| 摘要 |
PURPOSE:To know the modulation factor of intensity modulation by converting optically modulated light into an electric signal by a photodetector which has a narrower photodetection range than the modulation range of the optical modulation and finding the time mean ratio of the DC and AC components of the electric signal. CONSTITUTION:This transmitter receiver is equipped with light source 2, an optical modulator 4 which imposes intensity modulation upon light from the light source, a bias circuit 6 which applies a bias voltage to the optical modulator, an optical branching circuit 10 which branches light from the optical modulator, the photodetector 12 which converts one light beam branched by the optical branching circuit photoelectrically, a DC level detecting circuit 14, an AC level detecting circuit 16, etc. The optically modulated light is converted into the electric signal by the photodetector 12 which has the narrower photodetection sensitivity range than the modulation band of the optical modulation, the DC and AC components of the electric signal are separated and detected, and the time mean ratio of the DC and AC components is found to monitor the modulation factor of the optical modulation. Further, the bias voltage applied to the optical modulator is so controlled that the time mean ratio of the DC and AC components becomes constant, thereby stabilizing the modulation factor. |
