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Hari Datta Bhatta

Bio: Hari Datta Bhatta is an academic researcher from Tel Aviv University. The author has contributed to research in topics: Time domain & Total harmonic distortion. The author has an hindex of 3, co-authored 8 publications receiving 22 citations. Previous affiliations of Hari Datta Bhatta include École Polytechnique Fédérale de Lausanne.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors extend the capabilities of chirped-pulse phase-sensitive optical time-domain reflectometry to the measurement of large dynamic strains over hundreds of meters of standard single-mode fiber.
Abstract: This paper extends the capabilities of chirped-pulse phase-sensitive optical time-domain reflectometry to the measurement of large dynamic strains over hundreds of meters of standard single-mode fiber. Benefitting from single-shot strain measurements, this technique has already demonstrated dynamic strains of the order of submicrostrains with a sensitivity of picostrains-per-root-Hertz. Yet, for large dynamic strains, it relies on the accumulation of incremental measurements, where each trace is cross correlated with its predecessor to determine the relative change of strain. However, practical time records of measured high slew-rate applied perturbations contain disturbing outliers. We then detail and analyze a post-processing strategy to mitigate this limitation. Through this strategy, we are able to achieve for the first time (to our knowledge) high signal-to-noise Rayleigh-backscattering-based distributed measurements of large and fast dynamic strains of a longitudinally vibrating 4 m section at the end of 210 m of a single-mode fiber: from peak to peak 150–1190 μϵ at vibration frequency of 400 Hz and 50 Hz, respectively.

29 citations

Journal ArticleDOI
TL;DR: In this article, a novel and improved version of SA-BOTDA, having a significantly wider drift tolerance for the interrogation point was proposed, using a 14 ns pump pulse and a judicious choice of the frequency of the loss probe.
Abstract: Slope-assisted Brillouin optical time domain analysis (SA-BOTDA) is a fast and distributed sensing technique that interrogates the Brillouin gain spectrum (BGS) near the middle of the linear region of its slope, allowing the measurement of high frequency vibrations. However, environmentally-induced deviations of the interrogation point from the rather small linear region around the optimum frequency position, result in harmonic distortion and changes in the slope value, which determines the gain-to-frequency conversion factor. Engineering the BGS by adding a loss probe, we propose a novel and improved version of SA-BOTDA, having a significantly wider drift tolerance for the interrogation point. Here, using a 14 ns pump pulse and a judicious choice of the frequency of the loss probe, we demonstrate an engineered BGS having a 70% wider frequency range (as compared with the conventional BGS), where the interrogation point can drift without compromising either the prescribed level of harmonic distortion or the given slope tolerance, further benefiting the flexibility and usage of SA-BOTDA.

10 citations

Proceedings ArticleDOI
24 Sep 2018
TL;DR: In this article, a chirped pulse phase-sensitive OTDR was used to measure large and fast dynamic strains with SNR of > 24dB and signal smoothing and impact of error accumulation were discussed.
Abstract: It is experimentally demonstrated that a chirped pulse phase-sensitive OTDR can measure large and fast dynamic strains (~100’s of μe, ~100’s of Hz) with SNR of > 24dB. Signal smoothing and impact of error accumulation are also discussed.

4 citations

Proceedings ArticleDOI
13 May 2018
TL;DR: In this paper, it was shown that signal distortion is inherently present in dynamic fiber-optic strain sensing techniques, which use frequency scanning to determine the value of the measurand.
Abstract: It is shown, theoretically and experimentally, that signal distortion is inherently present in dynamic fiber-optic strain sensing techniques, which use frequency scanning to determine the value of the measurand. The resulting harmonic distortion and ways to reduce it are described.

