System and method for manufacturing waveguide unit

Abstract

Systems and methods for fabricating waveguide cells are disclosed. Systems for fabrication of waveguide cells according to various embodiments can be configured and implemented in many different ways. In many embodiments, various deposition mechanisms are used to deposit layer(s) of optical recording material onto a transparent substrate. A second transparent substrate can be provided, and the three layers can be laminated to form a waveguide cell. Suitable optical recording materials can vary widely depending on the given application. In some embodiments, the deposited optical recording material has a similar composition throughout the layer. In many embodiments, the optical recording material varies spatially in composition, allowing for the formation of optical elements with varying properties. Regardless of the composition of the optical recording material, any method of placing or depositing the optical recording material onto the substrate can be utilized.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 201880085893.0, filed on November 28, 2018, entitled "System and method for manufacturing waveguide units".

[0002] Cross-reference to related applications

[0003] This application claims the benefit and priority of the following patent applications, which are filed under 35 USC §119(e): U.S. Provisional Patent Application No. 62 / 663,864, filed April 27, 2018, entitled “Method and Apparatus for Fabricating Holographic Gratings”; U.S. Provisional Patent Application No. 62 / 614,813, filed January 8, 2018, entitled “Low Haze Liquid Crystal Materials”; U.S. Provisional Patent Application No. 62 / 614,831, filed January 8, 2018, entitled “Liquid Crystal Materials and Formulations”; U.S. Provisional Patent Application No. 62 / 614,932, filed January 8, 2018, entitled “Methods for Fabricating Optical Waveguides”; and U.S. Provisional Patent Application No. 62 / 614,932, filed May 7, 2018, entitled “Method and Apparatus for Copying a Diversity of Hologram Prescriptions from a Common U.S. Provisional Patent Application No. 62 / 667,891 entitled "Master" and U.S. Provisional Patent Application No. 62 / 703,329 entitled "Systems and Methods for Fabricating a Multilayer Optical Structure" filed on July 25, 2018. The disclosures of U.S. Provisional Patent Application 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 entirety for all purposes. Technical Field

[0004] The present invention generally relates to processes and apparatus for manufacturing waveguide units, and more specifically, to manufacturing waveguide units using deposition and printing techniques. Background Technology

[0005] A waveguide can be described as a structure that has the ability to confine and guide waves (i.e., to confine the spatial region in which waves can propagate). One class of waveguides includes optical waveguides, which are structures that can guide electromagnetic waves, typically in the visible spectrum. Waveguide structures can be designed to use many different mechanisms to control the propagation path of waves. For example, a planar waveguide can be designed to use a diffraction grating to diffract and couple incident light into the waveguide structure, allowing the in-coupled light to continue traveling within the planar structure via total internal reflection (“TIR”).

[0006] Waveguide fabrication can include the use of material systems that allow holographic optical elements to be recorded within the waveguide. One class of such materials includes polymer-dispersed liquid crystal (“PDLC”) mixtures, which are mixtures comprising photopolymerizable monomers and liquid crystals. Another 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 illuminating the material with two mutually coherent laser beams. During the recording process, the monomers polymerize and the mixture undergoes phase separation induced by photopolymerization, resulting in regions densely filled with liquid crystal droplets, interspersed with clear polymer regions. Alternating liquid crystal-rich and liquid crystal-poor regions form the fringe plane of the grating.

[0007] Waveguide optics, as described above, can be considered for a range of display and sensor applications. In many applications, various waveguide systems and material systems can be used to realize waveguides containing one or more grating layers encoding multiple optical functions, enabling new innovations in near-eye displays for augmented reality (“AR”) and virtual reality (“VR”), compact head-up displays (“HUD”) for aerospace and land transportation, and sensors for biometric and lidar (“LIDAR”) applications. Summary of the Invention

[0008] One embodiment includes a method for manufacturing a waveguide unit, the method comprising: providing a first substrate; determining predefined grating characteristics; and using at least one deposition head to deposit an optical recording material layer onto the first substrate, wherein the optical recording material deposited on the grating region is configured to achieve the predefined grating characteristics.

[0009] In another embodiment, the method further includes: providing a second substrate; placing the second substrate onto a deposited optical recording material layer; and laminating the first substrate, the optical recording material layer, and the second substrate.

[0010] In a further embodiment, depositing the optical recording material layer includes providing a first mixture of optical recording materials, providing a second mixture of optical recording materials, and using the at least one deposition head to deposit the first mixture of optical recording materials and the second mixture of optical recording materials into the first substrate in a predetermined pattern.

[0011] In another embodiment, the first mixture of the optical recording material includes a first bead, and the second mixture of the optical recording material includes a second bead of a different size from the first bead.

[0012] In a further embodiment, the first mixture of the optical recording materials has a different weight percentage of liquid crystal than the second mixture of the optical recording materials.

[0013] In another embodiment, the method further includes defining a grating region and a non-grating region on the first substrate, wherein the first mixture of optical recording materials includes liquid crystal and monomers, the second mixture of optical recording materials includes monomers, and depositing the first mixture of optical recording materials and the second mixture of optical recording materials onto the first substrate in a predetermined pattern includes depositing the first mixture of optical recording materials on the grating region and depositing the second mixture of optical recording materials on the non-grating region.

[0014] In a further embodiment, the first mixture of the optical recording material is a liquid crystal mixture comprising a polymer dispersion of monomers, liquid crystal, photoinitiator dyes and coinitiators.

[0015] In another additional embodiment, the polymer-dispersed liquid crystal mixture includes additives selected from the group consisting of: photoinitiators, nanoparticles, low-functionality monomers, additives for reducing switching voltage, additives for reducing switching time, additives for increasing refractive index modulation, and additives for reducing haze.

[0016] In a further additional embodiment, the at least one deposition head includes at least one inkjet printhead.

[0017] In another embodiment, depositing the optical recording material layer includes providing a first mixture of optical recording materials, providing a second mixture of optical recording materials, printing a first point of the first mixture of optical recording materials using the at least one inkjet printhead, and printing a second point of the second mixture of optical recording materials adjacent to the first point using the at least one inkjet printhead.

[0018] In a further embodiment, the at least one inkjet printhead includes a first inkjet printhead and a second inkjet printhead, and depositing the optical recording material layer includes providing a first mixture of optical recording materials, providing a second mixture of optical recording materials, printing the first mixture of optical recording materials onto the first substrate using the first inkjet printhead, and printing the second mixture of optical recording materials onto the first substrate using the second inkjet printhead.

[0019] In yet another embodiment, the predefined grating characteristics include characteristics selected from the group consisting of: refractive index modulation, refractive index, birefringence, liquid crystal director alignment, and grating layer thickness.

[0020] In a further embodiment, the predefined grating characteristics include spatial variations of characteristics selected from the group consisting of: refractive index modulation, refractive index, birefringence, liquid crystal director alignment, and grating layer thickness.

[0021] In yet another additional embodiment, the predefined grating characteristics result in an exposed grating, wherein the grating has spatially varying diffraction efficiency.

[0022] A further embodiment includes a system for manufacturing a grating, the system comprising at least one deposition head connected to at least one container containing at least one mixture of optical recording materials, a first substrate having at least one predefined region for supporting the grating, 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 materials onto the first substrate using the positioning element, and the deposited material provides predefined grating properties within at least one predefined grating region after holographic exposure.

[0023] In yet another embodiment, the at least one deposition head is connected to a first container containing a first mixture of optical recording materials and a second container containing a second mixture of optical recording materials.

[0024] In yet another embodiment, the first mixture of the optical recording material comprises liquid crystal and monomers, and the second mixture of the optical recording material comprises monomers, wherein the at least one deposition head is configured to deposit the first mixture of the optical recording material onto the at least one predefined grating region.

[0025] In yet another embodiment, the at least one deposition head includes at least one inkjet printhead.

[0026] In a further additional embodiment, the predefined grating characteristics include characteristics selected from the group consisting of: refractive index modulation, refractive index, birefringence, liquid crystal director alignment, and grating layer thickness.

[0027] In yet another embodiment, the predefined grating characteristics result in an exposed grating, wherein the grating has spatially varying diffraction efficiency.

[0028] Additional embodiments and features are set forth in part in the description which follows, and will become apparent to those skilled in the art upon review of the specification, or may be recognized by practice of the invention. A further understanding of the nature and advantages of the invention can be achieved by referring to the accompanying drawings and the remainder of the specification, which form a part of this disclosure. Attached Figure Description

[0029] This description will be more fully understood with reference to the accompanying drawings and figures, which are presented as exemplary embodiments of the invention and should not be construed as a complete exposition of the scope of the invention. It will be apparent to those skilled in the art that the invention can be practiced using some or all of the invention disclosed in the following description.

[0030] Figure 1A A cross-sectional view of a waveguide unit according to an embodiment of the present invention is illustrated conceptually.

[0031] Figure 1B A waveguide unit with a wedge-shaped profile according to an embodiment of the present invention is illustrated conceptually.

[0032] Figure 1C A top view of a waveguide unit according to an embodiment of the present invention is shown conceptually.

[0033] Figure 2A A conceptual illustration of a work cell cluster system according to an embodiment of the present invention is provided.

[0034] Figure 2B A conceptual illustration is provided of a cell cluster system having two deposition cells according to an embodiment of the invention.

[0035] Figure 3A An isometric view of a deposition work cell according to an embodiment of the present invention is conceptually illustrated.

[0036] Figure 3B A top view of a deposition work cell according to an embodiment of the present invention is shown conceptually.

[0037] Figure 4A and Figure 4BThe illustrations conceptually depict the use of reverse ray tracing to calculate a compensating refractive index modulation pattern for a coating, according to various embodiments of the invention.

[0038] Figure 5A and Figure 5B The basic structural differences between SBG and SRG are conceptually illustrated.

[0039] Figure 6 A waveguide unit having a marking region for a grating is conceptually illustrated according to an embodiment of the present invention.

[0040] Figure 7A and Figure 7B The operation of a deposition mechanism utilizing a spraying module according to an embodiment of the present invention is conceptually illustrated.

[0041] Figure 8A and Figure 8B Two operating states of the spraying module according to an embodiment of the present invention are conceptually illustrated.

[0042] Figure 9 This is a flowchart that conceptually illustrates a method for fabricating a holographic grating using a selective coating process according to an embodiment of the present invention.

[0043] Figure 10 A deposition head for providing predefined grating characteristics within a grating region is conceptually illustrated according to an embodiment of the invention.

[0044] Figure 11 The illustration conceptually illustrates the operation of a deposition head according to an embodiment of the invention for depositing material in a region having predefined grating characteristics.

[0045] Figure 12 A deposition mechanism for depositing two grating layers according to an embodiment of the present invention is illustrated conceptually.

[0046] Figure 13 A conceptual illustration is provided of a grating layer for depositing materials and a system for holographically exposing the layer according to an embodiment of the invention.

