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 FPI s for the sensing cavity, and an FPI 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 FPI r and facilitates adjustments to the VE’s amplification degree. Experimental results reveal significant pressure sensitivities of −795.96pm/MPa and −3219.91pm/MPa, respectively, representing a 20-fold and 80-fold improvement compared to FPI s (−39.80pm/MPa). 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.