Optical fiber strain sensor with improved linearity range

A strain sensor is constructed from a two mode optical fiber. When the optical fiber is surface mounted in a straight line and the object to which the optical fiber is mounted is subjected to strain within a predetermined range, the light intensity of any point at the output of the optical fiber will have a linear relationship to strain, provided the following equation is less than 0.17 radians delta phi 01 - delta phi 11 = +TR where nco represents the refractive index of the core, k represents the wavenumber of the light, L represents the length of the optical fiber, S1 represents axial strain, V is U is a solution to the eigenvalue equation of the optical fiber, vf represents the Poisson ratio, Pef represents the effective strain-optic coefficient of the optical fiber and nln represents where K1 is the modified Bessel function of second kind of order/with argument given by where