Multi-vibration detection by probe pulses with ergodic SOPs in a POTDR system

Polarization optical time domain reflectometers (POTDR) can detect vibration of fiber via the change of the state of polarization (SOP) of the Rayleigh backscattered light. For traditional POTDR systems, one key problem is the high misdiagnosis rate when multiple vibrations are simultaneously applied on the sensing fiber due to the random birefringence along the fiber. To solve this problem, we propose in this paper a novel implementation of the POTDR using probe pulses with ergodic SOPs. A series of vibration spectra along the fiber are obtained by sweeping the SOP of the probe pulse. The sum of these vibration spectra, which should be immune to the birefringence of the sensing fiber, is used to analyze the vibration information. Numerical simulation and experiments are carried out to analyze the performance of the proposed system when the input SOPs are traversed with uniform distribution and random distribution. Results show that the misdiagnosis rate of detecting multi-vibration with different frequencies is greatly reduced. In addition, detection of more-than-two vibrations with the same frequency based on POTDR is successfully performed for the first time to the best of our knowledge.