Method for processing an optical waveguide

Abstract

To provide mastering systems and methods for fabricating waveguides, and waveguide devices using such mastering systems.SOLUTION: A mastering system for fabricating holographic waveguides may employ a step of using a master to control application of energy (e.g., laser, light, or magnetic beam) onto a liquid crystal substrate to fabricate a holographic waveguide into the liquid crystal substrate. Mastering systems for fabricating holographic waveguides according to embodiments of the present invention may include a variety of features.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention generally relates to a method for manufacturing a waveguide, and more specifically, to a method for a waveguide display.

Background Art

[0002] A waveguide can be referred to as a structure with the ability to confine and guide waves (i.e., limit the spatial region in which waves can propagate). One subclass includes optical waveguides, which are structures that can guide electromagnetic waves, typically those in the visible spectrum. Waveguide structures can be designed to control the propagation path of waves using several different mechanisms. For example, a planar waveguide can be designed to utilize a diffraction grating to diffract incident light and couple it into the waveguide structure, and thus the internally coupled light can continue to propagate within the planar structure via total internal reflection ("TIR").

[0003] The processing of waveguides can include the use of material systems that enable the recording of holographic optical elements within the waveguide. One class of such materials includes polymer dispersed liquid crystal ("PDLC") mixtures, which are mixtures containing a photopolymerizable monomer and a liquid crystal. A further subclass of such mixtures includes holographic polymer dispersed liquid crystal ("HPDLC") mixtures. Holographic optical elements such as volume phase gratings can be recorded in such liquid mixtures by irradiating the material with two mutually coherent laser beams. During the recording process, the monomer polymerizes and the mixture undergoes photoinduced phase separation, creating regions rich in liquid crystal microdroplets interspersed with regions of clear polymer. The alternating regions rich in liquid crystal and depleted in liquid crystal form the fringe planes of the grating.

[0004] The waveguide optical systems such as those described above can be considered for various display and sensor applications. In many applications, waveguides containing one or more grating layers encoding multiple optical functions are realized using various waveguide architectures and material systems, enabling new innovations in eyepiece displays for augmented reality ("AR") and virtual reality ("VR"), compact head-up displays ("HUD") for aviation and road traffic, and sensors for biometric and lidar ("LIDAR") applications. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0005] 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, and emitting at least one recording beam towards the master grating, wherein, in response to the interaction with the master grating, a portion of the at least one recording beam is diffracted towards the waveguide cell, and recording at least one volume grating in the waveguide cell using interference exposure formed from at least the diffracted portion of the at least one recording beam.

[0006] Again, a further embodiment includes a system for recording a holographic grating, the system comprising a waveguide cell comprising a layer of a polymer-dispersed liquid crystal mixture sandwiched between two substrates, a master grating, and a light source configured to emit at least one recording beam towards the master grating, wherein, in response to the interaction with the master grating, a portion of the at least one recording beam is diffracted towards the waveguide cell, and at least one volume grating is recorded in the waveguide cell through interference exposure formed from at least the diffracted portion of the at least one recording beam.

[0007] In another embodiment, the master grating includes an amplitude grating.

[0008] In a further embodiment, the master lattice includes a chirped lattice.

[0009] In yet another embodiment, the recorded volume lattice contains a rolled K-vector.

[0010] In still further embodiments, the recorded volume lattice contains a multiplexed lattice.

[0011] In another embodiment, the master lattice includes three separate lattices.

[0012] In still further embodiments, the three separate lattices are designed to record an input lattice, a folded lattice, and an output lattice.

[0013] In another additional embodiment, at least one volume lattice includes three volume lattices.

[0014] In a further additional embodiment, at least one recording beam includes three recording beams.

[0015] Again, in another embodiment, the interference exposure is formed from the zero-order beam and the diffracted portions of only one recording beam.

[0016] Additional embodiments and features are described in part in the following description and will be in part apparent to those skilled in the art in light of the discussion herein, or may be learned by practice of the invention. A further understanding of the nature and advantages of the present invention can be realized by reference to the remaining portions of this specification and the drawings which form a part of this disclosure.

[0017] The description is presented as an illustration of exemplary embodiments of the invention and should not be construed as an exhaustive listing of the scope of the invention. It will be more fully understood with reference to the following figures and data graphs. It will be apparent to those skilled in the art that the invention can be practiced using some or all of what is disclosed in the following description.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0019] For the purpose of describing the embodiments, some well-known features of optical technologies known to those skilled in the art of optical design and visual displays are omitted or simplified so as not to obscure the basic principles of the present invention. Unless otherwise specified, the term "on-axis" related to the direction of a ray or beam refers to propagation parallel to the axis normal to the surface of an optical component described in connection with the present invention. In the following description, the terms light, ray, beam, and direction are used synonymously and in relation to each other, and may indicate the direction of propagation of electromagnetic radiation along a straight-line trajectory. The terms light and illumination may be used in relation to the visible and infrared bands of the electromagnetic spectrum. Some of the following description will be presented using terminology commonly employed by those skilled in the art of optical design. As used herein, the term grating may, in some embodiments, include a grating consisting of a set of gratings. For illustrative purposes, it should be understood that the drawings are not drawn to scale unless otherwise specified.

[0020] Turning now to the drawings, a mastering system and method for fabricating a waveguide and a waveguide device using such a mastering system are described. A mastering system for fabricating a holographic waveguide can include using a mask to control the application of energy (e.g., a laser, light, or magnetic beam) onto a liquid crystal substrate and fabricating a holographic waveguide within the liquid crystal substrate. After fabrication, the final holographic waveguide can be incorporated into various display systems. These mastering systems can 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 reduce the wavefront errors found in two-beam systems caused by the different paths of the two beams. Thus, a single energy beam process can be compatible with high-volume manufacturing processes where thermal and vibration considerations can introduce various problems when aligning multiple energy beams. A mastering system for fabricating a holographic waveguide according to embodiments of the present invention can include various features. These features include, but are not limited to, a chirp related to a single input beam copy (near-field, i.e., hybrid contact copy), a double chirp grating (for input and output), a zero-order grating for transmittance control, an alignment reference grating, a 3:1 structure, a position adjustment turret to enable rapid alignment, a simultaneous optimization of lens and window thicknesses related to a plurality of roll axis rotation K-vector gratings, and avoidance of other orders and crossovers of diffracted beams. The waveguide structure, mastering system, and exposure process are described in further detail in the following sections. Waveguide Structure

[0021] Waveguide structures according to various embodiments can be implemented in many different ways. In many embodiments, the waveguide structure is designed to be an optical waveguide, which is a structure that can confine and guide electromagnetic waves or light within the visible spectrum. These optical waveguides can be implemented for use in several different applications, including but not limited to helmet-mounted displays, head-mounted displays ("HMDs"), and HUDs. The term HUD is typically utilized 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 the given application.

[0022] Optical waveguides according to various embodiments can be designed to manipulate light waves in a controlled manner using various methods and waveguide optics. For example, an optical waveguide can be implemented using a material with a higher refractive index than the surrounding environment to limit the area through which light can propagate. Light coupled into an optical waveguide made of such a material at a certain angle can be confined within the waveguide via total internal reflection. In a planar waveguide, the angle at which total internal reflection occurs can be given by Snell's law, which can determine whether light is refracted or completely reflected at the surface boundary.

[0023] In many embodiments, a waveguide incorporating a Bragg grating is implemented for HUD applications. The HUD can be incorporated in any of a variety of applications, including (but not limited to) eyepiece applications. A HUD utilizing a planar waveguide incorporating a Bragg grating, according to various embodiments of the present invention, can achieve a significantly wider field of view and have lower volume requirements than a HUD implemented using conventional optical components. In some embodiments, the HUD includes at least one waveguide incorporating several gratings. In further embodiments, the waveguide can incorporate at least three Bragg gratings, which can be implemented to provide various optical functions such as (but not limited to) biaxial beam expansion. For example, in some embodiments, the waveguide incorporates an input grating, a folding grating, and an output grating. A HUD utilizing a waveguide can be implemented using various numbers of waveguides. In many embodiments, the HUD is implemented using a single waveguide. In other embodiments, the HUD is implemented using a stack of waveguides. Multiple waveguides can be stacked and implemented to provide different optical functions such as (but not limited to) implementing a color display. In some embodiments, the HUD incorporates three separate waveguides, i.e., one waveguide for each of the red, green, and blue channels.

