High-performance reflection gratings in photorefractive polymers

To date highest external diffraction efficiency and two-beam coupling gain at moderate applied fields (about 30% and 260 cm − 1 , respectively, at 60 V ∕ μ m ) are obtained in photorefractive reflection gratings with grating periods of about 0.2 μ m using a standard low-glass-temperature polyvinylcarbazole based composite. Reflection gratings exhibit five times faster growth/erasure rates than conventional transmission gratings. Further, their performance is very sensitive to changes in the saturation field. This allows a reliable calculation of the photorefractive trap density, which shows a significant enhancement with the field. Finally, the theoretical analysis reveals the geometry-dependent competition between the birefringence and electro-optic contributions.