Modal-interference-based temperature sensing using plastic optical fibers: markedly enhanced sensitivity near glass-transition temperature

We developed strain and temperature sensors based on multimode interference in perfluorinated graded-index (GI) plastic optical fibers, and investigate their sensing performance at 1300 nm. At room temperature, we achieve ultra-high sensitivities of strain and temperature of -112 pm/mu epsilon and +49.8 nm/degrees C/m, the absolute value of which are approximately 7.2 and over 1800 times as large as those in silica GI multimode fibers, respectively. We also find that the temperature sensitivity is drastically enhanced with increasing temperature toward similar to 80 degrees C, where phase transition of core polymer partially occurs.