Simultaneous salinity and temperature measurement using multimode interference effect

A multimode interference (MMI) sensor based on an SGNS structure (single mode fiber-graded index multimode fiber-tapered no core fiber-single mode fiber) for simultaneous measurement of salinity and temperature is described and experimental results presented. The tapered no core fiber (TNCF) and graded index multimode fiber (GIMF) promotes the existence of high-order modes, increasing sensitivity to the variations in the external environment, whereas the GIMF with n/4 pitch (where n is an odd number) can play a collimation role to reduce losses. Experimental results show that the salinity and temperature sensitivities are 4.0951 nm/% and −0.5329 nm/oC, respectively. In addition, the MMI sensor exhibits good stability and repeatability, and the response times to salinity and temperature variations are 118 ms and 398 ms, respectively. The experimental results indicate that the sensor has the advantages of simple structure, high sensitivity, and low cost, proving that the sensor has excellent potential to simultaneously measure salinity and temperature in a liquid environment.