WO2020041620A1

WO2020041620A1 - Cmos-compatible single-layer waveguide display for augmented and virtual reality

Info

Publication number: WO2020041620A1
Application number: PCT/US2019/047754
Authority: WO
Inventors: Yoo Seung Lee; Chee Wei Wong; Tom G. LEE
Original assignee: University of California Berkeley; University of California San Diego UCSD
Current assignee: University of California Berkeley; University of California San Diego UCSD
Priority date: 2018-08-23
Filing date: 2019-08-22
Publication date: 2020-02-27
Anticipated expiration: 2021-02-23

Abstract

A waveguide display includes: (1) a waveguide including an input region and an output region spaced from the input region along a lengthwise axis of the waveguide, wherein the waveguide is configured to propagate a light beam from the input region towards the output region; (2) an input diffractive optical element adjacent to the input region and configured to focus the light beam into the waveguide, wherein the input diffractive optical element includes an input chirped grating; and (3) an output diffractive optical element adjacent to the output region and configured to focus the light beam out of the waveguide, wherein the output diffractive optical element includes an output chirped grating.

Description

CMOS-COMPATIBLE SINGLE-LAYER WAVEGUIDE DISPLAY FOR AUGMENTED AND VIRTUAL REALITY

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 62/722,086, filed August 23, 2018, the contents of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

[0002] This disclosure generally relates to a waveguide display.

BACKGROUND

[0003] For Augmented Reality (AR) display devices, diffractive optical elements (DOEs) or holographic optical elements (HOEs) with a glass waveguide have been proposed because they can reduce a size and a cost of the AR display devices. Diffraction angles of these optical elements are determined by a grating structure and a wavelength. Thus, comparative DOEs or HOEs for multiple wavelengths specify multiple structures such as a multi-layer stacked structure. Each wavelength ray is diffracted at a designed layer for the wavelength. However, formation of multi-layer stacked structures can involve numerous fabrication stages since the number of fabrication stages are multiplied by the number of wavelengths. Thus, fabrication cost can be increased because of increased fabrication difficulty and increased fabrication stages. Moreover, a total efficiency can be reduced since there is some power loss when light passes through each layer. Even though a grating structure in a particular layer is designed for one wavelength, it is not fully transparent for other wavelengths, and other wavelengths can be diffracted at unwanted diffraction angles at this layer.

[0004] It is against this background that a need arose to develop the embodiments described herein.

SUMMARY

[0005] In some embodiments, a waveguide display includes: (1) a waveguide including an input region and an output region spaced from the input region along a lengthwise axis of the waveguide, wherein the waveguide is configured to propagate a light beam from the input region towards the output region; (2) an input diffractive optical element (DOE) adjacent to the input region of the waveguide and configured to focus the light beam into the waveguide, wherein the input DOE includes an input chirped grating; and (3) an output DOE adjacent to the output region of the waveguide and configured to focus the light beam out of the waveguide, wherein the output DOE includes an output chirped grating.

[0006] In additional embodiments, a waveguide display includes: (1) a waveguide including an input region and an output region spaced from the input region along a lengthwise axis of the waveguide; (2) an input DOE on the input region of the waveguide, wherein the input DOE includes a first input DOE unit, a second input DOE unit, and a third input DOE unit that are laterally cascaded on the input region of the waveguide in a direction orthogonal to the lengthwise axis of the waveguide; and (3) an output DOE on the output region of the waveguide.

[0007] Other aspects and embodiments of this disclosure are also contemplated. The foregoing summary and the following detailed description are not meant to restrict this disclosure to any particular embodiment but are merely meant to describe some embodiments of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a better understanding of the nature and objects of some embodiments of this disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

[0009] Figure 1 | Overall architecture of a complementary metal-oxide- semiconductor (CMOS)-compatible waveguide display. The display includes a chirped diffractive optical element (DOE) in one-dimension (1D) at an input region and a chirped DOE in two-dimensions (2D) (or 1D) at an output region. An expanded collimated beam from three color lasers serve as an input from a display. After beam focusing with the input DOE, light is totally internally reflected across an about 3-mm thick waveguide and re focused to an eye box with the chirped output DOE.

