TY - JOUR A1 - Lu, Xin A1 - Krebber, Katerina T1 - Direct detection based φOTDR using the Kramers-Kronig receiver N2 - A Kramers-Kronig (KK) receiver is applied to a phase-sensitive optical time domain reflectometry based on direct detection. An imbalanced Mach-Zehnder interferometer with a 2× 2 coupler is used in sensing system to encode the phase information into optical intensity. The directly obtained signal is treated as the in-phase component, and the KK receiver provides the quadrature component by Hilbert transform of the obtained signal, so that the optical phase can be retrieved by IQ demodulation. The working principle is well explained, and the obtained phase variance is theoretically analyzed. The experiment demonstrates the functionality of the sensor and validates the theoretical analysis. KW - Kramers-Kronig detector KW - Distributed fiber sensing KW - Acoustic sensing PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-516803 UR - https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-24-37058&id=442839 DO - https://doi.org/10.1364/OE.405723 VL - 28 IS - 24 SP - 37058 EP - 37068 PB - Optical Society of America AN - OPUS4-51680 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Krebber, Katerina T1 - Characterizing detection noise in phase-sensitive optical time domain reflectometry N2 - Phase-sensitive optical time domain reflectometry (φOTDR) is an excellent distributed fiber sensing technique and has been applied in various areas. Its noise is however never been comprehensively studied to the best of our knowledge. The different detection noise sources in such a sensing system are thoroughly investigated. The impacts of thermal noise, shot noise and the beat between signal and the amplified spontaneous emission from a pre-amplifier have been theoretically and experimentally demonstrated. Due to the random nature of the φOTDR signal, the detection noise demonstrates distinct features at different fiber positions in a single measurement. The theoretical analysis and the experimental result explicitly affirm most of the fiber sections, and the difference at some positions may be explained by ambient noise. KW - Noise analysis KW - Acoustic sensing KW - Distributed fiber sensing PY - 2021 DO - https://doi.org/https://doi.org/10.1364/OE.424410 SN - 1094-4087 VL - 29 IS - 12 SP - 18791 EP - 18806 PB - Optical Society of America CY - Washington, DC AN - OPUS4-52757 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Krebber, Katerina T1 - Phase error analysis and unwrapping error suppression in phase-sensitive optical time domain reflectometry N2 - Phase-sensitive optical time domain reflectometry becomes an effective tool to realize distributed sensing, and the optical phase of the received light is usually used to quantify the strain for both dynamic and static measurement. The analysis on the overall phase error has been improved by considering the proportionality of the detection noise to the local optical power. The estimation accuracy is greatly improved by using the proposed theory, the probability density of the estimation accuracy over 99% is > 0.6, ∼39 times larger than the previously reported method. The phase unwrapping may malfunction due to the noisy signal, causing large phase errors. Point break detection algorithms are used to locate the incorrect phase unwrapping points, so the temporal evolution of the phase retrieved at each position can be divided into several sections with different offset. The phase unwrapping error is then suppressed by removing the offset. KW - Phase unwrapping KW - Distributed fiber sensing KW - Acoustic sensing PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-543919 DO - https://doi.org/10.1364/OE.446517 VL - 30 IS - 5 SP - 6934 EP - 6948 PB - Optica Publishing Group AN - OPUS4-54391 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Hicke, Konstantin A1 - Krebber, Katerina T1 - Dual functionality of wavelength scanning coherent optical time domain reflectometer N2 - Wavelength scanning coherent optical time domain reflectometer (WS-COTDR) is a good candidate to spatially resolve the environmental information at comparatively low frequency. This paper reveals it can also work as a traditional optical time domain reflectometer (OTDR) to identify Fresnel reflection by averaging the obtained signal over the wavelength scanning range. Simultaneous distributed vibration sensing and a traditional OTDR measurement are experimentally demonstrated using the WS-COTDR system. T2 - European Workshop on Optical Fibre Sensors (EWOFS 2023) CY - Mons, Belgium DA - 23.05.2023 