Highly sensitive optical fiber pressure sensor based on the FPI and Vernier effect via femtosecond laser plane-by-plane writing technology

In this paper, a highly sensitive pressure sensor based on fiber-optic Fabry-Perot interferometers (FPIs) and the Vernier effect (VE) is proposed and experimentally demonstrated. We employ a closed capillary-based F P I _s for the sensing cavity, and an F P I _r created through femtosecond laser refractive index modulation for the reference cavity, which remains impervious to pressure changes. Connecting these two FPIs in series produces a VE-based cascaded sensor with a clear spectral envelope. The femtosecond laser micromachining technique provides precise control over the length of F P I _r and facilitates adjustments to the VE's amplification degree. Experimental results reveal significant pressure sensitivities of -795.96p m/M P a and -3219.91p m/M P a, respectively, representing a 20-fold and 80-fold improvement compared to F P I _s (-39.80p m/M P a). This type of sensor has good sensitivity amplification and, due to its all-fiber structure, can be a promising candidate for high-temperature and high-pressure sensing, especially in harsh environments.