[0047] Figure 14 This is a flowchart conceptually illustrating a method for depositing a material film having regions with predefined grating properties according to an embodiment of the present invention.

[0048] Figure 15 A conceptual illustration of an inkjet printing modulation scheme according to an embodiment of the present invention is provided. Detailed Implementation

[0049] For the purposes of describing the embodiments, some well-known features of optical techniques known to those skilled in the art of optical design and visual displays have been omitted or simplified so as not to obscure the basic principles of the invention. Unless otherwise stated, the term "on-axis" regarding the direction of light rays or beams refers to propagation parallel to an axis perpendicular to the surface of the optical component described with respect to the invention. In the following description, the terms light, ray, beam, and direction are used interchangeably and are associated with each other to indicate the direction of propagation of light energy along a straight trajectory. The sections described below will be stated using terminology commonly used by those skilled in the art of optical design. For illustrative purposes, it should be understood that, unless otherwise stated, the drawings are not drawn to scale.

[0050] Turning now to the accompanying drawings, systems and methods for manufacturing waveguide units are illustrated. A waveguide unit can be defined as a device containing uncured and / or unexposed optical recording material in which optical elements, such as, but not limited to, gratings, can be recorded by exposure to electromagnetic radiation at certain wavelengths. Numerous techniques exist for the fabrication and construction of waveguide units. In many embodiments, a waveguide unit is constructed by placing a thin film of optical recording material between two transparent substrates. In a further embodiment, a work cell cluster manufacturing system is implemented to construct such waveguide units. A work cell can be defined as a collection of machines assigned to a specific manufacturing task. A cluster can be defined as a group of machines that collaboratively perform similar functions. In some embodiments, a work cell cluster includes a preparation work cell for preparing a substrate for deposition, a deposition work cell for depositing optical recording material onto the substrate, and a lamination work cell for laminating various layers together to form a waveguide unit.

[0051] Work cells and clusters of work cells according to various embodiments can be configured and implemented in many different ways. For example, a preparation work cell can be configured to prepare a substrate for material deposition through various processes, including but not limited to cleaning procedures and processes. In many embodiments, substrate preparation includes a glass cleaning procedure for removing contaminants and particles from the substrate surface. In some embodiments, procedures for increasing the surface adhesion properties of the substrate are implemented to further prepare the substrate for material deposition.

[0052] The deposition work unit can be configured to deposit one or more layers of optical recording material onto a transparent substrate using various deposition and printing mechanisms. In many embodiments, additive manufacturing techniques such as, but not limited to, inkjet printing are used to deposit one or more layers of optical recording material. In several embodiments, spraying techniques are used to deposit one or more layers of optical recording material. Suitable optical recording materials can vary widely depending on the given application. In some embodiments, the deposited optical recording material has a similar composition throughout the layer. In many embodiments, the optical recording material varies spatially in composition, thereby allowing the formation of optical elements with varying properties. Regardless of the composition of the optical recording material, any method of placing or depositing the optical recording material onto the substrate can be used.

[0053] Laminate working units can be configured to laminate various layers to form waveguide units. In many embodiments, laminate working units are configured to laminate and form a three-layer composite of an optical recording material and a transparent substrate. As will be readily appreciated, the number of layers and the type of materials used to construct the waveguide unit can vary and depend on the given application. For example, in some embodiments, the waveguide unit can be constructed to include a protective cladding, a polarization control layer, and / or an alignment layer. In some embodiments, the system is configured to produce curved waveguides and waveguide units. Specific materials, systems, and methods for constructing waveguide units are discussed in further detail below.

[0054] waveguide unit

[0055] According to various embodiments of the invention, waveguide units can be configured and constructed in many different ways. As discussed above, in many waveguide configurations, the waveguide unit includes a thin film of optical recording material sandwiched between two substrates. Various processes can be used to fabricate such waveguide units. In many embodiments, the waveguide unit can be constructed by coating a first substrate with an optical recording material capable of acting as an optical recording medium. Various 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 microdroplets). As can be readily appreciated, the type of mixture utilized and the selection of the optical recording material can depend on a given application. Various deposition techniques can be used to deposit the optical recording material. In many embodiments, the optical recording material can be deposited onto the first substrate by inkjet, spin-coating, and / or spray coating processes. The deposition process can be configured to deposit one or more types of optical recording materials. In some embodiments, the deposition process is configured to deposit an optical recording material whose composition spatially varies across the substrates. After the deposition of the optical recording material, a second substrate can be placed such that the optical recording material is sandwiched between the two substrates to form the waveguide unit. In several embodiments, the second substrate may be a thin protective film coated onto the exposure layer. In such embodiments, various techniques, including but not limited to spraying processes, can be used to coat the exposure layer with a desired material film. In many embodiments, the waveguide unit may include various additional layers, such as, but not limited to, a polarization control layer and / or an alignment layer. Other processes for manufacturing the waveguide unit may include filling the empty waveguide unit (composed of two substrates) with an optical recording material using processes such as, but not limited to, gravity filling and vacuum filling methods.

[0056] The substrate used to construct the waveguide unit is often made of a transparent material. In some embodiments, the substrate is an optical plastic. In other embodiments, the substrate can be made of glass. An exemplary glass substrate is a standard Corning Willow glass substrate (refractive index 1.51) with a thickness as low as 50 micrometers. The thickness of the substrate can vary depending on the application. In many embodiments, a 1 mm thick glass slide is used as the substrate. In addition to different thicknesses, substrates of different shapes can also be used depending on the application, such as, but not limited to, rectangular and curved shapes. Often, the shape of the substrate determines the overall shape of the waveguide. In many embodiments, the waveguide unit comprises two substrates with the same shape. In other embodiments, the substrates have different shapes. As can be readily appreciated, the shape, size, and material of the substrate can vary and depend on the specific requirements of a given application.

[0057] 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 to help prevent the two substrates from collapsing onto each other. In some embodiments, the waveguide unit is composed of an optical recording material layer sandwiched between two planar substrates. Depending on the type of optical recording material used, thickness control can be difficult to achieve due to the viscosity of some optical recording materials and the lack of boundary edges of the optical recording material layer. In many embodiments, the beads are relatively incompressible solids, which can allow the construction of waveguide units with a uniform thickness. The size of the beads can determine the local minimum thickness of the area around a single bead. Accordingly, the size of the beads can be selected to help obtain the desired thickness of the optical recording material layer. The beads can be made of any of a variety of materials, including but not limited to glass and plastic. In several embodiments, the material of the beads is selected such that its refractive index does not substantially affect the propagation of light within the waveguide unit.

[0058] In some embodiments, the waveguide unit is configured such that the two substrates are parallel or substantially 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 unit has a tapered profile. Tapered waveguide units 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 an increasing size pattern across the material layer, a tapered optical recording material layer can be formed when the material is sandwiched between two substrates.

[0059] Once constructed, the waveguide unit can be used in conjunction with various processes for recording optical elements within optical recording materials. For example, the disclosed processes can be incorporated into embodiments and teachings from materials and processes such as, but not limited to, those described in U.S. Patent Application No. 16 / 116,834, filed August 29, 2018, entitled “Systems and Methods for High-Throughput Recording of Holographic Gratings in Waveguide Cells” and U.S. Patent Application No. 16 / 007,932, filed June 13, 2018, entitled “Holographic Material Systems and Waveguides Incorporating Low Functionality Monomers”. The disclosures of U.S. Patent Application Nos. 16 / 116,834 and 16 / 007,932 are incorporated herein by reference in their entirety for all purposes.

[0060] Figure 1A The diagram illustrates a cross-sectional view of a waveguide unit 100 according to an embodiment of the invention. As shown, the waveguide unit 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, gratings). The optical recording material 102 can be any of a variety of compounds, mixtures, or solutions, such as, but not limited to, the HPDLC mixtures described in the preceding sections. In the illustrative embodiment, the optical recording material 102 is sandwiched between two parallel glass plates 104, 106. The substrates can be arranged in either a parallel or non-parallel configuration. Figure 1B A cross-sectional view of a tapered waveguide unit 108 utilizing beads 110, 112, and 114 according to an embodiment of the invention is conceptually illustrated. As shown, beads 110, 112, and 114 are different in size and are dispersed throughout an optical recording material 116 sandwiched between two glass plates 118 and 120. During the construction of the waveguide unit, the local thickness of a region of the optical recording material layer is limited by the size of the beads in that particular region. By dispersing the beads across the optical recording material in an increasing order of size, a tapered waveguide unit can be constructed when a substrate is placed in contact with the beads. As discussed above, the substrate used in the waveguide unit can vary in thickness and shape. In many embodiments, the substrate is rectangular in shape. In some embodiments, the shape of the waveguide unit is a combination of curved components. Figure 1C A top view of a waveguide unit 122 with a curved shape according to an embodiment of the present invention is shown conceptually.

[0061] Although Figures 1A-1C The illustration shows a specific waveguide unit construction and arrangement, but waveguide units can be constructed in many different configurations, and a variety of different materials can be used depending on the specific requirements of a given application. For example, the substrate can be made of a transparent plastic polymer instead of glass. Furthermore, the shape and size of the waveguide units can vary considerably 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, thereby allowing the production of waveguides with curved cross-sections.

[0062] grating structure

[0063] Waveguide units according to various embodiments of the present invention can incorporate various photosensitive materials. In many embodiments, the waveguide unit incorporates a holographic polymer-dispersed liquid crystal mixture that acts as an optical recording medium in which optical elements can be recorded. The optical elements can include many different types of gratings capable of exhibiting different optical properties. One type of grating that can be recorded in the waveguide unit is a volume Bragg grating, which can be characterized as a transparent medium having a periodic variation in its refractive index. This variation allows incident light of certain wavelengths to diffract at certain angles. Volume Bragg gratings can have high efficiency with almost no light diffracted into higher orders. The relative amounts of light in diffraction and in the zeroth order can be changed by controlling the refractive index modulation of the grating.

[0064] One type of grating used in holographic waveguide devices is the switchable Bragg grating (“SBG”). An SBG is a diffraction device formed by recording a volume phase grating in a mixture of HPDLC (although other materials can also be used). SBGs can be fabricated by first placing a thin film of a mixture of photopolymerizable monomers and liquid crystal material between glass plates or substrates, forming waveguide units. One or two glass plates can support electrodes, typically transparent tin oxide films, for applying an electric field. SBGs can be implemented as waveguide devices where HPDLC forms an evanescent coupling layer or waveguide core near the waveguide. The glass plates used to form the HPDLC units can provide a total internal reflection light guide structure. When the switchable grating diffracts light at an angle exceeding the TIR condition, light is coupled out of the SBG.