[0024] 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 having the same surface pitch size but different grating tilt angles can increase the overall coupled internal angle bandwidth of the waveguide. In some embodiments, one or more of the gratings within the waveguide incorporate a roll-axis rotation K-vector and / or tilt angle that varies across the grating 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 fringe, which can determine the optical efficiency for a given range of input and diffraction angles. By incorporating a grating with a roll-axis rotation K-vector (“RKV”), the grating can be designed to vary the diffraction efficiency in a manner that achieves desirable characteristics across the eye box of the HUD display. Other aspects regarding the configuration of the grating fringe (such as RKV) and the structure and implementation of the waveguide for use in a HUD are discussed in further detail below. Diffraction grating

[0025] An optical waveguide can incorporate different optical elements to manipulate the propagation of light waves. As can be readily understood, the type of grating selected can depend on the specific requirements of a given application. The optical structures recorded in the waveguide can include many different types of optical elements, such as, but not limited to, diffraction gratings. In many embodiments, the grating implemented is a Bragg grating (also referred to as a volume grating). A Bragg grating can have high efficiency such that most light is not diffracted to higher orders. The relative amount of light at the diffracted zero order can be varied by controlling the refractive index modulation of the grating, i.e., the property used to create a lossy waveguide grating for extracting light over a large pupil. By strategically placing a volume Bragg grating within the waveguide, the propagation of light within the waveguide can be affected in a controlled manner to achieve various effects. The diffraction of light incident on the grating can be determined by the properties of the light and the grating. As can be readily understood, volume Bragg gratings can be constructed to have different properties depending on the specific requirements of a given application. In some embodiments, the volume Bragg grating is designed to be a transmission grating. In other embodiments, the volume Bragg grating is designed to be a reflection grating. For a transmission grating, incident light that satisfies the Bragg condition is diffracted such that the diffracted light exits from the grating on the side where the incident light did not enter. For a reflection grating, the diffracted light exits from the same side of the grating as the side where the incident light entered.

[0026] Figures 1A and 1B conceptually illustrate two volume Bragg grating configurations according to various embodiments of the present invention. Depending on the side from which the light beam exits after diffraction, the grating can be classified as either a reflection grating 100 or a transmission grating 150. The conditions for refraction / reflection, or Bragg conditions, can depend on several factors, including, 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 shows a reflection grating 100 recorded in a transparent material. As shown, light beams 101, 102, having different wavelengths, are incident on the reflection grating 100 at the same angle and having fringes 103 parallel to the grating surface. Light beam 101 does not satisfy the Bragg condition and is transmitted through the grating. On the other hand, light beam 102 satisfies the Bragg condition and is reflected back through the same surface on which it is incident. Another type of grating is a transmission grating, which is conceptually illustrated in Figure 1B. In an illustrative embodiment, the transmission grating 150 has fringes 151 perpendicular to the grating surface. As shown, light beams 152, 153 with different wavelengths are incident on the transmission grating 150 at the same angle. Light beam 152 satisfies the Bragg condition, is refracted, and exits from the opposite side of the grating on which the light beam 152 is incident. Light beam 153 does not satisfy the Bragg condition and is transmitted through its original propagation path. Depending on the efficiency of the grating, the light can be partially reflected or refracted. Figures 1A and 1B illustrate specific volume grating structures, but any type of grating structure can be recorded in a waveguide cell according to various embodiments of the present invention. For example, the volume grating can be implemented with fringes that are graded and / or tilted with respect to the grating surface, which can affect the angle of diffraction / reflection. The above discussion represents the grating structure as either transmission or reflection, but both types of gratings behave in the same manner according to the standard grating equation.

[0027] The waveguide structures according to various embodiments of the present invention can implement gratings in several different ways. In addition to volume gratings, the gratings can be implemented as surface relief gratings. As the name indicates, a surface relief grating can be implemented by physically forming grooves or a periodic pattern on the surface of a substrate. The periodicity and angles formed by the grooves can determine the efficiency and other characteristics of the grating. Among other methods, but not limited to, any of several methods such as etching and photolithography can be used to form these grooves.

[0028] FIG. 2 conceptually illustrates a surface relief grating according to an embodiment of the present invention. As shown, the surface relief grating 200 contains periodic tilted grooves 201. When light is incident on the grooves 201, diffraction can occur under certain conditions. The tilt and periodicity of the grooves 201 can be designed to achieve a targeted diffraction behavior of the incident light.

[0029] FIGS. 1A-1B and 2 show specific grating structures, but it is readily understandable that the grating structures can be configured in several different ways depending on the specific requirements of a given application. Examples of such configurations are discussed in more detail in the following section. Switchable Bragg gratings

[0030] One class of gratings used in holographic waveguide devices is the switchable Bragg grating (“SBG”). The SBG can be fabricated by first placing a thin film of a mixture of a photopolymerizable monomer and a liquid crystal material between glass plates or substrates. In many cases, the glass plates are in a parallel configuration. One or both of the glass plates can support electrodes, typically transparent indium tin oxide films, for applying an electric field across the film. The grating structure within the SBG can be recorded in a liquid material (often referred to as a syrup) through photo-polymerization induced phase separation using interference exposure with spatially periodic intensity modulation. Factors such as, but not limited to, control of the irradiation intensity, volume fraction of the components of the materials in the mixture, and exposure temperature can determine the resulting grating morphology and performance. As can be readily understood, a wide variety of materials and mixtures can be used depending on the specific requirements of a given application. In many embodiments, HPDLC materials are used. During the recording process, the monomer polymerizes and the mixture undergoes phase separation. The LC molecules aggregate to form discrete or coalesced liquid droplets that are periodically dispersed within the polymer network on the scale of the optical wavelength. Alternating regions rich in liquid crystal and regions depleted of liquid crystal form the grating fringe planes, which can produce Bragg diffraction with a strong optical polarization resulting from the orientation order of the LC molecules in the droplets.

[0031] The resulting volume phase grating can exhibit very high diffraction efficiency, which can be controlled by the magnitude of the electric field applied across the film. When an electric field is applied to the grating through the transparent electrodes, the natural orientation of the LC droplets changes, reducing the refractive index modulation of the fringes and lowering the hologram diffraction efficiency to a very low level. Typically, the electrodes are configured such that the applied electric field will be perpendicular to the substrate. In some embodiments, the electrodes are fabricated from indium tin oxide (「ITO」). In the off state with no electric field applied, the extraordinary axis of the liquid crystal generally aligns normal to the fringes. The grating thus exhibits high refractive index modulation and high diffraction efficiency with respect to P-polarized light. When an electric field is applied to the HPDLC, the grating switches to the on state and the extraordinary axis of the liquid crystal molecules aligns parallel to the applied electric field and thus perpendicular to the substrate. In the on state, the grating exhibits lower refractive index modulation and lower diffraction efficiency with respect to both S- and P-polarized light. Thus, the grating region no longer diffracts light. Each grating region can be divided into a number of grating elements, such as a pixel matrix by the function of the HPDLC device, for example. Typically, the electrodes on one substrate surface are uniform and continuous, while the electrodes on the opposing substrate surface are patterned according to a number of selectively switchable grating elements.

[0032] Typically, the SBG element is switched clear at 30 μs, and the relaxation time for switching on is longer. It should be noted that the diffraction efficiency of this device can be adjusted using the applied voltage over a continuous range. In many cases, this device exhibits nearly 100% efficiency when no voltage is applied and essentially zero efficiency when a sufficiently high voltage is applied. In certain types of HPDLC devices, a magnetic field can be used to control the LC alignment. In some HPDLC applications, the phase separation of the LC material from the polymer can be carried out to such an extent that no recognizable droplet structure results. The SBG can also be used as a passive grating. In this mode, its main benefit is uniquely high refractive index modulation. The SBG can be used to provide a transmission or reflection grating for free-space applications. The SBG can be implemented as a waveguide device where the HPDLC forms either a waveguide core or an evanescent coupling layer adjacent to the waveguide. The glass plates used to form the HPDLC cell provide a total internal reflection ("TIR") light guiding structure. When a switchable grating diffracts light at an angle exceeding the TIR condition, the light can be coupled out from the SBG.

[0033] Figures 3A and 3B conceptually illustrate the switching properties of HPDLC SBG devices 300, 350 and the SBG according to various embodiments of the present invention. In Figure 3A, the SBG 300 is in the off state. As shown, the LC molecules 301 are aligned substantially normal to the fringe plane. Accordingly, the SBG 300 exhibits a high diffraction efficiency and the incident light can be easily diffracted. Figure 3B illustrates the SBG 350 in the on position. The applied voltage 351 aligns the optical axes of the LC molecules 352 within the droplet 353 to create an effective refractive index that matches the refractive index of the polymer, essentially creating a transparent cell where the incident light is not diffracted. In an illustrative embodiment, an AC voltage source is shown. As can be readily understood, various voltage sources can be utilized depending on the specific requirements of a given application.

