Research On Bending Resistant Large Mode Area Trench-assisted Segmented Cladding Fiber

As the representative of the third generation laser,fiber laser develops rapidly because of its higher output power and wider application.However,with the output power of fiber lasers increasing,some limited factors appear in high-power fiber lasers.The non-linear effects are main factors limiting the increase of the output power and the mode instability affects the beam quality of output.Large mode area fiber can reduce nonlinear effects effectively.Single-mode operation can improve beam quality effectively and good bending resistance is conducive to the miniaturization and integration of high-power fiber lasers.Therefore,the design of large mode area fiber with single-mode operation and bending resistance can effectively promote the development of high-power lasers.The main work content and innovation results of this paper are as follows:(1)The basic principles of the Finite Element Method(FEM)are clarified,and three common boundary conditions and bending equivalent models are introduced.The COMSOL software is used to analyze the Multi-Trench Fiber(MTF)and traditional Segmented Cladding Fiber(SCF).The simulation results are compared with previous conclusions to verify the accuracy of finite element method and the method of setting up perfect matched layer of Segmented Cladding Fiber.(2)A Double Trench-Assisted Fan-Segmented Cladding Fiber(DTA-FSCF)is proposed.With large core size,DTA-FSCF has larger mode area and better single-mode operation compared with the traditional Fan-Segmented Cladding Fiber(FSCF)and single Trench-Assisted Fan-Segmented Cladding Fiber(STA-FSCF).The parameters effect is studied and investigated on bending performance and mode area to optimize structural parameters.With the bending radius of 20cm and operating wavelength of1.55?m,the effective mode area of DTA-FSCF can reach 1096?m~2,and the loss ratio between lowest higher-order modes and fundamental mode is larger than 100.DTA-FSCF has excellent single-mode performance and large mode area.Besides,the fiber performance is not sensitive to the bending orientation.(3)The bending performance of traditional Segmented Cladding Fiber(SCF)is analyzed.The influence of segmented number,core radius and duty cycle on the performance of the fiber is studied.SCF has the characteristics of insensitive with bending direction.By optimizing the fiber parameters,the mode area of SCF can reach704?m~2 when the operating wavelength is 1.06?m at bending radius of 20 cm.The loss ratio between lowest higher-order modes and fundamental mode is larger than 20.(4)A Pixelated Trench-Assisted Segmented Cladding Fiber(PTA-SCF)is proposed.PTA-SCF has larger loss ratio between higher-order-modes and fundamental mode when the mode area is same with SCF.The parameters effect is studied and investigated on bending performance and mode area to optimize structural parameters.In order to obtain a larger mode area,the fiber parameters are adjusted.When the bending radius is 20cm,operating wavelength is 1.06?m and core radius is 25?m,the effective mode area of PTA-SCF can reach 914?m~2,and the loss ratio between lowest higher-order modes and fundamental mode is larger than 100.