Hetero-core structured Fabry-Perot fiber sensor for liquid refractive index and Hydrogen gas detection

In this paper, we have developed a hetero-core structured fiber optic Fabry-Perot (FP) sensor. The hetero-core interface is simply made by fusion splicing two fibers with different core diameters. The hetero-core insertion length plays a role as a FP cavity length. The cavity length could be easily tuned by the insertion length of the hetero-core fiber. Additionally, the sensor has smooth-faced reflector on the hetero-core interface due to fabrication process comprised of cleaving and fusion splicing. Firstly, in order to evaluate the characteristic of the hetero-core structured FP sensor, we carried out the refractive index change experiment with water and glycerin solution. As a result, we can experimentally obtain the refractive index sensing ability of the proposed hetero-core FP sensor. Secondly, we carried out the hydrogen detection experiment by the hetero-core fiber FP sensor which has the 5-nm Pd thin film. We also confirmed that the H2 gas detection by the proposed sensor could be achieved based on the amplitude change in the FP fringe.