Light guiding by artificial gauge fields

Abstract

†These authors contributed equally to this work.The use of artificial gauge fields enables systems of uncharged particles to behave as if affected by external fields. Generated by geometry or external modulation, artificial gauge fields have been instrumental in demonstrating topological phenomena in many physical systems, including photonics, cold atoms and acoustic waves. Here, we demonstrate experimentally for the first time waveguiding by means of artificial gauge fields. To this end, we construct artificial gauge fields in a photonic waveguide array, by using waveguides with nontrivial trajectories. First, we show that tilting the waveguide arrays gives rise to gauge fields that are different in the core and the cladding, shifting their respective dispersion curves, and in turn confining the light to the core. In a more advanced setting, we demonstrate waveguiding in a medium with the same artificial gauge field and the same dispersion everywhere, but with a phase-shift in the gauge as the only difference between the core and the cladding. The phase-shifted sinusoidal trajectories of the waveguides give rise to waveguiding via bound states in the continuum. Creating waveguiding and bound states in the continuum by means of artificial gauge fields is relevant to a wide range of physical systems, ranging from photonics and microwaves to cold atoms and acoustics.Waveguiding -the ability to confine light in a region and guide it within a structure is a fundamental building block in many photonics applications. The basic structure of a waveguide consists of a core region where the light is confined and a cladding region within which the core is embedded. Standard waveguide structures rely on total internal reflection, and are made up of a high refractive index core surrounded by a low refractive index cladding, or on metallic pipes where the electromagnetic fields are completely forbidden from escaping [1]. Other schemes rely on photonic systems with bandgaps [2-6], coupled resonator arrays [7], grating-mediated waveguiding [8], Kapitza-effect arrangements [9] or exploit the vectorial spin-orbit interaction of light in an anisotropic medium [10]. In all of these, the core and the cladding are made from media with a different dispersion relation. Recently, a conceptually new waveguiding mechanics was proposed: a waveguide where the cladding and core region have the same dispersion curve, but the core's dispersion is shifted by virtue of an artificial gauge field [11].Gauge fields are a fundamental concept in physics, describing the basic interactions between charged particles. Neutral particles (such as photons) are thus decoupled from real gauge fields.However, by properly engineering a physical system, one can generate artificial gauge fields that would govern the effective dynamics of the neutral particles. That is, most often an artificial gauge field can be induced through the geometric design of the system or through some specific external modulation, such that the effective dynamics of the system behaves as...

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