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Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To improve the signal-to-noise ratio (SNR) of vibration signals in a phase-sensitive optical time-domain reflectometer (Φ-OTDR) system, a principal component analysis variable step-size normalized least mean square (PCA-VSS-NLMS) denoising method was proposed in this study. First, the mathematical principle of the PCA-VSS-NLMS algorithm was constructed. This algorithm can adjust the input signal to achieve the best filter effect. Second, the effectiveness of the algorithm was verified via simulation, and the simulation results show that compared with the wavelet denoising (WD), Wiener filtering, variational mode decomposition (VMD), and variable step-size normalized least mean square (VSS-NLMS) algorithms, the PCA-VSS-NLMS algorithm can improve the SNR to 30.68 dB when the initial SNR is −1.23 dB. Finally, the PCA-VSS-NLMS algorithm was embedded into the built Φ-OTDR system, an 11.22 km fiber was measured, and PZT was added at 10.19–10.24 km to impose multiple sets of fixed-frequency disturbances. The experimental results show that the SNR of the vibration signal is 8.77 dB at 100 Hz and 0.07 s, and the SNR is improved to 26.17 dB after PCA-VSS-NLMS filtering; thus, the SNR is improved by 17.40 dB. This method can improve the SNR of the system's position information without the need to change the existing hardware conditions, and it provides a new scheme for the detection and recognition of long-distance vibration signals. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a theoretical analysis of how the excitation conditions affect the sapphire fiber Fabry-Perot interferometer (SFPI) visibility was performed. The conditions were considered, in which an SFPI was excited by a single-mode fiber (SMF), a multimode fiber (MMF), and a fiber collimator. The finite difference method (FDM) was used to realize the numerical solution of the modal electric fields, and then, the modal excited distributions in the sapphire fiber and the SFPI visibility were calculated. The results showed that different numbers of modes were excited in sapphire fibers under different excitation conditions and finally affected the fringe visibility of the SFPI. The fiber collimator excited the fewest modes and the visibility remained at the highest level. Finally, an experiment was performed, and the experimental results agreed well with the theoretical results.

Distributed optical fiber sensing is an important tool for understanding the dynamic evolution of mining rock movement, and the accuracy of monitoring data mainly depends on the fiber-rock coupling relationship. In this study, the 22207 working face of the Buertai Coal Mine in the Shenmu Mining Area was selected as the research object. The distributed optical fiber sensing technology was applied to similarity model tests, combined with the fiber-rock coupling relationship, to explore the inherent connection between the spatiotemporal evolution characteristics of mining-induced overlying strata vertical zoning and the peak strain data locations along the optical fiber. To address the issue of measurement errors caused by the influence of the fiber-rock coupling relationship on the strain data, a new method was proposed to characterize the fiber-rock coupling relationship using the percentage of fissures in the rock mass. Through the experiments on the fiber-rock coupling relationship, a linear function relationship between the fiber-rock strain transmission coefficient and the percentage of fissures in the rock mass was obtained. The binary method was used to process the model images and obtain the variation of fissures in each region. The strain transmission coefficients of the buried optical fiber in the mining-induced overlying strata were calculated in different zones, providing support for further exploring the relationship between the peak strain data and the vertical zoning characteristics of mining-induced overlying strata. The study showed that the peak strain data locations along the optical fiber can be used to characterize the key stratum position below and the zoning of the overlying strata. A model representing the key stratum position below and the zoning of the overlying strata was constructed. By using the peak detection algorithm, the positions of the key stratum were identified as 44, 68, and 107 cm, and the development heights of the falling zone and the water flowing fractured zone were determined to be 35 cm and 68 cm, respectively. The algorithm's identification results were consistent with the theoretically calculated values, and they were in line with the actual situation of the 22207 working face. The research findings have improved the accuracy of distributed optical fiber sensing technology in the field of monitoring dynamic deformation of mining rock, providing new research ideas for characterizing key stratum positions and rock zoning.

Pile foundations supporting high-rise buildings are generally subject to cyclic loading because of dynamic loading. The corrosion of steel materials in pile foundations is another major concern, especially for piles in a marine environment. In this study, a series of cyclic and static loading tests on model piles made of fiber-reinforced polymer (FRP) and seawater–sea sand concrete (SSC) and ended in a rock socket were reported. Three structural configurations (FRP tube–confined, FRP rebar cage–reinforced, and centered FRP rebar–reinforced) were adopted for the model piles. Strain along the depth of the piles was measured using fiber Bragg grating (FBG) optic sensors and an advanced distributed optical sensing technique known as optical frequency domain reflectometry (OFDR). Strain distribution, axial cyclic stiffness, and shaft friction mobilization of the piles under static and different modes of axial cyclic loading were analyzed and explored in detail. The test results indicated that the FRP tube–confined model pile showed higher confinement and cyclic capacity and lower stiffness degradation, leading to relatively more stable behavior. A high level of cyclic loading can cause microcracks to form and grow within the pile material, thereby decreasing pile stiffness. The strain profile of all the piles along the depth appeared to follow a similar trend, and fluctuations at certain points led to failure. Cyclic stiffness showed gains initially when cyclic load conditions were below a certain threshold level but degraded when loading was increased beyond it. Moreover, shaft resistance gradually increased with cycles, causing higher mobilization in the upper portion of the socket. The experimental results have provided the first systematic study on the performance of the FRP-SSC composite model piles ended in rock sockets under axial cyclic and static loadings. This will contribute to development of a potential predictive method for pile settlement and capacity for the better design of rock-socketed piles. [ABSTRACT FROM AUTHOR]

