Abstract
Suppressing mode instabilities (MI) by optimizing the fiber coiling methods has been studied numerically. By employing our semi-analytical model, the MI threshold of two typical high power fibers in various coiling methods has been calculated. It reveals that fiber laser systems with gain fibers being coiled in cylinder shape has higher MI threshold than those with gain fibers being coiled in spiral shape, and MI-free output power of fiber lasers can be scaled up to above 3 kW even with the typical commercial fibers in the co-pumped configurations.