Visible Quintuple Narrowband Metasurface Absorber Based on Gallium Arsenide Square Cavity for Multispectral Sensing Application

In this study, we introduce a novel five-band metasurface absorber (MSA) design for optical multispectral refractive index (RI) sensing. This design is built upon a square cavity nanostructure array of gallium arsenide (GaAs) that is seamlessly integrated with a continuous gold (Au) film, enabling high sensitivity in visible region. Simulation results show that the designed MSA achieves high absorbance of 97.7%, 99.8%, 96.9%, 92.3%, and 99.3% at 349.2 THz, 451.2 THz, 508.4 THz, 597.6 THz, and 656.1 THz, respectively, which are in agreement with the values obtained by coupling mode theory (CMT) calculation. The high Q-factors of about 68.47, 46.04, 33.01, 66.4, and 62.47 are also obtained, approaching the CMT values of 60.84, 40.23, 34.93, 68.25, and 53.71. The observed five-band stronger absorption of the designed MSA is mainly attributed to the hybridized coupling effects of surface plasmon polariton (SPP) mode, waveguide modes, and cavity modes excitations. The multi-band absorption properties of the designed MSA can be adjusted easily by changing the geometric parameters of the unit-cell. The MSA-based RI sensor has a higher Q-factor and narrow-bandwidth, yielding a sensitivity of about 16, 32, 68.8, 49.6, and 112 THz/refractive index unit (RIU). The proposed visible MSA has great potential in applications such as detecting, sensing, and enhanced spectroscopy.