Design And Research Of Measuring Method For Graphene's Complex Refractive Index And Conductivity

Graphene,as a two-dimensional material,has been widely used in the fabrication of optoelectronic devices.Its Complex refractive index and conductivity are two important parameters that reflect the electrical and optical properties.The traditional measurement of complex refractive index is ellipsometry measurement.Its instruments are expensive and the optical modeling is difficult.At the same time,the optical waveguide is not introduced in the measurement process,and the measurement results have little reference value for the design of graphene optoelectronic devices.For the traditional measurement of graphene's conductivity,metal electrode is needed to be plated on graphene's surface.The process is complicated and the contact resistance is introduced.Therefore,designing a graphene hybrid optical waveguide structure to measure graphene's composite refractive index and conductivity is of great significance for the study of graphene optoelectronic devices.Based on above research background,this paper proposes a Graphene-Long Period Fiber Grating(G-LPFG)hybrid waveguide structure to measure its complex refractive index and conductivity.The measurement theory and fabrication experiment of the hybrid waveguide are researched.The main works are as follows:Firstly,this paper elaborates graphene's basic optical properties and the theory of long-period fiber grating.And this paper has an in-depth discussion on the relationship of graphene's complex refractive index and conductivity,the regulation is also analyzed.Based on the coupled mode theory,the transmissivity of long period fiber gratings is analyzed and the transmission spectrum is simulated.These works lay the theoretical foundation for the modeling of G-LPFG hybrid waveguide.Secondly,this paper establishes cladding mode eigenvalue equation of the hybrid waveguide based on two methods.For the first kind of graphene composite refractive index cladding model,this paper solves the eigenvalue equation,The influences of the real and imaginary part of the graphene's complex refractive index on the solution are analyzed.The real and imaginary parts' effects on resonant wavelength are also studied.For the second kinds of surface current model,the cladding mode eigenvalue equation is deduced according to the electric field vector model and studied by graphic method.Thirdly,the fabrication of LPFG and graphene are introduced.And the graphene is characterized by Raman spectroscopy.The experiment of transferring graphen to long period fiber grating is performed,these works lays foundation for the subsequent experimental study on the propagation properties of the waveguide.Finally,experiments are performed to measure the G-LPFG hybrid waveguide's transmission spectrum.Graphene's complex refractive index and conductivity are estimated by comparing with previous theoretical model.And the measurement errors are analyzed.This hybrid waveguide structure enhances the LPFG's sensitivity to the external environment.Therefore,it can also be used to fabricating highly sensitive sensors for external environment,such as refractive index of liquid.