CN117642575A - Display device with waveguide-based taber illuminator - Google Patents

Abstract

A waveguide illuminator (104) for illuminating a display panel includes an input waveguide (106), a waveguide beam splitter (112) coupled to the input waveguide (106), and a waveguide array (116) coupled to the waveguide beam splitter (112). The waveguide array (116) includes an array of couplers (120) that couple out portions of the split beam to form an array of coupled-out beam portions (122) for illuminating the display panel. The coupled-out beam portions (122) undergo optical interference and form a taber pattern of illumination associated with the pixel array of the display panel, with an increase in luminous flux achieved by centering individual taber peaks on the display panel pixels.

Description

Display device with waveguide-based Taber illuminator

Technical field

The present disclosure relates to luminaires, visual display devices, and related components and modules.

Background technique

Visual displays provide information including still images, video, data, etc. to one or more viewers. Visual displays have applications in a variety of fields including entertainment, education, engineering, science, professional training, advertising, to name a few. Some visual displays (eg, televisions) display images to multiple users, while some visual display systems (eg, near-Eye displays (NED)) are intended for use by individual users.

Artificial reality systems typically include a NED (eg, a headset or a pair of glasses) configured to present content to a user. The near-eye display can display virtual objects, or combine images of real objects with images of virtual objects, such as in virtual reality (VR) applications, augmented reality (AR) applications, or mixed reality (MR) applications. Images are combined. For example, in an AR system, a user can view an image of a virtual object (eg, Computer-Generated Image (CGI)) superimposed on the surrounding environment by looking through a "combiner" component. Wearable display combiners are typically transparent to external light but include some light routing optics to direct display light into the user's field of view.

Because Head-Mounted Display (HMD) or NED displays are typically worn on the user's head, large, bulky, unbalanced, and/or heavy display devices with heavy batteries are difficult for users to wear It would be cumbersome and uncomfortable. As a result, head mounted display devices benefit from a compact and efficient construction that includes efficient light sources and illuminators that provide illumination of the display panel, high throughput viewing lenses, and other optical elements in the image formation chain.

Contents of the invention

According to a first aspect of the present disclosure, a display device is provided. The display device includes a display panel including a pixel array on a display substrate, and a waveguide illuminator. The waveguide illuminator is coupled to the display panel. The waveguide illuminator is coupled to the display panel. The illuminator is used to illuminate the pixel array, and the waveguide illuminator includes: an illuminator substrate; a beam splitter, the beam splitter is supported by the illuminator substrate, and the beam splitter is used to divide the input beam into a plurality of sub-beams; the waveguide array each waveguide is supported by the illuminator substrate and extends parallel to a row of pixels of the pixel array, wherein each waveguide in the array is configured to guide one of the plurality of beamlets in the waveguide; and an outcoupling grating array coupled to the waveguide array; wherein the outcoupling grating array extends along the pixel array to couple portions of the plurality of sub-beams for propagation through the display substrate And a Taber peak array is formed at the plane of the pixel array, wherein the position of each Taber peak in the Taber peak array corresponds to the position of each pixel in the pixel array.

The display device may further include a light source for providing the input beam to the beam splitter.

The light source may be tunable in wavelength; wherein, in operation, the position of the respective Taber peak may depend on the wavelength of the light source, and wherein the wavelength may be selected such that the Taber peak is within the pixel array centered on pixels.

The light source may have an emission bandwidth; wherein, in operation, the width of the Taber peak in the Taber peak array may depend on the emission bandwidth of the light source, and wherein the width of the Taber peak may be greater than the width of the pixels in the pixel array. width to overfill the pixel aperture to facilitate alignment of the waveguide illuminator with the display panel.

The light source may be a polychromatic light source for providing an input beam comprising light of a plurality of color channels.

The beam splitter may be configured to couple a plurality of the plurality of color channels into respective waveguides in the array of waveguides, wherein each waveguide in the array of waveguides may be configured to be guided in the waveguide The light for each of the multiple color channels.

The waveguide illuminator may further include a color selective reflector located in a light path between the coupling grating array and the substrate of the display panel, wherein the color selective reflector may be configured to Different color channels of light within the color channel provide different optical path lengths.

The color selective reflector may comprise a stack of dichroic reflectors configured to reflect portions of the plurality of beamlets out of the coupling grating array back. Propagate through the illuminator substrate to illuminate pixels in the pixel array.

The beam splitter may be configured to couple different color channels of the plurality of color channels into different waveguides in the waveguide array, wherein the different waveguides may be disposed at different depths within the illuminator substrate .

The waveguide array may include a ridge waveguide, wherein the gratings in the outcoupling grating array may be formed in the ridge waveguide in the waveguide array.

According to a second aspect of the present disclosure, there is provided a method for coupling a display panel including a pixel array to a waveguide illuminator including an outcoupling grating array coupled to the waveguide array, in which In the waveguide array, a plurality of sub-beams of an input light beam propagate in the waveguide parallel to rows of the pixel array, and the method includes: using the coupling-out grating array to couple the plurality of sub-beams propagating in the waveguide array. A plurality of portions are coupled out to propagate through the substrate of the display panel toward the pixel array; forming a Taber peak array at the plane of the pixel array; and tuning the central wavelength of the light beam such that each Taber peak array in the Taber peak array The position of the peak is centered on the pixel in this pixel array.

The method may also include using a light source to provide the input beam.

The method may also include splitting the input beam provided by the light source using a beam splitter coupled to the waveguide array.

The method may also include using a polychromatic light source with an input beam that includes multiple color channels of light.

The method may also include coupling a plurality of the plurality of color channels into respective waveguides in the waveguide array using a beam splitter; and directing the plurality of color channels in each waveguide in the waveguide array for each color channel in the light.

