The general field of the invention is that of optical guides for collimated images comprising a first and a second image conductor functioning by total reflection, each conductor comprising a plurality of plates that are planar, semi-reflective, mutually parallel and inclined with respect to the plane of the external faces of the image conductors. The two conductors are arranged so as to deliver a collimated image to a large pupil. The optical guide according to the invention comprises an optical beam doubler element having substantially the shape of a rectangular parallelepiped. In its basic version, it comprises four external planar facets, two internal semi-reflective planar mirrors, said mirrors being mutually perpendicular, a planar entrance face intended to receive a collimated image, and an exit face adhesively bonded to the injection section of one of the image conductors. The invention also relates to the whole of the display device associated with this optical guide.