Abstract
In this paper, we numerically demonstrate mid-IR nearly perfect resonant absorption and coherent thermal emission for both polarizations and wide angular region using multilayer designs of unpatterned films of hexagonal boron nitride (hBN). In these optimized structures, the films of hBN are transferred onto a Ge spacer layer on top of a one-dimensional photonic crystal (1D PC) composed of alternating layers of KBr and Ge. According to the perfect agreements between our analytical and numerical results, we discover that the mentioned optical characteristic of the hBN-based 1D PCs is due to a strong coupling between localized photonic modes supported by the PC and the phononic modes of hBN films. These coupled modes are referred as Tamm phonons. Moreover, our findings prove that the resonant absorptions can be red- or blue-shifted by changing the thickness of hBN and the spacer layer. The obtained results in this paper are beneficial for designing coherent thermal sources, light absorbers, and sensors operating within 6.2 μm to 7.3 μm in a wide angular range and both polarizations. The planar and lithography free nature of this multilayer design is a prominent factor that makes it a large scale compatible design.
Highlights
Thermal emission originates from the totally uncorrelated process of spontaneous radiation inside matter in local thermal equilibrium
Inspired by that point, Lee et al [45,46] demonstrated that a coherent thermal source can be designed using an unpatterned film of SiC that is coated on a 1D photonic crystals (1D PCs)
In order to match the photonic bandgap of the 1D PC to the second Reststrahlen band (RS band) of hexagonal boron nitride (hBN), we choose d1 = 923nm and d2 = 576 nm
Summary
Thermal emission originates from the totally uncorrelated process of spontaneous radiation inside matter in local thermal equilibrium. Inspired by that point, Lee et al [45,46] demonstrated that a coherent thermal source can be designed using an unpatterned film of SiC that is coated on a 1D PC They showed that the excitation of surface waves at the interface of the coated layer and the photonic crystal results in highly spectral and directional thermal emission in the mid-IR for both TE and TM waves [45,46]. To the best of our knowledge, this is the first analytical-numerical study of resonant absorption in hBN-based 1D PCs for both polarizations
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