Transfer films, optical films, optical waveguides and methods of making same

Abstract

A transfer film includes a release liner having a release surface and an optical film disposed on the release surface. The optical film includes an acrylate layer disposed on the release surface and having an average thickness in a range of about 10 to 1500 nm; a multilayer antireflective stack disposed on the acrylate layer opposite the release liner; and a multilayer grating disposed on the multilayer antireflective stack opposite the acrylate layer. An optical waveguide can be made by transferring the optical film from the transfer film to an optical core and then removing the release liner. The acrylate layer may be removed from the multilayer antireflective stack after the optical film has been transferred to the optical core.

Description

[0001] TRANSFER FILMS, OPTICAL FILMS, OPTICAL WAVEGUIDES AND METHODS OF MAKING SAME

[0002] TECHNICAL FIELD

[0003] The present description relates generally to optical film disposed on optical waveguides.

[0004] BACKGROUND

[0005] An optical waveguide can be configured to propagate light therealong primarily by total internal reflection.

[0006] SUMMARY

[0007] In some aspects, the present description provides a transfer film including a release liner having a release surface and an optical film disposed on the release surface. The optical film includes an acrylate layer disposed on the release surface and having an average thickness that can be in a range of about 10 to 1500 nm; a multilayer antireflective stack disposed on the acrylate layer opposite the release liner; and a multilayer grating disposed on the multilayer antireflective stack opposite the acrylate layer. An optical waveguide can be made by transferring the optical film from the transfer film to an optical core and then removing the release liner. The acrylate layer may be removed from the multilayer antireflective stack after the optical film has been transferred to the optical core.

[0008] In some aspects, the present description provides a transfer film including a release liner having a release surface; an acrylate layer disposed on the release surface and having an average thickness in a range of about 10 nm to about 1500 nm; a multilayer antireflective stack disposed on the acrylate layer opposite the release liner; and a multilayer grating disposed on the multilayer antireflective stack opposite the acrylate layer.

[0009] In some aspects, the present description provides an optical film including a multilayer grating including first and second layers, where each of the first and second layers has a structured first major surface and an opposite second major surface; and a multilayer antireflective stack disposed directly on, and substantially coextensive with, the second major surface of the first layer. The first major surfaces of the first and second layers are disposed on and substantially conform to one another. The second major surface of the first layer can be substantially smooth. The multilayer antireflective stack can include a plurality of inorganic A layers, where each A layer has a same first composition, and where the A layers of each pair of adjacent A layers are separated by at least one layer having a composition different from the first composition. The multilayer antireflective stack can include first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack, with the first A layer disposed between the multilayer grating and the second A layer. An average grain size of the first A layer can be greater than an average grain size of the second A layer. In some aspects, the present description provides an optical film including a multilayer grating including first and second layers, where each of the first and second layers has a structured first major surface and an opposite second major surface; and a multilayer antireflective stack disposed directly on, and substantially coextensive with, the second major surface of the first layer. The first major surfaces of the first and second layers are disposed on and substantially conform to one another. The second major surface of the first layer can be substantially smooth. An average minimum distance between the structured first major surface of the first layer and the multilayer antireflective stack is less than about 500 nm.

[0010] In some aspects, the present description provides a method of making a transfer film. The method includes, in sequence: disposing an acrylate layer on a release surface of a release liner, where the acrylate layer has an average thickness in a range of about 10 to 1500 nm; disposing a multilayer antireflective stack on the acrylate layer; and disposing a radiation-cured layer on the multilayer antireflective stack, where the radiation-cured layer has a major structured surface facing away from the multilayer antireflective stack, and where the major structured surface includes a plurality of alternating first ridges and first grooves.

[0011] In some aspects of the present description, an optical waveguide is provided, the optical waveguide including an optical core configured to propagate an optical mode at a first wavelength therealong, and a multilayer grating disposed on the optical core and configured to extract the optical mode that would otherwise propagate along the optical core along a first direction. The multilayer grating includes an adhesive layer and an inorganic layer. The adhesive layer has a major bottom surface facing the optical core and an opposing structured major top surface facing away and spaced apart from the optical core. The structured major top surface includes a plurality of substantially parallel linear grating elements extending along a same length direction of the grating elements and arranged along an orthogonal width direction of the grating elements. The inorganic layer is disposed on and conforms to the structured major top surface of the adhesive layer so that the inorganic layer has a thickness standard deviation that is less than about 50% of an average thickness of the inorganic layer. The optical waveguide can include a multilayer antireflective stack where the multilayer grating is disposed between the multilayer antireflective stack and the optical core.

[0012] In some aspects of the present description, an optical waveguide is provided, the optical waveguide including an optical core configured to propagate an image light therealong primarily by total internal reflection, a structured adhesive layer, and an inorganic layer. The structured adhesive layer includes a major bottom surface facing, and bonded to, the optical core and an opposing major structured top surface having a plurality of alternating ridges and grooves. An average spacing between the grooves and the optical core is greater than about 5 nm. The inorganic layer is conformally disposed on the major structured top surface of the structured adhesive layer so that opposing first and second major surfaces of the inorganic layer substantially conform to the major structured top surface of the structured adhesive layer and define an average spacing of between about 10 nm to about 100 nm therebetween. The optical waveguide can include a multilayer antireflective stack where the inorganic layer is disposed between the multilayer antireflective stack and the optical core.

[0013] In some aspects of the present description, an optical waveguide is provided, the optical waveguide including an optical core configured to propagate an image light therealong primarily by total internal reflection, and inorganic layer, and a structured adhesive layer. The inorganic layer is disposed on the optical core and defines a plurality of alternating first and second concavities. The first concavities are concave toward the optical core, and the second concavities are convex toward the optical core. The structured adhesive layer is disposed between and bonding the optical core to the inorganic layer, and substantially fills the first concavities. For each pair of adjacent first and second concavities, the first and second concavities are separated by a common side wall extending from a first rounded side wall comer joining the common side wall to a bottom of the second concavity to an opposite second rounded side wall comer joining the common side wall to a bottom of the first concavity. In a first planar cross-section substantially orthogonal to the common side wall, the first rounded side wall comer includes an outer first circumferential surface facing the optical core and having a first radius of curvature Rl, and the second rounded side wall comer having an outer second circumferential surface facing away from the optical core and having a second radius of curvature R2, such that Rl > R2 for at least a plurality of pairs of adjacent first and second concavities. The optical waveguide can include a multilayer antireflective stack where the inorganic layer is disposed between the multilayer antireflective stack and the optical core.

[0014] In some aspects of the present description, an optical waveguide is provided, the optical waveguide including an optical core configured to propagate an image light therealong primarily by total internal reflection, an inorganic layer, and a stmctured adhesive layer. The inorganic layer is disposed on the optical core and defines a plurality of alternating first and second concavities. The first concavities are concave toward the optical core, and the second concavities are convex toward the optical core. The stmctured adhesive layer is disposed between and bonding the optical core to the inorganic layer. The stmctured adhesive layer substantially fills the first concavities. For each pair of adjacent first and second concavities, the first and second concavities are separated by a common side wall extending from a first rounded side wall comer joining the common side wall to a bottom of the second concavity to an opposite second rounded side wall comer joining the common side wall to a bottom of the first concavity. The first rounded side wall comer is closer to the optical core and the second rounded side wall comer is farther from the optical core. In a first planar cross-section substantially orthogonal to the common side wall, the first rounded side wall comer includes an outer first circumferential surface facing the optical core and having a first outer radius of curvature Rl, and an inner first circumferential surface facing away from the optical core and having a first inner radius of curvature Rl ’, wherein Rl > Rl ’ for at least a plurality of pairs of adjacent first and second concavities. The optical waveguide can include a multilayer antireflective stack where the inorganic layer is disposed between the multilayer antireflective stack and the optical core. In some aspects of the present description, a method of making an optical waveguide is provided, the method including providing a carrier including an acylate layer, a multilayer antireflective stack disposed on the acrylate layer, and a radiation-cured layer disposed on the multilayer antireflective stack where the radiation-cured layer has a major structured surface facing away from the multilayer antireflective stack and having a plurality of alternating first ridges and first grooves; conformally disposing an inorganic layer on the major structured surface of the radiation-cured layer so that both a first major surface thereof facing the carrier and a second major surface thereof facing away from the carrier substantially conform to the major structured surface of the radiation-cured layer. The first and second major surfaces of the inorganic layer define a spacing average Savgand a spacing standard of deviation Ssd therebetween, such that Ssd / Savg is less than about 0.5 disposing an adhesive layer on the second major surface of the inorganic 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 opposing substantially planar major surface; and adhering the substantially planar major surface of the structured adhesive layer to a major surface of an optical core configured to propagate an image light therealong primarily by total internal reflection.

[0015] In some aspects of the present description, an optical waveguide is provided, the optical waveguide including an optical core configured to propagate an image light therealong, and first and second multilayer gratings disposed on the optical core. The first multilayer grating is configured to receive an image light from an image projector and inject at least a portion of the received image light into the optical core. The injected image light propagates along the optical core primarily by total internal reflection. The second multilayer grating is configured to receive at least a portion of the injected image light and extract at least a portion of the received injected image light from the optical core for viewing by a viewer. Each of the first and second multilayer gratings include an inorganic undulating layer and a planarizing adhesive layer. The inorganic undulating layer includes opposing outermost undulating major surfaces nestingly aligned with each other to create a wave-like shape along a width direction of the inorganic undulating layer and to form a plurality of substantially parallel ridges and grooves. The ridges and the grooves extend along an 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. The optical waveguide can further include at least one antireflective stack where at least one of the first and second multilayer gratings is disposed between the optical core and the at least one multilayer antireflective stack.

[0016] In some aspects of the present description, an optical waveguide is provided, the optical waveguide including an optical core configured to propagate an image light therealong, and a continuous seamless multilayer disposed on a major side of the optical core. The continuous seamless multilayer 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 undulated inorganic layer portions of an otherwise non-undulated inorganic layer. Each of the undulated inorganic layer portions includes opposing outermost undulating major surfaces nestingly aligned with each other and forming a plurality of substantially parallel ridges and grooves of the undulated inorganic layer portion extending along a length-direction of the undulated inorganic layer portion and arranged along an orthogonal width-direction of the undulated inorganic layer portion. The continuous seamless adhesive layer is disposed between the inorganic layer and the optical core and substantially conforms to the ridges and grooves of each of the undulated inorganic layer portion and bonds the inorganic layer to the optical core. A first undulated inorganic layer of the undulated inorganic layer portions is configured to receive an image light from an image projector and inject at least a portion of the received image light into the optical core. The injected image light propagates along the optical core primarily by total internal reflection. A second undulated inorganic layer portion of the undulated inorganic layer portions is configured to receive at least a portion of the injected image light along a first direction and redirect the injected image light as a redirected image light propagating along a different second direction along the optical core primarily by total internal reflection. A third undulated inorganic layer portion of the undulated 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. The optical waveguide can include at least one multilayer antireflective stack where at least one of the undulated inorganic layer portions is disposed between the optical core and the at least one multilayer antireflective stack.

[0017] In some aspects of the present description, a method of making an optical waveguide is provided, the method including providing a carrier including an acrylate layer, a multilayer antireflective stack disposed on the multilayer antireflective stack, and a radiation-cured layer disposed on the multilayer antireflective stack where the radiation-cured layer includes a major structured surface having, in a plurality of discrete spaced apart regions, a plurality of alternating first ridges and first grooves; conformally disposing an inorganic layer on the major structured surface of the radiation-cured layer so that both a first major surface thereof facing the carrier and a second major surface thereof facing away from the carrier substantially conform to the major structured top surface of the carrier to form a continuous seamless inorganic layer having a plurality of undulated inorganic layer portions in an otherwise non-undulated inorganic layer. In each of the undulated inorganic layer portions, the first and second major surfaces of the layer portion define a spacing average Savgand a spacing standard of deviation Ssd therebetween, such that Ssd / Savg is less than about 0.5; substantially conformally coating the second major surface of the inorganic 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 opposing substantially planar major surface; and adhering the substantially planar major surface of the structured adhesive layer to a major surface of an optical core configured to propagate an image light therealong primarily by total internal reflection. These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIGS. 1A and IB are schematic side or cross-sectional views of portions of an optical waveguide including a multilayer grating and a multilayer antireflective stack, in accordance with some embodiments of the present description.

[0020] FIG. 2 shows a scanning electron microscope image of a multilayer grating, in accordance with some embodiments of the present description.

[0021] FIGS. 3A and 3B are process flow diagrams schematically illustrating a method of making an optical waveguide with a multilayer grating and a multilayer antireflective stack, in accordance with an embodiment of the present description.

[0022] FIG. 4 is a schematic side or cross-sectional view of an optical waveguide including two multilayer grating sections, in accordance with some embodiments of the present description.

[0023] FIG. 5 provides an alternate schematic view of the optical waveguide of FIG. 4, in accordance with some embodiment of the present description.

[0024] FIGS. 6A and 6B include schematic side or cross-sectional views of the architecture of a multilayer grating, in accordance with some embodiments of the present description.

[0025] FIG. 7 is a schematic side or cross-sectional view of an optical waveguide including multilayer grating sections on opposing sides of an optical core, in accordance with some embodiments of the present description.

[0026] FIG. 8 is a schematic side or cross-sectional view of an optical waveguide, in accordance with some embodiments of the present description.

[0027] FIGS. 9A and 9B provide schematic top and side views, respectively, of an optical waveguide including three multilayer grating sections, in accordance with some embodiments of the present description.

[0028] FIGS. 10A and 10B provide schematic illustrative examples of shapes for features on a multilayer grating, in accordance with some embodiments of the present description.

