Anti-reflective coating on optical waveguide

Abstract

This disclosure relates to an anti-reflective coating on an optical waveguide. An anti-reflective waveguide assembly includes: a waveguide substrate having a first refractive index, a plurality of diffractive optical elements disposed on a first surface of the waveguide, and an anti-reflective coating disposed on a second surface of the waveguide. The anti-reflective coating preferably increases the absorption of light entering the waveguide through the surface on which the anti-reflective coating is applied, such that at least 97% of the light is transmitted. The anti-reflective coating consists of four material layers having different refractive indices, wherein the first refractive index and the virtual refractive index are less than 1 × 10⁻⁶. ‑3 However, it is preferably less than 5×10 ‑4 .

Description

[0001] This application is a divisional application of the application filed on December 10, 2018, with PCT international application number PCT / US2018 / 064686, Chinese national phase application number 201880079474.6, and entitled "Anti-reflective coating on optical waveguide".

[0002] Cross-references to related applications

[0003] This application claims priority to U.S. Provisional Patent Application No. 62 / 596,904, filed December 10, 2017, and U.S. Provisional Patent Application No. 62 / 751,240, filed October 26, 2018, the entire contents of each of which are incorporated herein by reference. Background Technology

[0004] Surface treatments for substrates such as windows or photovoltaic devices (e.g., solar panels) benefit from layered antireflective coatings. Reducing glare from light impacting glass, improving the retention of natural light to lower energy costs, or increasing the absorption of light impacting photovoltaic cells are some applications of antireflective coatings. Traditional antireflective coatings offer benefits for light paths that are substantially perpendicular to the substrate surface normal, but are generally designed to maximize antireflectivity for free-space light, which is expected to originate entirely outside the substrate. Traditional coatings also seek to improve transmittance. In addition to free-space origins, certain optical media manipulate light paths, thus requiring antireflective coatings to optimize the performance of such media. Summary of the Invention

[0005] Embodiments of the present invention generally relate to specific materials and layer thicknesses for antireflective coatings used in optical waveguides. More specifically, the embodiments and techniques described herein relate to antireflective coatings that must facilitate light propagation to achieve total internal reflection (TIR) ​​while minimizing reflections of light at orthogonal angles or other free-space light. The embodiments described herein do not involve seeking complete light transmission.

[0006] Some embodiments involve a waveguide substrate having a first refractive index, such as glass. The substrate can be planar or cylindrical (e.g., optical fiber). For a planar substrate, a plurality of diffractive optical elements (e.g., gratings) are disposed on a first surface, and an anti-reflective coating is disposed on the opposite surface. For a cylindrical waveguide, an anti-reflective coating is applied to the outer surface.

[0007] In some embodiments, the waveguide is configured to receive light and propagate it along an axis by total internal reflection. In a planar waveguide, light travels along an axis in a first direction, and is outcoupled in a substantially orthogonal direction when reflected from diffractive optical elements on the corresponding surface. In a cylindrical waveguide, light is reflected along an axis substantially parallel to the waveguide length and then outcoupled at the distal end.

[0008] The antireflective coating on such embodiments is configured to minimize the phase delay between the s and p polarization states of the received light, such that the bounce angles of each polarization component of the light through the TIR are substantially similar.

[0009] In some embodiments, the antireflective coating is a single magnesium fluoride (MgF2) layer with a thickness between 75 nanometers (nm) and 125 nanometers. In some embodiments, a silicon dioxide (SiO2) layer is applied as an outer layer to the coating.

[0010] In some embodiments, the antireflective coating has a density of less than 5 × 10⁻⁶. -4 The virtual refractive index value (which may be referred to herein as the absorption coefficient) k. In some embodiments, regardless of the number of coating layers, the k value of the complete coating is 5 × 10⁻⁶. -4 Up to 1×10 -3 In some embodiments, the coating is a single-layer material. In some embodiments, the coating alternates between two materials, one of which has a higher refractive index compared to the second material. In some embodiments, fewer than eight layers are used in total.

[0011] In some embodiments, titanium dioxide (TiO2) with a refractive index greater than 2 is used as the coating material; in some embodiments, SiO2 with a refractive index between 1.45 and 1.58 is alternated with layers having titanium dioxide.

[0012] These material and layer choices optimize the efficiency of light output from the optical waveguide, minimize phase delay to reduce optical defects such as streaks in images output from such waveguides, and minimize the labor and material costs of conventional layers. Attached Figure Description

[0013] Figure 1 The image shows a top view of an anti-reflective coating, which is understood in terms of its function of minimizing reflected light and maximizing light absorption in the waveguide.

