Numerical analyses of a spectral beam combining multiple Yb-doped fiber lasers for optimal beam quality and combining efficiency

Physical parameters of a spectral beam combining (SBC) system for multiple Yb-doped fiber lasers (YDFLs) were identified and numerically analyzed to obtain the optimal beam quality and the combining efficiency. We proposed an optimal range of the parameters that can be utilized in SBC systems. For a practical SBC system composed of a multi-layer dielectric grating and a transform mirror, we systematically varied input laser parameters such as the incident angle, beam diameter, laser linewidth, spectral spacing, number of beams, and their spatial separation. Characteristics of diffracted beams by the SBC system were numerically analyzed using a Fourier modal method (FMM). The beam quality M² and the combining efficiency, η, were optimized by varying the laser beam parameters. We found that M² and η were most affected by the angle of incidence and the laser linewidth, respectively. We presented the optimal parameters for three, five, and seven linear beam array SBCs along with a range of allowed parameters that could be used in the laser power scaling.