[0065] Grating structures in SBGs can be recorded in HPDLC films via photopolymerization-induced phase separation using interferometric exposure with spatially periodic intensity modulation. Factors such as, but not limited to, control of irradiation intensity, the volume fraction of the HPDLC material components, and exposure temperature determine the resulting grating morphology and properties. During the recording process, monomers polymerize and the mixture undergoes phase separation. LC molecules aggregate to form discrete or aggregated droplets, which are periodically distributed within a polymer network on an optical wavelength scale. Alternating liquid crystal-rich and liquid crystal-poor regions form the fringe plane of the grating, which can produce Bragg diffraction with strong optical polarization caused by the oriented alignment of LC molecules within the droplets. The resulting bulk-phase grating can exhibit very high diffraction efficiency, which can be controlled by the magnitude of the applied electric field across the HDPLC layer. When an electric field is applied to the hologram via a transparent electrode, the natural orientation of the LC droplets changes, causing a decrease in the refractive index modulation of the fringes, and the holographic diffraction efficiency drops to a very low level. The diffraction efficiency of the device can be adjusted by means of the applied voltage across a continuous range from near 100% efficiency without applied voltage to essentially zero efficiency with sufficiently high voltage. In some types of HPDLC devices, the phase separation of the LC material from the polymer can be achieved to the point that no discernible microdroplet structures are formed. SBGs can also be used as passive gratings. The main advantage in this mode is the unique 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, where HPDLCs form an evanescent coupling layer or waveguide core near the waveguide. The glass plate used to form the HPDLC cell provides a total internal reflection light guide structure. When the switchable grating diffracts light at an angle exceeding the TIR condition, light can be coupled out of the SBG.

[0066] In many embodiments, SBG is recorded in a homogeneous modulation material, such as POLICRYPS or POLIPHEM, which have a matrix of solid liquid crystal dispersed in a liquid polymer. Exemplary homogeneous modulation 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 entirety. The homogeneous modulation grating is 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 when no electric field is applied, and becomes diffracted in the presence of an electric field. Reverse-mode HPDLCs can be based on any formulation and process disclosed in PCT application No.: PCT / GB2012 / 000680 entitled "IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALS ANDDEVICES". The optical recording material system is discussed in more detail below.

[0067] Optical Recording Material Systems

[0068] HPDLC mixtures according to various embodiments of the present invention typically comprise LC, monomers, photoinitiator dyes, and co-initiators. The mixtures (often referred to as slurries) also frequently include surfactants. For the purposes of describing the invention, a surfactant is defined as any chemical agent that reduces the surface tension of the total liquid mixture. The use of surfactants in PDLC mixtures is known and traces back to the earliest studies of PDLCs. For example, the paper SPIE, Vol. 2689, 158-169, 1996, by RL Sutherland et al., describes PDLC mixtures comprising monomers, photoinitiators, co-initiators, chain extenders, and LC to which surfactants can be added; the disclosure of that paper is incorporated herein by reference. Surfactants are also mentioned in the paper Journal of Nonlinear Optical Physics and Materials, Vol. 5, No. I 89-98, 1996, by Natarajan et al., the disclosure of which is incorporated herein by reference. Furthermore, U.S. Patent No. 7,018,563 to Sutherland et al. discusses a polymer-dispersed liquid crystal material for forming polymer-dispersed liquid crystal optical elements, the polymer-dispersed liquid crystal material comprising: at least one acrylic monomer; at least one type of liquid crystal material; a photoinitiator dye; a co-initiator; and a surfactant. The disclosure of U.S. Patent No. 7,018,563 is incorporated herein by reference in its entirety.

[0069] Patents and scientific literature contain numerous examples of material systems and processes that can be used to fabricate waveguides for composite gratings, including studies on formulating such material systems to achieve high diffraction efficiency, fast response time, low drive voltage, and so on. Both Sutherland's U.S. Patent No. 5,942,157 and Tanaka et al.'s U.S. Patent No. 5,751,452 describe combinations of monomers and liquid crystal materials suitable for fabricating waveguides for composite gratings. Examples of formulations can also be found in papers dating back to the early 1990s, many of which disclose the use of acrylate monomers, including:

[0070] ·RL Sutherland et al., Chem. Mater., 5, 1533 (1993), describe the use of acrylate polymers and surfactants, the contents of which are incorporated herein by reference. Specifically, the formulations include crosslinked multifunctional acrylate monomers; chain extenders N-vinylpyrrolidone, LCE7, photoinitiator rose red, and co-initiator N-phenylglycine. Octanoic acid surfactant is added in some variants.

[0071] Fontecchio et al., SID 00 Digest 774-776, 2000, describe UV-curable HPDLCs comprising multifunctional acrylate monomers, LCs, photoinitiators, co-initiators, and chain terminators for reflective display applications, the contents of which are incorporated herein by reference.

[0072] YHCho et al., Polymer International, 48, 1085-1090, 1999, disclosed HPDLC formulations including acrylates, the contents of which are incorporated herein by reference.

[0073] Karasawa et al., Japanese Journal of Applied Physics, Vol. 36, 6388-6392, 1997, described acrylates of various functional orders, the contents of which are incorporated herein by reference.

[0074] • TJ Bunning et al., Polymer Science: Part B: Polymer Physics, Volume 35, 2825-2833, 1997, also describe multifunctional acrylate monomers, the contents of which are incorporated herein by reference.

[0075] ·G. S. Lannacchione et al., Europhysics Letters, Vol. 36(6), 425-430, 1996, describes a mixture of PDLCs comprising pentaacrylate monomers, LC, chain extenders, co-initiators and photoinitiators, the contents of which are incorporated herein by reference.

[0076] Acrylates offer advantages such as rapid kinetics, good mixing with other materials, and compatibility with film-forming processes. Because acrylates are cross-linked, they tend to be mechanically robust and flexible. For example, urethane acrylates with functionalities of 2 (di) and 3 (tri) have been widely used in HPDLC technology. Higher functionality materials such as penta- and hex-functional stems have also been used.

[0077] While the above discussion of HPDLC mixtures as suitable optical recording materials in waveguide units has addressed HPDLC mixtures with specific compositions, the specific formulation of optical recording materials can vary widely and depend on the specific requirements of a given application. Such considerations may include diffraction efficiency (“DE”), haze, solar immunity, transparency, and switching requirements.

[0078] Examples of S&P polarized RMLCM materials

[0079] The S and P polarization responses of a grating containing LCs can depend on the orientation of the average LC pointing vector relative to the grating's K vector. Typically, the pointing vector is substantially parallel to the K vector, thus giving a strong P response and a weaker S response. If the LC pointing vector is misaligned, the grating may have a strong S response. Many embodiments of the invention include reactive monomer liquid crystal mixture (“RMLCM”) material systems configured to combine a mixture of LCs and monomers (and other components, including photoinitiator dyes, co-initiators, and surfactants), which undergo phase separation under holographic exposure to provide a grating in which at least one LC and at least one monomer form a first HPDLC morphology providing a P polarization response, and at least one LC and at least one monomer form a second HPDLC morphology providing an S polarization response. In various such embodiments, the material system includes an RMLCM comprising a photopolymerizable monomer composed of suitable functional groups (e.g., acrylates, thiol-containing and other esters), a crosslinking agent, a photoinitiator, a surfactant, and a liquid crystal.

[0080] Turning to the components of the material formulation, any encapsulating polymer can be formed from any single photoreactive monomer material or a mixture of photoreactive monomer materials having a refractive index of approximately 1.5 to 1.9, which crosslinks and separates upon bonding. Exemplary monomeric functional groups that can be used in the material formulation according to the embodiments include, but are not limited to, acrylates, thiols, thioesters, fluorinated monomers, mercapto-containing, siloxane-based materials, and other esters. Polymer crosslinking can be achieved through different reaction types, including but not limited to photoinitiated photopolymerization, thermally initiated polymerization, and chemically initiated polymerization.

[0081] These photopolymers can be combined with a second liquid crystal material in a two-phase mixture. Any suitable liquid crystal material with a common refractive index and a very common refractive index that matches the polymer's refractive index can be used as a dopant to balance the refractive index of the final RMLCM material. Liquid crystal materials can be manufactured, refined, or exist naturally. Liquid crystal materials include all known phases of liquid crystallization, including nematic and smectic phases, cholesteric phases, and lyotropic disk phases. Liquid crystals can exhibit ferroelectric or antiferroelectric properties and / or behaviors.

[0082] Any suitable photoinitiator, co-initiator, chain extender, and surfactant (such as, for example, octanoic acid) suitable for use with monomers and LC materials can be used in the formulation of RMLCM materials. It will be understood that the photoinitiator can operate in any desired spectral band, including the UV and / or visible bands.

[0083] In various embodiments, LCs can interact to form LC mixtures, wherein two or more distinct LC molecules interact to form a non-axis structure that interacts with both S-polarization and P-polarization. The waveguide may also include LC alignment materials to optimize LC alignment for improved S- and P-performance. In many embodiments, the ratio of P-polarized to S-polarized diffraction efficiencies in the PDLC morphology is maintained at a relative ratio from 1.1:1 to 2:1, and in some embodiments, at approximately 1.5:1. In other embodiments, the measured diffraction efficiencies for P-polarized light range from greater than 20% to less than 60%, and for S-polarized light from greater than 10% to less than 50%, and in some embodiments, the PDLC morphology exhibits a diffraction efficiency of approximately 30% for P-polarization and approximately 20% for S-polarization. This can be compared to a conventional PDLC morphology, in which the P-polarized diffraction efficiency is approximately 60%, and the S-polarized diffraction efficiency is approximately 1% (i.e., conventional P-polarized materials have very low or negligible S-components).

[0084] Mixture of nanoparticles

[0085] In many embodiments, the reactive monomer liquid crystal mixture may further comprise chemically active nanoparticles deployed within LC domains. In some such embodiments, the nanoparticles are carbon nanotubes (“CNTs”) or nanoclay nanoparticle materials within LC domains. Embodiments also relate to methods for controlling the size, shape, and uniformity of the nanoclay particles. Methods for mixing and dispersing the nanoclay particles can determine the electrical and optical properties of the resulting device. The use of nanoclay in HPDLCs is discussed in PCT application No.: PCT / GB2012 / 000680, entitled “IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALS ANDDEVICES”.

[0086] Nanoclay nanoparticles can be formed from any naturally occurring or manufactured ingredients, as long as they can be dispersed in a liquid crystal material. The specific nanoclay material to be chosen depends on the specific application of the film and / or device. The concentration and method of dispersion also depend on the specific application of the film and / or device. In many embodiments, the liquid crystal material is selected such that its ordinary refractive index matches that of the nanoclay material. Due to the dispersion of the nanoclay particles, the resulting composite can have forced alignment of liquid crystal molecules, and the optical quality of the film and / or device is not affected. The composite mixture comprising liquid crystal and nanoclay particles can be ultrasonically mixed to an isotropic state. The mixture can then be combined with optically crosslinkable monomers (such as photoinitiated acrylic or urethane resins) and sandwiched between substrates to form units (or alternatively applied to the substrate using a coating process).

