Multi-Pulse Parallel Demodulation for High-Precision Measurement in Raman-Distributed Optical Fiber Sensing

Raman distributed temperature sensors enables distributed measurement of temperature along the sensing fiber, which is widely used in production. Due to the limitation of the optical time-domain reflection principle, the temperature measurement accuracy of the sensors will be seriously affected when the length of the temperature variation region is shorter than the pulse width. In this work, the relationship between pulse width, fiber under test (FUT) length and FUT temperature is firstly studied. Then, a multi-pulse parallel demodulation scheme is proposed. The experiments depict that a temperature measurement accuracy is optimized from over 30 °C to 1.55 °C with a 0.2 m temperature variation region over 5.6 km. The scheme is based on multi-pulse parallel measurements combined with numerical simulations to achieve equivalent short pulse measurements of the small-region temperature variation without changing the hardware structure of the sensors. This scheme reduces the hardware requirements of the sensors and avoids the problems of sensing distance reduction and signal-to-noise ratio deterioration caused by shortening the pulse width.