Intermediate layer with adjusted color and gradient

Abstract

An optical system including: (1) a light-directing optical element (LOE) formed from a transparent material and having at least first and second mutually parallel outer major surfaces for supporting propagation of an image by internal reflection; and (2) an intermediary layer adjacent to at least one of the first and second mutually parallel outer major surfaces, wherein the intermediary layer is configured such that (1) at angles less than a critical angle, a reflectance of light averaged over the visible spectrum of light coupled within the LOE and propagated between the at least first and second mutually parallel outer major surfaces is greater than the reflectance expected in the absence of the intermediary layer, and (2) a pure white reflectance is closer to the pure white point in the angular range from angles less than the critical angle to the critical angle than the reflectance expected in the absence of the intermediary layer.

Description

[Technical field]

[0001] The present invention relates to optical systems, and more particularly to optical systems for displaying images to a user, that include a color and tilt tuned intervening layer to reduce the haze effect. [Background technology]

[0002] Consumer demand for better and more comfortable human-computer interfaces is driving the demand for smaller geometries, wider fields of view (FOVs), longer battery life, and clear augmented images in head mounted displays (HMDs) and smart glasses. Head mounted displays that use a waveguide (LOE) to direct the augmented images from a compact projector to the user's eyes have the advantage of reducing the overall size of the HMD device. However, such displays often result in undesirable color haze. Summary of the Invention [Problem to be solved by the invention]

[0003] In one embodiment of the present invention, color haze is mitigated by controlling the reflection intensity and the angle at which the reflection intensity is based at optical interfaces (or boundaries) in the waveguide coatings on the major surfaces of the LOE.

[0004] Light propagating in a waveguide reflects different amounts depending on the angle of incidence. It is convenient to define three angular ranges: low angles of incidence (LR range), where a low reflection (LR) coefficient is desired, intermediate angles of incidence, and high angles of incidence. The boundary between the intermediate and high angles of incidence is defined by the critical angle, where all incident light at angles greater than the critical angle undergoes total internal reflection (TIR); this angular range is sometimes referred to as the TIR range. The intermediate range is characterized by a steep dependence of the reflection intensity on the angle of incidence. [Means for solving the problem]

[0005] The teachings of one embodiment of the present invention provide an optical system that may include a light-guide optical element (LOE) formed from a transparent material and having at least first and second mutually parallel outer major surfaces for supporting (or maintaining) propagation of an image by internal reflection, and an intermediary layer (or intermediate layer or mediating layer) adjacent to at least one of the first and second mutually parallel outer major surfaces, the intermediary layer configured such that (1) at angles less than a critical angle, a reflectance of light averaged over the visible spectrum of light coupled within the LOE and propagated between the at least first and second mutually parallel outer major surfaces is greater than the reflectance expected in the absence of the intermediary layer, and (2) a pure white reflectance is closer to a pure white point (or pure white color point) in the angular range from angles less than the critical angle to the critical angle than the reflectance expected in the absence of the intermediary layer.

[0006] The accompanying drawings, which are incorporated in and form a part of this specification, depict various exemplary systems, methods, and the like, illustrating various embodiments of the aspects of the present invention. It should be understood that the boundaries of the illustrated components in the figures (e.g., boxes, collections of boxes, or other shapes) are illustrative of example boundaries. Those skilled in the art will appreciate that a component may be configured as multiple components, and multiple components may be configured as a component. A component shown as an internal part of another component may be implemented as an external part, and vice versa. Additionally, the components may not be drawn to scale. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary optical system for a near-eye display (NED). [Figure 2A] 2A is a schematic diagram of a cross-sectional side view of the lens and LOE of the NED of FIG. [Figure 2B] 2B is a schematic diagram of an enlarged cross-sectional side view of the lens and LOE of the NED of FIG. [Figure 2C] FIG. 2C is a schematic side view of light traveling through the LOE of FIGS. 2A and 2B. [Figure 3A] FIG. 3A is a graph of reflection versus incidence angle for an interface between a glass LOE and air. [Figure 3B] FIG. 3B is a diagram of a portion of the CIE 1931 XYZ color space gamut showing example reflectance color coordinates for reflection in a waveguide with a BK7 glass core and air over different angular ranges for wavelengths from 430 nm to 660 nm. [Figure 4] FIG. 4 is a diagram of an exemplary LOE having defects or imperfections that cause scattering. [Diagram 5]FIG. 5 shows the color coordinates (CIE 1931 XYZ color space gamut) in the mid-angle range II for reflection in a waveguide with a BK7 glass core and air, over the wavelength range from 430 nm to 660 nm. [Figure 6] FIG. 6 is a first graph of “reflectivity versus incidence angle” at an interface between a BK7 glass waveguide (glass) and a low-refractive index adhesive (low RI adhesive) and a second graph of “reflectivity versus incidence angle” at an interface between a BK7 glass waveguide and an MCSML, including the mid-range II. [Figure 7] Figure 7A is a diagram of color coordinates (CIE 1931 XYZ color space gamut) over the intermediate angle range II for reflection in a waveguide with a BK7 glass core and low refractive index adhesive (low RI adhesive) for wavelengths from 430 nm to 660 nm, and Figure 7B is a diagram of color coordinates over the intermediate angle range II for reflection in a waveguide with a BK7 glass core with MCSML. [Figure 8] FIG. 8 is a plot of three graphs illustrating the effect of coherence length on adhesive layer thickness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Embodiments of the present invention provide an optical system (or optics) for a head up display (HUD) or, most preferably, a near eye display (NED), e.g. a virtual reality display or an augmented reality (AR) display, which includes a light-guide optical element (LOE) that allows for an expanded optical aperture for said purpose.

