Light-guide optical elements using complementary-coated partial reflectors and light-guide optical elements with reduced light scattering

Abstract

The reflectivity of a partially reflective surface is sensitive to various parameters of the incident light, including spectral range, polarization direction, and angle of incidence.SOLUTION: The transparent substrate has two parallel surfaces and guides the collimated image light by internal reflection. The first set of internal surfaces is disposed in the substrate oblique to the parallel planes. The second set of interior surfaces is disposed within the substrate parallel to the first set of interior surfaces, alternating with the first set of interior surfaces, and in an overlapping relationship with the first set of interior surfaces. Each of the first set of internal surfaces includes a first coating having a first reflective characteristic that is at least partially reflective to at least a first subset of components of incident light. Each of the second set of internal surfaces includes a second coating having a second reflective characteristic complementary to the first reflective characteristic to at least partially reflect at least a second subset of components of the incident light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 943,867, filed December 5, 2019, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to display systems, and in particular to light-directing optical elements suitable for use in displays. [Background technology]

[0003] One particular display technology, particularly suited to head-up displays (HUDs) such as near-eye displays (NEDs) for virtual reality and augmented reality applications, uses a light-guiding optical element, also referred to as a "light guide" or "light-transmitting substrate," having a series of internal, oblique, mutually parallel, partially reflective surfaces. An image projector is optically coupled to the waveguide and inputs light corresponding to a collimated image into the waveguide, such that the light propagates through the waveguide by internal reflection. The propagating light is gradually coupled out of the waveguide toward the observer's eye by reflection off the series of partially reflective surfaces, thereby expanding the effective optical aperture on the side opposite the eye compared to the output aperture of the image projector.

[0004] The reflectance of a partially reflective surface is sensitive to various parameters of the incident light, including the spectral range, polarization direction, and angle of incidence. Partially reflective surfaces are typically coated with optical coatings to produce a desired reflectance pattern. Summary of the Invention

[0005] The present invention is a light-guiding optical element.

[0006] Certain preferred embodiments according to one aspect of the invention provide light-guide optical elements having internal partial reflectors coated according to an optical coating scheme that allows spectral, polarization, and angular uniformity requirements to be simultaneously met. In other embodiments of this aspect of the invention, the aforementioned requirements are met while simultaneously minimizing reflections in undesired directions. Certain preferred embodiments according to another aspect of the invention provide light-guide optical elements having an amount of reflection-repressing material applied to an exterior surface or one or more regions of the surface of the light-guide optical element that reduces light scattering within the light-guide optical element.

[0007] In accordance with the teachings of an embodiment of the present invention, an optical device is provided, comprising: an optically transmissive substrate having at least two parallel major exterior surfaces for guiding light exhibiting a collimated image by internal reflection at the major exterior surfaces; a first set of mutually parallel interior surfaces disposed within the substrate at an angle relative to the exterior surfaces; and a second set of mutually parallel interior surfaces disposed within the substrate parallel to the first set of interior surfaces, alternating with and overlapping the first set of interior surfaces, wherein at least a portion of each of the first set of interior surfaces includes a first coating having first reflective properties such that the first coating is at least partially reflective to at least a first subset of components of incident light, and at least a portion of each of the second set of interior surfaces includes a second coating having second reflective properties complementary to the first reflective properties such that the second coating is at least partially reflective to at least a second subset of components of incident light, such that the sets of interior surfaces cooperate to reflect all components of light from the first and second subsets.

[0008] Optionally, the first subset of components includes light corresponding to a first color, and the second subset of components includes light corresponding to a second color.

[0009] Optionally, a first subset of components comprises light having a first polarization direction, and a second subset of components comprises light having a second polarization direction.

[0010] Optionally, at least one of the first coating or the second coating includes a structural polarizer.

[0011] Optionally, at least one of the first coating or the second coating comprises a dielectric coating.

[0012] Optionally, at least one of the first coating or the second coating comprises a metal coating.

[0013] Optionally, the first coating is configured to reflect light having a wavelength corresponding to a first color with a first reflection efficiency, reflect light having a wavelength corresponding to a second color with a second reflection efficiency, and reflect light having a wavelength corresponding to a third color with a third reflection efficiency less than the first reflection efficiency, and the second coating is configured to reflect light having a wavelength corresponding to the first color with a reflection efficiency greater than the third reflection efficiency, such that the combined reflection efficiency of the third color by the first and second coatings is greater than or equal to the first reflection efficiency.

[0014] Optionally, the second reflection efficiency is less than the first reflection efficiency, and the second coating is configured to reflect light having a wavelength corresponding to the second color with a reflection efficiency greater than the second reflection efficiency, such that the combined reflection efficiency of the second color by the first and second coatings is greater than or equal to the first reflection efficiency.

[0015] Optionally, the second coating is configured to reflect light having a wavelength corresponding to the first color with a reflective efficiency approximately equal to the first reflective efficiency.

[0016] Optionally, the first coating is configured to reflect light having wavelengths corresponding to a first color with a first reflection efficiency, reflect light having wavelengths corresponding to a second color with a second reflection efficiency less than the first reflection efficiency, and reflect light having wavelengths corresponding to a third color with a third reflection efficiency less than the first reflection efficiency, and the second coating is configured to reflect light having wavelengths corresponding to the first color with a reflection efficiency greater than the second and third reflection efficiencies, reflect light having wavelengths corresponding to the second color with a reflection efficiency greater than the second and third reflection efficiencies, and reflect light having wavelengths corresponding to the third color with a reflection efficiency greater than the second and third reflection efficiencies.

[0017] Optionally, the first coating comprises a patterned coating comprising several portions of reflective material arranged in a predetermined pattern on each of the first set of interior surfaces.

[0018] Optionally, each portion of reflective material has a circular shape in the plane of the interior surface.

[0019] Optionally, each portion of reflective material has an oval shape in the plane of the interior surface.

[0020] Optionally, the reflective material is a dielectric material.

[0021] Optionally, the reflective material is a metallic material.

[0022] Optionally, the spaces formed between the portions of reflective material are transparent.

[0023] Optionally, a second reflective material is disposed on an interior surface in spaces formed between the portions of reflective material.

[0024] Optionally, the second reflective material comprises a dielectric material.

[0025] Optionally, the second reflective material is disposed in a predetermined pattern on the interior surface.

[0026] Optionally, at least one of the number of moieties or the size of the moieties on the first set of interior surfaces increases with respect to the primary direction of propagation of light through the substrate.

[0027] Optionally, the optical device further comprises an amount of light reflection suppressing material disposed between the reflective material and at least a portion of the first set of interior surfaces.

[0028] Optionally, the light reflection suppressing material includes a light absorbing material.

[0029] Optionally, the light reflection suppressing material includes a light scattering material.

[0030] A first coating is disposed on a first portion of each of the first set of interior surfaces, a second coating is disposed on a second portion of each of the first set of interior surfaces, a second coating is disposed on a first portion of each of the second set of interior surfaces, and a first coating is disposed on a second portion of each of the second set of interior surfaces, the first and second portions of the first set of interior surfaces being non-overlapping portions, and optionally the first and second portions of the second set of interior surfaces being non-overlapping portions.

[0031] Optionally, the first and second sets of internal surfaces reflect a percentage of light guided by internal reflection at the major external surface away from the substrate towards the viewer's eyes.

[0032] Optionally, the first and second sets of internal surfaces reflect a proportion of light guided by internal reflection at the major external surface out of the substrate so as to be coupled to the second optically transparent substrate for guidance by internal reflection at the external surface of the second optically transparent substrate.

[0033] Optionally, the substrate is configured to guide light in one dimension through the substrate.

[0034] Optionally, the substrate is configured to guide light in two dimensions through the substrate.

[0035] Optionally, at least one of the interior surfaces from at least one of the first set or the second set includes an edge region associated with a first of the exterior surfaces of the substrate that defines a boundary region between the at least one interior surface and the substrate, the first of the exterior surfaces having a quantity of light-absorbing material positioned in a recess formed in the first of the exterior surfaces at the boundary region.

[0036] Also provided is an optical device according to embodiments of the present teachings, comprising: an optically transmissive substrate having at least two parallel major exterior surfaces for directing light exhibiting a collimated image by internal reflection at the major exterior surfaces; and a plurality of mutually parallel interior surfaces disposed within the substrate at an angle relative to the exterior surfaces, wherein at least a portion of a first subset of the interior surfaces comprises a patterned coating including portions of a reflective material arranged in a predetermined pattern on the interior surfaces of the first subset, the patterned coating being at least partially reflective to at least a first subset of components of incident light, and a second subset of the interior surfaces being at least partially reflective to at least a second subset of components of incident light, the interior surfaces of the first subset being in an overlapping relationship with the interior surfaces of the second subset, such that the subsets of interior surfaces cooperate to reflect all components of light from the first and second subsets.

[0037] Optionally, each portion of reflective material has a circular shape in the plane of the first subset of interior surfaces.

[0038] Optionally, each portion of reflective material has an oval shape in the plane of the first subset of interior surfaces.

[0039] Optionally, the reflective material is a dielectric material.

[0040] Optionally, the reflective material is a metallic material.

[0041] Optionally, the spaces formed between the portions of reflective material are transparent.

[0042] Optionally, a second reflective material is disposed in spaces formed between the portions of reflective material.

[0043] Optionally, the second reflective material comprises a dielectric material.

[0044] Optionally, the second reflective material is disposed in a predetermined pattern on the interior surfaces of the first subset.

[0045] Optionally, at least one of the number of moieties or the size of the moieties on the interior surface of the first subset increases with respect to the direction of propagation of light through the substrate.

[0046] Optionally, the optical device further comprises an amount of light reflection suppressing material disposed between the reflective material and the first subset of inner surfaces.

[0047] Optionally, the light reflection suppressing material includes a light absorbing material.

[0048] Optionally, the light reflection suppressing material includes a light scattering material.

[0049] Optionally, the interior surfaces of the first subset alternate with the interior surfaces of the second subset.

[0050] Optionally, a surface of the first subset of interior surfaces is coplanar with a surface of the second subset of interior surfaces.

[0051] Optionally, the interior surface reflects a percentage of light guided by internal reflection at the major exterior surface back out of the light-transmitting substrate towards the viewer's eyes.

[0052] Optionally, the interior surface reflects a proportion of light guided by internal reflection at the major exterior surface from the light-transmitting substrate so as to be coupled to the second light-transmitting substrate for guidance by internal reflection at the exterior surface of the second light-transmitting substrate.

[0053] Optionally, the substrate is configured to guide light in one dimension through the substrate.

[0054] Optionally, the substrate is configured to guide light in two dimensions through the substrate.

[0055] Optionally, at least one of the interior surfaces includes an edge region associated with a first of the exterior surfaces of the substrate that defines a boundary region between the at least one interior surface and the substrate, the first of the exterior surfaces having a quantity of light-absorbing material positioned in a recess formed in the first of the exterior surfaces at the boundary region.

[0056] An optical device according to an embodiment of the present teachings is also provided, comprising: a light-transmitting substrate having at least two parallel major exterior surfaces for guiding light by internal reflection at the major exterior surfaces; at least one at least interior surface disposed within the substrate at an angle relative to the exterior surfaces, the at least one interior surface having an edge region associated with a first one of the exterior surfaces of the substrate that defines a boundary region between the interior surface and the substrate; and a quantity of light-absorbing material positioned in a recess formed in the first one of the exterior surfaces at the boundary region.