[0034] In waveguide cell designs, in addition to the components described above, adhesives and spacers are placed between substrates to attach the layers of elements together and maintain the cell gap or thickness dimension. In these devices, the spacers can take many forms, including but not limited to materials, sizes, and geometries. The materials can include, for example, plastics (such as divinylbenzene), silica, and conductive spacers. They can take any suitable geometry, including but not limited to rods and spheres. The spacers can be of any suitable size. In many cases, the size of the spacers ranges from 1 to 30 μm. The use of these adhesive materials and spacers may be necessary in LC cells using conventional materials and manufacturing methods, but they can contribute to cell clouding that degrades the optical properties and performance of the waveguides and devices. HPDLC material system

[0035] HPDLC mixtures according to various embodiments of the present invention generally include an LC, a monomer, a photoinitiator dye, and a co-initiator. The mixture (often referred to as a syrup) also frequently includes a surfactant. For the purpose of explaining the present invention, a surfactant is defined as any chemical that reduces the surface tension of the entire liquid mixture. The use of surfactants in PDLC mixtures is known and dates back to the earliest investigations of PDLCs. For example, the paper by R.L Sutherland et al., SPIE Vol. 2689, 158 - 169, 1996 (the disclosure of which is incorporated herein by reference) describes a PDLC mixture including a monomer, a photoinitiator, a co-initiator, a chain extender, and an LC into which a surfactant can be added. Surfactants are also mentioned in the paper by Natarajan et al., Journal of Nonlinear Optical Physics and Materials, Vol. 5 No. 1 89 - 98, 1996 (the disclosure of which is incorporated herein by reference). Further, U.S. Patent No. 7,018,563 by Sutherland et al. discusses a polymer-dispersed liquid crystal material for forming a polymer-dispersed liquid crystal optical element including at least one acrylic acid 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.

[0036] Patents and scientific literature contain many examples of material systems and processes that can be used to fabricate SBG, including investigations into formulating such material systems to achieve high diffraction efficiency, rapid response times, low drive voltages, etc. Both U.S. Patent No. 5,942,157 by Sutherland and U.S. Patent No. 5,751,452 by Tanaka et al. describe monomer and liquid crystal material combinations suitable for fabricating SBG devices. Examples of recipes can also be found in papers dating back to the early 1990s. Many of these materials use acrylate monomers, including: · R. L. Sutherland et al., Chem. Mater. 5, 1533 (1993) (the disclosure of which is incorporated herein by reference) describes the use of acrylate polymers and surfactants. Specifically, the recipe includes a crosslinkable polyfunctional acrylate monomer, the chain extender N-vinylpyrrolidinone, LC E7, the photoinitiator rose bengal, and the co-initiator N-phenylglycine. The surfactant octanoic acid was added in one variation. · Fontecchio et al., SID 00 Digest 774-776, 2000 (the disclosure of which is incorporated herein by reference) describes a UV curable HPDLC for reflective display applications that includes polyfunctional acrylate monomers, LC, photoinitiators, co-initiators, and chain terminators. · Y.H. Cho, et al., Polymer International, 48, 1085-1090, 1999 (the disclosure of which is incorporated herein by reference) discloses an HPDLC recipe containing acrylate. · Karasawa et al., Japanese Journal of Applied Physics, Vol. 36, 6388-6392, 1997 (the disclosure of which is incorporated herein by reference) describes acrylates in various functional states.·T.J. Bunning et al., Polymer Science: Part B: Polymer Physics, Vol. 35, 2825-2833, 1997 (the disclosure of which is incorporated herein by reference) also describes multifunctional acrylate monomers. ·G.S. Iannacchione et al., Europhysics Letters Vol. 36 (6), 425-430, 1996 (the disclosure of which is incorporated herein by reference) describes a PDLC mixture comprising a pentaacrylate monomer, an LC, a chain extender, a co-initiator, and a photoinitiator.

[0037] Acrylates offer the benefits of rapid kinetics, good mixing with other materials, and compatibility with the film-forming process. Since acrylates are crosslinked, they tend to be mechanically robust and flexible. For example, functional 2 (di) and 3 (tri) urethane acrylates have been widely used with respect to HPDLC technology. Higher functionality materials such as penta and hexa functional stems have also been used.

[0038] One of the known attributes of transmissive SBGs is that LC molecules tend to align with the average direction normal to the lattice fringe plane (i.e., parallel to the lattice or K vector). The effect of LC molecule alignment is that transmissive SBGs efficiently diffract P-polarized light (i.e., light with a polarization vector in the plane of incidence), but have near-zero diffraction efficiency with respect to S-polarized light (i.e., light with a polarization vector normal to the plane of incidence). Recording mechanism for volume gratings

[0039] Volume gratings can be recorded within a waveguide cell using many different methods according to various embodiments of the present invention. Recording of optical elements within an optical recording material can be accomplished using any number and type of electromagnetic radiation source. Depending on the application, the exposure source and / or recording system can be configured to record the optical elements using various levels of exposure output and duration. As discussed above with respect to SBG, techniques for recording volume gratings can include exposure of an optical recording material using two mutually coherent laser beams, and the superposition of the two beams creates a periodic intensity distribution along the interference beam. The optical recording material can form a grating structure that exhibits a refractive index modulation pattern that matches the periodic intensity distribution. In an HPDLC mixture, the light intensity distribution results in diffusion and polymerization of the monomers into the high-intensity regions and simultaneous diffusion of the liquid crystal into the dark regions. This phase separation creates alternating liquid-crystal-rich regions and liquid-crystal-depleted regions that form the fringe planes of the grating. The grating structure can be formed with tilted or non-tilted fringes depending on how the recording beams are configured. FIGS. 4A-4D conceptually illustrate a two-beam recording process according to various embodiments of the present invention. As shown, two methods can be used to create two different types of Bragg gratings, namely, a transmission grating 400 and a reflection grating 401. Depending on how the two recording beams 402, 403 are positioned, the interference pattern 404 can record either a transmission or a reflection grating within the 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 reflection volume grating are typically substantially parallel to the surface of the substrate, and the fringes of a transmission grating are typically substantially perpendicular to the surface of the substrate). During playback, a beam 406 incident on the transmission grating 400 can result in a diffracted beam 407 that is transmitted. On the other hand, a beam 408 incident on the reflection grating 401 can result in a reflected beam 409.

[0040] Another method for recording a volume grating within an optical recording material involves the use of 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. Depending on the interaction with the master grating, the single beam can be diffracted. The first-order diffraction and the zero-order beam can overlap and create an interference pattern, which can then expose the optical recording material to form the desired volume grating. A single-beam recording process utilizing an amplitude grating, according to an embodiment of the present invention, is conceptually illustrated in FIG. 5. As shown, a beam 500 from a single laser source (not shown) is directed through an amplitude grating 501. Depending on the interaction with the grating 501, the beam 500 can be diffracted, for example, as in the case of the rays interacting with the black shaded regions of the amplitude grating, or the beam 500 can propagate through the amplitude grating with substantially no deviation as the zero-order beam, for example, as in the case of the rays interacting with the cross-hatched regions of the amplitude grating. The first-order diffracted beam 502 and the zero-order beam 503 can overlap and create an interference pattern that exposes the optical recording layer 504 of the waveguide cell. In an illustrative embodiment, a spacer block 505 is positioned between the grating 501 and the optical recording layer 504 to modify the distance between the two components.

[0041] Specific methods for recording volume gratings are discussed and shown in FIGS. 4A-4D and 5, but recording systems according to various embodiments of the present invention can be configured to implement any of several methods for recording volume gratings. Roll-axis Rotating K-Vector Gratings and Multiplexed K-Vector Gratings

[0042] When dealing with limited ranges of wavelength and angle (over which diffraction occurs in a volume Bragg grating), several methods can be utilized 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 some embodiments, the variations transverse to the roll axis rotation K vector are typically such that the direction of the change in the K vector is out of the plane of the waveguide or grating element. The varying fringes or roll axis rotation K vectors can be implemented in several different ways. In some embodiments, the fringes of the grating are designed to vary in a progressive manner across the grating. In other embodiments, different discrete sets of gratings with different fringes are installed in succession. Gratings with roll axis rotation K vectors can be designed and configured in various ways. In many embodiments, the roll axis rotation K vector is designed such that the peak diffraction efficiency of each grating section is optimized with respect to its corresponding output angle at that position. In some embodiments, the peak diffraction efficiency of each grating at different positions is offset from its corresponding output angle at that position. It has been shown that by introducing this offset, the eyebox uniformity can be improved. In some embodiments, the offset can improve the overall image brightness by a factor of two compared to only matching the peak diffraction efficiencies at different positions.

[0043] The roll-axis-rotated K-vector grating can be used to maximize the peak diffraction efficiency of the internal coupling light, according to certain embodiments of the present invention. The use of the roll-axis-rotated K-vector enables high-efficiency input coupling into the grating and also enables the beam divergence angle to be optimized to minimize the waveguide thickness, which may require balancing the waveguide thickness, the angular bandwidth of the grating, and the spread of the field of view angle at any given point on the grating. The low-angle response of the grating when the K-vector is roll-axis rotated (and the surface pitch is maintained) can prevent output coupling and enable the waveguide thickness to be minimized. In some embodiments, the design goal is to ensure maximum input coupling at a point and minimize angular diversity such that the grating thickness can be minimized without external coupling to each other at different points.

