Abstract
Infrared metasurface anomalous reflector with ultra-high efficiency and broad band operation is designed via multi-sheet graphene layer with triangular holes. The anomalous reflection angle covers the range of 10° to 90° with the efficiency higher than 80%, over a broad spectral range from 7 μm–40 μm of infrared spectrum. It reaches above 92% at the center wavelength in the spectral response. By increasing the periodicity of phase gradient, we can expand this frequency band even further without losing efficiency. The compact design of metasurface affords the adjustability of the electrochemical potential level of graphene by means of gating. Additionally, the impact of the number of graphene sheets for the optimum efficiency of the proposed structure is investigated. By adding the secondary graphene metasurface with opposite direction of phase gradient, we demonstrated the tunability of the reflection angle from θr to −θr with bias voltage.
Highlights
Plasmonic metasurfaces with a phase gradient have the ability to alter and tilt the wavefront of electromagnetic waves[23,24,25,26]
Our design achieved the anomalous reflection angle, covering a range of 10° to 90° with an efficiency higher than 80% over a broad spectral range from 7 μm–40 μm
The effective phase gradient is generated from the triangular shape on the graphene layers
Summary
Plasmonic metasurfaces with a phase gradient have the ability to alter and tilt the wavefront of electromagnetic waves[23,24,25,26] In this regard, the structures with low quality factors are the center of interests[27,28,29,30]. Each graphene ribbon has a specific width, chosen to have a certain plasmon resonance frequency This provides the strong near-field interaction, and highly efficient anomalous reflections. Both the periodicity of the phase gradient direction (x-direction) and the periodicity of the polarization direction (y-direction) are considered to design a structure and to investigate the behavior of its reflection with the assistance of the Finite-difference time-domain (FDTD) method. By leveraging the tunability of the Fermi level of the graphene sheets[43,44,45,46,47], we propose uniquely tunable graphen plasmonic reflector structure in this work
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