Zero index metamaterials with PT symmetry in a waveguide system.

Inspired by the concept of parity-time symmetry, we propose a new waveguide system consisting of zero index metamaterials with an air gap. Based on analytical calculations and numerical simulations, we demonstrate that there are two exceptional points in such a system, which can induce unidirectional transparency. However, the introduced air gap could effectively manipulate the property of the waveguide system with PT symmetry. In particular, coherent perfect absorber-laser modes could be excited in PT broken phase, if a specific phase difference in the air gap is obtained. More interestingly, when Fabry-Pérot resonances take place in the air gap, the PT symmetry property will be suppressed, i.e., the value of loss/gain could not affect transmission and reflection of the waveguide. As a result, perfect bidirectional transmission without reflection can occur in the waveguide system.