The method may further include using a color selective reflector in a light path between the coupling grating array and the display panel to provide different light path lengths for light in different color channels of the plurality of color channels.

The method may further include using a beam splitter to couple different color channels of the plurality of color channels into different waveguides in the waveguide array, wherein the different waveguides may be disposed at different locations within the substrate of the illuminator. at depth.

According to a third aspect of the present disclosure, there is provided a method for coupling a display panel including a pixel array to a waveguide illuminator including an outcoupling grating array coupled to the waveguide array, the The method includes: using a light source to provide an input beam having an emission bandwidth; using a beam splitter to split the input beam into a plurality of sub-beams; causing the plurality of sub-beams to propagate in the waveguide parallel to the rows of the pixel array; using The decoupling grating array couples portions of the plurality of beamlets propagating in the waveguide array to propagate through the substrate of the display panel toward the pixel array; and forming a Taber peak array at the plane of the pixel array; Wherein, the width of the Taber peak in the Taber peak array depends on the emission bandwidth of the light source, and the width of the Taber peak is greater than the width of the pixels in the pixel array to overfill the aperture of the pixel to facilitate the waveguide. Alignment of the illuminator with the display panel.

The light source may be a polychromatic light source that provides an input beam comprising light of a plurality of color channels. The beam splitter can couple a plurality of the plurality of color channels into respective waveguides in the waveguide array.

The method may further include using a color selective reflector in a light path between the coupling grating array and the display panel to provide different light path lengths for light in different color channels of the plurality of color channels.

The light source may be a polychromatic light source that provides an input beam comprising light of a plurality of color channels. The beam splitter can couple different color channels of the plurality of color channels into different waveguides in the waveguide array. The different waveguides may be disposed at different depths within the substrate of the illuminator.

Description of drawings

Exemplary embodiments will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic plan view of a waveguide illuminator of the present disclosure;

Figure 2 is a schematic plan view of an embodiment of the illuminator of Figure 1;

3A is a schematic top view of a polychromatic waveguide illuminator of the present disclosure having a surface relief grating on a ridge waveguide;

3B is a schematic top view of a portion of the multicolor waveguide illuminator of FIG. 3A overlaid with a single RGB pixel of the display panel;

Figure 3C is a three-dimensional schematic diagram of the ridge waveguide of the multi-color waveguide illuminator of Figure 3A;

4A is a schematic cross-sectional view of a display device of the present disclosure;

4B is an enlarged cross-sectional view of the pixel array of the display device of FIG. 4A, wherein the pixel array is superposed with a peaked Talbot optical power density distribution of the illumination light;

Figure 5 is a calculated Taber plot of optical power density distribution through the thickness of the display panel substrate of the display device of Figure 4A;

6 is a side cross-sectional view of the display device of FIG. 4A illustrating a Taber pattern of optical power density inside the display substrate;

Figure 7 is a schematic diagram of the cross-sectional view of Figure 6, showing the principle of wavelength tuning of the Taber peak position;

Figure 8 is a schematic diagram of the cross-sectional view of Figure 6, illustrating the principle of overfilling the pixel aperture with broadband illumination light;

Figure 9 is a cross-sectional exploded view of an embodiment of a waveguide illuminator with a buried dichroic mirror;

Figure 10 is a schematic diagram of a multi-color embodiment of the waveguide illuminator of Figure 4A;

Figure 11 is a flow chart of a method of coupling a waveguide illuminator to a display panel under wavelength tuning;

12 is a flowchart of a method of coupling a waveguide illuminator to a display panel with pixel aperture overfill;

13 is a view of an augmented reality (AR) display of the present disclosure having the form factor of a pair of glasses; and

Figure 14 is a three-dimensional view of a head mounted display (HMD) of the present disclosure.

Detailed ways

Although the present teachings are described in connection with various embodiments and examples, there is no intention to limit the present teachings to such embodiments. On the contrary, as those skilled in the art will appreciate, the present teachings cover various alternatives and equivalents. All statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Furthermore, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

As used herein, the terms "first", "second" and the like are not intended to imply a sequential order but are intended to distinguish one element from another unless expressly stated otherwise. Similarly, the sequential order of the method steps does not imply a sequential order of their performance unless expressly stated.

In visual displays that include an array of pixels coupled to an illuminator, light utilization efficiency depends on the ratio of the geometric area occupied by each pixel to the total area of the display panel. For near-eye displays and/or microdisplays commonly used in head-mounted displays, this ratio may be lower than 50%. Color filters on display panels that transmit no more than 30% of incident light on average further hinder efficient backlight utilization. In addition, for polarization-based display panels (eg, Liquid Crystal (LC) display panels), there may be a 50% polarization loss. All these factors greatly reduce the display's light utilization and overall wall plug efficiency, which is undesirable.

According to the present disclosure, the light utilization efficiency and electro-optical conversion efficiency of a backlight display can be improved by providing a waveguide illuminator that generates a peak distribution of optical power density at the display panel, where individual peaks of the optical power density overlap with the display pixels. In displays where the illuminator emits light in primary colors such as red, green and blue, the color of the illumination light can be matched to the color filter, or the color filter can be omitted entirely. For polarization-based displays, the polarization of the emitted light can be matched to a predefined input polarization state. By matching the spatial distribution, transmission wavelength, and/or transmission polarization characteristics of the display panel's pixels, the useful portion of the display light that is not absorbed or reflected by the display panel on its way to the viewer's eyes can be significantly increased, thereby significantly improving the performance of the display. Electro-optical conversion efficiency.