[0009] 1 illustrates, using the numeral 100, an implementation of a near-eye display device according to the teachings of one embodiment of the present invention, using a LOE 10. The near-eye display device 100 is optically coupled to a compact image projector or picture projector (or POD) 114 that can project an image into the LOE (which can be interchangeably referred to as a "waveguide," "substrate," or "slab") 10, where the image light is captured in one dimension by total internal reflection at a set of mutually parallel flat exterior (or major) surfaces.

[0010] Optical aperture expansion is accomplished within LOE 10 by one or more configurations that progressively redirect image illumination, typically using a set of partially reflective surfaces (which term can be interchangeably referred to as "facets" or the like) that are parallel to one another and angled obliquely with respect to the propagation direction of the image light, with each successive facet deflecting a percentage (or portion) of the image light in the deflected direction. In one-dimensional aperture expansion, the facets couple-out the image light toward the user's eye. In some cases, as illustrated, two-dimensional aperture expansion is accomplished within region 116 of LOE 10 using a first set of facets that progressively redirect and capture / guide image illumination within LOE 10 by total internal reflection. The deflected image illumination then enters a second substrate region 118 of LOE 10, which may be implemented as a separate adjacent substrate or as a contiguous portion of a single substrate, in which a coupling arrangement (e.g., a further set of partially reflective facets) progressively couples out a percentage of the image illumination towards an observer's eye located within a region defined as an eye-motion box (EMB), thereby providing an expansion of the optical aperture in two dimensions. A similar function can be performed using diffractive optical elements (DOEs) for redirecting and / or coupling out the image illumination in one or both of regions 116 and 118. While the following description and figures focus on embedded refractive optical elements, the invention is equally applicable to near-eye displays based on refractive or diffractive optical elements.

[0011] The entire device can be implemented separately for each eye, and preferably, each LOE 10 facing the user's corresponding eye is supported on the user's head. In one particularly preferred option, as shown, the support arrangement is implemented as a set of lenses (e.g., Rx lenses, sunglasses, etc., colloquially referred to herein as "glasses") attached to the face, including lenses 112 to which the LOEs 10 are operatively connected, and a frame including sides 120 that support the device against the user's ears. However, other forms of support structure are possible, including, but not limited to, a headband, visor, or device suspended from a helmet.

[0012] In the illustrated embodiment, the X-axis extends horizontally, which generally corresponds to the extension of the first region of LOE 10, and the Y-axis extends perpendicular to the X-axis, i.e., vertically. In very approximate terms, the first region 116 of LOE 10 can be considered to provide an expansion of the aperture in the X-direction, and the second region 118 of LOE 10 can be considered to provide an expansion of the aperture in the Y-direction.

[0013] The near-eye display 100 may include various additional components, and typically includes a controller (or control) 122 that operates the image projector 114, typically using power from a small on-board battery (not shown) or some other suitable power source. The controller 122 may include all the required electronic components, such as at least one processor or processing circuitry for driving the image projector.

[0014] In this disclosure, various features of certain embodiments of the invention are illustrated in the context of an eyeglass lens (see FIG. 1), and in particular in the context of an interface between an eyeglass lens and a waveguide, however, it is understood that all features disclosed herein are equally applicable to any waveguide interface implementation.

