Abstract
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 ${{\rm FPI}_s}$ for the sensing cavity, and an ${{\rm FPI}_r}$ 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 ${{\rm FPI}_r}$ and facilitates adjustments to the VE’s amplification degree. Experimental results reveal significant pressure sensitivities of ${-}{795.96}\;{\rm pm/MPa}$ and ${-}{3219.91}\;{\rm pm/MPa}$, respectively, representing a 20-fold and 80-fold improvement compared to ${{\rm FPI}_s}$ (${-}{39.80}\;{\rm pm/MPa}$). 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.
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