Observation of Bloch oscillations in complex PT-symmetric photonic lattices

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.

Parity‐Time‐Symmetric Optical Lattice with Alternating Gain and Loss Atomic Configurations

“…More importantly, the gain and loss coefficients can be adjusted more independently, which will be easier to control the gain, loss, and coupling coefficients to realize the PT‐symmetric condition and study related effects. Furthermore, by taking advantage of the large parametric space in multi‐level atomic configurations, such newly demonstrated periodic gain/loss optical lattices can provide a more flexible platform to investigate the diverse effects such as solitons in PT‐symmetric nonlinear lattices and unidirectional light transport resulting from the interplay between non‐Hermitian Hamiltonian and nonlinear effects, and various beam dynamical properties such as non‐Hermitian Bloch oscillation predicted in non‐Hermitian optical lattices. Also, this EIT‐based scheme can be extended to various atom‐like solid materials, and hopefully create useful PT‐symmetric optical devices.…”

“…So far, experimental realizations of periodically arranged PT‐symmetric potentials have been limited only to a few optical settings, such as a time‐domain lattice realized in a network of coupled gain/loss fiber loops, and an optical waveguide array with a lossy (without gain) background . The known exact PT‐symmetric optical lattice with spatially periodic gain and loss channels was realized in a four‐level N ‐type atomic configuration .…”

Anderson localization in synthetic photonic lattices

“…A number of important effects have been demonstrated in SPLs, including random walks of single particles 11 , Bloch oscillations and unidirectional invisibility associated with parity-time symmetry 12, 15 , scattering on defect states 16 , and diametric drive acceleration 17 . Furthermore, SPLs are naturally suitable for observation of Anderson localization, since any degree of disorder can be introduced through programmable electro-optic phase-modulation of individual propagating pulses at specific time slots of the lattice.…”

Super Bloch oscillation in aPTsymmetric system

“…Although the nonHermitian Hamiltonian considered in [20] is PT symmetric, the total power was observed to be changed in time. In the experiment [21], pseudo-Hermitian wave packet propagation with a vanishing net increase in power was observed by controlling the period of the Bloch oscillation in a global and local PT symmetric mesh lattice. A resonant restoration of PT symmetry and secondary emissions, which occurs each time the wave packet passes through the exceptional point was also observed in that experiment.…”