KEYWORDS: Fiber Bragg gratings, Denoising, Sensing systems, Signal to noise ratio, Wavelets, Wavelength division multiplexing, Time division multiplexing, Temperature metrology, Random lasers, Light
In this paper, a novel fiber Bragg grating (FBG) sensing system is proposed with large capacity and long transmission
distance to achieve multi-parameter measurements. Record system performances are achieved via the use of high-order
random lasing and remote optical pumping amplifications as well as the combination of time-division multiplexing and
wavelength-division multiplexing technologies. The experimental results show that the sensing distance can reach 150km
with single-end amplification and the optical signal-to-noise ratio (OSNR) is >4dB with good linearity of 0.9992 for 308
FBGs. We also proposed a new denoising method based on deep-learning, and the OSNR is enhanced to 10.2dB from
4.1dB, which is much better than the wavelet and empirical mode decomposition (EMD) methods reported, ensuring the
high accuracy of the center wavelength detection with deep-learning denoising correspondingly.
The paper is about real-time compensating the time-skew and phase-mismatch in one of orthogonal polarizations of the 90° optical hybrid, which is a key module of heterodyne distributed acoustic sensing system.
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.
We report a low threshold, high efficiency random fiber laser with hybrid Erbium-Raman gain. The numerical analysis is made to describe the power performance of the proposed Erbium-Raman random fiber laser and reveal the high efficiency generation in this simple configuration. Thanks to the hybrid gain, the experimentally achieved laser threshold has been reduced to 60 mW. The optical conversion efficiency is of record high in the 1.5 μm regime, reaching 61.5% when pump power is 2 W. This work provides an effective way to generate high efficiency stable 1.5 μm random lasing, which could have important applications in optical fiber sensing and communication.
A repeater-less Brillouin optical time-domain analyzer (BOTDA) with 157.68km sensing range is demonstrated, using
the combination of random fiber laser Raman pumping and low-noise laser-diode-Raman pumping. With optical pulse
coding (OPC) and Non Local Means (NLM) image processing, temperature sensing with ±0.70°C uncertainty and 8m
spatial resolution is experimentally demonstrated. The image processing approach has been proved to be compatible with
OPC, and it further increases the figure-of-merit (FoM) of the system by 57%.
We propose a high-resolution optical time domain reflectometry (OTDR) based on an all-fiber supercontinuum source. The source simply consists of a laser with moderate power and a section of fiber which has a zero dispersion wavelength near the laser’s central wavelength. Spectrum and time domain properties of the source are investigated, showing that the source has great capability in nonlinear optics, such as correlation OTDR. We analyze one of the key factors limiting the operational range of such an OTDR, i.e., sampling time. Finally, we experimentally demonstrate a correlation OTDR with 25km sensing range and 5.3cm spatial resolution, as a verification of theoretical analysis.
A high resolution optical time domain reflectometry (OTDR) based on an all-fiber chaotic source is demonstrated. We analyze the key factors limiting the operational range of such an OTDR, e.g., integral Rayleigh backscattering and the fiber loss, which degrade the optical signal to noise ratio at the receiver side, and then the guideline for counter-act such signal fading is discussed. The experimentally demonstrated correlation OTDR presents ability of 100km sensing range and 8.2cm spatial resolution (1.2 million resolved points), as a verification of the theoretical analysis. To the best of our knowledge, this is the first time that correlation OTDR measurement is performed over such a long distance with such high precision.
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.
Highly stable single-wavelength and broadband random fiber lasers are reported as potential light sources for use in photonic sensing, for the first time, which are based on the hybrid pumping with mixing of Er-doped fiber (EDF) and single-mode fiber (SMF).
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.
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.
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.
The random distributed feedback fiber laser (RDFB-FL), firstly proposed and demonstrated by S. K. Turitsyn et al.,
has been designated as the significant breakthrough in the fields of laser physics and nonlinear optics. In this paper,
the fully distributed Raman amplification approach, based on the novel concept of RDFB-FL, is proposed and
presented for the first time. As a typical proof-of-concept, the high-performance distributed sensing with ±1°C
temperature accuracy and ±2m spatial resolution, over entire 122km long-range Brillouin optical time-domain
analyzer (BOTDA), has been demonstrated using the fully distributed second-order Raman amplification based on
RDFB-FL proposed. The experimental results confirmed its unique ultra-low noise performance for the proposed
distributed amplification. We believe it's the best sensing result for such a length of BOTDA so far. The underlined
physical mechanisms associated with its quasi-lossless transmission and partial coherence characteristics, are also
presented, in order to account for this much attractive feature.
The novel concept of utilizing the second-order random fiber laser (RFL) to realize long-distance fiber-optic pointsensing
systems is proposed. The sensing system consists of a pump laser, a fiber Bragg grating (FBG) at the pump side
and 100km single mode fiber (SMF), and another FBG at the end of the SMF. The first FBG is used to enhance the
lasing efficiency, and the second FBG is use as the remotely-located sensing head. The Bragg wavelengths of the two
FBGs correspond to the first-order and the second-order random lasing spectrum, respectively. Its ability for remote
temperature sensing is experimentally demonstrated.
Long-period fiber gratings (LPFGs) written in nano-engineered bend insensitive single-mode fiber (NEBI-SMF) were
reported. It is found that, only when the pitches of the gratings are in two wavelength ranges (270-305 μm and 420-480
μm), obvious resonance peaks can be obtained within the band of 1200-1650 nm, due to the cladding mode separation
caused by the nano-engineered ring in the fiber cladding. The strain sensitivity of the LPFG with a pitch of 295 μm in the
range of 270-305 μm is 2.8 pm/με, while the LPFG with a pitch of 470 μm in the range of 420-480 μm is insensitive to
strain. The temperature sensitivities of the two LPFGs are 0.145 nm/oC and 0.098 nm/oC, respectively. Due to the special
structure of the NEBI-SMF, more interesting phenomenon could be explored by carrying out further theoretical and
experimental study of these novel LPFGs, such as the bending and twisting characteristics, etc.
The novel concept of utilizing a random fiber laser (RFL) to extend the sensing distance of fiber-optic sensing systems is
proposed for the first time to our knowledge. In this paper, two schemes based on the RFL with a fiber Bragg grating
(FBG) are experimentally demonstrated to verify the concept. The first one is a 100km FBG temperature sensing system,
in which a 100km RFL provides an effective way to enhance the sensing signal of the FBG sensor due to its strong lasing
radiation across the 100km fiber span. It is the first time to find that the RFL without the FBG is a temperatureinsensitive
distributed lasing cavity, which offers stable long-distance transmission for the sensing signal. The second
one is a 100km Brilloiun optical time domain analyzer (BOTDA), in which the generated random lasing is used as a
fully distributed Raman pump and hence stable Raman amplification can be obtained to enhance the Brilloiun sensing
signal. In principle, such a novel concept can be adopted for any type of distributed fiber-optic sensors as the RFL can be
used as a stable distributed Raman pump for sensing signal amplification along the whole length of the fiber.
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