Method and apparatus for optical sensing

摘要

A system for monitoring a pipeline structure, comprising a (DAS) system which includes an optical sensing fibre deployed along the structure and an interferometer arranged to receive backscattered light from along the fibre. The interferometer comprises at least two optical paths 105, 106 with a path length difference there-between. The backscattered light interferers in the interferometer to produce interference components and the DAS system further comprises a photodetector means to measure the interference components and also a processor that is arranged to determine optical phase angle data therefrom. The apparatus further comprises an acoustic source arranged to move within the pipeline structure where the DAS system measures the acoustic transmission through the pipe structure wall to track the position of the acoustic source. The interferometer may also comprise an optical coupler 104 which introduces a phase shift between the interference components. Other preferred features include: an optical-amplifier 101 amplifying the received backscattered light; an optical-filter 102 filtering out Amplified Spontaneous Emission (ASE) noise generated by the optical-amplifier. The processor may be arranged to process the optical phase angle data to identify acoustic perturbations along the fibre. The interferometer may be further arranged to receive reflected light from along the fibre.