The sensitivity and noise of an all-fiber optic current transformer (AFOCT) scheme named resonant AFOCT are analyzed, which senses the current information by measuring the frequency difference between clockwise and counterclockwise resonances inside a fiber ring resonator (FRR). Compared with polarization-type and interference-type AFOCT, the sensitivity of the resonant AFOCT can be improved by increasing the finesse of the FRR. The mathematical model of the resonant AFOCT is established, and the sensitivity expression of the resonant AFOCT limited by the sensitivity of the photodetector is derived. For the small current measurement of 1 mA level, the carrier suppression level of phase modulation is required to be better than ${{\rho }_{\text{ccw}}}{{\rho }_{\text{cw}}}{\rm{ = }} - \mathrm{110 \, dB}$, and the intensity of unwanted polarization eigenstate of the FRR should be suppressed to less than −68 dBm. The non-ideal characteristics of fiber quarter-waveplate and the residual linear birefringence of spun fiber mainly affect the scale factor of the resonant AFOCT. The resonant AFOCT will be an important way to achieve high-precision of the current transformer.

In some special working environments, such as high temperatures, strong electromagnetic fields, dark and narrow spaces, existing technologies such as laser doppler velocimetry (LDV) and high-speed photography velocimetry (HSP) cannot effectively measure the velocity of objects. Multi-core fiber (MCF) is a new type of microstructure optical fiber, which combines the characteristics of traditional optical fibers such as high temperature resistance and electromagnetic field resistance. At the same time, its structure is more compact and its volume is smaller, making it very suitable for working in harsh environments. In this article, we will use the special core layout structure of MCF, combined with their compact volume, to measure the velocity of object. The effects of distance between adjacent fiber cores and the number of cores on average coupling efficiency of spatial light are analyzed. Velocity error caused by the uniformity of fiber core layout is analyzed. An experimental comparison between MCF method and HSP method is conducted to verify the feasibility of the method.

The rapid development of information and communication technology has driven the demand for higher data transmission rates. Multi-core optical fiber, with its ability to transmit multiple signals simultaneously, has emerged as a promising solution to meet this demand. Additionally, due to its characteristics such as multi-channel transmission, high integration, spatial flexibility, and versatility, multi-core optical fibers hold vast potential in sensing applications. However, the manufacturing technology of multi-core fiber is still in its early stages, facing challenges such as the design and fabrication of high-quality cores, efficient coupling between cores, and the reduction of crosstalk. In this paper, an overview of the current status and future prospects of multi-core fiber manufacturing technology has been presented, and their limitations will be discussed. Some potential solutions to overcome these challenges will be proposed. Their potential applications in optical fiber sensing will also be summarized. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical analysis of how the excitation conditions affect the sapphire fiber Fabry-Perot interferometer (SFPI) visibility was performed. The conditions were considered, in which an SFPI was excited by a single-mode fiber (SMF), a multimode fiber (MMF), and a fiber collimator. The finite difference method (FDM) was used to realize the numerical solution of the modal electric fields, and then, the modal excited distributions in the sapphire fiber and the SFPI visibility were calculated. The results showed that different numbers of modes were excited in sapphire fibers under different excitation conditions and finally affected the fringe visibility of the SFPI. The fiber collimator excited the fewest modes and the visibility remained at the highest level. Finally, an experiment was performed, and the experimental results agreed well with the theoretical results. [ABSTRACT FROM AUTHOR]

Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aiming at the pattern recognition of disturbance events in distributed optical fiber sensing systems, a multi-dimensional feature extraction method of optical fiber sensing signals is proposed. A total of 65 features on time domain, amplitude domain, frequency domain and time–frequency domain, respectively, are extracted from the denoised signals. In order to solve the problem that there are invalid features, redundant features and too many dimensions of feature sets in the original feature set, the original feature set is screened by Relief F algorithm, correlation coefficient analysis method and principal component analysis method, so as to obtain a feature combination with strong classification ability and small dimensions. For three disturbance events, two SVM (Support Vector Machine) two-classifiers are used to achieve classification. The classifier model was trained and tested based on 563 experimental samples, with pattern recognition accuracy of 100% (408/408) and 99.67% (303/304), respectively. It verifies the effectiveness and feasibility of the multi-dimensional feature extraction method of sensing signals in this paper. [ABSTRACT FROM AUTHOR]

