Secondary phase difference measurement method for compensating frequency drift in phase sensitive optical time domain reflectometer

Abstract

The invention discloses a secondary phase difference measurement method for a phase sensitive optical time domain reflectometer (phi-OTDR), which is used for compensating the effects of frequency drift of laser in phi-OTDR. The measuring structure comprises a laser module, a phi-OTDR sensing module, a data acquisition card and a processor. The laser module comprises a laser and a first coupler. The phi-OTDR sensing module comprises an acousto-optic modulator, a pulse signal generator, an optical amplifier, a circulator, a sensing fiber and a photodetector. The measurement method is based on the conventional phi-OTDR, uses a secondary phase difference algorithm to differentiate the phase information in the signal according to a certain interval, and performs phase difference again by selecting two points with certain interval in a non-vibration area in order to eliminate the phase signal drift caused by the frequency drift of the laser, reduce the effect of frequency drift noise on phi-OTDR sensing performance, and improve the accuracy of the system for quantitative measurement of vibration events and the ability to detect low frequency signals.

Description

technical field [0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to a method for compensating frequency drift in a phase sensitive optical time domain reflectometer (Φ-OTDR). Background technique [0002] Φ-OTDR (Phase Sensitive Optical Time Domain Reflectometry, Phase Sensitive Optical Time Domain Reflectometry) has a fast response speed. It is a distributed optical fiber sensing technology that uses Rayleigh scattered light in the optical fiber. It passes Rayleigh scattering in the optical fiber Coherent effect sensing, when the optical fiber is not disturbed by external events, the Rayleigh scattering signal returned in the optical fiber will present a stable coherent waveform, that is, the fluctuations on each optical power curve have the same shape and will not change with time . Conversely, if a certain place on the optical fiber is disturbed by an external event, the coherent waveform of the returned Rayleigh sca...

AI Technical Summary

Problems solved by technology

In addition, due to the hysteresis of the temperature control system in the laser, the internal temperature of the laser will eventually fluctuate within a certain range, which will also cause the frequency drift of the laser

The frequency of the laser does not drift steadily to a single direction. The direction of the drift is random. Its drift trajectory is similar to random walk noise, and it can also produce a large drift in a short time, because the Φ-OTDR curve is for the frequency of the light source. Drift is relatively sensitive, so it will cause distortion of the Φ-OTDR curve, and the acquired information such as the position and frequency of the disturbance event will be inaccurate, thereby reducing the sensing performance of the Φ-OTDR system

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