Quasi-distributed Optical Fiber Research Articles

Quasi-distributed optical fiber hydrogen leakage detecting system based on bus chain topology structure

Micro-mirror optical fiber hydrogen sensors have the advantages of compact structure and fast demodulation speed. All-optical sensor networks consisting of micro-mirror optical fiber hydrogen sensors are essentially necessary across the hydrogen value chain. A bus chain topology structure hydrogen leakage detecting system based on micro-mirror sensors is proposed and experimentally demonstrated. A compensating optical path with constant power supply is introduced, and the power dissipation scheme is theoretically and experimentally proposed by designating the splitting ratios of the splitters array. By constructing such a network with twenty micro-mirror hydrogen sensors, the system has been experimentally verified with good repeatability and stability under different concentrations of hydrogen. By employing this bus chain topology strategy, a quasi-distributed optical fiber hydrogen leakage detection system with micro-mirror hydrogen sensors array is realized. It will provide a promising solution with high feasibility on multi-point leakage detecting in hydrogen infrastructures.

Quasi-distributed optical fiber sensing for the coupled vibration analysis of high-speed train-bridge coupled system under earthquakes

Due to the extensive construction of high-speed rail lines passing through seismically active areas, the possibility of a sudden earthquake occurring during train operation is very high. Additionally, the earthquake will intensify the dynamic response of trains and bridges, causing serious bridge damage. In this work, the dynamic response behavior of the bridge structures in the coupled train-bridge system under the earthquake is investigated based on the 4-table shaking table system. Shaking table experiments are also conducted on a high-speed railroad model of simple-supported girder bridge at a scale of 1/10 with the simulated layers of China Railway Track System type II (CRTS II) ballastless track slabs. The strain responses of various components, including rails, track plates, base plates, and beams, were measured on the bridge using quasi-distributed fiber optic gratings, both with and without seismic actions. Additionally, the seismic isolation characteristics of the fasteners and the CA mortar layer were investigated. The dynamic performance of the coupled train-bridge system under earthquakes was studied in both the time and frequency domains.

Dynamic responses of a train-track-bridge coupled system under earthquakes

The probability of a train running over a bridge when an earthquake occurs is increasing with the total mileage of China’s high-speed railway network expanding. To study this issue, a three-dimensional train-track-bridge dynamic interaction system subjected to seismic excitations is established based on commercial mathematical software. Besides, a set of motion equations of the system are derived according to the multibody dynamics, the finite element method theory and the bridge seismic theory. Moreover, in order to study the dynamic response of high-speed railway bridges under earthquake, a series of experiments are conducted on a scaled high-speed railway simple supported bridge model with a ballastless track slab excited by shaking table tests. Meanwhile, the strain of rails, track slabs, base plates and girder in various working conditions are measured by quasi-distributed optical fiber sensing stuck in bridge members. At last, the dynamic response of each structure member is demonstrated in the time and frequency domains. Furthermore, the seismic isolation performance of bridge members, such as fasteners, cement asphalt (CA) mortar layer and so on, is explained in details.

Investigations on the shearing performance of ballastless CRTS II slab based on quasi-distributed optical fiber sensing

With the continuous development of high-speed railway technology, there are higher expectations for train operation and running safety. Shear failure is the main form of damage to the ballastless CRTS II slab as an essential part of the ballastless track system, and its interlayer shearing performance and damage mechanism play an important role in ensuring railroad safety. This paper employs quasi-distributed optical fiber technology to investigate the force characteristics, ductility performance, and damage mechanism of ballastless CRTS II plate in shear failure. The influences of shear reinforcement on the shear bearing capacity of ballastless track structure are also investigated. It is concluded that shearing force in each layer of the CRTS II ballastless track exhibits obvious nonlinear characteristics, and the introduction of shear reinforcement can improve the seismic performance. The quasi-distributed optical fiber sensing has good performance in the field of ballastless track monitoring, which compensates for the limitation that traditional monitoring methods are difficult to be used in concealed CA mortar layer in long-term service and provides reasonable recommendations for ballastless track design and subsequent maintenance.

