WO2023079041A1

WO2023079041A1 - Lightguide and method of making the same

Info

Publication number: WO2023079041A1
Application number: PCT/EP2022/080751
Authority: WO
Inventors: Andrew Mark; Darren Ihmels; Harjit Bhambra; Yaroslav Urzhumov; Lutz Körner; Daniel PIOTROWSKI
Original assignee: Meta Materials Inc.
Priority date: 2021-11-05
Filing date: 2022-11-03
Publication date: 2023-05-11

Abstract

A method of forming a lightguide includes dispensing a continuous line of a flowable curable sealant on a surface of a first plate, contacting a surface of a second plate to the curable sealant while maintaining a separation between the surfaces of the first and second plates using one or more spacers, curing the flowable curable sealant by exposing the flowable curable sealant to actinic radiation to form a solid gasket sealing a mold volume between the first and second plates while maintaining the separation between the surfaces, filling the mold volume with a prepolymer composition, curing the prepolymer composition in the mold volume to form a polymer layer, demolding the polymer layer to separate the polymer layer from the first and second plates, and obtaining the lightguide from the polymer layer.

Description

LIGHTGUIDE AND METHOD OF MAKING THE SAME

FIELD OF THE DISCLOSURE

[0001] This disclosure relates to the field of optical components, and more specifically to lightguides, such as lightguides that are useful for augmented reality (AR) displays, and methods for making such lightguides.

BACKGROUND

[0002] Lightguides are used in a variety of applications to confine and transport light from one point to another. For example, lightguides are used in head mounted displays, such as for AR applications. One or more lightguides can be used to direction light from a projector to a wearer’s eye, for example.

[0003] In such applications, stringent manufacturing tolerances may be necessary to ensure adequate optical performance. For example, extremely flat and/or extremely smooth surfaces may be needed in order for the lightguide to perform appropriately. Consistently achieving such surface characteristics in a plastic lightguide can be challenging.

SUMMARY

[0004] Techniques for forming lightguides with well controlled optical and mechanical properties are disclosed.

[0005] In a first aspect, the present disclosure is directed to a method of forming a lightguide that includes: dispensing a continuous line of a flowable curable sealant on a surface of a first plate; contacting a surface of a second plate to the curable sealant while maintaining a separation between the surfaces of the first and second plates using one or more spacers; curing the curable sealant to form a gasket sealing a mold volume between the first and second plates; filling the mold volume with a prepolymer composition; curing the prepolymer composition in the mold volume to form a polymer layer conforming to the mold volume; demolding the polymer layer to separate the polymer layer from the first and second mold plates; and obtaining the lightguide from the polymer layer. [0006] Implementations of the method can include one or more of the following features. The gasket, having been formed by curing the curable sealant, may be referred to as a solid gasket. For example, the mold volume can be vertically oriented while filling the mold volume with the prepolymer composition.

[0007] The gasket can include an opening and the prepolymer composition may be delivered to the mold volume through the opening.

[0008] The flowable curable sealant can be cured by exposing the curable sealant to actinic radiation. The prepolymer composition can be cured by exposing the prepolymer composition to actinic radiation, by heating the prepolymer composition, and/or by mixing reagents to form the prepolymer composition.

[0009] The flowable curable sealant can have a viscosity in a range from about 5,000 cP to about 100,000 cP. The first plate can have a lateral dimension in a range from about 10 mm to about 500 mm. In some examples, the first plate has a lateral dimension of about 200 mm, about 300 mm, or about 450 mm.

[0010] The surface of the first plate can be a planar surface. The surface of the second plate can also be a planar surface.

[0011] The separation between the surfaces of the first and second plates can be constant across the mold volume. The separation between the surfaces of the first and second plates can be in a range from about 10 pm to about 1,000 pm. In some examples, the separation between the surfaces of the first and second plates is about 500 pm or less.

[0012] The continuous line of the flowable curable sealant can be a circular line. The continuous line of the flowable curable sealant can be in a shape of an eyepiece.

[0013] The mold volume can be filled through an opening (e.g., one or more openings) in the solid gasket. The opening(s) can have a width of about 50 mm or less. [0014] The method can include dispensing a continuous line of an opaque material next to the solid gasket prior to filing the mold volume with the prepolymer composition.