[0087] In various embodiments, the nanoparticles are composed of nanoclay nanoparticles, preferably spherical or sheet-like, wherein the particle size is on the order of 2-10 nanometers in the shortest dimension and on the order of 10 nanometers in the longest dimension. Desiredly, the liquid crystal material is selected such that the ordinary refractive index of the liquid crystal matches that of the nanoclay material. Alternatively, the nanoparticles may be composed of a material with ferroelectric properties, thereby inducing a ferroelectric alignment effect on the liquid crystal molecules, thereby enhancing the electro-optic switching characteristics of the device. In another embodiment of the invention, the nanoparticles are composed of a material with ferromagnetic properties, thereby inducing a ferromagnetic alignment effect on the liquid crystal molecules, thereby enhancing the electro-optic switching characteristics of the device. In yet another embodiment of the invention, the nanoparticles have an induced electric or magnetic field, thereby inducing an alignment effect on the liquid crystal molecules, thereby enhancing the electro-optic switching characteristics of the device. Exemplary nanoparticles for use in other environments, including thermoplastics, polymer adhesives, etc., are disclosed in U.S. Patent Nos. 7,068,898; 7,046,439; 6,323,989; 5,847,787; and U.S. Patent Publications Nos. 2003 / 0175004; 2004 / 0156008; 2004 / 0225025; 2005 / 0218377; and 2006 / 0142455, the disclosures of which are incorporated herein by reference.

[0088] Nanoclays with naturally occurring surface properties can be used, or the surface can be chemically treated for specific bonding, electrical, magnetic, or optical properties. Preferably, the nanoclay particles are intercalated so that they are uniformly dispersed in the liquid crystal material. The general term "nanoclay" as used in this discussion can refer to naturally occurring montmorillonite nanoclay, intercalated montmorillonite nanoclay, surface-modified montmorillonite nanoclay, and surface-treated montmorillonite nanoclay. Nanoparticles may be commercially available, or they may require size reduction or morphological modification. 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 dry or in a liquid suspension. The liquid suspension can be a buffer, solvent, inert liquid, or liquid crystal material. An exemplary ball milling process provided by Spex LLC (Metuchen, NJ) is called the Spex8000 high-energy ball mill. Another exemplary process provided by Retsch (France) uses planetary ball milling to reduce micron-sized particles to nano-sized particles.

[0089] Nanoparticles can be dispersed in a liquid crystal material prior to polymer dispersion. Before polymer dispersion, dried or solvent-suspended nanoparticles can be ultrasonically mixed with the liquid crystal material or monomers to achieve isotropic dispersion. Depending on the specific material used, it may be necessary to prepare wet particles for dispersion in the liquid crystal. If the particles are in a solvent or liquid buffer, the solution can be dried, and the dried particles 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 having a vapor pressure lower than that of the liquid crystal material, the solution can be directly mixed with the liquid crystal, and one of the above methods can be used to evaporate the solvent, leaving the liquid crystal / nanoparticle dispersion. In one embodiment of the invention, the optical film comprises a liquid crystal material and nanoclay nanoparticles, wherein the nanoparticles are material particles having a size of less than one micrometer in at least one dimension. The film can be isotropically distributed.

[0090] Although nanoclay materials have been discussed, CNTs have been used as an alternative to nanoclays in many embodiments as a means of reducing voltage. EHKim et al. reviewed the properties of CNTs in relation to PDLC devices in Polym. Int. 2010; 59: 1289-1295, the contents of which are incorporated herein by reference in their entirety. PDLC films have been fabricated with varying amounts of multi-walled carbon nanotubes (“MWCNTs”) to optimize the electro-optic properties of the PDLC films. MWCNTs were well dispersed in the prepolymer mixture, up to 0.5 wt%, meaning that polyurethane acrylate (“PUA”) oligomer chains encapsulate MWCNTs along their length, resulting in high diffraction efficiency and good phase separation. Due to the reinforcing effect of MWCNTs with their inherently good mechanical properties, the hardness and elastic modulus of the polymer matrix increase with increasing MWCNT amounts. The increased elasticity of the PUA matrix and the immiscibility between the matrix and the liquid crystal gradually increase the diffraction efficiency of the PDLC film. However, due to the high viscosity of the reaction mixture, poor phase separation between the matrix and the LC causes a decrease in the diffraction efficiency of the PDLC film with more than 0.05 wt% MWCNT. Using 0.05 wt% MWCNT at 40 wt% LC can yield a PDLC film exhibiting a low driving voltage (75%).

[0091] In embodiments where PDLC materials incorporate such nanoparticles, improvements in the electro-optical properties and reductions in the switching voltage of polymer-dispersed liquid crystal films and / or polymer-dispersed liquid crystal devices can be achieved by including nanoparticles within the liquid crystal domains. The inclusion of nanoparticles serves to align liquid crystal molecules and alters the birefringence properties of the film through refractive index averaging. Furthermore, the inclusion of nanoparticles improves the switching response of the liquid crystal domains.

[0092] Monomer Functionality

[0093] RMLCM material systems according to various embodiments can be formulated in various 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 component mixing and its percentage composition, along with several factors such as, but not limited to, recording beam power / wavelength, grating periodicity, and grating thickness, can determine the diffraction efficiency of the resulting HPDLC grating. Inhomogeneous polymerization caused by the spatially periodic irradiation intensity of the exposure can be a driving force for separating monomers from the LC and aligning the orientation of LC molecules, which can affect the diffraction efficiency of the HPDLC grating. Often, the diffusion coefficient of monomers depends on their molecular weight and reactivity. Various monomer molecular weights or functional numbers have been shown to produce complex distributions of polymer and LC phases. In many cases, molecular functionality can be critical in achieving efficient phase separation and the formation of gratings with high diffraction efficiency. Accordingly, many embodiments of the invention include material systems formulated with specific mixtures of monomers, which are selected, at least in part, because of their functionality, to influence 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 characteristics of the recording beam and the thickness of the grating. For the purposes of describing this invention, the functionality of a monomer refers to the number of reaction sites on each monomer unit.

[0094] The effects of different monomer functionalities in HPDLC material systems have been studied to some extent in the scientific literature. Such studies generally examine the effect of the effective or average functionality of the mixtures related to grating formation and performance. For example, in the paper by Pogue et al., Polymer 41 (2000) 733-741, studies were conducted in floodlit PDLC and holographic PDLC gratings to show that a reduction in effective monomer functionality generally leads to reduced LC phase separation, the contents of which are incorporated herein by reference.

[0095] Many embodiments of the invention include studies of mixtures of specific blends of low-functionality monomers that can lead to the formation of gratings with high diffraction efficiency and efficient phase separation. While the scientific literature generally emphasizes the use of high-functionality monomers, various embodiments of the invention focus on the use of low-functionality monomers in certain applications. In some embodiments, the monomers in the mixture are monofunctional or bifunctional monomers. In many embodiments, trifunctional monomers are also included. Such mixtures typically include low concentrations of trifunctional monomers, such as less than 5 wt%.

[0096] Mixtures comprising low-functional monomers can behave differently depending on various factors such as, 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, studies of PDLC material systems typically include UV-sensitive systems, as material reactivity is generally poor for visible light systems. However, formulations according to various embodiments of the invention have enabled the use of low-functionality monomers sensitive to visible light (polymerization) to achieve high diffraction efficiencies (>80%) with low haze. In further embodiments, the material system comprises monomers sensitive to green light (such as light with wavelengths ranging from 495-570 nm). Besides different illumination systems, the performance of HPDLC mixtures can also depend on the thickness of the waveguide units in which the gratings are formed. For example, for a given material system, deposited films of different thicknesses can form waveguides with different haze measures. While the thickness of the gratings has been explored in patents and the scientific literature, such studies have focused on relatively thick gratings. In many embodiments, the material system is formulated for use in waveguides with thin form factors. In a further embodiment, the material system is configured for use in fabricating waveguides with HPDLC layers less than 10 μm thick and gratings with a diffraction efficiency greater than 80%. In a further embodiment, the material system is configured for use in waveguides with HPDLC layers 2-3 μm thick and gratings with a diffraction efficiency of 80-90%. The material system can also be configured for fabricating such waveguides with low haze. In several embodiments, the material system can form HPDLC layers with a haze of less than 1%. Waveguide haze is the integrated effect of light interacting with material and surface inhomogeneities at numerous beam bounces. The effect on ANSI contrast (the average ratio of white to black measured from a checkerboard pattern) can be significant due to scattering contributions to the black level. Haze is primarily caused by wide-angle scattering from 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 be at least partly caused by narrow-angle scattering resulting from large-scale inhomogeneities, leading to a loss of see-through quality and reduced image sharpness. Some waveguide applications, such as aircraft HUDs, using 1-D beam extension in thick waveguides produce as few as seven bounces, allowing for contrast ratios up to 80:1. However, in thin waveguides of this type used in near-eye displays, the number of bounces can increase tenfold, making the need for haze control even more urgent.

[0097] The RMLCM formulation can be optimized for the specific thickness of the HPDLC layer. In many embodiments, the RMLCM formulation is optimized for a uniform modulation grating of ~3 μm thickness designed to have a refractive index modulation of ~0.16. As can be readily appreciated, the specific thickness of the waveguide component to be fabricated can vary and can depend on the specific requirements of a given application. In many embodiments, the waveguide component can be fabricated to have 90% transmittance and 0.3% haze. In other embodiments, the waveguide component can be fabricated to have ~0.1% haze (having ~0.01% haze recorded in an unexposed sample of the same material). In some embodiments, the RMLCM can be formulated to fabricate a waveguide component containing less than 0.05% haze.

[0098] Transmitted haze can be defined as the percentage of light that deviates from the desired beam direction by an average of more than 2.5 degrees (according to ASTM D1003). Waveguide sharpness can be characterized by the amount of light scattered at narrow angles (at angles less than 2.5° to 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 perpendicular to the waveguide's TIR surface. To assess holographic haze, scattering can be measured around the principal diffraction direction (through the center of the eye-tracking range). Measurement procedures for haze, sharpness, and transmittance are defined in the ASTM D1003 international testing standard, where "Procedure A" uses a haze meter and "Procedure B" uses a spectrophotometer. An exemplary instrument for measuring haze is the BYK-Gardner HAZE Guard II equipment.

[0099] In many embodiments, the RMLCM mixture comprises a complex mixture of liquid crystal mixtures, acrylates, and acrylates. MEMO and photoinitiator. In a further embodiment, the RMLCM includes EHA and DFHA. Depending on the specific mixing of the components and their percentage composition, the resulting grating can have very different properties. In some embodiments, the weight percentage of LC is greater than 30%. In a further embodiment, the proportion of LC is greater than 35 wt%. In some embodiments, the mixture includes a liquid crystal with high birefringence. In a further embodiment, the high birefringence liquid crystal accounts for more than 20 wt% of the mixture. In many embodiments, the dye and photoinitiator account for less than 5 wt% of the mixture.

