An interferometric fiber optic vibration sensor based on random phase modulation

A stable homodyne interferometric fiber optic vibration sensor is proposed and demonstrated by using a probe pulse, which is generated based on random phase modulation. The first half of the probe pulse is divided into three time slots. Each time slot is subjected to random and different phase modulation. The last half of the probe pulse is not modulated. An unequal-arm Michelson interferometer is used as the sensing unit of vibration sensor. By using a simple direct detection scheme, the interference signals of three time slots can be distinguished in the time domain. Two time slots' interference signals are selected and extracted as the signal to be demodulated. The vibration signal to be measured can be quantitatively measured by using ellipse fitting algorithm and arctangent algorithm. Compared with the traditional 3 × 3 coupler-based scheme, the system structure is simple and can form a large-scale sensor array. Moreover, the interference light signal in each time slot can provide multiple channels for averaging, resulting in a better demodulation signal-to-noise ratio (SNR) performance. By multi-channel averaging, the SNR is improved by at least 5.2 dB.