Parametric reflection of the quasi-distributed optical fiber sensors with flexible packaging layer for bending strain measurement

The health condition assessment of long-span structures (i.e., pipes) has always been important for tracking the service safety state. Effectively monitoring the large-scale deformation of the pipe structures can be adopted to diagnose the structural performance and identify the possible damage. Considering the local interfacial debonding between the distributed optical fiber and the pipe induced testing failure, improved packaging design is expected to enhance the feasibility and durability of the sensor. Therefore, a flexible silicone elastomer packaged quasi-distributed optical fiber sensor with cross section in semi-circle shape is proposed and tested on the pipe structures. Comparison analysis on the bending strain measurement with bare fiber Bragg grating (FBG) and packaged FBGs in series has been conducted. Parametric reflection method is theoretically proposed for the packaged sensor subjected to bending action. Simulation analysis based on software ANSYS has also been performed to validate the effectiveness of the proposed sensor and the corrected calibration coefficient deduced from the theoretical analysis. Results show that the flexible packaged optical fiber sensor has stable performance for measuring the bending induced compressive or tensile deformation of the pipe. The proposed parametric reflection method can accurately calibrate the quasi-distributed and distributed optical fiber sensors. The study can promote the precise and feasible application of distributed optical fiber sensors in bending strain measurement.

Design of an Er-doped surface plasmon resonance-photonic crystal fiber to improve magnetic field sensitivity.

In order to meet the demand for large-scale magnetic field testing, this paper proposes a D-shaped magneto-refractive photonic crystal fiber (MRPCF) based on surface plasmon resonance (SPR) by using the erbium-doped materials. The four different structures of Models A, B, C, and D are designed by changing the diameter, the position, and the number of layers of the air holes, and the corresponding magnetic field sensing characteristics are analyzed. The results show that in the magnetic field range of 5-405 mT, the magnetic field sensitivities of Models A, B, C, and D are 28 pm/mT, 48 pm/mT, 36 pm/mT, and 21 pm/mT, respectively. Meanwhile, the figure of merit (FOM) of the four MRPCF-SPR sensors is investigated, which have FOMs of 4.8 × 10-4 mT-1, 6.4 × 10-4 mT-1, 1.9 × 10-4 mT-1, 0.9 × 10-4 mT-1. Model B has higher sensitivity and larger FOM. In addition, the effect of the structural parameters of Model B on the sensing performance is also studied. By optimizing each parameter, the magnetic field sensitivity of the optimized Model B is increased to 53 pm/mT, and its magneto-refractive sensitivity and FOM are 2.27 × 10-6 RIU/mT and 6.2 × 10-4 mT-1, respectively. It shows that the magneto-refractive effect of MRPCF can be effectively enhanced by optimizing the structural design of fiber. The proposed MRPCF is an all-solid-state fiber, which solves the instability problem of the magnetic fluid-filled fiber and reduces the complexity of the fabrication process. The all-solid-state MRPCF can be used in the development of quasi-distributed optical fiber magnetic field sensors and has broad applications in the fields of geological exploration, earthquake and tsunami monitoring, and military navigation.

