Half-spectral unidirectional invisibility in non-Hermitian periodic optical structures

TL;DR

This paper introduces half-spectral unidirectional invisibility in non-Hermitian periodic optical structures, where the medium appears invisible from one side below the Bragg frequency and from the opposite side above it, using tailored index and gain gratings.

Contribution

It presents a novel phenomenon of half-spectral invisibility in non-PT-symmetric optical structures achieved through Hilbert transform-based index and gain gratings.

Findings

Achieves unidirectional invisibility below and above the Bragg frequency

Uses tailored real and imaginary refractive index distributions

Demonstrates control of optical transparency in periodic structures

Abstract

The phenomenon of half-spectral unidirectional invisibility is introduced for one-dimensional periodic optical structures with tailored real and imaginary refractive index distributions in a non-$\mathcal{PT}$-symmetric configuration. The effect refers to the property that the optical medium appears to be invisible, both in reflection and transmission, below the Bragg frequency when probed from one side, and above the Bragg frequency when probed from the opposite side. Half-spectral invisibility is obtained by a combination of in-phase index and gain gratings whose spatial amplitudes are related each other by a Hilbert transform.