Quantitative amplitude measuring φ-OTDR using multiple uncorrelated Rayleigh backscattering realizations.

We propose and demonstrate a technique to perform quantitative strain sensing using the amplitude of the Rayleigh backscattered light in a modified φ-OTDR system. While standard amplitude measuring φ-OTDR sensors can identify the presence of strain, they cannot perform quantitative measurements because the amplitude of the Rayleigh backscattered light exhibits a non-linear and unpredictable strain response. Here, we demonstrate a technique to computationally recover a linear strain response from a set of uncorrelated Rayleigh backscattering measurements. Using a combination of frequency and polarization multiplexing, we constructed a φ-OTDR system capable of recording 18 uncorrelated Rayleigh backscattering measurements in parallel. By combining information from these 18 measurements, the sensor achieves a linear strain response with total harmonic distortion below -35 dB. The sensor is immune to signal fading, has a minimum detectable strain of 5 pɛ/√Hz and a bandwidth of 500 kHz.