[0100] Nematic liquid crystal materials can provide a range of birefringence (which can be translated into refractive index modulation). Low to medium birefringence typically covers the range of 0.09–0.12. However, much lower birefringence values ​​can be used to design gratings, including gratings in which the birefringence varies along the grating. Such gratings can be used to extract light from a waveguide at low efficiency at one end and high efficiency at the other end to provide spatially uniform output illumination. High birefringence (nematic LC) is typically in the range of 0.2–0.5. Even higher values ​​are possible. The paper “High Birefringence Liquid Crystals” by R. Dabrowski et al. (Crystals; 2013; 3; 443–482) reviews mixtures, composites, and nematic liquid crystals with positive dielectric anisotropy (i.e., LCs with a greater dielectric constant on the long molecular axis than in other directions), the contents of which are incorporated herein by reference.

[0101] The functionality of monomers in a mixture can significantly affect the diffraction efficiency of the resulting grating. In many embodiments, the mixture comprises at least one monofunctional monomer and at least one polyfunctional monomer at varying concentrations. In several embodiments, the concentration of the monofunctional monomer in the mixture ranges from 1 to 50 wt%. The monofunctional monomer may include aliphatic / aromatic groups and a binder. In some embodiments, the proportion of polyfunctional monomers present in the mixture ranges from 2 to 30 wt%. The polyfunctional monomers according to various embodiments of the invention typically comprise low-functionality monomers. In many embodiments, the mixture comprises low concentrations of bifunctional monomers. In further embodiments, the mixture comprises less than 15 wt% of bifunctional monomers. Depending on the type and concentration of the bifunctional monomers in the mixture, sufficient phase separation and grating formation can occur. In illustrative embodiments, the monofunctional monomer, bifunctional monomer, and LC have relative weight ratios of 30%, 14%, and 40%, which results in the formulation of records that allow for diffraction efficiencies higher than 90% and refractive index modulation of approximately 0.12.

[0102] As can be readily recognized, the percentage of each component within an RMLCM can vary widely. Such material systems can be formulated to achieve certain properties in the resulting grating. In many cases, RMLCMs are formulated to have the highest possible diffraction efficiency.

[0103] Working cell clusters for manufacturing waveguide units

[0104] Waveguide unit manufacturing systems according to various embodiments of the present invention can be implemented as clusters of work units. Modular systems can be achieved by dividing different manufacturing steps into work units. In many embodiments, the work unit cluster includes: a preparation work unit for preparing a substrate for material deposition; a deposition work unit for depositing optical recording materials onto the substrate; and a lamination work unit for laminating various layers together to construct waveguide units. The work units can be configured in various ways to implement different manufacturing processes for the waveguide units. In some embodiments, the work units are linked and configured such that the output of one work unit is transferred to another work unit, thereby forming a manufacturing assembly line. Transfer mechanisms can be implemented in various ways, such as, but not limited to, the use of robotic arms, suction and / or conveyor systems. In several embodiments, the products are transferred manually. Figure 2A A conceptual illustration shows a work cell cluster system 200 according to an embodiment of the present invention. In an illustrative embodiment, system 200 includes a preparation work cell 202, a deposition work cell 204, and a lamination work cell 206. As shown, arrow 208 indicates the sequential workflow relationship within the work cells.

[0105] One advantage of modular systems is the ability to increase productivity by varying the number of work cells used for a specific task, thereby optimizing work cell usage and reducing work cell downtime. For example, waveguide cells made with different optical recording materials can result in different deposition times. In such embodiments, the number of deposition work cells can be varied accordingly to balance the task completion time of each work cell, such as minimizing the total downtime of the work cells. Figure 2B A conceptual illustration shows a cell cluster system 210 with two deposition cells 212, 214 according to an embodiment of the invention. In the illustrative embodiment, system 210 includes a preparation cell 216, two deposition cells 212, 214, and a lamination cell 218. Dotted arrow 220 indicates that the output from the preparation cell 216 can be received by either deposition cell 212, 214. Such a system is ideally implemented when the completion time of a single deposition process is approximately twice the completion time of the other processes.

[0106] Although Figure 2A and Figure 2B The conceptual illustration shows a specific configuration of a cell-of-work cluster system, but cell-of-work clusters according to various embodiments of the invention can be configured in many ways depending on the specific requirements of a given application. For example, a cell-of-work cluster can be configured to have different workflow paths, cell types, and / or cell numbers.

[0107] Due to the sensitive nature of some materials and processes associated with waveguide unit fabrication, the working unit can be configured to provide protection against ambient light and contaminants. In many embodiments, filters cover the working unit 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 working unit can be arranged with appropriate filters that prevent certain wavelengths of light from entering the working unit and exposing the optical recording material. In addition to reducing / preventing light pollution, the working unit can also be configured to reduce particulate contamination. In several embodiments, the working unit is configured to operate in an environment with minimal air pollution. Low-particulate environments can be achieved in many different ways, including, but not limited to, the use of air filters. In many embodiments, air filters employing laminar airflow principles are implemented. Contamination reduction / prevention systems such as those described above can be implemented individually or in combination. While specific systems have been described, working units according to various embodiments of the invention can be constructed in various ways to modify the working environment in a desired manner. For example, in several embodiments, the working unit is configured to operate in a vacuum. Specific working units and their implementations and constructions will be described in further detail in the following sections.

[0108] Preparation work unit

[0109] Waveguide units according to various embodiments of the present invention typically consist of an optical recording material layer sandwiched between two substrates. Manufacturing techniques for constructing such waveguide units according to various embodiments of the present invention may include a deposition step in which the optical recording material layer is deposited onto one of the substrates. In many embodiments, a preparation unit may be implemented to perform a cleaning / preparation process on the substrate to prepare it for use in the deposition step. Preparing a substrate, such as, but not limited to, a glass plate, may include removing surface contaminants and increasing surface adhesion properties for better material deposition.

[0110] The preparation unit can be configured to perform various cleaning and preparation processes. A robotic arm and / or suction device can be used to manipulate the substrate throughout the unit. In many embodiments, the preparation unit is configured to clean the glass substrate using various solvents and solutions, including but not limited to soap solutions, pickling solutions, acetone, and various types of alcohols. In some embodiments, several types of solvents and / or solutions are used in combination. For example, in several embodiments, methanol or isopropanol can be applied after acetone to wash away excess acetone. In many embodiments, deionized water is used to wash away excess solvent or solution. Solvents can be applied in several ways, including but not limited to the use of nozzles and baths. After cleaning, the unit can be configured to dry the substrate using an inert gas such as nitrogen and / or a heating element.

[0111] 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 adhering to the substrate. The duration of this treatment can vary depending on several factors, and the treatment can be performed on different types of substrates. Depending on the type of contaminant and the type of substrate, deionized water or a cleaning solution / solvent can be used.

[0112] In many embodiments, the preparation unit is configured to realize a plasma chamber for plasma treatment of the substrate surface. In some embodiments, the substrate is made of glass. Plasma, existing in the form of ions and electrons, is essentially an ionized gas that carries excess electrons in both negative and positive states. Plasma can be used to treat the substrate surface to remove contaminants and / or to prepare the surface for material deposition by increasing surface energy to improve adhesion properties. In many embodiments, the preparation unit includes a vacuum pump that can be used to generate a vacuum under which plasma treatment can be performed.

[0113] As will be readily appreciated, the preparation work unit according to various embodiments of the invention can be configured to perform combinations of various steps to achieve a specific cleaning process according to the requirements of a given application. Although specific preparation work units for preparing glass plates have been discussed above, preparation work units can be implemented to perform various preparation steps for various different substrates, including but not limited to plastics.

[0114] Deposition working unit

[0115] Waveguide unit fabrication systems can utilize various techniques for placing optical recording materials between two substrates. Fabrication systems according to various embodiments of the invention can utilize a deposition process in which an optical recording material film is deposited onto a substrate, and the composite is laminated together with a second substrate to form a three-layer laminate. In many embodiments, the fabrication system is a cluster of work units comprising deposition work units for depositing optical recording material films onto substrates. Such deposition work units can be configured to receive substrates from preparation work units. In some embodiments, a deposition work unit includes a stage for supporting the substrate and at least one deposition mechanism for depositing material onto the substrate. Any of a variety of deposition heads can be implemented as a deposition mechanism. In several embodiments, a spraying mechanism, such as, but not limited to, a nozzle, is implemented to deposit optical recording material onto the substrate. In some embodiments, a printing mechanism is used to deposit the optical recording material. Depending on the type of deposition mechanism / head implemented, several different deposition capabilities can be achieved. In many embodiments, the deposition head can allow the deposition of different materials and / or mixtures with varying component concentrations. As can be readily appreciated, the specific deposition mechanism utilized can depend on the specific requirements of a given application.

[0116] Components within a 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 certain axes 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 in three-dimensional Euclidean space), allowing for the deposition of multiple layers onto the substrate. In many embodiments, the deposition head is configured to move only on two axes to deposit a single layer. In other embodiments, the stage, and thus the substrate, is configured to move in three dimensions, while the deposition head is 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 one or more printheads and / or stages. The stage and deposition head can be configured such that a 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 several embodiments, the deposition head is configured to move back and forth to deposit material on one axis, while the stage moves on different axes, thereby allowing for the deposition of material in a two-dimensional Euclidean plane. In many embodiments, a conveyor belt is used to realize the worktable. The system can be designed such that the conveyor belt receives substrates from different work cells, such as preparation work cells. Once received, the conveyor system can move the substrate along with the deposition head as it deposits a layer of material onto the substrate. At the end of the conveyor path, the substrate can be delivered to another work cell.

[0117] In many embodiments, the deposition work unit includes an inkjet printhead configured to deposit optical recording material onto a substrate. Conventionally, inkjet printing refers to a printing method that deposits a matrix of ink dots to form a desired image. In typical operation, an inkjet printhead comprises 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 produce complex patterns and structures with high precision due to the size and number of nozzles in a typical inkjet printhead. Applying these principles to waveguide unit manufacturing applications, inkjet printing can be used to print uniform or near-uniform layers of optical recording material in terms of thickness and composition. Depending on the application and the inkjet printhead, one or more layers of optical recording material can be printed onto the substrate. Various optical recording materials, such as those described in the sections above, can be used in conjunction with inkjet printheads. In addition to the ability to print on different materials, the printing system can also be configured for use with various types of substrates. As can be readily appreciated, 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 based on printing stability and accuracy. Other considerations may include, but are not limited to, viscosity, surface tension, and concentration, which can affect several factors, such as, but not limited to, droplet formation and the ability to form layers of uniform thickness.

