CROSS-PHASE MODULATION IN FIBER LINKS WITH MULTIPLE OPTICAL AMPLIFIERS AND DISPERSION COMPENSATORS

We have theoretically and experimentally investigated the cross-phase modulation (XPM) effect in optical fiber links with multiple optical a mplifiers and dispersion compensators, Our theory suggests that the XP M effect can be modeled as a phase modulator with inputs from the inte nsity of copropagating waves, The frequency response of the phase modu lator corresponding to each copropagating wave depends on fiber disper sion, wavelength separation, and fiber length, The total XPM-induced p hase shift is the integral of the phase shift contributions from all f requency components of copropagating waves, In nondispersive fibers, X PM is frequency-independent; in dispersive fibers, XPM's frequency res ponse is approximately inversely proportional to the product of freque ncy, fiber dispersion, and wavelength separation, In an N-segment ampl ified link, the frequency response of XPM is increased N-fold, but onl y in very narrow frequency bands, In most other frequency bands, the a mount of increase is limited and almost independent of N. However, in an N-segment amplified link with dispersion compensators, the frequenc y response of XPM is increased N-fold at all frequencies if the disper sion is compensated for within each fiber segment, Thus, the XPM-induc ed phase shift is smaller in systems employing lumped dispersion compe nsation than in systems employing distributed dispersion compensation.