Abstract
To reduce the loss of the metal–insulator–metal waveguide structure in the near-infrared region, a plasmonic nanosensor structure based on a racetrack resonant cavity is proposed herein. Through finite element simulation, the transmission spectra of the sensor under different size parameters were analyzed, and its influence on the sensing characteristics of the system was examined. The analysis results show that the structure can excite the double Fano resonance, which has a distinctive dependence on the size parameters of the sensor. The position and line shape of the resonance peak can be adjusted by changing the key parameters. In addition, the sensor has a higher sensitivity, which can reach 1503.7 nm/RIU when being used in refractive index sensing; the figure of merit is 26.8, and it can reach 0.75 nm/°C when it is used in temperature sensing. This structure can be used in optical integrated circuits, especially high-sensitivity nanosensors.
Highlights
Based on Racetrack Resonant Cavity.Surface plasmon polaritions (SPPs) are evanescent waves propagating along the surface of a metal, formed by the coupling of free electrons and photons on the metal’s surface [1,2,3,4,5]
This interference effect exhibits asymmetric resonance that is different from the traditional Lorentz line spectrum. Because this asymmetrical Fano resonance spectrum has sharp lines, low radiation loss, and the resonance frequency is highly correlated with the refractive index and structural parameters of the filling material, it can be applied to the field of nanosensing with a higher figure of merit (FOM) and sensitivity (S) [16,17]
Micromachines 2021, 12, 1359 structure with a short rod and a cup-shaped resonant cavity coupling [21], which serves as a refractive index sensor with a sensitivity of 600 nm/RIU
Summary
Nanosensor structures of different shapes based on Fano resonance have been proposed by researchers, such as cup cavity [21], splitting ring cavity [22], notched cavity [23], and multiple ring cavity [24]. These structures can integrate and contact the sensing medium. Micromachines 2021, 12, 1359 structure with a short rod and a cup-shaped resonant cavity coupling [21], which serves as a refractive index sensor with a sensitivity of 600 nm/RIU. The structure potentially has great applications in optical communications and high-density integrated optics, especially in nano-optical sensing
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