Optimization of Thickness of Polymeric Photorefractive Thin Film for Large Two-Beam Coupling Strength in Reflection Beam Arrangement

Beam fanning was reduced for a large strength of two-beam coupling by using a two-prism configuration to couple incident beams into a polymeric photorefractive thin film. The experimental results of the dependence of the coupling coefficient on the external electric field coincided well with the theoretical results obtained using the coupled-wave equations for two-beam coupling, in which the fanning effect was treated as an electric-field dependent absorbance. Parameters dominating the fanning were the sample thickness and the direction and magnitude of the electric field. The coupling strength reached 2.2, which corresponds to the coupling coefficient of 150 cm-1 and the interaction length of 145 µm.