Common aperture spectral beam combination of fiber lasers with 5 kW power high-efficiency and high-quality output

Common Aperture Spectral Beam Combination (SBC) of multiple high power fiber lasers output into a composite beam via a multi-layer dielectric (MLD) gratingis 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.