Method for manufacturing an optical waveguide

Abstract

The present application relates to a method for manufacturing optical waveguides. A mastering system and methods for manufacturing waveguides and waveguide devices using such a mastering system are described. The mastering system for manufacturing holographic waveguides may include using a master to control the application of energy (e.g., laser, optical, or magnetic beams) to a liquid crystal substrate to manufacture the holographic waveguide within the liquid crystal substrate. The mastering system for manufacturing holographic waveguides according to embodiments of the present invention may include various features. These features include, but are not limited to: chirping for a single input beam replica (i.e., near hybrid contact replicas), double-chirped gratings (for input and output), a zero-order grating for transmission control, an alignment reference grating, a 3:1 configuration, a position adjustment tool to enable rapid alignment, simultaneous optimization of lens and window thicknesses for multiple RKVs, and avoidance of crossover of diffracted beams and other orders.

Description

[0001] This application is a divisional application of the invention patent application with an international filing date of January 8, 2019, national application number 201980007747.0, and invention name “Method for Manufacturing Optical Waveguide”. Technical Field

[0002] The present invention relates generally to methods for the manufacture of waveguides, and more particularly to waveguide displays. Background Art

[0003] A waveguide can be referred to as a structure that has the ability to confine and guide waves (i.e., limit the spatial region 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 many different mechanisms. For example, a planar waveguide can be designed to utilize a diffraction grating to diffract and couple 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] The fabrication of waveguides can include the use of material systems that allow for the 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, can be recorded in such liquid mixtures by illuminating the material with two mutually coherent laser beams. During the recording process, the monomers polymerize and the mixture undergoes photopolymerization-induced phase separation, resulting in regions densely populated with liquid crystal droplets interspersed with regions of clear polymer. The alternating liquid crystal-rich and liquid crystal-poor regions form the fringe plane of the grating.

[0005] Waveguide optics such as those described above can be considered for a range of display and sensor applications. In many applications, waveguides containing one or more grating layers encoding a variety of optical functions can 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 biometric and laser radar ("LIDAR") applications. Summary of the Invention

[0006] One embodiment includes a method for recording a hologram, the method comprising providing a waveguide cell comprising a layer of a polymer-dispersed liquid crystal mixture sandwiched between two substrates, providing a master grating, emitting at least one recording beam toward the master grating, wherein upon interaction with the master grating, a portion of the at least one recording beam is diffracted toward the waveguide cell, and recording at least one volume grating within the waveguide cell using an interferometric exposure formed by at least the diffracted portion of the at least one recording beam.

[0007] Further embodiments also include a system for recording a holographic grating, the system comprising a waveguide unit including a polymer-dispersed liquid crystal mixture layer sandwiched between two substrates, a master grating, and a light source configured to emit at least one recording beam toward the master grating, wherein after interacting with the master grating, a portion of the at least one recording beam is diffracted toward the waveguide unit and at least one volume grating is recorded within the waveguide unit by interference exposure formed by at least the diffracted portion of the at least one recording beam.

[0008] In another embodiment, the master grating comprises an amplitude grating.

[0009] In a further embodiment, the master grating comprises a chirped grating.

[0010] In yet another embodiment, the recorded volume grating includes a scrolled K-vector.

[0011] In a still further embodiment, the recorded volume grating comprises a multiplexed grating.

[0012] In yet another embodiment, the master grating comprises three separate gratings.

[0013] In a still further embodiment, three separate gratings are designed to record the input grating, the fold grating and the output grating.

[0014] In another additional embodiment, the at least one volume grating includes three volume gratings.

[0015] In a further additional embodiment, the at least one recording beam comprises three recording beams.

[0016] In yet another embodiment, the interferometric exposure is formed by the zeroth order beam and the diffracted portion of only one recording beam.

[0017] Additional embodiments and features are set forth to some extent in the following description and will become apparent to those skilled in the art upon review of the specification or may be learned through practice of the invention. A further understanding of the nature and advantages of the invention may be realized by reference to the drawings and the remaining portions of the specification, which form a part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] This description will be more fully understood with reference to the accompanying drawings and data diagrams below, which are presented as exemplary embodiments of the present invention and should not be construed as a complete elaboration of the scope of the present invention. It will be apparent to those skilled in the art that the present invention may be practiced with some or all of the invention disclosed in the following description.

[0019] Figure 1A and Figure 1B Two volume Bragg grating configurations are conceptually illustrated according to various embodiments of the present invention.

[0020] Figure 2 Surface relief grating according to an embodiment of the present invention is conceptually illustrated.

[0021] Figure 3A and Figure 3B HPDLC SBG devices and switching characteristics of the SBG according to various embodiments of the present invention are conceptually illustrated.

[0022] Figures 4A-4D A two-beam recording process according to various embodiments of the present invention is conceptually illustrated.

[0023] Figure 5 A single beam recording process using an amplitude grating according to an embodiment of the present invention is conceptually illustrated.

[0024] Figure 6A and Figure 6B Two implementations of a scrolled K-vector raster are conceptually illustrated according to various embodiments of the present invention.

[0025] Figure 7 A multiplexed K-vector grating according to an embodiment of the present invention is conceptually illustrated.

[0026] Figure 8 A waveguide utilizing coupling gratings to diffract light into and out of the waveguide is conceptually illustrated in accordance with an embodiment of the present invention.

[0027] Figure 9 and Figure 10 A waveguide using an output grating for exit pupil expansion in one dimension is conceptually illustrated in accordance with an embodiment of the present invention.

[0028] Figure 11 A waveguide system utilizing two planar waveguides to provide exit pupil expansion in two dimensions is conceptually illustrated in accordance with an embodiment of the present invention.

[0029] Figure 12 A waveguide utilizing a triple grating structure to provide two-dimensional exit pupil expansion is conceptually illustrated in accordance with an embodiment of the present invention.

[0030] Figure 13 A cross-sectional view of an RGB stack of waveguides is conceptually illustrated in accordance with an embodiment of the present invention.

[0031] Figure 14 A dual-axis extended waveguide display with two grating layers is conceptually illustrated in accordance with an embodiment of the present invention.

[0032] Figure 15 A plan view of a single grating layer according to an embodiment of the present invention is conceptually illustrated.

[0033] Figure 16 Conceptually illustrated is a plan view of a two grating layer configuration according to an embodiment of the present invention.

[0034] Figure 17 A dual-axis extended waveguide display according to an embodiment of the present invention is conceptually illustrated.

[0035] Figure 18 An eye tracking display according to an embodiment of the present invention is conceptually illustrated.

[0036] Figure 19 A dual extended waveguide display with a dynamic focusing element and an eye tracker is conceptually illustrated in accordance with an embodiment of the present invention.

[0037] Figure 20A and Figure 20B A waveguide display coupled to an input image node through an opto-mechanical interface is conceptually illustrated in accordance with an embodiment of the present invention.

[0038] Figure 21-24 Various input image node configurations according to various embodiments of the invention are conceptually illustrated.

[0039] Figure 25 A system diagram showing components for a waveguide display, in accordance with an embodiment of the present invention, is conceptually illustrated.

[0040] Figure 26 An exposure process using a chirped amplitude grating according to an embodiment of the present invention is conceptually illustrated.

[0041] Figure 27A and Figure 27BAn exposure process for simultaneously forming three gratings according to an embodiment of the present invention is conceptually illustrated.

[0042] Figure 28 A fabrication setup for simultaneously exposing red, blue, and green gratings according to an embodiment of the present invention is conceptually illustrated.

[0043] Figures 29A-29C Various methods for generating RKV gratings according to various embodiments of the present invention are conceptually illustrated.

[0044] Figure 30A and Figure 30B Various applications of chirped gratings according to various embodiments of the present invention are conceptually illustrated.

[0045] Figure 31 A mastering system utilizing a zero-order grating in conjunction with a chirped grating is conceptually illustrated in accordance with an embodiment of the present invention.

[0046] Figure 32 A mastering system utilizing a reference grating according to an embodiment of the present invention is conceptually illustrated.

[0047] Figure 33 A mastering system configured to avoid generating other order beams and / or to avoid interfering with an energy beam focused on a liquid crystal substrate is conceptually illustrated in accordance with an embodiment of the present invention.

[0048] Figure 34 Conceptual illustration of the effect of the position of the master grating on the resulting diffraction. DETAILED DESCRIPTION

[0049] 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 description below, the terms light, ray, beam and direction can be used interchangeably and associated with each other to indicate the direction of propagation of electromagnetic radiation along a straight line trajectory. With respect to the visible and infrared bands of the electromagnetic spectrum, the terms light and illumination can be used. The portions described below will be stated using terms commonly used by those skilled in the art of optical design. As used herein, in some embodiments, the term grating can encompass gratings comprising a collection of gratings. For illustrative purposes, it is to be understood that the drawings are not drawn to scale unless otherwise stated.

[0050] Turning now to the accompanying drawings, a mastering system and methods for using such a mastering system to manufacture waveguides and waveguide devices are described. A mastering system for manufacturing holographic waveguides may include using a master to control the application of energy (e.g., laser, optical, or magnetic beams) to a liquid crystal substrate to manufacture the holographic waveguide within the liquid crystal substrate. After manufacture, the completed holographic waveguide can be incorporated into various display systems. These mastering systems may employ one or more energy beams. In many embodiments, the mastering system uses a single energy beam, which can simplify the alignment of various components within the mastering system and can reduce wavefront errors caused by the different paths of the two beams found in two-beam systems. As such, a single energy beam process can be compatible with high-volume manufacturing processes where thermal and vibration considerations may introduce various complexities in aligning multiple energy beams. A mastering system for manufacturing holographic waveguides according to embodiments of the present invention may include various features. These features include, but are not limited to: chirping for a single input beam replica (i.e., near hybrid contact replica), double-chirped gratings (for input and output), a zero-order grating for transmission control, an alignment reference grating, a 3:1 configuration, a position adjustment tool to enable fast alignment, simultaneous optimization of lens and window thicknesses for multiple rolled K-vector gratings, and avoidance of crossover of diffracted beams and other orders. The waveguide structure, mastering system, and exposure process are described in further detail in the following sections.

