Abstract

Bi-tunable asymmetric light transmission (AT) and nearly perfect resonant absorption functionalities are achieved by a Lorentz-reciprocal metamaterial for the operation at the mid-infrared (MIR) wavelengths and transverse magnetic polarization. The bi-tunable metamaterial with bi-functional features and a total thickness of 1.8 μm is based on an hBN/graphene/hBN heterostructure that is bounded by a Ge grating on the upper side and a hybrid ${\mathrm{VO}}_2/\mathrm{Au}$ grating on the lower side. Through analytical calculations, we first investigate how the dispersion characteristics of the high-$\beta$ hyperbolic phonon polaritons of hBN can be controlled and hybridized through the insulator ($\mathrm{i}\text{-}{\mathrm{VO}}_2$) to metal ($\mathrm{m}\text{-}{\mathrm{VO}}_2$) transition of ${\mathrm{VO}}_2$ in a bare $\mathrm{hBN}/{\mathrm{VO}}_2$ heterostructure. Then, at the absence of graphene and owing to the support of the hybridized high-$\beta$ modes, a broad and efficient AT with forward-to-backward contrast exceeding 40% is obtained by numerical calculations for the $\mathrm{i}\text{-}{\mathrm{VO}}_2$ case, as the first functionality of the structure. Moreover, it is found that for the $\mathrm{m}\text{-}{\mathrm{VO}}_2$ case, the device is no longer transmittive and a nearly perfect resonant absorption response, as the second functionality, is observed for backward illumination. Finally, by introducing multilayer graphene into the structure and considering the intermediate states of ${\mathrm{VO}}_2$ in the calculations, the bi-tunable transmission and absorption characteristics of the device are investigated. We believe the designed metamaterial is well-suited for MIR optical diodes, sensors, and thermal emitters.

© 2019 Optical Society of America

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