| 摘要 |
A novel acoustic vibration sensor and novel acoustic vibration sensing system are described having principal application to hydrophones and operating upon the optical heterodyning principle. The sensor employs a pair of single mode fibers, optically coupled by a path whose length is varied by the acoustic vibrations, and including a partially reflecting discontinuity at the sensitive end of each fiber. Optical signals of one frequency are supplied to one fiber, and of another frequency to the other fiber. Optical signals of the same difference frequency emerge from the "dry end" of each fiber. When these two emergent signals are photodetected, and the phase or frequency difference is obtained, the acoustic vibration is sensed. The process effectively cancels out noise pickup in the single mode fibers and in other parts of the system, such as laser noise and oscillator instabilities.
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