Holographic waveguides including birefringence control and methods for their manufacture

Abstract

The invention relates to holographic waveguides including birefringence control and methods for their manufacture. Many embodiments according to the present invention are directed to waveguides that implement birefringence control. In some embodiments, the waveguide includes a birefringent grating layer and a birefringent control layer. In further embodiments, the birefringence control layer is compact and efficient. Such structures may be used in a variety of applications, including, but not limited to: compensating for polarization dependent losses in holographic waveguides; providing a three-dimensional LC director arrangement in the Bragg grating based waveguide; and spatially varying the angle / spectral bandwidth for homogenizing the output from the waveguide. In some embodiments, polarization maintaining, wide angle, and highly reflective waveguide cladding with polarization compensation is achieved for grating birefringence. In several embodiments, a thin polarization control layer is implemented for providing quarter-wave or half-wave delay.

Description

[0001] This application is a divisional application of an invention patent application with an international application date of March 18, 2019, a national application number of 201980029130.9, and an invention name of “Holographic waveguides comprising birefringence control and methods for their manufacture”. Technical Field

[0002] The present disclosure relates to optical waveguides, and more particularly, to waveguide displays using birefringent gratings. Background Art

[0003] Waveguides can be referred to as structures that have the ability to confine and guide waves (i.e., limit the region of space in which waves can propagate). A subclass includes optical waveguides, which are structures that can guide electromagnetic waves, typically in the visible spectrum. Waveguide structures can be designed to control the propagation path of waves using a variety of different mechanisms. For example, a planar waveguide can be designed to utilize a diffraction grating to diffract incident light and couple the incident light into the waveguide structure so that the in-coupled light can continue to travel within the planar structure via total internal reflection ("TIR").

[0004] Fabrication of waveguides may include the use of material systems that allow for recording of holographic optical elements 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 may be recorded in such liquid mixtures by irradiating the material with two mutually coherent laser beams. During the recording process, the monomers polymerize and the mixture undergoes photopolymerization-induced phase separation, resulting in regions densely populated with liquid crystal droplets interspersed with regions of transparent polymer. Alternating liquid crystal-rich and liquid crystal-poor regions form the fringe plane of the grating.

[0005] Waveguide optics such as those described above may be considered for a range of display and sensor applications. In many applications, waveguides containing one or more grating layers encoding multiple optical functions may be implemented using various waveguide architectures and material systems, enabling new innovations in near-eye displays for augmented reality ("AR") and virtual reality ("VR"), compact heads-up displays ("HUD") for aviation and land transportation, and sensors for biometrics and laser radar ("LIDAR") applications. Summary of the invention

[0006] Below, below is a more detailed description of various concepts and embodiments thereof for innovative optical displays and methods for displaying information. It should be understood that the various concepts introduced above and discussed in more detail below can be implemented in any of numerous ways, because the disclosed concepts are not limited to any particular implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes. A more complete understanding of the present invention can be obtained by considering the detailed description below in conjunction with the accompanying drawings, in which similar reference numerals indicate similar components. For the purpose of clarity, details related to technical materials known in the technical field related to the present invention are not described in detail.

[0007] One embodiment includes a waveguide comprising: at least one waveguide substrate, at least one birefringent grating; at least one birefringent control layer, a light source for outputting light, an input coupler for directing the light into a total internal reflection path within the waveguide, and an output coupler for extracting light from the waveguide, wherein interaction of the light with the birefringent control layer and the birefringent grating provides predefined characteristics of the light extracted from the waveguide.

[0008] In another embodiment, the interaction of the light with the birefringence control layer provides at least one of: an angular or spectral bandwidth change, a polarization rotation, a birefringence change, an angular or spectral dependence of at least one of beam transmission or polarization rotation, and a light transmission change in at least one direction in the plane of the waveguide substrate.

[0009] In a further embodiment, said predefined characteristic varies across said waveguide.

[0010] In yet another embodiment, the predefined characteristic is due to a cumulative effect of the interaction of the light with the birefringence control layer and the birefringence grating along at least one light propagation direction within the waveguide.

[0011] In yet a further embodiment, the predefined characteristic comprises at least one of: uniform illumination and uniform polarization over the range of angles of the light.

[0012] In yet another embodiment, the birefringence control layer provides compensation for polarization rotation introduced by the birefringence grating along at least one direction of light propagation within the waveguide.

[0013] In yet a further embodiment, the birefringence control layer is a liquid crystal and polymer material system.

[0014] In another additional embodiment, the birefringence control layer is a liquid crystal and polymer system aligned using directional ultraviolet radiation.

[0015] In further additional embodiments, the birefringence control layer is arranged by at least one of: electromagnetic radiation, electric or magnetic fields, mechanical forces, chemical reactions, and thermal exposure.

[0016] In yet another embodiment, the birefringence control layer affects the alignment of LC directors in a birefringent grating formed in a liquid crystal and polymer system.

[0017] In yet a further embodiment, the birefringence controlling layer has an anisotropic refractive index.

[0018] In yet another embodiment, the birefringence control layer is formed on at least one of an inner optical surface or an outer optical surface of the waveguide.

[0019] In a yet further embodiment, the birefringence control layer comprises at least one stack of refractive index layers disposed on at least one optical surface of the waveguide, wherein at least one layer in the stack of refractive index layers has an isotropic refractive index and at least one layer in the stack of refractive index layers has an anisotropic refractive index.

[0020] In yet another additional embodiment, the birefringence control layer provides a highly reflective layer.

[0021] In yet further additional embodiments, the birefringence control layer provides optical power.

[0022] In yet another embodiment, the birefringence control layer provides an environmental isolation layer for the waveguide.

[0023] In yet a further embodiment, the birefringence control layer has a gradient refractive index structure.

[0024] In yet another additional embodiment, the birefringence control layer is formed by stretching a layer of optical material to spatially vary its refractive index in the plane of the waveguide substrate.

[0025] In yet further additional embodiments, the light source provides collimated light in angular space.

[0026] In yet another embodiment, at least one of the input coupler and the output coupler comprises a birefringent grating.

[0027] In a still further embodiment, the birefringent grating is recorded in a material system comprising at least one polymer and at least one liquid crystal.

[0028] In yet another additional embodiment, the at least one birefringent grating includes at least one birefringent grating for providing at least one of: beam expansion in a first direction, beam expansion in a second direction and extracting light from the waveguide, and coupling light from a source into a total internal reflection path in the waveguide.

[0029] In still further additional embodiments, the light source comprises a laser and the arrangement of LC directors in the birefringent grating is spatially varied to compensate for illumination banding.

[0030] Yet another additional embodiment includes a method of manufacturing a waveguide, the method comprising providing a first transparent substrate, depositing a layer of grating recording material, exposing the layer of grating recording material to form a grating layer, forming a birefringence control layer, and applying a second transparent substrate.

[0031] In yet a further additional embodiment, the grating recording material layer is deposited onto the substrate, the birefringence control layer is formed on the grating layer, and the second transparent substrate is applied over the birefringence control layer.

[0032] In yet another additional embodiment, the grating recording material layer is deposited onto the substrate, the second transparent substrate is applied over the grating layer, and the birefringence control layer is formed on the second transparent substrate.

[0033] In yet a further additional embodiment, the birefringence control layer is formed on the first transparent substrate, the grating recording material layer is deposited onto the birefringence control layer, and the second transparent substrate is applied over the grating layer.

[0034] In yet a further embodiment, the method further comprises depositing a layer of liquid crystal polymer material and aligning the liquid crystal polymer material using directed UV light, wherein the layer of grating recording material is deposited onto the substrate and the second transparent substrate is applied over the aligned liquid crystal polymer layer.

[0035] In yet yet another additional embodiment, the liquid crystal polymer material layer is deposited onto one of the grating layer or the second transparent substrate.

[0036] In yet another additional embodiment, the layer of liquid crystal polymer material is deposited onto the first transparent substrate, the layer of grating recording material is deposited onto the aligned liquid crystal polymer material, and the second transparent substrate is applied over the grating layer.

[0037] Additional embodiments and features are partially set forth in the following description, and will become partially clear to those skilled in the art after reviewing the specification, or may be learned through practice of the invention. A further understanding of the nature and advantages of the invention may be achieved by reference to the remainder of the specification and drawings which form a part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying data and drawings, in which:

[0039] Figure 1 A schematic cross-sectional view of a waveguide including a birefringent grating and a birefringence control layer according to an embodiment of the present invention is conceptually illustrated.

[0040] Figure 2 A schematic cross-sectional view of a waveguide including a birefringence grating and a birefringence control layer for compensating for grating birefringence according to some embodiments of the present invention is conceptually illustrated.

[0041] Figure 3 A schematic cross-sectional view of a waveguide including a birefringence control layer and a birefringence grating for providing uniform output illumination from the waveguide in accordance with an embodiment of the present invention is conceptually illustrated.

[0042] Figure 4 A schematic cross-sectional view conceptually illustrates a birefringence control layer formed by combining a multilayer structure of an isotropic refractive index layer and an anisotropic refractive index layer according to an embodiment of the present invention.

[0043] Figure 5 A schematic cross-sectional view of a birefringence control layer formed by combining a multilayer structure of an isotropic refractive index layer and an anisotropic refractive index layer integrated with a birefringent grating layer according to an embodiment of the present invention is conceptually illustrated.

[0044] Figure 6 A plan view of a double extended waveguide with a birefringence control layer according to an embodiment of the present invention is conceptually illustrated.

[0045] Figure 7 A schematic cross-sectional view of a waveguide including a birefringence control layer and a birefringence grating for correcting birefringence introduced by an optical element in an output light path from the waveguide is conceptually illustrated in accordance with an embodiment of the present invention.

[0046] Figure 8 A schematic plan view conceptually illustrates an apparatus for aligning a birefringence control layer by applying a force to an edge of the layer according to an embodiment of the present invention.

[0047] Figure 9A-9F Process steps and apparatus for fabricating a waveguide including a birefringent grating and a birefringence control layer according to various embodiments of the present invention are conceptually illustrated.

[0048] Figures 10A-10F Process steps and apparatus for fabricating a waveguide including a birefringence control layer and a birefringence grating applied to the outer surface of the waveguide according to various embodiments of the present invention are conceptually illustrated.

[0049] Figures 11A-11F Process steps and apparatus for fabricating a waveguide including a birefringent grating and a birefringence control layer according to various embodiments of the present invention are conceptually illustrated.

[0050] Fig.12 A flow chart showing a method of fabricating a waveguide including a birefringent grating and a birefringence control layer is conceptually illustrated in accordance with an embodiment of the present invention.

[0051] Fig.13 A flow chart showing a method of fabricating a waveguide including a birefringence control layer and a birefringence grating applied to an outer surface of the waveguide is conceptually illustrated in accordance with an embodiment of the present invention.

[0052] Fig.14 A flow chart showing a method of fabricating a waveguide including a birefringent grating and a birefringence control layer is conceptually illustrated, wherein forming the birefringence control layer is performed before recording the grating layer, according to an embodiment of the present invention.

[0053] Fig.15 A schematic side view of a waveguide having a birefringence control layer applied at the waveguide to air interface in accordance with an embodiment of the present invention is conceptually illustrated.

[0054] Fig.16 A schematic side view of a waveguide having a birefringence control layer applied to the waveguide-to-air interface to isolate the waveguide from its environment is conceptually illustrated in accordance with an embodiment of the present invention.

[0055] Fig.17 A schematic side view of an apparatus for fabricating a structure including a birefringent grating layer overlying a birefringent control layer through which a grating recording beam propagates is conceptually illustrated in accordance with an embodiment of the present invention.

