Pulse Propagation in Multimode Dielectric Waveguides

S. D. Personick 1 was the first to realize that coupling between the guided modes of a multimode waveguide is capable of reducing the pulse dispersion t h a t is caused by the fact that modes with higher group velocity arrive at the receiver earlier than modes with lower group velocity. Multimode pulse dispersion can, of course, be avoided by designing the waveguide to operate with only a single mode. However, single-mode waveguides cannot be excited efficiently by incoherent 1199 1200 THE BELL SYSTEM TECHNICAL JOURNAL, JULY-AUGUST 1972 light sources such as luminescent diodes. A simple communications system using luminescent diodes instead of more expensive lasers as light sources needs multimode optical waveguides as the transmission medium. Unless multimode pulse dispersion can be reduced by some means, the information-carrying capacity of a multimode optical fiber is severely limited. Even though Personick 1 pointed the way for achieving an improvement in the multimode pulse dispersion he did not give design criteria for their construction nor did he discuss the loss penalty that inevitably must be paid for any improvement in pulse dispersion. Furthermore, Personick's paper deals primarily with two modes even though some thought is given to the multimode case. H. E. Rowe and D. T. Young 2 rederived Personick's results using a more rigorous analysis but also limited themselves to the two-mode case. Patent applications by E. A. J. Marcatili, S. E. Miller, and S. D. Personick are pending.