Reduction of Multimode Pulse Dispersion by Intentional Mode Coupling

Optical fibers supporting many guided modes suffer from multimode dispersion. A pulse launched into a multimode fiber excites many modes, each traveling at a different group velocity. At the far end of the fiber the pulse is spread out in time because of the different group delays of each mode. This multimode dispersion effect is usually more serious than the single-mode dispersion caused by the dispersive effect of the dielectric material of the waveguide core and by the inherently dispersive nature of mode guidance. Discussions of multimode dispersion in the absence of mode coupling can be found in Refs. 1, 2, and 3. S. D. Personick discovered that multimode dispersion in fibers can be reduced by intentional (or unintentional) mode coupling. If the power carried in the fiber transfers back and forth between slow and fast modes, averaging takes place, so that the pulse no longer breaks up into a sequence of pulses but is forced to travel at an average group delay with a concomitant reduction in pulse spreading. Although the spread of a pulse carried by uncoupled modes is proportional to the 1795