Dual subwavelength-grating topology for building polarization beam splitters

A polarization beam splitter (PBS) is key for building polarization-diversity systems in optical communication networks. Here, we propose a compact and easy-to-fabricate PBS based on a dual subwavelength-grating (DSWG) structure positioned between two Si waveguides on a silicon-on-insulator platform. The coupling strengths of the transverse-electric (TE) and transverse-magnetic (TM) modes were selectively modified, with TE mode suppression and TM mode enhancement. By optimizing the duty cycles along transverse and longitudinal directions of the DSWG structure, the device length is reduced by approximately 40%, and the polarization extinction ratio (PER) of the TM mode is improved by ∼5 dB at a wavelength of 1.55 μ m, compared to a single subwavelength grating structure. Numerical simulations revealed high PERs and low insertion losses (ILs) of 26.7 dB (0.1 dB) for TE mode and 23.2 dB (0.28 dB) for TM mode, with a compact footprint of 1.34 × 2.86 μ m ^2 . Across a bandwidth of ∼90 nm within the C-band (1.53–1.56 μ m), the proposed PBS achieves a TM mode PER of ∼20 dB, a TE mode PER greater than 25 dB, and ILs below 0.25 dB for both modes. This approach, utilizing biaxial anisotropic metamaterials, offers a flexible method for integrating PBSs into photonic integrated circuits using standard semiconductor fabrication processes.