KW - Structural health monitoring KW - Distributed fiber sensing KW - Acoustic sensing PY - 2023 DO - https://doi.org/10.1117/12.2678098 VL - 12643 SP - 1 EP - 4 PB - SPEI AN - OPUS4-57590 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Hicke, Konstantin A1 - Krebber, Katerina T1 - Dual-functionality of WS-COTDR for ground movement monitoring N2 - Wavelength scanning coherent optical time domain reflectometer (WS-COTDR) is a good candidate to spatially resolve the environmental information at comparatively low frequency. This paper reveals it can also work as a traditional optical time domain reflectometer (OTDR) to identify Fresnel reflection by averaging the obtained signal over the wavelength scanning range. Simultaneous distributed vibration sensing and a traditional OTDR measurement are experimentally demonstrated using the WS-COTDR system. T2 - European Workshop on Optical Fibre Sensors (EWOFS 2023) CY - Mons, Belgium DA - 23.05.2023 KW - Distributed fiber sensing KW - Acoustic sensing KW - Structural health monitoring PY - 2023 AN - OPUS4-57591 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Krebber, Katerina T1 - Novel fading suppression method for distributed optical fiber acoustic sensing N2 - A universal method based on alternating pulse widths is proposed to suppress the signal fading for all distributed acoustic sensors (DASs) and experimentally demonstrated by one DAS system based on a Mach-Zehnder interferometer. T2 - Optica Sensing Congress CY - Munich, Germany DA - 30.07.2023 KW - Distributed fiber sensing KW - Acoustic sensing KW - Fading suppression KW - Structural health monitoring PY - 2023 SP - 1 EP - 2 AN - OPUS4-58048 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Krebber, Katerina T1 - Novel fading suppression method for distributed optical fiber acoustic sensing N2 - A universal method based on alternating pulse widths is proposed to suppress the signal fading for all distributed acoustic sensors (DASs) and experimentally demonstrated by one DAS system based on a Mach-Zehnder interferometer. T2 - Optica Sensing Congress CY - Munich, Germany DA - 30.07.2023 KW - Distributed fiber sensing KW - Acoustic sensing KW - Structural health monitoring KW - Fading suppression PY - 2023 AN - OPUS4-58049 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Thomas, P. T1 - Phase Error Evaluation via Differentiation and Cross-Multiplication Demodulation in Phase-Sensitive Optical Time-Domain Reflectometry N2 - Phase-sensitive optical time-domain reflectometry (jOTDR) is a technology for distributed vibration sensing, where vibration amplitudes are determined by recovering the phase of the backscattered light. Measurement noise induces phase errors, which degrades sensing performance. The phase errors, using a differentiation and cross-multiplication (DCM) algorithm, are investigated theoretically and experimentally in a jOTDR system based on a phase retrieval configuration consisting of an imbalanced Mach–Zehnder interferometer (IMZI) and a 3 x 3 coupler. Analysis shows that phase error is highly dependent on the AC component of the obtained signal, essentially being inversely proportional to the product of the power of the light backscattered from two locations. An analytical expression was derived to estimate the phase error and was confirmed by experiment. When applied to the same measurement data, the error is found to be slightly smaller than that obtained using in-phase/quadrature (I/Q) demodulation. The error, however, increases for longer measurement times. KW - Distributed fiber sensing KW - Phase-sensitive optical time-domain reflectometry KW - Phase error PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-580501 UR - https://www.mdpi.com/2304-6732/10/5/514 DO - https://doi.org/10.3390/photonics10050514 SN - 2304-6732 VL - 10 IS - 5 SP - 1 EP - 14 PB - MDPI CY - Basel AN - OPUS4-58050 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Hicke, Konstantin A1 - Krebber, Katerina T1 - Distributed acoustic sensing to monitor ground motion/movement at multi-frequency bands N2 - A novel distributed acoustic sensing technique is proposed that exploits both phase and amplitude of the Rayleigh backscattered light to quantify the environmental variation. The system employs a wavelength-scanning laser and an imbalanced Mach-Zehnder interferometer to acquire the reflection spectra and the phase of the detected light, respectively. Fading-free and low-frequency measurements are realized via the crosscorrelation of the reflection spectra. The discrete crosscorrelation is used to circumvent the nonlinear