ABSTRACT
This chapter discusses the principles of thin-film designs involving phase change materials. The increase in refractive index of one of the films will make the phases of the H and L films unequal. Returning to the VO2 thin film, we can place it in the center of a cavity as H2R5HIR4HH2 to increase resonant absorption and to reduce the light intensity required to induce switching. The refractive index values of the two phases are quite different, which can be exploited in optical thin-film designs to create tunable devices just like VO2. The end result is that a red shift of the long-pass edge is observed as the refractive index of the H film increases in value. The cavity structure is in resonance when the VO2 film is in the cold state. As a result, the reflection falls to zero at the reference wavelength. The transmission is about 35%, with the remainder absorbed due to resonance-enhanced absorption.
