SWITCH POWER DRIFT IN OPTICALLY BISTABLE ZnSe INTERFERENCE DEVICES.

Optically bistable devices based on nonlinear thin-film interference filters have been reported by Smith et al and Weinberger et al and have been shown to be suitable for use as logic elements in digital optical circuits and pattern recognition applications. These devices use ZnSe or ZnS as the active material and rely on thermally induced changes in the refractive index to provide the required nonlinear response. Early experiments with optically bistable interference filters showed highly irreproducible input-output characteristics. In particular switch-up powers increased rapidly with time and the bistable region was seen to expand on each scan of input power. We have observed similar effects with nonlinear filters grown on low temperature substrates and consequently made up of less dense thin-film layers.