Research On Surface Plasmon Polarization-Controlled Optical Switch With Composite Metasurface Structure

Surface plasmon is an electromagnetic mode generated by the incident light and free electrons on the surface of precious metals.It has the ability to enhance the local field.The device reaches the sub-wavelength size that can break the optical diffraction limit.The metasurface structure based on surface plasmons can manipulate photons on the nanometer scale,which provides an effective way to realize highly integrated,miniaturized and high-performance nanophotonic devices.As the basic logic device of integrated optical path,the development of optical switch is particularly important for the construction of integrated optical path.At present,optical switches based on various principles and control methods have been proposed and designed one after another.The polarization state is a basic element of light,and its optical properties play a decisive role in the interaction between light and matter.The realization of polarization control on light will have very important research significance.In this paper,based on the finite element method,the effects and performance of polarization control optical switches of several different nanorod structures are studied.The main work is as follows:First,a T-like composite metasurface structure composed of three sets of parallel double nanorods is designed to realize polarization-controlled Fano optical switch.The structure is composed of four horizontal nanorods and two vertical nanorods.When the polarization angle of the incident light changes by??14?2,the optical switch function can be realized,with the switch ratios of 16.3 dB and 18.5 dB,respectively.This structure has a high sensitivity of 1147.8nm/RIU.At the same time,the effect of structural parameter changes on the transmission spectrum was studied.The response characteristics of the optical switch can be adjusted by changing the length of the nanorods and nanorods l₁,l₂.In addition,it was found that when the nanorod spacing d₂ is reduced,the transmission spectrum a new transmission valley is produced.Next,when the upper and lower spacing d₂=0nm of the T-like nanorod hexamer structure is changed,a double IL Nanorod metasurface structure composed of two L nanorods and two horizontal nanorods placed on top of it is formed.The optical switching characteristics of the T-like structure formed by the L-shaped nanorods were studied,and it was found that the L-shaped nanorods have two transmission valleys at?=0°,and a transmission window is generated in the middle of the transmission valleys.This special transmission phenomenon is called equal.Plasmon induced transparency?PIT?,adjust the transmission valley at?=90°so that it is right at the transmission window,so when the polarization angle changes?/2,three wavelengths can be switched simultaneously.They all have a high switching ratio.The switching ratios are 12.2 dB,11.8 dB,14.2 dB,and the sensitivity is 986.7 nm/RIU.Finally,a type of rectangular nanorod tetramer super surface structure was designed.The study found that when the polarization angle of the incident light changes?/2,the switching ratio can reach up to 27.8 dB.Because the nano double rods are arranged side by side,an optical resonant cavity can be formed,and the local light intensity is bound in the cavity,which can greatly reduce the radiation loss,and the quality factor FOM is up to 151.6.At the same time,the effect of structural parameter changes on the transmission spectrum was studied,and it was found that the response characteristics of the optical switch can be adjusted by changing the structure period size P,nanorod spacing d₁,and nanorod length l₁,l₂.The above research results can provide a new design ideas for the research of nano-optical switches,and provide a research basis for the design of high-performance polarization state optical switches.In addition,the nanorod RC resonant cavity and surface lattice resonance also laid the foundation for the research of extremely narrow-band and high-Q Fano optical switches and PIT optical switches.