Systems and methods for manufacturing waveguide cells

Abstract

To allow systems for manufacturing waveguide cells in accordance with various embodiments to be configured and implemented in many different ways.SOLUTION: In many embodiments, various deposition mechanisms are used to deposit a layer(s) of an optical recording material(s) onto a transparent substrate. A second transparent substrate can be provided, and the three layers can be laminated to form a waveguide cell. A suitable optical recording material can vary widely depending on a given application. In some embodiments, the optical recording material deposited has a similar composition throughout a layer. In a number of embodiments, the optical recording material spatially varies in composition, enabling formation of optical elements with varying characteristics. Regardless of the composition of the optical recording material, any method of placing or depositing the optical recording material onto a substrate can be utilized.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application is a joint venture under 35 U.S.C. § 119(e) with U.S. Provisional Patent Application No. 62 / 663,864, entitled "Method and Apparatus for Fabricating Holographic Gratings," filed April 27, 2018; U.S. Provisional Patent Application No. 62 / 614,813, entitled "Low Haze Liquid Crystal Materials," filed January 8, 2018; U.S. Provisional Patent Application No. 62 / 614,831, entitled "Liquid Crystal Materials and Formulations," filed January 8, 2018; and U.S. Provisional Patent Application No. 62 / 614,932, entitled "Methods for Fabricating Optical Waveguides," filed January 8, 2018; This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62 / 667,891, entitled "Systems and Methods for Fabricating a Multilayer Optical Structure," filed May 7, 2018, and U.S. Provisional Patent Application No. 62 / 703,329, entitled "Systems and Methods for Fabricating a Multilayer Optical Structure," filed July 25, 2018. The disclosures of U.S. Provisional Patent Applications Nos. 62 / 663,864, 62 / 614,813, 62 / 614,831, 62 / 614,932, 62 / 667,891, and 62 / 703,329 are incorporated herein by reference in their entireties for all purposes.

[0002] The present invention relates generally to processes and apparatus for fabricating waveguide cells, and more particularly to processes and apparatus for fabricating waveguide cells utilizing deposition and printing techniques. [Background technology]

[0003] A waveguide can be referred to as a structure with the ability to confine and guide waves (i.e., restrict the spatial region through which waves can propagate). One class of waveguides includes optical waveguides, which are structures that can guide electromagnetic waves, typically those in the visible spectrum. Waveguide structures can be designed to control the propagation path of waves using several different mechanisms. For example, planar waveguides can be designed utilizing diffraction gratings to diffract and couple incident light into the waveguide structure, so that the internally coupled light can continue traveling within the planar structure via total internal reflection ("TIR").

[0004] Waveguide fabrication can include the use of material systems that enable the recording of holographic optical elements within the waveguide. One class of such materials includes polymer-dispersed liquid crystal ("PDLC") mixtures, which are mixtures containing a photopolymerizable monomer and a liquid crystal. A further subclass of such mixtures includes holographic polymer-dispersed liquid crystal ("HPDLC") mixtures. Holographic optical elements, such as volume phase gratings, can be recorded in such liquid mixtures by irradiating the material with two mutually coherent laser beams. During the recording process, the monomer polymerizes, and the mixture undergoes photopolymerization-induced phase separation, creating regions densely populated with liquid crystal microdroplets interspersed with regions of clear polymer. The alternating liquid crystal-rich and liquid crystal-depleted regions form the fringe planes of the grating.

[0005] Waveguide optics such as those described above can be considered for a variety of display and sensor applications. In many applications, waveguides containing one or more grating layers encoding multiple optical functions can be realized using various waveguide architectures and material systems, enabling new innovations in eyepiece displays for augmented reality ("AR") and virtual reality ("VR"), compact head-up displays ("HUDs") for aviation and road traffic, and sensors for biometric and laser radar ("LIDAR") applications. Summary of the Invention [Means for solving the problem]

[0006] One embodiment includes a method for manufacturing a waveguide cell, the method including the steps of providing a first substrate, determining predetermined grating characteristics, and depositing a layer of optical recording material onto the first substrate using at least one deposition head, wherein the optical recording material deposited over the grating region is formulated to achieve the predetermined grating characteristics.

[0007] In another embodiment, the method further includes providing a second substrate, placing the second substrate on the deposited layer of optical recording material, and laminating the first substrate, the layer of optical recording material, and the second substrate.

[0008] In a further embodiment, depositing the layer of optical recording material comprises providing a first mixture of optical recording material, providing a second mixture of optical recording material, and depositing the first and second mixtures of optical recording material onto the first substrate in a predetermined pattern using at least one deposition head.

[0009] In yet another embodiment, the first mixture of optical recording material includes first beads and the second mixture of optical recording material includes second beads that are a different size than the first beads.

[0010] In still further embodiments, the first mixture of optical recording material has a different weight percentage of liquid crystal than the second mixture of optical recording material.

[0011] In yet another embodiment, the method further includes defining grating regions and non-grating regions on the first substrate, wherein the first mixture of optical recording material comprises a liquid crystal and a monomer, and the second mixture of optical recording material comprises a monomer, and depositing the first and second mixtures of optical recording material on the first substrate in the predetermined pattern includes depositing the first mixture of optical recording material over the grating regions and depositing the second mixture of optical recording material over the non-grating regions.

[0012] In yet a further embodiment, the first mixture of the optical recording material is a polymer dispersed liquid crystal mixture comprising a monomer, a liquid crystal, a photoinitiator dye, and a coinitiator.

[0013] In another additional embodiment, the polymer dispersed liquid crystal mixture comprises an additive selected from the group comprising a photoinitiator, nanoparticles, a low functionality monomer, an additive for reducing switching voltage, an additive for reducing switching time, an additive for increasing refractive index modulation, and an additive for reducing haze.

[0014] In further additional embodiments, the at least one deposition head includes at least one inkjet print head.

[0015] Again, in another embodiment, the step of depositing the layer of optical recording material includes the steps of providing a first mixture of optical recording material, providing a second mixture of optical recording material, printing a first dot of the first mixture of optical recording material using at least one inkjet print head, and printing a second dot of the second mixture of optical recording material adjacent to the first dot using at least one inkjet print head.

[0016] Again, in a further embodiment, the at least one inkjet print head includes a first inkjet print head and a second inkjet print head, and the step of depositing the layer of optical recording material includes the steps of providing a first mixture of optical recording material, providing a second mixture of optical recording material, printing the first mixture of optical recording material onto a first substrate using the first inkjet print head, and printing the second mixture of optical recording material onto the first substrate using the second inkjet print head.

[0017] In yet another embodiment, the predetermined grating property comprises a property selected from the group comprising refractive index modulation, refractive index, birefringence, liquid crystal director matching, and grating layer thickness.

[0018] In still yet a further embodiment, the predetermined grating property comprises a spatial variation of a property selected from the group comprising refractive index modulation, refractive index, birefringence, liquid crystal director matching, and grating layer thickness.

[0019] In yet another additional embodiment, the predetermined grating characteristics result in a grating after exposure, the grating having a spatially varying diffraction efficiency.

[0020] Still further additional embodiments include a system for fabricating a grating, the system including at least one deposition head connected to at least one reservoir containing at least one mixture of optical recording material; a first substrate having at least one predetermined area for supporting the grating; and a positioning element capable of positioning the at least one deposition head across the first substrate, wherein the at least one deposition head is configured to deposit the at least one mixture of optical recording material onto the first substrate using the positioning element, the deposited material providing predetermined grating characteristics within the at least one predetermined grating area after holographic exposure.

[0021] Again, in yet another additional embodiment, at least one deposition head is connected to a first reservoir containing a first mixture of optical recording materials and a second reservoir containing a second mixture of optical recording materials.

[0022] Again, in still a further embodiment, the first mixture of optical recording material comprises a liquid crystal and a monomer, and the second mixture of optical recording material comprises a monomer, and the at least one deposition head is configured to deposit the first mixture of optical recording material onto at least one predetermined grating area.

[0023] In yet another additional embodiment, the at least one deposition head includes at least one inkjet print head.

[0024] In still further additional embodiments, the predetermined grating property comprises a property selected from the group comprising refractive index modulation, refractive index, birefringence, liquid crystal director alignment, and grating layer thickness.

[0025] Again, in yet another embodiment, the predetermined grating characteristics result in a grating after exposure, the grating having a spatially varying diffraction efficiency.

[0026] Additional embodiments and features are set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of this specification or may be learned by practice of the invention. A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and drawings that form a part of this disclosure.

[0027] The description will be more fully understood with reference to the following figures and data graphs, which are presented as exemplary embodiments of the invention and should not be construed as a complete recitation of the scope of the invention. It will be apparent to those skilled in the art that the present invention may be practiced using some or all of the invention as disclosed in the following description. [Brief explanation of the drawings]

[0028] [Figure 1] Figure 1A conceptually illustrates a profile view of a waveguide cell according to an embodiment of the present invention, Figure 1B conceptually illustrates a waveguide cell with a wedge-shaped profile according to an embodiment of the present invention, and Figure 1C conceptually illustrates a top view of a waveguide cell according to an embodiment of the present invention. [Figure 2A] 1 conceptually illustrates a work cell cluster system, in accordance with one embodiment of the present invention. [Figure 2B] 1 conceptually illustrates a work cell cluster system with two deposition work cells, according to one embodiment of the present invention. [Figure 3] 3A and 3B conceptually illustrate an isometric view and a top view of a deposition work cell, respectively, in accordance with one embodiment of the present invention. [Figure 4] 4A and 4B conceptually and diagrammatically illustrate the use of reverse ray tracing to calculate a compensated refractive index modulation pattern for a coating, according to various embodiments of the present invention. [Figure 5] 5A and 5B conceptually illustrate the fundamental structural differences between SBG and SRG. [Figure 6] 10 conceptually illustrates a waveguide cell with a marked area relative to the grating, according to one embodiment of the present invention. [Figure 7] 7A and 7B conceptually illustrate the operation of a deposition mechanism utilizing a spray module, according to one embodiment of the present invention. [Figure 8] 8A and 8B conceptually illustrate two operational states of a spray module, according to one embodiment of the present invention. [Figure 9] 1 is a flowchart conceptually illustrating a method for fabricating a holographic grating using a selective coating process, in accordance with one embodiment of the present invention. [Figure 10] 1 conceptually illustrates a deposition head for providing predetermined grating characteristics within a grating region, according to an embodiment of the present invention. [Figure 11]1 conceptually illustrates the operation of a deposition head to deposit a material having regions with predetermined lattice properties, according to an embodiment of the present invention. [Figure 12] 1 conceptually illustrates a deposition mechanism for depositing two grating layers according to one embodiment of the present invention. [Figure 13] 1 conceptually illustrates a system for depositing a grating layer of material and holographically exposing the layer, according to one embodiment of the present invention. [Figure 14] 1 is a flowchart conceptually illustrating a method of depositing a film of material with regions having predetermined lattice properties, in accordance with an embodiment of the present invention. [Figure 15] 1 conceptually illustrates an inkjet printing modulation scheme, in accordance with one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] For purposes of describing embodiments, some well-known features of optical technology known to those skilled in the art of optical design and visual displays have been omitted or simplified so as not to obscure the underlying principles of the present invention. Unless otherwise noted, the term "on-axis" in reference to a light ray or beam direction refers to propagation parallel to an axis normal to the surface of the optical component described in connection with the present invention. In the following drawings, the terms light, ray, beam, and direction are used synonymously and interrelatedly and may refer to the direction of propagation of light energy along a straight trajectory. Portions of the following description will be presented using terminology commonly employed by those skilled in the art of optical design. It should be understood that for illustrative purposes, the drawings are not drawn to scale unless otherwise noted.