[0010] Figure 2 | Baseline implementation of DOEs based on chirped input and output gratings with first-order diffraction a, Tuned for input drive lasers of about 645.80 nm (red), about 520.47 nm (green), and about 442.35 nm (blue) wavelength, an input DOE has an x-direction chirped grating period as shown b, Output grating period in the x-direction. c, Output grating period in the y-direction. Each chirped DOE is optimized for the red-green- blue wavelengths, with 405 nm illustrated for reference.

[0011] Figure 3 | Second implementation of chirped input grating with second-order diffraction a, Schematic of second-order grating parameters b, Substantially uniform color ratio across diffraction angles, with optimized differential DOE thicknesses for red-green- blue. c, Substantially uniform DOE thickness with trade-off in color ratios across diffraction angles d, Example respective DOE efficiencies for the color gamut, different ray angles and DOE thicknesses.

[0012] Figure 4 | Third implementation based on slanted input grating for improved efficiencies a, Schematic of slanted grating parameters b, Parameters of designed slanted gratings c, Slanted grating efficiency versus grating height, with additional about 405 nm and about 460 nm wavelengths included for comparison d, Example respective DOE efficiencies for the color gamut, different ray angles and DOE thicknesses. A substantially uniform color ratio is achieved based on non-uniform DOE thicknesses. Top inset: cross-section of the DOE. e, Substantially uniform DOE thicknesses at about 430-nm, with resulting non-uniform color ratio. Top inset: cross-section of the DOE.

[0013] Figure 5 | Third implementation with vertical input grating mounted on an angled prism, for improved efficiencies. Schematic shows an input DOE with 1D chirp, total internal reflection waveguiding, and an output DOE with 2D (or 1D) chirp for refocusing onto an eye box.

[0014] Figure 6 | Third implementation with vertical input grating mounted on an angled prism, for improved efficiencies a, Schematic of the grating mounted at an about 30° angle and oblique incident beam, with first-order diffraction b, Parameters of designed vertical gratings mounted on an angled prism c, Prism-mounted grating efficiency versus grating height, designed with oblique incident angles d, Example respective DOE efficiencies for the color gamut, different ray angles and DOE thicknesses. A relatively uniform color ratio is achieved based on non-uniform DOE thicknesses, with about 370-nm for blue, about 450-nm for green and about 570-nm for red. Top inset: cross-section of the DOE. e, Substantially uniform DOE thicknesses at about 480-nm, with resulting non-uniform color ratio. Top inset: cross-section of the DOE.

[0015] Figure 7 | Input DOE - 1D cascaded array of DOE units. The 1D cascaded array aids to balance color gamut, with each individual chirped DOE unit optimized for one of red, green, and blue. [0016] Figure 8 | Color balancing of 1D cascaded grating. A first-order grating is considered, with balanced efficiency across red, green, and blue.

[0017] Figure 9 | Output DOE - 2D cascaded array.

[0018] Figure 10 | 2D cascaded array, with lateral cascading of DOE units in the y- direction.

[0019] Figure 11 | 2D cascaded array, with lateral cascading of DOE units in the x- direction.

[0020] Figure 12 | 2D out-coupling chirped grating (x-axis) design via rigorous coupled- wave analysis simulations. Grating periods are shown as a function of the grating x- axis position for red, blue and green wavelengths and target diffraction angle (first-order) is shown as a function of the grating x-axis position.

[0021] Figure 13 | 2D out-coupling chirped grating (y-axis) design via rigorous coupled- wave analysis simulations. Grating periods are shown as a function of the grating y- axis position for red, blue and green wavelengths and target diffraction angle (first-order) is shown as a function of the grating y-axis position.

[0022] Figure 14 | a, Scanning electron micrograph of an example DOE. B, Magnified section of a DOE shown for illustration.

[0023] Figure 15 | Experiment on second implementation including an in-coupling DOE (second-order grating), a 3-mm thick glass waveguide, and an out-coupling DOE (second-order grating).

