High-performance silicon polarization switch based on a Mach–Zehnder interferometer integrated with polarization-dependent mode converters

As the key element for optical systems, polarization controllers with versatile functionalities are highly desired. Here, a CMOS-compatible polarization switch is proposed and realized by using a Mach–Zehnder interferometer integrated with two polarization-dependent mode converters (PDMCs) at the input/output ends. The PDMCs, which utilize the mode hybridness and adiabatic mode evolution in a silicon-on-insulator (SOI) ridge waveguide taper, provide a low-loss adiabatic transmission for the launched TE0 mode as well as efficient mode conversion from the launched TM0 mode to the TE1 mode. For the MZI structure, there are two 1 × 2 dual-mode 3-dB power splitters based on a triple-core adiabatic taper, and two thermally-tunable phase-shifters embedded in the arms. The polarization state and the polarization extinction ratio (PER) of the transmitted light can be dynamically tuned by introducing some phase difference between the MZI arms electrically. The fabricated device has an excess loss of ∼0.6 dB for the TE0 and TM0 modes. When the switch is off, the TE0 and TM0 modes go through the device without exchange. In contrast, when the switch is on, the TE0–TM0 conversion occurs and the measured PER is about 20 dB.