A review on various optical fibre sensing methods for batteries

Batteries have rapidly evolved and are widely applied in both stationary and transport applications. The safe and reliable operation is of vital importance to all types of batteries, herein an effective battery sensing system with high performance and easy implementation is critically needed. This also requires the sensing system to monitor the states of batteries in real time. Among the available methods, optical fibre sensors have shown a significant advantage due to their advanced capabilities of which include the fast measurement of multiple parameters with high sensitivity, working without interfering the battery performance, being able to be composited in multiplexed configurations and being robust to various harsh environment conditions. This paper mainly discusses the current optical fibre sensing methods for batteries in terms of the working principles and critical reviews the sensing performance corresponding to different sensing parameters. Moreover, the challenges and outlooks for future research on battery sensing are derived

Ultimate spatial resolution realisation in optical frequency domain reflectometry with equal frequency resampling

A method based on equal frequency resampling is proposed to suppress laser nonlinear frequency sweeping for the ultimate spatial resolution in optical frequency domain reflectometry. Estimation inaccuracy of the sweeping frequency distribution caused by the finite sampling rate in the auxiliary interferometer can be efficiently compensated by the equal frequency resampling method. With the sweeping range of 130 nm, a 12.1 µm spatial resolution is experimentally obtained. In addition, the sampling limitation of the auxiliary interferometer-based correction is discussed. With a 200 m optical path delay in the auxiliary interferometer, a 21.3 µm spatial resolution is realised at the 191 m fibre end. By employing the proposed resampling and a drawing tower FBG array to enhance the Rayleigh backscattering, a distributed temperature sensing over a 105 m fibre with a sensing resolution of 1 cm is achieved. The measured temperature uncertainty is limited to ±0.15 °C

High sensing accuracy realisation with millimetre/sub-millimetre resolution in optical frequency domain reflectometer

By effectively suppressing the nonlinear sweep noise and random range of wavelength sweep in the optical frequency domain reflectometer, the theoretical spatial resolution and uniform sweep distribution are delivered for high sensing accuracy. A strain accuracy of 0.51 is realised with a 5 mm sensing resolution, while the accuracy is 5.89 with a 1 mm sensing resolution. Theoretical limitation between the strain accuracy and sensing resolution is further studied for the sub-millimetre resolution sensing. It is found that signal to noise ratio and frequency bandwidth of the calculated cross-correlation are critical factors in measuring accuracy. Increasing the sweep range can provide a better spatial frequency step for a high signal to noise ratio in the cross-correlation. With a 130 nm sweep range, the measurement accuracy is limited to 19.31 with a 0.5 mm sensing resolution. Besides, for the long-distance sensing of 104m, the measurement accuracy is 8.72 with a 1 mm sensing resolution

High-resolution ϕ-OFDR using phase unwrap and nonlinearity suppression

Phase-sensitive optical frequency domain reflectometer (Φ-OFDR) is investigated to deliver an accurate distributed measurement with high spatial resolution. It is found that random phase noise and quadrant discrimination during phase calculation are the main reasons for the random hopping in Φ-OFDR. By efficiently eliminating random hopping in the phase unwrap and suppressing the laser-induced nonlinear sweep for the theoretical spatial resolution, the proposed Φ-OFDR is proved to be able to decouple the limitation between resolution and accuracy in coherent OFDR (C-OFDR). Distributed strain measurement with 20 mm spatial resolution in Φ-OFDR is obtained and analysed. Measurement with little deviation and uniform sensitivity between applied strain and phase change both validate the efficient noise suppression for extreme resolution measurement. Then the influence of the initial sweep frequency between two times measurements is studied. With a further reduced 800 µm spatial resolution, the proposed Φ-OFDR is able to retain accurate distributed measurement compared to conventional C-OFDR methods. Besides, the computation time of the Φ-OFDR is only 3.2% of the C-OFDR

High-performance fibre-based and silicon photonics-based optical frequency domain reflectometry for battery sensing

Optical fibre sensors have attracted increasing attention in battery sensing. This thesis is dedicated to the development of two outstanding distributed optical fibre sensors based on optical frequency domain reflectometry (OFDR) for batteries. The research commences with a comprehensive analysis of the OFDR system, achieved through the establishment of a function-module-based theoretical model. This model enables modular analysis, single-device verification, and systematic comparison, providing a solid theoretical foundation for the research. Especially, an innovative equal frequency resampling method is proposed in this thesis to effectively compensate for the nonlinear frequency tuning noise, significantly enhancing the performance of the OFDR system. A fibre-based OFDR, optimizing the operating parameters and implementing the equal frequency resampling method, achieves remarkable experimental results. In this thesis, an unprecedented spatial resolution of 12.1 µm is obtained, setting a world record. This spatial resolution represents the ultimate spatial resolution attainable by a fibre-based OFDR up to this point in time. Moreover, this fibre-based OFDR is employed to conduct distributed temperature and strain sensing with exceptional performance. In this thesis, the distributed temperature measurements showcase a temperature uncertainty of 0.13 °C over an 8 m measurement range and 0.15 °C over a 102 m measurement range. Similarly, distributed strain measurements exhibit a strain accuracy of 0.51 µε at a 4 m fibre end and 1.86 µε at a 104 m fibre end, with an effective sensing spatial resolution of 5 mm. Additionally, a strain accuracy of 19.31 µε is achieved with an effective sensing spatial resolution of 0.5 mm. Furthermore, a real on-chip OFDR based on Rayleigh backscattering is proposed and demonstrated for the first time. In this thesis, an integrated OFDR utilizing silicon photonics technology is fabricated on a Silicon-on-Insulator (SOI) platform, replacing the fibre-based main interferometer module and auxiliary interferometer module with the on-chip photonic circuits. A distributed refractive index measurement confirms the potential and effectiveness of the silicon photonics-based OFDR, achieving an impressive experimental spatial resolution of 8.28 µm which is reaching its theoretical level. Both the fibre-based OFDR and the silicon photonics-based OFDR demonstrate exceptional sensing performance, fulfilling the requirements for battery sensing. The outcomes of this thesis contribute to the advancement of battery sensing and pave the way for the development of smart batteries

