Compensation of fibre chromatic dispersion by spectral inversion

The introduction of erbium-doped-fibre optical amplifiers (EDFAs) has eliminated fibre loss as a fundamental limit to achievable transmission distance. However, system containing EDFAs must operate at a wavelength near 1.55 mu m, whereas most of the embedded singlemode fibre in the world is ´normal-dispersion´ fibre with the zero in the group-velocity dispersion located at 1.3 mu m. Because this fibre has a dispersion of approximately +17 ps/km/nm at 1.5 mu m, chromatic dispersion is now a primary limitation in high-speed amplified systems. A chromatic dispersion compensation technique employing phase conjugation is used to transmit a directly-modulated 2.5 Gbit/s signal at 1.5 mu m wavelength through 400 km of normal-dispersion fibre.