1.4 kW 1030 nm all-fiber amplifier with ∼3.5 GHz linewidth assisted by confined Yb-doped active fiber and cascaded phase modulation technique.

This study presents a high power 1030 nm narrow linewidth fiber amplifier employing confined-doped fiber. Through comparative analysis of conventional fully-doped and novel confined-doped fibers (both with 30/250 µm core/cladding diameter), we demonstrate the latter's superior performance in high-power short-wavelength operation, exhibiting enhanced threshold of transverse mode instability while maintaining high laser efficiency and amplified spontaneous emission suppression. As a result, a 1430 W signal laser with 3.5 GHz linewidth is obtained. To the best of our knowledge, this is the highest average power for an all-fiber laser reported so far operating at 1030 nm just within several GHz spectral linewidth. Furthermore, by narrowing the linewidth of the seed laser, an 848 W signal laser with 1.71 GHz linewidth is achieved. This work demonstrates the significant advantages of the confined-doped fiber design in high-power, short-wavelength, and narrow linewidth fiber laser applications.