Recent Advances in Phase-Sensitive Optical Time Domain Reflectometry (Ф-OTDR)

Abstract

Phase-sensitive optical time domain reflectometry (Ф-OTDR) is an effective way to detect vibrations and acoustic waves with high sensitivity, by interrogating coherent Rayleigh backscattering light in sensing fiber. In particular, fiber-optic distributed acoustic sensing (DAS) based on the Ф-OTDR with phase demodulation has been extensively studied and widely used in intrusion detection, borehole seismic acquisition, structure health monitoring, etc., in recent years, with superior advantages such as long sensing range, fast response speed, wide sensing bandwidth, low operation cost and long service lifetime. Significant advances in research and development (R&D) of Ф-OTDR have been made since 2014. In this review, we present a historical review of Ф-OTDR and then summarize the recent progress of Ф-OTDR in the Fiber Optics Research Center (FORC) at University of Electronic Science and Technology of China (UESTC), which is the first group to carry out R&D of Ф-OTDR and invent ultra-sensitive DAS (uDAS) seismometer in China which is elected as one of the ten most significant technology advances of PetroChina in 2019. It can be seen that the Ф-OTDR/DAS technology is currently under its rapid development stage and would reach its climax in the next 5 years.

Polarization fading mitigation in distributed acoustic sensors based on a high-speed polarization rotator

“…Techniques adopted for eliminating phase fading are tailored to the DAS sensing approach [2,13]. Interferometric DAS systems, for instance, use two approaches: 1) a 3×3 coupler to create three signals 2π/3 out of phase [14][15][16] and 2) phase generated carrier which relies on the modulation of the phase of light in one arm of the interferometer and its mixture with the light from the other arm to generate a beat signal [17,18].…”

Realization of a polarization-insensitive optical frequency-domain reflectometer using an I/Q homodyne detection

“…Note that although there exist advanced methods for enhancing the performance of phase-sensitive optical time-domain reflectometry (Ф-OTDR) systems [14][15][16], they mostly focus on extending the sensing distance or measurand resolution of the sensor. On the contrary, the best approach to improve the spatial resolution down to the centimetric level is to use an OFDR configuration.…”

“…On the contrary, the best approach to improve the spatial resolution down to the centimetric level is to use an OFDR configuration. For this reason, the OFDR system here implemented and described above in this section allows for a spatial resolution of a few cm, representing an improvement of about 2 orders of magnitude in the spatial resolution of Ф-OTDR sensors [14][15][16].…”

Long Range Raman-Amplified Distributed Acoustic Sensor Based on Spontaneous Brillouin Scattering for Large Strain Sensing

“…The sensitivity of DAS systems based on Phase-sensitive Optical Time-domain Reflectometry (φ-OTDR) has seen a continuous improvement over the past decade, reaching levels as low as several tens of pε/ √ Hz [7][8][9][10][11][12][13][14]. Although the lower strain limit of φ-OTDR based DAS (φ-DAS) systems are extended to sub nε levels, the ceiling of the strain range of these systems is limited to several tens of µε due to the trade-off between the maximum sampling rate and the length of the sensing fiber [15,16] (detailed explanation of this trade-off is provided in Section 2). This limitation restricts the use of φ-DAS in applications that require measurement of high strain-rates over long distances such as analysis of large-magnitude earthquakes or evaluation of railway track behavior [3,17].…”