[0029] FIGS. 11A and 1 IB provide schematic additional illustrative examples of shapes for the features on a multilayer grating, in accordance with some embodiment of the present description.

[0030] FIG. 12 is an illustrative example of methods for measuring dimensions on an undulating layer of a multilayer grating, in accordance with some embodiments of the present description.

[0031] FIG. 13 is a schematical cross-sectional view of a multilayer antireflective stack 150 including a plurality of alternating A and B layers, according to some embodiments.

[0032] FIG. 14 schematically illustrates plan and side or cross-sectional views of layers of a multilayer antireflective stack that have different grain sizes, in accordance with some embodiment of the present description. DETAILED DESCRIPTION

[0033] In the following description, reference is made to the accompanying drawings that form a part hereof 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 are contemplated and is made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.

[0034] Nano-structured fdms are useful in optical laminates or as transfer fdms based on subwavelength optics such as diffractive optical elements and optical meta-surfaces. Transfer fdms is used to fabricate image-preserving waveguides for augmented reality devices. The optical performance of these waveguides is dependent upon the index contrast (i.e., difference in refractive index) between the grating structure and the surrounding medium, which could be the template fdm (e.g., polymer, with a refractive index around 1.5) or air (if the template is removed in a subsequent process step). Therefore, there is a need for methods to increase or maximize the refractive index of a templated nanostructure for use in its final article.

[0035] Fabrication of high-index, sub-wavelength gratings and nanostructures is typically done using “batch processing” with methods developed for the semiconductor industry. The process starts by depositing a dense layer of TiCf on a substrate (e.g., high index glass wafer). The TiCf layer is coated with a polymeric resist, which is then patterned via a lithographic technique such as photolithography, nano-imprint lithography, or e-beam lithography to define the desired pattern in the resist. The pattern in the resist is then transferred into the TiCf layer by etching and finally the resist is removed, leaving behind the patterned TiCf.

[0036] The transfer film approach described herein is fundamentally different from the batch processing approach typically used and is far more suitable to high-volume and lower cost production of subwavelength optical structures. The transfer film approach achieves this by fabricating the high-index TiO2sub-wavelength structure on a polymeric structure on a carrier film. In some embodiments, the carrier film includes a carrier substrate, a thin acrylate layer (e.g., no more than about 1.5 micrometers thick) and a multilayer antireflective stack disposed on the acrylate layer. It has been found that depositing the thin acrylate layer on the carrier substrate before depositing the multilayer antireflective stack provides a substantially smooth surface for the multilayer optical stack and allows a structured radiation-cured layer having a thin (e.g., less than about 500 nm) land region to be formed on the multilayer antireflective stack. A multilayer antireflective stack is generally a stack of at least two layers that is configured to provide reduced reflectance when applied to a substrate. A multilayer antireflective (AR) stack may include layers having thicknesses selected to produce destructive interference for reflected light of at least one wavelength and at at least one angle of incidence, as would be appreciated by those of ordinary skill in the art. The layer may be designed to be antireflective as part of the final optical waveguide. Once the structure is made on the carrier film including the AR stack, the structure and AR stack can be transferred to a final substrate (e.g., a high-index glass wafer) with an ultra-thin adhesive (e.g., less than 500 nm and preferably less than 100 nm thick to maintain good optical coupling), and the carrier substrate and optionally the acrylate layer can then be removed. This enables use of high-capacity roll-to-roll processing to create the high index structures, along with a multilayer antireflective stack, on the final substrate.

[0037] According to some aspects of the present description, a transfer film (see, e.g., transfer film 250 schematically illustrated in FIG. 3B) includes a release liner having a release surface; an acrylate layer disposed on the release surface and having an average thickness in a range of about 10 nm to about 1500 nm; a multilayer antireflective stack disposed on the acrylate layer opposite the release liner; and a multilayer grating disposed on the multilayer antireflective stack opposite the acrylate layer. In some embodiments, the average thickness of the acrylate layer is at least about 20, 30, 40, or 50 nm. In some such embodiments, or in other embodiments, the average thickness of the acrylate layer is no more than about 1400, 1200, 1000, 800, 600, or 500 nm.

[0038] In some embodiments, the multilayer grating includes a first layer disposed on the acrylate layer and having a structured major surface facing away from the acrylate layer; an inorganic layer disposed on and substantially conforming (e.g., conforming, or nominally conforming, or conforming up to variations small (e.g., less than about 30, 25, 20, 15, 10, or 5 percent) compared to a feature size (e.g., height) of the major surface) to the structured major surface of the first layer; and a second layer disposed on the inorganic layer opposite the first layer, where the second layer may substantially planarize the inorganic layer. Substantially planarizing the inorganic layer generally means substantially filling (e.g., filling greater than 90, 95, or 97 percent of a total volume) volume between structures of the inorganic layer and forming a substantially planar surface (e.g., planar, or nominally planar, or planar up to variations small (e.g., less than 10, 8, 6, or 5 percent) of a width of the inorganic layer. Conformally coating, or conformally deposing, a layer on a structured surface means that the resulting layer substantially conforms to the structured surface (e.g., conformally disposing a layer on a structured surface may include small variations about an ideal conformal coating). In some embodiments, the first layer is a radiation-cured layer. The radiation-cured layer can be made from any (e.g., actinic) radiation-curable materials. Suitable radiation-curable materials include ultraviolet (UV) or electron-beam curable acrylates, for example. In some embodiments, the second layer is an adhesive layer. In some embodiments, an average minimum distance (e.g., the mean over the minimum distance for each of the structures of the structured major surface) between the structured major surface of the first layer and the multilayer antireflective stack, or between the inorganic layer and the multilayer antireflective stack, is less than about 500, 400, 300, 200, 150, 100, 90, or 80 nm. In some such embodiments, or in other embodiments, the average minimum distance is at least about 1, 5, 10, 15, or 20 nm.

[0039] In some embodiments, the inorganic layer has opposing first and second major surfaces defining a spacing average Savgand a spacing standard deviation Ssd therebetween, where Ssd / Savg can be less than about 0.5 or can be in any range described elsewhere herein. In some embodiments, the inorganic layer defines a plurality of alternating first and second concavities (see, e.g., first and second concavities 63 and 64 illustrated in FIG. 2), where the first concavities are convex toward the multilayer antireflective stack, and the second concavities are concave toward the multilayer antireflective stack. In some embodiments, for each pair of adjacent first and second concavities, the first and second concavities are separated by a common side wall extending from a first rounded side wall comer joining the common side wall to a bottom of the second concavity to an opposite second rounded side wall comer joining the common side wall to a bottom of the first concavity, such that in a first planar cross-section substantially orthogonal to the common side wall, the first rounded side wall comer has an outer first circumferential surface facing the second layer and having a first radius of curvature Rl, and the second rounded side wall comer has an outer second circumferential surface facing the first layer and having a second radius of curvature R2. In some embodiments, Rl > R2 for at least a plurality of pairs of adjacent first and second concavities. In some embodiments, Rl - R2 is at least 5 nm, or at least 10 nm, or at least 20 nm, or at least 30 nm, or at least 40 nm, or at least 50 nm. In some such embodiments, or in other embodiments, embodiments, Rl - R2 is no more than about 500, 400, 300, or 200 nm.

[0040] In some embodiments, the inorganic layer defines a plurality of alternating first and second concavities (see, e.g., first and second concavities 63 and 64 illustrated in FIG. 2), where the first concavities are convex toward the multilayer antireflective stack, and the second concavities are concave toward the multilayer antireflective stack. In some embodiments, for each pair of adjacent first and second concavities, the first and second concavities are separated by a common side wall extending from a first rounded side wall comer joining the common side wall to a bottom of the second concavity to an opposite second rounded side wall comer joining the common side wall to a bottom of the first concavity, such that in a first planar cross-section substantially orthogonal to the common side wall, the first rounded side wall comer has an outer first circumferential surface facing the optical core and having a first outer radius of curvature Rl, and an inner first circumferential surface facing away from the optical core and having a first inner radius of curvature Rl'. In some embodiments, Rl > Rl' for at least a plurality of pairs of adjacent first and second concavities. In some embodiments, Rl - Rl' is at least 5 nm, or at least 10 nm, or at least 20 nm, or at least 30 nm, or at least 40 nm, or at least 50 nm. In some such embodiments, or in other embodiments, embodiments, Rl - Rl' is no more than about 500, 400, 300, or 200 nm.

[0041] In some embodiments, the multilayer grating includes first and second layers, where each of the first and second layers has a structured first major surface and an opposite second major surface. The first major surfaces of the first and second layers can be disposed on and substantially conform to one another. For example, one of the first and second layers can be a radiation-cured layered structured via a cast and cure process, for example, and the other of the first and second layers can be a backfill layer that can have a refractive index different from that of the radiation-cured layer for at least one visible wavelength (e.g., in a range of about 400 nm to about 700 nm). An inorganic layer may be disposed between the first major surfaces of the first and second layers. In this case, the first major surfaces can still substantially conform to one another when the inorganic layer is thin compared to the sizes of the structures of the structured first major surfaces, for example. In some embodiments, the multilayer grating includes an undulating inorganic layer disposed between the first and second layers, where the first major surfaces of the first and second layers are disposed on and substantially conform to the inorganic layer.

[0042] In some embodiments, the multilayer antireflective stack includes a plurality of inorganic A layers, where each A layer has a same first composition and the A layers of each pair of adjacent A layers are separated by at least one layer having a composition different from the first composition. The composition and fabrication of the A layers and B layers are typically chosen such that they have different refractive indexes for at least one wavelength in a range of about 400 nm to about 700 nm. The multilayer antireflective stack includes first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack where the first A layer is disposed between the multilayer grating and the second A layer. An average grain size of the first A layer can be greater than an average grain size of the second A layer. In some embodiments, an average grain size of the first A layer is greater than an average grain size of the second A layer. In some embodiments, the average grain size of the first A layer is at least about 5, 10, 15, 20, or 25 percent greater than the average grain size of the second A layer. In some such embodiments, or in other embodiments, the average grain size of the first A layer is no more than about 50, 20, 10, or 5 times greater than the average grain size of the second A layer. The average grain size may be taken to be the mean of the area of the grains in a cross-section. Grain sizes are described further elsewhere herein (see, e.g., FIG. 14 and the discussion thereof).

[0043] In some embodiments, the multilayer antireflective stack includes one or more B layers, where the A and B layers alternate with one another along a thickness direction of the multilayer antireflective stack. Each B layer can have a same second composition different from the first composition. In some embodiments, each layer of the transfer film, or the optical film, disposed between the first layer of the multilayer grating and the acrylate layer is an A layer or has a composition different from the first composition. In some embodiments, no more than one layer (e.g., a single B layer or no layer) separates the first A layer and the first layer of the multilayer grating. In some embodiments, no more than one layer (e.g., a single B layer or no layer) separates the second A layer and the acrylate layer.

[0044] In some embodiments, the multilayer antireflective stack includes a plurality of alternating A and B layers, where each A layer has the same first composition, and each B layer has a same second composition different from the first composition, where the plurality of alternating A and B layers include the first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack. In some embodiments, the first composition is an inorganic composition. An inorganic composition is generally a composition that consist essentially (e.g., greater than 96, 97, 98, or 99% by weight) of inorganic materials. Inorganic materials include compounds of carbon such as carbides (e.g., silicon carbide), some carbonates, and some cyanides that do not include carbon bound to hydrogen. An inorganic composition can be an inorganic element or compound or a blend or alloy of inorganic elements or compounds. In some embodiments, the second composition is an inorganic composition. In some embodiments, the second composition is an organic composition. In some embodiments, each A layer is an inorganic layer. In some embodiments, each B layer is an inorganic layer. In other embodiments, each B layer is an organic layer.

[0045] In some aspects of the present description, a method of making a transfer fdm (see, e.g., FIGS. 3A-3B) is provided. The method includes, in sequence: disposing an acrylate layer on a release surface of a release liner; disposing a multilayer antireflective stack on the acrylate layer (e.g., via chemical vapor deposition, physical vapor deposition, atomic layer deposition, sputtering, spin-coating, or any appropriate combination thereof); disposing a radiation-cured layer on the multilayer antireflective stack, where the radiation-cured layer has a major structured surface facing away from the antireflective stack, and where the major structured surface includes a plurality of alternating first ridges and first grooves. In some embodiments, the method further includes, in sequence (after disposing the radiation-cured layer), conformally disposing an inorganic layer on the major structured surface of the radiation-cured layer so that both a first major surface thereof facing the radiation-cured layer and a second major surface thereof facing away from the radiation-cured layer substantially conform to the major structured surface of the radiation-cured layer; and disposing an adhesive layer on the second major surface of the inorganic layer such that the adhesive layer substantially planarizes the inorganic layer to form a structured adhesive layer having a major structured surface facing and substantially conforming to the second major surface of the inorganic layer and an opposing substantially planar major surface. In some embodiments, the acrylate layer has an average thickness of at least about 10, 20, 30, 40, or 50 nm. In some such embodiments, or in other embodiments, the average thickness of the acrylate layer is up to about 1500, 1400, 1200, 1000, 800, 600, or 500 nm. For example, in some embodiments, the acrylate layer has an average thickness in a range of about 10 nm to about 1500 nm, or about 30 nm to about 1000 nm, or about 50 nm to about 500 nm. In some embodiments, the inorganic layer has a thickness standard deviation that is less than about 50% of an average thickness of the inorganic layer. The ratio of the thickness standard deviation to the average thickness can be in any of the ranges described elsewhere herein for Ssd / Savg. In some other embodiments, the inorganic layer has a thickness standard deviation of greater than 50% of the average thickness of the inorganic layer. For example, a vertical sidewall may be thinner than the top or bottom portions of the undulation such that the thickness standard deviation is greater than 50% of the average thickness of the inorganic layer. As another example, the inorganic layer can be deposited at angle (e.g., by setting the sample at an oblique angle to vapor flux in a vapor deposition processes) so that the thickness of one vertical sidewall is thicker than a thickness of an opposite vertical sidewall and this may result in the thickness standard deviation being greater than 50% of the average thickness of the inorganic layer. The step of disposing the multilayer antireflective stack on the acrylate layer can result in different layers of the multilayer antireflective stack having different grain sizes as described further elsewhere herein. In some embodiments, the step of disposing the radiation-cured layer on the multilayer antireflective stack includes: providing a tool having a major structured surface including a plurality of alternating ridges and grooves; disposing a radiation-curable material on the major structured surface of the tool, and on the multilayer antireflective stack opposite the acrylate layer, to form a radiation-curable layer having a major structured surface facing and substantially conforming to the major surface of the tool and an opposite major surface disposed on the multilayer antireflective stack; and irradiating the radiation-curable layer to form the radiation-cured layer. Such processes for making a structured radiation-cured layer may be referred to as cast and cure processes and are generally described in U.S. Pat. Nos. 5,175,030 (Lu et al.) and 5,183,597 (Lu) and in U.S. Pat. Appl. Pub. No. 2012 / 0064296 (Walker, JR. et al.), for example.