[0118] Figure 3A and Figure 3B The diagram illustrates a deposition work unit 300 according to an embodiment of the present invention. Figure 3A An isometric view of the deposition work unit 300 is shown, while Figure 3B A top view of the same deposition work unit 300 is shown. As shown, the deposition work unit 300 is constructed of a frame that can hold optical glass filters to prevent particulate contamination and exposure of the optical recording material within the work unit 300 to ambient light. The work unit includes a chamber for receiving a substrate and chambers 302, 304 for outputting waveguide units. In an illustrative embodiment, the stage is implemented as a conveyor belt 306 that moves the received substrate in one direction. The deposition work unit 300 also includes an inkjet printer 308 implemented as a deposition mechanism. The inkjet printer 308 is configured to print in a direction different from the movement of the conveyor belt 306, thereby allowing the deposition of an optical recording material layer on the planar surface of the substrate. Furthermore, the deposition work unit 300 implements a roller laminator 310 for laminating the printed layers and two substrates to construct the waveguide units. The work unit 300 is also implemented as a glove box with a glove 312, which allows for manual operation of the equipment within the work unit 300 while maintaining a clean environment.

[0119] Although Figure 3A and Figure 3BA specific deposition work unit configuration has been described, but according to various embodiments of the invention, the deposition work unit can be configured in many ways. For example, the laminator can be implemented in a separate lamination work unit. In several embodiments, automated system configuration can be implemented. In many embodiments, multiple inkjet printheads are used. In other embodiments, spray nozzles are used as the deposition mechanism.

[0120] Modulation of material composition

[0121] High brightness and excellent color fidelity are crucial factors in AR waveguide displays. High uniformity across the field of view (FOV) is essential in every case. However, the fundamental optics of waveguides can introduce inhomogeneities due to gaps or overlaps in the beams bouncing along the waveguide. Defects in the grating and the non-planarity of the waveguide substrate can create further inhomogeneities. In SBGs, further polarization rotation problems can arise due to birefringent gratings. The greatest challenge is with folded gratings, where multiple intersections of the beam with the grating fringes result in millions of optical paths. According to various embodiments of the invention, inhomogeneities can be overcome by carefully managing grating characteristics, particularly refractive index modulation.

[0122] Of the numerous possible beam interactions (diffraction or zero-order transmission), only a subset contributes to the signal presented at the eye-tracking range. By tracing back from the eye-tracking range, the folding regions that contribute to a given field point can be clearly identified. The precise correction of the modulation required to send more signal to the dark regions of the output illumination can then be calculated. After bringing the output illumination uniformity of one color to the target, the process can be repeated for other colors. Once the refractive index modulation pattern is established, the design can be output to the deposition apparatus, where each target refractive index modulation is translated into a unique deposition setting on the substrate to be coated for each spatial resolution cell. In many embodiments, the spatial pattern can be implemented with a fully repeatable resolution of 30 micrometers.

[0123] Figure 4A and Figure 4B The illustrations conceptually depict the use of reverse ray tracing to calculate a compensating refractive index modulation pattern for a coating, according to various embodiments of the invention. This process can determine the refractive index modulation variation on the folded grating required to improve uniform illumination within the eye-tracking range, as well as the optimized available area of ​​the folded grating. Figure 4AA mathematical model of a basic waveguide system is shown, comprising an input grating 402, a folded grating divided into a computational grid 404, and an output grating 406. By tracing the rays passing through the output grating and the folded grating from points within the eye-tracking range (FOV), the folded grating cells contributing to eye-tracking illumination in a given FOV direction can be identified. The reverse beam path from the output grating is indicated by rays 408-414. By repeating the ray trajectories for different FOV angles, the maximum extent of the folded grating required to fill the eye-tracking range can be determined. This ensures that the area of ​​HPDLC material to be deposited / printed is kept minimal, thereby reducing haze in the finished waveguide component. This procedure can also identify which cells need to have their refractive index modulation increased (or decreased) to maintain illumination uniformity across the eye-tracking range. For example, in Figure 4A In this embodiment, most of the folded grating region has a refractive index modulation of 0.03. However, certain computational units surrounded by 416 (e.g., such as unit 418) and certain computational units surrounded by 420 (e.g., such as unit 422) should have a refractive index modulation of 0.07, while the computational units located within the rectangular region 424 should have a refractive index modulation of 0.05. Typically, the mapping of the refractive index modulation values ​​is output as an AutoCAD DXF (Graphics Exchange Format) file to the processor controlling the deposition mechanism. Figure 4B This is a plan view 450 of the final waveguide component 452, on which a refractive index modulation pattern of a printed grating layer is superimposed (and...). Figure 4A (The model corresponds to this), as will be revealed by examining the printed grating under a cross-polarizer. The grating region includes an input grating 454, an output grating 456, and a folded grating 458. In an illustrative embodiment, the folded grating includes... Figure 4A The high refractive index modulation regions 460, 462, and 464 corresponding to the units identified in regions 416, 420, and 424. Figure 4B The grating region is surrounded by the polymer region 466. Although Figure 4A and Figure 4B The illustration shows a specific method for calculating a compensated refractive index modulation pattern, but such a pattern can be calculated using any technique available.

[0124] Compared to waveguides utilizing surface topography gratings (“SRGs”), SBG waveguides employing fabrication techniques according to various embodiments of the invention allow for dynamic adjustment of grating design parameters affecting efficiency and uniformity, such as refractive index modulation and grating thickness, during the deposition process. Consequently, a new master plate is not required for the grating recording process. For SRGs where modulation is controlled by etching depth, such a scheme would be impractical, as each change to the grating would necessitate repeating complex and costly tooling processes. Furthermore, achieving the desired etching depth accuracy and resist imaging complexity can be extremely difficult. Figure 5A and Figure 5B The basic structural differences between SBG and SRG are conceptually illustrated. Figure 5A A cross-sectional view 500 of a portion of the SRG is shown. In an illustrative embodiment, the grating includes a substrate 502 supporting inclined surface topography elements 504 separated by an air gap 506. Typically, the surface topography elements and the substrate are formed of a common material. The grating pitch is indicated by the symbol p, and the grating depth is indicated by the symbol h. Figure 5B A cross-sectional view 550 of the SBG is shown. Compared to the SRG, the SBG comprises alternating tilted Bragg fringes formed by low-refractive-index rich monomer fringes (such as 552) and higher-refractive-index rich LC fringes (such as 554). The refractive index difference is characterized by refractive index modulation δn, which plays an equivalent role in determining the grating diffraction efficiency as the grating depth in the SRG. Variations in refractive index modulation are represented by a curve 556, which is a superposition of refractive index modulation versus a distance z along the grating. In some embodiments, the refractive index modulation has, for example, Figure 5B The sinusoidal profile shown is illustrated. In embodiments where the SBG is formed with uniformly modulated HPLCD, the refractive index modulation profile may include near-rectangular LC-rich and polymer-rich regions.

[0125] The deposition process according to various embodiments of the present invention can provide for the adjustment of grating design parameters by controlling the type of material to be deposited. Similar to multi-material additive manufacturing, various embodiments of the present invention can be configured to deposit different materials or different material compositions in different regions of a substrate. In many embodiments, the optical recording material layer can be deposited with different materials in different regions. For example, the deposition process can be configured to deposit HPDLC material onto regions of the substrate intended to be grating regions, and to deposit monomers onto regions of the substrate intended to be non-grating regions. In several embodiments, the deposition process is configured to deposit optical recording material layers with spatially varying compositional properties, thereby allowing for the modulation of various aspects of the deposited material. Modulation schemes and deposition processes for different types of materials and mixtures are discussed in further detail below.

[0126] The choice of material to be printed in a specific area can depend on the optical elements that will later be recorded in that area. For example, in some embodiments, the deposition head is configured to deposit an optical recording material layer for waveguide units intended to be recorded with three different gratings. This layer can be deposited such that the material printed in each of the areas assigned to the three gratings is different from each other. Figure 6 A waveguide unit 600 with marked regions intended for recording various gratings is conceptually illustrated according to an embodiment of the invention. As shown, outlines of regions for the input grating 602, the folded grating 604, and the output grating 606 are depicted. Depending on the given application, such regions can be constructed from different materials or different mixtures. In many embodiments, different materials can be deposited to produce different diffraction efficiencies in the recorded gratings. In the illustrative embodiment, the waveguide unit is curved and is designed, along with the grating's position, size, and shape, for near-eye applications.

[0127] The deposition of materials with different compositions can be achieved in several different ways. In many embodiments, more than one deposition head can be used to deposit different materials and mixtures. Each deposition head can be coupled to a different material / mixture container. Such implementations can be used in a variety of applications. For example, different materials can be deposited for the grating region and non-grating region of a waveguide unit. In some embodiments, HPDLC material is deposited on the grating region, while only monomers are deposited on the non-grating region. In several embodiments, the deposition apparatus can be configured to deposit mixtures with different component compositions.

[0128] In some embodiments, the spray nozzle can be configured to deposit multiple types of materials onto a single substrate. In waveguide applications, the spray nozzle can be used to deposit different materials for grating regions and non-grating regions of the waveguide. Figure 7A and Figure 7B The operation of a deposition mechanism utilizing a spraying module according to an embodiment of the invention is conceptually illustrated. As shown, the apparatus 700 includes a coating module 702, which includes a first spraying module 704 connected via a conduit 706 to a first container 708 containing a first mixture of a first material, and a second spraying module 710 connected via a conduit 712 to a second container 714 containing a second mixture of a second material. In the illustrative embodiment, the first material includes at least liquid crystal and monomers, while the second material includes only monomers. Such a configuration allows for the deposition of optical recording material layers having defined grating regions and non-grating regions. As will be readily appreciated, any configuration of different mixtures may be utilized as appropriate, depending on the specific application.

[0129] exist Figure 7A and Figure 7BIn this device, a first spraying module and a second spraying module provide spraying of droplets at controllable divergence angles indicated by 716 and 718. The device also includes support for a transparent substrate 720 having predefined regions for supporting a grating, as illustrated in shaded areas 722-726, regions of the grating that do not transmit light into the eye-tracking range, as indicated by 728 and 730, and a region surrounding the grating, indicated by 732. In some embodiments, regions 728 and 730 are identified by waveguide-guided reverse ray tracing from the eye-tracking range. During operation, regions supporting the grating that provide diffracted light into the eye-tracking range are coated with a first mixture. Regions 728 and 730 are coated with a second mixture. The device also includes a positioning device 734 connected to the coating apparatus via a control link 736 for reciprocating movement of the coating apparatus across the substrate. The device also includes a switching mechanism for activating the first coating module and deactivating the second coating module when the coating device is positioned above a substrate area for supporting the grating, and for deactivating the first coating module and activating the second coating module when the coating device is positioned above a substrate area that does not support the grating.

[0130] exist Figure 8A and Figure 8B The diagrams conceptually illustrate two operating states of the device, and these diagrams show details of the substrate. (For example...) Figure 8A As shown, when the coating apparatus is above the non-grating support region 800 (located in the upper region of the strip defined by edges 802, 804), the second coating module is activated and the first coating module is deactivated, allowing a layer of monomer 806 to be coated onto the substrate. Figure 8B As shown, when the coating apparatus is above the essentially grating support region 808 (located in the lower region of the strip defined by edges 802, 804), the second coating module is deactivated and the first coating module is activated, such that a layer of liquid crystal and monomer mixture 810 is coated onto the substrate.

