Abstract

Most multimode fibres have discrete defects in their profiles such as the central dip, and such a defect introduces a small shift in the mean group velocity of a small number of modes from the mean velocity of the main group. This results in the modes travelling as two separate groups, so that a small pulse is produced in the impulse response of a single length of fibre. Experience has shown that when lengths of such fibres are spliced together the overall impulse is of the form of figure 1, in which there is a series of side pulses of decending order. J. Wright et al (1) suggested that this could be explained by assuming 50% of mode mixing at each splice, so that there is a continual interchange of energy between the two modal groups. As it is not possible to accumulate enough fibres to explore experimentally the effect of variations in the magnitude and displacement of the minor group on the concatenated bandwidth, a computer simulation based on this relatively simple concept, was established to determine the variation.