Design On The Square Concave Ring Structure Micro-nano Optical Functional Device Based On Surface Plasmon Polaritons

With the rapid development of modern communication technology,light as a transfer carrier has made great progress in the transmission of high-speed and large-capacity information.But the performance and size of conventional photonic devices could not meet the current needs for highspeed information transmission due to the diffraction limit.Surface plasmon polaritons(SPPs)are electromagnetic surface waves that propagate at the interface between metal and dielectric.They have the perperties of breaking the traditional optical diffraction limit and strong locality,and they could guide and manipulate the propagation of light at the subwavelength level.In the common three-layer structure of SPPs,the metal-insulator-metal(MIM)structure could not only manipulate and propagate the light at the nanometer level,but also support the sub-wavelength high group velocity mode over a wide spectrum.In this paper,based on surface plasmon polaritons,a square concave ring MIM waveguide structure is proposed to realize the design of micro-nano optical functional devices by using the boundary coupling method.The magnetic field distributions,the transmission spectrums and resonant wavelength distribution curves of the waveguide structures are calculated by COMSOL numerical analysis software,which is based on the finite element method(FEM).For the constructed square concave ring cavity structure,the minimum transmittance of its stopband is as low as 0.01,the maximum transmittance of its passband can reach up to 0.96 and the top of passband is smooth.The above results indicate that the structure can be used as a band-stop filter with excellent performance.Researches have found that increasing structural parameters I and H could cause a significant red shift in the transmission line,and the stopband transmittance of different modes will also change at the same time;increasing structural parameter D will increase the transmission of valley 1 to 0.80,and finally disappear,while valley 2 and valley 3 are almost unchanged;The resonant wavelength has a linear relationship with the effective refractive index of the medium;After optimizing the structural parameters,the quality factor of the waveguide structure can be raised from 14.82 to 17.07;It has also been found that changes in the direction and the number of the notches would result in splitting of different valley patterns.Afterwards,the two kinds of extended structures are analyzed and studied.When the medium of concave ring transversal cavity is changed to silver,the structure can still be used as a band-stop filter,but the range of passband bandwidth is become wider.When the medium of waveguide corresponding to the notch is changed to silver,Due to the introduction of a metal baffle,the structure produces a Fano resonance phenomenon with a sensitivity of 960 nm/RIU and the system quality factor of 1412.After the further optimization of structure parameters,its sensitivity can reach up to 1000 nm/RIU and the quality factor can be increased to 1660.The above three kinds of square concave ring waveguide structures designed in this paper could have certain application value in the band-stop filter,optical switch and biological trace sensor.