Tatsuya Hatano, Daeyoul Yoon and Kazuyou Mizuno
In designing a network architecture to offer greater flexibility and higher reliability in the wavelength-division multiplexing (WDM) systems of the future, an architecture that uses the optical add-drop multiplexer (OADM) for signal I/O with respect to the transmission path has been proposed. It is known that changes in the gain of the erbium-doped fiber amplifier (EDFA) that accompany fluctuation in the signal light input to the OADM and changes in Raman gain generated in the transmission path occur in the sub-millisecond order. It is also known that this gain change is gain tilt occurring in the wavelength direction, constituting a factor in the degradation of transmission characteristics due to the power level deviations among signals. We have developed a fast gain tilt compensator that is capable of operation in the microsecond order and uses a lithium niobate (LN) polarization transformer to compensate for the gain tilt due to these gain changes.