[0057] Optionally, at least one interior surface comprises a plurality of mutually parallel partially reflective surfaces.

[0058] Optionally, at least one internal surface is configured to couple light guided within the substrate out of the substrate by internal reflection.

[0059] Optionally, at least one internal surface is configured to couple light into the substrate for propagation within the substrate by internal reflection.

[0060] Optionally, the at least one internal surface is configured to couple light guided within the substrate by internal reflection into the second optically transmissive substrate so as to propagate within the second substrate by internal reflection.

[0061] Optionally, the light absorbing material comprises black absorbing paint.

[0062] Optionally, the amount of light absorbing material is sufficient to fill the recess.

[0063] Optionally, the inner surface has a second end region associated with a second one of the outer surfaces of the substrate defining a second boundary region between the inner surface and the substrate, and the optical device further comprises a quantity of light-absorbing material positioned in a recess formed in the second one of the outer surfaces at the second boundary region.

[0064] Also provided is a method for manufacturing an optical device according to an embodiment of the present teachings, comprising: obtaining a light-transmitting substrate having at least two parallel major exterior surfaces for guiding light by internal reflection at the major exterior surfaces, the substrate having at least one interior surface disposed between and obliquely relative to the exterior surfaces, the interior surface having an edge region associated with a first of the exterior surfaces of the substrate and defining a boundary region between the interior surface and the first of the exterior surfaces; and depositing a quantity of light-absorbing material within a recess formed in the first of the exterior surfaces at the boundary region.

[0065] Optionally, depositing the amount of light-absorbing material includes applying the light-absorbing material to substantially the entire first of the exterior surfaces.

[0066] Optionally, the method further comprises polishing the first one of the exterior surfaces to remove the light absorbing material from substantially all portions of the first one of the exterior surfaces outside the recess.

[0067] Optionally, obtaining the light-transmitting substrate includes attaching a set of coated transparent plates together to form a stack, slicing the stack diagonally to form a substrate having at least two parallel major exterior surfaces and an interior surface at an angle to the exterior surfaces, and polishing the exterior surfaces.

[0068] Optionally, polishing the exterior surfaces causes a first one of the exterior surfaces to form a recess in the boundary region.

[0069] Optionally, the amount of light absorbing material is sufficient to fill the recess.

[0070] Optionally, the inner surface has a second end region associated with a second one of the outer surfaces of the substrate to define a boundary region between the inner surface and a second one of the outer surfaces, and the method further includes depositing a quantity of light-absorbing material in a recess formed in the second one of the outer surfaces at the boundary region between the inner surface and the second one of the outer surfaces.

[0071] An optical device according to an embodiment of the present teachings is also provided, comprising: an optically transmissive substrate having first and second pairs of parallel major exterior surfaces forming a rectangular cross-section, the substrate configured to guide light by internal reflection at the major exterior surfaces; at least one interior surface disposed within the substrate at an angle to a direction of elongation of the substrate configured to couple light out of the substrate; and a quantity of light-absorbing material positioned in a defect formed in an exterior region of the substrate.

[0072] Optionally, the defect comprises a scratch formed on one of the exterior surfaces.

[0073] Optionally, the defect comprises a chip at an edge formed between one of the exterior surfaces of the first pair of exterior surfaces and one of the exterior surfaces of the second pair of exterior surfaces.

[0074] Optionally, the defect includes a chip in a corner formed between one of the exterior surfaces of the first pair of exterior surfaces and one of the exterior surfaces of the second pair of exterior surfaces.

[0075] Optionally, the interior surface includes at least a first end region associated with one of the exterior surfaces of the substrate so as to define a boundary region between the interior surface and the substrate.

[0076] Optionally, the defect comprises a depression formed in the boundary region.

[0077] Optionally, the light absorbing material comprises black absorbing paint.

[0078] Unless otherwise defined herein, all technical and / or scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. In carrying out or testing embodiments of the present invention, methods and materials similar or equivalent to those described herein may be used, but exemplary methods and / or materials are described below. In case of conflict, the present patent specification, including definitions, will prevail. Furthermore, the materials, methods, and examples are merely illustrative and are not necessarily intended to be limiting. [Brief explanation of the drawings]

[0079] Some embodiments of the present invention are described herein, by way of example only, with reference to the accompanying drawings. With specific reference to the drawings in detail, it is emphasized that the details shown are by way of example and for purposes of illustrative discussion of embodiments of the present invention. In this regard, the description taken together with the drawings will make apparent to those skilled in the art how embodiments of the present invention may be practiced.

[0080] Turning now to the drawings, in which like reference numbers or letters indicate corresponding or similar elements, [Figure 1] 1 is a schematic side view representation of a light-directing optical element (LOE) constructed and operative in accordance with the teachings of one embodiment of the present invention, illustrating the progression of components of image radiation through a series of alternating sets of internal partially reflective surfaces having complementary sets of coatings. [Figure 2] 1 shows the reflectance curves of coatings that may be used on some of the internal partially reflecting surfaces as a function of angle of incidence for p-polarized and s-polarized light. [Figure 3] 1 is a schematic representation of image radiation components reflected by an internal partially reflective surface at different reflection angles. [Figure 4] 1 is a schematic representation of a patterned reflective coating having portions of reflective material that can be used to compensate for lower reflection of some of the illumination components. [Figure 5] 5 is a schematic representation of a patterned reflective coating similar to that of FIG. 4, but with portions of reflective material having shapes different from those of the portions of reflective material in FIG. 4. [Figure 6] 1 is a schematic representation of a coating having two reflective patterns on a single coating. [Figure 7] 1 illustrates reflectance curves as a function of wavelength for coatings that may be used on some of the internal partially reflective surfaces. [Figure 8] 7 shows the reflectance curve achieved when using the coating of FIG. 7 in combination with complementary coatings used on some of the internal partially reflective surfaces. [Figure 9] 10 shows reflectance curves as a function of wavelength for different coatings that may be used on some of the internal partially reflective surfaces. [Figure 10] 9 shows the reflectance curves achieved when using the coating of FIG. 9 in combination with complementary coatings used on some of the internal partially reflective surfaces. [Figure 11] 1 is a schematic representation of a series of internal partially reflective surfaces having two complementary coatings disposed in alternating order on each of the internal partially reflective surfaces. [Figure 12A] 1A-1C are schematic side and front views of an optical device having two optical waveguides each having a set of partially reflective internal surfaces that may have complementary coatings for performing optical aperture expansion in two dimensions. [Figure 12B] 1A-1C are schematic side and front views of an optical device having two optical waveguides each having a set of partially reflective internal surfaces that may have complementary coatings for performing optical aperture expansion in two dimensions. [Figure 13] 1 is a schematic representation of another optical device having two optical waveguides each having a partially reflective internal surface that may have a complementary coating for performing optical aperture expansion in two dimensions. [Figure 14] 1 is a schematic representation of an LOE having a set of internal partially reflective surfaces, showing the progression of image radiation through the LOE and an undesired reflection from one of the internal partially reflective surfaces. [Figure 15A] 15 is a schematic representation of one of the internal partially reflective surfaces of FIG. 14 implemented with a patterned reflective coating similar to the patterned reflective coatings of FIGS. 4 and 5 , illustrating the transmission and reflection of light incident on the front side of the internal partially reflective surface. [Figure 15B] 15B is a schematic representation of the partially reflective surface of FIG. 15A showing the transmission and reflection of light incident on the back side of the internal partially reflective surface. [Figure 16A]FIG. 15C is a schematic representation of an internal partially reflective surface similar to that of FIGS. 15A and 15B , constructed and operative in accordance with the teachings of one embodiment of the present invention, having an amount of reflection-suppressing material disposed between the reflective portion of the patterned reflective coating and the front side of the internal partially reflective surface, illustrating the transmission and reflection of light incident on the front side of the internal partially reflective surface. [Figure 16B] 16B is a schematic representation of the partially reflective surface of FIG. 16A showing the transmission of light incident on one region behind the internal partially reflective surface and the suppression by the reflection-reducing material of light incident on another region behind the internal partially reflective surface. [Figure 17] 1 is a schematic representation of a section of a light-directing optical element (LOE) showing defects in the form of dimples formed in the interior partially reflective surface of the LOE and in the boundary region between the interior partially reflective surface and the exterior surface of the LOE. [Figure 18] 18 is a schematic representation corresponding to FIG. 17 showing the progression of image radiation through the LOE and the scattering effect on image radiation imparted by the depression. [Figure 19] 19 is a schematic representation of a section of a light-directing optical element (LOE) constructed and operative in accordance with the teachings of one embodiment of the present invention, similar to the LOE of FIGS. 17 and 18, but having a quantity of light-absorbing material applied in the recess and illustrating absorption of image radiation by the light-absorbing material. [Figure 20] 12B is a side view similar to FIG. 12A, but showing a defect in the form of a chipped corner or edge of one of the optical waveguides. [Figure 21] 21 is a side view corresponding to FIG. 20, showing an amount of light absorbing material applied at a chamfered corner or edge, according to the teachings of one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0081] Embodiments of the present invention provide various light-directing optical elements with internal partial reflectors, including light-directing optical elements having coatings in which the internal partial reflectors are applied according to a complementary coating scheme, and light-directing optical elements having reflection-suppressing material applied to an exterior surface or one or more regions of a surface of the light-directing optical element.

[0082] The principles and operation of various light-directing optical elements according to the present invention may be better understood with reference to the drawings accompanying the description.

[0083] Before describing at least one embodiment of the present invention in detail, it should be understood that the present invention is not necessarily limited in its application to the details of construction and arrangement of components and / or methods set forth in the following description and / or illustrated in the drawings and / or examples. The present invention may be practiced or carried out in other embodiments or in various ways. Initially, references are made herein to directions, such as front-to-back, up-down, and left-to-right. These directional references are exemplary only for the purpose of illustrating the present invention and its embodiments.

[0084] Referring now to the drawings, Figure 1 shows an optical device in the form of a light-directing optical element (LOE), generally designated 10, constructed and operative in accordance with a non-limiting embodiment of the present invention. LOE 10 is formed as an optically transmissive substrate composed of a transparent material (such as glass) having a pair of parallel faces (also referred to as "major exterior surfaces" or "surfaces") 12, 14, and a plurality of planar partially reflective surfaces 16a, 16b, 16c, 18a, 18b, 18c disposed within the substrate at oblique angles relative to parallel faces 12, 14. In the illustrated non-limiting embodiment, LOE 10 forms a slab waveguide, i.e., the other two dimensions of LOE 10 are at least an order of magnitude greater than the distance between parallel faces 12, 14. The partially reflective surfaces (hereinafter interchangeably referred to as "internal surfaces," "internal partial reflectors," "partial reflectors," or "facets") 16a, 16b, 16c, 18a, 18b, 18c are subdivided into two sets of internal object surfaces: a first set 16 having internal surfaces 16a, 16b, 16c, and a second set 18 having internal surfaces 18a, 18b, 18c. For ease of presentation, each of the sets 16, 18 is shown herein as having three internal surfaces, although it should be understood that either or both sets can have any suitable number of internal surfaces.

