Ultra-compact digital metasurface polarization beam splitter via integrated TE and TM mode coupling gratings

Inverse design promotes the miniaturization of integrated photonic devices by leveraging subwavelength structures. Based on the physics-constrained inverse design (PCID) method, we propose an ultra-compact polarization beam splitter (PBS), featuring integrated coupling gratings inversely designed to simultaneously and efficiently couple TE and TM modes. This PBS consists of a standard silicon-on-insulator (SOI) substrate and a two-dimensional digital metasurface composed of tunable air-silicon column structures. This achieves efficient polarization splitting within a compact footprint of 5 × 2.7 μm². The integrated coupling gratings, inversely designed for simultaneous and efficient coupling of both TE and TM modes, significantly mitigate fabrication errors and ensure consistent measurement conditions for each polarization state. Consequently, experimental measurements closely match our simulated predictions, demonstrating low insertion losses(-1.58 dB for TE mode and -1.65 dB for TM mode) and high extinction ratios over an 80 nm bandwidth covering the entire C-band.