| 摘要 |
PCT No. PCT/GB97/00647 Sec. 371 Date Nov. 6, 1997 Sec. 102(e) Date Nov. 6, 1997 PCT Filed Mar. 10, 1997 PCT Pub. No. WO97/33390 PCT Pub. Date Sep. 12, 1997A method and apparatus for increasing the operational bandwidth of a multimode optical fiber communications system is provided. The method comprises launching optical radiation into the core of the multimode fiber away from the center of the core so as to strongly excite mid order modes of the multimode fiber, but to only weakly excite low order and high order modes of the multimode fiber. 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 fiber refractive index profile. Modal noise performance is also enhanced. Embodiments of the invention employ a singlemode fiber, a multimode fiber or a lens to illuminate an end face of a multimode fiber with a small spot offset from the optical axis of the fiber. |
