Direct coupling stacking for improved image quality in optical devices

Abstract

This invention provides a directly coupled stacked structure for improved image quality in optical devices. [Solution] Optical surfaces are planarized and plasma activated to laminate them together, and then a direct bond is formed between the two surfaces without adhesive or an adhesive layer. This process provides an improved optical element with higher image brightness, lower light scattering, better resolution, and higher image fidelity. Direct bonding also provides a heat-resistant interface that can withstand much higher temperatures than conventional optical adhesives. Exemplary processes can be used to manufacture many types of improved optical components such as improved laminated lenses, mirrors, beam splitters, collimators, prism systems, optical conduits, and specular waveguides for smart glasses and head-up displays (HUDs), which provide better image quality and elimination of dark lines of sight that are apparent to the human observer when conventional adhesives are used in conventional lamination.

Description

Technical Field

[0001] The present invention relates to direct-bonded laminates in optical devices. (Cross-reference to related applications) This application claims the benefit of U.S. Provisional Application No. 62 / 645,633, filed Mar. 20, 2018, and U.S. Non-Provisional Application No. 16 / 176,191, filed Oct. 31, 2018, under 35 U.S.C. § 119(e)(1), the entire contents of which are incorporated herein by reference.

Background Art

[0002] Optical components often include various laminated combinations of optical layers of glass, reflective metals, transparent polymers, dielectrics, and adhesives. The adhesives between the bonding layers or laminate layers do not themselves serve an optical purpose, but their presence is taken for granted even though they detrimentally introduce additional material into the optical path. Each additional change in the material within the optical path results in some kind of image loss, such as loss of brightness or loss of resolution. This loss of image quality can be due to simple scattering of light at each new interface, or due to partial absorption of light by the adhesive material, or due to a change in the refractive angle between materials, or both.

[0003] The amount by which light slows down in a given material is explained by its refractive index. The refractive index of a material is defined by dividing the speed of light c in a vacuum by the speed of light through the material. Optically dense media have a large refractive index. In optical devices, different types of glass, polymers, ceramics such as transparent spinels, and optical adhesives can have slightly different refractive indices. Thus, when light accelerates as it passes from one material to another, or conversely when light slows down between materials, the refractive angle is larger (or smaller) than the angle of incidence, causing some image loss or distortion along the optical path. The adhesive layer between transparent materials within an optical device is thin, but it robs the image of some of the integrity it might have had for a human observer.

[0004] Smart glasses and head-up displays (HUDs) for augmented reality (AR) and virtual reality (VR) devices rely on numerous optical components such as waveguides, prisms, collimators, convex lenses, reflectors, concave mirrors, combiners, and beam splitters to achieve near-eye optics in smart glasses and visual fusion in head-up displays. Because the optical path passes through many layered optical components, the detrimental effects of conventional adhesive layers are combined. [Overview of the project]

[0005] Direct bonding lamination is provided for improved image quality in smart glasses and other optical devices. An exemplary process involves planarizing and plasma-activating optical surfaces to laminate them together, then forming a direct bond between the two surfaces without adhesive or a bonding layer. This process provides improved optical elements with higher image brightness, lower light scattering, better resolution, and higher image fidelity. Direct bonding also provides a heat-resistant interface that can withstand much higher temperatures than conventional optical adhesives. The exemplary process can be used to manufacture many types of improved optical components for smart glasses and head-up displays (HUDs), such as improved laminated lenses, mirrors, beam splitters, collimators, prism systems, optical tubes, and specular waveguides, which provide better image quality and elimination of the dark line of sight that is apparent to the human observer when conventional adhesives are used in conventional lamination.