[0015] The actinic radiation may be ultraviolet radiation.

[0016] The solid gasket can be absorptive at operative wavelengths of the lightguide. For example, the solid gasket can be black.

[0017] The prepolymer composition can be cured by exposure to second actinic radiation, by heating the prepolymer composition, and/or by mixing reagents to form the prepolymer composition. The second actinic radiation may be ultraviolet radiation.

[0018] The method can include post-curing the polymer layer prior to the demolding. The post-curing can include heating the polymer layer.

[0019] Obtaining the lightguide from the polymer material can include separating the polymer material from the solid gasket. Obtaining the lightguide from the polymer material can include singulating the lightguide from the polymer material

[0020] The method can include integrating the lightguide into a display, such as a headmounted display (e.g., an augmented reality head-mounted display).

[0021] In a second aspect, the present disclosure is directed to a method of forming a lightguide, including: dispensing a continuous line of a flowable curable sealant on a surface of a first plate; contacting a surface of a second plate to the curable sealant while maintaining a separation between the surfaces of the first and second plates using one or more spacers; curing the flowable curable sealant by exposing the flowable curable sealant to actinic radiation to form a solid gasket sealing a mold volume between the first and second plates while maintaining the separation between the surfaces; filling the mold volume with a prepolymer composition; curing the prepolymer composition in the mold volume to form a polymer layer; demolding the polymer layer to separate the polymer layer from the first and second plates; and obtaining the lightguide from the polymer layer.

[0022] In a third aspect, the present disclosure is directed to an article, including: first and second mold plates arranged with respective surfaces facing each other; one or more spacers between the respective surfaces defining a gap of 500 pm or less between the respective surfaces; a gasket comprising a continuous line of a cured sealant sealing the gap and defining a mold volume; and a flowable prepolymer composition at least partially filling the mold volume. The gasket can be in the shape of an eyepiece (e.g., teardrop shaped). The gasket can include an opening sized and shaped to receive the prepolymer composition.

[0023] Examples of the article can include one or more of the following features and/or features of other aspects. For example, the gasket can be in the shape on an eyepiece. The gasket can include an opening sized and shaped to receive the prepolymer composition.

[0024] Among other advantages, implementations can provide efficient, high-yield, high quality lightguides suitable for display applications (e.g., head mounted displays). For example, the techniques described here can provide lightguides from materials with high optical homogeneity and optically smooth surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The foregoing and other objects of the present disclosure, the various features thereof, as well as the disclosure itself may be more fully understood from the following description of specific examples, when read together with the accompanying drawings in which:

[0026] FIG. 1 is a schematic diagram showing steps in an example process for forming a lightguide plate;

[0027] FIG. 2A is a cross-sectional diagram of an example mold with spacers and a gasket for molding a lightguide plate; [0028] FIG. 2B is a plan view diagram of the example mold with spacers and gasket shown in FIG. 2A;

[0029] FIG. 3 is a plan view of another example of a mold in which the gasket is shaped as an eyepiece; and

[0030] FIG. 4 is a plan view of yet a further example of a mold in which the gasket is shaped as an eyepiece.

[0031] In the drawings, like symbols denote like elements.

DETAILED DESCRIPTION

[0032] The disclosures of these patents, patent applications, and publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art as known to those skilled therein as of the date of the invention described and claimed herein. The instant disclosure will govern in the instance that there is any inconsistency between the patents, patent applications, and publications and this disclosure.

[0033] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The initial definition provided for a group or term herein applies to that group or term throughout the present specification individually or as part of another group, unless otherwise indicated.

[0034] For the purposes of explaining the invention well-known features of optics and optical component manufacturing known to those skilled in the art have been omitted or simplified in order not to obscure the basic principles of the invention. Parts of the following description will be presented using terminology commonly employed by those skilled in the art of optical design. It should also be noted that in the following description of the invention repeated usage of the phrase “in one example” does not necessarily refer to the same example. [0035] As used herein, the articles “a” and “an” refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element. Furthermore, use of the term “including” as well as other forms, such as “include,” “includes,” and “included,” is not limiting.

