Research On Design Optimization And Characteristic Of All-optical Diode Based On Surface Plasmon Polariton

The most basic device in the integrated photon circuit is the all-optical diode.It will be of great significance for the preparation of complex photonic circuits in the future if the diode devices can be made dynamically modulated.Surface plasmon optics can effectively break the diffraction limit and realize the control and constraint of electromagnetic waves at the sub-wavelength scale,which provides a theoretical basis for the fabrication of all-optical devices at the nanoscale.In this thesis,the numerical simulation software of COMSOL Multiphysics based on the full vector finite element method is used to design two types of all-optical diode from the perspective of structural innovation and method innovation,and the one-way transmission characteristics are analyzed systematically.An all-optical diode structure composed of charged metal nanowires embedded in magneto-optical materials named Bismuth iron garnet(BIG)is proposed and the asymmetric excitation characteristics of Surface Plasmon Polariton(SPP)are studied.It is found that the induced magnetic field generated by the charged nanowires can break the symmetry of SPP at both ports of the structure.With the change of current direction,the port that effectively activates the SPP also changes.The wavelength range with asymmetric transmission is analyzed,in which SPP is effectively excited at the high potential port of nanowire structures,while the excitation of SPP is inhibited at the lower one.For silver nanowires,a maximum extinction ratio of 6.7d B can be obtained within the operating wavelength and the one-way excitation characteristics of the gold nanowires are more stable.In the above two structures,the SPP electric field intensity of gold nanowires is relatively weak,but it can be improved by increasing the strength of the in-line current.However,with the increase of current value,the non-reciprocity of the structure will not change.An all-optical diode device with slit-groove structures on silver film surface is proposed and the extraordinary optical transmission characteristics are evaluated theoretically.It is shown that the phenomenon of transmission enhancement occurs in the silver film structure with single-slit,which is caused by the coupling of incident light and surface plasmon.In a metal film structure with subwavelength grooves and single-slit,the transmission characteristics of light source change with the location of the grooves.In this paper,the effects of the number and location of grooves on the one-way transmission characteristics of single-slit silver film structure are discussed in detail,and an optimal structure is obtained by etching five pairs of grooves above the silver film and two pairs of grooves below.When the wavelength of incident light is 780nm-1100nm,the incident light passes through the device with a high extinction ratio,but its forward transmittance does not exceed 50%.After optimizing the above structure,we proposes a structure with double-slit and multi-groove,which can obtain an extinction ratio of up to 90d B,the corresponding transmittance contrast is 10~9,and the forward transmittance of the light source is up to 80%.In addition,the wavelength range of extinction exceeding 20d B is 145nm in the double-slit structure.