Research On Coherent Beam Combining Technology Of Fiber Laser Array With Large Numbers Of Elements

Fiber laser has the advantages of good beam quality,compact structure,high conversion efficiency and convenient thermal management.It has broad application prospects in the fields of industry,national defense and medical care.However,due to the factors such as thermal damage,nonlinear effects,mode instability,and the brightness of pumping source,the output power of a single fiber laser has limits.The realization of fiber laser coherent combination can achieve the purpose of improving the laser output power while maintaining high beam quality.Expanding the number of combining channels is an important research direction of coherent combination.In this paper,we choose the coherent beam combining technology of fiber laser array with large numbers of elements as the research object to conduct related theoretical and experimental research.The research content of the thesis mainly includes the following aspects:1.Based on the theoretical model of the fiber laser array beam emission system,the theoretical model of the fiber laser array beam coherent combining system is established,which provides a theoretical basis for the parameter selection of the large array element fiber laser array coherent combining system.Based on the generalized Huygens-Fresnel principle,the far field intensity distribution function of large array element coherent combining is theoretically analyzed,and the numerical simulation is carried out by using fast Fourier transformation.2.Based on the theoretical analysis of the large array element coherent combining system,a fiber laser collimator array which can be used for coherent combining of 127-channel fiber laser array was fabricated,and the corresponding phase control module was fabricated to build a experiment setup containing large numbers of elements for coherent beam combining.3.Based on the coherent combining system with large numbers of elements,the grouping method is proposed to study the effect of grouping on the effect of coherent combining.The simulation results show that it can reduce the difficulty and cost of production without greatly reducing the effect of coherent combining.It has strong feasibility.4.The fiber laser array coherent combining experimental system with MOPA structure was designed and built,and the fiber laser coherent combining experiments with seven elements,nineteen elements,thirty-seven elements and sixty elements were carried out.In the experiment,after the phase-locking control is applied,stable interference fringes can be formed in the far field,and the power in the bucket is effectively improved,and good experimental results are obtained.5.On the basis of the six-sided dense arrangement of the circular sub-aperture,the efficient splicing method of fiber laser aperture separation combining is studied.Two new unit sub-aperture splicing schemes are proposed to calculate the energy of two sub-calibers.Through the functional relationship between the ratio and the cutoff coefficient,the optimal values of the truncation coefficients of the two new schemes are obtained.On this basis,the coherent combining effects of three sub-aperture schemes are compared by using the Gaussian beam as the sub-beam simulation analysis.The simulation results show that the two new sub-aperture stitching schemes are compared with the circular sub-aperture regular hexagonal filling.The solution can increase the power consumption in the far field bucket by 9.2% and 13.9%.