TY - JOUR A1 - Lu, Xin A1 - Chruscicki, Sebastian A1 - Schukar, Marcus A1 - Münzenberger, Sven A1 - Krebber, Katerina T1 - Application of Intensity-Based Coherent Optical Time Domain Reflectometry to Bridge Monitoring N2 - Although distributed fiber sensing techniques have been widely used in structural health monitoring, the measurement results of bridge monitoring, particularly under destructive testing, have rarely been reported. To the best of our knowledge, this paper is the first report of distributed vibration measurement results, which we obtained during a three-day destructive test on an abolished bridge. A coherent optical time domain reflectometry (COTDR) was used to acquire the vibration information while the bridge was being sawed. The obtained signal was analyzed in time and frequency domain. Some characteristics of the sawing-induced vibration were retrieved by the short-time Fourier transform; the vibration exhibited several high frequency components within the measured range up to 20 kHz and all the components appeared in the same time slot. Some unexpected signals were also detected. Thorough analysis showed that they are quite different from the sawing-induced vibration and are believed to originate from internal damage to the bridge (probably the occurrence of cracks). KW - Destructive testing KW - Structural health monitoring KW - Distributed fiber sensing KW - Distributed acoustic sensing PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-547451 DO - https://doi.org/10.3390/s22093434 VL - 22 IS - 9 SP - 3434 PB - MDPI AN - OPUS4-54745 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krenek, S. A1 - Eisermann, R. A1 - Failleau, G. A1 - Lu, Xin A1 - Thomas, P. A1 - Kjeldsen, H. A1 - Anhalt, K. T1 - Fibre-optic thermometry to support the clean energy transition N2 - The measurement and control of temperature plays a key role in achieving the European Green Deal targets for a low carbon energy system. Fibre-optic thermometry is an emerging technology that can improve temperature measurement in extreme environments for energy providers and industry due to its distributed sensing and immunity to electromagnetic fields. Various applications for optimisation and monitoring in the energy sector are described, covering the whole range from energy generation to transmission and consumption. However, fibre-optic thermometers have cross sensitivities to other quantities (e.g., strain and humidity) and ageing effects that need to be investigated, quantified and minimised to obtain traceable and reliable measurements. This is particularly important so that applications in critical infrastructure can benefit from future measurements that are not possible with conventional sensors. The European INFOTherm project aims to overcome the limitations that currently prevent the widespread use of fibre-optic thermometry by creating a dedicated European metrology infrastructure for research, development and calibration. First results on measurement uncertainty, improvement of measurement techniques and practical field tests are presented. KW - Industrial processes optimisation KW - Fibre-optic thermometry KW - Distributed temperature sensing KW - Traceability KW - Thermal energy storage KW - Electrical grid resilience PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-640075 DO - https://doi.org/10.1515/teme-2025-0044 SN - 2196-7113 VL - 92 IS - 9-10 SP - 392 EP - 405 PB - De Gruyter Brill AN - OPUS4-64007 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Christensen, J. A1 - Thomas, P. A1 - Failleau, G. A1 - Eisermann, R. A1 - Hicke, Konstantin A1 - Krenek, S. T1 - Fiber artefact for performance evaluation of time domain distributed fiber sensor interrogators N2 - Distributed fiber sensing (DFS) is a powerful tool for structural health monitoring (SHM), allowing continuous and seamless measurements of temperature and strain along the fiber. The spatial accuracy of a DFS interrogator, as a key parameter of the system, is vital for precisely locating structural perturbations or defects. Its evaluation and calibration methods however attract little attention. A fiber optic artefact based on a fiber loop is developed to evaluate distance accuracy and signal quality for both self-developed and commercial sensing systems based on Rayleigh, Raman, and Brillouin scattering effects, respectively. The measured distance is corrected to remove the influence of the pulse width. Additionally, the obtained SNRs are compared for different loop trips and pulse widths, assisting to assess signal quality for SHM applications. KW - Structural health monitoring KW - Distributed fiber sensing KW - Distributed temperature sensing KW - Fiber artefact KW - Spatial correction PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-648966 DO - https://doi.org/10.1088/1361-6501/ae214e VL - 36 IS - 11 SP - 1 EP - 10 PB - IOP Publishing Ltd CY - Bristol, UK AN - OPUS4-64896 