Critical-phenomenon-based optical bistability in vanadium dioxide

Abstract

Vanadium dioxide undergoes large changes in its optical properties at the metal-semiconductor thermodynamic phase transition at 68°C. The most pronounced changes occur in the infrared. By combining low power nonlinearity from the metal-semiconductor phase transition with a thin film interference filter, we demonstrate optical bistability at 1.06 μm. Highly stable bistable operation has been obtained. By biasing at the critical point, an all-optical external switching between the semiconducting and metallic states has been demonstrated. A contrast ratio of 15:1 has been achieved. The other characteristic parameters are as follows: switching energy density = 380 pJ/μm2, switching intensity ≈0.9 W/cm2, switching time ≈10 ms, and the nonlinear index of refraction ≈0.5 cm2/W. It should be stressed, however, that these numbers are only representative and not the optimum values for these parameters. An attractive feature of the vanadium dioxide is the tunability of the transition temperature and the width of the bistable region through doping and other techniques. This tunability provides control to tune the characteristic parameters, such as switching powers and switching speeds, over a wide range.