[0044] Figures 6A and 6B conceptually illustrate two implementations of a roll-axis-rotated K-vector grating according to various embodiments of the present invention. Referring first to FIG. 6A, in some embodiments, the roll-axis-rotated K-vector grating can be implemented as a waveguide section containing discrete grating elements 600 having different K-vectors. Referring next to FIG. 6B, in some embodiments, the roll-axis-rotated K-vector grating can be implemented as a waveguide section containing grating elements 601 in which the K-vector undergoes a smooth monotonic variation in direction. As shown, the change in the direction of the K-vector is out of the plane of the waveguide.

[0045] In many embodiments, different sets of discrete fringes are superimposed within the same lattice to create a multiplexed lattice with multiple essentially overlapping lattices within the same volume that function independently and without interfering with each other. For example, if two volume lattices are recorded within the same device for two different Bragg wavelengths at the same angle of incidence, the device can diffract two selected wavelengths into different output directions with limited crosstalk. Multiplexing can be used to generate an improved angular profile, extend the diffraction efficiency angular bandwidth, and provide better luminance uniformity and color balance across the exit pupil and field of view by combining two lattices of similar prescription. Multiplexing can also be used to encode two distinct diffraction prescriptions that are designed to project light into clearly different fields of a region or diffract light of two different wavelengths into a given field of view region. Measures can be taken to ensure that there is no competition between the lattices during recording that would lead to unequal diffraction efficiencies and crosstalk between the lattices during playback. Multiplexing can also provide a significant benefit in reducing the number of layers within a waveguide structure. In some embodiments, at least one of the input, folding, or output lattices can combine two or more angular diffraction prescriptions to expand the angular bandwidth. Similarly, in some embodiments, at least one of the input, folding, or output lattices can combine two or more spectral diffraction prescriptions to expand the spectral bandwidth. For example, a color multiplexing lattice may be used to diffract two or more of the primary colors.

[0046] FIG. 7 conceptually illustrates a multiplexed K-vector grating according to an embodiment of the present invention. As shown, the multiplexed grating 700 contains two sets of fringes 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 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 in different directions. During operation, both multiplexed gratings 701, 702 are active and can provide a wider incident and diffraction bandwidth. The angular bandwidth θ of the incident light with respect to the multiplexed grating i covers an angular range including overlapping θ i1 and θ i2 . The angular bandwidth θ of the diffraction with respect to the multiplexed gratings 701, 702 d covers an angular range including overlapping θ d1 and θ d2 . In some embodiments, more than two gratings are multiplexed.

[0047] Specific grating structures with varying fringes are discussed above, but any of several fringe configurations can be utilized according to the specific requirements of a given application. For example, any number of gratings can be multiplexed as enabled by manufacturing constraints. The roll-axis rotated K-vector grating can be designed to have a K-vector that is rotated about the roll axis in any discrete unit. A waveguide implementing pupil expansion

[0048] The gratings can be implemented in the waveguide in a variety of different ways. In some embodiments, the gratings are present on the outer surface of the waveguide. In other embodiments, a volume grating is implemented inside the waveguide. The gratings can also be implemented to perform different optical functions such as, but not limited to, coupling light, directing light, and preventing light transmission. FIG. 8 conceptually illustrates a waveguide that utilizes a coupling grating to diffract light both inside and outside the waveguide according to an embodiment of the present invention. As shown, the 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 is incident on 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 such that the refracted light 806 is incident on the second surface 802 at an angle at which total internal reflection can occur. Thus, the light 805 is coupled into the waveguide and confined within the first and second surfaces 801, 802 of the waveguide 800. In an illustrative embodiment, the light travels through the waveguide 800 until it interacts with the output grating 804, which refracts the light out of the waveguide 800 and couples it into the user's eye 807.

[0049] In many embodiments, the diffraction grating can be used to preserve the eye box size while reducing the lens size by effectively expanding the exit pupil of the collimating optical system. The exit pupil can be defined as a virtual aperture, and only the light rays passing through this virtual aperture can be incident on the user's eye. FIGS. 9 and 10 conceptually illustrate a waveguide that utilizes an output grating for exit pupil expansion in one dimension according to an embodiment of the present invention. The waveguide 900 in FIG. 9 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 by the input grating 902 and can propagate through the waveguide 900 via total internal reflection. In an illustrative embodiment, the output grating 904 is designed and expanded to refract a portion of the guided light. The light is refracted such that the refracted light 906 is incident on the second surface 902 at an angle at which total internal reflection does not occur, enabling the light 906 to be coupled out of the waveguide 900. This lossy extraction allows for exit pupil expansion because the remaining light can continue to propagate 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 expanded exit pupil can also be achieved with the correct design, as shown in FIG. 10.

[0050] Expanding on the concepts of FIGS. 9 and 10, the optical waveguide can be designed to expand the exit pupil in two dimensions. In many embodiments, two waveguides can be stacked together, and the light coupled into the waveguide stack can create a system capable of achieving exit pupil expansion in two dimensions. FIG. 11 conceptually illustrates a waveguide system that utilizes two planar waveguides to provide exit pupil expansion in two dimensions, according to an embodiment of the present invention. As shown, system 1100 includes a first waveguide 1101 and a second waveguide 1102. The first waveguide 1101 can include a first input coupling grating 1103 and a first output coupling grating 1104, and the second waveguide 1102 can include a second input coupling grating 1105 and a second output coupling grating 1106. The first input coupling grating 1103 can be designed to couple collimated light 1107 from image source 1108 into the first waveguide 1101. Similar to the systems described in FIGS. 9 and 10, the 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 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 that is expanded in a 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 expanded 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 light out of the second waveguide 1102. As a result, the exit pupil is expanded in two dimensions, enabling a smaller lens size relative to the eye box size 1109.

[0051] In many embodiments, the optical waveguide utilizes a folded grating, which can provide exit pupil expansion in one dimension while directing light within the waveguide. In further embodiments, the folded grating directs the light toward an output grating, which can provide exit pupil expansion in a second dimension different from the first direction, and also couples the light out of the waveguide. By using a folded grating, the waveguide display can require fewer layers than other systems and methods of displaying information. In addition, by using a folded grating, light can travel by total internal reflection within the waveguide in a single right angle prism defined by the waveguide exterior surface while achieving dual pupil expansion. As a result, two-dimensional exit pupil expansion can be achieved using a single waveguide. FIG. 12 conceptually illustrates a waveguide utilizing a three-grating structure to provide two-dimensional exit pupil expansion, according to an embodiment of the present invention. As shown, the waveguide 1200 includes an input grating 1201, a folded grating 1202, and an output grating 1203. The arrows 1204-1206 on the gratings 1201-1203 indicate the k-vector associated with each grating. In many embodiments, the folded grating 1202 can be designed to provide exit pupil expansion in one dimension and redirect the direction of light propagating from the input grating 1201 via total internal reflection. In an illustrative embodiment, the fringes of the folded grating 1202 are offset 45 degrees from either of the other two gratings 1201, 1203. Light entering the folded grating is redirected 1207, 1208 and propagates towards the output grating 1203, which provides exit pupil expansion in a second dimension and couples the light out of the waveguide 1200.

[0052] While the above discussion in conjunction with Figures 8-12 describes specific waveguide structures, it will be readily appreciated that any number of waveguide structure configurations may be utilized according to the specific requirements of a given application. For example, a grating that provides an exit pupil expansion can be designed with a gradient efficiency such that the fraction of light that is refracted varies with the entrance area. Waveguide Layer Stack

[0053] Waveguides according to various embodiments of the present invention can be stacked together to implement a certain optical function. For example, in many embodiments, the device can include a stack of RGB diffractive layers, each layer comprising an input and an output grating. In each layer, the SBG is recorded to provide a peak diffraction efficiency versus wavelength characteristic that is offset from the peak wavelength by a small increment (along the waveguide). In some embodiments, RGB SBG layers are used and can be switched continuously and synchronously with an RGB LED image source. FIG. 13 conceptually illustrates a contour view of an RGB stack of waveguide 1300 according to an embodiment of the present invention. In an illustrative embodiment, wavelength selective absorption layers 1301-1303 are used to selectively absorb unwanted light within each waveguide layer 1304-1306. The dashed lines represent weak couplings due to polarization off or Bragg off. The stack of waveguides further includes various filters and waveplates 1307-1311. The polarization orientation is depicted with respect to the input grating.