[0030] Turning now to the drawings, systems and methods for fabricating waveguide cells are illustrated. A waveguide cell can be defined as a device containing uncured and / or unexposed optical recording material onto which optical elements, such as, but not limited to, a grating, can be recorded through exposure to electromagnetic radiation of a certain wavelength. Many techniques exist for the fabrication and construction of waveguide cells. In many embodiments, a waveguide cell is constructed by placing a thin film of optical recording material between two transparent substrates. In further embodiments, a workcell cluster manufacturing system is implemented to construct such waveguide cells. A workcell can be defined as a set of machines assigned to a specific manufacturing task. A cluster can be defined as a group of machines that cooperatively perform similar functions. In some embodiments, the workcell cluster includes a preparation workcell for preparing a substrate for deposition, a deposition workcell for depositing the optical recording material onto the substrate, and a lamination workcell for laminating various layers together to form the waveguide cell.

[0031] Work cells and work cell clusters according to various embodiments can be configured and implemented in many different ways. For example, a preparation work cell can be configured to prepare substrates for material deposition through various processes, including, but not limited to, cleaning procedures and protocols. In many embodiments, substrate preparation includes a glass cleaning procedure to remove contaminants and particles from the surface of the substrate. In some embodiments, procedures to increase the surface adhesion properties of the substrate are implemented to further prepare the substrate for material deposition.

[0032] The deposition work cell can be configured to deposit one or more layers of optical recording material onto a transparent substrate using a variety of different deposition and printing mechanisms. In many embodiments, additive manufacturing techniques such as, but not limited to, inkjet printing are used to deposit the layers of optical recording material. In some embodiments, spraying techniques are utilized to deposit the layers of optical recording material. Suitable optical recording materials can vary widely depending on a given application. In some embodiments, the deposited optical recording material has a similar composition throughout the layer. In some embodiments, the optical recording material varies spatially in composition, allowing for the formation of optical elements with various properties. Regardless of the composition of the optical recording material, any method of placing or depositing the optical recording material onto a substrate can be utilized.

[0033] A lamination work cell can be configured to laminate various layers to form a waveguide cell. In some embodiments, the lamination work cell is configured to laminate and form a three-layer composite of optical recording material and transparent substrate. As can be readily appreciated, the number of layers and types of materials used to construct a waveguide cell can vary and depend on a given application. For example, in some embodiments, a waveguide cell can be constructed to include a protective cover layer, a polarization control layer, and / or a matching layer. In some embodiments, the system is configured for the production of curved waveguides and waveguide cells. Specific materials, systems, and methods for constructing waveguide cells are discussed in further detail below. Waveguide Cell

[0034] Waveguide cells can be configured and constructed in many different ways according to various embodiments of the present invention. As discussed above, in many waveguide configurations, the waveguide cell includes a thin film of optical recording material sandwiched between two substrates. Such waveguide cells can be manufactured using a variety of processes. In many embodiments, the waveguide cell can be constructed by coating a first substrate with an optical recording material capable of acting as an optical recording medium. A variety of optical recording materials can be used. In some embodiments, the optical recording material is a holographic polymer dispersed liquid crystal mixture (e.g., a matrix of liquid crystal droplets). As can be readily appreciated, the choice of optical recording material and the type of mixture utilized can depend on a given application. The optical recording material can be deposited using a variety of deposition techniques. In some embodiments, the optical recording material can be deposited on the first substrate through inkjet, spin coating, and / or spraying processes. The deposition process can be configured to deposit one or more types of optical recording material. In some embodiments, the deposition process is configured to deposit an optical recording material that spatially varies in composition across the substrate. After deposition of the optical recording material, a second substrate can be placed so that the optical recording material is sandwiched between the two substrates, forming a waveguide cell. In some embodiments, the second substrate can be a thin protective film coated on the exposure layer. In such embodiments, various techniques, including but not limited to, spray processes, can be used to coat the exposure layer with a film of the desired material. In some embodiments, the waveguide cell can include various additional layers, such as, but not limited to, polarization control layers and / or matching layers. Other processes for fabricating waveguide cells can include filling an empty waveguide cell (constructed from two substrates) with optical recording material using processes such as, but not limited to, gravity filling and vacuum filling methods.

[0035] Substrates used in the construction of waveguide cells are often made from transparent materials. In some embodiments, the substrate is an optical plastic. In other embodiments, the substrate may be fabricated from glass. An exemplary glass substrate is standard Corning Willow glass substrate (refractive index 1.51), which is available in thicknesses up to 50 micrometers. The thickness of the substrate can vary from application to application. In many embodiments, 1 mm thick glass slides are used as substrates. In addition to different thicknesses, substrates of different shapes, such as, but not limited to, rectangular and curved shapes, can also be used depending on the application. In many cases, the shape of the substrate can determine the overall shape of the waveguide. In some embodiments, a waveguide cell contains two substrates that are identical in shape. In other embodiments, the substrates are different shapes. As can be easily understood, the shape, dimensions, and materials of the substrates can vary and depend on the specific requirements of a given application.

[0036] In many embodiments, beads or other particles are dispersed throughout the optical recording material to help control the thickness of the optical recording material layer and prevent the two substrates from collapsing relative to one another. In some embodiments, waveguide cells are constructed with an optical recording material layer sandwiched between two planar substrates. Depending on the type of optical recording material used, thickness control can be difficult due to the viscosity of some optical recording materials and the lack of a boundary edge for the optical recording material layer. In some embodiments, the beads are relatively incompressible solids, which can enable the construction of waveguide cells with consistent thicknesses. The size of the beads can determine the local minimum thickness relative to the area surrounding each individual bead. Therefore, the dimensions of the beads can be selected to help achieve a desired optical recording material layer thickness. The beads can be made from any of a variety of materials, including, but not limited to, glass and plastic. In some embodiments, the bead material is selected so that its refractive index does not substantially affect the propagation of light within the waveguide cell.

[0037] In some embodiments, the waveguide cells are constructed such that the two substrates are parallel or nearly parallel. In such embodiments, beads of relatively similar size can be dispersed throughout the optical recording material to help achieve a uniform thickness throughout the layer. In other embodiments, the waveguide cells have a tapered profile. Tapered waveguide cells can be constructed by dispersing beads of different sizes across the optical recording material. As discussed above, the size of the beads can determine the local minimum thickness of the optical recording material layer. By dispersing the beads in a pattern of increasing size across the material layer, a tapered layer of optical recording material can be formed when the material is sandwiched between two substrates.

[0038] Once constructed, the waveguide cells can be used in conjunction with various processes for recording optical elements in optical recording materials. For example, the disclosed processes may incorporate embodiments and teachings from materials and processes such as, but not limited to, those described in U.S. patent application Ser. No. 16 / 116,834, entitled "Systems and Methods for High-Throughput Recording of Holographic Gratings in Waveguide Cells," filed Aug. 29, 2018, and U.S. patent application Ser. No. 16 / 007,932, entitled "Holographic Material Systems and Waveguides Incorporating Low Functionality Monomers," filed June 13, 2018. The disclosures of U.S. patent application Ser. Nos. 16 / 116,834 and 16 / 007,932 are incorporated herein in their entireties for all purposes.

[0039] A profile view of a waveguide cell 100 according to one embodiment of the present invention is conceptually illustrated in FIG. 1A. As shown, the waveguide cell 100 includes a layer of optical recording material 102, which can be used as a recording medium for optical elements such as, but not limited to, a grating. The optical recording material 102 can be any of a variety of compounds, mixtures, or solutions, such as, but not limited to, the HPDLC mixture described in the previous section. In an illustrative embodiment, the optical recording material 102 is sandwiched between two parallel glass plates 104, 106. The substrates can be arranged in both parallel and non-parallel configurations. FIG. 1B conceptually illustrates a profile view of a tapered waveguide cell 108 utilizing beads 110, 112, and 114 according to one embodiment of the present invention. As shown, the beads 110, 112, and 114 vary in size and are dispersed throughout the optical recording material 116 sandwiched between two glass plates 118, 120. During construction of a waveguide cell, the local thickness of an area of ​​the optical recording material layer is limited by the size of the beads in that particular area. By distributing beads of increasing size across the optical recording material, a tapered waveguide cell can be constructed when a substrate is placed in contact with the beads. As discussed above, the substrate utilized in the waveguide cell can vary in thickness and shape. In many embodiments, the substrate is rectangular in shape. In some embodiments, the shape of the waveguide cell is a combination of curved components. Figure 1C conceptually illustrates a top view of a waveguide cell 122 having a curved shape in accordance with one embodiment of the present invention. While Figures 1A-1C illustrate a specific waveguide cell structure and arrangement, waveguide cells can be constructed in many different configurations and can use a variety of different materials depending on the specific requirements of a given application. For example, the substrate can be made of a transparent plastic polymer instead of glass. Additionally, the shape and size of the waveguide cells can vary greatly and can be determined by various factors such as, but not limited to, the application of the waveguide, ergonomic considerations, and economic factors. In many embodiments, the substrate is curved, allowing for the production of waveguides with curved cross-sections.

[0040] lattice structure Waveguide cells according to various embodiments of the present invention can incorporate various photosensitive materials. In many embodiments, the waveguide cells incorporate a holographic polymer-dispersed liquid crystal mixture, which serves as an optical recording medium onto which optical elements can be recorded. The optical elements can include many different types of gratings, which can exhibit different optical properties. One type of grating that can be recorded within a waveguide cell is a volume Bragg grating, which can be characterized as a transparent medium with a periodic variation in its refractive index. This variation can allow diffraction of certain wavelengths of incident light at certain angles. Volume Bragg gratings can have high efficiency, with little light being diffracted into higher orders. The relative amount of light in the zeroth order diffracted can be varied by controlling the refractive index modulation of the grating.

[0041] One class of grating used in holographic waveguide devices is the switchable Bragg grating ("SBG"). SBGs are diffractive devices that can be formed by recording a volume phase grating in an HPDLC mixture (although other materials can also be used). SBGs can be fabricated by first placing a thin film of a mixture of photopolymerizable monomer and liquid crystal material between glass plates or substrates, which forms the waveguide cell. One or both glass plates can support electrodes, typically transparent tin oxide films, to apply an electric field across the film. SBGs can be implemented as waveguide devices in which the HPDLC forms either the waveguide core or an evanescent coupling layer adjacent to the waveguide. The glass plates used to form the HPDLC cell can provide a total internal reflection light-guiding structure. When the switchable grating diffracts light at angles beyond the TIR condition, the light is coupled out of the SBG.

