Bending sensor with tilted fiber Bragg grating interacting with multimode fiber

A new type fiber bending sensor based on a tilted fiber Bragg grating (TFBG) interacting with a multimode fiber (MMF) is presented. The sensing head is formed by insertion of a small section of MMF between single-mode fiber (SMF) and the TFBG. The reflection light from this sensor head includes two parts, i.e., the reflected Bragg mode and cladding modes. The latter were first coupled from the core mode to counter-propagating cladding modes by the TFBG and then coupled back into the core as a function of the MMF. The power of the cladding modes changes as the fiber is bent while the Bragg one keeps unchanged. The average reflective power in the cladding modes decreased with the increase of curvature. The measurement range of the curvature from 0m⁻¹ to 2.5m⁻¹ with a measurement sensitivity of −802.4nW/m⁻¹ is achieved.