[0085] In certain preferred, but non-limiting, embodiments, the interior surfaces of the two sets 16, 18 alternate, such that one or more of the interior surfaces 16a, 16b, 16c are disposed between adjacent pairs of interior surfaces 16a, 16b, 16c, 18a, 18b, 18c, and vice versa. Preferably, the interior surfaces alternate between the interior surfaces of the two sets 16, 18, such that for each pair of adjacent interior surfaces 16a, 16b, 16c, there is one of the interior surfaces 18a, 18b, 18c, and vice versa. This alternating configuration is shown in FIG. 1.

[0086] Here, projected image 20, represented schematically by beam 20 of illumination including sample rays 20A and 20B, is coupled into LOE 10 (i.e., within the substrate) by optical inward-coupling configuration 22, represented schematically as an inward-coupling reflector. Other suitable inward-coupling configurations for coupling image illumination into LOE 10 are known in the art, such as by the use of suitably angled coupling prisms or diffractive optical elements. Image illumination 20 is guided within LOE 10 by repeated internal reflections off parallel faces 12, 14 (i.e., image illumination 20 is trapped by internal reflections within the LOE substrate). In certain preferred, but non-limiting, implementations, propagation through LOE 10 by internal reflection is a form of total internal reflection (TIR), whereby incident propagating image illumination 20 on parallel faces 12, 14 at angles greater than a critical angle causes reflection of the illumination at parallel faces 12, 14. In other non-limiting implementations, propagation through LOE 10 by internal reflection is achieved by reflective coatings (eg, angle-selective reflective coatings) applied to parallel faces 12, 14.

[0087] Image illumination 20 propagates through LOE 10 until it reaches a series of interior surfaces 16a, 16b, 16c, 18a, 18b, and 18c, where a portion of the image intensity is reflected from LOE 10 as rays 24A and 24B. In certain embodiments, such as the embodiment shown in FIG. 1, interior surfaces 16a, 16b, 16c, 18a, 18b, and 18c reflect the image illumination as reflected rays 24A and 24B to couple a portion of the image intensity from LOE 10 toward the viewer's eye. As will be discussed, in other embodiments, interior surfaces 16a, 16b, 16c, 18a, 18b, and 18c reflect the image illumination as reflected rays 24A and 24B and couple it into another LOE for directing between the parallel faces of the other LOE and for coupling outward toward the viewer's eye by a set of interior surfaces disposed within the other LOE.

[0088] The image illumination 20 typically includes multiple components of illumination, including, for example, different polarization components and different color (i.e., spectral) components. The interior surfaces 16a, 16b, 16c, 18a, 18b, 18c are preferably formed from transparent plates or slabs having a coating applied to at least a portion of the sides or surfaces of the plates or slabs. The coatings are designed with reflective properties so that the coatings at least partially reflect incident light having specific corresponding characteristics to generate desired reflectance patterns for the components of illumination, as described in more detail below. Generally, at least a portion of the interior surfaces 16a, 16b, 16c have coatings with reflectance properties so that specific components of the image illumination are reflected by the interior surfaces 16a, 16b, 16c. At least a portion of interior surfaces 18a, 18b, 18c also have a coating having reflective properties complementary to the reflectivity properties of interior surfaces 16a, 16b, 16c, so that components of the imaging illumination that are not sufficiently reflected by interior surfaces 16a, 16b, 16c are preferably and sufficiently reflected by interior surfaces 18a, 18b, 18c.

[0089] Before describing the design details of reflectors 16a, 16b, 16c, 18a, 18b, 18c in more detail, it should be noted that the projected image illumination 20 is a collimated image, i.e., each pixel is represented by a beam of parallel rays at a corresponding angle, corresponding to light from the scene far away from the observer (a collimated image may be referred to as "infinitely collimated"). Note that while image 20 is represented here simply as a single ray corresponding to a single point in the image, typically the image's center of gravity, the image actually comprises a range of angles to each side of the central ray, which are coupled into and out of the substrate at corresponding ranges of angles, thereby producing a field of view corresponding to the portion of the image that reaches the observer's eye in the direction that the image reaches.

[0090] Each interior surface has opposing ends that define where the interior surface begins and stops, respectively. These opposing ends are referred to as the "start end" and "stop end." For example, looking at interior surfaces 16a and 18a, it can be seen that interior surface 16a has start end 17a-1 and stop end 17a-2, and interior surface 18a has start end 19a-1 and stop end 19a-2. Interior surfaces 16a, 16b, and 16c are preferably disposed within LOE 10 so that each interior surface 16b, 16c begins where the previous interior surface 16a, 16b ends within the projection plane of the interior surfaces. In other words, start end 17b-1 of interior surface 16b is aligned with stop end 17a-2 of interior surface 16a, and start end 17c-1 of interior surface 16c is aligned with stop end 17b-2 of interior surface 16b. In such an arrangement, facets 16a, 16b, 16c appear continuous and non-overlapping in the plane of projection, and in the non-limiting implementation shown in FIG. 1, are planar, parallel to the planes of surfaces 12, 14. This arrangement ensures that there are no gaps between adjacent interior surfaces 16a, 16b, 16c in the primary light propagation direction through LOE 10 (arbitrarily illustrated as being from left to right along the horizontal axis in FIG. 1), thereby maintaining continuous aperture expansion (i.e., aperture multiplication) for the components of light reflected by first set 16. Similarly, interior surfaces 18a, 18b, 18c are preferably arranged within LOE 10 so that each interior surface 18b, 18c starts where the previous interior surface 18a, 18b ends, thereby maintaining continuous aperture expansion for the components of light reflected by second set 18. In other words, the starting edge 19b-1 of the inner surface 18b is aligned with the stopping edge 19a-2 of the inner surface 18a, and the starting edge 19c-1 of the inner surface 18c is aligned with the stopping edge 19b-2 of the inner surface 18b.

[0091] In embodiments in which the interior surfaces of the two sets 16, 18 alternate, the two sets 16, 18 also preferably have an overlapping relationship, whereby at least some of the interior surfaces of the first set 16 overlap some of the interior surfaces of the second set 18, and vice versa. In certain cases, the overlapping relationship is such that there is at least one interior surface of one of the sets 16, 18 having a starting end located at a position in the projection plane that is between a starting end and a stopping end of a single interior surface of the other of the sets 16, 18, and a stopping end of an interior surface of one of the sets 16, 18 located at a position in the projection plane that is between a starting end and a stopping end of another single interior surface of one of the sets 16, 18.

[0092] FIG. 1 shows the two sets 16, 18 in an alternating and overlapping configuration, with the starting end 19a-1 of inner surface 18a positioned at a position in the projection plane between starting end 17a-1 and stop end 17a-2 of inner surface 16a, the stop end 19a-2 of inner surface 18a positioned at a position in the projection plane between starting end 17b-1 and stop end 17b-2 of inner surface 16b, the starting end 19b-1 of inner surface 18b positioned at a position in the projection plane between starting end 17b-1 and stop end 17b-2 of inner surface 16b, the stop end 19b-2 of inner surface 18b positioned at a position in the projection plane between starting end 17c-1 and stop end 17c-2 of inner surface 16b, and the starting end 19c-1 of inner surface 18c positioned at a position in the projection plane between starting end 17c-1 and stop end 17c-2. Similarly, stop end 17a-2 of inner surface 16a is positioned at a position in the projection plane between start end 19a-1 and stop end 19a-2 of inner surface 18a, start end 17b-1 of inner surface 16b is positioned at a position in the projection plane between start end 19a-1 and stop end 19a-2 of inner surface 18a, stop end 17b-2 of inner surface 16b is positioned at a position in the projection plane between start end 19b-1 and stop end 19b-2 of inner surface 18b, start end 17c-1 of inner surface 16c is positioned at a position in the projection plane between start end 19b-1 and stop end 19b-2 of inner surface 18b, and stop end 17c-2 of inner surface 16c is positioned at a position in the projection plane between start end 19c-1 and stop end 19c-2 of inner surface 18c.

[0093] Preferably, the overlapping configuration between the interior surfaces of the two sets 16, 18 is such that the start and stop ends of the interior surface of one of the sets 16, 18 are at a midpoint between the start and stop ends of the interior surface of the other of the sets 16, 18. Note that in certain instances, an "overlapping relationship" may include a complete overlapping configuration such that the interior surfaces of set 16 and set 18 are coplanar, whereby the start and stop ends of the facets of set 16 coincide with the start and stop ends, respectively, of the facets of set 18. Further details of optical waveguides using overlapping interior surfaces with conventional coating architectures can be found in commonly owned U.S. Patent No. 10,481,319, which is incorporated herein by reference in its entirety.

[0094] The following paragraphs describe coating designs for the sets of interior surfaces 16, 18 according to embodiments of the present invention. The interior surfaces 16a, 16b, 16c, 18a, 18b, 18c have coatings with complementary reflectivity properties such that components of the image illumination that are not sufficiently reflected by one of the interior surfaces 16a, 16b, 16c are preferably and sufficiently reflected by one of the interior surfaces 18a, 18b, 18c. Specifically, as described in detail below, the interior surfaces 16a, 16b, 16c have coatings configured to reflect a proportion of the intensity of each illumination component in a subset of the components of the image illumination, and the interior surfaces 18a, 18b, 18c have coatings configured to reflect a proportion of the intensity of each illumination component in another subset of the components of the image illumination, such that the coatings of the two sets of interior surfaces 16, 18 cooperate to reflect a combined proportion of the intensities of all illumination components within the two subsets. The combined percentage of intensity reflected by the coatings of the two sets 16, 18 cooperatively is equal to or greater than the percentage of intensity reflected by the coatings of the two sets 16, 18 individually.

[0095] When the interior surfaces are alternated according to an alternating configuration, as shown in FIG. 1 , the complementary coatings of pairs of adjacent interior surfaces from two different sets allow the interior surfaces from the two sets to cooperate to reflect all components of the image illumination over a portion of the projection plane of the interior surfaces to maintain continuous aperture expansion.

[0096] As part of a first non-limiting example, consider image illumination 20 including spectral components corresponding to different spectral components of illumination, e.g., red, green, and blue light. In this example, interior surfaces 16a, 16b, 16c may include a first coating configured to reflect red light (i.e., light having a wavelength near 638 nm) with high efficiency, partially reflect green light (i.e., light having a wavelength near 532 nm) with moderate efficiency, but partially reflect blue light (i.e., light having a wavelength near 456 nm) with low efficiency. To compensate for the moderate reflection efficiency of green light and the low reflection efficiency of blue light provided by interior surfaces 16a, 16b, 16c, interior surfaces 18a, 18b, 18c can include a second coating configured to reflect blue light with high efficiency (comparable to the efficiency provided by interior surfaces 16a, 16b, 16c on red light) and partially reflect green light with moderate efficiency (comparable to the efficiency provided by interior surfaces 16a, 16b, 16c on green light). The coating on interior surfaces 18a, 18b, 18c can also partially reflect red light with low efficiency. As a result, light ray 24A carries high efficiency red light, medium efficiency green light, and low efficiency blue light, and light ray 24B carries high efficiency blue light and medium efficiency green light, so that the overall reflected image resulting from reflection off the two alternating and overlapping sets 16, 18 has little or no color difference across the three colors while maintaining continuous aperture expansion (due to the alternating internal surfaces). Any residual color difference that cannot be eliminated by coating the two sets 16, 18 can be compensated for by adjusting the colored light sources used to generate the collimated image illumination 20.

