On Optical Frequency Domain Reflectometry Research Articles

A silicone rubber packaged distributed optical fiber sensing tape for strain-crack monitoring based on OFDR technique

A novel silicone rubber (SR)-packaged distributed optical fiber sensor (DOFS) tape based on optical frequency domain reflectometry (OFDR) technique was developed to effectively monitor substrate cracking. The analytical strain distribution of this sensor tape is derived based on the current strain transfer model and then used to determine the parameter sensitivity to provide a scientific basis for the selection of packing parameters and bond length. A calibration test of the sensor tape on steel plates was performed, and the feasibility of the sensing tape for accurately measuring the substrate strain and crack width was demonstrated. A test is conducted to monitor adjacent double cracks, and the test results show that the sensor tape has the ability to identify crack positions with crack spacings greater than 40 mm. The sensor tape is applied to the monitoring of concrete cracking induced by corrosion, and the test results demonstrate that the DOFS sensing tape has advantages for monitoring large cracks. Both the analytical and experimental results show that the novel SR-packaged DOFS tape is effective and feasible.

Improvement of high sensitivity ICR characteristics and its application in OFDR

Coherent optical sensing technology faces significant challenges in practical applications due to the extremely weak signal light, necessitating highly sensitive coherent receivers. A high-sensitivity, highly integrated, and low-noise coherent receiver module based on germanium-silicon photonic chips has been developed. A testing system was constructed to assess the performance of the coherent receiver module, revealing a reception sensitivity of -70dBm, with physical dimensions of 33×40×8.6 mm3 and an output noise voltage of ±4mV. Additionally, a distributed sensing system based on optical frequency domain reflectometry (OFDR) was established to verify the module’s application in OFDR systems, achieving a spatial resolution of 1mm.

Improve accuracy and measurement range of sensing in km-level OFDR using spectral splicing method.

In this paper, we propose and demonstrate a spectral splicing method (SSM) for distributed strain sensing based on optical frequency domain reflectometry (OFDR), which can achieve km level measurement length, µɛ level measurement sensitivity and 104 µɛ level measurement range. Based on the traditional method of cross-correlation demodulation, the SSM replaces the original centralized data processing method with a segmented processing method and achieves precise splicing of the spectrum corresponding to each signal segment by spatial position correction, thus realizing strain demodulation. Segmentation effectively suppresses the phase noise accumulated in the large sweep range over long distances, expands the sweep range that can be processed from the nm level to the 10 nm level, and improves strain sensitivity. Meanwhile, the spatial position correction rectifys the position error in the spatial domain caused by segmentation, which reduces the error from the 10 m level to the mm level, enabling precise splicing of spectra and expanding the spectral range, thus extending the strain range. In our experiments, we achieved a strain sensitivity of ±3.2 µɛ (3σ) over a length of 1 km with a spatial resolution of 1 cm and extended the strain measurement range to 10,000 µɛ. This method provides, what we believe to be, a new solution for achieving high accuracy and wide range OFDR sensing at the km level.

Shape and Flow Sensing in Arterial Image Guidance From UV Exposed Optical Fibers Based on Spatio-Temporal Networks.

Minimally invasive revascularization procedures such as percutaneous transluminal angioplasty seek to treat occlusions in peripheral arteries. However their ability to treat long occlusions are hampered by difficulties to monitor the location of intravascular devices such as guidewires using fluoroscopy which requires continuous radiation, and lack the capacity to measure physiological characteristics such as laminar blood flow close to occlusions. Fiber optic technologies provide means of tracking by measuring fibers under strain, however they are limited to known geometrical models and are not used to measure external variations. We present a navigation framework based on optical frequency domain reflectometry (OFDR) using fully-distributed optical sensor gratings enhanced with ultraviolet exposure to track the three-dimensional shape and surrounding blood flow of intra-vascular guidewires. To process the strain information provided by the continuous gratings, a dual-branch model learning spatio-temporal features allows to predict the output measures based on scattered wavelength distributions. The first network determines the 3D shape appearance of the guidewire using the input backscattered wavelength shift data in combination with prior segmentations, while a second network (graph temporal convolution network) produces estimates of vascular flow velocities using ground-truth 4D-flow MRI acquisitions. Experiments performed on synthetic and animal models, as well as in a preliminary human trial shows the capability of the model to generate accurate 3D shape tracking and blood flow velocities differences below 2 cm/s, thus providing realistic physiologic and anatomical properties for intravascular techniques. The study demonstrates the feasibility of using the device clinically, and could be integrated within revascularization workflows for treating occlusions in arteries, since the navigation framework involves minimal manual intervention.

