Lumus Patent | Virtual image delivery system for near eye displays

The constraint given by expression (2) requires that for a same intensity of light propagated in the input FOV of the given input virtual image along any two different or same angular directions, the facets reflect substantially a same intensity of light toward the EMB along the same respective angular directions in the output FOV of the output virtual image. The constraint operates to preserve relative brightness of features in the input virtual image to better than 8% in the projected output virtual image projected by GOODIS to the EMB. The constraint also provides for uniformity to better than 8% of intensity of light in an output FOV of the projected output virtual image independent of location of the output FOV in the EMB. In accordance with an embodiment of the disclosure the coatings on the facets in at least one of the x-waveguide and y-waveguide are configured to advantageously satisfy the constraints.

In an embodiment the coatings may be determined responsive to iterative Monte Carlo ray tracing for different configurations of coatings and a cost function that indicates when a given configuration of coatings converges to a configuration that provides GOODIS with a desired fidelity. Among a plurality of degrees of freedom available for modeling and determining coatings for the facets in accordance with an embodiment of the disclosure are at least one or any combination of more than one of reflectivity of an optionally dielectric coating as a function of incident angle for s polarized light and/or p polarized light, a number of facets, spacing between facets and/or their respective tilt angles. A configuration of coatings may be considered to provide a desired fidelity and advantageously satisfy the constraints when the configuration satisfies a criterion responsive to the value of the cost function.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF FIGURES

Non-limiting examples of embodiments of the disclosure are described below with reference to figures attached hereto that are listed following this paragraph. Identical features that appear in more than one figure may be labeled with a same label in multiple figures in which they appear. A label labeling an icon representing a given feature of an embodiment of the disclosure in a figure may be used to reference the given feature. Dimensions of features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale.

FIG. 1 schematically shows the geometry of a good image delivery system, a GOODIS, comprising first and second LOEs that cooperate to expand in two dimensions an input aperture located in the first LOE to an output aperture located in the second LOE, in accordance with an embodiment of the disclosure;

FIG. 2 schematically illustrates light propagation as a function of the geometry of the GOODIS shown in FIG. 1, in accordance with an embodiment of the disclosure;

FIG. 3A shows schematic graphs of reflectivity of a dielectric coating as a function of angle of incidence for p and s light incident on facets of the GOODIS in the first LOE that contribute to providing an advantageous fidelity that characterizes the GOODIS, in accordance with an embodiment of the disclosure;

FIG. 3B shows schematic graphs of reflectivity of a dielectric coating as a function of angle of incidence for p and s light incident on the facets of the GOODIS in the second LOE that contribute to providing an advantageous fidelity that characterizes the GOODIS, in accordance with an embodiment of the disclosure;

FIG. 3C shows a schematic graph of dependence of s and p polarization light reflected into the second LOE from the first LOE assuming that light from a virtual image input into the first LOE is substantially p polarized with respect to TIR surfaces of the first LOE, in accordance with an embodiment of the disclosure; and

FIG. 4 schematically illustrates operation of a GOODIS having facets coated with the dielectric coatings shown in FIGS. 3A and 3B, in accordance with an embodiment of the disclosure.

DETAILED DESCRIPTION

In the discussion, unless otherwise stated, adjectives such as “substantially” and “about” modifying a condition or relationship characteristic of a feature or features of an embodiment of the disclosure, are understood to mean that the condition or characteristic is defined to within tolerances that are acceptable for operation of the embodiment for an application for which it is intended. Wherever a general term in the disclosure is illustrated by reference to an example instance or a list of example instances, the instance or instances referred to, are by way of non-limiting example instances of the general term, and the general term is not intended to be limited to the specific example instance or instances referred to. Unless otherwise indicated, the word “or” in the description and claims is considered to be the inclusive “or” rather than the exclusive or, and indicates at least one of, or any combination of more than one of items it conjoins.

FIG. 1 schematically shows a GOODIS 20 comprising an x-LOE 30 having a waveguide 31 and facets 40 embedded in the waveguide and a y-LOE 50 having a waveguide 51 and facets 60 embedded in the waveguide in accordance with an embodiment of the disclosure. For convenience of presentation features and geometry of GOODIS 20 are spatially referenced relative to a coordinate system 21.