[0051] waveguide structure

[0052] The waveguide structures according to various embodiments can be implemented in many different ways. In many embodiments, the waveguide structure is designed as an optical waveguide, which is a structure that can confine and guide electromagnetic waves or light in the visible spectrum. These optical waveguides can be implemented for use in many different applications, such as, but not limited to, helmet-mounted displays, head-mounted displays ("HMDs"), and HUDs. The term HUD is generally used to describe a class of devices that incorporate a transparent display that presents data without requiring the user to change their normal field of view. Optical waveguides can integrate various optical functions into a desired form factor depending on a given application.

[0053] Optical waveguides according to various embodiments can be designed to manipulate light waves in a controlled manner using a variety of methods and waveguide optics. For example, optical waveguides can be implemented using materials with a higher refractive index than the surrounding environment to limit the area within which light can propagate. Light coupled into an optical waveguide made of such materials at specific angles can be confined within the waveguide via total internal reflection. In a planar waveguide, the angle at which total internal reflection occurs is given by Snell's law, which determines whether light is refracted or totally reflected at a surface boundary.

[0054] In many embodiments, waveguides incorporating Bragg gratings are implemented for HUD applications. HUDs can be incorporated into any of a variety of applications, including, but not limited to, near-eye applications. Compared to HUDs implemented using conventional optical components, HUDs utilizing planar waveguides incorporating Bragg gratings according to various embodiments of the present invention can achieve a significantly larger field of view and have lower volume requirements. In some embodiments, the HUD includes at least one waveguide incorporating multiple gratings. In further embodiments, the waveguide incorporates at least three Bragg gratings that can be implemented to provide various optical functions, such as, but not limited to, biaxial beam spreading. For example, in many embodiments, the waveguide incorporates an input grating, a folding grating, and an output grating. HUDs utilizing waveguides can be implemented using varying numbers of waveguides. In many embodiments, a single waveguide is used to implement the HUD. In other embodiments, a stack of waveguides is used to implement the HUD. Multiple waveguides can be stacked and implemented to provide different optical functions, such as, but not limited to, implementing a color display. In several embodiments, the HUD incorporates three separate waveguides, one for each of the red, green, and blue color channels.

[0055] Waveguides utilizing Bragg gratings according to various embodiments of the present invention can be designed to have different types of fringes. The use of multiple waveguides with the same surface pitch size but different grating tilt angles can increase the overall couple-in angular bandwidth of the waveguide. In many embodiments, one or more of the gratings within the waveguide incorporates a tilt angle that varies across the grating and / or a rolling K-vector to modify the diffraction efficiency of the grating. The K-vector can be defined as a vector orthogonal to the plane of the associated grating fringes, which can determine the optical efficiency for a given range of input and diffraction angles. By incorporating a grating with a rolling K-vector ("RKV"), the grating can be designed to change the diffraction efficiency in a manner that achieves desired characteristics across the eyebox of a HUD display. The configuration of grating fringes (such as RKV) and other aspects related to the structure and implementation of waveguides used in HUDs are discussed in further detail below.

[0056] Diffraction grating

[0057] Optical waveguides can incorporate various optical elements to manipulate the propagation of light waves. As will be readily appreciated, the type of grating chosen can depend on the specific requirements of a given application. 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 implemented grating is a Bragg grating (also known as a volume grating). Bragg gratings can have high efficiency, with virtually no light diffracted into higher orders. The relative amounts of light in the diffracted and zeroth orders can be varied by controlling the refractive index modulation of the grating, a property that can be used to create lossy waveguide gratings for extracting light from large pupils. By strategically placing a volume Bragg grating within a waveguide, the propagation of light within the waveguide can be influenced in a controlled manner to achieve a variety of effects. The diffraction of light incident on the grating can be determined by the characteristics of the grating and the light. As will be readily appreciated, a volume Bragg grating can be constructed with different characteristics depending on the specific requirements of a given application. In many embodiments, the volume Bragg grating is designed as a transmission grating. In other embodiments, the volume Bragg grating is designed as a reflection grating. In a transmission grating, incident light that meets the Bragg condition is diffracted so that the diffracted light exits the grating on the side that the incident light did not enter. For a reflection grating, the diffracted light exits on the same side of the grating as the incident light entered.

[0058] Figure 1A and Figure 1B Two volume Bragg grating configurations according to various embodiments of the present invention are conceptually illustrated. Depending on the side from which the light exits after diffraction, the grating can be classified as a reflection grating 100 or a transmission grating 150. The conditions of refraction / reflection, or Bragg conditions, can depend on several factors, such as, but not limited to, the refractive index of the medium, the grating period, the wavelength of the incident light, and the angle of incidence. Figure 1A A reflection grating 100 recorded in a transparent material is shown. As shown, light rays 101, 102 have different wavelengths and are incident at the same angle on the reflection grating 100, which has fringes 103 parallel to the grating surface. Light ray 101 does not satisfy the Bragg condition and is transmitted through the grating. On the other hand, light ray 102 does satisfy the Bragg condition and is reflected back through the same surface through which it entered. Another type of grating is a transmission grating, which is a type of grating that is used in a variety of applications. Figure 1B 150 is conceptually illustrated in FIG. In the illustrative embodiment, the transmission grating 150 has fringes 151 perpendicular to the grating surface. As shown, light rays 152, 153 having different wavelengths are incident on the transmission grating 150 at the same angle. Light ray 152 satisfies the Bragg condition and is refracted, exiting on the opposite side of the grating from which light ray 152 entered. Light ray 153 does not satisfy the Bragg condition and is transmitted through according to its original propagation path. Depending on the efficiency of the grating, the light may be partially reflected or refracted. Although Figure 1A and Figure 1B While specific volume grating structures are illustrated, any type of grating structure can be recorded in a waveguide cell according to various embodiments of the present invention. For example, a volume grating can be implemented with fringes that are skewed and / or tilted relative to the grating surface, which can affect the angles of diffraction / reflection. While the above discussion depicts grating structures as either transmissive or reflective, both types of gratings can be represented in the same manner according to standard grating equations.

[0059] Waveguide structures according to various embodiments of the present invention can implement gratings in many different ways. In addition to volume gratings, gratings can also be implemented as surface topography gratings. As the name implies, surface topography gratings can be achieved by physically forming grooves or a periodic pattern on the surface of a substrate. The periodicity and angle formed by the grooves can determine the efficiency and other characteristics of the grating. Any of a number of methods can be used to form these grooves, such as, but not limited to, etching and photolithography.

[0060] Figure 2 A surface topography grating according to an embodiment of the present invention is conceptually illustrated. As shown, surface topography grating 200 includes periodically tilted grooves 201. When light is incident on grooves 201, diffraction may occur under certain conditions. The tilt and periodicity of grooves 201 can be designed to achieve a desired diffraction behavior for the incident light.

[0061] Although Figure 1A-1B and Figure 2 A specific grating structure is shown, but it will be readily appreciated that the grating structure may be configured in many different ways depending on the specific requirements of a given application. Examples of such configurations are discussed in further detail in the following sections.

[0062] Switchable Bragg grating

[0063] One type of grating used in holographic waveguide devices is the switchable Bragg grating ("SBG"). An SBG can be fabricated by first placing a thin film of a mixture of photopolymerizable monomers and 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, typically transparent tin oxide films, for applying an electric field across the films. The grating structure in the SBG can be recorded in a liquid material (often referred to as a slurry) by photopolymerization-induced phase separation using interferometric exposure with spatially periodic intensity modulation. Factors such as, but not limited to, control of the radiation intensity, the volume fractions of the components in the mixture, and the exposure temperature can determine the resulting grating morphology and performance. As can be readily appreciated, a 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 within the polymer network on the scale of the optical wavelength. The 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 resulting from the orientation alignment of the LC molecules in the droplet.

[0064] 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 transparent electrodes, the natural orientation of the LC droplets can be altered, causing the refractive index modulation of the fringes to decrease and the holographic diffraction efficiency to drop to very low levels. Typically, the electrodes are configured so that the applied electric field is perpendicular to the substrate. In many embodiments, the electrodes are made of indium tin oxide ("ITO"). In the off (OFF) state, with no applied electric field, the extraordinary axis of the liquid crystal is typically aligned perpendicular to the fringes. As a result, 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 the on (ON) state, in which the extraordinary axis of the liquid crystal molecules is aligned 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- and P-polarized light. Consequently, the grating regions no longer diffract light. Depending on the function of the HPDLC device, each grating area can be divided into multiple grating elements such as 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 multiple selectively switchable grating elements.

