Submillimeter-spatial-resolution φ-OFDR strain sensor using femtosecond laser induced permanent scatters.

A φ-optical frequency domain reflectometry (OFDR) strain sensor with a submillimeter-spatial-resolution of 233 µm is demonstrated by using femtosecond laser induced permanent scatters (PSs) in a standard single-mode fiber (SMF). The PSs-inscribed SMF, i.e., strain sensor, with an interval of 233 µm exhibited a Rayleigh backscattering intensity (RBS) enhancement of 26 dB and insertion loss of 0.6 dB. A novel, to the best of our knowledge, method, i.e., PSs-assisted φ-OFDR, was proposed to demodulate the strain distribution based on the extracted phase difference of P- and S-polarized RBS signal. The maximum measurable strain was up to 1400 µε at a spatial resolution of 233 µm.