Distributed Rayleigh scatter dynamic strain sensing above the scan rate with optical frequency domain reflectometry

Luna recently demonstrated a novel optical phase-based algorithm for removing the adverse effects of fiber motion at frequencies far above the scan rate on high-resolution measurements of Rayleigh scatter using Optical Frequency Domain Reflectometry (OFDR) for static strain and temperature measurements. By comparing dynamic OFDR Rayleigh scatter measurements to a static reference, it is possible to extract the time-varying phase signal in real time. The same algorithm, applied to successive segments along an unbonded single mode fiber, is an effective means of monitoring the spatial distribution of high frequency optical phase perturbations caused by vibration and acoustic wave propagation in the fiber. We will discuss tradeoffs between scan speed, scan duration, range, spatial resolution, vibration sensitivity and vibration frequency range, provide measurement examples, predict limiting specifications for practical system performance based on current commercial OFDR products, and compare these limits to those of distributed acoustic sensing techniques based on Optical Time Doman Reflectometry.