Polarization-insensitive 2 × 2 thermo-optic Mach-Zehnder switch on silicon.

A polarization-insensitive 2×2 thermo-optic Mach-Zehnder switch (MZS) on silicon is proposed and demonstrated experimentally by utilizing silicon-on-insulator (SOI) nanophotonic waveguides with a 340-nm-thick silicon core layer. The present MZS consists of two 2×2 3 dB multimode interference (MMI) couplers, which are designed to be polarization-insensitive by choosing the core width optimally. Meanwhile, the MZS arms are designed with square SOI nanophotonic waveguides with a cross section of 340  nm×340  nm in order to achieve polarization-insensitive phase shift. The fabricated silicon MZS has an excess loss of 1∼4  dB and an extinction ratio of >20  dB in the C-band (1530∼1565  nm) for both TM and TE polarizations.