DETAILED DESCRIPTION

[0024] Overview:

[0025] Embodiments relate to a complementary metal-oxide- semiconductor (CMOS)-compatible waveguide display for high-resolution, high-performance Augmented and Virtual Reality. In some embodiments, the display is lightweight and thin-film implementable on eyeglasses, with at least 1080P resolution (1920 x 1080) and field-of-view in excess of ± 35 degrees. In some embodiments, the display is based on a chirped grating design along with red-green-blue cascade for color and chromatic aberration balancing. A diffractive optical element (DOE) of some embodiments has a 20 mm x 15 mm cross-section covering the human eye box, in pupil and gazing field size. The waveguide display supports a variable range of image pixel pitches such as 2.8-mhi (0.22” diagonal), 4.5-mhi (0.39” diagonal) and other dimensions. The diffractive, holographic-like optical element has high transparency of about 85% or more, high brightness, and high contrast ratio. A waveguide thickness is designed and implemented between about l.5-mm to about 3-mm and can be thinner when specified. The waveguide display architecture includes an input chirped DOE and an output chirped DOE (Figure 1), chirped in two-dimensions (2D) or one-dimension (1D) and with laterally cascaded color balancing within a single-layer structure. Desirable physical optical concepts are implemented for the waveguide display, along with co optimization in the numerical designs, CMOS -compatible fabrication, and prototype measurement demonstrations.

[0026] DOEs with a glass waveguide are desirable because they can reduce a size and a cost of Augmented and Virtual Reality display devices. Diffraction angles of these optical elements are determined by a grating structure (e.g., implemented as a Bragg grating, a volume grating, a surface relief grating, a blazed grating, and so forth) and a wavelength. Comparative DOEs for multiple wavelengths include multiple structures such as a multi-layer stacked structure. However, fabrication cost can be increased because of increased fabrication difficulty and increased fabrication stages of such multi-layer structures. Moreover, a total efficiency can be reduced since there is some power loss when light passes through each layer, and wavelengths other than a design wavelength for a particular layer can be diffracted at unwanted diffraction angles at this layer.

[0027] Figure 1 shows an overall single-layer architecture, including an expanded collimated beam with a display information from a display 102 entering a left- side of a waveguide 104 (e.g., a glass waveguide). Positioned on an input or in-coupling region of the waveguide 104, an input or in-coupling DOE 106, implemented as a chirped grating, focuses a chromatic light path into multiple total internal reflection bounces across the waveguide 104. As illustrated in a top view in Figure 1, the input DOE 106 includes an array of diffractive components 110, each extending lengthwise along a widthwise y-axis of the waveguide 104, and spaced from one another with a grating period spatially varying along a lengthwise x-axis of the waveguide 104. Positioned on an output or out-coupling region of the waveguide 104 laterally spaced from the input region along the lengthwise x-axis of the waveguide 104, an output or out-coupling DOE 108, implemented as a second chirped grating, focuses the chromatic light path to an eye box. As illustrated in a top view in Figure 1, the output DOE 108 includes an array of diffractive components 112 spaced from one another with a grating period that is spatially varying along the lengthwise x-axis of the waveguide 104, and with a grating period that is spatially varying along the widthwise y-axis of the waveguide 104. Several successive design variations of both the input and output DOEs 106 and 108 are described in the following for 1080P resolution, in a performance trade-off space of efficiency, field-of-view, color balancing and aberration correction, high transparency-brightness and contrast ratio, fabrication ease and measurement demonstration.

[0028] In the design approach, ray tracing simulation tools are used to model a chief ray propagation, considering the chromatic and monochromatic aberration, modulation transfer function (MTF), and distortion. Custom simulation tools support the waveguide display design and further verified with rigorous coupled-wave analysis (RCWA), finite- difference time-domain (FDTD), or finite element method (FEM) for DOE efficiencies. Surface relief gratings are primary chosen in the approach but metamaterial or Bragg gratings can also be considered. DOEs can be fabricated with CMOS-compatible deposition, lithography, and etching techniques. Silicon-rich nitride, with its higher refractive index, can reduce a silicon nitride thickness, allowing easier fabrication. Other ceramics also can be used.

