Design Of Nanostructured Filter Based On Surface Plasmon Polaritons

Surface plasmon polaritons(SPPs)is an electromagnetic mode propagated at the interface of a metal medium by the interaction of electrons and photons.It has been widely concerned in the field of nanoscale optics because of its good localization and its ability to break through the traditional diffraction limit.It is considered as an effective basis for the realization of nanoscale optical devices.The filter,as the basic device of optical communication,is very important.Based on SPPs basic theory,this paper studies the structure of MIM waveguide which can realize filtering function,discusses the influence of structure parameters on the filtering performance,and proposes three narrow-band filters based on the plasmon-induced transparency responses(PIT).The main content of this article is as follows.Firstly,the basic principle of the surface equiexcimer is discussed.We derive the dispersion equation of surface equiexcitations from maxwell's equations and obtain the excitation conditions of surface equiexcitations.Then the SPPs in the metal-dielectric interface and MIM waveguide are studied.The characteristic parameters of SPPs including wavelength,propagation length and penetration depth are discussed.The understanding of the SPPs is the theoretical basis for the subsequent design and research.Secondly,the MIM waveguide with ring cavity and trapezoidal cavity is discussed and numerically simulated by finite element method.The influences of structure parameters such as ring cavity radius,coupling distance,bottom edge width and trapezoidal cavity height on waveguide filtering performance are discussed.The researchs show that the radius r of the ring cavity,the bottom width w2 of the trapezoidal cavity and the height h have a great influence on the resonant frequency of the resonator,while the coupling distance has a great influence on the transmission because it affects the coupling efficiency between the cavity and the waveguide.At the same time,by changing the coupling mode between the ring cavity and the waveguide,the bandpass performance and bandstop performance of the structure can be converted.This chapter lays a foundation for the new structure.Finally,according to the parameter characteristics of the above structure,we proposed three narrow-band filter structures based on plasma induced transparency:the band-stop filter with trapezoidal cavity and ring cavity,the band-pass filter with trapezoidal cavity and ring cavity,and the band-stop tunable filter with double ring resonator.Structure 1 is based on ring resonator and trapezoid resonator,trapezoid cavity is directly connected with waveguide.The structure has the characteristics of narrow-band-pass filtering.The trapezoidal cavity of structure two is coupled with the waveguide.The structure has the characteristic of narrow band resistance.However,due to the limitation of PIT generation conditions,the above filters cannot be tunable at the center wavelength.Based on this,we proposed a tunable narrow band-stop filter with double ring resonator.When the radius of the inner and outer ring cavity is 1:2,the PIT responses can be generated,and the position of the PIT transmission peak has a linear relationship with the radius of the ring cavity.The tunable band stop filter is designed by adjusting the inner and outer ring cavity radii at the same time according to the ratio of 1:2.The band-stop filter has the advantages of low transmittance,narrow stopband and high Q value.In conclusion,we explored the structure and function of resonator filter based on the SPPs MIM waveguide and proposed new narrow-band filters based on PIT responses.