Bistability and beam steering via grating couplers in ZnS waveguides

It is now well established that when high-power lasers are coupled via prisms into waveguides, whose refractive index varies with power, the coupling efficiency decreases with increasing power, and bistability occurs when the nonlinearities are nonlocal.1 This occurs since the wave vector of the guided wave becomes power-dependent, and, as the guided wave power changes in the coupling region, the phase mismatch between the guided wave field and the incident field changes. This effect is inherent in a distributed coupler and should, therefore, also occur in a grating coupler. We report on bistability on coupling into a thin-film ZnS waveguide via a grating coupler. Since the wave vector of the guided wave undergoes an abrupt change when switching occurs, a weak probe beam, which uses the same grating as an output coupler, also experiences an abrupt change in output angle at the point of switching, steering the probe beam in space.