Adaptive dispersion equalization by monitoring relative phase shift between spacing-fixed WDM signals

This paper proposes a novel adaptive dispersion equalization system that equalizes the temperature-induced dispersion fluctuation in long-span ultra-high-speed optical transmission systems. The system monitors the dispersion fluctuation by measuring the relative delay between two wavelength division multiplexed (WDM) signals, and equalizes the dispersion fluctuation by wavelength tuning. A variable-dispersion equalizer can be used instead of wavelength tuning. Adaptive equalization is successfully demonstrated in 40-Gb/s (8-ps-RZ pulses) 400-km transmission. Furthermore, the proposed equalization system is shown to be applicable to WDM systems that use dispersion and dispersion slope compensation. Since the sensitivity to the dispersion fluctuation is improved by extending the wavelength spacing of the signal and monitor channels, the system is shown to operate even when polarization-mode dispersion (PMD) of the transmission fiber must be taken into account.