# Switchable linear to circular polarization conversion in reflection and transmission modes based on vanadium-dioxide

## TL;DR

This paper introduces a terahertz polarization converter that can switch between transmission and reflection modes using vanadium dioxide.

## Contribution

A switchable dual-mode linear-to-circular polarization converter based on vanadium dioxide in the THz band is proposed.

## Key findings

- The converter operates in transmission mode with LTC polarization conversion at specific THz frequency bands when VO2 is insulating.
- In metallic state, VO2 enables reflection mode with circular polarization conversion across two frequency ranges.
- The device achieves high polarization conversion efficiency and low axial ratios suitable for THz communication systems.

## Abstract

A design of a switchable dual-mode linear-to-circular polarization converter (LTC-PC) in the terahertz (THz) band is reported based on vanadium dioxide (VO2). Adjusting the VO2 state allows the converter to alternate between the transmission and reflection modes. In the insulating state, VO2 enables transmission mode operation for a forward x- or y-polarized wave. LTC polarization conversion occurs within the frequency bands of 1.26–1.47 THz and 1.83–1.85 THz. Moreover, this mode yields an LTC polarization conversion at a frequency of 1.7 THz. The polarizer operates in reflection mode when VO2 is in the metallic state. Two conversion bands are identified for circular polarization within the frequency bands of 0.93–1.67 THz and 1.80–1.86 THz. The dual-mode polarization converter achieves axial ratios below 3 dB and a polarization conversion efficiency greater than 0.8. Surface current distributions reveal the polarization conversion mechanisms. Furthermore, we analyze the polarization ellipses of both reflected and transmitted waves at various frequencies across the operational bands. We anticipate that the proposed design, featuring high performance and dual functionality, will be applicable in THz communication systems and sensors.