Dual-Band Infrared Near-Perfect Absorption by Fabry-Perot Resonances and Surface Phonons

In this article, we present a simple absorber design which enables dual-band near-perfect absorption at infrared (IR) frequencies. The absorber is an unpatterned hBN/dielectric/hBN triple layer, with a 1150-nm-thick hBN film as the top layer, a 850-nm-thick dielectric film as the middle layer, and a hBN substrate. Unlike the metal/dielectric/metal triple layer, it is found that the high efficiency absorption at specific wavelengths is mainly mused by two mechanisms: Fabry-Perot (FP) resonances and surface phonons. The absorption response is found sensitive to the top and middle layers. The two mechanisms can be coupled to affect the absorption spectra by choosing a proper thickness of the top and middle layers.