Single-mode waveguides or few-mode waveguides (e.g., ridge waveguides) combined with laser illumination allow efficient control of light properties such as color and directionality. When light propagates in a single spatial mode, the output can be diffraction-limited and highly directional. Single-mode propagation allows light to be coupled out at specific points on the waveguide and can be combined with focusing couplers if required. Narrow spectrum laser illumination enables large color gamut display. Additionally, single-mode waveguides can maintain polarization, which enables highly polarized output from a backlight unit without the need for a polarizer.

The Taber effect can be used to generate peak illumination of display panels. One challenge associated with this approach is the alignment of the illuminator with the display panel, which is required to align the spots of the illumination pattern with the pixels of the display panel. Wavelength tuning of the display panel may be employed to tune the Taber pattern with respect to the pixels of the display panel. In some embodiments, the wavelength spectrum of the illumination light is broad enough to overfill the apertures of the pixels of the display panel.

According to the present disclosure, there is provided a display device including a display panel and a waveguide illuminator coupled to the display panel. The display panel has a pixel array on a display substrate. The waveguide illuminator includes: an illuminator substrate; a beam splitter supported by the illuminator substrate for dividing an input beam into a plurality of sub-beams; and a waveguide array, each waveguide being supported by the illuminator substrate and extending parallel to the rows of pixels of the pixel array, wherein each waveguide in the array is configured to guide one of the plurality of beamlets in the waveguide; and an array of outcoupling gratings, the outcoupling grating An array is coupled to the waveguide array. The decoupling grating array extends along the pixel array to couple portions of the plurality of sub-beams to propagate through the display substrate and form a Taber peak array at the plane of the pixel array. The position of each Taber peak in the Taber peak array corresponds to the position of each pixel of the pixel array.

A light source may be provided for generating an input beam and coupling the input beam to the beam splitter. The light source may be tunable in wavelength, and the position of the individual Taber peaks may depend on the wavelength of the light source. The wavelength can be chosen so that the Taber peak is centered on the pixel in the pixel array. The width of the Taber peaks in the Taber peak array generally depends on the emission bandwidth of the light source. In some embodiments, the width of the Taber peak can be made larger than the width of the pixels in the pixel array for overfilling the aperture of the pixels to facilitate alignment of the waveguide illuminator with the display panel.

In some embodiments, the waveguide array includes ridge waveguides. The gratings in the outcoupling grating array may be formed in ridge waveguides in the waveguide array.

In embodiments where the light source is a polychromatic light source for providing an input beam comprising a plurality of color channels of light, the beam splitter may be configured to couple a plurality of the plurality of color channels into the waveguide array. in each waveguide. Each waveguide in the array of waveguides may be configured to guide light in the waveguide for each of a plurality of color channels. In such embodiments, the waveguide illuminator may further include a color-selective reflector located in the optical path between the coupling-out grating array and the substrate of the display panel.

The color selective reflector may be configured to provide different optical path lengths for light in different color channels of the plurality of color channels. To this end, the color selective reflector may comprise a stack of dichroic reflectors configured to couple the portions of the plurality of beamlets out of the decoupling grating array. The reflection propagates back through the illuminator substrate to illuminate the pixels in the pixel array. Alternatively or additionally, the beam splitter may be configured to couple different color channels of the plurality of color channels to different waveguides in the waveguide array, the different waveguides being disposed at different locations within the illuminator substrate. at depth.

In accordance with the present disclosure, there is provided a method for coupling a display panel including a pixel array to a waveguide illuminator including an outcoupling grating array coupled to the waveguide array, in the waveguide array , multiple sub-beams of the input beam propagate in waveguides parallel to the rows of the pixel array. The method includes using the outcoupling grating array to couple portions of beamlets propagating in the waveguide array to propagate through a substrate of the display panel toward the pixel array; forming a Taber peak array at a plane of the pixel array ; and tuning the central wavelength of the light beam so that the position of each Taber peak in the Taber peak array is centered on the pixel in the pixel array. The method may also include using a light source to provide an input beam, and using a beam splitter coupled to the waveguide array to split the input beam provided by the light source.

In embodiments where the method uses a polychromatic light source for an input beam of light that includes multiple color channels, the method may further include using a color selective reflector in the light path between the outcoupling grating array and the display panel to provide The light of different color channels in the plurality of color channels provides different optical path lengths. The method may also include using a beam splitter to couple different ones of the plurality of color channels into different waveguides in the waveguide array, the different waveguides being disposed at different depths within the substrate of the illuminator.

In accordance with the present disclosure, there is also provided a method for coupling a display panel including a pixel array to a waveguide illuminator including an outcoupling grating array coupled to the waveguide array. The method includes: using a light source to provide an input beam with an emission bandwidth; using a beam splitter to split the input beam into a plurality of sub-beams; causing the plurality of sub-beams to propagate in a waveguide parallel to a row of the pixel array; using the coupling a grating array to couple portions of the plurality of beamlets propagating in the waveguide array to propagate through the substrate of the display panel toward the pixel array; and forming a Taber peak array at a plane of the pixel array.

The width of the Taber peaks in the Taber peak array may generally depend on the emission bandwidth of the light source. The width of the Taber peak can be made larger than the width of the pixels in the pixel array to overfill the aperture of the pixels to facilitate alignment of the waveguide illuminator with the display panel.

In embodiments where the light source is a polychromatic light source providing an input beam comprising a plurality of color channels of light and a beam splitter couples a plurality of the plurality of color channels into respective waveguides in the waveguide array, the The method may further include using a color selective reflector in the optical path between the coupling grating array and the display panel to provide different optical path lengths for light in different color channels of the plurality of color channels.

In some embodiments, the beam splitter can couple different ones of the plurality of color channels into different waveguides in the waveguide array, the different waveguides being disposed at different depths within the substrate of the illuminator. .

