Low-complexity Φ-OTDR system based on phase shifting modulation technique

Phase modulation is one of the key techniques for the phase-sensitive optical time domain reflectometer (Φ-OTDR) system. This paper proposes a novel phase modulation method by utilizing the phase shifting technique based on unbalanced Michelson interferometer (MI-PST) to reduce the computation complexity of the Φ-OTDR system. One arm of the MI is winded on a piezoelectric ceramic transducer (PZT) to introduce the modulation phase. Three shifting phases in the sequence of π/2, -π/2 and 0 are generated through the PZT. The signal phase can be directly calculated according to the three light intensities modulated by the shifting phases without calling for any complicate signal processing. In the experiment of 2 km sensing range, the system can accurately detect the signal information at any vibration position along the fiber, and the obtained signal-to-noise ratio can reach 44.21 dB with the background noise of 7.94×10-3 rad/√Hz. The proposed method is simple in both hardware implementation and signal calculation which reduces the computational complexity of the Φ-OTDR system.