[0006] This summary is not intended to identify any important or essential features of the claimed subject matter, nor is it intended to be used to help limit the scope of the claimed subject matter. Hereinafter, specific embodiments of this disclosure will be described with reference to the accompanying drawings, where similar reference numerals indicate similar elements. However, it should be understood that the accompanying drawings illustrate various implementations described herein and are not intended to limit the scope of the various technologies described herein. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows a bonded optical component, illustrating an exemplary component having a directly bonded optical layer for optical clarity, compared to conventional components bonded by an adhesive layer. [Figure 2] This is a diagram of an exemplary specular optical waveguide that may be improved, having directly bonded surfaces between optical layers instead of surfaces bonded with conventional adhesives. [Figure 3] This is an exemplary method for fabricating a specular optical waveguide using optical components that have surfaces directly bonded together instead of being bonded together with an adhesive material. [Figure 4] This is an exemplary method for joining or laminating optical layers having directly bonded surfaces instead of conventional optically high-density adhesives. [Modes for carrying out the invention]

[0008] This disclosure describes direct-bonded stacking for improved clarity in optical devices. In one implementation, the exemplary direct-bonding technique aims to minimize or eliminate optical adhesives and glues between optical layers that could cause loss of image quality in the optical device. In one implementation, direct oxide bonding between surfaces, such as silicon dioxide-silicon dioxide bonding, or direct bonding between surfaces using other semiconductor-nonmetallic combinations, is used to bond or laminate optical layers made of glass or other materials for optical precision. Besides silicon dioxide, other materials such as silicon nitride (ShN4), silicon oxynitride (SiON), silicon carbonitride (SiCN), and other compounds may be used for direct bonding. Eliminating separate adhesives or bonding layers between the surfaces of the optical layers improves optical performance, such as higher fidelity of light transmission. Direct bonding between optical surfaces also provides a heat-resistant interface between the first and second optical surfaces, improving the thermal budget of the entire optical component. Conventional glues and adhesives used to join two glass pieces together degrade, for example, at higher temperatures, or for specific light wavelengths, specific light intensities, and when used with high-power lasers; therefore, these conventional optical components, including conventional adhesives, are limited to lower operating temperatures and lower-power lasers. Direct bonding processes described herein, such as the ZiBond® brand direct bonding, eliminate this conventional limitation. Direct bonding, which incidentally provides a heat-resistant interface, has the same coefficient of thermal expansion as when one or both flat optical surfaces are joined together, and direct bonding, which provides a heat-resistant interface, also has much higher heat resistance and higher temperature resistance than conventional optical glues and adhesives.

[0009] The exemplary bonding technique allows for minimal or no interface between optical layers when molecules between two opposing surfaces made of the same material are directly bonded to each other. Eliminating adhesives, even to a thickness of just a few microns, can reduce some visual artifacts during device use, such as vertical line bulges visible to users of conventional near-eye optics. For example, the exemplary method applies direct bonding to improve various basic waveguides used in near-eye optics in smart glasses and HUDs, which have spaced reflective surfaces within the waveguide.

[0010] Figure 1 shows an exemplary optical component having surfaces that are directly bonded together instead of cemented together. Two optical blanks 50 and 52 are conventionally bonded together with an adhesive or intervening adhesive layer 54. The direct bonding interface 100 can bond equivalent optical blanks 102 and 104, which offer improved optical properties because there is no interfering and optically detrimental adhesive layer 54 as seen in conventionally bonded blanks 50 and 52.

[0011] Achromatic lenses, such as achromatic doublets 56 consisting of a convex element 58 and a concave element 60, are conventionally bonded together with cement 62. Achromatic lenses are corrected to focus two wavelengths, such as blue and red, on the same plane. The convex element 58 and concave element 60 in an achromatic doublet are typically made from different glasses having different dispersions, such as crown glass and flint glass. The chromatic aberration of one lens 58 is offset by the chromatic aberration of the other lens 60. Conventional designs attempt to minimize the impact of the presence of conventional cement 62 on calculations for chromatic and spherical aberration correction by keeping the cement layer as thin as possible and maintaining refractive properties that match those of crown glass and flint glass.

[0012] Despite the glass materials of the bonded optical elements being made from molecularly different materials (crown glass and fling glass), the direct bonding interface 100 can bond equivalent achromatic lens elements 106 and 108 without the intervening conventional cement 62. The direct bonding interface 100 provides a better achromatic doublet than those made using conventional cement 62.