[0042] Grating structures within SBGs can be recorded in films of HPDLC materials through photopolymerization-induced phase separation using interference exposure with spatially periodic intensity modulation. Factors such as, but not limited to, controlling the irradiation intensity, the volume fraction of the HPDLC material's components, and the exposure temperature can determine the resulting grating morphology and performance. During the recording process, the monomer polymerizes and the mixture undergoes phase separation. LC molecules aggregate to form discrete or coalesced droplets that are periodically dispersed within the polymer network on the scale of optical wavelengths. Alternating liquid crystal-rich and liquid crystal-depleted regions form the fringe planes of the grating, which can generate Bragg diffraction with strong optical polarization resulting from the orientational order of the LC molecules within the droplets. The resulting volume phase grating can exhibit very high diffraction efficiency, which can be controlled by the magnitude of the electric field applied across the HPDLC layer. When an electric field is applied to the hologram through transparent electrodes, the natural orientation of the LC droplets is altered, reducing the refractive index modulation of the fringes and reducing the hologram diffraction efficiency to very low levels. The diffraction efficiency of this device can be adjusted using the applied voltage over a continuous range from nearly 100% efficiency when no voltage is applied to essentially zero efficiency when a sufficiently high voltage is applied. In some types of HPDLC devices, phase separation of the LC material from the polymer can be achieved to the point where no discernible droplet structure results. SBGs can also be used as passive gratings. In this mode, its primary benefit is the uniquely high refractive index modulation. SBGs can be used to provide transmission or reflection gratings for free-space applications. SBGs can be implemented as waveguide devices in which the HPDLC forms either the waveguide core or the evanescent coupling layer adjacent to the waveguide. The glass plates used to form the HPDLC cell provide a total internal reflection light-guiding structure. When the switchable grating diffracts light at angles beyond the TIR condition, light can be coupled out of the SBG.

[0043] In many embodiments, the SBGs are recorded in a uniformly modulated material such as POLICRYPS or POLIPHEM, which has a matrix of solid liquid crystal dispersed in a liquid polymer. Exemplary uniformly modulated liquid crystal polymer material systems are disclosed in U.S. Patent Application Publication No. US2007 / 0019152 by Caputo et al. and PCT Application No. PCT / EP2005 / 006950 by Stumpe et al., both of which are incorporated herein by reference in their entireties. Uniformly modulated gratings are characterized by high refractive index modulation (and therefore high diffraction efficiency) and low scattering. In some embodiments, at least one of the gratings is recorded in a reverse-mode HPDLC material. Reverse-mode HPDLC differs from conventional HPDLC in that the grating is passive in the absence of any applied electric field and becomes diffractive in the presence of an electric field. Reverse mode HPDLC may be based on any of the recipes and processes disclosed in PCT Application No. PCT / GB2012 / 000680, entitled "IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES." Optical recording material systems are discussed in more detail below. Optical Recording Material System

[0044] HPDLC mixtures according to various embodiments of the present invention generally include LC, monomer, photoinitiator dye, and coinitiator. The mixture (often referred to as a syrup) also frequently includes a surfactant. For purposes of describing the present invention, a surfactant is defined as any chemical that reduces the surface tension of the overall liquid mixture. The use of surfactants in PDLC mixtures is known and dates back to the earliest investigations of PDLC. For example, an article by R.L. Sutherland et al., SPIE Vol. 2689, pp. 158-169, 1996 (the disclosure of which is incorporated herein by reference), describes a PDLC mixture containing a monomer, photoinitiator, coinitiator, chain extender, and LC to which a surfactant may be added. Surfactants are also mentioned in an article by Natarajan et al., Journal of Nonlinear Optical Physics and Materials, Vol. 5, No. 1, 89-98, 1996 (the disclosure of which is incorporated herein by reference). Additionally, U.S. Patent No. 7,018,563 to Sutherland et al. discusses a polymer dispersed liquid crystal material for forming a polymer dispersed liquid crystal optical element, the material including at least one acrylic acid monomer, at least one type of liquid crystal material, a photoinitiator dye, a coinitiator, and a surfactant. The disclosure of U.S. Patent No. 7,018,563 is incorporated herein by reference in its entirety.

[0045] The patent and scientific literature contains many examples of material systems and processes that can be used to fabricate waveguides incorporating volume gratings, including investigations into formulating such material systems to achieve high diffraction efficiency, fast response times, low drive voltages, etc. U.S. Patent No. 5,942,157 to Sutherland and U.S. Patent No. 5,751,452 to Tanaka et al. both describe suitable monomer and liquid crystal material combinations for fabricating waveguides incorporating volume gratings. Recipe examples can also be found in papers dating back to the early 1990s, many of which disclose the use of acrylate monomers, including the following: R.L. Sutherland et al., Chem. Mater. 5, 1533 (1993), the disclosure of which is incorporated herein by reference, describes the use of acrylate polymers and surfactants. Specifically, the recipe includes a crosslinking multifunctional acrylate monomer, the chain extender N-vinylpyrrolidinone, LC E7, the photoinitiator Rose Bengal, and the coinitiator N-phenylglycine. The surfactant octanoic acid was added in some variations. Fontecchio et al., SID 00 Digest 774-776, 2000 (the disclosure of which is incorporated herein by reference) describe a UV-curable HPDLC for reflective display applications that includes a multifunctional acrylate monomer, a LC, a photoinitiator, a co-initiator, and a chain terminator. YH Cho, et al., Polymer International, 48, 1085-1090, 1999, the disclosure of which is incorporated herein by reference, discloses HPDLC recipes containing acrylates. Karasawa et al., Japanese Journal of Applied Physics, Vol. 36, 6388-6392, 1997, the disclosure of which is incorporated herein by reference, describes various functionalized acrylates. TJ Bunning et al., Polymer Science: Part B: Polymer Physics, Vol. 35, 2825-2833, 1997, the disclosure of which is incorporated herein by reference, also describes multifunctional acrylate monomers. G.S. Iannacchione et al., Europhysics Letters Vol. 36 (6). 425-430, 1996, the disclosure of which is incorporated herein by reference, describe PDLC mixtures containing pentaacrylate monomers, LC, chain extenders, coinitiators, and photoinitiators.

[0046] Acrylates offer the benefits of fast kinetics, good mixing with other materials, and compatibility with film-forming processes. Because acrylates are crosslinked, they tend to be mechanically robust and flexible. For example, urethane acrylates with functionalities of 2 (di) and 3 (tri) have been widely used for HPDLC technology. Higher functionality materials, such as penta- and hexa-functional stems, have also been used.

[0047] Although HPDLC mixtures with specific components are discussed above in connection with their suitable use as optical recording materials in waveguide cells, the specific formulation of the optical recording material can vary widely and can depend on the specific requirements of a given application. Such considerations can include diffraction efficiency ("DE"), haze, solar resistance, transparency, and switching requirements. S- and P-polarized RMLCM material embodiments

[0048] The S- and P-polarized responses of gratings containing LCs can depend on the average LC director orientation relative to the grating K vector. Typically, the director is approximately parallel to the K vector, giving a strong P response and a weaker S response. If the LC directors are misaligned, the grating can have a strong S response. Many embodiments of the present invention include reactive monomer liquid crystal mixture ("RMLCM") material systems configured to incorporate a mixture of LCs and monomers (and other components, including photoinitiator dyes, co-initiators, and surfactants), which, under holographic exposure, undergo phase separation to provide a grating in which at least one of the LCs and at least one of the monomers form a first HPDLC morphology that provides a P-polarized response, and at least one of the LCs and at least one of the monomers form a second HPDLC morphology that provides an S-polarized response. In various such embodiments, the material system includes an RMLCM, which includes photopolymerizable monomers composed of suitable functional groups (e.g., acrylates, mercaptos, and other esters, among others), crosslinkers, photoinitiators, surfactants, and liquid crystals.

[0049] Turning to the components of the material formulation, any single photoreactive monomer material or any encapsulating polymer formed from a mixture of photoreactive monomer materials with a refractive index of about 1.5-1.9 that crosslinks and phase separates when combined can be utilized. Exemplary monomer functional groups that can be used in material formulations according to embodiments include, but are not limited to, acrylates, thiolenes, thiol esters, fluoromonomers, mercaptos, siloxane-based materials, and other esters. Polymer crosslinking can be achieved through different reaction types, including, but not limited to, light-induced photopolymerization, thermally-induced polymerization, and chemically-induced polymerization.

[0050] These photopolymerizable materials can be combined in a two-phase formulation with a second liquid crystal material. Any suitable liquid crystal material with ordinary and extraordinary refractive indices matching those of the polymer can be used as a dopant to balance the refractive index of the final RMLCM material. The liquid crystal material can be manufactured, purified, or naturally occurring. Liquid crystal materials include all known phases of liquid crystallinity, including nematic and smectic phases, cholesteric phases, and lyotropic discotic phases. Liquid crystals can exhibit ferroelectric or antiferroelectric properties and / or behavior.

[0051] Any suitable photoinitiators, coinitiators, chain extenders, and surfactants (e.g., octanoic acid, etc.) suitable for use in conjunction with the monomers and LC materials can be used in the RMLCM material formulations. It should be understood that the photoinitiator can operate within any desired spectral band, including within the UV and / or visible bands.

[0052] In various embodiments, LCs can interact to form LC mixtures, where molecules of two or more different LCs interact to form non-axial structures that interact with both S and P polarized light. The waveguide can also contain an LC matching material to optimize LC matching for optimal S and P performance. In many embodiments, the ratio of diffraction efficiencies for P and S polarized light in the PDLC configuration is maintained at a relative ratio of 1.1:1 to 2:1, and in some embodiments, approximately 1.5:1. In other embodiments, the measured diffraction efficiency for P polarized light is greater than 20% to less than 60%, while the diffraction efficiency for S polarized light is greater than 10% to less than 50%. In some embodiments, the diffraction efficiency of the PDLC configuration for P polarized light is approximately 30%, and the diffraction efficiency of the PDLC configuration for S polarized light is approximately 20%. This can be compared to conventional PDLC configurations, which have diffraction efficiencies for P polarized light of approximately 60% and S polarized light of approximately 1% (i.e., conventional P polarizing materials have a very low or negligible S component). Mixtures incorporating nanoparticles

[0053] In many embodiments, the reactive monomer liquid crystal mixture can further include chemically active nanoparticles disposed within the LC regions. In some such embodiments, the nanoparticles are carbon nanotube ("CNT") or nanoclay nanoparticle materials within the LC regions. Embodiments are also directed to methods for controlling nanoclay particle size, shape, and uniformity. Methods for formulating and dispersing the nanoclay particles can determine the resulting electrical and optical properties of the device. The use of nanoclays in HPDLC is discussed in PCT Application No. PCT / GB2012 / 000680, entitled "IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES."

[0054] Nanoclay nanoparticles can be formed from any naturally occurring or manufactured composition, as long as they can be dispersed in the liquid crystal material. The specific nanoclay material to be selected depends on the specific application of the film and / or device. The concentration and dispersion method also depend on the specific application of the film and / or device. In many embodiments, the liquid crystal material is selected to match the ordinary refractive index of the liquid crystal with that of the nanoclay material. The resulting composite material can have a forced alignment of the liquid crystal molecules due to the nanoclay particle dispersion, and the optical quality of the film and / or device can be unaffected. The composite mixture containing the liquid crystal and nanoclay particles can be mixed to an isotropic state by sonication. The mixture can then be combined with an optically crosslinkable monomer, such as a photoinitiated acrylate or urethane resin, and sandwiched between substrates to form a cell (or alternatively, applied to the substrates using a coating process).

[0055] In various embodiments, the nanoparticles comprise nanoclay nanoparticles, preferably spheres or platelets with a particle size of about 2-10 nanometers in the shortest dimension and about 10 nanometers in the longest dimension. Desirably, the liquid crystal material is selected to match the normal refractive index of the liquid crystal with the nanoclay material. Alternatively, the nanoparticles may comprise a material with ferroelectric properties, causing the particles to induce a ferroelectric matching effect on the liquid crystal molecules, thereby enhancing the electro-optical switching properties of the device. In another embodiment of the invention, the nanoparticles comprise a material with ferromagnetic properties, causing the particles to induce a ferromagnetic matching effect on the liquid crystal molecules, thereby enhancing the electro-optical switching properties of the device. In another embodiment of the invention, the nanoparticles have an induced electric or magnetic field, causing the particles to induce a matching effect on the liquid crystal molecules, thereby enhancing the electro-optical switching properties of the device. Exemplary nanoparticles for use in other contexts, including thermoplastics, polymer binders, and the like, are disclosed in U.S. Pat. Nos. 7,068,898, 7,046,439, 6,323,989, 5,847,787, and U.S. Patent Publication Nos. 2003 / 0175004, 2004 / 0156008, 2004 / 0225025, 2005 / 0218377, and 2006 / 0142455, the disclosures of which are incorporated herein by reference.