[0097] In another non-limiting example, consider an image illumination 20 that includes two orthogonal linearly polarized components, namely, an s-polarized component and a p-polarized component, where two sets of interior surfaces 16, 18 include coatings that selectively reflect the orthogonal polarizations in a complementary manner, such that one interior surface of set 16 primarily reflects light polarized in one of the polarization directions (e.g., p-polarized light) to its surface, and the other interior surface of set 18 primarily reflects light polarized in the orthogonal polarization direction (e.g., s-polarized light) to its surface.

[0098] One type of coating that can provide such polarization-selective reflectivity is a dielectric coating. Figure 2 shows the reflectivity characteristics of such a dielectric coating for p- and s-polarized light across the angle of incidence (AOI). As can be seen, at lower AOIs, e.g., in the 0-20 degree range (i.e., near normal to the interior surface), both s- and p-polarized light are reflected with approximately the same efficiency; that is, the reflectivity of s- and p-polarized light is nearly the same (slightly above 25%). As the AOI increases over a given range, the reflectivity of the two polarizations diverges. Specifically, at higher AOIs, e.g., in the 20-55 degree range, the reflectivity of p-polarized light decreases compared to the reflectivity of s-polarized light. For example, at an AOI of approximately 40 degrees, the reflectivity of s-polarized light is slightly above 50% (thereby acting as a nearly perfect partial reflector), while the reflectivity of p-polarized light is less than 15%.

[0099] To produce an image with a wide viewer field of view, different angles are reflected from different interior surfaces. Figure 3 shows an LOE 10 in which all interior surfaces 16a, 16b, 16c, 18a, 18b, and 18c include a dielectric coating with the reflective properties described above with reference to Figure 2. In this configuration, the image radiation propagating through the LOE has both s-polarized and p-polarized components. Illustratively, some of the image radiation propagating through LOE 10 strikes interior surface 18c at a lower AOI, such that the dielectric coating reflects both polarizations with approximately the same efficiency. As a result, reflected ray R 18c The s-polarized components of the reflected ray R are of approximately equal intensity. However, some of the image radiation impinges on the interior surfaces 18a, 18b, 16b at the higher range of the AOI, so that the dielectric coatings on the interior surfaces 18a, 18b, 16b reflect primarily s-polarized light. As a result, the reflected ray R 18a , R 18b , R 16b The s-polarized component of each of the 18a, 18b is the dominant component. To compensate for the reduced p-polarized component in a particular AOI range, the interior surfaces 18a, 18b are redesigned to reflect primarily p-polarized light (or to reflect both polarizations with approximately equal efficiency).

[0100] According to certain embodiments, to achieve the desired reflectivity of p-polarized light, the internal surfaces 18 a, 18 b further include an orientation-sensitive polarizing reflector (or “structured polarizer”) that transmits one incident polarization and reflects the orthogonal polarization according to the reflector’s unique axial orientation. One non-limiting example of a structured polarizer is a birefringent dielectric coating or film commercially available from 3M Company (Minnesota, USA). Another non-limiting example of a structured polarizer is a wire grid film commercially available from Moxtek Inc. (Utah, USA). Yet another non-limiting example of a structured polarizer is a patterned partially reflective coating having multiple portions of reflective material arranged in a pattern on a thin film or transparent substrate.

[0101] With continued reference to FIGS. 1-3, reference is now made to FIG. 4, which shows a diagram of a non-limiting example of a patterned reflective coating (also referred to as a "reflective pattern coating") 30, according to a non-limiting embodiment of the present invention. Coating 30 has reflective properties such that light polarized in one polarization direction (e.g., s-polarized or p-polarized) is primarily / largely reflected by coating 30, and light polarized in the orthogonal polarization direction (e.g., p-polarized or s-polarized) is primarily / largely transmitted by coating 30. Preferably, the reflected polarized light exhibits greater than 90% reflection (referred to as "substantially complete reflection"), and most preferably, greater than 95% reflection. Conversely, the transmitted polarized light preferably exhibits greater than 90% transmission (referred to as "substantially complete transmission"), and most preferably, greater than 95% transmission.

[0102] The coating 30 includes amounts 34 of reflective material (hereinafter referred to as "portions" 34) disposed in a spaced-apart relationship and arranged in a predetermined pattern on a planar base surface 32. The base surface 32 is preferably, but not necessarily, transparent to light, so that spaces 35 on the base surface 32 formed between and around the portions 34 of reflective material are optically transparent. In certain embodiments, the planar base surface 32 is a thin film or substrate that can be bonded to a transparent plate to form an internal, partially reflective surface. In other embodiments, the planar base surface 32 itself is a faceted transparent plate, and the portions 34 of reflective material are deposited directly on the transparent plate. In certain embodiments, the reflective material is a dielectric material. In other, sometimes more preferred, embodiments, the reflective material is a metallic material, such as silver. Each portion 34 of reflective material has a shape that allows light of one polarization direction to induce a current flow. Thus, light polarized in the polarization direction that induces current flow will cause coating 30 to act as a reflector when incident on coating 30, and light polarized in the orthogonal polarization direction will cause coating 30 to act as an optical transmissive material when incident on coating 30.

[0103] 4, each of the portions 34 is identical in size and each has a generally circular shape in the plane of the base surface 32 (i.e., in the plane of the interior surface), where the portions 34 are circularly symmetrical dots (in the plane of the base surface 32) of reflective material deposited on the base surface 32 in the arranged pattern. In this configuration, the portions 34 are arranged in the predetermined pattern so that they are uniformly spaced apart, such that the distance between the centers of each pair of adjacent dots is constant throughout the coating 30.

[0104] FIG. 5 illustrates another non-limiting example of a coating 30 in which portions 36 of reflective material having non-circular symmetry in the plane of the base surface 32 are arranged on the base surface 32 in a predetermined pattern. Here, the portions 36 have a generally elliptical or oval shape (two orthogonal axes of symmetry) in the plane of the base surface 32 (i.e., in the plane of the interior surface). The orientation of the portions 36 in the plane of the base surface 32 determines the dominant reflected polarization. For example, in the configuration of portions 36 shown in FIG. 5, the dominant reflected polarization may be p-polarized light, while rotating the portions 36 90 degrees in the plane of the base surface 32 may switch the dominant reflected polarization to s-polarized light. Other shapes of reflective material besides circular and oval shapes are contemplated herein; for example, the portions of reflective material may be arranged in a pattern of lines on the base surface 32.

[0105] By using internal surfaces 18a, 18b with coating 30, internal surfaces 18a, 18b can reflect a subset of the illumination components (in this case, the p-polarized components) that are not completely reflected by internal surface 16b. In other words, for a given AOI within the higher AOI range, internal surface 16a reflects a first subset of the illumination components (in the form of s-polarized components) with high reflectivity and a second subset of the illumination components (in the form of p-polarized components) with low reflectivity. For the same given AOI, internal surfaces 18a, 18b reflect the low-reflectivity components, i.e., the second subset of the illumination components (in this case, the p-polarized components), with high reflectivity to compensate for the low reflectivity imparted by internal surface 16b. As a result, internal surfaces 18a, 16b, 18b cooperate to reflect both polarization components (i.e., components from both subsets) and maintain the continuity of aperture doubling. The two subsets of components of the image illumination are complementary, meaning that the combination of components from the two subsets accounts for all of the components of the propagated image illumination. In this particular example, the s- and p-polarized components are complementary because they make up the polarization components of the image illumination.

[0106] In certain embodiments, two different coatings may be implemented on the same interior surface plane using a single coating. For example, a dielectric coating may be disposed in the spaces between portions 34. As a result, portions 34 or 36 may be implemented as one type of dielectric or metallic coating, and the spaces 35 on base surface 32 formed between and around portions 34 or 36 may be implemented as another type of dielectric coating. FIG. 6 schematically illustrates an example of such a coating 31, in which portions 38 of a second reflective material are deposited in a predetermined pattern in the spaces 35 on base surface 32 formed between and around portions 34. In the non-limiting example shown in FIG. 6, each of portions 34 is generally circular in shape, while each of portions 38 is generally elliptical in shape.

[0107] As discussed, the coating designs of embodiments of the present invention are equally applicable to situations in which the image illumination includes different visible color components. In such situations, some of the principles of patterned reflector coatings described above with reference to Figures 4-6 can be used to address the color non-uniformity issue. For example, the interior surfaces 16a, 16b, and 16c can include a coating that partially reflects a first subset of three colors with a suitable reflection efficiency, and the interior surfaces 18a, 18b, and 18c can include a coating that partially reflects a second subset of three colors with a suitable efficiency, where the second subset of colors includes colors that are not preferably reflected by the interior surfaces 16a, 16b, and 16c. In general, the subsets of color components of the image illumination are complementary, meaning that the combination of components from the subsets accounts for all of the color components of the propagated image illumination. The following paragraphs describe various examples of coating designs for the interior surfaces of the two sets 16 and 18 to maintain color uniformity.

[0108] As a preamble, it is preferable to arrange the reflective material portions 34, 36 in a relatively small pattern so that the observer perceives a uniform image. In particular, it is preferable to arrange the reflective material portions 34, 36 in a geometric arrangement according to the size of the observer's eye pupil, e.g., as a circle with a diameter of approximately 2 mm (human eye pupils typically have diameters in the range of 2-4 mm under bright lighting conditions). However, reflective material portions having a small size and arranged in a small pattern tend to diffract incident light into large angles, thereby reducing image resolution. Therefore, in a non-limiting implementation of the present invention, the inner surfaces of the two sets 16, 18 are implemented using a reflective patterned coating (described above with reference to Figures 4-6) in combination with a dielectric coating.

[0109] In one non-limiting example, interior surfaces 16a, 16b, 16c are implemented with a dielectric coating to be at least partially reflective to red, green, and blue light, and interior surfaces 18a, 18b, 18c are implemented with a patterned coating 30 in which the reflective material of coating 30 is a metallic material (e.g., silver). The dielectric coating of interior surfaces 16a, 16b, 16c has reflective characteristics according to the graph shown in Figure 7, where the dielectric coating of interior surfaces 16a, 16b, 16c reflects a first subset of components of image illumination in the form of green light (i.e., light having a wavelength near 532 nm) with reasonably high efficiency (approximately 10% reflectance), but reflects a second subset of components of image illumination in the form of red light and blue light (i.e., light having wavelengths near 638 nm and 456 nm, respectively) with lower efficiency (approximately 4% reflectance) than it reflects green light. Coating 30 on interior surfaces 18a, 18b, and 18c has reflective properties that reflect both subsets of components with sufficient efficiency to compensate for the lower reflectivity of the second subset of components. The overall reflectivity provided by the combination of the dielectric coatings on interior surfaces 16a, 16b, and 16c and coating 30 on interior surfaces 18a, 18b, and 18c is shown in FIG. 8. As can be inferred, coating 30 reflects the second subset of components of the image illumination (i.e., red and blue light) with a reflectivity of at least approximately 6%, which is a higher efficiency than that provided to the second subset of components by the dielectric coatings on interior surfaces 16a, 16b, and 16c. Coating 30 also reflects the first subset of components of the image illumination (i.e., green light) with a reflectivity of approximately 4%. The two subsets of color components are complementary in that the combination of the two subsets (the first subset with high green light efficiency and the second subset with high red and blue light efficiency) accounts for all three color components of the image illumination. As a result, the overall reflected image has a higher resolution green component than the red and blue color components, but with reduced color differences.However, the human eye is most sensitive to the resolution of the green light component of an image, and therefore an overall image with higher resolution of the green component may be perceived by an observer as not having any noticeable loss of resolution.

