MONITORING CONTROL SYSTEM FOR OPTICAL REPEATER

摘要

PURPOSE:To keep the gain of a semiconductor light amplifier used in an optical repeater by modulating the intensity of signal light with a modulation index less than a signal bit rate frequency by a sine wave of low frequency, and using the signal as a control monitoring signal. CONSTITUTION:An optical demultiplexing circuit 2 demultiplexes the partial demultiplex light L3 of output amplification light L2 from the semiconductor light amplifier, and an optical/electrical (O/E) conversion circuit 4 outputs to convert it to an electrical signal S1. The amplification light L2 outputted from the light amplifier 2 is comprised of amplified signal light and natural emission light L0 which becomes noise light generated from the semiconductor light amplifier 2. The intensity of the amplified signal light is modulated by the sine wave of low frequency, however, no modulation is applied on the natural emission light L0. Therefore, the output signal S2 of a filter 5 is obtained as the sine wave for control in proportion to the signal light L1. The gain can be kept constant by detecting the fluctuation of the gain of the semiconductor light amplifier 2 from the fluctuation of the output signal S2 of the filter 5, and controlling an injection current Ii by an amplifier driving circuit 7 receiving a driving control signal S3 from an automatic gain control(AGC) circuit 6 so as to keep the level of the sine wave constant.