High order mode evolution in large mode area fiber lasers with suppressing strategies

In this paper, we present systematically theoretical analysis of the high order mode (HOM) oscillation in large mode area (LMA) fiber oscillator. A detailed numerical laser oscillator model based on LMA fiber has been built. Model analysis shows that the HOM begins oscillating in fiber laser oscillator when the fiber core diameter reaches 25μm. This HOM oscillation could seriously degrade the beam quality of laser output. In order to suppress the HOM oscillation in LMA fiber laser, we put forward two fiber device models which are partially inscribed fiber Bragg gratings (FBGs) and partially doped gain fiber. Simulation proves the inhibition ability against HOM oscillation of these two devices. Our work provides a complete and concise analysis on the mode characteristics in high power fiber laser oscillator.

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