Optical fiber sensor with enhanced strain sensitivity based on the Vernier effect in a three-FBG cascaded Fabry–Perot configuration

The Vernier effect has attracted significant attention in the past decade as an effective method for improving measurement sensitivity. In this study, we introduce and validate a sensitivity-enhanced optical fiber strain sensor utilizing cascaded Fabry–Perot interferometers (FPIs), which are constructed by inscribing three fiber Bragg gratings (FBGs) in series. Experimental results show that the proposed structure provides a strain sensitivity of up to 23.3 pm $\mu {\varepsilon }^{-1}$, which is approximately 16 times higher than that of the single-sensing FPI, which has a sensitivity of 1.45 pm $\mu {\varepsilon }^{-1}$. Beyond demonstrating high sensitivity, we systematically analyze the sensor’s detection limit and dynamic range by varying the cavity lengths, highlighting key performance trade-offs. Experimental results show strong agreement with simulations and validate the practical utility of the design. The proposed sensor is simple to fabricate, cost-effective, and well-suited for deployment in low-resource environments or multiplexed sensor networks.