Optical waveguide and manufacturing method thereof

Abstract

An optical waveguide (200) includes: an optical core (30) configured to propagate image light along the optical core; and a first multi-layer grating and a second multi-layer grating (40), the first multi-layer grating and the second multi-layer grating being disposed on the optical core (30). The first multilayer grating (40a) is configured to receive image light from an image projector (70a) and to inject at least a portion of the received image light into the optical core (30). The injected image light propagates along the optical core (30) by total internal reflection. The second multilayer grating (40b) is configured to receive a portion of the injected image light and to extract the received portion of the injected image light from the optical core (30) for viewing. Each of the first multi-layer grating and the second multi-layer grating (40) includes an inorganic relief layer (60) having an undulating shape in a width direction, and a flattening adhesive layer (50) disposed between the relief layer (60) and the optical core (30) and flattening one of the relief major surfaces of the inorganic relief layer (60).

Description

SUMMARY OF THE INVENTION

[0001] In some aspects of the present specification, an optical waveguide is provided. The optical waveguide includes: an optical core configured to propagate image light along the optical core; and a first multilayer grating and a second multilayer grating disposed on the optical core. The first multilayer grating is configured to receive image light from an image projector and direct at least a portion of the received image light into the optical core. The directed image light propagates along the optical core mainly by total internal reflection. The second multilayer grating is configured to receive at least a portion of the directed image light and extract at least a portion of the received directed image light from the optical core for viewing by a viewer. Each of the first multilayer grating and the second multilayer grating includes an inorganic undulating layer and a planarizing adhesive layer. The inorganic undulating layer includes two opposite outermost undulating major surfaces that are aligned nestedly with each other to produce a wavy shape along the width direction of the inorganic undulating layer and form a plurality of substantially parallel ridges and grooves. These ridges and grooves extend along the orthogonal length direction of the inorganic undulating layer. The planarizing adhesive layer is disposed between the inorganic undulating layer and the optical core, and substantially planarizes one of the undulating major surfaces of the inorganic undulating layer and bonds the inorganic undulating layer to the optical core.

[0002] In some aspects of the present specification, an optical waveguide is provided, which includes: an optical core configured to propagate image light along the optical core; and a continuous seamless multi-layer disposed on a main side surface of the optical core. The continuous seamless multi-layer includes a continuous seamless inorganic layer and a continuous seamless adhesive layer. The continuous seamless inorganic layer undulates in a plurality of discrete spaced-apart regions of the inorganic layer to form a plurality of spaced-apart undulating inorganic layer portions of the originally non-undulating inorganic layer. Each of the undulating inorganic layer portions in the undulating inorganic layer portions includes two opposite outermost undulating main surfaces that are nested and aligned with each other, and forms a plurality of substantially parallel ridges and grooves that extend along the length direction of the undulating inorganic layer portion and are arranged in the orthogonal width direction of the undulating inorganic layer portion. The continuous seamless adhesive layer is disposed between the inorganic layer and the optical core, and is substantially conformal to the ridges and the grooves of each of the undulating inorganic layer portions in the undulating inorganic layer portions and bonds the inorganic layer to the optical core. A first undulating inorganic layer portion of the undulating inorganic layer portion is configured to receive image light from an image projector and direct at least a portion of the received image light into the optical core. The directed image light propagates along the optical core mainly by total internal reflection. A second undulating inorganic layer portion in the undulating inorganic layer portions is configured to receive at least a portion of the directed image light received in a first direction and redirect the directed image light as redirected image light that propagates along the optical core mainly by total internal reflection in a different second direction. A third undulating inorganic layer portion in the undulating inorganic layer portions is configured to receive at least a portion of the redirected image light and extract at least a portion of the received redirected image light from the optical core for viewing by a viewer.

[0003] In some aspects of the present specification, a method of fabricating an optical waveguide is provided, the method including: providing a temporary carrier including a main structured surface having a plurality of alternating first ridges and first grooves in a plurality of discrete spaced-apart regions; conformally disposing an inorganic layer on the main structured surface of the temporary carrier such that both a first main surface of the inorganic layer facing the temporary carrier and a second main surface of the inorganic layer facing away from the carrier are substantially conformal to the main structured top surface of the temporary carrier to form a continuous seamless inorganic layer having a plurality of undulating inorganic layer portions in the originally non-undulating inorganic layer. In each of the undulating inorganic layer portions in the undulating inorganic layer portions, an average spacing value S avg and a spacing standard deviation S sd are defined between the first main surface and the second main surface of the layer portion such that S sd / S avgLess than about 0.5; coating the second major surface of the inorganic layer substantially conformally with an adhesive layer and substantially planarizing the inorganic layer to form a structured adhesive layer having a major structured top surface facing and substantially conforming to the second major surface of the inorganic layer and an opposite substantially planar major surface; bonding the substantially planar major surface of the structured adhesive layer to a major surface of an optical core configured to propagate image light along the optical core primarily by total internal reflection; and removing the temporary carrier from the first major surface of the inorganic layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1A and Figure 1B A side view of a portion of an optical waveguide including a multilayer grating in accordance with an embodiment of the present specification;

[0005] Figure 2 is a scanning electron microscope of a multilayer grating in accordance with an embodiment of the present specification;

[0006] Figure 3 is a process flow diagram illustrating a method of fabricating an optical waveguide having a multilayer grating in accordance with an embodiment of the present specification;

[0007] Figure 4 is a side view of an optical waveguide including two multilayer grating sections in accordance with an embodiment of the present specification;

[0008] Figure 5 There is provided in accordance with an embodiment of the present specification Figure 4 an alternative view of the optical waveguide;

[0009] Figure 6A and Figure 6B a side view of the architecture of a multilayer grating in accordance with an embodiment of the present specification;

[0010] Figure 7 is a side view of an optical waveguide including multilayer grating sections on opposite sides of an optical core in accordance with an alternative embodiment of the present specification;

[0011] Figure 8 is a side view of an optical waveguide in accordance with another alternative embodiment of the present specification;

[0012] Figure 9A and Figure 9B respectively provide a top view and a side view of an optical waveguide including three multilayer grating sections in accordance with an alternative embodiment of the present specification;

[0013] Figure 10A and Figure 10B provides an illustrative example of an alternative shape for features on a multilayer grating in accordance with an embodiment of the present specification;

[0014] Figure 11A and Figure 11B provides additional illustrative examples of alternative shapes for features on a multilayer grating according to embodiments of this specification; and

[0015] Figure 12 is an illustrative example of a method for measuring dimensions on a relief layer of a multilayer grating according to embodiments of this specification. Detailed Description

[0016] In the following description, reference is made to the accompanying drawings, which form a part of this disclosure and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments may be conceived and effected without departing from the scope or essence of this specification. Accordingly, the following detailed description should not be taken in a limiting sense.

[0017] The nanostructured film can be used in an optically laminated article or as a transfer film for subwavelength optical devices such as diffractive optical elements and optical metasurfaces. The transfer film can be used to fabricate image retention waveguides for augmented reality devices. The optical properties of these waveguides depend on the refractive index contrast (i.e., refractive index difference) between the grating structure and the surrounding medium, which can be a template film (e.g., a polymer with a refractive index of about 1.5) or air (in the case where the template is removed in a subsequent processing step). Thus, methods are needed to maximize the refractive index of the templated nanostructures used in the final articles of templated nanostructures.

[0018] The fabrication of high refractive index, subwavelength gratings and nanostructures is typically accomplished using "batch processing" and methods developed for the semiconductor industry. The process begins by depositing a dense TiO 2 layer on a substrate (e.g., a high refractive index glass wafer). The TiO 2 layer is coated with a polymer resist, which is then patterned via lithographic techniques such as photolithography, nanoimprint lithography, or electron beam lithography to define the desired pattern in the resist. The pattern in the resist is then transferred to the TiO 2 layer by etching, and finally the resist is removed, leaving the patterned TiO 2 .

[0019] The transfer film method described herein is fundamentally different from the commonly used batch processing methods and may be more suitable for high-volume and low-cost production of subwavelength optical structures. The transfer film method fabricates a high refractive index TiO 2A sub - wavelength structure is used to achieve this. Once the structure is fabricated, it is transferred to the final substrate (e.g., a high - refractive - index glass wafer) using an ultrathin adhesive (less than 500 nm and preferably less than 100 nm thick to maintain good optical coupling), and the carrier substrate and optionally the template layer are removed. This enables the use of high - volume roll - to - roll processing to create high - refractive - index structures on the final substrate.

[0020] According to some aspects of the present specification, an optical waveguide includes: an optical core configured to propagate an optical mode at a first wavelength along the optical core; and a multilayer grating disposed on the optical core and configured to extract an optical mode that would otherwise propagate along the optical core in a first direction (e.g., on the x - axis relative to the waveguide).

[0021] In some embodiments, the multilayer grating may include an adhesive layer and an inorganic layer. In some embodiments, the adhesive layer may include a main bottom surface facing the optical core and an opposite structured main top surface facing away from and spaced from the optical core. In some embodiments, the structured main top surface may include a plurality of substantially parallel linear grating elements that extend along the same length direction (e.g., the y - axis) of the grating element and are arranged along the orthogonal width direction (e.g., the x - axis) of the grating element. In some embodiments, the plurality of substantially parallel linear grating elements may form a periodic pattern along the width direction of the grating element. In some such embodiments, the periodic pattern may have a period in the range of about 100 nm to about 1000 nm, or about 150 nm to about 750 nm, or about 200 nm to about 700 nm, or about 250 nm to about 600 nm, or about 300 nm to about 550 nm, or about 300 nm to about 500 nm or about 300 nm to about 450 nm. In some embodiments, the width direction of the grating element may be substantially parallel to the first direction.

