Bending-Loss-Resistant Brillouin Optical Time-Domain Analysis Based on Thin-Diameter Fiber

Bending-induced optical loss will shorten the sensing performance of distributed optical fiber sensors. In some extreme conditions, a sharp bend will cause the sensing signal to vanish along the whole sensing fiber in a two-end-access distributed optical fiber sensor, such as Brillouin optical time-domain analysis. In this letter, a bending-loss-resistant distributed Brillouin time-domain sensor based on thin-diameter fiber with a depressed index profile region near the fiber core is proposed. The thin-diameter fiber of 60 (Y60) and
$80~\mu $
m (Y80) were compared with the standard single-mode fiber and the one without the depressed region, in terms of bending-induced optical loss. Results show that Y60 displays neglectable optical loss even when the bending radius is reduced to 1 mm, which demonstrates that distributed fiber sensing can be conducted with this kind of fiber. To the best of our knowledge, this is the highest value that the distributed fiber sensing can withstand. Moreover, the proposed thin-diameter fiber has the advantages of low transmitted loss, low cost, and simple structure, which shows the potential application for distributed measurement of temperature and strain in compact structures, such as batteries, gyroscopes, and shape sensing of smart structures.