Intensity-modulated bend sensor by using a twin core fiber: theoretical and experimental studies.

A new optical fiber bend sensor is proposed and demonstrated based on a sandwich structure created by splicing a segment of twin core fiber (TCF) between two segments of single mode fibers (SMFs). One core of the TCF is aligned with the cores of two segments of SMFs. An incident beam is directed into the TCF by the lead-in SMF. Light couples back and forth between two cores. The bend sensing performance of the sensor is investigated by intensity-modulated method. The intensity of the operation wavelength is modulated by the change of refractive index and geometrical deformation in the bent TCF. Experimental results show such a bend sensor achieves sensitivity of +0.671 /m-1 and resolution of 0.003 m-1 in the range of 0 to 1.25 m-1. In addition, the sensitivity and bend measurement range can be flexibly adjusted through selection of the length of TCF and sensing configuration. As such, the proposed sensor can be further developed for large or small bend ranges measurement.