[0056] Nanoclays can be used with their naturally occurring surface properties, or the surface can be chemically treated for specific bonding, electrical, magnetic, or optical properties. Preferably, the nanoclay particles will be intercalated so that they are uniformly dispersed in the liquid crystal material. The generic term "nanoclay" as used in the discussion of the present invention can refer to naturally occurring montmorillonite nanoclay, intercalated montmorillonite nanoclay, surface-modified montmorillonite nanoclay, and surface-treated montmorillonite nanoclay. The nanoparticles can be available as commercially purchased, or they may need to be reduced in size or modified in morphology. Processes that can be used include chemical particle size reduction, particle growth, grinding of wet or dry particles, milling of large particles or raw materials, vibratory milling of large particles or raw materials, ball milling of particles or raw materials, centrifugal ball milling of particles or raw materials, and vibratory ball milling of particles or raw materials. All of these techniques can be performed either dry or using a liquid suspension. The liquid suspension can be a buffer, solvent, inert liquid, or liquid crystal material. One exemplary ball milling process offered by Spex LLC (Metuchen, NJ) is known as the Spex 8000 High Energy Ball Mill. Another exemplary process offered by Retsch (France) uses a planetary ball mill to reduce micrometer-sized particles to nanoscale particles.

[0057] Nanoparticles can be dispersed in the liquid crystal material prior to polymer dispersion. Dry or solvent-suspended nanoparticles can be ultrasonically mixed with the liquid crystal material or monomer prior to polymer dispersion to achieve an isotropic dispersion. Wet particles may need to be prepared for dispersion in the liquid crystal, depending on the specific material used. If the particles are in a solvent or liquid buffer, the solution can be dried and the dried particles can be dispersed in the liquid crystal as described above. Drying methods include evaporation in air, vacuum evaporation, purging with an inert gas such as nitrogen, and heating the solution. If the particles are dispersed in a solvent or liquid buffer with a lower vapor pressure than the liquid crystal material, the solution can be mixed directly with the liquid crystal, and the solvent can be evaporated using one of the methods described above, leaving a liquid crystal / nanoparticle dispersion. In one embodiment of the present invention, an optical film comprises a liquid crystal material and nanoclay nanoparticles, where the nanoparticles are particles of a material with a size of less than 1 micrometer in at least one dimension. The film can be isotropically distributed.

[0058] Although nanoclay materials are discussed, in many embodiments, CNTs are used as an alternative to nanoclays as a means to reduce voltage. The properties of CNTs relevant to PDLC devices have been reviewed by E.H. Kim et al. in Polym. Int. 2010; 59: 1289-1295 (the disclosure of which is incorporated herein by reference in its entirety). PDLC films were fabricated with various amounts of multi-walled carbon nanotubes ("MWCNTs") to optimize the electro-optical performance of the PDLC films. MWCNTs were well dispersed in the prepolymer mixture up to 0.5 wt %, implying that polyurethane acrylate ("PUA") oligomer chains wrapped around the MWCNTs along their length, resulting in high diffraction efficiency and good phase separation. The hardness and elastic modulus of the polymer matrix were enhanced with increasing amounts of MWCNTs due to the reinforcing effect of MWCNTs, which are inherently good mechanical properties. The increased elasticity of the PUA matrix and the immiscibility between the matrix and the liquid crystal gradually increased the diffraction efficiency of the PDLC film. However, the diffraction efficiency of PDLC films with MWCNTs above 0.05 wt.% was reduced, which was caused by poor phase separation between the matrix and the LC due to the high viscosity of the reactive mixture. PDLC films exhibiting low driving voltages (75%) could be obtained using 0.05 wt.% MWCNTs in 40 wt.% LC.

[0059] In embodiments in which the PDLC material incorporates such nanoparticles, reduced switching voltages and improved electro-optical properties of polymer dispersed liquid crystal films and / or devices can be obtained by including nanoparticles within the liquid crystal regions. The inclusion of nanoparticles serves to align the liquid crystal molecules and modify the birefringent properties of the film through refractive index averaging. Additionally, the inclusion of nanoparticles improves the switching response of the liquid crystal regions. Monomer Functionality

[0060] RMLCM material systems according to various embodiments can be formulated in a variety of ways. In many embodiments, the material system is an RMLCM comprising at least one LC, at least one multifunctional monomer, a photoinitiator, a dye, and at least one monofunctional monomer. The specific mixture of components and their percent composition, along with several factors such as, but not limited to, the recording beam power / wavelength, grating periodicity, and grating thickness, can determine the diffraction efficiency of the resulting HPDLC grating. Heterogeneous polymerization due to the spatially periodic irradiation intensity of the exposure light can be a driving force for separating the monomer and LC and ordering the orientation of the LC molecules, which can affect the diffraction efficiency of the HPDLC grating. In many cases, the diffusion coefficient of the monomers depends on their molecular weight and reactivity. It has been shown that varying monomer molecular weights or functionality can result in complex distributions of polymer and LC phases. In many cases, molecular functionality can be important in achieving efficient phase separation and the formation of gratings with high diffraction efficiency. Thus, many embodiments of the present invention include material systems formulated with specific mixtures of monomers selected, at least in part, for their functionality to affect the diffraction efficiency and refractive index modulation of the resulting grating structure. Other considerations in formulating such mixtures may include, but are not limited to, the nature of the recording beam and the thickness of the grating. For purposes of describing the present invention, the functionality of a monomer refers to the number of reactive sites on each monomer unit.

[0061] The effects of various monomer functionalities in HPDLC material systems have been studied to some extent in the scientific literature. Such studies generally consider the effect of the effective or average functionality of the mixture on grating formation and performance. For example, in the paper by Pogue et al., Polymer 41 (2000) 733-741 (the disclosure of which is incorporated herein by reference), investigations were carried out on flood PDLC and holographic PDLC gratings to show that a decrease in effective monomer functionality generally leads to reduced LC phase separation.

[0062] Many embodiments in accordance with the present invention involve investigations into mixtures involving specific formulations of low-functionality monomers that can result in the formation of gratings with high diffraction efficiency and efficient phase separation. While the scientific literature typically emphasizes the use of high-functionality monomers, various embodiments in accordance with the present invention focus on the use of low-functionality monomers in certain applications. In some embodiments, the monomers in the mixture are either monofunctional or difunctional monomers. In some embodiments, trifunctional monomers are also included. In such mixtures, the trifunctional monomers are typically included at low concentrations, such as less than 5% by weight.

[0063] Mixtures containing low-functionality monomers can behave differently depending on various factors, including, but not limited to, the wavelength sensitivity of the material system, the thickness of the HPDLC to be formed, and the exposure temperature. In the scientific literature, investigations into PDLC material systems typically involve UV-sensitive material systems, since material reaction efficiency is generally poor in visible light systems. However, formulations according to various embodiments of the present invention have been able to reach high diffraction efficiencies (>80%) with low haze using low-functionality monomers that are sensitive (polymerize) to visible light. In further embodiments, the material system includes a monomer that is sensitive to green light, such as light with wavelengths ranging from 495 to 570 nm. In addition to different optical systems, the performance of HPDLC mixtures can depend on the thickness of the waveguide cell in which the grating is formed. For example, for a given material system, different thicknesses of the deposited film can form waveguides with different amounts of haze. While grating thickness has been explored in patent and scientific literature, such investigations have focused on relatively thick gratings. In some embodiments, the material system is formulated for use in waveguides with thin form factors. In a further embodiment, the material system is formulated for use in fabricating waveguides having HPDLC layers with thicknesses below 10 μm and gratings with diffraction efficiencies greater than 80%. In a further embodiment, the material system is formulated for use in waveguides having HPDLC layers 2-3 μm thick and gratings with diffraction efficiencies of 80-90%. The material system can also be formulated to fabricate such waveguides with low haze. In some embodiments, the material system can form HPDLC layers with haze less than 1%. Waveguide haze is the integrated effect of light interacting with material and surface inhomogeneities over many beam bounces. The impact on ANSI contrast, i.e., the ratio of averaged white to black measurements obtained from a checkerboard pattern, can be dramatic due to scattering contributions to the black level. Haze is largely due to wide-angle scattering by LC droplets and other small particles or scattering centers resulting from incomplete phase separation of the LC / monomer mixture during grating recording.Haze can also result, at least in part, from narrow-angle scattering generated by large-scale nonuniformities, leading to a loss of see-through quality and reduced image clarity. Some waveguide applications, such as aircraft HUDs, that use 1D beam expansion in thick waveguides produce as few as seven bounces, allowing for contrasts of up to 80:1. However, in thin waveguides of the type used in eyepiece displays, the number of bounces can increase by a factor of ten, making haze control even more necessary.

[0064] The RMLCM recipe can be optimized for a specific thickness of the HPDLC layer. In many embodiments, the RMLCM recipe is optimized for a uniformly modulated grating of about 3 μm thick, designed to have a refractive index modulation of about 0.16. As can be readily appreciated, the specific thickness of the waveguide section to be fabricated can vary and depend on the specific requirements of a given application. In some embodiments, the waveguide section can be fabricated with 90% transmission and 0.3% haze. In other embodiments, the waveguide section can be fabricated with about 0.1% haze (about 0.01% haze is recorded in an unexposed sample of the same material). In some embodiments, the RMLCM can be formulated to fabricate waveguide sections containing less than 0.05% haze.

[0065] Transmission haze can be defined as the percentage of light that deviates, on average, by more than 2.5 degrees from the desired beam direction (according to the ASTM D1003 standard). Waveguide transparency can be characterized by the amount of narrow-angle scattered light (at angles less than 2.5 degrees from the normal to the waveguide surface). Transmittance can be defined as the amount of light transmitted through the waveguide without being scattered. To assess general material haze, scattering can be measured around a vector normal to the waveguide TIR surface. To assess holographic haze, scattering can be measured around the principal diffraction direction (passing through the center of the eyebox). Procedures for measuring haze, transparency, and transmittance are defined in the ASTM D1003 international test standard, with "Procedure A" using a haze meter and "Procedure B" using a spectrophotometer. An exemplary instrument for measuring haze is the BYK-Gardner HAZE Guard II instrument. In many embodiments, the RMLCM mixture includes a liquid crystal mixture, a complex mixture of acrylates and acrylate esters, Dynasylan® MEMO, and a photoinitiator. In further embodiments, the RMLCM includes EHA and DFHA. Depending on the specific mixture of components and their percent composition, the resulting lattices can have very different properties. In some embodiments, the proportion of LC by weight is greater than 30%. In further embodiments, the proportion of LC is greater than 35% by weight. In some embodiments, the mixture includes a liquid crystal with high birefringence. In further embodiments, the high birefringence liquid crystal comprises more than 20% by weight of the mixture. In some embodiments, the dye and photoinitiator comprise less than 5% by weight of the mixture.

