Article

High-resolution distributed shape sensing using phase-sensitive optical time-domain reflectometry and multicore fibers

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Abstract

In this paper, a highly-sensitive distributed shape sensor based on a multicore fiber (MCF) and phase-sensitive optical time-domain reflectometry (φ-OTDR) is proposed and experimentally demonstrated. The implemented system features a high strain sensitivity (down to ∼0.3 µɛ) over a 24 m-long MCF with a spatial resolution of 10 cm. The results demonstrate good repeatability of the relative fiber curvature and bend orientation measurements. Changes in the fiber shape are successfully retrieved, showing detectable displacements of the free moving fiber end as small as 50 µm over a 60 cm-long fiber. In addition, the proposed technique overcomes cross-sensitivity issues between strain and temperature. To the best of our knowledge, the results presented in this work provide the first demonstration of distributed shape sensing based on φ-OTDR using MCFs. This high-sensitivity technique proves to be a promising approach for a wide range of new applications such as dynamic, long distance and three-dimensional distributed shape sensing.

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... 8 In 2019, MCF (multicore fiber) was combined with Φ-OTDR to achieve a high strain sensitivity over 24-m-long distance with a spatial resolution of 10 cm. 9 In earlier works, researchers obtained the location and frequency of external disturbance by extracting the amplitude fluctuation curve of Rayleigh backscattering (RBS) light. However, the intensity change of amplitude is not linear with the external disturbance strength, which makes the quantitative measurement and signal identification difficult. ...
... In the next step, we used a binary matrix mask to represent the removal degree of Δφ 0 ðt; dÞ. Removal degree represents how we suppress the inaccurate phase, the value of mask is given by E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 9 ; 1 1 6 ; 6 6 3 Mðt; dÞ ¼ 1; Δφ 0 ðt; dÞ RMSE ≤ θ 0; Δφ 0 ðt; dÞ RMSE > θ ; (9) where Mðt; dÞ means the mask value of each phase difference change Δφ 0 ðt; dÞ. ...
... (9) and(10), Figs. 10(a) and 10(b) show the masks of laboratory experimental results when the accuracy threshold θ is set as 0.45 and 0.35 rad. ...
... Detecting both the bending orientation and angle is crucial in reliably estimating the shape of the fiber and thereby, the shape of the element being sensed. Recently, distributed sensing techniques have been explored for the detection of bending using MCF like Brillouin optical time domain analysis (BOTDA) [17], and more recently phase-sensitive optical time-domain reflectometry (φ-OTDR) [18], which presents a higher sensitivity level. These techniques allow both bending orientation and radius to be detected, but distributed sensing requires complex architectures and interrogations systems, which increases the difficulty and costs of such systems. ...
... In order to theoretically reconstruct the bend angle and tip deviation based on the loss measurements of the proposed fiber, we have followed a method similar to the one presented in [18]. From the measurement data we created 6 points in a 3D space defined as: where x i , and y i represent the location of i-th core in the crosssection of the fiber, and z i depicts the losses in dBs of the i-th core. ...
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In this article we present an all-fiber vector bend sensor by means of a self-fabricated micro-structured multicore optical fiber. The reported solution is based on differential intensity variations of the light transmitted along the cores whose changes are influenced by the bending angle and orientation. The unique asymmetric structure of the air-holes in the optical fiber provides each core with different confinement losses of the fundamental mode depending on the bending radius and orientation, making each of the cores bend-sensitive in a range of at least 80°. It has been experimentally demonstrated that the reported sensor enables the bending angle and orientation to be detected in a full range of 360° without any dead-zones, and the possibility of end point detection with millimeter precision. Additionally, a reconstruction of the bending vector has been carried out theoretically, and a good match can be observed between the experimental and theoretical data.
... This laboratory study demonstrates the potential for higher stability and high measurement accuracy when using this fiber as a distributed curvature sensor. It should be noted that similar studies were carried out earlier, on typical multicore fibers, using the technique of frequency domain reflectometry and other methods [53]- [55]. No doubt they do not require the creation of special variation of multicore fibers, but they have lower precision. ...
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This paper describes the state-of-art features of special optical fibers and integrated-optical circuits distributed parameters study by methods of optical reflectometry. Attention is paid to the study of the internal structure of fibers that preserve the polarization of the introduced radiation, active optical fibers, and waveguides inside the integrated chips, optical circuits, and other technological created media.