[0131] Although Figures 7A-8BThe illustrations depict specific applications and configurations of a spraying mechanism, but spraying and deposition mechanisms can generally be constructed and used for a variety of applications. In many embodiments, the spraying mechanism is configured for printing gratings in which a coating apparatus with at least two selectable spray heads can be used to control at least one of material composition, birefringence, and thickness. In some embodiments, the deposition working unit provides means for depositing grating recording material optimized for control of laser striping. In several embodiments, the deposition working unit provides means for depositing grating recording material optimized for control of polarization inhomogeneity. In some embodiments, the deposition working unit provides means for depositing grating recording material optimized for control of polarization inhomogeneity associated with an alignment control layer. In many embodiments, the deposition working unit can be configured to deposit additional layers such as beam splitting coatings and environmental protection layers. Furthermore, although Figures 7A-8B The capabilities of the spray nozzle have been discussed, but these capabilities can also be achieved in other deposition mechanisms. For example, inkjet printheads can also be implemented to print different materials in raster and non-raster regions of a substrate.

[0132] Figure 9 This 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. (Reference) Figure 9Method 900 includes providing (902) a transparent substrate for coating. A grating-supported region and a non-grating-supported region of the substrate can be defined (904). Depending on the specific application, gratings of various sizes and shapes can be defined. In some embodiments, the grating region supports an input grating, a folded grating, or an output grating. In many embodiments, the substrate has a region defined for a grating made from a combination of gratings of the aforementioned types. A first mixture for coating, comprising liquid crystal and monomers, and a second mixture for coating, comprising monomers, can be provided (906). A first spray head can be provided (908) for coating the first mixture onto the substrate. A second spray head can be provided (910) for coating the second mixture. The integrated first and second spray heads can be considered a coating apparatus. The coating apparatus can be set (912) to its initial position (k=1). The coating apparatus can be moved (914) to a current position above the substrate. A decision can be made regarding whether the current coating apparatus is located above the grating-supported region or the non-grating-supported region (916). If the coating device is above the grating region, the first spray head can be activated and the second spray head can be deactivated (918). If the coating module is above the grating support region, the first spray head can be deactivated and the second spray head can be activated (920). A decision regarding the coating state can be made (922). If all designated areas have been coated, the process can be terminated (924). If not all designated areas have been coated, the next area to be coated (increment k) can be selected (926), and the deposition step can be repeated.

[0133] Although Figure 9 The illustration shows a specific method for depositing different materials on a substrate, but the deposition apparatus can be configured to produce material films with properties that can vary spatially and across regions. Figure 10 A deposition head for providing predefined grating characteristics within a grating region is conceptually illustrated according to an embodiment of the invention. (Reference) Figure 10The deposition head 1000 includes a first spraying module 1002 fed via a conduit 1004 from a container 1006 containing at least one of a liquid crystal and a monomer. This mixture is dispersed through the spraying module 1002 into a spray stream 1008 for coating a transparent substrate. The substrate has predefined regions for supporting gratings. An XY displacement controller 1010 is also provided for reciprocating the spraying module on the substrate, and means for controlling the spraying characteristics from the module in each grating region to deposit a film providing predefined grating characteristics within the grating regions after holographic exposure. Holographic exposure can be performed using any current holographic process, including any process disclosed in the references. In an illustrative embodiment, the deposition head 1000 also includes a mixture controller 1012 for controlling one or more of the temperature, dilution, and relative concentration of the chemical components of the mixture. The deposition head 1000 may 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 on and off states. In several embodiments, predefined grating characteristics include one or more of refractive index modulation, refractive index, birefringence, liquid crystal director alignment, and grating layer thickness. As will be readily appreciated, the deposition head can be implemented and configured in many different ways. In many embodiments, any combination and subset of XY displacement controllers, mixture controllers, and spray controllers can be utilized. In some embodiments, an additional controller is used to configure the spray mechanism and the material to be deposited.

[0134] Figure 11 The diagram conceptually illustrates the operation of a deposition head for depositing material having regions with predefined grating characteristics, according to an embodiment of the invention. As discussed above, the deposition head can be configured to deposit material having spatial variations in one or more of the following on the grating region: refractive index modulation, refractive index, birefringence, liquid crystal director alignment, and grating layer thickness. Figure 11 As shown, the spraying module 1100 follows a spraying path 1102 across substrate 1104. For example, spraying can be dynamically controlled during transitions along path 1102 to alter predefined grating characteristics in regions such as 1106, 1108, or other predefined grating areas. In some embodiments, the deposition mechanism provides a grating with spatially varying diffraction efficiency after exposure. For example, referring again... Figure 11 The coated regions 1106 and 1108 (after holographic exposure) exhibit diffraction efficiency (DE) characteristics with respect to angle (U), as represented by curves 1110 and 1112, respectively.

[0135] Figure 12 A deposition mechanism for depositing two grating layers according to an embodiment of the present invention is conceptually illustrated. As shown, system 1200 is similar to... Figure 11 The system includes a second spraying module 1202 that provides a jet 1204 for coating the second grating layer 1206. In many embodiments, different mixture components are used to coat the grating layer. In some embodiments, similar to Figure 7A The system includes a first spraying module connected to a first container containing a first mixture, the first mixture including at least one of a first liquid crystal and a first monomer; and a second spraying module connected to a second container containing a second mixture, the second mixture including at least one of a second liquid crystal and a second monomer.

[0136] Figure 13 A conceptual illustration shows a system for depositing a grating material layer and for holographically exposing the layer using a recording beam having on and off states synchronized with a coating module. As shown, system 1300 includes a system similar to... Figure 12 A coating apparatus provides predefined grating regions 1306, 1308 following a spraying path 1302 across substrate 1304. During the coating process, a holographic exposure apparatus 1310, providing a recording beam 1312, can expose the coated predefined grating regions 1314. In many embodiments, the holographic exposure apparatus is based on a master grating that replicates the desired grating contacts within the predefined grating regions.

[0137] Figure 14This is a flowchart conceptually illustrating a method for depositing a material film having regions with predefined grating characteristics according to an embodiment of the present invention. As shown, method 1400 includes providing (1402) a transparent substrate for coating. Grating-supported regions and non-grating-supported regions of the substrate can be defined (1404). A mixture comprising liquid crystal and monomer can be provided (1406). In several embodiments, the material utilized includes one or more of photoinitiators, nanoparticles, low-functionality monomers, additives for reducing switching voltage, additives for reducing switching time, additives for increasing refractive index modulation, and additives for reducing haze. A spraying module for coating the mixture onto the substrate can be provided (1408). The spraying module can be set (1410) to its initial position (k=1). The spraying module can be moved (1412) to its current position above the substrate. A decision can be made regarding whether the current coating device is located above the grating-supported region or the non-grating-supported region (1414). If the coating apparatus is above the grating region, the spraying module can be activated (1416) to provide spraying characteristics for achieving predefined grating characteristics within the grating region. The grating region can be coated (1418). A decision regarding the coating state can be made (1420). If all designated areas have been coated, the process can be terminated (1422). If not all designated areas have been coated, the next area to be coated can be selected (1424), and the deposition step can be repeated with increments of k.

[0138] Although Figures 10 to 14 The illustrations depict specific embodiments and methods of depositing material in regions with predefined grating characteristics, but any configuration can be implemented across a variety of setups. For example, in many embodiments, multiple spraying modules or deposition heads are utilized. Depending on the specific application, various predefined grating characteristics can be controlled and / or modulated. The modulation of material composition using more than one deposition head is discussed in further detail below.

[0139] As discussed above, the deposition process can be configured to deposit optical recording materials with spatially varying compositional components. Modulation of the material composition can be achieved in many different ways. In many embodiments, an inkjet printhead can be configured to modulate the material composition by utilizing various inkjet nozzles within the printhead. By changing the composition on a "point-to-point" basis, an optical recording material layer can be deposited such that it has varying compositional components across planar surfaces. Such a system can be implemented using various devices, including but not limited to inkjet printheads. Similar to how color systems use toning of only a few colors to produce a spectrum of millions of discrete color values ​​(such as the CMYK system in printers or the overlay RGB system in display applications), inkjet printheads according to various embodiments of the invention can be configured to print optical recording materials with varying compositions using only containers of a few different materials. Different types of inkjet printheads can have different levels of precision and can print at different resolutions. In many embodiments, a 300 DPI ("dots per inch") inkjet printhead is utilized. Depending on the level of precision, the discretization of a given number of varying material components across a given region can be determined. For example, given two types of materials to be printed and an inkjet printhead with a precision level of 300 DPI, for a given volume of printed material, if the location of each dot can contain either of the two types of materials, then there are 90,001 possible discrete values ​​for the composition ratio of the two types of materials per square inch. In some embodiments, each dot location can contain either or both of the two types of materials. In several embodiments, more than one inkjet printhead is configured to print layers of optical recording material with spatially varying compositions. While the print dots for dual-material applications are essentially a binary system, in practical applications, averaging the print dots across regions allows for discretization of the sliding scale of the ratio of the two materials to be printed.

[0140] Figure 15A conceptual illustration of an inkjet printing modulation scheme according to an embodiment of the present invention is provided. As shown, eighteen discrete unit squares can each be printed with varying ratios of two different types of materials. In the illustrated embodiment, the inkjet printhead is capable of printing sixty-four dots within each of the eighteen unit squares. Each dot can be printed using either of the two types of materials. A close-up view 1500 of unit square 1502 shows all sixty-four dot positions within the unit square printed with the first material. Similarly, a close-up view 1504 of unit square 1506 is printed entirely with the second material. Unit square 1508 shows an intermediate composition, where thirty of the sixty-four dot positions are printed with the first material, while the remaining dot positions are printed with the second material. Thus, as a whole, unit square 1508 contains intermediate concentration levels from both materials. Using this modulation scheme, patterns with any variation in material properties can be achieved.

[0141] The number of discrete levels of possible concentration / ratio across a unit square is given by the number of point locations that can be printed within the unit square. In an illustrative embodiment, sixty-four discrete points can be printed within a unit square, which thus results in sixty-five different concentration combinations possible for each unit square, ranging from 100% of the first material to 100% of the second material. Although Figure 15 The regions are discussed in terms of unit squares, but these concepts apply to actual units and can be determined by the precision level of the inkjet printhead. Although specific examples of modulating the material composition of the printed layer are discussed, it is readily apparent that the concept of using an inkjet printhead to modulate the material composition can be extended to using more than two different material containers and can vary at the precision level, primarily depending on the type of printhead used.