[0066] Nematic LC materials can offer a range of birefringence (which can be translated into refractive index modulation). Low to moderate birefringence typically covers the range of 0.09 to 0.12. However, gratings can be designed using much lower birefringence values, including gratings where the birefringence varies along the grating. Such gratings can be used to extract light from a waveguide with low efficiency at one end of the grating and high efficiency at the other end of the grating to provide spatially uniform output illumination. High birefringence (nematic LC) typically ranges from 0.2 to 0.5. Even higher values ​​are possible. Nematic liquid crystals, compounds, and mixtures with positive dielectric anisotropy (i.e., LCs with a dielectric constant greater in the long molecular axis than in other directions) are reviewed in the paper by R. Dabrowski et al., "High Birefringence Liquid Crystals"; Crystals; 2013;3;443-482, the disclosure of which is incorporated herein by reference.

[0067] The functionality of the monomers in the mixture can greatly affect the diffraction efficiency of the resulting grating. In many embodiments, the mixture contains at least one monofunctional monomer and at least one multifunctional monomer in various concentrations. In some embodiments, the concentration of the monofunctional monomer in the mixture ranges from 1 to 50% by weight. The monofunctional monomer can include an aliphatic / aromatic group and an adhesion promoter. In some embodiments, the proportion of multifunctional monomer present in the mixture is in the range of 2 to 30% by weight. Multifunctional monomers according to various embodiments of the present invention typically contain low-functionality monomers. In some embodiments, the mixture contains a low concentration of a difunctional monomer. In further embodiments, the mixture contains less than 15% by weight of a difunctional monomer. Depending on the type and concentration of the difunctional monomer in the mixture, proper phase separation and grating formation can occur. In an illustrative embodiment, the monofunctional monomer, the difunctional monomer, and the LC had relative weight ratios of 30%, 14%, and 40%, which resulted in a formulation that allowed recording of gratings with diffraction efficiencies higher than 90% and refractive index modulations of about 0.12.

[0068] As can be readily appreciated, the percent composition of each component within an RMLCM can vary widely. The formulation of such a material system can be designed to achieve certain properties in the resulting grating. In many cases, an RMLCM is formulated to have the highest possible diffraction efficiency.

[0069] Work cell cluster for fabricating waveguide cells Waveguide cell manufacturing systems according to various embodiments of the present invention can be implemented as a work cell cluster. By compartmentalizing different manufacturing steps into work cells, a modular system can be implemented. In many embodiments, the work cell cluster includes a preparation work cell for preparing a substrate for material deposition, a deposition work cell for depositing optical recording material onto the substrate, and a stacking work cell for stacking various layers together to build the waveguide cell. The work cells can be configured in various ways to implement different manufacturing processes for the waveguide cell. In some embodiments, the work cells are coupled and configured so that the output of one work cell is transferred to another work cell to form a manufacturing assembly line. The transfer mechanism can be implemented in various ways, such as, but not limited to, the use of mechanical arms, suction, and / or conveyor systems. In some embodiments, the products are transferred manually. FIG. 2A conceptually illustrates a work cell cluster system 200 according to an embodiment of the present invention. In the illustrative embodiment, the system 200 includes a preparation work cell 202, a deposition work cell 204, and a stacking work cell 206. As shown, arrows 208 indicate sequential workflow relationships between workcells.

[0070] One advantage of a modular system is the ability to vary the number of work cells dedicated to specific tasks, optimizing work cell usage and improving throughput by reducing work cell downtime. For example, waveguide cells manufactured using different optical recording materials may result in different deposition times. In such embodiments, the number of deposition work cells may be varied accordingly to balance the task completion time of each work cell, such as to minimize overall work cell downtime. FIG. 2B conceptually illustrates a work cell cluster system 210 with two deposition work cells 212, 214, in accordance with an embodiment of the present invention. In the illustrative embodiment, the system 210 includes a preparation work cell 216, two deposition work cells 212, 214, and a lamination work cell 218. The dotted arrow 220 indicates that output from the preparation work cell 216 can be received by either of the deposition work cells 212, 214. Such a system can ideally be implemented when the completion time for a single deposition process is approximately twice as long as the completion time for the other process.

[0071] 2A and 2B conceptually illustrate specific workcell cluster system configurations, workcell clusters according to various embodiments of the present invention can be configured in numerous ways depending on the specific requirements of a given application. For example, workcell clusters can be configured to have different workflow paths, types of workcells, and / or numbers of workcells.

[0072] Due to the sensitive nature of some materials and processes associated with waveguide cell processing, the work cell can be configured to provide protection from environmental light and contaminants. In many embodiments, an optical filter coats the work cell to reduce and / or prevent unwanted light from interacting with the optical recording material, which is typically a photosensitive material. Depending on the specific type of optical recording material, the deposition work cell can be lined with an appropriate optical filter that prevents certain wavelengths of light from entering the work cell and exposing the optical recording material. In addition to reducing / preventing light contamination, the work cell can also be configured to reduce particulate contamination. In some embodiments, the work cell is configured to operate in an environment with little or no air contamination. A low-particulate environment can be achieved in many different ways, including, but not limited to, the use of air filters. In some embodiments, air filters employing laminar airflow principles are implemented. Contamination reduction / prevention systems such as those described above can be implemented separately or in combination. While specific systems are described, work cells according to various embodiments of the present invention can be constructed in a variety of ways to modify the work environment in desired ways. For example, in some embodiments, the work cells are configured to operate in a vacuum. Specific work cells and their implementations and constructions are described in further detail in the following sections.

[0073] Preparation work cell Waveguide cells according to various embodiments of the present invention typically consist of a layer of optical recording material sandwiched between two substrates. Fabrication techniques for constructing such waveguide cells according to various embodiments of the present invention can include a deposition step in which a layer of optical recording material is deposited on one of the substrates. In many embodiments, a preparation work cell can be implemented to perform cleaning / preparation procedures on the substrates to prepare them for the deposition step. Preparing a substrate, such as a glass plate, can include, but is not limited to, removing contaminants from the surface and enhancing surface adhesion properties for better material deposition.

[0074] The preparation work cell can be configured to implement a variety of cleaning and preparation protocols. Mechanical arms and / or suction devices can be used to maneuver substrates throughout the work cell. In many embodiments, the preparation work cell is configured to clean glass substrates using a variety of solvents and solutions, including, but not limited to, soap solutions, acid cleaners, acetone, and various types of alcohols. In some embodiments, several types of solvents and / or solutions are used in combination. For example, in some embodiments, methanol or isopropanol can be dispensed after acetone to rinse away excess acetone. In some embodiments, deionized water is used to rinse away excess solvent or solution. Solvents can be dispensed in several ways, including, but not limited to, the use of nozzles and baths. After cleaning, the work cell can be configured to dry the substrates using an inert gas, such as nitrogen, and / or a heating element.

[0075] In many embodiments, the cleaning process includes an ultrasonic treatment step. In some embodiments, the substrate is placed in a chamber containing a solution, and a transducer is used to generate ultrasonic waves. The ultrasonic waves can agitate the solution and remove contaminants adhered to the substrate. The treatment can vary in duration depending on several factors and can be performed with different types of substrates. Deionized water or a cleaning solution / solvent can be used depending on the type of contamination and the type of substrate.

[0076] In many embodiments, the preparation work cell incorporates a plasma chamber and is configured to plasma-treat the surface of a substrate. In some embodiments, the substrate is made of glass. Existing in the form of ions and electrons, plasma is essentially an ionized gas charged with excess electrons in both negative and positive states. The plasma can be used to treat the surface of the substrate, remove contaminants, and / or prepare the surface for material deposition by increasing surface energy and improving adhesion properties. In some embodiments, the work cell includes a vacuum pump, which can be used to generate the vacuum under which plasma processing can be performed.

[0077] As can be readily appreciated, preparation work cells according to various embodiments of the present invention can be configured to perform various combinations of steps and implement specific cleaning protocols according to the requirements of a given application. Although a specific preparation work cell for preparing glass plates is discussed above, the preparation work cell can be implemented to perform various preparation steps for a variety of different substrates, including, but not limited to, plastics.

[0078] Deposition Work Cell Waveguide cell manufacturing systems can utilize various techniques for placing optical recording material between two substrates. Manufacturing systems according to various embodiments of the present invention can utilize a deposition process in which a film of optical recording material is deposited on a substrate and the composite is laminated with a second substrate to form a three-layer stack. In many embodiments, the manufacturing system is a work cell cluster including a deposition work cell for depositing a film of optical recording material on a substrate. Such a deposition work cell can be configured to receive the substrate from a preparation work cell. In some embodiments, the deposition work cell includes a stage for supporting the substrate and at least one deposition mechanism for depositing material on the substrate. Any of a variety of deposition heads can be implemented to function as the deposition mechanism. In some embodiments, a spray mechanism, such as, but not limited to, a spray nozzle, is implemented to deposit the optical recording material on the substrate. In some embodiments, the optical recording material is deposited using a printing mechanism. Depending on the type of deposition mechanism / head implemented, several different deposition capabilities can be achieved. In some embodiments, the deposition head can enable the deposition of different materials and / or mixtures with varying component concentrations. As can be readily appreciated, the particular deposition mechanism utilized may depend on the specific requirements of a given application.

[0079] Components within the deposition work cell can be configured to move in various ways to deposit optical recording material onto a substrate. In many embodiments, the deposition head and / or stage are configured to move across an axis to deposit one or more layers of optical recording material. In some embodiments, the deposition head is configured to move and deposit material across three dimensions, such as within three-dimensional Euclidean space, allowing for the deposition of multiple layers onto a substrate. In some embodiments, the deposition head is configured to move in only two axes to deposit a single layer. In other embodiments, the stage, and therefore the substrate, is configured to move in three dimensions while the deposition head remains stationary. As can be readily appreciated, deposition applications can be implemented to deposit material in various dimensions by configuring the degrees of freedom of motion of the print head and / or stage. The stage and deposition head can be configured such that the combination of their degrees of freedom of motion allows for the deposition of material in n-dimensional Euclidean space, where n is the desired dimension. For example, in some embodiments, the deposition head is configured to move back and forth to deposit material in one axis while the stage moves in a different axis, allowing for deposition of material in a two-dimensional Euclidean plane. In some embodiments, the stage is implemented using a conveyor belt. The system can be designed so that the conveyor belt receives the substrate from a different work cell, such as a preparation work cell. Once received, the conveyor system can move the substrate while the deposition head deposits a layer of material on the substrate. At the end of the conveyor path, the substrate can be delivered into another work cell.

[0080] In some embodiments, the deposition work cell includes an inkjet print head configured to deposit an optical recording material onto a substrate. Traditionally, inkjet printing refers to a printing method that deposits a matrix of ink dots to form a desired image. In typical operation, an inkjet print head contains a large number of small individual nozzles, each capable of depositing a dot of material. In additive manufacturing applications, inkjet printing can be used to create complex patterns and structures with high precision due to the size and number of nozzles in a typical inkjet print head. Applying these principles to waveguide cell manufacturing applications, inkjet printing can be used to print a layer of optical recording material that is uniform or nearly uniform in terms of thickness and composition. Depending on the application and inkjet print head, one or more layers of optical recording material can be printed onto a substrate. Various optical recording materials, such as those described in the above sections, can be used in conjunction with inkjet print heads. In addition to the ability to print on different materials, the printing system can be configured for use with various types of substrates. As can be readily understood, the choice of material to be printed and the substrate used can depend on the specific requirements of a given application. For example, the choice of material system can be selected based on printing stability and accuracy. Other considerations may include, but are not limited to, viscosity, surface tension, and density, which may affect several factors such as, but not limited to, beading and the ability to form a layer of uniform thickness.

