Narrowband thermal emitter based on quasi-Tamm phonon polaritons in uniaxial hyperbolic materials

Narrowband mid-infrared emitters have garnered considerable attention due to their promising applications in fields such as chemical and biological sensing, as well as efficient thermal energy management. In this paper, we present a novel design for a narrowband mid-infrared thermal emitter based on quasi-Tamm phonon-polaritons (quasi-TPhPs) in hyperbolic materials. The structure replaces traditional one-dimensional symmetric photonic crystals with two pairs of asymmetric Ge/SiO 2 thin films, enabling enhanced reflection. By incorporating hexagonal boron nitride (hBN) at the substrate, the quasi-TPhPs are efficiently excited within the type-II hyperbolic band for both transverse electric and transverse magnetic waves. The emitter achieves near-unity emission at a wavelength of 6.717 μm, with a quality factor greater than 210. Notably, a substantial enhancement of the electric field at the interface between hBN and the Ge/SiO 2 stack further substantiates the presence of TPhPs. Additionally, we examine the influence of incident angle and polarization state on emitter performance. Moreover, the resonance wavelength and emission strength of the TPhPs mode can be finely tuned by adjusting the spacer layer thickness. This approach offers a highly efficient and tunable method for achieving narrowband thermal radiation, making it a promising candidate for applications in mid-infrared gas sensing and thermophotovoltaics power generation.