Review and Analysis of Peak Tracking Techniques for Fiber Bragg Grating Sensors

Fiber Bragg Grating (FBG) sensors are among the most popular elements for fiber optic sensor networks used for the direct measurement of temperature and strain. Modern FBG interrogation setups measure the FBG spectrum in real-time, and determine the shift of the Bragg wavelength of the FBG in order to estimate the physical parameters. The problem of determining the peak wavelength of the FBG from a spectral measurement limited in resolution and noise, is referred as the peak-tracking problem. In this work, the several peak-tracking approaches are reviewed and classified, outlining their algorithmic implementations: the methods based on direct estimation, interpolation, correlation, resampling, transforms, and optimization are discussed in all their proposed implementations. Then, a simulation based on coupled-mode theory compares the performance of the main peak-tracking methods, in terms of accuracy and signal to noise ratio resilience

Monitoring temperature and vibration in a long weak grating array with short-pulse generation using a compact gain-switching laser diode module

© 2019 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited.[EN] Quasi-distributed temperature sensing and single point vibration sensing were performed. Ultrashort pulses generated by a gain-switching laser were used to interrogate a fiber Bragg gratings (FBG) array sensor. Temperature changes were measured down to 1 degrees C with sub-centimeter spatial resolution. The advantages of our fast interrogation setup were exploited, as the higher frequency limit of a dynamic measure that can be sensed is limited by the time needed to generate the optical pulse and to acquire the data from the sensor. The experimental approach described in this paper can sense mechanical vibrations up to a frequency of 245 kHz and a strain resolution as low as 1.2 mu epsilon.H2020 Marie Sklodowska-Curie Actions (MSCA-ITN-ETN-722509); Ministerio de Economia y Competitividad (DIMENSION TEC2017 88029-R); Generalitat Valenciana (PROMETEO 2017/103).Sartiano, D.; Sales Maicas, S. (2019). Monitoring temperature and vibration in a long weak grating array with short-pulse generation using a compact gain-switching laser diode module. Optics Express. 27(26):38661-38669. https://doi.org/10.1364/OE.379106S38661386692726Tosi, D. (2017). Review and Analysis of Peak Tracking Techniques for Fiber Bragg Grating Sensors. Sensors, 17(10), 2368. doi:10.3390/s17102368Mihailov, S. J. (2012). Fiber Bragg Grating Sensors for Harsh Environments. Sensors, 12(2), 1898-1918. doi:10.3390/s120201898Chan, P. K. C., Jin, W., Gong, J. M., & Demokan, N. S. (1999). Multiplexing of fiber Bragg grating sensors using a FMCW technique. IEEE Photonics Technology Letters, 11(11), 1470-1472. doi:10.1109/68.803082Pastor-Graells, J., Martins, H. F., Garcia-Ruiz, A., Martin-Lopez, S., & Gonzalez-Herraez, M. (2016). Single-shot distributed temperature and strain tracking using direct detection phase-sensitive OTDR with chirped pulses. Optics Express, 24(12), 13121. doi:10.1364/oe.24.013121Martins, H. F., Martin-Lopez, S., Corredera, P., Filograno, M. L., Frazao, O., & Gonzalez-Herraez, M. (2013). Coherent Noise Reduction in High Visibility Phase-Sensitive Optical Time Domain Reflectometer for Distributed Sensing of Ultrasonic Waves. Journal of Lightwave Technology, 31(23), 3631-3637. doi:10.1109/jlt.2013.2286223Ou, Y., Zhou, C., Qian, L., Fan, D., Cheng, C., & Guo, H. (2015). Large-capacity multiplexing of near-identical weak fiber Bragg gratings using frequency-shifted interferometry. Optics Express, 23(24), 31484. doi:10.1364/oe.23.031484Hervas, J., Barrera, D., Madrigal, J., & Sales, S. (2018). Microwave Photonics Filtering Interrogation Technique Under Coherent Regime For Hot Spot Detection on a Weak FBGs Array. Journal of Lightwave Technology, 36(4), 1039-1045. doi:10.1109/jlt.2018.2793161Ricchiuti, A. L., Hervás, J., & Sales, S. (2016). [INVITED] Cascade FBGs distributed sensors interrogation using microwave photonics filtering techniques. Optics & Laser Technology, 77, 144-150. doi:10.1016/j.optlastec.2015.09.003Nonaka, K., Mizuno, H., Song, H., Kitaoka, N., & Otani, A. (2008). Low-Time-Jitter Short-Pulse Generator Using Compact Gain-Switching Laser Diode Module With Optical Feedback Fiber Line. Japanese Journal of Applied Physics, 47(8), 6754-6756. doi:10.1143/jjap.47.6754Cusano, A., Cutolo, A., Nasser, J., Giordano, M., & Calabrò, A. (2004). Dynamic strain measurements by fibre Bragg grating sensor. Sensors and Actuators A: Physical, 110(1-3), 276-281. doi:10.1016/j.sna.2003.10.031Takahashi, N., Yoshimura, K., & Takahashi, S. (2001). Fiber Bragg Grating Vibration Sensor Using Incoherent Light. Japanese Journal of Applied Physics, 40(Part 1, No. 5B), 3632-3636. doi:10.1143/jjap.40.3632Tsuda, H. (2010). Fiber Bragg grating vibration-sensing system, insensitive to Bragg wavelength and employing fiber ring laser. Optics Letters, 35(14), 2349. doi:10.1364/ol.35.002349Lau, K. Y. (1988). Gain switching of semiconductor injection lasers. Applied Physics Letters, 52(4), 257-259. doi:10.1063/1.9948

