Design,Fabrication And Properties Of Heterogeneous Helical Cladding Large Mode Field Single Mode Fiber

Because the threshold power generated by the non-linear effect is proportional to the effective mode area of the fiber,the most direct way to solve the problem of non-linear effect and optical damage in the process of increasing the power density of the fiber laser is to use large mode area fiber.By investigating the common large mode field optical fibers,this paper presents the structure of heterogenous helical cladding large mode field optical fibers.The simulation analysis of the fiber is carried out by COMSOL Multiphysics software.The Nd-doped phosphate heterogenous helical cladding large mode field optical fibers are designed and fabricated,and the performance of the fiber is tested in a series.At the same time,the experimental study of the fiber amplifier is completed.The work is as follows:Firstly,The theoretical simulation of optical fibers is carried out by COMSOL Multiphysics software,mainly using finite element method.The Cartesian coordinate system and traditional PML are introduced,and the conversion between spiral coordinate system and spiral PML is realized through theoretical derivation.Then the three-dimensional model of optical fibers is simplified to two-dimensional model,which simplifies the complex problems and makes the calculation and analysis process simpler and faster.The structure of the optical fiber designed in this paper is introduced in detail,and the two-dimensional modeling process using COMSOL Multiphysics software is demonstrated.The effects of core diameter,pitch and high refractive index cladding size on the limiting loss of the optical fiber are studied respectively,and the mode area characteristics of the optical fiber are also studied.Secondly,Design and fabrication of optical glass.The preparation technology of bulk glass materials was investigated.Large laser glass,large refractive index cladding glass and small refractive index cladding glass were prepared.A series of performance indexes of laser glass materials,such as transmission spectrum and absorption spectrum,were tested.The content of hydroxyl OH-hydroxyl in laser glass was calculated.It lays a solid foundation for the subsequent fiber drawing.Finally,According to the structure of optical fibers,the fabrication of hetero-cladding optical fibers prefabricated rods is carried out by using the prepared core laser glass and cladding glass,and the pulling of hetero-helical cladding optical fibers is completed.Large mode field optical fibers with different radius and pitch are successfully fabricated.The stimulated radiation spectrum,absorption and loss of optical fibers are tested,and the performance data of optical fibers are obtained,and the loss of optical fibers are analyzed.The main reason of high consumption is the design of optical fiber amplifier,and the obvious effect of optical signal amplification is obtained.