Micro-scale fiber optic ocean salinity sensor

Abstract A micro-scale fiber (MSF) sensor for measuring ocean salinity is proposed and experimentally demonstrated. The sensor is fabricated by tapering a single-mode fiber (SMF) to a diameter of approximately 8 μm through the flame-brushing technique. In the tapered region, light energy will leak out to the external environment, forming an evanescent field that is sensitive to the external environment’s refractive index (RI). Experimental results demonstrate a salinity sensitivity of 0.536 nm/‰ for salinity levels ranging from 5‰ to 40‰ at 5‰ intervals. The standard deviation of the sensor is only 3.29 pm when the stability test lasts 60 min. The temperature sensitivity of the sensor is only −0.046 nm °C −1 , so the temperature effect can be neglected as it accounts for less than one-tenth of the salinity sensitivity. The MSF salinity sensor offers the advantages of simple fabrication, cost-effectiveness, and strong confinement, making it suitable for ocean environment detection.