[0056] Fig.18 A schematic side view of an apparatus for fabricating a structure comprising a birefringence control layer overlying a birefringent grating layer, wherein the birefringence control layer is aligned by UV radiation propagating through the grating, in accordance with an embodiment of the present invention is conceptually illustrated.

[0057] Fig.19A cross section of a waveguide including a substrate sandwiching a grating layer is conceptually illustrated.

[0058] Fig. 20 A waveguide with a quarter wave polarization layer inserted is conceptually illustrated according to an embodiment of the present invention.

[0059] Fig.21 A schematic cross-sectional view showing a portion of a waveguide illustrating the use of a quarter wave polarization layer with an RKV grating in accordance with an embodiment of the present invention is conceptually illustrated.

[0060] Fig. 22 A polarizing layer architecture comprising an LCP quarter wave cell and a reactive monomer liquid crystal mixture (RMLCM) cell separated by an index matching oil layer is conceptually illustrated in accordance with an embodiment of the present invention.

[0061] Fig.23 An example of a polarization architecture based on a grating unit having a RMLCM grating material layer in direct contact with a bare LCP film according to an embodiment of the present invention is conceptually illustrated.

[0062] Fig.24 A cross-sectional view schematically illustrating an example of a polarization layer architecture in which a bare LCP layer is bonded to a bare RMLCM layer in accordance with an embodiment of the present invention is conceptually illustrated.

[0063] Fig.25 A cross-sectional view schematically illustrating an example of a polarization layer architecture using an RMLCM layer as a polarization layer according to an embodiment of the present invention is conceptually illustrated.

[0064] Fig.26 An example of a polarization layer architecture including features for compensating for polarization rotation introduced by a birefringent grating is conceptually illustrated in accordance with an embodiment of the present invention.

[0065] Fig. 27 The schematic diagram of an embodiment of the present invention is conceptually illustrated. Fig.26 A plan view of a waveguide display featuring an embodiment.

[0066] Fig.28 and Fig.29 A cross-sectional view schematically showing an example of a polarization layer architecture including an upper substrate, an LCP layer with a hard encapsulation layer, an RMLCM layer, and a lower substrate according to various embodiments of the present invention is conceptually illustrated.

[0067] Fig.30 A plan view schematically showing a first example of a two-region polymer film according to an embodiment of the present invention is conceptually illustrated.

[0068] Fig.31A plan view schematically showing a second example of a two-region polymer film according to an embodiment of the present invention is conceptually illustrated.

[0069] Fig.32 A plan view schematically showing a third example of a two-region polymer film according to an embodiment of the present invention is conceptually illustrated.

[0070] Fig.33 A diagram showing a transparent aperture layout according to an embodiment of the present invention is conceptually illustrated.

[0071] Fig.34 A plan view schematically illustrating a waveguide including an output grating, a turn grating, and an input grating including a K-vector for each grating and an alignment layer fast axis direction is conceptually illustrated according to an embodiment of the present invention. DETAILED DESCRIPTION

[0072] For the purpose of describing the embodiments, some well-known features of optical technology known to those skilled in the art of optical design and visual displays have been omitted or simplified so as not to obscure the basic principles of the invention. Unless otherwise stated, the term "on-axis" with respect to the direction of a ray or beam refers to propagation parallel to an axis perpendicular to the surface of the optical component described with respect to the present invention. In the following description, the terms light, ray, beam and direction can be used interchangeably and associated with each other to indicate the propagation direction of electromagnetic radiation along a straight track. The terms light and illumination can be used with respect to the visible band and infrared band of the electromagnetic spectrum. Parts of the following description will be presented using terms commonly used by those skilled in the art of optical design. In the following description, the term grating can be used to indicate any kind of diffraction structure used in a waveguide, including a hologram and a Bragg or volume hologram. The term grating can also encompass gratings comprising grating groups. For example, in some embodiments, the input grating and the output grating each include two or more gratings multiplexed in a single layer. For the purpose of illustration, it is to be understood that the drawings are not drawn to scale unless otherwise stated.

[0073] Referring generally to the accompanying drawings, systems and methods related to waveguide applications involving birefringence control according to various embodiments of the present invention are illustrated. Birefringence is an optical property of a material having a refractive index that depends on the polarization and propagation direction of light. A birefringent grating may be referred to as a grating having such a property. In many cases, a birefringent grating is formed in a liquid crystal polymer material system such as, but not limited to, a HPDLC blend. The polarization properties of such a grating may depend on the average relative permittivity and the relative permittivity modulation tensor.

[0074] Many embodiments according to the present invention are directed to waveguides that implement birefringence control. In some embodiments, the waveguide includes a birefringent grating layer and a birefringence control layer. In further embodiments, the birefringence control layer is compact and efficient. Such a structure can be used for various applications, including but not limited to: compensating for polarization-dependent losses in holographic waveguides; providing a three-dimensional LC director arrangement in a Bragg grating-based waveguide; and spatially varying the angle / spectral bandwidth for homogenizing the output from the waveguide. In some embodiments, a polarization-maintaining, wide-angle, and highly reflective waveguide cladding with polarization compensation is implemented for grating birefringence. In several embodiments, a thin polarization control layer is implemented for providing a quarter-wave or half-wave delay. In multiple embodiments, a polarization-maintaining, wide-angle birefringence control layer is implemented for modifying the polarization output of the waveguide to balance the birefringence of an external optical element used with the waveguide.

[0075] In many embodiments, the waveguide includes at least one input grating and at least one output grating. In further embodiments, the waveguide may include additional gratings for various purposes, such as but not limited to turn gratings for beam expansion. The input grating and the output grating may each include a multiplexing grating. In some embodiments, the input grating and the output grating may each include two overlapping grating layers that are in contact or vertically separated by one or more thin optical substrates. In some embodiments, the grating layers are sandwiched between glass or plastic substrates. In some embodiments, two or more such grating layers may form a stack within which total internal reflection occurs at the external substrate and air interface. In some embodiments, the waveguide may include only one grating layer. In some embodiments, electrodes may be applied to the face of the substrate to switch the grating between a diffractive state and a transparent state. The stack may also include additional layers such as beam splitting coatings and environmental protection layers. The input grating and the output grating shown in the figures may be provided by any of the above-described grating configurations. Advantageously, the input grating and the output grating may be designed to have a common surface grating pitch. In the case where the waveguide also includes (one or more) gratings in addition to the input grating and the output grating, the gratings can be designed to have a grating pitch such that the vector sum of the grating vectors is substantially zero. The input gratings can be combined with gratings oriented so that each grating diffracts the polarization of the incident unpolarized light into the waveguide path. The output grating can be configured in a similar manner so that the light from the waveguide path is combined and coupled out of the waveguide as unpolarized light. Each grating is characterized by at least one grating vector (or K vector) in 3D space, which in the case of a Bragg grating is defined as a vector perpendicular to the Bragg fringes. The grating vectors can determine the optical efficiency for a given range of input angles and diffraction angles. In some embodiments, the waveguide includes at least one surface topography grating. Waveguide grating structures, material systems, and birefringence control are discussed in further detail below.

[0076] Switchable Bragg grating

[0077] The optical structure recorded in the waveguide can include many different types of optical elements such as, but not limited to, diffraction gratings. In many embodiments, the grating implemented is a Bragg grating (also known as a volume grating). A Bragg grating can have high efficiency with little light being diffracted into higher orders. The relative amount of light in the diffracted order and the zeroth order can be changed by controlling the refractive index modulation of the grating, and this property of the refractive index modulation of the grating can be used to make a lossy waveguide grating for extracting light in a large pupil. One type of grating used in holographic waveguide devices is a switchable Bragg grating ("SBG"). SBGs can be made by first placing a thin film of a mixture of a photopolymerizable monomer and a liquid crystal material between glass plates or substrates. In many cases, the glass plates are in a parallel configuration. One or both of the glass plates can support electrodes (usually transparent tin oxide films) for applying an electric field to the film. The grating structure in the SBG can be recorded in a liquid material (usually called a syrup) by phase separation induced by photopolymerization using interferometric exposure with spatial periodic intensity modulation. Factors such as, but not limited to, controlling the radiation intensity, the component volume fractions of the materials in the mixture, and the exposure temperature can determine the resulting grating morphology and performance. As can be readily appreciated, a wide variety of materials and mixtures can be used, depending on the specific requirements of a given application. In many embodiments, HPDLC materials are used. During the recording process, the monomers polymerize and the mixture undergoes phase separation. The LC molecules aggregate to form discrete or coalesced droplets that are periodically distributed in the polymer network on the scale of the optical wavelength. 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 due to the orientational ordering of the LC molecules in the droplets.

[0078] The resulting volume phase grating can exhibit very high diffraction efficiency, which can be controlled by the magnitude of the electric field applied to the film. When an electric field is applied to the grating via the transparent electrodes, the natural orientation of the LC droplets can change, resulting in a reduction in the refractive index modulation of the fringes and a drop in the holographic diffraction efficiency to a very low level. Typically, the electrodes are configured so that the applied electric field will be perpendicular to the substrate. In several embodiments, the electrodes are made of indium tin oxide ("ITO"). In the OFF state, where no electric field is applied, the extraordinary axis of the liquid crystal is arranged substantially perpendicular to the fringes. Thus, the grating exhibits high refractive index modulation and high diffraction efficiency for P-polarized light. When an electric field is applied to the HPDLC, the grating switches to an ON state in which the extraordinary axis of the liquid crystal molecules is arranged parallel to the applied electric field and therefore perpendicular to the substrate. In the ON state, the grating exhibits lower refractive index modulation and lower diffraction efficiency for both S-polarized light and P-polarized light. Thus, the grating area no longer diffracts light. Depending on the function of the HPDLC device, each grating area can be divided into a plurality of grating elements, such as, for example, a pixel matrix. Typically, the electrodes on one substrate surface are uniform and continuous, while the electrodes on the opposite substrate surface are patterned according to a plurality of selectively switchable grating elements.

[0079] One of the known properties of transmissive SBGs is that the LC molecules tend to align with an average direction perpendicular to the plane of the grating fringes (i.e., parallel to the grating or K-vector). The effect of the LC molecular alignment is that the transmissive SBG diffracts P-polarized light (i.e., light with a polarization vector in the plane of incidence) efficiently, but has almost zero diffraction efficiency for S-polarized light (i.e., light with a polarization vector perpendicular to the plane of incidence). As a result, transmissive SBGs cannot generally be used at near grazing incidence when the angle between the incident and reflected light is small, because the diffraction efficiency of any grating for the P polarization drops to zero. Furthermore, in holographic displays that are sensitive to only one polarization, illumination light with mismatched polarizations is not efficiently captured.

[0080] HPDLC Material System

[0081] HPDLC mixtures according to various embodiments of the present invention typically include LC, monomers, photoinitiator dyes, and co-initiators. The mixture (commonly referred to as a slurry) often also includes a surfactant. For the purpose of describing the present invention, a surfactant is defined as any chemical agent that reduces the surface tension of the total liquid mixture. The use of surfactants in HPDLC mixtures is known and dates back to the earliest studies on HPDLC. For example, a paper by RL Sutherland et al., SPIE, Vol. 2689, 158-169, 1996, describes a PDLC mixture including monomers, photoinitiators, co-initiators, chain extenders, and LC to which a surfactant can be added, the disclosure of which is incorporated herein by reference. Surfactants are also mentioned in a paper by Natarajan et al., Journal of Nonlinear Optical Physics and Materials, Vol. 5, No. I89-98, 1996, the disclosure of which is incorporated herein by reference. In addition, U.S. Patent No. 7,018,563 to Sutherland et al. discusses a polymer dispersed liquid crystal material for forming a polymer dispersed liquid crystal optical element, the 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.