Dataset to support the article "High-resolution 𝜙-OFDR using phase unwrap and nonlinearity suppression"

This dataset is used for realizing high resolution of phase-sensitive Optical Frequency Domain Reflectometer. It is associated with the research paper: Guo Z, Yan J, Han G, Yu Y, Greenwood D and Marco J (2023) &quot;High-Resolution &phi;-OFDR Using Phase Unwrap and Nonlinearity Suppression&quot;. Journal of Lightwave Technology, 41 (9), 2885-2891. (https://doi.org/10.1109/JLT.2023.3236775). The data is presented as an excel file: High_resolution_OFDR_using_phase_unwrap_and_nonlinearity_suppression.xlsx This work was funded by High Value Manufacturing Catapult and the Engineer and Physical Sciences Research Council - EPSRC EP/V000624/1. The author Gaoce Han would like to acknowledge the China Scholarship Council for sponsoring.</span

Dataset to support the article &quot;High Sensing Accuracy Realisation with Millimetre/sub-Millimetre Resolution in Optical Frequency Domain Reflectometer&quot;

This dataset is used for realizing high sensing accuracy and sub-millimetre resolution of Optical Frequency Domain Reflectometer. It is associated with the research paper &quot;High Sensing Accuracy Realisation with Millimetre sub-Millimetre Resolution in Optical Frequency Domain Reflectometer&quot; in Journal: Journal of Lightwave Technology. This work was funded by High Value Manufacturing Catapult, grant reference, 160080 CORE (WMG), titled &lsquo;Smart Sensing for Future Batteries&rsquo; and the EPSRC (Engineering and Physical Sciences Research Council), grant reference EP/R004927/1, titled &lsquo;Prosperity Partnership&rsquo;. The author Gaoce Han would like to acknowledge the China Scholarship Council for sponsoring.</span

Dataset supporting the University of Southampton Doctoral Thesis &quot;High-performance Fibre-based and Silicon Photonics-based Optical Frequency Domain Reflectometry for Battery Sensing&quot;

This dataset contains: both simulation and experimental results pertinent to the thesis. The dataset is accessible through Microsoft Excel or other similar software for comprehensive review. The data is presented as: Dataset_for_High-performance_Fibre-based_and_Silicon_Photonics-based_Optical_Frequency_Domain_Reflectometry_for_Battery_Sensing.xlsx</span

Integrated silicon photonics OFDR system for high-resolution distributed measurements based on Rayleigh backscattering

Optical frequency domain reflectometry (OFDR) has high spatial resolution and measurement accuracy, driving its popularity in various fields. Integration of OFDR technology has made it accessible, cost-effective and deployable in many applications, including battery management and photonic integrated circuits. An integrated OFDR system based on Rayleigh backscattering and silicon photonics technology on an SOI platform has been developed for the first time. The system's simplified configuration was simulated, fabricated and characterized in detail, achieving an experimental spatial resolution of 8.28 μm, matching the theoretical level. This system shows high potential for sensing, monitoring and detection where precise spatial information is crucial. OFDR's accessibility and high performance in distributed measurements make it a promising technology for future advancements

High sensing accuracy realisation with millimetre/sub-millimetre resolution in optical frequency domain reflectometer

By effectively suppressing the nonlinear sweep noise and random range of wavelength sweep in the optical frequency domain reflectometer, the theoretical spatial resolution and uniform sweep distribution are delivered for high sensing accuracy. A strain accuracy of ±0.51 με is realised with a 5 mm sensing resolution, while the accuracy is ±5.89 με with a 1 mm sensing resolution. Theoretical limitation between the strain accuracy and sensing resolution is further studied for the sub-millimetre resolution sensing. It is found that signal to noise ratio and frequency bandwidth of the calculated cross-correlation are critical factors in measuring accuracy. Increasing the sweep range can provide a better spatial frequency step for a high signal to noise ratio in the cross-correlation. With a 130 nm sweep range, the measurement accuracy is limited to ±19.31 με with a 0.5 mm sensing resolution. Besides, for the long-distance sensing of 104m, the measurement accuracy is ±8.72 με with a 1 mm sensing resolutio