The invention of the erbium fiber amplifier just a half-dozen years ago1,2 paved the way for development of wide-band, "all-optical," long distance fiber transmission systems. There were two principal incentives for the development of these systems. First, the huge bandwidth of the optical amplifiers would limit neither the fundamental bit rate nor the potential for extensive wavelength-division-multiplexing (WDM). Second, save for the amplifiers themselves, the system would be strictly passive, so that the many expensive, rate-limiting, active components of electronic regeneration, with their potential for failure, would be eliminated. It was also important that most other properties.
by Linn F. Mollenauer