[0022] In some embodiments, the inorganic layer may be disposed on the structured main top surface of the adhesive layer and may conform to the structured main top surface such that the thickness standard deviation of the inorganic layer is less than about 50%, or less than about 45%, or less than about 40%, or less than about 35%, or less than about 30%, or less than about 25% or less than about 20% of the average thickness of the inorganic layer.

[0023] In some embodiments, the optical core may have an average thickness between about 100 microns and about 2000 microns, or between about 150 microns and about 1500 microns, or between about 200 microns and about 1250 microns, or between about 250 microns and about 1250 microns or between about 300 microns and about 1000 microns. In some embodiments, the optical core may have a thickness of at most 5000 microns, or at most 7500 microns or at most 10,000 microns.

[0024] In some embodiments, the minimum spacing between the optical core and the main top surface of the adhesive layer may be greater than about 5 nm, or greater than about 10 nm, or greater than about 15 nm, or greater than about 20 nm, or greater than about 25 nm, or greater than about 30 nm, or greater than about 35 nm, or greater than about 40 nm, or greater than about 45 nm or greater than about 50 nm.

[0025] In some embodiments, the optical waveguide may further include a cover layer disposed on the inorganic layer and substantially planarizing the inorganic layer. In some embodiments, the inorganic layer may comprise titanium dioxide (TiO 2 ), zirconium oxide (ZrO x ), titanium oxide (TiO x ), SiO 2 , Al 2 O 3 , CeO 2 , ZnO, Nb 2 O 5 , Ta 2 O 5 , HfO 2 , SiAlOxNy, Si 3 N 4 , Nb-doped TiO 2 and ZrO 2 or one or more of them. In some embodiments, at a first wavelength, the refractive index of the cover layer may be at least 0.5, or at least 0.6, or at least 0.7, or at least 0.8, or at least 0.9, or at least 1.0 or at least 1.2 smaller than the refractive index of the inorganic layer.

[0026] In some embodiments, an optical system may include any of the optical waveguides described herein; at least one light source configured to inject light at a first wavelength into the optical core of the optical waveguide such that the injected light propagates as an optical mode along the optical core in a first direction.

[0027] According to some aspects of the present specification, an optical waveguide includes: an optical core configured to propagate image light along the optical core mainly by total internal reflection; a structured adhesive layer; and an inorganic layer. In some embodiments, the structured adhesive layer may include a main bottom surface facing the optical core and bonded to the optical core and an opposite main structured top surface including a plurality of alternating ridges and grooves. In some embodiments, the average spacing between the grooves and the optical core may be greater than about 5 nm, or about 10 nm, or about 15 nm, or about 20 nm, or about 25 nm, or about 30 nm, or about 35 nm, or about 40 nm, or about 45 nm or about 50 nm. In some embodiments, the average spacing between the grooves and the optical core may be less than about 500 nm, or about 450 nm, or about 400 nm, or about 350 nm, or about 300 nm, or about 250 nm, or about 200 nm, or about 150 nm or about 100 nm. In some embodiments, the minimum spacing between the grooves and the optical core may be greater than about 5 nm, or about 10 nm, or about 15 nm, or about 20 nm, or about 25 nm, or about 30 nm, or about 35 nm, or about 40 nm, or about 45 nm, or about 50 nm.

[0028] As used herein, the terms "ridge" and "groove" shall be defined as follows. A ridge is any undulation in a layer for which the material of the layer is "pushed" "upward" away from the optical core, thereby forming a protrusion extending in a direction away from the optical core. Conversely, a groove is any undulation in a layer for which the material of the layer is "pushed" "downward" toward the optical core, thereby forming a recess extending in a direction toward the optical core.

[0029] Both the ridge and the groove can be considered "depressions" in the layer, but the depressions face different directions. For example, each depression has an open end and a closed end (e.g., a "cup-shaped" shape). In the "ridge" depression, the open end of the depression "faces" the optical core "downward" (negative z-direction in FIG. 1), and the closed end protrudes "upward" away from the optical core (positive z-direction indicated by the arrow on the coordinate system graph in FIG. 1). Conversely, the "groove" depression has an open end facing "upward" away from the optical core and a closed end facing the optical core "downward". These definitions are provided for a clear understanding of the drawings and language of the present specification.

[0030] In some embodiments, for at least one visible wavelength in the visible (visually perceptible by humans) wavelength range extending from about 420 nm to about 680 nm, the structured adhesive has a refractive index between about 1.35 and about 2.5. In some embodiments, for at least one visible wavelength in the visible wavelength range extending from about 420 nm to about 680 nm, the structured adhesive has a refractive index of about 1.5.

[0031] In some embodiments, the inorganic layer may be conformally disposed on the main structured top surface of the structured adhesive layer such that the opposite first and second main surfaces of the inorganic layer are substantially conformal to the main structured top surface of the structured adhesive layer, and the first and second main surfaces of the inorganic layer define an average spacing between about 10 nm and about 100 nm, or about 20 nm and about 90 nm, or about 30 nm and about 80 nm, or about 40 nm and about 70 nm or about 40 nm and about 60 nm. In some embodiments, the inorganic layer may have a refractive index greater than about 1.5, or about 1.6, or 1.7, or 1.8, or 1.9, or 2.0, or 2.1, or 2.2, or 2.3 or 2.4 at a wavelength of about 580 nm.

[0032] In some embodiments, the optical core may have a refractive index greater than about 1.5, or greater than about 1.6, or greater than about 1.7, or greater than about 1.8, or greater than about 1.9 or greater than about 2.0 at a wavelength of about 580 nm. In some embodiments, the optical core may comprise one or more of tantalum, niobium, lanthanum, lead, barium, titanium, zirconium, and bismuth. In some embodiments, the optical core may be a polymer. In some embodiments, the optical core may include, but is not limited to, one or more of polymethacrylate, polycarbonate, polyester, polyphosphonate, polysulfone, siloxane, epoxy resin, or polyimide components. In some embodiments, the optical core may comprise nanoparticles. In some embodiments, the optical core may comprise nanoparticles of titanium dioxide or zirconia.

[0033] According to some aspects of the present specification, an optical waveguide includes: an optical core configured to propagate image light along the optical core mainly by total internal reflection; an inorganic layer; and a structured adhesive layer. In some embodiments, the inorganic layer may be disposed on the optical core and may define a plurality of alternating first recesses and second recesses, wherein the first recesses are recessed toward the optical core and the second recesses are protruded toward the optical core. In some embodiments, the structured adhesive layer may be disposed between the optical core and the inorganic layer and bond them to each other. In some embodiments, the structured adhesive layer may substantially fill the first recesses.

[0034] For each pair of adjacent first and second recesses, the first and second recesses may be separated by a common sidewall that extends from a first rounded sidewall corner that connects the common sidewall to the bottom of the second recess to an opposite second rounded sidewall corner that connects the common sidewall to the bottom of the first recess. In a first planar cross-section that is substantially orthogonal to the common sidewall (e.g., in the xz plane of an optical waveguide), the first rounded sidewall corner may include an outer first circumferential surface that faces the optical core and has a first radius of curvature R1. In some embodiments, the second rounded sidewall corner may include an outer second circumferential surface that faces away from the optical core and has a second radius of curvature R2. In some embodiments, for at least a plurality of pairs of adjacent first and second recesses, R1 may be greater than R2.

[0035] According to some aspects of the present specification, an optical waveguide may include: an optical core configured to propagate image light along the optical core primarily by total internal reflection; an inorganic layer; and a structured adhesive layer. In some embodiments, the inorganic layer may be disposed on the optical core and may define a plurality of alternating first and second recesses. In some embodiments, the first recesses may be recessed toward the optical core, and the second recesses may be protruded toward the optical core.

[0036] In some embodiments, the structured adhesive layer may be disposed between the optical core and the inorganic layer and may bond the optical core to the inorganic layer. In some embodiments, the structured adhesive layer may substantially fill the first recesses. In some embodiments, for each pair of adjacent first and second recesses, the first and second recesses may be separated by a common sidewall that extends from a first rounded sidewall corner that connects the common sidewall to the bottom of the second recess to an opposite second rounded sidewall corner that connects the common sidewall to the bottom of the first recess. In some embodiments, the first rounded sidewall corner may be closer to the optical core and the second rounded sidewall corner may be farther from the optical core.

[0037] In some embodiments, in a first planar cross-section that is substantially orthogonal to the common sidewall (e.g., the xz plane of the optical waveguide), the first rounded sidewall corner may include an outer first circumferential surface that faces the optical core and has a first outer radius of curvature R1 and an inner first circumferential surface that faces away from the optical core and has a first inner radius of curvature R1. In some embodiments, for at least a plurality of pairs of adjacent first and second recesses, R1 may be greater than R1'. In some embodiments, the value of R1–R1' may be at least 10 nm, or at least 20 nm, or at least 30 nm, or at least 40 nm, or at least 50 nm.

[0038] According to some aspects of the present specification, a method of fabricating an optical waveguide may include: providing a temporary carrier including a primary structured surface having a plurality of alternating first ridges and first trenches; conformally disposing an inorganic layer on the primary structured surface of the temporary carrier such that both a first primary surface of the inorganic layer facing the temporary carrier and a second primary surface of the inorganic layer facing away from the carrier are substantially conformal to the primary structured top surface of the temporary carrier, such that an average spacing S is defined between the first primary surface and the second primary surface of the inorganic layer avg and a spacing standard deviation S sd , S sd / S avg is less than about 0.5, or about 0.4, or about 0.3, or about 0.2, or about 0.17, or about 0.15, or about 0.12, or about 0.1; disposing an adhesive layer on the second primary surface of the inorganic layer and substantially planarizing the inorganic layer to form a structured adhesive layer having a primary structured top surface facing and substantially conformal to the second primary surface of the inorganic layer and an opposite substantially planar primary surface; and bonding the substantially planar primary surface of the structured adhesive layer to a primary surface of an optical core configured to propagate image light along the optical core primarily by total internal reflection; and removing the temporary carrier from the first primary surface of the inorganic layer. For additional details regarding the values of S avg and S sd and how measurements may be determined, reference the discussion herein Figure 12 .