[0046] As is known in the art, an optical core of an optical waveguide can be configured to propagate a light therealong primarily by total internal reflection (TIR). When light propagates along an optical core of an optical waveguide primarily by TIR, most of the light propagating along the optical core that is incident on an outer surface of the optical core is reflected back into the optical core via TIR at the outer surface of the optical core.

[0047] According to some aspects of the present description, a method of making an optical waveguide is provided. The method includes making a transfer film according to any of the methods described elsewhere herein for making a transfer film; adhering the substantially planar major surface of the structured adhesive layer of the transfer film to a major surface of an optical core configured to propagate an image light therealong primarily by total internal reflection; and removing the release liner from the acrylate layer. In some embodiments, the method further includes, after the adhering and removing steps, removing the acrylate layer to expose the multilayer antireflective stack.

[0048] According to some aspects of the present description, an optical film includes a multilayer grating including first and second layers, where each of the first and second layers has a structured first major surface and an opposite second major surface, where the first major surfaces of the first and second layers are disposed on and substantially conform to one another, and where the second major surface of the first layer is substantially smooth; and a multilayer antireflective stack disposed directly on, and substantially coextensive with, the second major surface of the first layer. In some embodiments, the optical film includes an undulating inorganic layer disposed between the first and second layers. In some embodiments, the multilayer grating includes an undulating inorganic layer disposed between the first and second layers, where the first major surfaces of the first and second layers are disposed on and substantially conform to the inorganic layer. In some embodiments, an optical film includes a multilayer grating including an undulating inorganic layer disposed between first and second layers, where each of the first and second layers has a structured first major surface and an opposite second major surface, the first major surfaces of the first and second layers are disposed on and substantially conform to the undulating inorganic layer, and the second major surface of the first layer is substantially smooth; and a multilayer antireflective stack disposed directly on, and substantially coextensive with, the second major surface of the first layer. A substantially smooth major surface may be free of engineered microstructures or nanostructures, and / or a substantially smooth major surface may be sufficiently smooth (e.g., optically smooth and / or a surface roughness Ra less than 10, 7, 5, 4, 3, 2 or 1 nm) that any deviation from smoothness has a negligible effect on optical properties of the surface (e.g., reflection from the surface). In some embodiments, the multilayer antireflective stack includes a plurality of inorganic A layers, where each A layer has a same first composition, and where the A layers of each pair of adjacent A layers are separated by at least one layer having a composition different from the first composition. The multilayer antireflective stack can include first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack, where the first A layer is disposed between the multilayer grating and the second A layer, and where an average grain size of the first A layer can be greater than an average grain size of the second A layer. The difference between the grain sizes of the first and second A layers can be as described further elsewhere herein. In some embodiments, the multilayer antireflective stack includes one or more B layers, where the A and B layers alternate with one another along a thickness direction of the multilayer antireflective stack, and where each B layer can have a same second composition different from the first composition. In some embodiments, no more than one layer (e.g., one B layer or no layer) separates the first A layer and the first layer of the multilayer grating. In some embodiments, the first layer of the multilayer grating is a radiation-cured layer, and the second layer of the multilayer grating is an adhesive layer. In some embodiments, the optical film further includes an acrylate layer having an average thickness in a range of about 10 to 1500 nm (or in a range described elsewhere herein), where the multilayer antireflective stack is disposed between, and directly contacting, the acrylate layer and the first layer. In some embodiments, each layer of the optical film disposed between the first layer of the multilayer grating and the acrylate layer is an A layer or has a composition different from the first composition. In some embodiments, no more than one layer (e.g., one B layer or no layer) separates the second A layer and the acrylate layer.

[0049] Layers or elements can be described as substantially coextensive with each other if at least about 60% by area of each layer or element is coextensive with at least about 60% by area of each other layer or element. Here, area refers to the area of a major surface of the layer or element. In some embodiments, for layers or elements described as substantially coextensive, at least about 70%, or at least about 80%, or at least about 90% by area of each layer or element is coextensive with at least about 70%, or at least about 80%, or at least about 90% by area of each other layer or element.

[0050] In some embodiments, an optical waveguide includes an optical core and the optical film (or any optical film of the present description) disposed on the optical core, with the multilayer grating between the optical core and the multilayer antireflective stack. In some embodiments, an optical system includes the optical waveguide and an image projector configured to emit an image light, where the multilayer grating is configured to receive the emitted image light and inject at least a portion of the received image light into the optical core. In some embodiments, an optical system includes the optical waveguide, where the multilayer grating is configured to receive at least a portion of a light propagating in the optical core and extract at least a portion of the light from the optical core for viewing by a viewer. In some embodiments, an optical system includes the optical waveguide and an image projector configured to emit an image light, where a first portion of the multilayer grating is configured to receive the emitted image light and inject at least a portion of the received image light into the optical core, and a different second portion of the multilayer grating is configured to receive at least a portion of the injected image light and extract at least a portion of the received injected image light from the optical core for viewing by a viewer.

[0051] In some embodiments, an optical waveguide includes an optical core and first and second optical films disposed on the optical core, where each of the first and second optical films is the optical film (or any optical film of the present description), where for each of the first and second optical films, the multilayer grating is disposed between the optical core and the multilayer antireflective stack. In some embodiments, an optical system includes the optical waveguide and an image projector configured to emit an image light, where the multilayer grating of the first optical film is configured to receive the emitted image light and inject at least a portion of the received image light into the optical core, and the multilayer grating of the second optical film is configured to receive at least a portion of the injected image light and extract at least a portion of the received injected image light from the optical core for viewing by a viewer.

[0052] In some embodiments, an augmented reality system includes any of the optical systems of the present description.

[0053] According to some aspects of the present description, an optical film includes: a multilayer grating including first and second layers, where each of the first and second layers has a structured first major surface and an opposite second major surface, the first major surfaces of the first and second layers are disposed on and substantially conform to one another, and the second major surface of the first layer is substantially smooth; and a multilayer antireflective stack disposed directly on, and substantially coextensive with, the second major surface of the first layer. In some embodiments, an undulating inorganic layer is disposed between the first and second layers. In some embodiments, the multilayer grating includes an undulating inorganic layer disposed between the first and second layers, where the first major surfaces of the first and second layers are disposed on and substantially conform to the inorganic layer. In some embodiments, an optical film includes: a multilayer grating including an undulating inorganic layer disposed between first and second layers, where each of the first and second layers has a structured first major surface and an opposite second major surface, the first major surfaces of the first and second layers are disposed on and substantially conform to the inorganic layer, and the second major surface of the first layer is substantially smooth; and a multilayer antireflective stack disposed directly on, and substantially coextensive with, the second major surface of the first layer. In some embodiments, an average minimum distance between the structured first major surface of the first layer and the multilayer antireflective stack, or between the undulating inorganic layer and the multilayer antireflective stack, is less than about 500, 400, 300, 200, 150, 100, 90, or 80 nm (or the average minimum distance can be in any range described elsewhere herein). In some embodiments, the multilayer antireflective stack includes a plurality of inorganic A layers, where each A layer has a same first composition, and where the A layers of each pair of adjacent A layers are separated by at least one layer having a composition different from the first composition. In some embodiments, the multilayer antireflective stack includes first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack, where the first A layer is disposed between the multilayer grating and the second A layer. In some embodiments, an average grain size of the first A layer is greater than an average grain size of the second A layer. The difference between the grain sizes of the first and second A layers can be as described further elsewhere herein. In some embodiments, the first layer of the multilayer grating is a radiation-cured layer, and the second layer of the multilayer grating is an adhesive layer.

[0054] In some embodiments, an optical waveguide includes an optical core and at least one optical film of the present description disposed on the optical core, where for each of the at least one optical film, the multilayer grating is disposed between the optical core and the multilayer antireflective stack. In some embodiments, an augmented reality system includes the optical waveguide and an image projector in optical communication with the at least one optical film. The term “optical communication” as applied to two objects means that light can be transmitted from one object to the other either directly or indirectly using optical methods (for example, reflection, diffraction, refraction).

[0055] According to some aspects of the present description, an optical waveguide includes an optical core configured to propagate an optical mode at a first wavelength therealong, a multilayer grating disposed on the optical core and configured to extract the optical mode that would otherwise propagate along the optical core along a first direction (e.g., in an x-axis relative to the waveguide), and a multilayer antireflective stack where the multilayer grating is disposed between the multilayer antireflective stack and the optical core.

[0056] In some embodiments, the multilayer antireflective stack includes a plurality of inorganic A layers, where each A layer has a same first composition, and where each pair of adjacent A layers are separated by at least one layer having a composition different from the first composition; where the multilayer antireflective stack includes first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack, with the first A layer disposed between the multilayer grating and the second A layer, and where an average grain size of the first A layer being greater than an average grain size of the second A layer.

[0057] In some embodiments, the multilayer grating includes an adhesive layer and an inorganic layer. In some embodiments, the adhesive layer includes a major bottom surface facing the optical core and an opposing structured major top surface facing away and spaced apart from the optical core. In some embodiments, the structured major top surface incudes a plurality of substantially parallel linear grating elements extending along a same length direction (e.g., a y-axis) of the grating elements and arranged along an orthogonal width direction (e.g., an x-axis) of the grating elements. In some embodiments, the plurality of substantially parallel linear grating elements forms a periodic pattern along the width direction of the grating elements. In some such embodiments, the periodic pattern has a period in a range from about 100 nm to about 1000 nm, or from about 150 nm to about 750 nm, or from about 200 nm to about 700 nm, or from about 250 nm to about 600 nm, or from about 300 nm to about 550 nm, or from about 300 nm to about 500 nm, or from about 300 nm to about 450 nm. In some embodiments, the width direction of the grating elements is substantially parallel to the first direction.

[0058] In some embodiments, the inorganic layer is disposed on and may conform to the structured major top surface of the adhesive layer so that the inorganic layer has a thickness standard deviation that 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 an average thickness of the inorganic layer. In other embodiments, the inorganic layer may have a larger thickness standard deviation as described further elsewhere herein.

[0059] In some embodiments, the optical core has an average thickness of 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 has a thickness of up to 5000 microns, or up to 7500 microns, or up to 10,000 microns.

[0060] In some embodiments, a minimum spacing between the optical core and the major top surface of the adhesive layer 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. In some embodiments, the minimum spacing is less than about 500 nm, less than about 450 nm, less than about 400 nm, less than about 350 nm, less than about 300 nm, less than about 250 nm, less than about 200 nm, less than about 150 nm, less than about 100 nm, less than about 90 nm, or less than about 80 nm.

[0061] In some embodiments, the optical waveguide further includes a (e.g., polymeric) layer disposed on and substantially planarizing the inorganic layer. Such a layer is a radiation-cured layer and / or is referred to as a planarizing layer. The planarizing layer can be or include a radiation-cured layer. The multilayer antireflective stack can be disposed on the planarizing layer opposite the inorganic layer. In some embodiments, the inorganic layer incudes one or more of titanium dioxide (TiCf). zirconium oxide (ZrOx), titanium oxide (TiOx), silicon carbide (SiC2), SiCh, AI2O3, CeCh, ZnO, Nb2Os, Ta2Os, HfCf. SiAlOxNy, S N-i. Nb-doped TiCf. and ZrCf. In some embodiments, at the first wavelength, an index of refraction of the planarizing layer is less than an index of refraction of the inorganic layer by 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.

[0062] In some embodiments, an optical system includes any of the optical waveguides described herein, at least one light source disposed so as to inject light at the first wavelength into the optical core of the optical waveguide, such that the injected light propagates along the optical core along the first direction as the optical mode. According to some aspects of the present description, an optical waveguide includes an optical core configured to propagate an image light therealong primarily by total internal reflection, a structured adhesive layer, an inorganic layer, and a multilayer antireflective stack. The inorganic layer can be disposed between the multilayer antireflective stack and the optical core. In some embodiments, the structured adhesive layer incudes a major bottom surface facing, and bonded to, the optical core and an opposing major structured top surface including a plurality of alternating ridges and grooves. In some embodiments, an average spacing between the grooves and the optical core 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, the average spacing between the grooves and the optical core is 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, or about 90 nm, or about 80 nm. In some embodiments, a minimum spacing between the grooves and the optical core 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. The optical waveguide may further include a planarizing layer disposed on the inorganic layer and including a major structured bottom surface facing the inorganic layer and an opposite major substantially smooth (e.g., optically smooth) top surface, where the multilayer antireflective stack is disposed on the major substantially smooth top surface of the radiation-cured layer. The planarizing layer can be or include a radiation-cured layer.

