Single-channel 2R regeneration has been widely demonstrated in the past using highly nonlinear fiber (HNLF)-based regenerators that exploit the self-phase modulation (SPM) effect. However, the direct extension of these regenerators to include multi-wavelength (multi-X) operation is not feasible due to the debilitating nonlinear interaction between the WDM channels, associated with the cross-phase modulation effect (XPM). In the present paper two appropriately modified fiber-based schemes for multi-4 regeneration at 40 Gb/s and even higher data rate are presented. The schemes utilize multiple fibers with alternating dispersion, minimizing the effect of XPM and resulting in regeneration of the degraded WDM channels. INTRODUCTIONAs wavelength division multiplexing (WDM) becomes the natural choice for all kinds of optical networks, the extension of today's single-channel 2R regeneration schemes to multi-4 operation is considered as a strategic goal for making optical networking a powerful and economically viable solution. It is a widely-held opinion that the development of multi-4 regenerators has the potential to follow the paradigm of optical amplification and its application in WDM systems, introducing another major revolution in optical communications. The significance of the targeted multi-4 operation is associated with the ability to handle a number of channels using a single element rather than having to demultiplex the individual channels and apply regeneration discretely to each one of them. Fiber-based subsystems are considered as excellent candidates for the realization of such elements, having the additional potential of efficient operation at high bit rates, since the nonlinearity for the regenerative functionality originates in their case from the Kerr effect, and thus it can be considered practically instantaneous.