[0014] Figure 2 This is a top view illustrating a planar waveguide according to some embodiments, which couples out multiple light beams propagating through the waveguide via total internal reflection.

[0015] Figure 3This is a top view showing a multi-waveguide stack according to some embodiments, which couples out multiple beams as optical bundles.

[0016] Figure 4 This is a front view of a planar waveguide having three diffractive optical element regions according to some embodiments.

[0017] Figure 5 This is a front view showing an orthogonal pupil expander that diffracts light across its span according to some embodiments.

[0018] Figure 6A This is a top view showing multiple light bounces through a waveguide according to some embodiments.

[0019] Figure 6B This is a front view of an interferometer network that transmits energy through waveguides configured to support total internal reflection, according to some embodiments.

[0020] Figure 7 It is a graph showing the phase delay relationship as a function of layers in the antireflective coating, according to some embodiments.

[0021] Figure 8A The image shows a captured image of an eyepiece design for blue light (455 nm) on a substrate where the anti-reflective coating has layers with different n values.

[0022] Figure 8B A simulated image of an eyepiece design for blue light (455 nm) is shown on a substrate in which the anti-reflective coating has layers with different n values.

[0023] Figure 8C The image shows a captured image of an eyepiece design for red light (625 nm) on a substrate in which the anti-reflective coating has layers with different n values.

[0024] Figure 8D A simulated image of an eyepiece design for red light (625 nm) is shown on a substrate in which the anti-reflective coating has layers with different n values.

[0025] Figures 9A to 9D This is a graph showing the efficiency attenuation of light energy output from the waveguide as the number of anti-reflective coating layers and the value of k vary according to some embodiments. Detailed Implementation

[0026] Antireflective coatings are typically configured to produce out-of-phase reflections on layers of materials with different refractive indices. Typically, a single-layer antireflective coating seeks a refractive index n equal to the square root of the refractive index of the substrate being coated, and a thickness t equal to one-quarter of the wavelength λ of the light targeted by the antireflective coating.

[0027] Equation 1 ncoating = √(n substrate )

[0028] Equation 2 t = λ target light / (4·n coating )

[0029] Figure 1 An antireflection diagram is shown, in which light L 100 strikes medium 110 and reflects light R 101, while simultaneously transmitting to medium 120 and reflecting light R 103, thereby producing constructive interference with light R 101; the remaining light L 105 is transmitted into medium 103. Many variations are known to increase the total amount of transmitted light L 105. For example, broadband antireflection with increased transmission of multiple wavelengths using a single coating is achieved by utilizing additional and / or varying thickness layers.

[0030] although Figure 1 The coating arrangement shown can function as intended for free-space light, but some optical systems employ waveguide technology; augmented or mixed reality systems, in particular, maximize this technology in the outgoing pupil expander system to deliver light from the light source, which is then propagated through the waveguide via TIR and coupled out to the user's eye.

[0031] Figure 2 A simplified form of this system is shown. One waveguide is shown, but it should be understood that other waveguides are stacked together (see reference below). Figure 3 (Furthermore,) it can function similarly. Light 400 is injected into waveguide 1182 at input surface 1382 and propagates within waveguide 1182 via TIR. Input surface 1382 can be an incoupling grating formed by diffractive optical elements, thereby diffracting light 400 into waveguide 1382 at an angle supporting TIR. At the point where light 400 strikes outcoupling diffractive optical element 1282, a sampled portion is emitted from the waveguide as multiple outgoing beams 402.

[0032] Each outgoing beam is a sampled sub-beam of light 400, increasing the likelihood that any sampled sub-beam will be seen by the viewer's eye 4. Therefore, it is important that waveguide 1182 maintains TIR to generate multiple outgoing beams across its span; otherwise, the outgoing beams 402 would not be dispersed, and the resulting outgoing pupils would only be visible at certain locations on the eye 4, limiting the applicability and flexibility of the system.