[0082] The patent and scientific literature contains many examples of material systems and processes that can be used to make SBGs, including research into formulating such material systems to achieve high diffraction efficiency, fast response time, low drive voltage, etc. U.S. Patent No. 5,942,157 to Sutherland and U.S. Patent No. 5,751,452 to Tanaka et al. both describe combinations of monomers and liquid crystal materials suitable for making SBG devices. Examples of formulations can also be found in papers dating back to the early 1990s, many of which use acrylate monomers, including:

[0083] RL Sutherland et al., Chem. Mater., 5, 1533 (1993), describes the use of acrylate polymers and surfactants, the disclosure of which is incorporated herein by reference. Specifically, the formulation includes a crosslinking multifunctional acrylate monomer; a chain extender N-vinyl pyrrolidone, LC E7, a photoinitiator Rose Bengal, and a co-initiator N-phenylglycine. In some variations, a surfactant, octanoic acid, is added.

[0084] • Fontecchio et al., SID 00 Digest 774-776, 2000, describe UV-curable HPDLCs comprising multifunctional acrylate monomers, LC, photoinitiators, co-initiators, and chain terminators for reflective display applications, the disclosure of which is incorporated herein by reference.

[0085] • YH Cho et al., Polymer International, 48, 1085-1090, 1999, disclose HPDLC formulations including acrylates, the disclosure of which is incorporated herein by reference.

[0086] • Karasawa et al., Japanese Journal of Applied Physics, Vol. 36, 6388-6392, 1997, describe acrylates of various functional orders, the disclosure of which is incorporated herein by reference.

[0087] • TJ Bunning et al., Polymer Science: Part B: Polymer Physics, Vol. 35, 2825-2833, 1997, also describe multifunctional acrylate monomers, the disclosure of which is incorporated herein by reference.

[0088] G Slannacchione et al., Europhysics Letters, Vol. 36(6), 425-430, 1996, describe PDLC mixtures comprising a pentaacrylate monomer, LC, a chain extender, a co-initiator, and a photoinitiator, the disclosure of which is incorporated herein by reference.

[0089] Acrylates offer the advantages of fast kinetics, good mixing with other materials, and compatibility with film-forming processes. Since acrylates are cross-linked, they tend to be mechanically robust and flexible. For example, urethane acrylates with functional 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.

[0090] Birefringence Overview

[0091] HPDLC-based holographic waveguides offer the benefits of switchability and high refractive index modulation, but suffer from inherent birefringence due to the alignment of the liquid crystal directors along the grating vectors during LC polymer phase separation. While this results in a large degree of polarization selectivity that can be advantageous in many applications, adverse effects such as polarization rotation can occur in gratings designed to turn and expand the waveguide beam in the waveguide plane (known as turn gratings). This polarization rotation can lead to efficiency losses and output light inhomogeneities.

[0092] Two common methods for modifying the alignment of the LC directors include the application of an alignment layer and rubbing. Typically, by such means, the LC directors in a plane parallel to the alignment layer can be rearranged within that plane. In HPDLC Bragg gratings, the problem is made more challenging by the natural alignment of the LC directors along the grating K-vector, making the alignment of all but the simplest gratings a complex three-dimensional problem, and rendering the traditional techniques of using rubbing or polyamide alignment layers impractical. Other methods may include applying electric fields, magnetic fields, and mechanical pressure during curing. These methods have shown limited success when applied to reflective gratings. However, such techniques are generally not easily converted to transmission Bragg grating waveguides.

[0093] The main design challenge in the waveguide is to couple the image content from the external projector into the waveguide efficiently and in such a way that the waveguide image is free of dispersion and brightness non-uniformity. In order to overcome the dispersion and achieve fairly good collimation, the use of lasers can be implemented. However, lasers can suffer from the problem of pupil banding artifacts, which manifest themselves as output illumination non-uniformity. Banding artifacts can be formed when the collimated pupil is replicated (expanded) in the TIR waveguide. Basically, each time the beam interacts with the grating, the beam diffracted from the waveguide can have gaps or overlaps, resulting in illumination ripples. In many cases, the waviness varies with changes in field angle, waveguide thickness, and aperture thickness. The banding effect can be smoothed by dispersion, which is usually exhibited by broadband sources such as LEDs. However, LED illumination is not completely free of banding issues, and in addition, this tends to result in bulky input optics and increase the thickness of the waveguide. De-banding is minimized using a pupil shifting technique for configuring the light coupled into the waveguide so that the input grating has an efficient input aperture that varies with the TIR angle. Techniques for performing pupil shifting are described in International Application No. PCT / US2018 / 015553, entitled “Waveguide Device with Uniform Output Illumination,” the disclosure of which is incorporated herein by reference in its entirety.

[0094] In some cases, the polarization rotation that occurs in the turn grating (described above) can compensate for illumination banding in a waveguide using laser illumination. The mechanism is that the large number of grating interactions in the turn grating combined with the small polarization rotation of each interaction can average out the banding (caused by imperfect matching of the TIR beam and other related optical effects such as, but not limited to, parasitic gratings left over from the recording process, interaction of stray light with the grating and waveguide surfaces, etc.). The process of birefringence compensation can be aided by fine-tuning the spatial variation of birefringence in the turn grating (alignment of the LC director).

[0095] A further problem caused in waveguide displays is that contact with moisture or surface combinations may inhibit waveguide total internal reflection (TIR), resulting in image gaps. In such cases, the scope of using a protective outer layer may be limited by the need for low refractive index materials that will provide TIR within the waveguide angular bandwidth. A further design challenge in waveguides is to maintain high efficiency within the angular bandwidth of the waveguide. An exemplary solution would be a polarization-maintaining, wide-angle and highly reflective waveguide cladding. In some applications, a quarter-wave retardation layer or a half-wave retardation layer applied to one or both of the main reflective surfaces of the waveguide can be used to achieve polarization balance within the waveguide. However, in some cases, the actual retardation film may add an unacceptable thickness to the waveguide. Thin-film coatings of the required formulation will generally require expensive and time-consuming vacuum coating steps. An exemplary method of achieving the coating includes, but is not limited to, using inkjet printing or an industry standard spin coating process. In many embodiments, the coating can be applied directly to the printed grating layer. Alternatively, the coating can be applied to the external optical surface of the assembled waveguide.

[0096] In some applications, waveguides are combined with conventional optics to correct aberrations. Such aberrations are introduced when waveguides are used in applications such as, but not limited to, automotive HUDs that project images onto the car windshield for reflection into the eyebox of the observer. The curvature of the windshield can introduce significant geometric aberrations. Since many waveguides operate with collimated beams, it can be difficult to pre-compensate for distortion within the waveguide itself. One solution involves mounting pre-compensating optics near the output surface of the waveguide. In many cases, the optics are molded in plastic and can introduce severe birefringence that should be balanced by the waveguide.

[0097] In view of the above, many embodiments of the present invention are directed to birefringence control layers designed to solve one or more of the problems set forth above. For example, in many embodiments, compact and efficient birefringence control layers are implemented for compensating polarization-dependent losses in holographic waveguides, for providing three-dimensional LC director arrangements in Bragg grating-based waveguides, for spatially varying the angle / spectral bandwidth to homogenize the output from the waveguide, and / or for isolating the waveguide from its environment while ensuring the confinement of the waveguide beam. In some embodiments, polarization-maintaining, wide-angle, and highly reflective waveguide claddings with polarization compensation are implemented for grating birefringence. In several embodiments, thin polarization control layers are implemented for providing quarter-wave or half-wave delays. The polarization control layer can be implemented as a thin layer directly on top of the grating layer using standard spin coating or inkjet printing processes, or the polarization control layer is implemented into one or both of the waveguide substrates. In multiple embodiments, polarization-maintaining, wide-angle birefringence control layers are implemented for changing the polarization output of the waveguide to balance the birefringence of external optical elements used with the waveguide. Other implementations and specific configurations will be discussed in further detail below.

[0098] Waveguide applications including birefringence control

[0099] Many different techniques can be used to implement waveguides and waveguide displays implementing birefringence control techniques according to various embodiments of the present invention. In some embodiments, the waveguide includes a birefringent grating layer and a birefringent control layer. In further embodiments, a compact and efficient birefringent control layer is implemented. The birefringent control layer can be implemented for various functions, such as, but not limited to: compensating for polarization-dependent losses in holographic waveguides; providing a three-dimensional LC director arrangement in a Bragg grating-based waveguide; and efficient and cost-effective integration within the waveguide for spatially varying the angular / spectral bandwidth for homogenizing the output from the waveguide. In any embodiment to be described, the birefringent control layer can be formed on any optical surface of the waveguide. For the purpose of understanding the present invention, the optical surface of the waveguide can be one of a TIR surface, a surface of a grating layer, a surface of a waveguide substrate sandwiching a grating layer, or a surface of any other optical substrate implemented in the waveguide (e.g., a beam splitter layer for improving uniformity).

[0100] Figure 1A waveguide implementing a birefringent control layer is conceptually illustrated in accordance with an embodiment of the present invention. In the illustrated embodiment, the waveguide device 100 includes an optical substrate 101 that includes a birefringent grating layer 102 and a birefringent control layer 103. As shown, light 104 propagating under TIR within the waveguide interacts with both layers. For example, a ray 104A having an initial polarization state represented by symbol 104B has its polarization rotated to state 104C after propagating through the grating region around point 102A. The birefringent control layer 103 rotates the polarization vector to state 104D, which is the polarization state for achieving a certain predefined diffraction efficiency for ray 104E when ray 104E interacts with the grating around point 102B and is diffracted into direction 104F with a polarization state 104G that is approximately similar to state 104D. As will be shown in the following description, many different configurations of birefringent control layers and birefringent gratings may be implemented in accordance with various embodiments of the present invention.

[0101] Figure 2 A waveguide device 200 is conceptually illustrated, comprising at least one optical substrate 201 and a coupler 202 for deflecting light 203A, 203B (covering a range of incident angles) from an external source 204 to TIR paths 205A, 205B in the waveguide substrate. The light in the TIR path can interact with an output grating, which can be configured to extract a portion of the light each time the TIR light satisfies the grating diffraction condition. In the case of a Bragg grating, extraction can occur when the Bragg condition is met. More precisely, efficient extraction can occur when the light incident on the grating is within the angular bandwidth and spectral bandwidth around the Bragg condition. These bandwidths are defined based on some measure of acceptable diffraction efficiency (such as, but not limited to, 50% of the peak DE). For example, light in the TIR light paths 205A, 205B is diffracted by the output grating to output directions 206A, 206B, 207A, and 207B at different points along the output grating. It should be clear from basic geometric optics that a unique TIR angle can be defined by each angle of incidence of light at the input grating.

[0102] Many different types of optical elements can be used as couplers. For example, in some embodiments, the coupler is a grating. In several embodiments, the coupler is a birefringent grating. In many embodiments, the coupler is a prism. The device also includes at least one birefringent grating 208 for providing beam expansion in a first direction and light extraction from the waveguide and at least one birefringent control layer 209 having anisotropic refractive index properties. In the embodiment to be discussed, the source 204 can be an input image generator including a light source, a microdisplay panel, and an optical device for collimating light. As can be easily understood, various input image generators can be used, including input image generators that output non-collimated light. In many embodiments, the input image generator projects an image displayed on the microdisplay panel so that each display pixel is converted into a unique angular direction within the substrate waveguide. The collimating optical device can include lenses and reflectors, which can be diffractive lenses and reflectors. In some embodiments, the source can be configured to provide illumination that is not modulated with image information. In several embodiments, the light source can be a laser or an LED, and can include one or more lenses for changing the angular characteristics of the illumination beam. In various embodiments, the image source may be a microdisplay or an image scanner.

