High-resolution and wide-dynamic-range fiber temperature sensing enabled by a photopolymer self-growing micro-cones dual FPI cavity

This paper presents an advanced optical fiber temperature sensor with features such as its high resolution and extensive dynamic range. The sensor incorporates two Fabry-Pérot interference (FPI) cavities, created by first growing a high-refractive-index UV-photopolymer micro-cone over the fiber facet and then coating a low-refractive-index UV-photopolymer. Owing to their significantly different optical path lengths, these two FPIs operate independently and generate a Vernier effect. This approach successfully overcomes the traditional sensitivity-range trade-off. Furthermore, it simplifies signal interrogation by allowing direct analysis of the envelope and comb spectra, eliminating the need for Fourier transform filtering. The primary FPI cavity (FPI1) has a temperature detection range of approximately 63.27 °C. Meanwhile, the secondary FPI cavity (FPI2) achieves a significantly higher temperature sensitivity of 2.64 nm/°C. Additionally, the ultra-compact sensor is not only easy to deploy but also immune to external environmental perturbations, showcasing its promising potential for a wide range of engineering applications.