Multiple PT symmetry and tunable scattering behaviors in a heterojunction cavity

Abstract

We study a heterojunction cavity with one vacuum gap inserted between two dielectric slabs with conjugate complex refractive indices, i.e., of balanced gain and loss. This cavity is found to exhibit a multiple parity-time (PT) symmetry characterized by alternating symmetric and broken phases, when examined in terms of both of the eigenvalues of the scattering matrix. Scattering behaviors, including reflection and transmission, however, should be classified into three distinct types because a transition region may exist between the symmetric and broken phases. It is of particular interest that vanishing reflectance could occur for light waves input from both the left and right sides, though of different wave vectors, in the symmetric phases. Moreover, it is viable to attain unidirectional invisibility for light waves only input from the left side and simultaneously realize coherent perfect absorption and lasing for a given wave vector in the transition regions. These unique scattering behaviors can be easily tuned to suit a wide range of wave vectors by adjusting the gap width.