Abstract :
We have developed a recyclable, transmission type photoconductivity controlled liquid crystal light valve suitable for real or quasi real-time optical reconstruction of long wave holograms. This device combines an organic photoconductor PVK/TNF (Poly-N-vinylcarbazole/2,4, 7-trinitro-9-fluorenone) film and a thin liquid crystalline layer. While several types of photoactivated light valves have been developed for a variety of purposes, the current one differs from previous versions in that the fabrication of the device is probably the easiest and least expensive, because of the type of photoconductor and the mode of operation involved. Most importantly, it is capable of reconstructing excellent optical images from long wave holograms. The reconstruction of holograms, even at long wave range, is probably one of the most stringent performance tests for any light valve intended to be used as a noncoherent-to-coherent optical image converter, or as an optical-to-optical interface device. Thus, we have not merely characterized the device by MTF measurement for its resolution capability, and optimized its performance in sensitization, addressing irradiance and applied voltage. In addition, we have evaluated and demonstrated its performance with the aid of a microwave test hologram transparency in an optical-bench simulation of a real-time reconstruction. The retrieved image is probably the first of its kind from a light valve. The experimental data are further explained by the proposed macroscopic device model, which governs the possible optimal operating conditions and suggests potential design flexibilities. A general assessment of the device is discussed, based on the quality of the reconstructed image, the device structure and the operating conditions.
