Optical waveguides, which route light between optical devices much like metal wires routing electrons on a silicon chip, are the fundamental building blocks of integrated photonics. The most widely used waveguide is a dielectric waveguide in which a high-index core is surrounded by a low-index cladding; light is confined in the core because of total internal reflection. We propose a new waveguiding mechanism based on an effective gauge field for photons. Unlike dielectric waveguides, our proposed waveguide allows light to propagate in only one direction, eliminating undesirable back reflections.
We provide a theoretical framework to understand a gauge-field waveguide, where a gauge field can displace, in wave vector space, otherwise identical states in the core and cladding, thus producing light confinement in the core. Even though photons are neutral and therefore have no naturally analogous magnetic field, effective gauge fields for photons can be realized by controlling the phase of dynamic modulations that drive photonic transitions. We use standard waveguide theory to describe an inhomogeneous effective gauge-field waveguide constructed from a square lattice of dynamically coupled resonators, and we illustrate its novel features such as nonreciprocity and single-mode, one-way guiding over certain frequency ranges. In such a system, the effective gauge field for photons is mapped to the modulation phases, which one can readily control in real time, allowing for the reconfiguration of the routing scheme dynamically, without changing the underlying device structure.
Our work highlights new possibilities in controlling the flow of light and exemplifies a rich set of gauge-field physics that can be studied in photonic systems. Experimental realization of our proposal could be feasible with the rapid development of on-chip silicon photonics.
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