Multilayer coating structure minimizing phase shift

Abstract

A multilayer coating structure is provided that minimizes phase shift. An apparatus comprising a waveguide and one or more partially reflective surfaces embedded inside the waveguide, wherein each of the one or more partially reflective surfaces comprises a multilayer coating structure, wherein a first portion of the multilayer coating structure causes a total phase shift of light propagating through the first portion of the multilayer coating structure, and wherein a second portion of the multilayer coating structure is selected to reduce the total phase shift.

Description

Technical Field

[0001] This disclosure relates to multilayer coated structures, manufacturing methods, waveguides, and head-mounted displays. More specifically, in some embodiments, this disclosure relates to multilayer coated structures, manufacturing methods, waveguides having specific and / or minimized cumulative relative phases through multilayer coated structures, and head-mounted displays. Background Technology

[0002] Refractive head-mounted displays are based on partially reflective surfaces embedded within waveguides. These partially reflective surfaces can be made from highly precise nanoscale multilayer coating structures designed and fabricated to achieve specific reflection, polarization, and color properties.

[0003] As light propagates through a medium or free space, it accumulates phase. Light traveling a certain distance through different materials will accumulate different phases. Therefore, different regions of a beam propagating through a complex structure will accumulate different phases, affecting the phase front of the beam and thus the beam quality in far-field images, as well as reducing the optical resolution of the image.

[0004] This disclosure focuses on refractive waveguides, but is also applicable to bulk grating or surface grating waveguides. The techniques described in this disclosure can also be applied to control the phase front of an expanded output beam, for example, to generate beam equalizers, optical diffusers, or expanded flat-top beams. The advantage of such structures is that they are transparent and can be fabricated such that light propagating through them is only slightly distorted during transmission, while expanding the injected input beam (thus compactly replacing cumbersome classical optics and propagation distance) and generating diffuse or complex phase fronts. Summary of the Invention

[0005] In one embodiment, an apparatus is disclosed comprising a waveguide and one or more partial reflective surfaces embedded within the waveguide, wherein each of the one or more partial reflective surfaces comprises a multilayer coating structure, wherein a first portion of the multilayer coating structure causes a total phase shift of light propagating through the first portion of the multilayer coating structure, and wherein a second portion of the multilayer coating structure is selected to reduce the total phase shift.

[0006] In another embodiment, a method for manufacturing a waveguide is disclosed, wherein the method includes: providing one or more partial reflective surfaces embedded within the waveguide, wherein each of the one or more partial reflective surfaces is provided by forming a multilayer coating structure, wherein a first portion of the multilayer coating structure is provided to cause a total phase shift of light propagating through the first portion of the multilayer coating structure, and wherein a second portion of the multilayer coating structure is selected to reduce the total phase shift.

[0007] In another embodiment, a non-transitory computer-readable storage medium is disclosed, which stores instructions for designing one or more partial reflective surfaces embedded within a waveguide, wherein the instructions cause one or more processors to execute at least one multilayer coating structure for each of the one or more partial reflective surfaces, wherein a first portion of the multilayer coating structure is provided to cause a total phase shift of light propagating through the first portion of the multilayer coating structure, and wherein a second portion of the multilayer coating structure is selected to reduce the total phase shift.

[0008] In another embodiment, an apparatus is disclosed comprising a waveguide and one or more partially reflective surfaces embedded within the waveguide, wherein each of the one or more partially reflective surfaces comprises a multilayer coating structure, and wherein one or more layers of the multilayer coating structure are selected to limit the total phase shift of light propagating through one or more other layers of the multilayer coating structure to below a predetermined threshold.

[0009] In another embodiment, a non-transitory computer-readable storage medium is disclosed, which stores instructions for designing one or more partially reflective surfaces embedded within a waveguide, wherein the instructions cause one or more processors to execute at least one multilayer coating structure for each of the one or more partially reflective surfaces, wherein each of the one or more partially reflective surfaces includes a multilayer coating structure, and wherein one or more layers of the multilayer coating structure are selected to limit the total phase shift of light propagating through one or more other layers of the multilayer coating structure to below a predetermined threshold. Attached Figure Description

[0010] Figure 1A A refractive waveguide having a set of partially reflective surfaces embedded inside the waveguide is shown according to an embodiment of the present disclosure.

