Patent ID: 12242098

DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Initially, throughout this document, references are made to directions such as, for example, front and back, upper and lower, left and right, and the like. These directional references are exemplary only to illustrate the invention and embodiments thereof.

Referring now to the drawings,FIG.1illustrates an optical device in the form of a light-guide optical element (LOE), generally designated10, constructed and operative according to a non-limiting embodiment of the present invention. The LOE10is formed as a light-transmitting substrate, constructed from a transparent material (such as glass), that has a pair of parallel faces (also referred to as “major external surfaces” or “surfaces”)12,14, and a plurality of planar partially reflective surfaces16a,16b,16c,18a,18b,18cdeployed within the substrate at an oblique angle to the parallel faces12,14. In the non-limiting illustrated embodiment, the LOE10forms a slab-type waveguide, i.e., where the other two dimensions of the LOE10are at least an order of magnitude greater than the distance between the parallel faces12,14. The partially reflective surfaces (referred to hereinafter interchangeably as “internal surfaces”, “internal partial reflectors”, “partial reflectors” or “facets”)16a,16b,16c,18a,18b,18care subdivided into two sets of internals surfaces, namely a first set16having the internal surfaces16a,16b,16c, and a second set18having the internal surfaces18a,18b,18c. For simplicity of presentation each of the sets16,18is illustrated here as having three internal surfaces, however it should be understood that either or both of the sets could have any suitable number of internal surfaces.

In certain preferred but non-limiting embodiments, the internal surfaces of the two sets16,18are interleaved, such that one or more of the internal surfaces16a,16b,16cis positioned between a pair of adjacent internal surfaces16a,16b,16c,18a,18b,18c, and vice versa. Preferably, the internal surfaces alternate between the internal surfaces of the two sets16,18, such that for each pair of adjacent internal surfaces16a,16b,16cthere is a single one of the internal surfaces18a,18b,18c, and vice versa. This alternating configuration is illustrated inFIG.1.

A projected image20, represented here schematically by a beam of illumination20including sample light rays20A and20B, is coupled into the LOE10(i.e., into the substrate) by an optical coupling-in configuration22, represented schematically as a coupling-in reflector. Other suitable coupling-in configurations for coupling image illumination into the LOE10, such as by use of a suitably angled coupling prism or a diffractive optical element, are well-known in the art. The image illumination20is guided within the LOE10by repeated internal reflection at the parallel faces12,14(i.e., the image illumination20is trapped by internal reflection within the LOE substrate). In certain preferred but non-limiting implementations, the propagation through the LOE10by internal reflection is in the form of total internal reflection (TIR), whereby incidence of the propagating image illumination20at the parallel faces12,14at angles greater than a critical angle causes reflection of the illumination at the parallel faces12,14. In other non-limiting implementations, the propagation through the LOE10by internal reflection is effectuated by a reflective coating (e.g., an angularly selective reflective coating) applied to the parallel faces12,14.

The image illumination20propagates through the LOE10until reaching the series of internal surfaces16a,16b,16c,18a,18b,18c, where part of the image intensity is reflected out of the LOE10as light rays24A,24B. In certain embodiments, such as the embodiment illustrated inFIG.1, the internal surfaces16a,16b,16c,18a,18b,18creflect the image illumination as reflected light rays24A,24B so as to coupled part of the image intensity out of the LOE10toward the eye of an observer. As will be discussed, in other embodiments the internal surfaces16a,16b,16c,18a,18b,18creflect the image illumination as reflected light rays24A,24B so as to be coupled into another LOE for guiding between parallel faces of the other LOE and for coupling out toward the observer's eye by a set of internal surfaces deployed within the other LOE.

The image illumination20typically includes multiple components of illumination, including, for example, different polarization components and different color (i.e., spectral) components. The internal surfaces16a,16b,16c,18a,18b,18care preferably formed from transparent plates or slabs having coatings applied to at least part of the sides or surfaces of the plates or slabs. The coatings are designed with reflective characteristics such that the coatings are at least partially reflective to incident light having particularly corresponding characteristics in order to generate a desired reflectivity pattern for the components of the illumination, the details of which will be described in detail below. In general, at least part of the internal surfaces16a,16b,16chave a coating with a reflectivity characteristic such that certain components of the image illumination are reflected by the internal surfaces16a,16b,16c. At least part of the internal surfaces18a,18b,18calso have a coating with a reflectivity characteristic that is complementary to the reflection characteristic of the internal surfaces16a,16b,16c, such that components of the image illumination that are not sufficiently reflected by the internal surfaces16a,16b,16care suitably and sufficiently reflected by the internal surfaces18a,18b,18c.

Before explaining the details of the design of the reflectors16a,16b,16c,18a,18b,18cin further detail, it is noted that the projected image illumination20is a collimated image, i.e., where each pixel is represented by a beam of parallel rays at a corresponding angle, equivalent to light from a distant scene far from the observer (the collimated image may be referred to as being “collimated to infinity”). Although the image20is represented here simplistically as a single ray corresponding to a single point of the image, typically the centroid of the image, it is noted that the image in fact includes a range of angles to each side of the central ray, which are coupled into the substrate with a corresponding range of angles, and are similarly coupled out of the substrate at corresponding angles thereby creating a field of view corresponding to parts of the image arriving in directions to the eye of the observer.

Each internal surface has opposing ends that define where the internal surface respectively starts and stops. These opposing ends are referred to as a “starting end” and a “stopping end”. Looking at the internal surfaces16aand18a, for example, it can be seen that the internal surface16ahas a starting end17a-1and a stopping end17a-2, and the internal surface18ahas a starting end19a-1and a stopping end19a-2. The internal surfaces16a,16b,16care preferably deployed within the LOE10such that each of the internal surfaces16b,16cstarts where the previous internal surfaces16a,16bends in a projection plane of the internal surfaces. In other words, the starting end17b-1of the internal surface16bis aligned with the stopping end17a-2of the internal surface16a, and the starting end17c-1of the internal surface16cis aligned with the stopping end17b-2of the internal surface16b. In such a deployment, the facets16a,16b,16cappear as continuous and non-overlapping in the projection plane, which in the non-limiting implementation illustrated inFIG.1is a plane that is parallel to the planes of the surfaces12,14. This deployment ensures that there are no gaps between adjacent internal surfaces16a,16b,16cin the primary light propagation direction through the LOE10(arbitrarily illustrated as being from left to right along the horizontal axis inFIG.1), thereby preserving continuous aperture expansion (i.e., aperture multiplication) for the components of light reflected by the first set16. Similarly, the internal surfaces18a,18b,18care preferably deployed within the LOE10such that each of the internal surfaces18b,18cstarts where the previous internal surfaces18a,18bends, thereby preserving continuous aperture expansion for the components of light reflected by the second set18. In other words, the starting end19b-1of the internal surface18bis aligned with the stopping end19a-2of the internal surface18a, and the starting end19c-1of the internal surface18cis aligned with the stopping end19b-2of the internal surface18b.

