Micro-scale fiber optic ocean salinity sensor

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 mu m 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/parts per thousand for salinity levels ranging from 5 parts per thousand to 40 parts per thousand at 5 parts per thousand 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 degrees 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.