Referring now to FIG. 1 , a waveguide illuminator 104 includes an illuminator substrate 101 that supports an input waveguide 106 for directing an input beam 108 . Input beam 108 may be provided by a light source 110 (eg, a laser light source). As used herein, the term "waveguide" means a light guide structure that confines light propagation in two dimensions, like a lightwire, and operates in a single transverse mode or in several transverse modes (e.g., up to 12 propagation mode) to guide light. Waveguides can be straight, curved, etc. An example of a waveguide is a ridge waveguide. Waveguide illuminator 104 may be implemented in a Photonic Integrated Circuit (PIC).

Waveguide beam splitter 112 is coupled to input waveguide 106 . The function of the waveguide beam splitter 112 is to split the input beam 108 into a plurality of beamlets 114 . An array of waveguides 116 is coupled to a waveguide beam splitter 112 for directing beamlets 114 in the waveguides 116 . As shown, waveguides 116 extend parallel to each other. Each waveguide 116 is configured to direct one of the plurality of beamlets 114 from the waveguide beam splitter 112 to an end 129 of the waveguide 116 .

The array of rows 119 of coupling-out gratings 120 is supported by the substrate 101 of the waveguide illuminator 104 . Coupling gratings 120 of each row 119 are coupled to a waveguide 116 along the length of the waveguide 116 for coupling a plurality of one of a plurality of beamlets 114 propagating in the waveguide 116 . Part 122 is coupled out. The plurality of portions 122 coupled out by the couplers 120 of all rows 119 form a two-dimensional array of beamlet portions 122 that couple out from the waveguide array and exit at, for example, an acute or right angle to the substrate 101 . The X- and Y-spacing of the two-dimensional array of beamlet portions 122 may, but need not, match the X- and Y-spacing of the display panel illuminated by the waveguide illuminator 104 .

Referring now to FIG. 2 , waveguide illuminator 204 includes light source 210 and PIC 234 . Light source 210 provides input beam 208 to PIC 234. PIC 234 includes optical scheduling circuitry 241 coupled to light source 210 . Optical scheduling circuitry 241 is configured to receive beam 208 and split the beam into a plurality of beamlets that propagate in respective waveguides. To split the beam 208 into multiple sub-beams, the optical scheduling circuit 241 may include a binary tree of 1×2 waveguide beam splitters 244 coupled to each other through waveguides 245 . Other configurations of the optical scheduling circuit 241 are also possible, for example, these configurations can be based on trees of Mach-Zehnder interferometers, slab waveguide interferometers, etc., and can include different wavelengths (e.g., different colors). The wavelength of the channel) is a separate waveguide tree for the light source component.

PIC 234 also includes an array of waveguides 216 coupled to optical scheduling circuit 241 for receiving beamlets from optical scheduling circuit 241. The waveguides 216 extend parallel to each other so that the beamlets propagate in the waveguides. PIC 234 also includes an array of outcoupling gratings 220 optically coupled to each waveguide 216 in the waveguide array for coupling out portions of the beamlets propagating in each waveguide 216. As shown, the outcoupling grating 220 is disposed parallel to the XY plane and performs the same or similar function as the outcoupling grating 120 of the waveguide illuminator 104 of FIG. 1 . Coupling gratings 220 couple out the beamlet portions from corresponding waveguides 216 such that these beamlet portions propagate through the substrate of the display panel and due to the Talbot planes separated from the array of outcoupling gratings 220 The optical power density peak array is formed by the Bo effect, as will be explained in more detail below.

Figures 3A-3C illustrate possible implementations of PIC 234 of Figure 2. Referring first to Figures 3A and 3B, PIC illuminator 304 includes a substrate 306 and an array of waveguides 307 supported by substrate 306 and extending along the pixel array of the display panel to be illuminated. In the PIC illuminator 304 shown in Figure 3A, each waveguide 307 includes an array of "red waveguides" 307R for transmitting light of red wavelengths, an array of "green waveguides" 307G for transmitting light of green wavelengths, and an array of "green waveguides" 307G for transmitting light of green wavelengths. An array of "blue waveguides" 307B that transmit blue wavelength light. Light of different wavelengths 308 may be generated by multi-wavelength light source 310 and distributed among different waveguides 307R, 307G, and 307B by optical scheduling circuitry 319 that is part of the PIC. The function of the optical scheduling circuit 319 is to spread the light along the Y direction and reroute the light into the waveguide 307 array. Similar to optical scheduling circuit 241 of Figure 2, optical scheduling circuit 319 may include a binary tree of beam splitters. A row of pixels among the plurality of pixels of the display panel may be disposed across all of the waveguides 307R of the red channel, the waveguide 307G of the green channel, and the waveguide 307B of the blue channel, respectively, which waveguides are vertically illustrated in FIG. 3A extend. A row of pixels is outlined by a dashed rectangle 313 in Figure 3A.

Figure 3B is an enlarged view of the three color channel waveguides located below a single pixel 303 of the display panel. Each of the three color sub-pixels corresponds to one of the red (R) channel, green (G) channel, and blue (B) channel of the image. For example, in the RGGB scheme, more than three color sub-pixels can be provided. Light portions may be coupled out or redirected from ridge waveguides 307R, 307G and 307B by respective gratings 312R, 312G and 312B shown in Figure 3C, forming an array of respective gratings for each color channel. Gratings 312R, 312G, and 312B may be chirped to focus the outcoupled beam in a direction along the waveguide (ie, vertically (ie, along the X-axis) in Figures 3A and 3B). Additionally, the grating grooves can be curved to focus the light in the horizontal direction in Figures 3A and 3B (ie, along the Y-axis). In the example of Figure 3C, gratings 312R, 312G, and 312B are formed in waveguides 307R, 307G, and 307B, respectively, but in some embodiments, the grating array may be formed separately and optically coupled to the waveguide 307 array.

