Application of the cascaded multi-channel fiber optic sensors with bent structures for internal supercapacitor...

Supercapacitors are widely used in various applications due to their high power density and long cycle life. However, monitoring the electrolyte concentration and temperature remains challenging. Conventional sensors often suffer from instability, polar plate degradation, and interference caused by the corrosive internal environment. To solve these issues, we develop a cascaded multi-channel fiber optic sensor using a bending mode leakage coupling mechanism to excite the core-cladding mode interference. Four independent sensing units are fabricated on a single-mode fiber via a non-destructive geometrical tuning process, forming robust multi-channel multiplexed sensing units without chemical coatings. This design reduces sensor fragility in the corrosive supercapacitor environment. Additionally, a mathematical model correlating wavelength shift, electrolyte concentration, and capacitance is established. Experimental results demonstrate a strong correlation (R² = 0.9981) between concentration, capacitance, and wavelength offset, validating the model's accuracy. The method enables non-contact capacitance measurement, improving system stability and durability, and provides a novel approach for in-situ supercapacitor monitoring.