[0013] Similarly, partially specular partially reflective surfaces 64 that also partially transmit incident light are used in many other devices such as beam splitters, near-eye optics, and interferometers. A beam splitter may be two triangular glass prisms bonded together with an epoxy, polyester, or urethane adhesive. The thickness of the adhesive layer 66 may be calculated to reflect half of the incident light and transmit the other half in different directions. Some beam splitters may use glass or plastic with aluminum or silver sputtered from vapor as a semi-transparent coating. Dichroic optical coatings may also be used in beam splitters for laser power or to separate certain wavelengths. The reflectance-to-transmittance ratio of light depends on the wavelength of the incident light. Conventional designs may attempt to incorporate the properties of the adhesive layer 66 into the partially reflective surface 64. An exemplary direct bonding interface 100 can eliminate the obstruction posed by the adhesive layer 66 in some situations. The exemplary direct bonding interface 100 can provide a simpler and more accurate partial reflective surface 110 for beam splitters and other optical devices, which simplifies manufacturing and eliminates unwanted light absorption by the conventional adhesive layer 66. By including the direct bonding interface 100 together with the partial reflective surface 110 having an optically pure interface, the perception of bands or dark lines in optical devices using laminated mirrors can be eliminated.

[0014] Prismatic systems in binoculars, such as paired Porro prisms or roof prisms like the Schmidt-Péchanm prism 68, may conventionally use an adhesive interface 70, or they may use an air interface to avoid the use of the conventional adhesive interface 70. The exemplary direct bonding interface 100 can provide a better combination of prisms 12, in comparison, having a truly transparent interface between the directly bonded surfaces of the same glass material, or having no interface at all.

[0015] The direct coupling interface 100 may also be used to mount other types of layers and coatings within a layered optical component. Often, the light-receiving and light-emitting surfaces are optically coated to minimize light loss, and a given coating may have good anti-reflective or good reflective properties. An exemplary direct coupling interface 100 is particularly useful for internal reflective (specular) coatings and anti-reflective coatings mounted between the glass layer of a coated element and the laminate stack.

[0016] The exemplary direct bonding interface 100 also provides a superior optical element when a dielectric coating is used instead of a metallic mirror coating. The exemplary direct bonding interface 100 provides a stack of multiple dielectric mirrors, which can provide a much better visible light reflectivity than either an aluminum or silver metallic coating.

[0017] The exemplary direct bonding and lamination methods can be applied to many common and specialized optical elements and devices and can replace and replace conventional techniques and conventional materials for bonding optical elements together, such as polyester, epoxy, urethane, resin adhesives, Canada balsam, and other one and two component adhesives 54, 62, 66, and 70 for bonding optical elements.

[0018] Figure 2 shows wearable computer glasses 200 that add information alongside, or in addition to, what the user observes through the lenses. Such smart glasses 200 can benefit from optical elements incorporating the exemplary direct coupling interface 100 described herein. Exemplary conventional smart glasses or their conventional specular waveguides are manufactured by companies such as Lumus (Rechovot, Israel), Optinvent (Rennes, France), and Journey Technologies (Beijing, China). The exemplary waveguide assembly 202 may use a series of partially reflective surfaces 204 to reflect the projected image, as described in U.S. Patents 6,829,095 and 8,432,614 (both incorporated herein). The partially reflective surfaces 204 allow an external real-time image 206 to pass through the lenses of the smart glasses 200 while simultaneously reflecting the projected image 208 to a human observer. Due to the relatively small dimensions of the optical components, conventional optical adhesives used to laminate lenses and multiple glass layers together introduce extra material layers in the optical path, reducing image quality. This lamination using conventional adhesives can create perceived visible lines in the field of view that are undesirable to the observer, particularly at the interface of the reflective mirrors 204. The exemplary lamination process described herein for creating a direct bonding interface 100 can laminate optical layers together without conventional adhesives, resulting in a more accurate image and the elimination of artificial lines in the field of view. The exemplary direct bonding interface 100 described herein allows for better clarity for both the pass-through image 206 and the projected image 208 reflected from the array of partially reflective mirrors 204 to a human observer.