[0065] Typically, an SBG element is switched off within 30 μs and switched on with a longer relaxation time. It has been noted that the diffraction efficiency of the device can be tuned over a continuous range via the applied voltage. In many cases, the device exhibits near-100% efficiency without an applied voltage and essentially zero efficiency with a sufficiently high applied voltage. In certain types of HPDLC devices, a magnetic field can be used to control the LC orientation. In some HPDLC applications, the phase separation of the LC material and the polymer can be so great that no discernible droplet structure results. SBGs can also be used as passive gratings. In this mode, their primary advantage is the unique high refractive index modulation. SBGs can be used to provide transmission or reflection gratings for free-space applications. SBGs can be implemented as waveguide devices, with the HPDLC forming either an evanescent coupling layer near the waveguide or the waveguide core. The glass plates used to form the HPDLC cell provide a total internal reflection ("TIR") light-guiding structure. Light can be coupled out of the SBG when the switchable grating diffracts light at angles exceeding the TIR condition.

[0066] Figure 3A and Figure 3B The HPDLC SBG devices 300 and 350 and the switching characteristics of the SBG according to various embodiments of the present invention are conceptually illustrated. Figure 3A In FIG. 3 , the SBG 300 is in the OFF state. As shown, the LC molecules 301 are aligned substantially perpendicular to the stripe plane. As such, the SBG 300 exhibits high diffraction efficiency, and incident light can be easily diffracted. Figure 3B SBG 350 is shown in the ON position. An applied voltage 351 can orient the optical axes of LC molecules 352 within droplet 353 to produce an effective refractive index that matches that of the polymer, thereby creating a substantially transparent cell in which incident light is not diffracted. In the illustrative embodiment, an AC voltage source is shown. As can be readily appreciated, a variety of voltage sources can be utilized depending on the specific requirements of a given application.

[0067] In waveguide cell designs, in addition to the components described above, adhesives and spacers may be placed between the substrates to adhere the layers of the element together and maintain the cell gap or thickness dimension. In these devices, the spacers can take many forms, such as, but not limited to, materials, sizes, and geometries. Materials can include, for example, plastics (e.g., divinylbenzene), silicon dioxide, and conductive spacers. They can take any suitable geometry, such as, but not limited to, rods and spheres. The spacers can take any suitable size. In many cases, the size of the spacers ranges from 1 to 30 μm. While the use of these adhesives and spacers may be necessary in LC cells using conventional materials and manufacturing methods, they can introduce blurring into the cell, thereby degrading the optical properties and performance of the waveguide and device.

[0068] HPDLC Material System

[0069] HPDLC mixtures according to various embodiments of the present invention typically include LC, monomers, photoinitiator dyes, and co-initiators. The mixture (often referred to as a slurry) often also includes a surfactant. For the purposes of describing the present invention, a surfactant is defined as any chemical agent that reduces the surface tension of the overall liquid mixture. The use of surfactants in PDLC mixtures is known and dates back to the earliest research on PDLC. For example, RL Sutherland et al., SPIE, Vol. 2689, 158-169, 1996, describes PDLC mixtures 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 Natarajan et al., Journal of Nonlinear Optical Physics and Materials, Vol. 5, No. I 89-98, 1996, the disclosure of which is incorporated herein by reference. Additionally, U.S. Patent No. 7,018,563 to Sutherland et al. discusses a polymer-dispersed liquid crystal material for forming a polymer-dispersed liquid crystal optical element, the 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.

[0070] 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, and the like. 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 these materials use acrylate monomers, including:

[0071] 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 coinitiator, N-phenylglycine. In some variations, the surfactant octanoic acid is added.

[0072] • Fontecchio et al., SID 00 Digest 774-776, 2000, describe UV-curable HPDLC comprising multifunctional acrylate monomers, LC, photoinitiator, co-initiator and chain terminator for reflective display applications, the disclosure of which is incorporated herein by reference.

[0073] • YH Cho et al., Polymer International, 48, 1085-1090, 1999, disclose HPDLC formulations including acrylates, the disclosure of which is incorporated herein by reference.

[0074] • 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.

[0075] • 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.

[0076] 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.

[0077] Acrylates offer the advantages of fast kinetics, good mixing with other materials, and compatibility with film-forming processes. Because acrylates are cross-linked, they tend to be mechanically robust and flexible. For example, 2(di)- and 3(tri)-functional urethane acrylates have been widely used in HPDLC technology. Higher functionality materials such as penta- and hexafunctional stems have also been used.

[0078] 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 fringe (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).

[0079] Recording mechanism for volume grating

[0080] According to various embodiments of the present invention, volume gratings can be recorded in waveguide elements using a number of different methods. Any number and type of electromagnetic radiation sources can be used to achieve recording of optical elements in optical recording materials. Depending on the application, the exposure source(s) and / or recording system can be configured to record the optical elements using varying durations and exposure power levels. As discussed above with respect to SBGs, techniques for recording volume gratings can include exposure of the optical recording material using two mutually coherent laser beams, where the superposition of the two beams produces a periodic intensity distribution along an interference pattern. The optical recording material can be formed into a grating structure exhibiting a refractive index modulation pattern that matches the periodic intensity distribution. In an HPDLC mixture, the light intensity distribution causes monomers to diffuse and polymerize into high-intensity regions, while liquid crystals diffuse into dark regions. This phase separation produces alternating liquid crystal-rich and liquid crystal-poor regions that form the fringe plane of the grating. Depending on how the recording beams are configured, the grating structure can be formed with tilted or non-tilted fringes. Figures 4A-4DA two-beam recording process according to various embodiments of the present invention is conceptually illustrated. As shown, two methods can be used to generate two different types of Bragg gratings—i.e., a transmission grating 400 and a reflection grating 401. Depending on how the two recording beams 402, 403 are positioned, an interference pattern 404 can record either a transmission or a reflection grating in an optical recording material 405. The difference between the two types of gratings can be seen in the orientation of the fringes (i.e., the fringes of a reflector grating are generally substantially parallel to the surface of the substrate, and the fringes of a transmission grating are generally substantially perpendicular to the surface of the substrate). During playback, beam 406 incident on transmission grating 400 can result in a transmitted diffracted beam 407. On the other hand, beam 408 incident on reflection grating 401 can result in a reflected beam 409.

[0081] Another method for recording volume gratings in an optical recording material involves using a single beam to form an interference pattern on the optical recording material. This can be achieved through the use of a master grating. In many embodiments, the master grating is a volume grating. In some embodiments, the master grating is an amplitude grating. After interacting with the master grating, the single beam can be diffracted. The first order diffraction and the zeroth order beam can overlap to produce an interference pattern that can then expose the optical recording material to form the desired volume grating. Figure 5 , a single-beam recording process utilizing an amplitude grating according to an embodiment of the present invention is conceptually illustrated in FIG. As shown, a beam 500 from a single laser source (not shown) is directed through an amplitude grating 501. Upon interacting with the grating 501, the beam 500 may diffract, as occurs when light interacts with a dark shaded region of the amplitude grating, or may propagate through the amplitude grating without substantial deviation, as occurs when light interacts with a cross-hatched region of the amplitude grating. The first-order diffracted beam 502 and the zeroth-order beam 503 may overlap to produce an interference pattern that exposes an optical recording layer 504 of a waveguide unit. In the illustrative embodiment, a spacer 505 is positioned between the grating 501 and the optical recording layer 504 to modify the distance between the two components.

[0082] Although Figures 4A-4D and Figure 5 Specific methods of recording volume gratings are discussed and illustrated in , but recording systems according to various embodiments of the present invention may be configured to implement any of a number of methods for recording volume gratings.

[0083] Rolling K-vector grating and multiplexed K-vector grating

[0084] To address the limited range of wavelengths and angles over which diffraction occurs in a volume Bragg grating, several approaches can be used to increase the diffraction bandwidth of the grating. In many embodiments, the gratings can employ fringes that vary with respect to their K vectors. In many embodiments, the variation in the K vector across the roll is typically such that the direction of the change in the K vector is not in the plane of the waveguide or grating elements. Varying fringes or a roll-over K vector can be implemented in many different ways. In some embodiments, the fringes of the grating are designed to vary in a gradual manner across the grating. In other embodiments, separate sets of gratings with different fringes are placed sequentially. Gratings with a roll-over K vector can be designed and configured in various ways. In many embodiments, the roll-over K vector is designed so that the peak diffraction efficiency of each grating section is optimized for its corresponding output angle at that location. In some embodiments, the peak diffraction efficiency of each grating at different locations is offset according to its corresponding output angle at that location. Introducing this offset has been shown to improve eye-tracking uniformity. In some embodiments, the offset can improve overall image brightness by a factor of two compared to simply matching the peak diffraction efficiency at different locations.

[0085] According to embodiments of the present invention, a rolled K-vector grating can be used to maximize the peak diffraction efficiency of the incoupled light. The use of a rolled k-vector enables high-efficiency input coupling into the grating and also allows optimization of the beam expansion angle to minimize the thickness of the waveguide; this may require balancing the thickness of the waveguide, the angular bandwidth of the grating, and the spread of the field angle at any given point on the grating. With the K-vector rolled (and maintaining the surface pitch), the low angular response of the grating can prevent outcoupling, allowing the waveguide thickness to be minimized. In many embodiments, the design goal is to ensure maximum input coupling at a certain point and minimize angular diversity, so that the grating thickness can be minimized without coupling to each other at different points.

[0086] Figure 6A and Figure 6B Conceptually illustrating two implementations of a rolling K-vector raster according to various embodiments of the present invention. Figure 6A In some embodiments, a rolled K-vector grating can be implemented as a waveguide portion comprising separate grating elements 600 having different K-vectors. Figure 6B In several embodiments, a rolled K-vector grating can be implemented as a waveguide portion comprising a grating element 601 within which the K-vector undergoes a smooth, monotonic change in direction. As illustrated, the change in direction of the K-vector is not in the plane of the waveguide.