[0054] FIG. 13 illustrates the specific structure of the waveguide stack, but any of several stack configurations can be used according to the specific requirements of a given application. For example, in many embodiments, only two layers, namely red and blue / green, are used to implement the RGB stack. Such a system can be achieved using several methods. In some embodiments, multiplexed gratings containing different sets of gratings, each correlated with an RGB color, are used to implement multiple color waveguides within a single waveguide layer. Waveguide display

[0055] Waveguide displays according to various embodiments of the present invention can be implemented and constructed in many different ways. For example, a waveguide display can contain various numbers of waveguide layers and different exit pupil expansion schemes. FIG. 14 conceptually illustrates a biaxial expansion waveguide display with two grating layers, according to an embodiment of the present invention. 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 grating layers between glass or plastic substrates, forming a stack in which total internal reflection occurs at the outer substrate and air interfaces. In some embodiments, the stack can further include additional layers such as beam splitting coatings and environmental protection layers. In an illustrative embodiment, each grating layer contains input gratings 1405A, 1405B, folding grating exit pupil expanders 1406A, 1406B, and output gratings 1407A, 1407B, where the letters A and B refer to the first and second waveguide layers. The input grating, folding grating, and output grating can be holographic gratings such as switchable or non-switchable SBG. As used herein, the term grating may include a grating that can include a set of gratings such as a multiplexed grating or a set of discrete roll axis rotation K vector gratings. In an illustrative embodiment, IIN 1403 integrates a microdisplay panel 1402, a light source 1401, and the optical components required to illuminate the display panel, separate the reflected light, and collimate it into the required FOV. In the embodiment of FIG. 14 and the embodiments to be described below, at least one of the input, folding, and output gratings can be electrically switchable. In many embodiments, all three grating types are passive (i.e., non-switchable). In some embodiments, the IIN can project an image displayed on the microdisplay panel such that each display pixel is converted in a unique angular direction within the substrate waveguide. The collimation optics contained within the IIN can include lenses and mirrors.In a further embodiment, the lens and mirror are diffractive lens and mirror.

[0056] In an illustrative embodiment, the optical path from the source to the waveguide through the IIN is shown by light rays 1408 - 1411. The input gratings 1405A, 1405B of each grating layer can couple a portion of the light into the TIR paths within the waveguide 1404, such paths being represented by light rays 1412, 1413. The output gratings 1407A, 1407B can diffract the light from the waveguide into the angular ranges of collimated light 1414, 1415, respectively, for viewing by the eye 1416. The angular range corresponding to the field of view of the display can be defined by the IIN optics. In some embodiments, the waveguide grating can encode an optical output for adjusting the collimation of the output. In some embodiments, the output image is at infinity. In other embodiments, the output image may be formed at a distance of several meters from the eyebox. Typically, the eye is positioned within the exit pupil or eyebox of the display.

[0057] Different 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 contains a beam splitter for directing light onto a microdisplay and transmitting the reflected light towards a waveguide. In many embodiments, the beam splitter is a grating recorded within an HPDLC, and the inherent polarization selectivity of such a grating is used to separate the light illuminating the display and the image modulated light reflected from the display. In some embodiments, the beam splitter is a polarizing beam splitter cube. In some embodiments, the IIN incorporates a despeckler. The despeckler is 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).

[0058] The light source can be a laser or an LED and can include one or more lenses for modifying the illumination beam angle characteristics. The image source can be a microdisplay or a laser-based display. The LED can provide better uniformity than the laser. When laser illumination is used, there is a risk of illumination banding occurring at the waveguide output. In many embodiments, laser illumination banding in the waveguide can be overcome using the techniques and teachings disclosed in U.S. Patent Application No. 15 / 512,500, titled "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 some embodiments, the image source is a liquid crystal display (LCD) microdisplay or a liquid crystal on silicon (LCoS) microdisplay on a silicon substrate.

[0059] In some embodiments, as shown in FIG. 14, each grating layer addresses half of the entire field of view. Typically, the folding grating is shifted 45 degrees clockwise (i.e., graded in the waveguide plane) to ensure an appropriate angular bandwidth for the folded light. In other embodiments, other clockwise angles can be used to satisfy spatial constraints regarding the positioning of the gratings that can occur in the ergonomic design of the display. In some embodiments, at least one of the input and output gratings has a roll-axis rotating K vector. Rotating the K vector about the roll axis can enable the angular bandwidth of the grating to be expanded without the need to increase the waveguide thickness.

[0060] In many embodiments, the angular bandwidth of the folded grating can be enhanced by designing the grating prescription to provide a double interaction of the guided light with the grating. Exemplary embodiments of double interaction folded gratings are disclosed in U.S. Patent Application No. 14 / 620,969, entitled "Waveguide Grating Device", the disclosure of which is incorporated herein by reference in its entirety.

[0061] FIG. 15 conceptually illustrates a plan view 1500 of a single grating layer similar to that used in FIG. 14, according to an embodiment of the present invention. The grating layer 1501 optically coupled to IIN 1502 includes an input grating 1503, a first beam splitter 1504, a folded grating 1505, a second beam splitter 1506, and an output grating 1507. The beam splitter can be a partially transmissive coating that homogenizes the guided light by providing multiple reflection paths within the waveguide. Each beam splitter can include more than one coating layer, and each coating layer is applied to a transparent substrate. A typical beam path from IIN to the eye 1508 is shown by the light rays 1509 - 1513.

[0062] FIG. 16 conceptually illustrates a plan view 1600 of a two-grating layer configuration, according to an embodiment of the present invention. As shown, the grating layers 1601A, 1601B optically coupled to IIN 1602 include input gratings 1603A, 1603B, first beam splitters 1604A, 1604B, folded gratings 1605A, 1605B, second beam splitters 1606A, 1606B, and output gratings 1607A, 1607B, where the letters A and B refer to the first and second grating layers, respectively. In the illustrated embodiment, the two layers of gratings and beam splitters are substantially overlapping.

[0063] In many embodiments, the grating layer can be divided 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, a third layer can include an input grating. In such embodiments, several layers can then be laminated together on a single waveguide substrate. In some embodiments, the grating layer includes several components, including an input coupler, a folded grating, and an output grating (or portions thereof), which are laminated together to form a single substrate waveguide. The components can be separated by optical glue or other transparent materials with a refractive index that matches or is substantially similar to that of the components.

[0064] In many embodiments, the grating layer can be formed via a cell fabrication process that creates cells of a desired grating thickness and vacuum-fills each cell with SBG material for each of the input coupler, the folded grating, and the output grating. In some embodiments, the cells can be formed by positioning a plurality of glass plates with gaps between glass plates that define the desired grating thickness for the input coupler, the folded grating, and the output grating. In some embodiments, one cell can be fabricated with a plurality of openings such that separate openings are filled with different pockets of SBG material. Any intervening space can then be separated by a separator (e.g., glue, oil, etc.) to define separate areas. In some embodiments, the SBG material can be spin-coated onto a substrate and then covered by a second substrate after the material has cured.

[0065] In many embodiments, the input coupler, the folded grating, and the output grating are created by interfering two light waves at an angle within the substrate to create a holographic wavefront, thereby creating bright and dark fringes that are set within the waveguide substrate at the desired angle. Additionally, such optical elements can also be processed using any of the various methods described in the above sections.

[0066] In one embodiment, the input coupler, the folded grating, and the output grating embodied as SBGs can be Bragg gratings recorded in a holographic polymer dispersed liquid crystal (HPDLC) (e.g., a matrix of liquid crystal droplets), but the SBGs can also be recorded in other materials. In one embodiment, the SBGs are recorded in a homogeneous modulation material such as POLICRYPS or POLIPHEM having a matrix of solid liquid crystals dispersed in a liquid polymer. The SBGs can be essentially switched or non-switched. In its non-switched form, the SBGs have advantages over conventional holographic optical polymer materials that can provide a high refractive index modulation due to their liquid crystal component. Exemplary homogeneous modulation liquid crystal polymer material systems are disclosed in U.S. Patent Application Publication No. US2007 / 0019152 by Caputo et al. and PCT Application No. PCT / EP2005 / 006950 by Stumpe et al., both of which are incorporated herein by reference in their entirety. The homogeneous modulation gratings are characterized by high refractive index modulation (and thus high diffraction efficiency) and low scattering.

[0067] In many embodiments, the input coupler, the folding grating, and the output grating are made from a reverse-mode HPDLC material. Reverse-mode HPDLC is passive when no electric field is applied to the grating and becomes diffractive in the presence of an electric field, which is different from conventional HPDLC. The reverse-mode HPDLC may be based on any of the recipes and processes disclosed in PCT application No. PCT / GB2012 / 000680 entitled "Improvements to Holographic Polymer Dispersed Liquid Crystal Materials and Devices", the disclosure of which is incorporated herein by reference in its entirety. The grating is recorded in any of the above material systems but can be used in a passive (non-switching) mode. The processing process is the same as that used for switching, but the electrode coating step is omitted. LC polymer material systems are highly desirable in terms of their high refractive index modulation. In some embodiments, the grating is recorded in the HPDLC but cannot be switched.