[0015] 2A and 2B are schematic illustrations of possible cross-sectional side views and close-up cross-sectional side views, respectively, of LOE 10. Here, a major surface (or major outer surface) 11 of LOE 10 is attached to a lens 112 of a pair of glasses via an intermediate layer (or intermediate layer or mediating layer) 20. A separate intermediate layer 30 is attached to the other major surface 12 of LOE 10. Note that FIGS. 2A and 2B are illustrated for illustrative purposes and are not illustrated to scale. Intermediate layer 20 insulates LOE 10 from lens 112 and acts as a spacer to maintain total internal reflection of any image projected onto LOE 10. Intermediate layer 30 allows LOE 10 to be insulated from the environment (e.g., air, humidity, and dirt).

[0016] The intermediary layers described herein may be disposed on or as part of an optical layer (e.g., a low RI adhesive, or an effective low RI coating) that is also capable of shifting the critical angle (or boundary angle) for total internal reflection. In this case, the intermediary layer shifts the critical angle and thus affects the amount of angle available for guiding an image inside the LOE 10. However, this is not required. In other examples, the intermediary layers described herein may not shift the critical angle when used to achieve the purposes described herein. In summary, the intermediary layers described herein may or may not be part of an optical layer that is also capable of shifting the critical angle.

[0017] 2A and 2B, an intermediary layer may be used (e.g., bonded) between an isolated waveguide (e.g., LOE 10) and a separate waveguide or lens, in which case the intermediary layer may be referred to in the art as an insulating layer or isolation layer, a more common term.

[0018] 2A, LOE 10 is disposed between lens 112 on one side and air on the other side. Similarly, LOE 10 may be disposed between two lenses, or LOE 10 may be disposed beside air on both sides, or LOE 10 may be bonded to any other material that has sufficient contrast in refractive index between the substrate material of LOE 10.

[0019] FIG. 2C illustrates a simplified cross-section of LOE 10 with lens 112 coupled to one side of LOE 10. In this figure, ray AA corresponds to a single region of the guided image. Ray AA makes an angle α with respect to the normal to LOE major surfaces 11 and 12. As ray AA propagates through the waveguide, it is reflected off major surfaces 11 and 12 until it strikes recessed partially reflective surface 22, which redirects the ray to BB, coupling it out of LOE 10 and into the eyebox.

[0020] The reflectance of the primary surfaces 11 and 12 depends on different parameters, such as the wavelength, polarization and incidence angle α of the illuminating light, and can be determined from the Fresnel equations, which describe the behavior of electromagnetic waves at the interface between two media with different (wavelength-based) refractive indices.

[0021] In FIG. 3A, an exemplary reflectance profile is shown as a function of the angle of incidence for s-polarized light, averaged over the entire visible spectrum. As can be seen, the reflectance profile varies with the critical angle θ c Regarding the above, it can be divided into three intervals (or ranges or regions).

[0022]

number

[0023] I. The above formula represents the angular range for leakage. At this low incidence angle, the reflectivity is low so the light leaks out of the waveguide quickly and cannot be guided in the waveguide.

[0024]

number

[0025] II. The above formula represents the weakly guided angle range (middle range). This angle is below the critical angle but close to the critical angle, and the reflectivity is relatively large, but below 100%. As a result, the light is weakly guided in the waveguide.

[0026]

number

[0027] III. The above formula represents the angle range when guided. In this case, 100% reflection occurs at the critical angle θ c The light is guided in the waveguide by total internal reflection because it is above the critical angle. Here, the critical angle is defined as follows.

[0028]

number

[0029] In the above equation (Eq.1), n surroundings denotes the refractive index of the cladding or mediating layer (i.e., the low refractive index medium), and n LOE denotes the refractive index of the LOE (i.e., the high refractive index medium) through which the trapped ray may travel.

[0030] In Fig. 3B, the color characteristics in these three angle ranges are illustrated. Within these ranges, x, y coordinates in the CIE 1931 XYZ color space gamut are illustrated for different angles of incidence, which are for a BK7 substrate waveguide with ambient air for a uniform distribution of wavelengths between 430 nm and 660 nm, approximately in the visible spectrum. In Fig. 3B I, the color coordinates are illustrated for a first angle range of incidence (see equation 1 above), which spans an angle range from 0 degrees to 39 degrees. In Fig. 3B III, the color coordinates are illustrated for a third angle range (see equation 3 above), which spans an angle range from 42 degrees to 90 degrees. As can be seen from Fig. 3B I and 3B III, these reflections are achromatic and can be defined as being located near the pure white point (0.333, 0.333). In Fig. 3B II, the color coordinates are illustrated for a second angle range (see equation 2 above), which spans an angle range from 39 degrees to 42 degrees. As can be seen from FIG. 3B, II, the reflections within this angular range are chromatic and lie further away from the pure white point (0.333, 0.333).

