Keiichi Aiso, Yoshio Tashiro, Tsuneo Suzuki, Takeshi Yagi
The increasing capacity of wavelength-division multiplexing (WDM) transmission systems requires higher optical output power of erbium doped fiber amplifiers (EDFAs). Higher output causes in the EDFA adverse nonlinear effects --four-wave mixing (FWM) and cross-phase modulation (XPM) etc.-- that result in signal distortion. In the past fiber parameters of Er-doped fibers (EDFs) have been optimized from the standpoint of improving amplification efficiency, but designs that improve efficiency increase nonlinearity. This makes it difficult to achieve low nonlinearity with EDF. Here the authors have developed fibers that are co-doped with erbium and ytterbium. This Er, Yb co-doped fiber (EYDF) successfully realizes low nonlinearity without degrading amplification efficiency, and when pumped using a 1480-nm laser diode, EYDFAs achieve both lower nonlinearity and higher output power.