Fiber Bragg gratings in soft glass fibers

In this chapter, we provide an overview of femtosecond laser inscription of Fiber Bragg Gratings (FBGs) into soft glass fibers. In the first section, we will start by introducing the FBG and the general methods that were originally developed in the context of germanosilicate fibers and will then outline the main difficulties that arise when working with soft glass fibers. Next, we will provide an overview of the various techniques that have successfully been employed to fabricate FBGs into soft glass fibers using femtosecond laser inscription. In the second section of this chapter, the phase-mask writing technique with femtosecond pulses applied to fluoride and chalcogenide glass fibers will be detailed. Experimental results of FBGs written in ZrF₄-based, InF₃-based and As₂S₃ glass fibers will be presented. Thermal stability of those FBGs will also be discussed. The last section of this chapter will detail the direct ultrafast writing of FBGs by using the point-by-point and line-by-line writing technique applied to fluoride glass fibers. The physical mechanisms responsible for the laser-induced refractive index change in these soft glass fibers will be discussed. Finally, we will conclude this chapter with a short summary and an outlook toward future work.