frequency sweeping of the laser. Based on the phase of the backscattered light, it is possible to quantify fast environmental variations. The whole system requires no hardware modification of the existing system and its functionality is experimentally validated. The proposed system has the potential to monitor ground motion/movement at very low frequency band like subsidence around mining areas and at high frequency band like earthquakes and vibrations induced by avalanches. KW - Distributed acoustic sensing KW - DAS KW - Distributed fiber optic sensing KW - Ground motion detection KW - Subsidence monitoring PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-596129 DO - https://doi.org/10.1109/JLT.2024.3358495 VL - 42 IS - 18 SP - 1 EP - 8 PB - Optical Society und IEEE Photonics Society AN - OPUS4-59612 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Hicke, Konstantin A1 - Krebber, Katerina T1 - Approaching distributed ground motion sensing at high and low frequency ranges N2 - The phase and reflection spectrum of a standard distributed acoustic sensor based on an interferometer are used for fast and slow dynamic measurements, respectively, enabling the system to simultaneously measure various types of ground movement. T2 - 28th International Conference on Optical Fiber Sensors (OFS-28) CY - Hamamatsu, Japan DA - 20.11.2023 KW - Distributed acoustic sensing KW - Ground movement monitoring KW - Geomonitoring KW - Interferometer-based KW - DAS PY - 2023 SP - 1 EP - 4 PB - Optica CY - Washington D.C., USA AN - OPUS4-59098 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin T1 - Introduction to group 8.6 N2 - A brief introduction of group 8.6 and the research work on the application of fiber sensing. T2 - DIU Besuch CY - Berlin, Germany DA - 05.05.2023 KW - Structural health monitoring KW - Distributed fiber sensing KW - Distributed acoustic sensing KW - Practical application PY - 2023 AN - OPUS4-57430 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Krebber, Katerina T1 - Configuration simplification and data reduction in a DAS system for monitoring large infrastructures N2 - The distributed acoustic sensor based on an imbalanced Mach-Zehnder interferometer with a 3×3 coupler is simplified by using a balanced detector instead of three identical photodetectors. The obtained data is reduced by two third accordingly. T2 - Optica Sensing Congress 2024 CY - Toulouse, France DA - 15.07.2024 KW - Data reduction KW - Distributed fiber optic sensing KW - System simplification PY - 2024 SP - 1 EP - 2 PB - Optica CY - Washington D.C., USA AN - OPUS4-60840 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin T1 - Configuration simplification and data reduction in a DAS system for monitoring large infrastructures N2 - The distributed acoustic sensor based on an imbalanced Mach-Zehnder interferometer with a 3×3 coupler is simplified by using a balanced detector instead of three identical photodetectors. The obtained data is reduced by two third accordingly. T2 - Optica Sensing Congress 2024 CY - Toulouse, France DA - 15.07.2024 KW - Distributed fiber sensing KW - System simplification KW - Data reduction PY - 2024 AN - OPUS4-60841 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Hicke, Konstantin A1 - Lu, Xin A1 - Chruscicki, Sebastian A1 - Krebber, Katerina T1 - Measurement of Slowly Changing and Quasi-Static Strain Signals for Ground Motion Monitoring Applications using Distributed Acoustic Sensing N2 - The suitability of wavelength-scanning COTDR for distributed dynamic strain sensing (DAS) along buried fiber cables for long-term geotechnical monitoring applications is demonstrated by experiments showing the method’s capability to demodulate slowly varying and quasi-static signals. T2 - Optica Sensing Congress 2024 CY - Toulouse, France DA - 15.07.2024 KW - Ground motion KW - Ground movement monitoring KW - Distributed fiber optic sensing KW - Quasi-static signals KW - Geomonitoring PY - 2024 SP - 1 EP - 2 PB - Optica CY - Washington D.C., USA AN - OPUS4-60816 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Krebber, Katerina T1 - Suppression of Rayleigh fading induced errors in φOTDR by different pulse widths for improving the reliability of civil infrastructure monitoring N2 - Rayleigh fading is a widely observed phenomenon in the many fields, such as wireless communication and optical imaging. It is also the main factor limiting the performance of the phase-sensitive optical time domain reflectometry (φOTDR). The low SNR at the fading points results in a large measurement error, severely affecting the reliability of civil