Distributed and dynamic strain sensing with high spatial resolution and large measurable strain range

Abstract

A distributed and dynamic strain sensing system based on frequency-scanning phase-sensitive optical time domain reflectometry is proposed and demonstrated. By utilizing an RF pulse scheme with a fast arbitrary waveform generator, a train of optical pulses covering a large range of different optical frequencies, short pulse width, and high extinction ratio is generated. Also, a Rayleigh-enhanced fiber is used to eliminate the need for averaging, allowing single-shot operation. Using direct detection and harnessing a dedicated least mean square algorithm, the method exhibits a record high spatial resolution of 20 cm, concurrently with a large measurable strain range (80 µε, 60 demonstrated), a fast sampling rate of 27.8 kHz (almost the maximum possible for a 55 m long fiber and 60 frequency steps), and low strain noise floor (<1.8 nε/ √ Hz for vibrations below 700 Hz and <0.7 nε/ √ Hz for higher frequencies).

Phase Noise Effects on Phase-Sensitive OTDR Sensors Using Optical Pulse Compression

“…Finally, there is yet another kind of methods that are based on using the dependence on wavelength of the interference from the signals coming from a particular location in the fiber. These can work by directly changing the wavelength of the interrogating pulses launched into the fiber [2] [3] or by using chirped pulses in which the wavelength dependence of the interference is translated to a time dependence [4]. In either case, the excitation affecting the fiber can be quantified by the shift that it induces in the interference pattern.…”

10-cm spatial resolution distributed acoustic sensor based on an ultra low-loss enhanced backscattering fiber

“…The enhancement in the intensity of the backscattered signal has been achieved by either forming a continuous grating along the fibre 32 or inscribing individual reflectors at fixed intervals in the core of the fibre 33 . In 2020, Zhang et al 34 have shown that the spatial resolution of a conventional DAS system that operates based on φ -OTDR interrogation technique can be reduced to as low as 20 cm if a continuous grating enhanced backscattering (CGEB) fibre is used as a sensing medium. In the following year, Xiong et al 35 have used CGEB fibre to demonstrate a DAS system with 28 cm resolution, but over a much longer sensing range of up to 920 m. Despite these successful demonstrations, since the intensity of the backscattered light in a CGEB fibre is proportional to the duration of the probe pulse, DAS systems based on this fibre still encounter the same trade-off between the spatial resolution and SNR.…”

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

“…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]. Although, a number of φ-DAS systems capable of measuring relatively large strain levels have recently been demonstrated, the sensing range in none of those studies were exceeding [18][19][20][21].…”