Quantitative measurement of dynamic nanostrain based on a phase-sensitive optical time domain reflectometer

TLDR

The authors propose a phase‑sensitive OTDR‑based sensing system that uses coherent detection and I/Q demodulation to quantitatively measure large‑range dynamic nanostrain in real time. The system applies precise nanostrain to fiber via a nanopositioning translation stage and extracts phase and amplitude of Rayleigh backscatter through coherent detection and I/Q demodulation. Experimental results show the system can measure nanostrain from 10 to 1000 nε with 1–2 nε resolution, determine strain‑refractive‑index parameters (8.714 mrad/(nε·m) and –0.3751 ε⁻¹), and capture dynamic signals such as a 12 Hz triangular wave of 100 nε amplitude and a 188 Hz resonant tone.

Abstract

A sensing system is proposed for quantitative measurement of large-range dynamic nanostrain based on a phase-sensitive optical time domain reflectometer, where the coherent detection and I/Q demodulation methods are employed to demodulate both the phase and the amplitude of the Rayleigh scattering light in real time. A nanopositioning translation stage is utilized to apply precise nanostrain to fiber. By measuring phase differences between two adjacent sections, the quantitative nanostrain with a large measurement range is demonstrated; this is also a method to measure the strain parameter of refractive index. For the Panda polarization-maintaining fiber under test in the experiment, the strain parameter of phase difference is measured to be 8.714 mrad/(nε·m), while the strain parameter of refractive index is measured to be -0.3751ε-1. As a proof of the concept, the dynamic strain sensing with a range of 10-1000 nε is experimentally demonstrated, and the strain resolution is 1 or 2 nε, corresponding to 5 or 2.5 m spatial resolution, respectively. The experimental measurement also shows a triangular wave with a 12-Hz vibrating frequency and a 100-nε strain amplitude as well as a 188-Hz resonant signal of the tensile section.