[0068] 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 direct the light through total internal reflection between a first surface and a second surface to the folding grating within the waveguide. The input coupler can be oriented directly towards or at an angle with respect to the folding grating. For example, in some embodiments, the input coupler can be set to be slightly tilted with respect to the folding grating. In some embodiments, the folding grating can be oriented in a diagonal direction. The folding grating can be configured to provide pupil expansion in a first direction and direct light to the output grating through total internal reflection inside the waveguide.

[0069] In many embodiments, the vertical edges of each folded grating are angled with respect to the axis of alignment of the input coupler such that each folded grating is set diagonally with respect to the propagation direction of the display light. The folded grating can be angled such that light from the input coupler is redirected to the output grating. In some embodiments, the folded grating is set at a 45-degree angle with respect to the direction in which the display image is emitted from the input coupler. This feature can direct the display image propagating through the folded grating towards the output grating. For example, in some embodiments, the folded grating can direct the image towards the output grating by 90 degrees. In this way, a single waveguide can provide biaxial pupil expansion in both the horizontal and vertical directions. In some embodiments, each of the folded gratings can have a partial diffraction structure. In some embodiments, each of the folded gratings can have a full diffraction structure.

[0070] The output grating can be configured to provide pupil expansion in a second direction different from the first direction and to emit light from the waveguide from the first surface or the second surface. The output grating can receive the 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 includes a plurality of layers of the substrate, thereby comprising a plurality of layers of the output grating. Thus, there is no requirement that the grating be in one plane within the waveguide, and the gratings can be stacked on top of each other (e.g., the cells of the gratings are stacked on top of each other).

[0071] In many embodiments, a quarter-wave plate on the substrate waveguide rotates the polarization of the light ray and maintains efficient coupling with the SBG. The quarter-wave plate can be coupled or adhered 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 optical wave polarization management. Such polarization management can help to keep the alignment of the light ray with the intended optical axis by compensating for the skew wave in the waveguide. The quarter-wave plate is optional and can enhance the efficiency of the optical design in the implementation. In some embodiments, the waveguide does not include a quarter-wave plate. The quarter-wave plate may be provided as a multilayer coating.

[0072] In many embodiments, the waveguide display can be operated in a single color. In some embodiments, the waveguide display can be operated in color. Color operation can be achieved using a stack of single-color waveguides of a design similar to that of FIG. 14. This design can use red, green, and blue waveguide layers as shown, or alternatively, red and blue / green layers. FIG. 17 conceptually illustrates a biaxial magnified waveguide display 1700 according to an embodiment of the present invention, including a light source 1701, a microdisplay panel 1702, and an IIN 1703 optically coupled to red, green, and blue waveguides 1704R, 1704G, 1704B, where each waveguide includes two grating layers. In an illustrative embodiment, the three waveguides are separated by a void. In some embodiments, the waveguides are separated by a low refractive index material such as a nanoporous film. As shown, the red grating layer labeled R includes input gratings 1705R, 1706R, folding grating exit pupil expanders 1707R, 1708R, and output gratings 1709R, 1710R. The grating elements of the blue and green waveguides are labeled using the same numbers with B, G designating blue and green. In some embodiments, all of the input, folding, and output gratings are passive, i.e., non-switchable. In some embodiments, at least one of the gratings is switchable. In some embodiments, the input grating within each layer is 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 and blue and green waveguides. In various embodiments, the color waveguides can be implemented using only one grating layer within each single-color waveguide.

[0073] FIG. 18 conceptually illustrates an eye tracker display according to an embodiment of the present invention. A waveguide device-based eye tracker is 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 by reference in their entireties). Looking again at FIG. 18, the eye tracking display 1800 includes a two-axis magnifying waveguide display based on any of the embodiments described above. The waveguide display can include a waveguide 1801 containing at least one grating layer incorporating input, folding, and output gratings, an IIN 1802, an eye tracker 1803 including the waveguide, an infrared detector 1804, and an infrared source 1805. The eye tracker and the display waveguide can be separated by a void or by a low refractive index material. As described in the above references, the eye tracker can comprise separate illumination and detector waveguides. In an illustrative embodiment, the optical path from the infrared source to the eye is indicated by rays 1806-1808, and the backscattered signal from the eye is indicated by rays 1809, 1810. The optical path from the input image node through the display waveguide to the eye box is indicated by rays 1811-1813.

[0074] In many embodiments, the dual - magnification waveguide display can further include a dynamic focusing element. FIG. 19 conceptually illustrates a dual - magnification waveguide display 1900 with a dynamic focusing element 1901 and an eye tracker disposed proximate to the major surface of the waveguide display, according to an embodiment of the present invention. In some embodiments, the dynamic focusing element is an LC device. In some embodiments, the LC device combines an LC layer and a diffractive optical element. In some embodiments, the diffractive optical element is an electrically controllable LC - based device. In various embodiments, the dynamic focusing element is disposed between the waveguide display and the eye tracker. In various embodiments, the dynamic focusing element can be disposed proximate to the surface of the display waveguide that is farthest from the eye.

[0075] The dynamic focusing device can provide a number of image planes 1902. In light - field display applications, at least four image planes can be used. The dynamic focusing element can be based on the dynamic focusing element described in U.S. Patent Application No. 15 / 553,120, titled "Electrically Focus Tunable Lens", the disclosure of which is incorporated herein by reference in its entirety. In some embodiments, a dual - magnification waveguide display having a dynamic focusing element and an eye tracker can provide a light - field display, such as one based on the teachings disclosed in U.S. Patent Application No. 15 / 543,013, titled "Holographic Waveguide Light Field Displays", the disclosure of which is incorporated herein by reference in its entirety.

[0076] Specific waveguide structures are discussed above, but any of several waveguide structures can be implemented depending on the specific requirements of a given application. For example, in many waveguide configurations, the input, turning, and output gratings are formed within a single layer sandwiched by transparent substrates. Such a configuration is shown in FIG. 14 where two layers are stacked in that manner. In some embodiments, the waveguide includes only one grating layer. In some embodiments, switching transparent electrodes are applied to opposing surfaces of the substrate layer sandwiching the switching grating. In some embodiments, the cell substrate can be fabricated from glass. One glass substrate that can be used is a standard Corning Willow glass substrate (refractive index 1.51) that is available in thicknesses up to 50 micrometers. In other embodiments, the cell substrate can be an optical plastic.

[0077] In many embodiments, the waveguide display is coupled to the IIN by an opto-mechanical interface that enables the waveguide to be easily retracted from the IIN assembly. The basic principle is conceptually illustrated in FIG. 20A. FIG. 20A shows a two-axis magnified waveguide display 2000 that includes a waveguide 2001 containing an input grating 2002, a folding grating 2003, and an output grating 2004, and an IIN 2005. The apparatus further includes an optical link 2006 connected to the waveguide, a first optical interface 2007 that terminates the optical link, and a second optical interface 2008 that forms an output optical port of the IIN. The first and second optical interfaces can be decoupled as shown by a gap 2009 shown in FIG. 20B. In some embodiments, the optical link is a waveguide. In some embodiments, the optical link is curved. In some embodiments, the optical link is a GRIN image relay device. In various embodiments, the optical connection is established using a mechanical mechanism. In some embodiments, the optical connection is established using a magnetic mechanism. The advantage of decoupling the waveguide from the IIN in a helmet-mounted display application is that the eyepiece portion of the display can be removed when not in use. In some embodiments where the waveguide includes a passive grating, the eyepiece optics can be disposable.

[0078] Figure 21 conceptually illustrates an IIN 2100 having a microdisplay panel 2101, a spatially varying NA component 2102, and a microdisplay optical system 2103, according to an embodiment of the present invention. As shown, the microdisplay optical system 2103 receives light 2104 from an illumination source (not shown) and deflects the light onto the microdisplay in the direction indicated by ray 2105. Light reflected from the microdisplay is represented by diverging ray pairs 2106 - 2108 having a numerical aperture (NA) angle that varies along the X axis. In an illustrative embodiment, the spatially varying NA component is disposed between the microdisplay optical system and the microdisplay. In other embodiments, the spatially varying NA component is disposed adjacent to the output surface of the microdisplay optical system. Figure 22 conceptually illustrates such an embodiment, represented by the spatially varying NA component 2200.

[0079] 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 illustrates an IIN 2300 including a backlight 2301, a microdisplay 2302, and a variable NA component 2303, according to an embodiment of the present invention. Typically, light from the backlight, represented by rays 2304 - 2306 having a uniform NA across the backlight, irradiates the back of the microdisplay and is converted to output image modulated light represented by diverging ray pairs 2307 - 2309 having an NA angle that varies along the X axis after propagation through the variable NA component.

