Study on Sensor for Solution Concentration and Temperature Based on Fused Tapering Optical Fiber Coupler

A simple and high-degree accuracy sensor for solution concentration and temperature based on fused tapering optical fiber coupler is fabricated. The change of refractive index in the evanescent field on the fused region of an optical fiber coupler shifts the output coupling visibility. Therefore the coupling visibility is changed with variation of solution concentration (refractive index) and temperature surrounding the fused tapering zone of the coupler. The sodium chloride solution is studied experimentally. Based on the experiment data and the least square method, the concentration accuracy of the coupler sensor is evaluated to be 10^-3 and the temperature accuracy is about 0.823°C. The stability of the sensor system with the optical coupler can reach the order of 10^-4. This simple, low-cost, good-stability and high-degree accuracy coupler sensor is suitable to be used in the environmental monitoring, analytical chemistry, and food safety testing.