Mid-infrared Ge-based thermo-optic phase shifters with an improved figure of merit

Abstract

We demonstrate a power-efficient and fast thermo-optic phase shifter on a Ge platform for mid-infrared applications. Several approaches are implemented to improve the performance. Air trenches and Si-Ge multilayers with ultra-low thermal conductivity are introduced to provide thermal insulation. Few-layer graphene is used to enhance the thermal conductivity between the heater and the waveguide for efficient heat injection and subtraction. The optimized design has a power consumption of 3.9 mW and a time constant of 1.8 µs, resulting in a very small figure-of-merit of merely 7.0 mW·µs, 4 times smaller than the previously reported value.