Polypyrrole-Coated Polarization Maintaining Fiber-Based Vernier Effect for Isopropanol Measurement

A fiber optic isopropanol sensor based on polypyrrole-coated polarization maintaining fiber (PMF) is demonstrated. The sensor configuration is based on the combination of the Vernier effect of a single fiber Sagnac loop and the isopropanol sensitive material of polypyrrole, which swells in corresponding to the change of isopropanol concentration. And this swell effect can induce the strain effect on the fiber Sagnac loop. In this paper, the sensitivity of the proposed sensor exhibits ~4.2 times (239 pm/ppm) higher than the conventional Sagnac interferometer (56.89 pm/ppm) from the range of 0 to 42 ppm with a satisfactory stability and linearity.