High-performance, ultra-broadband silicon polarization beam splitter utilizing mode conversion Bragg gratings

High-performance polarization beam splitters (PBSs) are essential for maintaining signal integrity and minimizing interference in advanced photonic applications. This paper experimentally demonstrates a high-performance, ultra-broadband on-chip silicon PBS that integrates a mode conversion Bragg grating (MC-BG) with an adiabatic asymmetric directional coupler (ADC). The MC-BG is implemented by etching a hole-structured grating array into a multimode waveguide, serving as a polarization-dependent broadband mode router. It directs the input TM₀ and TE₀ modes in opposite directions while simultaneously converting the TE₀ mode into a higher-order TE₂ mode. The transformed TE₂ mode is then extracted from the multimode waveguide via a specially designed broadband adiabatic ADC, exiting through the cross port. This design achieves theoretically high performance with an extinction ratio (ER) of >30 dB/15 dB and an insertion loss (IL) of <0.9 dB/2 dB over bandwidths of 265 nm (1410-1675 nm) and 375 nm (1300-1675 nm), respectively. Fabricated on a standard 220 nm silicon-on-insulator (SOI) wafer using a single-step etching process, experimental results reveal that, for a device length of 91.7 μm, the bandwidth with ERs exceeding 30 dB spans more than 220 nm. To our knowledge, this is the first demonstration of a PBS on a 220 nm SOI platform achieving an experimentally verified ER exceeding 30 dB over a bandwidth greater than 200 nm. Furthermore, our analysis indicates that performance can be further improved by incorporating a TM₂ mode stripper, extending the 30 dB bandwidth to nearly 295 nm.