Modulated single-longitudinal mode semiconductor laser and fiber transmission characteristics at 1.55 µm

A laser light injection technique was studied to realize a semiconductor laser transmitter oscillating in a 1.55 μm single-longitudinal mode. When -15 dBm optical power was injected into the directly modulated laser, no dispersion degradation was observed in the error rate characteristics after transmitting through 44.3 km single-mode fibers at 100 Mbits/s. Effective gain coefficient , measured by the light injection method, was 45 cm^-1near threshold. As this gain was sufficiently saturated at the -15 dBm injection power, undesired longitudinal modes in the modulated laser were suppressed.