This work presents the implementation of an optical system for fiber Bragg grating writing by using the phase mask technique. The method consists of radiating a photosensitive optical fiber with a suitable intensity pattern of UV light that generates a spatial modulation of the fiber core refraction index and creates the Bragg grating. As light source a beam of an Nd-YAG pulsed laser, of quadrupled frequency, and 266 nm emission, was used. The proposed system is described, the results are analyzed, and applications developed with fiber Bragg grating are mentioned.Centro de Investigaciones ÓpticasFacultad de Ingeniería