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., TE₀ and TM₀, 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 TE₀ and TM₀ 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.