Metasurface With WS2 Based on Quasi-Bound States in the Continuums for Refractive Index Sensing

Optical metasurfaces are widely used in the field of sense due to their small size, freedom of design, and easy manipulation of the light field. At present, researchers usually focus on either sensitivity or full-width at half-maximum (FWHM) to pursue better sensor performance. Metal materials are used to excite the surface plasmon resonance (SPR) to improve the sensitivity, or all-dielectric materials are used to reduce the FWHM, but they are mutually constraining. To solve this problem, a double rectangular structure of the metasurface is proposed. Through structural parameter design, the metasurface can generate three types of peaks: guided mode resonance (GMR), Fano resonance, and quasi-bound states in the continuums (Q-BIC). The surface electric field intensity of the metasurface is enhanced after coating tungsten disulfide (WS2), which is combined with the characteristics of Q-BIC high-quality factor and achieves good results in refractive index sensing. Through simulation calculation, the surface electric field intensity of the sensor is increased by about three times, and the sensitivity is increased to 107.5 nm/RIU, which is 2.5 times more than without WS2. The FWHM remains at less than 0.01 nm and the figure of merit (FOM) of the sensor increased by 1.9 times. The sensor effectively limits the increase of FWHM while improving the sensitivity; it has great potential in the detection of trace substances and biosensing.