A Quasi-Distributed Optical Fiber Monitoring System for Movement of Roof Strata in Mines

A Quasi-Distributed Optical Fiber Monitoring System for Movement of Roof Strata in Mines

Discrete curvature-based shape configuration of composite pipes for local buckling detection based on fiber Bragg grating sensors

For the high strength, good corrosion resistance and stability, carbon fiber reinforced polymer (CFRP) composites can be made into pipes to transfer gasses and oils in submarine environment. Structural performance and shape of CFRP composite pipes are particularly important to sustain the regular operation of the delivery system. To obtain the in-field shape and identify the local buckling of CFRP composite pipes, quasi-distributed optical fiber sensing techniques have been developed based on the multiplex of fiber Bragg grating (FBG) sensors. Theoretical investigation on shape profile configuration of the pipes based on the measured strains has been performed. Relationship between the accuracy of configuration algorithm and the sensor layout has also been explored. Experiments have been conducted to check the effectiveness and accuracy of the proposed sensing technique and curve configuration algorithm. Results validate good measurement performance of the proposed sensors and high accuracy of the shape-configuration algorithm. Suggestions on the sensor layout of long-distance pipe structures are provided with the comprehensive consideration of overall structural shape control and economical factor. The study can be adopted to instruct the establishment of the structural health monitoring system, identify the buckling and assess the safety operation of pipe structures.

Design of leakage monitoring system based on optical fiber side coupling effect

Aiming at the problems of the existing quasi-distributed optical fiber sensing measurement technology, such as complexity, low accuracy and slow response time, a quasi-distributed optical fiber water leakage monitoring system with high real-time performance and lower cost is designed; the system is mainly composed of sensitive detection. It is composed of needle, low light detection unit, main control unit and data transmission unit. The lateral coupling effect forms a series of sensing probes after the LED light source is scanned. Light enters the polymer fiber through the lateral coupling structure. When the medium between the LED and the coupling structure changes, the coupling light intensity increases, and the output light intensity at both ends of the fiber increases accordingly, so the liquid leakage event can be converted into a coupling medium change To measure and cooperate with several other modules to complete the construction of a water leakage monitoring system; the results show that the designed fiber-optic water leakage monitoring system has the ability to detect and locate water leakage signals, and the positioning accuracy is less than or equal to 10 cm. Basically realize the functions of liquid leakage detection and leakage point positioning, which conforms to the characteristics of quasi-distributed measurement.

Dynamic Performance Detection of CFRP Composite Pipes based on Quasi-Distributed Optical Fiber Sensing Techniques

For the high strength, corrosion resistance, and good stability, carbon fiber–reinforced polymer (CFRP) composites have been made into pipes to transfer gasses and oils in subsea environment. Structural performance of CFRP composite pipes is particularly important to sustain the regular operation of the delivery system. To obtain the in-field behavior of the CFRP composite pipes, quasi-distributed optical fiber sensing techniques are developed based on the multiple configuration of fiber Bragg grating (FBG) sensing elements. Theoretical investigation on the dynamic response of the pipes is performed. Experiments on cantilever CFRP pipes with surface-attached FBGs in series and packaged FBG sensors have been conducted to check the feasibility and effectiveness of the proposed sensing technique. Results validate the good measurement performance of the proposed sensors and the accuracy of the vibration analysis. The study can be adopted to instruct the establishment of the structural health monitoring system of CFRP composite pipes and assess the safety operation state of the pipe systems.

Interrogation technology for quasi-distributed optical fiber sensing systems based on microwave photonics

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Apparatus development for contact mechanics of energy pile-soil interface

An Energy Pile-Soil Interface Characteristic Apparatus (EPSICA) was developed to investigate the contact mechanics of the pile-soil interface. In the center of the apparatus, there is an energy pile model, around which different soil can be filled to simulate pile in different subsoil. The soil can be saturated. By applying loads on the top of the soil, the different depths were simulated. The temperature of energy piles was controlled by the cycling fluid with a water bath. The Pt100 sensors were installed in the pile and soil to measure the temperature changes. The miniature earth pressure cells were installed on the pile surface to measure the normal stress of the pile-soil interface. The FBG quasi-distributed optical fiber technology was used to measure the hoop strain to evaluate the circumferential deformation of the pile model. Taking the sand foundation as an example, the mechanical behavior of pile-soil contact behavior during the heating and cooling cycle was studied based on the temperature of pile and soil, normal stress of pile-soil interface and hoop strain of pile. The developed apparatus provides a new method for the study of thermos-mechanical behavior of energy pile.