[0063] 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 “up” away from the optical core, forming a projection extending in a direction that is away from the optical core. Conversely, a groove is any undulation in a layer for which the material of the layer is pushed “down” toward the optical core, forming a depression extending in a direction toward the optical core.

[0064] Both ridges and grooves is considered “concavities” in a layer, but concavities facing in different directions. For example, each concavity has an open end and a closed end (e.g., a “cup-like” shape). In a “ridge” concavity, the open end of the concavity faces “down” toward the optical core (the negative z- direction of FIG. 1) and the closed end is projected “up” away from the optical core (the positive z- direction of FIG. 1, shown by the arrow on the coordinate system graphic). A “groove” concavity, conversely, has an open end that faces “up” away from the optical core, and a closed end that faces “down” toward the optical core. These definitions are provided for clarity in understanding the figures and language of this specification.

[0065] In some embodiments, for at least one visible wavelength in a visible (human-visible) wavelength range extending from about 420 nm to about 680 nm, the structured adhesive has an index of refraction of between about 1.35 to about 2.5. In some embodiments, for at least one visible wavelength in a visible wavelength range extending from about 420 nm to about 680 nm, the structured adhesive has an index of refraction of about 1.5. In some embodiments, the inorganic layer is conformally disposed on the major structured top surface of the structured adhesive layer so that opposing first and second major surfaces of the inorganic layer substantially conform to the major structured top surface of the structured adhesive layer, and the first and second major surfaces of the inorganic layer define an average spacing of between about 10 nm to about 100 nm, or about 20 nm to about 90 nm, or about 30 nm to about 80 nm, or about 40 nm to about 70 nm, or about 40 nm to about 60 nm, therebetween. In some embodiments, the inorganic layer has an index of refraction of greater than about 1.5, or about 1.6, or about 1.7, or about 1.8, or about 1.9, or about 2.0, or about 2.1, or about 2.2, or about 2.3, or about 2.4 at a wavelength of about 580 nm.

[0066] In some embodiments, the optical core has an index of refraction of 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 incudes one or more of tantalum, niobium, lanthanum, lead, barium, titanium, zirconium, and bismuth. In some embodiments, the optical core is or includes a polymer. In some embodiments the optical core includes one or more of, but is not limited to, polymethacrylate, polycarbonate, polyester, polyphosphonate, polysulfone, silicone, epoxy, or polyimide constituents. In some embodiments, the optical core incudes nanoparticles. In some embodiments, the optical core includes nanoparticles of titania, or zirconia.

[0067] According to some aspects of the present description, an optical waveguide includes an optical core configured to propagate an image light therealong primarily by total internal reflection, an inorganic layer, a structured adhesive layer, and a multilayer antireflective stack. In some embodiments, the inorganic layer is disposed between the multilayer antireflective stack and the structured adhesive layer. In some embodiments, the inorganic layer is disposed on the optical core and defines a plurality of alternating first and second concavities, where the first concavities are concave toward the optical core, and the second concavities are convex toward the optical core. In some embodiments, the structured adhesive layer is disposed between the optical core and the inorganic layer and bonding them to each other. In some embodiments, the structured adhesive layer substantially fills the first concavities (e.g., fills at least 70, 80, 90, or 95 percent of a total volume of the first concavities). In some embodiments, a radiation-cured layer is disposed on the inorganic layer and separates the inorganic layer from the antireflective stack. In some embodiments, the radiation-cured layer substantially fills the second concavities.

[0068] For each pair of adjacent first and second concavities, the first and second concavities is separated by a common side wall extending from a first rounded side wall comer joining the common side wall to a bottom of the second concavity to an opposite second rounded side wall comer joining the common side wall to a bottom of the first concavity. In a first planar cross-section (e.g., in an xz-plane of the optical waveguide) substantially orthogonal to the common side wall, the first rounded side wall comer may include an outer first circumferential surface facing the optical core and having a first radius of curvature Rl. In some embodiments, the second rounded side wall comer includes an outer second circumferential surface facing away from the optical core and having a second radius of curvature R2. In some embodiments, R1 is greater than R2 for at least a plurality of pairs of adjacent first and second concavities.

[0069] According to some aspects of the present description, an optical waveguide includes an optical core configured to propagate an image light therealong primarily by total internal reflection, an inorganic layer, a structured adhesive layer, and a multilayer antireflective stack. In some embodiments, the inorganic layer is disposed on the optical core and defines a plurality of alternating first and second concavities. In some embodiments, the first concavities are concave toward the optical core, and the second concavities are convex toward the optical core. In some embodiments, the inorganic layer is disposed between the multilayer antireflective stack and the structured adhesive layer.

[0070] In some embodiments, the structured adhesive layer is 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 substantially fills the first concavities. In some embodiments, a radiation-cured layer substantially fills the second concavities. In some embodiments, for each pair of adjacent first and second concavities, the first and second concavities are separated by a common side wall extending from a first rounded side wall comer joining the common side wall to a bottom of the second concavity to an opposite second rounded side wall comer joining the common side wall to a bottom of the first concavity. In some embodiments, the first rounded side wall comer is closer to the optical core and the second rounded side wall comer is farther from the optical core.

[0071] In some embodiments, in a first planar cross-section (e.g., an xz-plane of the optical waveguide) substantially orthogonal to the common side wall, the first rounded side wall comer includes an outer first circumferential surface facing the optical core and having a first outer radius of curvature Rl, and an inner first circumferential surface facing away from the optical core and having a first inner radius of curvature Rl ’ . In some embodiments, Rl is greater than Rl ’ for at least a plurality of pairs of adjacent first and second concavities. In some embodiments, the value of Rl - Rl’ is at least 10 nm, or at least 20 nm, or at least 30 nm, or at least 40 nm, or at least 50 nm. In some embodiments, Rl - Rl ’ is no more than about 500, 400, 300, 200 nm.

[0072] According to some aspects of the present description, a method of making an optical waveguide includes providing a carrier including an acylate layer, a multilayer antireflective stack disposed on the acrylate layer, and a radiation-cured layer disposed on the multilayer antireflective stack where the radiation-cured layer includes a major structured surface having a plurality of alternating first ridges and first grooves; conformally disposing an inorganic layer on the major structured surface of the radiation- cured layer so that both a first major surface thereof facing the carrier and a second major surface thereof facing away from the carrier substantially conform to the major structured surface of the radiation-cured layer such that the first and second major surfaces of the inorganic layer define a spacing average Savgand a spacing standard of deviation Ssd therebetween, Ssd / Savg can be 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 major surface of the inorganic 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 opposing substantially planar major surface; and adhering the substantially planar major surface of the structured adhesive layer to a major surface of an optical core configured to propagate an image light therealong primarily by total internal reflection. In other embodiments, Ssd / Savg may be greater than about 0.5. Refer to the discussion of FIG. 12 herein for additional detail on the values of Savgand SSdand how the measurements are determined.

[0073] In some embodiments, the step of providing the carrier includes providing a tool having a major structured surface including a plurality of alternating ridges and grooves; and disposing a radiation- curable material on the major structured surface of the tool to form a radiation-curable layer having a major structured surface facing and substantially conforming to the major surface of the tool; and irradiating the radiation-curable layer to for the radiation-cured layer.

[0074] In some embodiments, the method further includes, after the adhering step, removing the acrylate layer. In some embodiments, the step of removing the acrylate layer is done by one or more of plasma etching, wet etching, solvent dissolution, laser ablation, chemo-mechanical polishing (CMP), or any other appropriate method.

[0075] In some embodiments, the carrier includes an acrylate layer disposed on a carrier substrate having a separable release layer where the multilayer antireflective stack is disposed on the acylate layer, and the major structured surface is deposited on the multilayer antireflective stack. In some embodiments, the carrier includes a separable release layer, where the acrylate layer is deposited on the separable release layer, and where the method further includes, after the adhering step, removing the separable release layer. Suitable acrylates include those formed from volatilizable acrylate or methacrylate monomers, for example. Examples of carrier substrates including a separable release liner with an acrylate layer disposed thereon are described in International Pat. Appl. Pub. No. WO 2023 / 111729 (Gotrik et al.), for example. As described in Gotrik et al., the release liner may include a substrate, a first (or planarizing) acylate layer disposed on the substrate (the acylate layer disposed on the release liner may then be referred to as a second acrylate layer or a transferrable acrylate layer), and a release layer disposed on the first acrylate layer, where the release layer may include a metal layer or a doped semiconductor (e.g., aluminum-doped silicon) layer. Suitable materials for the (first and / or second) acrylate layer are described in Gotrik et al. and include tricyclodecane dimethanol diacrylate, for example, which may be applied by ultrasonic atomization and flash evaporation followed by curing via electron beam curing, for example.

[0076] According to some aspects of the present description, an optical waveguide includes an optical core configured to propagate an image light therealong; first and second multilayer gratings disposed on the optical core; and at least one multilayer antireflective stack where at least one of the first and second multilayer gratings is disposed between the optical core and the at least one multilayer antireflective stack. In some embodiments, the at least one multilayer antireflective stacks includes first and second antireflective stacks where the first and second multilayer gratings are disposed between the optical core and the respective first and second antireflective stacks. In some embodiments, the first multilayer grating is configured to receive an image light from an image projector and to inject at least a portion of the received image light into the optical core. In some embodiments, the injected image light propagates along the optical core primarily by total internal reflection. In some embodiments, the second multilayer grating is configured to receive at least a portion of the injected image light and extract at least a portion of the received injected image light from the optical core for viewing by a viewer (e.g., a human observer). In some embodiments, the first and second multilayer gratings has different width directions (e.g., the x axes relative to each multilayer grating may define a non-zero angle therebetween if overlaid). In some embodiments, the optical core has an index of refraction of 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 incudes one or more of tantalum, niobium, lanthanum, lead, barium, titanium, zirconium, and bismuth. In some embodiments, the optical core is a polymer. In some embodiments the optical core incudes one or more of polymethacrylate, polycarbonate, polyester, polyphosphonate, polysulfone, silicone, epoxy, or polyimide constituents. In some embodiments, the optical core incudes nanoparticles. In some embodiments, the optical core incudes nanoparticles of titania, or zirconia. In some embodiments, each of the first and second multilayer gratings incudes an inorganic undulating layer and a planarizing adhesive layer. In some embodiments, the inorganic undulating layer incudes opposing outermost undulating major surfaces nestingly aligned with each other to have a wave-like shape along a width direction (e.g., along an x-axis) of the inorganic undulating layer and forming a plurality of substantially parallel ridges and grooves. In some embodiments, the ridges and the grooves extend along an orthogonal length direction (e.g., a y- axis) of the inorganic undulating layer. In some embodiments, an undulation amplitude of at least one of the first and second multilayer gratings varies along the width direction thereof.

[0077] As used herein, the phrase “undulating layer” refers to the layer having a wave-like pattern, shape, or profile in the width direction of the layer with successive curves in the layer in alternate directions forming alternating peaks and valleys, or ridges and grooves, on each major side of the layer along the width direction and extending along the length direction of the layer. Examples of undulating layers include, but are not limited to, layers having a sinusoidal wave pattern, shape, or profile, and layer having a triangular wave, slanted, or blazed pattern, shape, or profile. Other examples of undulating layers include layers featuring a two-dimensional (2D) pattern of posts and / or holes, where a crosssection taken through a linear collection (e.g., a row) of posts or holes creates an undulating pattern across the layer.

[0078] In some embodiments, the planarizing adhesive layer is disposed between the inorganic undulating layer and the optical core and substantially planarizing one of the undulating major surfaces of the inorganic undulating layer and bonding the inorganic undulating layer to the optical core.

[0079] In some embodiments, the planarizing adhesive layer defines a minimum distance dmin between the inorganic undulating layer and the optical core. In some such embodiments, dmin 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 run, or about 40 nm, or about 45 nm, or about 50 nm. In some such embodiments, or in other embodiments, is less than about 500 nm, or about 400 nm, or about 300 nm, or about 200 nm, or about 150 nm, or about 100 nm, or about 90 nm, or about 80 nm. In some embodiments, for at least one of the first and second multilayer gratings, a minimum separation between the optical core and the grooves of the multilayer gratings changes along the width of the multilayer grating.

[0080] In some embodiments, for at least one of the first and second multilayer gratings, in a planar cross-section (e.g., an xz-plane) of the multilayer grating that is orthogonal to the length direction (e.g., a y-axis) of the multilayer gratings, for two different locations on the multilayer grating LI and L2, each location including one ridge and one directly adjacent groove, where the ridge and groove have a combined width of Wi and W2 at the respective locations LI and L2, the area between the optical core and the ridge at LI is Ari, the area between the optical core and the groove at LI is Agi, the area between the optical core and the ridge at L2 is Ar2, and the area between the optical core and the groove at L2 is Ag2 (see, e.g., FIG. 6B). In some embodiments, (Ari+ Agi) / Wi is within 30% of (Ar2 + Ag2) / W2, or within 20%, or within 10%, or within 5%, or within 2% of (A^ + Ag2) / W2.

