Space-Charge Fields in Photorefractive Crystals for Volume Holographic Interconnections.

In this dissertation, the space-charge fields in photorefractive crystals due to the illumination of light interference patterns have been analyzed for volume holographic interconnections. Volume holograms stored in a three-dimensional medium such as a photorefractive crystal is considered as a promising candidate for the implementation of neural network. This volume holographic interconnection scheme has a potential for a dramatic increase in the number of interconnections and for implementing real-time learning in the optical domain because of the dynamic characteristics of the photorefractive material. Criteria for optimal implementation of the volume holographic interconnections utilizing photorefractive materials are presented. Theoretical formulation for photorefractive space-charge fields generated by the illumination of multiple noncollinear plane light interference patterns was achieved by substituting the complex Fourier series of the space -charge field and free-carrier density into Kukhtarev's nonlinear differential equations. Steady-state space-charge fields generated by the light interference patterns, each of them formed by a pair of optical plane waves, are analyzed. Analytic solutions of the steady-state space-charge fields in photorefractive crystals are derived for small laser intensity at large modulation depth. Numerical solutions for the photorefractive crystal BSO are also obtained by utilizing Powell's method without the assumption of small laser intensity, and they are compared with the analytic solutions in both cases of stationary and moving light interference patterns. The intermode space-charge fields, which may cause the second -order cross-talk problem in volume holographic interconnections, are described. The data regions are obtained in which the effect of intermode space-charge fields are suppressed and the criteria for optimal implementation of volume holographic interconnections are satisfied. Temporal behaviors of the space-charge field generation and interaction between multiple light and space-charge field gratings are also investigated based on the general theoretical formulation for the photorefractive space-charge field.