Plasmonic nanohelix-based 3D metasurfaces for refractive index sensing applications: A numerical parameter study

We conducted a numerical study of a metasurface consisting of a core-shell SiO 2 @Au plasmonic helix array to analyze how variations in its geometrical parameters affect its sensitivity to changes in the refractive index of the surrounding environment, demonstrating its potential as a highly tunable element for advanced optical sensing. Differential transmission spectra revealed that the helix array exhibited asymmetric optical responses to circularly polarized light of opposite handedness. The peak wavelength of the differential transmission spectrum was employed to investigate how geometric variations affect the sensitivity of the helix array. This was achieved by systematically modifying the geometric parameters of the helices—namely, the major radius, metal shell thickness, total height, and core radius—in parallel with adjustments to the refractive index of the surrounding medium. A linear fit of the relationship between the differential transmission peak position and the refractive index of the surrounding medium revealed a geometry-dependent sensitivity to changes in the refractive index, with sensitivity values ranging from approximately 471 to 541 nm/RIU. An evaluation of the figure of merit (FoM) indicates that the helix's major radius is the dominant factor influencing sensitivity, achieving a FoM of 7.7 RIU −1 . The metal shell thickness plays a secondary role, yielding a lower FoM of 3.9 RIU −1 . In contrast, total height shows a limited correlation with sensitivity, while core radius has a negligible impact, corresponding to FoM values of 0.45 RIU −1 and 0.29 RIU −1 , respectively. The results reveal that geometric design impacts sensing performance and guides metasurface optimization for refractive index sensing.