[0039] In some embodiments, the method of fabricating an optical waveguide may further include: disposing a cover material on the first primary surface of the inorganic layer; and substantially planarizing the inorganic layer to form a structured cover layer having a primary structured surface facing and substantially conformal to the first primary surface of the inorganic layer and an opposite substantially planar primary surface. In some embodiments, the step of providing a temporary carrier includes providing a tool having a primary structured surface including a plurality of alternating ridges and trenches; and disposing a temporary carrier material on the primary structured surface of the tool to form a temporary carrier having a primary structured surface facing and substantially conformal to the primary surface of the tool and including a plurality of alternating first ridges and first trenches

[0040] In some embodiments, the step of removing the temporary carrier from the first primary surface of the inorganic layer may include removing the temporary carrier by plasma etching, wet etching, solvent dissolution, laser ablation, chemical mechanical polishing (CMP), or any other suitable method

[0041] In some embodiments, the temporary carrier may include a carrier substrate having a separable release layer, where the primary structured surface is deposited on the separable release layer. Examples of carriers having a separable release layer are described in co-pending U.S. Patent Application No. 63 / 265,650, filed December 17, 2021.

[0042] In such embodiments, the step of removing the temporary carrier involves removing the carrier substrate and then removing the remaining "primary structured surface" by plasma etching, wet etching, solvent dissolution, laser ablation, chemical mechanical polishing (CMP), or any other suitable method.

[0043] According to some aspects of the present specification, an optical waveguide may include an optical core configured to propagate image light along the optical core; and a first multilayer grating and a second multilayer grating disposed on the optical core. In some embodiments, the first multilayer grating may be configured to receive image light from an image projector and direct at least a portion of the received image light into the optical core. In some embodiments, the directed image light may propagate along the optical core mainly by total internal reflection. In some embodiments, the second multilayer grating may be configured to receive at least a portion of the directed image light and extract at least a portion of the received directed image light from the optical core for viewing by a viewer (e.g., a human observer). In some embodiments, the first multilayer grating and the second multilayer grating may have different width directions (e.g., a non-zero angle may be defined therebetween when the x-axes of each multilayer grating are overlapping). In some embodiments, the optical core may have a refractive index greater than about 1.5, or greater than about 1.6, or greater than about 1.7, or greater than about 1.8, or greater than about 1.9 or greater than about 2.0 at a wavelength of about 580 nm. In some embodiments, the optical core may comprise one or more of tantalum, niobium, lanthanum, lead, barium, titanium, zirconium, and bismuth. In some embodiments, the optical core may be a polymer. In some embodiments, the optical core may include one or more of a polymethacrylate, polycarbonate, polyester, polyphosphonate, polysulfone, silicone, epoxy resin, or polyimide component. In some embodiments, the optical core may comprise nanoparticles. In some embodiments, the optical core may comprise nanoparticles of titanium dioxide or zirconium oxide. In some embodiments, each of the first multilayer grating and the second multilayer grating may include an inorganic relief layer and a planarizing adhesive layer. In some embodiments, the inorganic relief layer may include two opposite outermost relief main surfaces that are nested and aligned with each other to have a wavy shape along the width direction of the inorganic relief layer (e.g., along the x-axis), and form a plurality of substantially parallel ridges and grooves. In some embodiments, the ridges and grooves may extend along the orthogonal length direction of the inorganic relief layer (e.g., the y-axis). In some embodiments, the relief amplitude of at least one of the first multilayer grating and the second multilayer grating may vary along its width direction.

[0044] As used herein, the phrase "undulating layer" refers to a layer having a wavy pattern, shape, or profile in the width direction of the layer, wherein connected curves in alternating directions in the layer form alternating peaks and valleys or ridges and grooves on each major side of the layer in the width direction, and extend along the length direction of the layer. Examples of undulating layers include, but are not limited to, layers having a sine wave pattern, shape, or profile, and layers having a triangular wave, tilted, or blazed pattern, shape, or profile. Other examples of undulating layers include layers characterized by a two-dimensional (2D) pattern of pillars and / or holes, wherein a cross-section taken through a linear collection of pillars or holes (e.g., a row of pillars or holes) across the layer produces an undulating pattern.

[0045] In some embodiments, a planarizing adhesive layer may be disposed between the inorganic undulating layer and the optical core, and substantially planarize one of the undulating major surfaces of the inorganic undulating layer and bond the inorganic undulating layer to the optical core.

[0046] In some embodiments, the planarizing adhesive layer may define a minimum distance d between the inorganic undulating layer and the optical core min . In some such embodiments, d min may be greater than about 5 nm, or about 10 nm, or about 15 nm, or about 20 nm, or about 25 nm, or about 30 nm, or about 35 nm, or about 40 nm, or about 45 nm or about 50 nm. In some embodiments, for at least one of the first multilayer grating and the second multilayer grating, the minimum spacing between the optical core and the trench of the multilayer grating may vary along the width of the multilayer grating.

[0047] In some embodiments, for at least one of the first multilayer grating and the second multilayer grating, in a plane cross-section (e.g., xz plane) orthogonal to the length direction (e.g., y-axis) of the multilayer grating, for two different positions L1 and L2 on the multilayer grating, each position including a ridge and a directly adjacent trench, wherein the area between the optical core and the ridge at L1 is A r1 , the area between the optical core and the trench at L1 is A g1 , the area between the optical core and the ridge at L2 is A r2 , and the area between the optical core and the trench at L2 is A g2 , A r1 +A g1 differs from A r2 +A g2 by within 30% of A r2 +A g2 , or within 20%, or within 10%, or within 5% or within 2%.

[0048] In some embodiments, for at least one of the first multilayer grating and the second multilayer grating, the multilayer grating may further include a planarizing overcoat that conformally covers the inorganic undulating layer and substantially planarizes the inorganic undulating layer, opposite to the planarizing adhesive layer. In some embodiments, the first multilayer grating and the second multilayer grating may be disposed on the same side of the optical core, or may be disposed on two opposite major sides of the optical core. In some embodiments, the first multilayer grating and the second multilayer grating may be spaced apart, while in other embodiments, the first multilayer grating and the second multilayer grating may be in contact or overlap.

[0049] In some embodiments, the optical waveguide may further include: a connecting adhesive portion disposed between the planarizing adhesive layers of the first multilayer grating and the second multilayer grating and continuously and seamlessly connecting the planarizing adhesive layers. In some embodiments, the optical waveguide may further include: a connecting substantially non-undulating inorganic layer disposed between the inorganic undulating layers of the first multilayer grating and the second multilayer grating and continuously and seamlessly connecting the inorganic undulating layers.

[0050] In some embodiments, each of the first multilayer grating and the second multilayer grating may further include a planarizing overcoat that conformally covers the inorganic undulating layer and substantially planarizes the inorganic undulating layer, opposite to the planarizing adhesive layer. In some such embodiments, the optical waveguide may further include: a substantially planar connecting overcoat disposed between the planarizing overcoats of the first multilayer grating and the second multilayer grating and continuously and seamlessly connecting the planarizing overcoats.

[0051] In some embodiments, for at least one visible wavelength in the range of human visible wavelengths extending from about 420 nm to about 680 nm, the refractive index of the planarizing overcoat is at least 0.5, or at least 0.6, or at least 0.7, or at least 0.8, or at least 0.9, or at least 1.0 or at least 1.2 less than the refractive index of the inorganic undulating layer.

[0052] In some embodiments, for at least one of the first multilayer grating and the second multilayer grating, a plurality of substantially parallel ridges and grooves may form a periodic pattern along the width direction of the inorganic undulating layer. In some such embodiments, the periodic pattern may have a period in the range of about 100 nm to about 1000 nm, or about 150 nm to about 750 nm, or about 200 nm to about 700 nm, or about 250 nm to about 600 nm, or about 300 nm to about 550 nm, or about 300 nm to about 500 nm or about 300 nm to about 450 nm.

[0053] In some embodiments, the optical core may have an average thickness between about 100 microns and about 2000 microns, or between about 150 microns and about 1500 microns, or between about 200 microns and about 1250 microns, or between about 250 microns and about 1250 microns or between about 300 microns and about 1000 microns. In some embodiments, the optical core may have a thickness of at most 5000 microns, or at most 7500 microns or at most 10,000 microns. In some embodiments, the minimum thickness of the planarizing adhesive layer may be greater than about 5 nm, or about 10 nm, or about 15 nm, or about 20 nm, or about 25 nm, or about 30 nm, or about 35 nm, or about 40 nm, or about 45 nm or about 50 nm.

[0054] In some embodiments, the layer of inorganic undulations may comprise titanium dioxide (TiO 2 ), zirconium oxide (ZrO x ), titanium oxide (TiO x ), SiO 2 , Al 2 O 3 , CeO 2 , ZnO, Nb 2 O 5 , Ta 2 O 5 , HfO 2 , SiAlOxNy, Si 3 N 4 , Nb-doped TiO 2 and zirconium dioxide (ZrO 2 ) or one or more of them.

[0055] In some embodiments, an optical system may include any of the optical waveguides described herein and an image projector configured to emit image light, wherein the first multilayer grating may be configured to receive the emitted image light and direct at least a portion of the received image light into the optical core of the optical waveguide.

