Mid infrared polarization engineering via sub-wavelength biaxial hyperbolic van der Waals crystals

TL;DR

This paper demonstrates how biaxial hyperbolic van der Waals crystals, specifically $ ext{α-MoO}_3$, can be used to miniaturize mid-infrared photonic devices like polarizers and waveplates by exploiting their natural optical anisotropy.

Contribution

The study provides a comprehensive theoretical analysis and device optimization of $ ext{α-MoO}_3$ for mid-IR photonic applications, highlighting its potential for device miniaturization.

Findings

Significant reduction in device footprint for polarizers with high extinction ratio.

Effective subwavelength-thick waveplate design using $ ext{α-MoO}_3$.

Validation through analytical and full wave simulations.

Abstract

Recently, in-plane biaxial hyperbolicity has been observed in $\alpha$-MoO${_3}$ --a van der Waal crystal-- in the mid-infrared frequency regime. Here, we present a comprehensive theoretical analysis of thin film $\alpha$-MoO${_3}$ for application to two mid-IR photonic devices -- a polarizer and a waveplate. We show the possibility of a significant reduction in the device footprint while maintaining an enormous extinction ratio from $\alpha$-MoO${_3}$ based polarizers in comparison with that of conventional polarizers. Secondly, we carry out device optimization of $\alpha$-MoO${_3}$ based waveplates with subwavelength thickness. We explain our results using natural in-plane hyperbolicity of $\alpha$-MoO${_3}$ via analytical and full wave simulations. This work will build a foundation for miniaturization of mid-infrared photonic devices by exploiting the optical anisotropy of $\alpha$-MoO${_3}$.