Optical sensing and switching in the visible light spectrum based on the bound states in the continuum formed in GaP metasurfaces

We propose dielectric metasurfaces supporting BICs in the visible light spectrum based on GaP cuboids. An artificial "molecule" composed of two identical GaP cuboids, which exhibits highly directional scattering, is used as the unit cell to construct the metasurfaces. It is found that the Q factor of the BIC is extremely sensitive to the gap width between the two GaP cuboids. A Q factor as high as 2 x 107 can be achieved when the gap width of all GaP cuboids in the metasurface becomes equal. An exponential decrease in the Q factor is observed when the gap width deviates from the optimum value. We show that optical sensing with sensitivities of 135 nm/RIU and 45 nm/RIU can be realized by using x-and y-polarized white light. By integrating a tungsten disulfide (WS2) monolayer on such a metasurface, we demonstrate that the BIC in the hybrid metasurface can be optically manipulated by injecting excitons and trions in the WS2 monolayer. Our findings are helpful for understanding the physical origin for the BIC formed in a metasurface and useful for constructing novel photonic functional devices by combining such metasurfaces with two-dimensional materials.