Optimization of fabrication process for Si metasurface-based mid-wavelength infrared polarizers

Metasurfaces, as a novel class of subwavelength artificial structures, offer advantages such as compactness, ease of integration, and high design flexibility. In particular, dielectric grating-based metasurfaces can provide wavelength-selective polarization filtering in the mid-wavelength infrared (MWIR, 3-5 µm) band with low optical loss and high transmittance, as demonstrated by our simulations. In this work, we develop and optimize a high-fidelity nanofabrication process for an amorphous silicon grating-based metasurface polarizer on a sapphire substrate. The process employs two key SiO2 layers—an interfacial layer for adhesion and a hard mask for patterning—enabling high‑precision fabrication and robust structural integrity. This approach provides a practical fabrication route toward high-performance, low-cost, and flip‑chip compatible MWIR polarization filters for next‑generation highly-miniaturized multispectral polarimeters.