Phase Interrogation of Diaphragm-Based Optical Fiber Acoustic Sensor Assisted by Wavelength-Scanned Spectral Coding

In this paper, we proposed a phase interrogation method for diaphragm-based interferometric optical fiber acoustic sensor based on the spectral coding process. The information of the sound wave is coded on the optical spectrum of the sensor head by wavelength scanning, which builds a map between time and wavelength. The acoustic signal can be reconstructed from the sound-encoded spectrum. The sound-induced phase variation of the sensor can be interrogated by comparing the sound-encoded spectrum with the initial spectrum curve, which can be acquired from the sinusoidal fitting method. In order to eliminate the phase ambiguity, a diaphragm-based Michelson interferometer is set up using a commercial 3 × 3 fiber coupler and two synchronized channels with 120° phase difference are employed for the interrogation. Experimental results indicate that the proposed method can provide stable demodulation results under random environmental fluctuations, while the commonly used edge filtering technique shows fluctuations of more than 10 dB under the same condition.