Broadband Polarization-Insensitive Thermo-Optic Switches on a 220-nm Silicon-on-Insulator Platform

We demonstrate a polarization-insensitive 2 x 2 thermo-optic switch on a 220-nm silicon-on-insulator platform. This device is based on a balanced Mach-Zehnder interferometer with arms consisting of square-cross-section waveguides. In simulations, the Mach-Zehnder switch (MZS) exhibits extinction ratios (ERs) > 9.5 dB for the transverse electric (TE) and transverse magnetic (TM) polarized modes from 1500 nm to 1600 nm. Experimental results verify the broadband operation of the MZS: switching the two polarizations with ERs > 10 dB over an 85-nm wavelength range. Across the C-band (1530 similar to 1565 nm), the fabricated MZS has insertion losses of 0.2 similar to 43 dB and ERs > 16 dB (14 dB) at the cross (bar) port for both the TE and TM polarizations. The polarization-dependent losses are around 2 dB within a 100-nm wavelength range, showing the low polarization diversity of the MZS. The proposed MZS is a promising building block for implementing on-chip polarization-division-multiplexed optical interconnects.