Enhanced photorefractive two-beam coupling in low-T_g polymeric materials with a new device structure

Abstract

Large two-beam coupling gain with a low driving voltage and a small grating spacing was observed by use of a novel device structure in a photorefractive polymer with a low glass-transition temperature (Tg). A net gain (Γ−α)L close to 1 was observed for an external electric field of ∼40 V/μm and a grating spacing of 0.42 μm. The enhanced coupling strength was the result of optimized parameters and improved, effective electro-optical coefficient, phase shift, space-charge field, and effective interaction length compared with those of a conventional device structure. Moreover, mechanism for this enhancement of coupling strength was found to be applicable to typical efficient low-Tg polymeric materials.