A novel ring-core photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) is designed for ultra-low refractive index detection. A gold nanowire is coated on the outer surface of the PCF as a plasma material, greatly facilitating the manufacturing of the sensor. To achieve real-time detection, the analyte is located on the outside of the sensor. The mode coupling effect and main performance parameters are analyzed through finite element method. In addition, by optimizing several important structural parameters, the overall performance of the sensor has been greatly improved. The optimized sensor shows a maximum wavelength sensitivity of 26,000 nm/RIU in the refractive index range of 1.14–1.26, maximum amplitude sensitivity of 300 RIU − 1 , as well as minimum resolution of 3. 8 5 × 1 0 − 6 RIU. The PCF-SPR sensor with outstanding properties has great potential in applications such as oil logging, biosensing, and chemical monitoring. [ABSTRACT FROM AUTHOR]

With the proposal of a "smart battery," real-time sensing by rechargeable batteries has become progressively more important in both fundamental research and practical applications. However, many traditional sensing technologies suffer from low sensitivity, large size, and electromagnetic interference problems, rendering them unusable in the harsh and complicated electrochemical environments of batteries. The optical sensor is an alternative approach to realize multiple-parameter, multiple-point measurements simultaneously. Thus, it has garnered significant attention. Through analyzing these measured parameters, the state of interest can be decoded to monitor a battery's health. This review summarizes current progress in optical sensing techniques for batteries with respect to various sensing parameters, discussing the current limitations of optical fiber sensors as well as directions for their future development. [ABSTRACT FROM AUTHOR]

To improve the signal-to-noise ratio (SNR) of vibration signals in a phase-sensitive optical time-domain reflectometer (Φ-OTDR) system, a principal component analysis variable step-size normalized least mean square (PCA-VSS-NLMS) denoising method was proposed in this study. First, the mathematical principle of the PCA-VSS-NLMS algorithm was constructed. This algorithm can adjust the input signal to achieve the best filter effect. Second, the effectiveness of the algorithm was verified via simulation, and the simulation results show that compared with the wavelet denoising (WD), Wiener filtering, variational mode decomposition (VMD), and variable step-size normalized least mean square (VSS-NLMS) algorithms, the PCA-VSS-NLMS algorithm can improve the SNR to 30.68 dB when the initial SNR is −1.23 dB. Finally, the PCA-VSS-NLMS algorithm was embedded into the built Φ-OTDR system, an 11.22 km fiber was measured, and PZT was added at 10.19–10.24 km to impose multiple sets of fixed-frequency disturbances. The experimental results show that the SNR of the vibration signal is 8.77 dB at 100 Hz and 0.07 s, and the SNR is improved to 26.17 dB after PCA-VSS-NLMS filtering; thus, the SNR is improved by 17.40 dB. This method can improve the SNR of the system’s position information without the need to change the existing hardware conditions, and it provides a new scheme for the detection and recognition of long-distance vibration signals.

In the context of sustainability, the development of optical fiber sensing technology and 3D printing technology brings new sustainable manufacturing solutions for the furniture industry. Based on the current status and development situation of the application of optical fiber sensing technology and 3D-printed furniture, this paper proposes the concept of applying embedded optical fiber sensing technology to traditional furniture manufacturing as the intersection of traditional furniture design and 3D printing technology. This design method is applied in furniture design cases, the stability of the 3D-printed structure after the optical fiber is embedded in the structure is verified through experiments, and the integration of the embedded optical fiber light-inducing and monitoring technology is used to assess the intelligence of furniture. It is found that by applying optical fiber sensors to furniture intelligence, the real-time monitoring of the environment, temperature, humidity, and other parameters during the use of furniture can be achieved, thus improving the energy efficiency and comfort of furniture. This innovative design idea and method provides a new direction for the sustainable development of furniture products and encourages the furniture industry to move forward in a more environmentally friendly and intelligent direction. [ABSTRACT FROM AUTHOR]

This study discussed the application of optical fibers in addressing the problem of insufficient light harvesting and sensing health monitoring in ancient buildings. Based on three-dimensional (3D) printing technology to fix the light-harvesting lens and conducting optical fiber, develop the replacement parts that can be buried into the optical fiber of ancient buildings. By introducing the experimental application to improve the experimental quality of research and teaching. Firstly, it highlights the advantage that the optical fiber plus lens structure design can make the natural light introduced for a long time; secondly, it points out that the buried optical fiber structure design does not affect the warmth and sound insulation of the building; finally, the health monitoring of the building is realized through the proposed method of buried optical fiber sensing. The design scheme adopts a fiber optic light transmission and sensing system, which can realize the whole system's corrosion resistance, after laying buried and low-cost operation. [ABSTRACT FROM AUTHOR]

