Distributed transverse-force sensing along a single-mode fiber using polarization-analyzing OFDR.

We report what we believe to be the first demonstration of a direct distributed transverse-force (TF) sensing along a single-mode fiber (SMF) using a self-built polarization-analyzing optical frequency-domain reflectometry (PA-OFDR). The transverse line-force (TLF) distribution along a SMF can be directly obtained from the absolute measurement of birefringence induced by the TF via photo-elastic effect at different locations along the fiber, without the need of complicated force-to-strain conversion. We show that our system is capable of sensing a weight of merely 0.68 g but yet has a large dynamic range of over 44 dB. In particular, we obtained a maximum detectable TLF of 16.8 N/mm, a minimum detectable TLF of 6.61×10 N/mm, a TLF measurement uncertainty of <2.432%, a TF sensing spatial resolution of 3.7 mm and a TF sensing distance of 103.5 m. We also experimentally investigated the influence of different fiber coatings on the TF sensing and found that the polyimide coating is a better choice due to its high TF measurement sensitivity and response speed, although it induces relatively high residual birefringence in the SMF to limit the minimum detectable TLF. Our work is an important step forward for practical distributed TF sensing and shall prove useful for engineers and scientists to implement the PA-OFDR technology for distributed TF sensing with low cost SMFs.