Nonlinear effects in optical fibers impose different limitations on the communications link, and an understanding of such effects is almost a prerequisite for actual lightwave-system designers. On the other hand, they offer a variety of possibilities for all-optical signal processing, amplification and regeneration. The nonlinear effects are enhanced dramatically, and new phenomena are observed in the so-called photonic crystal fibers. In this paper, we review the effects — both detrimental and potentially beneficial — of optical nonlinearities in conventional and in photonic crystal fibers.
