Nonlocal Polarization Effect in Phase-Sensitive Optical Time-Domain Reflectometry

In coherent phase-sensitive optical time-domain reflectometry (Φ-OTDR) systems, polarization fading occurs when the polarization state of the optical local oscillator is orthogonal to that of the backscattered signal. While polarization diversity detection is generally deemed as a solution to address polarization fading problem, the evolving polarization state along the fiber can lead to the nonlocal polarization-related noise from external disturbances, thus affecting the subsequent Rayleigh backscattered signal. To clarify this nonlocal effect, we introduce a novel one-dimensional model extension for polarization-division multiplexing Rayleigh scattering signals, by introducing a unitary Jones matrix assigned to each scattering segment in Φ-OTDR systems. Simulation results confirm that observable rotations of the local state of polarization induce severe phase noise in the distal sensing fiber, yielding the impairment from the nonlocal polarization effect. In response, by utilizing the orthogonal polarization division multiplexed optical pulses, we establish a polarization-division-based multi-input and multi-output (MIMO) system to mitigate the nonlocal polarization-related impairments. In the simulations and experiments, the polarization-division-based MIMO system is demonstrated to be immune to the nonlocal effect, even under extreme conditions.