[0029] Diffractive Optical Element:

[0030] First Baseline Implementation: A first baseline implementation is based on chirped input and output gratings with first-order diffraction. The implementation is tuned to three input drive lasers of wavelengths of about 645.80 nm (red), about 520.47 nm (green), and about 442.35 nm (blue). The input DOE 106 has an x-direction length of about 7-mm, with a chirped grating period spatially varying along the lengthwise x-axis of the waveguide 104 as illustrated in Figure 2a. For each of the wavelengths at about 645.80 nm, about 520.47 nm, and about 442.35 nm, a periodicity and a chirp of the input DOE 106 are optimized according to a respective and different spatially varying profile along the x-direction and, in particular, with a grating period generally increasing towards the output DOE 108, and with a larger grating period at each grating position for a longer wavelength relative a shorter wavelength, as illustrated in Figure 2a. A reference DOE at about 405 nm is also illustrated for comparison. After the input DOE 106, total internal reflection with five bounces crosses the waveguide 104 to the eye box as shown in Figure 1. The resulting optimized output DOE 108 is designed as a two-dimensional array, with the x-axis grating period chirped between about l-pm to about 200-nm for the red, green and blue color gamut as illustrated in Figure 2b. For each of the wavelengths at about 645.80 nm, about 520.47 nm, and about 442.35 nm, a periodicity and a chirp of the output DOE 108 are optimized according to a respective and different spatially varying profile along the x-direction and, in particular, with a grating period generally increasing towards the input DOE 106, and with a larger grating period at each grating position for a longer wavelength relative a shorter wavelength. There is less stringent criteria on the y-axis focusing into the eye box and hence, in the y-axis, the grating period is intrinsically wider. The optimized design is illustrated in Figure 2c, averaging about 25-pm in periodicity of the output DOE 108 and has a chirp that spans from about 2-pm to about 55-pm. An about 405 nm reference is also illustrated for the output DOE 108.

[0031] Second Implementation: A second implementation is based on second-order diffraction, to ease fabrication with larger DOE grating periods along with a trade-off of lower overall display efficiencies. Figure 3a illustrates geometries of a second-order implementation of the input DOE 106, including the array of diffractive components 110 having a grating period P and separated from one another by a gap G, and each having a width W and a height H (corresponding to a thickness of the input DOE 106). Two cases of color balancing are illustrated in Figure 3b and 3c. In Figure 3b, a substantially uniform color ratio for the red, green and blue color gamut is achieved via differential thickness control; in Figure 3c, a substantially uniform thickness of about 4l0-nm is enforced across the DOE for ease in CMOS fabrication at the expense of non-uniform color ratio. Figure 3d provides a table setting forth resulting efficiencies for each angled ray, with examples of 50° to 65° illustrated and at about 50% duty cycle. To balance the color gamut, an about 340-nm DOE thickness is chosen for blue, an about 4l0-nm DOE thickness is chosen for green, and an about 5l0-nm DOE thickness is chosen for red, with the respective efficiencies illustrated. For a substantially uniform thickness of about 4l0-nm the respective efficiencies are set forth in Figure 3d, along with the efficiencies versus diffraction angles shown in Figure 3c.

[0032] Third Implementation: To further increase overall diffraction efficiencies, Figure 4a illustrates a third implementation of the input DOE 106 based on a slanted angle grating. As illustrated, the input DOE 106 includes the array of diffractive components 110 having a grating period P and separated from one another by a gap G, and each having a width W, a height H (corresponding to a thickness of the input DOE 106), and a non-zero slanted angle (e.g., in a range of about 10° to about 45°) relative to a thickness- wise z-axis of the waveguide 104. Figure 4b summarizes the implemented slanted grating parameters, with an increasing thickness for longer wavelengths. Figure 4c plots DOE efficiencies versus modeled height, via a simplified modal method (SMM) simulation and DOE efficiencies versus diffraction angles, via RCWA simulation. Reference wavelengths of about 405 nm and about 460 nm are also included for comparison. To balance the different efficiencies for red- green-blue, a slanted grating DOE with non-uniform (or differential) height is illustrated in Figure 4d, allowing a substantially uniform color ratio. Figure 4e correspondingly shows a substantially uniformly thick slanted grating DOE and the respective efficiencies for the red, green and blue colors.

