Characterization of an inorganic photorefractive liquid crystal hybrid cell

摘要

High birefringent liquid crystals are attractive for photorefractive applications but device operation, Usually restricted to the Raman-Nath regime, can be degraded by small phase shifts between the optical and refractive index gratings and coarse grating spacings with narrow beam intersection angles. Applying external electric fields and having to tilt the cell at an angle to the grating k-vector cause further complications. In this paper, two-beam coupling in hybrid photorefractive cells comprising a nematic liquid crystal layer between inorganic photorefractive windows is described. Photorefractive properties are determined by the windows, while the liquid crystal amplifies the overall refractive index modulation. Bragg matched liquid crystal gain coefficients > 1600 cm(-1) grating periods < 300 nm and wide beam intersection angles with perfect 90 degrees phase shifts between the optical and refractive index gratings at normal incidence viithout the need for an external field are demonstrated.