Long Range Static and Dynamic Strain Measurement by Using Phase-Noise-Compensated OFDR

We present long-range strain measurements using phase-noise-compensated optical frequency domain reflectometry (PNC-OFDR) over 1.5 km with a strain range of 1000 μϵ. In conventional OFDR, the observed Rayleigh scattering spectral correlation cannot be maintained over the coherence length of the laser. The use of PNC-OFDR extends this correlation distance by a factor of 100 or more, confirming high Rayleigh correlation over the entire 1.5 km section. As a result, we achieved strain measurements of up to 1000 μϵ at the end of the fiber under test (FUT), with a spatial resolution of 10 cm. In addition, we develop a scheme to observe fast dynamic strain by decomposing the Rayleigh scattering spectrum into sub-bands. Thanks to a newly proposed statistical processing technique, such a scheme eliminates the need for prior measurement of the reference spectrum in a stationary state. With our scheme, we observed dynamic strain up to 200 Hz at a measurement distance over 200 m. Such a result greatly surpasses the conventional dynamic strain measurement by OFDR.