The finite element method (FEM) was used to investigate the optical–mechanical behavior of a Fabry–Perot Interferometer (FPI) composed of a capillary segment spliced between two sections of standard optical fiber. The developed FEM model was validated by comparing it with theory and with previously published experimental data. The model was then used to show that the absolute strain on the host substrate is usually smaller than the strain measurement obtained with the sensor. Finally, the FEM model was used to propose a cavity geometry that can be produced with repeatability and that yields the correct absolute strain experienced by the host substrate, without requiring previous strain calibration. [ABSTRACT FROM AUTHOR]

This study introduces an innovative phase-sensitive optical time-domain reflectometer (φ-OTDR) technology based on orthogonal frequency-division multiplexing (OFDM) and nonlinear frequency modulation (NLFM) pulse modulation sequences. The proposed approach addresses the inherent trade-offs among spatial resolution, frequency response range, and sensing distance that conventional φ-OTDR systems encounter. This method optimizes spatial resolution and sensing distance by modulating both the frequency and phase of optical pulses. Moreover, it enhances sidelobe suppression by adjusting the nonlinearity of frequency modulation, reducing interference between adjacent signals, and improving the signal-to-noise ratio (SNR). Additionally, orthogonal frequency-division multiplexing expands the frequency response range. This paper elucidates the fundamental principles and implementation of OFDM-NLFM time-domain pulse modulation techniques and designs, experimentally validates a φ-OTDR system based on this method, and conducts comprehensive testing and analysis of the system's performance. The experimental results demonstrate that the proposed φ-OTDR system achieves an 11 m spatial resolution and a frequency response range of 1–10 kHz over a 16.3 km optical fiber, utilizing a 65 MHz frequency bandwidth with multiplexed signals across four frequencies. This innovative approach reduces hardware resource consumption, opening up promising prospects for various practical engineering applications in optical fiber sensing technology. [ABSTRACT FROM AUTHOR]

Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the rapid development of energy, power electronic equipment plays a crucial role in renewable energy. Modular multilevel converter (MMC) has turned into cutting-edge inverter topology in flexible HVDC and offshore wind power situations. However, under the conditions of high humidity and high voltage, the internal submodules lifetime of MMC might be affected. The system reliability mainly depends on good running of the submodules, so stable performance of the submodules serious threat to the normal operation of the inverter. Therefore, this paper proposes a model based on Peck accelerated life predictable model, and model predictive control (MPC) strategy is improved, at the same time without affecting the external characteristics can better control the submodule voltage fluctuations. What is more, real time monitoring of the working environment of the converter through the optical fiber sensing module. Finally, the experimental and simulative outcomes show that the proposed control strategy can effectively reduce the voltage fluctuations in the small module, and the life parameters of the submodules can be obtained in real time by bringing the results into the proposed life prediction model. By comparing the results, the results can be obtained the proposed control strategy can effectively increase the reliability of the submodule.

In order to accurately measure the Dissolved Oxygen (DO) concentration, and enhance the sensitivity and stability of sensor head, two fluorinated dry gel oxygen sensitive materials 3, 3, 3-Trifluoropropyltrimethoxy/Tetraethyl Orthosilicate (TFP-TriMOS/TEOS) and 3, 3, 3-Trifluoropropyltrimethoxy/1, 2-Bis (triethoxysilyl) Ethane (TFP-TriMOS/BTESE) fluorinated hybrid dry gel dope with Ruthenium (Ru) complex were developed by improved sol-gel technology. Oxygen sensing head was made by dip coating plastic optical fiber into the above prepared sol-gel. Its oxygen sensing performance was studied under different precursor ratios. Experimental results show that all the fabricated DO sensing heads have good oxygen sensing performance, and the detection limits are 0.135 and 0.118 mg/L, respectively. Compared with the fiber optic oxygen sensing head coated with a single precursor (TEOS, BTESE and TFP-TriMOS), the fiber optic oxygen sensing head based on fluorinated dry gel shows higher linearity and lower detection lower limit. The stability of the fluorinated DO sensing head and the influence of pH the intensity of fluorescence signal was studied. The results show that the two kinds of fiber optic dissolved oxygen sensing head have good stability and anti-interference ability.