[0033] Figure 2A single waveguide system is shown, but those skilled in the art will understand that if a single waveguide 1182 provides a sampling portion of the light 400, other waveguides performing similar functions can provide other sampling portions to produce rich light effects, such as multicolor component images or depth sensing. Figure 3 A multilayer system is illustrated having three waveguides 1210, 1220, and 1230 for propagating light via TIR. When each optical path 1240, 1242, and 1244 is coupled at positions 1212, 1222, and 1232, respectively, it strikes a corresponding coupled-out diffracting optical element 1214, 1224, or 1234 (coupled light from paths 1222 and 1232 is not shown) arranged on waveguides 1210, 1220, and 1230, which diffracts multiple sub-beams in two directions: one direction toward the viewer (e.g., ...). Figure 2 The eye 4 in the image is represented by beam 3010; the other direction, away from the viewer, is represented by beam 3020.

[0034] If beam 3020 is reflected from the subsequent waveguide 1220, it may cause undesirable effects, such as interference with beam 3010, increased ambiguity due to any angular changes that may be caused by reflection, etc. Here, applying an anti-reflective coating to the surface of the waveguide opposite its coupled diffractive optical element would help reduce these effects. However, conventional coatings intended to increase transmission will degrade the optical paths 1240, 1242, and 1244 as they propagate through TIR across waveguides 1210, 1220, and 1230. This degradation introduces uniformity disturbances at coupling and results in poor image quality.

[0035] Waveguide optics systems employing pupil expander technology exacerbate this problem. In systems such as... Figure 2 In the pupil expander system shown, the light is distributed not only in a substantially perpendicular direction, but also in a direction orthogonal to the path of the outgoing beam. Figure 4 An orthogonal pupil expander (OPE) 3706 is shown mounted on waveguide 3704. Figure 4 Also shown is an exit pupil expander (EPE) 3708 for coupling out a progressively exiting beam of TIR light, which is similar to Figure 2 The coupled-out diffraction optical element 1282 shown also shows a similar Figure 2 The input surface 1382 has a coupling grating (ICG) 3702. Figure 4 In the waveguide system, light is coupled into the waveguide through a coupling grating and diffracted toward the orthogonal pupil expander.

[0036] Figure 5 The image shows light sampling across the orthogonal pupil expander. (Source: [Original Source Name]) Figure 4The light 4410B coupled into the grating encounters the grating 4420B (e.g., a series of diffractive optical elements), which diffracts a sample of light in a first direction and a sample of the same light 4430B in a second direction; the specific direction of diffraction varies with the specific geometry of the diffractive optical elements.

[0037] Figure 6A A cross-sectional view of the optical path is shown, where a waveguide includes a grating 662 on one surface and an anti-reflective coating 664 on the opposite surface. As light propagates through the waveguide via TIR, it is alternately reflected from an orthogonal pupil expander and from the surface opposite the orthogonal pupil expander. Those skilled in the art will understand that a similar function also occurs in the exit pupil expander region of the waveguide. To reduce reference... Figure 3 The reflection described by beam 3020 is achieved by applying an anti-reflective coating to the opposing surface. Accumulated light interferometers can be derived from this interaction, for example... Figure 6B The unit cell inferometer shown is... Figure 6B In this process, each interaction with the orthogonal pupil expander samples the light into two paths, with a reflection occurring between each successive reflection from the orthogonal pupil expander and the anti-reflection coating side. Each reflection from either the orthogonal pupil expander side or the anti-reflection side can further cause a change in the polarization of the light, causing each successive bounce to perturb the polarization state and alter the energy at each output node.

[0038] By decomposing polarization into s-state and p-state components, the resulting electric field E is a function of the light amplitude A and phase φ, and is shown for each s- and p-path as follows:

[0039] Equation 3

[0040] Equation 4

[0041] Where i indicates the value of the variable at the input.

[0042] Each interaction (indicated by the directional arrows below, with...) Figure 6B The optical path correlation at the output node can be described as a 2×2 matrix multiplied by the energies of the s and p elements in equations 3 and 4, making...

[0043] Equation 5

[0044] The left and down directions indicate light diffracted to the left and down, respectively. Figure 6B The output node is shown at 662, where η is the diffraction efficiency of the conversion and φ is the phase shift of the conversion.

[0045] Furthermore, each bounce from the AR coating can be described by a 2×2 matrix. In a planar coating, the off-diagonal elements of this matrix are 0, and since the layers are parallel in a planar coating, the diagonal elements must be 1. Since there is no diffraction from the AR coating, there are only the following two matrices: AR ↓↓ and AR ←← .

[0046] Equation 6

[0047] Equation 7

[0048] Now, the electric field state that causes the output node to propagate downwards (towards the exit pupil expander) can be related to the electric field input state.