[0036] As used herein, the term “about” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which it is used. As used herein when referring to a measurable value such as an amount, a temporal duration, and the like, the term “about” is meant to encompass variations of ±20% or ±10%, including ±5%, ±1%, and ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.

[0037] As used herein, the term “planar lightguide” refers to a lightguide having two opposing planar surfaces that are parallel. Geometric relationships such as “planar” and “parallel” refer to geometric relationships to within fabrication tolerances and/or to within intended performance thresholds. Mathematical precision of such relationships on a microscope level is not intended.

[0038] As used herein, the term “actinic radiation” refers to electromagnetic radiation that can produce a photochemical reaction in a prepolymer composition, such as a polymerization reaction.

[0039] The present disclosure relates, at least in part, to lightguides and to processes for making lightguides.

[0040] Referring to FIG. 1, a process 100 for forming a lightguide includes the following steps. First, a continuous line of curable sealant is dispensed onto a planar surface of first mold plate defining a perimeter shape of a mold volume (step 110). The curable sealant is flowable (e.g., a liquid) and can be dispensed from a syringe, for example. The temperature of the curable sealant can be regulated to control its viscosity. For example, the curable sealant can be heated to decrease its viscosity relative to its room temperature viscosity. Generally, the viscosity of the curable sealant should be sufficiently low so that it can be easily dispensed in a continuous line, but it should be high enough so that the line retains its shape after being dispensed. The curable sealant can have a visocity in a range from about 5,000 cP to about 100,000 cP (e.g., about 8,000 cP or more, about 10,000 cP or more, about 20,000 cP or more, about 80,000 cP or less, about 50,000 cP or less, about 30,000 or less, such as about 15,000 cP to about 25,000 cP). The curable sealant can be dispensed manually or by an autodispense. The surfaces of the mold plates may be coated with antireflection (AR) coatings to improve the transmission of radiation used for curing materials during the molding process. A sufficient amount of curable sealant is dispensed for adequate wetting of, and adhesion to, the opposing surfaces of the mold plates, taking into account any sealant shrinkage during curing. In some cases, a sufficient amount of sealant can correspond to a line width of about 1 mm to about 5 mm. Additionally, the sealant has sufficient adhesion to the mold plates and elasticity to remain adhered to the mold plate surfaces should shrinkage occur.

[0041] Next, precision spacers (also referred to as gauges) are placed onto the surface of first mold plate (step 120). The spacers define the thickness of the mold volume for molding the lightguide (discussed further below). In many cases, the thickness of the mold volume is relatively small, such as 1 mm or less. Any appropriate spacers can be used to provide the desired thickness. The spacers should have relatively stable dimensions under conditions used during the molding process to avoid changes in the thickness of the mold. In certain examples, the spacers can be formed from materials with appropriately chosen thermal expansion coefficients that strain (shrink) by an appropriate ratio as the molded material is cured, accommodating any shrinkage of the cured material. In some examples, carbide gauges can be used as the spacers.

[0042] A second mold plate is aligned and mated with the first mold plate (step 130) to enclose the mold volume. The second mold plate also has a planar surface that faces the planar surface of the first mold plate, supported by the spacers to provide the mold volume with a controlled thickness. The curable sealant perimeter contacts the inner surface of the second mold plate, forming a seal between the mold plates. [0043] The assembly composed of the two mold plates, spacers, and curable sealant is exposed to actinic radiation to cure the curable sealant to form a solid gasket composed of cured sealant (step 140). For example, the assembly can be exposed to UV radiation at sufficient intensity and for a sufficient time to cure the sealant. The gasket provides a robust seal between the mold plates, maintaining the shape of the mold volume during the remainder of the molding process.

[0044] Generally, a variety of curable materials can be used as the curable sealant. In general, the curable sealant should be able to provide a seal between the surfaces of the mold plates sufficient to contain a flowable material, such as a prepolymer composition used for making the lightguide. Commercially available curable sealants can be used, such as Loctite branded sealants (from Henkel, Rocky Hill, CT), Tri Glass Ultraviolet resin (from Triglass, Inc., triglassinc.com), and UV Cure Silicone sealants (e.g., from Novagard® Industrial, Cleveland, OH).

