Strain and curvature optical fiber laser sensor based on an accurate RI-regulated FMF with high modal power balance

In this paper, a ring fiber laser sensor based on a three layered-core few modes fiber (TL-FMF) is proposed. The home-made TL-FMF is spliced with two pieces of single mode fiber (SMF) at both sides as the sensing and filtering component. In the TL-FMF, an intermediate with higher refractive index (RI) is sandwiched between a central dip and a sub-high RI layer. Due to the special RI, the TL-FMF has an equidistant modal effective RI difference and a balanced modal power of different modes, enabling a highly uniform interference spectrum. Then applying the TL-FMF in proposed ring fiber laser sensor, the sensing experimental results show that its sensitivities in strain and curvature are -2.78 pm/pa and -6.17 nm/m-1, respectively, and shows an excellent characteristic of temperature insensitivity. This fiber laser sensor implements the dual-parameter measurement with anti-cross sensitivity, which offers a promising candidate in fiber fabrication monitoring, deformation measurement and bending detection.