Multipoint Temperature-Independent Vector Bending Sensing With Coupled-Core Fibers

Fiber optic bending sensing has potential use in industrial and medical applications. Thus, so far, several configurations have been reported with that end, but the state-of-the-art sensors are either complex, temperature dependent, or cannot be multiplexed easily. To circumvent these important limitations, we have developed a sensing platform based on an asymmetric coupled-core optical fiber that is combined with conventional Bragg gratings. The asymmetric fiber was designed with three cores arranged in an equilateral triangle. The said fiber supports supermodes that suffer drastic changes when it is bent. Consequently, the reflection of a Bragg grating inscribed close to the asymmetric fiber changes drastically, but its wavelength position is not altered. We demonstrate experimentally that our sensing platform allows the development of highly sensitive bending sensors that have important practical assets. The latter include compactness and simple fabrication, capability of distinguishing the direction of bending and simultaneous detection of temperature and bending. Moreover, the sensors can be multiplexed easily and can be interrogated with commercially available fiber optic sensor read out units.