Polarization vortices of thermal emission

Polarization vortices, crucial constituents of singular optics, manifest as vortices of polarization states around singularities. Recent progress has linked polarization vortices with bound states in the continuum (BICs) in optical waves. However, this association has not been explored in the realm of thermal emission, which holds the potential for generating arbitrary polarizations in a single thermal emitter. Here, we implement a polarization vortex thermal emitter (PVTE) based on BICs in a photonic crystal slab (PCS), allowing for the generation of various polarization states simultaneously along different directions. Using a custom-designed polarized angle-resolved thermal emission spectrometer (PARTES), we experimentally confirm polarization vortices of thermal emission originating from BICs with different charges and types. The proposed PVTEs present effective strategies for controlling thermal emission and show promising applications in infrared optical technology.