4.5 kW, 1050 nm bidirectional output near-single-mode all-fiber laser oscillator

High-power fiber laser oscillators have been widely used in industrial processing, material processing, biomedical and other fields due to their compact structure, simple logic and strong power scalability. With the increasing demand for laser performance in industrial applications, bidirectional output fiber laser based on a single resonator structure has a broad application prospect. In this work, we first establish a theoretical model for a 1050-nm bidirectional output fiber laser oscillator based on the steady-state rate equation, and simulate the relationship between the length of the gain fiber and output power, efficiency, and the intensity of stimulated Raman scattering (SRS). A high-power bidirectional output fiber laser with a central wavelength of 1050 nm is built using an ytterbium-doped fiber with a core/cladding diameter of 20/400 μm. The output characteristics of the 1050-nm bidirectional output fiber laser oscillator under different pump methods (unidirectional pump, bidirectional pump) are experimentally studied in detail. With a total pump power of 5262 W, A-end output power reaches 1419 W and B-end output power reaches 3051 W. Therefore, a total output power of 4470 W with an optical-to-optical conversion efficiency of 84.9% is achieved. The corresponding beam qualities (<i>M</i><sup>2</sup> factor) of both ends are 1.27 and 1.31 when the output powers reach 1458 W and 2733 W, respectively. By further optimizing the length of the gain fiber, the amplified spontaneous emission (ASE) and SRS are effectively suppressed. With a total pump power of 5262 W, the Raman suppression ratios at A-end and B-end are enhanced by ~6.6 dB and ~8.1 dB, respectively. It is expected that higher output power can be achieved by increasing the pump power and optimizing the laser structure in the future.