Mid-Infrared Polarization Engineering via Sub-wavelength Biaxial Hyperbolic vdW Crystals

Authors

Saurabh Dixit, Nihar Ranjan Sahoo, Abhishek Mall and Anshuman Kumar

Abstract

Mid-infrared (IR) spectral region is of immense importance for astronomy, medical diagnosis, security and imaging due to the vibrational modes of many molecules in this band. Two-dimensional van der Waals (vdW) crystals like α-MoO₃ and α-V₂O₅ exhibit natural in-plane biaxial hyperbolicity in the mid-IR at room temperature. Here, we harness this hyperbolic anisotropy to design lithography-free, sub-wavelength mid-IR photonic devices for polarization engineering. We demonstrate a dramatic footprint reduction while maintaining high extinction ratios using thin films of these vdW crystals. By precisely controlling polarization rotation, ellipticity, and phase via full-wave simulations and analytical models, we create miniaturized polarizers and waveplates with performance rivals traditional metasurfaces—providing a compact, integrable platform for IR photonics.