In embodiments in which the internal surfaces of the two sets16,18are interleaved, it is preferable that the two sets16,18are also in overlapping relation whereby at least some of the internal surfaces of the first set16overlap with some of the internal surfaces of the second set18, and vice versa. In certain cases, the overlapping relation is such that there is at least one internal surface of one of the sets16,18that has its starting end located at a position in the projection plane that is between the starting and stopping ends of a single internal surface of the other of the sets16,18, and such that the stopping end of the internal surface of the one of the sets16,18is located at a position in the projection plane that is between the starting and stopping ends of another single internal surface of the other of the sets16,18.

FIG.1shows the two sets16,18in an interleaved and overlapping configuration in which the starting end19a-1of the internal surface18ais located at a position in the projection plane that is between the starting end17a-1and the stopping end17a-2of the internal surface16a, the stopping end19a-2of the internal surface18ais located at a position in the projection plane that is between the starting end17b-1and the stopping end17b-2of the internal surface16b, the starting end19b-1of the internal surface18bis located at a position in the projection plane that is between the starting end17b-1and the stopping end17b-2of the internal surface16b, the stopping end19b-2of the internal surface18bis located at a position in the projection plane that is between the starting end17c-1and the stopping end17c-2of the internal surface16b, and the starting end19c-1of the internal surface18cis located at a position in the projection plane that is between the starting end17c-1and the stopping end17c-2. Likewise, the stopping end17a-2of the internal surface16ais located at a position in the projection plane that is between the starting end19a-1and the stopping end19a-2of the internal surface18a, the starting end17b-1of the internal surface16bis located at a position in the projection plane that is between the starting end19a-1and the stopping end19a-2of the internal surface18a, the stopping end17b-2of the internal surface16bis located at a position in the projection plane that is between the starting end19b-1and the stopping end19b-2of the internal surface18b, the starting end17c-1of the internal surface16cis located at a position in the projection plane that is between the starting end19b-1and the stopping end19b-2of the internal surface18b, and the stopping end17c-2of the internal surface16cis located at a position in the projection plane that is between the starting end19c-1and the stopping end19c-2of the internal surface18c.

Preferably the overlapping configuration between the internal surfaces of the two sets16,18is such that the starting/stopping end of an internal surface of one of the sets16,18is at the midpoint between the starting and stopping ends of the internal surface of the other of the sets16,18. It should be noted that in certain instances “overlapping relation” may include configurations in which an internal surface of the set16and an internal surface of the set18are entirely overlapping such that they are coplanar, whereby the starting and stopping ends of a facet of the set16are respectively coincident with the starting and stopping ends of a facet of the set18. Further details of optical waveguides that employ overlapping internal surface having conventional coating architectures can be found in the applicant's commonly owned U.S. Pat. No. 10,481,319, which is incorporated by reference in its entirety herein.

The following paragraphs describe the coating designs for the sets16,18of internal surfaces according to embodiments of the present invention. The internal surfaces16a,16b,16c,18a,18b,18chave coatings with complementary reflectivity characteristics such that components of the image illumination that are not sufficiently reflected by one of the internal surfaces16a,16b,16care suitably and sufficiently reflected by the one of the internal surfaces18a,18b,18c. In particular, and as will be described in detail below, the internal surfaces16a,16b,16chave coatings configured to reflect a proportion of intensity for each illumination component in a subset of the components of the image illumination, and the internal surfaces18a,18b,18chave coatings configured to reflect a proportion of intensity for each illumination component in another subset of the components of the image illumination, such that the coatings of the two sets16,18of internal surfaces cooperate to reflect a combined proportion of intensity of all illumination components in the two subsets. The combined proportion of intensity cooperatively reflected by the coatings of the two sets16,18is greater than or equal to the proportion of intensity reflected individually by the coatings of the two sets16,18.

When the internal surfaces are interleaved according to the alternating configuration as illustrated inFIG.1, the complementary coatings of pairs of adjacent internal surfaces from two different sets enable the internal surfaces from the two sets to cooperate to reflect all of the components of the image illumination across portions of the projection plane of the internal surfaces so as to preserve continuous aperture expansion.

As part of a first non-limiting example, image illumination20that includes different spectral components of illumination, for example spectral components corresponding to red light, green light, and blue light, is considered. In this example, the internal surfaces16a,16b,16cmay include a first coating that is configured to reflect red light (i.e., light having wavelengths near 638 nm) with high efficiency and to partially reflect green light (i.e., light having wavelengths near 532 nm) with moderate efficiency, but is configured to partially reflect blue light (i.e., light having wavelengths near 456 nm) with low efficiency. In order to compensate for the moderate reflection efficiency of green light and the low reflection efficiency of blue light imparted by the internal surfaces16a,16b,16c, the internal surfaces18a,18b,18ccan include a second coating that is configured to reflect blue light with high efficiency (on par with the efficiency imparted by the internal surfaces16a,16b,16con red light) and to partially reflect green light with moderate efficiency (on par with the efficiency imparted by the internal surfaces16a,16b,16con green light). The coating of the internal surfaces18a,18b,18cmay also partially reflect red light with low efficiency. As a result, the light rays24A convey high efficiency red light, moderate efficiency green light, and low efficiency blue light, and the light rays24B convey high efficiency blue light and moderate efficiency green light, such that the overall reflected image resultant from the reflection by the two interleaved and overlapping sets16,18has little to no color difference across the three colors while preserving continuous aperture expansion (due to the interleaving of the internal surfaces). Any residual color difference that cannot be eliminated by the coatings of the two sets16,18can be compensated for by adjustment of colored light sources that are used for generating the collimated image illumination20.

In another non-limiting example, image illumination20that includes two orthogonal linear polarization components, namely s-polarization and p-polarization components, is considered. Here, the two sets16,18of internal surfaces include coatings that are selectively reflective to the orthogonal polarizations in a complementary fashion, whereby the internal surfaces of one of the sets16primarily reflect light that is polarized in one of the polarization directions (e.g., p-polarization) with respect to the surface of the internal surfaces of the set16, and the internal surfaces of the other set18primarily reflect light that is polarized in the orthogonal polarization direction (e.g., s-polarization) with respect to the surface of the internal surfaces of the set18.

