High Spatial Resolution Raman Distributed Optical Fiber Sensing Using Self-Pulse Time-Domain Delay Differential Demodulation

A primary problem in Raman distributed optical fiber sensing is balancing the sensing distance and spatial resolution. Owing to the optical time-domain reflection (OTDR) positioning principle and pulse-broadening effects, the sensing spatial resolution of existing schemes working at kilometer-level distances is limited to the order of meters. In this work, a self-pulse time-domain delay differential demodulation for Raman distributed optical fiber sensing was proposed and demonstrated experimentally. The Raman anti-Stokes scattering signal is first delay differentially reconstructed such that its intensity is related to the intensity difference between the first and last discrete sub-pulses, rather than being modulated by the light intensity within the entire pulse. The proposed scheme changes the physics-imposed of traditional spatial resolution which is determined by the pulse width. The sensing spatial resolution of the proposed demodulation scheme is theoretically determined by a systematic sampling rate and bandwidth. Its sensing spatial resolution is optimized to 0.3 m under the modulation of a 10 ns pulse width over a sensing distance of more than 3.0 km. Moreover, it also maintains a 0.08 $^{\circ }$C temperature accuracy. This scheme provides a novel approach for most distributed optical fiber sensing based on the OTDR positioning principle.