In order to focus the coupled out light beam in the horizontal direction in Figure 3B, a ID microlens 318 can be provided as shown. As used herein, the term "1D microlens" refers to a lens that focuses light primarily in one dimension, for example, a cylindrical lens. Instead of ID lenses, 2D lenses (ie lenses that focus light in two orthogonal planes) may be provided. An array of microlenses 318 disposed in the optical path between gratings 312R, 312G, and 312B and pixels 303R, 303G, and 303B may be used to at least partially focus light redirected by gratings 312R, 312G, and 312B to propagate through the corresponding Sub-pixels 303R, 303G and 303B. A configuration for one white pixel 303 is shown in Figure 3B. The white pixel configuration can be repeated for each white pixel of the display panel.

FIG. 4A shows a display device 400 using the waveguide illuminator 104 of FIG. 1 . The waveguide illuminator 204 of Figure 2 and/or the PIC illuminator 304 of Figure 3A may also be used. The display device 400 of FIG. 4A includes a display panel 402 illuminated by a waveguide illuminator 104. Display panel 402 includes an array of pixels 406 supported by a display substrate 408 . As a non-limiting example, display panel 402 may be a liquid crystal (LC) panel that includes a thin layer of LC fluid between a pair of substrates, one substrate carrying an array of electrodes defining transmissive LC pixels. Light source 110 provides an input beam 108 which is split by beam splitter 112 into beamlets propagating in waveguides 116 in a waveguide array, as explained above with reference to FIG. 1 . Coupling grating 120 couples out portions 122 of beamlets 114 from waveguide illuminator 104 such that the outcoupled beam portions 122 propagate through display substrate 408 and form light at the array of pixels 406 due to the Talbot effect. Array of power density peaks 422 (Fig. 4B), the Taber effect is further illustrated below in Figs. 5 and 6. The location of optical power density peak 422 (FIG. 4) corresponds to the location of pixel 406, for example, optical power density peak 422 may be centered on pixel 406. Since the optical power density peak 422 is centered on the pixel 406, most of the illumination light propagates through the pixel 406 and is not blocked by the opaque inter-pixel area 407, thereby increasing the overall luminous flux and therefore increasing the electro-optical conversion efficiency of the display device 400 . As shown, one peak 422 may be provided for each pixel 406. In some embodiments, the distance between peaks 422 may be equal to M times p, where p is the pitch of the pixel array and M is an integer greater than or equal to 1 (≥1). For example, in embodiments where a Taber pattern is generated at several wavelengths of illumination light, a peak 422 at a wavelength of a specific color channel may be set for each color sub-pixel of the pixel array, with several sub-pixels forming one RGB pixel.

The beam portion 122 forming the array of Taber peaks 422 is spatially modulated by the array of pixels 406 and propagates toward an ocular lens 423. Viewing lens 423 collimates beam portion 122 and redirects the beam portion toward eyebox 424 of display device 400 . The function of the viewing lens 423 is to form an image in the angular domain at the eye zone 424 from the image in the linear domain displayed by the display panel 402 . In this context, the term "image in the linear domain" refers to an image in which the individual pixels of the image are represented by the coordinates of a beam whose color and/or brightness represents the color and/or brightness of those pixels. The term "image in the angular domain" therefore refers to an image in which the individual pixels of the image are represented by the beam angle of a beam whose color and/or brightness represents the color and/or brightness of those pixels.

FIG. 5 shows the Taber stripe pattern 500 as an optical power density map in the display substrate 408 ( FIG. 4A ) of the display panel 402 . The horizontal direction in FIG. 5 is the direction through the thickness of the substrate of the display panel 402 . Taber stripe pattern 500 originates from a first plane 501 disposed parallel to the XY plane in Figure 4A. The decoupling grating 120 is arranged in the first plane 501 . In FIG. 5 , light propagates from left to right, forming an array of optical power density peaks at different distances from the first plane 501 . The optical power density distribution at the first plane 501 is repeated at a second plane 502 which is separated from the first plane 501 by a Taber pattern period T, which in this example is equal to 0.5 mm. The array of pixels 406 may be located at the second plane 502 . For embodiments where the array of coupling gratings 120 is disposed on the surface of the illuminator that engages the display substrate 408, as shown in Figure 4A, the Taber pattern period (in the thickness direction of the display substrate 408) may simply be equal to the thickness of the substrate.

More generally, according to the following equation (1), the distance D between the plane of the coupling grating and the plane of the pixel may include only a part of the Taber pattern, or several such patterns.

D = KT ² /(N λ), (1)

Where, K and N are integers greater than or equal to 1 (≥1), and λ is the wavelength of the light beam in the display substrate 408 . In the above equation (1), K is the number of repetitions of the Taber pattern, and N defines Taber peak sub-planes with higher pitch. For example, at the intermediate plane 503 which is 0.25 mm apart from the first plane 501 and the second plane 502, this spacing is doubled.

Turning to FIG. 6 , a Taber pattern 600 showing the optical power density distribution within the substrate 408 is formed by optical interference between different portions of the beamlets 114 propagating in the waveguide 116 . As such, the position of optical power density peak 422 relative to pixel 406 of display panel 402 depends on the relative phase between the portions of beamlet 114 coupled out by coupling out grating 120 . The relative phase depends on the wavelength; therefore, the optical power density peak 422 can be shifted by tuning the wavelength of the beamlet 114 . Providing a wavelength tunable light source (eg, a tunable laser) and tuning the wavelength can center the optical power density peak 422 on the pixel 406 of the display panel 402 . When the wavelength of light source 110 is tuned, optical power density peak 422 shifts as shown by arrow 630.