[0019] In an exemplary process for fabricating a mirror waveguide 202 that uses an array of mirror surfaces 204 for near-eye optics, a plurality of glass layers or parts 210 are coated with a layer that is at least partially reflective and then directly bonded together into a stack 212. A direct-bond interface 100 can create a reflective surface 204 between each layer 210. The stacked stack 212 is then die-cut at an angle oblique to the perpendicular of the reflective surface 204 to produce a mirror waveguide 202 having a reflective surface 204 placed at an angle useful for directing a projected image 208 into a human eye.

[0020] FIG. 3 shows an exemplary process for fabricating an exemplary mirror waveguide 202 having a directly oxidized bonded reflective surface. In one implementation, a thin layer of a fully or partially reflective mirror coating 204 is deposited on a glass wafer or panel 210. Then, a thin layer 304 of silicon oxide (e.g., SiO2) having a thickness of about 0.01 - 5.00 pm is deposited on the thin mirror coating 204 on the glass wafer or panel 210. The glass panel 210 is directly oxidized and bonded to the next glass panel 210 through each oxide layer 304.

[0021] In another implementation, a thin layer of silicon nitride (Si3N4), silicon oxynitride (SiON), or silicon carbonitride (SiCN) can be deposited as an alternative to the SiO2 layer 304. In another implementation, a combination of the above layers (SiO2, Si3N4, SiON, and / or SiCN) can be deposited on the thin mirror coating 204 on the glass wafer or panel 210.

[0022] By repeating the above coating and bonding steps, a multi-wafer or multi-panel stack 212 is created. If the stack is vertical, the stack 212 is die-cut or singulated at an angle 306 perpendicular as shown to produce individual mirror waveguides 202.

[0023] In various implementations, an exemplary apparatus may include a first optically transparent substrate including a first flat surface, a second optically transparent substrate including a second flat surface, and a direct chemical bond between the material of the first flat surface of the first optically transparent substrate and the material of the second flat surface of the second optically transparent substrate.

[0024] The material of the first flat surface and the material of the second flat surface may include the same material bonded to itself across the direct bond. The direct bond itself may include a direct silicon oxide - silicon oxide bond between the first flat surface and the second flat surface. If a metal component such as a fixture or conductor is involved in the direct bond interface, the direct bond may be a contact bond that forms spontaneously at room temperature, such as a direct bond of the ZiBond® brand or a hybrid direct bond of the DBI® brand, and both bonding technologies are available from Invensas Bonding Technologies, Inc. (formerly Ziptronix, Inc.), Xperi company (see, for example, U.S. Patent Nos. 6,864,585 and 7,485,968, which are incorporated herein in their entirety).

[0025] As part of the direct bond process, the first flat surface and the second flat surface can be polished flat by a chemical mechanical polishing (CMP) tool. Then, the first flat surface and the second flat surface can be activated by a plasma process in preparation for the formation of a direct chemical bond, such as a nitrogen - based plasma etching process or a reactive ion plasma etching process.

[0026] The direct bond is formed at room temperature and can then be strengthened by annealing at a high temperature of about 150°C or higher after formation.

[0027] As a specular waveguide 202, an exemplary apparatus has at least a partially reflective coating 204 on one or both of the first and second flat surfaces. The fully or partially reflective coating may be, for example, aluminum, silver, gold, platinum, mercury, magnesium fluoride, titanium dioxide, silicon dioxide, zinc sulfide, tantalum pentoxide, reflective dielectric, or Bragg mirror, or a combination of two or more such coatings. Other partially or fully reflective coatings not included in the above list may also be used.

