All‐Dielectric Thermal Emitter With Highly‐Coherent Narrowband Directional Radiation

ABSTRACT This research explores the advancement of a highly directional all‐dielectric thermal emitter. It illustrates that a coupled photonic device—a directional thermal emitter based on resonance metagratings integrated with a band‐pass filter utilizing distributed Bragg reflectors—can function as a distinctive thermal emitter. This thermal emitter emits an extremely narrow band of electromagnetic waves in only two specific, distinct directions, exhibiting a discrete dispersion curve. With a peak emissivity of ε ∼ 0.9 and a Q‐factor of approximately 243, this coupled thermal emitter demonstrates an angular spread ( Δθ ) of about 0.5°. Since the device is composed entirely of dielectric materials, its spatial coherence length is high, estimated to be around 115 λ . Furthermore, the device parameters can be customized to manipulate the emitting wavelength and angle across a wide range. By introducing a new class of highly directional thermal emitters, this research deepens our understanding of thermal radiation principles and offers practical implications for various thermal‐engineering applications.