Temperature profiling of ex-vivo organs during ferromagnetic nanoparticles-enhanced radiofrequency ablation by fiber Bragg grating arrays

In this paper, we present real-time profiles of temperature during a ferromagnetic nanoparticles (NPs)enhanced radiofrequency ablation (RFA). A minimally invasive RFA setup has been prepared and applied ex vivo on a liver phantom; NPs (with concentration of 5 mg/mL) have been synthetized and injected within the tissue prior to perform the ablation, in order to facilitate the heat distribution to the peripheral sides of the ablated tissue. Temperature detection has been realized in situ with a network of 15 fiber Bragg grating (FBG) sensors in order to highlight the impact of the NPs on the RFA mechanism. Obtained temperature profiles and thermal maps confirm that nanoparticles injection ensures better heat penetration than in case of pristine RFA procedure. The results show that adding NPs solution leads to extending the successfully ablated area achieving a double-sized lesion

Multicore optical fiber shape sensors suitable for use under gamma radiation

© 2019 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited.[EN] We have designed and implemented a fiber optic shape sensor for high-energy ionizing environments based on multicore optical fibers. We inscribed two fiber Bragg gratings arrays in a seven-core optical fiber. One of the arrays has been inscribed in a hydrogen-loaded fiber and the other one in an unloaded fiber in order to have two samples with very different radiation sensitivity. The two samples were coiled in a metallic circular structure and were exposed to gamma radiation. We have analyzed the permanent radiation effects. The radiation-induced Bragg wavelength shift (RI-BWS) in the hydrogen-loaded fiber is near ten times higher than the one observed for the unloaded fiber, with a maximum wavelength shift of 415 pm. However, the use of the multiple cores permits to make these sensors immune to RI-BWS obtaining a similar curvature error in both samples of approximately 1 cm without modifying the composition of the fiber, pre-irradiation or thermal treatment.Ministerio de Economia y Competitividad (DIMENSION TEC2017 88029- R); Generalitat Valenciana (IDI/FEDER/2018, PROMETEO 2017/103); H2020 Marie Sklodowska-Curie Actions (MSCA-ITN-ETN-722509); Universitat Politecnica de Valencia (PAID-01-18); Ministerio de Ciencia, Innovacion y Universidades (IJCI-2017-32476).Barrera, D.; Madrigal-Madrigal, J.; Delepine-Lesoille, S.; Sales Maicas, S. (2019). Multicore optical fiber shape sensors suitable for use under gamma radiation. Optics Express. 27(20):29026-29033. https://doi.org/10.1364/OE.27.029026S2902629033272

