Distributed Fiber Acoustic System (DAS)

A distributed fiber optic vibration and acoustic sensing system based on Rayleigh scattering phase demodulation is an advanced technology that transforms standard telecommunication fibers into highly sensitive distributed sensors. Also known as Phase-sensitive Optical Time Domain Reflectometry (φ-OTDR) or Distributed Acoustic Sensing (DAS), this system detects vibrations, acoustic waves, and strain variations with exceptional spatial and temporal resolution.

​

The fundamental principle relies on Rayleigh scattering, where coherent laser pulses interact with microscopic irregularities within the fiber core. These irregularities create a stable scattering pattern that acts as a distributed reflector array, generating continuous backscattered signals as light propagates through the fiber.

​

Phase demodulation constitutes the core sensing mechanism by analyzing interference patterns of backscattered light. External mechanical disturbances induce minute changes in the fiber's optical path length, altering the phase relationship of scattered light and creating detectable interference variations that precisely correlate to the magnitude, frequency, and spatial location of the original disturbance.