We report a miniature optical fiber chemical sensor that consists of a fused-biconical single-mode optic fiber coupler. The absorption of the evanescent wave changes when the waist cladding refractive index n2 is slightly modified. Consequently, the coupling visibility also changes. By putting the device in the water polluted, the trace amounts of chromium and nitrite in water can be detected. The coupler fabrication and design of the chemical sensor are described. The performance and characteristic of this system clearly establish the usefulness of the technique for detecting very low concentrations of the dissolved contaminants. And the sensor has shown preferable sensitivity and time response.
An optical fiber temperature sensor based on optical fiber coupler and evanescent wave is presented. The overall goal of our research is to design a temperature sensor system which is used to monitor temperature accurately. Coupler is used as the sensor probe. Such kind of coupler uses standard communication SM fiber to be a sensing component of evanescent wave. The probe is obtained by replacing the cladding of coupler region with temperature sensitive material. The whole system is then exposed in a thermal bath. A numerical modeling of the sensor based on supermode theory is studied and the result is simulated. At last, the system for temperature measurement in experiment is simply described.