Fano Resonance Effect And Its Sensing Application In Plasmon Polaritons Waveguide Structures

Surface Plasmons Polaritons(SPPs)are electromagnetic oscillations formed by the interaction of electrons and photons that can move freely over the Surface of a metal.SPPS can break through the diffraction limit and propagate forward at the interface between the metal and the dielectric.Its energy is mainly bound at this interface,so it will have a strong limiting effect.And because it decays exponentially along the vertical interface,SPPs can manipulate optical signals in the subwavelength range.Therefore,it will be possible to achieve nanoscale miniaturization of optical devices.The metal-dielectric-metal(MDM)waveguide structure can transmit SPPs.And MDM waveguide has strong binding to SPPS.And MDM waveguide structure is relatively simple,can transmit a long distance,easy to prepare and many other advantages are also more attention.Based on the propagation characteristics of surface plasmons in metal-dielectric-metal(MDM)waveguides,an H-type resonator near field coupled direct waveguide structure with baffle is proposed.MDM straight waveguides containing metal panel due to the effect of reflection of the baffle to produce low transmittance continuous transmission spectrum,and the scale of 300 x 300nm2 H cavity structure can produce center wavelength of 810nm and 1350nm respectively mode of vertical and horizontal first order resonance,contains two resonant mode coupling into baffle straight waveguide will produce has the dual Fano of antisymmetric linear resonance transmission peak.The finite element method was used to analyze the dependence of the transmission lines of the waveguide structure on the structure parameters and the refractive index of the filling medium.The sensitivity of the refractive index sensing for two asymmetric transmission peaks was calculated as750nm/RIU and 1360nm/RIU,respectively.Then a concave resonator coupled single baffle MDM waveguide structure is designed.The coupling of the wide continuous state formed by the metal single baffle and the discrete state formed by the concave cavity forms the Fano resonance peak in the two modes.The causes of the Fano resonance and the transmission characteristics are analyzed,and the influence of different structural parameters and refractive index media on the sensing characteristics of the structure is studied.The optimal FOM value is4.5089×10~4,and the refractive index sensing sensitivity of the two asymmetric transmission peaks is 750nm/RIU and 1500nm/RIU,respectively.Then it is proposed to add a concave cavity under the straight waveguide with baffle to become a double-coupled concave cavity MDM waveguide structure,and the quadruple Fano resonance tuning appears.When different structural parameters of the upper and lower resonators are changed respectively,the Fano resonance generated by the upper and lower concave cavities are non-interference.The concave cavity on each side can affect two resonant transmission peaks,thus achieving independent tuning of the four resonant transmission peaks.By using this characteristic,the application function of Fano resonance can be broadened.By applying this characteristic to the field of differential sensing,the influence of some interference factors on the measurement results can be reduced and the accuracy of the measurement results can be improved.