[0045] After forming the gasket, the mold is vertically oriented and the mold volume is filled with a prepolymer composition (step 150). In some examples, the gasket includes an opening through which the prepolymer composition is dispensed into the volume. Alternatively, the dispensing device can pierce the gasket to provide access for filling the mold volume. For example, the dispensing device can include a canula which can pierce the gasket material and provide a channel through which the prepolymer composition can be supplied.

[0046] In general, the prepolymer composition is a flowable material that can be cured in the mold volume to provide the lightguide. Accordingly, the prepolymer composition has a viscosity suitably low that it can be dispensed into and fill the mold volume. The prepolymer composition can be at an elevated temperature (with respect to room temperature) to reduce the viscosity and promote its flowability.

[0047] As illustrated in FIG. 1, the vertical orientation of the mold ensures that the mold volume fills from the bottom. Accordingly, having the opening at the top of the mold ensures a channel for gas to exit the mold volume as it is displaced by the prepolymer composition. This can reduce bubble formation in the prepolymer composition and/or cured lightguide. Generally, a variety of other approaches can be used to reduce bubble formation in the prepolymer composition in the mold volume, in addition to or as an alternative to vertically orienting the mold. For example, the prepolymer composition can be pressure filled to facilitate displacement of gas. In some examples, a vacuum can be applied to the mold volume to draw gas from the volume and/or draw the prepolymer into the volume. Alternatively, or additionally, an actuator can be used to vibrate or tilt back and forth the mold to avoid bubble formation. It is also useful to have the entire filling process done in vacuum. Other options include centrifuging the mold, e.g., during or after filling the mold volume, to push the prepolymer composition against one side of the mold and displace bubbles from it by virtue of artificial bubble buoyancy generated by the centrifugal force.

[0048] It can also be useful to heat the fluid before or during delivery to the mold volume, so that it holds less gas. This can be done by warming the prepolymer composition itself and/or the apparatus used to dispense the composition (e.g., heating a delivery tube). A further option is to use a needle that is sufficiently long, inserted through the gasket at the top of the mold volume that extends close to the bottom to fill the volume from the bottom and then withdrawn the needle from the top. Dispensing the prepolymer composition can be performed manually or can be computer controlled.

[0049] Generally, the prepolymer composition includes a polymerizable component (e.g., composed of monomers and/or oligomers). A variety of chemistries can be used including acrylate chemistries (e.g., PMMA), non-acrylate chemistries, urethane chemistries, etc. The prepolymer composition can include other components in addition to the polymerizable component. For example, the composition can include one or more photoinitiators, co-initiators, viscosity enhancers, stabilizers, etc. In some examples, the prepolymer composition is a commercially-available formulation such as CR39 or trivex prepolymer. In some examples, the composition includes suspended micro- or nanoparticles having, for example, a relatively high refractive index, high conductivity, or high magnetic susceptibility of paramagnetic, diamagnetic or ferromagnetic kind. Generally, the prepolymer composition may be a different material from the curable sealant. [0050] After filling the mold volume, the prepolymer composition is cured (step 160) to form a solid, polymeric lightguide material. In this example, the prepolymer composition is cured by exposure to actinic radiation, such as UV radiation or appropriate wavelengths of visible light. The mold is illuminated by actinic radiation at sufficient intensity and for a sufficient length of time to solidify substantially all the prepolymer. The result is a solid polymer layer that substantially fills the mold volume.

[0051] In some examples, the mold can be illuminated with actinic radiation of uniform brightness from one or both sides. Alternatively, non-uniform exposure can be used. For example, higher intensity radiation can be used closer to the perimeter of the mold volume than in the center. Alternatively, or additionally, the volumetric distribution of actinic radiation inside the material being cured can be adjusted or controlled by adding optical components to the top, bottom or periphery of the mold. Such optical components include, for example, mirrors, dielectric partial reflectors, refracting elements (e.g., prisms), diffusers and other geometrical optics components, polarization filters, color/wavelength filters, as well as anti-reflection coatings, diffraction gratings, holograms and other diffractive optical elements. Alternatively, or additionally, different regions of the mold volume can be exposed at different times. For instance, in certain cases, the center of the volume can be exposed first, then later, the sides can be exposed. Sequentially curing different portions of the prepolymer composition can mitigate the effects of shrinking of the cured material.