[0081] In some embodiments, the structures of the multilayer grating are arranged at an average pitch of at least about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, or 350 nm. In some such embodiments, or in other embodiments, the average pitch is no more than about 20, 10, 7, 5, 4, 3, 2, 1, 0.8, 0.7, 0.6, 0.5, 0.45, or 0.4 micrometers. In some such embodiments, or in other embodiments, the average height of the structures is at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, or 30 nm. In some such embodiments, or in other embodiments, the average height is no more than about 20, 10, 7, 5, 4, 3, 2, 1, 0.8, 0.7, 0.6, 0.5, 0.45, or 0.4 micrometers. For example, in some embodiments, the average pitch is from about 50 nm to about 5000 nm and the average height is in a range of about 5 nm to about 5000 nm; or the average pitch is from about 300 nm to about 450 nm and the average maximum height is in a range of about 5 nm to about 500 nm. Here, the average height may refer to either the average undulation amplitude (e.g., mean of the undulation amplitude Am) or the average maximum height (e.g., mean of distance from the optical core to the peaks of the structures). That is, either or both the average undulation amplitude or the average maximum height can be in any of the ranges described for the average height.

[0082] In some embodiments, for at least one of the first and second multilayer gratings, the multilayer grating further includes a planarizing polymeric layer conformally covering the inorganic undulating layer opposite the planarizing adhesive layer and substantially planarizing the inorganic undulating layer. In some embodiments, the first and second multilayer gratings are disposed on the same side of the optical core, or are disposed on opposite major sides of the optical core. In some embodiments, the first and second multilayer gratings are spaced apart, while in other embodiments, the first and second multilayer gratings are in contact or overlap. In some embodiments, the optical waveguide further includes a connecting adhesive portion disposed between, and continuously and seamlessly connecting, the planarizing adhesive layers of the first and second multilayer gratings. In some embodiments, the optical waveguide further includes a connecting substantially non-undulating inorganic layer disposed between, and continuously and seamlessly connecting, the inorganic undulating layers of the first and second multilayer gratings.

[0083] In some embodiments, each of the first and second multilayer gratings further includes a planarizing polymeric layer conformally covering the inorganic undulating layer opposite the planarizing adhesive layer and substantially planarizing the inorganic undulating layer. In some such embodiments, the optical waveguide further includes a substantially planar connecting polymeric layer disposed between, and continuously and seamlessly connecting, the planarizing polymeric layers of the first and second multilayer gratings.

[0084] In some embodiments, for at least one visible wavelength in a human-visible wavelength range extending from about 420 nm to about 680 nm, an index of refraction of the planarizing polymeric layer is less than the index of refraction of the inorganic undulating layer by 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.

[0085] In some embodiments, for at least one of the first and second multilayer gratings, the plurality of substantially parallel ridges and grooves forms a periodic pattern along the width direction of the inorganic undulating layer. In some such embodiments, the periodic pattern has a period in a range from about 100 nm to about 1000 nm, or from about 150 nm to about 750 nm, or from about 200 nm to about 700 nm, or from about 250 nm to about 600 nm, or from about 300 nm to about 550 nm, or from about 300 nm to about 500 nm, or from about 300 nm to about 450 nm.

[0086] In some embodiments, the optical core has an average thickness of between about 100 microns and about 2000 microns, or about 150 microns and about 1500 microns, or about 200 microns and about 1250 microns, or about 250 microns and about 1250 microns, or about 300 microns and about 1000 microns. In some embodiments the optical core has a thickness of up to 5000 microns, or up to 7500 microns, or up to 10,000 microns. In some embodiments, a minimum thickness of the planarizing adhesive layer 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.

[0087] In some embodiments, the inorganic undulating layer includes one or more of titanium dioxide (TiCh), zirconium oxide (ZrOx), titanium oxide (TiOx), SiCh, AI2O3, CeCh, ZnO, Ta2Os, HfCf. SiAlOxNy, S N-i. Nb-doped TiCf. and zirconium dioxide (ZrCf).

[0088] In some embodiments, an optical system includes any of the optical waveguides described herein, and the image projector configured to emit the image light, where the first multilayer grating is configured to receive the emitted image light and inject at least a portion of the received image light into the optical core of the optical waveguide.

[0089] In some embodiments, for at least one visible wavelength in a visible wavelength range extending from about 420 nm to about 680 nm, the planarizing adhesive layer has an index of refraction of between about 1.35 to about 2.5. In some embodiments, for at least one visible wavelength in a visible wavelength range extending from about 420 nm to about 680 nm, the planarizing adhesive layer has an index of refraction of about 1.5. In some embodiments, the inorganic undulating layer has an index of refraction of 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.

[0090] In some embodiments, a minimum spacing between the optical core and the plurality of substantially parallel ridges and grooves 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, as average spacing between the grooves and the optical core is 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.

[0091] According to some aspects of the present description, an optical waveguide includes an optical core configured to propagate an image light therealong, a continuous seamless multilayer grating disposed on a major side of the optical core, and at least one multilayer antireflective stack.

[0092] In some embodiments, the continuous seamless multilayer includes a continuous seamless inorganic layer and a continuous seamless adhesive layer. In some embodiments, 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 undulated inorganic layer portions of an otherwise non-undulated inorganic layer. In some embodiments, the at least one of the undulated inorganic layer portions is disposed between the optical core and the at least one multilayer antireflective stack. In some embodiments, for each of the at least one multilayer antireflective stack, an undulated inorganic layer portion of the at least one undulated inorganic layer portion is disposed between the optical core and the multilayer antireflective stack.

[0093] In some embodiments, each of the undulated inorganic layer portions includes opposing outermost undulating major surfaces nestingly aligned with each other and forming a plurality of substantially parallel ridges and grooves of the undulated inorganic layer portion extending along a length-direction (e.g., a x-axis) of the undulated inorganic layer portion and arranged along an orthogonal width-direction (e.g., a y-axis) of the undulated inorganic layer portion.

[0094] In some embodiments, the continuous seamless adhesive layer is disposed between the inorganic layer and the optical core and may substantially conform to the ridges and grooves of each of the undulated inorganic layer portion and bonding the inorganic layer to the optical core.

[0095] In some embodiments, a first of the undulated inorganic layer portions is configured to receive an image light from an image projector and inject at least a portion of the received image light into the optical core. In some embodiments, the injected image light propagates along the optical core primarily by total internal reflection. In some embodiments, a second of the undulated inorganic layer portions is configured to receive at least a portion of the injected image light along a first direction and redirect the injected image light as a redirected image light propagating along a different, second direction along the optical core primarily by total internal reflection. In some embodiments, a third of the undulated 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.

[0096] When used herein, the term “seamless” used in conjunction with the term “layer” (as in “seamless adhesive layer”) shall be defined to mean a layer which was formed as a continuous piece and which substantially does not contain gaps within the layer. In some embodiments, a “seamless” layer contains small cracks (e.g., cracks formed unintentionally as a result of a manufacturing or processing step) which do not significantly affect the intended function of the otherwise continuous layer. In addition, a layer containing intentional discontinuities between two substantially similar sections of the layer, where the two sections are otherwise in direct contact with each other (e.g., a butt-joint between two sections) and where the layer otherwise functionally performs substantially as a continuous layer, shall be considered seamless.

[0097] According to some aspects of the present description, a method of making an optical waveguide includes the steps of providing a carrier including an acrylate layer, a multilayer antireflective stack disposed on the acrylate layer, and a radiation-cured layer disposed on the multilayer antireflective stack where the radiation-cured layer includes a major structured surface having, in a plurality of discrete spaced apart regions, a plurality of alternating first ridges and first grooves; conformally disposing an inorganic layer on the major structured surface of the radiation-cured layer (e.g., so that both a first major surface thereof facing the carrier and a second major surface thereof facing away from the carrier substantially conform to the major structured top surface of the radiation-cured layer) to form a continuous seamless inorganic layer having a plurality of undulated inorganic layer portions in an otherwise non-undulated inorganic layer, such that in each of the undulated inorganic layer portions, the first and second major surfaces of the layer portion define a spacing average Savgand a spacing standard of deviation Ssd therebetween, Ssd / Savg 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 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 opposing substantially planar major surface; and adhering the substantially planar major surface of the structured adhesive layer to a major surface of an optical core configured to propagate an image light therealong primarily by total internal reflection. The method may further include, after the adhering step, removing the acrylate layer.

[0098] Turning now to the figures, FIG. 1A includes a side view of an embodiment of an optical waveguide according to the present description. In FIG. 1A, an embodiment of an optical system 300 is shown. In some embodiments, optical system 300 includes an optical waveguide 200 and at least one light source 70 / 71. FIG. IB includes a side view of a portion of the optical waveguide of FIG. 1A. In some embodiments, optical waveguide 200 includes an optical core 30, a multilayer grating 40, and a multilayer antireflective stack 150. In some embodiments, multilayer grating 40 is disposed on optical core 30 and configured to extract an optical mode that would otherwise propagate along optical core 30.

[0099] In some embodiments, light source 70 / 71 is disposed so as to inject light 20 / 21 at a first wavelength in a human-visible (visible) wavelength range into optical core 30, where the injected light 20 / 21 propagates along optical core 30 along a first direction (e.g., a direction along the x-axis, as shown in FIG. 1A) of the optical core 30 as the optical mode. Light 20 / 21 propagates along optical core 30 until it impinges on multilayer grating 40, where it may pass into multilayer grating 40 and be extracted from optical core 30 (where it is viewed by a viewer, not shown in FIG. 1A, but shown elsewhere herein). It should be noted that the first wavelength may also be outside of the visible wavelength range (e.g., is an infrared wavelength).

[0100] In some embodiments, multilayer grating 40 includes an adhesive layer 50 and an inorganic layer 60. In some embodiments, adhesive layer 50 incudes a major bottom surface 51 facing optical core 30 and an opposing structured major top surface 52 facing away and spaced apart from optical core 30. In some embodiments, the structured major top surface 52 incudes a plurality of substantially parallel linear grating elements 53 extending along a same length direction (e.g., the y-axis as shown in FIG. 1A) of the grating elements 53 and arranged along an orthogonal width direction (e.g., the x-axis as shown in FIG. 1A) of the grating elements 53.

[0101] In some embodiments, the plurality of substantially parallel linear grating elements 53 form a periodic pattern along the width direction (e.g., the x-direction shown in FIG. 1A) of the grating elements 53. In some embodiments, the width direction of the grating elements is substantially parallel to the first direction. In some such embodiments, the periodic pattern has a period in a range from about 100 nm to about 1000 nm, or from about 150 nm to about 750 nm, or from about 200 nm to about 700 nm, or from about 250 nm to about 600 nm, or from about 300 nm to about 550 nm, or from about 300 nm to about 500 nm, or from about 300 nm to about 450 nm.

[0102] In some embodiments, the optical core has an average thickness tcof between about 100 microns and about 2000 microns, or about 150 microns and about 1500 microns, or about 200 microns and about 1250 microns, or about 250 microns and about 1250 microns, or about 300 microns and about 1000 microns. In some embodiments, a minimum spacing, db, between the optical core and the major top surface of the adhesive layer 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.

[0103] In some embodiments, the inorganic layer 60 is disposed on and may conform to the structured major top surface 52 of adhesive layer 50 so that the inorganic layer 60 has a thickness standard deviation that is less than about 50%, or about 45%, or about 40%, or about 35%, or about 30%, or about 25%, or about 20% of an average thickness of the inorganic layer 60. In some embodiments, inorganic layer 60 has a first major surface 61 facing away from optical core 30 and a second major surface 62 facing toward optical core 30 and substantially conforming to the major structured top surface 52 of adhesive layer 50. In some embodiments, inorganic layer 60 defines a plurality of alternating first concavities 63 and second concavities 64, where the first concavities 63 are concave toward the optical core 30 and the second concavities 64 are convex toward optical core 30. In some embodiments, inorganic layer 60 incudes one or more of titanium dioxide (TiCE), zirconium oxide (ZrOx), titanium oxide (TiOx), SiCh, AI2O3, CeCh, ZnO, bfthOs, Ta2O5. HfO2. SiAlOxNy, SijN^ Nb-doped TiC , and zirconium dioxide (ZrO2).

[0104] In some embodiments, the multilayer grating 40 of the optical waveguide 200 further includes a (e.g., polymeric, radiation-cured, and / or planarizing) layer 80 disposed on and substantially planarizing the inorganic layer 60. In some embodiments, at the first wavelength, an index of refraction of the layer 80 is less than the index of refraction of the inorganic layer 60 by at least 0.5.

[0105] FIG. IB shows additional detail on adhesive layer 50. Adhesive layer 50 is structured and include a major bottom surface 51 and an opposing major structured top surface 52. In some embodiments, major structured top surface 52 includes a plurality of alternating ridges 54 and grooves 155. In some embodiments, an average spacing dabetween the bottoms of grooves 155 and the optical core 30 is greater than about 5 nm, or about 10, or about 15, or about 20, or about 25, or about 30, or about 35, or about 40, or about 45, or about 50 nm.

[0106] FIG. 2 shows an image from a scanning electron microscope (SEM) of a multilayer grating on an optical core, according to an embodiment of the present description. A multilayer grating 40 is disposed on an optical core 30. In the embodiment shown in FIG. 2, the multilayer grating 40 includes an adhesive layer 50, an inorganic layer 60 conforming to the adhesive layer 50, and a layer 80 planarizing the top of the multilayer grating 40. A multilayer antireflective stack 150 (not part of the SEM image) is schematically indicated to be disposed on layer 80 opposite the inorganic layer 60. Optical film 140 includes multilayer antireflective stack 150 and multilayer grating 40. The major surface of layer 80 that faces layer 50, and the major surface of the layer 50 that faces layer 80 may be described as substantially conforming to one another.

