Controllable Light Scattering on Fiber Bragg Gratings in Multimode Fibers: Tailoring Angular Emission for Advanced Fiber-Based Light Sources

We study lateral light scattering on fiber Bragg gratings (FBG) with the goal of creating an optical fiber-based linear light source with controllable emission angles. The scattering from two FBGs was measured for polar angles (measured from the fiber axis) in the range θ = 27.1–152.9° and for all azimuth angles around the fiber. The observed light emission is strongly concentrated in one or more scattering cones around the fiber axis, showing four intensity peaks on opposite sides. These scattering phenomena are described and explained using the volume current method. This method shows a novel and simple way to understand the side scattering on FBGs as a combined effect of the grating’s longitudinal period, the grating harmonics, and its transversal shape. Further, this work contributes to a better understanding of the azimuth FBG-scattering caused by an interplay of the transversal grating shape and the fiber modes. The presented method can generate tailored side emissions for fiber light source applications, create light power sensors, or suppress unwanted scattering on FBGs for low optical loss applications.