Multimode control of quasi-bound states in the continuum through symmetry engineered multipolar diversity

Abstract

We present a dimeric all dielectric metasurface that enables multimode refractive-index sensing via symmetry-engineered quasi-bound states in the continuum. A single rotation of one silicon pillar breaks the C2v symmetry and simultaneously activates four spectrally isolated resonances as electric quadrupole, magnetic dipole, magnetic quadrupole, and electric dipole, with quality factors up to 2388.7 and sensitivities ranging from 111.5–446.9nm Riu−1. Crucially, the distinct multipolar characters endow each mode with a unique susceptibility to geometric fabrication tolerances, angular misalignment, and ambient refractive-index changes. This differentiated response is exploited for a differential self-referencing readout that cancels thermal drift and lithographic imperfections without requiring separate reference channels or recalibration. The device is compatible with standard electron-beam lithography and reactive ion etching, and operates in the near-infrared telecommunication band, offering a theoretical route toward future lab-on-chip integration. Compared with conventional single-mode sensors, our platform offers higher measurement robustness against environmental noise and fabrication-induced errors, reduces the need for post-fabrication trimming, and provides multiple independent spectral channels for simultaneous multi-parameter monitoring. This work translates multipolar diversity into a practical engineering advantage, offering a promising theoretical blueprint for compact, high-precision optical sensing in resource-limited settings where calibration-free operation and long-term stability are essential.