Design And Optimization Of Optical Fiber Connector Using In Metal-insulator-metal Waveguides

Nanowaveguides based on surface plasma enable optical systems to break through the diffraction limit thus can be used in areas such as super-resolution optical imaging,optical communications,and ultra-high-density information storage.Metal-Insulator-Metal(MIM)devices are one of the most promising structures of those nanostructures because they can greatly reduce the losses generated during nano-focusing.However,due to its own problems,such as length limitation and excitation of surface plasmon,it is difficult to apply on actual focusing process.Aiming at the problem of MIM waveguide in nano-focusing,this paper creatively proposes a new structure: optical fiber-MIM connector based on basic electromagnetic theory and near-field optics theory.It connects the fiber core to the MIM waveguide.The principle is that the electromagnetic energy in the fiber is coupled into the MIM waveguide through the connector and finally completes the nano-focusing process in the MIM waveguide.The main work of this paper is as follows:(1)A fiber-MIM waveguide connector was designed.The connector consists of two parts: a "cup"-shaped structure made of photoplastic epoxy SU-8 with a "cup" structure for the fiber core inserted;the other part is attached to the back of the "cup" : a metal screen with a thickness of several tens of nanometers.It has a rectangular hole on the metal screen for MIM waveguideinserted.According to the basic electromagnetic theory and near-field theory,the connector is theoretically analyzed,and the analysis shows that the connector has high optical efficiency.Based on this,a possible method of making this connectors is proposed.(2)The designed fiber-MIM waveguide connector is numerically simulated by the finite difference time domain(FDTD)method.The numerical calculation results are in line with the theoretical expectation: the connector excites the surface plasmon in the MIM waveguide efficiently.And the energy coupling efficiency is very high.We designed an optimization strategy to obtain the optimal parameters and the highest energy coupling efficiency.The result is: when the thickness of the metal screen is 50 nm and the aluminum is used as the metal screen material,the energy coupling efficiency of the connector is maximized.The value is 79.5%;when the MIM waveguide is connected to the connector,the energy coupling efficiency is as high as 83.7%.In addition,we found that the background radiation noise emitted from the MIM pedestal is greatly weakened because the thickness of the metal screen is greater than the penetration depth of the surface plasmon,which means that the MIM waveguide doesn't need to reduce the background radiation by increasing its length.