| 摘要 |
PURPOSE:To make possible the stable controlling of light power by delaying the change speed of bias voltage by an LPF at the resetting of transmission power controlling bias point to the feedback circuit for controlling the transmission light power of a light modulator by crystal. CONSTITUTION:The intensity modulated light from modulator 2 which makes use of polarization by the electro-optic effect of crystal is detected and fed back by way of a photo detector and the transmitted light power of the modulator 2 is controlled constant. The sinusoidal bias voltage-transmission light power curve including linear portions fluctuates according to the change of temperature, etc. and therefore if the bias voltage of the modulator 2 is re-adjusted by a reset switch 17, the switches 15, 16 of the specified clock period feedback circuit are turned ON and a switch 14 is turned OFF by a signal generating circuit 18 according to the ON and OFF of the switch 17 and the change speed of the bias voltage at the resetting is delayed from the response speed of the transmission light power by the LPF by a resistance R1 and capacitor C, whereby the stable controlling of the transmission light is accomplished without saturation, etc. of the bias voltage. |
