Abstrac The mathematic mode based on rate equations and power propagation equations of Tm^3＋-doped silica fiber lasers is established and calculated by Matlab software. Output mirror reflectivities of the laser power, optimization of the fiber length and dopant concentrations may significantly improve the slope efficiency of fiber lasers. The evolution of small signal gain coefficient without upconversion and with upconversion is showed for different pump powers. The distributions of the pump light and laser along the fiber and the ion concentrations at every energy level are analyzed. The relation between the small signal gain and incident pumping power, as well as the relation between the pumping light and laser powers with gain medium length are investigated at different dopant concentrations. The relation between output powers and different output coupling mirror reflectivities is studied at different pumping powers. And the further research is also carried out on the relation of slope efficiency and pumping threshold versus fiber lengths for different pump absorption coefficient. The results indicate that there are optimal fiber length and optimal coupling output transmissivity for the maximum of laser output power.

By means of numerical analysis, the distribution of pump light and the output laser power along the fiber with different fiber length has been investigated. The experimental research of the Nd^3 ＋ -doped polarization-maintaining fiber laser is reported, which is pumped by 808 nm semiconductor laser. The influence of different fiber winding radius on output power and polarization characteristic of the laser are studied. Double wavelength peaks at 1060 nm and 1092 nm are obtained. The maximum output power of the laser is 7.35 W at 1060 nm, the slope efficiency is 58.3 %.

Using two fiber loop mirrors（FLPs） as end mirrors and inserting a comb-filter with a flexible F-P cavity into one of the FLPs, stable multiwavelength oscillation of ytterbiumdoped fiber-line laser has been obtained at room temperature when wavelength spacing is larger than 1.3 nm. The F-P cavity length can be adjusted and the laser wavelength spacings are hence tunable.

The output characteristics and their influence factors of continuous wave （CW） high power Yb^3＋-doped double clad fiber laser （YDCFL） are experimentally investigated. The results show that the slant angle of the dichroic mirror （DM） with respect to the fiber axes affects the threshold and the output power of the laser. The threshold increases and the output power decreases with the increase of the slant angle, however, such influences may be neglected if the slant angle is smaller than ±2°. The effective gain length of the doped fiber may also influence the threshold and the output power, and determine the lasing wavelength. The lasing wavelength shifts to longer wavelength as the effective gain length of the doped fiber increases.