Transmission–Reflection Analysis in high scattering optical fibers: A comparison with single-mode optical fiber

Abstract Raman distributed optical fiber sensing has been demonstrated to be a mature and versatile scheme that presents great flexibility and effectivity for the distributed temperature measurement of a wide range of engineering applications over other established techniques. The past decades have witnessed its rapid development and extensive applicability ranging from scientific researches to industrial manufacturing. However, there are four theoretical or technical bottlenecks in traditional Raman distributed optical fiber sensing: (i) The difference in the Raman optical attenuation, a low signal-to-noise ratio (SNR) of the system and the fixed error of the Raman demodulation equation restrict the temperature measurement accuracy of the system. {ii) The sensing distance and spatial resolution cannot be reconciled. (iii) There is a contradiction between the SNR and measurement time of the system. (iv) Raman distributed optical fiber sensing cannot perform dual-parameter detection. Based on the above theoretical and technical bottlenecks, advances in performance enhancements and typical applications of Raman distributed optical fiber sensing are reviewed in this paper. Integration of this optical system technology with knowledge based, that is, demodulation technology etc. can further the performance and accuracy of these systems. 

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Physics and applications of Raman distributed optical fiber sensing

A high-sensitivity surface plasmon resonance (SPR) sensor is designed and analyzed numerically. The sensor is constructed on the eightfold U-shaped photonic quasi-crystal fiber (PQF) and coated with indium tin oxide (ITO). The coupling between the core mode and surface plasmon polariton mode is enhanced due to shortening of the distance between the core and the ITO layer, so that the PQF-SPR sensor exhibits high refractive index (RI) sensitivity in the near-infrared region. The maximum wavelength sensitivity and the corresponding resolution of this sensor are 42,000 nm/RIU and 2.38×10−6RIU, respectively. The average wavelength sensitivity is 12,750 nm/RIU in the refractive index range of 1.306–1.386. This advanced sensor is suitable for the determination of RIs in the near-infrared region.

Surface plasmon resonance sensor based on U-shaped photonic quasi-crystal fiber

We report the experimental demonstration of a reference-free Distributed Anti-Stokes Raman Thermometry (DART) scheme for real-time power line monitoring in overhead power transmission (OPGW/OPC) cables. Our work is based on the loop configuration in which only the anti-Stokes intensity is captured and processed to determine the temperature, thereby providing a self-calibrated solution that is tailor-made for a rugged field measurement. Temperature experienced by the optical fiber embedded in the power cable is estimated through a simple heat transfer model and is experimentally validated using a homebuilt DART system with a root mean square (RMS) temperature error of 0.33 °C.

Reference-Free Real-Time Power Line Monitoring Using Distributed Anti-Stokes Raman Thermometry for Smart Power Grids

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We propose and experimental demonstrate a Dynamic Threshold Identification Method (DTIM) based on the Raman distributed fiber sensor (RDFS) system for detecting the pipeline leak. The DTIM can detect the position of pipeline leak according to distributed temperature measured by the RDFS. The DTIM includes three steps, which are the space segmentation detection, $3\sigma $ criterion and identification of historical data. The experimental results show that the proposed RDFS can detect and accurately locate the leak position by using the DTIM, and the positioning accuracy is 1 m. In addition, the temperature change rate of the leak position performs a quadratic function relationship with the leak rate, and the leak rate can be estimated by this method. It provides an effective distributed monitoring method for the leak monitoring of pipeline.

Pipeline Leak Detection Using Raman Distributed Fiber Sensor With Dynamic Threshold Identification Method

A novel Rayleigh noise suppression method is proposed to improve temperature accuracy and resolution for Raman distributed fiber-optics sensors. The proposed temperature demodulation method can eliminate temperature measurement inaccuracy caused by Rayleigh noise. The experimental results indicate that the temperature accuracy is optimized from 6.2°C to 1.7°C at a sensing distance of 9.1 km by using the proposed method, and the temperature resolution leads to about 1.5°C improvement compared with the tradition demodulation method at a sensing distance of 10.0 km. The proposed method provides a robust and reliable high performance for long sensing ranges.