[0080] In many embodiments, the principles of the present invention may be applied to emissive displays. Examples of emissive displays for use in conjunction with the present invention include those based on LED arrays and emissive polymer arrays. FIG. 24 conceptually illustrates an IIN 2400 having an emissive microdisplay 2401 and a spatially varying NA component 2402, according to an embodiment of the present invention. Typically, light from the microdisplay, indicated by light rays 2403 - 2405, having a uniform NA across the emission surface of the display, irradiates the spatially varying NA component and is converted to output image modulated light, indicated by diverging light ray pairs 2406 - 2408, where the NA angle varies along the X-axis.

[0081] In many embodiments, the microdisplay optics includes a polarizing beam splitter cube. In some embodiments, the microdisplay optics includes an inclined plate to which a beam splitter coating is applied. In some embodiments, the microdisplay optics includes a waveguide device with an SBG that acts as a polarization selective beam splitter. Details regarding such embodiments are discussed in U.S. Patent Application No. 13 / 869,866, titled "Holographic Wide Angle Display" and U.S. Patent Application No. 13 / 844,456, titled "Transparent Waveguide Display", the disclosures of which are incorporated herein by reference in their entirety. In some embodiments, the microdisplay optics contains at least one of a refractive component and a curved reflective surface or diffractive optical element for controlling the numerical aperture of the illumination light. In some embodiments, the microdisplay optics contains a spectral filter for controlling the wavelength characteristics of the illumination light. In some embodiments, the microdisplay optics contains apertures, masks, filters, and coatings for controlling stray light. In many embodiments, the microdisplay optics incorporates a birdbath optics.

[0082] Figures 14-24 illustrate a specific waveguide display and structure, although any waveguide display system and configuration can be used to be suitable for the specific requirements of a given application. At its core, the waveguide is simply used to manipulate the direction of light. This nature can generally be used in a variety of different systems. An example of a general system that can utilize a waveguide is shown in FIG. 25. FIG. 25 conceptually illustrates a system diagram showing components related to 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 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 further includes a microdisplay panel and the optical components necessary to illuminate the display panel. In further embodiments, light source 2501 includes a collimator and other optical components for manipulating the light into a desired form prior to incidence into the waveguide. In other embodiments, light source 2501 is natural light. Once light source 2501 outputs light into waveguide 2502, waveguide 2502 can then manipulate and redirect the light in a desired manner both inside and outside of the light receiver 2503. The waveguide can be any general waveguide known in the art and / or one of the waveguides as described above. The light receiver can be any of several components capable of receiving light from the waveguide. In many embodiments, light receiver 2503 is the user's eye. In some embodiments, light receiver 2503 is another waveguide. In some embodiments, light receiver 2503 is a display capable of displaying the light from waveguide 2502. In further embodiments, the display is simply glass that can reflect the light onto another light receiver. System 2500 can optionally include a switching device 2504 and electrical components for use in combination with SBG. In many embodiments, switching device 2504 can receive data from the light source to introduce a voltage to direct SBG to the on position at an appropriate time.Waveguide exposure process and mastering system.

[0083] In addition to the exposure scheme described in FIGS. 4A - 4D for recording both transmissive and reflective waveguides, many mastering techniques can be used to perform such recordings and form various waveguide structures and gratings. In various embodiments, the mastering system includes the use of an amplitude grating (“AG”). Such gratings can be used to form various types of gratings with different configurations. In many embodiments, an amplitude master grating is used to form an RKV grating within a waveguide. In further embodiments, the amplitude grating contains a linear variation of the grating period, called a chirp. Chirped gratings can be utilized in many different ways. FIG. 26 conceptually illustrates an exposure process utilizing a chirped amplitude grating according to an embodiment of the present invention. As shown, the process includes the use of an input beam 2600 that interacts with a focusing element 2601 to provide a 1D focus. A zeroth - order input beam 2602 is directed towards the chirped AG 2603 and can provide a diffraction profile with a linear variation. The two beams can then be combined to form the desired interference pattern and expose a waveguide substrate 2604. As shown, the separation distance from the exposure surface and the origin of the diffracted beam can be important. In an illustrative embodiment, a transparent spacer block 2605 is used to control the separation distance.

[0084] In many embodiments, a single beam exposure system can be used in combination with an amplitude grating to form a grating within a waveguide. FIG. 5 conceptually illustrates one such embodiment. The use of a single beam in the near-contact copying mode can be considered a hybrid between direct contact copying and two-beam contact copying distinct from direct contact copying, i.e., hybrid contact copying. This approach can be useful when direct contact copying is not possible, such as when the separation distance from the master surface to the exposure surface cannot be ignored. In such situations, the separation distance can be important. For example, in an exposure process for an RKV grating, the separation distance can be important and should be considered to preserve the surface projection fringe period that traverses the complete RKV grating (without which the mutual relationship of the complete waveguide path cannot be maintained). In some embodiments, a single plane wavefront input beam can be configured to interact with a cylindrical lens to provide a 1D focus. In further embodiments, at least a portion of the light can generate diffracted beams through interaction with a chirp master, and another portion can pass through as the zero order (with attenuation) while preserving the original 1D focusing function of the cylindrical lens.

[0085] In many embodiments, a master can be designed to incorporate more than one amplitude grating. By incorporating multiple amplitude gratings within a single master, alignment errors can be reduced compared to a system that uses a single master for each grating. In some embodiments, a mastering system includes a master with three amplitude gratings. In some embodiments, the master can be developed to incorporate RKV functionality in the simultaneous exposure of three patterns written in one plate. The input and / or output master gratings can be chirp gratings and can optionally include additional gratings in the zero order region with no overlap with the chip.

[0086] In many embodiments, mastering of a plurality of grating elements within a waveguide structure can involve the use of multiple exposures. In such embodiments, a multi-step process can be used, where different regions corresponding to different grating elements of a contact copy element are exposed. In many such embodiments, the process can include the step of continuously exposing the contact copy. For example, the process can include first exposing an output grating region (e.g., using a large area O / P only master or a portion of a multi-grating master), and then exposing multiple times to form a folded-back grating region.

[0087] Masters incorporating more than one amplitude grating can also be utilized for the simultaneous exposure of more than one grating. In such a system, a collimated or coherent incident light beam is generally focused through the master AG, through an optical system, and through a suitable transparent substrate material onto the desired area for contact printing. FIGS. 27A and 27B conceptually illustrate an exposure process for simultaneously forming three gratings according to an embodiment of the present invention. As shown, in many such embodiments, the optical system is used to simultaneously direct collimated light onto the desired grating areas, resulting in the formation of multiple gratings (e.g., input, output, and feedback) in a single exposure. In an illustrative embodiment, the process includes the use of a master 2700 containing a grating, a glass plate 2701 for adjusting the separation distance, and a contact printing substrate 2702 as the material on which the grating is recorded. The process utilizes a collimated beam 2703 directed at three mirrors 2704 - 2706, which redirects the beam 2703 towards the master grating 2700. Once the beam 2703 is incident on the master grating 2700, an exposure / curing process similar to that described in FIG. 5 occurs, allowing three different gratings to be simultaneously formed on the contact print 2702. In many embodiments, a 3:1 mastering process can be utilized to fabricate a holographic waveguide having input, feedback, and output gratings in a single exposure. In various such embodiments, the input, feedback, and / or output gratings are RKV gratings. In some embodiments, the feedback grating may be partitioned into multiple zones. Any number of zones can be utilized according to the requirements of a particular application, but in some embodiments of the present invention, the feedback grating may be divided into five sections.

[0088] Figures 27A and 27B show the specific number and arrangement of gratings to be formed, but it should be understood that any number and arrangement of such gratings can be provided. Similarly, any number and arrangement of illumination beams can be provided. For example, as shown in FIG. 28, if a three-color waveguide is required, the beams can be optically arranged such that the beams for the red 2800, green 2801, and blue 2802 channels are incident on the contact copy area through the master. FIGS. 27A, 27B, and 28 show conceptual diagrams of the mastering system and arrangement, but it should be understood that these conceptual elements can take the form of any suitable optical frame, movable adapter, exposure plate, etc. required to enable the fixation of the optical elements with respect to the master and the contact copy area.

[0089] As described above, the holographic waveguide implemented in connection with the mastering and processing embodiments can be a single component and / or a stack of waveguides according to the requirements of the specific application of the embodiments of the present invention. For example, the holographic waveguide can include three layers, i.e., one layer for each of red, blue, and green. A conceptual diagram of a holographic waveguide having three layers is shown and discussed in connection with FIG. 13.

[0090] In a typical RKV grating, the grating vectors rotate about the roll axis within the same plane as the incident plane of the structural beam. In a folded grating, the grating vectors can rotate about the roll axis perpendicular to the incident plane of the structural beam. Turning to FIGS. 29A-29C here, conceptual diagrams of various approaches for generating an RKV grating according to some embodiments of the present invention are shown. Many embodiments include a stepped folded RKV, and the angles in each segment vary orthogonally to the K vector direction, as shown in FIGS. 29B and 29C. The cross-term MUX limit is overcome by the single input angle of the scanned beam in any single-pass approach. Some embodiments include a scanned RKV folded grating, where the scanned beam exposes the RKV at different angles in discrete steps across the aperture of a planar folded master grating to generate a stepped master. As discussed above, in some embodiments, only a single input beam angle is used to irradiate the folded master at any given time.