One type of coating that can provide such polarization selective reflectivity is a dielectric coating.FIG.2shows the reflectivity characteristics of such a dielectric coating for p-polarization and s-polarization across angle of incidence (AOI). As can be seen, at a lower range of AOIs, for example AOIs in the range of 0-20 degrees (i.e., close to perpendicular the internal surfaces), both s and p-polarizations are reflected with approximately the same efficiency, i.e., the reflectance of s and p-polarizations is approximately the same (slightly above 25%). As the AOI increases over a given range, the reflectance of the two polarizations deviates. Specifically, at a higher range of AOIs, for example AOIs in the range of 20-55 degrees, the reflectance for p-polarization is reduced relative to the reflectance for s-polarization. For example, at AOI of approximately 40 degrees, the reflectance for s-polarization is slightly above 50% (thereby operating as an almost perfect partial reflector), whereas the reflectance for p-polarization is below 15%.

In order to generate an image having wide field of view for the observer, different angles are reflected from different internal surfaces.FIG.3shows the LOE10in which all of the internal surfaces16a,16b,16c,18a,18b,18cinclude the dielectric coating having the reflectance characteristics described above with reference toFIG.2. In this configuration, the image illumination that propagates through the LOE has both s-polarization and p-polarization components. By way of illustration, some of image illumination that propagates through the LOE10impinges on the internal surface18cat an AOI in the lower range such that the dielectric coating reflects both polarizations with approximately the same efficiency. As a result, the polarization components of the reflected light ray Rige are of approximately equal intensity. However, some of the image illumination impinges on the internal surfaces18a,18b,16bat AOIs in the higher range, such that the dielectric coating of the internal surfaces18a,18b,16bprimarily reflects the s-polarized light. As a result, the s-polarization component of each of the reflected light rays R18a, R18b, R16bis the dominant component. In order to compensate for the reduced p-polarization component at the particular AOI range, the internal surfaces18a,18bare re-designed so as to reflect primarily p-polarized light (or to reflect both polarizations with approximately equal efficiency).

According to certain embodiments, in order to achieve the desired reflectivity for p-polarized light, the internal surfaces18a,18badditionally include an orientation sensitive polarization reflector (or “structural polarizer”) that transmits one incident polarization and reflects the orthogonal polarization according to the reflector's inherent axis orientation. One non-limiting example of a structural polarizer is a birefringent dielectric coating or film commercially available from the 3M Company of Minnesota, USA. Another non-limiting example of a structural polarizer is a wire-grid film, for example commercially available from Moxtek Inc. of Utah, USA. Yet another non-limiting example of a structural polarizer is a patterned partially reflective coating having a number of portions of reflective material deployed in a pattern on a thin film or transparent substrate.

With continued reference toFIGS.1-3, refer now toFIG.4, which shows an illustration of a non-limiting example of a patterned reflective coating (also referred to as a “reflective pattern coating”)30according to non-limiting embodiments of the present invention. The coating30has reflective characteristics such that light that is polarized in one polarization direction (e.g., s-polarized or p-polarized) is primarily/majority reflected by the coating30, and light that is polarized in the orthogonal polarization direction (e.g., p-polarized or s-polarized) is primarily/majority transmitted by the coating30. Preferably, the reflected polarization exhibits more than 90% reflection (referred to as “substantially completely reflective”), and most preferably over 95% reflection. Conversely, the transmitted polarization preferably exhibits more than 90% transmission (referred to as “substantially completely transmissive”), and most preferably over 95% transmission.

The coating30includes an amount34of reflective material (referred to hereinafter as “portions”34) deployed in spaced relation and arranged in a prescribed pattern on a planar base surface32. The base surface32is preferably, but not necessarily, transparent to light such that the spaces35on the base surface32that are formed between and around the portions34of reflective material are light-transparent. In certain embodiments, the planar base surface32is a thin-film or thin-substrate that can be bonded to a transparent plate to form the internal partially reflective surface. In other embodiments, the planar base surface32is itself the transparent plate from which the facet is formed, and the portions34of 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 portion34of the reflective material has a shape that enables light in one polarization direction to induce flow of electrical current. Therefore, light that is polarized in the polarization direction that induces current flow sees the coating30as a reflector when incident to the coating30, whereas light that is polarized in the orthogonal polarization direction sees the coating30as light-transmissive when incident to the coating30.

In the non-limiting example illustrated inFIG.4, each of the portions34is identical in size and each has a generally circular shape in the plane of the base surface32(i.e., in the plane of the internal surface). Here, the portions34are effectively circularly symmetric (in the plane of the base surface32) dots of reflective material deposited on the base surface32in the arranged pattern. In this configuration, the portions34are arranged in a prescribed pattern so as to be uniformly spaced such that the distance between the centers of each pair of adjacent dots is constant across the entire coating30.

FIG.5shows another non-limiting example of the coating30in which portions36of reflective material having non-circular symmetry in the plane of the base surface32are deployed on the base surface32in a prescribed pattern. Here, the portions36have a generally elliptical or oblong shape (two orthogonal axes of symmetry) in the plane of the base surface32(i.e., in the plane of the internal surface). The orientations of the portions36in the plane of the base surface32determine the dominant reflective polarization. For example, in the configuration of the portions36illustrate inFIG.5, the dominant reflected polarization may be p-polarization, whereas rotating the portions36by 90-degrees in the plane of the base surface32may switch the dominant reflected polarization to s-polarization. Other shapes of the reflective material besides circular and oblong shapes are contemplated herein, for example, the portions of reflective material may be deployed in a pattern of lines on the base surface32.

By employing internal surfaces18a,18bthat have the coating30, the internal surfaces18a,18bare able to reflect the subset of the illumination components (in this case the p-polarization components) that is not fully reflected by the internal surface16b. In other words, for a given AOI in the higher AOI range, the internal surface16areflects a first subset of components of the image illumination (in the form of the s-polarization components) with high reflectance and reflects a second subset of components of the image illumination (in the form of the p-polarization components) with low reflectance. For the same given AOI, the internal surfaces18a,18breflect the low reflectance components, i.e., the second subset of components of the image illumination (in this case the p-polarization components) with high reflectance, so as to compensate for the low reflectance imparted by the internal surface16b. As a result, the internal surfaces18a,16b,18bcooperate to reflects both polarization components (i.e., the components from both subsets) to preserve continuity of aperture multiplication. The two subsets of components of image illumination are complementary, meaning that the union of the components from the two subsets accounts for all of the components of the propagating image illumination. In this particular example, the s and p-polarization components are complementary since they make up the polarization components of the image illumination.

In certain embodiments, two different coatings may be implemented on the same internal surface plane using a single coating. For example, a dielectric coating can be deployed in the spaces between the portions34. As a result, the portions34or36can be implemented as one type of dielectric coating or metallic coating, and the spaces35on the base surface32that are formed between and around the portions34or36can be implemented as another type of dielectric coating.FIG.6schematically illustrates an example of such a coating31, in which portions38of a second reflective material are deposited in a prescribed pattern in the spaces35on the base surface32formed between and around the portions34. In the non-limiting example illustrated inFIG.6, each of the portions34is generally circular in shape, whereas each of the portions38is generally elliptical in shape.