[0103] For any direction of light, the interaction of the light with the birefringence control layer 209 and the birefringence grating 208 integrated along the total internal reflection path can provide predefined characteristics of the light extracted from the waveguide. In some embodiments, the predefined characteristics include at least one of uniform polarization or uniform illumination over a range of angles of the light. Figure 2 Also illustrated is how the birefringence control layer 209 and grating 208 provide uniform polarization. In many embodiments, the input state will correspond to P polarization, which can be used for the grating recorded in the HPDLC. For the purposes of explaining the present invention, an initial polarization state represented by 210 is assumed. The interaction of light near the grating interaction region along the TIR path 205A with the birefringence control layer is represented by polarization states 211, 212, which show the rotation of the polarization vector before and after propagation through the thickness AB of the birefringence control layer 209. This polarization rotation can be designed to balance the polarization rotation of the thickness CD of the adjacent grating region encountered by the light along the TIR path 205A. Thus, the polarization of the light extracted by the grating can be aligned parallel to the input polarization vector, as indicated by polarization state 213. In some embodiments, the output polarization state can be different from the input polarization state. In a case such as Figure 2 In various embodiments, such as the embodiment shown in , the birefringent grating has at least a partial overlap with the birefringent control layer. In several embodiments, the two are separated by a portion of the waveguide path.

[0104] Figure 3A waveguide device 300 is conceptually illustrated in which a birefringent control layer and a grating provide uniform output illumination according to an embodiment of the present invention. In the illustrated embodiment, the waveguide device 300 includes at least one optical substrate 301 and a coupler 302 for deflecting light 303 from an external source 304 to a TIR path 305 in the waveguide substrate. The device 300 also includes at least one birefringent grating 306 for providing beam expansion in a first direction and light extraction from the waveguide and at least one birefringent control layer 307 having anisotropic refractive index properties. As shown, light in the TIR ray path 305 can be diffracted by the output grating to output directions 308, 309. For the purpose of explaining the present invention, an initial beam illumination (I) versus angle (U) distribution represented by 310 is assumed. The interaction of light near the grating interaction region along the TIR path 305 with the birefringent control layer 307 is characterized by the illumination distribution (311) before propagating through the thickness AB of the birefringent control layer and the illumination distribution (312) after propagation. In some applications such as, but not limited to, display applications, the waveguide device 300 may be designed to have uniform illumination with respect to angle at the exit pupil of the waveguide. This may be achieved by matching the birefringence properties with respect to angle of the birefringence control layer to the angular bandwidth of the grating (along the grating path CD in the vicinity of the approach path AB) so that light extracted by the grating (indicated by 308, 309) integrated at the waveguide exit pupil provides uniform illumination with respect to angle distribution 313. In some embodiments, the properties of the grating and the birefringence control layer vary across the aperture of the waveguide.

[0105] Implementing a birefringence control layer

[0106] A variety of materials and manufacturing processes may be used to provide the birefringence control layer. In many embodiments, the birefringence control layer has an anisotropic refractive index property that can be controlled during manufacturing to provide a spatial distribution of birefringence such that for light from any direction, the interaction of the light with the birefringence control layer and the birefringence grating integrated along the total internal reflection path provides predefined characteristics of the light extracted from the waveguide. In some embodiments, the layer may be implemented as a thin stack comprising more than one layer.

[0107] Depending on the grating configuration, alignment of HPDLC gratings can present significant challenges. In the simplest case of a planar grating, polarization control can be constrained to a single plane orthogonal to the grating plane. Rolled K-vector gratings may require changes in alignment across the grating plane. Turn gratings, especially those with tilted Bragg fringes, can have much more complex birefringence, requiring 3D alignment and, in some cases, much higher spatially resolved alignment.

[0108] The following examples of birefringence control layers used with the present invention are illustrative only. In each case, it is assumed that the layer is treated so that the properties are changed across the surface of the layer. It is also assumed that the birefringence control layer is disposed within a waveguide containing a grating or on an optical surface of a waveguide. In some embodiments, the birefringence control layer is in contact with the grating layer. In several cases, the birefringence control layer is split into separate portions and disposed on different surfaces of the waveguide. In a number of embodiments, the birefringence layer may include a plurality of layers.

[0109] In some embodiments, the present invention provides a thin polarization control layer that can provide quarter wave or half wave retardation. The polarization control layer can be implemented as a thin layer directly on top of the grating layer or into the waveguide substrate using standard spin coating or inkjet printing processes, or both.

[0110] In one set of embodiments, a birefringence control layer is formed using a material that can utilize a liquid crystal and polymer network that can be 3D aligned using directional UV light. In some embodiments, the birefringence control layer is formed at least in part by a liquid crystal polymer (LCP) network. LCPs, also referred to in the literature as reactive polyarylates, are polymerizable liquid crystals containing liquid crystal monomers that include, for example, reactive acylated ends that polymerize with each other in the presence of a photoinitiator and directional UV light to form a rigid network. The mutual polymerization of the ends of the liquid crystal molecules can freeze their orientation into a three-dimensional pattern. The process typically includes coating a material system containing a liquid crystal polymer on a substrate, and prior to annealing, selectively aligning the LC director using a directional / spatially controllable UV source. In some embodiments, the birefringence control layer is formed at least in part by a photoalignment layer, which is also referred to in the literature as a linearly polymerized photopolymer (LPP). LPP can be configured to align the LC director parallel or perpendicular to the incident linearly polarized UV light. LPP can be formed as a very thin layer (typically, 50nm) to minimize the risk of scattering or other parasitic optical effects. In some embodiments, the birefringence control layer is formed of LCP, LPP and at least one dopant. The birefringence control layer based on LCP and LPP can be used to arrange the LC director in the complex three-dimensional geometric shape characteristics of the rolling K-vector grating and the turning grating formed in the thin film (2 to 4 microns). In some embodiments, the birefringence control layer based on LCP or LPP also includes a dichroic dye, a chiral dopant for realizing a narrow or broadband cholesteric filter, a twisted delay agent or a negative c-plate delay agent. In many embodiments, the birefringence control layer based on LCP or LPP provides a quarter or half wave delay layer.

[0111] In some embodiments, the birefringence control layer is formed of a multilayer structure combining an isotropic refractive index layer and an anisotropic refractive index layer (eg, Figure 4 ). Figure 4 In FIG. 4 , multilayer structure 400 includes isotropic layers 401, 402 and anisotropic refractive index layers 403, 404. In some embodiments, the multilayer stack may include a large number of layers such as, but not limited to, tens or hundreds of layers. Figure 5 A multilayer structure 500 is conceptually illustrated, comprising isotropic layers 501, 502 and anisotropic refractive index layers 503, 504 in combination with a birefringent grating layer 505. When the birefringence is on the same order of magnitude as the in-plane refractive index variation between adjacent material layers in the stack, improved control of the reflectivity of P-polarized light may be achieved. Generally, in isotropic materials, Brewster's law dictates that for any interface, there exists an angle of incidence (the Brewster's angle) at which the P-polarized reflectivity vanishes. However, at other angles, the reflectivity may increase dramatically. The limitations imposed by the Brewster's angle may be overcome by applying the basic principles discussed in "Giant Birefringent Optics in Multilayer Polymer Mirrors" by Weber et al., Science, Vol. 287, March 31, 2000, pp. 2451-2456. Because the optical properties of the system of isotropic / anisotropic refractive index layers are based on the fundamental physics of interface reflections and phase thicknesses rather than on a specific multilayer interference stack design, new design freedoms are possible. If the Brewster angle limitation is eliminated, the design of wide-angle broadband applications is simplified, especially for birefringence control layers immersed in a high refractive index medium such as a waveguide substrate. A further advantage with respect to waveguide displays is that color fidelity can be maintained for all angles of incidence and polarizations.

[0112] A birefringent grating will typically have polarization rotation properties that vary with angular wavelength. A birefringent control layer may be used to modify the angular, spectral, or polarization properties of a waveguide. In some embodiments, the interaction of light with the birefringent control layer may provide efficient angular bandwidth variation along the waveguide. In many embodiments, the interaction of light with the birefringent control layer may provide efficient spectral bandwidth variation along the waveguide. In several embodiments, the interaction of light with the birefringent control layer may provide polarization rotation along the waveguide. In several embodiments, the grating birefringence may be varied across the waveguide by spatially varying the composition of the liquid crystal polymer mixture during grating fabrication. In some embodiments, the birefringent control layer may provide a birefringence variation in at least one direction in the plane of the waveguide substrate. The birefringent control layer may also provide a means for optimizing optical transmission (for different polarizations) within the waveguide. In many embodiments, the birefringent control layer may provide a transmission variation in at least one direction in the plane of the waveguide substrate. In several embodiments, the birefringent control layer may provide an angular dependency of at least one of beam transmission or polarization rotation in at least one direction in the plane of the waveguide substrate. In various embodiments, the birefringence control layer may provide spectral dependence of at least one of beam transmission or polarization rotation in at least one direction in the plane of the waveguide substrate.

[0113] In many embodiments, birefringent gratings can provide input couplers, turn gratings, and output gratings in a wide range of waveguide architectures. Figure 6 A plan view of a double extended waveguide with a birefringence control layer according to an embodiment of the present invention is conceptually illustrated. In the illustrated embodiment, the waveguide 600 comprises an optical substrate 601 comprising an input grating 602, a turning grating 603 and an output grating 604 covered by polarization control layers 605, 606, 607, respectively.

[0114] In some embodiments, the present invention provides a polarization-maintaining, wide-angle birefringence control layer for modifying the polarization output of a waveguide to balance the birefringence of an external optical element used with the waveguide. Figure 7 An embodiment of the present invention is conceptually illustrated for an automotive HUD that reflects a collimated image off the windshield into the eye-tracking field. Any windshield curvature will generally result in aberrations and other geometric distortions that cannot be corrected in certain waveguide implementations where the beam is required to remain substantially collimated. One solution to this problem is to mount a corrective element near the output surface of the waveguide, which can be a conventional refractive element or a diffractive element. In such an implementation, the birefringent corrective component can avoid interfering with the light path originating from the waveguide and can be achromatic. The compensator technology used can provide a spatially varying configuration, low haze and high transmittance. In Figure 7In the illustrated embodiment of , the waveguide 700 includes: an optical substrate 701 including a grating coupler 702 for deflecting light 703 from an external source of image modulated light (not shown) into a TIR path 704 in the waveguide; a birefringent grating 705 for providing beam expansion in a first direction and extracting light from the waveguide; and a birefringence control layer 706. The device 700 also includes an optical element 707, which is disposed proximate to the waveguide for correcting geometric distortion and other aberrations introduced by reflections at the windshield. In some embodiments, the optical element 707 is a refractive lens. In other embodiments, the optical element 707 can be a diffractive lens. For a wide field of view HUD that provides a large eye movement range, the corrector will typically have a large package with a horizontal dimension (along the dashboard) of up to 400 mm. However, if the corrector is molded from plastic, it will tend to encounter birefringence. Therefore, in Figure 7 In the embodiment of FIG. 7 , the birefringence control element 706 can be designed to compensate for both the grating polarization and the polarization rotation introduced by the optical element 707. Referring again to FIG. Figure 7 , assuming an initial polarization state corresponding to P polarization. Symbols 708-711 represent the polarization state after propagation through the birefringent grating, birefringent control layer and correction element. The polarization state represents the interaction of the light with the birefringent control layer near the grating interaction region along the TIR path. Figure 7 In some embodiments, the polarization of the light 712, 713 extracted by the grating is aligned parallel to the input polarization vector. In some embodiments, the birefringence control layer 706 can be configured to rotate the output light polarization vector through ninety degrees.

