Abstract

To date erbium amplifiers have been based on fiber doped with 10 to 1000 ppm erbium oxide, providing several tens of dB gain in lengths of 100 m or less.[1–4] However, communications systems which use such high gain, "lumped" amplifiers subject the signal to large excursions in amplitude, which can cause significant interchannel interference in a wavelength division multiplexed system. Of equal importance, the amplified spontaneous emission (ASE) is significantly smaller when distributed amplification is used, and a larger signal to noise is obtained when the signal is sustained at a high level throughout the system.[5] We show here that fibers can indeed be made with the controlled, very low Er doping (10–100 ppb Er averaged over the core), required for such distributed amplification. Some of our fibers allowed for just enough gain per unit length (0.2–0.3 dB/Km) to cancel fiber loss, without at the same time introducing significant impurities or other defects.

© 1990 Optical Society of America