FIELD MICROSTRUCTURE AND TEMPORAL AND SPATIAL INSTABILITY OF PHOTONICBLOCH WAVES IN NONLINEAR PERIODIC MEDIA

The nonlinear dispersion relation of monochromatic optical Bloch modes in a periodic half-space is derived for both normal and oblique incid ence. It is shown that strong nonlinear beam steering can occur in the vicinity of the Bragg condition. By studying the field microstructure , and making use of diagrams of wavevector versus frequency, a fresh p erspective is gained on the physical mechanisms that govern the behavi our of light in nonlinear periodic media. A linearised analysis is use d to identify parameter ranges of temporal and spatial instability, an d to quantify the gain of the associated modulational instability.