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A new technique for measuring chirp evolution of Gaussian-like pulses transmitted on single-mode fiber is presented. It is used in a recirculation loop experiment to characterize propagation in anomalous-dispersion regime over megametrical distances. In-quadrature periodical variations of the two characteristic parameters of pulses (i.e., spectral width and chirp) are measured versus distance for different values of prechirp and in-line power. This constitutes the first experimental evidence of pseudoperiodical soliton propagation in dispersion-managed links. It also demonstrates that the prechirp is a key element for the control of nonlinearity as predicted by the theory.

A 40-Gb/s single-channel soliton transmission was performed on a dispersion-shifted fiber (DSF) embedded in a link connecting Rome to Pomezia. The soliton system was based on the transmission of pulses with orthogonal states of polarization (alternate polarizations) to limit the impairments due to the soliton interaction. The performance of the system operating in the field has been compared with results obtained in the laboratory. While in the laboratory the system showed a nearly-stable error-free transmission over 700 km, strong temporal fluctuations of the performance have been observed in the field trial. Numerical simulations have shown that such a degradation, and in particular the fluctuation of the Q factor, is mainly due to a polarization mode dispersion of the installed cables larger than that of the fibers used in the laboratory. However, 500 km error-free transmission was observed in the field for time interval longer than one hour, demonstrating the potentiality of a 40 Gb/s soliton system with alternate polarizations operating with long amplifier spacing (100 km) without in-line control.

We present a simple and efficient model which takes gain stabilization and internal filtering for gain equalization into account. This model allowed the optimization of the filter position in the doped fiber to obtain the best gain stabilization and lowest noise figure. Finally, we demonstrate that equalized and stabilized gain amplifiers are efficient devices for wavelength division multiplexing (WDM) transmissions.