We demonstrate a new refractive index (RI) and salinity sensor based on a lossy mode resonance (LMR) effect which combines fiber-optic side-polishing and radio-frequency (RF) sputtering techniques. The side-polished fiber can enhance optical fibers to generate an evanescent field in sensing applications. Gallium-doped zinc oxide (GZO) thin films produce a high attenuation lossy mode resonance effect that permits a highly sensitive refractive index and salinity fiber sensor. GZO thin film was prepared by an RF magnetron sputtering method. The thickness of the D-shaped fiber sensing device was 74.7 μm, and a GZO film thickness of 67 nm was deposited on the polished surface of the D-shaped fiber to fabricate LMR type liquid salinity sensors. The sensitivity of 3637.8 nm/RIU was achieved in the RI range of 1.333 to 1.392. To investigate the sensitivities of LMR salinity sensors, the NaCl solution salinities of 0%, 50%, 100%, 150%, 200%, and 250% were measured in this work. The experimental result shows that the sensitivity of the salinity sensor is 0.964 nm per salinity unit (SU).
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