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 grating on the lower side. Through analytical calculations, we first investigate how the dispersion characteristics of the high- hyperbolic phonon polaritons of hBN can be controlled and hybridized through the insulator () to metal () transition of in a bare heterostructure. Then, at the absence of graphene and owing to the support of the hybridized high- modes, a broad and efficient AT with forward-to-backward contrast exceeding 40% is obtained by numerical calculations for the case, as the first functionality of the structure. Moreover, it is found that for the 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 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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