Electrostatic steering of thermal emission with active metasurface control of delocalized modes

We theoretically describe and experimentally demonstrate a graphene-integrated metasurface structure that enables electrically-tunable directional control of thermal emission. This device consists of a dielectric spacer that acts as a Fabry-Perot resonator supporting long-range delocalized modes bounded on one side by an electrostatically tunable metal-graphene metasurface. By varying the Fermi level of the graphene, the accumulated phase of the Fabry-Perot mode is shifted, which changes the direction of absorption and emission at a fixed frequency. We directly measure the frequency- and angle-dependent emissivity of the thermal emission from a fabricated device heated to 250 degrees C. Our results show that electrostatic control allows the thermal emission at 6.61 mu m to be continuously steered over 16 degrees, with a peak emissivity maintained above 0.9. We analyze the dynamic behavior of the thermal emission steerer theoretically using a Fano interference model, and use the model to design optimized thermal steerer structures. Dynamic angular tuning of thermal emission is a problem in the field of thermal metasurfaces. Here, the authors make a thermal emission device using electrostatic gates, opening an avenue for radiative heat management and mid-infrared communication.