Abstract

Lightwave systems using optical amplifiers as repeaters offer the advantage of ease of capacity enhancement through the use of either high data rates or wavelength-multiplexed channels. Besides optical fiber nonlinearities, potential limitations of such lightwave systems include the effects of optical amplifier saturation and the accumulation of amplified spontaneous emission. Simulations show that transmission at gigabit-per-second rates over transoceanic distances is possible if erbium-doped fiber amplifiers are used as repeaters. The upper limit on amplifier spacing imposed by noise accumulation is approximately 100 km for a 10000 km, 2.5 Gb/s transmission system. Reduced amplifier spacing lowers the total noise and expands the range of signal powers that satisfy the required signal-to-noise ratio and constraints related to optical-fiber nonlinearities. Best noise performance is obtained with distributed amplification in which the transmission fiber is lightly doped with erbium and optically pumped, so that the gain just compensates the loss. Depending on the supervisory methods, amplified lightwave systems might be operated with regulated optical power or might be free-running, a choice that affects the signal power, efficiency, saturation, and noise figure of the fiber amplifier.

© 1990 Optical Society of America