Multi-parameter measurement: distributed optical fiber sensing technology with multi-mechanism fusion

IoT technology has been a hot topic in recent years. In the IoT network architecture, the lowest perception layer is composed of a variety of sensors, which are mainly responsible for external information collection. Compared with traditional electrical sensors, fiber optic sensors have their irreplaceable advantages. Optical fiber sensor is small in size, anti-electromagnetic interference, long life, not easy to enter water and be corroded; Low cost, simple wiring, and extremely low loss, so it supports long-distance, large-scale sensing; Light has high sensitivity and large dynamic range for measuring changes in the environment in which the fiber is located. Therefore, optical fiber sensors have been widely used in many fields such as aerospace, biosensing, power grid, building monitoring, etc.

The distributed optical fiber sensor is based on the backscatter effect and distributed positioning technology in the optical fiber to realize fully distributed sensing along the optical fiber to be measured. Existing systems generally measure only a certain parameter of the environment in which the fiber is located. In the application of multi-aspect simultaneous monitoring of the monitoring object of optical fiber sensing, multiple independent optical fiber sensing systems need to be erected. Obviously, this increases the complexity and cost of the project.

In order to solve this problem, the team of Fan Xinyu and He Zuyuan of Shanghai Jiao Tong University and the team of Yan Lianshan, Southwest Jiaotong University proposed a distributed optical fiber sensing technology with multi-mechanism fusion.

This technology combines multiple sensing mechanisms in a distributed optical fiber sensing system to realize the simultaneous measurement of multiple parameters. This method greatly improves the multi-parameter measurement efficiency of the structure to be measured, reduces the system application cost, and is convenient for laying and installation. Compared with the multi-parameter measurement system that uses special optical fiber and discrete optical fiber sensing element for sensing, the distributed sensing system with multi-mechanism fusion can realize multi-parameter measurement based on ordinary single-mode optical fiber for communication, which greatly reduces the cost of the sensor.

The results were published in Light: Advanced Manufacturing under the title “Single-end hybrid Rayleigh Brillouin and Raman distributed fibre-optic sensing system.”

The team designed a distributed sensing system that combines Rayleigh scattering, stimulated Brillouin scattering, and spontaneous Raman scattering phenomena on the same sensing fiber to simultaneously sense and quantitatively measure vibration, temperature, and strain along the fiber. The system drives two adjacent optical pulses into the fiber in a single probe, uses the Rayleigh scattered light of the previous pulse to achieve vibration measurement, and simultaneously forms the detection light and pump pulse of the temperature/strain measurement system with the latter pulse, and stimulated Brillouin scattering occurs. Combined with pulse coding to adjust the time interval between the two pulses, the spontaneous Raman scattered light of the two pulses is distinguished in the time domain for temperature measurement, which solves the problem of cross-sensitivity of temperature strain in stimulated Brillouin scattering sensing.

Instead of a simple patchwork of three measurement systems, this system uses the same light source and simultaneously senses vibration, temperature, and strain by receiving only one pulse of Rayleigh scattered light, and temperature sensing by receiving Raman scattered light. This technology realizes simultaneous measurement of multiple parameters with a streamlined system, improves the measurement feedback speed, reduces the complexity of the system by single-ended measurement method, and realizes the measurement indicators of positioning accuracy less than 10 meters, vibration noise floor 10pε/√Hz, Brillouin frequency shift measurement accuracy of 0.58MHz, and temperature measurement accuracy of 0.5°C at a measurement distance of 9 km, realizing the complete separation of strain temperature parameters.

The distributed optical fiber sensing system with multi-mechanism integration expands the application scenarios of distributed optical fiber sensing, thanks to its great sensing scale and excellent sensing performance, and the system cost is much lower than that of traditional sensor networks. (Source: Advanced Manufacturing WeChat public account)

Figure 1: Schematic diagram of a distributed optical fiber sensing system with multi-mechanism fusion

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