Research On Key Technologies And Engineering Of High Power CW Fiber Laser

The fiber laser has a wide range of applications because of high conversion efficiency,good beam quality,compact structure and free maintenance.With the maturation of technology in fiber manufacturing process and semiconductor production,ytterbium-doped fiber laser has been widely applied in the fields of laser processing,medical treatment,militaryand optical communication.With the explanation of application fields,the fiber lasers have been developing towards higher power and more integration.In the course of development,it is necessary to solve the key technical problems such as thermal effect,reflection and beam combination of fiber lasers.Project supported by the National Science and Technique Major Project of the Ministry of Science and Technique of China(Grant No.2010ZX04013-052)-Development of high power all fiber laser for industrial,based on current problems of high power CW fiber lasers,the theoretical simulation and experimental study of high power CW fiber laser are carried out,and finally the project is completed and the engineering of high power CW fiber laser is realizedin this dissertation.The main research contents and results are as follows:1.Based on the energy level structure and spectral characteristics of the ytterbium-ionsand the steady-state rate equation of ytterbium-doped double-clad fiber laser,the approximate analytical formula of ytterbium-doped double-clad fiber laser is deduced,and the theoretical simulation of end pumped and side pumpedis carried out.In the end pumped fiber laser model,the distribution characteristics of pump power and laser power in the fiber are discussed,and the influence of the structural parameters on the output characteristics of fiber laser is analyzed.Based on the boundary conditions of multi-point pumping,the fiber laser model with side-pumped is established and the numerical simulation is also carried out.By comparing the two simulation results,we can see that,with the multi-point pumping in the fiber laser,the distribution of the laser power in the fiber is more flat.Meanwhile,the output power of the fiber laser could increase only by increasing the number of pumping points.2.Combined with the theoretical simulation,ytterbium-doped double-clad fiber laser is designed,and the experimental study is carried out.According to the main parameters of the coupler and the testing method,the influence of the coupler parameters on the performance of the fiber laser is analyzed.Finally,a double-clad fiber laser and an amplifier are built using the self-made cascade pump coupler.In the fiber laser,the coupler has the isolation effect on the reverse pump power,so it can be applied in the backward pumping structure.So,the experimental study of fiber laser in the structure of forward pumped,backward pumped and bidirectional pumpedis carried out.In the experiment ofbidirectional pumped fiber laser,with the 975 nm pump power of 1096 W,the 780 W of laser power is obtained with the optical to optical conversion efficiency of 71%,and the central wavelength of fiber laser is 1080 nm.In the amplifier,the seed power of 206 W is amplified to 635 W with the pump power of 546 W,and the optical-optical conversion efficiency is 78%.3.The optical fiber thermal model is establishedon the basis of heat conduction equation,and the processing technology of optical fiber is optimized.Based on the optimization of fiber processing technology and the design of fiber cooling device,the production line of laser products iscompleted,with the small batch production and application of fiber laser.Based on the method of water cooling,in the end pumped fiber laser,the single-mode fiber laser of 1kW is conducted successfully with master oscillator power amplifier structure.In the fiber laser,output power of 1024 W is obtained with thetotal pumping power of 1496 W at 975 nm,and the optical to optical conversion efficiency is 68.5%.Meanwhile,in the structure of end-pumped,the 1080 nm laser module with output power of 600 W is completed,which provides stable light source for 4kW high power fiber laser.Based on the experiment and encapsulation of the laser module,the control of the key process of 500 W fiber laser production is realized,and the small batch production of 500 W fiber laser is realized.Based on the special optical fiber isolation and light stripping technology,a passive anti reflection fiber laser is designed.In the laser cutting experiment,it is proved that the laser can work stably for a long time in the process of metal processing,and it can also work stably when the high reflective material such as aluminum and copper is processed.4.According to the requirements of the national special project for laser power combining,a high power fiber combiner is developed.The mode field distribution of tapered fiber is simulated and analyzed,and the fiber combiner is fabricated on the basis of optical fiber fused/biconical taper processing platform and quartz glass bushing method.The 7×1 fiber combiner with the input fiber of 20/130?m and the output fiber of 100?mis fabricated.The average transmission efficiency of combiners is 93%.Finally,the 600 W laser module is combinered to developed the 4kW high beam quality output fiber laser.