Post-chemical etching of tapered seven-core fiber sensor towards the dispersion turning point for ultra-high sensitivity

Optical fibers have been widely applied for sensitive detection due to the advantages of high sensitivity, compact size and remote sensing capability. In this work, a post-chemical etching process is applied to approach the dispersion turning point (DTP) in a tapered strongly-coupled seven-core fiber to enhance the sensitivity. Ultra-high sensitivity is achieved by targeting a specific diameter via the controlled post-chemical etching technique, rather than relying solely on extensive size reduction of the fiber structure. Across the DTP, i.e., when the sign of the dispersion factor changes, the dips in the interference pattern shift in opposite directions in response to external variations. The refractive index sensitivity reaches as high as 5437.51 nm/RIU (refractive-index unit) near the DTP, of which the magnitude is about 27 times higher compared to that of the fiber without etching. The measured maximum temperature sensitivity is 182.45 pm/^∘C, mainly dominated by the dispersion property and the thermo-optic effect. This work provides a competitive approach for significantly enhancing sensitivity while better maintaining structural robustness and steadiness, showing great potential for future detector applications.