[0081] A deposition work cell 300 according to one embodiment of the present invention is conceptually illustrated in FIGS. 3A and 3B. FIG. 3A shows an isometric view of the deposition work cell 300, while FIG. 3B shows a top view of the same deposition work cell 300. As shown, the deposition work cell 300 is constructed with a frame that can hold an optical glass filter to prevent particulate contamination and ambient light from exposing the optical recording material within the work cell 300. The work cell includes chambers 302, 304 for receiving a substrate and outputting a waveguide cell. In the illustrative embodiment, the stage is implemented as a conveyor belt 306 that moves the received substrate along one direction. The deposition work cell 300 further includes an inkjet printer 308 implemented as a deposition mechanism. The inkjet printer 308 is configured to print across a direction different from the movement of the conveyor belt 306, allowing for the deposition of a layer of optical recording material across the planar surface of the substrate. Additionally, deposition work cell 300 implements a roller laminator 310 for laminating printed layers and two substrates to build a waveguide cell. Work cell 300 is also implemented as a glove box with gloves 312, which allows for manual manipulation of devices within work cell 300 while maintaining a clean environment.

[0082] 3A and 3B depict a specific deposition work cell configuration, the deposition work cell can be configured in many ways according to various embodiments of the present invention. For example, the deposition device can be implemented in a separate deposition work cell. In some embodiments, an automated system configuration can be implemented. In many embodiments, multiple inkjet print heads are used. In other embodiments, spray nozzles are used as the deposition mechanism.

[0083] Modulation of material composition High luminance and excellent color fidelity are important factors in AR waveguide displays. In each case, high uniformity across the FOV can be essential. However, the basic optics of the waveguide can lead to non-uniformities due to gaps or overlaps of beams bouncing back and forth along the waveguide. Further non-uniformities can arise from imperfections in the grating and non-planarity of the waveguide substrate. In SBGs, there can be the additional problem of polarization rotation due to birefringent gratings. The greatest challenge is with folded gratings, where millions of optical paths exist resulting from multiple intersections of the beam with the grating fringes. Careful management of the grating properties, particularly the refractive index modulation, can be utilized to overcome non-uniformities according to various embodiments of the present invention.

[0084] Of the many possible beam interactions (diffraction or zero-order transmission), only a subset contributes to the signal presented to the eyebox. By tracing back from the eyebox, the folding regions contributing to a given field point can be pinpointed. The precise correction to the modulation needed to further transmit the output illumination into the dark region can then be calculated. Once the output illumination uniformity for one color is returned to the target, the procedure can be repeated for the other color. Once the refractive index modulation pattern is established, this design can be exported to a deposition mechanism, where each target refractive index modulation is translated into a unique deposition setting for each spatial resolution cell on the substrate to be coated. In many embodiments, spatial patterns can be implemented down to 30 micrometer resolution with perfect repeatability.

[0085] 4A and 4B conceptually and diagrammatically illustrate the use of reverse ray tracing to calculate a compensated refractive index modulation pattern for a coating, according to various embodiments of the present invention. This procedure can determine the optimal usable area of ​​the folded grating and the refractive index modulation variation across the folded grating needed to provide uniform illumination in the eyebox. FIG. 4A shows a mathematical model of a basic waveguide architecture, including an input grating 402, a folded grating 404 divided into a computational mesh, and an output grating 406. By tracing rays from a point traversing the eyebox through the output grating and through the folded grating, the folded grating cells that contribute to the eyebox illumination for a given FOV direction can be identified. The reverse beam path from the output grating is shown by rays 408-414. By repeating the ray tracing for different FOV angles, the maximum extent of the folded grating needed to fill the eyebox can be determined. This ensures that the area of ​​HPDLC material to be deposited / printed can be kept to a minimum, thereby reducing haze in the final waveguide section. This procedure can also identify cells whose refractive index modulation needs to be increased (or decreased) to maintain illumination uniformity across the eyebox. For example, in the embodiment of FIG. 4A, most of the folded grating region has a refractive index modulation of 0.03. However, some computational cells surrounded by 416 (e.g., cell 418) and some computational cells surrounded by 420 (e.g., cell 422) should have a refractive index modulation of 0.07, while computational cells located within rectangular area 424 should have a refractive index modulation of 0.05. Typically, the map of refractive index modulation values ​​is exported as an AutoCAD DXF (Drawing Interchange Format) file to a processor controlling the deposition mechanism. FIG. 4B shows a top view 450 of the final waveguide section 452, onto which is superimposed the refractive index modulation map of the printed grating layer (corresponding to the model of FIG. 4A), as would be revealed by viewing the printed grating under crossed polarizers. The grating region includes an input grating 454, an output grating 456, and a folded grating 458.In the illustrative embodiment, the folded grating contains high refractive index modulation regions 460, 462, and 464, which correspond to the cells identified in regions 416, 420, and 424 in Figure 4A. The grating regions in Figure 4B are surrounded by clear polymer regions 466. While Figures 4A and 4B illustrate a specific method for calculating a compensated refractive index modulation pattern, any of a variety of techniques can be utilized to calculate such a pattern.

[0086] Compared to waveguides utilizing surface relief gratings (“SRGs”), SBG waveguides implementing fabrication techniques according to various embodiments of the present invention can allow grating design parameters affecting efficiency and uniformity, such as refractive index modulation and grating thickness, to be dynamically adjusted during the deposition process. Thus, there is no need for a new master for the grating recording process. With SRGs, where modulation is controlled by etch depth, such a scheme would be impractical because each variation in the grating would require repeating a complex and expensive tooling process. Additionally, achieving the required etch depth precision and resist imaging complexity can be very difficult. Figures 5A and 5B conceptually illustrate the fundamental structural differences between SBGs and SRGs. Figure 5A shows a cross-sectional view 500 of a portion of an SRG. In the illustrative embodiment, the grating includes a substrate 502 supporting sloped surface relief elements 504 separated by air gaps 506. Typically, the surface relief elements and the substrate are formed from a common material. The grating pitch is indicated by the symbol p, and the grating depth is indicated by the symbol h. FIG. 5B shows a cross-sectional view 550 of an SBG. In contrast to an SRG, an SBG contains alternating slanted Bragg fringes formed from low-index monomer-rich fringes, such as 552, and higher-index LC-rich fringes, such as 554. The refractive index difference is characterized by the refractive index modulation δn, which plays an equivalent role in determining the grating diffraction efficiency relative to the grating depth of an SRG. The variation in the refractive index modulation is represented by a superimposed plot 556 of the refractive index modulation versus the distance z along the grating. In some embodiments, the refractive index modulation has a sinusoidal profile, as shown in FIG. 5B. In embodiments in which the SBG is formed in a uniformly modulated HPDLC, the refractive index modulation profile can include approximately rectangular LC-rich and polymer-rich regions.

[0087] Deposition processes according to various embodiments of the present invention can provide for adjustment of grating design parameters by controlling the type of material to be deposited. Similar to multi-material additive manufacturing techniques, various embodiments of the present invention can be configured to deposit different materials or different material compositions in different areas on a substrate. In many embodiments, layers of optical recording material can be deposited using different materials in different areas. For example, a deposition process can be configured to deposit HPDLC material on areas of the substrate intended to be grating regions and monomer on areas of the substrate intended to be non-grating regions. In some embodiments, a deposition process can be configured to deposit layers of optical recording material with spatially varying component compositions, allowing for modulation of various aspects of the deposited material. Modulation schemes and deposition processes for different types of materials and mixtures are discussed in more detail below.

[0088] The choice of material printed within a particular area may depend on the optical element that will later be recorded within that area. For example, in some embodiments, a deposition head is configured to deposit layers of optical recording material for a waveguide cell intended to be recorded with three different gratings. The layers can be deposited so that the materials printed in each of the areas designated for the three gratings are all different from each other. FIG. 6 conceptually illustrates a waveguide cell 600 with marked areas intended to be recorded with various gratings, according to one embodiment of the present invention. As shown, areas for an input grating 602, a folded grating 604, and an output grating 606 are outlined. Each such area can be composed of a different material or a different blend composition, depending on a given application. In some embodiments, different materials can be deposited to produce different diffraction efficiencies between the recorded gratings. In an illustrative embodiment, the waveguide cell is curvilinear, which, along with the location, size, and shape of the gratings, is designed to be a waveguide for an ocular application.

[0089] Deposition of materials with different compositions can be implemented in several different ways. In many embodiments, more than one deposition head can be utilized to deposit different materials and mixtures. Each deposition head can be coupled to a different material / mixture reservoir. Such implementations can be used for a variety of applications. For example, different materials can be deposited for the grating and non-grid areas of a waveguide cell. In some embodiments, HPDLC material is deposited on the grating regions, while only monomer is deposited on the non-grid regions. In some embodiments, the deposition mechanism can be configured to deposit mixtures with different component compositions.

[0090] In some embodiments, a spray nozzle can be implemented to deposit multiple types of materials on a single substrate. In waveguide applications, a spray nozzle can be used to deposit different materials for the lattice and non-lattice areas of a waveguide. Figures 7A and 7B conceptually illustrate the operation of a deposition mechanism utilizing a spray module, according to an embodiment of the present invention. As shown, an apparatus 700 includes a coating module 702 including a first spray module 704 connected via a pipe 706 to a first reservoir 708 containing a first mixture of a first material, and a second spray module 710 connected via a pipe 712 to a second reservoir 714 containing a second mixture of a second material. In an illustrative embodiment, the first material includes at least a liquid crystal and a monomer, while the second material includes only a monomer. Such a configuration enables the deposition of a layer of optical recording material with defined lattice and non-lattice areas. As can be easily understood, any configuration of different mixtures can be utilized as appropriate depending on the specific application.

[0091] In Figures 7A and 7B, the first and second spray modules provide droplet jets over controllable divergence angles, as represented by 716 and 718. The apparatus further includes a support for a transparent substrate 720 having predetermined areas for supporting the grating, as illustrated by the areas of the grating that do not transmit light into the eyebox, as indicated by shaded areas 722-726, 728, and 730, and the area surrounding the grating, as indicated by 732. In some embodiments, areas 728 and 730 are identified by back-ray tracing of the waveguide from the eyebox. During operation, the areas for supporting the grating that provide diffracted light entering the eyebox are coated with a first mixture. Areas 728 and 730 are coated with a second mixture. The apparatus further includes a positioning device 734 connected to the coating device by a control link 736 for traversing the coating device across the substrate. The apparatus further includes a switching mechanism for activating the first spray module and deactivating the second spray module when the coating apparatus is positioned over a substrate area for supporting a grating, and for deactivating the first spray module and activating the second spray module when the coating apparatus is positioned over a substrate area that does not support a grating.

[0092] Two operating states of the apparatus are conceptually illustrated in Figures 8A and 8B, which show details of the substrate. As shown in Figure 8A, when the coating apparatus is over a non-lattice support area 800 (located in the upper region of the strip bounded by edges 802, 804), the second spray module is activated and the first spray module is deactivated so that a layer of monomer 806 is sprayed onto the substrate. As shown in Figure 8B, when the coating apparatus is over a substantially lattice support area 808 (located in the lower region of the strip bounded by edges 802, 804), the second spray module is deactivated and the first spray module is activated so that a layer of liquid crystal and monomer mixture 810 is sprayed onto the substrate.

