Inscription of polymer optical fiber Bragg grating at 962 nm and its potential in strain sensing

Fiber Bragg grating (FBG) with a 962-nm Bragg wavelength was fabricated in trans-4-stilbenemethanol doped poly(methyl methacrylate) polymer optical fibers (POFs) using a phase mask with 17% zeroth-order diffraction for the inscription wavelength of 325 nm. The effect of zeroth-order diffraction of the phase masks on FGB in POF was first examined by observing micrographs of the gratings. A linear relationship between the fiber axial strain and shift of the FBG was observed up to 6.5% tensile strain with a strain sensitivity of 0.916 pm/με. However, this shift was notably affected by the time-dependent stress relaxation in the fiber, especially when the FBG was subject to a relatively higher strain > 2%.