Nonreciprocal absorption and omnidirectional band gap in the biaxial hyperbolic metamaterials with black phosphorus

Abstract

Hyperbolic metamaterials (HMs) stacked by black phosphorus (BP) and silver are proposed, whose permittivities of three orthogonal directions are theoretically investigated. Four structures are designed by the HMs, of which the quasi-periodic structure 4 with gradient thickness and the filter element is adopted. The simulated results show that the hyperbolic properties can be found in several distinct regions for the dielectric constant of BP. In the proposed structure 4, the absorption peaks of transverse electric (TE) wave and transverse magnetic (TM) wave can be observed at different incident angles and frequency positions during the forward transmission. The peak value of TM wave is larger than that of TE wave at a sharp angle, which is more suitable for realizing the sensors and its sensitivity is 1.49 THz·degree−1 in the linear range. For the backward transmission, the entire structure is presented with the photonic band gap in the incident angle range of 0°–70° and in the frequency range of 630–740 THz, which can be called the omnidirectional band gap. Thus, the phenomenon of the nonreciprocal transmission of electromagnetic waves along two directions can be obtained. The cross stacking of the x- and y-directions of the dielectric constant of BP and the x- and y-axes of the coordinate axis is also considered. There is little difference with the above results, only the sensitivity of the sensor is enhanced slightly. The calculated results can apply for realizing the nonreciprocal absorbers, sensor, and an omnidirectional reflector.