STUDIES ON OPTIMIZATION OF AN ERBIUM-DOPED FIBER AMPLIFIER SUITABLE FOR AN OPTICAL-TRANSMISSION LINE CONTAINING AN AMPLIFIER REPEATER

Optical amplifier structures suitable for a 622 Mbit/s repeater in an optical communication system containing one in-line amplifier have bee n investigated. Two wavelengths of 1.533 mum and 1.549 mum are conside red for two cases, i.e., single-channel transmission and two-channel w avelength division multiplexing transmission. The basic amplifier stru cture is of a two-stage type where forward pumped and backward pumped erbium-doped fibers are connected with each other through intermediate optical filters and an optical isolator. First, the effect of the int ermediate optical filters was clarified in optical gain and bit error rate characteristics. Then, the erbium-doped fiber length was optimize d on the basis of the allowable optical loss of the optical system whi ch was operated at a bit error rate of 10(-9). As a result, the approp riate length of the for-ward pumped erbium-doped fiber was found to be about 20 m for both cases of single-channel and two-channel wavelengt h multiplexing amplifiers. With the designed amplifier used in the sys tem, the calculated allowable optical line loss was more than 90 dB fo r both the cases.