Silicon Multimode Anti-Symmetric Apodized Bragg Gratings for Ultra-Broadband High-Extinction-Ratio Polarization Beam Splitter

A polarization beam splitter (PBS) is the basic building block for polarization management in coherent communications and quantum entanglement. Compared to discrete polarization elements, photonic integrated circuits (PICs) exhibit significant advantages of a small footprint, scalability, reduced power consumption, and enhanced processing stability. However, polarization beam splitting in PICs is usually sensitive to wavelength due to high-index contrast and suffers from moderate polarization extinction ratio. Here, we design and experimentally demonstrate a high-performance integrated PBS with a record-wide bandwidth of high-extinction-ratio (> 30 dB) covering the entire S + C + L band (similar to 190 nm). We achieve this utilizing mode coupling in multimode anti-symmetric apodized waveguide Bragg gratings and adiabatic directional coupler-based mode (de)multiplexers on a conventional SOI platform. The PBS also features low average insert losses (ILs) of 1/0.4 dB for TE-/TM-polarization from 1415 to 1675 nm. Our demonstration paves the way for implementing efficient polarization diversity circuits for large-capacity telecom systems and high-degree quantum information applications.