Exploring the Design of Mid-Infrared Thermal Emitters Using Graphene-Si Hybrid Resonances with Coupled Mode Theory

Thermal emission is typically spontaneous, broadband, and isotropic. Modifying the emissivity and absorptivity of a nanostructure allows for the development of devices for heat management and leads to advances in beamforming metasurfaces for generally incoherent light or emissive sources. Here we discuss the use of coupled-mode theory to design metasurfaces whose working principle couples the guided mode resonance of a silicon photonic crystal to the localized surface plasmons of a graphene ribbon array. The resultant devices are predicted to have a Q factor of greater than 10,000 and can be tuned through the application of a gate voltage from a peak emissivity of more than 0.98 to nearly 0. We show that predictions made using coupled mode theory run two orders of magnitude faster than equivalent FEM simulations, allowing us to quickly define the phase space of device geometries that produce critically coupled, narrowband TM-polarized thermal emission. We will also present results of experimental measurements of tunable graphene resonators coupled to high quality factor photonic crystals. We show through the choice of realistic material parameter modelling, the resultant structures are amenable for fabrication.<br/><br/>A. Nagpal, M. Zhou, O. Ilic, Z. Yu, H. Atwater, "Thermal Metasurface with Tunable Narrowband Absorption from a Hybrid Graphene/Silicon Photonic Crystal Resonance," <i>Opt. Express</i>, (2022).