[0033] Since a slanted grating can be relatively difficult for CMOS fabrication, in Figure 5, the waveguide display is illustrated including the input DOE 106, implemented as a vertical grating mounted at a non-zero angle (e.g., in a range of about 10° to about 45° or about 30°) relative to the input region of the waveguide 104, such as on a prism 502, for improved efficiencies. The corresponding design is illustrated in Figure 6a, with oblique incident angle and first-order diffraction. The prism is chosen at about 30° in this design. The resulting DOE parameters are summarized in Figure 6b, in addition to angled grating height versus efficiency plots for red-green-blue. Fikewise, Figure 6c plots the DOE efficiencies versus modeled height, for the oblique incident light. For color balancing, a non-uniform DOE thickness is illustrated in Figure 6d with about 370-nm for blue, about 450-nm for green and about 570-nm for red. For ease of CMOS -compatible fabrication, Figure 6e shows a designed substantially uniformly thick DOE for an optimized thickness of about 480-nm, with tolerable variations in waveguide display efficiencies which can be compensated by controlling drive laser input powers.

[0034] Cascaded Diffractive Optical Element:

[0035] 1D Cascaded Array of DOE Units for In-coupling: Once focused into a waveguide, electromagnetic wave guidance based on total internal reflection has negligible losses. The next design consideration is thus that of a multi-wavelength or multi-color DOE such as a red-green-blue (RGB) DOE. A 1D cascaded array is first explained, followed by a 2D cascaded array. A comparative approach based on stacking of three RGB gratings is illustrated in Figure 7 on the upper right comer. To facilitate the CMOS-compatible fabrication, a thin-film, input DOE is based on a cascade implementation as shown on the lower right in Figure 7. An input DOE includes a first group of first input DOE units 702 (e.g., blue input units), a second group of second input DOE units 704 (e.g., green input units), and a third group of third input DOE units 706 (e.g., red input units). A DOE unit 702, 704, or 706 in each particular group is optimized for a respective and different laser color for that group, and each DOE unit 702, 704, or 706 includes an array of diffractive components 708, 710, or 712 chirped along a lengthwise x-axis of the waveguide. Hence, a periodicity and a chirp of a DOE unit 702, 704, or 706 in each particular group are optimized according to a respective and different spatially varying profile along the x-axis; namely, the first DOE units 702 in the first group have a first spatially varying profile along the x-axis, the second DOE units 704 in the second group have a second spatially varying profile along the x-axis, and the third DOE units 706 in the third group have a third spatially varying profile along the x-axis, where the first profile, the second profile, and the third profile at different from one another. The first DOE units 702, the second DOE units 704, and the third DOE units 706 are laterally cascaded along a widthwise y-axis of the waveguide in an ABC-ABC lateral periodic configuration.

[0036] To balance the color gamut, Figure 8 shows the y-axis tuning of area widths (a, b, and c as illustrated in Figure 8a) of the first DOE units 702, the second DOE units 704, and the third DOE units 706. For example, if the blue, green and red DOE efficiencies are 0.90, 0.80 and 0.70, the respective widths a, b, and c can have different and respective values of 0.293, 0.333 and 0.377 (in arbitrary or relative units), with the third DOE units 706 designed for a longer wavelength (red) having a greater width than the second DOE units 704, and with the second DOE units 704 designed for a longer wavelength (green) having a greater width than the first DOE units 702 (Figure 8b). An example efficiency based color balancing is shown in Figure 8c. With tuning of the widths, an example resulting balanced color gamut is shown in Figure 8d.

