On Four-Wave Mixing Suppression in Dispersion-Managed Fiber-Optic OFDM Systems With an Optical Phase Conjugation Module

Coherent optical orthogonal frequency-division multiplexed (OFDM) systems with uniform chromatic dispersion can efficaciously combat both fiber dispersion by utilizing the properties of the cyclic prefix and four-wave mixing (FWM) among the individual subcarriers via the phased-array effect in dispersive fiber links. Such excellent performance, however, often implies appreciable sacrifices in data rate, since a long cyclic prefix is required to compensate for the dispersion accumulated at the receiver. The spectral efficiency of such OFDM systems may be substantially improved by dispersion management. Dispersion-compensating fibers placed periodically along the transmission line can significantly shorten the channel memory thereby allowing a reduction in the cyclic prefix overhead. However, the FWM tolerance of such dispersion-managed (DM) links may suffer considerably. In this work, the application of optical phase conjugation (OPC) to DM OFDM systems is investigated. Several systems set-ups are considered, and the degrees of inter-subcarrier FWM suppression are estimated analytically for arbitrary dispersion map parameters. A comparison is also made against links with uniform chromatic dispersion. Despite their inherently inferior FWM tolerance properties, DM OFDM systems can be made quite competitive with the application of OPC.