Active Compensation Method for Light Source Frequency Drifting in <inline-formula> <tex-math notation="LaTeX">$\Phi $ </tex-math></inline-formula>-OTDR Sensing System

Abstract

Phase-sensitive optical time-domain reflectometry ( -OTDR) has the ability to make a measurement on external disturbance dynamically along the sensing fiber by monitoring the interference fading pattern variance of the Rayleigh backscattering waveform through continuous probe pulse injection. However, even if there is no disturbance, the received -OTDR trace will still show slow but noteworthy distortion due to light source frequency drifting (LSFD). This trace-to-trace slow distortion makes it challenging to capture low-frequency event. In this letter, an active compensation method based on laser frequency sweep and cross-correlation calculation has been proposed to suppress the influence of LSFD. With the proposed active compensation method, the tracking of LSFD can be realized, and the trace-to-trace distortion can be greatly suppressed. The experimental result has shown that a vibration event of 0.5 Hz has been identified successfully under mean frequency drifting speed of 1.68 MHz/s, which extends the application realm of the -OTDR sensing system to quasi-static measurement.Index Terms-Distributed optical fiber sensors, phase sensitive optical time domain reflectometry ( -OTDR), laser frequency drift compensation.

Recent Progress in the Performance Enhancement of Phase-Sensitive OTDR Vibration Sensing Systems

“…For a given SR (probe pulse-width), several Φ-OTDR-based vibration sensor schemes have been proposed to increase the SNR and the DR of the vibration measurement not necessarily by increasing the input probe light peak power but by reducing or controlling the noise present in the system [14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. In [14], a coherent detection-based Φ-OTDR system has been proved to have a better SNR than that of a direct detection system.…”

“…These trace to trace fluctuation act as a noise that fixes the minimum detectable vibration frequency to a higher value. The authors in [17] proposed the wavelength diversity technique to actively compensate the influence of laser source frequency drift, which enabled them to detect a vibration of 0.5 Hz frequency under a laser source frequency drift of mean value of 1.68 MHz/s. The basis of the method is the use of a wavelength tunable laser source to modulate the laser output frequency through the parameters sweep number N and frequency sweep step Δf .…”

Ultra-high resolution strain sensor network assisted with an LS-SVM based hysteresis model

“…Due to the high sensitivity, high spatial and temporal resolution, DAS has been developed and used for broadband seismic monitoring in oil/gas exploration 17 . Nevertheless, the frequency shift of the laser source, as well as the cross-sensitivity between temperature and strain, severely ruin the signal to noise ratio (SNR) of the DAS in low frequency band 18,19 . The noise in ultra-low frequency band of the DAS system limits the availabilities for nature earthquake recording and earth tide monitoring.…”

Optical Fiber Vibration Sensor Using Least Mean Square Error Algorithm

“…On the other hand, the noise elimination is mainly dependent on a signal processing algorithm in time domain and frequency domain [16][17][18][19]. A fast Fourier transform is performed on the original signal matrix to separate the noise and vibration signals in the frequency domain to obtain a high SNR for the vibration location [16].…”

“…A fast Fourier transform is performed on the original signal matrix to separate the noise and vibration signals in the frequency domain to obtain a high SNR for the vibration location [16]. An active frequency scanning method is combined with a cross-correlation algorithm to dynamically reduce the noise caused by frequency drift [17]. A multi-scale wavelet decomposition method is used to decompose the time signal by the selective rearrangement in order to improve the SNR [18].…”