[0087] In many embodiments, different sets of discrete fringes are superimposed into the same grating, resulting in a multiplexed grating with essentially multiple gratings operating independently within the same volume without interfering with each other. For example, if two volume gratings are recorded in the same device for two different Bragg wavelengths at the same angle of incidence, the device can diffract the two selected wavelengths into different output directions with limited crosstalk. Multiplexing can be used to produce an improved angular distribution by combining two gratings of similar prescription to extend the diffraction efficiency angular bandwidth and give better brightness uniformity and color balance across the exit pupil and field of view. Multiplexing can also be used to encode two different diffraction prescriptions that can be designed to project light into different area fields, or to diffract two different wavelengths of light into a given field of view. Steps can be taken to ensure that there is no competition between gratings during recording that would result in unequal diffraction efficiencies and crosstalk between gratings during playback. Multiplexing can also provide the significant advantage of reducing the number of layers in the waveguide structure. In some embodiments, at least one of the input grating, the folded grating, or the output grating can combine two or more angular diffraction schemes to extend the angular bandwidth. Similarly, in several embodiments, at least one of the input grating, the folded grating, or the output grating can combine two or more spectral diffraction schemes to extend the spectral bandwidth. For example, a color multiplexing grating can be used to diffract two or more primary colors.

[0088] Figure 7 A multiplexed K-vector grating according to an embodiment of the present invention is conceptually illustrated. As illustrated, a multiplexed grating 700 includes two fringe sets 701, 702. The first set 701 is depicted by solid diagonal lines and has a K-vector K1 and a period Λ1. The second multiplexed grating 702 is illustrated by dot-dashed lines and has a K-vector K2 and a period Λ2. In the illustrated embodiment, the two grating periods are the same, but the K-vectors are different in direction. In operation, both of the multiplexed gratings 701, 702 are active and can provide wider incident and diffraction bandwidths. The incident angle bandwidth θ of the multiplexed grating is i Coverage includes overlapping θ i1 and θ i2 The diffraction angle bandwidth θ of the multiplexed gratings 701 and 702 is d Coverage includes overlapping θ d1 and θ d2 In some embodiments, more than two gratings are multiplexed.

[0089] While specific grating structures with varying stripes are discussed above, any of a number of stripe configurations can be utilized, depending on the specific requirements of a given application. For example, any number of gratings can be multiplexed, as permitted by manufacturing constraints. A scrolled K-vector grating can be designed with a K-vector that scrolls in any discrete unit.

[0090] Waveguides for pupil expansion

[0091] Gratings can be implemented in waveguides in a variety of ways. In some embodiments, the grating resides on the outer surface of the waveguide. In other embodiments, a volume grating is implemented within the waveguide. Gratings can also be implemented to perform different optical functions, such as, but not limited to, coupling light, guiding light, and preventing light from being transmitted. Figure 8 A waveguide utilizing a coupling grating to diffract light into and out of the waveguide is conceptually illustrated in accordance with an embodiment of the present invention. As shown, waveguide 800 includes a first surface 801, a second surface 802, an input grating element 803, and an output grating element 804. Collimated light 805 from a projection lens enters the waveguide through the first surface 801 at an orthogonal angle. The light travels through the waveguide 800 at its original angle and interacts with the input grating element 803 before reaching the second surface 802 on the other side of the waveguide 800. The input grating element 803 can be designed to diffract the light 805 at an oblique angle so that the refracted light 806 is incident on the second surface 802 at an angle at which total internal reflection can occur. In this manner, the light 805 is coupled into the waveguide and confined within the first surface 801 and the second surface 802 of the waveguide 800. In the illustrative embodiment, light travels within the waveguide 800 until it interacts with the output grating 804 , which refracts and couples the light out of the waveguide 800 and into the user's eye 807 .

[0092] In many embodiments, a diffraction grating can be used to reduce lens size while maintaining the size of the eyebox by effectively expanding the exit pupil of the collimating optical system. The exit pupil can be defined as a virtual aperture, where only light that passes through this virtual aperture can enter the user's eye. Figure 9 and Figure 10 A waveguide utilizing an output grating for exit pupil expansion in one dimension is conceptually illustrated in accordance with an embodiment of the present invention. Figure 9The waveguide 900 in FIG. 1 includes a first surface 901, a second surface 902, an input grating element 903, and an output grating element 904. As shown, light 905 is coupled into the waveguide 900 through the input grating 902 and can travel through the waveguide 900 via total internal reflection. In the illustrative embodiment, the output grating 904 is extended and designed to refract a portion of the light being waveguided. The light can be refracted so that the refracted light 906 is incident on the second surface 902 at an angle where total internal reflection does not occur, thereby allowing the light 906 to be coupled out of the waveguide 900. This lossy extraction allows the exit pupil to expand because the remaining light can continue to travel within the waveguide 900, and once the light is incident on the output grating 904 again, the scenario described above can occur again. Using this technique, a continuously expanding exit pupil can also be achieved with appropriate design, such as Figure 10 As shown in .

[0093] exist Figure 9 and Figure 10 Expanding on the ideas in

[0015] , optical waveguides can be designed to expand the exit pupil in two dimensions. In many embodiments, two waveguides can be stacked together to create a system in which light coupled into the waveguide stack can achieve exit pupil expansion in two dimensions. Figure 11 A waveguide system is conceptually illustrated that utilizes two planar waveguides to provide exit pupil expansion in two dimensions according to an embodiment of the present invention. As shown, the system 1100 includes a first waveguide 1101 and a second waveguide 1102. The first waveguide 1101 may include a first input coupling grating 1103 and a first output coupling grating 1104, and the second waveguide 1102 may include a second input coupling grating 1105 and a second output coupling grating 1106. The first input coupling grating 1103 may be designed to couple collimated light 1107 from an image source 1108 into the first waveguide 1101. Similar to Figure 9 and Figure 10In the system described in

[15] , confined light can travel through the first waveguide 1101 via total internal reflection until the light reaches the first output coupling grating 1104. In an illustrative embodiment, the first output coupling grating 1104 is designed to provide lossy exit pupil expansion in a first dimension and couple the light out of the first waveguide 1101. The second input coupling grating 1105 can be designed to receive the light output from the first waveguide 1101, expanded in the first dimension, and refract the received light so that the received light travels through the second waveguide 1102 via total internal reflection. In many embodiments, the first output coupling grating 1104 and the second input coupling grating 1106 are stretched in a similar manner. The light traveling through the second waveguide 1102 can then interact with the second output coupling grating 1106. In an illustrative embodiment, the second output coupling grating 1106 is designed to provide lossy exit pupil expansion in a second dimension, different from the first dimension, and couple the light out of the second waveguide 1102. As a result, the exit pupil expands in two dimensions, allowing for a smaller lens size with respect to the eyebox size 1109 .

[0094] In many embodiments, an optical waveguide utilizes a folded grating that can guide light within the waveguide while providing an exit pupil expansion in one dimension. In further embodiments, the folded grating guides light toward an output grating that can provide an exit pupil expansion in a second dimension, different from the first, and also couples the light out of the waveguide. By using a folded grating, a waveguide display can require fewer layers compared to other systems and methods for displaying information. Furthermore, by using a folded grating, light can travel through a single rectangular prism defined by the waveguide's outer surface via total internal reflection within the waveguide, simultaneously achieving dual pupil expansion. As a result, a single waveguide can achieve two-dimensional exit pupil expansion. Figure 12 A waveguide utilizing a three-grating structure to provide two-dimensional exit pupil expansion according to an embodiment of the present invention is conceptually illustrated. As shown, waveguide 1200 includes an input grating 1201, a folded grating 1202, and an output grating 1203. Arrows 1204-1206 on gratings 1201-1203 illustrate the k-vector associated with each grating. In many embodiments, folded grating 1202 can be designed to provide exit pupil expansion in one dimension and redirect light propagating via total internal reflection from input grating 1201. In an illustrative embodiment, the fringes of folded grating 1202 are offset by 45 degrees from either of the other two gratings 1201 and 1203. Light 1207 incident on the folded grating is redirected 1208 to propagate toward output grating 1203, which provides exit pupil expansion in a second dimension and couples light out of waveguide 1200.

[0095] Although the above Figures 8-12 The discussion has described specific waveguide structures, but it will be readily appreciated that any number of waveguide structure configurations may be utilized, depending on the specific requirements of a given application. For example, a grating providing exit pupil expansion may be designed with a gradient efficiency such that the portion of refracted light varies depending on the region of incidence.

[0096] Waveguide layer stack

[0097] Waveguides according to various embodiments of the present invention can be stacked together to achieve certain optical functions. For example, in many embodiments, a device can include a stack of RGB diffraction layers, each layer including an input grating and an output grating. The SBGs in each layer are recorded to provide peak diffraction efficiency with respect to wavelengths that are offset (along the waveguide) by small increments from the peak wavelength. In some embodiments, RGB SBG layers are used and can be switched sequentially and synchronously with an RGB LED image source. Figure 13 A cross-sectional view of an RGB stack of waveguides 1300 is conceptually illustrated, in accordance with an embodiment of the present invention. In the illustrative embodiment, wavelength-selective absorption layers 1301-1303 are used to selectively absorb unwanted light in each waveguide layer 1304-1306. Dashed lines represent weak coupling due to polarization mismatch, or Bragg mismatch. The waveguide stack also includes various filters and waveplates 1307-1311. Polarization orientation is depicted relative to the input grating.

