Theoretical and experimental study of Bragg modulational instability in a dynamic fiber grating

We study theoretically and experimentally nonlinear wave propagation in dynamic optical Bragg gratings, Such gratings are obtained through cross-phase modulation with the beating wave that results from two intense laser beams of different frequencies propagating in a highly birefringent fiber, We show that wave propagation in these gratings obeys the standard coupled-mode equations of static nonlinear Bragg gratings, which makes our study relevant to a wide class of problems related to nonlinear wave propagation in periodic media. The main advantage of the dynamic Bragg gratings is that they make it possible to study experimentally nonlinear wave dynamics close to the bandgap where static gratings cannot be investigated because of their high reflectivity. We illustrate this advantage through the study of Bragg modulational instability. (C) 2002 Optical Society of America.