[0115] In some embodiments, the birefringence control layer may be provided by various techniques using mechanical, thermal or electromagnetic treatment of the substrate. For example, in some embodiments, the birefringence control layer is formed by applying a mechanical stress that varies spatially across the surface of the optical substrate. Figure 8 Conceptually illustrated is an apparatus 800 for arranging a birefringence control layer 801 that applies forces in the directions indicated by 802-805, resulting in an anisotropic birefringence profile 806. In many embodiments, not all of the illustrated forces necessarily need to be applied to the layer. In some embodiments, the birefringence control layer 801 is formed by inducing a thermal gradient in an optical substrate. In a number of embodiments, the birefringence control layer 801 is provided by a HPDLC grating in which an electric or magnetic field is used to align the LC director during curing. In several embodiments, two or more of the above techniques may be combined.

[0116] Fabrication of waveguides implementing birefringence control layers

[0117] The present invention also provides methods and apparatus for manufacturing waveguides containing birefringent gratings and birefringent control layers. The construction and arrangement of the apparatus and methods as shown in various exemplary embodiments are illustrative only. Although only a few embodiments are described in detail in this disclosure, many modifications are possible (e.g., for improving processing efficiency and the quality of the finished waveguide, minimizing process differences, monitoring processes and other additional steps). Any process step involving the formation of a layer should be understood to cover multiple such layers. For example, where a process step for recording a grating layer is described, this step can be extended to recording a stack containing two or more grating layers. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. According to alternative embodiments, the order or sequence of any process or method steps can be changed or reordered. Without departing from the scope of the present disclosure, other substitutions, modifications, changes and omissions may be made to the design of the process equipment, operating conditions and arrangements of the exemplary embodiments. For the purpose of explaining the present invention, the description of the process will involve a birefringent control layer based on a liquid crystal polymer material system as described above. However, it should be clear from the description that these processes can be based on any implementation of the birefringent control layer described herein.

[0118] Figure 9A-9F Process steps and apparatus for fabricating a waveguide including a birefringent grating and a birefringence control layer according to various embodiments of the present invention are conceptually illustrated. Fig. 9A A first step 900 of providing a first transparent substrate 901 is shown. Fig. 9B An apparatus 910 for applying a holographic recording material to a substrate 901 is shown. In the illustrated embodiment, the apparatus 910 includes a coating apparatus 911 that provides a spray pattern 912 that forms a grating recording material layer 913 on the substrate 901. In some embodiments, the spray pattern may include a narrow jet or blade that sweeps or steps across the surface to be coated. In several embodiments, the spray pattern may include a diffuse stream for simultaneously covering a large area of ​​the surface. In a number of embodiments, the coating apparatus may be used in conjunction with one or more master plates to provide selective coating of an area on the surface. In many embodiments, the coating apparatus is based on a standard spin coating or inkjet printing process that is an industry standard.

[0119] Fig. 9CAn apparatus 920 for exposing a layer of grating recording material to form a grating layer is conceptually illustrated in accordance with an embodiment of the present invention. In the illustrated embodiment, the apparatus 920 includes a master grating 921 for contacting that replicates the grating in the recording material and a laser 922. As shown, the master grating 921 diffracts incident light 923 to provide zero order 924 and diffracted light 925, which interfere within the grating material layer to form a grating layer 926. The apparatus may have further features such as, but not limited to, a stop and master for overcoming stray light from higher diffraction orders or other sources. In some embodiments, several gratings may be recorded into a single layer using the principle of multiplexed holograms. Fig.9D An apparatus 930 for coating a layer of liquid crystal polymer material onto a grating layer is conceptually illustrated in accordance with an embodiment of the present invention. In the illustrated embodiment, the apparatus 930 includes a coating apparatus 931 configured to deliver a spray pattern 932 to form a material layer 933. The coating apparatus 931 may have similar features to a coating apparatus for applying grating recording materials. Fig.9E An apparatus 940 for providing an aligned liquid crystal polymer material layer according to an embodiment of the present invention is conceptually illustrated. In the illustrated embodiment, the apparatus 940 comprises a UV source (which may include collimation, beam steering and beam shaping optics depending on the specific requirements of a given application) 941 that provides directed UV light 942 for forming an aligned LC polymer layer 943. Fig.9F The completed waveguide 950 is conceptually illustrated after the step of applying a second substrate 951 over the aligned liquid crystal polymer layer 943 .

[0120] In some embodiments, the exposure of the grating recording material can use a conventional cross-beam recording process instead of the mastering process described above. In many embodiments, further processing of the grating layer may include annealing, heat treatment and / or other processes for stabilizing the optical properties of the grating layer. In some embodiments, an electrode coating can be applied to the substrate. In many embodiments, a protective transparent layer can be applied over the grating layer after exposure. In multiple embodiments, the liquid crystal polymer material is based on the LCP, LPP material system discussed above. In several embodiments, the arrangement of the liquid crystal polymer can cause the arrangement of the liquid crystal director to be parallel to the UV beam direction. In other embodiments, the arrangement is ninety degrees to the UV beam direction. In some embodiments, the second transparent substrate can be replaced by a protective layer applied using a coating device.

[0121] Figures 10A-10F Process steps and apparatus for fabricating a waveguide including a birefringence control layer and a birefringence grating applied to the outer surface of the waveguide according to various embodiments of the present invention are conceptually illustrated. Fig. 10AA first step 1000 of providing a first transparent substrate 1001 according to an embodiment of the present invention is conceptually illustrated. Fig. 10B An apparatus 1010 for applying a holographic recording material to a substrate according to an embodiment of the present invention is conceptually illustrated. In the illustrated embodiment, the apparatus 1010 includes a coating apparatus 1011 that provides a spray pattern 1012 that forms a grating recording material layer 1013 on a substrate 1001 . Fig. 10C Conceptually illustrates an apparatus 1020 for exposing a grating recording material layer to form a grating layer according to an embodiment of the present invention. In the illustrated embodiment, the apparatus 1020 includes a master grating 1021 for contacting that replicates the grating in the recording material and a laser 1022. As shown, the master 1021 converts light 1023 from the laser 1022 into a zero-order 1024 and diffracted light 1025, which interfere within the grating material layer 1013 to form a grating layer 1026. Fig. 10D A partially completed waveguide 1030 is conceptually illustrated after a step of applying a second substrate 1031 over the exposed grating layer in accordance with an embodiment of the present invention. Fig. 10E An apparatus 1040 for applying a layer of liquid crystal polymer material onto a second substrate is conceptually illustrated in accordance with an embodiment of the present invention. In the illustrated embodiment, the apparatus 1040 includes a spray applicator 1041 for delivering a spray pattern 1042 to form a layer 1043 of material. Fig.10F Conceptually illustrated is an apparatus 1050 for aligning a liquid crystal polymer material in accordance with an embodiment of the present invention. In the illustrated embodiment, the apparatus 1050 includes a UV source 1051 that provides directional UV light 1052 for forming an aligned liquid crystal polymer layer 1053, which can be configured to realign the LC director of the grating layer 1026.

[0122] Figures 11A-11F Conceptually illustrates process steps and apparatus for fabricating a waveguide including a birefringent grating and a birefringent control layer according to various embodiments of the present invention. Unlike the above embodiments, the step of forming the birefringent control layer may be performed before recording a grating layer formed above the birefringent control layer. Fig.11A A first step 1100 of providing a first transparent substrate 1101 is conceptually illustrated. Fig. 11B An apparatus 1110 for coating a layer of liquid crystal polymer material onto a first substrate is conceptually illustrated in accordance with an embodiment of the present invention. In the illustrated embodiment, the apparatus 1110 includes a coating apparatus 1111 configured to deliver a spray pattern 1112 to form a layer 1113 of material. Fig. 11CAn apparatus 1120 for aligning a liquid crystal polymer material in accordance with an embodiment of the present invention is conceptually illustrated. In the illustrated embodiment, the apparatus 1120 includes a UV source 1121 that provides directed UV light 1122 for forming an aligned liquid crystal polymer layer 1123. Fig.11D An apparatus 1130 for applying holographic recording material to a substrate according to an embodiment of the present invention is conceptually illustrated. In the illustrated embodiment, the apparatus 1130 includes a coating apparatus 1131 for providing a spray pattern 1132 to form a grating recording material layer 1133 on top of a liquid crystal polymer layer 1123. Fig.11E Conceptually illustrates an apparatus 1140 for exposing a grating recording material layer to form a grating layer according to an embodiment of the present invention. In the illustrated embodiment, the apparatus 1140 includes a master grating 1141 for contacting that replicates the grating in the recording material and a laser 1142. As shown, the master grating 1141 converts light 1142 from the laser into zero-order 1143 and diffracted light 1144, which interfere in the grating material layer 1133 to form a grating layer 1123 arranged by a liquid crystal polymer material layer 1123. Fig.11F The completed waveguide 1150 is conceptually illustrated after a step of applying a second substrate 1151 over the exposed grating layer in accordance with an embodiment of the present invention.

[0123] Fig.12 A flow chart illustrating a method of fabricating a waveguide including a birefringent grating and a birefringent control layer according to an embodiment of the present invention is conceptually illustrated. Fig.12 , method 1200 includes providing (1201) a first transparent substrate. A layer of grating recording material may be deposited (1202) onto the substrate. The layer of grating recording material may be exposed (1203) to form a grating layer. A layer of liquid crystal polymer material may be deposited (1204) onto the grating layer. The liquid crystal polymer material may be aligned (1205) using directed UV light. A second transparent substrate may be applied (1206) over the alignment layer.

[0124] Fig.13 A flow chart illustrating a method of manufacturing a waveguide including a birefringence control layer and a birefringence grating applied to an outer surface of the waveguide according to an embodiment of the present invention is conceptually illustrated. Fig.13 , method 1300 includes providing (1301) a first transparent substrate. A layer of grating recording material may be deposited (1302) onto the substrate. The layer of grating recording material may be exposed (1303) to form a grating layer. A second transparent substrate may be applied (1304) over the exposed grating layer. A layer of liquid crystal polymer material may be deposited (1305) onto the second transparent substrate. The liquid crystal polymer material may be aligned (1306) using directional UV light.

[0125] Fig.14 A flow chart illustrating a method of manufacturing a waveguide including a birefringent grating and a birefringent control layer, wherein forming the birefringent control layer is performed before recording the grating layer, according to an embodiment of the present invention is conceptually illustrated. Fig.14 , method 1400 includes providing (1401) a first transparent substrate. A layer of liquid crystal polymer material may be deposited (1402) onto the substrate. The liquid crystal polymer material may be aligned (1403) using directed UV light. A layer of grating recording material may be deposited (1404) onto the aligned liquid crystal polymer material. The layer of grating recording material may be exposed (1405) to form a grating layer. A second transparent substrate may be applied (1406) over the grating layer.

[0126] although Figure 12-14 A specific process for fabricating a waveguide containing a birefringent grating and a birefringent control layer is illustrated, but many other fabrication processes and equipment may be implemented to form such a waveguide in accordance with various embodiments of the present invention. For example, the order or sequence of any process or method steps may be changed or reordered in accordance with alternative embodiments. Other substitutions, modifications, changes, and omissions may be made to the design of the process equipment, operating conditions, and arrangements of the exemplary embodiments without departing from the scope of the present disclosure.

