Mode instability in high power all-fiber amplifier with large-mode-area gain fiber

We studied the mode instability (MI) of the signal light in high power all-fiber amplifier with large-mode-area (LMA) gain fiber experimentally. The MI phenomenon of the output beam was observed and analyzed in the all-fiber amplifier, and the MI power threshold was compared by coiling gain fiber with different radii in multi-kilowatt level (more than 3 kW). In the experiments, MI power threshold was improved and optimized with coil radius reduction of the LMA gain fiber in the all-fiber amplifier.