Lateral offset optical fiber modal interferometer sensor for simultaneous measurement of seawater temperature and salinity

An optical fiber sensor for simultaneous measurement of seawater temperature and salinity was designed and implemented based on a lateral offset Modal interferometer (MI) using a suspended core photonic crystal fiber (SCPCF). The MI was made by fusing single mode fiber and multimode fiber (SMF-MMF) structures with a lateral offset SCPCF coated with UV adhesive film on the inner wall. In the experiment, the response of the sensor to the change of seawater temperature and salinity was measured respectively. The results have shown that the temperature sensitivity of 1.486 nm/°C was obtained within the temperature range from 5 °C to 45 °C and the salinity sensitivity of 2.495 nm/‰ was obtained within the salinity range from 0‰ to 50‰. The sensor resolves the problem of cross-sensitivity between seawater temperature and salinity and provides a simple structure with low cost and high sensitivity.