Numerical Analysis Of A Near-infrared Plasmonic Filter With High Figure Of Merit Based On Fano Resonance

In this paper,the MIM waveguide structure is taken as the research object and the finite-difference time domain method is used to study the influence of the coupled cavity structure on the transmission performance of the waveguide.The general characteristics of the coupling cavity,such as the transmission performance of the waveguide,the radiation mode of the coupling cavity under the excitation condition and the mode resonance law between the coupling cavity,were obtained.Using the FDTD simulation software in the article,the effect of the coupling cavity on the waveguide performance under different conditions was investigated.The calculation verifies a reinforcing effect on the transmission for the direct coupling cavity and for the indirect coupling cavity a weakening effect on the transmission which was analyzed by the energy level theory and the radiation field model.The relationship between the resonance conditions of different modes in the nanocavity and the dipole resonance was found and the position between them could determine the dipole resonance.In addition,the EIT-like phenomenon in the combined coupling structure was obtained,which is found that the coupling distance and the dielectric constant affect the transmission peak in the waveguide transmission.On the base of the above results,we designed a high quality filtering structure which was found that the higher the mode of resonance occurs,the better the channel of the transmission spectrum.However,the surface plasmon resonance in the near-infrared region corresponds to the resonance of the low-order mode and lower quality was obtained for the direct coupling through the nanocavity.The structure designed in this chapter has higher-quality transmission channels in the near-infrared region by using a variety of low-order modes of hybridization.In particular,using the zero-order mode generated by the air cavity and the first-order mode generated by the silicon cavity,Fano resonance could be clearly observed.The calculation results showed that its transmission efficiency T is up to 92% at 1562 nm while the optical resolution FWHM is 5 nm and its optical resolution FWHM is 12 nm corresponding to the transmission efficiency T over 99%.