Incoherent Optical Frequency-Domain Reflectometry Based on Homodyne Electro-Optic Downconversion for Fiber-Optic Sensor Interrogation.

Fiber-optics sensors using interrogation based on incoherent optical frequency-domain reflectometry (I-OFDR) offer benefits such as the high stability of interference in the radio-frequency (RF) domain and the high SNR due to narrowband RF detection. One of the main impairments of the technique, however, is the necessity of high-frequency detectors and vector network analyzers (VNA) in systems requiring high resolution. In this paper, we report on two C-band implementations of an I-OFDR architecture based on homodyne electro-optic downconversion enabling detection without VNA and using only low-bandwidth, high-sensitivity receivers, therefore alleviating the requirements of conventional I-OFDR approaches. The systems are based on a pair of modulators that are synchronized to perform modulation and homodyne downconversion at a reference frequency of 25.5 kHz. In the first system, we attain centimeter resolution with a sensitivity down to −90 dB using the modulation frequency range comprised between 3.2 and 14.2 GHz. In the second, we measured, for the first time using this approach, Rayleigh backscattering traces in standard single mode fiber with resolution of 6 m and a sensitivity of −83 dB by use of the 10.1–30.1 MHz range. These results show the feasibility of these simple, homodyne downconversion I-OFDR systems as compact interrogators for distributed or quasi-distributed optical fiber sensors.

Signal Analysis, Signal Demodulation and Numerical Simulation of a Quasi-Distributed Optical Fiber Sensor Based on FDM/WDM Techniques and Fabry-Pérot Interferometers.

In civil engineering quasi-distributed optical fiber sensors are used for reinforced concrete monitoring, precast concrete monitoring, temperature monitoring, strain monitoring and temperature/strain monitoring. These quasi-distributed sensors necessarily apply some multiplexing technique. However, on many occasions, two or more multiplexing techniques are combined to increase the number of local sensors and then the cost of each sensing point is reduced. In this work, a signal analysis and a new signal demodulation algorithm are reported for a quasi-distributed optic fiber sensor system based on Frequency Division Multiplexing/Wavelength Division Multiplexing (FDM/WDM) and low-precision Fabry-Pérot interferometers. The mathematical analysis and the new algorithm optimize its design, its implementation, improve its functionality and reduce the cost per sensing point. The analysis was corroborated by simulating a quasi-distributed sensor in operation. Theoretical analysis and numerical simulation are in concordance. The optimization considers multiplexing techniques, signal demodulation, physical parameters, system noise, instrumentation, and detection technique. Based on our analysis and previous results reported, the optical sensing system can have more than 4000 local sensors and it has practical applications in civil engineering.

Investigation on temperature characteristics of weak fiber Bragg gratings in a wide range

A weak fiber Bragg grating (WFBG) is an ideal quasi-distributed optical fiber sensor. Special attention should be paid to the spectrum and sensing performance of the WFBG at extreme temperatures due to its poor reflection intensity. In this Letter, the temperature characteristics of the WFBG from −252.75°C to 200.94°C are experimentally investigated. Five WFBGs with reflectivity from ∼0.25% to ∼10% are used in the experiments. The reflectivity variations and wavelength shifts at different temperatures are studied. Experimental results show that the WFBG can survive and work at extreme temperatures, but the performance is affected significantly. The reflectivity is affected significantly by both cryogenic temperature and high temperature. The temperature responses of Bragg wavelengths in the wide temperature range are also obtained.

