High-isolation polarization splitter rotator in standard silicon photonic platforms

Silicon photonics enables the realization of compact and cost-effective photonic integrated circuits (PICs). However, the strong birefringence of silicon-on-insulator (SOI) waveguides introduces polarization dependence, requiring solutions for polarization diversity. In this work, we present the design and experimental demonstration of a compact polarization splitter-rotator (PSR) operating in the extended C band wavelength range (i.e., 1500–1600 nm), fully compatible with silicon photonic foundries that employ 220 nm silicon-on-insulator wafers and a 70 nm partial etch, typically used for grating couplers. We demonstrate a high-isolation device that integrates a two-stage adiabatic directional coupler for polarization splitting, a custom-shaped bi-level taper for TM0-to-TE1 rotation, an ultracompact TE1-to-TE0 mode converter, and clean-up filters to enhance the polarization extinction ratio (PER). The proposed PSR exhibits negligible insertion loss in the TE branch and a TM-to-TE conversion loss of 0.71 dB at 1550 nm. PER measurements demonstrate excellent performance, with a worst-case value of 30.95 dB near 1550 nm across all input/output polarization combinations for which the PSR is expected to reject optical signal transmission. We compare the high-isolation version with a single-stage PSR without clean-up filters, confirming the effectiveness of the improved design. These results demonstrate a compact and highly-compatible solution for large-scale integration in polarization-diverse silicon photonic systems.