Abstract: A pumping module having a cascaded Raman laser for Raman amplified optical transmission systems. Non-linear parametric phenomena, such as Raman-assisted three-wave mixing, in Raman amplified signals from a cascaded Raman pump are strongly reduced by substantially suppressing from the output spectrum of the Raman pump the emission peaks at wavelengths shorter than that of the desired pumping wave on a specific wavelength ?n, and within a given spacing from ?n. The pumping non-zero dispersion fibres have zero dispersion between the wavelength range of the transmission signal and the wavelength range of the pump signal.

Abstract: The modification is accomplished on the basis of the solution known as spectral inversion (or optical phase conjugation). The device (1) comprises a medium, such as typically a dispersion shifted optical fiber (4), into which the signal to be modified is injected together with a pump signal at such a level as to induce modulation instability in the fiber (4). At the output of fiber (4) a spectrally inverted optical signal is available, which signal is translated in wavelength and is obtained with high conversion efficiency. Preferably, in order to avoid stimulated Brillouin scattering, the pump signal is subjected to spectrum broadening, for instance by means of a modulator (5).

Abstract: A train of rectangular pulses is sent into a fiber, which pulses have such a wavelength that fiber operates under anomalous dispersion conditions, such a peak power as to cause modulation instability in the fiber and such a ratio between duration and repetition period that the average power is lower than the threshold at which stimulated Brillouin effect takes place. The maximum value of instability gain is measured in the spectrum of the pulses exiting the fiber and the Kerr non linearity coefficient is obtained from the maximum measured value of modulation instability gain by minimizing the error, in the range of power values used for the measurement, with respect to a theoretical curve expressing such maximum gain as a function of the peak power. The device to realize the method is also provided.