Temperature and strain-independent curvature sensor based on a singlemode/multimode fiber optic structure

This work describes a fiber optic sensing structure that is sensitive to curvature, and features a low temperature- and strain cross-sensitivity. It is based on multimode interference, and relies on a singlemode-step index multimode-singlemode fiber structure. It was observed that the transmitted optical power in such a layout is highly sensitive to the wavelength of operation, and to the length of the multimode fiber. The optical spectrum exhibits two dominant loss bands, at wavelengths that have similar responses both to temperature and strain, but different responses to curvature. Based on this result, an interrogation approach is proposed that permits substantial sensitivity to curvature (8.7 0.1 nm m) and residual sensitivities to temperature and strain (0.3 0.1 pm °C^-1 and (-0.06 0.01) × 10^-6 m m^-1, respectively). The beam-propagation method was employed for modeling the propagation of light along the optical fiber sensing device proposed.