Abstract: An optically bistable device comprises a Fabry-Perot etalon containing intracavity liquid crystal material. Etalon mirros of deposited silver are overlaid on indium tin oxide electrodes. The electrodes provide electrical biasing means for the material, which exhibits both optical nonlinearity and electro-optic tunability of refractive index. The etalon has an interference fringe maximum at a wavelength .lambda..sub.m1. the fringe is tunable to .lambda..sub.m2 by applying a bias voltage across the mirrors. A light beam illuminates the etalon, the beam having a wavelength .lambda..sub.s where .lambda..sub.m2 is between .lambda..sub.s and .lambda..sub.m1. The beam intensity is sufficient to induce bistable etalon switching for a fringe at .lambda..sub.m2 but not for a fringe at .lambda..sub.m1. Tuning the etalon fringe electro-optically from .lambda..sub.m1 to .lambda..sub.