A Novel Mid-Infrared Transverse Magnetic Mode Pass Periodic Waveguide Polarizer With Low Reflections

We propose a transverse magnetic (TM) pass polarizer based on a periodic waveguide on a silicon-on-insulator platform. The design is implemented on a 500nm-thick silicon layer surrounded by SiO₂. The polarizer operates in the mid-infrared (MIR) wavelength range of 3.1 μm to 3.6 μm, a crucial band for chemical and biological sensing, as well as environmental monitoring. While there is extensive documentation on polarizers in the near-infrared (NIR), there is a significant scarcity of research reports on polarizers in the MIR. This proposed polarizer demonstrates outstanding performance, characterized by ultra-low loss for the transmitted TM mode, minimal reflections of the undesired transverse electric (TE) mode, and exceptionally high loss for the transmitted TE mode. The TM insertion loss remains below 0.5dB over a wavelength range of 3.2 μm to 3.6 μm, as the TM mode operates in the subwavelength and low-loss radiation regimes. The transmitted TE power is remarkably small, falling below -30dB over a 300nm wavelength range. This is attributed to the TE mode operating in the high-loss radiation regime and the band gap region of the dispersion diagram. Furthermore, the reflected power of the undesired TE mode is significantly reduced (below .20dB) by incorporating the periodic waveguide in a directional coupler setup. The footprint of the polarizer is compact, measuring just 30 μm × 7 μm.