Quasi-Distributed Optical Fiber Transducer for Simultaneous Temperature and Vibration Sensing in High-Power Generators

Quasi-Distributed Optical Fiber Transducer for Simultaneous Temperature and Vibration Sensing in High-Power Generators

Quasi-distributed sol-gel coated fiber optic oxygen sensing probe

In the field of aquaculture, optical sensor technology is beginning to provide alternatives to the conventional electrical sensor. Hence, the development and characterization of a multipoint quasi-distributed optical fiber sensor for oxygen measurement is reported. The system is based on 1 mm core diameter plastic optical fiber where sections of cladding have been removed and replaced with three metal complexes sol-gel films to form sensing points. The sensing locations utilize luminophores that have emission peaks at 385 nm, 405 nm and 465 nm which associated with each of the sensing points. Interrogation of the optical sensor system is through a fiber optic spectrometer incorporating narrow bandpass emission optical filter. The sensors showed comparable sensitivity and repeatability, as well as fast response and recovery towards oxygen.

Water Pipe Condition Assessment Using Submersible Quasi-distributed Optical Fibre based Pressure Transducers

Transient based technique is known as one of the most economical ways for pipeline condition assessment. This technique involves monitoring and analysing pressure transient profiles at multiple points in a distributed system. Its application is restricted due to its low spatial resolution (10 m). It is hypothesised that by increasing the number of pressure transducers and reducing the gauge length (distance between the transducers), the spatial resolution of the measurements would highly be improved. However, the deployment of pressure transducers is restricted to the location of the hydrants. In this paper, a submersible quasi-distributed optical fibre based pressure sensors were proposed, constructed and tested in laboratory to verify this concept. For this context, this paper describes the proposed optical device and presents some preliminary analysis and results obtained from a set of experiments. The experimental results show that using the quasi-distributed optical fibre based pressure transducers for pressure transient analysis can potentially detect small anomalies (200 mm) and measure the growth of the anomalies along a water pipe.

Study on the Deformation Measurement of the Cast-In-Place Large-Diameter Pile Using Fiber Bragg Grating Sensors.

Compared with conventional piles such as the circle pile, the cast-in-place large-diameter pile (PCC pile) has many advantages: the lateral area of PCC pile is larger and the bearing capacity of PCC pile is higher. It is more cost-effective than other piles such as square pile under the same condition. The deformation of the PCC pile is very important for its application. In order to obtain the deformation of the PCC pile, a new type of quasi-distributed optical fiber sensing technology named a fiber Bragg grating (FBG) is used to monitor the deformation of the PCC pile. The PCC model pile is made, the packaging process of the PCC model pile and the layout of fiber sensors are designed, and the strains of the PCC model pile based on FBG sensors are monitored. The strain of the PCC pile is analyzed by the static load test. The results show that FBG technology is successfully applied for monitoring the deformation of the PCC pile, the monitoring data is more useful for the PCC pile. It will provide a reference for the engineering applications.

A Surface Strain Monitoring Technique for Slope of Mountainous Area Substation Based on FBG Sensor

Geological structure health in mountainous area substation is complex, and the climate is changeable, it is easy to appear the geological disasters like landslide and subsidence in substation, Aiming at the strong electromagnetic interference in substation and other factors, to monitor of slope surface strain of mountainous area substation with FBG strain sensor, in order to reflect the stability of the slope. Combined with the actual situation of slope of Yunnan 220kV mountainous area substation, the surface type FBG strian sensors are installed on the surface of upstream and downstream slope of mountainous area substation, the lower reaches of the substation, the serial network forms a quasi distributed optical fiber sensing network. they form a quasi-distributed optical fiber sensing network through the serial networking methods.When the slope surface occurs deformation due to the soil sliding, it will drive the FBG strain sensor and transfer the equal strain to the FBG strain sensor. By measuring the center wavelength shift of the FBG strian sensor, the strian value of slope surface at each point can be reflected. The monitoring results show that, the period from May 9th to June 6th, the maximum strain of upstream slope is 171uɛ, it appears at the location of marked as US4 FBG strain sensor, the maximum strain of downstream slope is 112uɛ,it appears at the location of marked as DS1 FBG strain sensor.