Observation of Bloch oscillations in complex PT-symmetric photonic lattices

TL;DR

This paper reports the first experimental observation of Bloch oscillations in complex PT-symmetric photonic lattices, revealing unique properties and a method to reconstruct the band structure by monitoring light evolution.

Contribution

It introduces the first experimental demonstration of Bloch oscillations in PT-symmetric lattices and a novel method to analyze their band structure through light evolution monitoring.

Findings

Observation of Bloch oscillations in PT-symmetric lattices

Detection of secondary emissions and resonant PT symmetry restoration

Method for reconstructing real and imaginary band components

Abstract

Light propagation in periodic environments is often associated with a number of interesting and potentially useful processes. If a crystalline optical potential is also linearly ramped, light can undergo periodic Bloch oscillations, a direct outcome of localized Wannier-Stark states and their equidistant eigenvalue spectrum. Even though these effects have been extensively explored in conservative settings, this is by no means the case in non-Hermitian photonic lattices encompassing both amplification and attenuation. Quite recently, Bloch oscillations have been predicted in parity-time-symmetric structures involving gain and loss in a balanced fashion. While in a complex bulk medium, one intuitively expects that light will typically follow the path of highest amplification, in a periodic system this behavior can be substantially altered by the underlying band structure. Here, we report the first experimental observation of Bloch oscillations in parity-time-symmetric mesh lattices. We show that these revivals exhibit unusual properties like secondary emissions and resonant restoration of PT symmetry. In addition, we present a versatile method for reconstructing the real and imaginary components of the band structure by directly monitoring the light evolution during a cycle of these oscillations.