % benzaldehyde-diphenyl hydrazone is typical of the epoxy-based photorefractive polymers recently shown to be photorefractive.1

In the last three years, a number of researchers have succeeded in making polymers which exhibit the photorefractive effect.1-4 These polymers have numerous potential applications in integrated optics, optical processing, optical data storage, optical computing, communications, image processing, optical switching, thresholding, laser resonators, simulation of neural networks, and studies of nonlinear dynamics. Elements of these applications have been implemented in the laboratory using high-performance photorefractive crystals. However, the cost of crystal growth and preparation has been a primary impediment to commercial application of crystal photorefractive devices. Photorefractive polymers, on the other hand, have very low production cost and will be particularly suitable for formation of waveguide devices for use in, e.g., integrated optics. The photorefractive performance of the polymers must be greatly improved, to meet or exceed the performance of available crystals.

We report the photorefractive properties of a new polymer mixture composed of 40 wt. % benzaldehyde-diphenyl hydrazone dissolved in Bisphenol A 4,4'-nitroaminostilbene. The polymer has a response time of 0.11±0.02 sec at 1 W/cm2, an overall photorefractive sensitivity (index change per unit absorbed energy density) of 1.8±0.5 × 10−6 cm3/J.

We report the performance of photorefractive polymers that have improved response time and phase stability. The polymers studied consist of a host polymer, an attached nonlinear optical moiety, plus a hole transport agent, similar to those previously reported.1 One such composition consists of the host polymer Bisphenol-A with the moiety 4′-amino-4′-nitrostilbene and the hole transport agent diethyl-aminobenzaldehyde-diphenyl hydrazone. Samples 145 μm thick exhibit a diffraction efficiency of 0.01% and an exponential response time constant of 0.1 s with an applied field of 90 kV/cm at a wavelength of 650 nm, 1.6 μm grating spacing, and an intensity of 0.3 W/cm2. These results represent a 1,000-fold improvement in sensitivity (at comparable absorbance) over the results reported in Ref. 1. There is no observable decrease in the photorefractive or photoconductive sensitivities of a sample stored 20 days at room temperature. This is also the first report, to our knowledge, of photorefractivity in a non-cross-linking electro-optic polymer. We also discuss the influence of the polymer composition, polymer processing, and experimental conditions on photorefractive performance and comparison with direct measurements of electro-optic and photorefractive response.