Effect of polarisation on pulse broadening in multimode graded-index optical fibres

A formulation of ray optics that takes the polarisation of electromagnetic waves into account shows that the maximum difference in time delay between corresponding HE and EH modes is, for almost any multimode graded-index fibre, of the order of 10 000 (¿n/n)2/V ns/km, where V is the V-number of the fibre and ¿n is the variation of the refractive index between axis and cladding. The effect of polarisation on pulse broadening is found to be negligible if the V-number of the fibre is much larger than about 20.