Fig. 1. Schematic of the structure of semi-open cavity MZI sensor

Fig. 2. Sensor fabrication process and micrograph. (a) Manufacturing process of MZI sensor; (b) diagram of geometric relationship between modified offset parameters set in the fusion splicer and the actual lateral offset amount, the offset between the X and Y views is actually the modified offset parameter in the fusion splicer; (c) microscopic images of SMSMS structure

Fig. 3. Schematic of testing device, physical diagram, and seawater sample. (a) Sensing characteristic testing system; (b) physical photos of sensors fixed with UV glue; (c) prepared seawater solution

Fig. 4. Comparison of interference spectra. (a) Interference spectra with d=62.5 μm and varied L; (b) interference spectra with L=950 μm and varied d

Fig. 5. Temperature response characteristics. (a) Transmission spectrum changes; (b) Dip 1 and Dip 2 data fitting curves; (c) quadratic polynomial fitting curves of Dip 1 data at different salinities; (d) Dip 1 wavelength offset at different salinities; (e) quadratic polynomial fitting curves of Dip 2 data at different salinities; (f) Dip 2 wavelength offset at different salinities

Fig. 6. Salinity response characteristics. (a) Transmission spectrum changes; (b) Dip 1 and Dip 2 data fitting curves; (c) Dip 1 data fitting curves at different temperatures; (d) Dip 1 wavelength offset at different temperatures; (e) Dip 2 data fitting curves at different temperatures; (f) Dip 2 wavelength offset at different temperatures

Fig. 7. Surface fitting results of MZI interference dip wavelength variation with temperature and salinity. (a) Quadratic polynomial surface fitting for Dip 1 data; (b) quadratic polynomial surface fitting for Dip 2 data; (c) paraboloid fitting of Dip 1 data; (d) paraboloid fitting of Dip 2 data

Fig. 8. Comparison of calculation results of nonlinear decoupling algorithm with standard values. (a) MZI spectral curves; (b) comparison of calculation results

Fig. 9. Spectral stability test results. (a) MZI spectral changes; (b) fluctuations in the interference dip wavelength

Fig. 10. Repeated test results. (a) Temperature repeatability tests; (b) salinity repeatability tests