[0031] In more practical aspects, imperfections within LOE 10 can result in detrimental scattering artifacts. For example, LOE 10 can have manufacturing or impact defects, such as machining defects on the surface or chips on the edges of facets. Also, the waveguide can become dirty. For example, dust or user sweat can accumulate on the surface of the waveguide. Or, stray light can enter the waveguide from projector 114.

[0032] FIG. 4 illustrates a LOE 10 similar to FIG. 2C, but in this case includes defects or imperfections F1 and F2 that can cause scattering. F1 is a defect inside the LOE 10, and F2 is a defect on the surface of the LOE 10. As can be seen from FIG. 4, these defects F1, F2 scatter a portion of the light from ray AA. In the low reflectivity range I, some of the harmful scattered light impinging on the LOE 10 can escape. Some of the scattered light can be guided or partially guided inside the LOE 10. The scattered light can impinge on a core-cladding interface in the intermediate angle range II of FIGS. 3A, 3B, or in the angle range III when guided, until it finally reaches the semi-reflective facet 22. From the facet 22, some of it can be coupled out of the LOE 10 toward the user's eye, as illustrated by ray CC. Thus, the scattered light can be viewed as a weak background that degrades the desired image and reduces contrast. As a function of core-cladding reflectance and chromaticity (see FIGS. 3A and 3B), scattered light can produce a chromatic and / or achromatic haze that is superimposed on the augmented image ray BB.

[0033] Although background haze is undesirable, often weak haze can be tolerable to the human eye, provided that the haze does not present problems from strong intensity gradients or color non-uniformity. Typically, such haze is fully guided in the waveguide by TIR (angular range III) and can be essentially uniform in intensity and achromatic. However, light that is only weakly guided (angular range II) can present problems from strong intensity gradients (or slopes) and color non-uniformity, which can then be more noticeable and more disruptive to the eye.

[0034] To understand the effect of weakly guided haze, consider a ray incident on a major surface of LOE 10 at an angle α and wavelength λ, and the reflectance R(α, λ) in the weakly guided mid-range II, given by the following equation:

[0035]

number

[0036] If the incident light is reflected N times off the major surfaces before being coupled out of the waveguide, the intensity I(α) before being coupled out of the waveguide is illustrated by the following equation:

[0037]

number

[0038] In the above equation (Eq.2), I 0 corresponds to the initial intensity. Here we only focus on the effect of reflections from the major surfaces and ignore other artifacts, e.g. reflections from different embedded elements in the waveguide. The intensity gradient can also be found from the partial derivative with respect to the field of view (FoV) and wavelength (λ):

[0039]

number

[0040] In the above formula, applicants have neglected the dependence of N on α and applied the right-hand side approximation, i.e., R~1, which is valid near the critical angle. That is, applicants have concluded that the normalized partial derivative of the reflectance is enhanced by a factor of N in the normalized partial derivative of the intensity. This N is typically of the order of several tens of years, and reflectance is usually sensitive to the incidence angle and wavelength at angles of incidence near (below) the critical angle, so the gradient of the intensity I is sensitive to the incidence angle and also to the wavelength. In Figure 5, the color coordinates (CIE 1931 XYZ color space gamut) in the mid-angle range II are illustrated for reflection in a waveguide with a BK7 glass core and air over wavelengths from 430 nm to 660 nm. As can be seen from Fig. 5, in the angular range from 12 degrees to 39 degrees the scattered light is achromatic, in the angular range from 40.7 degrees to 41.2 degrees the scattered light is chromatic (i.e. the reflection lies further away from the pure white point (0.333, 0.333)), and in the angular range from 41.248 degrees to 45 degrees the scattered light can again be achromatic. Furthermore, when the glass / air reflectivity is low (below the angular range I of leakage in Fig. 3A), the scattered light is rapidly attenuated and cannot reach the user's eye. The chromatic / achromatic and intensity profile in the intermediate range II determines the perceived haze profile.

[0041] In the consumer product of AR glasses illustrated in FIG. 1, the LOE 10 is integrated with an optical lens 112. As illustrated in FIG. 2A and FIG. 2B, an intermediary layer 20 can be implemented between the lens 112 and the LOE 10, and an intermediary layer 30 can be implemented between the LOE 10 and the environment. Considering all the above, these intermediary layers 20, 30 can be designed not only to support low reflection at low angles and high reflection at high angles (i.e., to support TIR), but also to solve the color haze problem, and in one embodiment, these intermediary layers 20, 30 can be designed to control the reflection intensity at the core (LOE) cladding (environment) interface. In this case, the applicant introduces color and tilt-tuned intermediary layers (MCSML) 20, 30. Considering the broader case, a higher RI waveguide kept in a lower RI surrounding can typically create undesirable haze problems, and a MCSML solution is needed to manage such problems.