[0098] Although Figure 13 A specific structure of a waveguide stack is shown, but any of a number of stacking configurations can be used, depending on the specific requirements of a given application. For example, in many embodiments, only two layers, red and blue / green, are used to implement an RGB stack. Several approaches can be used to implement such a system. In some embodiments, multiplexed gratings, containing different sets of gratings, each associated with an RGB color, are used to implement multiple color waveguides in a single waveguide layer.

[0099] Waveguide Display

[0100] Waveguide displays according to various embodiments of the present invention may be implemented and constrained in many different ways. For example, a waveguide display may contain varying numbers of waveguide layers and different exit pupil expansion schemes. Figure 14A conceptual illustration of a dual-axis expanded waveguide display with two grating layers, according to an embodiment of the present invention, is provided. As shown, waveguide display 1400 includes a light source 1401, a microdisplay panel 1402, and an input image node ("IIN") 1403 optically coupled to a waveguide 1404 having two grating layers. In some embodiments, the waveguide is formed by sandwiching the grating layers between glass or plastic substrates to form a stack, within which total internal reflection occurs at the outer substrate-air interface. In several embodiments, the stack may also include additional layers, such as beam-splitting coatings and environmental protection layers. In the illustrative embodiment, each grating layer includes an input grating 1405A, 1405B, a folded grating exit pupil expander 1406A, 1406B, and an output grating 1407A, 1407B, where the characters A and B refer to the first and second waveguide layers, respectively. The input grating, folded grating, and output grating may be holographic gratings, such as switchable or non-switchable SBGs. As used herein, the term grating may encompass gratings that may include a collection of gratings, such as a multiplexed grating or a collection of discrete scrolling K-vector gratings. In the illustrative embodiment, the IIN 1403 integrates the microdisplay panel 1402, the light source 1401, and the optical components required to illuminate the display panel, split the reflected light, and collimate it into the required FOV. Figure 14 In embodiments described herein and in embodiments to be described below, at least one of the input grating, the fold grating, and the output grating can be electrically switchable. In many embodiments, all three grating types are passive (i.e., non-switching). In many embodiments, the IIN can project an image displayed on a microdisplay panel such that each display pixel is translated into a unique angular orientation within the substrate waveguide. The collimating optics included in the IIN can include lenses and mirrors. In further embodiments, the lenses and mirrors are diffractive lenses and mirrors.

[0101] In the illustrative embodiment, the light path from the source through the IIN to the waveguide is indicated by rays 1408-1411. The input gratings 1405A and 1405B of each grating layer can couple a portion of the light into a TIR path in the waveguide 1404, represented by rays 1412 and 1413. The output gratings 1407A and 1407B can diffract the light from the waveguide into a range of angles for collimated light 1414 and 1415, for viewing by the eye 1416. The IIN optics can define an angular range corresponding to the display's field of view. In some embodiments, the waveguide gratings can encode optical power for adjusting the collimation of the output. In some embodiments, the output image is at infinity. In other embodiments, the output image can be formed at a distance of several meters from the eye's field of view. Typically, the eye is within the display's field of view, or exit pupil.

[0102] Various IIN implementations and embodiments can be utilized as discussed and taught in U.S. Patent Application No. 13 / 869,866, entitled “Holographic Wide Angle Display,” and U.S. Patent Application No. 13 / 844,456, entitled “Transparent Waveguide Display,” the disclosures of which are incorporated herein by reference in their entireties. In some embodiments, the IIN includes a beam splitter for directing light onto the microdisplay and transmitting reflected light toward the waveguide. In many embodiments, the beam splitter is a grating recorded in the HPDLC, and the inherent polarization selectivity of such a grating is used to separate the light illuminating the display from the image-modulated light reflected from the display. In several embodiments, the beam splitter is a polarizing beam splitter cube. In many embodiments, the IIN incorporates a despeckler. Despecklers are discussed in U.S. Patent No. 8,565,560, entitled “Laser Illumination Device,” the disclosure of which is incorporated herein by reference in its entirety.

[0103] The light source can be a laser or an LED and can include one or more lenses for modifying the angular characteristics of the illumination beam. The image source can be a microdisplay or a laser-based display. LEDs can provide better uniformity than lasers. If laser illumination is used, there is a risk of illumination banding at the waveguide output. In many embodiments, the laser illumination banding in the waveguide can be overcome using the techniques and teachings disclosed in U.S. patent application Ser. No. 15 / 512,500, entitled “Method and Apparatus for Generating Input Images for Holographic Waveguide Displays,” the disclosure of which is incorporated herein by reference in its entirety. In some embodiments, the light from the light source is polarized. In several embodiments, the image source is a liquid crystal display (LCD) microdisplay or a liquid crystal on silicon (LCoS) microdisplay.

[0104] In some embodiments, similar to Figure 14The grating layers shown in FIG. 5 , each grating layer addresses half of the total field of view. Typically, the folded gratings are clocked at 45 degrees (i.e., tilted in the waveguide plane) to ensure sufficient angular bandwidth of the folded light. In other embodiments, other clock angles can be used to meet spatial constraints on grating positioning that may arise in the ergonomic design of the display. In some embodiments, at least one of the input grating and the output grating has a scrolled k-vector. Scrolling the k-vector can allow the angular bandwidth of the grating to be extended without increasing the waveguide thickness.

[0105] In many embodiments, the grating scheme can be designed to provide a dual interaction between the guided light and the grating to enhance the angular bandwidth of the folded grating. An exemplary embodiment of a dual interaction folded grating is disclosed in U.S. Patent Application No. 14 / 620,969, entitled “Waveguide Grating Device,” the disclosure of which is incorporated herein in its entirety.

[0106] Figure 15 Conceptually illustrates a device similar to an embodiment of the present invention. Figure 14 Figure 1500 shows a plan view of a single grating layer used in an optical system. Grating layer 1501, optically coupled to an IIN 1502, includes an input grating 1503, a first beam splitter 1504, a fold grating 1505, a second beam splitter 1506, and an output grating 1507. The beam splitters can be partially transmissive coatings that homogenize the guided light by providing multiple reflection paths within the waveguide. Each beam splitter can include more than one coating, each applied to a transparent substrate. Typical beam paths from the IIN to the eye 1508 are indicated by rays 1509-1513.

[0107] Figure 16 A plan view 1600 of a two-grating layer configuration according to an embodiment of the present invention is conceptually illustrated. As shown, grating layers 1601A and 1601B optically coupled to an IIN 1602 include input gratings 1603A and 1603B, first beam splitters 1604A and 1604B, folding gratings 1605A and 1605B, second beam splitters 1606A and 1606B, and output gratings 1607A and 1607B, where the characters A and B refer to the first and second grating layers, respectively. In the illustrated embodiment, the two grating layers and beam splitters substantially overlap.

[0108] In many embodiments, the grating layer can be decomposed into separate layers. For example, in some embodiments, the first layer includes a folded grating, while the second layer includes an output grating. In further embodiments, the third layer can include an input grating. In such embodiments, these multiple layers can then be laminated together into a single waveguide substrate. In several embodiments, the grating layer includes multiple sheets, including an input coupler, a folded grating, and an output grating (or portions thereof), that are laminated together to form a single substrate waveguide. These sheets can be separated by optical glue or other transparent materials with a refractive index that matches or is substantially similar to the refractive index of the sheets.

[0109] In many embodiments, the grating layer can be formed via a cell fabrication process by creating cells of the desired grating thickness and vacuum filling each cell with SBG material for each of the input coupler, fold grating, and output grating. In some embodiments, the cell can be formed by positioning multiple glass plates with gaps between the glass plates that define the desired grating thickness for the input coupler, fold grating, and output grating. In several embodiments, a cell can be made with multiple apertures, such that different apertures are filled with different pockets of SBG material. Any intervening spaces can then be separated by a spacer material (e.g., glue, oil, etc.) to define the separation regions. In many embodiments, the SBG material can be spin-coated onto a substrate and then covered with a second substrate after the material cures.

[0110] In many embodiments, input couplers, folded gratings, and output gratings can be created by interfering two light waves at a certain angle within the substrate to generate a holographic wavefront, thereby producing light and dark fringes arranged at desired angles in the waveguide substrate. Furthermore, such optical elements can be fabricated using any of the various methods described in the previous sections.

[0111] In one embodiment, the input coupler, fold grating, and output grating implemented as SBGs can be Bragg gratings recorded in a holographic polymer dispersed liquid crystal (HPDLC) (e.g., a matrix of liquid crystal droplets), although SBGs can also be recorded in other materials. In one embodiment, the SBGs are recorded in a uniformly modulated material, such as POLICRYPS or POLIPHEM, which has a matrix of solid liquid crystals dispersed in a liquid polymer. SBGs can be switching or non-switching in nature. In their non-switching form, SBGs have an advantage over conventional holographic photopolymer materials in that they can provide high refractive index modulation due to their 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.

[0112] In many embodiments, the input coupler, folded grating, and output grating are made of 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 in the presence of an electric field. 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 Polymer Dispersed Liquid Crystal Materials and Devices," the disclosure of which is incorporated herein in its entirety. The grating can be recorded in any of the above material systems, but used in a passive (non-switching) mode. The manufacturing process is the same as that used for switching mode, but the electrode coating stage is omitted. LC polymer material systems are highly desirable given their high refractive index modulation. In some embodiments, the grating is recorded in the HPDLC, but is not switched.

