Bilaterally asymmetric reflection and transmission of light by a grating structure containing a topological insulator

A boundary-value problem was formulated to investigate the reflection and transmission of light by a device consisting of an orthorhombic dielectric material that sits atop a 1D grating and is coated with a 3D topological insulator. In view of the periodicity of the grating, the electromagnetic field phasors were represented in terms of Floquet harmonics and the analysis was conducted by using the rigorous coupled-wave approach. We found that the device can exhibit bilaterally asymmetric reflection and transmission in the mid-infrared wavelength regime, provided that the surface admittance of the topological insulator is sufficiently high. This bilateral asymmetry is exhibited in narrow regimes for both the free-space wavelength and the angle of incidence. Bilateral asymmetry is exhibited more significantly by the specular components than by the nonspecular components of the reflected and transmitted plane waves.