Monochromatic Polarization‐Sensitive Photothermoelectric Detection via Plasmonic Quasi‐BICs

Abstract Bound states in the continuum (BICs) provide a robust mechanism for enhancing the resonance quality factor ( Q ‐factor) by confining light in non‐radiative modes. Due to the large intrinsic losses, the Q ‐factors of plasmonic resonances are typically limited. A plasmonic photothermoelectric metasurface based monochromatic polarization detector with a high polarization ratio () is proposed and simultaneously realize linear sensing with the polarization angle sensitivity of 0.67 µA (W·deg) −1 by the excitation of high‐ Q quasi‐BICs resonances. In general, with the purpose to achieve the maximal circular dichroism ( CD ) response, symmetry breaking is introduced, which inevitably leads to the radiative losses and the significantly decreased Q ‐factor, therefore fundamentally limiting the simultaneous realization of polarization modulation and high monochromaticity. Herein, a circular polarization‐sensitive device is further realized () with a high CD (>0.9) response under the situation of intrinsic chirality. Such simultaneous performance of high PR, CD , and sharp resonance are related to the fact that optical absorption is primarily dominated by the grating walls while the offset of the geometry perturbation serves only to break the mirror symmetry and generate the CD response. Our research provides a novel approach for on‐chip optical devices in high‐speed monochromatic detection.