[0011] Figure 1B Another exemplary refractive waveguide having two sets of partially reflective surfaces embedded inside the waveguide is shown according to an embodiment of the present disclosure.

[0012] Figures 2A to 2C Different angle regions for waveguide design according to embodiments of this disclosure are shown.

[0013] Figure 3 The following embodiments according to the present disclosure are shown. Figure 2A The typical distribution of the average reflectivity (averaged over the visible spectrum) of the waveguide's reflecting surface varies with the incident angle.

[0014] Figure 4AThe case of a simple finite plate with thickness d and refractive index n1 placed in an ambient material with refractive index n0 is shown, along with a parallel ray (plane wave) propagating at an angle θ0 relative to the normal of the main surface of the plate.

[0015] Figure 4B A coating structure with multiple layers is shown, which causes a cumulative phase difference between light propagating through the multilayer coating structure and light not propagating through the multilayer coating structure.

[0016] Figure 4C Two multilayer coating structures are shown, through which light can propagate at incident angles θ0 and θ0'.

[0017] Figure 5A This illustrates the "unfolding" of the optical path of light rays inside the refracting waveguide.

[0018] Figure 5B The “unfolding” optical path of light inside the refracting waveguide is shown, where the small facet does not extend all the way to the main surface.

[0019] Figure 6 The phase preceding the discrete jump is shown.

[0020] Figure 7A The diagram shows a coating structure of two materials with four layers and two refractive indices placed in an environmental material.

[0021] Figure 7B It shows the relationship with Figure 7A The same structure as shown, but with an additional thick layer whose refractive index is close to that of the surrounding material.

[0022] Figure 7C It shows: targeting Figure 7A and Figure 7B The structure in the coating, which varies with the incident angle, represents the phase difference between light propagating through the coating and light that will travel through the environmental material without passing through the coating.

[0023] Figure 7D Showing the target Figure 7A and Figure 7B A comparison of reflectivity as a function of incident angle for the two scenarios presented.

[0024] Figure 8A An exemplary coating structure of two materials with two refractive indices placed within an environmental material is shown, wherein the coating structure is designed for specific requirements that do not include low phase shift requirements.

[0025] Figure 8BExemplary coating structures of three materials with three refractive indices placed within an environmental material are shown, wherein the coating structures are designed to have low reflectivity and induce a phase difference that is compensated for. Figure 8A The phase difference of the coating structure in the middle.

[0026] Figure 8C It shows that Figure 8B The coating structure is placed Figure 8A The combined structure on top of the coating structure.

[0027] Figure 9 It is a multilayer coating structure with different refractive indices placed in environmental materials, wherein the structure is designed by specialized software to meet all specification requirements, including low phase shift. Detailed Implementation

[0028] Phase shift caused by thin film coating inside the waveguide

[0029] Figure 1A An exemplary refractive waveguide 2 is shown, wherein a set of partially reflective surfaces (facets) 10 are embedded inside the waveguide 2. Figure 1B Another exemplary refractive waveguide 2 is shown, in which two sets of partially reflective surfaces (planes) 10 and 11 are embedded within the waveguide 2. The partially reflective surfaces in each set can be coparallel. More complex structures (e.g., three or more sets of coparallel surfaces, homogenizing elements, quadruple rectangular waveguides) are also possible. An image can be injected into the waveguide 2 via a coupling element 20 (which can be refracted, reflected, or diffracted) or directly through the main surface. The injected image propagates within the waveguide 2 until it is reflected by the partially reflective surface 10, which couples the light out of the waveguide 2 toward a predetermined eye-tracking box (EMB) 1, assuming the user's eye is located within the predetermined EMB 1.