[0042] In the configuration of FIG. 1, an adhesive is used to bond the LOE 10 to the lens 112. This configuration, without the MCSML, may be prone to introducing color haze into the user's eyes due to imperfections (e.g., due to chips, dirt, sweat, etc.), as discussed above. The MCSML 20, 30 tailors the reflectance in mid-range II compared to that of the prior art adhesive / insulation layers, making the overall haze of the LOE 10 more tolerable. Furthermore, the MCSML 20, 30 tailors the reflectance in mid-range II compared to that of the prior art adhesive / insulation layers, making the tailored reflectance substantially achromatic, such that the reflection intensity at the core (LOE) cladding (environment) interface does not vary excessively as a function of incidence angle below a critical angle.

[0043] FIG. 6 illustrates a first graph of “Reflectance vs. Incident Angle (Tilt Rs vs. Angle)” at an interface between a BK7 glass waveguide (glass) and a low refractive index adhesive (low RI adhesive), including the mid-range II. FIG. 6 also illustrates a second graph of “Reflectance vs. Incident Angle” at an interface between a BK7 glass waveguide and MCSML 20. As can be seen from FIG. 6, MCSML 20, 30 adjusts the slope (or tilt) of the mid-range II to increase the reflectance averaged over the visible spectrum of light, which is incident at a critical angle θ C Near the angle θ (θ<θ C ), is coupled into the LOE 10 and weakly trapped between the major outer surfaces. Thus, the reflection of the MCSML 20, 30 is greater than the reflection expected without the MCSML 20, 30. In one embodiment, the MCSML 20, 30 adjusts the slope of the mid-range II to reduce the critical angle θ C 6, the reflectance averaged over the visible spectrum of light that is coupled into the LOE 10 and weakly trapped between the major exterior surfaces is at least 10%, 15%, 20%, or 25% greater than the critical angle θ of 54 degrees (as can be seen in FIG. 6). C = approximately 10 degrees below 64 degrees) the reflectance is greater than 20%. This adjustment to the Mid-Range II slope makes the overall LOE10 haze more tolerable.

[0044] In FIG. 7A, the color coordinates (CIE 1931 XYZ color space gamut) in the intermediate angle range II are illustrated for the reflection in a waveguide with a BK7 glass core and a low refractive index adhesive (low RI adhesive) at wavelengths from 430 nm to 660 nm. As can be seen from FIG. 7A, the scattered light can be chromatic in the intermediate angle range between approximately 59.6 degrees and 63.1 degrees (i.e., the reflection is located further away from the pure white point (0.333, 0.333)). In FIG. 7B, the color coordinates in the same intermediate angle range II are illustrated for the reflection in a waveguide with a BK7 glass core with MCSML 20, 30. As can be seen from FIG. 7B, in comparison with the prior art adhesive / insulation layer, MCSML 20, 30 adjust the reflection in the intermediate range II, so that the adjusted reflection is substantially achromatic (i.e., the reflection is located close to the pure white point (0.333, 0.333)).

[0045] Therefore, in one embodiment, the critical angle θ C From an angle 10 degrees below the critical angle θ C For the angular range from 10 degrees below the critical angle to 10 degrees above the critical angle θ 1 , in the CIE 1931 XYZ color space or gamut, for reflection in a waveguide with a BK7 glass core and MCSML 20, 30, the reflectance of pure white light lies closer to the pure white point (0.333, 0.333) than the reflection in the same waveguide without MCSML 20, 30. For example, in one embodiment, for reflection in a waveguide with a BK7 glass core and MCSML 20, 30, in the CIE 1931 XYZ color space or gamut, the reflectance of pure white light lies closer to the pure white point (0.333, 0.333) than the reflection in the same waveguide without MCSML 20, 30. C In the angular range from 0.333 to 0.333, the reflectance of pure white light lies within a color radius of 0.01 or 0.015 or 0.02 or 0.025 or 0.03 or 0.035 or 0.04 from the transmitted pure white point (0.333, 0.333). Such reflectances are generally considered achromatic, for example, when compared to the reflectances illustrated in FIG. 7A.

[0046] From the point of view of coating design, different solutions can be envisaged, but it is often beneficial to (1) use low refractive index (RI) materials for the requirements of the TIR range III and (2) use multi-layer coatings for the slope in the TIR (intermediate) range II and the anti-reflection range I (low degree).

