Low-Strain Crosstalk Curvature MZI Based on the Cascaded of Step-Index Fiber and Graded Index Fiber

Mach fiber interferometric curvature sensors are susceptible to strain crosstalk when working. In this article, a low-strain crosstalk curvature Mach–Zehnder interferometer (MZI) was constructed using graded index fiber cascaded with step-index fiber. When the sensor is subjected to axial strain modulation, the optical path difference between modes in the graded index fiber increases, while the optical path difference between modes in the step-index fiber decreases. The changes in the optical path difference cancel each other, reducing the strain sensing sensitivity. The experimental results indicate that when the length of the two fibers is 14.35 and 4 cm, respectively, the sensor becomes insensitive, with a sensitivity of −0.097 pm/
$\mu \varepsilon $
. The curvature sensing sensitivity is −21.97 nm/
$\text{m}^{{-{1}}}$
, with high sensitivity. The curvature strain cross sensitivity of the sensor is
${4.415} \times {10}^{{-{6}}} \text{m}^{{-{1}}}/\mu \varepsilon $
, reducing strain crosstalk during curvature sensing.