Design And Optimization Of Multifunctional Filter With Rectangular Cavity Based On The Surface Plasmon Polaritons

Today,with the invention of semiconductor laser,the communication techniques using light as a way of carrying information develop gradually.At the same time,the performance and size of traditional photoelectric device can not meet people's need.As a surface wave propagating along the interface between metal and dielectric,surface plasmon polaritons have strong confinement in the direction which is perpendicular to the propagating direction,and in this way,the electromagnetic field can be squeezed into a small region,which provides the possibility of breaking diffraction limits.Various devices,like filter and switch,are designed based on different structures.Therefore,surface plasmon polaritons have become a hot choice of realizing highly integrated optical circuits in nanoscale.Till now,most of filters prefer using silver as metal layer and air as dielectric layer.As for the coupling method,straight coupling and side coupling are applied in general articles.Besides those two methods,there is another type of structure with cascaded grooves which can result in good performance.Considering that the straight coupling and side coupling sometimes have to sacrifice the coupling length between waveguides and resonant cavity for higher transmittance,this article aims to relatively ease this situation.Firstly,we place two silicon baffles on the both sides of rectangular cavity and increase the length of silicon.The transmittance spectra can move towards infrared domain and more peaks emerge under this change.Through changing other structural parameters,we can not only obtain a good band-pass filter which can reach 90% transmittance but also get an excellent flat-top band-pass filter.Secondly,by placing a notch at the center of rectangular cavity,we get a dual channel band-pass filter with transmittance over 70%,and after optimization,this new type of filter can even reach 80% transmittance for both channel.Moreover,the distance between two channels is tunable and the second channel can be tuned individually.Results are simulated by COMSOL Multiphysics 5.0 based on the finite element method.The structures proposed here may provide a new option for the highly integrated optical circuits in nanoscale.