In this manuscript, complex degree of coherence (CDC) is proposed to depict the spectral characteristics of narrow-linewidth fiber lasers in coherent beam combining (CBC) system. Both the theoretical and experimental demonstrations are shown that the CDC of individual narrow-linewidth fiber laser is directly proportional to its combining efficiency of CBC system. Compared with the multiplicity of typical ‘spectral linewidth’ concepts, such as full wave at half maximum (FWHM), spectral power ratio (SPR) and RMS value, CDC can be directly acted as a unified metric to evaluate the spectrally and temporally coherent capacity of narrow-linewidth fiber lasers with different spectral distributions. Finally, the impacts of spectral distribution and delay time on CDC are also theoretically and experimentally investigated.

在本手稿中，提出了复相干度 (CDC) 来描述窄线宽光纤激光器在相干光束组合 (CBC) 系统中的光谱特性。理论和实验证明，单个窄线宽光纤激光器的CDC与其CBC系统的合路效率成正比。与典型的“频谱线宽”概念的多样性相比，例如半高全波 (FWHM)、频谱功率比 (SPR) 和 RMS 值，CDC 可以直接作为统一度量来评估频谱和时间相干容量具有不同光谱分布的窄线宽光纤激光器。最后，还从理论上和实验上研究了光谱分布和延迟时间对 CDC 的影响。