Figure 7 further illustrates the principle of wavelength tuning. Schematic diagram 700 depicts the optical path of the outcoupled portion of beamlet 114 . The first path pair is shown in solid lines. The first path pair results in a local interference maximum 721 at the inter-pixel region 407 . The left path length 701A is equal to a, and the right path length 701B is equal to b+c. The condition for the local interference maximum can be written as

b + c – a = nλ, (2)

where n is an integer and λ is the wavelength of beamlet 114 in the corresponding medium.

The second path pair 702A, 702B is shown in dashed lines. The second path pair results in a local interference maximum 722 centered on pixel 406 . The left path length 702A is equal to a’, and the right path length 701B is equal to b+c’, where b is the distance between adjacent outcoupling gratings 120. The condition for the local interference maximum in this case can be written as

b+c’–a’=nλ(3a)

By selecting a wavelength λ that satisfies condition (3a), the local interference maximum 722 (ie, Taber optical power density peak 422) can be centered on the pixel 406. When c’=a’, as shown in Figure 7, condition (3a) is simplified to

b=nλ(3b)

Adjusting the location of the local interference maximum 722 of the Taber pattern 600 by tuning the wavelength of the light source 110 enables maximum transmission of light emitted by the waveguide illuminator 104 through the display panel 102 when the display device 400 is assembled. This adjustment may be particularly advantageous for miniature display panels with small pixels on the order of several microns and for tight pixel pitches.

Instead of tuning the wavelength of the light source, it is possible to provide a light source with a bandwidth that is wide enough so that the Taber peak overfills the aperture of the pixels of the display panel. Referring to the illustrative example of FIG. 8 , a schematic diagram 800 depicts an optical path 802 of a portion of a beamlet 114 that is coupled out of a coupling grating 120 . In this example, it is assumed that condition (3b) is satisfied at the center wavelength of the light source, whereby a local interference maximum occurs at the center of the pixel 406 of the display panel 402. The width of the Taber peaks 822 in the Taber peaks 822 array depends on the emission bandwidth of the light source 110 . By selecting a sufficiently wide emission bandwidth of the light source, the Taber peak 822 can be made wide enough such that the width of the Taber peak is larger than the width (aperture) of the pixels 406 of the display panel. In other words, Taber peak 822 overfills the aperture of pixel 406 to facilitate alignment of waveguide illuminator 104 with display panel 102 .

In some embodiments of display device 400 (FIG. 4A), light source 110 is a polychromatic light source that provides an input beam that includes multiple color channels. Since the Taber distance D depends on the wavelength defined by equation (1) above, the optical configuration of the waveguide illuminator needs to be adapted so that the Taber planes for different color channels overlap at the pixel array of the display panel. In embodiments in which beam splitter 112 (Figs. 1 and 4) is configured to couple a plurality of color channels into separate waveguides 116, the light of the plurality of color channels in separate waveguides 116 propagates and couples out from the same plane. To ensure that the Taber planes for different color channels overlap at the array of display pixels 406 of display panel 402 (FIG. 4), optical components may be provided to make the optical path between the outcoupling grating 120 and the plane of the pixels 406 dependent on the wavelength. Referring to FIG. 9 , as a non-limiting illustrative example, waveguide illuminator 904 includes the elements of illuminator 204 of FIG. 2 . The waveguide structure of the optical scheduling circuit 241 is formed in the core layer 952 supported by the illuminator substrate 954, which waveguide structure includes a waveguide beam splitter and couples the linear waveguide with the linear waveguide 220 array. The illuminator 904 also includes a color selective reflector 956 located in the optical path of the light beam 208 between the array of coupling gratings 220 formed in the core layer 952 and the substrate 908 of the display panel. Color selective reflector 956 is configured to provide different optical path lengths for different wavelengths of light beam components (ie, for different color channels of light). To this end, the color-selective reflector 956 may comprise a stack of a first reflector 961 , a second reflector 962 and a third reflector 963 consisting of Reflector substrate 964 is supported at different depths (ie, different Z coordinates) within reflector substrate 964 . The first reflector 961 and the second reflector 962 may be dichroic reflectors. The first reflector 961 reflects the light of the first wavelength and transmits the light of the second wavelength and the third wavelength, and the second reflector 962 transmits the light of the first wavelength and the third wavelength and reflects the light of the second wavelength. The third reflector 963 may be a mirror that reflects 100% of light of all wavelengths, or it may be a dichroic mirror that only reflects light of a third wavelength to reduce color channel crosstalk.

In operation, the light beam 208 carries a first beam component 271 , a second beam component 272 and a third beam component 273 , respectively represented by for carrying light of the first wavelength, light of the second wavelength and light of the third wavelength. For example, first beam component 271, second beam component 272, and third beam component 273 may be at red, green, and blue wavelengths, respectively. The decoupling grating 220 decouples out the light portion 212 carrying all beam components. The first beam component 271 is reflected by the first reflector 961 and the remaining beam components 272 and 273 are transmitted through the first reflector. The second beam component 272 is reflected by the second reflector 962 and the third beam component 273 is transmitted through the second reflector. Finally, the third beam component 273 is reflected by the third reflector 963 . Due to split beam propagation, different beam components will travel different distances before they reach the substrate 908 of the display panel. Different distances can be selected to compensate for different distances of light of different wavelengths to the Taber plane as defined by equation (1) above, so that the peaked Taber patterns overlap at the pixel plane of the display panel. The color selective reflector 956 reflects portions of the beamlets (ie, beam components of different wavelengths or colors) coupled out of the array of outcoupling gratings 220 as propagating back through the illuminator substrate 954 to illuminate the display panel. on pixels.