[0028] The lamination bonding between optical surfaces may include one or more thin layers of silicon oxide or ShN4, SiON, and / or SiCN coating each reflective coating 204 before direct oxide bonding or direct oxide-oxide bonding. Since the oxide layer(s) are ultrathin, about 0.01 to 5.00 pm, the resulting bond may be considered optically transparent or a significant improvement over much thicker layers of optically dense adhesives as conventionally used. The given apparatus may also have one or more layers of optically transparent dielectrics coating each reflective coating 204, as is desirable for a given application. Other optical elements and display components can be added as a specular waveguide 202 to create smart glasses, head-up displays (HUDs), or other optical devices.

[0029] Figure 4 shows an exemplary method 400 for fabricating a multilayer optical layer having direct bonding instead of a thicker layer of conventional optically high-density adhesive. In Figure 4, the individual operations are shown as separate blocks.

[0030] In block 402, the first surface of the first optically transparent substrate is planarized to a low surface roughness.

[0031] In block 404, the second surface of the second optically transparent substrate is also planarized to a low surface roughness.

[0032] In block 406, the first surface of the first optically transparent substrate and the second surface of the second optically transparent substrate are placed in contact with each other to form a direct bond between the first surface and the second surface.

[0033] In exemplary method 400, the first and second optically transparent substrates may be glass (e.g., quartz, quartz glass, borosilicate glass, sapphire, crown glass, flint glass, etc.), but may also be polymers, ceramics, and other materials. The first and second optically transparent substrates may be layers of optical devices such as optical waveguides, prisms, collimators, lenses, reflectors, mirrors, combiners, beam splitters, and diffraction gratings.

[0034] The first surface of the first optically transparent substrate and the second surface of the second optically transparent substrate are brought into contact with each other at ambient room temperature to form a bond between the first and second surfaces at room temperature. After the bond is formed, the process may optionally include heating the first and second optically transparent substrates, or their bonded surfaces, to a temperature of about 150°C to strengthen the bond. Subsequent annealing processes or the passage of time strengthen the bond, resulting in low bond strain, minimal bond stress, and increased bond sealing (watertight and airtight). If annealing is used, the first and second optically transparent substrates are then cooled to room temperature.

[0035] Exemplary method 400 also works with substrates and materials that are opaque or even non-transparent.

[0036] Planarizing the first surface of the first optically transparent substrate and the second surface of the second optically transparent substrate to a low surface roughness may involve polishing the first and second surfaces with chemical mechanical polishing (CMP) tools. Alternatively, the surfaces may be made sufficiently flat during their formation or manufacture.

[0037] The exemplary method 400 may also include activating the first and second surfaces with a plasma process in preparation for the spontaneous formation of a bond between the two surfaces at room temperature. The plasma process may be a nitrogen-based etching process or a reactive ion etching process. Subsequent heat treatment and time improve the bond strength.

[0038] To fabricate a specular waveguide, Method 400 includes depositing a reflective coating on one or both of a first or second surface. The reflective coating may be partially reflective for transmission or HUD applications. The reflective coating may be aluminum, silver, gold, platinum, or mercury, or magnesium fluoride, titanium dioxide, silicon dioxide, zinc sulfide, tantalum pentoxide, reflective dielectric, or Bragg mirror, or a combination of two or more such coatings may be used as layers.

[0039] The reflective coating may be covered with a thin layer (thickness 0.01 to 5.00 pm) of oxide or nitride. Spontaneous chemical bonding may consist of direct oxide-oxide bonding in the thin layers of oxide or nitride on the first and second optically transparent substrates. Alternatively, the reflective coating(s) may be covered with one or more layers of one or more optically transparent dielectrics.

[0040] This process is repeated to fabricate a stack of optically transparent substrates containing optical waveguides or specular optical waveguides. A reflective coating is added to at least some of the optically transparent substrates in the stack to fabricate a waveguide with multiple embedded specular arrays.

