High-Sensitivity Strain Sensor With Temperature Compensation Based on USFBG-FPIs and Vernier Effect

A fiber-optic strain sensor with amplified sensitivity and temperature compensation was demonstrated. The cascaded ultrashort fiber Bragg gratings (USFBGs) inscribed by femtosecond laser were used to construct Fabry-Perot interferometers (FPIs) and generate optical Vernier effect (OVE). Three sensor samples with sensitivity amplification factors of 41.8, 26.7, and 14.0 were fabricated and measured, the strain sensitivity is up to 50.1 pm/με, 32.0 pm/με, 16.8 pm/με, respectively. The femtosecond laser micromachining enables precise control of sensitivity amplification factor, significantly expanding the application scope of sensors and making it promising for a wide range of strain measurement scenarios from extreme to conventional scales. The proposed sensor is compact, the length of single USFBG is only 50 μm, and possesses outstanding structural integrity and simplified manufacturing process. The reflection spectrum exhibits a distinctive “dual-peak” characteristic different from conventional OVE, in which the lower envelope peak and upper envelope dip of USFBG-FPIs display different sensitivities, providing inherent temperature compensation. The sensing peak demonstrates the amplified sensitivity and the compensation dip maintains its original sensitivity, thereby effectively mitigating temperature cross-talk. Furthermore, the multiplexing capability of the sensor gives it greater potential for practical application.