Propagation of pulse fluctuations of multimode sources in optical fibers and waveguides with arbitrary chromatic dispersion

On long fibers the fluctuations depend only on the shape of the group delay curve, a monotonic delay separates the modes, whereas a symmetric delay leaves pairs of modes with identical intensity profiles and a persistent beat noise.

Dispersion downconverts the beats of overlapping modes to baseband, where receivers cannot filter them. The detected power follows random phasor statistics, and Gaussian estimates of fade probability can be wrong by orders of magnitude. Mode partition noise grows with dispersion and dominates in band limited links.