Research On Fabrication And Optical Modulation Characteristics Of Photonic Crystal Fiber Based On Graphene Directly Grown On Air-hole

Graphene has remarkable electrical and optical properties,in which the absorption of light by graphene materials can be effectively controlled by regulating the applied electric field and carrier concentration,which makes graphene have great potential in the field of optical modulation.Photonic crystal fiber(PCF)is a new type of fiber with multilayer air holes.The performance of G-PCF can be regulated by changing the aperture and spacing of the air hole,constructing a new type of fiber device.In order to integrate the advantages of graphene and PCF,the author and his research group propose a new type of PCF based on graphene directly grown on air-hole(G-PCF)composite waveguide by directly growing graphene onto inner hole walls of the PCF with atmospheric pressure chemical vapor deposition(APCVD).The G-PCF retains the structural integrity of the PCF waveguide,and gives full play to the graphene unique optical modulation characteristics.The flexible structure and all-optical control enable the G-PCF to have great potential in all-optical devices,including optical modulator,filter and optical switch.This paper focuses on the fabrication and characterization of G-PCF,the theory of electro-optical modulation and all-optical modulation,and the measurement of all-optical modulation.The main research contents are as followed.Firstly,the fabrication and application of graphene and G-PCF at home and abroad are reviewed.The electrical,optical,mechanical and thermal properties of graphene are briefly introduced.The characteristics of various graphene fabrication methods are summarized.The development history of graphene-based optical modulator is compared and analyzed.The characteristics of the optical modulator based on the integration of graphene and fiber are mainly analyzed.The existing problems in the fabrication and application of the optical modulator integrated with graphene and fiber are summarized.In view of these problems,the research content and theoretical basis for the research are proposed.Secondly,based on APCVD method,a novel composite waveguide is fabricated by directly growing graphene onto the inner hole walls of PCF without catalysis.The relationship between the growth temperature,growth duration,gas velocity of carbon source and the number of layers,uniformity and quality of the graphene in the holes of the PCF is established.Raman spectroscopy and scanning electron microscopy are used to characterize the graphene films,then the fabrication process of G-PCF is optimized.Thirdly,the theory and characteristics of electro-optic modulation based on G-PCF are studied.Based on the special zero-band-gap band structure and electro-optical modulation theory,the permittivity and the change of complex refractive index of graphene with Fermi energy level are studied.On this basis,the optical transmission and electrical absorption modulation characteristics of the G-PCF composite waveguide are analyzed by the finite element method,and the modulation laws of the G-PCF modulator are studied when the total internal reflection PCF and the photonic bandgap PCF are respectively used as optical devices.The relationship between the number and position of graphene layers and fiber structure parameters of G-PCF and the modulation depth of G-PCF are studied,based on which the electro-optical modulation characteristics of G-PCF are studied.Then,the theory and characteristics of all-optical modulation based on G-PCF are studied.The preferential absorption characteristic of graphene are studied and theoretical simulation is carried out.The transmission and all-optical modulation characteristics of G-PCF are tested through experiments,and the relevant parameters of all-optical amplitude modulator,such as loss and modulation depth,are also analyzed.In the end,the main work of this paper is summarized.Meanwhile,the limitations and the shortcomings of existing fabrication technology of graphene are analyzed.Then optimization of G-PCF modulator in modulation depth and modulation rate are discussed.Finally,the prospect of G-PCF for applications is prospected.