[0056] In some embodiments, for at least one visible wavelength in the visible wavelength range extending from about 420 nm to about 680 nm, the planarizing adhesive layer may have a refractive index between about 1.35 and about 2.5. In some embodiments, for at least one visible wavelength in the visible wavelength range extending from about 420 nm to about 680 nm, the planarizing adhesive layer may have a refractive index of about 1.5. In some embodiments, the inorganic undulation layer may have a refractive index greater than about 1.5, or greater than about 1.6, or greater than about 1.7, or greater than about 1.8, or greater than about 1.9, or greater than about 2.0, or greater than about 2.1, or greater than about 2.2, or greater than about 2.3 or greater than about 2.4 at a wavelength of about 580 nm.

[0057] In some embodiments, the minimum spacing between the optical core and the plurality of substantially parallel ridges and grooves may be greater than about 5 nm, or about 10 nm, or about 15 nm, or about 20 nm, or about 25 nm, or about 30 nm, or about 35 nm, or about 40 nm, or about 45 nm or about 50 nm. In some embodiments, the average spacing between the grooves and the optical core may be less than about 500 nm, or about 450 nm, or about 400 nm, or about 350 nm, or about 300 nm, or about 250 nm, or about 200 nm, or about 150 nm or about 100 nm.

[0058] According to some aspects of the present specification, an optical waveguide may include: an optical core configured to propagate image light along the optical core; and a continuous seamless multilayer disposed on a main side surface of the optical core.

[0059] In some embodiments, the continuous seamless multilayer may include a continuous seamless inorganic layer and a continuous seamless adhesive layer. In some embodiments, the continuous seamless inorganic layer may undulate in a plurality of discrete spaced-apart regions of the inorganic layer to form a plurality of spaced-apart undulating inorganic layer portions of the originally non-undulating inorganic layer.

[0060] In some embodiments, each of the undulating inorganic layer portions in the undulating inorganic layer portions may include two opposite outermost undulating main surfaces that are nested and aligned with each other, and form a plurality of substantially parallel ridges and grooves that extend along the length direction (e.g., the x-axis) of the undulating inorganic layer portion and are arranged along the orthogonal width direction (e.g., the y-axis) of the undulating inorganic layer portion.

[0061] In some embodiments, the continuous seamless adhesive layer may be disposed between the inorganic layer and the optical core, and may be substantially conformal to the ridges and grooves of each of the undulating inorganic layer portions in the undulating inorganic layer portion and bond the inorganic layer to the optical core.

[0062] In some embodiments, the first undulating inorganic layer portion in the undulating inorganic layer portion is configured to receive image light from an image projector and direct at least a portion of the received image light into the optical core. In some embodiments, the directed image light may propagate along the optical core mainly by total internal reflection. In some embodiments, the second undulating inorganic layer portion in the undulating inorganic layer portion may be configured to receive at least a portion of the directed image light received in a first direction and redirect the directed image light into redirected image light that propagates along the optical core mainly by total internal reflection in a different second direction. In some embodiments, the third undulating inorganic layer portion in the undulating inorganic layer portion may be configured to receive at least a portion of the redirected image light and extract at least a portion of the received redirected image light from the optical core for viewing by a viewer.

[0063] As used herein, the term "seamless" when used in combination with the term "layer" (as in "seamless adhesive layer") shall be defined to mean a layer that is formed as a continuous workpiece and that contains substantially no gaps within the layer. In some embodiments, a "seamless" layer may contain small cracks (e.g., cracks inadvertently formed due to manufacturing or processing steps) that do not significantly affect the intended function of the otherwise continuous layer. Additionally, a layer that contains an intentionally discontinuous portion between two substantially similar sections of the layer shall be considered seamless where the two sections are otherwise in direct contact with each other (e.g., a butting joint between the two sections) and where the layer otherwise functions substantially as a continuous layer.

[0064] According to some aspects of the present specification, a method of fabricating an optical waveguide may include the steps of: providing a temporary carrier including a primary structured surface having a plurality of alternating first ridges and first trenches in a plurality of discrete spaced-apart regions; conformally disposing an inorganic layer on the primary structured surface of the temporary carrier such that a first major surface of the inorganic layer facing the temporary carrier and a second major surface of the inorganic layer facing away from the carrier are substantially conformal to the primary structured top surface of the temporary carrier to form a continuous seamless inorganic layer having a plurality of undulating inorganic layer portions within an otherwise non-undulating inorganic layer, such that within each of the undulating inorganic layer portions in the undulating inorganic layer portions, an average spacing S avg and a spacing standard deviation S sd , S sd / S avg is less than about 0.5, or less than about 0.4, or less than about 0.3, or less than about 0.2, or less than about 0.17, or less than about 0.15, or less than about 0.12, or less than about 0.1; substantially conformally coating the second major surface of the inorganic layer with an adhesive layer and substantially planarizing the inorganic layer to form a structured adhesive layer having a primary structured top surface facing and substantially conformal to the second major surface of the inorganic layer and an opposite substantially planar major surface; bonding the substantially planar major surface of the structured adhesive layer to a major surface of an optical core configured to propagate image light along the optical core primarily by total internal reflection; and removing the temporary carrier from the first major surface of the inorganic layer.

[0065] Turning now to the drawings, Figure 1A and Figure 1B a side view of an embodiment of an optical waveguide according to the present specification. In Figure 1A , an embodiment of an optical system 300 is shown. In some embodiments, the optical system 300 includes an optical waveguide 200 and at least one light source 70 / 71.

[0066] In some embodiments, the optical waveguide 200 includes an optical core 30 and a multilayer grating 40. In some embodiments, the multilayer grating 40 may be disposed on the optical core 30 and configured to extract optical modes that would otherwise propagate along the optical core 30.

[0067] In some embodiments, the light source 70 / 71 may be arranged to inject light 20 / 21 having a first wavelength within the range of wavelengths visible (visible) to humans into the optical core 30, wherein the injected light 20 / 21 propagates as an optical mode along the optical core 30 in a first direction of the optical core 30 (e.g., in the direction along the x-axis, as Figure 1A shown). The light 20 / 21 propagates along the optical core 30 until the light impinges on the multilayer grating 40, where the light may enter the multilayer grating 40 and may be extracted from the optical core 30 (the light may be viewed by a viewer in the multilayer grating, not shown in Figure 1A but shown elsewhere herein). It should be noted that the first wavelength may also be outside the visible wavelength range (e.g., it may be an infrared wavelength).

[0068] In some embodiments, the multilayer grating 40 may include an adhesive layer 50 and an inorganic layer 60. In some embodiments, the adhesive layer 50 may include a main bottom surface 51 facing the optical core 30 and an opposite structured main top surface 52 facing away from the optical core 30 and spaced apart from the optical core. In some embodiments, the structured main top surface 52 may include a plurality of substantially parallel linear grating elements 53 that extend along the same length direction of the grating element 53 (e.g., the y-axis as Figure 1A shown) and are arranged along an orthogonal width direction of the grating element 53 (e.g., the x-axis as Figure 1A shown).

[0069] In some embodiments, the plurality of substantially parallel linear grating elements 53 form a periodic pattern along the width direction of the grating element 53 (e.g., the x-direction as Figure 1A shown). In some embodiments, the width direction of the grating element is substantially parallel to the first direction. In some such embodiments, the periodic pattern may have a period in the range of about 100 nm to about 1000 nm, or about 150 nm to about 750 nm, or about 200 nm to about 700 nm, or about 250 nm to about 600 nm, or about 300 nm to about 550 nm, or about 300 nm to about 500 nm or about 300 nm to about 450 nm.

[0070] In some embodiments, the optical core may have an average thickness t between about 100 microns and about 2000 microns, or between about 150 microns and about 1500 microns, or between about 200 microns and about 1250 microns, or between about 250 microns and about 1250 microns or between about 300 microns and about 1000 microns c . In some embodiments, the minimum spacing d between the optical core and the main top surface of the adhesive layer b is greater than about 5 nm, or greater than about 10 nm, or greater than about 15 nm, or greater than about 20 nm, or greater than about 25 nm, or greater than about 30 nm, or greater than about 35 nm, or greater than about 40 nm, or greater than about 45 nm or greater than about 50 nm.

[0071] In some embodiments, the inorganic layer 60 may be disposed on the structured main top surface 52 of the adhesive layer 50 and may conform to the structured main top surface such that the thickness standard deviation of the inorganic layer 60 is less than about 50%, or about 45%, or about 40%, or about 35%, or about 30%, or about 25% or about 20% of the average thickness of the inorganic layer 60. In some embodiments, the inorganic layer 60 may have a first main surface 61 facing away from the optical core 30 and a second main surface 62 facing the optical core 30 and substantially conforming to the main structured top surface 52 of the adhesive layer 50. In some embodiments, the inorganic layer 60 may define a plurality of alternating first recesses 63 and second recesses 64, wherein the first recesses 63 are recessed toward the optical core 30 and the second recesses 64 protrude toward the optical core 30. In some embodiments, the inorganic layer 60 may comprise titanium dioxide (TiO 2 ), zirconium oxide (ZrO x ), titanium oxide (TiO x ), SiO 2 , Al 2 O 3 , CeO 2 , ZnO, Nb 2 O 5 , Ta 2 O 5 , HfO 2 , SiAlO x N y , Si 3 N 4 , Nb-doped TiO 2 and zirconia (ZrO 2 ) or one or more of them.

[0072] In some embodiments, the multilayer grating 40 of the optical waveguide 200 may further include a cover layer 80 disposed on the inorganic layer 60 and substantially planarizing the inorganic layer. In some embodiments, at a first wavelength, the refractive index of the cover layer 80 may be at least 0.5 less than the refractive index of the inorganic layer 60.