[0091] In addition to the above discussion, a mastering system according to many embodiments of the present invention can employ a chirped grating for various other purposes, as shown in FIG. 30A. These chirped gratings can assist in correcting when the incident beam on the exposure surface is not collimated and due to differences between the master and the holographic waveguide being processed. For example, a holographic waveguide is typically inside a waveguide cell of finite thickness, while the master typically has a thin protective cover applied to prevent damage to the chrome. The chirped grating can be utilized to compensate for these additional layers. Any of various protective coatings, such as glass and SiO2 protective layers, can be utilized as appropriate for the requirements of the specific use of embodiments of the present invention.

[0092] A conceptual diagram of a dual chirped grating master according to an embodiment of the present invention is shown in FIG. 30B. The 3:1 dual chirped grating offers various advantages over prior art manufacturing techniques. RKV can dramatically improve the efficiency and uniformity of the holographic waveguide. The RKV input can provide additional input coupling to the waveguide, and the RKV output can provide better pupil formation and enable improved brightness. As discussed above, enabling simultaneous exposure of the RKV input and output gratings (and folds) can reduce the total manufacturing / process time. In many embodiments, both gratings share the same spacer and / or optical density between the master and the holographic waveguide, and thus the RKV profile and spacer window may be configured to be balanced.

[0093] According to embodiments of the present invention, various mastering systems utilize a zero-order grating. The zero-order grating can be used to control the transmittance of the zero-order beam, and thus it will be close to the transmittance of the chirped grating and enable a continuous beam ratio. This prevents discontinuities in the exposure (and thus the diffraction efficiency in the replicated grating portion). A conceptual diagram of a mastering system that utilizes a zero-order grating together with a chirped grating according to an embodiment of the present invention is shown in FIG. 31. In various embodiments, the zero-order grating has no diffraction order or the diffraction order does not interfere with the system. The orientation of the master and / or the energy beam can be used to control the direction of unwanted diffracted beams, 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 for obtaining an evanescent diffracted wave. In various embodiments, using a master grating with a transmittance and / or period similar to the chirped grating at the boundary enables seamless replication to be created within the liquid crystal substrate.

[0094] In many embodiments, the mastering system utilizes a reference grating to align the lens position and obtain an accurate grating period. A conceptual diagram of such a system is provided in FIG. 32, showing the input chirp (K 11 ) and 0th order plane (K 12 ) gratings, the output chirp (K 32 ) and 0th order plane gratings (K 32 ), and the reference gratings K 13 (input) and K 33 (output) for the folded grating (K2). The reference grating can help improve the 3:1 structure by enabling simultaneous exposure of the input, folded, and output gratings, which reduces the total manufacturing time, provides high accuracy, and the accuracy of grating alignment is given by a compact design that can be accurate up to 0.1 nm and is attractive for masters and larger volume manufacturing. In some embodiments, the energy beam is collimated. To ensure that a collimated incident beam is used for the generation of the RKV grating, back ray tracing can be employed by tracing the ideal structured ray from the holographic waveguide to the lens, and modifying the window thickness is used to change the focus of the beam with respect to the hologram plane, and shifting the lens can achieve a collimated beam output from the master to the liquid crystal substrate.

[0095] In some embodiments, the mastering system, as shown in FIG. 33, avoids having other order beams created and / or interfering with the energy beam focused on the liquid crystal substrate. To avoid unwanted order beams hitting the grating area, the window thickness can be adjusted, the glass can be modified, the RKV profile can be changed, the change in the lens and / or the incident beam angle can be changed, and / or a low refractive index material can be used to completely reflect the unwanted order by the low refractive index material.

[0096] In some embodiments, the mastering system utilizes one or more diffractive means, and the same position on the master needs to generate two different diffracted beams, which is not possible unless they are of different diffraction orders. To simplify the process, the master is arranged in a configuration where there are no crossovers of the diffracted beams. In various embodiments, the master is installed as close as possible to the liquid crystal substrate. In some embodiments, the master is installed far enough away from where the crossover ends, which can induce a large separation between the zero order and the diffracted beams. If the master is installed overly far away, crossovers of the diffracted beams can occur (see, for example, FIG. 34). If the master is installed overly close, unwanted diffraction orders can hit the liquid crystal substrate. Thus, the mastering system according to embodiments of the present invention limits the distance from the liquid crystal substrate to the master plate to a certain range. To increase this range, a high refractive index glass can be used to reduce the ray angle such that the traveling distance for the diffracted beams to cross over is longer. Additionally, short wavelength exposure can also reduce the ray angle, which is similarly useful. In many embodiments where a high refractive index plate is used in the master stack, Fresnel reflection needs to be managed, particularly with respect to the high refractive index plate between the master and the copy plane. Doctrine of equivalents

[0097] Specific systems and methods have been discussed above, but many different embodiments can be implemented in accordance with the present invention. Therefore, it should be understood that the present invention can be practiced in ways other than those specifically described without departing from the scope and spirit of the present invention. Accordingly, the embodiments of the present invention should be considered illustrative in all respects and not restrictive. Thus, the scope of the present invention should be determined by the appended claims and their equivalents, rather than by the illustrated embodiments. Although specific embodiments have been described in detail in this disclosure, many modifications (e.g., variations in the sizes, dimensions, structures, shapes, and proportions of various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) are conceivable. For example, the positions of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be modified or varied. Therefore, all such modifications are intended to be included within the scope of this disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the illustrative embodiments without departing from the scope of this disclosure.

Claims

1. 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; scanning at least one recording beam across the master grating, the scanned recording beam exposing the layer of the polymer-dispersed liquid crystal mixture in the waveguide cell in discrete steps across the apertures of the master grating, each discrete step corresponding to a different scanned recording beam angle; in response to the interaction with the master grating, a portion of the at least one scanned recording beam is diffracted as diffracted light towards the waveguide cell; another portion of the at least one scanned recording beam propagates towards the waveguide cell as zero-order light; the diffracted light and the zero-order light interfere to record a roll-axis rotated K-vector grating in the waveguide cell; each interfering diffracted light has a diffracted light direction, and the zero-order light has a zero-order light direction, and the diffracted light direction and the zero-order light direction both correspond to a unique K-vector in the waveguide cell.

2. The method according to 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 travels towards the waveguide cell through a transparent spacer block.

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

5. The method according to claim 1, wherein the roll-axis rotated K-vector grating contains a multiplexed grating.

6. The method according to 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 an input grating, a folded grating, and an output grating.

8. The method according to claim 1, wherein in the roll axis rotation K vector grating, the grating vector rotates in a plane perpendicular to the incident plane of the diffracted light and the zero-order light.

9. The method according to claim 1, wherein the recorded grating is a folded grating.

10. The method according to claim 1, wherein the roll axis rotation K vector grating has a constant surface pitch.

11. A system for recording a holographic grating, the system comprising: An optical waveguide cell comprising a layer of a polymer-dispersed liquid crystal mixture sandwiched between two substrates; A master grating; A beam scanner configured to scan at least one scanned recording beam across the master grating, The scanned recording beam is configured to expose the layer of the polymer-dispersed liquid crystal mixture in the optical waveguide cell in discrete steps across the aperture of the master grating, each step corresponding to a different scanned recording beam angle, In response to the interaction with the master grating, a portion of the at least one scanned recording beam is diffracted as diffracted light towards the optical waveguide cell, Another portion of the at least one scanned recording beam propagates towards the optical waveguide cell as zero-order light, The diffracted light and the zero-order light interfere to record a roll axis rotation K vector grating in the optical waveguide cell, Each interfering diffracted light has a diffracted light direction, and the zero-order light has a zero-order light direction. The diffracted light direction and the zero-order light direction both correspond to a unique K vector in the optical waveguide cell.

12. The system according to claim 11, wherein the master grating comprises an amplitude grating.

13. The system according to claim 12, further comprising a transparent spacer block, wherein a diffracted portion of the at least one recording beam travels through the transparent spacer block.

14. The system according to claim 11, wherein the roll-axis rotation K-vector lattice contains a multiplexed lattice.

15. The system according to claim 11, wherein the master lattice comprises three separate lattices.

16. The system according to claim 15, wherein the three separate lattices are designed to record an input lattice, a folding lattice, and an output lattice.

17. The system according to claim 15, wherein lattice vectors of the roll-axis rotation K-vector lattice rotate in a plane perpendicular to an incident plane of the diffracted light and the zero-order light.

18. The system according to claim 11, wherein the recorded lattice is a folding lattice.

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