Ultranarrow and Angle-Insensitive Thermal Emitters Enabled by Quasi-Bound States in the Continuum with Lattice Perturbation

Narrow-band thermal emission holds promising prospects in the field of energy devices. However, the angle dispersion causes a deviation from the desired wavelength, leading to energy dissipation and a significant decrease in energy utilization efficiency. Here, we demonstrate an avenue toward high Q factor and angle-insensitive thermal emitter design based on quasi-bound states in the continuum with geometric perturbations. The height perturbation and lattice perturbation affect the out-of-plane and in-plane mode couplings, respectively, contributing to tailoring the Q factor and regulating the angle dispersion. We have demonstrated an infrared emitter, compatible with wavelength tunability and large-scale on-chip fabrication, exhibiting a high Q factor of up to 650 and superior angle-insensitive performance over the full angle range. This has been further experimentally verified with measured angle-resolved absorption and emission spectra. Our results provide a significant improvement in achieving ultranarrow and angle-insensitive thermal emission, offering promising applications in high-precision detection and miniature on-chip spectrometers.