infrastructure monitoring. The proposed method involves changing the pulse width during measurements to suppress the impact of fading. Experimental result shows that the number of fading points is greatly reduced by ∼ 96 % and the measurement error is reduced by more than 5 times. Unlike existing methods, this approach requires no hardware modifications, making it applicable to almost all current phase-based φOTDR systems. The versatility and effectiveness of this method make it an excellent candidate for infrastructure monitoring and related fields. KW - Distributed fiber sensing KW - Optical fiber sensing KW - Phase-sensitive optical time domain reflectometry KW - Infrastructure monitoring KW - Rayleigh fading PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-614208 DO - https://doi.org/10.1016/j.optlastec.2024.111927 SN - 1879-2545 VL - 181 SP - 1 EP - 9 PB - Elsevier Ltd. AN - OPUS4-61420 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Hicke, Konstantin A1 - Krebber, Katerina T1 - Distributed fiber optic sensing for monitoring of underground facilities N2 - Distributed fiber optic sensing (DFOS) technique is a promising and robust non-destructive testing tool that can seamlessly acquire environmental conditions over large scales. Therefore, it has found extensive applications in structural health monitoring. Its appeal for monitoring underground facilities lies in the intrinsic properties of the optical fiber, such as immunity to magnetic interference, small size, chemical inertia, etc. This paper provides a concise overview of DFOS applications in underground facility monitoring. Following a brief introduction to the working principle of the DFOS technique, various examples are provided to demonstrate how distributed fiber sensors contribute to monitoring underground facilities. The paper presents unpublished field test results with an emphasis in the energy sector, including monitoring gas storage facilities, geothermal reservoir exploration, and ground movement detection. Furthermore, the paper identifies several directions for enhancing the DFOS system. T2 - SPIE Photonics Europe CY - Strasbourg, France DA - 07.04.2024 KW - Underground gas storage KW - Distributed fiber sensing KW - Geothermal borehole KW - Ground movement KW - Leakage detection KW - Structure health monitoring PY - 2024 AN - OPUS4-60146 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Hicke, Konstantin A1 - Krebber, Katerina T1 - Distributed fiber optic sensing for monitoring of underground facilities N2 - Distributed fiber optic sensing (DFOS) technique is a promising and robust non-destructive testing tool that can seamlessly acquire environmental conditions over large scales. Therefore, it has found extensive applications in structural health monitoring. Its appeal for monitoring underground facilities lies in the intrinsic properties of the optical fiber, such as immunity to magnetic interference, small size, chemical inertia, etc. This paper provides a concise overview of DFOS applications in underground facility monitoring. Following a brief introduction to the workingbnprinciple of the DFOS technique, various examples are provided to demonstrate how distributed fiber sensors contribute to monitoring underground facilities. The paper presents unpublished field test results with an emphasis in the energy sector, including monitoring gas storage facilities, geothermal reservoir exploration, and ground movement detection. Furthermore, the paper identifies several directions for enhancing the DFOS system. T2 - SPIE Photonics Europe CY - Strasbourg, France DA - 07.04.2024 KW - Structure health monitoring KW - Geothermal borehole KW - Distributed fiber optic sensing KW - Ground movement KW - Leakage detection PY - 2024 DO - https://doi.org/10.1117/12.3023571 SN - 0277-786X VL - 13001 SP - 1 EP - 10 PB - SPIE AN - OPUS4-60384 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Christensen, J. B. A1 - Jørgensen, A. A. A1 - Vandborg, M. H. A1 - Thomas, P. J. A1 - Lu, Xin A1 - Failleau, G. A1 - Eisermann, R. A1 - Grüner-Nielsen, L. A1 - Balslev-Harder, D. A1 - Lassen, M. A1 - Krenek, S. T1 - Fiber-artefact methodology and calibration framework for Brillouin-based fiber sensing N2 - We propose, and demonstrate, the use of a fiber-optical measurement artefact as a metrological tool for traceable distance calibration of distributed optical fiber sensors. The constructed fiber artefact consists of a lead-in fiber coupled to a fiber loop using a 3-dB coupler and is used to calibrate both a home-build Brillouin-OTDR setup and a custom version of a