[0030] Figures 2A to 2C Different angular regions are shown for the design of a set of partially reflecting surfaces (facets) 10 in waveguide 2. Although waveguides with only one set of facets are presented (such as...), Figure 1A However, these regions also apply to refractive waveguides with several sets of common parallel planes, such as... Figure 1B The refractive waveguide in the middle. Figures 2A to 2C The left column of each of them presents Figure 1AWaveguide 2 has a first set of facets 10 with different angular orientations. An input image is injected from a projector (not shown) through coupling element 20 and propagates within waveguide 2 as either a descending ray 31a or a rising ray 31b. Ultimately, the rising ray 31b is reflected from one of the facets 10 and reaches EMB 1. The descending ray 31a can also be reflected by the facets 10; however, this reflection is undesirable and would result in reduced output intensity (efficiency loss), and could also produce harmful ghosting images.

[0031] To minimize these effects, the reflectivity of facet 10 should be able to minimize the reflection of the falling ray 31a. Therefore, each facet 10 has a range of incident angles in which reflection is desired and defines the properties of the output image, and different angular ranges in which reflection should be minimized. To prevent degradation of color uniformity in the final image, the transmittance of ray 31a and the reflectivity and transmittance of ray 31b must be sufficiently uniform across the relevant wavelength bands. Clearly, these properties must be controlled under the relevant polarization states of the incident rays 31a and 31b.

[0032] Figures 2A to 2C The middle column of each describes the range of possible incident angles of the descending ray 31a and the rising ray 31b on the facet 10. The descending ray 31a illuminates the facet 10 at a specific angle region 42 (transmission window), while the rising ray 31b illuminates the facet 10 at a different angle region 41 (reflection window). Figures 2A to 2C The orientation of the facet 10, as described in the right column of each of them, also determines the angle region 43 of the incident light rays transmitted from the general world scene through the waveguide 2.

[0033] Figure 2A A small plane 10 is shown, typically at an angle of, for example, 23° to 29° relative to the main surface of waveguide 2. This makes the typical angle range of the reflection window 41, for example, 18° to 34°, the typical angle range of the transmission window 42, for example, 64° to 90°, and the typical angle range of the world scene window 43, for example, 5° to 63°.

[0034] Figure 2B A small plane 10 is shown that is typically at an angle of, for example, 31° to 43° relative to the main surface of waveguide 2. This makes the typical angle range of the reflection window 41, for example, 26° to 38°, the typical angle range of the transmission window 42, for example, 46° to 90°, and the typical angle range of the world scene window 43, for example, 1° to 69°.

[0035] Figure 2CA small plane 10 is shown that is typically at an angle of, for example, 47° to 68° relative to the main surface of waveguide 2. This makes the typical angle range of the reflection window 41, for example, 42° to 72°, the typical angle range of the transmission window 42, for example, 19° to 44°, and the typical angle range of the world scene window 43, for example, 30° to 90°.

[0036] As explained above, within these angular regions, the design of multilayer coating structures must be optimized to meet different optical properties, such as reflection and transmission, chromaticity, and polarization. For example, Figure 3 Demonstrated against Figure 2A The waveguide 2 shown in the diagram has a typical distribution of the average reflectivity of s-polarized light (averaged over the visible spectrum from 400 nm to 700 nm) on its reflecting surface 10 as a function of the incident angle. Clearly, the reflectivity reaches a desired finite value in the low-angle range (“reflection” window) and exhibits low reflectivity at high angles (“transmission” window).

[0037] In addition to controlling these properties of light in the design of multilayer coated structures, this disclosure also describes methods for controlling the phase properties of transmitted light through multilayer coated structures to minimize diffraction artifacts. More specifically, this disclosure describes methods for controlling the phase caused by the coating, such that the phase difference between light propagating through the coating and light propagating in the medium without propagating through the coating is limited to a certain threshold, or the phase difference between rising and falling rays propagating through the coating is limited to a certain threshold. For example, the methods described herein can control the phase caused by the coating such that the phase difference between light propagating through the coating and light propagating in the medium without propagating through the coating is limited to a predetermined threshold, such as within ±1°, ±10°, ±50°, or ±100°. Furthermore, for example, the methods described herein can limit the phase difference between rising and falling rays propagating through the coating to a predetermined threshold, such as within ±1°, ±10°, ±50°, or ±100°.