[0052] Still further strategies can be adopted to manage issues associated with shrinking and/or shape changes to the cured material. For example, to accommodate these changes, the spacing between the mold plates can be actively changed during the curing step. For example, a system using one or more gap sensors (e.g., a laser interferometry system) and one or more actuators for changing the gap thickness can be used in a feedback process to provide high spacing precision based on real time feedback.

[0053] In some implementations, a cured material can be subject to one or more post-cure steps. For example, the cured material can be heated for a period of time after curing. The cured material can be heated to a temperature in a range from about 60 °C to about 150 °C, for instance (such as from about 80 °C to about 120 °C, such as about 100 °C). The peak temperature for the post-cure step generally depends on the type of polymer material used. The peak post-cure temperature can be below the glass transition temperature for the polymer.

[0054] The period for which the material is heated can vary. The cured material can be held at a heated temperature for about 15 minutes to about five hours (e.g., about 30 minutes or more, about an hour or more, about two hours or more, about four hours or less, about three hours or less). Heating to a peak post-cure temperature from, e.g., room temperature, can be achieved by ramping up the temperature over a period of time, e.g., a series of discrete steps or continuously. Alternatively, or additionally, cooling can be performed with a down ramp.

[0055] The molds can be vertically oriented during the post-cure step or horizontal. In some cases, the orientation of the mold can be varied during the post-cure step.

[0056] Generally, post-curing can increase the degree of conversion of the cured material, reduce stress/birefringence in the cured material, and/or facilitate successful demolding).

[0057] After curing or post-curing, the plate is demolded (step 160), obtaining the lightguide (step 170). Demolding involves removing the lightguide from the mold while retaining the lightguide’s shape. Demolding can include inserting a bar into the gap between the mold plates at an edge and twisting the bar to lever apart the plates, separating at least one of the plates from the gasket. Generally, this removes one of the plates from the lightguide. The lightguide can then be manually delaminated from the other mold plate. Other methods for demolding can be performed, e.g., using a high-pressure fluid (e.g., water) jet; or a thermal shock, by heating and/or cooling down the molds quickly. One or more of the demolding methods can be used together.

[0058] The gasket can be removed from both surfaces and the mold plates reused after appropriate cleaning. [0059] Implementations can include additional or alternative steps. For example, in some cases, obtaining the lightguide can include trimming or edging the lightguide plate to shape the lightguide plate for incorporation into a specific device (e.g., an eyepiece for a head mounted display).

[0060] In some examples, the cured polymer is annealed after cure. For instance, the mold can be heated to a temperature at which stresses in the cured polymer are reduced. Annealing can also deepen the curing of the polymer.

[0061] Coatings can also be applied at the lightguide after demolding. For example, an alternate index material, anti-reflection materials, and/or protection materials (e.g., a hardcoat) can be applied. Coatings can be included that affect the optical properties of the waveguide (e.g., anti-reflection films and/or enhance reflective or transmissive properties, enhance the durability of the waveguide, or both.

[0062] Furthermore, while the foregoing example features a prepolymer composition curable by actinic radiation, alternative curing methods can be used. For example, in some cases, a thermally cured prepolymer composition can be used. A two-stage prepolymer composition can be used in which the two components are mixed immediately prior to its delivery into the mold volume and a reaction between the two components cures the composition.

[0063] Although the examples described above feature planar mold surfaces, other implementations are possible. For example, one or both of the surfaces of the mold plates can be patterned with surface features to provide optical features on one or both surfaces of the lightguide. For instance, the mold plate surfaces can be etched, e.g., with a grating or other diffractive structure.

[0064] Further, in some examples, the mold plate surfaces can be moved relative to each other during the process. For example, one can start with the mold surfaces at a first distance apart, and then move the molds during the curing process. For instance, as the polymer shrinks, the two mold plates can be brought closer together. [0065] In certain implementations, the mold surfaces can be placed horizontally (their large surfaces perpendicular to gravity). In that scenario, one mold can be placed and filled with the prepolymer composition before being covered with the second plate. Once the plates are pressed together, the prepolymer composition is cured.

[0066] In some examples, the mold plates can have a spacing ring or lip. In this way, the spacer(s) is (are) incorporated into the mold plates as single piece of material. The curable sealant can be better positioned in place this way.

