POF Bragg Gratings
This chapter looks in more depth at topics of photosensitivity, grating inscription, measurand sensitivity, the challenges posed by polymer fibers, and applications. Optical fiber Bragg gratings usually take the form of a periodic modulation of the effective index of the fiber core along a short length of fiber. The motivation for the development of polymer optical fiber Bragg gratings (POFBG) comes from the very different material properties of polymers compared to silica. Bragg grating sensors are almost always operated with single mode fiber, since the presence of other modes leads to additional peaks in the reflection spectrum, which significantly complicates the readout process. The first POFBGs were fabricated in polymethyl methacrylate-based fiber with a Bragg wavelength in the 1550 nm region. POF is a viscoelastic material and in general, if it is subject to a constant strain, the fiber stress will gradually reduce.