[0038] To understand this intuitively, such as Figure 4A As shown, consider a simple finite plate with thickness d and refractive index n1 placed in an ambient material with refractive index n0, and a parallel ray (plane wave) propagating at an angle θ0 relative to the normal to the main surface of the plate. The ray propagating through the plate is refracted into an angle. Furthermore, light propagates through a medium with a refractive index different from that of the surrounding environment. Therefore, the optical path length of light propagating through the plate differs from that of light propagating without passing through the plate. Specifically, the difference in optical path length between light propagating through the plate and light propagating without passing through the plate is:

[0039]

[0040] Therefore, there is a phase difference of Δ·k between the light rays that propagate through the plate and those that do not, where k is the wave number (k = 2π / λ, λ is the wavelength). When incident normally, Δ = d(n0 - n1), and the phase difference depends linearly on the refractive index difference.

[0041] Similarly, such as Figure 4B As shown, more complex multilayer coating structures with multiple layers will also cause a phase difference between light propagating through the multilayer coating structure and light not propagating through it. This phase difference can be calculated using various analytical or numerical methods (e.g., the transfer matrix method). Figure 4C As shown, the phase difference can also be calculated for the case where light can propagate through one of the two multilayered coating structures at incident angles θ0 and θ0'. In fact, the rising and falling rays of a single collimated beam propagating in waveguide 2 ( Figures 2A to 2C Different phases will accumulate when propagating through the small plane 10.

[0042] Next, consider Figure 5A It shows the optical path of light inside the refractive waveguide 2 (also referred to in this paper as a light-guiding optical element (LOE)). Figure 5A The first row shows a typical 1D structure, where the image is coupled into waveguide 2, and rising rays 31a and falling rays 31b propagate through waveguide 2 until they are reflected by one of the embedded facets 10 and coupled out of waveguide 2. The different trajectories of the rays are more easily understood by spreading the rays around the main surface of waveguide 2, where light is reflected by total internal reflection. This is in... Figure 5A The description is provided in lines two through four. Clearly, different rays of light illuminate the small plane 10 at different times and angles (i.e., as rising or falling rays). Therefore, the rays may differ from each other in amplitude and phase. Similarly, as... Figure 5B As shown, in the case where the facet 10 does not extend all the way to the main surface, the phase difference requirement will now also include the difference between light propagating between the coatings and light propagating through the coatings at different angles.

[0043] This ray diagram depicts the effect of facet 10 on the incident light field generated by a single pixel of the input image. As the field propagates through the LOE, it accumulates discrete jumps in amplitude and phase when illuminating (partially illuminating) facet 10. Amplitude jumps are inherent to refractive waveguide technology, and if the reflectivity of facet 10 is low, the effect of amplitude jumps on image quality is negligible. In contrast, phase jumps can be large and can have a significant impact on the image quality of the output image. Figure 6 A simplified front-phase image of a single optical field at the output of the waveguide is shown, assuming that diffraction within the waveguide is negligible.

[0044] Therefore, it is clear that the effects of accumulated phase differences during propagation through the facet 10 must be controlled to achieve high image quality. For example, for waveguide structures with 5 to 20 facets, the phase shift must be less than 50° to obtain an MTF value >0.3 per degree for 10 to 20 cycles. Methods for generating low phase shift optical coatings are described below.