[0041] Direct bonding, direct oxide bonding, or direct oxide-oxide bonding may be DBI® branded bonding or ZiBond® branded direct oxide bonding, both available from Invensas Bonding Technologies, Inc. (formerly Ziptronix, Inc.), Xperi company (see, e.g., U.S. Patents 6,864,585 and 7,485,968, both incorporated herein). For example, ZiBond® branded direct bonding is a low-temperature wafer-to-wafer or die-to-wafer or die-to-die bonding technology between wafers or dies having the same or different coefficients of thermal expansion (CTE) using low-temperature homogeneous (oxide-oxide) direct bonding technology. ZiBond direct bonding offers several advantages over conventional bonding technologies such as adhesives, anodic bonding, eutectic bonding, and glass frit. Bonding is performed at room temperature, which enhances overall yield and certainty by eliminating adverse effects associated with coefficient of thermal expansion (CTE) mismatch, warping, and strain. Higher throughput and lower holding costs are achieved by using industry-standard wafer alignment and bonding equipment. Without requiring high temperatures or pressures during bonding, the high throughput of ZiBond's direct bonding manufacturing process minimizes manufacturing costs during mass production for high-volume market applications. During ZiBond's direct bonding process, industry-standard dielectric surfaces, such as silicon dioxide or silicon carbonitride, are polished to a low surface roughness using conventional chemical mechanical polishing (CMP) tools, and nitrogen-based chemicals are applied through conventional plasma etching. The prepared wafer surfaces are then simply aligned and placed together, resulting in the spontaneous formation of chemical bonds between the die and / or wafers. Very strong, low-strain bonds with approximately half the bonding strength of silicon can be obtained at room temperature, and, for example, stronger, more secure, sealed bonds than silicon can be obtained after moderate heating to approximately 150°C in a batch process outside the alignment and placement tools.

[0042] In the specification and the following claims, the terms “connect,” “connection,” “connected,” “in connection with,” and “connecting” are used to mean “in direct connection with” or “in connection with, via one or more elements.” The terms “couple,” “coupling,” “coupled,” “coupled together,” and “coupled with” are used to mean “directly coupled together” or “coupled together via one or more elements.”

[0043] Although this disclosure discloses a limited number of embodiments, those skilled in the art who are interested in this disclosure will understand many possible modifications and variations from the given description. The appended claims are intended to encompass such modifications and variations as falling within the true spirit and scope of this disclosure.

Claims

1. A method for forming a mirror optical waveguide, Depositing one or more reflective coatings having at least partial reflectivity on at least a first substrate, To provide a dielectric layer on one or more reflective coatings that forms the first surface of the first substrate, To provide a second dielectric layer on a second substrate that forms the second surface of the second substrate, The first surface and the second surface are stacked together to form a stack, A fire-resistant interface is formed at room temperature via a direct bond between the first material of the first surface and the second material of the second surface, wherein the first material has a first coefficient of thermal expansion, the second material has a second coefficient of thermal expansion, and the first coefficient of thermal expansion is substantially identical to the second coefficient of thermal expansion. A method comprising dicing the stack at an oblique angle with respect to the perpendiculars of one or more of the reflective coatings.

2. The method according to claim 1, wherein the first substrate includes a first optically transparent substrate, and the second substrate includes a second optically transparent substrate.

3. The first substrate comprises one of the following: glass, quartz glass, quartz, sapphire, borosilicate, plastic, or ceramic. The method according to claim 1, wherein the second substrate comprises one of glass, quartz glass, quartz, sapphire, borosilicate, plastic, or ceramic.

4. The method according to claim 1, wherein the first surface and the second surface are superimposed at ambient temperature in order to form a spontaneous chemical bond between the first surface and the second surface.

5. After forming the spontaneous chemical bond, the first substrate and the second substrate are heated to a temperature of approximately 150°C to strengthen the spontaneous chemical bond. The method according to claim 4, further comprising cooling the first substrate and the second substrate to room temperature.

6. The method according to claim 1, wherein at least one of the one or more reflective coatings is perfectly reflective.

7. The method according to claim 1, wherein the one or more reflective coatings include one or more of aluminum, silver, gold, platinum, mercury, magnesium fluoride, titanium dioxide, silicon dioxide, zinc sulfide, tantalum pentoxide, a reflective dielectric, or a Bragg mirror.

