High Figure of Merit Refractive Index Sensor Derived From the Axial Length Ratio of Elliptically Polarized Light of Chiral Plasmonic Structure Arrays

The refractive index sensor based on the Fano resonance effect (that is, Fano sensor) is one promising branch of plasmonic sensing applications owing to its narrow spectral line shape. Further improvement in the sensitivity and figure of merit (FOM) is the main issue in this field. In contrast to the Fano sensor, herein, we report a novel ultra-sensitive refractive index sensor based on the axial length ratio of transmitted elliptically polarized light of chiral plasmonic structure arrays (that is, ratio sensor). Compared with the optimized Fano sensor in the same asymmetric chiral plasmonic structure arrays, the proposed ratio sensor shows a better sensitivity performance of 556.9 nm/RIU, that is, 1.31 times higher than that of the optimized Fano sensor. Specifically, the quality factor of the spectral line shape and FOM of the proposed ratio sensor reach 121.6 and 60, respectively, that are 2.14 and 2.92 times higher than those of the optimized Fano sensor, respectively. Our study proposes a potential path to achieve high-quality ultra-sensitive refractive index sensing.