[0045] Proper coating design can mitigate the phase shift effects between different optical paths caused by optical coatings. Specifically, the coating design should allow for the production of thin coatings with a minimum number of layers and should meet specific requirements for achromatic color, reflection, transmission, and phase shift as a function of angle. It has been found that using coating materials with a refractive index close to that of the surrounding immersion glass can be very beneficial in reducing the total number of layers and coating thickness. Since coating machines are typically limited to a few materials, it is necessary to use a mixture of at least two materials to create a new material with the desired refractive index. This can generally be described as selecting two or three visually transparent materials with certain inherent phase shift characteristics for reflection, transmission, and color requirements. These phase shift characteristics can be reduced if at least one of the materials used has a refractive index very close to that of the surrounding environment. If no visually transparent material with a refractive index very close to that of the ambient glass is available, a mixture of materials can be used to achieve the desired refractive index.

[0046] Using such manufactured materials, the phase shift caused by the coating can be mitigated or eliminated. One way to achieve this is to begin with a multilayer optical coating in an ambient material with a refractive index n1, where the optical coating adheres to all the requirements of a predefined coating specification, except that it causes a higher-than-expected phase shift. This phase shift can be mitigated or eliminated by adding another layer of material with a refractive index n2 and a thickness d, such that...

[0047]

[0048] in, The phase shift is caused by the first coating and needs to be mitigated (minimized) or eliminated. λ0 is the center wavelength or dominant wavelength in the relevant spectrum, θ1 is the incident angle of the central field when irradiating the facet, and θ2 = sin -1 [n2(λ0)sin(θ1) / n1(λ0)]. If the value of n2 is close to n1, the Fresnel reflection caused by this additional layer can be ignored, and thus the phase shift caused is mitigated, with only a slight effect on the coating's performance in other aspects (e.g., reflectivity and chromaticity).

[0049] The thickness d can be selected for the center wavelength or the dominant wavelength, or it can be calculated as the average or weighted average of the entire relevant optical spectrum, or as the average or weighted average of the entire relevant optical spectrum in which the weighting also takes into account the sensitivity of the human eye.

[0050] Furthermore, the thickness d can be chosen for the central field of view, or as a trade-off that minimizes phase shift across the entire field of view. For example, the tolerance of the thickness d can vary by ±40%, where such a range of variation does not preclude higher or lower values.

[0051] Figure 7A A four-layer coating structure of two materials with refractive indices n1 = 1.45 and n2 = 2.1 is shown, which is placed in an N-BK7 (n0 = 1.515) environmental material. Figure 7B The same structure is shown, but with an additional thick layer of n3 = 1.5, where the value of n3 is close to the refractive index of the surrounding material.

[0052] In the formula above, the thickness d is determined by taking into account the center wavelength λ0. Of course, other alternatives for determining the thickness d are possible. For example, the thickness can be chosen to provide optimal reduction across the entire relevant spectrum, or to reduce the green wavelength to which the human eye is most sensitive.

[0053] Figure 7C Comparison targeting Figure 7A (Solid line, shown as "A") and Figure 7B In the structure shown by the dashed line "B", for s-polarized light with wavelength λ = 530 nm, the phase difference between the light propagating through the coating and the light that will propagate through the environmental material without passing through the coating, varying with the incident angle. Clearly, Figure 7A The structure undergoes a large phase shift, and Figure 7B The structure exhibits very low phase shift up to an incident angle of ~60°. Figure 7D Comparison targeting Figure 7A (Solid line, shown as "A") and Figure 7B The structure shown in the dashed line (labeled "B") displays reflectance as a function of the incident angle. Clearly, despite the significant difference in phase shift, the reflectance distribution is almost identical in both cases.

[0054] More generally, the initial specification can be broken down into two separate coating designs, with one placed on top of the other. The first coating is the initial coating that meets all specification requirements (except those related to coating-induced phase shift); while the second coating is designed to mitigate the coating-induced phase shift of the first coating while maintaining high transmittance at all relevant angles, such as near 95% transparency. The second coating is expected to affect the coating-induced phase shift while maintaining very low reflectance. Therefore, the superimposed coating, consisting of both coating designs, is likely to meet all specification requirements.