Refractive Index and Temperature Sensing Using Inter-Core Crosstalk in Multicore Fibers

[EN] Multicore optical fibers are of great interest in the optical sensing field. Their core diversity and spatial distribution enable the development of sensing mechanisms that are not possible in single-core fibers. In this paper, we study the use of the inter-core crosstalk phenomena for the implementation of a surrounding refractive index (SRI) sensor. The selective inscription of a tilted fiber Bragg grating (TFBG) intentionally increases the inter-core crosstalk between the inscribed cores and makes it sensitive to the SRI. With this technique we simplify the measurement of the SRI and improve the identification and tracking of the excited cladding modes, as compared with the analysis of the transmission spectrum of a TFBG in single-core fibers. The proposed device is also sensitive to temperature. Temperature is obtained from the crosstalk wavelength shift with a measured sensitivity of 9.75 pm/degrees C. The SRI is obtained from the measurement of the crosstalk optical power. For increasing SRIs the cladding modes gradually fade, reducing the crosstalk optical power. We observed that the higher the tilt, the higher the sensor sensitivity. For a 7 degrees TFBG the SRI sensitivity obtained is -74.2 dB/RIU from 1.31 to 1.39 and -250.8 dB/RIU from 1.39 to 1.44.This work was supported in part by the Spanish Ministry of Economy and Competitiveness under the DIMENSION TEC2017 88029-R Project and in part by the Generalitat Valenciana by PROMETEO 2017/103 research excellency award and IDI/FEDER/2018 GVA Infraestructura. The work of J. Madrigal was supported by Universitat Politecnica de Valencia scholarship PAID-01-18. The work of D. Barrera was supported by Spanish MICINN fellowship IJCI-2017-32476.Madrigal-Madrigal, J.; Barrera Vilar, D.; Sales Maicas, S. (2019). Refractive Index and Temperature Sensing Using Inter-Core Crosstalk in Multicore Fibers. Journal of Lightwave Technology. 37(18):4703-4709. https://doi.org/10.1109/JLT.2019.2917629S47034709371

The study of internal structure of woven glass and carbon fiber reinforced composite materials with embedded fiber-optic sensors

In this work, samples from composite materials with embedded optical fibers are investigated. It is known that for unidirectional layered composite materials, under certain conditions, a distortion of the internal structure and the formation of such technological defect as resin pocket in the region of the embedded optical fiber occur. So it is important to evaluate the change in the internal structure for other types of reinforcement, in particular, woven reinforcement. Analysis of the internal structure of the studied materials with 2´2 twill weave style was carried out using a digital microscope. In addition, the reflected optical signal from the Bragg gratings after being embedded into the composite material is analyzed

Coupled-core fiber Bragg gratings for low-cost sensing

[EN] Sensors based on Bragg gratings inscribed in conventional single mode fibers are expensive due to the need of a sophisticated, but low-speed, interrogation system. As an alternative to overcome this issue, in this work, it is proposed and demonstrated the use of coupled-core optical fiber Bragg gratings. It was found that the relative reflectivity from such gratings changed when the coupled-core fiber was subjected to point or periodic bending. This feature makes the interrogation of such gratings simple, fast, and cost-effective. The reflectivity changes of the gratings are attributed to the properties of the supermodes supported by the coupled-core fiber. As potential applications of the referred gratings, intensity-modulated vector bending and vibration sensing are demonstrated. We believe that the results reported here can pave the way to the development of many inexpensive sensors. Besides, coupled-core fiber Bragg gratings may expand the use of grating technology in other areas.This work is part of the Projects No. PGC2018-101997-B-I00 and RTI2018-094669-B-C31 funded by the MCIN/AEI/10.13039/501100011033/and FEDER, Una manera de hacer Europa; and the scholarship PAID-01-18 Granted by the Universitat Politecnica de Valencia

Fiber Optic Refractive Index Distributed Multi-Sensors by Scattering-Level Multiplexing With MgO Nanoparticle-Doped Fibers