[0107] Inorganic layer 60 is disposed on optical core 30 and defines a plurality of alternating first 63 and second 64 concavities. In this embodiment, first concavities 63 are concave toward optical core 30, the second concavities 64 are convex toward optical core 30. Structured adhesive layer 50 is disposed between and bonds optical core 30 to inorganic layer 60 such that the structured adhesive layer 50 substantially fills first concavities 63.

[0108] In some embodiments, for each pair of adjacent first concavities 63a and second concavities 64a, the first 63a and second 64a concavities are separated by a common side wall 65 extending from a first rounded side wall comer 65a joining the common side wall 65 to a bottom 64al of the second concavity 64a to an opposite second rounded side wall comer 65b joining the common side wall 65 to a bottom 63al of first concavity 63a. In a first planar cross-section (e.g., the xz-plane shown in FIG. 2) substantially orthogonal to the common side wall 65, the first rounded side wall comer 65a includes an outer first circumferential surface 65al which faces the optical core 30 and has a first radius of curvature Rl, and the second rounded side wall comer 65b includes an outer second circumferential surface 65b 1 facing away from optical core 30 and having a second radius of curvature R2, such that Rl is greater than R2 for at least a plurality of pairs of adjacent first 63a and second 64a concavities.

[0109] Also, in the same first planar cross-section (i.e., the xz-plane), the first rounded side wall comer 65a has an inner first circumferential surface 65a2 facing away from the optical core and having a first inner radius of curvature Rl ’, such that Rl is greater than Rl ’ for at least a plurality of pairs of adjacent first 63a and second 64a concavities.

[0110] FIGS. 3A and 3B are process flow diagrams schematically illustrating a method of making an optical waveguide with a multilayer grating and a multilayer antireflective stack, in accordance with an embodiment of the present description.

[0111] FIG. 3A schematically illustrates the steps of disposing an acrylate layer 142 on a release surface 143 of a release liner 141, and then disposing a multilayer antireflective stack 150 on the acrylate layer 142 to provide a substrate 97 that can subsequently be used in making a transfer film (e.g., transfer film 250 schematically illustrated in FIG. 3B) and / or an optical waveguide. Suitable release liners and methods of depositing the acrylate layer 142 on the release liner are described in International Appl. No. WO 2023 / 111729 (Gotrik et al.), for example.

[0112] FIG. 3B is a process flow schematically illustrating one embodiment of a method of making an optical waveguide with multilayer grating according to the present description. The method may include steps A-H outlined herein. It should be noted that the flow of the process shown in FIG. 3B follows the arrows provided between steps in FIG. 3B and moves in a serpentine pattern from the top of FIG. 3B to the bottom of FIG. 3B (i.e., the steps are performed in order based on their alphabetical labels from Step A to Step H).

[0113] A radiation cured layer 90 with a major structured surface 91 having a plurality of alternating first ridges 92 and first grooves 93 is provided (Step D). In some embodiments, Step D incudes providing a tool 100 having a major structured surface 101 having a plurality of alternating ridges 102 and grooves 103 (Step A), disposing a material 90a on the major structured surface 101 of tool 100 to form a radiation-curable layer which can be cured in contact with substrate 97 resulting in a radiation-cured layer

[0114] 90 having a major structured surface 91 facing and substantially conforming to the major structured surface 101 of tool 100 and including the plurality of alternating first ridges 92 and first grooves 93 (Step B), and removing the layer 90 from tool 100 (Step C). In some embodiments, the land area (marked as L in Step D, representing the thickness between the bottom of one groove on the major structured surface

[0115] 91 and the opposing surface of the substrate) is 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. In some embodiments, this thickness, which can correspond to an average minimum distance between the inorganic layer 60 (see step E) and the multilayer antireflective stack 150, is less than about 500, 400, 300, 200, 150, 100, 90, or 80 nm.

[0116] In Step E, an inorganic layer 60 is conformally disposed on major structured surface 91 of radiation-cured layer 90. Conformally disposing the inorganic layer 60 on major structured surface 91 generally means disposing the inorganic layer 60 so that at least a first major surface 61 facing layer 90 substantially conforms to the major structured surface 91. In some embodiments, inorganic layer 60 is conformally disposed on major structured surface 91 of radiation-cured layer 90 so that both a first major surface 61 thereof facing layer 90 and a second major surface 62 thereof facing away from layer 90 substantially conform to the major structured top surface 91 of the layer 90. In some embodiments, the first major surface 61 and the second major surface 62 of the inorganic layer 60 defines a spacing average Savgand a spacing standard of deviation Ssd therebetween, such that Ssd / Savg 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 incudes a chemical vapor deposition (CVD) method, a sputter coating method, a physical vapor deposition (PVD) method, an atomic layer deposition (ALD) method, or any appropriate combination thereof.

[0117] In Step F, a layer of adhesive material is disposed on the second major surface 62 of inorganic layer 60 which substantially planarizes inorganic layer 60 to form a structured adhesive layer 50 having major structured top surface 52 which faces and substantially conforms to second major surface 62 of inorganic layer 60, and an opposing substantially planar major surface 51.

[0118] In some embodiments, the layer of adhesive material is a polymeric or monomeric adhesive layer and / or is an optically clear adhesive layer. Suitable optically clear adhesives include, but are not limited to, those available from Norland Products, Inc. (Cranbury, NJ), for example. Other suitable adhesives include thermosetting materials such as those available from the Dow Chemical Company (Midland, MI) under the CYCLOTENE tradename, for example. Still other suitable adhesives include heat-activated adhesives such as those available from KRATON Polymers (Houston, TX) under the KRATON tradename, for example. Suitable adhesive layers, including thin adhesive layers (e.g., less than 50 nm thick), are described in U.S. Pat. Nos. 7,521,727 (Khanarian et al.); 7,53,419 (Camras et al.); 6,709,883 (Y ang et al.); and 6,682,950 (Y ang et al.), for example.

[0119] In Step G, the substantially planar major surface 51 of the structured adhesive layer 50 is adhered to a major surface 31 of an optical core 30 configured to propagate an image light therealong primarily by total internal reflection. In Step H, the separable layer 141 is removed from the multilayer antireflective stack 150. The acrylate layer 142 may also optionally be removed from the multilayer antireflective stack 150 (e.g., the acrylate layer has been removed from the multilayer antireflective stack 150 in FIG. 1A and other figures). The acrylate layer may be removed by etching (e.g., oxygen plasma etching), for example. Removing the acrylate layer may result in a lower average reflectance (e.g., no more than about 8, 7, 6, or 5 percent) for substantially normally incident (e.g., within about 20, 15, 10, or 8 degrees of normal incidence) visible light (e.g., light in a wavelength range of about 400 nm to about 700 nm) which is desired for many applications. Leaving the acrylate layer can result in low average reflectance for substantially normally incident light in some wavelength regions (e.g., no more than about 8, 7, 6, or 5 percent in each of a red and a blue wavelength range) which may be desired for some applications.

[0120] FIG. 4 is a schematic side view of an embodiment of optical system having an optical waveguide featuring at least first and second multilayer gratings and at least first and second multilayer antireflective stacks, according to the present description. In some embodiments, optical system 400 includes an optical waveguide 305 (including a first multilayer grating 40a, a second multilayer grating 40b, a first multilayer antireflective stack 150a, a second multilayer antireflective stack 150b, and an optical core 30a), and an image projector 70a.

[0121] In some embodiments, optical core 30a of optical waveguide 305 is configured to propagate light therealong through total internal reflection. In some embodiments, first 40a and second 40b spaced-apart, multilayer gratings are disposed on optical core 30a. In some embodiments, first multilayer grating 40a is configured to receive image light 20 from image projector 70a and inject at least a portion 21 of the received image light into optical core 30a.

[0122] In some embodiments, the injected image light 21 propagates along the optical core as propagating image light 22 primarily by total internal reflection. In some embodiments, second multilayer grating 40b is configured to receive at least a portion 23 of the propagating image light 22 and extract at least a portion 24 of the received injected image light from optical core 30a for viewing by a viewer 55.

[0123] In some embodiments, each of the first 40a and second 40b multilayer gratings incudes an inorganic undulating layer 60a, 60b and a planarizing adhesive layer 50a, 50b. In some embodiments, inorganic undulating layer 60a, 60b incudes opposing outermost undulating major surfaces 61a, 61b, 62a, 62b nestingly aligned with each other to have a wave-like shape along a width direction (e.g., the x-axis as shown in FIG. 4 for 40a, or x’ axis shown in FIG. 5 for 40b) of the inorganic undulating layer 60a, 60b, and forming a plurality of substantially parallel ridges 62a, 62b and grooves 63b, 63b. In some embodiments, ridges 62a, 62b and grooves 63b, 63b extend along an orthogonal length direction (e.g., the y-axis of FIG. 4, or the y’-axis of FIG. 5) of the inorganic undulating layers 60a, 60b.

[0124] In some embodiments, planarizing adhesive layer 50a, 50b is disposed between inorganic undulating layer 60a, 60b and optical core 30a and may substantially planarize one of the undulating major surfaces 62a, 62b of inorganic undulating layer 60a, 60b and may bond the inorganic undulating layer 60a, 60b to optical core 30a.

[0125] In some embodiments, for at least one of the first 40a and second 40b multilayer gratings, the multilayer grating further includes a (e.g., planarizing and / or radiation cured) layer 80a, 80b conformally covering inorganic undulating layer 60a, 60b opposite the planarizing adhesive layer 50a, 50b and substantially planarizing the inorganic undulating layer 60a, 60b. Layers 80a, 80b, and / or 80 (described elsewhere herein) may correspond to layer 90 of FIG. 3B.

[0126] FIG. 5 provides an alternate view of the embodiment of the optical waveguide of FIG. 4. Like- numbered components common to both FIGS. 4 and 5 shall be assumed to serve similar functions unless specifically stated otherwise. That is, descriptions given for components in FIG. 4 shall be assumed to apply to like-numbered components in FIG. 5 and therefore these descriptions may not be repeated in the description of FIG. 5. In some embodiments, image light 20 is emitted by image projector 70a and enters optical core 30 via first multilayer grating 40a. This image light is propagated as propagating image light 22 (via total internal reflection within optical core 30a) until at least a portion of the light is extracted from optical core 30a via second multilayer grating 40b as extracted image light 24 for viewing by viewer 55. As shown in FIG. 5, the orientation of first multilayer grating 40a and second multilayer grating 40b (i.e., the width directions of the two gratings) may differ, as is desired by an application to direct the image light in an appropriate direction. In some embodiments, the ridges and grooves of first multilayer grating 40a are aligned with and extend in the x direction shown in FIG. 5 (left side of FIG. 5), while the ridges and grooves of second multilayer grating 40b are aligned with and extend in the x’ direction shown in FIG. 5 (right side of FIG. 5).

[0127] FIGS. 6A and 6B include side views of the architecture of an embodiment of a multilayer grating, such as multilayer gratings 40a, 40b of FIGS. 4 and 5. The multilayer grating will typically include a radiation-cured layer disposed on the inorganic layer and the optical waveguide including the multilayer grating will typically further include a multilayer antireflective stack disposed on the radiation- cured layer as described further elsewhere herein. FIGS. 6A and 6B is examined together for the following discussion. In some embodiments, at least one of multilayer gratings 40a, 40b has an undulation amplitude Am(e.g., the distance between the bottom of a groove to the top of an adjacent ridge) that varies along the width direction (e.g., the x-direction shown in FIGS. 6A-6B) thereof. In some embodiments, the planarizing adhesive layer 50a, 50b defines a minimum distance dmin between the inorganic undulating layer 60 and the optical core 30a, such that dmin 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 40a and second 40b multilayer gratings, a minimum separation d between the optical core 30a and the bottom of the grooves of the multilayer gratings 40a, 40b changes along the width of the multilayer grating 40a, 40b.

[0128] In some embodiments, for at least one of the first 40a and second 40b multilayer gratings, in a planar cross-section (e.g., the xz-plane shown in FIGS. 6A-6B) of the multilayer grating 40a, 40b that is orthogonal to the length direction (e.g., the y-axis) of the multilayer gratings 40a, 40b, and for two different locations on the multilayer grating LI and L2, each location including a single ridge and a single directly adjacent groove, where the area between the optical core and the ridge at LI is Ari, the area between the optical core and the groove at LI is Agi, the area between the optical core and the ridge at L2 is Ar2, and the area between the optical core and the groove at L2 is Ag2. In some embodiments, Ari+ Agiis within 30% of Ar+ Ag2, or within 30% of Ar2 + Ag2, or within 10% of Ar2 + Ag2, or within 5% of Ar2 + Ag2, or within 2% of Ar2 + Ag2. The ridge and groove can have a combined width of Wi and W2 at the respective locations LI and L2. In some embodiments, (Ari+ Agi) / Wi is within 30% of (Ar2 + Ag2) / W2, or within 30% of (Ar2 + Ag2) / W2, or within 10% of (A^ + Ag2) / W2, or within 5% of (Ar2 + Ag2) / W2, or within 2% of (Ar2+ Ag2) / W2.

[0129] FIG. 7 is a side view of an alternate embodiment of an optical system, including an optical waveguide with first and second multilayer gratings disposed on opposite side of an optical core. The embodiment shown in FIG. 7 is similar to the embodiment shown in FIG. 4 discussed elsewhere herein. Accordingly, like-numbered components common to both figures shall be assumed to have the same function unless specifically stated otherwise, and definitions may not be repeated from the discussion of FIG. 4 in the discussion of FIG. 7. In the embodiment of FIG. 7, the first 40a and second 40b spacedapart, multilayer gratings are disposed on opposite major sides 1 la and 1 lb of the optical core 30a (as opposed to on the same major side, as shown in FIG. 4). The basic function of optical waveguide 305 of FIG. 7 may be essentially the same as the basic function of optical waveguide 305 of FIG. 4 (i.e., the second multilayer grating 40b extracts a portion of light 23 and directs it as image light 24 for viewing by viewer 55, but viewer 55 is now on major side 1 lb of optical waveguide 305, and image projector 70a is on side 1 la of optical waveguide 305).

