The Research On Characteristics And Applications Of Novel Few Mode Fiber And Multi Core Fiber

With the rapid development of Internet and Internet of Things,the current optical transmission network based on single mode fiber is facing with great challenge because the fundamental capacity limit around 100 Tb/s of single mode fiber is approaching.Space division multiplexing either employing few mode fiber or multi core fiber has drawn significant attentions as a means to use space as an additional dimension to avert the capacity bottleneck of the existing single mode fiber optical networks limited by fiber nonlinear effect.As effective methods to realize space division multiplexing,the characteristics and applications of few mode fiber and multi core fiber have also been explored extensively.Related research works in the thesis are supported by the National 973 Project,the National 863 Project,and the National Natural Science Foundation of China.The main research achievements of this thesis are listed as follows:(1)The development and applications on mode division multiplexing and new optical device of few mode fiber are summerized.The mode characteristics in few mode fiber are analyzed in detail based on optical waveguide theory,including elliptical core few mode fiber.Fundamental steps of manufacturing optical fiber are presented,and the D shape elliptical core fiber supporting dual modes are designed and manufactured using MCVD method and drawing tower in the laboratory.The strain sensing property of the manufactured dual mode fiber is studied experimentally.Based on the D shape of special fiber structure,the special fiber supporting single linear polarization mode of the first order mode is designed,and influences of structural parameters on mode properties are discussed,which could provide new ideas of special few mode fiber design.(2)A compact dual mode interferometer is proposed.The device consists of a segment dual mode fiber manufactured in the laboratory sandwiched using core-offset splicing method between two single mode fibers,whose transmission spectrum shows obvious interference pattern.The spectrum characteristics and sensing properties of different lengths of dual mode fiber are studied in the experiment.The device is used to measure strain and temperature simultaneously with two different interference peaks or dips.The SMF-FBG and dual mode fiber inline sensing structure is proposed.Simultaneous measurement of strain and temperature are achieved by using transmission dip of FBG and one interference crest of dual modes.Based on coupled mode theory,the coupled mode transmission equations are simplified when involving dual mode fiber Bragg grating.The fourth-order Runge-Kutta method and transmission matrix method are used to investigate spectrum of uniform FBG and uniform phase-shifted FBG in dual mode fiber separately.Dual mode FBG is manufactured by phase mask method and is used to realize switchable dual-wavelength Erbium-doped fiber laser.(3)The characteristics of strong coupling multi core fiber in novel photonic lantern mode multiplexer and demultiplexer are discussed in detail.The method to calculate effective indices of supporting supermodes in various strong coupling multi core fiber is proposed,and the comparison results between proposed method and finite element method have witnessed the accuracy and validity of the former.The weak coupled seven core fiber are manufactured by MCVD method in the laboratory,and a novel optical fiber sensor capable of measuring strain,temperature and curvature is proposed and demonstrated.A segment manufactured seven core fiber(SCF)is spliced directly by fiber fusion machine between multi-mode fibers(MMF)whose length are both 1mm at two ends,then the MMF-SCF-MMF is sandwiched between SMFs directly,thus producing the whole Mach-Zehnder sensing structure.Experiment results show the sensitivities of strain,temperature and curvature are 0.8 pm/??,38.2 pm/? and 9.478 nm/m-1.(4)Two multi core large-mode-area fibers with air-hole cores structure are proposed.The strong coupling multi cores are arranged in circular or hexagonal shape,and strict dual mode are supporting by introducing the symmetrical distributed air-hole cores around the center.The mode characteristics and mode area are investigated with various structural parameters in different core numbers condition.Large mode areas of supporting supermodes are achieved with improved bending performance.