[0067] Non -flat, curved waveguide/shapes can be made if mold curvature is achieved. Flat or curved molds, or wedge, can be used. For curved surfaces, to avoid bubble formation, the fill surface should be always parallel to the ground.

[0068] In general, the size of the mold plates can vary as appropriate to accommodate the size of the mold volume desired. In some cases, the mold plates have a lateral dimension (e.g., diameter of 10 mm or more (e.g., about 20 mm or more, about 30 mm or more, about 40 mm or more, about 50 mm or more, about 55 mm or more, about 60 mm or more, about 70 mm or more, about 75 mm or more, about 80 mm or more, about 90 mm or more, or about 100 mm or more). Larger mold plates are also possible, such as (e.g., about 200 mm to about 500 mm, about 200 mm, about 220 mm, about 240 mm, about 260 mm, about 280 mm, or about 300 mm, about 400 mm, about 450 mm in diameter). In some cases, the mold plates can be the same size as wafer used in semiconductor manufacturing (e.g., 20 mm diameter, 30 mm diameter, and 450 mm diameter). At that size, many industry- compatible wafer-scale tools and processes can be used, such as cutting, curing, applying coatings, etc.

[0069] Referring to FIGS. 2A and 2B, an example of a mold 200 filled with a prepolymer composition 201 is shown in cross-section and plan view, respectively. Cartesian axes are provided for reference. In this example, three spacers 240 are used to establish a thickness, T, of the gasket 210 and lightguide formed by the mold. Here, the mold 200 is composed of two circular planar plates 220 and 230, each of which having inner planar surfaces separated by spacers 240. Plates 220 and 230 each have the same diameter, D. T is the thickness of spacers 240 in the z-direction, normal to the planar surfaces of the plates 220 and 230, which both extend parallel to the X- Y plane. The gasket 210 in this example is a circular gasket with an inner diameter, ID, and an outer diameter, OD. There is an opening 215 having a width, W, in the gasket 210 through which the system introduces the prepolymer composition. The spacers 240 are placed outside of the perimeter of gasket 210. In this way, they do not obstruct the prepolymer composition in the mold volume.

[0070] In general, the dimensions T, W, ID, OD, and D can vary as appropriate for the specific application. In some examples, T can be in a range from about 10 pm to about 10,000 pm (e.g., about 20 pm or more, about 50 pm or more, about 100 pm or more, about 150 pm or more, about 200 pm or more, about 300 pm or more, about 400 pm or more, such as about 5,000 pm or less, about 4,000 pm or less, about 3,000 pm or less, about 2,000 pm or less, about 1,000 pm or less, about 750 pm or less, about 600 pm or less, about 500 pm or less, such as in a range from about 250 pm to about 550 pm, about 300 pm to about 500 pm, or about 350 pm to about 450 pm).

[0071] ID can be about 50 mm or more (e.g., about 80 mm or more, about 100 mm or more, about 150 mm or more, about 200 mm or more). OD can be about 5 mm or more greater than ID (e.g., about 10 mm or more greater, about 15 mm or more greater, about 20 mm greater) In some examples, OD corresponds to the diameter of plate 220 and/or 230.

[0072] W is generally sufficiently large to provide a channel suitable for filling the mold volume with the prepolymer composition and allowing displaced air to escape. In some exampleexamples, W is in a range from about 0.5 mm to about 50 mm (e.g., about 1 mm or more, about 2 mm or more, about 3 mm or more, about 4 mm or more, such as about 40 mm or less, about 30 mm or less, about 20 mm or less). Generally, a wide channel facilitates filling of the mold volume. In certain examples, multiple channels can be provided. For example, where the mold volume is large and/or the mold volume thickness is small, more than one channel can allow for quicker fill than a comparable mold with only one channel. [0073] The OD of the gasket 210 is generally less than the diameter, D, of the planar plate surface sufficient to accommodate the spacers 240. For example, D can be about 10 mm or more than OD (e.g., about 15 mm or more, about 20 mm or more, such as about 100 mm or less, about 75 mm or less, about 50 mm or less).

