Ge-on-Si and Ge-on-SOI thermo-optic phase shifters for the mid-infrared.

Germanium-on-silicon thermo-optic phase shifters are demonstrated in the 5 µm wavelength range. Basic phase shifters require 700 mW of power for a 2π phase shift. The required power is brought down to 80 mW by complete undercut using focused ion beam. Finally an efficient thermo-optic phase shifter is demonstrated on the germanium on SOI platform. A tuning power (for a 2π phase shift) of 105 mW is achieved for a Ge-on-SOI structure which is lowered to 16 mW for a free standing phase shifter.