Optical device comprising a multi-layers waveguides

Abstract

It is proposed an optical device for delivering a polychromatic image to an eye box being an area positioned in front of an eye of a user wearing said optical device. The optical device is remarkable in that it comprises: • a light-engine for delivering said polychromatic image, said light engine being able to generate n different monochromatic light image beams [C, . . . , C, . . . , C, whom combination corresponds to said polychromatic image, each monochromatic light image Cbeing associated with a wavelength Ay, and wherein A>Afor all the i E [1, n], and wherein the monochromatic light image beams Cis in a transverse electric mode if j is odd, and the monochromatic light image beams Cis in a transverse magnetic mode if j is even; • n-waveguide elements () that are stack on each other, n being an integer greater or equal to three, each waveguide element, except the one closer to the eye of a user, comprising a diffraction grating that can deviate only one of said n monochromatic light image in the waveguide element by total internal reflection, a first output that delivers deviated light toward said eye box, and a second output that delivers non-deviated light by a waveguide element to a subsequent waveguide element, wherein said second output comprising an achromatic half-wave plate (506, 507), and wherein the waveguide element that is closer to the eye of the user comprises also a diffraction grating that can deviate only one of said n monochromatic light image in the waveguide element by total internal reflection, and an output that delivers deviated light toward said eye box, wherein each diffraction grating of said optical device is associated with a different wavelength, and, wherein the arrangement order of said n-waveguide is done according to the wavelength value, from the smallest to the highest, the smallest waveguide element being positioned closer to the light engine.