Twist dependencies of strain and temperature sensitivities of perfluorinated graded-index polymer optical fiber Bragg gratings

We measure the twist dependence of the reflected spectrum of a fiber Bragg grating (FBG) inscribed in a perfluorinated graded-index (PFGI) polymer optical fiber (POF). With increasing twist, the strain sensitivity decreases with a coefficient of -34.2 pm/%/turns/m, while the temperature sensitivity increases with a coefficient of 0.39 pm/°C/turns/m. At a twist of 150 turns m^-1, the temperature sensitivity is 3 times higher than that with no twist. The controllability of the strain and temperature coefficients without considerable cost is beneficial not only to highly sensitive temperature sensing but also discriminative sensing of strain and temperature using two PFGI-POF-FBGs.