High-sensitivity fiber salinity sensor based on an exposed-core microstructured fiber interferometer

A high-sensitivity salinity sensor based on a freedom-core mode Mach-Zehnder interferometer was proposed with a well-designed exposed-core microstructured optical fiber. The real-time salinity sensing was achieved by using an exposed-core microstructured optical fiber shortened to 228 µm. The proposed sensor has a salinity measurement range from 0 ‰ to 40 ‰ and a salinity sensitivity of around -2.29 nm/‰, corresponding to a refractive index sensitivity of -13103.16 nm/RIU. The measurement error caused by the temperature is only 0.02 ‰/°C, which can be neglected in practical applications. This kind of sensor also presents a Fabry-Perot interference phenomenon besides the Mach-Zehnder interferometer, which shows a flexible sensing structure. The proposed sensor offers an alternative method for accurate measurement of seawater salinity.