High-efficiency Ge thermo-optic phase shifter on Ge-on-insulator platform.

We report on a Ge thermo-optic (TO) phase shifter on a Ge-on-insulator (GeOI) platform for mid-infrared (MIR) integrated photonics. Numerical analysis showed that the Ge TO phase shifter can realize three times higher modulation efficiency than a Si TO phase shifter, owing to the large TO coefficient and refractive index of Ge. The Ge TO phase shifter, operating at a wavelength of 1.95 μm fabricated on a GeOI wafer, achieved an operating power of 7.8 mW for a phase shift of π, which was less than half of that in a previously reported Si TO phase shifter operating at a wavelength of 1.55 μm. Thus, the Ge TO phase shifter is promising for high-performance and low-power MIR photonic integrated circuits for various sensing and communication applications.