Method and system for indicating an optical transmit amplifier fault

Optical transmit amplifier (24) fault indicator system (46), (78), and (80) indicates the failure of optical transmit amplifier (24) and includes an input loss circuit (46), an output failure circuit (80), and a modulation detector circuit (78). The modulation detector circuit (78) receives a portion (76) of the optical output signal (74) for determining therefrom that a failure in modulation exists in optical output signal (74) of optical transmit amplifier (24). The modulation detector (78) includes a modulation conversion circuit (82) and (84) for converting modulation in the optical output signal (76) into a measurable signal having a level within a first predetermined range in the presence of modulation and a second predetermined range in the absence of modulation. The modulation detector circuit (78) converts the measurable signal to a DC signal and produces a loss of modulation alarm signal (114) in response to a loss of modulation.