Suppression of inter-modal four-wave mixing in high-power fiber lasers

For the inter-modal four-wave mixing (IMFWM) in high-power fiber lasers, the phase-matching frequency shift and coherence length are calculated to determine the fiber mode combinations corresponding to IMFWM peaks; then, the parameters of the laser are optimized accordingly to suppress the IMFWM. On the basis of laser parameter optimization, the fiber coiling method is applied to further suppress the IMFWM. To validate this method, a master oscillator power amplifier was configured with 20/400 fiber to produce IMFWM peaks at 1108 and 1071.6 nm in the output spectrum, and then those peaks were removed by reducing the bending radius of the fiber.