Analysis of a bistable thermally tunable waveguide

Abstract

The effect of thermal tuning on the optical properties of an SOI based suspended waveguide is analysed. This analysis is based on the model that a fixed-fixed suspended beam, which forms the optical waveguide, will buckle when thermal expansion causes an axial stress that exceeds the critical buckling pressure of the beam. The analysis of the waveguide response will be broken up into the pre- and post-buckle stages of thermal actuation. Each stage of actuation will have a separate relationship for the shift in optical response as a function of temperature, which will include a combination of the thermo-optic, photo-elastic, and thermo-elastic effects. Given a corrugated, or version of the waveguide, it will be shown that thermally tuning the Bragg wavelength involves a change in index via a change in temperature and stress, and a change in grating pitch via a change in temperature. Particular attention will be paid to the evolving stress field over the length of the waveguide and its relationship to the stress-optic effect. It will also be shown that the pre- and post-buckle temperatures are path-dependant. Finally, examples of device implementation will be explored.