Research On Fiber Thermal Effect Of High Power Fiber Laser And Its Heat Treatment Technology

High power fiber lasers are widely used in military and civilian.In recent years,the output power of double cladding fiber laser has been increasing continuously,resulting in serious optical fiber heating problem.Thermal effects limit the development of lasers.In order to achieve a stable output of high power laser,the theoretical factors of fiber heating phenomenon in fiber lasers are simulated,and experimental systems are built to verify the results.The systems were optimized and the heat suppression technology was improved.The factors affecting the thermal problems of the active optical fiber in fiber lasers are analyzed.The active optical fiber in fiber lasers with different structures in power,pumping mode,pumping wavelength and bandwidth,fiber parameters are simulated by numerical simulation.The corresponding lasers with different structures are constructed to verify the simulation results.The laser pumped at 915 nm has well-distributed heating power and is less affected by the pumping bandwidth.However,with the same output,the overall heating power is higher than that of the laser pumped at 976 nm.Increasing core diameter can reduce core temperature,but too large core diameter will lead to deterioration of beam quality and intensification of spectral broadening.Optimizing the structure of the fiber laser,the temperature rise of the active fiber is controlled,the temperature is well-distributed,and the output is higher.The heating sources of passive optical fibers are divided into three parts: splicing misalignment,packaging stresses,and coating incision.The heating model of optical fibers and the model of deformation on signal light are established.The simulation and experimental results show that the deformation of optical fibers caused by splicing misalignment and packaging stresses will cause the heating of optical fibers and the overall deterioration of the beam quality of the output.When the output is 100 W,the maximum change of M2 value caused by stress is 0.39 and the maximum temperature rise caused by stress is 12?.The temperature rise of the cladding power stripper using silastic is controlled within 5? and the M2 value change caused by stress is controlled within 0.05.The rougher the incision is,the higher the temperature rise of the optical fiber is.By using the method of segmental corrosion,a large amount of scattered light can be stripped from the cladding power stripper,which can improve the thermal condition of the coating incision before and after the stripper.Improving the operation of fiber,the fiber heating is suppressed,the beam quality deterioration is controlled,and the output is more stable.The heat suppression methods of fiber laser are designed and experimented.Using all liquid cooling design,the LMA-YDF-20/400-M optical fibers can withstand nearly 3 kW output light without being damaged by the core melting.The surface temperature of the optical fibers is 35? at 2820 W laser output.The conventional heat treatment methods are improved by replacing heat sink material and other measures.When the LMA-YDF-25/400 optical fiber is used as gain fiber,the final output temperature of 3237 W laser is 37.46?.