| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical phase control circuit which surely executes synchronous detection on minute modulation components, making it possible to exert stable operating point control of an optical modulator. <P>SOLUTION: An AGC amplifier 26 has its lower limit cutoff frequency of loop band set to be higher than the frequency of a minute modulation signal b4, and amplifies, in a variable gain amplifier 31, an electric signal b8 after being photoelectric converted so that it will be equal to a target amplitude value b10 on the basis of a gain control signal b9-1. In a peak detection circuit 32, it detects the output amplitude of the variable gain amplifier, and, in an integrator, it outputs as a gain control signal an output signal b9 which is derived by integrating a difference between the output amplitude and the target amplitude value to the variable gain amplifier and also outputs it as a synchronous detection signal b9-1 to a synchronous detector 27. The synchronous detector determines the direction of operating point control by synchronously detecting the synchronous detection signal, while a control circuit 28 outputs an operating point control signal on the basis of the determined direction of control, and an adder 29 outputs to the optical modulator an operating point control signal b6 consisting of the operating point control signal which has had a minute modulation signal superposed thereon. <P>COPYRIGHT: (C)2013,JPO&INPIT |