Waveguide 31, also referred to as x-waveguide 31 is optionally a rectangular prism having relatively large parallel face surfaces 32 and 33 parallel to the xy-plane of coordinate system 21 and parallel, relatively narrow top and bottom edge surfaces 34 and 35 parallel to the xz-plane. Light from images generated by a display engine such as a display engine 70 shown in FIG. 1 is coupled into waveguide 31 optionally by a prismatic input coupler 71 through an input aperture 36 located on an end surface 37 of the x-waveguide. Light entering x-waveguide 31 through input aperture 36 is repeatedly totally internally reflected (TIR) from face surfaces 32 and 33, also referred to as TIR surfaces 32 and 33, to bounce back and forth between the TIR surfaces and propagate along the positive x-direction in the x-waveguide to reach and be incident on facets 40.

By way of example a light ray input into x-waveguide 31 propagating in a midplane 38 of the x-waveguide parallel to the xz-plane and being totally internally reflected from TIR surfaces 32 and 33 to bounce back and forth between the TIR surfaces is schematically represented by arrows 23. Optionally, upon entry into x-waveguide 31 polarization of light in light ray 23 schematically indicated by a block arrow 25 is parallel to midplane 38, and since the midplane is a plane of incidence of the light ray with TIR surfaces 32 and 33 the light ray is p polarized with respect to the plane of incidence.

Facets 40 are optionally parallel to each other and perpendicular to TIR surfaces 32 and 33 and are tilted by a tilt angle β_x relative to bottom edge surface 35 and the x-axis. A normal 41 to each facet 40 is rotated relative to the y-axis by the tilt angle β_x. Each facet 40 as described below reflects a portion of light propagating in x-waveguide 31 that is incident on the facet through bottom edge surface 35 and into waveguide 51. For example when light ray 23 is incident on a facet 40 the facet reflects a portion of the light in the light ray into y-waveguide 51. It is noted that whereas light ray 23 is p polarized with respect to TIR surfaces 32 and 33, with respect to facets 40 because the normals 41 of the facets do not lie in the midplane, the light ray comprises both p and s polarized light.

Waveguide 51, also referred to as y-waveguide 51, is also optionally a rectangular prism. The waveguide has relatively large parallel TIR face surfaces 52 and 53 parallel to the xy-plane and parallel, relatively narrow left and right edge surfaces 54 and 55 respectively that are parallel to the yz-plane. Light reflected by facets 40 in x-waveguide 31 into y-waveguide 51 is repeatedly TIR reflected from face surfaces 52 and 53 to bounce back and forth between the TIR surfaces and propagate in y-waveguide 51 along the y-axis to reach and be incident on facets 60 of the y-waveguide. Facets 60 are optionally parallel to each other and perpendicular to side surfaces 54 and 55. The facets are tilted by a tilt angle β_y relative to TIR surface 52 and the y-axis. A normal 61 to each of facets 60 is rotated by tilt angle β_y relative to the z-axis. Each facet 60 as described below reflects a portion of light propagating in y-waveguide 51 along the y-axis that is incident on the facet through an output aperture 57 on TIR face surface 53 to an EMB 80 for viewing by a user (not shown).

GOODIS 20 as shown in FIG. 1 has height h, width w, and thickness of depth d. X-waveguide 31 has height h₁ and y-waveguide 51 height h₂. Both waveguides optionally have a same width substantially equal to the width w of GOODIS and a same thickness or depth, d. Height h may be equal to (h₁+h₂). By way of numerical example, in an embodiment h may have a value between about 30 mm (millimeters) and about 50 mm, height h between 30 mm and about 50 mm, and depth between about 1.0 mm to about 3 mm. Height h₁ of x-waveguide 31 in an embodiment may be between about 10 mm and about 20 mm, and height h₂ may be between about 10 mm and 40 mm. X-waveguide 31 may have between about 20 and about 30 facets 40 tilted at a tilt angle β_x between about 25° and about 65°. Y-waveguide 51 may have between about 8 and about 12 facets 60 tilted at a tilt angle β_y between about 20° and about 70°.

FIG. 2 schematically illustrates propagation of light rays from virtual images generated by display engine 70 that are coupled into GOODIS 20 by input coupler 71 to travel along x-waveguide 31 and be reflected into y-waveguide 51 by facets 40 and thereafter by facets 60 in the y-waveguide toward EMB 80.

In x-waveguide 31 a triangular cluster of arrows converging to a point on a facet 40 from which the facet reflects light rays into y-waveguide 51 represents a cross section in the xy-plane of a FOV comprising angular directions along which light rays received from display engine 70 are incident on the facet. By way of example, three FOV xy cross sections represented by triangular clusters 101, 102, and 103 of angular propagation directions of light rays are shown in FIG. 2 for a selection of facets 40 individualized by labels 40-1, 40-2, and 40-3 respectively. A light ray in a FOV xy cross section 101, 102, and 103 represented by a solid arrow 121 is reflected into y-waveguide 51 along an angular direction represented by a solid arrow 131 for which facets 60 in the y-waveguide successfully reflect light into EMB 80. However, not all light from light rays in the FOV of the virtual image that are incident on a facet 40 and reflected into y-waveguide 51 are successfully reflected into EMB 80. A dashed arrow 122 in a FOV cross section 101, 102, or 103 represents a light ray that facet 40-1, 40-2 or 40-3 respectively reflects into y-waveguide 51 along an angular direction represented by a dashed arrow 132 for which facets 60 reflect light that misses EMB 80. Solid arrows 131 representing angular directions of light rays from which light is successfully reflected into EMB 80 by facets 60 are shown pointing into output aperture 57. Dashed arrows 132 representing angular directions of light rays from which facets 60 reflect light that fails to reach EMB 80 are shown pointing towards regions outside of output aperture 57.

Shaded areas 401, 402, and 403 in FIG. 2 schematically indicate ranges of angular directions along which facets 40-1, 40-2, and 40-3 respectively reflect light rays from which facets 60 successfully reflect light into EMB 80. Median angular directions in ranges 401, 402, and 403 along which the facets respectively reflect incident light rays are indicated by relatively long solid arrows 131 in the ranges. The median angular directions for ranges 401, 402, and 403 are directed along angles θ₁, θ₂, and θ₃, relative to normals 41 of facets 40-1, 40-2 and 40-3 respectively. Angles θ₁, θ₂, θ₃, are angles of incidence and reflection of light rays that are reflected along the median angular directions in ranges. As a result of the locations of facets 40-1, 40-2 and 40-3 relative to outlet aperture 57, and as schematically shown in FIG. 2, θ₁>θ₂>θ₃. Quite generally, a median angular direction of incidence and corresponding angular direction of reflection along which a facet 40 reflects light rays and from which subsequently facets 60 successfully reflect light to EMB 80 decreases with distance of the facet from input aperture 36.

Similarly, median angular directions of light that facets 60 reflect into EMB 80 from light rays reflected into y-waveguide 51 by facets 40 decrease with distance of facets 60 from bottom surface 35 of x-waveguide 31. The median angular directions for a selection of facets 60 are represented by solid arrows 151. Angles of reflection between the median angular directions 151 and normals 61 for the selection of facets 60 are labeled φ₁, φ₂, and φ₃, where a larger subscript identifies an angle associated with a facet 60 further from bottom surface 35.

The above discussion indicates that different facets of GOODIS 20 reflect different angular portions of an input FOV of a virtual image from display engine 70 into EMB 80. And in general, to achieve a high fidelity output image, the farther a facet 40 in x-waveguide 31 is from input aperture 36 the larger should be reflectivity of the facet for light from portions of the input FOV having smaller angles of incidence, AOI, on the facet, which the facet reflects to larger values of x in the EMB. Similarly, the farther a facet 60 in y-waveguide 51 is from bottom edge surface 35 of x-waveguide 31, the larger should be reflectivity of the facet for light from portions of the input FOV having smaller AOIs on the facet, which the facet reflects to larger values of y in the EMB.

Let an “x” index such as k(x) designate a facet 40 in x-waveguide 31 and let the value of the index increase with distance of the designated facet 40 from input aperture 36. Similarly, let a “y” index, such as k(y) designate a facet 60 in y-waveguide 51 and let the value of the index increase with distance of the designated facet 60 from surface 35. The constraints for provision of a high fidelity output virtual image expressed by expressions (2) and (3) may be written to express constraints on facets 40, which may also be referred to as x-facets 40,

[(|TP°_k(x),m−TP°_j(x),n|/AVG(TP°_k(x),m,TP°_j(x),n))<δ%|I(α_m)=I(α_n),∀(j(x),k(x)),∀(m,n)] (3)