Investigation Of High Power Ytterbium-Doped Double-Clad Fiber Lasers

Cladding-pumped Ytterbium-doped double-clad fiber lasers developed very fast in recent years. They are attractive and have great potential in many fields for their high power, high efficiency, excellent beam quality, low cost, compactness, immunity from thermal effect and easy-maintenance.According to the principle and experimental condition, the high power fiber laser system is comprised of a 976-nm laser diode stack pump source, a spatial filter, an aspheric lens, a feedback component and a D-shape 600/650μm inner-cladding with a numerical aperture (NA) of 0.46 Yb3+-doped fiber. And the Yb3+-doped double-clad fiber is end pumped by the laser diode stack.The output characteristics of the Yb3+-doped double-clad fiber laser is theoretically analyzed by solving the governing equation of pump power and signal power in the fiber. The forward and backward distributions of pump power and signal power, the dependence of the fiber length, the transmission loss as well as the reflectivity of the end facet on the output power are also numerically modeled. Then the optimum experimental condition is obtained by means of those analyses.After investigating the propagation property of Gaussian beam, the appropriate parameters of lens coupling system is selected. The spatial filter is designed and fabricated to eliminate the high frequency components resulted from the possible faults in beam shaping, diffraction or nonlinear effect in the process of propagation. And some special methods are taken to avoid facet damage when the fiber is strongly pumped. In order to keep the high power fiber laser system running stably, an effective cooling system is deployed by analyzing the power distribution and the characteristics of the main components.Then the experimental platform of Yb3+-doped double-clad fiber laser system is constructed. Because of the increase of the coupling efficiency after the optimization of the experimental condition, the output power of this fiber laser system is gradually scaled up to a higher level. Finally 332-W CW with central wavelength of 1104nm output power is realized. The threshold of the system is about 7.6-W and the slope efficiency with respect to the launched pump power is 78.5%.There are some problems in the experiments and some improvement suggestions are presented.