[0127] Additional Embodiments and Applications

[0128] In some embodiments, a polarization-maintaining, wide-angle, highly reflective waveguide cladding with polarization compensating for grating birefringence can be achieved. Fig.15 One such embodiment is shown. In the illustrated embodiment, waveguide 1500 includes a waveguide substrate 1501 including a birefringent grating 1502 and a birefringent control layer 1503 overlying the waveguide substrate 1501. As shown, interaction of guided light 1504 with the birefringent control layer 1503 at the interface of the birefringent control layer 1503 and the waveguide substrate 1501 causes its polarization to rotate from a state indicated by symbol 1505 (resulting from a previous interaction with the grating) to a state indicated by 1506 (having a desired orientation for the next interaction with the grating, e.g., having an orientation that provides a predefined diffraction efficiency at some predefined point along the grating).

[0129] In many embodiments, a compact and efficient birefringence control layer for isolating a waveguide from its environment while ensuring efficient confinement of the waveguide beam can be achieved. Fig.16One such embodiment is illustrated. In the illustrated embodiment, an environmentally isolated waveguide 1600 includes a waveguide substrate 1601 including a birefringent grating 1602 and a birefringent control layer 1603 overlying the waveguide substrate 1601. As shown, the interaction of the guided light 1604 with the birefringent control layer 1603 at the interface of the birefringent control layer 1603 and the waveguide substrate 1601 causes its polarization to rotate from a state indicated by symbol 1605 to a state indicated by 1606. Environmental isolation of the waveguide can be provided by designing the birefringent control layer 1603 so that total internal reflection occurs at an interface 1607 between the birefringent control layer 1603 and the waveguide substrate 1601. In some embodiments, environmental isolation is provided by designing the birefringent control layer to have a gradient refractive index property so that only a small portion of the guided light is reflected at the air interface of the birefringent control layer. In several embodiments, the birefringent control layer can include a separate GRIN layer. In various embodiments, the GRIN layer may be based on the embodiments disclosed in U.S. Provisional Patent Application No.: 62 / 123,282, entitled “NEAR EYE DISPLAY USING GRADIENT INDEX OPTICS” and U.S. Provisional Patent Application No.: 62 / 124,550, entitled “WAVEGUIDE DISPLAY USING GRADIENT INDEX OPTICS”.

[0130] Fig.17 A device 1700 is conceptually illustrated according to an embodiment of the present invention, which can be used in combination with some of the above methods to manufacture a structure including a birefringent grating layer 1701 overlying a birefringent control layer 1702. Fig.17 1702. In the embodiment shown, the substrate supporting the birefringence control layer is not shown. The construction beam indicated by rays 1703, 1704 can be provided by a master grating or a cross-beam holographic recording arrangement. As shown, the construction beam propagates through the birefringence control layer 1702. In many embodiments, the construction beam is in the visible band. In some embodiments, the construction beam is in the UV band.

[0131] Fig.18 A device 1800 is conceptually illustrated according to an embodiment of the present invention, which can be used in combination with some of the above methods to manufacture a structure including a birefringence control layer 1801 overlying a birefringence grating layer 1802. Fig.18, the substrate supporting the grating layer is not shown. The direction of the recording beam is indicated by 1803. In many embodiments, the birefringence control layer is a liquid crystal polymer material system that is aligned using a directed UV beam. In some embodiments where the grating is recorded in a polymer and liquid crystal material system, the exposed grating may be erased during the process of aligning the birefringence control layer by applying an external stimulus such as heat, electric or magnetic fields, or light to effectively produce an isotropic phase of the liquid crystal.

[0132] Fig.19 Conceptually illustrated is a cross section of a waveguide 1900 comprising substrates 1901, 1902 sandwiching a grating layer 1903. As shown, a source 1904 emits collimated light 1905A, which is coupled by the grating layer into a total internal reflection (TIR) ​​path indicated by light rays 1905B, 1905C, and extracted by the grating layer 1903 into an output light path 1905D. In the illustrated embodiment, the source 1904 can be a variety of light sources, including but not limited to a laser or an LED.

[0133] Fig. 20 Conceptually illustrates a method for performing a Fig.19 A waveguide similar to the waveguide of FIG. 1900 has a quarter wave polarization layer inserted by replacing substrate 1902 with a quarter wave film 2001 sandwiched by substrates 2002 and 2003. The quarter wave polarization layer can benefit the holographic waveguide design in two ways. First, it can reduce the repeated interaction (outcoupling) of the rolled K-vector (RKV) input grating to increase the overall coupling efficiency of the input grating. Second, it can continuously mix the polarization of the light entering the turning grating and the output grating to provide better extraction. The quarter wave layer can be located on the waveguide surface along the light from the input grating. Generally, the waveguide surface can include one of the TIR surfaces of the wave or some intermediate surface formed inside the waveguide. The optical properties of the quarter wave layer can be optimized for the "waveguide angle" (i.e., the angle in the glass that exceeds the TIR angle). In some embodiments, the center field is designed to be approximately 55 degrees in the glass (corresponding to a refractive index of approximately 1.51 at a wavelength of 532nm). In many embodiments, in order to optimize the performance of the red, green and blue emitting waveguides, optimization for red, green and blue may be used. As will be shown in the embodiments to be described, there are several different ways of including a quarter wave film within the waveguide. In the embodiments below, we generally refer to a quarter wave polarizing layer provided by a liquid crystal polymer (LCP) material. However, it should be understood that other materials are used in the application of the present invention.

[0134] Fig.21A schematic cross-sectional view 2100 showing a portion of a waveguide is conceptually illustrated in accordance with an embodiment of the present invention, illustrating how the use of a quarter wave polarization layer with an RKV grating can overcome the problem of unwanted extraction of light along a propagation path in an input grating portion of a waveguide. Input light including P polarized light 2101A is illustrated as being coupled by the grating layer into a TIR path in the waveguide indicated by rays 2101B-2101L. The waveguide grating has a rolled K vector, examples of which are schematically illustrated by vectors 2102A-2102C as they appear at three points along the length of the waveguide. In the illustrated embodiment, the light 2101A diffractively coupled into the TIR by the input grating is P polarized with respect to the grating. In many embodiments, the TIR angle can be nominally 55 degrees in glass. Upon transmission through the quarter wave layer, the polarization of the light changes from P to circular polarization (2101C). After TIR at the lower surface of the waveguide, the polarization changes to circularly polarized light in the opposite direction (2101D), so that after passing through the quarter wave layer on the upstream path of the quarter wave layer, it becomes S polarized (2101E) with respect to the grating. Since S polarized light is both off-Bragg and "offpolarization" (because the grating has zero or low diffraction efficiency for S), the S polarized light passes through the grating without deviation (2101F) or actual loss. The light then undergoes TIR for a second time (2101G), thereby maintaining its S polarization. Therefore, with respect to the P polarization-sensitive grating, the light 2101G is now on-Bragg, but still unpolarized. Therefore, the light passes through the grating without diffraction (2101H). At this position, the RKV (2102B) has a slight roll relative to the RKV (2102A) near the light entry point on the I / P grating. If the light is "polarized", the "rolling" effect of the RKV will be small, and so the light will be strongly outcoupled. The S-polarized light that passes through the grating undergoes another complete cycle (2101H-2101M) in a manner similar to the cycle indicated by rays 2101B-2101G, and then returns to the P-polarization state for the next (2101M) Bragg interaction at the grating region with the K-vector 2102C. At this point, the light has performed two complete cycles of TIR bounces down the waveguide, increasing the angular separation of the K-vector and the angle of incidence at the grating, which strongly reduces the Bragg interaction.

[0135] To further clarify Fig.21Example, consider light at a 55 degree TIR angle in a 1 mm thick waveguide, with a 20 mm projector relief (the distance of the projector from the input grating), and a nominal 4.3 mm diameter projector exit pupil: the first interaction with the grating occurs at approximately 2.85 mm along the waveguide. This is equivalent to an angle of 8.1 degrees at the 20 mm projector relief. For comparison, the FWHM angular bandwidth of a typical 1.6 um grating is about 12 degrees in air (depending on the prescription), i.e., the angle subtended by the pupil is not much larger than the half width of the lens. This results in strong outcoupling if the polarization is not changed to S-polarization as described above. In fact, using a quarter wave layer doubles the TIR length to approximately 5.7 mm. This offset is equivalent to about 15.9 degrees (larger than the angular bandwidth of most waveguide gratings), thereby reducing the outcoupling interaction losses from the waveguide.

[0136] Fig. 22 A polarization layer architecture 2200 comprising an LCP quarter wave unit and a reactive monomer liquid crystal mixture (RMLCM) unit separated by an index matching oil layer (2201) according to an embodiment of the present invention is conceptually illustrated. The LCP unit includes a substrate 2202 and an LCP film 2203. The RMLCM unit includes substrates 2204, 2205 sandwiched with an RMLCM layer 2206. This configuration has the following advantages: the index matching oil bonding can provide a non-permanent bond to allow the polarization unit to be installed and removed for testing purposes. Adhesive can also be applied to the (pinned) edges for semi-permanent bonding. In some embodiments, the oil layer can be provided using an oil-filled unit.

[0137] Fig.23 An example of a polarization architecture 2300 based on a grating unit with a layer of RMLCM grating material 2301 in direct contact with a bare LCP film 2302 according to an embodiment of the present invention is conceptually illustrated. The two films are sandwiched by substrates 2303, 2304. This is a simple and cost-effective solution for implementing the LCP layer. If the beads are embedded directly on the LCP layer, it may be difficult to maintain thickness control of the RMLCM layer using spacer beads. Fig.23 Embodiments may require careful matching of the material properties of the RMLCM and the LCP to avoid deleterious interactions between the RMLCM and LCP layers. In many embodiments, holographic exposure of the RMLCM layer may be applied directly in the RMLCM without passing through the LCP layer. In some embodiments, if exposure construction through the LCP layer is unavoidable, the polarization rotation of the LCP layer may be pre-compensated.

[0138] Fig.24A cross-sectional view schematically illustrating an example of a polarization layer architecture 2400 in which a bare LCP layer is bonded to a bare RMLCM layer according to an embodiment of the present invention is conceptually illustrated. The device includes an upper substrate 2401, a bare LCP film 2402, an adhesive layer 2403, an exposed RMLCM layer 2404, and a lower substrate 2405. In many embodiments, the adhesive layer can be Norland NOA65 adhesive or a similar adhesive.

[0139] Fig.25 A cross-sectional view of an example of a polarization layer architecture 2500 schematically showing a polarization layer using an RMLCM layer as a polarization layer according to an embodiment of the present invention is conceptually illustrated. The device includes an upper substrate 2501, an upper RMLCM layer 2502, a transparent separator 2503, a lower RMLCM layer 2504, and a lower substrate 2505. Utilizing the inherent birefringence properties of the RMLCM material, one of the RMLCM layers can be used not only as a grating material, but also as a polarization rotation layer. The "polarization rotation grating" should have a period and / or k-vector direction so that its diffraction is minimized. In some embodiments, the RMLCM layer can be configured as a sub-wavelength grating. In some embodiments, the RMLCM layer can be arranged to be sandwiched between two release layers so that after the layer is cured, it can be removed and reapplied elsewhere.

[0140] Fig.26 An example of a polarization layer architecture 2600 including features for compensating for polarization rotation introduced by a birefringent grating in accordance with an embodiment of the present invention is conceptually illustrated. The device includes an upper substrate 2601, a polarization control layer 2602, a transparent substrate 2603, a grating layer 2604, and a lower substrate 2605. The grating layer includes a first grating 2606A and a second grating 2606B separated by a transparent region 2607. In some embodiments, the transparent region can be a polymer having a refractive index similar to that of the substrate. In many embodiments, other low refractive index materials can be used to provide the transparent region. The polarization control layer includes quarter-wave retardation regions 2608A, 2608B and a polarization compensation region that balances the polarization rotation introduced by the birefringent grating 2606A (when directing light to propagate from grating 2606A to grating 2606B).

