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The Raman gain enhancement of a regenerative ultrafast all-optical cross-phase modulation (XPM) wavelength converter (WC) is quantitatively investigated and experimentally demonstrated to operate error free at 40 and 80 Gb/s. The regenerative nature of the converter is shown by experimentally demonstrating a negative 2-dB power penalty at 80 Gb/s. It is also shown that the Raman gain greatly enhances the wavelength conversion efficiency at 80 Gb/s by 21 dB at a Raman pump power of 600 mW using 1 km of highly nonlinear fiber. An analytical theory based on nonlinear phase-shift enhancement of the fiber-effective length is presented and shows the relationship between a nonlinear enhancement and Raman gain as a function of pump power and fiber design parameters. Measured parameters are used in the analytical model, and a good fit between experiment and theory is shown for two different types of fiber: one dispersion-shifted and one highly nonlinear fiber. The ultrafast response time of Raman gain makes this technique applicable to fiber-based ultrafast WCs. In addition, the applicability to other nonlinear fiber wavelength conversion techniques is discussed.
Date of Publication: March 2005