For four decades, fiber Bragg grating (FBG) have delivered outstanding performance for applications in many fields of engineering and science, including sensing, lasers, dispersion management, and filters. However, most FBGs for these applications have been confined to lengths of less than 100mm. Recent developments have led to a demand for longer gratings (~ meter length) in applications such as Raman and Brillouin distributed feedback FBG lasers. Until recently, controlling the spatial characteristics of the FBG with a precision necessary for these applications has been difficult to achieve, since small errors accumulate leading to unpredictable and unrepeatable characteristics. These errors make it impossible to utilise long FBGs for linear and nonlinear applications routinely. By undertaking a step by step approach to understand the limitations of not only the technology of FBG inscription, but surprisingly, also from the uniformity of the optical fiber has led to near perfect ultra-long gratings. Although challenges remain, these advances have allowed the fabrication of single frequency fiber Raman and Brillouin DFB lasers with outstanding performance, also opening the doors to other nonlinear optical applications.
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