[0113] In many embodiments, the input grating can be replaced by another type of input coupler, such as, but not limited to, a prism and a reflective surface. In some embodiments, the input coupler can be a holographic grating, such as an SBG grating or a passive grating, which can be a passive SBG grating. The input coupler can be configured to receive collimated light from a display source and cause the light to travel within the waveguide to the fold grating via total internal reflection between the first surface and the second surface. The input coupler can be oriented directly toward the fold grating or at a certain angle relative to the fold grating. For example, in several embodiments, the input coupler can be arranged to be slightly tilted with respect to the fold grating. In many embodiments, the fold grating can be oriented in a diagonal direction. The fold grating can be configured to provide pupil expansion in a first direction and guide the light to the output grating via total internal reflection inside the waveguide.

[0114] In many embodiments, the longitudinal edges of each fold grating are oblique to the alignment axis of the input coupler so that each fold grating is arranged on a diagonal line with respect to the propagation direction of the display light. The fold grating can be angled so that light from the input coupler is redirected to the output grating. In some embodiments, the fold grating is arranged at a forty-five degree angle with respect to the direction of the display image released from the input coupler. This feature can cause the display image propagating along the fold grating to be transferred into the output grating. For example, in several embodiments, the fold grating can cause the image to be rotated 90 degrees into the output grating. In this way, a single waveguide can provide dual-axis pupil expansion in both the horizontal and vertical directions. In many embodiments, each fold grating can have a partial diffraction structure. In some embodiments, each fold grating can have a full diffraction structure.

[0115] The output grating can be configured to provide pupil expansion in a second direction different from the first direction and to cause light to exit the waveguide from the first surface or the second surface. The output grating can receive a display image from the folded grating via total internal reflection and can provide pupil expansion in the second direction. In many embodiments, the output grating comprises a multilayer substrate, thereby comprising a multilayer output grating. Accordingly, there is no requirement that the grating be in a single plane within the waveguide, and the gratings can be stacked on top of each other (e.g., units of the grating are stacked on top of each other).

[0116] In many embodiments, a quarter-wave plate on the substrate waveguide rotates the polarization of the light to maintain efficient coupling with the SBG. The quarter-wave plate can be coupled to or attached to the surface of the substrate waveguide. For example, in some embodiments, the quarter-wave plate is a coating applied to the substrate waveguide. The quarter-wave plate can provide polarization management of the light waves. Such polarization management can help the light maintain alignment with the intended observation axis by compensating for skew waves in the waveguide. The quarter-wave plate is optional and can increase the efficiency of the optical design in embodiments. In several embodiments, the waveguide does not include a quarter-wave plate. The quarter-wave plate can be provided as a multilayer coating.

[0117] In many embodiments, the waveguide display can be operated in monochrome. In some embodiments, the waveguide display can be operated in color. Figure 14 Color operation can be achieved by stacking similarly designed single-color waveguides. The design can use a red waveguide layer, a green waveguide layer, and a blue waveguide layer as shown, or alternatively use a red layer and a blue / green layer. Figure 17 A dual-axis extended waveguide display 1700 according to an embodiment of the present invention is conceptually illustrated and includes a light source 1701, a microdisplay panel 1702, and an IIN 1703 optically coupled to a red waveguide 1704R, a green waveguide 1704G, and a blue waveguide 1704B, each of which includes two grating layers. In the illustrative embodiment, the three waveguides are separated by an air gap. In some embodiments, the waveguides are separated by a low-refractive-index material such as a nanoporous membrane. As shown, the red grating layer, labeled R, includes input gratings 1705R and 1706R, folded grating exit pupil expanders 1707R and 1708R, and output gratings 1709R and 1710R. The grating elements of the blue and green waveguides are labeled using the same numbering, with B and G indicating blue and green. In some embodiments, the input grating, folded grating, and output grating are all passive, i.e., non-switching. In several embodiments, at least one of the gratings is switchable. In many embodiments, the input gratings in each layer are switchable to avoid color crosstalk between waveguide layers. In many embodiments, color crosstalk can be avoided by placing dichroic filters 1711, 1712 between the input grating regions of the red and blue waveguides, and the blue and green waveguides. In various embodiments, color waveguides can be implemented using only one grating layer in each monochromatic waveguide.

[0118] Figure 18An eye tracking display according to an embodiment of the present invention is conceptually illustrated. Eye trackers based on waveguide devices are discussed in PCT Application No. PCT / GB2014 / 000197 entitled “Holographic Waveguide Eye Tracker,” PCT Application No. PCT / GB2015 / 000274 entitled “Holographic Waveguide Optical Tracker,” and PCT Application No. PCT / GB2013 / 000210 entitled “Apparatus for Eye Tracking,” the disclosures of which are incorporated herein in their entirety. Figure 18 , the eye tracking display 1800 includes a dual-axis extended waveguide display based on any of the embodiments described above. The waveguide display may include: a waveguide 1801 including at least one grating layer incorporating an input fold and an output grating, an IIN 1802, an eye tracker 1803 including a waveguide, an infrared detector 1804, and an infrared source 1805. The eye tracker and the display waveguide may be separated by an air gap or by a low refractive material. As explained in the above references, the eye tracker may include separate illumination and detector waveguides. In the illustrative embodiment, the light path from the infrared source to the eye is indicated by rays 1806-1808, and the signal backscattered from the eye is indicated by rays 1809, 1810. The light path from the input image node through the display waveguide to the eye range is indicated by rays 1811-1813.

[0119] In many embodiments, the dual extended waveguide display may also include a dynamic focusing element. Figure 19 A dual extended waveguide display 1900 is conceptually illustrated having a dynamic focus element 1901 and an eye tracker disposed near a major surface of the waveguide display, in accordance with an embodiment of the present invention. In some embodiments, the dynamic focus element is an LC device. In several embodiments, the LC device combines an LC layer with a diffractive optical element. In many embodiments, the diffractive optical element is an electrically controllable LC-based device. In various embodiments, the dynamic focus element is disposed between the waveguide display and the eye tracker. In various embodiments, the dynamic focus element may be disposed near the surface of the display waveguide farthest from the eye.

[0120] The dynamic focus device can provide multiple image surfaces 1902. In light field display applications, at least four image surfaces can be used. The dynamic focus element can be based on the dynamic focus element described in U.S. Patent Application No. 15 / 553,120, entitled "Electrically Focus Tunable Lens," the disclosure of which is incorporated herein in its entirety. In some embodiments, a dual extended waveguide display with a dynamic focus element and an eye tracker can provide a light field display, such as those based on the teachings disclosed in U.S. Patent Application No. 15 / 543,013, entitled "Holographic Waveguide Light Field Displays," the disclosure of which is incorporated herein by reference in its entirety.

[0121] While specific waveguide structures are discussed above, any of a number of waveguide structures may be implemented depending on the specific requirements of a given application. For example, in many waveguide configurations, the input grating, folded grating, and output grating are formed in a single layer sandwiched between transparent substrates. Such configurations are Figure 14 , where the two layers are stacked as such. In some embodiments, the waveguide includes only one grating layer. In several embodiments, the switching transparent electrodes are applied to opposing surfaces of the substrate layers that sandwich the switching grating. In many embodiments, the unit substrate can be made of glass. One glass substrate that can be used is a standard Corning Willow glass substrate (refractive index 1.51), which can be as thin as 50 microns. In other embodiments, the unit substrate can be an optical plastic.

[0122] In many embodiments, the waveguide display is coupled to the IIN through an opto-mechanical interface that allows the waveguide to be easily retracted from the IIN assembly. The basic principle is conceptually illustrated in Figure 20A middle. Figure 20A A dual-axis extended waveguide display 2000 is shown, comprising a waveguide 2001 comprising an input grating 2002, a folded grating 2003, and an output grating 2004, and an IIN 2005. The device further comprises an optical link 2006 connected to the waveguide, a first optical interface 2007 terminating the optical link, and a second optical interface 2008 forming an output optical port of the IIN. The first optical interface and the second optical interface may be formed as shown by Figure 20BIn some embodiments, the optical link is a waveguide. In several embodiments, the optical link is curved. In many embodiments, the optical link is a GRIN image relay device. In various embodiments, a mechanical mechanism is used to establish the optical connection. In some embodiments, the optical connection is established using a magnetic mechanism. In helmet-mounted display applications, an advantage of decoupling the waveguide from the IIN is that the near-eye portion of the display can be moved away when not in use. In some embodiments, where the waveguide includes a passive grating, the near-eye optics can be disposable.

[0123] Figure 21 An IIN 2100 is conceptually illustrated having a microdisplay panel 2101, a spatially varying NA component 2102, and microdisplay optics 2103, in accordance with an embodiment of the present invention. As shown, microdisplay optics 2103 receives light 2104 from an illumination source (not shown) and deflects the light onto the microdisplay in a direction indicated by ray 2105. Light reflected from the microdisplay is indicated by diverging ray pairs 2106-2108, where the numerical aperture ("NA") angle varies along the X-axis. In the illustrative embodiment, the spatially varying NA component is disposed between the microdisplay optics and the microdisplay. In other embodiments, the spatially varying NA component is disposed adjacent to the output surface of the microdisplay optics. Figure 22 Such an embodiment is conceptually illustrated, shown by a spatially varying NA component 2200.

[0124] In many embodiments, the microdisplay is a reflective device. In some embodiments, the microdisplay is a transmissive device, typically a transmissive LCoS device. Figure 23 Conceptually illustrated is an IIN 2300 according to an embodiment of the present invention including a backlight 2301, a microdisplay 2302, and a variable NA component 2303. Light from the backlight, indicated by rays 2304-2306, which have generally uniform NA across the backlight, illuminates the back of the microdisplay and, after propagating through the variable NA component, is converted into output image modulated light, indicated by diverging ray pairs 2307-2309, where the NA angle varies along the X-axis.

