采用多层介质膜衍射光栅实现多路高功率光纤激光共孔径光谱合成有望成为光纤激光同时实现高功率、高效率和高光束质量的最具发展潜力的技术途径。搭建了一套基于双光栅色散补偿设计的5 kW共孔径光谱合成系统。采用国产多层介质膜衍射光栅实现了5路kW级窄谱子束激光的高效优质共孔径光谱合成,最大输出功率达5.07 kW,光束质量因子(M2)小于3,合成效率达到91.2%。初步研究表明: 多层介质膜衍射光栅在较高功率水平、较宽光谱范围内均能保持较高衍射效率,是实现高功率光纤激光高效率光谱合成的重要器件; 参与合成的子束自身的光束质量水平和线宽是影响合成输出光束质量的重要因素,光谱合成系统的输出功率主要受限于窄谱子束的输出功率和合成路数,增加窄谱子束的功率或合成路数均可进一步提升系统的输出功率。

Common Aperture Spectral Beam Combination (SBC) of multiple high power fiber lasers output into a composite beam via a multi-layer dielectric (MLD) grating is a promising approach for the fiber laser system to scale the output power further while maintaining high efficiency and excellent beam quality simultaneously. A common aperture SBC system with dual-grating dispersion compensation configuration based on five kW-level narrow-linewidth fiber amplifier chains in all-fiber format is set up. A common aperture combing beam is achieved with high efficiency and excellent beam quality in the system by using China-made MLD gratings. The maximum average output power of 5.07 kW of the combined beam and the combination efficiency of 91.2% are obtained. The beam quality factor M2 at a power level of 5 kW is less than 3. The preliminary experimental results have shown that MLD grating, which can maintain high diffraction efficiency in a wide spectrum range under high power level operation, is a perfect element for SBC of high power fiber laser. The results also demonstrate that the beam quality and the linewidth of the individual fiber laser are the key factors affecting the beam quality of the spectral combining beam. Presently, the output power is limited by the amount of the narrow-linewidth fiber amplifier chains and the output power of the individual narrow-linewidth fiber amplifier. So it can be expected that the common aperture SBC system output power can be further scaled.