SNR dependence of measurement stability of heterodyne phase-sensitive optical time-domain reflectometry

Abstract

Phase-sensitive optical time-domain reflectometry ( Φ -OTDR) implements distributed vibration measurements by demodulation of vibration-induced phase of Rayleigh backscattered light waves (RBLs), and suffers from measurement instability. The weak intensities of RBLs and the resulting low signal-to-noise ratios (SNRs) of intensity measurements are the dominating factors that cause the instability of vibration measurements. In this paper, dependence of the measurement stability of heterodyne Φ -OTDR on the SNR of the intensity measurement is investigated analytically and experimentally. An analytical solution of the probability density function of the demodulated phase as a function of SNR is obtained through rigorous derivation, and the dependence of the measurement stability on the SNR is investigated by analyzing the probability density function distribution of the demodulated phase. Both the theoretical predictions and experimental results reveal the impact of SNR on the measurement stability of heterodyne Φ -OTDR. This study fulfills the Φ -OTDR theory and would lead to an effective approach to stabilizing vibration quantization.

Distributed φ-OTDR signal classification based on VMD and SVM

“…Since the proposal of the phase-sensitive optical time domain reflectometer (φ-OTDR) in 1993 [1] , benefiting from its features including resistance to electromagnetic interference, corrosion resistance, high sensitivity, and distributed sensing capabilities [2] , this technology has been widely utilized in various fields such as oil and gas pipelines, construction, railway, highway safety inspection, and underwater detection [3][4][5][6][7] . Due to the coherent detection technique employed by the φ-OTDR, the output signal comprises coherent backscattered light [8] , which can lead to coherent and polarization fading phenomena, resulting in a decrease in the signal-to-noise ratio of the system. Additionally, during the recognition of perturbation signals, external disturbances and environmental factors often interfere, leading to a decline in the recognition performance of the sensing system and causing false alarms.…”

Interference-Fading-Suppressed Pulse-Coding Φ-OTDR Using Spectrum Extraction and Rotated-Vector-Sum Method

“…Utilizing the Rayleigh backscattering signal (RBS), phase sensitive optical time-domain reflectometry (Φ-OTDR) enables an optical fiber to detect the strain changes along the fiber with the advantages of high sensitivity and quantitative disturbance signal recovery [3]. However, the intensity of RBS light is usually weak, resulting in the low signal-to-noise ratio (SNR) of the detected signal, which will affect the reliability of vibration measurement [4]. In general, there are two common methods to improve the amplitude of RBS signal: one is to increase the peak power of the input pulse, which is limited by nonlinear impairments [5]; the other is to increase the pulse width, which will reduce the spatial resolution unfortunately.…”