The Impulse Response of an Optical Fiber With Parabolic Index Profile

The current interest in multimode optical waveguides is related to progress in the fabrication of luminescent diodes which have become cheap and dependable sources of incoherent light. Since incoherent light cannot be injected into a single-mode fiber with high efficiency, multimode waveguides must be used. A disadvantage of using multimode instead of single-mode waveguides is multimode pulse dispersion caused by the fact that the group velocity of the guided modes is not the same. Power injected at one end of the waveguide is shared by many or all of the possible guided modes. As each mode reaches the other end of the guide at a different time, the initial pulse is broadened. It is the purpose of this paper to calculate the impulse response of a graded-index, multimode fiber. 1-3 The index distribution is assumed to be given by the expression n = n0 - A^) Ogr^fl. (1)