Detecting pipeline leakage using active distributed temperature Sensing: Theoretical modeling and experimental verification

This paper presents a feasibility study on leak detection of buried pipelines using the active distributed temperature sensing (ADTS) method. The proposed solution involves the use of actively heated fiber optic (AHFO) cables arranged parallel to the pipelines, allowing for changes in the thermal properties of the surrounding soil to be captured and correlated with leakage accidents. This problem was modeled as an infinite cylindrical or linear heat source buried in porous media with seepage flowing inside. AHFO sensors were designed to verify the proposed method through scale-reduced model tests. The fiber optic temperature sensing technology based on optical frequency domain reflectometry (OFDR) was used to continuously monitor temperature profiles. The test results demonstrate that the ADTS solution has greatly improved the accuracy of passive temperature sensing methods. The feasibility of the solution was evaluated regarding different levels of leakage estimation, namely, identification, location, and quantification. This paper presents the first attempt to monitor the infiltration process associated with pipeline leaks using the AHFO-OFDR technique, which is a reliable method for structural health monitoring of underground pipelines.

Pressure test of a prestressed concrete cylinder pipe using distributed fiber optic sensors: Instrumentation and results

This paper presents an approach for measuring and visualizing the strain and loading responses of a pressurized prestressed concrete cylinder pipe (PCCP) using distributed fiber optic sensors based on optical frequency domain reflectometry (OFDR). The pipe has an inner diameter of 3400 mm and length of 5000 mm. The concrete core, steel cylinder, prestressing wires, and mortar coating of PCCP were instrumented with specific distributed fiber optical sensors that can also be installed in future field construction. This PCCP was tested under increasing internal water pressure until a large number of radial and longitudinal cracks appeared on the pipe surface. The crack measurements made by the distributed sensors are in good agreement with the actual observations and reflect the crack propagation with reasonable accuracy. This study demonstrates that distributed fiber optical sensors can be effectively installed in the PCCP production process, and the cracks on the concrete core and mortar coating can be monitored with a spatial resolution of 1 cm. It is expected that distributed sensing technology for structural health monitoring will be useful in new and existing pipeline structures.

A Novel Sensor for Undrained Shear Strength Measurement in Very Soft to Soft Marine Sediments Based on Optical Frequency Domain Reflectometry Technology.

Due to the short supply of conventional fill materials, such as sand, land reclamation using dredged marine deposits has recently been proposed, in which marine deposits with high water content are blow-filled into reclaiming areas. The strength development of the filled marine soils is of great importance during the sedimentation and consolidation to guide the filling process and construction of reclamation. In this study, a novel sensor based on optical frequency domain reflectometry (OFDR) technology with a simple design was developed for undrained shear strength measurement. The novel sensor consists of an optical fiber and a series of polyoxymethylene coins. Owing to the merits of OFDR technology on high resolution, fully distributed sensing, and immunity to electromagnetic interference, the novel sensor can be used to determine undrained shear strength profiles of very soft to soft marine sediments/soils with good accuracy. The sensor was calibrated in remolded marine deposits with different water contents. The good feasibility and performance of the novel sensor for undrained shear strength measurement were well validated in two physical model tests on marine deposits treated by horizontal drains with vacuum preloading.

Generalized Cross-Correlation Strain Demodulation Method Based on Local Similar Spectral Scanning.

Optical fiber measurement technology is widely used in the strength testing of buildings, the health testing of industrial equipment, and the minimally invasive surgery of modern medical treatment due to its characteristics of free calibration, high precision, and small size. This paper presents an algorithm that can improve the range and stability of strain measurements in order to solve the problems of the small range and measurement failure of optical fiber strain sensors based on optical frequency-domain reflectometry (OFDR). Firstly, a Rayleigh scattering model based on the refractive index perturbation of an optical fiber is proposed to study the characteristics of Rayleigh scattering and to guide the strain demodulation algorithm based on the spectral shift. Secondly, a local similar scanning method that can maintain a high similarity by monitoring local Rayleigh scattering signals (LSs) before and after strain is proposed. Thirdly, a generalized cross-correlation algorithm is proposed to detect spectral offset, solving the problem of demodulation failure in the case of a Rayleigh scattering signal with a low signal-to-noise ratio. Experiments show that the proposed method still has high stability when the spatial resolution is 3 mm. The measurement precision is 6.2 με, which proves that the multi-peaks or pseudo-peaks of the traditional algorithm in the case of a large strain, the high spatial resolution, and the poor signal-to-noise ratio are solved, and the stability of the strain measurement process is improved.

