Simulation And Research Of Large Mode Area Single Mode Fiber With Multi-trench Based On Coupling Effect

Fiber lasers have attracted attention among the researchers all over the world because of their stability,flexibility,good beam quality,concentrated energy and low loss.With the increasing demand,fiber lasers are gradually developed toward high power output.However,high power signals propagating in optical fibers will lead to nonlinear effects,and large mode area fibers are considered to be one of the most useful ways to overcome this difficulty.Therefore,the content of this paper is the structure design and performance analysis of a fiber with large mode area,low bending loss and single mode operation.The main work of this paper is as follows:(1)The research status of large mode area fibers is introduced,and the related simulation analysis methods and the boundary conditions setting are presented in this paper.The research is based on the finite element simulation method which combines with the perfect matching layer.At the same time,an equivalent refractive index model of the curved optical fiber is proposed for the phenomenon that the refractive index of an optical fiber is distorted because of bending.(2)The main performance indicators of this paper are explained and analyzed,including large mode area,low bending loss and single mode operation.These main performance indicators are implemented as follows:Large mode area is mainly achieved by coupling effect;Low bending loss is achieved by the increasing of numerical aperture;Single mode operation is achieved by suppressing higher order modes.(3)A two-layer core fiber based on gradient coupling ring and multi-trench is proposed,and the performance analysis is presented.The main design principles are:The two-layer core and gradient coupling ring contribute to the large mode area;In addition to the above function,the gradient coupling ring can improve the bending resistance ability;With the multi-trench,the numerical aperture increases which is beneficial to reduce the bending loss and improve the transmission efficiency.At a wavelength of 1550nm,the simulation result shows that large mode area of 2207?m2 can be achieved,and the bending loss is reduced to about 0.048dB/m,and the fiber can achieve single mode operation by suppressing the higher order modes.At the same time,the stability of the proposed fiber is illustrated by error analysis and wavelength dependence analysis.(4)A fiber based on gradient multi-layer core and multi-trench is proposed,and the performance is analyzed.In terms of the low bending loss,it is effectively reduced by introducing multi-trench,thereby achieving high transmission efficiency.In terms of large mode area,it is achieved by the coupling effect of the gradient multi-layer core,the mode field shifts to the outside due to coupling effect,thereby increasing the mode area.The simulation is performed at a wavelength of 1550nm.The result shows that the mode area can reach 2180?m2 and the bending loss is reduced to about 0.054dB/m,the single-mode operation is still achieved by suppressing higher order modes.At the same time,error analysis and wavelength dependence analysis are performed.