Optical Processing Using Photorefractive Crystals

Citation

Yu, Jeffrey Winston (1988) Optical Processing Using Photorefractive Crystals. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/q49d-bb74. https://resolver.caltech.edu/CaltechETD:etd-02012007-140044

Abstract

The ability of photorefractive crystals to holographically record an optical image in real time allows one to use them in a variety of optical information processing systems. A number of such systems are presented in this thesis. To form the ground work used in analyzing the performance of photorefractive optical processors, a comparison between the Kukhtarev and Moharam models was done. The regimes where each model sufficiently predicted the response of the photorefractive crystal was determined. In addition, a new model based on a higher perturbation expansion of Kukhtarev's material equation is presented. This method allows one to numerically derive the profile of the space charge field recorded in the crystal and predict the regime where the Kukhtarev and Moharam models are most accurate.

Three optical processing systems are presented. The first, a photorefractive incoherent to coherent converter (PICOC), utilizes a photorefractive crystal as a spatial light modulator. Both the Kukhtarev and higher expansion models were used to analyze the performance of the converter. In the second example, the use of a photorefractive crystal as a time integrating detector is presented. By utilizing this crystal in an acousto-optic time integrating correlator, the output correlation is presented without the bias inherent in standard time integrating architectures. This allows one to utilize the full dynamic range of the output detector, thereby increasing the processing gain of the system. The third example utilizes a photorefractive crystal in a VanderLugt correlator. Standard VanderLugt correlators using planar holograms have been used successfully in pattern classification. In this thesis, we will derive the capacity of this system and demonstrate that by using a photorefractive crystal as the storage medium, the volume holographic properties of the crystal results in an increase in the capacity of the system. In addition, the angular selectivity of the crystal allows one to perform multi-category classification. The effect of using a volume hologram in a VanderLugt correlator is analyzed and experimental results presented.

Thesis Files