Detection of salinity in the process of heating seawater by using a directional coupler of the multimode plastic optical fiber with a plane mirror as a reflector

Plastic optical fiber (POF) FD 620 10 has been widely used in various sensors with the basic principle of utilizing the intensity received because of reflection, one of which is used as a displacement sensor. In this study, POF was used as a directional coupler and was applied for the detection of the refractive index of sodium chloride (NaCl) solutions due to changes in concentration and detection of salinity in the process seawater heating. The results of this study indicate that the sensor system has succeeded in detecting the refractive index of the NaCl solution at a concentration of 0–20% and changes in the salinity of seawater due to the heating process. This sensor system is simple and easy to use, and the manufacturing cost is relatively cheap. The results of this study indicate that the sensor system has succeeded in detecting the refractive index of the NaCl solution at a concentration of 0–20% and changes in the salinity of seawater due to the heating process at the temperature range from 13 to 58 °C. This sensor system is simple and easy to use and the manufacturing cost is relatively cheap.