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

Method of manufacturing a monolayer diffractive combiner used in a head-up display device for an automobile vehicle, said head-up display comprising a projection unit provided with a display backlit by n≧1 light source(s) of wavelength(s) λi, where i=1 to n, said light source(s) illuminating at least one zone of said display, and sending a light beam towards said combiner at an angle θp, said method of manufacturing comprising the following steps:

• a) depositing a photosensitive layer having a uniform thickness on a plane surface of a solid substrate;
• b) exposing the photosensitive layer to an interference of two light beams R1 and R2 emanating from a single laser source to form exposed zones of interference fringes corresponding to the interference of the two light beams;
• c) converting the exposed zones to form a diffractive relief structure in the photosensitive layer, and manufacturing a mold for reproducing the diffractive relief structure;
• and
• d) using said mold to transfer the diffractive relief structure of the substrate onto an element made of homogeneous transparent plastic material effective to form the monolayer diffractive combiner characterized as having a diffractive surface, wherein step b) is carried out n times, by the two light beams R1 and R2 emanating from the single laser source, said two light beams characterized as having a wavelength λe, and each time distinguished by emanating with an angle θi, where i=1 to n, between the beam R1 and the beam R2 equal to θi=arcsin ((λe/λi)*sin(θp)), wherein one of the interfering beams is characterized as being divergent and having a spherical wave, and the other beam is characterized as being a plane wave, wherein their interference generates a diffractive network with variable pitch with curved fringe contour lines.