Low-loss nanoscale zero-index metawaveguides and metadevices

Abstract

Zero-index metamaterials exhibit a uniform spatial phase distribution, promising numerous applications such as efficient electromagnetic tunneling and high-fidelity optical computing. These applications necessitate an integrated, low-loss zero-index waveguide platform for guiding, routing, and interfering light. Nevertheless, existing zero-index metamaterials grapple with substantial footprints, high losses, and limited flexibility. Here, we present low-loss nanoscale zero-index metawaveguides enabled by quasi-bound states in the continuum, formed through destructive interferences along in-plane and out-of-plane directions. This metawaveguide’s propagation loss is 2 orders of magnitude lower than that of the state-of-the-art zero-index waveguide. Leveraging the low loss and flexibility of this metawaveguide, we realized a zero-index metaring for the first time. This low-loss zero-index metawaveguide offers a versatile platform for integrated photonic circuits with minimal phase errors for classical and quantum information processing.