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wang, Kun A1 - Schukar, Marcus A1 - Hicke, Konstantin A1 - Lu, Xin T1 - Effect of humidity on fiber-optic temperature sensing N2 - This study investigates the influence of ambient humidity on the temperature sensitivity, measurement accuracy, and uncertainty of optical fibers with different coatings, using a Rayleigh-based distributed sensing technique. Polymer-coated fibers (acrylate and polyimide) and metal-coated fibers (copper and gold) were tested under controlled humidity (30%–90% RH) and temperature (20–60 °C) conditions. Rayleigh-based measurements revealed a slight but consistent decrease in temperature sensitivity with increasing humidity for all polymer-coated fibers, attributed to humidity-induced changes in coating stiffness and strain transfer. In contrast, metal-coated fibers exhibited humidity-independent behavior and superior stability. These findings highlight the non-negligible role of ambient humidity in fiber-optic temperature sensing, particularly in Rayleigh-based systems using hygroscopic coatings. The results provide practical guidance for fiber and coating selection in humid environments and offer broader insight into humidity–strain–temperature coupling mechanisms relevant to other fiber-optic sensing mechanisms. KW - Distributed sensing KW - Humidity effect KW - Temperature sensing KW - Optical fiber coatings KW - Temperature uncertainty PY - 2026 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-650040 DO - https://doi.org/10.1016/j.measurement.2025.119905 SN - 0263-2241 VL - 261 SP - 1 EP - 9 PB - Elsevier Ltd. AN - OPUS4-65004 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Hicke, Konstantin T1 - Error suppression in wavelength scanning coherent optical time domain reflectometry by polarization diversity detection N2 - Wavelength scanning coherent optical time domain reflectometry (WS-COTDR) is a popular distributed fiber sensing technique that quantifies environmental changes based on the frequency shift of Rayleigh reflection spectra which are usually obtained by cross correlation. This method can cause large errors due to the spikes in the spectrum caused by the random interference of the Rayleigh backscattered light and the uncorrelated section in the reflection spectrum. Polarization diversity detection is applied to suppress this type of error. Two orthogonally polarized components of the Rayleigh backscattered light are detected in a single sensing system and processed separately by cross correlation. The correlation spectra of the two polarizations are averaged to determine the frequency shift, effectively mitigating the large error. Meanwhile, the polarization dependence helps avoid the large errors caused by Fresnel reflection and restrain null sensitivity positions, where the frequency shift is difficult to be determined due to the similarity of the spectra. The sensing performance improvement is experimentally validated, and the proposed system is tested in the field to monitor traffic along a busy street in Berlin, demonstrating its functionality and feasibility in practice. KW - Traffic monitoring KW - Coherent optical time domain reflectometry KW - Distributed fiber sensing KW - Polarization diversity detection KW - Optical fiber sensing PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-630320 DO - https://doi.org/10.1016/j.measurement.2025.117733 SN - 1873-412X VL - 253 SP - 1 EP - 11 PB - Elsevier Ltd. AN - OPUS4-63032 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Königsbauer, Korbinian A1 - Hicke, Konstantin T1 - Improved phase retrieval method for system simplification or fading suppression in interferometer-based φOTDR systems N2 - Phase sensitive optical time domain reflectometry (φOTDR) systems based on different types of interferometers for phase retrieval typically require two or three photodetectors to record the outputs from the interferometer. A novel signal processing principle is proposed for phase retrieval by taking the difference between two outputs as the quadrature component and reconstructing the in-phase component via Hilbert transformation of the Q component for IQ demodulation. Thus, only one balanced photodetector or two standard photodetectors are need, reducing system complexity and data volume. This principle can also be used to suppress fading effect for the traditional three-detector φOTDR systems by selecting optimal phases across detector pairs. Experiments with a φOTDR systems based on an imbalanced Mach-Zehnder interferometer validate the feasibility of this method and demonstrate a high fading suppression of about 90%. KW - Phase retrieval KW - Distributed fiber sensing KW - Structural health monitoring PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-652630 DO - https://doi.org/10.1364/OE.580984 SN - 1094-4087 VL - 33 IS - 26 SP - 54733 EP - 54746 PB - Optica Publishing Group AN - OPUS4-65263 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -