Diffraction based monochromatic head up display for airborne applications

Abstract

Optical display systems and methods for providing three-dimensional and two-dimensional convergence corrected images to a user are described. The optical display systems may include at least two image generators producing a plurality of rays forming a plurality of images. A diffraction enhanced imaging system may be configured to collect the rays produced and control convergence angle of each ray at specific wavelengths into an optical waveguide. An in-coupling diffraction system may couple the rays into the optical waveguide. A wavelength compensated beam expander may expand horizontal extension of the images and an output coupling and vertical expansion system may magnify the images in a vertical direction and direct light towards a user at specific angles creating a wide field of view.

What is claimed is: 
     
         1 . An optical display system for providing three-dimensional convergence corrected images to a user, comprising:
 at least one image generator producing a plurality of rays forming a limited color, two-dimensional image;   a diffraction enhanced imaging system configured to collect rays produced by the image generator and configured to control convergence angle of each ray at specific wavelengths into an optical waveguide such that rays at different wavelengths have different convergence angles;   an in-coupling diffraction system configured to couple the rays controlled by the diffraction enhanced imaging system into the optical waveguide via at least one of specific convergence angles and a specific divergence angle;   a wavelength compensated beam expander configured to simultaneously expand horizontal extension of the images and compensate for wavelength dispersion; and,   an output coupling and vertical expansion system configured to magnify the image in a vertical direction and direct a fraction of light toward the user at one or more specific angles creating a wide field of view.   
     
     
         2 . The optical display system of  claim 1 , wherein the in-coupling diffraction system uses diffraction to couple the rays into the optical waveguide at specific convergence angles such that at least one of the wavelength compensated beam expander and the output coupling and vertical expansion system produce an expanded beam of the rays having specific divergence angles. 
     
     
         3 . The optical display system of  claim 1 , wherein the wavelength compensated beam expander simultaneously expands horizontal extension of the images and compensate for wavelength dispersion such that a color component of each image pixel of each image overlap precisely at the output coupling and vertical expansion system. 
     
     
         4 . The optical display system of  claim 1 , wherein the diffraction enhanced imaging system includes at least one lens, the lens comprising at least one diffractive portion and at least one refractive portion configured to alter wavelength dispersion effect on image distance produced by the lens. 
     
     
         5 . The optical display system of  claim 4 , wherein the lens comprises:
 a first substrate layer formed of an optically clear material having known wavelength dispersion properties;   a first diffractive grating layer positioned adjacent to the first substrate layer, the first diffractive grating layer is formed of a holographic material and includes a plurality of gratings, the gratings configured with a grating period impacting wavelength dispersion;   a second diffractive grating layer positioned adjacent to the first diffractive grating layer and formed of substantially similar material and properties as the first diffractive grating layer, the second diffractive grating layer having a plurality of gratings; and,   a second substrate layer positioned adjacent to the second diffractive grating layer and formed of an optically clear material.   
     
     
         6 . The optical display system of  claim 5 , the lens further comprises a spacer layer formed of an optically clear material and positioned between the first diffractive grating layer and the second diffractive grating layer. 
     
     
         7 . The optical display system of  claim 5 , wherein the first substrate layer includes a first surface and a second surface and at least one of the first surface and the second surface is a curved surface. 
     
     
         8 . The optical display system of  claim 5 , wherein the second substrate layer includes a first surface and a second surface and at least one of the first surface and the second surface is a curved surface. 
     
     
         9 . The optical display system of  claim 5 , wherein peaks of the gratings of the second diffractive grating layer lie at a substantially similar position as valleys of the gratings of the first diffractive grating layer. 
     
     
         10 . The optical display system of  claim 5 , wherein at least one of the first substrate layer, first diffractive grating layer, second diffraction grating layer and second substrate layer consist of at least one material having a refractive index configured to be controlled by application of an electric field. 
     
     
         11 . The optical display system of  claim 5 , further comprising a wedge element configured to provide at least one image at a different angle from an optical axis of the lens and a different distance from an output plane of the lens. 
     
     
         12 . The optical display system of  claim 5 , further comprising a refractive element positioned adjacent to the lens, the refractive element being formed of dispersive material and configured to enhance wavelength dispersion of the lens. 
     
     
         13 . The optical display system of  claim 1 , wherein the in-coupling diffraction system includes a single diffraction grating having a period configured to direct rays entering the in-coupling diffraction system to exit the in-coupling diffraction system at an angle conducive to propagation within the optical waveguide by total internal reflection. 
     
     
         14 . The optical display system of  claim 13 , wherein period of the single diffraction grating, alters ray cone for each wavelength to create a new image point configured as an input image for the wavelength compensated beam expander. 
     
     
         15 . The optical display system of  claim 13 , wherein period of the single diffraction grating is configured to modify wavelength dispersion introduced by the diffraction enhanced imaging system. 
     
     
         16 . The optical display system of  claim 1 , wherein distance between the diffraction imaging system and the in-coupling diffraction system is determined such that beam width for each color at an input plane of the in-coupling diffraction system and axis of beams intercepting the in-coupling diffraction system results in a beam of light that includes wavelengths having substantially similar beam width and beam axis when exiting the wavelength compensated beam expander. 
     
     
         17 . The optical display system of  claim 1 , wherein the wavelength compensated beam expander includes at least two optical elements positioned in series and each configured to alter wavelength dispersion properties of rays. 
     
     
         18 . The optical display system of  claim 17 , wherein a first image produced by a first optical element is an input image for a second optical element. 
     
     
         19 . The optical display system of  claim 18 , wherein the second optical element may be configured to produce collimated light for each wavelength with position and propagation direction of each output beam overlapping with beams for other wavelengths. 
     
     
         20 . The optical display system of claim  118 , wherein each optical element includes at least one of a reflective mirror, a single-axis Fresnel reflector, and a reflection grating. 
     
     
         21 . The optical display system of  claim 1 , wherein the output coupling and vertical expansion system includes a vertically oriented waveguide having at least two reflecting elements configured to magnify images in a vertical direction and direct at least a fraction of light out of the vertically oriented waveguide and towards the user at specific angles; to create the wide field of view. 
     
     
         22 . A method, comprising:
 collecting a plurality of rays forming images produced by an image generator and altering convergence angle of the rays at each wavelength such that rays at different wavelengths have different convergence angles;   coupling the rays into an optical waveguide system using diffraction at specific convergence and divergence angles;   expanding horizontal extent of each image;   compensating for wavelength dispersion such that color components of each image pixel overlap;   magnifying each image in a vertical direction; and,   directing a fraction of light out of the optical waveguide system and toward a user at specific angles to create a wide field of view.   
     
     
         23 . An optical display system, comprising:
 an image generator producing a plurality of rays forming a color limited two-dimensional image; and,   a diffraction enhanced imaging system configured to collect rays produced by the image generator and configured to control convergence angle of each ray at specific wavelengths into an optical waveguide such that rays having different wavelengths have different convergence angles, the diffraction enhanced imaging system comprising a lens having at least one diffractive portion and at least one refractive portion configured to alter wavelength dispersion effect on image distance produced by the lens.