Polarization-insensitive optical switches based on mode-insensitive devices

Owing to the waveguide birefringence in most photonic integrated circuits, optical switches are typically sensitive to the light state of polarization (SOP). In certain application scenarios, optical switches are required to process light signals with random SOPs from single-mode fibers. This study presents a method to achieve polarization-insensitive optical switches based on mode-insensitive devices after transforming the fundamental mode of one polarization component in randomly polarized light into a high-order mode of its orthogonal polarization, without extra power consumption or significant size increase. For 2 × 2 silicon-based thermo-optic switches, the measured polarization-dependent losses (PDLs) in both CROSS and BAR states were less than 0.4 dB at a wavelength of 1315 nm. Ranging from 1309 to 1339 nm, the PDLs were less than 0.9 dB. A 4 × 4 optical switch was also experimentally demonstrated, whose PDLs for all routing paths in all BAR and CROSS states were less than 1.2 dB at a wavelength of 1334 nm. This method can potentially be used to construct polarization-insensitive on-chip integrated photonic systems for applications in fields such as optical communications and optical interconnections.