As discussed, the coating designs of the 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 the patterned reflector coatings described above with reference toFIGS.4-6can be used to address color non-uniformity issues. For example, the internal surfaces16a,16b,16ccan include a coating that partially reflects a first subset of the three colors at a suitable reflection efficiency, and the internal surfaces18a,18b,18ccan include a coating that partially reflects a second subset of the three colors at a suitable efficiency, where the second subset of the colors includes colors that are not suitably reflected by the internal surfaces16a,16b,16c. In general, the subsets of color components of image illumination are complementary, meaning that the union of the components from the subsets accounts for all of the color components of the propagating image illumination. The following paragraphs describe various examples of designs of the coatings of the internal surfaces of the two sets16,18for preserving color uniformity.

By way of introduction, it would be preferable to arrange the portions34,36of reflective material in a pattern that is relatively small so that the observer will perceive a uniform image. In particular, it would be preferable to deploy the portions34,36of reflective material in a geometric arrangement in accordance with the size of the pupil of the eye of the observer, for example as a circle having a diameter of approximately 2 mm (the pupil of the human eye typically has a diameter in the range of 2-4 mm in bright lighting conditions). However, portions of reflective material having small size and arranged in small patterns tend to diffract incident light to large angles, thereby reducing image resolution. Therefore, in non-limiting implementations of the present invention, the internal surfaces of the two sets16,18are implemented using the coatings having reflective patterns (described above with reference toFIGS.4-6) in combination with dielectric coatings.

In one non-limiting example, the internal surfaces16a,16b,16care implemented using a dielectric coating so as to be at least partially reflective to red, green and blue light, and the internal surfaces18a,18b,18care implemented using a patterned coating30in which the reflective material of the coating30is a metallic material (e.g., silver). The dielectric coating of the internal surfaces16a,16b,16chas reflection characteristics according to the graph illustrated inFIG.7. Here, the dielectric coating of the internal surfaces16a,16b,16creflects a first subset of components of the image illumination, in the form of green light (i.e., light having wavelengths near 532 nm), with reasonably high efficiency (approximately 10% reflectance), but reflects a second subset of components of the 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 than the green light reflection (approximately 4% reflectance). The coating30of the internal surfaces18a,18b,18chas reflection characteristics so as to be reflective for both subsets of components with enough efficiency in order to compensate for the low reflectance of the second subset of components. The overall reflectance imparted by the combination of the dielectric coating of the internal surfaces16a,16b,16cand the coating30of the internal surfaces18a,18b,18cis illustrated inFIG.8. As can be inferred, the coating30reflects the second subset of components of the image illumination (i.e., red light and blue light) with reflectance of at least approximately 6%, which is a higher efficiency than that imparted on the second subset of components by the dielectric coating of the internal surfaces16a,16b,16c. The coating30also reflects the first subset of components of the image illumination (i.e., green light) with reflectance of approximately 4% reflectance. The two subsets of color components are complementary in that the union of the two subsets (first subset having high efficiency green light, second subset having high efficiency red and blue light) accounts for all three of the color components of the image illumination. As a result, the overall reflected image has a reduced color difference, albeit while having a higher resolution of the green color components than the red and blue color components. The human eye, however, is most sensitive to the resolution of green light components of an image, and therefore an overall image having higher resolution of green color components would likely be perceived by the observer as not having any noticeable resolution degradation.

In an alternative configuration, the coating30can be implemented using a reflective material that has higher reflectance for red light and blue light than for green light (i.e., the coating30reflects mostly red light and blue light). As a result, the overall reflected image would have little to no noticeable color difference.

In another non-limiting example, the internal surfaces16a,16b,16care implemented using a dielectric coating that has reflection characteristics according to the graph illustrated inFIG.9. Here, the dielectric coating of the internal surfaces16a,16b,16creflects a first subset of components of the image illumination, in the form of green light and red light, with high efficiency (approximately 15% reflectance), but reflects a second subset of components of the image illumination, in the form of blue light, with lower efficiency than the green light and red light reflection (approximately 10% reflectance). In order to compensate for the low reflectance of the second subset of components, a particular implementation of the coating30is used for the internal surfaces18a,18b,18c. In this implementation, the portions of the reflective material (implemented as dielectric material or metallic material) are small (preferably in accordance with the human pupil size discussed above), and have reflection characteristics such that only blue light is reflected by the coating30. The overall reflectance imparted by the combination of the dielectric coating of the internal surfaces16a,16b,16cand the coating30of the internal surfaces18a,18b,18cis illustrated inFIG.10, whereby the overall reflectance is approximately constant at approximately 15% across the visible light spectrum. The result is a white balanced image without diffraction (blue light tends to be diffracted much less than green and red light).

FIG.11shows another implementation of using two coating schemes to preserve color uniformity according to a non-limiting example. Here, the internal surfaces16a,16b,16c,18a,18b,18chave two sets of coatings on each reflector arranged in an alternating configuration, where there is a lateral change in the coating of each internal surface. In the non-limiting illustrated example, each internal surface has two non-overlapping portions, namely a first portion and a second portion. The first portions40a,40b,40cof the internal surfaces16a,16b,16chave a first coating33, for example a dielectric coating having reflective characteristics according toFIG.7orFIG.9, and the second portions42a,42b,42cof the internal surfaces16a,16b,16chave a second coating37, for example the coating30. The first portions44a,44b,44cof the internal surfaces18a,18b,18chave the second coating37, and the second portions46a,46b,46cof the internal surfaces18a,18b,18chave the first coating33.

In the non-limiting example illustrated inFIG.11, the coatings33,37are deployed on alternating portions of successive internal surfaces, such that the coatings on each pair of adjacent internal surfaces (e.g., internal surfaces16a,18a, internal surfaces18a,16b, internal surfaces16b,18b, etc.) cooperate to reflect all of the components of subsets of the image illumination with reasonable efficiency so as to preserve color uniformity. In this particular configuration, the two sets of internal surfaces can be thought of as being effectively coplanar, whereby each internal surface has both coatings33,37. It is noted that althoughFIG.11shows each of the two portions of each of the internal surfaces constitutes approximately half of the internal surface plane, other configurations are possible, so long as the portions of the internal surfaces on which the coatings are deployed alternate between successive internal surfaces.

