Broadband mixing of ${\cal PT}$-symmetric and ${\cal PT}$-broken phases in photonic heterostructures with a one-dimensional loss/gain bilayer

TL;DR

This paper theoretically demonstrates broadband mixing of ${\cal PT}$-symmetric and ${\cal PT}$-broken phases in photonic heterostructures with loss/gain bilayers and polarization converters, enabling advanced control of electromagnetic wave transmission and absorption.

Contribution

It introduces novel heterostructure configurations that achieve broadband phase mixing of ${\cal PT}$ phases, expanding the potential for tunable photonic devices.

Findings

Broadband phase mixing achieved in four-channel heterostructures.

Configurations with polarization-converting components enable phase control.

Eigenvalue behaviour varies with loss/gain medium permittivity.

Abstract

Combining loss and gain components in one photonic heterostructure opens a new route to efficient manipulation by radiation, transmission, absorption, and scattering of electromagnetic waves. Therefore, loss/gain structures enabling ${\cal PT}$-symmetric and ${\cal PT}$-broken phases for eigenvalues have extensively been studied in the last decade. In particular, translation from one phase to another, which occurs at the critical point in the two-channel structures with one-dimensional loss/gain components, is often associated with one-way transmission. In this report, broadband mixing of the ${\cal PT}$-symmetric and ${\cal PT}$-broken phases for eigenvalues is theoretically demonstrated in heterostructures with four channels obtained by combining a one-dimensional loss/gain bilayer and one or two thin polarization-converting components (PCCs). The broadband phase mixing in the four-channel case is expected to yield advanced transmission and absorption regimes. Various configurations are analyzed, which are distinguished in symmetry properties and polarization conversion regime of PCCs. The conditions necessary for phase mixing are discussed. The simplest two-component configurations with broadband mixing are found, as well as the more complex three-component configurations wherein symmetric and broken sets are not yet mixed and appear in the neighbouring frequency ranges. Peculiarities of eigenvalue behaviour are considered for different permittivity ranges of loss/gain medium, i.e., from epsilon-near-zero to high-epsilon regime.