[0125] In many embodiments, the principles of the present invention can be applied to emissive displays.Examples of emissive displays for use with the present invention include emissive displays based on LED arrays and light emitting polymer arrays. Figure 24Conceptually illustrated is an IIN 2400 in accordance with an embodiment of the present invention having an emissive microdisplay 2401 and a spatially varying NA component 2402. Light from the microdisplay, indicated by rays 2403-2405, which generally have a uniform NA across the emitting surface of the display, illuminates the spatially varying NA component and is converted into output image modulated light, indicated by diverging ray pairs 2406-2408, having a varying NA angle along the X-axis.

[0126] In many embodiments, the microdisplay optics include a polarizing beam splitter block. In some embodiments, the microdisplay optics include a tilted plate to which a beam splitter coating has been applied. In many embodiments, the microdisplay optics include a waveguide device including an SBG that functions as a polarization-selective beam splitter. Details related to such embodiments are discussed in U.S. Patent Application No. 13 / 869,866, entitled "Holographic Wide Angle Display," and U.S. Patent Application No. 13 / 844,456, entitled "Transparent Waveguide Display," the disclosures of which are incorporated herein in their entireties. In several embodiments, the microdisplay optics include at least one of a refractive component and a curved reflective surface or a diffractive optical element for controlling the numerical aperture of the illumination light. In some embodiments, the microdisplay optics include a spectral filter for controlling the wavelength characteristics of the illumination light. In many embodiments, the microdisplay optics include apertures, masks, filters, and coatings for controlling stray light. In many embodiments, the microdisplay optics incorporate birdbath optics.

[0127] Although Figure 14-Figure 24 While specific waveguide displays and structures have been described, any waveguide display system and configuration can be used appropriately, depending on the specific requirements of a given application. At its core, a waveguide simply manipulates the direction of light. This property can be exploited in a variety of different systems. Figure 25 An example of a general system that can utilize waveguides is shown in . Figure 25A system diagram conceptually illustrates components for a waveguide display according to various embodiments of the present invention. As shown, system 2500 utilizes a light source 2501 that can output light into a waveguide 2502. The light source used can be a variety of different systems. In some embodiments, light source 2501 is from a projector. In many embodiments, light source 2501 also includes a microdisplay panel and the optical components required to illuminate the display panel. In further embodiments, light source 2501 includes a collimator and other optical components to manipulate the light into a desired form before entering the waveguide. In other embodiments, light source 2501 is natural light. Once light source 2501 outputs light into waveguide 2502, waveguide 2502 can manipulate and redirect the light in a desired manner into and out of a receiver 2503. The waveguide can be any general waveguide known in the art and / or one of the waveguides described above. The receiver can be any of a number of components capable of receiving light from a waveguide. In many embodiments, receiver 2503 is the user's eye(s). In some embodiments, receiver 2503 is another waveguide. In several embodiments, receiver 2503 is a display capable of displaying light from waveguide 2502. In further embodiments, the display is a simple glass that reflects light onto another receiver. System 2500 may optionally include a switch device 2504 and electrical components for use with the SBG. In many embodiments, switch device 2504 may optionally receive data from the light source in order to apply voltage to turn the SBG to the ON position at the appropriate time.

[0128] Waveguide exposure process and mastering system

[0129] Apart from Figures 4A-4D In addition to the exposure schemes described in

[15] for recording both transmissive and reflective waveguides, a number of mastering techniques can be used to perform such recording and form various waveguide structures and gratings. In various embodiments, the mastering system includes the use of amplitude gratings ("AG"). Such gratings can be used to form various types of gratings with different configurations. In many embodiments, amplitude master gratings are used to form RKV gratings within waveguides. In further embodiments, the amplitude gratings contain a linear variation of the grating period, known as chirp. Chirped gratings can be utilized in many different ways. Figure 26The exposure process using a chirped amplitude grating according to an embodiment of the present invention is conceptually illustrated. As shown, the process includes using an input beam 2600 that interacts with a focusing element 2601 to provide 1D focusing. The zero-order input beam 2602 can be directed toward the chirped AG 2603, thereby providing a diffraction profile with a linear variation. The two beams can then be combined to form a desired interference pattern to expose the waveguide substrate 2604. As shown, the separation distance from the exposure plane and the start of the diffracted beam(s) can be critical. In the illustrative embodiment, a transparent spacer 2605 is used to control the separation distance.

[0130] In many embodiments, a single beam exposure system can be used in conjunction with amplitude grating to form a grating within a waveguide. Figure 5 One such embodiment is conceptually illustrated. In a mode close to contact replication, the use of a single beam can be viewed as a hybrid between direct contact replication and separate two-beam contact replication - i.e., hybrid contact replication. This approach can be useful in cases where direct contact replication is not possible, such as where the separation distance from the master plane to the exposure plane is not negligible. In such cases, the separation distance can be critical. For example, during exposure of an RKV grating, the separation distance can be important and should be taken into account in order to maintain the surface projected fringe period across the RKV grating (without which it would be impossible to maintain full waveguide path reciprocity). In several embodiments, a single plane wavefront input beam can be configured to interact with a cylindrical lens to provide 1D focusing. In further embodiments, at least a portion of the light can generate a diffraction beam by interaction with the chirped master, and another portion can pass through as zero order (with attenuation), thereby maintaining the original 1D focusing function of the cylindrical lens.

[0131] In many embodiments, the master can be designed to incorporate more than one amplitude grating. By combining multiple amplitude gratings in a single master, alignment errors can be reduced compared to systems that utilize separate masters for each grating. In some embodiments, the master system includes a master with three amplitude gratings. In several embodiments, the master can be developed to incorporate RKV functionality in the simultaneous exposure of three patterns written in a single plate. The input master grating and / or the output master grating can be chirped gratings, with additional gratings as needed in the zero-order region that does not overlap with the chip.

[0132] In many embodiments, mastering a multi-grating element within a waveguide structure can involve the use of multiple exposures. In such embodiments, a multi-step process can be used in which different regions corresponding to different grating elements of a contact replica element are exposed. In many such embodiments, the process can include sequentially exposing the contact replica. For example, the process can include first exposing the output grating region (e.g., using only a portion of a large-area O / P master or multi-grating master), and then performing multiple exposures to form the folded grating region.

[0133] A master incorporating more than one amplitude grating can also be used to expose more than one grating simultaneously. In such a system, a collimated or coherent incident beam is typically focused through the master AG via optics and brought to the desired area of the contact replica through a suitable transparent substrate material. Figure 27A and Figure 27B An exposure process for simultaneously forming three gratings in accordance with an embodiment of the present invention is conceptually illustrated. As shown, in many such embodiments, optics are used to simultaneously direct collimated light onto the desired grating regions to achieve the formation of multiple gratings (e.g., input, output, and fold) in a single exposure. In an illustrative embodiment, the process includes the use of a master 2700 containing the gratings, a glass plate 2701 for adjusting the separation distance, and a contact replica substrate 2702 as the material in which the gratings are recorded. The process utilizes a collimated beam 2703 directed at three mirrors 2704-2706, which redirect the beam 2703 toward the master grating 2700. Once the beam 2703 is incident on the master grating 2700, a process similar to the process of FIG. 2 can occur. Figure 5 , three different gratings are simultaneously formed on contact replica 2702 using the exposure / curing process described in

[0015] . In many embodiments, a 3:1 mastering process can be utilized to fabricate a holographic waveguide having an input grating, a folded grating, and an output grating in a single exposure. In various such embodiments, the input grating, the folded grating, and / or the output grating are RKV gratings. In many embodiments, the folded grating can be divided into a plurality of regions. While any number of regions can be utilized depending on the requirements of a particular application, in some embodiments of the present invention, the folded grating can be divided into five regions.

[0134] Although Figure 27A and Figure 27B A specific number and arrangement of gratings to be formed is shown, but it will be understood that any number and arrangement of such gratings may be provided. Similarly, any number and arrangement of illumination beams may be provided. For example, Figure 28 As shown in , where a three color waveguide is required, the beams can be optically arranged to allow beams for the red 2800, green 2801 and blue 2802 channels to be incident on the contact replica area through the master. Figure 27A 、 Figure 27B and Figure 28 Conceptual diagrams of master systems and arrangements are shown, but it will be understood that these conceptual elements can take the form of any suitable optical frames, removable adapters, exposure plates, etc. required to allow for fixation of optical elements relative to the master and contact replica areas.

[0135] As previously mentioned, the holographic waveguide implemented in conjunction with the master and manufacturing embodiments can be a single piece and / or a stack of waveguides, depending on the requirements of the specific application of the embodiments of the present invention. For example, the holographic waveguide can include three layers, one for each of red, blue, and green. Figure 13 A conceptual illustration of a holographic waveguide having three layers is shown and discussed.

[0136] In a typical RKV grating, the grating vector rolls in the same plane as the incident plane of the beam. In a folded grating, the grating vector can roll perpendicular to the incident plane of the beam. Now go to Figures 29A-29C , shows a conceptual illustration of various methods for generating RKV gratings according to many embodiments of the present invention. Many embodiments include a stepped folded RKV, where the angle in each section changes perpendicular to the K vector direction, such as Figure 29B and Figure 29C As shown in . The cross-term MUX limitation can be overcome by scanning a beam with a single input angle close to the input angle at any single moment in time. Several embodiments include a scanned RKV fold grating, where the scanned beam exposes the RKV at different angles in discrete steps across the aperture of a planar fold master grating to generate a stepped master. As previously discussed, in many embodiments, only a single input beam angle is used to illuminate the fold master at any given moment in time.

