Strain and temperature discrimination by using temperature-independent FPI and FBG

We present a compact fiber sensor with a hybrid structure including a temperature-independent Fabry-Perot interferometer (FPI) and a fiber Bragg grating (FBG) for strain and temperature discrimination. The temperature-independent FP interferometer which used as a strain gauge is formed by inserting a segment of tapered fiber tip in the capillary and subsequently splicing the other end of the capillary to a single mode fiber (SMF), the tapered fiber end-face and the spliced face form the FP cavity. Because the inserted taper tip has the degree of freedom along the fiber axial, when the FP interferometer is subjected to temperature variation, the thermal expansion of the fiber taper tip will resist the FP cavity length change caused by the variation of capillary length, and when the inserted tapered fiber length is selected as 160 μm, the temperature sensitivity of the whole FP sensor can be entirely eliminated. The FBG which acts as a thermometer is fabricated using the standard phase masks technique. The experimental results demonstrate that the sensor prototypes can realize the strain and temperature discrimination by combining a FBG and the temperature-independent FP interferometer.