Lithography-free IR polarization converters via orthogonal in-plane phonons in a-MoO3 flakes

TL;DR

This paper demonstrates lithography-free IR polarization converters using a-MoO3 flakes that exploit orthogonal in-plane phonons, achieving high polarization-dependent absorption and conversion without nanoscale fabrication.

Contribution

It introduces a novel approach to IR polarization control using naturally orthogonal phonon modes in a-MoO3, enabling simplified, low-loss photonic devices.

Findings

Achieved over 80% polarization-dependent absorption in a-MoO3-based cavities.

Observed 15% power conversion into orthogonal polarization.

Demonstrated coupling between phonons and cavity resonances.

Abstract

Exploiting polaritons in natural vdW materials has been successful in achieving extreme light confinement and low-loss optical devices and enabling simplified device integration. Recently, a-MoO3 has been reported as a semiconducting biaxial vdW material capable of sustaining naturally orthogonal in-plane phonon polariton modes in IR. In this study, we investigate the polarization-dependent optical characteristics of cavities formed using a-MoO3 to extend the degrees of freedom in the design of IR photonic components exploiting the in-plane anisotropy of this material. Polarization-dependent absorption over 80% in a multilayer Fabry-Perot structure with a-MoO3 is reported without the need for nanoscale fabrication on the a-MoO3. We observe coupling between the a-MoO3 optical phonons and the Fabry-Perot cavity resonances. Using cross-polarized reflectance spectroscopy we show that the strong birefringence results in 15% of the total power converted into the orthogonal polarization with respect to incident wave. These findings can open new avenues in the quest for polarization filters and low-loss, integrated planar IR photonics and in dictating polarization control.