Metasurfaces are powerful structures for controlling far-field light propagation through the engineering of the amplitude, polarization, and phase at an interface. By incorporating active components into metasurfaces, it is possible to realize different optical functionalities such as lensing and far-field steering that can be adjusted in real time. There are a number of different ways to realize this active functionality, including mechanical modulation, phase change materials, and electrostatic control. Of these, electrostatic modulation offers the potential benefit of very fast switching speeds, as well as low power consumption and a small device footprint, making it a very promising approach for realizing practical photonic devices. We report here on gate-tunable graphene-based mid-IR metasurfaces, capitalizing on the dynamically tunable conductivity (and consequently permittivity) of graphene to demonstrate its utility for broadband thermal emission control and beam steering in a multi-pixel device.<br/><br/>First, we look at arrays of graphene nanoribbons and by tuning the plasmon-mediated cavity resonance, we achieve broadband (6-9um) tuning of its emission spectrum using a multipixel array. Second, we look at a sheet of graphene with a patterned Au layer and tune a gap plasmon using multiple macrocells to achieve beamsteering or dynamic angular control of emission. We demonstrate up to 237° of phase modulation at 8.5um and calculate expected steering efficiencies relative to the incident beam of 1% out to 30°. Furthermore, we demonstrate an inverse design algorithm using genetic algorithms (GA) that finds optimal phase profiles for beamsteering devices with non-ideal amplitude and phase ranges. A maximal increase of 84% in the optimized directivity compared to previously demonstrated forward designs in non-ideal devices is reported.

Reconfigurable graphene metasurfaces for thermal emission engineering and active beam steering in the mid-IR via inverse design

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.