[0055] Figures 8A to 8C The concept was demonstrated in the document. Figure 8A The refractive index n is shown in the environmental material with refractive index n0. 11 and refractive index n 12 An exemplary coating structure for two materials. This coating structure is designed for specific requirements that do not include low phase shift requirements. Figure 8B The refractive index n is shown in the environmental material with refractive index n0. 21 Refractive index n 22 and refractive index n 23 Exemplary coating structures for three materials. These coating structures are designed to have low reflectivity and induce a phase difference that is compensated for. Figure 8A The phase difference of the structure in the middle. Figure 8C The combined structure is shown, in which Figure 8B The coating structure is placed Figure 8A The top of the coating structure.

[0056] Alternatively, comprehensive optimization of all coating requirements can be performed for a single coating design. Here, a dedicated software program, including instructions stored on a non-transitory computer-readable medium, is used to numerically find a stable coating design that will satisfy all coating requirements. In principle, this can be achieved with standard materials; however, as explained above, it is often advantageous to add manufactured materials to increase the number of degrees of freedom in the design. Such a structure in Figure 9 Presented in the middle, where different refractive indices n 11 n 12 n 21 n 22 and n 23 The material is placed within an ambient material with a refractive index of n0. The structure is designed to comply with all specification requirements, including low phase shift.

[0057] Possible applications of alternatives

[0058] While this disclosure focuses on techniques for controlling coating-induced phase shift in the context of head-mounted displays, the described techniques can also be used in a wide range of beam expanders for various applications, such as generating broad, flat-top beams. Furthermore, the described techniques can also be applied to applications requiring coating-induced phase shift, such as generating controlled optical diffusers.

[0059] The above description typically refers to different phases of light originating from a projector. For example, a first ray of light or a portion of light from the projector that passes through a partially reflective surface may have a phase shift relative to a second ray of light from the projector that does not pass through the partially reflective surface (e.g., the second ray may bypass the surface) or a portion of light. Alternatively, a first ray of light or a portion of light from the projector illuminating a partially reflective surface at a first angle of incidence may have a phase shift relative to a second ray of light or a portion of light illuminating the partially reflective surface at a second angle of incidence.

[0060] In cases where the waveguide is configured to be semi-transparent and / or allows a viewer to see through a partially reflective surface (e.g., augmented reality), ambient light (e.g., light from the surroundings, environment, or world of the waveguide) can typically pass through the waveguide via the main surface. A first ray or portion of ambient light passing through the partially reflective surface may have a phase shift relative to a second ray or portion of ambient light that does not pass through the partially reflective surface.

[0061] Similar to light from a projector, the angle of incidence through a partially reflective surface can also cause a phase shift. For example, a first ray or a portion of ambient light passing through the partially reflective surface at a second angle may have a phase shift relative to a second ray or a portion of ambient light passing through the partially reflective surface at a first angle.

[0062] The coating structure used to mitigate such phase shift can be structurally similar to the structure described above. For example, the coating structure can have a first portion and a second portion, the first portion being configured to have various optical properties other than phase shift (e.g., related to images, enhancements, displays, etc., consumed by the user), and the second portion adjacent to the first portion being configured to mitigate phase shift. Alternatively, the coating structure can comprise a single structure of multiple staggered layers, configured to simultaneously create the desired optical properties and mitigate phase shift (e.g., related to...). Figure 9 (Similar). The phase shift to be mitigated can be between ambient light rays that pass through the coated structure and those that do not, and / or between ambient light rays that pass through the coated structure at different angles.

[0063] In some implementations, the coating structure can be configured to mitigate phase shifts between light rays from the projector and between light rays from the ambient light. In other words, the coating structure can be configured to reduce the phase shifts between projector light and ambient light that pass through the coating structure and projector light and ambient light that do not pass through the coating structure. In this way, the coating structure can mitigate phase shifts from multiple sources.