[0110] In an alternative configuration, coating 30 can be implemented using a reflective material that has a higher reflectivity for red and blue light than for green light (i.e., coating 30 reflects mostly red and blue light). As a result, the overall reflected image will have little or no noticeable color difference.

[0111] In another non-limiting example, the interior surfaces 16a, 16b, 16c are implemented using a dielectric coating having reflectivity characteristics according to the graph shown in Figure 9. Here, the dielectric coating on the interior surfaces 16a, 16b, 16c reflects a first subset of the components of the image illumination in the form of green and red light with high efficiency (approximately 15% reflectivity), but reflects a second subset of the components of the image illumination in the form of blue light with lower efficiency than the reflection of the green and red light (approximately 10% reflectivity). To compensate for the lower reflectivity of the second subset of components, a particular implementation of the coating 30 is used on the interior surfaces 18a, 18b, 18c. In this implementation, the portion of the reflective material (implemented as a dielectric or metallic material) is small (preferably according to the human pupil size discussed above) and has reflectivity characteristics such that only blue light is reflected by the coating 30. The overall reflectance provided by the combination of the dielectric coating on interior surfaces 16a, 16b, 16c and coating 30 on interior surfaces 18a, 18b, 18c is shown in Figure 10, whereby the overall reflectance is constant at approximately 15% across the visible light spectrum, resulting in a diffraction-free, white-balanced image (blue light tends to diffract much less than green and red light).

[0112] FIG. 11 shows, by way of non-limiting example, another implementation that uses two coating schemes to maintain color uniformity. Here, the interior surfaces 16a, 16b, 16c, 18a, 18b, 18c have two sets of coatings on each reflector arranged in an alternating configuration, with lateral variations in the coatings on each interior surface. In the non-limiting illustrated example, each interior surface has two non-overlapping portions: a first portion and a second portion. The first portions 40a, 40b, 40c of the interior surfaces 16a, 16b, 16c have a first coating 33, e.g., a dielectric coating having reflective properties according to FIG. 7 or FIG. 9, and the second portions 42a, 42b, 42c of the interior surfaces 16a, 16b, 16c have a second coating 37, e.g., coating 30. First portions 44a, 44b, 44c of the interior surfaces 18a, 18b, 18c have the second coating 37, and second portions 46a, 46b, 46c of the interior surfaces 18a, 18b, 18c have the first coating 33.

[0113] In the non-limiting example shown in Figure 11, coatings 33, 37 are disposed on alternating portions of successive interior surfaces, such that the coatings on each pair of adjacent interior surfaces (e.g., interior surfaces 16a, 18a; interior surfaces 18a, 16b; interior surfaces 16b, 18b, etc.) cooperate to reflect all of a subset of the components of the image illumination with reasonable efficiency to maintain color uniformity. In this particular configuration, the two sets of interior surfaces can be considered effectively coplanar, whereby each interior surface has both coatings 33, 37. Note that while Figure 11 shows that each of the two portions of each interior surface constitutes approximately half of the interior surface plane, other configurations are possible so long as the portions of the interior surfaces on which coatings are disposed alternate between successive interior surfaces.

[0114] Although embodiments for maintaining color uniformity have been described in the context of interior surfaces 16a, 16b, and 16c having a dielectric coating and interior surfaces 18a, 18b, and 18c having a coating implemented in accordance with coating 30, other embodiments in which interior surfaces 16a, 16b, 16c, 18a, 18b, and 18c alternate, as discussed above with reference to, for example, FIGS. 4-6, and other embodiments in which both types of coatings are implemented on a single interior surface are possible. For example, each of interior surfaces 16a, 16b, 16c, 18a, 18b, and 18c may comprise two coatings: 1) a first coating, such as coating 30, and 2) a second coating, such as a dielectric disposed in the space formed between portions 34 of coating 30. The second coating may have reflective properties according to FIG. 7 or FIG. 9, whereby a first subset of components of the image radiation is reflected by the second coating with greater efficiency than a second subset of components of the image radiation. The first coating can then have reflective properties that compensate for the lower reflectivity imparted to the second subset by the second coating, so that each individual interior surface achieves an overall reflectivity that is nearly uniform across the three colors, as shown, for example, in Figures 8 and 10. In such a configuration, the two sets 16, 18 do not need to be alternating. Instead, the interior surfaces of both sets 16, 18 are identically coated, so that the two sets 16, 18 are identical, and preferably arranged so that each interior surface begins where the previous interior surface ends.

[0115] In certain embodiments, to provide uniform intensity throughout the field of view, the patterned reflective coating 30 on the interior surface may be configured so that the number of portions 34, 36 on the interior surface and / or the size of the portions 34, 36 vary from facet to facet. For example, interior surfaces 16a, 16b, 16c may be implemented using a dielectric coating (as discussed above), while interior surfaces 18a, 18b, 18c may be implemented using a patterned reflective coating 30. As light propagates through the LOE, the intensity of the light striking each successive facet is less than the intensity of the light striking the previous facet. This is due to the fact that a certain percentage of the intensity of the light striking a particular facet is reflected back from the LOE by that particular facet. To compensate for the decrease in light intensity in the direction of light propagation, the reflectivity provided by each facet should generally increase compared to the reflectivity provided by the preceding facet. This can be achieved by increasing the density of reflective material on the coating 30 on the interior surfaces of the second set 18 relative to the primary propagation direction of light through the LOE, for example, by increasing the number of portions 34, 36 and / or the sizes of the portions 34, 36. For example, the coating 30 on the interior surface 18a can be implemented with a first number of portions 34, 36 and / or a first size of portions 34, 36, the coating 30 on the interior surface 18b can be implemented with a second number of portions 34, 36 and / or a second size of portions 34, 36, and the coating 30 on the interior surface 18c can be implemented with a third number of portions 34, 36 and / or a third size of portions 34, 36. The first number of portions is smaller than the second number of portions, which is smaller than the third number of portions, and the size of the first portions is smaller than the second size of portions, which is smaller than the size of the third portion.

[0116] While some of the embodiments described so far involve two sets of internal partial reflectors with complementary coatings, other embodiments are possible in which there are more than two sets of partial reflectors with complementary coatings. As a simple example, a third set of internal surfaces can be disposed parallel to and interleaved with the internal surfaces of the other two sets 16, 18. Each set of internal surfaces can include a coating configured to reflect a specific subset of components of the image illumination. For example, the coating of the internal surfaces of the first set can be configured to reflect primarily red light, the coating of the internal surfaces of the second set can be configured to reflect primarily green light, and the coating of the internal surfaces of the third set can be configured to reflect primarily blue light. As a result, a given group of three (preferably contiguous) internal surfaces (one internal surface from each of the three sets) can cooperate to reflect all three components of the image illumination.

[0117] The coating and facet deployment techniques discussed above are described within the context of non-limiting examples of image illumination having either different spectral or polarization components. However, it should be understood that image illumination often has both spectral and polarization components (e.g., linearly polarized red, green, and blue light). For image illumination impinging on a facet at a higher range of AOI (e.g., 20-50 degrees), facet coatings can be designed to meet both spectral and polarization requirements to achieve transmission uniformity over a wide field of view.

[0118] While the coating designs and internal surface arrangements have been described thus far in the context of LOEs in which light is guided through the LOE in one dimension and coupled out (as "unguided" light) by internal surfaces (facets) to perform aperture expansion in one dimension (performing what is referred to herein as "guided-to-unguided" image propagation), the coating designs and facet arrangements described herein in accordance with embodiments of the present invention are equally applicable to optical devices having at least two light guides that cooperate to guide light in two dimensions to perform aperture expansion in two dimensions. These types of optical devices perform what is referred to herein as "guided-to-guided" image propagation, whereby image illumination is guided through a first light guide (in one or two dimensions) and reflected by a set of facets arranged in the first light guide to be coupled into a second light guide. The image illumination is then guided (in one dimension) through a second optical waveguide and reflected by a set of facets disposed in the second optical waveguide so as to couple the image illumination out of the second optical waveguide for viewing by an observer. The following paragraphs provide examples of optical devices that perform guide-to-guidance image propagation.

[0119] 12A and 12B show schematic side and front views, respectively, of an optical device performing guided-to-guided image propagation through two optical waveguides 50, 60 optically coupled together. Optical waveguide 50 has an elongation direction arbitrarily illustrated as corresponding to the "x-axis" and includes two pairs of parallel faces (i.e., major exterior surfaces) 52a, 52b, 54a, 54b forming a rectangular cross-section. A plurality of mutually parallel internally partially reflective surfaces (i.e., facets) 58 at least partially traverse optical waveguide 50 at an oblique angle relative to the elongation direction. Optical waveguide 60 optically coupled to optical waveguide 50 has a pair of parallel faces 62a, 62b forming a slab-type waveguide. Again, a plurality of mutually parallel internally partially reflective surfaces (i.e., facets) 64 at least partially traverse optical waveguide 60 at an oblique angle relative to the parallel faces 62a, 62b. The plane containing facet 58 is oblique to the plane containing facet 64 .

[0120] The optical coupling between light guides 50, 60, and the arrangement and configuration of partially reflective surfaces 58, 64 are such that when an image having an initial propagation direction at an oblique coupling angle relative to both the first and second pairs of parallel faces 52a, 52b, 54a, 54b is coupled into light guide 50, the image travels along light guide 50 by four internal reflections (i.e., in two dimensions) with a percentage of the image intensity reflected off partially reflective surface 58 to be coupled out of light guide 50 into light guide 60, and propagates through two internal reflections (i.e., in one dimension, similar to LOE 10) into light guide 60 with a percentage of the image intensity reflected off partially reflective surface 64 to be coupled out of light guide 60 as a visible image seen by the observer's eye. As a result of this construction, light propagating through light guide 50 is guided (in two dimensions by light guide 50), and light reflected by partially reflective surface 58 is also guided (in one dimension by light guide 60).

[0121] Coating design principles and / or facet alternation principles according to embodiments of the present invention can be applied to either or both sets of internally partially reflecting surfaces 58, 64. Further details of such optical devices using two optical waveguides 50, 60 can be found in commonly owned U.S. Patent No. 10,133,070, which is incorporated herein by reference in its entirety.

[0122] 13 shows a schematic diagram of an optical device that performs guided-to-guided image propagation through two slab light guides 70, 80 optically coupled together. Light guide 70 has two pairs of parallel faces 72a, 72b, 74a, 74b that form the slab waveguide (in the figure, faces 72a, 72b are at the front and back faces of light guide 70, respectively, and faces 74a, 74b are at the left and right sides of light guide 70, respectively). A plurality of mutually parallel internally partially reflective surfaces (i.e., facets) 76 at least partially traverse light guide 70 at oblique angles to the parallel faces 72a, 72b, 74a, 74b. Light guide 80 has two pairs of parallel faces 82a, 82b, 84a, 84b that form a slab waveguide (in the figures, faces 82a, 82b are on the front and back faces, respectively, of light guide 80, and faces 84a, 84b are on the left and right sides, respectively, of light guide 80). A plurality of mutually parallel internally partially reflective surfaces (i.e., facets) 86 at least partially traverse light guide 80 at oblique angles to parallel faces 82a, 82b, 84a, 84b. Furthermore, the plane containing facets 86 may be oblique or perpendicular to the plane containing facets 86.

