Abstract
In this paper, a multichannel refractive index sensor based on a subwavelength metal–insulator–metal (MIM) waveguide coupled with tangent-ring resonators is proposed. When two tangent-ring resonators were placed above the MIM waveguide, Fano resonance with asymmetrical line shape appeared in the transmission spectrum due to the interference between the light–dark resonant modes. The sensitivity and figure of merit were as high as 880 nm/RIU and 964, respectively. Through adding more tangent-ring resonators, multiple Fano resonances with ultrasharp peaks/dips were achieved in the wavelength range of 800–2000 nm. Besides, negative group delays were also observed in the Fano resonant dips. Two-dimensional finite-difference time-domain (FDTD) method was used to simulate and analyze the performances of the proposed structures. These kinds of multiring structures can find important applications in the on-chip optical sensing and optical communication areas.
Highlights
Subwavelength metal–insulator–metal (MIM) waveguides based on surface plasmon polariton (SPP), which is one of the promising methods to control the light transmission at nanoscale, have vigorously pushed forward the development of integrated photonics circuits [1]
Waveguides with dual side-coupled slot cavities or dual parallel grooves [22,23,24]. In the former researches, single Fano resonance was firstly investigated to obtain the high performances of figure of merit (FOM) and refractive-index sensitivity, and dual Fano resonance was investigated in the MIM structures to improve the on-chip integration [25,26]
The transmission characteristics of MIM waveguide based on SPPs in multi-tangent-ring
Summary
Subwavelength metal–insulator–metal (MIM) waveguides based on surface plasmon polariton (SPP), which is one of the promising methods to control the light transmission at nanoscale, have vigorously pushed forward the development of integrated photonics circuits [1]. Sharp and asymmetric Fano-line spectra are found in the MIM waveguides with dual side-coupled slot cavities or dual parallel grooves [22,23,24] In the former researches, single Fano resonance was firstly investigated to obtain the high performances of FOM and refractive-index sensitivity, and dual Fano resonance was investigated in the MIM structures to improve the on-chip integration [25,26]. In this case, more Fano peaks/dips are preferred in the single. Fano channels can of be structure obtained with proposed multichannel on-chip sensor, and it meets the development of integrated photonics.
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