| 摘要 |
PURPOSE:To make optical modulation of an optical signal outputted from a semiconductor laser constant at all times. CONSTITUTION:A DC bias voltage is applied to a terminal 1, a modulation signal is inputted to a terminal 2, a rear light of a semiconductor laser 4 driven by a drive circuit 3 is converted into an electric signal by a light receiving element 5, a detection circuit 6 detects the intensity of a DC component of the signal and a band pass filter 7 extracts a modulation component, a peak detection circuit 8 detects the intensity, a signal ratio detection circuit 9 detects a ratio of the intensity of the DC component and that of the modulation component, a control circuit 10 controls an amplification factor of a variable amplifier 11 and an attenuation of a variable attenuator 12 so that the ratio is made constant thereby controlling the modulation signal inputted to the drive circuit 3. The DC bias voltage applied to the drive circuit 3 may be controlled similarly and the intensity of the DC component and that of the modulation component in the semiconductor laser drive current may be similarly detected. |
