Coupling mechanism in multimode fibers

The steady increase of bandwidth demand in worldwide communications has revived the interest about multi-mode optical fibers and their use in spatial division multiplexed systems. Roughly speaking, in these systems transmission capacity is increased by using modes as separate channels, resorting to either special fiber with negligible mode coupling, or to MIMO technology to compensate mode dispersion. In this framework, understanding the mechanisms that originate mode coupling is of crucial importance, for it would lead to the development of more accurate propagation models and optimized fiber designs. The paper analyzes the most common sources of mode coupling and their effects.