The foundation of intelligent collaborative control of a shearer, scraper conveyor, and hydraulic support (three-machines) is to achieve the precise perception of the status of the three-machines and the full integration of information between the equipment. In order to solve the problems of information isolation and non-flow, independence between equipment, and weak cooperation of three-machines due to an insufficient fusion of perception data, a fusion method of the equipment's state perception system on the intelligent working surface was proposed. Firstly, an intelligent perception system for the state of the three-machines in the working face was established based on fiber optic sensing technology and inertial navigation technology. Then, the datum coordinate system is created on the working surface to uniformly describe the status of the three-machines and the spatial position relationship between the three-machines is established using a scraper conveyor as a bridge so that the three-machines become a mutually restricted and collaborative equipment system. Finally, an indoor test was carried out to verify the relational model of the spatial position of the three-machines. The results indicate that the intelligent working face three-machines perception system based on fiber optic sensing technology and inertial navigation technology can achieve the fusion of monitoring data and unified expression of equipment status. The research results provide an important reference for building an intelligent perception, intelligent decision-making, and automatic execution system for coal mines. [ABSTRACT FROM AUTHOR]

A porous anodic alumina film is proposed to construct an optical fiber temperature and humidity sensor. In the sensor structure, a fiber Bragg grating is used to detect the environment temperature, and the porous film is used to detect the environment humidity. The proposed porous anodic alumina film was fabricated by anodic oxidation reaction, and it is suitable for the use of humidity detection due to its porous structure. Experimental results show the temperature sensitivity of the proposed sensor was 10.4 pm/°C and the humidity sensitivity of the proposed sensor was 185 pm/%RH. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Engineering Technology is the property of Editorial Department of Electric Power Engineering Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Study on Optical Communications / Guangtongxin Yanjiu is the property of Study on Optical Communications Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to realize the simultaneous measurement of magnetic field and temperature, a Mach-Zehnder interferometer based on sphere-thin core fiber-sphere sensing structure was fabricated. The double parameter sensing was studied by using magnetic fluid as the sensing structure external environment. When the external magnetic field and temperature change, the refractive index of magnetic fluid changes regularly, and the magnetic field and temperature can be measured at the same time. But the extinction ratio of the structure is poor, so a spherical-multi mode fiber-thin core fiber-sphere sensor structure is improved. The results show that the magnetic field and temperature sensitivity of the sphere-thin core fiber-sphere sensing structure obtained by single-peak demodulation are -0.0967 nm/mT and 0.0667 nm/°C, respectively. The improved sphere- multi mode fiber-thin core fiber-sphere structure has a good interference effect, and the magnetic field and temperature sensitivity are 0.1267 nm/mT and -0.1213 nm/°C, respectively. It has the characteristics of low cost, high sensitivity, noise resistance and good application. The research can provide reference for the design of magnetic field and temperature double parameter sensor. [ABSTRACT FROM AUTHOR]

The traditional convergence instrument, 3D laser scanning and other monitoring technologies for the deformation of surrounding rock in the mine roadway can not meet the comprehensive monitoring requirements of complex projects. The technologies have low real-time and automatic monitoring degree, and do not have the capability of long-distance, high-precision and large-area monitoring. The existing optical fiber sensing technology only monitors the single parameter of the surrounding rock in the roadway. It can not comprehensively analyze the stability of the surrounding rock in the roadway. Taking the main adit of a coal mine as the engineering background, the stability of surrounding rock before and after the filling above the adit is studied by numerical simulation. The results show that the filling engineering causes the bearing pressure of surrounding rock on both sides of the adit to rise with asymmetric distribution. The maximum subsidence of the top plate increases from 8.3 mm before filling to 22.1 mm. The maximum floor heave increases from 4.0 mm to 8.5 mm. The maximum increase of the displacement of the two sides is 16.2 mm. The deformation of the surrounding rock corresponds strongly to the bearing pressure, which increases with the thickness of the filling above the adit. The fiber Bragg grating (FBG) sensor is used to construct the adit surrounding rock deformation monitoring system. The FBG sensor is set at the adit section to monitor the opening of the adit arch crown crack, the deformation of the roof, floor and both sides, and the stress and strain of the section. The local deformation of the surrounding rock is analyzed through the real-time spectrum. The results show that the adit roof is obviously under pressure under the influence of the disturbance of the overburden load under the existing condition of stone masonry arch support. The maximum subsidence of the roof is about 30 mm, forming a crack about 2 mm wide. The monitoring results are consistent with the numerical simulation and field observation results. The result verifies the effectiveness of the FBG-based adit surrounding rock stability monitoring method. According to the monitoring results, the reinforcement support scheme of bolt+T-shaped steel plate is proposed for the weak part of the adit support. The support effect is verified by numerical simulation. The results show that after the optimized support scheme, the maximum subsidence of the adit roof under the disturbance of overburden load is 11.3 mm. The maximum displacement of the two sides is 12.04 mm, and the average reduction of the surrounding rock deformation is 48.8%. The scheme improves the stability of the surrounding rock.

