Flexible Fiber-Optic Sensor Based on Upconversion Fluorescence in Tellurite Glass for Dual Parametric Monitoring of Temperature and Pressure

In this paper, a flexible single-point sensor integrated into a fiber-optic path, capable of simultaneously detecting temperature and pressure with inherent crosstalk immunity, is presented through the development of a hybrid tellurite glass/polydimethylsiloxane composite probe. Temperature measurement is achieved through the fluorescence intensity ratio technique utilizing the thermally coupled levels (<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11/2</sub> and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup>S3/2) of Er<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. Meanwhile, pressure sensing is realized by exploiting the temperature-insensitive characteristic of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11/2</sub> emission within a limited temperature range, combined with the polydimethylsiloxane-induced optical transmission loss under elastic deformation. To the best of our knowledge, this represents the first implementation of simultaneous temperature and pressure sensing based on upconversion fluorescence in Er<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>-doped tellurite glass. Compared with conventional dual-parameter fiber-optic sensors, our design eliminates the requirement for complex dual-sensing configurations or sophisticated signal decoupling algorithms, accomplishing dual-parameter detection using a single sensing element. The developed sensor exhibits outstanding features including compact structure, low-cost fabrication, simple signal interrogation, and excellent flexibility for wearable applications, showing great potential in healthcare monitoring, human-machine interfaces, and motion recognition systems.