Circularly Polarized Thermal Radiation From Nonequilibrium Coupled Antennas

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.

Thermal spin photonics in the near-field of nonreciprocal media

“…It paves the way for new fundamental and technological avenues related to thermal spin photonics. In particular, it will be useful in the near future for shaping spin-angular momentum related radiative heat transport phenomena such as our recent work on circularly polarized thermal light sources [11].…”

“…Our work utilizes fluctuational electrodynamics and is fundamentally beyond the regime of Kirchhoff's laws which is valid only for far-field thermal emission from bodies at equilibrium. One striking example where spin angular momentum of thermal radiation is not captured by Kirchhoff's laws, is circularly polarized thermal emission from coupled non-equilibrium antennas demonstrated in our recent work [11]. This approach of exploiting interacting non-equilibrium bodies is fundamentally unrelated to conventional approaches of achieving spin angular momentum of light based on either polarization conversion or structural chirality.…”

“…The spin angular momentum density(3) has so far been studied primarily for non-thermal light [31,32], where it leads to proportionate optical torque on small, absorptive particles [35,36]. We have generalized it here and in our recent work [11] to thermally generated electromagnetic fields in vacuum. We calculate both electric and magnetic type thermal spin angular momentum density given by ( ) S E and ( ) S H respectively.…”

Angular momentum radiation from current-carrying molecular junctions

“…However, for the symmetric couplings at para position, the net AM is 0 despite of the applied biases. These properties imply the possibility to design smart optical devices that can control the generation of AM radiation by simply applying an electric bias to the molecule junction, a convenient way compared with controlling AM radiation using a temperature bias [48,49] or an external magnetic field [50].…”

Multi-Layer Aperiodic Dielectric Stack Structures for High Performance Electromagnetic Spectral Shaping from mm-Wave to mid-IR Frequencies

“…Having a high-Q emission peak maximizes the detection resolution, where individual elements, molecules, or gases can be detected in a medium with minimal error. Several emitters have been reported to produce these narrowband emissions [46,47,48,49,50,51,52,7,53,6,8,54,29], based on various methods that can be classified as follows.…”