In order to further strengthen the operation protection measures of the optical cable and realize real-time monitoring of the hidden danger of external force damage in the optical cable line area, this paper uses the principle of Rayleigh backscattering and coherent detection to design and construct an optical cable external damage event monitoring based on distributed optical fiber vibration sensing early warning system. Using Phase Sensitive Optical Time Domain Reflectometer (Φ-OTDR) technology, the optical fiber vibration signal is collected in real time. The key characteristics of vibration sensing are extracted, and the type of hidden danger is sent to the operation and maintenance staff to locate and warn the hidden danger of external force damage in real time. Field verification results show that the system can simultaneously detect and locate multiple vibration sources along the sensing fiber, and can identify various types of disturbance signals. The monitoring and early warning system has a complete system and a simple structure. The recognition rate of various construction signals is as high as 95%. It realizes double early warning of the type of external breakage and precise location, which can effectively prevent and stop external damage events and improve the work efficiency of anti-external breakage of optical cables.

In order to further strengthen the operation protection measures of the optical cable and realize real-time monitoring of the hidden danger of external force damage in the optical cable line area, this paper uses the principle of Rayleigh backscattering and coherent detection to design and construct an optical cable external damage event monitoring based on distributed optical fiber vibration sensing early warning system. Using Phase Sensitive Optical Time Domain Reflectometer (Φ-OTDR) technology, the optical fiber vibration signal is collected in real time. The key characteristics of vibration sensing are extracted, and the type of hidden danger is sent to the operation and maintenance staff to locate and warn the hidden danger of external force damage in real time. Field verification results show that the system can simultaneously detect and locate multiple vibration sources along the sensing fiber, and can identify various types of disturbance signals. The monitoring and early warning system has a complete system and a simple structure. The recognition rate of various construction signals is as high as 95%. It realizes double early warning of the type of external breakage and precise location, which can effectively prevent and stop external damage events and improve the work efficiency of anti-external breakage of optical cables.

The rapid development of information and communication technology has driven the demand for higher data transmission rates. Multi-core optical fiber, with its ability to transmit multiple signals simultaneously, has emerged as a promising solution to meet this demand. Additionally, due to its characteristics such as multi-channel transmission, high integration, spatial flexibility, and versatility, multi-core optical fibers hold vast potential in sensing applications. However, the manufacturing technology of multi-core fiber is still in its early stages, facing challenges such as the design and fabrication of high-quality cores, efficient coupling between cores, and the reduction of crosstalk. In this paper, an overview of the current status and future prospects of multi-core fiber manufacturing technology has been presented, and their limitations will be discussed. Some potential solutions to overcome these challenges will be proposed. Their potential applications in optical fiber sensing will also be summarized.

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A straight-line-type Sagnac optic fiber acoustic sensing system is proposed in this paper to adopt the application needs of no man's plateau borderline for monitoring mechanical invasion. The Sagnac interference fiber loop is replaced by a straight-line fiber and a 1 × 2 coupler, and the length of the Sagnac interference fiber loop is shortened by close to 50%. The influences of delay fiber and sensing fiber on the sensing system are analyzed by theory calculation and simulation and the optimal lengths of delay fiber and sensing fiber were decided. The experiment system was set, and the sensing fiber was wound into titanium alloy cylinder to compose the sensing element. Experimental results show that the sensing system has a good response to 50−8000 Hz and 70 dB sinusoidal acoustical signals and can well distinguish the signals of different frequencies. Using a small-scale helicopter audio signal as the acoustical signal, the test results show that the response curve is consistent with the simulation results and the sensitivity reaches 30.67 mV/Pa. [ABSTRACT FROM AUTHOR]

For investigation of the temperature variation characteristics of the overhead transmission line under different meteorological conditions and the influence of wind speed on the effectiveness of the overhead transmission line icing monitoring based on the distributed optical fiber sensing technology,a 3D temperature field model for the ice-covered optical phase conductor is established. The variation characteristics of optical fiber temperature under different ambient temperature,wind speed and icing-thickness are analyzed and obtained using the finite element analysis. From this,the results reveal that the temperature difference between the icing part and the non-icing part is independent of the initial value of the ambient temperature,and the critical wind speed expression separately considering the rate of ambient temperature change or icing-thickness is provided. In addition,the critical wind speed value under the ambient temperature change rate and icing-thickness within the common range is presented. Based on the wind speed value and interpolation,a more accurate critical wind speed value can be given under the ambient temperature change rate and icing-thickness within the common range. It provides a reference for researching the temperature variation characteristics of ice-covered overhead transmission lines under different meteorological conditions and the influence of wind speed on the effectiveness of overhead transmission line icing monitoring based on distributed optical fiber sensing technology.

