Research On The Design Of Surface Plasmon-based Subwavelength Optical Devices And Their Coupling Mechanism

Surface plasmon is localized surface electromagnetic wave at the interface between metal and dielectric,which derive from the resonance of incident photon and metal electron.Owing to their unique properties beyond the diffraction limit,it has attracted tremendous attention.In the past few decades,surface plasmon has achieved remarkable results in the fields of physics,chemistry,biology,and material.In this paper,the design principles of metal surface plasmon-based and graphene surface plasmon-based filter,intersection and biosensor are studied by the method of FDTD and TMM.Moreover,the tunable mechanism is studied.The main research results are as follows:1.A compact nano-filter device based on metal surface plasmon is designed theoretically.The device is consist of metal MIM waveguide with a right-handed Archimedes spiral groove,and it realizes multi-channel filtering by the resonance of the Archimedes spiral waveguide.In addition,the resonance wavelengths depend on the resonance condition,and the number of channels is determined by the rotation angle(length)of the Archimedes spiral.The transmission spectrum and the field distribution are simulated by the FDTD method,and the simulation results agree well with the theory results.Thanks to the employment of coiled Archimedes spiral,the structure enables to realize the multi-channel filtering with small lateral and vertical dimensions,and it can be applied to design the highly integrated photonic system.2.A multi-channel tunable filter based on graphene surface plasmon is studied theoretically.The structure is composed of monolayer graphene and the Fibonacci sequence grating.The reasons for the blue shift and red shift of the transmission curve are theoretically explained by analyzing the dispersion relation of the cell construction waveguide,and the results obtained by FDTD method show that the characteristic of multi-channel filtering can be tuned by changing the chemical potential of graphene,Fibonacci sequence and the parameters of air trench.The discovery of these results will provide a new way to design the multi-channel filtering in the mid-infrared region,and it helps to realize the nanometer integration circuit.3.A filter based on monolayer graphene and layered waveguide with different thickness is designed in theory.The transmission spectrum of the structure is investigated by the FDTD method,and the results show that it can realize the tunable band-stop filter in the mid-infrared region.Besides,the position of the forbidden band can be tuned by applying voltage on graphene or changing chemical doping in graphene.In addition,in order to obtain a relatively wide band gap in practical applications,it can be achieved by adjusting the contrast of the thickness of the air layer and silicon in the substrate.It provides a feasible guide for the realization of tunable wideband filtering in the mid-infrared region.4.An intersection structure based on graphene nanoribbon is theoretically studied.The structure consists of four identical graphene nanoribbon waveguides symmetrically surrounding one graphene nanoring.One of the ports is chosen as the input port,and the coupling mechanism of the whole structure can be obtained by analyzing the transmission at other ports.It can be seen from the results of 3D FDTD simulation that the device has not only the multi-port splitting function but also the energy cross-transfer function.It is also found that the energy in the nanoring can only be coupled out when the surrounding branch waveguide is located at the magnetic field nodes.The discovery of these results can provide an important theoretical support for designing the multi-port energy splitting and tunable intersection.5.A biosensor based on the hybrid structure of graphene and molybdenum disulfide is designed in theory.The reflectance spectra of the sensor are investigated by using the transfer matrix method.The parameters of the structure are optimized layer by layer with sensitivity as a reference,and the biosensor with ultra-high sensitivity can be achieved,the sensitivity can be as high as 540.8°/RIU.In addition,the reasons for the high sensitivity of the structure are given by analyzing the field distribution of each layer in the model and the selection of the coupling prism.Meanwhile,the research of designing ultra-high sensitive biosensor is proposed,which provides a feasible reference for the realization of ultra-high sensitive SPR biosensor.