[0093] While Figures 7A-8B illustrate specific applications and configurations of the spray mechanism, the spray mechanism and deposition mechanism can generally be configured and utilized for a variety of applications. In many embodiments, the spray mechanism is configured to print a grating, and at least one of material composition, birefringence, and thickness can be controlled using a coating apparatus having at least two selectable spray heads. In some embodiments, the deposition work cell provides an apparatus for depositing a grating-recorded material optimized for control of laser banding. In some embodiments, the deposition work cell provides an apparatus for depositing a grating-recorded material optimized for control of polarization non-uniformity. In some embodiments, the deposition work cell provides an apparatus for depositing a grating-recorded material optimized for control of polarization non-uniformity in association with a matching control layer. In some embodiments, the deposition work cell can be configured for the deposition of additional layers, such as beam-splitting coatings and environmental protection layers. Additionally, although Figures 7A-8B discuss the capabilities of a spray nozzle, these capabilities can be implemented in other deposition mechanisms. For example, an inkjet print head can also be implemented to print different materials in grating and non-grating regions of a substrate.

[0094] FIG. 9 is a flowchart conceptually illustrating a method for fabricating a holographic grating using a selective coating process, according to an embodiment of the present invention. Referring to FIG. 9, method 900 includes providing a transparent substrate for coating (902). Grating-supporting and non-grating-supporting regions of the substrate can be defined (904). Gratings of various sizes and shapes can be defined depending on the specific application. In some embodiments, the grating regions support input, folded, or output gratings. In many embodiments, the substrate has areas defined for gratings made from combinations of the aforementioned types of gratings. A first mixture for coating containing a liquid crystal and a monomer and a second mixture for coating containing a monomer can be provided (906). A first spray head can be provided for coating the first mixture onto the substrate (908). A second spray head can be provided for coating the second mixture (910). The first and second spray heads integrated together can be considered a coating apparatus. The coating apparatus can be set to its starting position (k=1) (912). The coating apparatus can be moved to a current position over the substrate (914). A determination can be made whether the current coating apparatus is positioned over a grid-supported area or a non-grid-supported area (916). If the coating apparatus is over a grid-supported area, the first spray head can be activated and the second spray head can be deactivated (918). If the coating module is over a grid-supported area, the first spray head can be deactivated and the second spray head can be activated (920). A determination can be made regarding the coating status (922). If all defined areas have been coated, the process can be terminated (924). If not all defined areas have been coated, the next area to be coated (increment k) can be selected (926), and the deposition step can be repeated.

[0095] While Figure 9 illustrates a specific method for depositing different materials across a substrate, the deposition mechanism can be configured to produce a film of material with properties that can vary spatially and across regions. Figure 10 conceptually illustrates a deposition head for providing predetermined grating properties within a grating region, according to one embodiment of the present invention. Referring to Figure 10, the deposition head 1000 includes a first spray module 1002 fed via a pipe 1004 from a reservoir 1006 containing a mixture of at least one of a liquid crystal and a monomer, which is dispersed by the spray module 1002 into a spray jet 1008 to coat the transparent substrate. The substrate has a predetermined region for supporting the grating. Also provided are an XY displacement controller 1010 for traversing the spray module across the substrate and a means for controlling the spray properties from the module across each grating region to deposit a film that provides the predetermined grating properties within the grating region following holographic exposure. The holographic exposure may be performed using any current holographic process, including any of the processes disclosed in the referenced documents. In an illustrative embodiment, the deposition head 1000 further includes a mixture controller 1012 for controlling one or more of the temperature, dilution, and relative concentrations of the mixture's chemical components. The deposition head 1000 can also include a spray controller 1014 for controlling one or more of the spray angle relative to the substrate, the spray divergence angle, and the duration of the spray's on and off states. In some embodiments, the predetermined grating characteristics include one or more of the refractive index modulation, refractive index, birefringence, liquid crystal director alignment, and grating layer thickness. As can be readily appreciated, the deposition head can be implemented and configured in many different ways. In many embodiments, any combination or subset of an XY displacement controller, a mixture controller, and a spray controller can be utilized. In some embodiments, additional controllers are utilized to configure the spray mechanism and the material being deposited.

[0096] FIG. 11 conceptually illustrates the operation of a deposition head to deposit a material having regions with predetermined grating properties, according to one embodiment of the present invention. As discussed above, the deposition head can be configured to deposit a material having spatial variations across a grating region in one or more of the following: refractive index modulation, refractive index, birefringence, liquid crystal director alignment, and grating layer thickness. As shown in FIG. 11, a spray module 1100 follows a spray path 1102 across a substrate 1104. The spray can be dynamically controlled during its passage along path 1102 to vary the predetermined grating properties within the area of ​​the predetermined grating region, e.g., 1106, 1108. In some embodiments, the deposition mechanism provides a grating with spatially varying diffraction efficiency after exposure. For example, referring again to FIG. 11, the coated areas 1106, 1108 (after holographic exposure) exhibit diffraction efficiency (DE) versus angle (U) characteristics represented by curves 1110, 1112, respectively.

[0097] FIG. 12 conceptually illustrates a deposition mechanism for depositing two grating layers according to an embodiment of the present invention. As shown, system 1200 is similar to that of FIG. 11 but further includes a second spray module 1202 that provides a jet 1204 for coating second grating layer 1206. In many embodiments, the grating layers are coated using different mixture compositions. In some embodiments, similar to that of FIG. 7A, the system includes a first spray module connected to a first reservoir containing a first mixture including at least one of a first liquid crystal and a first monomer, and a second spray module connected to a second reservoir containing a second mixture including at least one of a second liquid crystal and a second monomer.

[0098] Figure 13 conceptually illustrates a system for depositing a grating layer of material and holographically exposing the layer using a recording beam with on and off states synchronized with a coating module. As shown, system 1300 includes a coating apparatus similar to that of Figure 12 that follows a spray path 1302 across a substrate 1304 providing predetermined grating areas 1306, 1308. During the coating process, a holographic exposure apparatus 1310 providing a recording beam 1312 can expose the coated predetermined grating area 1314. In many embodiments, the holographic exposure apparatus is based on a master grating that contact copies the desired grating into the predetermined grating area.

[0099] FIG. 14 is a flowchart conceptually illustrating a method for depositing a film of material with regions having predetermined lattice properties, according to one embodiment of the present invention. As shown, method 1400 includes providing a transparent substrate for coating (1402). Grid-supported and non-grid-supported regions of the substrate can be defined (1404). A mixture containing a liquid crystal and a monomer can be provided (1406). In some embodiments, the materials utilized include one or more of a photoinitiator, nanoparticles, a low-functionality monomer, an additive for reducing switching voltage, an additive for reducing switching time, an additive for increasing refractive index modulation, and an additive for reducing haze. A spray module can be provided for coating the mixture onto the substrate (1408). The spray module can be set to its starting position (k=1) (1410). The spray module can be moved to a current position across the substrate (1412). A determination can be made whether the current coating device is positioned over the grid-supported or non-grid-supported regions (1414). If the coating device is over the grid area, a spray module can be activated (1416) to provide spray characteristics to achieve the predetermined grid characteristics within the grid area. The grid area can be coated (1418). A determination regarding the coating status can be made (1420). If all defined areas have been coated, the process can be terminated (1422). If not all defined areas have been coated, the next area to be coated can be selected (1424), the deposition step can be repeated, and k can be incremented.

[0100] 10-14 illustrate specific implementations and methods for depositing material with regions having predetermined lattice properties, any of a variety of configurations can be implemented. For example, in many embodiments, multiple spray modules or deposition heads are utilized. The various predetermined lattice properties can be controlled and / or modulated depending on the specific application. Modulation of material composition utilizing more than one deposition head is discussed in further detail below.

[0101] As discussed above, a deposition process can be configured to deposit optical recording materials with spatially varying component compositions. Modulation of material composition can be implemented in many different ways. In some embodiments, an inkjet printhead can be configured to modulate material composition by utilizing various inkjet nozzles within the printhead. By modifying the composition on a "dot-by-dot" basis, a layer of optical recording material can be deposited so that it has a variety of compositions across the planar surface of the layer. Such a system can be implemented using a variety of devices, including, but not limited to, an inkjet printhead. Similar to how color systems, such as the CMYK system in printers or the additive RGB system in display applications, use a palette of only a few colors to generate a spectrum of millions of discrete color values, inkjet printheads according to various embodiments of the present invention can be configured to print optical recording materials with varying compositions using only a few reservoirs of different materials. Different types of inkjet printheads can have different levels of precision and print at different resolutions. In many embodiments, a 300 DPI ("dots per inch") inkjet printhead is utilized. Depending on the level of precision, discretization of various compositions of a given number of materials can be determined across a given area. For example, given two types of materials to be printed and an inkjet print head with a precision level of 300 DPI, if each dot location can contain either one of the two types of materials, there are 90,001 possible discrete values ​​of the composition ratio of the two types of materials across a square inch for a given volume of printed material. In some embodiments, each dot location can contain either one of the two types of materials or both materials. In some embodiments, more than one inkjet print head is configured to print a layer of optical recording material with a spatially varying composition.Printed dots for two-material applications are essentially a binary system, but in practical applications, averaging the printed dots across an area can allow for a sliding-scale discretization of the ratio of the two materials to be printed.

[0102] FIG. 15 conceptually illustrates an inkjet printing modulation scheme according to one embodiment of the present invention. As shown, 18 discrete unit squares can each be printed with various ratios of two different types of material. In the illustrated embodiment, the inkjet print head is capable of printing 64 dots within each of the 18 unit squares. Each dot can be printed using either one of the two types of material. A magnification 1500 of unit square 1502 shows all 64 dot locations within the unit square printed using a first material. Similarly, a magnification 1504 of unit square 1506 is printed entirely using a second material. Unit square 1508 shows an intermediate composition, with 30 of the 64 dot locations printed using the first material, while the remaining dot locations are printed using the second material. Thus, unit square 1508 overall contains intermediate levels of concentration from both materials. Using this modulation scheme, any pattern of varying material properties can be achieved.

[0103] The amount of possible discrete levels of concentration / ratio across a unit square is given by the number of dot locations that can be printed within the unit square. In an illustrative embodiment, 64 discrete dots can be printed within the unit square, thus resulting in each unit square having 65 different possible concentration combinations, ranging from 100% of the first material to 100% of the second material. While FIG. 15 discusses area in terms of unit squares, the concept is applicable to actual units and can be determined by the level of precision of the inkjet printhead. While a specific example of modulating the material composition of a printed layer is discussed, it can be readily understood that the concept of modulating material composition using an inkjet printhead can be extended to use more than two different material reservoirs and can vary in precision, which is highly dependent on the type of printhead used.

[0104] Varying the composition of the printed material can be advantageous for several reasons. For example, in many embodiments, varying the composition of the material during deposition can enable waveguides with gratings that have varying diffraction efficiencies across different areas of the grating. In embodiments utilizing HPDLC mixtures, this can be achieved by modulating the relative concentrations of liquid crystals within the HPDLC mixture during the printing process, which creates a composition that, when exposed to light, can produce gratings with varying diffraction efficiencies. In some embodiments, a first HPDLC mixture with a concentration of liquid crystal and a second HPDLC mixture without liquid crystal are used as printing palettes in an inkjet printhead to modulate the diffraction efficiency of the gratings that can be formed in the printed material. In such embodiments, the discretization can be determined based on the precision of the inkjet printhead. For example, if a 150 DPI inkjet printhead is utilized, each square inch can be printed with 22,501 discrete levels of liquid crystal concentration. The discrete levels can be given by the concentration / ratio of the material printed across an area. In this example, the discrete levels range from no liquid crystal to the maximum concentration of liquid crystal in the first PDLC mixture.