Gravity measurement can realize the detection of matter based on density characteristics, and has been paid attention to in geophysics, physics, engineering and other fields. In this paper, we report the development of a gravity measurement system based on the fiber-optic gyroscope. A two-mass structure to sense the gradient of gravity field is designed and implemented. The structure converts the torque generated by the gradient into rotational motion, which is observed by a fiber-optic gyroscope. In a short-period experiment, the resolution of the gradient corresponds to 0.39 E @ 100 s. In a long-period observation, the noise level of the system can reach 1.92 × 10 − 2 E / Hz. The experimental results show that the fiber-optic gyroscope based gravity measurement system has a good prospect in gravimetry. • The advantages of fiber-optic sensing, including high sensitivity and easy miniaturization, are extended to gravimetry. • The configuration of the gravity gradient instrumentation is simplified since only one sensing element is employed. • The results in non-ideal environments demonstrate its ultra-low noise level and good environmental adaptability. [ABSTRACT FROM AUTHOR]

• A fiber optic respiratory sensor based on optical fibers and silicon tube is proposed. • Static and accurate performance testing of fiber optic respiratory sensors is proposed. • The proposed respiratory sensors show high sensitivity and wide measurement range detection. An optical fiber sensor based on the principle of intensity modulation is proposed, which is composed of plastic optical fibers and silicone tubes. The displacement measurement is achieved by stretching the optical fibers to cause changes in the angle between the end faces, resulting in changes in the coupling efficiency between the end faces. To address the challenges in the performance calibration of fiber optic respiratory sensors, it is proposed to convert the dynamic characteristics measurement of the respiratory sensor into the static performance analysis of the displacement sensor, so as to obtain the characteristics such as sensitivity, linearity, and repeatability, etc. It is further proposed to use a stepper motor to simulate the periodic stretching process of the optical fibers caused by the respiratory process, enabling the analysis of frequency measurement accuracy under different respiratory strengths. Simulation and experimental results demonstrate that the proposed sensor has high linearity, good repeatability, high sensitivity, and a wide measurement range. It can accurately measure respiratory frequency and display amplitude information, providing comprehensive information for respiratory monitoring. [ABSTRACT FROM AUTHOR]

This study discussed the application of optical fibers in addressing the problem of insufficient light harvesting and sensing health monitoring in ancient buildings. Based on three-dimensional (3D) printing technology to fix the light-harvesting lens and conducting optical fiber, develop the replacement parts that can be buried into the optical fiber of ancient buildings. By introducing the experimental application to improve the experimental quality of research and teaching. Firstly, it highlights the advantage that the optical fiber plus lens structure design can make the natural light introduced for a long time; secondly, it points out that the buried optical fiber structure design does not affect the warmth and sound insulation of the building; finally, the health monitoring of the building is realized through the proposed method of buried optical fiber sensing. The design scheme adopts a fiber optic light transmission and sensing system, which can realize the whole system’s corrosion resistance, after laying buried and low-cost operation.

The finite element method (FEM) was used to investigate the optical–mechanical behavior of a Fabry–Perot Interferometer (FPI) composed of a capillary segment spliced between two sections of standard optical fiber. The developed FEM model was validated by comparing it with theory and with previously published experimental data. The model was then used to show that the absolute strain on the host substrate is usually smaller than the strain measurement obtained with the sensor. Finally, the FEM model was used to propose a cavity geometry that can be produced with repeatability and that yields the correct absolute strain experienced by the host substrate, without requiring previous strain calibration.

This study introduces an innovative phase-sensitive optical time-domain reflectometer (φ-OTDR) technology based on orthogonal frequency-division multiplexing (OFDM) and nonlinear frequency modulation (NLFM) pulse modulation sequences. The proposed approach addresses the inherent trade-offs among spatial resolution, frequency response range, and sensing distance that conventional φ-OTDR systems encounter. This method optimizes spatial resolution and sensing distance by modulating both the frequency and phase of optical pulses. Moreover, it enhances sidelobe suppression by adjusting the nonlinearity of frequency modulation, reducing interference between adjacent signals, and improving the signal-to-noise ratio (SNR). Additionally, orthogonal frequency-division multiplexing expands the frequency response range. This paper elucidates the fundamental principles and implementation of OFDM-NLFM time-domain pulse modulation techniques and designs, experimentally validates a φ-OTDR system based on this method, and conducts comprehensive testing and analysis of the system’s performance. The experimental results demonstrate that the proposed φ-OTDR system achieves an 11 m spatial resolution and a frequency response range of 1–10 kHz over a 16.3 km optical fiber, utilizing a 65 MHz frequency bandwidth with multiplexed signals across four frequencies. This innovative approach reduces hardware resource consumption, opening up promising prospects for various practical engineering applications in optical fiber sensing technology.