[0047] 2B, two different combinations of low RI refractive index materials and multi-layer coatings can be used for the intermediary layers 20 and 30. The intermediary layer 20 disposed between the LOE 10 and the lens 112 can include an adhesive 22, which can simultaneously function as an adhesive and a low RI material that operably connects the LOE 10 to the lens 112. On the other hand, the intermediary layer 30 disposed between the LOE 10 and the environment (e.g., air) can include a multi-layer low RI coating 32 as a low RI material. The intermediary layers 20 and 30 also include multi-layer coatings 24, 34 to accommodate a tilt to the non-reflective range I (low degree) and the TIR (intermediate) range II, respectively. Various layers are illustrated herein in a specific stacking order. However, the present invention is not limited to any particular order of the layers, and the order of the layers can be changed.

[0048] In one embodiment, the low RI material 32 (e.g., MgF having a refractive index of about 1.38) 2 , or AlF 4 having a refractive index of about 1.36 3 ) may be a thick coat layer with an optical thickness (optical thickness = physical thickness x refractive index) of over 700 nm, while the low RI material 22 may be a low RI index adhesive (Noland optical adhesive with a refractive index of about 1.34) with a thickness (from 0.5 μm to 100 μm). Other candidates for low RI index adhesives include NOA adhesives, as well as epoxies, acrylics, and silicones, which may be selected based on their particular (low) refractive index, adhesive strength, and other properties.

[0049] While the thickness of thin coatings is well controlled, the thickness of adhesive (or pressure sensitive) materials is generally more difficult to control and can often vary substantially from sample (or item) to sample or product to product. Thus, it is difficult to design and control the chromaticity and angular reflectance profile of the adhesive well. Thin layers of adhesive can cause problems with angle and wavelength sensitive profiles due to coherence artifacts, which can result in color artifacts in the background haze as described above. Therefore, there can be advantages in designing and manufacturing a thick layer (or layers) of adhesive compared to the coherence length of the illumination source. In one embodiment, the layer 22 of low RI adhesive is thicker than half the coherence length of the illumination source (e.g., POD 114) to the optical system. Such a thick layer generally allows for smooth removal of coherence artifacts and better control of the color characteristics of the background haze.

[0050] The effect of coherence length on adhesive layer thickness is illustrated in Figure 8, which illustrates the expected reflectance at the interface between the BK7 glass layer of LOE 10 and low RI adhesive 22 when illuminated with a green light source having a uniform spectral bandwidth of 20 nm between wavelengths of 520 nm and 540 nm. As is evident from Figure 8, varying the adhesive thickness (from 1 μm to 10 μm and to 100 μm) has a strong effect on the expected overall reflectance.

[0051] The use of a low RI adhesive 22 is advantageous in meeting the TIR range requirements because it reduces the overall requirements for the multi-layer coating 24. In general, as the angular range over which a coating must support a given performance specification increases, the optical performance of the coating may decrease. This is because a more complex and thicker coating may be required to achieve a given level of performance over a larger angular range. On the other hand, as the angular range over which a coating must support a given performance specification decreases, a simpler and thinner coating may be sufficient to achieve the desired performance. Because the multi-layer coating 24 must support a smaller angular range, when using a low RI adhesive 22, the coating 24 is simplified, reducing its overall optical thickness from about 3 μm to about 0.5 μm and reducing its number of layers by about 33%. When implementing the MCSML 20 on the first full facet LOE 10, the overall coating thickness and number of layers required may be reduced, allowing for higher profits, higher production cycles, lower stress / curvature, etc.

[0052] In another embodiment, a layer of coating or adhesive with a refractive index close to that of the LOE 10 (index matching layer) is placed on top of the LOE 10 in front of the low RI materials 22, 32. An index matched layer (IML) is a thin layer of material applied to the surface of a waveguide in a near-eye display. The purpose of the IML is to reduce the amount of light that is reflected at the interface, which may cause undesirable glare and reduce the contrast and brightness of the display. The IML may be fabricated from a material with a refractive index that matches that of the LOE 10, in which case the IML can act as a buffer layer at the interface. By matching the refractive index of the IML to that of the LOE 10, the IML can help reduce the amount of light that is reflected at the interface. This allows the display to have higher contrast and brightness, as well as less glare. In addition to reducing reflections, the IML can also help alleviate problems such as scattering, which can occur when light is scattered by imperfections in the surface of the waveguide. The IML can help reduce scattering and improve image quality by filling these defects with a material that has the same refractive index as that of the waveguide. In this configuration, the IML can minimize the effects of scattering caused by imperfections in the LOE 10, thereby reducing overall haze and improving image contrast.

