Experimental observations of bistability and instability in a two-dimensional nonlinear optical superlattice

Optical bistability in a two-dimensional nonlinear superlattice, resulting from the index-modulation mechanism, was observed in experiment for the first time. The two-dimensional nonlinear superlattice was constructed by recording a two-dimensional refractive index grating into a photorefractive material, a Fe-doped ${\mathrm{LiNbO}}_3$ single crystal. Optical instability was also observed in this experiment.