Optimization Design And Manufacture Of Fiber Combiner In High Power Fiber Laser

High power fiber laser has the characteristics of good beam quality,compact structure,easy heat dissipation and so on.It has important applications in industrial processing,military defense and other fields.Fiber combiner is an important part of high-power fiber laser,which can beam multi-channel fiber coupled semiconductor laser to a single fiber output,thus providing pump source for fiber laser.The performance of the combiner directly determines the upper limit of the output power of the fiber laser.In this paper,we optimize the design and manufacture of the high-power fiber combiner from two aspects of the pump coupling efficiency and the thermal effect in the cone region.The main work is as follows:Firstly,based on the geometrical optics theory,the influence of the incident angle of the pump light and the taper ratio on the normalized leakage position of the pump light is studied.By using the simulation model,the influence of the taper parameters of the pump fiber and the melting depth between the pump fiber and the signal fiber on the performance of the combiner is analyzed comprehensively.Finally,the optimal parameters of the side pump / signal combiner are obtained.Secondly,the heat generation mechanism of OH-ion in the taper region glass of the combiner was studied.The finite element analysis method is used to establish the simulation models of the combiner taper region in the air and heat sink structures.The simulation model is used to comprehensively analyze the temperature field distribution of the combiner cone area under transient and steady state conditions.The results show that the temperature gradient of the thermal effect is mainly distributed in the axial direction,and the temperature at the output end is the highest.Thirdly,a(2+1)×1 pump / signal combiner is fabricated by the biconical method.In the process of fabrication,a 14/250 ?m double clad fiber with smaller mode field area,better output beam quality and lower cost is used as the signal fiber.The coupling efficiency of the beam combiner and the insertion loss of the forward and reverse signals are measured.The coupling efficiency of the beam combiner is 95%,and the insertion loss of the forward and reverse signals is 0.065 d B and 0.125 d B respectively.The side coupling scheme of the beam combiner effectively guarantees the transmission efficiency of signal light on the premise of a small loss of pump coupling efficiency.Fourthly,a(6+1)×1 end-pumped beam combiner was fabricated by the twist-knot method,and a 14/250 ?m double-clad fiber was also used in the production of the signal fiber.The pump coupling efficiency of the combiner and the temperature change before and after the cone area package were tested.The pump coupling efficiency of the end-pumped combiner is 98.1%.At100 W input power,the temperature rise of the cone area of the combiner after packaging is1.3°C,which is 71% lower than that before packaging,which is in line with the simulation results.The design parameters and manufacturing process of the beam combiner can provide taper and heat dissipation guidance for higher power laser beam combiners.