8. The one or more reflective coatings are covered with one or more layers of silicon oxide, silicon nitride, silicon carbonitride, or silicon oxynitride. The method according to claim 1, further comprising forming spontaneous chemical bonds between each layer of silicon oxide, silicon nitride, silicon carbonitride, or silicon oxynitride on the first substrate and the second substrate.

9. The first surface includes a first non-conductive material and a first plurality of conductive components. The method according to claim 1, wherein the second surface comprises a second nonconductive material and a second plurality of conductive components.

10. The first nonconductive material is directly bonded to the second nonconductive material, The method according to claim 9, further comprising directly bonding the first plurality of conductive components to the second plurality of conductive components.

11. The method according to claim 10, wherein the first plurality of conductive components comprises at least one of a plurality of mounting fixtures or a plurality of conductors.

12. The method according to claim 1, wherein the dielectric layer includes an inorganic dielectric.

13. A method for forming a mirror optical waveguide, (i) depositing one or more reflective coatings having at least partial reflectivity on at least one of the first surface of the first substrate or (ii) the second surface of the second substrate, Activating the first surface and the second surface by a nitrogen-based plasma process, After the activation, the first surface and the second surface are directly superimposed to form a stack, wherein the first surface and the second surface are directly superimposed at ambient temperature, and a spontaneous chemical bond is formed between the first surface and the second surface. At room temperature, a refractory interface is formed between the first surface and the second surface via a direct inorganic dielectric, A method comprising dicing the aforementioned stack.

14. The method according to claim 13, wherein the first substrate includes a first optically transparent substrate, and the second substrate includes a second optically transparent substrate.

15. The method according to claim 13, wherein the nitrogen-based plasma process comprises one of (i) a nitrogen-based etching process or (ii) a reactive ion etching process.

16. The method according to claim 13, further comprising covering one or more reflective coatings with one or more layers of one or more optically transparent dielectrics.

17. The first surface includes a first non-conductive material and a first plurality of conductive components. The method according to claim 13, wherein the second surface comprises a second nonconductive material and a second plurality of conductive components.

18. The first nonconductive material is directly bonded to the second nonconductive material, The method according to claim 17, further comprising directly coupling the first plurality of conductive components to the second plurality of conductive components.

19. The method according to claim 18, wherein the first plurality of conductive components comprises at least one of a plurality of mounting fixtures or a plurality of conductors.

20. A first substrate comprising a first plasma activation surface and a first inorganic dielectric layer that at least partially defines the first plasma activation surface of the first substrate, A second substrate comprising a second plasma activation surface, one or more reflective coatings on the second substrate, and a second inorganic dielectric layer on the one or more reflective coatings, wherein the second inorganic dielectric layer at least partially defines the second plasma activation surface of the second substrate, and the one or more reflective coatings are at least partially reflective, Direct bonding between the first inorganic dielectric layer and the second inorganic dielectric layer, An apparatus comprising a fire-resistant interface between the first plasma-activated surface and the second plasma-activated surface, The first material of the first plasma-activated surface has a first coefficient of thermal expansion, and the second material of the second plasma-activated surface has a second coefficient of thermal expansion, and the first coefficient of thermal expansion is substantially the same as the second coefficient of thermal expansion. The apparatus has a surface that is die-cut at an oblique angle with respect to the perpendicular of one or more reflective coatings.

21. The apparatus according to claim 20, wherein the first substrate includes a first optically transparent substrate, and the second substrate includes a second optically transparent substrate.

22. The apparatus according to claim 20, wherein the first surface and the second surface comprise the same material bonded to each other via the direct bond.

23. The apparatus according to claim 20, wherein the direct bond includes one direct bond between the first surface and the second surface, which is silicon oxide, silicon nitride, silicon carbonitride, or silicon oxynitride.