[0073] Figure 1B Additional details regarding the adhesive layer 50 are shown. The adhesive layer 50 may be structured and include a main bottom surface 51 and an opposite main structured top surface 52. In some embodiments, the main structured top surface 52 may include a plurality of alternating ridges 54 and trenches 55. In some embodiments, the average spacing d between the bottom of the trench 55 and the optical core 30 a may be greater than about 5 nm, or about 10 nm, or about 15 nm, or about 20 nm, or about 25 nm, or about 30 nm, or about 35 nm, or about 40 nm, or about 45 nm or about 50 nm.

[0074] Figure 2 is a scanning electron microscope (SEM) image from a multilayer grating on an optical core according to an embodiment of the present specification. The multilayer grating 40 is disposed on the optical core 30. In Figure 2 the embodiment shown, the multilayer grating 40 includes an adhesive layer 50, an inorganic layer 60 conforming to the adhesive layer 50, and a cover layer 80 planarizing the top of the multilayer grating 40.

[0075] The inorganic layer 60 is disposed on the optical core 30 and defines a plurality of alternating first recesses 63 and second recesses 64. In this embodiment, the first recesses 63 are recessed toward the optical core 30, and the second recesses 64 are protruded toward the optical core 30. The structured adhesive layer 50 is disposed between the optical core 30 and the inorganic layer 60 and bonds the optical core to the inorganic layer such that the structured adhesive layer 50 substantially fills the first recesses 63.

[0076] For each pair of adjacent first recesses 63a and second recesses 64a, the first recess 63a and the second recess 64a are separated by a common sidewall 65 that extends from a first rounded sidewall corner 65a connecting the common sidewall 65 to the bottom 64a1 of the second recess 64a to an opposite second rounded sidewall corner 65b1 connecting the common sidewall 65 to the bottom 63a1 of the first recess 63a.

[0077] In a first plane cross-section substantially orthogonal to the common sidewall 65 (e.g., Figure 2In the xz plane shown in [description], the first rounded sidewall corner 65a includes an outer first circumferential surface 65a1 facing the optical core 30 and having a first radius of curvature R1, and the second rounded sidewall corner 65b includes an outer second circumferential surface 65b1 facing away from the optical core 30 and having a second radius of curvature R2, such that for at least multiple pairs of adjacent first recesses 63a and second recesses 64a, R1 is greater than R2.

[0078] Additionally, in the same first plane cross-section (i.e., the xz plane), the first rounded sidewall corner 65a has an inner first circumferential surface 65a2 facing away from the optical core and having a first inner radius of curvature R1', such that for at least multiple pairs of adjacent first recesses 63a and second recesses 64a, R1 is greater than R1'.

[0079] Figure 3 is a process flow illustrating an embodiment of a method of fabricating an optical waveguide having a multilayer grating according to this specification. The method may include steps A-J outlined herein. It should be noted that Figure 3 the flow of the process shown in [description] follows Figure 3 the arrows set between the respective steps in [description], and moves in a serpentine pattern from Figure 3 the top of [description] to Figure 3 the bottom of [description] (i.e., these steps are executed sequentially based on their alphabetical labels from step A to step J).

[0080] Provide a temporary carrier 90 having a master-structured surface 91 (step D), the master-structured surface having a plurality of alternating first ridges 92 and first trenches 93. In some embodiments, step D may include: providing a tool 100 having a master-structured surface 101 with a plurality of alternating ridges 102 and trenches 103 (step A); disposing a temporary carrier material 90a on the master-structured surface 101 of the tool 100 to form a temporary carrier 90 having a master-structured surface 91 that faces and is substantially conformal to the master-structured surface 101 of the tool 100 and includes a plurality of alternating first ridges 92 and first trenches 93 (step B); removing the temporary carrier 90 from the tool 100 (step C). In some embodiments, the temporary carrier 90 may include a separable substrate 97 for handling and / or transfer. In some embodiments, the landing area (labeled L in step D, representing the thickness between the bottom of one trench on the master-structured surface 91 and the opposite surface of the temporary carrier) may be less than 10 microns, or less than 5 microns, or less than 2 microns, or less than 1 micron or less than 0.5 microns thick.

[0081] In step E, the inorganic layer 60 is conformally disposed on the main structured surface 91 of the temporary carrier 90 such that both the first main surface 61 of the inorganic layer facing the temporary carrier 90 and the second main surface 62 of the inorganic layer facing away from the carrier 90 are substantially conformal to the main structured top surface 91 of the temporary carrier 90. In some embodiments, an average spacing S and a spacing standard deviation S may be defined between the first main surface 61 and the second main surface 62 of the inorganic layer 60 such that S / S is less than about 0.5, or about 0.4, or about 0.3, or about 0.2, or about 0.17, or about 0.15, or about 0.12 or about 0.1. In some embodiments, suitable deposition methods may include chemical vapor deposition (CVD) methods, sputtering coating methods, physical vapor deposition (PVD) methods, atomic layer deposition (ALD) methods, or any suitable combination thereof. avg and a spacing standard deviation S sd , such that S sd / S avg is less than about 0.5, or about 0.4, or about 0.3, or about 0.2, or about 0.17, or about 0.15, or about 0.12 or about 0.1. In some embodiments, suitable deposition methods may include chemical vapor deposition (CVD) methods, sputtering coating methods, physical vapor deposition (PVD) methods, atomic layer deposition (ALD) methods, or any suitable combination thereof.

[0082] In step F, an adhesive material layer is disposed on the second main surface 62 of the inorganic layer 60, and the adhesive material layer substantially planarizes the inorganic layer 60 to form a structured adhesive layer 50 having a main structured top surface 52 facing the second main surface 62 of the inorganic layer 60 and being substantially conformal thereto and an opposite substantially planar main surface 51.

[0083] In some embodiments, the adhesive material layer may be a polymeric or monomeric adhesive layer and / or may be an optically clear adhesive layer. Suitable optically clear adhesives include, but are not limited to, for example, those available from Norland Products Inc. (Cranbury, NJ). Other suitable adhesives include thermosetting materials such as those available under the trade name CYCLOTENE from Dow Chemical Company (Midland, MI). Still other suitable adhesives also include thermally activated adhesives such as those available under the trade name KRATON from KRATON Polymers (Huston, TX). Suitable adhesive layers, including thin adhesive layers (e.g., less than 50 nm thick) are described, for example, in the following U.S. patents: U.S. Patent 7,521,727 (Khanarian et al.); 7,53,419 (Camras et al.); U.S. Patent 6,709,883 (Yang et al.); and U.S. Patent 6,682,950 (Yang et al.).

[0084] In step G, a substantially planar major surface 51 of the structured adhesive layer 50 is bonded to a major surface 31 of the optical core 30, which is configured to propagate image light along the optical core primarily by total internal reflection. In step H, the separable substrate (if present) is removed from the temporary carrier 90. In step I, the temporary carrier 90 is removed from the first major surface 61 of the inorganic layer 60.

[0085] In some embodiments, a cover material may be disposed on the first major surface 61 of the inorganic layer 60 to substantially planarize the inorganic layer 60, thereby forming a structured cover layer 80 (step J). In some embodiments, the structured cover layer 80 may have a major structured surface 81 facing and substantially conforming to the first major surface 61 of the inorganic layer 60 and an opposite substantially planar major surface 82.

[0086] Figure 4 is a side view of an embodiment of an optical system having an optical waveguide characterized by at least a first micro-layer grating and a second micro-layer grating according to the present specification. In some embodiments, the optical system 400 includes an optical waveguide 305 (including a first multi-layer grating 40a, a second multi-layer grating 40b, and an optical core 30a) and an image projector 70a.

[0087] In some embodiments, the optical core 30a of the optical waveguide 305 may be configured to propagate light along the optical core by total internal reflection. In some embodiments, the spaced-apart first multi-layer grating 40a and second multi-layer grating 40b are disposed on the optical core 30a. In some embodiments, the first multi-layer grating 40a may be configured to receive image light 20 from the image projector 70a and direct at least a portion 21 of the received image light into the optical core 30a.

[0088] In some embodiments, the directed image light 21 propagates as propagating image light 22 along the optical core primarily by total internal reflection. In some embodiments, the second multi-layer grating 40b may be configured to receive at least a portion 23 of the propagating image light 22 and extract at least a portion 24 of the received directed image light from the optical core 30a for viewing by a viewer 55.

[0089] In some embodiments, each of the first multi-layer grating 40a and the second multi-layer grating 40b may include an inorganic relief layer 60a, 60b and a planarizing adhesive layer 50a, 50b. In some embodiments, the inorganic relief layers 60a, 60b may include opposite outermost relief major surfaces 61a, 61b, 62a, 62b, which are nested and aligned with each other along the width direction of the inorganic relief layers 60a, 60b (e.g., the x-axis as shown for 40a, or Figure 4 as shown for Figure 5has a wavy shape with respect to the x'-axis shown in 40b and forms a plurality of substantially parallel ridges 62a, 62b and grooves 63b, 63b. In some embodiments, the ridges 62a, 62b and grooves 63b, 63b extend along an orthogonal length direction of the inorganic undulating layers 60a, 60b (e.g., Figure 4 the y-axis of Figure 5 or the y'-axis of

[0090] In some embodiments, a planarizing adhesive layer 50a, 50b may be disposed between the inorganic undulating layers 60a, 60b and the optical core 30a, and may substantially planarize one of the undulating major surfaces 62a, 62b of the inorganic undulating layers 60a, 60b and bond the inorganic undulating layers 60a, 60b to the optical core 30a.

[0091] In some embodiments, for at least one of the first multilayer grating 40a and the second multilayer grating 40b, the multilayer grating may further include a planarizing cover layer 80a, 80b that conformally covers the inorganic undulating layers 60a, 60b contrary to the planarizing adhesive layer 50a, 50b and substantially planarizes the inorganic undulating layers 60a, 60b.

