| In traditional optical communication,multiplexing technology improves communi-cation capacity by multiplexing light waves from wavelength,frequency and space.How-ever,the communication capacity is close to the Shannon limit,and new technologies are urgently needed to solve the communication capacity crisis,while Orbital Angular Mo-mentum（OAM）is an effective method to solve the transmission capability of single-mode fiber,and it is a current research hotspot.The OAM has a spirally distributed phase,and the different OAM modes are orthogonal to each other.Theoretically,It provides a set of infinite orthogonal bases,which application to space division multiplexing（SDM）communication technology can greatly improve the communication capability and the efficiency of data transmission.Although there is a mathematical relationship between the OAM mode and the regular vector mode,its phase singularity light field center has no light field distribution.Therefore,special research and design of OAM fiber must be carried out.In this paper,a graded-index ring-core fiber supporting OAM mode is studied.By analyzing arbitrary refractive index distributions,a nanostructured fiber for OAM transmission is proposed for the first time with minimal nonlinearity.coefficients and confinement losses,and finally discuss the feasibility of nanostructured OAM fiber fabrication,therefore,this structure has great potential in optical communication.In this paper,a graded-index ring-core fiber supporting OAM mode is studied,and a nanostruc-tured fiber for OAM transmission is proposed for the first time by analyzing any refractive index distribution.The fiber has a very small nonlinear coefficient and limiting loss in the1.5-1.6μm band.Finally,the feasibility of nanostructured OAM fiber fabrication is dis-cussed.Therefore,this structure has great potential in optical communication.The main content and work of this thesis are as follows:（1）The application and classification of OAM fibers and the current problems to be solved are briefly introduced,and the mathematical relationship between OAM modes and eigenmodes is deduced after proposing and summarizing the principles and advan-tages of nanostructured fibers.The transmission characteristics of the OAM fiber are summarized,including effective refractive index,dispersion,confinement loss and non-linear coefficient,etc.（2）The relationship between the refractive index distribution and the optical fiber characteristics is studied,and the influence mechanism of the refractive index distribu-tion and the transmission characteristics of the OAM fiber is summarized.The influence of the refractive index convexity index change on the effective refractive index,nonlinear coefficient and dispersion is explored from the three angles of the inner ring,the outer ring and the vertex position of the transmission layer.An ideal parabolic refractive in-dex distribution of the nanostructure OAM fiber is designed.The simulation results from the Finite Element Method show that there are 34 transport modes by the OAM nanos-tructured fiber,of which the dispersion curve is regular and flat.The signal loss by the fiber can stay within 10-10d B/m,which is better than most of the OAM fibers.At the wavelength of 1550 nm,the nonlinear coefficient of nanostructured OAM fiber is about0.40.6 W-1/km,which is lower than that of single mode fiber.the nanostructure pix-elated fiber design method is used to realize the OAM fiber with any refractive index distribution,a Monte Carlo method is designed to invert the nanostructure,and the pix-elated fiber design structure is obtained,and the preparation is discussed.The preform is composed of 4836 fluorine-doped glass rods and germanium-doped glass rods.The final distribution of the nanorods in the core is determined by a special simulated anneal-ing algorithm.By arranging and stacking,the nanostructured OAM fiber with the same refractive index distribution is obtained. |
