Vectorial distributed acoustic sensing based on a multicore fiber and phase-sensitive optical time-domain reflectometry

Remote vectorial vibration sensing based on locally stabilized Mach-Zehnder interferometers using multi-core fiber and optical phase-locking

We report on remote sensing of vectorial vibration based on locally stabilized Mach-Zehnder interferometers (MZIs) using commercial multi-core fiber (MCF). Hexa-MZIs with a shared common reference arm are constructed by a 7-core MCF to acquire remotely vectorial vibration. A set of corresponding local receivers consisting of optical phase-locked loops (OPLLs) for not only eliminating the impact of environmental perturbations but also maintaining the stable operation and relative stability among the MZIs, allows guaranteed stabilized remote sensing. It moreover ensures a linearized phase detection, and thus an improved sensing sensitivity and dynamic range. This way, by exploiting the symmetrically geometric distribution for the cores of 7-core MCF, the proposed all-fiber design can enable highly precise remote extraction of vibration in a vectorial manner with a simplified remote structure. We achieve vectorial remote sensing for vibrations with ∼0.1076° and ∼0.3603 µm precision for the angle and displacement, respectively, over 10 km.

Quantitative quasi-distributed vibration sensing by φ-OFDR for multiple events over spatially consecutive sensing spatial resolutions

We report on a quantitative quasi-distributed vibration sensing (DVS) system enabled by phase-sensitive optical frequency domain reflectometry (φ-OFDR), which allows for multiple vibration events over consecutive spatial resolutions. To achieve effective crosstalk suppression and mitigation of the instability during the phase extraction, fiber with embedded ultra-weak grating arrays has been adopted as the sensing fiber. It exhibits a particularly customized low spatial duty cycle, that is, high ratio between the size of the gratings and their spacing and the spacing is additionally designed to match the integer multiple of the theoretical spatial resolution. In combination with a rectified frequency-modulated continuous-wave optical probe enabled by the optical phase-locked loop, it allows to achieve quantitative quasi-DVS for multiple events over consecutive sensing spatial resolution as high as ∼2.5 cm along the distance over ∼2200 m. The ability to simultaneously retrieve arbitrary multi-point vibration events over spatially consecutive sensing spatial resolutions with consistently linear response and sensitivity up to a few nano-strain level even at long distances has shown great potentials for the application of φ-OFDR from a practical point of view.