commercial Brillouin-OTDR interrogator build for distributed temperature sensing. For both interrogators, we demonstrate distance calibrations with 1-meter uncertainty (k=1) in the offset length and 0.1 % (1 m/km) uncertainty (k = 1) in the distance scale factor. In addition, it is shown that the fiber artefact can be used to assess undesired distance-dependent measurement biases. KW - Distributed temperature sensing KW - Metrology KW - Distributed optical fiber sensing KW - Brillouin optical time-domain reflectrometry PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-618853 DO - https://doi.org/10.1364/OE.544659 SN - 1094-4087 VL - 32 IS - 26 SP - 45483 EP - 45493 PB - Optica Publishing Group AN - OPUS4-61885 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin T1 - Progress review N2 - We report on the progress on calibration and characterization of distributed temperature sensing systems as a part of the European INFOTherm project. The most research results were achieved in the framework of the Work Package 2. T2 - Midterm meeting of INFOTherm project CY - Copenhagen, Denmark DA - 25.03.2025 KW - Humidity sensor KW - Optical fibre sensors KW - Distributed temperature sensing PY - 2025 AN - OPUS4-63007 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Hicke, Konstantin A1 - Breithaupt, Mathias A1 - Strangfeld, Christoph T1 - Distributed Humidity Sensing in Concrete Based on Polymer Optical Fiber N2 - We present a preliminary investigation on distributed humidity monitoring during the drying process of concrete based on an embedded polymer optical fiber (POF). The water dissipated into the POF changes several properties of the fiber such as refractive index, scattering coefficient and attenuation factor, which eventually alters the Rayleigh backscattered light. The optical time Domain reflectometer (OTDR) technique is performed to acquire the backscattered signal at the wavelengths 650 nm and 500 nm, respectively. Experimental results show that the received signal increases at 650 nm while the fiber attenuation factor clearly increases at 500 nm, as the concrete dries out. In the hygroscopic range, the information retrieved from the signal change at 650 nm agrees well with the measurement result of the electrical humidity sensors also embedded in the concrete sample. KW - Distributed fiber optic sensing KW - Distributed humidity sensing KW - Polymer optical fibers KW - Concrete drying KW - Material moisture KW - Embedded humidity sensors PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-537644 DO - https://doi.org/10.3390/polym13213755 SN - 2073-4360 VL - 13 IS - 21 SP - 3755 PB - MDPI CY - Basel, Switzerland AN - OPUS4-53764 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin T1 - Humidity response analysis of optical fibers with hygroscopic coatings based on Lamé’s equations N2 - Optical fibers with hygroscopic coatings are widely used for humidity sensing, where the coating expands upon absorbing water, inducing strain in the fiber. This strain is then used to determine humidity. However, previous studies have oversimplified the strain generation process. A comprehensive three-dimensional model of the mechanical interaction between the coating and the fiber is built based on Lamé’s equations. An analytical expression for the induced strain is derived. The proposed model predicts larger humidity-induced strain compared to the reported ones, given the same Young’s modulus or coefficient of humidity expansion for the coating. Interestingly, the effect of coating thickness on strain response are quite similar for both methods. Experimental validation using fibers with a polyimide coating shows strong agreement with the theoretical predictions. T2 - 29th International Conference on Optical Fiber Sensors CY - Porto, Portugal DA - 26.05.2025 KW - Distributed fiber sensing KW - Humidity sensors KW - Lamé’s equations KW - Reflectometry KW - Optical fiber sensors KW - Rayleigh scattering KW - Structural health monitoring PY - 2025 AN - OPUS4-63261 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin T1 - Polarization diversity detection based wavelength scanning coherent optical time domain reflectometry N2 - Although wavelength scanning coherent optical time-domain reflectometry (WS-COTDR) system is immune to fading effect, it suffers from occasional and localized large errors caused by the false peak in the correlation spectrum due to the large signal generated in the random interference of the backscattered light. Polarization diversity detection is applied to a standard WS-COTDR system to suppress large measurement