Robust light transport in non-Hermitian photonic lattices

TL;DR

This paper explores how non-Hermitian properties in 1D photonic lattices can enable robust, disorder-insensitive light transport through asymmetric amplification and damping, offering an alternative to topological protection.

Contribution

It introduces non-Hermitian transport mechanisms in 1D photonic lattices, demonstrating robustness against disorder via imaginary gauge fields and non-Hermitian delocalization transitions.

Findings

Non-Hermitian lattices exhibit asymmetric, disorder-robust light transport.

A mobility edge arises from non-Hermitian delocalization transition.

Engineered coupled-resonator structures can realize these effects experimentally.

Abstract

Combating the effects of disorder on light transport in micro- and nano-integrated photonic devices is of major importance from both fundamental and applied viewpoints. In ordinary waveguides, imperfections and disorder cause unwanted back-reflections, which hinder large-scale optical integration. Topological photonic structures, a new class of optical systems inspired by quantum Hall effect and topological insulators, can realize robust transport via topologically-protected unidirectional edge modes. Such waveguides are realized by the introduction of synthetic gauge fields for photons in a two-dimensional structure, which break time reversal symmetry and enable one-way guiding at the edge of the medium. Here we suggest a different route toward robust transport of light in lower-dimensional (1D) photonic lattices, in which time reversal symmetry is broken because of the {\it non-Hermitian} nature of transport. While a forward propagating mode in the lattice is amplified, the corresponding backward propagating mode is damped, thus resulting in an asymmetric transport that is rather insensitive to disorder or imperfections in the structure. Non-Hermitian transport in two lattice models is considered: a tight-binding lattice with an imaginary gauge field (Hatano-Nelson model), and a non-Hermitian driven binary lattice. In the former case transport in spite of disorder is ensured by a mobility edge that arises because of a non-Hermitian delocalization transition. The possibility to observe non-Hermitian delocalization induced by a synthetic 'imaginary' gauge field is suggested using an engineered coupled-resonator optical waveguide (CROW) structure.