[0053] "Definition" The following are definitions of selected terms used in this specification. These definitions include various examples or forms of components that fall within the scope of the terms and that may be used in implementations. The examples are not intended to be limiting. Also, either the single form or the multiple forms of these terms may be included in the definitions.

[0054] An "operable connection," or a connection in which entities (e.g., entities, objects, etc.) are "operably connected," refers to a connection that allows signals, physical communications, or logical communications to be sent or received. Typically, an operable connection includes a physical interface, an electrical interface, or a data interface, but it should be noted that an operable connection may include different combinations of these, or other types of these connections, sufficient to allow operable control. For example, two entities may be operably connected directly to communicate signals with each other, or may be operably connected through one or more intermediate entities, such as a processor, operating system, logic, software, or other entity, to communicate signals with each other. Logical or physical communication channels may be utilized to form an operable connection.

[0055] Whenever the term "includes" or "including" is used in the detailed description or claims, it is intended to be used in an inclusive sense, in the same manner that the term "comprising" is used in the claims as a transitional term. Furthermore, when the term "or" is used in the detailed description or claims (e.g., A or B), it is intended to be used in the sense of "A or B or both." If the applicant intends "only A or B, but not both," then a term such as "only A or B, but not both" should be used. Thus, the use of the term "or" herein is inclusive and not exclusive. See, e.g., Bryan A. Garner, A Dictionary of Modern Legal Usage, p. 624 (2nd ed., 1995), for related purposes.

[0056] The above embodiments have been described to illustrate exemplary systems, methods, etc. Although the embodiments have been described in considerable detail, the applicant does not intend to limit the scope of the present invention to such detail. Of course, for the purposes of describing the systems, methods, etc. described herein, it is not possible to describe all conceivable combinations of components or methodologies. Further advantages and improvements will be readily apparent to those skilled in the art. Thus, the present invention is not limited to the detailed description, exemplified apparatus, and embodiments shown and described. The present application is intended to embrace all such changes, modifications, and variations that fall within the scope of the appended claims. Moreover, the above description is not intended to limit the scope of the present invention. Rather, the scope of the present invention may be determined by the scope of the appended claims and their equivalents.

Claims

1. an optical system for directing an image toward a viewing user, the optical system comprising a light directing optical element (LOE) and an intermediary layer; the LOE is formed of a transparent material and has at least first and second mutually parallel outer major surfaces that support propagation of light corresponding to an image by total internal reflection when an angle of incidence of light thereon is greater than a critical angle, the LOE having an input coupling arrangement for coupling the image into the LOE and an output coupling arrangement for coupling the image out towards an eye of the user; the intermediary layer is adjacent to at least one of the at least first and second mutually parallel outer major surfaces and is coupled into the LOE at angles 10 degrees below a critical angle such that a reflectance averaged over the visible spectrum of light propagated between the at least first and second mutually parallel outer major surfaces is at least 10% greater than the reflectance expected in the absence of the intermediary layer, and the intermediary layer is configured such that, within a CIE 1931 XYZ color space or gamut, a pure white reflectance is located closer to the propagated pure white point (0.333, 0.333) in the angular range from 10 degrees below the critical angle to the critical angle than the reflectance expected in the absence of the intermediary layer. Optical system.

2. The optical system of claim 1 , wherein the intermediate layer comprises a low refractive index adhesive layer having a thickness between 0.5 μm and 100 μm.

3. The optical system of claim 2 , comprising an illumination source configured to generate the image, and wherein the low refractive index adhesive layer is thicker than half a coherence length of the illumination source.

4. The intermediate layer is a multi-layer coating layer of low refractive index having an optical thickness greater than 700 nm; an index matching layer disposed between at least one of said at least first and second mutually parallel outer major surfaces and said intermediate layer; The optical system of claim 1 , comprising at least one of:

5. 2. The optical system of claim 1, wherein the reflectance of a pure white light source lies within a color radius of 0.04 from a transmitted pure white point (0.333, 0.333) in the angular range from 10 degrees below the critical angle to the critical angle, within the CIE 1931 XYZ color space or gamut.

6. an optical system for directing an image toward a viewing user, the optical system comprising a light directing optical element (LOE) and an intermediary layer; The LOE is formed of a transparent material and has at least first and second mutually parallel outer major surfaces, the first and second outer major surfaces being such that the angle of incidence of light thereon is less than a critical angle θ C and supporting propagation of light corresponding to an image by total internal reflection when the LOE has an input coupling arrangement for coupling the image into the LOE and an output coupling arrangement for coupling the image out towards an eye of the user. The intermediate layer is adjacent to at least one of the at least first and second mutually parallel major outer surfaces and has a critical angle θ C Near the angle θ (θ < θ C wherein the intermediary layer is configured such that a reflectance averaged over a visible spectrum of light coupled into the LOE and propagated between the at least first and second mutually parallel major exterior surfaces is greater than a reflectance expected in the absence of the intermediary layer. Optical system.

