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/degrees C when the humidity is controlled and the heating/cooling rate is relatively low (<= 0.14 degrees C/min). The humidity sensitivity at a fixed temperature (25 degrees C) is 22.3 pm/%RH. Finally, the axial strain sensitivity is determined to be 1.35 pm/mu epsilon. (C) 2021 Optical Society of America

Automated summary

In this study, highly reflective fiber Bragg gratings were fabricated in perfluorinated polymer optical fibers using 800 nm femtosecond pulses and line-by-line inscription method. It was demonstrated that grating inscription could be achieved without damage with energy below 27 nJ, and the reflectivity of the grating continued to increase over several hours. The temperature-dependent behavior of the grating reflectivity and Bragg wavelength, as well as the sensitivity to humidity and axial strain, were also investigated.