[0037] 2D Cascaded Array of DOE Units for Out-coupling: To focus within an eye box for both the x- and y-directions, a 2D cascaded output DOE is specified. The above implementation for 1D is scaled to a 2D cascade as illustrated in Figure 9. A comparative approach based on stacking of three RGB gratings is illustrated in Figure 9 on the upper right corner. There are two ways to scale the 2D cascade. The first approach is to scale the ABC- ABC cascade in the y-direction. The output DOE includes a first group of first output DOE units 902 (e.g., blue output units), a second group of second output DOE units 904 (e.g., green output units), and a third group of third output DOE units 906 (e.g., red output units). A DOE unit 902, 904, or 906 in each particular group is optimized for a respective and different laser color for that group, and each DOE unit 902, 904, or 906 includes an array of diffractive components 908, 910, or 912 having dual chirp, namely chirped along a lengthwise x-axis of a waveguide, and along a widthwise y-axis of the waveguide. The first DOE units 902, the second DOE units 904, and the third DOE units 906 are laterally cascaded along the widthwise y-axis of the waveguide in an ABC-ABC lateral periodic configuration, as shown in Figure 10. Since the y-direction grating period can be about 20x larger than that of the x- direction grating period, another option is to laterally cascade the red-green-blue units 902, 904, and 906 in the x-direction, as shown in Figure 11.

[0038] Grating periods for the x-direction and the y-direction are determined by incident light angle and diffracted angle with diffraction equation. Incident angles are same as diffracted angles from an in-coupling DOE. For cascading in the x-direction, diffracted angles are from about -26.7 degrees to about +26.7 degrees as shown in Figure 12. Corresponding grating periods for x-direction are shown in Figure 12, and ranges from about 200-nm to about l-pm. Here the grating period decreases while diffraction angle is increased, or wavelength is decreased. For cascading in the y-direction, incident angle is a normal incident angle (0 degree) because the in-coupling DOE is an x-direction chirped grating which has x-direction light diffraction modes. Diffraction angles are from about -19.3 degrees to about +19.3 degrees as shown in Figure 13, with grating periods ranging from about 2-pm to about 55-pm. Positive and negative angles have a same grating period since incident light angle is normal incident. For the 2D cascaded grating, cascade direction can be in either the x-direction or the y-direction. However, if the y-direction grating period is longer than the x- direction grating period, then the x-direction cascade array is a more desirable approach for implementation, as shown in Figure 11. Similar to color non-uniformity correction for 1D cascaded grating, 2D cascaded grating efficiency for each wavelength depends on the y-axis area width of an output DOE unit for that wavelength. Thus the color uniformity caused by different diffraction efficiency for each wavelength can be addressed by tuning respective widths of output DOE units for different wavelengths.

[0039] Test Measurements:

[0040] Based on the above design implementations and optimizations, fabrication is made of DOEs from silicon nitride on a 3-mm thick waveguide, with example scanning electron micrographs shown in Figure 14.

[0041] Inset in Figure 15 shows a setup for waveguide display measurements. Each waveguide is installed on an optical table. A projection lens aligns a display to an in-coupling DOE. To measure virtual image, a sensor front lens and a CMOS image sensor or a charge- coupled device (CCD) is placed in an eye box region and a focal plane of the lens, respectively.

[0042] In-coupling and out-coupling DOEs for the second implementation are developed and tested for green wavelength (about 520 nm). In-coupling grating is a second- order chirped grating which can magnify a beam size. Then, out-coupling grating focuses the beam at the eye box region.

[0043] Example Embodiments:

[0044] In a first aspect according to some embodiments, a waveguide display includes: (1) a waveguide including an input region and an output region spaced from the input region along a lengthwise axis of the waveguide, wherein the waveguide is configured to propagate a light beam from the input region towards the output region; (2) an input DOE adjacent to the input region of the waveguide and configured to focus the light beam into the waveguide, wherein the input DOE includes an input chirped grating; and (3) an output DOE adjacent to the output region of the waveguide and configured to focus the light beam out of the waveguide, wherein the output DOE includes an output chirped grating.

[0045] In some embodiments of the first aspect, the input chirped grating is chirped in a direction along the lengthwise axis of the waveguide.

[0046] In some embodiments of the first aspect, the output chirped grating is chirped in the direction along the lengthwise axis of the waveguide and in a direction orthogonal to the lengthwise axis of the waveguide.

