Active Singularity Metadevices Enabled by Bound States in the Continuum

Abstract Losses are a fundamental aspect of nature, often limiting the performance of various physical processes, including bound states in the continuum (BICs). Although BICs theoretically exhibit infinite quality factors, they are practically constrained by losses from both intrinsic and extrinsic channels. Since these losses are unavoidable, it becomes essential to explore alternative approaches that leverage them. Here, phase singularities—analogous to the singularities of BICs in reciprocal space—emerge in the phase spectra of dielectric metadevices, where losses play a crucial role in reaching these special points. These phase singularities are robust within the parameter space, characterized by abrupt phase changes highly sensitive to external perturbations. The BIC‐enabled metadevices can customize the resonance quality factors associated with phase singularities, thereby improving the sensing figure of merit with enhanced local fields. An external pump channel is introduced to the metadevices, serving as a tunable mechanism for adjusting nonradiative losses. The tuning channel not only controls the operating conditions and sensitivity but also provides a modulation pathway to improve the signal‐to‐noise ratio in the measurement apparatus. The scheme provides a versatile platform for accessing phase singularities, advancing ultrasensitive optoelectronic devices used in sensing and detection applications.