Dual-FBG and F-P Cavity Compound Optical Fiber Sensor for Simultaneous Measurement of Bending, Temperature and Strain

A dual-FBG and F-P cavity compound optical fiber sensor based on a multi-core fiber (MCF) is proposed. A hollow core fiber (HCF) was fused between a single-mode fiber (SMF) and a MCF to form the F-P cavity. Two FBGs with different reflective wavelength were prepared on a side core (SC) and the central core (CC) of MCF respectively. An asymmetric 45° reflector was fabricated at the end of the MCF to make the optical path of the dual-FBG and the F-P cavity in series. The combination of the F-P cavity and the FBG on the CC can measure temperature and axial strain, simultaneously, while both of them are insensitive to bending. The FBG on the SC is sensitive to bending and can be used for curvature measurement, and the temperature and axial strain compensation can be achieved by the combination of the F-P cavity and FBG on the CC. Therefore, the curvature, axial strain and temperature can be measured simultaneously by the compound sensor on a single optical fiber.