1 citations

Proceedings ArticleDOI
28 Aug 2019
TL;DR: In this article, the performance of the differential pulse-width pair Brillouin optical time domain analysis (DPP-BOTDA) is evaluated experimentally using either the gain from log normalization or linear normalization for the subtraction of traces collected with pump pulses of slightly different pulse widths.
Abstract: The performance of the differential pulse-width pair Brillouin optical time domain analysis (DPP-BOTDA) is evaluated experimentally using either the gain from log normalization or linear normalization for the subtraction of traces collected with pump pulses of slightly different pulse widths. Using pump pulses widths of 43 ns and 40 ns, amplified Brillouin time domain probe traces were obtained for 10 km of standard single mode fiber. Two hotspots of length 30 cm and 6 m, separated by more than the spatial resolutions of the individual pulses and kept in a temperature controlled hot bath facility, were interrogated with temperature variations from 5 to 70°C, having probe signal gain of ~ 40% at the Brillouin Frequency Shift (BFS). This research work demonstrates, for the first time, that the use of linear gains for the subtraction step in creating the Brillouin gain spectrum, produces results for small to medium Brillouin frequency shifts (≤30 MHz), that deviate from the results of the subtraction of the logarithmic gains by as much as 2 MHz (~ 2°C), particularly for hotspots of the order of the spatial resolution of the DPP-BOTDA. For hotspots longer than the spatial resolution of the technique, the difference between results of the two processing methods show BFS deviations only at the end of the hotspots.

Cited by
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Journal ArticleDOI
TL;DR: In this paper, the principles involved in DAS system, including three types of reflectometry to locate the Rayleigh backscattering (RBS) along the fiber, and the methods to recover the vibration waveform by the phase or spectrum of RBS.
Abstract: Fiber-optic distributed acoustic sensor (DAS) is one of the most attractive and promising fiber-optic sensing technologies in the recent decade. It can simultaneously detect and retrieve multiple vibrations over a long distance, and the high sampling rate provides abundant information of the environment. This article reviews the principles involved in DAS system, including three types of reflectometry to locate the Rayleigh backscattering (RBS) along the fiber, and the methods to recover the vibration waveform by the phase or spectrum of RBS. The technologies and recent progresses on DAS systems are introduced, and two kinds of typical applications of DAS are reviewed. Finally, the possible research trends are discussed.

77 citations

Journal ArticleDOI
09 Oct 2019-Sensors
TL;DR: The principle of operation of CP-ΦOTDR is revisited, highlighting the particular performance characteristics of the technique and offering a comparison with alternative distributed sensing methods (with focus on coherent-detection-based ΦotDR).
Abstract: In 2016, a novel interrogation technique for phase-sensitive (Φ)OTDR was mathematically formalized and experimentally demonstrated, based on the use of a chirped-pulse as a probe, in an otherwise direct-detection-based standard setup: chirped-pulse (CP-)ΦOTDR. Despite its short lifetime, this methodology has now become a reference for distributed acoustic sensing (DAS) due to its valuable advantages with respect to conventional (i.e., coherent-detection or frequency sweeping-based) interrogation strategies. Presenting intrinsic immunity to fading points and using direct detection, CP-ΦOTDR presents reliable high sensitivity measurements while keeping the cost and complexity of the setup bounded. Numerous technique analyses and contributions to study/improve its performance have been recently published, leading to a solid, highly competitive and extraordinarily simple method for distributed fibre sensing. The interesting sensing features achieved in these last years CP-ΦOTDR have motivated the use of this technology in diverse applications, such as seismology or civil engineering (monitoring of pipelines, train rails, etc.). Besides, new areas of application of this distributed sensor have been explored, based on distributed chemical (refractive index) and temperature-based transducer sensors. In this review, the principle of operation of CP-ΦOTDR is revisited, highlighting the particular performance characteristics of the technique and offering a comparison with alternative distributed sensing methods (with focus on coherent-detection-based ΦOTDR). The sensor is also characterized for operation in up to 100 km with a low cost-setup, showing performances close to the attainable limits for a given set of signal parameters [≈tens-hundreds of pe/sqrt(Hz)]. The areas of application of this sensing technology employed so far are briefly outlined in order to frame the technology.

