Fig. 1. Structure of the micro-nano fiber sensor

Fig. 2. Spectra of the double-tapered micro-nano fiber structure. (a) Interference spectrum when the ambient refractive index is 1.34; (b) optical field transmission diagram of the dip A; (c) optical field transmission diagram of the peak B

Fig. 3. Structure of micro-nano fiber. (a) Schematic diagram of fabrication; (b) microcone point under microscope

Fig. 4. Fabrication of micro-nano fiber interferometer. (a) Micro-nano fiber taper platform; (b) micro-nano fiber microscope view with a diameter of 20 μm

Fig. 5. Structure of the fiber ring laser

Fig. 6. Fiber spectrogram. (a) ASE spectrum and laser spectrum of erbium-doped fiber; (b) transmission spectrum of micro-nano fiber interferometer

Fig. 7. Diagram of experimental setup for measuring refractive index and gadolinium nitrate solution

Fig. 8. Refractive index sensing curves of micro-nano fibers with different diameters. (a)-(c) Refractive index response spectra with diameters of 125, 50, and 20 μm, respectively; (d)-(f) sensing curves with diameters of 125, 50, and 20 μm, respectively

Fig. 9. Sensitivity detection of mass concentration of gadolinium nitrate solution. (a) Response spectra; (b) sensing curve