# Circularly polarized thermal radiation from nonequilibrium coupled antennas

## TL;DR

This paper introduces a novel method for generating circularly polarized thermal radiation using coupled anisotropic antennas at different temperatures, enabling reconfigurable polarization without structural chirality or magnetic fields.

## Contribution

It reveals a new mechanism for circularly polarized thermal emission from nonequilibrium coupled antennas, supported by rigorous electrodynamic analysis and practical experimental proposals.

## Key findings

- Thermal emission from anisotropic antenna dimers can be highly circularly polarized.
- Reversing antenna temperatures flips the polarization handedness.
- The mechanism operates without magnetic fields or structural chirality.

## Abstract

Circularly polarized light can be obtained by using either polarization conversion or structural chirality. Here we reveal a fundamentally unrelated mechanism of generating circularly polarized light using coupled nonequilibrium sources. We show that thermal emission from a compact dimer of subwavelength, anisotropic antennas can be highly circularly polarized when the antennas are at unequal temperatures. Furthermore, the handedness of emitted light is flipped upon interchanging the temperatures of the antennas, thereby enabling reconfigurability of the polarization state lacked by most circularly polarized light sources. We describe the fundamental origin of this mechanism using rigorous fluctuational electrodynamic analysis and further provide practical examples for its experimental implementation. Apart from the technology applications in reconfigurable devices, communication, and sensing, this work motivates new inquiries of angular-momentum-related thermal-radiation phenomena using thermal nonequilibrium, without applying magnetic field.