errors. In this way, the orthogonally polarized components of backscattered light can be obtained and processed separately. Due to the birefringence of the sensing fiber, the components experience different interference processes, so the average of their correlation spectrum can suppress the false peaks and finally reduce the occurrence of larger errors. The effectiveness of the proposed method is validated in laboratory for monitoring of sinusoidal vibrations and in field for tracking the bus movement via a dark fiber. T2 - 29th International Conference on Optical Fiber Sensors CY - Porto, Portugal DA - 26.05.2025 KW - Coherent optical time domain reflectometry KW - Traffic monitoring KW - Polarization diversity detection KW - Distributed fiber sensing PY - 2025 AN - OPUS4-63260 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Schukar, Marcus A1 - Großwig, S. A1 - Weber, U. A1 - Krebber, Katerina T1 - Monitoring acoustic events in boreholes using wavelengthscanning coherent optical time domain reflectometry in multimode fiber N2 - A distributed acoustic sensor (DAS) based on wavelength-scanning coherent optical time domain reflectometer (WS-COTDR) is tested in an underground gas storage based on a multimode fiber for the first time to the best of our knowledge. The WS-COTDR acquires the reflection spectrum by scanning the wavelength of the laser and uses the spectra to calibrate strain. It overcomes the fading problem which is common for all DAS systems, and possesses the advantage of simple configuration and low-cost. The working principle of the system is well explained and the measurement results are presented. Various artificial and natural acoustic events have been successfully detected by the WS-COTDR. Such a sensor demonstrates several advantages over the traditional DAS systems, so it is supposed to be widely used in the oil and gas industry. T2 - EAGE GeoTech 2021 Second EAGE Workshop on Distributed Fibre Optic Sensing CY - Online meeting DA - 01.03.2021 KW - Leakage detection KW - Distributed acoustic sensing KW - Distributed fiber optic sensing PY - 2021 DO - https://doi.org/10.3997/2214-4609.202131010 SP - Paper 10, 1 PB - European Association of Geoscientists & Engineers CY - Houten, Niederlande AN - OPUS4-52248 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Schukar, Marcus A1 - Großwig, S. A1 - Weber, U. A1 - Krebber, Katerina T1 - Monitoring acoustic events in boreholes using wavelengthscanning coherent optical time domain reflectometry in multimode fiber N2 - A distributed acoustic sensor (DAS) based on wavelength-scanning coherent optical time domain reflectometer (WS-COTDR) is tested in an underground gas storage based on a multimode fiber for the first time to the best of our knowledge. The WS-COTDR acquires the reflection spectrum by scanning the wavelength of the laser and uses the spectra to calibrate strain. It overcomes the fading problem which is common for all DAS systems, and possesses the advantage of simple configuration and low-cost. The working principle of the system is well explained and the measurement results are presented. Various artificial and natural acoustic events have been successfully detected by the WS-COTDR. Such a sensor demonstrates several advantages over the traditional DAS systems, so it is supposed to be widely used in the oil and gas industry. T2 - EAGE GeoTech 2021 CY - Online meeting DA - 01.03.2021 KW - Borehole monitoring KW - Distributed fiber sensing KW - Acoustic sensing PY - 2021 DO - https://doi.org/10.3997/2214-4609.202131010 SP - 1 EP - 5 AN - OPUS4-52152 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krebber, Katerina A1 - Weege, S. A1 - Großwig, S. A1 - Obermöller, M. A1 - Perk, M. A1 - Lu, Xin A1 - Schukar, Marcus A1 - Weber, U. A1 - Pfeiffer, T. A1 - Rembe, M. T1 - Kombinierte faseroptische Messungen in Bohrlöchern helfen bei der Detektion von Kleinstleckagen N2 - Seit November 2019 läuft ein breit angelegtes und vom BMWi gefördertes ZIM-Kooperationsprojekt zwischen der Bundesanstalt für Materialforschung und -prüfung (BAM), der IAB'Weimar gGmbH, der GKSO GmbH & Co. Projekt KG, der DEEP.KBB GmbH sowie der Rembe Consulting PartG mbB. Ziel des Forschungsvorhabens sind sowohl die Lokalisierung als auch die Quantifizierung insbesondere sehr kleiner Leckagen in einer Bohrlochverrohrung durch die Nutzung faseroptischer Messtechnik. Durch Messdatenkopplung und den Wegfall bewegungsbedingter Nachteile einer Messsonde werden wesentlich präzisere Ergebnisse zur Bewertung der Bohrlochintegrität als üblich erwartet. T2 - DGMK/ÖGEW-Frühjahrstagung 2020 CY - Meeting