[0141] Fig. 27 A schematic diagram of an embodiment of the present invention is conceptually illustrated. Fig.26 A plan view of a waveguide display 2700 having features of an embodiment of the present invention. The waveguide display 2700 includes a waveguide substrate 2701, an input grating 2702, a turning grating 2703, and an output grating 2704. Fig.26 According to the principle of the embodiment of the present invention, the polarization control regions 2705 and 2706 apply compensation to the grating depolarization.

[0142] Fig.28 A cross-sectional view schematically illustrating an example of a polarizing layer architecture 2800 including an upper substrate 2801, an LCP layer 2802 with a hard encapsulation layer 2803, an RMLCM layer 2804, and a lower substrate 2805 in accordance with an embodiment of the present invention is conceptually illustrated. In many embodiments, the hard encapsulation layer or film can be designed to protect the fragile LCP film from mechanical contact so that standard cleaning processes will not damage the film. Advantageously, the hard encapsulation layer can be made of a material that is resistant to spacer beads pushed into it by the lamination process, and chemically resistant to refractive index matching oils and adhesives.

[0143] Fig.29 A cross-sectional view schematically illustrating an example of a polarizing layer architecture 2900 including an upper substrate 2901, an LCP layer 2902 with a soft encapsulant layer 2903, an RMLCM layer 2904, and a lower substrate 2905 in accordance with an embodiment of the present invention is conceptually illustrated. The polarizing alignment film can be encapsulated with a soft encapsulant layer or film designed to protect the fragile LCP film from mechanical contact so that standard cleaning processes such as mopping with, for example, isopropyl alcohol will not damage the film. In some embodiments, the soft encapsulant can provide some resistance to spacer beads during the lamination process.

[0144] Fig.30 A plan view of a first example 3000 schematically illustrating a two-region polymer film according to an embodiment of the present invention is conceptually illustrated. This example uses a non-encapsulated LCP film 3001 supported by a 0.5 mm thick Eagle XG substrate with dimensions of 77.2 mm×47.2 mm. For a wavelength of 524 nm, region 1 is characterized by a fast axis of 75° relative to the horizontal, and a quarter-wave retardation at a 55° glass internal angle, 45° ellipticity ±5°. For a wavelength of 524 nm, region 2 is characterized by a fast axis of 105° relative to the horizontal, and a quarter-wave retardation at a 55° glass internal angle, 45° ellipticity ±5°. Typically, regions 1 and 2 extend horizontally to ±2 mm from the midpoint.

[0145] Fig.31A plan view of a second example 3100 schematically illustrating a two-region polymer film according to an embodiment of the present invention is conceptually illustrated. This example uses an encapsulation of an LCP layer 3101 by a protective film 3102, which is supported by a 0.5 mm thick Eagle XG substrate with dimensions of 77.2 mm × 47.2 mm. For a wavelength of 524 nm, region 1 is characterized by 75° relative to the horizontal fast axis, and a quarter-wave retardation at a 55° glass internal angle, 45° ellipticity ±5°. For a wavelength of 524 nm, region 2 is characterized by 105° relative to the horizontal fast axis, and a quarter-wave retardation at a 55° glass internal angle, 45° ellipticity ±5°. Typically, regions 1 and 2 extend horizontally to a midpoint of ±2 mm. The encapsulation layer can seal the polarizing layer so that the performance is not affected when covered by an oil layer such as Cargille Series A with a refractive index of 1.516. The encapsulation layer may seal the polarizing layer so that when covered by an additional layer of liquid crystal based photopolymer, the performance is not affected.

[0146] Fig.32 A plan view of a third example 3200 schematically showing a two-region polymer film according to an embodiment of the present invention is conceptually illustrated. This example uses glass encapsulation of LCP. A 0.5 mm thick Eagle XG substrate with dimensions of 77.2 mm × 47.2 mm supports an LCP layer 3201, an adhesive layer 3202, and a 0.2 mm thick Willow glass cover 3203. For a wavelength of 524 nm, region 1 is characterized by 75° relative to the horizontal fast axis, and a quarter-wave delay at a 55° glass internal angle, 45° ellipticity ±5°. For a wavelength of 524 nm, region 2 is characterized by 105° relative to the horizontal fast axis, and a quarter-wave delay at a 55° glass internal angle, 45° ellipticity ±5°. Advantageously, the glass used for LCP encapsulation is 0.5 mm EagleXG or 0.2 mm Willow glass. Typically, regions 1 and 2 extend horizontally to ±2 mm at the midpoint.

[0147] Fig.33 Conceptually illustrates an embodiment of the present invention. Figure 30-Figure 32 FIG. 3 is a diagram of a transparent aperture layout 3300 of an embodiment illustrated in FIG. The transparent aperture is highlighted with a dotted line. All dimensions are in mm.

[0148] Fig.34 The schematic diagram of the embodiment of the present invention includes a K vector for each grating and an arrangement layer fast axis direction based on Figure 30-Figure 33 A plan view 3400 of a waveguide 3401 having an input grating 3402, a turning grating 3403, and an output grating 3404 of an embodiment of FIG. Fig.34As shown in , the K vector and the fast axis direction for the input grating K vector are: 30 degrees; for the turning grating K vector is: 270 degrees; and for the output grating K vector is: 150 degrees.

[0149] The above description covers only some of the possible embodiments in which the LCP layer (or equivalent delay layer) can be combined with the RMLCM layer in the waveguide structure. In many of the above embodiments, the substrate can be made of 0.5 mm thick Corning Eagle XG glass. In some embodiments, thinner or thicker substrates can be used. In several embodiments, the substrate can be made of plastic. In multiple embodiments, the substrate and the optical layer encapsulated by the substrate can be curved. Any embodiment can include additional layers for protection from chemical contamination or damage caused during processing and manipulation. In some embodiments, additional substrate layers can be provided to achieve the required waveguide thickness. In some embodiments, additional layers can be provided to perform at least one function of illumination homogenization spectrum filtering, angle selective filtering, stray light control and de-striping. In many embodiments, the bare LCP layer can be directly bonded to the exposed RMLCM layer. In several embodiments, an intermediate substrate can be arranged between the LCP layer and the RMLCM layer. In multiple embodiments, the LCP layer can be combined with an unexposed layer of RMLCM material. In many embodiments, the LCP layer with or without encapsulation can have a haze characteristic of <0.25% and preferably 0.1% or less. It should be noted that the haze characteristics quoted are based on bulk material scattering and are independent of surface scattering losses, which are largely lost after immersion. The LCP and encapsulation layers can withstand exposure to 100C (>80C for thermal UM exposure). In many embodiments, the LCP encapsulation layer can be drag resistant to allow layer cleaning. In the above embodiments, there can be constant delay and no bubbles or voids within the film transparent aperture. The LCP and adhesive layers can match the optical flatness standards met by the waveguide substrate.

[0150] A color waveguide according to the principles of the present invention will typically include a stack of monochromatic waveguides. The design may use a red waveguide layer, a green waveguide layer, and a blue waveguide layer, or alternatively, a red layer and a blue layer / green layer. In some embodiments, the gratings are all passive, that is, non-switching. In some embodiments, at least one of the gratings is switched. In some embodiments, the input grating in each layer is switchable to avoid color crosstalk between the waveguide layers. In some embodiments, color crosstalk can be avoided by arranging a dichroic filter between the input grating regions of the red and blue waveguides and the blue and green waveguides. In some embodiments, the thickness of the birefringence control layer is optimized for the wavelength of light propagating in the waveguide to provide uniform birefringence compensation over the spectral bandwidth of the waveguide display. The wavelength and spectral bandwidth bands of red, green, and blue wavelengths commonly used in waveguide displays are red: 626nm±9nm, green: 522nm±18nm; and blue: 452nm±11nm. In some embodiments, the thickness of the birefringence control layer is optimized for the three colors of light.

[0151] In many embodiments, the birefringence control layer is provided by a sub-wavelength grating recorded in the HPDLC. Such gratings are known to exhibit shape birefringence phenomena and can be configured to provide a range of polarization functions including quarter-wave and half-wave retardation. In some embodiments, the birefringence control layer is provided by a liquid crystal medium in which the LC director is aligned by irradiating an azo dye-doped alignment layer with polarized or unpolarized light. In many embodiments, the birefringence control layer is patterned to provide an LC director orientation pattern with a sub-micron resolution step. In some embodiments, the birefringence control layer is processed to provide a continuous change in the orientation of the LC director. In several embodiments, the birefringence control layer provided by combining one or more of the above techniques is combined with a rubbing process or a polyimide alignment layer. In some embodiments, the birefringence control layer provides optical power. In many embodiments, the birefringence control layer provides a gradient refractive index structure. In several embodiments, the birefringence control layer is provided by a stack comprising at least one HPDLC grating and at least one alignment layer. In many embodiments, the birefringence grating may have a rolling K vector. The K vector is a vector aligned perpendicular to the grating plane (or fringe) that determines the optical efficiency for a given range of input angles and diffraction angles. Rolling the K vector allows the angular bandwidth of the grating to be extended without increasing the waveguide thickness. In many embodiments, the birefringent grating is a turning grating for providing exit pupil expansion. The turning grating can be based on any of the embodiments disclosed in PCT Application No.: PCT / GB2016000181 entitled "WAVEGUIDE DISPLAY" and the embodiments discussed in the other references given above.

[0152] In some embodiments, the device is used in a waveguide design to overcome the problem of laser banding. A waveguide according to the principles of the present invention can provide a pupil shift device for configuring the light coupled into the waveguide so that the input grating has an efficient input aperture that varies with the change of the TIR angle. Several embodiments of the pupil shift device will be described. The effect of the pupil shift device is a continuous light extraction from the waveguide through the output grating set to provide a substantially flat illumination profile for any light incident angle at the input grating. The pupil shift device can be implemented using a birefringent control layer to change at least one of the amplitude, polarization, phase and wavefront shift in 3D space as the angle of the incident light changes. In each case, the effect is to provide an effective aperture that can give a uniform extraction on the output grating for any light incident angle at the input grating. In some embodiments, pupil shifting means are provided at least in part by designing the optics of the input image generator according to various embodiments to have a NA variation that smoothly varies from a high numerical aperture (NA) on one side of the microdisplay panel to a low NA range at the other side, such as similar to those disclosed in PCT Application No.: PCT / GB2016000181 entitled “WAVEGUIDE DISPLAY”, the disclosure of which is incorporated herein in its entirety. Typically, a microdisplay is a reflective device.

[0153] In some embodiments, the grating layer can be broken down into individual layers. Multiple layers can then be laminated together into a single waveguide substrate. In many embodiments, the grating layer comprises several pieces, including input couplers, turn gratings, and output gratings (or portions thereof), that are laminated together to form a single substrate waveguide. The pieces can be separated by optical glue or other transparent materials whose refractive index matches that of the pieces. In several embodiments, the grating layer can be formed via a cell manufacturing process by creating cells of the desired grating thickness and vacuum filling each cell with SBG material for each of the input couplers, turn gratings, and output gratings. In one embodiment, the cell is formed by placing multiple glass plates with gaps between the glass plates defining the desired grating thickness of the input couplers, turn gratings, and output gratings. In one embodiment, a cell can be made to have multiple apertures so that the separated apertures are filled with different SBG material packages. Any intermediate spaces can then be separated by a separation material (e.g., glue, oil, etc.) to define the separated regions. In one embodiment, the SBG material can be spin-coated onto the substrate and then covered by a second substrate after the material is cured. By using a turning grating, the waveguide display advantageously requires fewer layers than previous systems and methods for displaying information according to some embodiments. In addition, by using a turning grating, light can travel in a single rectangular prism defined by the outer surface of the waveguide by total internal reflection within the waveguide, while achieving a dual pupil expansion. In another embodiment, the input coupler, the grating can be produced by two waves of light interfering at a certain angle within the substrate to produce a holographic wavefront, thereby producing light and dark stripes arranged in the waveguide substrate at the desired angle. In some embodiments, the grating in a given layer is recorded in a step-by-step manner by scanning or stepping a recording laser beam across the grating area. In some embodiments, the grating is recorded using a master and contact printing process currently used in the holographic printing industry.