Although the embodiments for preserving color uniformity have been described within the context of the internal surfaces16a,16b,16chaving dielectric coatings, and the internal surfaces18a,18b,18chaving the coatings implemented according to the coating30, and in which the internal surfaces16a,16b,16cand18a,18b,18care interleaved, other embodiments are possible in which both types of coatings are implemented on a single internal surface, for example as discussed above with reference toFIGS.4-6. For example, each of the internal surfaces16a,16b,16c,18a,18b,18cmay include two coatings: 1) a first coating, for example the coating30, and 2) a second coating, for example a dielectric deployed in the spaces formed between the portions34of the coating30. The second coating may have the reflection characteristics according toFIG.7orFIG.9, whereby a first subset of the components of the image illumination is reflected by the second coating with higher efficiency than a second subset of components of the image illumination. The first coating may then have reflection characteristics which compensate for the low reflectance imparted on the second subset by the second coating, such that each individual internal surface achieves an overall reflectance that is approximately uniform across the three colors, for example as illustrated inFIG.8andFIG.10. In such a configuration, it is not necessary for the two sets16,18to be interleaved. Instead, since the internal surfaces of both of the sets16,18are identically coated, the two sets16,18are one in the same, and are preferably deployed such that each internal surface starts where the previous internal surface ends.

In certain embodiments, the patterned reflective coating30of the internal surfaces may be configured such that the number of portions34,36and/or or the size of the portions34,36on the internal surfaces varies from facet to facet in order to provide uniform intensity across the entire field of view. For example, the internal surfaces16a,16b,16cmay be implemented using dielectric coatings (as discussed above), and the internal surfaces18a,18b,18cmay be implemented using the patterned reflective coating30. As light propagates through the LOE, the intensity of the light that impinges on each successive facet is less than the intensity of the light that impinges on the preceding facet. This is due to the fact that a proportion of the intensity of light that impinges on a particular facet is reflected out of the LOE by that particular facet. In order to compensate for the decrease in light intensity in the light propagation direction, the reflectance imparted by each facet should generally increase compared to the reflectance imparted by the preceding facet. This can be effectuated by increasing the density of the reflective material on the coating30on the internal surfaces of the second set18with respect to the primary propagation direction of light through the LOE by, for example, increasing the number of portions34,36and/or or the size of the portions34,36. For example, the coating30of the internal surface18acan be implemented with a first number of portions34,36and/or or a first size of the portions34,36, the coating30of the internal surface18bcan be implemented with a second number of portions34,36and/or or a second size of the portions34,36, and the coating30of the internal surface18ccan be implemented with a third number of portions34,36and/or or a third size of the portions34,36. The first number of portions is less than the second number of portions, which is less than the third number of portions, and the first size of the portions is less than the second size of the portions, which is less than the third size of the portions.

Although some of the embodiments described thus far have pertained to two sets of internal partial reflectors that have complementary coatings, other embodiments are possible in which there are more than two sets of partial reflectors having complementary coatings. As a simple example, a third set of internal surfaces can be deployed parallel to, and interleaved with, the internal surfaces of the other two sets16,18. Each set of internal surfaces can include a coating that is configured to reflect a particular subset of components of the image illumination. For example, the coating of the internal surfaces of the first set can be configured to primarily reflect red light, the coating of the internal surfaces of the second set can be configured to primarily reflect green light, and the coating of the internal surfaces of the third set can be configured to primarily reflect blue light. As a result, a given group of three (preferably consecutive) internal surfaces (the group having one internal surface from each of the three sets) is able cooperate to reflect all three components of image illumination.

The coating and facet deployment methodologies discussed above have been described within the non-limiting example context of image illumination having either different spectral components or different polarization components. However, it should be appreciated that image illumination often has both spectral and polarization components (e.g., linearly polarized red, green, and blue light). For image illumination that impinges on the facets at a higher range of AOIs, e.g., 20-50 degrees, the coatings of the sets of facets can be designed to satisfy both spectral and polarization requirements to achieve transmission equalization across a wide field of view.

Although the coating designs and the deployment of the internal surfaces have thus far been described within the context of an LOE in which light is guided through the LOE in one dimension and is coupled-out (as “unguided” light) by the internal surfaces (facets) so as to perform aperture expansion in one dimension (performing what is referred to herein as “guided-to-unguided” image propagation), the coating design and facet deployment described herein according to embodiments of the present invention are equally applicable to optical devices having at least two optical waveguides that cooperate to guide light in two-dimensions in order 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 optical waveguide (in one or two dimensions) and is reflected by a set of facets deployed in the first optical waveguide so as to be coupled into a second optical waveguide. The image illumination is then guided through the second optical waveguide (in one dimension) and is reflected by a set of facets deployed 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 guided-to-guided image propagation.

FIGS.12A and12Bshow schematic side and front views, respectively, of an optical device that performs guided-to-guided image propagation by way of two optical waveguides50,60that are optically coupled together. The optical waveguide50has a direction of elongation illustrated arbitrarily as corresponding to the “x-axis”, and includes two pairs of parallel faces (i.e., major external surfaces)52a,52b,54a,54bforming a rectangular cross-section. A plurality of mutually parallel internal partially reflecting surfaces (i.e., facets)58at least partially traverse the optical waveguide50at an oblique angle to the direction of elongation. The optical waveguide60, optically coupled to the optical waveguide50, has a pair of parallel faces62a,62bforming a slab-type waveguide. Here too, a plurality of mutually parallel internal partially reflecting surfaces (i.e., facets)64at least partially traverse the optical waveguide60at an oblique angle to the parallel faces62a,62b. The planes containing the facets58are oblique to the planes containing the facets64.

The optical coupling between the optical waveguides50,60, and the deployment and configuration of partially reflecting surfaces58,64are such that, when an image is coupled into the optical waveguide50with an initial direction of propagation at a coupling angle oblique to both the first and second pairs of parallel faces52a,52b,54a,54b, the image advances by four-fold internal reflection along the optical waveguide50(i.e., in two dimensions), with a proportion of intensity of the image reflected at the partially reflecting surfaces58so as to be coupled out of the optical waveguide50and into the optical waveguide60, and then propagates through two-fold internal reflection within the optical waveguide60(i.e., in one dimension, similar to as in the LOE10), with a proportion of intensity of the image reflected at the partially reflecting surfaces64so as to be coupled out of the optical waveguide60as a visible image seen by the eye of an observer. As a result of this construction, the light that propagates through the optical waveguide50is guided (in two dimensions by the optical waveguide50), and the light that is reflected by the partially reflecting surfaces58is also guided (in one dimension by the optical waveguide60).

The coating design principles and/or the facet interleaving principles according to the embodiments of the present invention can be applied to either or both of the sets of internal partially reflecting surfaces58,64. Further details of such an optical device that employs two optical waveguides50,60can be found in the applicant's commonly owned U.S. Pat. No. 10,133,070, which is incorporated by reference in its entirety herein.

