Abstract
I consider the problem of two-wave mixing caused by Bragg scattering in a permanent volume index grating that is composed of a periodic distribution of nonlinear particles embedded in a linear matrix. Applying coupled-wave theory, I obtain exact solutions for the nonlinear diffraction efficiency. Two types of Bragg grating are explored, one that is due to both linear and nonlinear contributions and the other to only nonlinear contributions to the index grating. I find interesting regions of intensity-dependent beam modulation, such as beam deflection, beam combining, and switching. One can control these effects by varying the input intensity, the modulation depth, or the phase difference between the intensity pattern and the particle grating. Abrupt beam switching can occur for both types of grating. In the first type, switching is seen with small changes in the input phase. A threshold modulation depth exists for the second type, and abrupt beam switching occurs when the input modulation depth is varied in the vicinity of this value. Intensity requirements for observing these phenomena in polymer-dispersed liquid-crystal gratings are estimated to be approximately 6–60 kW/cm2.
© 1991 Optical Society of America
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