[0130] FIG. 8 is a side view of another alternate embodiment of optical waveguide 305, and also shares common, like-numbered components with both FIGS. 4 and 7, which shall be assumed to have similar functions unless specifically stated otherwise. In the embodiment of optical waveguide 305 of FIG. 8, 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 40a and second 40b multilayer gratings. In some embodiments, optical waveguide 305 further includes a connecting, substantially non-undulating (e.g., nominally non-undulating but possibly including ordinary manufacturing variations) inorganic layer 111 disposed between, and continuously and seamlessly connecting, the inorganic undulating layers 60a, 60b of the first 40a and second 40b multilayer gratings. In some embodiments, where each of the first 40a and second 40b multilayer gratings further includes a planarizing layer 80a, 80b conformally covering the inorganic undulating layer 60a, 60b opposite the planarizing adhesive layer 50a, 50b and substantially planarizing the inorganic undulating layer 60a, 60b, the optical waveguide 305 further includes a substantially planar connecting layer 112 disposed between, and continuously and seamlessly connecting, the planarizing layers 80a, 80b of the first 40a and second 40b multilayer gratings. In some such embodiments, for at least one visible wavelength in a human- visible wavelength range extending from about 420 nm to about 680 nm, an index of refraction of the planarizing layer 112, 80a, 80b is less than index of refraction of the inorganic undulating layer 60a, 60b by at least 0.5.

[0131] FIGS. 9A and 9B provide top and side views, respectively, of yet another embodiment of an optical waveguide. FIGS. 9A and 9B should be examined together for the following discussion. In some embodiments, optical waveguide 310 incudes an optical core 30a configured to propagate an image light therealong and a continuous seamless multilayer 40s disposed on a major side 1 la of optical core 30a. In some embodiments, continuous seamless multilayer 40s incudes a continuous seamless inorganic layer 60 and a continuous seamless adhesive layer 50.

[0132] In some embodiments, continuous seamless inorganic layer 60 is undulated in a plurality of discrete spaced apart regions 100a, 100b, 100c (FIG. 9B) of the inorganic layer 60 to form a plurality of spaced apart undulated inorganic layer portions 60a, 60b, 60c of an otherwise non-undulated inorganic layer 60. In some embodiments, each of the undulated inorganic layer portions 60a, 60b, 60c incudes opposing outermost undulating major surfaces 61a, 61b, 61c; 62a, 62b, 62c nestingly aligned with each other and forming a plurality of substantially parallel ridges 63a, 63b, 63c and grooves 64a, 64b, 64c of the undulated inorganic layer portion 60a, 60b, 60c extending along a length-direction (see, e.g., y-, y’-, and y”-axis depictions in FIG. 9A) of the undulated inorganic layer portion 60a, 60b, 60c and arranged along an orthogonal width-direction (e.g., y-, y’-, and y”-axis) of the undulated inorganic layer portion 60a, 60b, 60c.

[0133] In some embodiments, the continuous seamless adhesive layer 50 is disposed between the inorganic layer 60 and the optical core 30a and may substantially conform to the ridges 63 and grooves 64 of each of the undulated inorganic layer portions 60a, 60b, 60c and bond the inorganic layer 60 to the optical core 30a.

[0134] In some embodiments, a first undulated inorganic layer portion 60a is configured to receive an image light 20 from an image projector 70a and inject at least a portion 21 of the received image light into optical core 30a. In some embodiments, the injected image light 21 propagates along optical core 30a primarily by total internal reflection.

[0135] In some embodiments, a second undulated inorganic layer portion 40c is configured to receive at least a portion 25 of the injected image light 21 along a first direction 25a and redirect the injected image light as a redirected image light 26 propagating along a different second direction 26a along the optical core 30a primarily by total internal reflection.

[0136] In some embodiments, a third undulated inorganic layer portion 40b is 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 a viewer 55.

[0137] FIGS. 10A and 10B provide illustrative examples of alternative shapes for the features on a multilayer grating. FIGS. 10A-10B show respective multilayer gratings 40c and 40d disposed on an optical core 30 and multilayer antireflective stack 150 disposed on the multilayer grating. In some embodiments, multilayer grating 40c includes an adhesive layer 50, an inorganic layer 60, and a radiation-cured or planarizing layer 80. Similarly, in some embodiments, multilayer grating 40d includes an adhesive layer 50, an inorganic layer 60, and a radiation-cured or planarizing layer 80. In some embodiments, inorganic layer 60 defines a plurality of alternating first concavities 63 and second concavities 64, wherein the first concavities 63 are concave toward the optical core 30 and the second concavities 64 are convex toward optical core 30. In the embodiment 40c of FIG. 10A, the first concavities 63 and second concavities 64 have a slanted square wave shape. In FIG. 10B, the plurality of alternating first concavities 63 and second concavities 64 of multilayer grating 40d have a triangular or “blazed” shape.

[0138] Although the examples discussed herein thus far have demonstrated a one-dimensional pattern of undulations, multilayer gratings exhibiting a two-dimensional array of features are also within the scope of the present description. For example, FIG. 11 A shows an example of a grating 40e which exhibits a two-dimensional array of posts, comparable to ridges 63, with the area between the posts comparable to grooves 64. Similarly, FIG. 1 IB shows a grating 40f with a two-dimensional array of holes, where each hole is similar in function to a groove 64 and the area between holes is comparable to ridges 63. In both FIGS. 11A and 1 IB, the cross-section of the gratings 40e and 40f (disposed on optical core 30) shown in the figures illustrates the same undulating pattern of the inorganic layer 60 and adhesive layer 50. A radiation-cured or planarizing layer and a multilayer antireflective stack can be further included as described further elsewhere herein.

[0139] As discussed elsewhere herein, the ridges and grooves (or first and second concavities) of the multilayer gratings discussed herein may have any appropriate shape. The embodiments of FIGS. 10A, 10B, 11A, and 1 IB are examples only and not intended to be limiting in any way.

[0140] FIG. 12 is an illustrative example of possible methods for measuring dimensions on an undulating layer of a multilayer grating according to the present description. For example, one method of measuring the thickness of the undulating inorganic layer is to take multiple measurements of the distance between the first major surface and the second major surface of the inorganic layer 60, such as the measurements si through s8 shown in FIG. 12. One method of doing this is to randomly select a number of points on the first major surface 61 of inorganic layer 60 and then to draw a straight line to the closest corresponding point on the second major surface 62. Then the spacing average Savg is determined by taking the average of these measurements, and the spacing standard of deviation Ssd is determined.

[0141] In some embodiments, the multilayer antireflective stack 150 is an interference stack including at least 2, 3, 4, or 5 alternating A and B layers. In some such embodiments, or in other embodiments, the stack 150 includes no more than 50, 40, 30, 25, 20, or 15 of the alternating A and B layers in total. The A and B layers can be, for at least one wavelength in a range of 400 to 700 nm, respective higher and lower refractive index layers.

[0142] FIG. 13 is a schematical cross-sectional view of a multilayer antireflective stack 150 including a plurality of alternating A and B layers, according to some embodiments. In some embodiments, at least some of the layers of the multilayer antireflective stack 150 are inorganic layers. For example, every other layer of the stack 150 can be an inorganic layer (e.g., the higher index layers can be inorganic and the lower index layers can be organic), or every layer of the stack 150 can be an inorganic layer. For example, in some embodiments, each A layer is an inorganic layer, while each B layer may be an inorganic layer having a different composition than the A layers or each B layer may be an organic layer. Suitable materials for the layers of the stack 150 include metal fluorides such as yttrium fluoride and magnesium fluoride, for example, and metal oxides (oxides of metalloids will herein be considered metal oxides) such as TiOx or SiOx, for example. In some embodiments, at least some the layers (e.g., the inorganic layers) of the stack 150 are polycrystalline and can be characterized by grain sizes of the layers.

[0143] FIG. 14 is a schematic illustration of grain sizes of layers of a multilayer antireflective stack, according to some embodiments. Plan and side (or cross-section) views 201a and 201b for a first layer 211 and plan and side (or cross-section) views 202a and 202b for a different second layer 212 are schematically illustrated. The first layer 211 can be a first A layer (e.g., the outermost A layer facing the multilayer grating) of a multilayer antireflective stack and the second layer 212 can be a second A layer (e.g., the outermost layer A layer facing away from the multilayer grating). Grain boundaries 205 are indicated. The average grain sizes can be determined from transmission electron microscopy (TEM) images, or (e.g., a grazing incidence) x-ray diffraction, or atomic force microscopy (AFM), or scanning electron microscopy (SEM) images, of the layers in, a plan view of a thin section or in a cross-sectional view, as the mean of the areas of the grains in the image. The mean of the areas can be taken to be the inverse of the number of grains per unit area which can be determined according to the ASTM El 12- 13(2021) test standard, for example.

[0144] In some embodiments, the multilayer antireflective stack 150 is disposed on a second major surface of a first layer of a multilayer grating as described further elsewhere herein. In some embodiments, the multilayer antireflective stack 150 includes a first outermost layer, or outermost first A layer, facing the second major surface of the first layer of the multilayer grating and an opposing second outermost layer, or outermost second A layer, where the first and second outermost layers or first and second A layers have respective first and second average grain sizes, and the first average grain size is greater than the second average grain size. The second and first outermost layers, or first and second A layers, can be the initial and final layers, or initial and final A layers, respectively, deposited on the acrylate layer 142 in making the multilayer antireflective stack 150 (see, e.g., FIG. 3A). The final layer of the stack 150 is typically deposited on a layer (the earlier deposited layers in the stack) that is at a higher temperature than the layer (the acrylate layer 142) on which the initial layer of the stack 150 is deposited. The final layer, or final A layer, may have a larger average grain size than that of the initial layer, or initial A layer, because of recrystallization at the higher temperature at which the final layer, or final A layer, is deposited, for example. In some embodiments, the multilayer antireflective stack includes a plurality of alternating A and B layers, where each A layer has a same inorganic first composition, and each B layer has a same second composition different from the first composition, where the plurality of alternating A and B layers include first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack, where the first A layer is disposed between the multilayer grating and the second A layer, and where an average grain size of the first A layer is greater than an average grain size of the second A layer. The second and first A layers can be the initial and final A layers, respectively, deposited on the acrylate layer 142 in making the multilayer antireflective stack 150 (see, e g., FIG. 3A). EXAMPLES

[0145] Materials

[0146] Substrate with Separation Packet

[0147] A substrate with separation packet was made by depositing a separation packet on ST504 polyethylene terephthalate (PET) film according to methods described in International Pat. Appl. Pub. No. WO 2023 / 111729 (Gotrik et al.). The acrylate coating acting as the first layer of the separation packet on SiA10xfor release was made on a roll-to-roll vacuum coater similar to the coater described in U.S. Patent Appl. Pub. No. 2010 / 0316852 (Condo, et al.) with the addition of a second evaporator and curing system located between the plasma pretreatment station and the first sputtering system, and using evaporators as described in U.S. Patent No. 8,658,248 (Anderson et al.).

[0148] This coater was outfitted with a substrate in the form of an indefinite length roll of 0.05 mm thick, 9 inch (22.86 cm) wide ST504. The substrate was prepared for coating by subjecting it to a nitrogen plasma treatment to improve the adhesion of the planarizing acrylate layer to the PET. The film was treated with a nitrogen plasma operating at 50 W using a titanium cathode, using a web speed of 8.0 meters / min and maintaining the backside of the film in contact with a coating drum chilled to 0° C.

[0149] On this prepared ST504 PET substrate, a planarizing acrylate layer of SR833 was formed. The acrylate layer was applied by ultrasonic atomization and flash evaporation to make a coating width of 9 inches (22.68 cm). The flow rate of this mixture into the atomizer was 0.67 ml / min to achieve a 375 nm layer, the gas flow rate was 60 standard cubic centimeters per minute (SCCM), and the evaporator temperature was 260° C. Once condensed onto the PET substrate, this monomeric coating was cured immediately with an electron beam curing gun operating at 7.0 kV and 4.0 mA.

[0150] The release layer of SiA10xwas deposited in-line with the previous acrylate coating step. This silicon aluminum oxide layer was laid down using an alternating current (AC) reactive sputter deposition process employing a 40 kHz AC power supply from a SiAl target. The voltage for the cathode during sputtering was controlled by a feed-back control loop that monitored the voltage and controlled the oxygen flow such that the voltage would remain constant. The system was operated at 16 kW of power to deposit an 11 nm thick layer of silicon aluminum oxide onto the planarizing organic acrylate layer. The transferrable acrylate layer (separation packet) of SR833 was deposited in-line with the previous SiA10xdeposition. The acrylate layer was applied by ultrasonic atomization and flash evaporation to make a coating width of 9 inches (22.68 cm). The flow rate of this mixture into the atomizer was 0.67 ml / min to achieve a 375 nm layer, the gas flow rate was 60 standard cubic centimeters per minute (SCCM), and the evaporator temperature was 260° C. Once condensed onto the SiA10xlayer, this monomeric coating was cured immediately with an electron beam curing gun operating at 7.0 kV and 4.0 mA.

