Influence of fringe bending on the enhancement of the diffraction efficiency of bismuth silicate gratings recorded under strong modulation and applied electric fields

摘要

The diffraction efficiency of bismuth silicate photorefractive gratings recorded in a nonlinear regime (light modulation depth, 1) was numerically calculated; phase coupling and off-Bragg reading conditions were taken into account. We considered gratings recorded with different applied electric dc fields under strong light modulation. We calculated the amplitude and the phase of the refractive-index variation of the gratings by numerically solving first the material rate equations to obtain the phase and the amplitude of the space-charge field and then the wave coupling equations for writing. We also obtained numerical solutions of the wave coupling equations for reading, considering angular deviations from the Bragg condition and bending of the fringes along the thickness of the sample. The diffraction efficiency for a 2-cm bismuth silicate sample recorded with an applied electric field of 2.5 kV/cm and a light modulation depth of 0.9 can be enhanced from 14% to 70% by use of an angular deviation of 3 X 10(-4) rad from the Bragg condition during reading. (C) 2003 Optical Society of America. [References: 11]