Boosting the spatial resolution in chirped pulse phi-OTDR using sub-band processing

Chirped pulse phase-sensitive optical time-domain reflectometry (chirped pulse phi-OTDR) allows the interrogation of tens of kilometers of optical fiber with high sensitivity and linearity, but typically with spatial resolution limited to ten meters to ensure proper processing and signal-to-noise ratio (SNR). In this paper, we propose a method to increase the spatial resolution of a chirped pulse phi-OTDR without reducing the pulse width. The improvement is achieved by adding an optical carrier to the input chirped pulse and by applying digital filtering to the measured backscatter traces. Experimental results validate the method, demonstrating a 10-fold resolution improvement with minimum impact on the measurement SNR.