| 摘要 |
PURPOSE:To obtain an output applied with optical modulation with a fixed amplitude at all times, by detecting both maximum and minimum levels of a laser light output to be optically modulated and then controlling the working point and amplitude of the modulated signal based on the detected signal. CONSTITUTION:In the case of an ambient temperature TO in a steady mode, an input video signal ein undergoes modulation of amplitude by a modulated signal aO given from a comparator 3 through a modulating circuit 2. Thus the signal ein is turned into a driving current to be modulated and supplied to a semiconductor laser oscillator 4. For the output signal of a monitor diode 5, the mean value PO of an output PTO to be optically modulated is clamped 6. Then the output signal of the diode 5 is supplied to detecting circuits 7 and 8 respectively. At the same time, the circuits 7 and 8 detect the maximum value EA and the minimum value EB with a clamping pulse generated 9 based on a modulated output. Each detected value is converted into a control signal by the comparator 3 and then supplied to a modulating circuit 2 in the form of a driving current. As a result, an optical output PT1 of the oscillator 4 is set equal to the maximum and minimum levels of the output PTO applied with optical modulation which are obtained in a steady mode. |
