Nonlinear effects in coherent multichannel transmission through optical fibers

Various nonlinear optical interactions in single-mode fibers that are used in coherent FDM (frequency division multiplexed) transmission systems are examined. It is these nonlinearities that lead to crosstalk between channels, power losses, and deleterious fluctuations, which in turn limit the power of the transmitted light and the number of allowed channels, and dictate the channel allocations. It is shown that, for long-haul transmission systems with fiber lengths exceeding 100 km, typical channel separation of 10 GHz, and few channels, the maximum allowed input power per channel, P_max, is limited by SBS (stimulated Brillouin scattering) to about 5 dBm. As the number of channels increases, FWM (four wave mixing) becomes the limiting process with P_max of about -5 dBm, whereas above several hundred channels SRS (stimulated Raman scattering) becomes dominant with P_max of about -5 dBm. For local area networks with shorter lengths, the results are similar, except that the values of P_max are uniformly higher by about 5 dB