was canceled DA - 15.04.2020 KW - Wasserstoffspeicher KW - Kavernenspeicher KW - Verteilte faseroptische akustische Sensorik PY - 2020 VL - 6 SP - 43 EP - 43 PB - DVV Media Group CY - Hamburg AN - OPUS4-52233 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Schukar, Marcus A1 - Krebber, Katerina T1 - Characterizing vibration response of fiber cables for distributed acoustic sensing N2 - The vibration responses of two fiber cables are characterized up to 16 kHz and compared with a standard tight-buffered 900 um fiber. The response of the cables is suppressed due to the cable protection. T2 - 27th International Conference on Optical Fiber Sensors (OFS-27) CY - Alexandria, VA, USA DA - 29.08.2022 KW - Distributed fiber sensing KW - Acoustic sensing KW - Response characterization PY - 2022 AN - OPUS4-56099 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Schukar, Marcus A1 - Weege, S. A1 - Roske, T. A1 - Krebber, Katerina T1 - Leakage detection at a borehole simulator using distributed acoustic sensing N2 - A distributed acoustic sensing system is used to detect the leakage in a borehole simulator by measuring the leakage induced vibration. The leakage location can be clearly determined by frequency spectrum analysis. T2 - 27th International Conference on Optical Fiber Sensors (OFS-27) CY - Alexandria, VA, USA DA - 29.08.2022 KW - Leakage detection KW - Structural health monitoring KW - Distributed fiber sensing KW - Distributed acoustic sensing PY - 2022 SP - 1 EP - 4 PB - Optica CY - Washington D.C., USA AN - OPUS4-56097 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Schukar, Marcus A1 - Krebber, Katerina T1 - Characterizing vibration response of fiber cables for distributed acoustic sensing N2 - The vibration responses of two fiber cables are characterized up to 16 kHz and compared with a standard tight-buffered 900 um fiber. The response of the cables is suppressed due to the cable protection T2 - 27th International Conference on Optical Fiber Sensors (OFS-27) CY - Alexandria, VA, USA DA - 29.08.2022 KW - Response characterization KW - Distributed fiber sensing KW - Acoustic sensing PY - 2022 SP - 1 EP - 4 PB - Optica CY - Washington D.C., USA AN - OPUS4-56096 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Schukar, Marcus A1 - Weege, S. A1 - Roske, T. A1 - Krebber, Katerina T1 - Leakage detection at a borehole simulator using distributed acoustic sensing N2 - A distributed acoustic sensing system is used to detect the leakage in a borehole simulator by measuring the leakage induced vibration. The leakage location can be clearly determined by frequency spectrum analysis. T2 - 27th International Conference on Optical Fiber Sensors (OFS-27) CY - Alexandria, VA, USA DA - 29.08.2022 KW - Structural health monitoring KW - Distributed fiber sensing KW - Distributed acoustic sensing KW - Leakage detection PY - 2022 AN - OPUS4-56098 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wang, Kun A1 - Lu, Xin A1 - Schukar, Marcus A1 - Hicke, Konstantin T1 - Water absorption effects on distributed temperature sensing using polyimide-coated optical fiber N2 - Polyimide-coated fibers are becoming more popular for distributed temperature sensing (DTS) because this coating can withstand much higher temperatures than the standard acrylate coating. As a hygroscopic material, polyimide can absorb water from the air, changing its properties, which may result in a modified temperature response of the sensing fiber. This study investigates the effect of water absorption on the performance of polyimide-coated optical fibers with different sizes and properties. The thermal response of these fibers was determined experimentally from 20°C to 90°C at a broad relative humidity level ranging from 10% to 90%. The results show that all the fibers experienced a decrease in temperature sensitivity as humidity increased, with the most noticeable non-linear spectral shift observed at higher humidity levels. These findings highlight the importance of optimizing fiber design and coating properties to balance stability and sensitivity, ensuring the reliable performance of DTS systems under extreme environmental conditions. T2 - 29th International Conference on Optical Fiber Sensors CY - Porto, Portugal DA - 26.05.2025 KW - Humidity sensing KW - Distributed temperature sensing KW - Optical fiber sensors KW - Temperature sensing KW - Water absorption KW - Polyimide-coated fiber PY - 2025 SN - 978-1-5106-9187-2 DO - https://doi.org/10.1117/12.3062748 VL - 13639 SP - 136393W-1 EP - 136393W-4 PB - SPIE AN - OPUS4-63642 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Schukar, Marcus