Dynamic Refractive Index Sensing Using a Tapered U-Shaped Fiber and an Interrogator with Real-Time Spectral Waterfall Visualization

This paper presents a refractive index (RI) sensing system based on a tapered U-shaped single mode–tapered seven core–single mode interferometer structure, combined with an interrogator capable of acquiring transmission spectra at 1 Hz. The focus of the work is on real-time dynamic monitoring of RI changes using intuitive waterfall spectral visualization. The fabricated sensor achieves a sensitivity of 2554.37 nm/RIU. The proposed system is portable and suited for continuous environmental and biochemical sensing. Experimental results using aqueous solutions with varying refractive indices demonstrate the system's ability to track spectral shifts reliably over time. This compact system offers promising potential for environmental and biomedical sensing applications.