Unidirectional transparency in epsilon-near-zero based rectangular waveguides induced by parity-Time symmetry

Abstract

Epsilon-near-zero (ENZ) metamaterials present exciting features such as an almost infinite effective wavelength and phase velocity. However, a major challenge when using such artificial media is to achieve impedance matching due to their vanishing permittivity. To address this, it has recently been shown that wave propagation within ENZ media combined with parity-Time (PT) symmetry concepts can exhibit asymmetric reflection and enhanced transmission. Here, we exploit this technique by studying a PT-symmetric ENZ structure consisting of a rectangular waveguide operating near the cutoff frequency of the dominant TE10 mode (emulating an ENZ metamaterial) and placed between balanced thin loss and gain blocks. Theoretical studies based on the transmission line theory, eigenvalue problems, and full-wave numerical simulations are performed. It is shown how unbroken and broken PT-symmetric phases can exist with exceptional points in between, demonstrating asymmetric reflection and enhanced transmission while preserving the ENZ behavior of the system.