[0092] Figure 5 Provided Figure 4 is an alternative view of an embodiment of the optical waveguide provided. Unless otherwise specifically stated, Figure 4 and Figure 5 components with the same reference numerals in both should be assumed to have similar functions. That is, the description given for the components in Figure 4 should be assumed to apply to the components with the same reference numerals in Figure 5 and thus these descriptions may not be repeated in the description of Figure 5 . In some embodiments, the image light 20 is emitted by the image projector 70a and enters the optical core 30 via the first multilayer grating 40a. This image light propagates as propagating image light 22 (via total internal reflection within the optical core 30a) until at least a portion of the light is extracted from the optical core 30a via the second multilayer grating 40b as the extracted image light 24 for viewing by the viewer 55. As Figure 5 shown, the orientations (i.e., the width directions of the two gratings) of the first multilayer grating 40a and the second multilayer grating 40b may be different, as required by the application of guiding the image light in the appropriate direction. In some embodiments, the ridges and grooves of the first multilayer grating 40a may be aligned with the Figure 5 x-direction shown in Figure 5 the left side of Figure 5 and extend in that x-direction, while the ridges and grooves of the second multilayer grating 40b may be aligned with the Figure 5aligned to the right side) and extends in the x' direction.

[0093] Figure 6A and Figure 6B including embodiments of a multi-layer grating (such as Figure 4 and Figure 5 the multi-layer gratings 40a, 40b). A side view of the architecture of the embodiment can simultaneously inspect Figure 6A and Figure 6B for the following discussion. In some embodiments, at least one of the multi-layer gratings 40a, 40b may have a varying undulation amplitude A Figures 6A to 6B in the width direction thereof (e.g., the x direction as shown in m (e.g., the distance between the bottom of the trench and the top of the adjacent ridge). In some embodiments, the planarizing adhesive layers 50a, 50b may define a minimum distance d min between the inorganic undulation layer 60 and the optical core 30a such that d min is greater than about 5 nm, or about 10 nm, or about 15 nm, or about 20 nm, or about 25 nm, or about 30 nm, or about 35 nm, or about 40 nm, or about 45 nm or about 50 nm. In some embodiments, for at least one of the first multi-layer grating 40a and the second multi-layer grating 40b, the minimum spacing d between the optical core 30a and the bottom of the trench of the multi-layer gratings 40a, 40b may vary along the width of the multi-layer gratings 40a, 40b.

[0094] In some embodiments, for at least one of the first multi-layer grating 40a and the second multi-layer grating 40b, in a plane cross-section (e.g., the xz plane as shown in Figures 6A to 6B ) orthogonal to the length direction (e.g., the y-axis) of the multi-layer gratings 40a, 40b, and for two different positions L1 and L2 on the multi-layer grating, each position including a single ridge and a single directly adjacent trench, where the area between the optical core and the ridge at L1 is A r1 , the area between the optical core and the trench at L1 is A g1 , the area between the optical core and the ridge at L2 is A r2 , and the area between the optical core and the trench at L2 is A g2 , A r1 + A g1 differs from A r2 + A g2 by within 30% of A r2 + A g2 , or within 30% of A r2 + A g2 , or within 10% of A r2 + A g2 + Ar2 +A g2 within 5% of or at A r2 +A g2 within 2% of. Figure 7 is a side view of an alternative embodiment of an optical system that includes an optical waveguide having a first multilayer grating and a second multilayer grating disposed on opposite sides of an optical core. Figure 7 The embodiment shown is similar to the Figure 4 embodiment shown elsewhere herein. Accordingly, unless otherwise specifically stated, components with the same reference numerals in both figures should be assumed to have the same function and may not be repeated in the Figure 7 discussion from Figure 4 the discussion of Figure 7 In the embodiment of Figure 4 the spaced-apart first multilayer grating 40a and second multilayer grating 40b are disposed on two opposite major sides 11a and 11b of the optical core 30a (different from being located on the same major side as shown in Figure 7 The basic function of the optical waveguide 305 of Figure 4 is substantially the same as the basic function of the optical waveguide 305 of

[0095] Figure 8 is a side view of another alternative embodiment of the optical waveguide 305 and also shares components with the same reference numerals with both Figure 4 and Figure 7 Accordingly, unless otherwise specifically stated, these components with the same reference numerals should be assumed to have similar functions. In Figure 8In an embodiment of the optical waveguide 305, the optical waveguide 305 further includes a connecting adhesive portion 110 disposed between and continuously and seamlessly connecting the planarizing adhesive layers 50a, 50b of the first multilayer grating 40a and the second multilayer grating 40b. In some embodiments, the optical waveguide 305 further includes a substantially non-rippled inorganic layer 111 for connection, which is disposed between and continuously and seamlessly connects the inorganic rippled layers 60a, 60b of the first multilayer grating 40a and the second multilayer grating 40b. In some embodiments, wherein each of the first multilayer grating 40a and the second multilayer grating 40b further includes planarizing cover layers 80a, 80b that conformally cover the inorganic rippled layers 60a, 60b opposite to the planarizing adhesive layers 50a, 50b and substantially planarize the inorganic rippled layers 60a, 60b, the optical waveguide 305 may further include a substantially planar connecting cover layer 112 disposed between and continuously and seamlessly connecting the planarizing cover layers 80a, 80b of the first multilayer grating 40a and the second multilayer grating 40b. In some such embodiments, for at least one visible wavelength in the range of visible wavelengths extending from about 420 nm to about 680 nm, the refractive index of the planarizing cover layers 112, 80a, 80b is at least 0.5 less than the refractive index of the inorganic rippled layers 60a, 60b.

[0096] Figure 9A and Figure 9B Top and side views of another embodiment of the optical waveguide are provided, respectively. It should be checked simultaneously Figure 9A and Figure 9B for the following discussion. In some embodiments, the optical waveguide 310 may include an optical core 30a configured to propagate image light therethrough and a continuous seamless multilayer 40s disposed on the main side surface 11a of the optical core 30a. In some embodiments, the continuous seamless multilayer 40s may include a continuous seamless inorganic layer 60 and a continuous seamless adhesive layer 50.

[0097] In some embodiments, the continuous seamless inorganic layer 60 may have a plurality of discrete spaced-apart regions 100a, 100b, 100c in the inorganic layer 60 ( Figure 9B) undulates to form a plurality of spaced-apart undulating inorganic layer portions 60a, 60b, 60c of the originally non-undulating inorganic layer 60. In some embodiments, each of the undulating inorganic layer portions 60a, 60b, 60c may include opposite outermost undulating major surfaces 61a, 61b, 61c; 62a, 62b, 62c, which are nested and aligned with each other, and form a plurality of substantially parallel ridges 63a, 63b, 63c and grooves 64a, 64b, 64c of the undulating inorganic layer portions 60a, 60b, 60c, and these plurality of substantially parallel ridges and grooves extend along the length direction of the undulating inorganic layer portions 60a, 60b, 60c (see, for example Figure 9A depicted by the y-axis, y'-axis, and y''-axis in

[0098] In some embodiments, a continuous seamless adhesive layer 50 may be disposed between the inorganic layer 60 and the optical core 30a and may be substantially conformal to the ridges 63 and grooves 64 of each of the undulating inorganic layer portions 60a, 60b, 60c and bond the inorganic layer 60 to the optical core 30a.

[0099] In some embodiments, the first undulating inorganic layer portion 40a may be configured to receive image light 20 from the image projector 70a and direct at least a portion 21 of the received image light into the optical core 30a. In some embodiments, the directed image light 21 may propagate along the optical core 30a mainly by total internal reflection.

[0100] In some embodiments, the second undulating inorganic layer portion 40c may be configured to receive at least a portion 25 of the directed image light 21 received along the first direction 25a and redirect the directed image light as redirected image light 26 that propagates along the optical core 30a mainly by total internal reflection in a different second direction 26a.

[0101] In some embodiments, the third undulating inorganic layer portion 40b may be configured to receive at least a portion 27 of the redirected image light and extract at least a portion 24 of the received redirected image light from the optical core 30a for viewing by the viewer 55.

[0102] Figure 10A and Figure 10B Illustrative examples of alternative shapes of features on the multilayer grating are provided. Figure 10AShows a multilayer grating 40c disposed on an optical core 30. In some embodiments, the multilayer grating 40c may include an adhesive layer 50 and an inorganic layer 60. In some embodiments, the inorganic layer 60 may define a plurality of alternating first recesses 63 and second recesses 64, where the first recesses 63 are recessed toward the optical core 30 and the second recesses 64 protrude toward the optical core 30. In Figure 10A embodiment 40c, the first recesses 63 and the second recesses 64 may have an inclined square wave shape. In Figure 10B , the plurality of alternating first recesses 63 and second recesses 64 of the multilayer grating 40d may have a triangular or "blazed" shape.

[0103] Although the examples discussed herein have thus far shown one-dimensional relief patterns, multilayer gratings exhibiting two-dimensional feature arrays are also within the scope of this specification. For example, Figure 11A shows an example of a grating 40e that exhibits a two-dimensional array of columns comparable to ridges 63, and the area between the columns is similar to trenches 64. Similarly, Figure 11B shows a grating 40f having a two-dimensional array of holes, where each hole is functionally similar to trench 64 and the area between the holes is comparable to ridge 63. In Figure 11A and Figure 11B both, the cross-sections of the gratings 40e and 40f (disposed on the optical core 30) shown in the figures illustrate the same relief pattern of the inorganic layer 60 and the adhesive layer 50.

[0104] As discussed elsewhere herein, the ridges and trenches (or first and second recesses) of the multilayer gratings discussed herein may have any suitable shape. Figure 10A , Figure 10B , Figure 11A and Figure 11B embodiments are merely examples and are not intended to be limiting in any way.