Monitoring and early detection of soil desiccation cracking using distributed fibre optical sensing

Desiccation cracking can significantly affect the hydro-mechanical behaviour of soil in various engineering applications. Characterising the evolution of desiccation-induced shrinkage strain in soils is a key step in understanding the cracking mechanism. This study presents a novel framework for monitoring and early detecting soil cracking by utilising the distributed fibre optical sensing (DFOS) technique based on optical frequency domain reflectometry (OFDR). DFOS-OFDR was integrated into a set of experimental testing to simultaneously monitor water content, crack pattern and strain state. OFDR with 1 με strain measurement accuracy was employed to monitor the initiation and propagation of cracks. The results reveal a strong correlation between the spatiotemporal evolution of soil strain and crack, confirming the efficacy and reliability of the proposed framework. During the drying process, the compressive strain induced by soil shrinkage increases first and starts to decrease when cracking is initiated. Further, DFOS-OFDR demonstrated promising results to predict the position of cracks. Compared to traditional strain monitoring methods with discrete measurements, DFOS-OFDR offers a non-destructive, accurate yet efficient, high-resolution and continuous technique for monitoring and early detection of soil desiccation cracking.

Distributed temperature profile in hydrogen flame measured by telecom fiber and its durability under flame by OFDR.

The distributed temperature profile of hydrogen flame based on optical frequency-domain reflectometry (OFDR) was experimentally demonstrated for the first time. Spatial temperature field at different flow rate of H2 flame was monitored by OFDR via a telecom fiber (Corning SMF-28, CPC6) inside the flame over seconds, and the highest temperature is on the sides of center flame separated by ∼1.4mm with difference of 140∼190°C over the flame dimension of 2.5 mm above 900°C. Uniformity level of temperature is studied by varying the distance between fiber and tube entrance, and the largest uniform region over 1-millimeter length of fiber is obtained. Rayleigh scatters correlation coefficient decreases with temperature to 90% around 400°C, further reduces to 70% about 800°C, and 50% roughly at 1000°C. It indicates that a nonlinear thermal sensitivity of SMF is expected for temperature higher than 400°C with OFDR measurement. The durability of single-mode fiber under H2 flame is studied via decorrelation time at various temperature. It maintains 20s at 880°C with correlation coefficient around 68% and drops to 50% decorrelation at 1000°C over 20s. This information is important for high temperature measurement using telecom fiber over 800°C based on OFDR. A maximum temperature of 1100°C was measured by OFDR, and it is possible for higher temperature measurement beyond of 1100°C with quicker system response time (<1s).

Distributed high-temperature sensing based on optical frequency domain reflectometry with a standard single-mode fiber.

Distributed temperature sensing up to 600°C at a fiber length of 100.75 m based on optical frequency domain reflectometry (OFDR) was demonstrated using a standard single-mode fiber (SMF) without any treatment. The spatial resolution was 2.5 mm. An algorithm, instantaneous optical frequency resampling (IOFR), to eliminate the nonlinearity of the laser source was proposed and used to obtain calibrated reference and measurement signals that were used for temperature demodulation. Moreover, the temperature response stability of the annealed SMF was better than that of un-annealed SMF, where the temperature sensitivity was 1.96 GHz/°C at 600°C.

Multiparameter Distributed Fiber Sensor Based on Optical Frequency-Domain Reflectometry and Bandwidth-Division Multiplexing

We demonstrate a multiparameter distributed sensing system based on optical frequency-domain reflectometry (OFDR) with a bandwidth-division multiplexing (BDM) technique. With the BDM-assisted OFDR, the sensor system can help interrogate multiple parallel sensing optical fibers by scanning the fibers within distinct spectral ranges without any cross talk. A dual-parameter distributed sensing system was set up by multiplexing two types of sensing fibers for the simultaneous independent measurement of strain and temperature. The rms deviations between the applied and measured values of the two parameters are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$19~ {\mu } {\varepsilon } $ </tex-math></inline-formula> and 1.4 °C, respectively, for a sensing spatial resolution of 10 cm. The proposed multiparameter distributed sensor system offers inexpensive potential solution to continuously monitor various parameters and is effective for the health monitoring of complex distributed structures.

