Spectral density of the intensity at the receiver in dispersive fiber links

Summary form only given. The conversion of laser phase noise to intensity noise by the effect of group velocity dispersion (GVD) in a single-mode optical fiber is well-known. In fiber links such as analog "supertrunk" CATV links and digital dispersion supported transmission (DST) links which span moderate to long distances at 1.55 /spl mu/m, this effect leads to requirements for narrow source laser linewidths. Previous authors have addressed this problem theoretically using a variety of approximate methods which are generally sufficient for consideration of the above applications. None of these models, however, can account conceptually for the large phase variations which inevitably result from phase diffusion, i.e. the "random walk" of the laser phase. Thus for large linewidths or long fiber lengths they eventually will fail. We have found that the spectral density of intensity variations after propagation in a fiber exhibiting only lowest-order group velocity dispersion has an exact solution in terms of the 4th order correlation function of the input field envelope.