[0151] A multilayer antireflective (AR) stack was then deposited using electron beam evaporation as a vacuum deposition process on the transferable acrylate layer surface. The deposited layers included 7 layers in total of SiOx and TiOx alternating with one another (starting and ending with SiOx) and having thickness of 84, 116, 37, 22, 50, 23, and 9 nm from the layer of the stack closest to the acrylate layer to the opposite layer of the stack.

[0152] A sample of the substrate with the multilayer antireflective stack was tested as follows. A layer of FG1901 adhesive was spin-coated onto the multilayer antireflective stack and the substrate with the stack was attached to a high index glass waver. The substrate was then removed leaving the antireflective stack and the transferable acylate layer disposed on the glass wafer. The transferable acrylate layer was then removed by oxygen plasma etching. The glass wafer with and without the antireflection stack had an average visible reflectance for substantially normally incident light of about 5% and 13%, respectively. Before removing the acrylate layer, the average reflectance of the wafer was increased to greater than 13%, but the reflectance in some wavelength ranges (a blue wavelength range and a green wavelength range) were reduced (e.g., to about 5% or less) compared to that of the glass wafer without the antireflective stack.

[0153] Nanostructure Tooling Film

[0154] A nanostructure tooling film was prepared by die coating a photocurable acrylate resin mixture (prepared by combining and mixing PHOTOMER 6210, SR238, SR351 and TPO in weight ratios of 60 / 20 / 20 / 0.5) onto ST505 film. The coated film was pressed against a nanostructured nickel surface attached to a steel roller controlled at 60° C using a rubber covered roller at a speed of 15.2 meters / min. The nanostructured nickel surface consisted of subwavelength gratings arranged as a 2D exit pupil expander pattern. The pattern has three grating regions that function as the input coupler, exit-pupil expander, and output coupler when attached to an appropriate substrate.

[0155] The coating thickness of the acrylate resin mixture on the film was sufficient to fully wet the nickel surface and form a rolling bead of resin as the coated film was pressed against the nanostructured nickel surface. The film was exposed to radiation from two Fusion UV lamp systems (obtained under the trade designation “F600” from Fusion UV Systems, Gaithersburg, MD) fitted with D bulbs both operated 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 fdm was exposed again to radiation from a single Fusion UV lamp system.

[0156] A silicon containing release film layer assembled according to 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.) was applied to the nanostructure tooling film in a parallel plate capacitively coupled plasma reactor. The chamber had a central cylindrical powered electrode with a surface area of 1.7 m2(18.3 ft2).

[0157] The nanostructured tooling film was placed on the powered electrode, and the reactor chamber was pumped down to a base pressure of less than 1.3 Pa (2 mTorr). O2 gas was flowed into the chamber at a rate of 1000 SCCM. Treatment was carried out using a plasma enhanced CVD method by coupling radiofrequency (RF) power into the reactor at a frequency of 13.56 MHz and an applied power of 2000 Watts. Treatment time was controlled by moving the nanostructure tooling film through the reaction zone at rate of 9. 1 meter / min (30 ft / min) resulting in an approximate exposure time of 10 seconds. After completing the deposition, RF power was turned off and gasses were evacuated from the reactor.

[0158] After the first treatment, a second plasma treatment was carried out in the same reactor without returning the chamber to atmospheric pressure. HMD SO gas is flowed into the chamber at approximately 1750 SCCM to achieve a pressure of 9 mTorr. 13.56 MHz RF power was subsequently coupled into the reactor with an applied power of 1000 W. The film was then carried through the reaction zone at a rate of 9.1 meter / min (30 ft / min) resulting in an approximate exposure time of 10 seconds. At the end of this treatment time, the RF power and the gas supply were stopped, the chamber was returned to atmospheric pressure, and the release-treated nanostructure tooling film was removed from the chamber.

[0159] Radiation-Cured Uayer

[0160] To demonstrate making a multilayer grating, a sample was made as described above but with the AR stack omitted. The substrate with separation packet was corona treated at an energy density of 1,000 J / cmA2. An acrylate solution was prepared by adding 74 wt% PHOTOMER 6210 with 25 wt% SR238 and 0.014% TPO to create Acrylate Resin A. Acrylate Resin A was diluted to make a solution of 10 wt% Acrylate Resin A, 54 wt% PGME, and 36% MEK. The diluted solution was slot-die coated onto the corona treated substrate with separation packet at a rate of 3 meters / minute. The solution was coated 10.16 cm wide and pumped with a syringe pump (Harvard Apparatus, Holliston, Massachusetts) at a rate of 3 SCCM.

[0161] The film was then dried at ambient conditions for 3 minutes before entering a nip. At the nip, the coated substrate with separation packet was laminated to the release treated nanostructure tooling film made in the previous step.

[0162] The nip consisted of a 90-durometer rubber roll and a steel roll set at 54°C. The nip was engaged by two Bimba air cylinders (Bimba, University Park, IL) pressurized to 0.55 MPa. The coated acrylate solution was cured using a Fusion D bulb (Fusion UV Systems, Gaithersburg, MD) and the cured acrylate mixture was separated from the release treated tooling fdm leaving behind the cured acrylate coating with a replica of the subwavelength gratings on the substrate with separation packet. Web tensions were set to be approximately 0.0057 N / m.

[0163] Transfer Film

[0164] A transfer fdm was prepared using a sputtering coater to deposit the high index (n~2.4) TiOxlayer onto the radiation-cured layer described above. Three TiOxtargets powered at 3kW were used to deposit 15 nm of TiOxat 0.9 m / min sequentially in four passes using a DC reactive process with an argon / oxygen gas mixture (~2% O2) to result in a nominally 60 nm thick layer of TiOx(after deposition, x is approximately equal to 2). The transferrable acrylate film with the TiOxcoating had a thickness of nominally 350-550 nm.

[0165] A single pattern was cut from the roll of transfer film. A thin layer of FG1901 was applied over the TiOxsurface by spin-coating at 200 rpm for 5 seconds followed by 4000 rpm for 30 seconds at 0.48% solids dilution in Cyclohexane / Toluene (9 ,05%:90.95% by weight) to result in a ~45 nm thick layer.

[0166] Waveguide

[0167] The above adhesive-coated TiOx / gratings were laminated onto a High Index Glass Wafer by placing the paired substrates in a 120mm CNI nanoimprint tool (NIL Technologies ApS, Lyngby, Denmark) at a temperature of 140 C and pressure of 6 bars for 5 minutes. Once the laminated pair had cooled to room temperature, the PET film of the substrate with separation packet was removed. This resulted in the transfer acrylate, and TiOx / grating being left behind on the glass wafer.

[0168] The remaining transfer acrylate was removed from the TiOxgrating by O2 plasma etching using a 40kHz YES G-1000 plasma system (Yield Engineering Systems, Fremont, CA) for 140 minutes at 500W and 230 millitorr of oxygen pressure, on a grounded electrode.

[0169] The completed waveguide was illuminated with a projector (Venus III 40D, Coretronic Corporation, Hsinchu, Taiwan) directed onto the input coupler grating and an image was observed at the output coupler, confirming that it functioned as an image preserving waveguide.

[0170] The radiation-cured layer and the TiOxlayer can be formed on the AR stack described above and the resulting stack can be laminated onto a High Index Glass Wafer as described above to result in the transfer acrylate, the AR stack, and TiOx / grating being left behind on the glass wafer after the PET film of the substrate with separation packet is removed.

[0171] Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1. 1, and that the value could be 1.

[0172] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially equal” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially equal” will mean about equal where about is as described above. If the use of “substantially parallel” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially parallel” will mean within 30 degrees of parallel. Directions or surfaces described as substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees of parallel, or is parallel or nominally parallel. If the use of “substantially aligned” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially aligned” will mean aligned to within 20% of a width of the objects being aligned. Objects described as substantially aligned may, in some embodiments, be aligned to within 10% or to within 5% of a width of the objects being aligned.

[0173] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0174] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed:

1. A transfer film, comprising: a release liner having a release surface; an acrylate layer disposed on the release surface and having an average thickness in a range of about 10 nm to about 1500 nm; a multilayer antireflective stack disposed on the acrylate layer opposite the release liner; and a multilayer grating disposed on the multilayer antireflective stack opposite the acrylate layer.

2. The transfer film of claim 1, wherein the multilayer grating comprises: a first layer disposed on the acrylate layer and having a structured major surface facing away from the acrylate layer; an inorganic layer disposed on and substantially conforming to the structured major surface of the first layer; and a second layer disposed on the inorganic layer opposite the first layer, the second layer substantially planarizing the inorganic layer.

3. The transfer film of claim 2, wherein an average minimum distance between the inorganic layer and the multilayer antireflective stack is less than about 500 nm.

4. The transfer film of claim 2, wherein the inorganic layer has opposing first and second major surfaces defining a spacing average Savgand a spacing standard deviation Ssd therebetween, Ssd / Savg less than about0.5.

5. The transfer film of claim 2, wherein the inorganic layer defines a plurality of alternating first and second concavities, the first concavities convex toward the multilayer antireflective stack, the second concavities concave the multilayer antireflective stack; wherein for each pair of adjacent first and second concavities, the first and second concavities are separated by a common side wall extending from a first rounded side wall comer joining the common side wall to a bottom of the second concavity to an opposite second rounded side wall comer joining the common side wall to a bottom of the first concavity, such that in a first planar cross-section substantially orthogonal to the common side wall, the first rounded side wall comer comprises an outer first circumferential surface facing the second layer and having a first radius of curvature Rl, and the second rounded side wall comer comprises an outer second circumferential surface facing the first layer and having a second radius of curvature R2, wherein Rl > R2 for at least a plurality of pairs of adjacent first and second concavities.

6. The transfer film of claim 2, wherein the inorganic layer defines a plurality of alternating first and second concavities, the first concavities convex toward the multilayer antireflective stack, the second concavities concave toward the multilayer antireflective stack; wherein for each pair of adjacent first and second concavities, the first and second concavities are separated by a common side wall extending from a first rounded side wall comer joining the common side wall to a bottom of the second concavity to an opposite second rounded side wall comer joining the common side wall to a bottom of the first concavity, such that in a first planar cross-section substantially orthogonal to the common side wall, the first rounded side wall comer comprises an outer first circumferential surface facing the optical core and having a first outer radius of curvature Rl, and an inner first circumferential surface facing away from the optical core and having a first inner radius of curvature Rl ’, wherein Rl > Rl ’ for at least a plurality of pairs of adjacent first and second concavities.

7. The transfer film of claim 1, wherein the multilayer antireflective stack comprises a plurality of inorganic A layers, each A layer having a same first composition, the A layers of each pair of adjacent A layers being separated by at least one layer having a composition different from the first composition, the multilayer antireflective stack comprising first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack, the first A layer disposed between the multilayer grating and the second A layer, an average grain size of the first A layer being greater than an average grain size of the second A layer.

8. An optical film, comprising: a multilayer grating comprising first and second layers, each of the first and second layers having a structured first major surface and an opposite second major surface, the first major surfaces of the first and second layers disposed on and substantially conforming to one another, the second major surface of the first layer being substantially smooth; and a multilayer antireflective stack disposed directly on, and substantially coextensive with, the second major surface of the first layer, wherein the multilayer antireflective stack comprises a plurality of inorganic A layers, each A layer having a same first composition, the A layers of each pair of adjacent A layers being separated by at least one layer having a composition different from the first composition, the multilayer antireflective stack comprising first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack, the first A layer disposed between the multilayer grating and the second A layer, an average grain size of the first A layer being greater than an average grain size of the second A layer.

9. The optical film of claim 8 further comprising an acrylate layer having an average thickness in a range of about 10 nm to about 1500 nm, the multilayer antireflective stack disposed between, and directly contacting, the acrylate layer and the first layer.

10. The optical film of claim 8, wherein the multilayer grating comprises an undulating inorganic layer disposed between the first and second layers, the first major surfaces of the first and second layers disposed on and substantially conforming to the inorganic layer.

11. An optical film, comprising: a multilayer grating comprising first and second layers, each of the first and second layers having a structured first major surface and an opposite second major surface, the first major surfaces of the first and second layers disposed on and substantially conforming to one another, the second major surface of the first layer being substantially smooth; and a multilayer antireflective stack disposed directly on, and substantially coextensive with, the second major surface of the first layer, wherein an average minimum distance between the structured first major surface of first layer and the multilayer antireflective stack is less than about 500 nm.

12. The optical film of claim 11, wherein the multilayer antireflective stack comprises a plurality of inorganic A layers, each A layer having a same first composition, the A layers of each pair of adjacent A layers separated by at least one layer having a composition different from the first composition, the multilayer antireflective stack comprising first and second A layers as the A layers farthest apart from one another in the multilayer antireflective stack, the first A layer disposed between the multilayer grating and the second A layer, an average grain size of the first A layer being greater than an average grain size of the second A layer.

13. An optical waveguide comprising an optical core and at least one optical film according to any one of claims 8 to 12 disposed on the optical core, wherein for each of the at least one optical film, the multilayer grating is disposed between the optical core and the multilayer antireflective stack.

14. An augmented reality system comprising the optical waveguide of claim 13 and an image projector in optical communication with the at least one optical film.

15. A method of making a transfer film, the method comprising, in sequence: disposing an acrylate layer on a release surface of a release liner, the acrylate layer having an average thickness in a range of about 10 nm to about 1500 nm; disposing a multilayer antireflective stack on the acrylate layer; and disposing a radiation-cured layer on the multilayer antireflective stack, the radiation-cured layer comprising a major structured surface facing away from the multilayer antireflective stack, the major structured surface comprising a plurality of alternating first ridges and first grooves.

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