Polarization-modulating switchable and selectable image display through an ultrathin quasi-bound-state-in-the-continuum metasurface

Active manipulation on absorption takes an essential place in nanophotonic light modulators, which always suffer from static tuning ability, limited depth, and insufficient modulating efficiency. In this study, we propose an alternative strategy utilizing the symmetry-protected-type bound state in the continuum (SPBIC) to satisfy a tunable critical-coupling absorber with high modulating mobility. To demonstrate our concept, we illustrate an ultrathin critical-coupling absorbing system composed of germanium metasurface and monolayer graphene through elaborately maneuvered quasi-SPBIC, which provides substantial local field enhancement to boost the light absorption of graphene. The intensity of such critical-coupling absorption can be efficiently tuned by modulating the polarization of the incident waves with an efficiency of 97.1%. Via this polarization control, we demonstrate digital switch ``0-1'' and switchable and selectable image-displaying functions in simulation. Such functions are obtained in one single-designed array by incident polarization while requiring no additional structural change. Our results may pave the way for next-gen nanophotonic metadevices.