This study presents the dependence of strain sensitivity on cavity length in conventional Fabry–Perot (F‐P) sensors. A high number of F‐P sensors were required and to ensure their reproducibility, a manufacturing process was developed to obtain similar sensors but with different types of lengths. A hollow‐core silica tube was used to fabricate several F‐P cavities by fusion splicing it between two sections of SMF28 fiber. The fabricated F‐P has a varying length ranging from 15 to 2500 μm. The cavities were measured under a microscope and the reflected spectrum was acquired for each one. Strain measurements were performed for a maximum strain of 1000 με. The strain sensitivity showed a highly linear correlation with ∆λFSR. Small length variations for short cavities heavily affect the FSR value. The smallest and longest cavities present sensitivities of 8.71 and 2.68 pm/με, respectively. Thermal characterization for low‐ and high‐temperature regimes was also performed and is constant for tested sensors. [ABSTRACT FROM AUTHOR]

We review recent advances in distributed fiber optic sensing (DFOS) and their applications. The scattering mechanisms in glass, which are exploited for reflectometry-based DFOS, are Rayleigh, Brillouin, and Raman scatterings. These are sensitive to either strain and/or temperature, allowing optical fiber cables to monitor their ambient environment in addition to their conventional role as a medium for telecommunications. Recently, DFOS leveraged technologies developed for telecommunications, such as coherent detection, digital signal processing, coding, and spatial/frequency diversity, to achieve improved performance in terms of measurand resolution, reach, spatial resolution, and bandwidth. We review the theory and architecture of commonly used DFOS methods. We provide recent experimental and field trial results where DFOS was used in wide-ranging applications, such as geohazard monitoring, seismic monitoring, traffic monitoring, and infrastructure health monitoring. Events of interest often have unique signatures either in the spatial, temporal, frequency, or wavenumber domains. Based on the temperature and strain raw data obtained from DFOS, downstream postprocessing allows the detection, classification, and localization of events. Combining DFOS with machine learning methods, it is possible to realize complete sensor systems that are compact, low cost, and can operate in harsh environments and difficult-to-access locations, facilitating increased public safety and smarter cities. [ABSTRACT FROM AUTHOR]

With the development of information transmission, there is an increasing demand for state monitoring of fiber-optic communication networks to improve the security and self-healing ability of the network. Distributed optical fiber sensing is one of the most attractive methods because it can achieve real-time detection of the whole network without additional sensing heads. However, when the sensing network is introduced into the communication network, the failure probability should be efficiently suppressed with limited sensing resources. In this paper, the fuzzy logic system is used to evaluate the impact of different sensing resource allocation on optical cable network quality. The link failure probability and path failure probability under the condition of uniform and non-uniform sensing resource allocation are simulated and analyzed, respectively. As shown in the analysis results, the failure probability under non-uniform allocation is significantly lower than under uniform allocation. In this paper, we discussed and addressed the allocation of the optical fiber sensing and communication integrated (OFSCI) network with the limited sensing resource for the first time. The results are helpful to develop an allocation strategy for optical fiber sensing and a communication integrated network with a higher robustness. [ABSTRACT FROM AUTHOR]

Optical fiber sensors present several advantages in relation to other types of sensors. These advantages are essentially related to the optical fiber properties, i.e., small, lightweight, resistant to high temperatures and pressure, electromagnetically passive, among others. Sensing is achieved by exploring the properties of light to obtain measurements of parameters, such as temperature, strain, or angular velocity. In addition, optical fiber sensors can be used to form an Optical Fiber Sensing Network (OFSN) allowing manufacturers to create versatile monitoring solutions with several applications, e.g., periodic monitoring along extensive distances (kilometers), in extreme or hazardous environments, inside structures and engines, in clothes, and for health monitoring and assistance. Most of the literature available on this subject focuses on a specific field of optical sensing applications and details their principles of operation. This paper presents a more broad overview, providing the reader with a literature review that describes the main principles of optical sensing and highlights the versatility, advantages, and different real-world applications of optical sensing. Moreover, it includes an overview and discussion of a less common architecture, where optical sensing and Wireless Sensor Networks (WSNs) are integrated to harness the benefits of both worlds. [ABSTRACT FROM AUTHOR]

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The foundation of intelligent collaborative control of a shearer, scraper conveyor, and hydraulic support (three-machines) is to achieve the precise perception of the status of the three-machines and the full integration of information between the equipment. In order to solve the problems of information isolation and non-flow, independence between equipment, and weak cooperation of three-machines due to an insufficient fusion of perception data, a fusion method of the equipment’s state perception system on the intelligent working surface was proposed. Firstly, an intelligent perception system for the state of the three-machines in the working face was established based on fiber optic sensing technology and inertial navigation technology. Then, the datum coordinate system is created on the working surface to uniformly describe the status of the three-machines and the spatial position relationship between the three-machines is established using a scraper conveyor as a bridge so that the three-machines become a mutually restricted and collaborative equipment system. Finally, an indoor test was carried out to verify the relational model of the spatial position of the three-machines. The results indicate that the intelligent working face three-machines perception system based on fiber optic sensing technology and inertial navigation technology can achieve the fusion of monitoring data and unified expression of equipment status. The research results provide an important reference for building an intelligent perception, intelligent decision-making, and automatic execution system for coal mines.