[0105] Finally, Figure 12 is an illustrative example of a possible method according to this specification for measuring dimensions on the relief layer of a multilayer grating. For example, one method of measuring the thickness of the relief inorganic layer is to make multiple measurements of the distance between the first major surface and the second major surface of the inorganic layer 60, such as Figure 12 the measurements s1 to s8 shown in. One way to do this is to randomly select a plurality of points on the first major surface 61 of the inorganic layer 60 and then draw straight lines to the closest corresponding points on the second major surface 62. Then the average spacing S avg is determined by taking the average of these measurements, and the spacing standard deviation S sd is determined.

[0106] Embodiment

[0107] Substrate with separated packages

[0108] The substrate with the release package is prepared by depositing the release package on an ST504 PET film according to the method described in co-pending U.S. Patent Application No. 63 / 265,650, filed Dec. 17, 2021 (Gotrik et al.). The acrylate coating that serves as the first layer of the release package on SiAlO x is prepared on a roll-to-roll vacuum coater similar to the coater described in U.S. Patent Application 2010 / 0316852 (Condo et al.) by adding a second evaporator and a curing system between a plasma pretreatment station and a first sputtering system and using an evaporator as described in U.S. Patent No. 8,658,248 (Anderson et al.).

[0109] The coater is equipped with a substrate in the form of an infinitely long roll of ST504 that is 0.05 mm thick and 9 inches (22.86 cm) wide. The substrate is prepared for coating by subjecting it to nitrogen plasma treatment to improve the adhesion of the planarizing acrylate layer to the PET. Using a titanium cathode, a web speed of 8.0 meters per minute is used and the back side of the film is kept in contact with a coating drum cooled to 0 °C, and the film is treated with nitrogen plasma operating at 50 W.

[0110] On the prepared ST504 PET substrate, a planarizing acrylate layer of SR833 is formed. The acrylate layer is applied by ultrasonic atomization and flash evaporation, with the coating width being 9 inches (22.68 cm). The flow rate of the mixture into the atomizer is 0.67 ml / min, resulting in a layer that is 375 nm thick, the gas flow rate is 60 standard cubic centimeters per minute (SCCM), and the evaporator temperature is 260 °C. Once condensed onto the PET substrate, the monomer coating is immediately cured with an electron beam curing gun operating at 7.0 kV and 4.0 mA.

[0111] SiAlO x The release layer of is deposited in-line with the previous acrylate coating step. The silicon aluminum oxide layer is laid down from a SiAl target using an AC reactive sputter deposition process employing a 40 kHz alternating current (AC) power supply. During sputtering, the voltage of the cathode is controlled by a feedback control loop that monitors the voltage and controls the oxygen flow rate such that the voltage remains constant. The system is operated at a power of 16 kW to deposit an 11 nm thick silicon aluminum oxide layer onto the planarizing organic acrylate layer.

[0112] The transferable acrylate layer (release package) of SR833 is with the previous SiAlO xDeposition On-line deposition. An acrylate layer is applied by ultrasonic atomization and flash evaporation, with a coating width of 9 inches (22.68 cm). The flow rate of the mixture into the atomizer is 0.67 ml / min, resulting in a layer of 375 nm, a gas flow rate of 60 standard cubic centimeters per minute (SCCM), and an evaporator temperature of 260 °C. Once condensed onto the SiAlO x layer, the monomer coating is immediately cured with an electron beam curing gun operating at 7.0 kV and 4.0 mA.

[0113] Nanostructured mold film

[0114] The nanostructured mold film is prepared by spin-coating a photocurable acrylate resin mixture (prepared by combining and mixing PHOTOMER 6210, SR238, SR351, and TPO in a weight ratio of 60 / 20 / 20 / 0.5) onto a ST505 film. The coated film is pressed against a nanostructured nickel surface, which is attached to a steel roller controlled at a speed of 15.2 meters per minute using a rubber-covered roller at 60 °C. The nanostructured nickel surface consists of sub-wavelength gratings arranged in a 2D exit pupil expander pattern. The pattern has three grating regions, which serve as an input coupler, an exit pupil expander, and an output coupler when attached to an appropriate substrate.

[0115] The coating thickness of the acrylate resin mixture on the film is sufficient to completely wet the nickel surface, and a rolling bead of resin is formed when the coated film is pressed against the nanostructured nickel surface. The film is exposed to radiation from a two-Fusion UV lamp system equipped with D bulbs (obtained from Fusion UV Systems, Gaithersburg, MD under the trade name "F600"), both bulbs operating at 142 W / cm while in contact with the nanostructured nickel surface. After peeling the film from the nanostructured nickel surface, the nanostructured side of the film is again exposed to radiation from a single-Fusion UV lamp system.

[0116] A silicone release film layer assembled according to the methods described in U.S. Patent Nos. 6,696,157 (David et al.) and 8,664,323 (Iyer et al.) and U.S. Patent Application Publication No. 2013 / 0229378 (Iyer et al.) is applied to the nanostructured mold film in a parallel plate capacitively coupled plasma reactor. The chamber has a central cylindrical energized electrode with a surface area of 1.7 m 2 (18.3 ft 2 ).

[0117] Place the nanostructured mold on the energized electrode and pump down the reaction chamber to a base pressure of less than 1.3 Pa (2 mTorr). Allow O 2 gas to flow into the chamber at a rate of 1000 SCCM. The treatment is carried out using a plasma-enhanced CVD method by coupling radio frequency (RF) power to the reactor at a frequency of 13.56 MHz and an applied power of 2000 watts. The treatment time is controlled by moving the nanostructured mold film through the reaction zone at a rate of 9.1 meters per minute (30 ft / min), resulting in an exposure time of approximately 10 seconds. After completion of the deposition, the RF power is turned off and the gas is evacuated from the reactor.

[0118] After the first treatment, a second plasma treatment is carried out in the same reactor without returning the reaction chamber to atmospheric pressure. Allow HMDSO gas to flow into the chamber at approximately 1750 SCCM to achieve a pressure of 9 mTorr. Subsequently, 13.56 MHz RF power is coupled to the reactor at an applied power of 1000 W. Then the film is transported through the reaction zone at a rate of 9.1 meters per minute (30 ft / min), resulting in an exposure time of approximately 10 seconds. At the end of this treatment time, the RF power and gas supply are stopped, the chamber is returned to atmospheric pressure, and the release-treated nanostructured mold film is removed from the chamber.

[0119] Template substrate

[0120] The substrate with the release package is corona-treated at an energy density of 1,000 J / cm^2. An acrylate solution is prepared by adding 74 wt% PHOTOMER 6210, 25 wt% SR238, and 0.014% TPO to produce acrylate resin A. Acrylate resin A is diluted to obtain a solution of 10 wt% acrylate resin A, 54 wt% PGME, and 36% MEK. The diluted solution is slot-coated onto the corona-treated substrate at a rate of 3 meters per minute with the release package. The solution is coated 10.16 cm wide and pumped at a rate of 3 SCCM using an injection pump (Harvard Apparatus, Holliston, MA, USA).

[0121] Then, the film is dried for 3 minutes under ambient conditions before entering the nip. At the nip, the coated substrate layer with the release package is laminated onto the release-treated nanostructured mold film produced in the previous step.

[0122] The nip consists of a rubber roll with a hardness of 90 and a steel roll set at 54 °C. The nip is engaged by two Bimba cylinders (Bimba, University Park, IL) pressurized to 0.55 MPa.

[0123] The coated acrylate solution is cured using a Fusion D lamp (Fusion UV Systems, Gaithersburg, MD), and the cured acrylate mixture is separated from the release-treated template film, leaving a cured acrylate coating with sub-wavelength grating replicas on the substrate with the separation package. The web tension is set to approximately 0.0057 N / m.

[0124] Transfer film

[0125] An exemplary transfer film is prepared by depositing a high refractive index (n ~ 2.4) TiO x layer onto the above template substrate using a sputter coater. Three TiO x targets powered by 3 kW are used to deposit 15 nm of TiO 2 in four sequential passes at 0.9 m / min using a DC reactive process with an argon / oxygen gas mixture (approx. 2% O x ), to produce a nominally 60 nm thick TiO x layer (after deposition, x is approximately equal to 2). The transferable acrylate film with the TiO x coating has a nominal thickness of 350 nm - 550 nm.

[0126] Individual patterns are cut out from the transfer film roll. The FG1901 thin layer is applied onto the TiO x surface by spin coating at 200 rpm for 5 seconds in a 0.48% solids in cyclohexane / toluene dilution (by weight 9.05%:90.95%), followed by spin coating at 4000 rpm for 30 seconds to obtain a layer approximately 45 nanometers thick.

[0127] Waveguide

[0128] The above adhesive-coated TiO x / The grating is laminated onto the high refractive index glass wafer by placing the paired substrates in a 120 mm CNI nanoimprint tool (NIL Technologies ApS, Lyngby, Denmark) at a temperature of 140°C and a pressure of 6 bar for 5 minutes. Once the laminate pair has cooled to room temperature, the template substrate is pulled away from the surface of the glass wafer, thereby initiating cracks at the separation interface between the carrier substrate and the transferred acrylate. This results in the transferred acrylate and TiO x / grating remaining on the glass wafer.

[0129] The remaining acrylate template is removed from the TiO 2 grating by performing O x plasma etching for 140 minutes at 500 W and an oxygen pressure of 230 mTorr using a 40 kHz YES G-1000 plasma system (Yield Engineering Systems, Fremont, CA).

[0130] The completed waveguide is irradiated with a projector (VenusIII 40D, Coretronic Corporation, Hsinchu, Taiwan, China) directed onto the input coupler grating, and the image is observed at the output coupler to confirm that the completed waveguide functions as an image storage waveguide.