24. The first substrate includes glass, quartz glass, quartz, sapphire, borosilicate, plastic, or ceramic. The apparatus according to claim 20, wherein the second substrate includes glass, quartz glass, quartz, sapphire, borosilicate, plastic, or ceramic.

25. The apparatus according to claim 20, wherein at least one of the one or more reflective coatings is perfectly reflective.

26. The apparatus according to claim 20, wherein the one or more reflective coatings include one or more of aluminum, silver, gold, platinum, mercury, magnesium fluoride, titanium dioxide, silicon dioxide, zinc sulfide, tantalum pentoxide, a reflective dielectric, and a Bragg mirror.

27. The apparatus according to claim 20, further comprising a layer of silicon oxide, silicon nitride, silicon carbonitride, or silicon oxynitride on the one or more reflective coatings.

28. The apparatus according to claim 20, wherein the first inorganic dielectric layer comprises one or more optically transparent dielectric layers on the one or more reflective coatings.

29. The apparatus according to claim 20, wherein the first and second surfaces are sufficiently flat to form a direct bond between the first surface and the second surface without the use of adhesive.

30. The apparatus according to claim 20, wherein the first and second surfaces are polished using chemical mechanical polishing before the formation of the direct bond.

31. The first surface includes a first non-conductive material and a first plurality of conductive components. The second surface includes a second non-conductive material and a second plurality of conductive components. The first nonconductive material is directly bonded to the second nonconductive material. The apparatus according to claim 20, wherein the first plurality of conductive components are directly coupled to the second plurality of conductive components.

32. The apparatus according to claim 31, wherein the first plurality of conductive components comprises at least one of a plurality of fixtures or a plurality of conductors.

33. The first surface and the second surface are activated by a plasma process, The apparatus according to claim 20, wherein the plasma process includes a nitrogen-based etching process or a reactive ion etching process.

34. The aforementioned direct bond includes an annealed direct bond. The apparatus according to claim 20, wherein the annealed direct bond is formed after heating the direct bond to a temperature of about 150°C.

35. Further comprising a stack of substrates directly coupled to each other, The apparatus according to claim 20, wherein the stack of substrates includes an optical waveguide.

36. The apparatus according to claim 35, further comprising one or more reflective coatings added to at least one substrate of the stack of substrates in order to form an optical waveguide having an array of multiple embedded mirror surfaces.

37. The apparatus according to claim 35 or 36, further comprising a display device optically connected to the optical waveguide.

38. The apparatus according to claim 20, wherein the first substrate and the second substrate are configured as layers of optical devices selected from the group consisting of optical waveguides, prisms, collimators, lenses, reflectors, mirrors, optical waveguides, combiners, beam splitters, and diffraction gratings.

39. The apparatus according to claim 20, wherein the direct coupling includes a direct coupling interface in a plane nonparallel to the outer surface of the apparatus, or includes a direct coupling interface in one or more planes different from the plane of the outer surface of the apparatus.

40. A first optical element comprising a first substrate, a reflective material, and a first bonding layer, wherein the reflective material is disposed on the first substrate and is located between the first substrate and the first bonding layer, A second optical element comprising a second substrate and a second bonding layer disposed on the second substrate, An optical waveguide comprising a direct bonding of dielectrics between the first bonding layer and the second bonding layer, An optical waveguide in which the first bonding layer has a first thickness in the range of 0.01 μm to 5.00 μm, and the second bonding layer has a second thickness in the range of 0.01 μm to 5.00 μm.

41. The optical waveguide according to claim 40, wherein the first substrate and the second substrate are optically transparent.

42. The optical waveguide according to claim 40, wherein the first bonding layer and the second bonding layer are superimposed at room temperature, thereby forming a spontaneous chemical bond between the first bonding layer and the second bonding layer.

43. The optical waveguide according to claim 40, further comprising direct bonding of conductors between the first bonding layer and the second bonding layer.

44. The optical waveguide according to claim 40, wherein the first bonding layer and the second bonding layer include silicon oxide, silicon nitride, silicon carbonitride, or silicon oxynitride.