Abstract

A difficult problem facing the designer of high bit-rate multimode systems is that of fibre bandwidth specification. For economic reasons, he must reject only those fibres from a jointed link which would otherwise prevent the necessary system bandwidth being achieved. The factors which are important in determining the resultant bandwidth include mode coupling, differential mode attenuation and the equalisation of modal delays between adjacent fibres. The first two effects may operate throughout the length of the fibre (due to micro-bending for instance) or be localised at the joints. Further complications arise because the bandwidth of a fibre is sensitive to the exact launch conditions and also to its enviroment, if this introduces significant micro-bending. These problems have been studied at BTRL over a number of years using a variety of dispersion and differential mode delay measurements (DMD) [1] on a number of different fibre links. The results of our most recent studies will be compared to our earlier work.