[0137] In addition to the above discussion, Figure 30A As shown in , the mastering system according to many embodiments of the present invention can employ chirped gratings for various other purposes. These chirped gratings can help correct for misalignment of the incident beam at the exposure plane and correct for differences between the master and the fabricated holographic waveguide. For example, holographic waveguides are typically within waveguide cells of finite thickness, while the master typically has a thin protective coating to prevent damage to the chrome. Chirped gratings can be used to compensate for these additional layers. Any of a variety of protective coatings, such as glass and SiO2 protective layers, can be utilized as appropriate to meet the requirements of the specific application of embodiments of the present invention.

[0138] exist Figure 30BA conceptual diagram of a double-chirped grating master according to an embodiment of the present invention is shown in Figure 2. The 3:1 double-chirped grating provides various advantages over prior art manufacturing techniques. The RKV can significantly improve the efficiency and uniformity of the holographic waveguide. The RKV input can provide more input coupling to the waveguide, while the RKV output can provide better pupil formation, allowing improved brightness. As discussed above, allowing simultaneous exposure of the RKV input and output gratings (and folds) can reduce the overall manufacturing / process time. In many embodiments, the two gratings share the same spacer and / or optical density between the master and the holographic waveguide, so the RKV distribution and spacer window can be configured to be balanced.

[0139] Various mastering systems according to embodiments of the present invention utilize a zero-order grating. The zero-order grating can be used to control the transmittance of the zero-order beam so that it approaches the transmittance of the chirped grating, allowing for a continuous beam ratio. This prevents discontinuities in the exposure (and therefore the diffraction efficiency in the replicated grating portion). Figure 31 A conceptual diagram of a master system utilizing a zero-order grating in conjunction with a chirped grating according to an embodiment of the present invention is shown in FIG. In various embodiments, the zero-order grating has no diffraction orders or the diffraction orders do not interfere with the system. The orientation of the master and / or the energy beam can be used to control the direction of the unwanted diffraction beam, but then the relative polarization of the grating and the zero-order beam needs to be considered. To eliminate diffraction, in various embodiments, the period of the grating can be less than the limit at which evanescent diffraction waves are obtained. In various embodiments, using a master grating with a similar transmittance and / or period as the chirped grating at the boundary allows for the creation of a seamless replica in the liquid crystal substrate.

[0140] In many embodiments, the mastering system utilizes a reference grating to align the lens position to obtain the exact grating period. Figure 32 A conceptual diagram of such a system is provided in , showing the relationship between the input chirp (K 11 ) and level 0 plane (K 12 ) grating, output chirp (K 32 ) and 0-level plane grating (K 32 ) and the reference grating K of the folded grating (K2) 13 (input) and K 33(output). The reference grating can help improve the 3:1 construction by allowing simultaneous exposure of the input grating, folded grating and output grating, which reduces the overall manufacturing time, provides high accuracy: the accuracy of the grating alignment is given by the master, which can be accurate to 0.1nm, and provides a compact design that is attractive for larger volume production. In several embodiments, the energy beam is collimated. To ensure that a collimated input beam or RKV grating is used for generation, reverse ray tracing can be employed by tracing the rays from the holographic waveguide to the ideal configuration of the lens, modifying the window thickness is used to change the focus of the beam relative to the holographic plane, and offsetting the lens can achieve a collimated beam output from the master to the liquid crystal substrate.

[0141] In some embodiments, the mastering system avoids generating beams of other orders and / or avoids interfering with the energy beam focused on the liquid crystal substrate, such as Figure 33 To prevent the beam of the unwanted order from hitting the grating area, the window thickness can be adjusted, the glass can be modified, the RKV distribution can be changed, the lens can be changed and / or the incident beam angle can be changed, and / or a low refractive index material can be used to cause the unwanted order to be totally reflected by the low refractive index material.

[0142] In many embodiments, the master system utilizes one or more diffraction devices, where the same position in the master is required to generate two different refracted beams, which is not possible unless they are different diffraction orders. To simplify manufacturing, the master is arranged in a configuration where there is no crossing of the diffracted beams. In various embodiments, the master is placed as close to the liquid crystal substrate as possible. In several embodiments, the master is placed far enough away from the end of the crossing, but this can cause a large separation between the 0th order and the diffracted beam. When the master is placed too far away, crossing of the diffracted beams can occur (see, for example, Figure 34 ). When the master is placed too close, unwanted diffraction orders may hit the liquid crystal substrate. Therefore, the master system according to an embodiment of the present invention limits the distance from the liquid crystal substrate to the master plate to a certain range. To increase this range, high refractive index glass can be used to reduce the light angle so that the diffracted beams cross over a longer distance. In addition, short wavelength exposure can also reduce the light angle, which also helps. In many embodiments where high refractive index plates are used in the master stack, Fresnel reflections need to be managed; especially for the high refractive index plates between the master and the replica plane.

[0143] Principle of Equivalence

[0144] Although specific systems and methods have been discussed above, many different embodiments can be implemented according to the present invention. Therefore, it is to be understood that, without departing from the scope and spirit of the present invention, the present invention can be practiced in a manner different from that specifically described. Thus, the embodiments of the present invention should be considered to be illustrative and not restrictive in all aspects. Accordingly, the scope of the present invention should not be determined by the embodiments shown, but should be determined by the appended claims and their equivalents. Although specific embodiments have been described in detail in this disclosure, many modifications are possible (for example, changes in the size, dimensions, structure, shape and proportion of various elements, the value of parameters, installation arrangements, use of materials, color, orientation, etc.). For example, the position of the elements can be reversed or changed in other ways, and the nature or quantity or position of the discrete elements can be changed or changed. Accordingly, all such modifications are intended to be included within the scope of this 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 this disclosure, other replacements, modifications, changes and omissions can be made in the design, operating conditions and arrangement of the exemplary embodiments.

Claims

1. A method for recording a hologram, the method comprising: providing a waveguide unit comprising a polymer dispersed liquid crystal mixture layer sandwiched between two substrates; Provide master grating; as well as scanning at least one recording beam across the master grating, wherein the scanned recording beam exposes the polymer dispersed liquid crystal mixture layer in the waveguide unit in discrete steps across the aperture of the master grating, and wherein each discrete step corresponds to a different scanned recording beam angle, wherein, after interacting with the master grating, a portion of at least one scanned recording beam is diffracted towards the waveguide unit, wherein another portion of the at least one scanned recording beam propagates toward the waveguide unit as zero-order light, wherein the diffracted light interferes with the zero-order light to record a rolling K-vector grating in the waveguide unit, and Each interfering diffracted light has a diffracted light direction, and the zero-order light has a zero-order light direction corresponding to a unique K vector.

2. The method of claim 1, wherein the master grating comprises an amplitude grating.

3. The method according to claim 2, wherein: The diffracted light of the at least one recording beam passes through a transparent spacer and travels toward the waveguide unit.

4. The method according to claim 1, wherein The master grating has a linear variation in the grating period.

5. The method according to claim 1, wherein The scrolling K-vector grating includes a multiplexed grating.

6. The method of claim 1, wherein: The master grating comprises three separate gratings.

7. The method according to claim 6, wherein: The three separate gratings are designed to record the input grating, the fold grating and the output grating.

8. The method of claim 1, wherein: The grating vectors in the rolling K-vector grating roll in a plane perpendicular to the incident plane of the diffracted light and the zero-order light.

9. The method of claim 1, wherein: The master grating is a planar grating.

10. The method of claim 1, wherein: The recorded grating is folded.

11. The method of claim 1, wherein: The scrolled K-vector grating has a constant spatial grating pitch.

12. A system for recording a holographic grating, the system comprising: a waveguide unit comprising a polymer dispersed liquid crystal mixture layer sandwiched between two substrates; Master grating; a beam scanner configured to raster scan at least one scanned recording beam across the master, wherein the scanned recording beam is configured to expose the polymer dispersed liquid crystal mixture layer in the waveguide unit in discrete steps across the aperture of the master grating, wherein each step corresponds to a different scanned recording beam angle, wherein, after interacting with the master grating, a portion of the at least one scanned recording beam is diffracted towards the waveguide unit, wherein another portion of the at least one scanned recording beam propagates toward the waveguide unit as zero-order light, wherein the diffracted light and the zero-order light interfere to record a rolling K-vector grating in the waveguide unit, and Each interfering diffracted light has a diffracted light direction, and the zero-order light has a zero-order light direction corresponding to a unique K vector.

13. The system of claim 12, wherein: The master grating includes an amplitude grating.

14. The system of claim 13, further comprising a transparent spacer block, wherein the diffracted portion of the at least one recording beam travels through the transparent spacer block.

15. The system of claim 12, wherein: The scrolling K-vector grating includes a multiplexed grating.

16. The system of claim 12, wherein: The master grating comprises three separate gratings.

17. The system of claim 16, wherein: The three separate gratings are designed to record the input grating, the fold grating and the output grating.

18. The system of claim 16, wherein: The grating vectors of the rolling K-vector grating roll in a plane perpendicular to the incident plane of the diffracted light and the zero-order light.

19. The system of claim 18, wherein the master grating is a planar grating.

20. The system of claim 12, wherein: The recorded grating is folded.

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