[0123] In the illustrated non-limiting implementation, light guides 70, 80 are optically coupled together in a configuration in which light guide 70 is stacked on top of light guide 80. However, it should be noted that light guides 70, 80 can be stacked front to back (e.g., with faces 72b, 82a facing each other). The optical coupling between light guides 70, 80 and the arrangement and configuration of partially reflective surfaces 76, 86 are such that when an image is coupled into light guide 70, the image propagates within light guide 70 between faces 72a, 72b in a first guided direction through double internal reflection to be coupled into light guide 80 from light guide 70 with a percentage of the image intensity reflected off partially reflective surface 76, and propagates from light guide 80 between faces 82a, 82b in a second guided direction (oblique to the first guided direction) through double internal reflection to be coupled out of light guide 80 as a visible image seen by the eye of an observer with a percentage of the image intensity reflected off partially reflective surface 86.

[0124] Coating design principles and / or alternating facets according to embodiments of the present invention can be applied to either or both sets of internally partially reflecting surfaces 76, 86. Further details of such optical devices using two optical waveguides 70, 80 can be found in commonly owned U.S. Patent No. 10,551,544, which is incorporated herein by reference in its entirety.

[0125] While the use of reflective pattern coatings disclosed herein has the advantage of maintaining color uniformity and intensity uniformity, the use of reflective pattern coatings can cause unwanted reflections from interior surfaces, which can result in ghost images. The general concept of unwanted reflections from interior surfaces is explained with reference to FIG. 14 , where LOE 100 has three mutually parallel, partially reflective interior surfaces 106 a, 106 b, 106 c disposed at an angle relative to a pair of parallel faces (major exterior surfaces) 102, 104. The thicknesses of interior surfaces 106 a, 106 b, 106 c are exaggerated in FIG. 14 to clearly show front sides 108 a, 108 b, 108 c and back sides 110 a, 110 b, 110 c of interior surfaces 106 a, 106 b, 106 c. The front and back sides of the interior surface are generally opposing sides, and the front side is the side of the interior surface that is coated with a coating (as described with reference to Figures 1-11) having reflective properties that enable reflection of propagating image illumination according to a desired reflectance pattern.

[0126] Image illumination 108, represented schematically by ray 108, is inwardly coupled into LOE 100 by inward-coupling reflector 110 (or any other suitable optical inward-coupling configuration, e.g., a coupling prism). Image illumination 108 propagates through LOE 100 by repeated internal reflections at faces 102, 104 (by total internal reflection or due to angle-selective reflective coatings applied to the faces) until it reaches a series of internal surfaces 106a, 106b, 106c, where a portion of the image intensity is reflected from LOE 100 as rays 116a-116d at front sides 108a, 108b, 108c of internal surfaces 106a, 106b, 106c. Looking at propagating image illumination 118, represented schematically by ray 118, a portion of the intensity of ray 118 is transmitted by interior surface 106a (as ray 120), after which ray 120 is reflected off face 102, and then a percentage of the intensity is reflected off front side 108a of interior surface 106a to be reflected off LOE 100 as ray 116b (the remaining intensity is transmitted by interior surface 106a so that the light continues to propagate through LOE 100). However, a portion of the intensity of ray 118 undergoes unwanted reflection at back side 110a of interior surface 106a, resulting in reflected ray 122. Reflected ray 122 can, in certain circumstances, undergo internal reflection off faces 102, 104, exemplified by the reflection off face 102, to produce reflected ray 124. Reflected ray 124 is reflected off front side 108b of interior surface 106b so as to be reflected from LOE 100 as ghost ray 126.

[0127] Figures 15A and 15B illustrate how reflective pattern coating 30 allows for both desired reflections on the front side of the interior surface and undesired reflections on the back side of the interior surface. Note that Figures 15A and 15B are not drawn to scale, and some of the dimensions of the interior surface and components of reflective pattern coating 30 are exaggerated for clarity of illustration.

[0128] Turning first to FIG. 15A , it is shown how any interior surface 130 (which may be one of the interior surfaces of set 18, for example) handles propagating image radiation 140 impinging on the front side 132 of the interior surface 130. The interior surface 130 has a reflective pattern coating 30 deposited on the front side 132 of the interior surface 130. In particular, a planar base surface 32 is deposited on the front side 132 such that portions 34 are arranged in a desired pattern on the front side 132. Alternatively, portions 34 may be deposited directly on the front side 132 in an arranged pattern without using the planar base surface 32. The propagating image radiation 140, represented schematically by rays 140A and 140B, impinges on different regions of the front side 132 of the interior surface 130. In this case, the propagating image radiation 140 is image radiation that has undergone reflection from the underside of the LOE (e.g., face 102 in FIG. 14 or face 12 in FIG. 1). A portion of the propagating image illumination, represented by ray 140A, impinges on an area of ​​interior surface 130 having reflective material, to be reflected (from the LOE) by one of the portions 34 of reflective material as reflected ray 142. A portion of the propagating image illumination, represented by ray 140B, impinges on an area of ​​interior surface 130 having spaces 35 between the portions 34 of reflective material, and is transmitted by interior surface 130 as ray 142 (i.e., because spaces 35 are transparent, ray 140B passes through interior surface 130 from front side 132 to back side 134 as ray 142). This ray 140B continues to propagate through the LOE, being reflected off faces of the LOE and / or reflected by subsequent interior surfaces. As a result, a portion of image illumination 140A is reflected from the LOE by interior surface 130, and a portion of image illumination 140B is transmitted by interior surface 130.

[0129] 15B, which illustrates how interior surface 130 handles propagating image illumination 118, represented schematically by rays 118A and 118B, that impinges on backside 134 of interior surface 130. In this case, the propagating image illumination is image illumination that has undergone reflection from the top surface of the LOE (e.g., surface 104 in FIG. 14 or surface 14 in FIG. 1). A portion of the propagating image illumination, represented by ray 118A, impinges on an area of ​​interior surface 130 having spaces 35 between portions 34 of reflective material and is therefore transmitted by interior surface 130 as ray 120 (i.e., because spaces 35 are transparent, ray 118A passes through interior surface 130 from backside 134 to frontside 132). A portion of the propagating image illumination, represented by ray 118B, passes through the backside 134 of interior surface 130 and strikes an area of ​​interior surface 130 having reflective material to be reflected by one of the portions 34 of reflective material as reflected ray 122. As discussed above, this ray 122 may undergo additional reflections at the faces of the LOE and ultimately be reflected off the front side of one interior surface to be reflected from the LOE as a ghost ray.

[0130] To combat these unwanted reflections, embodiments of the present invention provide a coating of reflection-suppressing material applied between the reflective material portion and the front side of the interior surface. Figures 16A and 16B illustrate the reflection-suppressing material and its effect on the transmitted image illumination. As with Figures 15A and 15B, Figures 16A and 16B are not drawn to scale for clarity of illustration.

[0131] 16A , a coating of reflection-suppressing material, designated as portion 150, is disposed between portions 34 of reflective material and front side 132 of interior surface 130. If coating 30 is implemented using a planar base surface 32 (e.g., a thin film), portions 150 can be deposited directly on surface 32, and portions 34 can then be deposited on portions 150. Preferably, the portions of reflection-suppressing material are arranged in the same pattern configuration as the portions of reflective material, such that portions 34 and 150 are identical in size, shape, and number. As seen in FIG. 16A , the reflection-suppressing material has little or no effect on the propagation of image illumination incident on front side 132 of interior surface 130. As discussed above with reference to FIG. 15A , a portion of the propagating image illumination, represented by ray 140A, strikes an area of ​​interior surface 130 having reflective material, to be reflected by one of portions 34 of reflective material as reflected ray 142. A portion of the propagating image illumination, represented by ray 140 B, strikes an area of ​​interior surface 130 having spaces 35 between portions 34 of reflective material and is transmitted by interior surface 130 as ray 142 .

[0132] 16B, which illustrates how an interior surface 130 having a reflection-inhibiting material handles propagating image illumination 118 that impinges on a back surface 134 of the interior surface 130. As discussed above with reference to FIG. 15B, a portion of the propagating image illumination, represented by ray 118A, impinges on an area of ​​the interior surface 130 having spaces 35 between portions 34 of reflective material and is therefore transmitted by the interior surface 130 as ray 120. However, unlike the configuration of FIG. 15B, a portion of the propagating image illumination, represented by ray 118B, passes through the back side 134 of the interior surface 130 and impinges on an area of ​​the interior surface 130 having portions 150 of the reflection-inhibiting material. Because the reflection-inhibiting material prevents back-side reflection of ray 118B, undesired reflections of the propagating image illumination do not occur.

[0133] The reflection-reducing material can be implemented in a variety of ways. In one non-limiting example, the reflection-reducing material is implemented as an amount of black absorbing paint that absorbs incident light. In another non-limiting example, the reflection-reducing material is implemented as an amount of light-scattering material (e.g., a diffusive material) that scatters incident light in multiple directions with an intensity that is orders of magnitude less than the intensity of the incident light. As a result, any scattered light that continues to propagate through the LOE and is reflected by subsequent internal surfaces will generally have an intensity that is too low to be noticeable to an observer.

[0134] The reflection-suppressing material is preferably deposited between the reflective material and the front side of the interior surface during fabrication of the LOE. The LOE is constructed by forming a stack of transparent plates (e.g., glass plates) with embedded interior surfaces, preferably bonded together with a suitable coating at their interface. Bonding is typically performed using optical cement. The coatings can include patterned reflective and / or dielectric coatings, all as described above. The coating can be constructed in a layer on a thin film or thin substrate (e.g., base surface 32) that is applied at the interface between the transparent plates before bonding the plates together. Alternatively, the coating can be constructed directly on the transparent plate before bonding the plates together, so that the transparent plate serves as base surface 32. When using a reflection-suppressing material to reduce ghost images, a layer of reflection-suppressing material can be constructed in a pattern (either directly on the transparent plate or on the thin film or thin substrate), and a layer of patterned reflective material is then constructed on the reflection-suppressing material, thereby sandwiching the reflection-suppressing material between the transparent plate and the reflective material.

[0135] Once the stack of transparent plates is bonded together at its boundaries with an appropriate coating (preferably a reflection-repressing material), the stack is cut (i.e., sliced) at an appropriate angle (corresponding to the desired oblique angle at which the interior surfaces will be disposed) to form an LOE with a partially reflective interior surface embedded between its parallel major exterior surfaces (i.e., faces). Slicing at the appropriate angle is referred to as an "oblique cut" or "oblique slice." The major exterior surfaces of the LOE are then polished to improve the optical quality at the major exterior surfaces. In embodiments where the LOE uses an inward-coupling reflector as an optical inward-coupling configuration, similar steps can be performed to produce a substrate with an embedded inward-coupling reflector.

