OPTICALLY BISTABLE THIN-FILM DEVICES USING WIDE-GAP II-VI COMPOUNDS

Optically bistable interference filters and single bistable absorption layers were prepared by thermal evaporation of II-VI semiconductors on glass and sapphire substrates. The bistable interference filters consist of a low absorption spacer, e.g. ZnS or CdS, with multilayer mirrors on both sides and an absorption layer, e.g. CdSe, on the beam exit side. Absorption leads to heating and thermooptic tuning of the spacer resulting in optical bistability and other types of nonlinear optic effects. Stable bistable switching is achieved for millions of cycles. Optical bistability due to increasing absorption is observed also in single ZnSe layers with an incident photon energy just below the band gap. The influence of different thin film preparation methods is studied. The switching elements were operated between 400 and 800 nm wavelength and needed switching powers of several mW. Switching times in the microsecond range were measured. The performance of the devices is optimized using theoretical models. © 1989.