Gap shift and bistability in two-dimensional nonlinear optical superlattices

We numerically investigate electromagnetic wave propagation in a two-dimensional optical superlattice with Kerr-type nonlinearity. We show that, with proper modulation depths of the refractive index, a stop gap in the spectrum is possible for a wave propagating at the Bragg angle of the structure. The location of the stop gap depends critically on the incident wave power. We demonstrate that this gap-shift effect can induce an intensity-dependent transmission. This property has important applications in optical bistable switching. {} 1996 The American Physical Society.