Propagation of Partially Coherent Light in non-Hermitian Lattices

TL;DR

This paper develops a band theory for partially coherent light in non-Hermitian lattices, revealing how coherence and gain/loss interplay to affect beam propagation, Bloch oscillations, and mode transitions.

Contribution

It introduces a formalism linking coherence theory with band structures in non-Hermitian lattices, highlighting the impact of spatial coherence on light dynamics.

Findings

Partially coherent light exhibits band and gap structures in correlation functions.

Bloch oscillations can be sustained in PT-symmetric lattices, depending on coherence.

A coherence-induced transition between breathing and oscillating modes is demonstrated.

Abstract

Band theory for partially coherent light is introduced by using the formalism of second-order classical coherence theory under paraxial approximation. It is demonstrated that the cross-spectral density function, describing correlations between pairs of points in the field, can have bands and gaps and form a correlation band structure. The propagation of a partially coherent beam in non-Hermitian periodic structures is considered to elucidate the interplay between the degree of coherence and the gain/loss present in the lattice. We apply the formalism to study partially coherent Bloch oscillations in lattices having parity-time symmetry and demonstrate that the oscillations can be sustained in such media but they are strongly dependent upon the spatial correlations of the beam. A transition between breathing and oscillating modes is shown to be induced by the degree of spatial coherence.