Diffractive combiner for multicolor and monochrome display, method of manufacture and head-up display device using same

A method for producing a single-layer diffractive combiner for a head-up display having a projection unit with n light sources of lambdai wavelength(s), where i=1 to n sending light towards the combiner at an angle thetap. The method includes forming interference fringes for each lambdai wavelength on a photosensitive layer with an interference of two light beams from a single laser source of wavelength lambdae, where the forming step is repeated n times, and each time the forming step is repeated an angle thetai between the two beams is determined according to thetai=arcsin ((lambdae/lambdai)*sin(thetap)), one of the interfering beams being divergent and having a spherical wave front and the other being a plane wave, the interference of the beams generating a diffractive network with an adjustable pitch and curved contour fringe lines.