[0136] While the polishing process has the desired effect of improving the optical quality of the parallel faces of the LOE, the polishing process can, in certain instances, produce defects in the interface region between the LOE substrate and the internal surfaces, which can adversely affect the optical performance and image quality at the LOE output. One type of defect that can be caused by the polishing process is a depression in one or both of the parallel faces of the LOE at the interface region between the internal surface of the substrate and the parallel faces. Such a defect is shown schematically in FIG. 17 (not drawn to scale), which shows a section of LOE 200 having parallel faces 202, 204, with internal partially reflective surface 206 disposed at an angle relative to faces 202, 204. Although not shown in the drawing, additional internal partially reflective surfaces are disposed within LOE 200 parallel to internal surface 206.

[0137] Inner surface 206 includes two opposing ends 208a, 208b (i.e., a start end and a stop end) at corresponding end regions 210a, 210b associated with faces 202, 204, respectively. Faces 202, 204 and their respective end regions 210a, 210b (and particularly their respective ends 208a, 208b) define interface regions 212a, 212b (designated by dashed circles) between inner surface 206 and the LOE substrate. A depression 214 is formed in one of faces 202 in the corresponding interface region 212a (although it may be formed in both faces, i.e., in both interface regions 212a, 212b), e.g., as a result of a polishing process. Indentation 214 is generally formed as a depression, recess, pit, cavity, or gap in the face of the LOE, such that a portion (albeit a small portion) of face 202 protrudes inward into the interior section of LOE 200 in which the interior surface is located. The protruding portion (i.e., protrusion) is generally designated 216 in FIG. 17.

[0138] Typically, dimples 214 form as a result of the polishing process due to pressure applied during polishing at boundary regions 212a, 212b, which may have reduced structural integrity compared to the remainder of surfaces 202, 204. Other causes besides polishing may cause dimples 214 to form, such as mishandling of the LOE (e.g., dropping).

[0139] As a result of the depression 214, image illumination propagating at or near the boundary region 212a may be scattered by the protrusion 216. This is shown schematically in FIG. 18 , where image illumination 218 (schematically represented by ray 218) is transmitted by the interior surface 206 and undergoes internal reflection at the surface 204 to generate reflected ray 220 (which is also part of the image illumination). Ray 220 enters the surface 202 at or near the protrusion 216 so as to strike the protrusion 216, causing the incident ray 220 to reflect in multiple directions (i.e., be scattered) by the protrusion 216, as schematically represented by scattered rays 222a-222c. The ray is scattered in various directions due to the varying surface profile of the protrusion 216. These scattered rays 222a-222b are unwanted reflections that propagate through LOE 200 to be reflected by one of the subsequent internal surfaces at an undesired angle and can result in a ghost image in the observer's eye, similar to ray 122 discussed above with reference to FIG. 15B.

[0140] 19 , a method is shown for combating the scattering effect caused by the depressions 214 by coating the portion of the surface 202 containing the depressions 214 with a light-absorbing material. In particular, an amount of light-absorbing material 224 is deposited on the portion of the surface 202 containing the depressions 214. Preferably, the amount of light-absorbing material 224 positioned within the depressions 214 is sufficient to fill the depressions 214 to the level of at least the defect-free portion of the surface 202. In one non-limiting example, the light-absorbing material 224 is implemented as black absorbing paint that is applied to the surface 202 in an amount sufficient to fill the depressions 214. The surface 202 is then preferably polished to remove any excess light-absorbing material from the surface 202, such that only the light-absorbing material positioned within the depressions 214 remains, and the level of the light-absorbing material 224 within the depressions 214 is the same as the defect-free portion of the surface 202.

[0141] The effect of light absorbing material 224 on the propagated image illumination is also shown in Figure 19. Similar to what was discussed above with reference to Figure 18, light ray 218 is transmitted by interior surface 206 and undergoes internal reflection at face 204 to produce reflected light ray 220. However, when light ray 220 strikes protrusion 216, it is absorbed by light absorbing material 224, thereby preventing light scattering by protrusion 216.

[0142] The light-absorbing material can be applied to any of the interface regions between the internal surface and the LOE substrate where such a depression exists, and then polished as described above. For example, the light-absorbing material can be applied to the depression formed in interface region 212b. Additionally, if an inward-coupling reflector (i.e., an internal reflective surface) is used as the optical inward-coupling configuration, a depression can be formed in the interface region between the internal reflective surface and the LOE substrate during the polishing process. Here, a small amount of light-absorbing material can also be applied to the interface region between the internal reflective surface and the LOE substrate to counteract the scattering effect induced by the depression.

[0143] While scattering reduction through the use of light-absorbing material applied to defects in the exterior region of the LOE has been described within the context of LOEs in which light propagates in one dimension and is outcoupled by an interior surface to perform aperture expansion in one dimension, the light-absorbing material may similarly be applied to defects in the exterior region or portions of a light guide that perform aperture expansion in two dimensions, such as the light guides that perform guided-to-guided image propagation described with reference to Figures 12A, 12B, and 13. These defects may include depressions formed in the boundary regions between various facets (e.g., facets 58, 64, 76, 86) and corresponding surfaces (e.g., surfaces 52a, 52b, 54a, 54b, 62a, 62b, 72a, 72b, 74a, 74b, 82a, 82b, 84a, 84b).

[0144] Light-absorbing material can also be used to repair defects in the form of scratches on the surfaces of the light guide and / or on chipped corners or edges of the light guide. For example, consider light guide 50 of FIGS. 12A and 12B, reproduced in FIG. 20. Here, a portion of the corner / edge formed by surfaces 52a, 54a has been chipped (e.g., due to mishandling of light guide 50), creating defect 230. Light propagating through light guide 50 by quadruple internal reflection that strikes the area of ​​defect 230 will be scattered or reflected in an undesired direction. As shown in FIG. 21, to prevent the scattering effect, a quantity of light-absorbing material 224 can be applied to defect 230. In FIG. 21, the amount of light-absorbing material positioned at the defect is sufficient to restore the rectangular cross-section of light guide 50. However, a smaller amount of light-absorbing material can be applied to defects that do not restore the light guide to its defect-free structure. Light absorbing material may be applied equally to any of the light guides 10, 50, 60, 70, 80, 100, for example, to fill scratches in the face of the light guide (both one-dimensional and two-dimensional expanded aperture optical devices).

[0145] It should be noted that certain aspects of the invention described herein may be used to advantage independently of other aspects of the invention. For example, complementary coating approaches used with or without alternating sets of facets may be used to advantage apart from defect correction techniques. Furthermore, defect correction techniques may be applied to LOEs or optical waveguides (which perform one- and two-dimensional aperture expansion) that otherwise have conventional coating architectures.

[0146] While only LOE and light guide structures are illustrated in the drawings, it will be understood that the various LOEs and light guides described herein are intended for use as part of a display, typically a head-up display (HUD), preferably a near-eye display (NED) such as a head-mounted display (HMD) or eyeglass-frame supported display, to provide images to a viewer's eyes. In certain preferred embodiments, the display is part of an augmented reality (AR) display system in which images provided to the viewer's eyes are overlaid on an external "real world" view. In other embodiments, the display is part of a virtual reality (VR) display system in which only images provided by the LOE / light guide are visible to the viewer. In all such cases, the display preferably includes a small form factor image projector that produces a collimated image that is optically coupled to the LOE / light guide via an optical inward coupling arrangement (e.g., inward coupling reflector 22, coupling prism, etc.) to introduce the collimated image into the LOE / light guide so that it propagates by internal reflection within the LOE / light guide and is gradually outward coupled by internal selectively reflective surfaces.

[0147] Examples of suitable image projectors for projecting illumination (i.e., light) corresponding to (i.e., indicative of) a collimated image are well known in the art, employing, for example, an illumination source, a spatial light modulator such as a liquid crystal on silicon (LCoS) chip, and collimating optics, typically all arranged on one or more surfaces of a polarization-selective beam splitter (PBS) cube or other prism arrangement.

[0148] It should be noted that when used within the context of an AR system, applying small amounts of light-absorbing material to defects in the external portion of the light guide may also provide the advantage of reducing or suppressing light scattering from the external scene.

[0149] When discussing the polarization properties of the image illumination and coatings, it should be noted that for each instance in which a particular polarization wave path is followed in the examples described herein, the polarizations are interchangeable, so that, for example, each reference to p-polarized light can be replaced with s-polarized light, and vice versa, in changing the polarization selective properties of the coating.

[0150] The description of various embodiments of the present disclosure is presented for illustrative purposes, but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terms used herein have been selected to best explain the principles of the embodiments, practical applications or technical improvements to technology found in the market, or to enable those skilled in the art to understand the embodiments disclosed herein.

[0151] As used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0152] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment described as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments and / or excludes the incorporation of features from other embodiments.

[0153] It will be understood that certain features of the invention that are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination, or in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperable without those elements.

[0154] To the extent that the appended claims have been drafted without multiple dependencies, this has been done solely to accommodate formal requirements in jurisdictions that do not permit such multiple dependencies. Note that all possible combinations of features implied by making the claims multiple dependent are expressly contemplated and should be considered part of the present invention.

[0155] While the present invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims.

Claims

1. 1. An optical device, comprising: an optically transmissive substrate having at least two parallel major exterior surfaces for directing light exhibiting a collimated image by internal reflection at said major exterior surfaces; a light-transmitting substrate; a first set of mutually parallel interior surfaces disposed within the substrate at an angle relative to the exterior surface; a second set of mutually parallel interior surfaces disposed within the substrate parallel to, alternating with, and in overlapping relationship with the first set of interior surfaces; an optical device, wherein at least a portion of each of the internal surfaces of the first set includes a first coating having first reflective properties such that the first coating is at least partially reflective to at least a first subset of components of incident light, and wherein at least a portion of each of the internal surfaces of the second set includes a second coating having second reflective properties complementary to the first reflective properties such that the second coating is at least partially reflective to at least a second subset of components of incident light, such that the sets of internal surfaces cooperate to reflect all components of light from the first and second subsets.

2. The optical device of claim 1 , wherein the first subset of components comprises light corresponding to a first color and the second subset of components comprises light corresponding to a second color.

3. The optical device of claim 1 , wherein the first subset of components comprises light having a first polarization direction and the second subset of components comprises light having a second polarization direction.

4. The optical device of claim 1 , wherein at least one of the first coating or the second coating comprises a structured polarizer.

5. The optical device of claim 1 , wherein at least one of the first coating or the second coating comprises a dielectric coating.

6. The optical device of claim 1 , wherein at least one of the first coating or the second coating comprises a metal coating.

7. 2. The optical device of claim 1, wherein the first coating is configured to reflect light having a wavelength corresponding to a first color with a first reflection efficiency, reflect light having a wavelength corresponding to a second color with a second reflection efficiency, and reflect light having a wavelength corresponding to a third color with a third reflection efficiency that is less than the first reflection efficiency; and the second coating is configured to reflect light having a wavelength corresponding to the first color with a reflection efficiency that is greater than the third reflection efficiency, such that a combined reflection efficiency of the third color by the first and second coatings is equal to or greater than the first reflection efficiency.

8. 8. The optical device of claim 7, wherein the second reflection efficiency is less than the first reflection efficiency, and the second coating is configured to reflect light having a wavelength corresponding to the second color with a reflection efficiency greater than the second reflection efficiency, such that the combined reflection efficiency of the second color from the first and second coatings is equal to or greater than the first reflection efficiency.

9. 9. The optical device of claim 8, wherein the second coating is configured to reflect light having a wavelength corresponding to the first color with a reflective efficiency approximately equal to the first reflective efficiency.

