Organic solvents in-diffusion probe based on Bragg reflectors inscribed in polypropylene no-core optical fibers

The utilization of polypropylene (PP) as an optical material offers a number of attractive features, such as biocompatibility, high tensibility, and high chemical stability, rendering PP suitable for use with a great number of organic and inorganic solvents. In this work, we present the use of Bragg reflectors inscribed in PP no-core optical fibers in probing the in-diffusion of organic solvents (OSs) such as xylene and toluene. We show that PP fibers keep being operable after long-term immersion in OS (up to 24 hours), while PP no-core optical fiber Bragg reflectors demonstrate gigantic red-shift (≈ 31 nm) after their immersion into toluene and xylene OSs, for characteristic times of 24 h. The transduction behavior is described using polymer matrix swelling and refractive index changes due to molecular in-diffusion.