| 摘要 |
The rotation sensing interferometer comprises a laser (10) and a modulator (11) introducing amplitude modulator light into a continuous length or strand of optical fibre (12), a portion of which is wound into a sensing loop (14). A phase modulator (38), driven by an a.c. generator (40), is mounted on the fibre (12). A similar phase modulator (39), but operating at a different frequency, is mounted at the centre of the loop (14). This modulator reduces the effects of back-scattered light. The output signal from the generator (40) is supplied to a lock-in amplifier (46) connected to receive the output of a photodetector (30) as well. This signal provides a reference for enabling the amplifier to detect the detector's output signal synchronously at the modulation frequency. The amplifier thus acts as a band-pass filter at the fundamented frequency. Counter-propagating waves are intensity modulated in accordance with a waveform selected to reduce the Kerr effect. The average value of the square of the intensity is equal to a contant times the average value of the waveform intensity squared, the constant having a value between 1.6 and 2.4. |
