VO₂-hBN-graphene-based bi-functional metamaterial for mid-infrared bi-tunable asymmetric transmission and nearly perfect resonant absorption

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 VO 2 ∕Au grating on the lower side. Through analytical calculations, we first investigate how the dispersion characteristics of the high-β hyperbolic phonon polaritons of hBN can be controlled and hybridized through the insulator (i-VO 2 ) to metal (m-VO 2 ) transition of VO 2 in a bare hBN∕VO 2 heterostructure. Then, at the absence of graphene and owing to the support of the hybridized high-β modes, a broad and efficient AT with forwardto-backward contrast exceeding 40% is obtained by numerical calculations for the i-VO 2 case, as the first functionality of the structure. Moreover, it is found that for the m-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 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.

Tunable plasmon-phonon polaritons in anisotropic 2D materials on hexagonal boron nitride

“…Besides being compatible with an A2DM, hBN has a very useful phononic property in the MIR rangeit behaves as a natural hyperbolic material within its RS bands and as a uniaxially anisotropic dielectric with low-losses outside of them [33][34][35][36][37][38][39]. In this section we analyze an A2DM/hBN/sub heterostructure [ Figure 1(c)] which is more functional than the suspended A2DM sheet and the A2DM/sub structure considered earlier.…”

“…This property allows hBN slabs to support subdiffractional volume-confined hyperbolic phonon polaritons with relatively low losses. Hereafter, the hyperbolic phonon polaritons of bare hBN and guided plasmon-phonon modes of graphene-hBN heterostructures inside (outside) of the RS band of hBN are denoted as HP 2 s and HP 3 s (SP 3 s), respectively [35][36][37][38]. As a result, the phonon polaritons in natural hBN exhibit an out-of-plane hyperbolic dispersion while their in-plane dispersion is isotropic.…”

“…This paper presents the exact dispersion relations for the guided SP 3 s and HP 3 s modes supported by an A2DM/hBN/sub heterostructure, where "sub" denotes substrate. These relations are then simplified to the case of an A2DM/sub structure to investigate the effect of substrate on the modal properties of SPPs supported by the plasmonic A2DM, which are denoted here as SP 2 s [35,37,38]. We calculate the EFCs, density plots, and electric field distributions of the guided modes supported by a suspended A2DM, A2DM/sub, and A2DM/hBN/sub heterostructures to analyze how the presence of hBN can lead to the topological transition of the guided modes.…”

Active metamaterial nearly perfect light absorbers: a review [Invited]

“…GST-based MPAs employed in patterned [184] and unpatterned [185] potential application of PCMs is not limited to the visible and IR regions; there are also some reports on taking advantage of PCMs' active optical responses in the microwave and THz regions [119,120]. Moreover, very recently, it has been theoretically reported that by combining VO 2 , hBN, and graphene in one structure it is possible to obtain a bi-tunable metamaterial with bi-functional MPA and asymmetric light transmitter characteristics in the MIR region [186], see Fig. 4(k).…”

Adaptive tuning of infrared emission using VO2 thin films

“…www.nature.com/scientificreports/ hBN heterostructures combined with Ge gratings on one side and a hybrid VO 2 /Au grating on the other side 24 . Specifically, a spectral absorption peak attributed to excitation of magnetic resonance can be excited below phase transition temperature, while above the phase transition temperature this magnetic resonance vanishes in the metallic state 24 . In Ref.…”