PT-symmetric transport in non-PT-symmetric bi-layer optical arrays

TL;DR

This paper investigates transport in non-PT-symmetric bi-layer optical arrays with balanced loss/gain, revealing spectral bands with real Bloch indices, regions of high transmission, unidirectional reflectivity, and Fabry-Perrot resonances.

Contribution

It demonstrates that non-PT-symmetric structures can exhibit PT-like transport properties and identifies conditions for spectral bands and resonances in such systems.

Findings

Spectral bands with real Bloch indices emerge in non-PT-symmetric arrays.

Regions with transmission coefficient T_N ≥ 1 and T_N ≤ 1 are identified.

Unidirectional reflectivity occurs at band borders, and Fabry-Perrot resonances are observed.

Abstract

We study transport properties of an array created by alternating $(a,b)$ layers with balanced loss/gain characterized by the key parameter $\gamma$. It is shown that for non-equal widths of $(a,b)$ layers, i.e., when the corresponding Hamiltonian is non-PT-symmetric, the system exhibits the scattering properties similar to those of truly PT-symmetric models provided that without loss/gain the structure presents the matched quarter stack. The inclusion of the loss/gain terms leads to an emergence of a finite number of spectral bands characterized by real values of the Bloch index. Each spectral band consists of a central region where the transmission coefficient $T_N \geq 1$, and two side regions with $T_N \leq 1$. At the borders between these regions the unidirectional reflectivity occurs. Also, the set of Fabry-Perrot resonances with $T_N=1$ are found in spite of the presence of loss/gain.