Experimental Observation of Dissipatively Coupled Bound States in the Continuum on an Integrated Photonic Platform

Abstract Bound states in the continuum (BICs) are a special type of waves that coexist with continuous waves without any radiation loss. Owing to eliminated dissipative coupling to the environment, the coupling between BICs is naturally considered to be dispersive. Here, dissipative coupling between BICs in coupled photonic waveguides is exploited on an etchless lithium niobate integrated platform, and for the first time, supermode BICs are experimentally observed on a chip. It is discovered that, under the variation of the waveguide gap, the two supermodes have complementarily varied loss rates and the supermode BIC appears periodically, which verifies respectively the dissipative nature of coupling and periodic variation of the coupling coefficient between the two coupled photonic waveguides. The observed dissipatively coupled BICs can enable many on‐chip applications such as high‐sensitivity sensing, optical communication, and topological physics.