| 摘要 |
PURPOSE:To facilitate drift reduction and to improve the sensitivity and accuracy by detecting the output light of each ultrasonic wave optical modulator (AOM) and controlling their frequency difference to a constant value, and thus removing the influence of reflected light. CONSTITUTION:The ultrasonic wave optical modulators (AOM) 12a and 12b impose frequency modulation upon light incident on a ring resonator 90 respectively and AOM drivers 13a and 13b drive the AOMs 12a and 12b at such different frequencies that their frequency difference is outside a detection band. A control means 19 detects the output light beams of the AOMs 12a and 12b and control the drivers 13a and 13b so that the frequency difference is invariably constant. Then, light beams which are propagated in the ring resonator 90 in the opposite clockwise and counterclockwise directions are given the frequency difference which is outside the detection band, and the frequency difference is held constant. Namely, the light beams which are propagated in the ring resonator 90 in the mutually opposite directions have the frequency difference, so interference components of the reflected light and signal light generate beats corresponding to the frequency difference. For the purpose, the frequency difference is set outside the band of a signal processor to remove the beat components, thereby eliminating the influence of the reflected light. |
