A role of non-linearity in self-organization in fiber laser arrays

Abstract

Along with rapid progress in characteristics of single-fiber lasers much attention is paid these days to the problem of phase locking of multi-core fiber lasers. It is known that only strong-coupled system has a chance to be phase locked despite non-identity of channels. In case of the strong inter-channel coupling the traditional theoretical approach based on expansion over modes of individual cores fails. We have developed 3D diffraction numerical code, and results of its implementation to simulations of 7-core hexagonal fiber structure experimentally studied recently are reported. Detailed analysis of light propagation in this system, where self-organization effect was observed, shows that the dominant mechanism of coherence formation in an array of co-propagating beams is mode spatial filtering produced by the gain assembly. Non-linear resonance refraction exerts a weak influence on appearance of self-organization. The ways to achieve better selection of a single array mode are discussed. For the first time, the tolerance limits on micro-core parameters for keeping phase-locking are numerically found.