Fig. 1. Principle diagram of acetone gas sensing based on fiber-tip micropillar

Fig. 2. Flow chart of device fabrication. (a) Photoresist solution dropped on end face of single-mode fiber, covered with coverslip; (b) two-photon polymerization for micropillar structure on end face of fiber; (c) coverslip on top of optical fiber removed and uncured photoresist washed away with mixed solution of isopropyl alcohol and acetone; (d) micropillar fabricated on end face of optical fiber

Fig. 3. SEM micrograph of polymerized micropillar fabricated on end face of optical fiber by two-photon polymerization. (a) Front view; (b) vertical view; (c) side view

Fig. 4. Reflection spectra of polymerized micropillars on end face of optical fiber with different design heights. (a) H₁＝20 μm; (b) H₂＝30 μm; (c) H₃＝40 μm

Fig. 5. Acetone gas sensitivity test. (a) Reflection spectra at different acetone concentrations ; (b) relationship between dip wavelength and acetone concentration

Fig. 6. Variation of dip wavelength in interference spectrum of polymerized micropillar when acetone concentration first decreases and then increases for three times in range of 1×10^－9 to 1×10^－3

Fig. 7. Temperature response of sensor; (a) Interference spectral response of polymerized micropillar sensor at different temperatures; (b) relationship between dip wavelength in interference spectrum and ambient temperature