Abstract: The invention relates to an exposure method for producing a Bragg grating on a photosensitive guide (120) or optical fiber (120), in which method the guide (the fiber) (120) is scanned by a light beam (300) and means (100, 220, 230) are provided for modulating the exposure time along the guide (the fiber) by varying the speed at which the beam (300) moves along the guide (the fiber) (120) so that it is located opposite each location of the guide (the fiber) (120) for a time period that varies with the location, the method including the step of disposing in front of the guide (the fiber) (110) a system (140) adapted to create interference fringes on the guide (the fiber) (120) and to scan the beam (300) over the interference system (140) at a speed that is modulated along the system (140), and furthermore the step of having the beam scan the guide (the fiber) (120) at a modulated speed without the interference system (140) on the path of the beam (300), the scanning with the interference system (140) being eff

Abstract: The invention relates to apparatus for measuring the index profile of an optical fiber preform that includes an outer envelope and a core. According to the invention, a deformable and transparent separation interface is provided between a deformable index isotropy medium and the outside surface of the envelope of the preform, said deformable separation interface adapting the deformable index isotropy medium to the outside surface of the envelope of the preform at least over an annular zone thereof, which zone corresponds to an optical measurement zone situated on the path of a light beam, said deformable and transparent interface, and inlet and outlet optical surfaces for the light beam all having an index close to the index of said medium.