High-sensitivity fiber optic temperature sensor based on Vernier effect in a polymethyl methacrylate capillary and barium titanate microsphere

This paper proposes and investigates a novel fiber Fabry–Perot interferometer (FPI) temperature sensor that leverages the Vernier effect for enhanced sensitivity. The sensor comprises a cascade of two FPIs formed by a short polymethyl methacrylate capillary, a barium titanate microsphere, and a cleaved single-mode fiber. The Vernier effect, induced by the dual Fabry–Perot cavities, amplifies the temperature sensitivity. The fabrication process involves the precise alignment and gluing of components, resulting in a simple, cost-effective sensor. The experimental results indicate a temperature sensitivity of 1.90 nm °C⁻¹. The sensor also exhibits excellent repeatability and stability, making it suitable for various temperature monitoring applications.