Highly Polarized Near-Infrared Photodetection in Monolayer WSe ₂ Enabled by Plasmonic Bound States in the Continuum

Polarization-sensitive near-infrared (NIR) photodetection plays a crucial role in applications such as object recognition, environmental monitoring, and navigation. While nanostructured or anisotropic two-dimensional (2D) materials offer a promising alternative for miniaturization, their polarization sensitivity often remains insufficient for practical implementation. To overcome these limitations, we present a highly polarization-sensitive NIR photodetector based on monolayer WSe2 operating below its intrinsic bandgap, enabled by anisotropic absorption and hot-carrier injection through plasmonic quasi-bound states in the continuum (quasi-BICs). By integrating asymmetrically paired gold nanorods in a long–short configuration on monolayer WSe2, a plasmonic quasi-BIC mode is excited, resulting in a polarization absorption ratio of 276 at the telecommunication wavelength of approximately 1.5 μm. The photodetector exhibits a high degree of linear polarization (DOLP) of 0.95 and a narrow full width at half-maximum (FWHM) of 70 nm, among the best performances for 2D-material-based photodetectors. Furthermore, we demonstrate its application in polarization-encoded telecommunication and polarization-resolved NIR imaging, highlighting its potential for practical applications. This work underscores the potential of integrating plasmonic quasi-BICs with 2D materials to realize compact, multifunctional NIR photodetectors with sub-bandgap operation, featuring simultaneously enhanced polarization sensitivity and spectral selectivity.