Fig. 1. Schematic diagram of the optical fiber sensor

Fig. 2. (a) Model of the SNS fiber structure with ZIF-8 film; (b) distribution of optical field in coreless fiber

Fig. 3. Energy distribution of the optical field in coreless fibers for different lengths. (a) 20 mm; (b) 30 mm; (c) 40 mm; (d) 50 mm

Fig. 4. Energy distribution of the optical field in coreless fibers and transmission spectra of the sensor the for different refractive index environment. (a) n_RI=1.34; (b) n_RI=1.35; (c) n_RI=1.36; (d) transmission spectra

Fig. 5. Schematic diagram of the process of growing a ZIF-8 film on the surface of a coreless fiber with in-situ crystallization technology

Fig. 6. SEM photos. (a) Cross-sectional view of the fiber without ZIF-8 film; (b) cross-sectional view of the fiber with ZIF-8 film; (c) further enlarged cross-sectional view of the fiber; (d) side view of the fiber with ZIF-8 film

Fig. 7. Diagram of experimental device for detecting trace ethanol in water

Fig. 8. Transmission spectra of the sensor in deionized water and ethanol solution without or with ZIF-8 film on coreless fiber surface. (a) Transmission spectra of the sensor without ZIF-8 film; (b) transmission spectra of the sensor with ZIF-8 film

Fig. 9. Transmission characteristics of the sensor in different volume fractions of ethanol solution. (a) Transmission spectra (simulation result); (b) transmission spectra (experimental result); (c) comparison of transmission peak offset between simulation and experimental results

Fig. 10. Response and recovery time of the sensor for different volume fractions of ethanol solution

Fig. 11. Transmission spectra of the sensor immersed in a 10% (volume fraction) ethanol solution for different temperatures