Fig. 1. Schematic diagram of sensor

Fig. 2. Manufacturing steps of sensor.(a) SMF end is discharged to form a ball; (b) SCF end is discharged to form a ball; (c) SMF is spliced with SCF to form a peanut structure; (d) cut SCF end; (e) SCF end is discharged to form a ball; (f) SCF is spliced with SMF to form second peanut structure

Fig. 3. Structural micrographs of sensor. (a) Micrograph of optical fiber ellipsoidal structure at end of SMF; (b) micrograph of optical fiber ellipsoidal structure at end of SCF; (c) micrograph of optical fiber “peanut structure”

Fig. 4. Transmission spectra of interferometers with different lengths

Fig. 5. Spatial frequency spectra of interferometer with different lengths

Fig. 6. Diagram of liquid level sensing experimental device

Fig. 7. Liquid level response spectra and sensitivity curves of interferometer. Transmission spectra of interferometer with length of (a) 24 mm; (b) 28 mm; (c) 32 mm at different liquid levels ; (d) linear fitting curves of liquid level sensitivity of interferometer

Fig. 8. Relationship between length of interferometer and liquid level sensitivity

Fig. 9. Temperature response spectra and sensitivity curves of interferometer. Transmission spectra of interferometer with length of (a) 24 mm; (b) 28 mm; (c) 32 mm at different water temperatures; (d) linear fitting curves of temperature sensitivity of interferometer