High-performance mid-infrared linear polarizers using Fabry–Pérot-resonant HSQ-based gratings via a simplified fabrication

Abstract

High-performance mid-infrared (MIR) linear polarizers are essential for advanced applications in polarimetric detection, thermal imaging and environmental monitoring. However, conventional implementations face a persistent challenge in simultaneously achieving high transverse magnetic (TM) wave transmission and extinction ratio (ER) while maintaining fabrication simplicity. Here, we present a 350 nm-pitch bilayer polarizer utilizing hydrogen-silsesquioxane (HSQ) gratings with collimated aluminum metallization. By leveraging HSQ's dual functionality as both the dielectric grating and electron-beam resist, our design enables a streamlined fabrication process: direct-write lithography followed by collimated thermal evaporation—eliminating the need for pattern transfer, a key limitation in conventional fabrication that degrades performance. A tailored spacer thickness can maximize TM transmission in the broadband MIR region by satisfying Fabry–Pérot resonance. Experimental results confirm the outstanding performance, including a 94% average transmission and a 30 dB extinction ratio across a 3–5 μm spectral range. The developed approach offers a promising strategy for MIR polarizers, successfully reconciling the traditionally competing demands of optical performance and easy fabrication.