Ultrasensitive strain sensor of dual parallel FPIs utilizing femtosecond laser processing and Vernier effect

This study proposes and develops a highly sensitive fiber optic strain sensor utilizing femtosecond laser processing and the Vernier effect. The sensor features two parallel Fabry-Pérot interferometers (FPI), with each FPI consisting of an air bubble and a tapered fiber optic cascade. FPI 2 serves as the sensing cavity, while FPI 1 acts as the reference cavity. The strain sensing capability of a single FPI 2 is measured at 6.67 p.m./με, while the parallel configuration of FPI 2 with FPI 1 achieves a sensitivity of 68.3 p.m./με, resulting in an amplification of 10.24. Furthermore, the proposed sensor demonstrates excellent repeatability, low-temperature cross-sensitivity, simple fabrication, and cost-effectiveness, making it a promising tool for strain measurement applications.