[0049] Equation 8

[0050] However, if the phase delay (the difference in phase shift between the s-path and the p-path at each bounce) is 0, then (θ) s =θ p If we consider the following equation, then this equation can be simplified. In this case, the anti-reflective coating no longer affects the energy output. In other words, equations 6 and 7 can be replaced with:

[0051] Equation 9

[0052] Equation 10

[0053] And the output is simplified to:

[0054] Equation 11

[0055] Therefore, if the AR coating has no phase delay, it only imparts a phase shift to the output without changing the polarization state or magnitude. If the AR coating does have a phase delay, it alters the output polarization state and magnitude, introducing negative optical effects. This is crucial when determining the number of antireflective coating layers on a TIR waveguide display device. Figure 7 The phase delay of TIR light at various incident angles is shown. Figure 8A The image shows a captured image of an eyepiece design for blue light (455 nm) on a substrate where the anti-reflective coating has layers with different n values. Figure 8B A simulated image of an eyepiece design for blue light (455 nm) is shown on a substrate in which the anti-reflective coating has layers with different n values. Figure 8C The image shows a captured image of an eyepiece design for red light (625 nm) on a substrate in which the anti-reflective coating has layers with different n values. Figure 8DA simulated image of an eyepiece design for red light (625 nm) is shown on a substrate where the anti-reflective coating layer has different n values. Significant variations in phase difference affect the emitted beam and can be used as... Figures 8A to 8D The "stripes" or uniformity disturbances shown were observed. The four-layer antireflective coating was found to have the best uniformity, thus outperforming [the previous method]. Figure 7 and 8A Other coatings shown in 8D. It should be understood that the effect of adjusting the number of antireflective layers is consistent across all wavelengths; that is, although... Figures 8A to 8D An eyepiece for a specific wavelength of light is shown, but the effect is similar for other wavelengths not shown (e.g., green).

[0056] To minimize this degradation and reduce inter-waveguide reflections while maintaining intra-waveguide reflections, embodiments of the present invention relate to an optimized anti-reflective coating. This optimization balances the refractive index of the anti-reflective material with the number and thickness of layers applied in the coating. This will be achieved by making θ s Basically equal to θ p This is to minimize the phase delay effect.

[0057] In some embodiments, an anti-reflective coating is applied to one side of a waveguide substrate within a waveguide stack constituting an eyepiece of an enhanced, hybrid, or virtual reality device. Preferably, the coated side is opposite to the side where the viewer's eye is intended to be placed, but the coated side being on the same side as the viewer's eye can serve a similar purpose. In some embodiments, a grating is applied to a surface on the waveguide opposite to the coated side. The anti-reflective coating preferably reduces reflections from the surface to which it is applied and increases transmission through that surface. The anti-reflective coating preferably increases light transmission to at least 97%.

[0058] The antireflective coating comprises at least one layer, but in a preferred embodiment, fewer than eight layers, and alternates between layers of two constituent materials having relatively high and relatively low refractive indices. In some embodiments, one of the constituent layers is titanium dioxide (TiO2). In some embodiments, one of the constituent layers is silicon dioxide (SiO2).

[0059] Those skilled in the art will understand that other candidate materials, such as SiN, ZrO2, ZnO2, Ta2O5, or NB2O5, or other metal oxides with low absorption rates in the visible wavelength range, are also available. Materials such as TiO2 and SiO2 are well known in the art for their use in achieving anti-reflective photovoltaic or glass processing.

[0060] In some embodiments, SiO2 is the final layer (i.e. the top layer) of the multilayer coating, serving as a protective layer against any wet chemicals (sulfuric acid, hydrogen peroxide, etc.) that accompany waveguide cleaning, treatment, or patterning.

[0061] The refractive index *n* of a material is composed of two elements: the known refractive index and the absorption coefficient *k* (or the virtual refractive index related to the attenuation of light passing through the material), such that *n* = *n* + *ik*. Different materials have different absorption coefficients, which can produce a wide variety of results, especially when multiple materials are layered together to produce a net *k* value for the coating. For example, titanium dioxide (a well-known antireflective material) and silicon nitride (SiN) have similar reflection spectra for normal incidence, but their *k* values ​​differ slightly. Although these differences are negligible in the normal / orthogonal light directions, when comparing the two materials, each light bounce at the surface at the TIR-supporting angle is attenuated with slightly different absorption. The cumulative effect of this slight difference in absorption coefficient in the coating, which manipulates light through multiple bounces across a TIR system, can severely impact overall image quality, especially uniformity and efficiency.

