A NEW DESIGN ARRANGEMENT OF TRANSMISSION FIBER DISPERSION FOR SUPPRESSING NONLINEAR DEGRADATION IN LONG-DISTANCE OPTICAL-TRANSMISSION SYSTEMS WITH OPTICAL REPEATER AMPLIFIERS

The invention of the erbium-doped fiber amplifier has opened the possibility of constructing long-distance optical transmission systems with 1.5-mum zero-dispersion wavelength shifted fibers. In such systems, nonlinear degradation due to four-wave mixing and self-phase modulation strictly limits the total span of systems and the length of the optical repeater spacing. There are proposals to use slightly normal group velocity dispersion fibers (D < 0) through the whole system or to arrange the various sections of different dispersion fiber in the cable for suppressing these nonlinearities [1]. However, these strategies are not so easily applied in real systems. In this paper, the authors have proposed a new arrangement of transmission fiber dispersion which easily suppresses these nonlinearities so as to expand the total span of the system or to increase the repeater spacings. The feasibility of the proposal has been experimentally confirmed.