FIG.13shows a schematic view of an optical device that performs guided-to-guided image propagation by way of two slab-type optical waveguides70,80that are optically coupled together. The optical waveguide70has two pairs of parallel faces72a,72b,74a,74bforming a slab-type waveguide (in the figure the faces72a,72bare at the front and back, respectively, of the optical waveguide70, and the faces74a,74bare at the left and right, respectively, of the optical waveguide70). A plurality of mutually parallel internal partially reflecting surfaces (i.e., facets)76at least partially traverse the optical waveguide70at an oblique angle to the parallel faces72a,72b,74a,74b. The optical waveguide80has two pairs of parallel faces82a,82b,84a,84bforming a slab-type waveguide (in the figure the faces82a,82bare at the front and back, respectively, of the optical waveguide80, and the faces84a,84bare at the left and right, respectively, of the optical waveguide80). A plurality of mutually parallel internal partially reflecting surfaces (i.e., facets)86at least partially traverse the optical waveguide80at an oblique angle to the parallel faces82a,82b,84a,84b. In addition, the planes containing the facets76are oblique or perpendicular to the planes containing the facets86.

In the illustrated non-limiting implementation, the optical waveguides70,80are optically coupled together in a configuration in which the optical waveguide70is stacked on top of the optical waveguide80. Note, however, the optical waveguides70,80can be stacked front to back (e.g., with the faces72b,82ain facing relation to each other). The optical coupling between the optical waveguides70,80, and the deployment and configuration of partially reflecting surfaces76,86are such that, when an image is coupled into the optical waveguide70, the image propagates through two-fold internal reflection within the optical waveguide70between the faces72a,72bin a first guided direction, with a proportion of intensity of the image reflected at the partially reflecting surfaces76so as to be coupled out of the optical waveguide70and into the optical waveguide80, and then propagates through two-fold internal reflection within the optical waveguide80between the faces82a,82bin a second guided direction (oblique to the first guided direction), with a proportion of intensity of the image reflected at the partially reflecting surfaces86so as to be coupled out of the optical waveguide80as a visible image seen by the eye of an observer.

The coating design principles and/or the facet interleaving principles according to the embodiments of the present invention can be applied to either or both of the sets of internal partially reflecting surfaces76,86. Further details of such an optical device that employs two optical waveguides70,80can be found in the applicant's commonly owned U.S. Pat. No. 10,551,544, which is incorporated by reference in its entirety herein.

While the use of the reflective pattern coatings disclosed herein has the benefit of preserving color uniformity and intensity uniformity, the use of the reflective pattern coatings may cause undesired reflections from the internal surfaces, which can lead to ghost images. The general concept of undesired reflections from the internal surfaces is described with reference toFIG.14. Here, LOE100has three mutually parallel partially reflective internal surfaces106a,106b,106cdeployed oblique to a pair of parallel faces (major external surfaces)102,104. The thickness of the internal surfaces106a,106b,106cis exaggerated inFIG.14for clarity of illustrating front sides108a,108b,108cand back sides110a,110b,110cof the internal surfaces106a,106b,106c. The front and back sides of an internal surface are generally opposing sides, where the front side is the side of the internal surface that is coated with the coatings (described with reference toFIGS.1-11) having the reflective characteristics that enable reflection of the propagating image illumination according to the desired reflectivity pattern.

Image illumination108, schematically represented by light ray108, is coupled into the LOE100by the coupling-in reflector110(or any other suitable optical coupling-in configuration, e.g., coupling prism, etc.). The image illumination108propagates through the LOE100by repeated internal reflection at the faces102,104(either by total internal reflection or due to an angularly selective reflective coating applied at the faces), until reaching the series of internal surfaces106a,106b,106c, where part of the image intensity is reflected, at the front sides108a,108b,108cof the internal surfaces106a,106b,106c, out of the LOE100as light rays116a-116d. Looking at the propagating image illumination118schematically represented by the light ray118, it can be seen that part of the intensity of the light ray118is transmitted by the internal surface106a(as light ray120) after which the light ray120is reflected at the face102and then a proportion of the intensity is reflected at the front side108aof the internal surface106aso as to be reflected out of the LOE100as light ray116b(the remaining intensity is transmitted by the internal surface106a, such that the light continues propagating through the LOE100). However, part of the intensity of the light ray118undergoes an undesired reflection at the back side110aof the internal surface106a, resulting in reflected ray122. The reflected ray122can, in certain circumstances, undergo internal reflection at the faces102,104, exemplified by the reflection at the face102, so as to generate reflected ray124. The reflected ray124is reflected at the front side108bof the internal surface106bso as to be reflected out of the LOE100as ghost light ray126.

FIGS.15A and15Bshow how the reflective pattern coating30enables both desired reflections at the front side of an internal surface and undesired reflections at the back side of the internal surface. It is noted thatFIGS.15A and15Bare not drawn to scale, and some of the dimensions of the internal surface and the components of the reflective pattern coating30are exaggerated for clarity of illustration.

Looking first atFIG.15A, there is shown how an arbitrary internal surface130(which can be for example one of the internal surfaces of the set18) handles propagating image illumination140that impinges on the front side132of the internal surface130. The internal surface130has the reflective pattern coating30deposited on the front side132of the internal surface130. In particular, the planar base surface32is deposited on the front side132such that the portions34are arranged in the desired pattern on the front side132. Alternatively, the portions34can be deposited directly on the front side132in the arranged pattern without the planar base surface32. Propagating image illumination140, represented schematically by light rays140A and140B, impinges on different regions of the front side132of the internal surface130. In this case, the propagating image illumination140is the image illumination that has undergone reflection at the lower face of the LOE (e.g., the face102inFIG.14or the face12inFIG.1). The part of the propagating image illumination represented by the light ray140A impinges on a region of the internal surface130having the reflective material so as to be reflected (out of the LOE) by one of the portions34of reflective material as reflected light ray142. The part of the of the propagating image illumination represented by the light ray140B impinges on a region of the internal surface130having spaces35between the portions34of reflective material, and is transmitted by the internal surface130as light ray142(i.e., the light ray140B passes through the internal surface130from the front side132to the back side134as light ray142, due to the spaces35being transparent). This light ray140B continues to propagate through the LOE, being reflected at the faces of the LOE and/or reflected by subsequent internal surfaces. As a result, part of the image illumination140A is reflected out of the LOE by the internal surface130, and part of the image illumination140B is transmitted by the internal surface130.