[0062] Figures 9A to 9D The light loss is shown as a percentage of output when using the energy output from a material with varying absorption coefficients k for various materials. Figure 9A The diagram illustrates how the loss of light energy output from the EPE varies with increasing layer number and k-value. As shown, in the case of an exemplary EPE efficiency of 5%, when the net k-value is less than approximately 5 × 10⁻⁶, the loss of light energy is significantly reduced. -4 At this point, most single-layer antireflective coatings maintain this efficiency in TIR systems (e.g., optical waveguides). However, the energy output efficiency at the EPE decreases exponentially with each increase in the number of layers or the net k-value. This is true regardless of the layer material or the number of layers, but the degree of attenuation varies, such as... Figure 9B and 9C As shown.

[0063] Figure 9D An EPE efficiency plot is shown, which demonstrates that although the increased number of layers has some benefits for antireflection known in the art, it also has an adverse effect on system performance due to increased losses.

[0064] In some embodiments, an antireflective coating with fewer than eight layers is used. In some embodiments, such as a MgF2 coating, only a single layer is used.

[0065] According to Equation 1, the target refractive index can be solved mathematically; however, the cumulative effect of a specific k value is not easily derived, and the cumulative target n is not easily obtained directly in alternating layer coatings. For example, if a conventional antireflective coating material such as titanium dioxide is applied to a glass substrate, Equation 1 is not satisfied. The refractive index of glass is typically between 1.5 and 1.6, therefore the refractive index of the antireflective coating on the glass should be between 1.22 and 1.27. In some embodiments of the present invention, a MgF2 antireflective coating is applied to the glass substrate (MgF2 has a refractive index of 1.38).

[0066] refer to Figure 3 Multiple waveguides can be used, each configured to propagate light of a specific wavelength. Different antireflective coating thicknesses can be produced for each waveguide based on its configured wavelength. For example, a MgF2 coating on glass configured to propagate green light (approximately 520 nm) requires a thickness of 94 nm. Alternatively, for a single-layer coating, a general thickness between 75 nm and 125 nm can be applied to any waveguide (to reduce the complexity of manufacturing applications) to universally reflect the visible spectrum, where it should be understood that the exact thickness selected is more advantageous for the specific wavelength of light determined by Equation 2.

[0067] Throughout this document, the terms "one embodiment," "some embodiments," "embodiment," or similar terms mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of these phrases in various places throughout this specification does not necessarily indicate the same embodiment. Furthermore, there is no limitation on how particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0068] The details shown herein are merely illustrative and are intended only to discuss preferred embodiments of the invention. These details are presented to provide the most useful and readily understood description of the principles and concepts believed to be present in various embodiments of the invention. In this regard, no structural details beyond those necessary for a basic understanding of the invention are attempted; the description, taken in conjunction with the accompanying drawings and / or examples, enables those skilled in the art to readily understand how to implement various forms of the invention in practice.

[0069] As used herein, unless otherwise specified, the terms “a” and “an” are understood to mean “one,” “at least one,” or “one or more.” Unless the context otherwise requires, the singular form used herein shall include the plural form, and the plural form shall include the singular form.

[0070] Unless the context clearly requires otherwise, throughout the specification and claims, the words “comprising,” “including,” etc., shall be understood to mean inclusive, not exclusive or exhaustive; that is, they shall be understood to mean “including but not limited to.” The term “or” as used herein shall be interpreted as inclusive or meaning any one or any combination thereof. Therefore, “A, B, or C” means any of the following: A; B; C; A and B; A and C; B and C; A, B, and C. Exceptions to this definition will only occur if the combination of elements, functions, steps, or actions is inherently mutually exclusive in some way.

[0071] Words used in singular or plural forms also include both singular and plural forms, respectively. Furthermore, when used in this disclosure, the words “this text,” “the preceding text,” and “the following text,” as well as words with similar meanings, should refer to this disclosure as a whole, and not to any particular part of this disclosure.

[0072] The description of embodiments in this disclosure is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. While specific embodiments and examples of this disclosure have been described herein for illustrative purposes, various equivalent modifications can be made within the scope of this disclosure, as will be appreciated by those skilled in the art. Such modifications may include, but are not limited to, changes in dimensions and / or materials shown in the disclosed embodiments.

