| 摘要 |
PURPOSE:To facilitate observing an intensity-modulated optical beam by detecting the difference between outputs of two low-pass filters by a differential amplifier to detect a DC variation and controlling a wide band DC amplifier with the detection output to stabilize its output DC component. CONSTITUTION:An optical beam A whose intensity is modulated by an optical modulator 5 has a part divided by a beam splitter 6 and is made incident on a photodetector 12. The output of the photodetector 12 is applied to a wide band DC amplifier 13 and a DC amplifier which has a low band and is stable with respect to temperature. The output of the DC amplifier 13 is applied to an oscilloscope 14 and a low pass filter 23. The output of the low-pass filter 23 is applied to a differential amplifier 26. The output of the DC amplifier 24 is applied to the differential amplifier through a low pass filter. If gains of DC amplifiers 13 and 24 are equalized, the DC variation of the DC amplifiers is detected by the output of the differential amplifier. The output of this differential amplifier is fed back to the DC amplifier 13 to improve the DC stability of the DC amplifier 13. |