© 2020 IEEE. Personal use of this material is permitted. Permissíon from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] In this work, we present the architecture of a multiplexed refractive index (RI) sensing system based on the interrogation of Rayleigh backscattering. The RI sensors are fabricated by fiber wet-etching of a high-scattering MgO nanoparticle-doped fiber, without the need for a reflector or plasmonic element. Interrogation is performed by means of optical backscatter reflectometry(OBR), which allows a detection with a millimeter-level spatial resolution. Multiplexing consists of a simultaneous scan of multiple fibers, achieved by means of scattering-level multiplexing (SLMux) concept, which uses the backscattered power level in each location as a diversity element. The sensors fabricated have sensitivity in the order of 0.473-0.568 nm/RIU (in one sensing point) and have been simultaneously detected together with a distributed temperature sensing element for multi-parameter measurement. An experimental setup has been prepared to demonstrate the capability of each sensing region to operate without cross-talk, while operating multi-fiber detection.This work was supported in part by the ORAU Programme at Nazarbayev University (LIFESTART and FOSTHER Grants), in part by the Agence Nationale de la Recherche (ANR) Project NanoSlim under Grant ANR-17-17-CE08-0002, in part by the National Natural Science Foundation for Excellent Youth Foundation of China under Grant 61722505, in part by the Key Program of Guangdong Natural Science Foundation under Grant 2018B030311006, and in part by The Spanish Ministry of Economy and Competitiveness under Grant DIMENSION TEC2017 88029-R. The associate editor coordinating the review of this article and approving it for publication was Prof. Marco Petrovich.Ayupova, T.; Shaimerdenova, M.; Korganbayev, S.; Sypabekova, M.; Bekmurzayeva, A.; Blanc, W.; Sales Maicas, S.... (2020). Fiber Optic Refractive Index Distributed Multi-Sensors by Scattering-Level Multiplexing With MgO Nanoparticle-Doped Fibers. IEEE Sensors Journal. 20(5):2504-2510. https://doi.org/10.1109/JSEN.2019.2953231S2504251020

Accurate Peak Detection for Optical Sensing with Reduced Sampling Rate and Calculation Complexity

Fiber Bragg gratings (FBGs) are widely applied in optical sensing systems due to their advantages including being simple to use, high sensitivity, and having great potential for integration into optical communication systems. A common method used for FBG sensing systems is wavelength interrogation. The performance of interrogation based sensing systems is significantly determined by the accuracy of the wavelength peak detection processing. Direct maximum value readout (DMVR) is the simplest peak detection method. However, the detection accuracy of DMVR is sensitive to noise and the sampling resolution. Many modified peak detection methods, such as filtering and curve fitting schemes, have been studied in recent decades. Though these methods are less sensitive to noise and have better sensing accuracy at lower sampling resolutions, they also confer increased processing complexity. As massive sensors may be deployed for applications such as the Internet of things (IoT) and artificial intelligence (AI), lower levels of processing complexity are required. In this paper, an efficient scheme applying a three-point peak detection estimator is proposed and studied, which shows a performance that is close to the curve fitting methods along with reduced complexity. A proof-of-concept experiment for temperature sensing is performed. 34% accuracy improvement compared to the DMVR is demonstrated

Single-peak fiber Bragg gratings in suspended-core optical fibers

Femtosecond laser inscribed fiber Bragg gratings in pure-silica suspended-core optical fibers have previously been demonstrated as a promising platform for high temperature sensing. However, the density of gratings that could be written on a single fiber was limited by undesired reflections associated with higher order modes in these high numerical aperture fibers. This resulted in a complex, broadband reflection spectrum with limited multiplexing capability. In this work we utilize modifications to the fine structure of the suspended core optical fibers to fine tune the relative confinement loss of the optical fiber modes, thus reducing the contribution from such higher order modes. The effects of these changes on mode propagation are modeled, giving a range of fibers with different confinement loss properties which can be tailored to the specific length scale of a desired application. We achieve single-peak reflections from individual fiber Bragg gratings, significantly improving performance for multipoint sensing and demonstrate this technique by writing 20 gratings onto a single fiber.Erik P. Schartner, Stephen C. Warren-Smith, Linh V. Nguyen, Dale Otten, Zheng Yu, David G. Lancaster and Heike Ebendorff-Heideprie