Bending-loss-resistant distributed Brillouin curvature sensor based on an erbium-doped few-mode fiber.

We developed a bending-loss-resistant distributed Brillouin curvature sensor based on an erbium-doped few-mode fiber (Er-FMF) and differential pulse-width pair Brillouin optical time-domain analysis. With Er ion amplification compensating for bending-induced optical loss, radii in the ∼0.3 to 2.02 cm range could be monitored correctly. The corresponding Brillouin frequency shift variations were in the range of 91.7 to 9 MHz, which agrees well with theoretical calculations. The sensitivity of the Er-FMF device increased inversely with the bending radius, with the optimal sensitivity of 292.7 MHz/cm obtained at a radius of 0.3 cm. To the best of our knowledge, this is the smallest radius of curvature detected and highest sensitivity reported to date, indicating potential applications in distributed sharp-bend sensing, such as intelligent robotics and structural health monitoring.