Dynamic Phase Extraction in an Ameliorated Distributed Vibration Sensor Using a Highly Stable Homodyne Detection

In this work, a highly stable homodyne phase demodulation scheme is proposed and experimentally demonstrated in an ameliorated distributed vibration sensor (DVS) using dual-wavelength probes and direct-detection receivers. According to the difference between central wavelengths of two probes, the vibration location and the frequency information can be simultaneously demodulated using a reflectometer and an interferometer in direct-detection receivers. An improved phase demodulation scheme is then employed in the interferometer part for the vibration sensing, since it is robust against the high-order harmonic distortion (due to nonlinearity) and the light intensity disturbance, and it is also fully independent of the applied modulation depth. Different patterns of piezoelectric transducer induced vibration are applied to the fiber under test. Experimental results demonstrate that the low harmonic distortion and the accurate phase extraction in the improved phase demodulation scheme make a good agreement with the theoretical analysis. This indicates that the proposed scheme will greatly extend the detected scope of the DVS, in which the quantitative measurement of vibrations is necessary.