Vibration-Induced Beat Frequency Offset Compensation in Distributed Acoustic Sensing Based on Optical Frequency Domain Reflectometry

We investigate the impact of the frequency modulation induced by vibration occurring at a preceding distance in distributed acoustic sensing (DAS) based on optical frequency domain reflectometry (OFDR), which analyzes a vibration waveform by calculating the spectrum shift of Rayleigh backscattered light in the same manner as a fiber Bragg grating. When the measurement time of a beat signal is shorter than the period of the vibration at the preceding distance, the vibration-induced frequency modulation can be treated as a frequency offset for the backscattered light. The frequency offset becomes a distance offset through the distance - beat frequency allocation of OFDR, and the distance offset forces us to interrogate the Rayleigh backscattered light spectra at unintentional distances for each measurement since the distance offset is time-varying. Since the spectra at unintentional distances are uncorrelated, the spectrum shift calculated with an uncorrelated spectrum results in a spurious vibration, which is a measured waveform that is different from the actual vibration waveform and that constitutes a measurement error in a DAS measurement. We propose a technique to compensate for the spurious vibration. The technique estimates the vibration-induced distance offset by calculating the cross-correlation between Rayleigh backscattered light waveforms and shifts the spectrum analysis range by the estimated offset in order to track the consistent spectrum. We perform a DAS measurement on a sensing fiber that experiences simultaneous vibrations at different distances and confirm the validity of the proposed technique.

Measuring the Two-Dimensional Temperature Profile of Carbon Fiber Reinforced Polymers During Drilling Using Distributed Fiber Sensing

The spatio-temporal evolution of the temperature induced over carbon fiber reinforced polymer (CFRP) laminates during drilling is monitored in real-time using a distributed optical fiber sensor based on optical frequency-domain reflectometry (OFDR). The proposed distributed measurement technique enables the simultaneous monitoring of thousands independent points on a CFRP plate during machining, being of special interest to measure the internal temperature of a workpiece. Experimental results validate the use of distributed OFDR-based sensing for this novel application, demonstrating a precise reconstruction of the two-dimensional (2D) temperature profile around the drilled hole, with a 2 mm spatial resolution and a sampling rate of 23.8 Hz (corresponding to a measurement interval of 42 ms). The high spatial and temporal resolutions provided by OFDR sensing offer unique features for this application, allowing for an accurate identification of the temporal evolution and spatial distribution of the 2D temperature profile originated during drilling. By embedding the sensing optical fiber in the interface between CFRP laminates and metals, a full map of the internal (interlayer) temperature of the CFRP plate can be obtained, demonstrating a feature that cannot be obtained by any other sensing technology. The proposed method can constitute a relevant tool for the identification of potential high temperatures occurring during machining, which could affect the quality of the borehole, induce material defects, and compromise the safety of an entire composite structure in service.

Intra-Arterial Image Guidance With Optical Frequency Domain Reflectometry Shape Sensing.

Intra-arterial liver cancer therapies, such as trans-arterial chemoembolization, are the preferred therapeutic approaches for advanced hepatocellular carcinoma. However, these palliative techniques are challenging for delivering therapeutic agents selectively in the tumor without real-time 3-D visualization of the catheter within the hepatic arteries. The objective of this paper is to develop and evaluate in pre-clinical tests an advanced interventional guidance platform using a distributed strain sensing device based on optical frequency-domain reflectometry (OFDR) to track the tip and shape of a catheter. The scattering properties of a fiber triplet are enhanced by focusing an ultraviolet beam on these fibers, producing a fully distributed strain sensor, which avoids interpolation errors observed with traditional shape tracking systems. A 3-D roadmap of the hepatic arteries is obtained from a combined fully convolutional and residual networks trained on MR angiography and combined with a 4-D flow dynamic sequence enabling to map blood flow velocities. An anisotropic curvature matching method is proposed to map the sensed data onto pre-operative MR and using 3-D ultrasound to correct for non-rigid deformations. Experiments were conducted in a controlled environment setting as well as in both synthetic phantoms and in five porcine models to assess the performance for device navigation, yielding satisfactory tracking accuracy with 3-D mean errors of 2.8 ± 0.9 mm. We present the first pilot study of MR-compatible UV-exposed OFDR optical fibers for non-ionizing device guidance in intra-arterial procedures, with the potential of avoiding multiple hospitalizations required to perform invasive selective chemoembolizations.