Referring to Figure 10, a waveguide illuminator 1004 is similar to the waveguide illuminator 104 of Figure 1, includes similar components, and may be implemented as a PIC. The waveguide illuminator 1004 of Figure 10 also includes a first coupler 1041, a second coupler 1042, and a third coupler 1043 (eg, an edge coupler). The detector and the third coupler are used to couple the light of the first light source 1051, the second light source 1052 and the third light source 1053 (eg, laser light source) into the waveguide illuminator 1004. The first, second, and third light sources 1051 , 1052 , and 1053 may respectively emit light 1061 , light 1062 , and light 1063 of a first color channel (eg, red light such as a red channel, green light for the green channel and blue light for the blue channel).

The wavelength multiplexer 1070 is coupled to the first coupler 1041, the second coupler 1042 and the third coupler 1043, and is used to separate the light 1061 of the first color channel and the light 1062 of the second color channel. and the third color channel light 1063 are combined into the input beam 108 and the input beam 108 is coupled into the input waveguide 106 . The abbreviation "CWM" in Figure 10 represents a "coarse" wavelength multiplexer with wavelength spacing of 20 nm or more. Waveguide beam splitter 1012 is an embodiment of waveguide beam splitter 112 of waveguide illuminator 104 of FIG. 1 . The waveguide beam splitter 1012 of Figure 10 includes a 1×N beam splitter 1072, where N is an integer, used to divide the input beam 108 into N portions 1008, each portion in N output waveguides. 1016 propagates in an output waveguide. 1×N beam splitter 1072 may include, for example, a 1×2 beam splitter array arranged as a binary tree in waveguide illuminator 204 of FIG. 2 . The N portions 1008 may all have the same optical power.

The waveguide beam splitter 1012 also includes N wavelength demultiplexers 1074, each wavelength demultiplexer coupled to a specific output waveguide among the N output waveguides 1016, for respectively dividing the light of the first color channel 1061, The light of the second color channel 1062 and the light of the third color channel 1063 separate to couple to and propagate in different color channels in different waveguides 116 in the waveguide array 1080 . Different waveguides may be disposed at different depths within the illuminator substrate to ensure that the Taber plane of light 1061 of the first color channel, light 1062 of the second color channel, and light 1063 of the third color channel is within the pixel array of the display panel. overlap on the plane. In other words, different depths of the waveguides in waveguide array 1080 can be selected such that the Taber peaks of light for different color channels are focused at the pixel plane.

Turning to FIG. 11 , and referring also to FIGS. 1 , 4A, and 4B, FIG. 11 presents a diagram for coupling a display panel (eg, display panel 402 of FIG. 4A ) to a waveguide illuminator (eg, FIGS. 1 and 4A Method 1100 of waveguide illuminator 104). Optional steps of method 1100 are represented by dashed rectangles. Method 1100 of Figure 11 may include providing (1102) an input beam using a light source (eg, light source 110 of Figure 4A). The light source 110 may be a monochromatic light source or a multi-color light source. Method 1100 may include splitting an input beam provided by light source 110 using a beam splitter (eg, beam splitter 112 coupled to an array of waveguides 116) (1104). Method 1100 includes using an array of outcoupling gratings (eg, outcoupling grating 120 (FIG. 4A)) to couple (1108) portions of a beamlet propagating in a waveguide array into pixels propagating through display panel 402 toward an array of pixels 406. Substrate 408. An array of Taber peaks (eg, Taber peak 422 in Figure 4B) is formed (1110) at the plane of the array of pixels 406. The center wavelength of the beam 108 provided by the light source 108 is tuned (1112) so that the position of each Taber peak 422 in the Taber array is centered on the pixel 406 in the pixel array.

In embodiments in which light source 110 is a polychromatic light source that generates an input beam carrying multiple color channels of light, method 1100 may include coupling 1105 a plurality of the plurality of color channels using a beam splitter. Light for each of the plurality of color channels in each waveguide of the waveguide array is then directed (1106) in each of the waveguides in the waveguide array. A color-selective reflector (eg, color-selective reflector 956 in FIG. 9) may be used (FIG. 11; 1109) in the optical path between the output coupling grating array and the display panel to provide color-selective reflectors for different ones of the multiple color channels. The light provides different optical path lengths, as explained above with reference to Figure 9.

12 illustrates a method for coupling a display panel (eg, display panel 402 of FIG. 4A) to a waveguide illuminator (eg, waveguide illuminator 104 of FIGS. 1 and 4A) and/or waveguide illuminator 1004 of FIG. 10 Method 1200. Method 1200 includes using a light source to provide (1202) an input beam with a sufficiently wide emission bandwidth. A beam splitter (eg, beam splitter 112 in Figure 1 or beam splitter 1012 in Figure 10) is used to divide the input beam into (Figure 12; 1204) a plurality of sub-beams. The plurality of beamlets propagate in waveguides parallel to the rows of the pixel array (1206). The decoupling grating array is used to decouple (1208) portions of the beamlets propagating in the waveguide array through the substrate of the display panel toward the pixel array, for example, as shown in Figure 4A. Method 1200 also includes forming (1210) an array of Taber peaks at a plane of the pixel array, for example, as shown in Figure 4B. The width of the Taber peaks in the Taber peak array depends on the emission bandwidth of the light source. To facilitate alignment of the waveguide illuminator with the display panel, the bandwidth needs to be wide enough such that the width of the Taber peak is larger than the width of the pixels in the pixel array to overfill the aperture of the pixels, as explained above and as shown in Figure 8 of.