[0154] In many embodiments, the grating is a Bragg grating recorded in a holographic polymer dispersed liquid crystal (HPDLC) as already discussed, although SBGs may be recorded in other materials as well. In one embodiment, the SBG is recorded in a uniformly modulated material such as POLICRYPS or POLIPHEM having a solid liquid crystal matrix dispersed in a liquid polymer. The SBG can be switching or non-switching in nature. In its non-switching form, the SBG has advantages over conventional holographic photopolymer materials that can provide high refractive index modulation due to its liquid crystal composition. Exemplary uniformly modulated liquid crystal-polymer material systems are disclosed in U.S. Patent Application Publication No.: US2007 / 0019152 to Caputo et al. and PCT Application No.: PCT / EP2005 / 006950 to Stumpe et al., both of which are incorporated herein by reference in their entirety. Uniformly modulated gratings are characterized by high refractive index modulation (and therefore high diffraction efficiency) and low scattering. In some embodiments, at least one of the gratings is a surface topography grating. In some embodiments, at least one of the gratings is a thin (or Raman-Nath) hologram.

[0155] In some embodiments, the grating 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 diffractive when an electric field is present. Reverse mode HPDLC can be based on any of the formulations and processes disclosed in PCT Application No.: PCT / GB2012 / 000680 entitled "IMPROVEMENTS TO HOLOGRAPHIC POLYMERDISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES". The grating can be recorded in any of the above material systems, but is used in passive (non-switching) mode. The manufacturing process can be the same as that used for switching, but the electrode coating stage is omitted. LC polymer material systems can be used for their high refractive index modulation. In some embodiments, the grating is recorded in the HPDLC, but is not switched.

[0156] In many embodiments, a waveguide display in accordance with the principles of the present invention may be integrated into a window, for example, in a windshield integrated HUD for road vehicle applications. In some embodiments, the window integrated display may be based on the embodiments and teachings disclosed in U.S. Provisional Patent Application No.: 62 / 125,064, entitled "OPTICAL WAVEGUIDE DISPLAYS FOR INTEGRATION IN WINDOWS" and U.S. Patent Application No.: 15 / 543,016, entitled "ENVIRONMENTALLY ISOLATED WAVEGUIDE DISPLAY". In some embodiments, a waveguide display in accordance with the principles of the present invention may include a light pipe for providing beam expansion in one direction based on the embodiments disclosed in U.S. Patent Application No.: 15 / 558,409, entitled "WAVEGUIDE DEVICE INCORPORATING A LIGHT PIPE". In some embodiments, the input image generator may be based on a laser scanner as disclosed in U.S. Patent No. 9,075,184, entitled "COMPACT EDGE ILLUMINATED DIFFRACTIVE DISPLAY". Embodiments of the present invention can be used in a wide range of displays, including HMDs for AR and VR, helmet mounted displays, projection displays, head up displays (HUDs), head down displays (HDDs), autostereoscopic displays, and other 3D displays. Some of the embodiments and teachings of this disclosure can be applied to waveguide sensors such as (for example) eye trackers, fingerprint scanners, and LIDAR systems, as well as illuminators and backlights.

[0157] It should be emphasized that the drawings are exemplary and the dimensions have been exaggerated. For example, the thickness of the SBG layer has been greatly exaggerated. An optical device based on any of the above embodiments may be implemented using a glass substrate utilizing materials and processes disclosed in PCT Application No.: PCT / GB2012 / 000680 entitled "IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES". In some embodiments, the dual extended waveguide display may be curved.

[0158] Although the specification has provided specific embodiments of the present invention, additional information related to the technology can be found in the following patent applications, which are hereby incorporated by reference in their entirety: U.S. Patent No. 9,075,184 entitled “COMPACT EDGE ILLUMINATED DIFFRACTIVE DISPLAY”, U.S. Patent No. 8,233,204 entitled “OPTICALDISPLAYS”, PCT Application No.: US2006 / 043938 entitled “METHOD AND APPARATUS FOR PROVIDINGA TRANSPARENT DISPLAY”, PCT Application No.: GB2012 / 000677 entitled “WEARABLE DATA DISPLAY”, U.S. Patent Application No.: 13 / 317,468 entitled “COMPACT EDGE ILLUMINATED EYEGLASSDISPLAY”, and U.S. Patent Application No.: 13 / 317,468 entitled “HOLOGRAPHIC WIDE ANGLE DISPLAY”. and U.S. Patent Application No. 13 / 869,866 entitled “TRANSPARENT WAVEGUIDE DISPLAY” and U.S. Patent Application No. 13 / 844,456 entitled “WAVEGUIDE GRATING DEVICE”, U.S. Patent Application No. 14 / 620,969 entitled “ELECTRICALLY FOCUS TUNABLE LENS”, U.S. Patent Application No. 15 / 553,120 entitled “ELECTRICALLY FOCUS TUNABLE LENS”, U.S. Patent Application No. 15 / 558,409 entitled “WAVEGUIDE DEVICE INCORPORATING A LIGHT PIPE”, U.S. Patent Application No. 15 / 512,500 entitled “METHOD AND APPARATUS FOR GENERATING INPUT IMAGES FOR HOLOGRAPHIC WAVEGUIDE DISPLAYS”, and U.S. Patent Application No. 15 / 513,500 entitled “NEAR EYE DISPLAY USING GRADIENT INDEX OPTICS”, U.S. Provisional Patent Application No.: 62 / 123,282, entitled “WAVEGUIDEDISPLAY USING GRADIENT INDEX OPTICS”, U.S. Provisional Patent Application No.: 62 / 124,550, entitled “OPTICAL WAVEGUIDE DISPLAYS FOR INTEGRATION IN WINDOWS”, and U.S. Provisional Patent Application No.:: 62 / 125,064, U.S. Patent Application No. 15 / 543,016 entitled “ENVIRONMENTALLY ISOLATED WAVEGUIDE DISPLAY”, U.S. Provisional Patent Application No. 62 / 125,089 entitled “HOLOGRAPHIC WAVEGUIDE LIGHT FIELDDISPLAYS”, U.S. Patent No. 8,224,133 entitled “LASER ILLUMINATION DEVICE”, U.S. Patent No. US8,565,560 entitled “LASER ILLUMINATION DEVICE”, U.S. Patent No. 6,115,152 entitled “HOLOGRAPHIC ILLUMINATION SYSTEM”, PCT Application No. PCT / GB2013 / 000005 entitled “CONTACT IMAGE SENSOR USING SWITCHABLE BRAGG GRATINGS”, and U.S. Patent Application No. 15 / 125,016 entitled “HOLOGRAPHIC WAVEGUIDE LIGHT FIELDDISPLAYS”. PCT Application No.: PCT / GB2012 / 000680 entitled “POLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES”, PCT Application No.: PCT / GB2014 / 000197 entitled “HOLOGRAPHIC WAVEGUIDE EYE TRACKER”, PCT Application No.: PCT / GB2013 / 000210 entitled “APPARATUS FOR EYE TRACKING”, PCT Application No.: GB2013 / 000210 entitled “APPARATUS FOR EYE TRACKING”, PCT / GB2015 / 000274 entitled “HOLOGRAPHIC WAVEGUIDE OPTICALTRACKER”, PCT Application No.: PCT / GB2016 / 000276 entitled “SYSTEM AND METHOD OF EXTENDING VERTICAL FIELD OF VIEW IN HEAD UP DISPLAY USING AWAVEGUIDE COMBINER”, U.S. Patent No. 8,903,207, entitled “COMPACT WEARABLE DISPLAY”, U.S. Patent No. 8,639,072, entitled “COMPACT HOLOGRAPHIC EDGE ILLUMINATED EYEGLASSDISPLAY”, U.S. Patent No.8,885,112, U.S. Patent Application No. 16 / 086,578 entitled “METHOD AND APPARATUS FOR PROVIDING APOLARIZATION SELECTIVE HOLOGRAPHIC WAVEGUIDE DEVICE”, U.S. Provisional Patent Application No. 62 / 493,578 entitled “WAVEGUIDE DISPLAY APPARATUS”, PCT Application No. PCT / GB2016000181 entitled “WAVEGUIDE DISPLAY”, U.S. Patent Application No. 62 / 497,781 entitled “APPARATUS FOR HOMOGENIZING THE OUTPUT FROM A WAVEGUIDE DEVICE”, and U.S. Patent Application No. 62 / 499,423 entitled “WAVEGUIDE DEVICE WITH UNIFORM OUTPUT ILLUMINATION”.

[0159] Principle of Equivalence

[0160] The construction and arrangement of the system and method as shown in various exemplary embodiments are merely illustrative. Although only several embodiments are described in detail in the present disclosure, many modifications are possible (for example, the size, dimension, structure, shape and ratio of various elements, the value of parameter, installation arrangement, the use of material, color, the change of orientation, etc.). For example, the position of the element can be reversed or otherwise changed, and the property or quantity or position of the discrete element can be changed or changed. Accordingly, all such modifications are intended to be included in the scope of the present disclosure. According to alternative embodiments, the order or sequence of any process or method step can be changed or reordered. Without departing from the scope of the present disclosure, other replacements, modifications, changes and omissions can be made in the design, operating conditions and arrangement of the exemplary embodiments.

Claims

1. A waveguide, comprising: at least one waveguide substrate; at least one birefringent grating; at least one birefringence control layer; A light source, the light source is used to output light; an input coupler for guiding the light into a total internal reflection path G within the waveguide; as well as An output coupler for extracting light from the waveguide, wherein interaction of the light with the birefringence control layer and the birefringence grating provides predefined characteristics of the light extracted from the waveguide.

2. The waveguide according to claim 1, wherein interaction of the light with the birefringence control layer provides at least one of: angular or spectral bandwidth variation; polarization rotation; birefringence variation; angular or spectral dependence of at least one of beam transmission or polarization rotation; and a variation in light transmission in at least one direction in the plane of the waveguide substrate.

3. The waveguide according to claim 1, wherein The predefined characteristic varies across the waveguide.

4. The waveguide according to claim 1, wherein: The predefined characteristic is due to the cumulative effect of the interaction of the light with the birefringence control layer and the birefringence grating along at least one direction of light propagation within the waveguide.

5. The waveguide according to claim 1, wherein The predefined characteristic comprises at least one of: uniform illumination and uniform polarization over the range of angles of the light.

6. The waveguide according to claim 1, wherein The birefringence control layer provides compensation for polarization rotation introduced by the birefringence grating along at least one direction of light propagation within the waveguide.

7. The waveguide according to claim 1, wherein: The birefringence control layer is a liquid crystal and polymer material system.

8. The waveguide according to claim 1, wherein The birefringence control layer is a liquid crystal and polymer system aligned using directional ultraviolet radiation.

9. The waveguide according to claim 1, wherein: The birefringence control layer is arranged by at least one of: electromagnetic radiation; electric or magnetic fields; mechanical forces; chemical reactions; and thermal exposure.

10. The waveguide according to claim 1, wherein The birefringence control layer affects the alignment of the LC directors in a birefringent grating formed in a liquid crystal and polymer system.

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