Investigation on Power Scalability of Diffraction-Limited Yb-Doped Fiber Lasers

The power scalability of diffraction-limited Yb-doped fiber lasers is investigated with a new model which takes into consideration the spectrums of absorption and emission cross sections of active ions. It is found that the maximum output power of a fiber laser is not only dependent on the pump wavelength, but also depends on the core size and cladding-to-core area ratio of active fiber. To increase the pump wavelength is not sufficient to improve the maximum output power, where at the same time the large core, small cladding, high pump brightness and dopant concentration are simultaneously required. Further investigations show that to maximize the output power, the best choice of pump wavelength is highly dependent on parameters such as the pump brightness, dopant concentration, core size and cladding-to-core area ratio. It is found that the pump wavelength with the largest absorption cross section should be the best choice when the core size is small. Besides, the upper limitation of pump brightness for elevating the output power of fiber lasers is given.