Azimuthal Alignment Method for Optimizing Bragg Grating Inscription in Photonic Crystal Fibers

An accurate (≤5°) and straightforward implementation optical method for determining the azimuthal lattice orientation of a microstructured optical fiber with respect to the side illumination beam used for Bragg grating recording is presented. This method is based on the diffraction pattern generated backward of the photonic crystal fiber cladding upon a continuous-wave visible laser light illumination. This optical fiber alignment and coordination method is experimentally demonstrated, describing in detail characteristic light scattering patterns used for the azimuthal orientation of the fiber with respect to the side-coming laser beam. Moreover, this alignment method is theoretically validated using standard ray tracing beam scattering software. Bragg grating recordings performed in this photonic crystal fiber (PCF) using 193-nm excimer laser radiation are also presented to depict the impact of the azimuthal alignment of the fiber with the inscription beam on the photosensitivity refractive index changes induced in the optical fiber.