... In 2019, S. Mikhailov et al. utilized this approach to measure the hydrostatic pressure along a highly birefringent photonic crystal fiber (PCF) 180 . The pressure applied on the asymmetric micro-structured fiber would cause an asymmetric strain in the fiber core, inducing a local birefringence variation. ...
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Phase-sensitive optical time-domain reflectometry (Φ-OTDR) has attracted numerous attention due to its superior performance in detecting the weak perturbations along the fiber. Relying on the ultra-sensitivity of light phase to the tiny deformation of optical fiber, Φ-OTDR has been treated as a powerful technique with a wide range of applications. It is fundamental to extract the phase of scattering light wave accurately and the methods include coherent detection, I/Q demodulation, 3 by 3 coupler, dual probe pulses, and so on. Meanwhile, researchers have also made great efforts to improve the performance of Φ-OTDR. The frequency response range, the measurement accuracy, the sensing distance, the spatial resolution, and the accuracy of event discrimination, all have been enhanced by various techniques. Furthermore, lots of researches on the applications in various kinds of fields have been carried out, where certain modifications and techniques have been developed. Therefore, Φ-OTDR remains as a booming technique in both researches and applications.
... Szostkiewicz et al. used a phase-sensitive optical time-domain reflectometry (phase-OTDR) to achieve DSS. Although the strain sensing sensitivity of phase-OTDR is up to nano-strain level, the spatial resolution of this system is still not high, about 10 cm [10]. In addition, the static strain measurement using phase-OTDR is not very stable because the phase is easily influenced by extern environment vibration. ...
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In distributed shape sensing, the shape reconstruction error is more and more sensitive to the strain measuring error along with curvature radius of reconstructed shape increasing, which causes a notable challenge for large curvature radius shape reconstructing. In this paper, we demonstrate a large curvature radius shape sensing using optical frequency domain reflectometry (OFDR) in multi-core fibers. We construct a theoretical model of strain measuring error and curvature radius reconstructing errors under different curvature radius. In the experiment, by this reconstructing error model, we optimally select the measurable strain resolution and the sensing spatial resolution to realize the shape reconstruction with a large curvature radius and reconstruct two-dimensional (2D) circle shapes of curvature radii from 5 cm to 100 cm. To verify the accuracy of three-dimensional (3D) shape reconstruction, we present a 3D shape sensing validation method based on 3D printing technology. We fabricate a 3D phantom containing a groove with a variable curvature radius of 5 cm to 100 cm. The presented distributed shape sensing system realize to reconstruct this complicated 3D shape. The root-mean-square error of curvature radius between the reconstructed and designed 3D space curves is 7.2 mm and the mean Euclidean distance is 3.4 mm.
... Over the past 10 years there has been an increasing interest in shape sensors based on optical fibres for various applications. Since 2000, when the first bent sensor based on multicore fibre was reported [1], extensive research efforts have been focused on the development of shape sensors using multicore fibres and fibre bundles and exploiting Rayleigh [2] and Brillouin [3] scattering and fibre Bragg gratings (FBGs) [4]. These technologies use different interrogation principles to measure strain along the length of an optical fibre. ...
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In order to provide high accuracy in shape measurement with multicore optical fibres, characterization and calibration procedures are an important part of sensor preparation. Some procedures can be considered mandatory for adequate shape reconstruction, while others can help to enhance the measurement accuracy. Several of such procedures are discussed and experimentally applied for demonstrating the possible performance enhancement of curvature sensing, a fundamental phase of the shape reconstruction process. The maximum error observed in curvature calculation for a test object has been proved to be almost halved, decreasing from 2.48% to 1.36%, by applying such calibration corrections. The overall average relative accuracy of curvature measurement was improved from 0.89% to 0.5% (an improvement of 44%).
... Zafeiropoulou et al. measured the curvature of a D-shaped multicore fiber using Brillouin optical time-domain reflectometry [158] . Szostkiewicz et al. distributedly sensed the curvature of an MCF using phase-sensitive Optical Time-Domain Reflectometry ( -OTDR)[159] . ...
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... Szostkiewicz et al. have also demonstrated a distributed curvature sensor based on phasesensitive Optical Time-Domain Reflectometry (φ-OTDR) [12]. However, like the OFDR-based distributed shape sensors, this technique also requires a reference measurement with a straight fibre since it is not capable of measuring the absolute strain-level. ...
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