Patent ID: 6825987
Filing Date: 2004-11-30
Classification: G02B

Abstract:
A light guide for display devices of the head-mounted or head-up type, comprising:a body of the light guide at least in part transparent to visible light; a coupling device associated to the body of the light guide and designed to couple the body to an optical system designed to generate an image, the coupling device being obtained in such a way that the light beams coming from said optical system enter the body of the light guide and propagate in the body by total internal reflection; and an image-extraction grating designed to extract the light beams which propagate in the body of the light guide so as to enable an observer to visualize the extracted image on a background visible in transparency through the body of the light guide; wherein said extraction grating is set in the proximity of one of the outer surfaces of the guide; said extraction grating has a saw-tooth profile; said extraction grating is coated with a partially reflecting coating deposited prevalently on the surfaces of the teeth that are least inclined with respect to the surfaces of the guide; and said coating is in turn coated with a layer of material having a refractive index that is substantially the same as that of the body of the light guide and having a surface facing the extraction grating, which follows the saw-tooth profile, and another plane surface which is substantially parallel to the outer surface of the guide in an area corresponding to which the grating is made.