Measurement of the nonlinear refractive index of long dispersion-shifted fibers by self-phase modulation at 1.55 /spl mu/m

We measure a value of N/sub 2/=2.45/spl times/10/sup -16/ cm/sup 2//W (/spl plusmn/5%) by self-phase modulation (SPM) in two 20 km dispersion-shifted fibers for random polarization at 1.55 /spl mu/m. There is still some dispersive broadening and we find that an accurate determination of N/sub 2/ requires fitting the experimental (SPM) spectra with a computer simulation to account for the variation in pulse shape and fiber properties along the length of the fiber. We also show that spectral information provides information about the input pulse properties.