Enhanced VOCs and humidity detection via DTP-regulated and surface-modified tapered seven-core fiber sensors

Fiber optic sensors exhibit unique advantages in environmental monitoring and biomedicine, yet conventional designs face limitations in detection limits and sensitivity. To overcome these challenges, a tapered seven core fiber (SCF) sensing system based on dispersion turning point (DTP) modulation and surface modification enhancement is innovatively proposed in this work. The wavelength sensitivity near the DTP approaches infinity, and the DTP can also serve as an intrinsic self-referencing point during sensing. In humidity (1–92 %RH) sensing, the bare fiber achieved a wavelength sensitivity of 0.2025 nm/%RH and an intensity sensitivity of 0.086 dB/%RH near the DTP. In volatile organic compounds (VOCs) detection, silica sol-gel surface modification amplified the response to polar molecules by 2–4 times, enabling ppb-level pollutant sensing. Specifically, the maximum wavelength sensitivity for ethyl acetate exceeded 1094.2 pm/ppm. This study provides a novel integrated solution for the detection of low-concentration VOCs, offering broad application prospects.