Study On The Characteristics Of Laser Beam Quality In Compact Spectral Beam Combining System

In order to achieve the goal of high power,high beam quality output and compact miniaturization of fiber laser,a compact spectral beam combining system based on compact fiber array is proposed in this paper.Through quantitative analysis of the influence of fiber array displacement and pointing disturbance deviation on the M~2factor pf combined laser,the effective control of combined laser beam quality is realized.According to the Heisenberg’s uncertainty principle and diffraction propagation theory,the expression of M~2factor of combined laser beam in the presence of horizontal displacement,horizontal directional disturbance and axial displacement disturbance of compact fiber array is systematically derived.The variation law of the M~2factor of the combined laser and its statistical distribution under the random deviation are simulated and analyzed when the single/multiple sub beams have displacement and pointing deviation respectively under the constant number of sub beams,and the error analysis of the M~2factor of the combined laser under the different number of sub beams with certain random displacement and pointing deviation is carried out,and the control requirements of various errors are given.According to the theoretical analysis results,an experiment platform was built.Based on the two sub beams,the variation law of the M~2factor of combined laser with respect to the fiber array was studied through preliminary experiment.The results are as follows:(1)The simulation analysis and experimental research show that the M~2factor of the combined laser is the most sensitive to the disturbance along the horizontal(x-axis)direction of the end face of the fiber,which needs to be controlled in the order of microns;(2)The quantitative relationship between the random disturbance and the M~2factor of the combined laser in the fiber array is determined by simulation analysis,and the precision requirements for the displacement and pointing control of the fiber array are put forward;(3)The simulation results show that when the number of sub beams exceeds 23,the statistical mean of M~2factor of the combined laser tends to_~2=1.37、_~2=1.34、_~2=1.25,and the standard deviation tends to 0.05,0.06 and 0.04 respectively;(4)In the experiment,the center wavelengths of the two lasers are 1052.74 nm and 1054.96 nm respectively,the linewidths are 0.0415 nm and 0.0398 nm respectively,the M~2factor of the two sub beams and the combined laser are 1.05,1.06,1.10 respectively,and the combining efficiency is 97.97%;(5)In the experiment of controlling the main error of fiber array,the law of the quality change of the combined laser after artificially increasing the disturbance deviation is consistent with the theoretical analysis results.The compact spectral beam combining system shows good stability,which better verifies the technical feasibility of the compact spectral beam combining system,and provides a certain reference for the subsequent development of higher power laser output.