[0074] While FIGS. 2A and 2B depict a circular gasket, other implementations are possible. In some examples, the gasket can be shaped according to the desired shape of the lightguide for its ultimate application. For example, referring to FIG. 3, another instance of a mold 300 includes a gasket 310 formed in the shape of an eyepiece for a head mounted display (e.g., tear drop shaped). Here, gasket 310 includes an opening 315 allowing the mold to be filled with prepolymer composition 301. Forming a gasket in a desired shape, such as gasket 310, can improve manufacturing efficiency by eliminating having to cut or singulate the light guide from a plate that is a different shape. More efficient use prepolymer composition can also result.

[0075] In some examples, the process includes over molding a black edge around the light guide. For example, referring to FIG. 4, a process includes applying a black edge 410 along the interior edge of the gasket 310 prior to filling the mold 400 with the prepolymer composition 401. For instance, the curable sealant for the gasket and a curable black material can be coextruded when the gasket is formed. When the prepolymer composition is then added to the mold volume it can cross link to the black material. Ultimately when the shaped lightguide is demolded, the black material will stay bonded to the light guide and break free from the gasket. Once the lightguide is removed from the mold, the black edge absorbs stray light that would otherwise exit the light guide for the edges and illuminate the guide edge. Conventionally, the black edge is applied in a separate step after forming the lightguide. Thus, including the black edge in the molding process can eliminate this additional post process step.

[0076] In some implementations, the sealant itself can serve as the edge of the lightguide, e.g., as an edge that blocks stray light. For example, the sealant can be an opaque material (e.g., a light absorbing, such as a black material). In some cases, a light absorbing compound (e.g., a dye or pigment) can be incorporated into the sealant to provide an opaque gasket. Examples of suitable materials can include commercially-available UV-curable masking resins, such as CM MASK® UV-curable masking resins from Composition Materials Co., Inc. (Milford, CT) and UV resin masks from Panacol-USA (Torrington, CT). The light absorbing compound can be selected to preferably absorb light at the wavelength (or wavelengths) of operation of the lightguide (e.g., preferably absorb red, green, and/or blue light). Further, the composition of both the gasket sealant and the lightguide can be selected to ensure adhesion between the gasket and the lightguide so that they remain attached when the lightguide is removed from the mold.

[0077] Generally, the methods disclosed here may be used to provide lightguides having precisely controlled mechanical characteristics, such as relatively low surface roughness (e.g., Sa (arithmetical mean height) of about 3 nm or less, about 2 nm or less, about 1 nm or less, about 0.8 nm or less, about 0.5 nm, or less), relatively low waviness (e.g., about 0.3 wv/cm or less, about 0.2 wv/cm or less, about 0.1 wv/cm or less, about 0.08 wv/cm or less, about 0.05 wv/cm or less), relatively low bow (e.g., about 50 pm or less, about 40 pm or less, about 30 pm or less, about 20 pm or less, about 15 pm or less, about 10 pm or less, about 8 pm or less), and/or relatively small TTV (e.g., about 10 pm or less, about 8 pm or less, about 5 pm or less, about 4 pm or less, about 3 pm or less, about 2 pm or less, about 1 pm or less). In examples of planar lightguides, the lightguide can have a relative low wedge angle (e.g., about 1 arcmin or less, about 45 arcsec or less, about 30 arcsec or less, about 20 arcsec or less, about 15 arcsec or less, about 10 arcsec or less).

[0078] Alternatively, or additionally, the methods disclosed here may be used to provide lightguides having precisely controlled optical characteristics. For example, the lightguides can have relatively high optical transmission at one or more wavelengths of operation (e.g., about 90% or more, about 91% or more, about 92% or more, about 93% or more, about 94% or more, about 95% or more, about 96% or more, about 97% or more, about 98% or more, e.g., @589 nm), relatively low haze (e.g., about 0.5% or less, about 0.3% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less), and/or a relatively homogenous refractive index (e.g., maximum variations in refractive index across the waveguide can be about 0.01 or less, such as about 0.005 or less, such as about 0.002 or less, such as less than about 0.001 or less). In some implementations the lightguide can have relatively low birefringence (e.g., An can be about 0.001 or less, about 0.0005 or less, about 0.0002 or less, about 0.0001 or less). [0079] In general, lightguides made using the methods described above may be used in a variety of applications. In some implementations, one or more lightguides can be included in a head mounted display, such as a head mounted display for augmented reality (AR). Examples of such displays are described in US20120092328A1, for example. Other applications for the lightguides include direct view displays, automotive display, avionics displays, signage, and general illumination. For example, the lightguides can be a lightguide for a backlit or frontlit liquid crystal display.