[0064] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” are also intended to include the plural forms. It will also be understood that, when used in this specification, the terms “comprising” and / or “including” specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0065] The corresponding structures, materials, actions, and equivalents of all means or steps plus functional elements (if any) in the appended claims are intended to include any structure, material, or action for performing a function in conjunction with other claimed elements of the specific claim. The disclosed embodiments of the invention have been presented for purposes of illustration and description, but are not intended to be exhaustive or limited to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. These embodiments were chosen and described to illustrate the principles and practical application of the invention and to enable others skilled in the art to understand the various embodiments of the invention with various modifications suitable for the particular purpose contemplated.

Claims

1. A waveguide, comprising: Environmental materials; as well as A plurality of partially reflective parallel surfaces, said plurality of partially reflective parallel surfaces being at least partially surrounded by said environmental material, each of said plurality of partially reflective parallel surfaces comprising: The first part includes one or more first layers, the one or more first layers being configured to exclude one or more optical properties with low phase shift, the one or more first layers being configured to cause a first portion of light from the periphery of the waveguide passing through the one or more first layers to have a phase shift relative to a second portion of light from the periphery of the waveguide that does not pass through the one or more first layers; as well as The second part includes one or more second layers configured to reduce the phase shift caused by the first part on light illuminating the one or more first layers from the surrounding area of ​​the waveguide.

2. The waveguide according to claim 1, wherein, The waveguide is configured to allow light from the surrounding area of ​​the waveguide to enter the waveguide through a first primary surface and exit the waveguide through a second primary surface.

3. The waveguide according to claim 2, wherein, The waveguide is configured such that: A first portion of the light from the periphery of the waveguide passes through the plurality of portions and is reflected parallel to the surface; and In this process, a second portion of the light from the surrounding area of ​​the waveguide does not pass through the partially reflective parallel surface.

4. The waveguide according to claim 1, wherein, The one or more second layers include a single second layer having a single refractive index.

5. The waveguide according to claim 4, wherein, The single second layer is in contact with the first portion and the environmental material.

6. The waveguide according to claim 4, wherein, The individual refractive index corresponds to the refractive index of the environmental material.

7. The waveguide according to claim 4, wherein, The thickness of the single second layer is greater than the thickness of any one of the one or more first layers.

8. The waveguide according to claim 4, wherein, The thickness of the individual second layer is based on the center wavelength or dominant wavelength to be propagated through the waveguide.

9. The waveguide according to claim 4, wherein, The thickness of a single second layer is based on the central field of view.

10. The waveguide according to claim 4, wherein, The thickness of the individual second layer is based on the phase shift, the center wavelength or dominant wavelength, the angle of incidence, the refractive index of the ambient material, and the refractive index of the individual second layer.

11. The waveguide according to claim 4, wherein, The thickness of a single second layer is based on a weighted average of the wavelengths to be propagated through the waveguide.

12. The waveguide according to claim 11, wherein, The weights of the weighted average are based on the sensitivity of the human eye.

13. The waveguide according to claim 1, wherein, The one or more second layers comprise a plurality of second layers having their own refractive indices.

14. The waveguide according to claim 13, wherein, The plurality of second layers are configured to have a transmittance of 95% or greater.

15. The waveguide according to claim 13, wherein, The plurality of second layers include at least three refractive indices.

16. The waveguide according to claim 13, wherein, The plurality of second layers includes an even number of layers.

17. The waveguide according to claim 1, wherein, The one or more optical properties include one or more of reflection, transmission, chromaticity, or polarization.

18. The waveguide according to claim 1, wherein, The one or more first layers are adjacent to the one or more second layers.

19. The waveguide according to claim 1, wherein, The one or more first layers are interleaved with the one or more second layers.

20. A waveguide, comprising: Environmental materials; as well as A plurality of partially reflective parallel surfaces, said plurality of partially reflective parallel surfaces being at least partially surrounded by said environmental material, each of said plurality of partially reflective parallel surfaces comprising: A multi-layer coating structure, the multi-layer coating structure comprising: One or more layers are configured to limit the total phase shift of light from the surrounding area of ​​the waveguide that passes through the multilayer coated structure relative to light from the surrounding area of ​​the waveguide that does not pass through the multilayer coated structure to below a predetermined threshold.

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