[0105] The ability to vary diffraction efficiency across a waveguide can be used for a variety of purposes. Waveguides are typically designed so that light can be reflected multiple times between the two planar surfaces of the waveguide. These multiple reflections can allow the light path to interact with the grating multiple times. In many embodiments, the waveguide cells can be printed with various compositions so that the gratings formed from the optical recording material layer have various diffraction efficiencies, compensating for light loss during interaction with the grating and enabling uniform output intensity. For example, in some waveguide applications, the output grating is configured to provide exit pupil expansion in one direction while also coupling light out of the waveguide. The output grating can be designed so that when the light in the waveguide interacts with the grating, only a certain percentage of the light is refracted out of the waveguide. The remaining portion continues on the same optical path, remaining in the TIR and continuing to be reflected within the waveguide. Again, upon a second interaction with the same output grating, another portion of the light is refracted out of the waveguide. During each refraction, the amount of light still traveling within the waveguide is reduced by the amount refracted out of the waveguide. Thus, the portion refracted at each interaction gradually decreases with respect to the overall intensity. By varying the diffraction efficiency of the grating so that it increases with propagation distance, the decrease in output intensity along each interaction can be compensated for, allowing for a uniform output intensity.

[0106] Varying the diffraction efficiency can also be used to compensate for other attenuation of light within the waveguide. All objects have a certain degree of reflectivity and absorptivity. Light trapped within the TIR in a waveguide is continuously reflected between the two substrates of the waveguide. Depending on the materials comprising the surfaces, some of the light may be absorbed by the material during each interaction. In many cases, this attenuation is small, but can be significant across a large area where many reflections occur. In many embodiments, the waveguide cells can be printed with various compositions so that the gratings formed from the optical recording material layers have different diffraction efficiencies to compensate for the absorption of light from the substrate. Depending on the substrate, certain wavelengths may be more easily absorbed by the substrate. In multilayer waveguide designs, each layer can be designed to couple light of a range of wavelengths. Therefore, the light coupled by these individual layers can be absorbed in different amounts by the layer's substrate. For example, in some embodiments, the waveguide is made from a three-layer stack to implement a color display, with each layer designed for one of red, green, and blue. In such an embodiment, the gratings in each of the waveguide layers can be formed to have different diffraction efficiencies and to perform color balance optimization by compensating for color imbalance due to loss in transmission of certain wavelengths of light.

[0107] In addition to varying the liquid crystal concentration within the material to vary the diffraction efficiency, another technique involves varying the thickness of the waveguide cell. This can be accomplished through the use of beads. In many embodiments, beads are dispersed throughout the optical recording material for structural support during construction of the waveguide cell. In some embodiments, beads of different sizes are dispersed throughout the optical recording material. The beads can be dispersed in increasing size across one direction of the layer of optical recording material. When the waveguide cell is constructed through stacking, the substrates sandwich the optical recording material, creating a wedge-shaped layer of optical recording material with structural support from the beads of various sizes. Beads of various sizes can be dispersed similarly to the modulation process described above. Additionally, modulating bead size can be combined with modulating the material composition. In some embodiments, reservoirs of HPDLC material, each suspended with beads of different sizes, are used to print layers of HPDLC material with the beads of various sizes strategically dispersed to form wedge-shaped waveguide cells. In some embodiments, bead size modulation is combined with material composition modulation by providing a reservoir volume equal to the product of the number of differently sized beads and the number of different materials used. For example, in one embodiment, an inkjet printhead is configured to print various concentrations of liquid crystal with two different bead sizes. In such an embodiment, four reservoirs can be prepared: a liquid crystal-free mixture suspension with beads of a first size, a liquid crystal-free mixture suspension with beads of a second size, a liquid crystal-rich mixture suspension with beads of a first size, and a liquid crystal-rich mixture suspension with beads of a second size. Stacking Work Cell

[0108] In many embodiments, the work cell cluster includes a lamination work cell for laminating the waveguide cells. After deposition of the optical recording material on the substrate, a second substrate can be placed on the optical recording material to create a three-layer composite. Often, the second substrate will be made from the same material and with the same dimensions as the first substrate. In many embodiments, the deposition work cell is configured to place the second substrate on the optical recording material. In other embodiments, the lamination work cell is configured to place the second substrate on the optical recording material. The second substrate can be placed manually or through the use of a mechanical arm and / or suction mechanism. Once the second substrate is placed, the three-layer composite may be too unstable to handle manually; therefore, in many embodiments, a lamination device is implemented to consolidate the composite.

[0109] The three-layer composite can be laminated in a variety of ways. In many embodiments, a press is implemented to provide downward pressure on the composite. In other embodiments, the lamination work cell is configured to feed the composite through a roller laminator. The adhesive nature of the consolidated composite and the optical recording material can result in the waveguide cells being manually handled with sufficient stability. In some embodiments, the layer of optical recording material includes beads. As a result, these relatively incompressible beads can define the height of the layer of optical recording material within the consolidated composite. As discussed in the section above, differently sized beads can be placed throughout the optical recording material. Depending on the lamination, the size of the beads can respectively determine the local thickness of the waveguide cells. By varying the size of the beads, wedge-shaped waveguide cells can be constructed. As can be readily understood, lamination of substrate-optical recording material layer composites can be achieved using a lamination work cell that can be configured and implemented in many different ways. In some embodiments, the lamination work cell is a modular work cell within a work cell cluster. In other embodiments, the lamination work cell is simply a lamination device implemented within a deposition work cell such as that shown in Figures 3A and 3B.

[0110] While specific systems and methods for manufacturing waveguide cells are discussed above, many different configurations can be implemented in accordance with the many different embodiments of the present invention. It should therefore be understood that the present invention may be practiced otherwise than as specifically described without departing from the scope and spirit of the present invention. Accordingly, the present embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention should, therefore, be determined not by the embodiments exemplified, but by the appended claims and their equivalents.

Claims

1. A method for manufacturing a waveguide cell, comprising: providing a first substrate; depositing a layer of optical recording material onto said first substrate using at least one deposition head; and exposing the layer of optical recording material to holographic light; depositing the layer of optical recording material on the first substrate Providing a first mixture of optical recording material; providing a second mixture of optical recording material; using the at least one deposition head to deposit a first mixture of the optical recording material onto a first region of the first substrate and a second mixture of the optical recording material onto a second region of the first substrate to produce a predetermined pattern including a grating region; the first mixture of optical recording material has a different weight percentage of liquid crystal than the second mixture of optical recording material; wherein the optical recording material deposited on the grating region is formulated to achieve predetermined grating characteristics after the holographic exposure, including a spatial variation in refractive index modulation and a spatial variation in refractive index, the predetermined grating characteristics resulting in a grating after the holographic exposure, the grating after the holographic exposure having a diffraction efficiency that varies spatially in response to the spatial variation in refractive index modulation and the spatial variation in refractive index.

2. Providing a second substrate; placing the second substrate over the deposited layer of optical recording material; 10. The method of claim 1, further comprising laminating the first substrate, the layer of optical recording material, and the second substrate.

3. The first mixture of optical recording material comprises first beads, The method of claim 1 , wherein the second mixture of optical recording material includes second beads of a different size than the first beads.

4. A method for manufacturing a waveguide cell, comprising: providing a first substrate; depositing a layer of optical recording material onto said first substrate using at least one deposition head; and exposing the layer of optical recording material to holographic light; depositing the layer of optical recording material on the first substrate Providing a first mixture of optical recording material; providing a second mixture of optical recording material; using the at least one deposition head to deposit the first mixture of optical recording material and the second mixture of optical recording material onto the first substrate in a predetermined pattern comprising grated regions and non-grated regions; the optical recording material deposited on the grating region is formulated to achieve predetermined grating characteristics after holographic exposure, including a spatial variation of refractive index modulation and a spatial variation of refractive index, the predetermined grating characteristics resulting in a grating after the holographic exposure, the grating after the holographic exposure having a diffraction efficiency that varies spatially in response to the spatial variation of refractive index modulation and the spatial variation of refractive index; the first mixture of the optical recording material comprises a liquid crystal and a monomer; the second mixture of optical recording material comprises a monomer; the first mixture of optical recording material has a different weight percentage of liquid crystal than the second mixture of optical recording material; Depositing the first mixture of optical recording material and the second mixture of optical recording material on the first substrate in the predetermined pattern includes: depositing a first mixture of the optical recording material on the grating region; and depositing a second mixture of said optical recording material on said non-grating regions.

5. The method of claim 1, wherein the first mixture of optical recording material is a polymer dispersed liquid crystal mixture comprising a monomer and a liquid crystal.

6. The method of claim 5, wherein the polymer dispersed liquid crystal mixture comprises an additive selected from the group consisting of nanoparticles, an additive for reducing switching voltage, an additive for reducing switching time, an additive for increasing refractive index modulation, and an additive for reducing haze.

7. The method of claim 1, wherein the at least one deposition head comprises at least one inkjet printing head.

8. The method of claim 7, wherein said depositing a layer of optical recording material comprises: Providing a first mixture of optical recording material; providing a second mixture of optical recording material; printing first dots of a first mixture of said optical recording material using at least one inkjet printhead; and printing, using the at least one inkjet printhead, a second dot of a second mixture of the optical recording material adjacent to the first dot.

9. The at least one inkjet print head comprises a first inkjet print head and a second inkjet print head; depositing the layer of optical recording material Providing a first mixture of optical recording material; providing a second mixture of optical recording material; printing a first mixture of the optical recording material onto the first substrate using the first inkjet printhead; and printing a second mixture of the optical recording material onto the first substrate using the second inkjet printhead.

10. The method of claim 1, wherein the predetermined grating properties further include properties selected from the group consisting of birefringence, liquid crystal director alignment, and grating layer thickness.

11. The method of claim 1, wherein the predetermined grating characteristic further includes spatial variation of a characteristic selected from the group consisting of birefringence, liquid crystal director alignment, and grating layer thickness.

12. A system for machining a grating, comprising: at least one deposition head connected to a first reservoir containing a first mixture of optical recording material, the first mixture being a mixture of monomer and liquid crystal, and a second reservoir containing a second mixture of optical recording material; a first substrate having at least one predetermined grating area for supporting a grating; a positioning element for positioning the at least one deposition head over the first substrate; a holographic exposure apparatus for exposing the first substrate; the at least one deposition head is configured to deposit a first mixture of the optical recording material onto a first region of the first substrate and a second mixture of the optical recording material onto a second region of the first substrate in a predetermined pattern; the holographic exposure device is configured to holographically expose at least one predetermined grating area of ​​the first substrate after depositing the first mixture of optical recording material and the second mixture of optical recording material on the first substrate; the deposited optical recording material provides a predetermined grating characteristic including a spatial variation of refractive index modulation and a spatial variation of refractive index within said at least one predetermined grating region; the predetermined grating characteristics result in a grating after holographic exposure, the grating after holographic exposure having a diffraction efficiency that varies spatially in response to the spatial variation of the refractive index modulation and the spatial variation of the refractive index; A system wherein the first mixture of optical recording material has a different weight percentage of liquid crystal than the second mixture of optical recording material.

13. The system described in claim 12, wherein the first mixture of optical recording material includes a liquid crystal and a monomer, the second mixture of optical recording material includes a monomer, and the at least one deposition head is configured to deposit the first mixture of optical recording material onto the at least one predetermined grating area.

14. The system described in claim 12, wherein the at least one deposition head comprises at least one inkjet print head.

15. The system described in claim 12, wherein the predetermined grating characteristics further include a characteristic selected from the group consisting of birefringence, liquid crystal director alignment, and grating layer thickness.

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