74 citations

Journal ArticleDOI
Haijun He1, Lianshan Yan1, Heng Qian1, Xinpu Zhang1, Bin Luo1, Wei Pan1 
TL;DR: An approach based on two-wavelength probe is proposed and demonstrated to improve the measurable range of the dynamic strain in Φ-OTDR, and by utilizing the difference between the two phases acquiring with two different lasers, the large dynamic strain can be recovered.
Abstract: Phase-sensitive optical time domain reflectometry (Φ-OTDR) realizes quantitative measurement of the dynamic strain employing phase demodulation. Unfortunately, it is difficult to measure the large dynamic strain with the conventional Φ-OTDR due to the restriction of the unwrapping algorithm. In this work, an approach based on two-wavelength probe is proposed and demonstrated to improve the measurable range of the dynamic strain in Φ-OTDR. By utilizing the difference between the two phases acquiring with two different lasers, the large dynamic strain can be recovered. In experiments, dynamic strains with peak values from 10.32 uɛ to 24.08 uɛ are retrieved accurately, which cannot be recovered with the conventional Φ-OTDR. Moreover, the tunable sensitivity is also demonstrated through adjusting the wavelengths of the probe. With the increment of the wavelength interval from 9.06 nm to 23.06 nm, the normalized sensitivity increases from 0.4 to 1 accordingly. That agrees well with the theoretical prediction. Foreseeably, the proposed method will extend the scope of application fields for Φ-OTDR, which requires large dynamic strain recognition.

36 citations

Journal ArticleDOI
TL;DR: In this paper, a sub-chirped-pulse extraction algorithm (SPEA) is proposed to replace the time-consuming sweeping process in conventional COTDR, and a single-shot coherent optical time domain reflectometry (SS-COTDR) for dynamic strain sensing is demonstrated with very high performance.
Abstract: Distributed optical fiber sensing, which uses telecom fiber as sensing medium, can realize high-precision temperature/strain monitoring along the fiber, making it an indispensable tool for structural health monitoring, security monitoring, seismic wave detection, etc. In this article, for the first time, a novel sub-chirped-pulse extraction algorithm (SPEA) is proposed to replace the time-consuming sweeping process in conventional COTDR, and a single-shot coherent optical time domain reflectometry (SS-COTDR) for dynamic strain sensing is demonstrated with very high performance. In order to quantitatively evaluate the maximum measurand change that can be measured per unit time, the measurement slew rate (SR) as an important parameter of COTDR has been analyzed in phase-demodultion scheme and in our scheme. As the proof-of-concept experiments, ultra-high strain sensitivities $\text{2.3 } p\varepsilon /\sqrt{\text{Hz}}$ is demonstrated in $\text{134} \text{ m}$ fiber with $\text{2} \text{ m}$ spatial resolution. Without distributed amplification, high-performance distributed strain measurements are demonstrated on $\text{75} \text{ km}$ fiber with strain sensitivity better than $\text{100} \,p\varepsilon /\sqrt{\text{Hz}}$ . In addition, this scheme is inherently immune to interference fading, which is disadvantageous for phase demodulation scheme.

35 citations

Journal ArticleDOI
TL;DR: Evaluating the statistical performance of a recently proposed DAS technique, namely, chirped-pulse ϕOTDR, in terms of sensitivity and signal-to-noise ratio (SNR), shows behavioral trends that significantly differ from those of traditional DAS.
Abstract: Distributed acoustic sensors (DAS) based on phase-sensitive optical time-domain reflectometry (ϕOTDR) have demonstrated interesting performance for many applications ranging from seismology to pipeline protection. However, the sensitivity of traditional DAS relying on coherent detection is strongly dependent on the system noise and trace fading points, offering poor reliability of the results in the spatial dimension. In this manuscript, we evaluate the statistical performance of a recently proposed DAS technique, namely, chirped-pulse ϕOTDR, in terms of sensitivity and signal-to-noise ratio (SNR). Our results show behavioral trends that significantly differ from those of traditional DAS. In particular, the acoustic SNR distribution in chirped-pulse DAS is notably narrower than that in the traditional case, allowing to ensure a large system dynamic range across all the points of the optical trace. Hence, chirped-pulse ϕOTDR offers localized perturbation detection with very high reliability, almost independent of trace fading points, along the complete reachable range of the sensor.

32 citations