Real-time observation of frequency Bloch oscillations with fibre loop modulation

Hao Chen,Peixiang Lu,Chi Zhang,Chengzhi Qin,Wenwan Li,Tianwen Han,Xinliang Zhang,Weiwei Liu,Kai Wang,Hua Long,Ningning Yang,Bing Wang

doi:10.1038/s41377-021-00494-w

Abstract

Bloch oscillations (BOs) were initially predicted for electrons in a solid lattice to which a static electric field is applied. The observation of BOs in solids remains challenging due to the collision scattering and barrier tunnelling of electrons. Nevertheless, analogies of electron BOs for photons, acoustic phonons and cold atoms have been experimentally demonstrated in various lattice systems. Recently, BOs in the frequency dimension have been proposed and studied by using an optical micro-resonator, which provides a unique approach to controlling the light frequency. However, the finite resonator lifetime and intrinsic loss hinder the effect from being observed practically. Here, we experimentally demonstrate BOs in a synthetic frequency lattice by employing a fibre-loop circuit with detuned phase modulation. We show that a detuning between the modulation period and the fibre-loop roundtrip time acts as an effective vector potential and hence a constant effective force that can yield BOs in the modulation-induced frequency lattices. With a dispersive Fourier transformation, the pulse spectrum can be mapped into the time dimension, and its transient evolution can be precisely measured. This study offers a promising approach to realising BOs in synthetic dimensions and may find applications in frequency manipulations in optical fibre communication systems.

Highlights

Bloch oscillations (BOs) describe the periodic movement of electrons in solids to which an external static electric field is applied[1,2] and are associated with a variety of interesting phenomena concerning the ultrafast transport of electrons
Analogies of electron BOs for neutral particles such as photons, acoustic phonons and cold atoms have been demonstrated in waveguide arrays[3,4,5], acoustic cavities[6,7] and optical lattices[8,9], which offer alternative platforms to investigate BOs more conveniently
Much research interest has been devoted to BOs in synthetic frequency lattices, which are usually formed by imposing temporal modulation on dielectric waveguides or fibres[22,23,24]

Summary

Introduction

Bloch oscillations (BOs) describe the periodic movement of electrons in solids to which an external static electric field is applied[1,2] and are associated with a variety of interesting phenomena concerning the ultrafast transport of electrons. Optical BOs in waveguide arrays stem from discrete diffraction[10,11,12,13,14]. This concept has been extended to synthetic dimensions of time[15,16], frequency[17,18,19] and angular momenta[20,21]. Much research interest has been devoted to BOs in synthetic frequency lattices, which are usually formed by imposing temporal modulation on dielectric waveguides or fibres[22,23,24]. Frequency BOs have been theoretically demonstrated in micro-resonators under temporal modulation[24], in which the frequency lattice is

Methods

Results

Conclusion