[0131] Material

[0132]

[0133]

[0134] Terms such as "about" will be understood in the context in which they are used and described by those of ordinary skill in the art in this specification. If it is not clear to those of ordinary skill in the art in the context in which they are used and described in this specification how "about" applies to the use of quantities expressing feature sizes, amounts, and physical properties, then "about" will be understood to mean within 10% of the specified value. A quantity given as about a specified value may precisely be the specified value. For example, if it is not clear to those of ordinary skill in the art in the context in which they are used and described in this specification, a quantity having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and the value may be 1.

[0135] One of ordinary skill in the art will understand terms such as "substantially" in the context in which they are used and described in this specification. If the use of "substantially equal" is not clear to one of ordinary skill in the art in the context in which it is used and described in this specification, then "substantially equal" will mean approximately the case of about as described above. If the use of "substantially parallel" is not clear to one of ordinary skill in the art in the context in which it is used and described in this specification, then "substantially parallel" will mean within 30 degrees of being parallel. In some embodiments, directions or surfaces described as being substantially parallel to each other may be within 20 degrees or 10 degrees of being parallel, or may be parallel or nominally parallel. If the use of "substantially aligned" is not clear to one of ordinary skill in the art in the context in which it is used and described in this specification, then "substantially aligned" will mean being aligned within 20% of the width of the object being aligned. In some embodiments, objects described as being substantially aligned may be aligned within 10% or 5% of the width of the object being aligned.

[0136] All of the above-cited references, patents, and patent applications are hereby incorporated by reference in their entirety in a consistent manner. In the event of any inconsistencies or contradictions between the incorporated reference sections and this application, the information in the foregoing description shall control.

[0137] Unless otherwise indicated, the description of an element in the figures shall be understood to apply equally to the corresponding elements in other figures. While specific embodiments have been illustrated and described herein, one of ordinary skill in the art will appreciate that many alternative and / or equivalent specific implementations may be used in place of the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any modifications or variations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. An optical waveguide, the optical waveguide comprising: an optical core configured to propagate image light along the optical core; and a first multi-layer grating and a second multi-layer grating, the first multi-layer grating and the second multi-layer grating being disposed on the optical core, the first multi-layer grating being configured to receive image light from an image projector and direct at least a portion of the received image light into the optical core, the directed image light propagating along the optical core mainly by total internal reflection, the second multi-layer grating being configured to receive at least a portion of the directed image light and extract at least a portion of the received directed image light from the optical core for viewing by a viewer, each of the first multi-layer grating and the second multi-layer grating comprising: an inorganic undulating layer including two opposite outermost undulating main surfaces, the undulating main surfaces being aligned nestedly with each other to have a wavy shape in the width direction of the inorganic undulating layer and forming a plurality of substantially parallel ridges and grooves, the ridges and the grooves extending in an orthogonal length direction of the inorganic undulating layer; and a planarizing adhesive layer disposed between the inorganic undulating layer and the optical core and substantially planarizing one of the undulating main surfaces of the inorganic undulating layer and bonding the inorganic undulating layer to the optical core.

2. The optical waveguide according to claim 1, wherein the first multi-layer grating and the second multi-layer grating have different width directions.

3. The optical waveguide according to claim 1, wherein the undulation amplitude of at least one of the first multi-layer grating and the second multi-layer grating varies along its width direction.

4. The optical waveguide according to claim 1, wherein the planarizing adhesive layer defines a minimum distance d between the inorganic undulating layer and the optical core min , and wherein d min > 5 nm.

5. The optical waveguide according to claim 1, wherein for at least one of the first multi-layer grating and the second multi-layer grating, the minimum spacing between the optical core and the grooves of the multi-layer grating changes along the width of the multi-layer grating.

6. The optical waveguide according to claim 1, wherein for at least one of the first multilayer grating and the second multilayer grating, in a plane cross-section of the multilayer grating orthogonal to the length direction of the multilayer grating, and for two different positions L1 and L2 on the multilayer grating, each position including a ridge and a directly adjacent trench, wherein the area between the optical core and the ridge at L1 is A r1 , the area between the optical core and the trench at L1 is A g1 , the area between the optical core and the ridge at L2 is A r2 , and the area between the optical core and the trench at L2 is A g2 , A r1 +A g1 differs from A r2 +A g2 by within 30% of A r2 +A g2 .

7. The optical waveguide according to claim 1, wherein for at least one of the first multi-layer grating and the second multi-layer grating, the multi-layer grating further comprises a planarizing cover layer that conformally covers the inorganic undulating layer opposite to the planarizing adhesive layer and substantially planarizes the inorganic undulating layer.

8. The optical waveguide according to claim 1, wherein the first multi-layer grating and the second multi-layer grating are disposed on two opposite main side surfaces of the optical core.

9. The optical waveguide according to claim 1, the optical waveguide further comprising: a connecting adhesive portion disposed between the planarizing adhesive layers of the first multi-layer grating and the second multi-layer grating and continuously and seamlessly connecting the planarizing adhesive layers.

10. The optical waveguide according to claim 1, the optical waveguide further comprising: a connecting substantially non-undulating inorganic layer disposed between the inorganic undulating layers of the first multi-layer grating and the second multi-layer grating and continuously and seamlessly connecting the inorganic undulating layers.

11. The optical waveguide according to claim 1, wherein each of the first multilayer grating and the second multilayer grating further includes a planarizing cover layer that conformally covers the inorganic undulating layer opposite to the planarizing adhesive layer and substantially planarizes the inorganic undulating layer, and wherein the optical waveguide further includes a substantially planar connecting cover layer that is disposed between the planarizing cover layers of the first multilayer grating and the second multilayer grating and continuously and seamlessly connects the planarizing cover layers.

12. The optical waveguide according to claim 11, wherein for at least one visible wavelength in the visible wavelength range extending from about 420 nm to about 680 nm, the refractive index of the planarizing cover layer is at least 0.5 less than the refractive index of the inorganic undulating layer.

13. The optical waveguide according to claim 1, wherein the inorganic undulating layer contains titanium dioxide (TiO 2 ), zirconium oxide (ZrO x ), titanium oxide (TiO x ), SiO 2 , Al 2 O 3 , CeO 2 , ZnO, Nb 2 O 5 , Ta 2 O 5 , HfO 2 , SiAlO x N y , Si 3 N 4 , Nb-doped TiO 2 and ZrO 2 or one or more of them.

14. An optical system, the optical system comprising: The optical waveguide according to claim 1 and the image projector configured to emit the image light, wherein the first multilayer grating is configured to receive the emitted image light and direct at least a portion of the received image light into the optical core.

15. The optical waveguide according to claim 1, wherein for at least one visible wavelength in the visible wavelength range extending from about 420 nm to about 680 nm, the planarizing adhesive layer has a refractive index between about 1.35 and about 2.

5.

16. The optical waveguide according to claim 1, wherein for at least one visible wavelength in the visible wavelength range extending from about 420 nm to about 680 nm, the planarizing adhesive layer has a refractive index of about 1.

5.

17. The optical waveguide according to claim 1, wherein the minimum spacing between the optical core and the plurality of substantially parallel ridges and grooves is greater than about 5 nm.

18. The optical waveguide according to claim 1, wherein the average spacing between the grooves and the optical core is less than about 500 nm.

19. An optical waveguide, the optical waveguide comprising: An optical core configured to propagate image light along the optical core; And a continuous seamless multilayer disposed on a main side of the optical core and including: A continuous seamless inorganic layer that undulates in a plurality of discrete spaced-apart regions of the inorganic layer to form a plurality of spaced-apart undulating inorganic layer portions of the originally non-undulating inorganic layer, each of the undulating inorganic layer portions including two opposite outermost undulating main surfaces that are nested and aligned with each other, and forming a plurality of substantially parallel ridges and grooves that extend along the length direction of the undulating inorganic layer portion and are arranged in the orthogonal width direction of the undulating inorganic layer portion; and A continuous seamless adhesive layer disposed between the inorganic layer and the optical core and substantially conforming to the ridges and the grooves of each of the undulating inorganic layer portions and bonding the inorganic layer to the optical core, wherein: The first undulating inorganic layer portion in the undulating inorganic layer portion is configured to receive image light from an image projector and direct at least a portion of the received image light into the optical core, and the directed image light propagates along the optical core mainly by total internal reflection; The second undulating inorganic layer portion in the undulating inorganic layer portion is configured to receive at least a portion of the directed image light received along a first direction and redirect the directed image light into redirected image light that mainly propagates along the optical core in a different second direction by total internal reflection; and The third undulating inorganic layer portion in the undulating inorganic layer portion is configured to receive at least a portion of the redirected image light and extract at least a portion of the received redirected image light from the optical core for viewing by a viewer.

20. A method of fabricating an optical waveguide, the method of fabricating an optical waveguide comprising: providing a temporary carrier including a main structured surface that includes a plurality of alternating first ridges and first trenches in a plurality of discrete spaced-apart regions; The inorganic layer is conformally disposed on the main structured surface of the temporary carrier such that both the first main surface of the inorganic layer facing the temporary carrier and the second main surface of the inorganic layer facing away from the carrier are substantially conformal to the main structured top surface of the temporary carrier to form a continuous seamless inorganic layer having a plurality of undulating inorganic layer portions in an otherwise non-undulating inorganic layer, such that in each of the undulating inorganic layer portions of the undulating inorganic layer portions, an average spacing value S is defined between the first main surface and the second main surface of the layer portion avg and a spacing standard deviation S sd such that S sd / S avg is less than about 0.5; coating the second main surface of the inorganic layer substantially conformally with an adhesive layer and substantially planarizing the inorganic layer to form a structured adhesive layer having a main structured top surface facing and substantially conforming to the second main surface of the inorganic layer and an opposite substantially planar main surface; bonding the substantially planar main surface of the structured adhesive layer to a main surface of an optical core configured to propagate image light along the optical core mainly by total internal reflection; and removing the temporary carrier from the first main surface of the inorganic layer.

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