Turning now toFIG.15B, there is shown how the internal surface130handles propagating image illumination118, represented schematically by light rays118A and118B, that impinges on the back side134of the internal surface130. In this case, the propagating image illumination is the image illumination that has undergone reflection at the upper face of the LOE (e.g., the face104inFIG.14or the face14inFIG.1). The part of the of the propagating image illumination represented by the light ray118A impinges on a region of the internal surface130having spaces35between the portions34of reflective material, and is therefore transmitted by the internal surface130as light ray120(i.e., the light ray118A passes through the internal surface130from the back side134to the front side132, due to the spaces35being transparent). The part of the propagating image illumination represented by the light ray118B passes through the back side134of the internal surface130and impinges on a region of the internal surface130having the reflective material so as to be reflected by one of the portions34of reflective material as reflected light ray122. This light ray122, as discussed above, can undergo additional reflections at the faces of the LOE and ultimately be reflected at the front side of one of the internal surfaces so as to be reflected out of the LOE as a ghost light ray.

In order to combat these undesired reflections, embodiments of the present invention provide a coating of reflection suppressing material applied between the portions of reflective material and the front side of the internal surfaces.FIGS.16A and16Bshow the reflection suppressing material and its effect on propagating image illumination. Similar to as inFIGS.15A and15B,FIGS.16A and16Bare not drawn to scale for clarity of illustration.

Looking first atFIG.16A, a coating of reflection suppressing material, designated as portions150, is deployed between the portions34of reflective material and the front side132of the internal surface130. If the coating30is implemented using a planar base surface32(e.g., thin-film), the portions150can be deposited directly on the surface32, and the portions34can then be deposited on the portions150. Preferably, the portions of the reflection suppressing material are arranged in the same pattern configuration as the portions of reflective material, such that the portions34and150are identical in size, shape, and number. As can be seen inFIG.16A, the reflection suppressing material has little to no effect on propagating image illumination that is incident to the front side132of the internal surface130. Similar to as discussed above with reference toFIG.15A, the part of the propagating image illumination represented by the light ray140A impinges on a region of the internal surface130having the reflective material so as to be reflected by one of the portions34of reflective material as reflected light ray142. The part of the of the propagating image illumination represented by the light ray140B impinges on a region of the internal surface130having spaces35between the portions34of reflective material, and is transmitted by the internal surface130as light ray142.

Turning now toFIG.16B, there is shown how the internal surface130with the reflection suppressing material handles propagating image illumination118that impinges on the back side134of the internal surface130. Similar to as discussed above with reference toFIG.15B, the part of the of the propagating image illumination represented by the light ray118A impinges on a region of the internal surface130having spaces35between the portions34of reflective material, and is therefore transmitted by the internal surface130as light ray120. However, unlike the configuration illustrated inFIG.15B, the part of the propagating image illumination represented by the light ray118B passes through the back side134of the internal surface130and impinges on a region of the internal surface130that has a portion150of the reflection suppressing material. The reflection suppressing material prevents the backside reflection of the light ray118B, and therefore no undesired reflection of propagating image illumination occurs.

The reflection suppressing material can be implemented in various ways. In one non-limiting example, the reflection suppressing material is implemented as an amount of black absorbing paint, which absorbs incident light. In another non-limiting example, the reflection suppressing material is implemented as an amount of light scattering material (such as a diffusive material), that scatters incident light in multiple directions at intensities that are orders of magnitude smaller than the intensity of the incident light. As a result, any scattered light that continues propagating through the LOE and is reflected by a subsequent internal surface will have an intensity that is generally too low to be noticeable to the observer.

The reflection suppressing material is preferably deposited between the reflective material and the front side of the internal surfaces during manufacturing of the LOE. The LOE, with embedded internal surfaces, is preferably constructed by forming a stack of transparent plates (e.g., glass plates) bonded together with suitable coatings at their interfaces. The boding is typically performed using optical cement. The coatings can include the patterned reflective coatings and/or dielectric coatings, all as described above. The coatings can be built up in layers on thin-films or thin-substrates (e.g., base surface32), which are applied at the interfaces between the transparent plates prior to bonding the plates together. Alternatively, the coatings can be built up directly on the transparent plates prior to bonding the plates together, such that the transparent plates serve as the base surface32. When employing a reflection suppressing material to reduce ghost images, layers of the reflection suppressing material can be built-up in a pattern (either directly on the transparent plates or on the thin-film or thin-substrate), with the layers of the pattern reflective material then built-up on the reflection suppressing material, thereby sandwiching the reflection suppressing material between the transparent plate and the reflective material.

Once the stack of transparent plates is bonded together, with appropriate coatings (and preferably reflection suppressing material) at the interfaces, the stack is cut (i.e., sliced) at an appropriate angle (corresponding to the desired oblique angle at which the internal surfaces are to be deployed) to form the LOE with partially reflective internal surfaces embedded between parallel major external surfaces (i.e., faces). The slicing at the appropriate angle is referred to as “diagonal cutting” or “diagonal slicing”. The major external surfaces of the LOE are then polished to increase optical quality at the major external surfaces. In embodiments in which the LOE uses a coupling-in reflector as the optical coupling-in configuration, similar steps can be performed in order to produce a substrate having an embedded coupling-in reflector.

Although the polishing process has the desired effect of increasing optical quality at the parallel faces of the LOE, the polishing process may, in certain instances, create blemishes at interface regions between the LOE substrate and the internal surface that can negatively affect optical performance and image quality at the LOE output. One type of blemish that can be caused by the polishing process is an indentation in one or both of the parallel faces of the LOE at the interface region between the internal surface and the parallel faces of the substrate. Such a blemish is illustrated schematically inFIG.17(not drawn to scale), which shows a section of an LOE200having parallel faces202,204with an internal partially reflective surface206deployed oblique to the faces202,204. Although not shown in the drawing, additional internal partially reflective surfaces are deployed within the LOE200, parallel to the internal surface206.

The internal surface206includes two opposing ends208a,208b(i.e., starting and stopping ends) at corresponding end regions210a,210bthat are respectively associated with the faces202,204. The faces202,204and the respective end regions210a,210b(and in particular the respective ends208a,208b) define interface regions212a,212b(designated by the dashed circles) between the internal surface206and the LOE substrate. An indentation214is formed, for example as a result of the polishing process, in one of the faces202at the corresponding interface regions212a(but can be formed in both faces, i.e., at both interface regions212a,212b). The indentation214is generally formed as a dent, depression, pit, cavity, or crevice in the face of the LOE, which causes a portion (albeit a small portion) of the face202to protrude inward into the interior section of the LOE200in which the internal surfaces are deployed. The protruding portion (i.e., the protrusion) is generally designated216inFIG.17.

Typically, the indentation214is formed as a result of the polishing process due to pressure applied during polishing at the interface regions212a,212b, which may have reduced structural integrity compared with the remaining portions of the faces202,204. Other sources besides polishing may cause the formation of the indentation214, for example, mishandling (e.g., dropping) of the LOE.

