A method for imprinting a plurality of slanted Bragg gratings into a photosensitive optical fiber by exposure of said fiber to a pattern of light shaped in space and/or time and of suitable wavelenth is presented. According to the invention a basic slanted Bragg grating of a determined period is imprinted into said fiber, while, simultanously, a periodic apodisation function is applied to said single slanted Bragg grating. In its preferred embodiment the imprinting light pattern is generated by a phase mask from a UV laser, the phase mask being dithered during the imprinting.