10. 2. The optical device of claim 1, wherein the first coating is configured to reflect light having a wavelength corresponding to a first color with a first reflection efficiency, reflect light having a wavelength corresponding to a second color with a second reflection efficiency lower than the first reflection efficiency, and reflect light having a wavelength corresponding to a third color with a third reflection efficiency lower than the first reflection efficiency; and the second coating is configured to reflect light having a wavelength corresponding to the first color with a reflection efficiency higher than the second and third reflection efficiencies, reflect light having a wavelength corresponding to the second color with a reflection efficiency greater than the second and third reflection efficiencies, and reflect light having a wavelength corresponding to the third color with a reflection efficiency greater than the second and third reflection efficiencies.

11. The optical device of claim 1 , wherein the first coating comprises a patterned coating comprising several portions of reflective material arranged in a predetermined pattern on each of the first set of interior surfaces.

12. The optical device of claim 11 , wherein each portion of the reflective material has a circular shape in the plane of the interior surface.

13. The optical device of claim 11 , wherein each portion of the reflective material has an oval shape in the plane of the interior surface.

14. The optical device of claim 11 , wherein the reflective material is a dielectric material.

15. The optical device of claim 11 , wherein the reflective material is a metallic material.

16. The optical device of claim 11 , wherein the spaces formed between the portions of the reflective material are transparent.

17. The optical device of claim 11 , wherein a second reflective material is disposed on the interior surface in spaces formed between the portions of the reflective material.

18. The optical device of claim 17 , wherein the second reflective material comprises a dielectric material.

19. 18. The optical device of claim 17, wherein the second reflective material is disposed in a predetermined pattern on the interior surface.

20. 12. The optical device of claim 11, wherein at least one of the number of portions or the sizes of the portions on the interior surface of the first set increases with respect to a primary direction of propagation of light through the substrate.

21. The optical device of claim 11 , further comprising an amount of light reflection suppressing material disposed between the reflective material and at least a portion of the interior surfaces of the first set.

22. The optical device of claim 21 , wherein the light reflection suppressing material comprises a light absorbing material.

23. The optical device of claim 21 , wherein the light reflection suppressing material comprises a light scattering material.

24. 2. The optical device of claim 1, wherein the first coating is disposed on a first portion of each of the internal surfaces of the first set, the second coating is disposed on a second portion of each of the internal surfaces of the first set, the second coating is disposed on a first portion of each of the internal surfaces of the second set, the first coating is disposed on a second portion of each of the internal surfaces of the second set, the first and second portions of the internal surfaces of the first set are non-overlapping portions, and the first and second portions of the internal surfaces of the second set are non-overlapping portions.

25. 10. The optical device of claim 1, wherein the first and second sets of internal surfaces reflect a percentage of light guided by internal reflection at the major external surface away from the substrate toward a viewer's eye.

26. 2. The optical device of claim 1, wherein the first and second sets of internal surfaces reflect a percentage of light guided by internal reflection at the major external surface from the substrate so as to be coupled to a second optically transparent substrate for guidance by internal reflection at the external surface of the second optically transparent substrate.

27. The optical device of claim 1 , wherein the substrate is configured to guide light in one dimension through the substrate.

28. The optical device of claim 1 , wherein the substrate is configured to guide light in two dimensions through the substrate.

29. 2. The optical device of claim 1, wherein at least one of the internal surfaces from at least one of the first set or the second set includes an edge region associated with a first of the external surfaces of the substrate that defines a boundary region between the at least one internal surface and the substrate, the first of the external surfaces having a quantity of light-absorbing material positioned in a recess formed in the first of the external surfaces at the boundary region.

30. 1. An optical device, comprising: an optically transmissive substrate having at least two parallel major exterior surfaces for directing light exhibiting a collimated image by internal reflection at said major exterior surfaces; an optical device comprising: a plurality of mutually parallel internal surfaces disposed within the substrate at an angle relative to the external surface, wherein at least a portion of a first subset of the internal surfaces comprises a patterned coating including portions of a reflective material arranged in a predetermined pattern on the internal surfaces of the first subset, the patterned coating being at least partially reflective to at least a first subset of components of incident light; a second subset of the internal surfaces being at least partially reflective to at least a second subset of components of incident light; and the internal surfaces of the first subset being in an overlapping relationship with the internal surfaces of the second subset, such that the subsets of internal surfaces cooperate to reflect all components of light from the first and second subsets.

31. 31. The optical device of claim 30, wherein each portion of the reflective material has a circular shape in the plane of the interior surface of the first subset.

32. 31. The optical device of claim 30, wherein each portion of the reflective material has an oval shape in the plane of the interior surface of the first subset.

33. 31. The optical device of claim 30, wherein the reflective material is a dielectric material.

34. 31. The optical device of claim 30, wherein the reflective material is a metallic material.

35. 31. The optical device of claim 30, wherein the spaces formed between the portions of the reflective material are transparent.

36. 31. The optical device of claim 30, wherein a second reflective material is disposed in spaces formed between the portions of the reflective material.

37. 37. The optical device of claim 36, wherein the second reflective material comprises a dielectric material.

38. 37. The optical device of claim 36, wherein the second reflective material is disposed in a predetermined pattern on the interior surfaces of the first subset.

39. 31. The optical device of claim 30, wherein at least one of the number of portions or the size of the portions on the interior surface of the first subset increases with respect to a direction of propagation of light through the substrate.

40. 31. The optical device of claim 30, further comprising an amount of light reflection suppressing material disposed between the reflective material and the interior surfaces of the first subset.

41. 41. The optical device of claim 40, wherein the light reflection suppressing material comprises a light absorbing material.

42. The optical device of claim 40 , wherein the light reflection suppressing material comprises a light scattering material.

43. 31. The optical device of claim 30, wherein the interior surfaces of the first subset alternate with the interior surfaces of the second subset.

44. 31. The optical device of claim 30, wherein a surface of the first subset of interior surfaces is coplanar with a surface of the second subset of interior surfaces.

45. 31. The optical device of claim 30, wherein the interior surface reflects a percentage of light guided by internal reflection at the major exterior surface away from the optically transmissive substrate toward the viewer's eye.

46. 31. The optical device of claim 30, wherein the internal surface reflects a percentage of light guided by internal reflection at the major external surface from the optically transparent substrate so as to be coupled to a second optically transparent substrate for guidance by internal reflection at an external surface of the second optically transparent substrate.

47. 31. The optical device of claim 30, wherein the substrate is configured to guide light in one dimension through the substrate.

48. 31. The optical device of claim 30, wherein the substrate is configured to guide light in two dimensions through the substrate.

49. 31. The optical device of claim 30, wherein at least one of the internal surfaces includes an edge region associated with a first of the external surfaces of the substrate that defines a boundary region between the at least one internal surface and the substrate, the first of the external surfaces having a quantity of light-absorbing material positioned in a recess formed in the first of the external surfaces at the boundary region.

50. 1. An optical device, comprising: an optically transparent substrate having at least two parallel major exterior surfaces for guiding light by internal reflection at said major exterior surfaces; at least one at least internal surface disposed within the substrate at an angle relative to the external surface, the at least one internal surface having an end region associated with a first one of the external surfaces of the substrate that defines a boundary region between the internal surface and the substrate; a quantity of light-absorbing material positioned in a recess formed in the first one of the exterior surfaces at the boundary region.

51. 51. The optical device of claim 50, wherein the at least one interior surface comprises a plurality of mutually parallel partially reflective surfaces.

52. 51. The optical device of claim 50, wherein the at least one internal surface is configured to couple light guided within the substrate out of the substrate by internal reflection.

53. 51. The optical device of claim 50, wherein the at least one internal surface is configured to couple light into the substrate for propagation within the substrate by internal reflection.

54. 51. The optical device of claim 50, wherein the at least one internal surface is configured to couple light guided within the substrate by internal reflection into a second optically transmissive substrate so as to propagate within the second substrate by internal reflection.

55. 51. The optical device of claim 50, wherein the light absorbing material comprises black absorbing paint.

56. 51. The optical device of claim 50, wherein the amount of the light-absorbing material is sufficient to fill the recess.

57. 51. The optical device of claim 50, wherein the inner surface has a second end region associated with a second one of the outer surfaces of the substrate that defines a second boundary region between the inner surface and the substrate, and the optical device further comprises a quantity of light-absorbing material positioned in a recess formed in the second one of the outer surfaces at the second boundary region.

58. 1. A method for manufacturing an optical device, the method comprising: Obtaining a light-transmitting substrate having at least two parallel major exterior surfaces for guiding light by internal reflection at the major exterior surfaces, said substrate having at least one interior surface disposed between and obliquely relative to said exterior surfaces, said interior surface having an edge region associated with a first one of said exterior surfaces of said substrate and defining a boundary region between said interior surface and said first one of said exterior surfaces; and depositing a quantity of light absorbing material within a recess formed in said first one of said exterior surfaces at said boundary region.

59. 60. The method of claim 58, wherein said depositing said amount of said light absorbing material comprises applying said light absorbing material to substantially the entirety of said first of said exterior surfaces.

60. 60. The method of claim 59, further comprising polishing the first one of the exterior surfaces to remove the light absorbing material from substantially all portions of the first one of the exterior surfaces outside the recess.

61. 59. The method of claim 58, wherein obtaining the light-transmitting substrate comprises attaching a set of coated transparent plates together to form a stack; slicing the stack diagonally to form the substrate having the at least two parallel major exterior surfaces and the interior surface at an angle to the exterior surfaces; and polishing the exterior surfaces.

62. 62. The method of claim 61, wherein said abrading said exterior surfaces causes said depression to form in said first one of said exterior surfaces at said boundary region.

63. 59. The method of claim 58, wherein the amount of the light absorbing material is sufficient to fill the recess.

64. 59. The method of claim 58, wherein the interior surface has a second end region associated with the second one of the exterior surfaces of the substrate to define a boundary region between the interior surface and a second one of the exterior surfaces, the method further comprising depositing a quantity of light-absorbing material in a recess formed in the second one of the exterior surfaces at the boundary region between the interior surface and the second one of the exterior surfaces.

65. 1. An optical device, comprising: an optically transmissive substrate having first and second pairs of parallel major exterior surfaces forming a rectangular cross-section, the substrate configured to guide light by internal reflection at the major exterior surfaces; at least one interior surface disposed within the substrate at an angle relative to an elongation direction of the substrate configured to couple light out of the substrate; a quantity of light-absorbing material positioned in a defect formed in an outer region of the substrate.

66. 66. The optical device of claim 65, wherein the defect comprises a scratch formed on one of the exterior surfaces.

67. 66. The optical device of claim 65, wherein the defect comprises a chip at an edge formed between one of the outer surfaces of the first pair of outer surfaces and one of the outer surfaces of the second pair of outer surfaces.

68. 66. The optical device of claim 65, wherein the defect comprises a chip in a corner formed between one of the exterior surfaces of the first pair of exterior surfaces and one of the exterior surfaces of the second pair of exterior surfaces.

69. 66. The optical device of claim 65, wherein the inner surface includes at least a first end region associated with one of the outer surfaces of the substrate to define a boundary region between the inner surface and the substrate.

70. 70. The optical device of claim 69, wherein the defect comprises a depression formed in the boundary region.

71. 66. The optical device of claim 65, wherein the light absorbing material comprises black absorbing paint.

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