[0142] For several reasons, altering the composition of the printed material can be advantageous. For example, in many embodiments, changing the material composition during deposition can allow a waveguide with a grating to have varying diffraction efficiencies across different regions of the grating. In embodiments utilizing HPDLC mixtures, this can be achieved by modulating the relative concentration of liquid crystals in the HPDLC mixture during the printing process, resulting in a composition that can produce a grating with varying diffraction efficiencies upon exposure. In several embodiments, a first HPDLC mixture with a certain concentration of liquid crystals and a second HPDLC mixture without liquid crystals are used as print toning in an inkjet printhead to modulate the diffraction efficiency of the grating that can be formed in the printing material. In such embodiments, discretization can be determined based on the precision of the inkjet printhead. For example, if a 150 DPI inkjet printhead is used, then 22,501 discrete levels of liquid crystal concentration can be printed per square inch. The discrete levels can be given by the concentration / ratio of material printed in a given area. In this example, the discrete levels range from no liquid crystals to the maximum concentration of liquid crystals in the first HPDLC mixture.

[0143] 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 allow the optical path to interact with the grating multiple times. In many embodiments, the waveguide unit can be printed with varying compositions so that the grating formed from layers of optical recording material has varying diffraction efficiencies to compensate for light loss during interaction with the grating, allowing for uniform output intensity. For example, in some waveguide applications, the output grating is configured to provide an exit pupil expansion in one direction while also coupling light out of the waveguide. The output grating can be designed such that when light within the waveguide interacts with the grating, only a certain percentage of the light is refracted out of the waveguide. The remainder continues in the same optical path, remaining within the TIR and continuing to be reflected within the waveguide. After 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, as is the amount of light refracted from the waveguide. Thus, at each interaction, the refracted portion gradually decreases in terms of total intensity. By changing the diffraction efficiency of the grating so that the refracted portion increases with the propagation distance, the reduction in output intensity along each interaction can be compensated, thus allowing for uniform output intensity.

[0144] Changing the diffraction efficiency can also be used to compensate for other attenuations of light within the waveguide. All objects have some degree of reflection and absorption. Light trapped in the TIR within the waveguide is continuously reflected between the two surfaces of the waveguide. Depending on the materials constituting the surfaces, a portion of the light can be absorbed by the material during each interaction. In many cases, this attenuation is small, but over large areas where many reflections occur, this attenuation can be considerable. In many embodiments, waveguide units can be printed with varying compositions, such that the grating formed from layers of optical recording material has varying diffraction efficiencies to compensate for light absorption from the substrate. Depending on the substrate, certain wavelengths may be more readily absorbed by the substrate. In multilayer waveguide designs, each layer can be designed to couple light within a certain wavelength range. Accordingly, light coupled by these individual layers can be absorbed by the substrate of these layers in different amounts. For example, in many embodiments, waveguides are made of three stacked layers to achieve color displays, where each layer is designed for one of red, green, and blue. In such an embodiment, the grating within each waveguide layer can be formed with varying diffraction efficiencies to perform color balance optimization by compensating for color imbalances caused by transmission losses due to certain wavelengths of light.

[0145] Besides altering the liquid crystal concentration within the material to change diffraction efficiency, another technique involves varying the thickness of the waveguide unit. This can be accomplished using beads. In many embodiments, beads are dispersed throughout the optical recording material during the fabrication of the waveguide unit for structural support. In some embodiments, beads of different sizes are dispersed throughout the optical recording material. The beads can be dispersed in ascending order of size in one direction of the optical recording material layer. When the waveguide unit is fabricated by lamination, the substrate sandwiches the optical recording material in the middle, creating a wedge-shaped optical recording material layer with structural support from the beads of varying sizes. Similar to the modulation process described above, beads of varying sizes can be dispersed. Furthermore, the modulation of bead size can be combined with the modulation of material composition. In several embodiments, containers of HPDLC material, each with beads of different sizes suspended, are used to print HPDLC material layers with strategically dispersed beads of varying sizes to form wedge-shaped waveguide units. In many embodiments, bead size modulation is combined with material composition modulation by providing a container quantity equal to the product of the number of beads of different sizes and the amount of different materials used. For example, in one embodiment, the inkjet printhead is configured to print liquid crystals of varying concentrations with two different bead sizes. In such an embodiment, four containers 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 the first size, and a liquid crystal-rich mixture-suspension with beads of the second size.

[0146] Lamination work unit

[0147] In many embodiments, the cluster of working cells includes lamination working cells for laminating waveguide units. After the optical recording material is deposited onto a substrate, a second substrate can be placed on the optical recording material to produce a three-layer composite. Often, the second substrate is made of the same material and has the same dimensions as the first substrate. In many embodiments, the deposition working cell is configured to place the second substrate on the optical recording material. In other embodiments, the lamination working cell is configured to place the second substrate on the optical recording material. The second substrate can be placed manually or by using a robotic arm and / or a suction mechanism. Once the second substrate is placed, the three-layer composite may be too unstable to be handled manually, and therefore, in many embodiments, the laminator is implemented as a compactor for the composite.

[0148] Three-layer composites can be laminated in various ways. In many embodiments, a press is implemented to apply downward pressure to the composite. In other embodiments, a lamination work unit is configured to feed the composite via a roller laminator. The compacted composite and adhesive properties of the optical recording material can result in waveguide units with sufficient stability to be manually processed. In some embodiments, the optical recording material layers comprise beads. Thus, these relatively incompressible beads can define the height of the optical recording material layers within the compacted composite. As discussed in the preceding sections, beads of different sizes can be placed throughout the optical recording material. After lamination, the size of the beads can each determine the local thickness of the waveguide unit. By varying the size of the beads, wedge-shaped waveguide units can be constructed. As will be readily appreciated, the lamination of substrate-optical recording material layer composites can be achieved using lamination work units that can be configured and implemented in many different ways. In several embodiments, the lamination work unit is a modular work unit within a cluster of work units. In other embodiments, the lamination work unit is simply a laminator implemented within a deposition work unit, such as... Figure 3A and Figure 3B As shown in the image.

[0149] While specific systems and methods for fabricating waveguide units have been discussed above, many different configurations can be implemented according to numerous different embodiments of the invention. Therefore, it is to be understood that the invention can be practiced in ways other than those specifically described without departing from the scope and spirit of the invention. Consequently, the embodiments of the invention should be considered illustrative rather than restrictive in all respects. Accordingly, the scope of the invention should not be determined by the illustrated embodiments, but rather by the appended claims and their equivalents.

Claims

1. A method for manufacturing a waveguide unit, the method comprising: Provide a first substrate; Determine the predefined grating characteristics; At least one deposition head is used to deposit an optical recording material layer onto the first substrate, wherein depositing the optical recording material layer includes: Provides a first mixture of optical recording materials; A second mixture of optical recording materials is provided; and The first mixture of optical recording materials and the second mixture of optical recording materials are deposited onto the first substrate in a predetermined pattern using the at least one deposition head; and Holographic exposure is performed on the optical recording material layer on the first substrate, wherein the optical recording material deposited on the grating region is configured to achieve the predefined grating characteristics after holographic exposure.

2. The method of claim 1, further comprising: Provide a second substrate; The second substrate is placed on the deposited optical recording material layer; as well as The first substrate, the optical recording material layer, and the second substrate are laminated.

3. The method of claim 1, wherein: The first mixture of optical recording materials includes a first bead; and The second mixture of optical recording materials includes a second bead of a different size than the first bead.

4. The method of claim 1, wherein the first mixture of optical recording materials has a different weight percentage of liquid crystal than the second mixture of optical recording materials.

5. The method of claim 1, further comprising defining a grating region and a non-grating region on the first substrate, wherein: The first mixture of optical recording materials includes liquid crystal and monomer; The second mixture of optical recording materials comprises monomers; as well as Depositing the first mixture of optical recording materials and the second mixture of optical recording materials onto the first substrate in a predetermined pattern includes: The first mixture of optical recording materials is deposited on the grating region; as well as The second mixture of optical recording materials is deposited on the non-grating region.

6. The method of claim 1, wherein the first mixture of optical recording materials is a polymer-dispersed liquid crystal mixture, the polymer-dispersed liquid crystal mixture comprising: monomer; liquid crystal; Photoinitiator dye; as well as Co-initiator.

7. The method of claim 6, wherein the polymer-dispersed liquid crystal mixture comprises an additive selected from the group consisting of: Photoinitiators, nanoparticles, low-functionality monomers, additives for reducing switching voltage, additives for reducing switching time, additives for increasing refractive index modulation, and additives for reducing haze.

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

9. The method of claim 8, wherein depositing the optical recording material layer comprises: Provides a first mixture of optical recording materials; A second mixture of optical recording materials is provided; The first point of the first mixture of optical recording materials is printed using the at least one inkjet printhead; as well as The second point of the second mixture of optical recording material adjacent to the first point is printed using the at least one inkjet printhead.

10. The method of claim 8, wherein: The at least one inkjet printhead includes a first inkjet printhead and a second inkjet printhead; as well as Depositing the optical recording material layer includes: Provides a first mixture of optical recording materials; A second mixture of optical recording materials is provided; The first mixture of optical recording material is printed onto the first substrate using the first inkjet printhead; and The second mixture of optical recording materials is printed onto the first substrate using the second inkjet printhead.

11. The method of claim 1, wherein the predefined grating characteristics include characteristics selected from the group consisting of: Refractive index modulation, refractive index, birefringence, liquid crystal pointing alignment, and grating layer thickness.

12. The method of claim 1, wherein the predefined grating characteristics include spatial variations of characteristics selected from the group consisting of: Refractive index modulation, refractive index, birefringence, liquid crystal pointing alignment, and grating layer thickness.

13. The method of claim 1, wherein the predefined grating characteristics result in an exposed grating having spatially varying diffraction efficiency.

14. A system for manufacturing gratings, the system comprising: A deposition head, which is connected to a container containing a mixture of optical recording materials; A first substrate having at least one predefined region for supporting a grating; A positioning element capable of positioning at least one deposition head across the first substrate; A holographic exposure apparatus is used to expose the first substrate, wherein: The deposition head is configured to deposit the mixture of optical recording materials onto the first substrate using the positioning element, wherein the deposition head is connected to a first container containing a first mixture of optical recording materials and a second container containing a second mixture of optical recording materials. The holographic exposure apparatus is configured to holographically expose at least one predefined region of the first substrate after the mixture of optical recording materials has been deposited onto the first substrate, and The deposited material provides predefined grating properties within the at least one predefined region after holographic exposure.

15. The system of claim 14, wherein the first mixture of optical recording materials comprises liquid crystal and monomers; and the second mixture of optical recording materials comprises monomers; wherein the at least one deposition head is configured to deposit the first mixture of optical recording materials onto the at least one predefined grating region.

16. The system of claim 14, wherein the deposition head comprises an inkjet printhead.

17. The system of claim 14, wherein the predefined grating characteristics include characteristics selected from the group consisting of: Refractive index modulation, refractive index, birefringence, liquid crystal pointing alignment, and grating layer thickness.

18. The system of claim 14, wherein the predefined grating characteristics result in a grating after holographic exposure, the grating having spatially varying diffraction efficiency.

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