7. The critical angle θ Ｃ 7. The optical system of claim 6, wherein at angles 10 degrees below the reflectance, the reflectance is at least 10%.

8. The optical system of claim 6 , wherein the intermediate layer comprises a low refractive index adhesive layer having a thickness between 0.5 μm and 100 μm.

9. The optical system of claim 8 , wherein the low index adhesive layer is thicker than half a coherence length of an illumination source for the optical system.

10. The optical system of claim 6 , wherein the intermediary layer comprises a low refractive index multi-coating layer having an optical thickness greater than 700 nm.

11. 7. The optical system of claim 6, wherein the intermediary layer comprises a multi-layer coating layer adjacent at least one of the at least first and second mutually parallel major exterior surfaces, and wherein the intermediary layer is configured such that, within a CIE 1931 XYZ color space or gamut, the reflectance of a pure white light source lies within a color radius of 0.04 from a transmitted pure white point (0.333, 0.333) in the angular range from 10 degrees below the critical angle to the critical angle.

12. 11. The optical system of claim 10, wherein the intermediary layer includes an index matching layer disposed between at least one of the at least first and second mutually parallel outer major surfaces and the intermediary layer.

13. an optical system for directing an image toward a viewing user, the optical system comprising a light directing optical element (LOE) and an intermediary layer; the LOE is formed of a transparent material and has at least first and second mutually parallel outer major surfaces that support propagation of light corresponding to an image by total internal reflection when an angle of incidence of light thereon is greater than a critical angle, the LOE having an input coupling arrangement for coupling the image into the LOE and an output coupling arrangement for coupling the image out towards an eye of the user; the intermediate layer is adjacent to at least one of the at least first and second mutually parallel major exterior surfaces, and the intermediate layer is configured such that, in a CIE 1931 XYZ color space or gamut, the reflectance of a pure white light source is within a color radius of 0.04 from a transmitted pure white point (0.333, 0.333) in an angular range from 10 degrees below the critical angle to the critical angle; Optical system.

14. The optical system of claim 13 , wherein the intermediate layer comprises a low refractive index adhesive layer having a thickness between 0.5 μm and 100 μm.

15. 15. The optical system of claim 14, comprising an illumination source for generating the image, and wherein the low refractive index adhesive layer is thicker than half a coherence length of the illumination source.

16. The optical system of claim 13 , wherein the intermediary layer comprises a low refractive index multi-coating layer having an optical thickness greater than 700 nm.

17. 14. The optical system of claim 13 including an index matching layer disposed between at least one of said at least first and second mutually parallel outer major surfaces and said intermediate layer.

18. an optical system for directing an image towards a viewing user, comprising: an illumination source configured to generate an image; an optical lens having at least first and second outer major surfaces; a light-guiding optical element (LOE); An intermediary layer; Equipped with the LOE is formed using a transparent material and has at least first and second mutually parallel outer major surfaces that support propagation of light corresponding to the image by total internal reflection when an angle of incidence of light thereon is greater than a critical angle; the LOE has an input coupling arrangement for coupling the image into the LOE and an output coupling arrangement for coupling the image out towards an eye of the user; the LOE is disposed adjacent to the optical lens such that one of the at least first and second mutually parallel outer major surfaces faces one of the at least first and second outer major surfaces of the optical lens; The intermediate layer is disposed between the optical lens and the at least first and second mutually parallel outer major surfaces and the LOE adjacent one of the at least first and second outer major surfaces of the optical lens, and has a critical angle θ C Near the angle θ (θ < θ C ), wherein the reflectance averaged over the visible spectrum of light coupled into the LOE and propagated between the at least first and second mutually parallel major exterior surfaces is greater than the reflectance expected in the absence of the intervening layer, and the intervening layer is configured such that, in the CIE 1931 XYZ color space or gamut, the reflectance of pure white lies within a radius of 0.04 color from the propagated pure white point (0.333, 0.333) for an angular range from 10 degrees below the critical angle to the critical angle. Optical system.

19. 20. The optical system of claim 18, wherein the intermediate layer comprises a low refractive index adhesive layer having a thickness between 0.5 μm and 100 μm, and the low refractive index adhesive layer is thicker than half the coherence length of the illumination source.

20. 20. The optical system of claim 18, wherein the intermediary layer comprises a low refractive index multi-coating layer having an optical thickness greater than 700 nm.

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