All-Fiber Curvature Sensor Based on Multimode Interference

A fiber-optic curvature sensor based on the single-mode-multimode-single-mode (SMS) fiber structure is developed. Several notches in the transmitted spectrum of the SMS fiber structure are generated due to the multimode interference effect. The dependence of the wavelength shifts and intensity changes of three transmission notches on the applied curvature are different from each other. The maximum sensitivities of wavelength-curvature and intensity-curvature relationships are - 10.38 nm/m^-1 and - 130.37 dB/m^-1 respectively. By properly choosing to measure wavelength shifts or intensity changes, high sensitivity measurement of curvature over a large scale can be obtained. The wavelength of the second notch is insensitive to the curvature change, offering the possibility for simultaneous measurement of curvature and other parameters such as temperature or strain.