High temperature mid-IR polarizer via natural in-plane hyperbolic Van der Waals crystals

TL;DR

This paper demonstrates a high-temperature mid-infrared polarizer using natural in-plane hyperbolic Van der Waals crystals, specifically $ extalpha$-MoO$_3$, which maintains high performance up to 140°C and offers a lithography-free, chip-compatible solution.

Contribution

First report of mid-IR optical response of $ extalpha$-MoO$_3$ above room temperature, showing its potential for high-temperature IR polarizers with natural hyperbolic anisotropy.

Findings

$ extalpha$-MoO$_3$ polarizer retains >10 dB extinction ratio up to 140°C.

Experimental validation of in-plane hyperbolic anisotropy in $ extalpha$-MoO$_3$.

Device operates without lithography, enabling easy integration.

Abstract

Integration of conventional mid to long-wavelength infrared polarizers with chip-scale platforms is restricted by their bulky size and complex fabrication. Van der Waals materials based polarizer can address these challenges due to its non-lithographic fabrication, ease of integration with chip-scale platforms, and room temperature operation. In the present work, mid-IR optical response of the sub-wavelength thin films of $\alpha$-MoO$_3$ is investigated for application towards high temperature mid-IR transmission and reflection type thin film polarizer. To our knowledge, this is the first report of above room temperature mid-IR optical response of $\alpha$-MoO$_3$ to determine the thermal stability of the proposed device. We find that our $\alpha$-MoO$_3$ based polarizer retains high extinction ratio with peak value exceeding 10 dB, up to a temperature of 140$^{\circ}$C. We explain our experimental findings by natural in-plane hyperbolic anisotropy of $\alpha$-MoO$_3$ in the mid-IR, high temperature X-ray diffraction and Raman spectroscopic measurements. This work opens up new avenues for naturally in-plane hyperbolic van der Waals thin-films to realize sub-wavelength IR optical components without lithographic constraints.