800 nm femtosecond pulses for direct inscription of FBGs in CYTOP polymer optical fiber.

We report the inscription of highly reflective fiber Bragg gratings in perfluorinated polymer (CYTOP) optical fibers using 800 nm femtosecond pulses and a line-by-line inscription method. We demonstrate that the energy for grating inscription without damage is below 27 nJ. After the writing process, we show that the grating reflectivity continues to rise for several hours. The obtained gratings show reflectivity degradation with temperature increase, while the Bragg wavelength undergoes a linear temperature dependence of 37.7 pm/°C when the humidity is controlled and the heating/cooling rate is relatively low (≤0.14/). The humidity sensitivity at a fixed temperature (25°C) is 22.3 pm/%RH. Finally, the axial strain sensitivity is determined to be 1.35 pm/µɛ.