T1 - Humidity response analysis of optical fibers with hygroscopic coatings based on Lamé’s equations N2 - Optical fibers with hygroscopic coatings are widely used for humidity sensing, where the coating expands upon absorbing water, inducing strain in the fiber. This strain is then used to determine humidity. However, previous studies have oversimplified the strain generation process. A comprehensive three-dimensional model of the mechanical interaction between the coating and the fiber is built based on Lamé’s equations. An analytical expression for the induced strain is derived. The proposed model predicts larger humidity-induced strain compared to the reported ones, given the same Young’s modulus or coefficient of humidity expansion for the coating. Interestingly, the effect of coating thickness on strain response are quite similar for both methods. Experimental validation using fibers with a polyimide coating shows strong agreement with the theoretical predictions. T2 - 29th International Conference on Optical Fiber Sensors CY - Porto, Portugal DA - 26.05.2025 KW - Reflectometry KW - Distributed fiber sensing KW - Humidity sensors KW - Lamé’s equations KW - Optical fiber sensors KW - Structural health monitoring KW - Rayleigh scattering PY - 2025 SN - 978-1-5106-9188-9 DO - https://doi.org/10.1117/12.3060891 VL - 13639 SP - 1 EP - 4 PB - SPIE AN - OPUS4-63257 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lu, Xin A1 - Hicke, Konstantin T1 - Polarization-diversity-detection-based wavelength-scanning coherent-optical-time-domain reflectometer and its application for bus monitoring N2 - Although wavelength scanning coherent optical time-domain reflectometry (WS-COTDR) system is immune to fading effect, it suffers from occasional and localized large errors caused by the false peak in the correlation spectrum due to the large signal generated in the random interference of the backscattered light. Polarization diversity detection is applied to a standard WS-COTDR system to suppress large measurement errors. In this way, the orthogonally polarized components of backscattered light can be obtained and processed separately. Due to the birefringence of the sensing fiber, the components experience different interference processes, so the average of their correlation spectrum can suppress the false peaks and finally reduce the occurrence of larger errors. The effectiveness of the proposed method is validated in laboratory for monitoring of sinusoidal vibrations and in field for tracking the bus movement via a dark fiber. T2 - 29th International Conference on Optical Fiber Sensors CY - Porto, Portugal DA - 26.05.2025 KW - Traffic monitoring KW - Coherent optical time domain reflectometry KW - Distributed fiber sensing KW - Polarization diversity detection PY - 2025 SN - 978-1-5106-9187-2 DO - https://doi.org/10.1117/12.3060889 VL - 13639 SP - 1 EP - 4 PB - SPIE AN - OPUS4-63258 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lu, Xin A1 - Schukar, Marcus T1 - Humidity response of optical fibres with hygroscopic coatings and its temperature dependence N2 - Optical fibres with hygroscopic coatings are widely used in structural health monitoring to acquire the humidity information. Water absorption-induced coating expansion leads to a strain change in the silica fibre, which can be measured by point and distributed strain fibre sensors and used to quantify the environmental humidity. In this paper, the strain transfer from the coating to the fibre is described by both 1D and 3D models. The impact of the coating property on the humidity induced strain is theoretically analysed. Since the properties of the sensing fibre are temperature-dependent, the humidity response obtained by the strain-based approach may change under different thermal conditions. The humidity response of fibres with different polyimide coatings is characterized by a commercial optical frequency domain reflectometer under different temperature conditions. The experimental results confirm the temperature dependence of the humidity response as the sensitivity of all the tested fibres decreases as the temperature increases. KW - Rayleigh scattering KW - Humidity sensor KW - Optical fibre sensors KW - Optical frequency domain reflectometer PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-629735 DO - https://doi.org/10.1088/2515-7647/adc85f VL - 7 IS - 2 SP - 1 EP - 11 PB - IOP Publishing Ltd CY - Bristol, UK AN - OPUS4-62973 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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 -