Temperature accuracy and resolution improvement for a Raman distributed fiber-optics sensor by using the Rayleigh noise suppression method.

In the field of temperature safety monitoring, it is important to quickly locate the position of temperature anomalies and start to alarm. The multimode fiber (MMF) has a certain temperature hysteresis effect when detecting the surrounding temperature along the sensing fiber, it deteriorates the warning-time of Raman distributed temperature sensor (R-DTS). This paper proposed and experimentally demonstrated an R-DTS with heat transfer functional model to perceive the surrounding temperature in advance. The temperature hysteresis effect of MMF cable in different temperature conditions are studied experimentally. The experimental results show that the temperature change rate of MMF and the surrounding temperature difference maintains a linear relationship after fitting. And this fitting relationship is used to perceive the surrounding temperature anomalies along the MMF for R-DTS system. The experimental results indicate that the warning-time of R-DTS can optimize from 23.4 s to 1.3 s at the temperature condition with 60 °C. It proves that this analytical model of the heat transfer function model can quickly perceive the environment temperature anomalies to avoid the temperature hysteresis effect of MMF at the difference temperature conditions. The research content can be applied in the temperature safety monitoring with high requirements for early-warning time, such as fire monitoring, power cable safety monitoring, and gas pipeline leakage detection.

R-DTS With Heat Transfer Functional Model for Perceiving the Surrounding Temperature

Solar cells can operate at a lower efficiency after a certain temperature, which is caused by a negative thermal coefficient. Therefore, the temperature prediction of photovoltaic (PV) modules is critical to accurately evaluate the efficiency of photovoltaic devices. We propose and experimentally demonstrate a Fuzzy Temperature Difference Threshold Method (FTDTM) based on Raman Distributed Temperature Sensor (RDTS) system for the detection and prediction of PV module temperature. The FTDTM consists of four steps, i.e., division of the universe, establishment of fuzzy relationships, definition of relationship matrix and calculation of predicted temperature. The experimental results show that the proposed RDTS can detect and accurately predict temperature trends by using the FTDTM. When the system window base of the FTDTM is set to 2, the average absolute error of the predicted temperature is 1.08 °C, and the fluctuation range of prediction error is ±3.7 °C. In addition, the experiment studied some factors affecting temperature distribution characteristics of PV modules, including solar radiation intensity, surface dust and inclination angle. We provide a solution for large-scale PV module temperature detection and early warning through RDTS systems with FTDTM.

Photovoltaic Panel Temperature Monitoring and Prediction by Raman Distributed Temperature Sensor With Fuzzy Temperature Difference Threshold Method

In recent years, optic-fiber sensors have been required to simultaneously measure the structure's crack and environmental temperature in the infrastructure monitoring system. We proposed and experimentally demonstrated a distributed optic-fiber sensor based on the Raman loop configuration and fiber loss characteristic for detecting the temperature and structure's crack. Among them, the Raman loop configuration with reference fiber is proposed to detect the temperature profile along the sensing fiber. It can eliminate the influence of external physical perturbation on the temperature measurement results, and do not require pre-calibration process before measurement. The temperature experimental results show that the temperature accuracy and spatial resolution can reach up to 0.28 °C and 1.2 m with the response time of 1.04 s. In addition, the information of crack is extracted by using the loss characteristics of Stokes, which is based on optical time domain reflectometry. The experiment results indicate that the fiber loss coefficient keeps a good linear variation between the crack ranges of 1.6 mm and 5.6 mm. The studies achieve the temperature and crack measurement only by one fiber.

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Yu Tao

Papers

Pipeline Leak Detection Using Raman Distributed Fiber Sensor With Dynamic Threshold Identification Method

Temperature accuracy and resolution improvement for a Raman distributed fiber-optics sensor by using the Rayleigh noise suppression method.

R-DTS With Heat Transfer Functional Model for Perceiving the Surrounding Temperature

Photovoltaic Panel Temperature Monitoring and Prediction by Raman Distributed Temperature Sensor With Fuzzy Temperature Difference Threshold Method

Temperature and Crack Measurement Using Distributed Optic-Fiber Sensor Based on Raman Loop Configuration and Fiber Loss