MULTIMODE COMMUNICATIONS SYSTEMS

摘要

A method and apparatus for increasing the operational bandwidth of a multimode optical fibre communications system is provided. The method comprises launching optical radiation into the core of the multimode fibre away from the centre of the core so as to strongly excite mid order modes of the multimode fibre, but to only weakly excite low order and high order modes of the multimode fibre. The mid order modes excited are predominately within a small number of mode groups and thus have similar propagation constants. This leads to a reduction in modal dispersion and thus to a significant increase in bandwidth compared to an overfilled launch. The offset launch of the invention is tolerant both to the launch conditions and to any imperfections in the fibre refractive index profile. Modal noise performance is also enhanced. Embodiments of the invention employ a singlemode fibre, a multimode fibre or a lens to illuminate an end face of a multimode fibre with a small spot offset from the optical axis of the fibre.