Flight demonstration of aircraft fuselage and bulkhead monitoring using optical fiber distributed sensing system

We have developed an optical fiber distributed sensing system based on optical frequency domain reflectometry (OFDR) that uses long-length fiber Bragg gratings (FBGs). This technique obtains strain data not as a point data from an FBG but as a distributed profile within the FBG. This system can measure the strain distribution profile with an adjustable high spatial resolution of the mm or sub-mm order in real-time. In this study, we applied this OFDR-FBG technique to a flying test bed that is a mid-sized jet passenger aircraft. We conducted flight tests and monitored the structural responses of a fuselage stringer and the bulkhead of the flying test bed during flights. The strain distribution variations were successfully monitored for various events including taxiing, takeoff, landing and several other maneuvers. The monitoring was effective not only for measuring the strain amplitude applied to the individual structural parts but also for understanding the characteristics of the structural responses in accordance with the flight maneuvers. We studied the correlations between various maneuvers and strains to explore the relationship between the operation and condition of aircraft.

Application of phosphate doped fibers for OFDR dosimetry

We employ phosphate doped optical fibers for distributed dosimetry based on Optical Frequency Domain Reflectometry (OFDR) and demonstrate the effect of limited Integrated Insertion Loss Dynamic Range (ILDR) on the system performance.

Long-Range High Spatial Resolution Distributed Temperature and Strain Sensing Based on Optical Frequency-Domain Reflectometry

A novel approach to realize long-range distributed temperature and strain measurement with high spatial resolution, as well as high temperature and strain resolution, is proposed based on optical frequency-domain reflectometry (OFDR). To maintain the high measurement resolution and accuracy while increasing the sensing length, an optimized nonlinearity compensation algorithm is implemented to ensure a large wavelength tuning range. The compensated OFDR trace exhibits improved sensing resolution at a short distance, and the spatial resolution gradually deteriorates at the far end due to accumulated phase noise induced by fast tuning of the laser wavelength. We demonstrated the spatial resolution of 0.3 mm over a single-mode fiber sensing length of over 300 m, and temperature and strain resolution of 0.7 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex></formula> and 2.3 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\varepsilon$</tex></formula> with spatial resolution of up to 7 cm, respectively.

Signal processing method based on group delay calculation for distributed Bragg wavelength shift in optical frequency domain reflectometry

A signal processing method based on group delay calculations is introduced for distributed measurements of long-length fiber Bragg gratings (FBGs) based on optical frequency domain reflectometry (OFDR). Bragg wavelength shifts in interfered signals of OFDR are regarded as group delay. By calculating group delay, the distribution of Bragg wavelength shifts is obtained with high computational efficiency. We introduce weighted averaging process for noise reduction. This method required only 3.5% of signal processing time which was necessary for conventional equivalent signal processing based on short-time Fourier transform. The method also showed high sensitivity to experimental signals where non-uniform strain distributions existed in a long-length FBG.

Lateral Load Measurements Based on a Distributed Sensing System of Optical Frequency-Domain Reflectometry Using Long-Length Fiber Bragg Gratings

In this paper, we demonstrate the measurements of lateral loads in a distributed manner using long-length fiber Bragg gratings (FBGs) based on optical frequency-domain reflectometry (OFDR). Birefringence is induced at specific areas of the long-length FBGs by lateral compression. The distributions of the Bragg peaks were monitored by the OFDR sensing system, from which we calculated the applied lateral loads. Theoretical calculation results confirmed the validity of the experimental results. In addition, position-wise beat signals of the power of the obtained spectra were observed with smaller lateral loads that were not sufficient to provide two distinguished Bragg peaks. This unique phenomenon for the frequency-domain reflectometry scheme is explained theoretically. We proposed a method for utilizing the beat cycle to calculate smaller lateral loads.