Equivalent Circuit Models of a Bifunctional Optical Metasurface for Beam Splitting and Refractive Index Sensing

Metasurfaces have attracted extensive attention in themicro/nano-opticsfield depending on their significant ability to modulate optical parameters.However, the current numerical simulation technology cannot meet thedemand of the design and analysis of metasurfaces efficiently dueto consuming substantial calculating time and memory. Besides, theycannot illustrate the physical mechanism straightforwardly behindthe optical responses. Herein, we propose and demonstrate two equivalentcircuit models systematically for a bifunctional metasurface withmetal-dielectric-metal structural meta-atoms based onpolarization multiplexing in the visible band. In the y-polarization state, the equivalent circuit model is establishedto interpret the phase shift exactly with a high goodness of fit of0.931, resulting in the beam splitting function from the anomalousreflection phenomenon. The polychromatic light splits from 34 to 69 & DEG;to produce the grating-type high-saturation structural colors witha large gamut of about 170.07% of the DCI-P3 standard. In the x-polarization state, the metasurface produces the surfacelattice resonance that is suitable for the refractive index sensingfunction due to the high sensitivity to environmental changes. Thesecond equivalent circuit model simulates the linewidth narrowingand red-shift phenomenon with a sensitivity relative error of 7.00%.We introduce a branch with a narrow-band-pass filter and a capacitorin series into the model to mimic the characteristic of Rayleigh anomalies.Both models extend the application of equivalent circuit theory inoptics further and provide a crucial approach to enhance the insightsinto the mechanism of metasurfaces.