[0047] In some embodiments of the first aspect, the input chirped grating includes an array of diffractive components that are slanted at a non-zero angle with respect to a direction orthogonal to a surface of the input region of the waveguide.

[0048] In some embodiments of the first aspect, the waveguide display further includes a display adjacent to the input DOE and configured to generate the light beam.

[0049] In a second aspect according to some embodiments, a waveguide display includes: (1) a waveguide including an input region and an output region spaced from the input region along a lengthwise axis of the waveguide; (2) an input DOE on the input region of the waveguide, wherein the input DOE includes a first input DOE unit, a second input DOE unit, and a third input DOE unit that are laterally cascaded on the input region of the waveguide in a direction orthogonal to the lengthwise axis of the waveguide; and (3) an output DOE on the output region of the waveguide.

[0050] In some embodiments of the second aspect, each of the first input DOE unit, the second input DOE unit, and the third input DOE unit is chirped in a direction along the lengthwise axis of the waveguide.

[0051] In some embodiments of the second aspect, the first input DOE unit has a grating period that is spatially varying according to a first profile along the lengthwise axis of the waveguide, the second input DOE unit has a grating period that is spatially varying according to a second profile along the lengthwise axis of the waveguide, the third input DOE unit has a grating period that is spatially varying according to a third profile along the lengthwise axis of the waveguide, and the first profile, the second profile, and the third profile at different from one another.

[0052] In some embodiments of the second aspect, the first input DOE unit has a first width in the direction orthogonal to the lengthwise axis of the waveguide, the second input DOE unit has a second width in the direction orthogonal to the lengthwise axis of the waveguide, the third input DOE unit has a third width in the direction orthogonal to the lengthwise axis of the waveguide, and the first width, the second width, and the third width at different from one another.

[0053] In some embodiments of the second aspect, the output DOE includes a first output DOE unit, a second output DOE unit, and a third output DOE unit that are laterally cascaded on the output region of the waveguide in the direction orthogonal to the lengthwise axis of the waveguide.

[0054] In some embodiments of the second aspect, each of the first output DOE unit, the second output DOE unit, and the third output DOE unit is chirped in a direction along the lengthwise axis of the waveguide and in the direction orthogonal to the lengthwise axis of the waveguide.

[0055] In some embodiments of the second aspect, the output DOE includes a first output DOE unit, a second output DOE unit, and a third output DOE unit that are laterally cascaded on the output region of the waveguide in a direction along the lengthwise axis of the waveguide.

[0056] In some embodiments of the second aspect, each of the first output DOE unit, the second output DOE unit, and the third output DOE unit is chirped in the direction along the lengthwise axis of the waveguide and in the direction orthogonal to the lengthwise axis of the waveguide.

[0057] In some embodiments of the second aspect, the waveguide display further includes a display optically coupled to the input diffractive optical element.

[0058] As used herein, the singular terms“a,”“an,” and“the” may include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an object may include multiple objects unless the context clearly dictates otherwise. [0059] As used herein, the term“set” refers to a collection of one or more objects. Thus, for example, a set of objects can include a single object or multiple objects. Objects of a set also can be referred to as members of the set. Objects of a set can be the same or different. In some instances, objects of a set can share one or more common characteristics.

[0060] As used herein, the terms“substantially” and“about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can refer to a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, a first numerical value can be“substantially” or“about” the same as a second numerical value if the first numerical value is within a range of variation of less than or equal to ±10% of the second numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0061] In the description of some embodiments, a component provided or disposed “on” or“over” another component can encompass cases where the former component is directly on (e.g., in physical or direct contact with) the latter component, as well as cases where one or more intervening components are located between the former component and the latter component.

[0062] Additionally, concentrations, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood flexibly to include numerical values explicitly specified as limits of a range, but also to include all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified. For example, a range of about 1 to about 200 should be understood to include the explicitly recited limits of about 1 and about 200, but also to include individual values such as about 2, about 3, and about 4, and sub-ranges such as about 10 to about 50, about 20 to about 100, and so forth. [0063] While the disclosure has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the disclosure as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, operation or operations, to the objective, spirit and scope of the disclosure. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while certain methods may have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not a limitation of the disclosure.