EQUIVALENTS

[0080] Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific embodiments described specifically herein. Such equivalents are intended to be encompassed in the scope of the following claims.

[0081] A number of embodiments are described. Other embodiments are in the following claims.

Claims

What is claimed is:

1. A method of forming a lightguide, comprising: dispensing a continuous line of a flowable curable sealant on a surface of a first plate; contacting a surface of a second plate to the curable sealant while maintaining a separation between the surfaces of the first and second plates using one or more spacers; curing the flowable curable sealant by exposing the flowable curable sealant to actinic radiation to form a solid gasket sealing a mold volume between the first and second plates while maintaining the separation between the surfaces; filling the mold volume with a prepolymer composition; curing the prepolymer composition in the mold volume to form a polymer layer; demolding the polymer layer to separate the polymer layer from the first and second plates; and obtaining the lightguide from the polymer layer.

2. The method of claim 1, wherein the flowable curable sealant has a viscosity in a range from about 5,000 cP to about 100,000 cP.

3. The method of claim 1 or claim 2, wherein the first plate has a lateral dimension in a range from about 10 mm to about 500 mm.

4. The method of claim 3, wherein the first plate has a lateral dimension of about 20 mm, about 30 mm, or about 450 mm.

5. The method of any one of the previous claims, wherein the surface of the first plate is a planar surface.

6. The method of claim 5, wherein the surface of the second plate is a planar surface.

7. The method of any one of the previous claims, wherein the continuous line of flowable curable sealant has a thickness in a range from about 0.5 mm to about 10 mm.

8. The method of any one of the previous claims, wherein the separation between the surfaces of the first and second plates is in a range from about 10 pm to about 10,000 pm.

9. The method of any one of the previous claims, wherein the separation between the surfaces of the first and second plates is constant across the mold volume.

10. The method of any one of the previous claims, wherein the continuous line of the flowable curable sealant is a circular line.

11. The method of any one of previous claims, wherein the continuous line of the flowable curable sealant is in a shape of an eyepiece.

12. The method of any one of the previous claims, wherein the mold volume is filled through an opening in the solid gasket.

13. The method of claim 12, wherein the opening has a width of about 50 mm or less.

14. The method of any one of the previous claims, further comprising dispensing a continuous line of an opaque material next to the solid gasket prior to filing the mold volume with the prepolymer composition.

15. The method of any one of the previous claims, wherein the actinic radiation is ultraviolet radiation.

16. The method of any one of the previous claims, wherein the solid gasket is absorptive at operative wavelengths of the waveguide.

17. The method of any one of the previous claims, wherein the prepolymer composition is cured by exposure to second actinic radiation, by heating the prepolymer composition, and/or by mixing reagents to form the prepolymer composition.

18. The method of claim 17, wherein the second actinic radiation is ultraviolet radiation.

19. The method of any one of the previous claims, further comprising post-curing the polymer layer prior to the demolding.

20. The method of claim 19, wherein the post-curing comprises heating the polymer layer.

21. The method of any one of the previous claims, wherein obtaining the lightguide from the polymer material comprises separating the polymer material from the solid gasket.

22. The method of any one of the previous claims, wherein obtaining the lightguide from the polymer material comprises singulating the lightguide from the polymer material.

23. The method of any one of the previous claims, further comprising integrating the lightguide into a display.

24. The method of claim 23, wherein the display is as a head- mounted display.

25. An article, comprising: first and second mold plates arranged with respective surfaces facing each other; one or more spacers between the respective surfaces defining a gap of about 10,000 pm or less between the respective surfaces; a gasket comprising a continuous line of a cured sealant sealing the gap and defining a mold volume; and a flowable prepolymer composition at least partially filling the mold volume.

26. The article of claim 25, wherein the gasket is in the shape of an eyepiece.

27. The article of claim 26, wherein the gasket comprises an opening sized and shaped to receive the prepolymer composition.