| 摘要 |
PROBLEM TO BE SOLVED: To provide an automatic frequency control circuit capable of detecting frequency variation and controlling a frequency of local oscillation light even when a large frequency difference between an optical signal and the local oscillation light occurs in a coherent optical receiver.SOLUTION: In an automatic frequency control circuit, a first frequency discriminator generates a first output voltage corresponding to a frequency of a first electric signal on the basis of the first electric signal converted from an optical signal inputted from an optical transmitter, and outputs the generated first output voltage. The second frequency discriminator generates a second output voltage corresponding to a frequency of a second electric signal on the basis of the second electric signal having the same frequency as the first electric signal converted from the optical signal, and outputs the generated second output voltage. A voltage detector controls a switch on the basis of the first output voltage, outputs any one of the first output voltage and the second output voltage to a local oscillation light source, and controls a frequency of local oscillation light outputted from the local oscillation light source to the same frequency as the optical signal or to a frequency having a predetermined offset to the frequency of the optical signal.SELECTED DRAWING: Figure 1 |
