Variation of Bragg condition in low-glass-transition photorefractive polymers when recorded in reflection geometry

Two low-glass transition photorefractive polymer composites were investigated in a symmetric reflection geometry. The holograms recorded in 105 μm thick devices have reached diffraction efficiencies as high as 60%. Unlike the gratings recorded in transmission geometry, holograms recorded in reflection geometry showed high angular selectivity and the Bragg condition was observed to be sensitive to the magnitude of the external bias field. We attribute this effect to poling-induced birefringence and give a theoretical analysis to describe the observed results.