The launch conditions (injected beam size/shape, radial/angular offset from the multimode fiber axis) may be varied to preferentially excite certain transverse modes of multimode optical fiber. To reduce multimode dispersion in the fiber, modes are excited having smaller amplitudes near fiber index defects....http://www.google.com/patents/US7228032?utm_source=gb-gplus-sharePatent US7228032 - Apparatus and methods for launching an optical signal into multimode optical fiber
