Slot waveguide-based, polarization-insensitive, thermo-optic phase shifters.

Polarization-insensitive, thermo-optic (TO), silicon photonic phase shifters using vertical slot waveguides are proposed. For such slot waveguides that support slot modes only for transverse-electric (TE) polarized modes, the TO coefficients of the fundamental TE and transverse-magnetic (TM) polarized modes (i.e., TE and TM, respectively) can be easily engineered to be the same by designing the widths of the slot and the total waveguide. In the experiments, the TO coefficients of the TE and TM modes for various slot waveguides are characterized by measuring the electrical switching powers of dual-polarization MZI optical switches using the slot waveguides as the TO phase shifters. A small switching power difference of <0.3% between the two polarization modes is observed for the switch using the slot waveguide engineered to act as a polarization-insensitive phase shifter. The performance of the developed optical switch is also experimentally characterized to prove the potential of the proposed phase shifters to realize polarization-independent switches.