An On-chip Hybrid Plasmonic Light Steering Concentrator Based On Metal-dielectric-metal Sandwich Structure

Surface plasmon polaritons(SPPs)modes can be used for efficiently delivering the electromagnetic energy to nanosized volumes that breaks the optical diffraction limit,thus causing extensive research interest in the field of nanophotonics.However,due to the inherent polarization dependence of surface plasmons,the excitation of surface plasmons with TE polarized incident light is a huge challenge for researchers.In addition,the intrinsic ohmic loss of the noble metal also limits the propagation distance of the surface plasmon polaritons,so the integration of plasmonic nanostructures has encountered obstacles.An on-chip hybrid plasmonic light steering concentrator based on a metal-dielectric-metal sandwich structure was proposed and designed in this paper.In the device,the TE-polarized light with the silicon-based waveguide as the carrier realizes the directional excitation of the surface plasmon polaritons through the coupling of the sandwich structure,which ultimately ensures the high efficient vertical steering of light wave and the high field intensity of the nanofocusing.Our work has opened up a new avenue for the integrated multi-nanofocus applications,such as on-chip trapping,sensing,and processing of the plasma-assisted functional components.In this paper,theoretical studies have been conducted on silicon-based photonic devices based on hybrid metal-dielectric-metal sandwich structures.It is mainly divided into two parts as follows: the first part of the work is mainly to propose,design and study the hybrid metal-dielectric-metal sandwich structure.The specific contents are:1.Using the finite element method(FEM)to analyze the single silver strip in free space and the single silver strip carried by a silicon-based substrate in the full frequency range,the different primary levels corresponding to different frequency bands in the two different cases are plotted and compared.Simultaneously,the new single-silver-strip hybrid mode,accompanied by a silicon-based substrate-mediated coupling is elucidated.2.The coupling effect generated by the multi-silver strips supported by the silicon-based substrate is illustrated by the “image charge” picture,supplemented by supermode analysis,resulting in different supermodes.3.In order to increase the coupling efficiency between the respective silver strips supported by the silicon-based substrate,a layer of silver plate with a specific thickness is added on top of it to form a metal-dielectric-metal sandwich structure.The minimum coupling length of the sandwich structure under the optimal parameter configuration is calculated based on the coupled-mode theory to ensure that it can achieve an integrated application at a minimum size.Finally,the analysis of the electric field distribution obtained by the three-dimensional simulation of the sandwich structure illustrates the excitation mechanism of the surface plasmon polaritons.The second part of the work is mainly to design an on-chip hybrid plasmonic light steering concentrator based on a hybrid metal-dielectric-metal sandwich structure.The overall coupling efficiency and nanofocusing performance of the device were further studied.Specific content includes:1.By introducing the lateral silver taper structure,the surface plasmons excited by the hybrid metal-dielectric-metal sandwich structure propagate along the edge of the silver taper,and finally achieve nanofocusing at the apex of it.2.For the loss mode and back reflection that occur throughout the whole coupling process,a time-averaged Poynting vector is introduced to calculate the coupling efficiency of the device under different parameter configurations.Based on the device's high-efficiency steering nanofocusing,a comprehensive evaluation of the device's nanofocusing performance is performed through the introduction of a series of parameters(adiabatic parameter,group/phase velocity,field amplitude enhancement factor,mode width,etc.).The main innovations of this article are:1.TE-polarized light is utilized to achieve high efficiency directional excitation of on-chip surface plasmon polaritons.By introducing the lateral silver taper structure,the surface plasmons excited by the hybrid metal-dielectric-metal sandwich structure propagate along the edge of the silver taper,and finally achieve nanofocusing at the apex of it.Hybrid metal-dielectric-metal sandwich structures have been proposed to overcome the ohmic loss of noble metals that limit the propogation distance of SPPs.2.A complete set of substrate-mediated coupling analysis theory for on-chip mode coupling of single/multiple metal strip has been proposed.For mode analysis of on-chip complex structures,a complementary mode analysis method that uses both global analysis and local analysis has been proposed for the first time.