As a result of the indentation214, image illumination that propagates at or near the interface region212amay undergo scattering by the protrusion216. This is illustrated schematically inFIG.18, where image illumination218(schematically represented by light ray218) is transmitted by the internal surface206, and undergoes internal reflection at the face204so as to generate reflected light ray220(which is also part of the image illumination). The light ray220is incident to the face202at or near the protrusion216so as to impinge on the protrusion216, causing the incident light ray220to be reflected in multiple directions (i.e., scattered) by the protrusion216, schematically represented by scattered light rays222a-222c. The light rays are scattered in various directions due to the varying surface profile of the protrusion216. These scattered light rays222a-222bare undesired reflections, and can propagate through the LOE200so as to be reflected by one of the subsequent internal surfaces at unwanted angles, resulting in ghost images at the eye of the observer, similar to the light ray122discussed above with reference toFIG.15B.

Referring now toFIG.19, there is shown a method for combating the scattering effects caused by the indentation214by coating a portion of the face202that includes the indentation214with a light absorbing material. In particular, an amount of a light absorbing material224is deposited on the portion of the face202that includes the indentation214. Preferably, the amount of the light absorbing material224that is located in the indentation214is sufficient to fill the indentation214to at least the level of the unblemished portions of the face202. In one non-limiting example, the light absorbing material224is implemented as black absorbing paint that is applied to the face202in an amount that is sufficient to fill the indentation214. The face202is preferably then polished to remove any excess light absorbing material from the face202, such that only the light absorbing material located in the indentation214remains, and the level of the light absorbing material224in the indentation214is flush with the unblemished portions of the face202

The effect of the light absorbing material224on propagating image illumination is also illustrated inFIG.19. Similar to as discussed above with reference toFIG.18, the light ray218is transmitted by the internal surface206, and undergoes internal reflection at the face204so as to generate reflected light ray220. However, the light ray220, upon impinging on the protrusion216, is absorbed by the light absorbing material224, thereby preventing scattering of light by the protrusion216.

The light absorbing material can be applied at any of the interface regions between the internal surfaces and the LOE substrate at which such indentations are present and then polished off as described above. For example, the light absorbing material can be applied to an indentation formed in the interface regions212b. In addition, when using a coupling-in reflector (i.e., an internal reflecting surface) as the optical coupling-in configuration, indentations may form at the interface regions between the internal reflecting surface and the LOE substrate during the polishing process. Here too an amount of light absorbing material can be applied at interface regions between the internal reflecting surface and the LOE substrate to combat scattering effects induced by the indentations.

Although the scattering reduction by use of a light absorbing material applied to blemishes at external regions of an LOE has been described within the context an LOE in which light propagates in one dimension and is coupled-out by internal surfaces so as to perform aperture expansion in one dimension, the light absorbing material can similarly be applied to blemishes on external regions or portions of optical waveguides that perform aperture expansion in two dimensions, such as the optical waveguides that perform guided-to-guided image propagation described with reference toFIGS.12A,12B and13. These blemishes can include indentations formed at interface regions between the various sets of facets (e.g., facets58,64,76,86) and the corresponding faces (e.g., faces52a,52b,54a,54b,62a,62b,72a,72b,74a,74b,82a,82b,84a,84b).

The light absorbing material can also be used to fix blemishes in the form of scratches on the faces of the optical waveguides and/or chipped corners or edges of the optical waveguides. For example, consider the optical waveguide50ofFIGS.12A and12B, reproduced inFIG.20. Here, a portion of the corner/edge that is formed by the faces52a,54ahas been chipped off (due to, for example, mishandling of the optical waveguide50), resulting in blemish230. Light propagating through the optical waveguide50by four-fold internal reflection that impinges on the region of the blemish230will be scattered or undergo reflections in undesired directions. As shown inFIG.21, an amount of light absorbing material224can be applied at the blemish230so as to prevent the scattering effect. InFIG.21, the amount of light absorbing material located at the blemish is sufficient so as to restore the rectangular cross-section of the optical waveguide50. However, a lesser amount of light absorbing material may be applied to blemishes which do not restore the optical waveguide to its unblemished structure. The light absorbing material can equally be applied to fill scratches at the faces of the optical waveguides (for both one-dimensional and two-dimensional aperture expanding optical devices), e.g., for any of the optical waveguides10,50,60,70,80,100.

It is noted that certain aspects of the present invention described herein can be used to advantage independently of other aspects of the present invention. For example, the complementary coating methodologies, used either with or without interleaved sets of facets, can be used to advantage separately from the blemish mending techniques. Moreover, the blemish mending techniques can be applied to LOEs or optical waveguides (performing one-dimensional or two-dimensional aperture expansion) having otherwise conventional coating architectures.

Although only the LOE and optical waveguide structures have been illustrated in the drawings, it will be understood that the various LOEs and optical waveguides described herein are intended for use as part of a display, typically a head-up display (HUD), which is preferably a near-eye display (NED), such as a head-mounted display (HMD) or glasses-frame supported display, for providing an image to an eye of an observer. In certain preferred embodiments, the display is part of an augmented reality (AR) display system, in which the image provided to the eye of the observer is overlaid on external “real-world” scenery. In other embodiments, the display is part of a virtual reality (VR) display system, in which only the image provided by the LOE/optical waveguide is viewable to the observer. In all such cases, the display preferably includes an image projector of small form factor that generates a collimated image, which is optically coupled to the LOE/optical waveguide so as to introduce the collimated image into the LOE/optical waveguide via an optical coupling-in configuration (e.g., the coupling-in reflector22, coupling prism, etc.) so as to propagate by internal reflection within the LOE/optical waveguide and gradually be coupled out by the internal selectively reflective surface.

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

It is noted that when used within the context of AR systems, application of small amounts of the light absorbing material on blemishes at external portions of the optical waveguides may also provide benefits of reducing or suppressing scattering of light from external scenery.

When discussing polarization properties of image illumination and coatings, it is noted that for each instance where a particular polarized wave path has been followed in the examples described herein, the polarizations are interchangeable, whereby, for example, on altering polarization selective properties of the coatings, each mention of p-polarized light could be replaced by s-polarized light, and vice versa.

The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

As used herein, the singular form, “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.

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 to exclude the incorporation of features from other embodiments.

It is appreciated that certain features of the invention, which 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, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable 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 inoperative without those elements.

To the extent that the appended claims have been drafted without multiple dependencies, this has been done only to accommodate formal requirements in jurisdictions which do not allow such multiple dependencies. It should be noted that all possible combinations of features which would be implied by rendering the claims multiply dependent are explicitly envisaged and should be considered part of the invention.

Although the 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.