[0073] All references cited herein are incorporated herein by reference. If necessary, aspects of this disclosure may be modified to provide further embodiments of this disclosure by incorporating the systems, functions, and concepts of the foregoing references. These and other changes may be made to this disclosure in accordance with the detailed description.

[0074] Any particular element of the foregoing embodiments may be combined or replaced with elements from other embodiments. Furthermore, although advantages associated with certain embodiments of this disclosure have been described in the context of these embodiments, other embodiments may also present these advantages, and not all embodiments need to present the advantages that fall within the scope of this disclosure.

[0075] Therefore, it should be understood that the invention can be practiced with modifications and variations within the spirit and scope of the appended claims. The description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. It should be understood that the invention can be practiced with modifications and variations, and that the invention is limited only by the claims and their equivalents.

Claims

1. An anti-reflection waveguide, comprising: A planar waveguide substrate with a first refractive index; Multiple diffractive optical elements are disposed on the first surface of the waveguide; as well as An anti-reflective coating is disposed on the second surface of the waveguide, wherein the waveguide is planar and configured to propagate light by total internal reflection between the plurality of diffractive optical elements and the anti-reflective coating in a substantially first direction, and to couple light out in a substantially orthogonal second direction to the first direction. The light propagating via total internal reflection includes an s-polarization component and a p-polarization component. The anti-reflection coating is configured to reduce the phase delay between the s-polarization component and the p-polarization component, such that, for a selected color of light, the incident angle of the s-polarization component through the waveguide is substantially similar to that of the p-polarization component.

2. The anti-reflection waveguide according to claim 1, wherein, The anti-reflective coating has no phase delay; it only imparts a phase shift to the output without changing the polarization state or magnitude.

3. The anti-reflection waveguide according to claim 2, wherein, Choosing a color with a first wavelength results in a similar reduction in phase delay for both the first wavelength and a second wavelength different from the first wavelength.

4. The anti-reflection waveguide according to claim 1, wherein, The anti-reflective coating reduces reflections from the second surface and increases the transmission of light entering the waveguide through the second surface.

5. The anti-reflection waveguide according to claim 4, wherein, At least 97% of the light is transmitted through the second surface.

6. The anti-reflection waveguide according to claim 1, wherein, The waveguide substrate is glass, and the anti-reflective coating includes a MgF2 layer.

7. The anti-reflection waveguide according to claim 6, wherein, The MgF2 layer has a thickness between 75 nm and 125 nm.

8. The anti-reflection waveguide according to claim 6, wherein, The anti-reflective coating includes a SiO2 layer.

9. The anti-reflection waveguide according to claim 7, wherein, The MgF2 layer is disposed adjacent to the second surface.

10. The anti-reflection waveguide according to claim 9, wherein, A SiO2 layer is disposed on the MgF2 layer.

11. The anti-reflection waveguide according to claim 10, wherein, The total refractive index of the antireflective coating is less than 5 × 10⁻⁶. -4 The virtual refractive index component value.

12. The anti-reflection waveguide according to claim 10, wherein, The total refractive index of the antireflective coating is 5 × 10⁻⁶. -4 Up to 1×10 -3 The virtual refractive index components between.

13. The anti-reflection waveguide according to claim 1, wherein, The anti-reflective coating comprises fewer than eight layers alternating between a first material and a second material.

14. The anti-reflection waveguide according to claim 13, wherein, The anti-reflective coating consists of four layers.

15. The anti-reflection waveguide according to claim 13, wherein, The first material has a higher refractive index compared to the second material.

16. The anti-reflection waveguide according to claim 13, wherein, The first material is TiO2.

17. The anti-reflection waveguide according to claim 13, wherein, Each TiO2 layer has a refractive index greater than 2.

18. The anti-reflection waveguide according to claim 13, wherein, The second material is SiO2.

19. The anti-reflection waveguide according to claim 18, wherein, Each SiO2 layer has a refractive index between 1.45 and 1.

58.

20. The anti-reflection waveguide according to claim 19, wherein, The total refractive index of the antireflective coating is less than 5 × 10⁻⁶. -4 The virtual refractive index component value.

21. The anti-reflection waveguide according to claim 19, wherein, The total refractive index of the antireflective coating is 5 × 10⁻⁶. -4 Up to 1×10 -3 The virtual refractive index components between.

22. The anti-reflection waveguide according to claim 1, wherein, The total refractive index of the antireflective coating is less than 5 × 10⁻⁶. -4 The virtual refractive index component value.

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