Complete Bragg diffraction and high two-beam coupling net gain in a photorefractive polymer

Photorefractive (PR) polymers are a new class of PR materials in which large (approximately 10-3) photoinduced refractive index changes can be generated with very low light power density (approximately 100 mW/cm2 or less). They offer structural flexibility, ease of processing and lower cost compared with commonly used inorganic PR crystals. We have developed a PR polymer composite with significantly enhanced performance compared with the existing PR polymers: For the first time, complete diffraction of an incident beam into the first (Bragg) diffraction order was observed in a 105 micrometers thick layer of a PR polymer. Absorption and reflection losses limit the measured maximum diffraction efficiency to 86%. The material also exhibits a net two-beam coupling gain of more than 200 cm-1. These results show that this class of materials presents a good practical alternative to the inorganic PR crystals.