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

Performance analysis of peak tracking techniques for fiber Bragg grating interrogation systems

In this paper, we propose a spectral correlation-based technique for tracking the wavelength shift of a fiber Bragg grating. We compared this approach, by means of a Monte Carlo numerical simulation, to the typical peak tracking techniques applied in classic interrogation systems. As result, we obtained a considerable gain in terms of noise tolerance (about 20 dB), which can be further incremented by selecting large-bandwidth gratings. This permits to increase the power budget of a fiber Bragg grating interrogator without changing the optical layout, overcoming classical limitations of commercial and custom systems. Penalties due to the non-idealities have been evaluated through the same Monte Carlo approach. Finally, we discuss a practical application of the peak tracking techniques to a fiber Bragg grating-based weight sensor, in which we applied the spectral correlation to track both the Bragg wavelength position, spectral deformations due to high strain, and spectral non-linearity

Performance analysis of peak tracking techniques for fiber Bragg grating interrogation systems

In this paper, we propose a spectral correlation-based technique for tracking the wavelength shift of a fiber Bragg grating. We compared this approach, by means of a Monte Carlo numerical simulation, to the typical peak tracking techniques applied in classic interrogation systems. As result, we obtained a considerable gain in terms of noise tolerance (about 20 dB), which can be further incremented by selecting large-bandwidth gratings. This permits to increase the power budget of a fiber Bragg grating interrogator without changing the optical layout, overcoming classical limitations of commercial and custom systems. Penalties due to the non-idealities have been evaluated through the same Monte Carlo approach. Finally, we discuss a practical application of the peak tracking techniques to a fiber Bragg grating-based weight sensor, in which we applied the spectral correlation to track both the Bragg wavelength position, spectral deformations due to high strain, and spectral non-linearity

Efficient large-scale multiplexing of fiber Bragg grating and fiber Fabry-Perot sensors for structural health monitoring applications

Fiber Bragg gratings have been demonstrated as a versatile sensor for structural health monitoring. We present an efficient and cost effective multiplexing method for fiber Bragg grating and fiber Fabry-Perot sensors based on a broadband mode-locked fiber laser source and interferometric interrogation. The broadband, pulsed laser source permits time and wavelength division multiplexing to be employed to achieve very high sensor counts. Interferometric interrogation also permits high strain resolutions over large frequency ranges to be achieved. The proposed system has the capability to interrogate several hundred fiber Bragg gratings or fiber Fabry-Perot sensors on a single fiber, whilst achieving sub-microstrain resolution over bandwidths greater than 100 kHz. Strain resolutions of 30n epsilon/Hz(1/2) and 2 n epsilon/Hz(1/2) are demonstrated with the fiber Bragg grating and fiber Fabry-Perot sensor respectively. The fiber Fabry-Perot sensor provides an increase in the strain resolution over the fiber Bragg grating sensor of greater than a factor of 10. The fiber Bragg gratings are low reflectivity and could be fabricated during the fiber draw process providing a cost effective method for array fabrication. This system would find applications in several health monitoring applications where large sensor counts are necessary, in particular acoustic emission

Advanced Interrogation of Fiber-Optic Bragg Grating and Fabry-Perot Sensors with KLT Analysis

The Karhunen-Loeve Transform (KLT) is applied to accurate detection of optical fiber sensors in the spectral domain. By processing an optical spectrum, although coarsely sampled, through the KLT, and subsequently processing the obtained eigenvalues, it is possible to decode a plurality of optical sensor results. The KLT returns higher accuracy than other demodulation techniques, despite coarse sampling, and exhibits higher resilience to noise. Three case studies of KLT-based processing are presented, representing most of the current challenges in optical fiber sensing: (1) demodulation of individual sensors, such as Fiber Bragg Gratings (FBGs) and Fabry-Perot Interferometers (FPIs); (2) demodulation of dual (FBG/FPI) sensors; (3) application of reverse KLT to isolate different sensors operating on the same spectrum. A simulative outline is provided to demonstrate the KLT operation and estimate performance; a brief experimental section is also provided to validate accurate FBG and FPI decoding

Polarization-resolved sensing with tilted fiber Bragg gratings: theory and limits of detection

Polarization based sensing with tilted fiber Bragg grating (TFBG) sensors is analysed theoretically by two alternative approaches. The first method is based on tracking the grating transmission for two orthogonal states of linear polarized light that are extracted from the measured Jones matrix or Stokes vectors of the TFBG transmission spectra. The second method is based on the measurements along the system principle axes and polarization dependent loss (PDL) parameter, also calculated from measured data. It is shown that the frequent crossing of the Jones matrix eigenvalues as a function of wavelength leads to a non-physical interchange of the calculated principal axes; a method to remove this unwanted mathematical artefact and to restore the order of the system eigenvalues and the corresponding principal axes is provided. A comparison of the two approaches reveals that the PDL method provides a smaller standard deviation and therefore lower limit of detection in refractometric sensing. Furthermore, the polarization analysis of the measured spectra allows for the identification of the principal states of polarization of the sensor system and consequentially for the calculation of the transmission spectrum for any incident polarization state. The stability of the orientation of the system principal axes is also investigated as a function of wavelength