Research on the effect of image noise on non-iterative fast mode decomposition technique in high-power fiber lasers

Abstract

High mode purity of high-power fiber lasers is strongly required in 3-dimensional printing, high brightness beam combing, and high accuracy material processing. Mode decomposition (MD) is an effective technique for diagnosing the mode composition of a high-power fiber laser. In particular, dynamic mode evolution could be commonly generated during power scaling process due to thermal and nonlinear effects. Consequently, the fast and accurate mode decomposition (MD) method is strongly required. The non-iterative fast mode decomposition based on matrix operation method is theoretically a promising technique to achieve ultra-fast MD with high accuracy. However, this technique of realizing MD is mainly limited by the noise of the light-spot image in a practical system. In this report, the effect of the image noise on the noniterative fast mode decomposition technique is carefully investigated. Simulation results show that the decomposition accuracy decreases as the intensity of noise increases. Nevertheless, the effect of image noise on the non-iterative fast mode decomposition method depends not only on the noise intensity but also on the coefficient matrix condition number of the matrix equations. Furthermore, the higher the condition number of coefficient matrix of linear equations is, the more influence of image noise on the non-iterative fast MD accuracy. The results presented could give instructive reference for further optimizing the non-iterative fast mode decomposition technique used in practical high-power fiber lasers.