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Though adding a groove to a plasmonic end-coupled perfect ring (PR) resonator, two additional resonance modes, which can be controlled by the length of the groove, will arise in this proposed ring-groove (RG) joint metal-insulator-metal (MIM) waveguide. By further cascading, the PR resonator and the RG joint resonator, single and dual Fano resonances with asymmetric line shapes are obtained due to the interference effects between the dark modes and the bright modes. High figure of merit and high refractive-index sensitivity are achieved, and thus this structure is suitable for the biochemistry sensing area. Interestingly, normal and abnormal dispersions are also investigated for the Fano peaks and dips, respectively. The performances of the proposed structure are investigated by using the finite-difference time-domain method. [ABSTRACT FROM AUTHOR]

In this paper, multiple Fano resonances preferred in the refractive index sensing area are achieved based on sub-wavelength metal-insulator-metal (MIM) waveguides. Two slot cavities, which are placed between or above the MIM waveguides, can support the bright modes or the dark modes, respectively. Owing to the mode interferences, dual Fano resonances with obvious asymmetrical spectral responses are achieved. High sensitivity and high figure of merit are investigated by using the finite-difference time-domain (FDTD) method. In view of the development of chip-scale integrated photonics, two extra slot cavities are successively added to the structure, and consequently, three and four ultra-sharp Fano peaks with considerable performances are obtained, respectively. It is believed that this proposed structure can find important applications in the on-chip optical sensing and optical communication areas. [ABSTRACT FROM AUTHOR]