Distributed fiber-optic sensing (DFOS) has drawn great attention in both academic research and industrial applications due to its unique advantages. Recent progress at University of Electronic Science and Technology of China (UESTC) in DFOS, mainly on ultra-long-distance Brillouin optical time-domain analysis (BOTDA) and phase-sensitive optical timedomain reflectometry (Φ-OTDR), is discussed in this paper, including research progress and real-life applications.
KEYWORDS: Signal to noise ratio, Edge detection, Safety, Wavelets, Denoising, Remote sensing, Reflectometry, Signal processing, Signal generators, Signal detection
It is essential to carry out real-time position and speed of trains to ensure the safety of railway operation. In this paper,
the phase-sensitive optical-time-domain reflectometry (Φ-OTDR) is proposed and demonstrated to overcome the
disadvantage of the track circuit that is currently used and has the risk to be damaged by lightening, for the first time, to
the best of our knowledge. A long sensing cable, buried nearby two parallel railways, is used to detect the vibration
signals generated by trains with Φ-OTDR and the real vibration signals of the trains are extracted/quantified utilizing
wavelet denoising. With the wavelet edge detection, the operation status of two nearby trains, including their relative
position and speed, are obtained over a 10.2 km measurement length in real-time. This work offers a new passive way for
safety monitoring of railway operation.
A long-range (124km) fully distributed fiber-optic vibration sensing system is demonstrated, based on phase-sensitive
optical time-domain reflectometry (Φ-OTDR) with counter-pumping distributed fiber Brillouin amplification (FBA).
FBA significantly enhances the probe pulse signal at the second half of the sensing fiber with less than 10dBm pump
power, and its amplification efficiency is demonstrated to be much higher than 26.9dBm counter-pumping Raman
amplification. As a result, demodulated intrusion signals along the whole sensing range can keep high signal to noise
ratio. The FBA scheme demonstrated in this work can also be incorporated in many other distributed fiber-optic sensing
systems for extension of sensing distance.
A phase-sensitive optical time-domain reflectometry with 175km sensing range is demonstrated using the combination of
co-pumping 2nd-order Raman amplification based on random fiber lasing, counter-pumping 1st-order Raman
amplification, and counter-pumping Brillouin amplification. With elaborate arrangements, each pumping scheme is
responsible for the signal amplification in one particular segment of the all three. To the best of our knowledge, this is
the first time that distributed vibration sensing is performed over such a long distance without inserting repeaters. The
novel hybrid amplification scheme demonstrated in this work can also be incorporated in other fiber-optic sensing
systems for extension of sensing distance.
Ultra-long-distance distributed fiber-optic sensing based on Brillouin optical time-domain analysis (BOTDA) is achieved by using a proposed configuration of hybrid distributed Raman amplification (H-DRA), that is realized by incorporating random fiber laser (RFL) based 2nd-order pump and low-noise laser-diode (LD) based 1st-order pump. A repeater-less sensing distance of up to 154.4km with 5m spatial resolution and ~±1.4°C temperature uncertainty is successfully demonstrated, which is the longest repeater-less BOTDA reported to date.
In this paper, we presented a successful field test of a fully distributed fiber-optical intrusion detection system for security monitoring of 220km long national borderline in China. Such a fiber fence shows its outstanding ability to operate at extreme weather conditions, like strong wind, heavy snow and storm, wide temperature range from -55℃ to +50℃, et al, which may be the most difficult and complicated environment for practical applications of fiber fences.
A novel distributed Raman amplification (DRA) scheme based on ultra-long fiber laser (UL-FL) pumping with a ring cavity rather than a linear cavity is proposed and demonstrated, for the first time. As a typical application of the proposed configuration, ultra-long-distance distributed sensing with Brillouin optical time-domain analysis (BOTDA) over 142.2km fiber with 5m spatial resolution and ± 1.5℃ temperature uncertainty is achieved, without any repeater, for the first time. The key point for the significant performance improvement is the system could offer both of uniform gain distribution and considerably suppressed pump-probe relative intensity noise (RIN) transfer, by optimized design of system structure and parameters.
A hybrid Raman distributed temperature sensor (RDTS) and low-reflective fiber Bragg grating (LR-FBG) sensing
system is proposed to achieve simultaneous measurement of distributed temperature and quasi-distributed strain. In this
system, a method based on wavelength-swept optical time domain reflectometry (OTDR) is applied to interrogate the
wavelength of reflective signal from the LR-FBGs with similar resonate wavelengths arranged in serial, while RDTS is
realized by using the same light source. It is proved that such a Raman sensor and the LR-FBG sensor can be integrated
into one system without interference by experiment.
A novel fiber-optic tip accelerometer based on Fabry-Perot (F-P) interferometer is proposed and
demonstrated, with potential to operate under high temperature, in this paper. Such a tip accelerometer is directed
fabricated on a large cladding fiber end by using the 157nm laser-micromachining technology. With the
calibration of a micro electro mechanical systems (MEMS) accelerometer, the sensitivity of such a fiber-optic F-P
accelerometer is 1.764 rad/g. The minimum detective acceleration is estimated to be 20μg.
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