Claims

What is claimed is:

1. A waveguide display comprising:

a waveguide including an input region and an output region spaced from the input region along a lengthwise axis of the waveguide, wherein the waveguide is configured to propagate a light beam from the input region towards the output region;

an input diffractive optical element adjacent to the input region of the waveguide and configured to focus the light beam into the waveguide, wherein the input diffractive optical element includes an input chirped grating; and

an output diffractive optical element adjacent to the output region of the waveguide and configured to focus the light beam out of the waveguide, wherein the output diffractive optical element includes an output chirped grating.

2. The waveguide display of claim 1, wherein the input chirped grating is chirped in a direction along the lengthwise axis of the waveguide.

3. The waveguide display of claim 2, wherein the output chirped grating is chirped in the direction along the lengthwise axis of the waveguide and in a direction orthogonal to the lengthwise axis of the waveguide.

4. The waveguide display of claim 1, wherein the input chirped grating includes an array of diffractive components that are slanted at a non-zero angle with respect to a direction orthogonal to a surface of the input region of the waveguide.

5. The waveguide display of any of claims 1 to 4, further comprising a display adjacent to the input diffractive optical element and configured to generate the light beam.

6. A waveguide display comprising:

a waveguide including an input region and an output region spaced from the input region along a lengthwise axis of the waveguide;

an input diffractive optical element on the input region of the waveguide, wherein the input diffractive optical element includes a first input diffractive optical element unit, a second input diffractive optical element unit, and a third input diffractive optical element unit that are laterally cascaded on the input region of the waveguide in a direction orthogonal to the lengthwise axis of the waveguide; and

an output diffractive optical element on the output region of the waveguide.

7. The waveguide display of claim 6, wherein each of the first input diffractive optical element unit, the second input diffractive optical element unit, and the third input diffractive optical element unit is chirped in a direction along the lengthwise axis of the waveguide.

8. The waveguide display of claim 6, wherein the first input diffractive optical element unit has a grating period that is spatially varying according to a first profile along the lengthwise axis of the waveguide, the second input diffractive optical element unit has a grating period that is spatially varying according to a second profile along the lengthwise axis of the waveguide, the third input diffractive optical element unit has a grating period that is spatially varying according to a third profile along the lengthwise axis of the waveguide, and the first profile, the second profile, and the third profile at different from one another.

9. The waveguide display of claim 6, wherein the first input diffractive optical element unit has a first width in the direction orthogonal to the lengthwise axis of the waveguide, the second input diffractive optical element unit has a second width in the direction orthogonal to the lengthwise axis of the waveguide, the third input diffractive optical element unit has a third width in the direction orthogonal to the lengthwise axis of the waveguide, and the first width, the second width, and the third width at different from one another.

10. The waveguide display of claim 6, wherein the output diffractive optical element includes a first output diffractive optical element unit, a second output diffractive optical element unit, and a third output diffractive optical element unit that are laterally cascaded on the output region of the waveguide in the direction orthogonal to the lengthwise axis of the waveguide.

11. The waveguide display of claim 10, wherein each of the first output diffractive optical element unit, the second output diffractive optical element unit, and the third output diffractive optical element unit is chirped in a direction along the lengthwise axis of the waveguide and in the direction orthogonal to the lengthwise axis of the waveguide.

12. The waveguide display of claim 6, wherein the output diffractive optical element includes a first output diffractive optical element unit, a second output diffractive optical element unit, and a third output diffractive optical element unit that are laterally cascaded on the output region of the waveguide in a direction along the lengthwise axis of the waveguide.

13. The waveguide display of claim 12, wherein each of the first output diffractive optical element unit, the second output diffractive optical element unit, and the third output diffractive optical element unit is chirped in the direction along the lengthwise axis of the waveguide and in the direction orthogonal to the lengthwise axis of the waveguide.

14. The waveguide display of any of claims 6 to 13, further comprising a display optically coupled to the input diffractive optical element.