Power Distribution among Modes in a Double-Clad Fiber Laser with a Multimode Fiber

The output powers of different modes from a double-clad fiber laser with a multimode fiber were studied by using the multimode rate equations. The variations of different mode powers along the fiber were calculated by using the fourth order Runge-Kutta algorithm to numerically solve the rate equations including the contribution of spontaneous emission to oscillating modes. In this work, calculations were carried out for two example fibers. The results show that, the total output power from the four-mode fiber laser is slightly larger than that from the two-mode fiber laser for the same pump level, the beam quality from the four-mode fiber laser is considerably worse than that from the two-mode fiber laser.