Ultralow Loss and High Extinction Ratio TM-Pass Polarizer in Silicon Photonics

TM-pass polarizers are pivotal components of photonic integrated circuits (PICs), especially those intended for biosensing applications. In the literature, several silicon TM-pass polarizers have been proposed, designed and experimentally demonstrated, but their insertion loss is not compatible with the current trend of silicon photonics aimed at exponentially increasing the component density within PICs. Herein, we propose and design a TM-pass polarizer whose insertion loss is carefully minimized to 0.05 dB at wavelength 1.55 μm by utilizing a combination of an asymmetric directional coupler and a mode evolution section. The adoption of appropriate technical solutions makes this record insertion loss value compatible with a high extinction ratio equal to 38 dB. With a device footprint of only 2.5 × 20 μm2, the design exhibits an insertion loss less than 1.7 dB and extinction ratio better than 30 dB over a large bandwidth of 200 nm. The design assumes the constraints of a typical silicon photonics open-access technological process and a standard 220 nm silicon-on-insulator (SOI) wafer. A very low sensitivity of the achieved performance to reasonable fabrication inaccuracies is demonstrated, with a worst-case insertion loss of only 0.32 dB at wavelength 1.55 μm.