BIT-ERROR-RATE CHARACTERIZATION OF IM-DD ULTRALONG-DISTANCE OPTICAL COMMUNICATION-SYSTEMS WITH ER-DOPED FIBER AMPLIFIERS USING A RECIRCULATING LOOP

We have evaluated the bit-error-rate characteristics of the IM-DD ultr along-distance optical communication systems employing Er-doped fiber amplifiers. 2.5- and 5-Gb/s IM-DD nonreturn-to-zero signal was analyze d by recirculating-loop experiments. We used a fiber loop of four Er-d oped fiber amplifiers and three spans of dispersion-shifted single-mod e fibers for the experiments. 16,000-km transmission at 2.5 Gb/s and 1 1,000-km transmission at 5 Gb/s were successfully achieved. The allowa ble wavelength-tunable range of the optical transmitter for 9000-km tr ansmission was also measured at the bit rate of 5 Gb/s. The experiment al results show the possibilities and limitations of transoceanic opti cal communication systems using Er-doped fiber amplifier repeaters.