The effects of periodic axis deformations on propagation in multimode optical fibers with single-mode excitation are investigated numerically and experimentally. The numerical study, based on ray theory, deals with helical rays in the presence of sinusoidal axis deformations for various shapes of index profile. The corresponding experimental observations and results, carried out on tubular modes, confirm the existence of resonance effects between the helical ray period and the fiber axis deformation. This technique permits the observation of mode-to-mode power transfer and provides a sensitive tool to investigate the mode-coupling mechanism in optical fibers.
© 1983 Optical Society of America
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