Mode coupling in a multimode optical fiber with microbends.

Experimental observations of the radiation pattern of a short multimode fiber with different induced deformations are reported here. Theoretical calculations are also made, based on the assumption of strong coupling between two particular modes of the fiber, and are in good agreement with experiment. We obtain numerical evaluations of the coupling coefficients and excess loss as a function of the amplitude of the deformation, and indications on the requirements to be met in cabling the fibers are derived from the experimental results.