In some embodiments, the light source may include a polychromatic light source that provides an input beam that includes multiple color channels of light. Beam splitter 112 may couple a plurality of color channels into respective waveguides 116 in the waveguide array. In such embodiments, method 1200 may further include using a color-selective reflector (eg, color-selective reflector 956 of FIG. 9) in the optical path between the coupling grating array and the display panel to provide color-selective reflectors in the plurality of color channels. Different color channels of light provide different optical path lengths (dashed rectangle at 1209). Alternatively, light of different color channels may be coupled into different waveguides in a waveguide array (eg, as in waveguide illuminator 1004 of Figure 10). For such embodiments, waveguides carrying light of different color channels may be provided at different depths within the substrate of the illuminator to achieve the same goal of providing different optical path lengths for different ones of the plurality of color channels.

Turning to Figure 13, a virtual reality (VR) near-eye display 1300 includes a frame 1301 that supports for each eye: a light source 1302; a waveguide illuminator 1306 that is operatively coupled to the light source 1302 and includes the components disclosed herein Any of the waveguide illuminators; (the light source may be built into the illuminator); a display panel 1318 that includes an array of display pixels, wherein the position of the decoupling grating in the waveguide illuminator 1306 is consistent with the polarization-tuned pixels of the display panel 1318 and a viewing lens 1332 for converting the image in the linear domain generated by the display panel 1318 into an image in the angular domain for direct viewing at the eye zone 1326 . A plurality of eye zone illuminators 1362 (shown as black dots) may be placed on the side of the waveguide illuminator 1306 facing the eye zone 1326. Eye tracking cameras 1342 may be provided for each eye zone 1326.

The purpose of the eye tracking camera 1342 is to determine the position and/or orientation of the user's two eyes. The eye zone illuminator 1362 illuminates the eye at the corresponding eye zone 1326, allowing the eye tracking camera 1342 to acquire an image of the eye and provide a reference reflection (ie, flicker). The flicker can be used as a reference point in the acquired image of the eye, thereby facilitating determination of the eye's gaze direction by determining the position of the eye's pupil image relative to the flicker image. In order to prevent the light of the eye zone illuminator 1362 from distracting the user's attention, the eye zone illuminator 1362 can be made to emit light that is invisible to the user. For example, infrared light may be used to illuminate eye zone 1326.

Turning to Figure 14, HMD 1400 is an example of an AR/VR wearable display system that surrounds a user's face to greater immerse the user in an AR/VR environment. HMD 1400 can generate fully virtual 3D images. HMD 1400 may include a front body 1402 and a strap 1404 that may be secured around a user's head. The front body 1402 is configured for placement in front of the user's eyes in a secure and comfortable manner. The display system 1480 may be disposed in the front body 1402 for presenting AR/VR images to the user. Display system 1480 may include any of those disclosed herein. The sides 1406 of the front body 1402 may be opaque or transparent.

In some embodiments, front body 1402 includes a localizer 1408 , an inertial measurement unit (IMU) 1410 for tracking the acceleration of HMD 1400 , and a position sensor 1412 for tracking the position of HMD 1400 . IMU 1410 is an electronic device that generates data indicative of the position of HMD 1400 based on measurement signals received from one or more position sensors 1412 that are generated in response to movement of HMD 1400 One or more measurement signals. Examples of position sensors 1412 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU 1410, Or some combination of them. Position sensor 1412 may be located external to IMU 1410, internal to IMU 1410, or some combination thereof.

The locator 1408 is tracked by an external imaging device of the virtual reality system so that the virtual reality system can track the position and orientation of the entire HMD 1400. Information generated by IMU 1410 and position sensor 1412 may be compared to the position and orientation obtained by tracking locator 1408 to improve tracking accuracy of the position and orientation of HMD 1400 . As a user moves and turns in 3D space, accurate position and orientation are important to present the appropriate virtual scene to that user.

HMD 1400 may also include a depth camera assembly (DCA) 1411 that collects data describing depth information of a local area around some or all portions of HMD 1400. Depth information can be compared with information from IMU 1410 to more accurately determine the position and orientation of HMD 1400 in 3D space.

HMD 1400 may also include an eye tracking system 1414 for determining the orientation and position of the user's eyes in real time. The acquired position and orientation of the eyes also allows the HMD 1400 to determine the user's gaze direction and adjust the image generated by the display system 1480 accordingly. The determined gaze direction and vergence angle may be used to adjust the display system 1480 to reduce vergence adjustment conflicts. As disclosed herein, direction and vergence may also be used for exit pupil steering of a display. Furthermore, the determined vergence and gaze angles can be used to interact with the user, highlight objects, bring objects to the foreground, create additional objects or pointers, etc. An audio system may also be provided, including a set of small speakers built into the front body 1402, for example.

Embodiments of the present disclosure may include or be implemented in conjunction with artificial reality systems. Artificial reality systems somehow adjust sensory information about the external world obtained through the senses (e.g., visual information, audio, touch (somatosensory) information, acceleration, balance, etc.) before being presented to the user. As non-limiting examples, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (Mixed Reality, MR), mixed reality (HybridReality), or some combination thereof and/or derivatives thereof. Artificial reality content may include fully generated content or generated content combined with captured (eg, real-world) content. Artificial reality content can include video, audio, somatic or tactile feedback or some combination thereof. Any of these contents may be presented in a single channel or in multiple channels (eg, in stereoscopic video that produces a three-dimensional effect to the viewer). Furthermore, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof that are used, for example, in artificial reality Create content in reality and/or otherwise use it in an artificial reality (e.g., perform activities in an artificial reality). Artificial reality systems that provide artificial reality content can be implemented on a variety of platforms, including wearable displays (e.g., HMDs connected to a host computer system), standalone HMDs, near-eye displays with the form factor of glasses, mobile devices or computing system or any other hardware platform capable of delivering artificial reality content to one or more viewers.

The scope of the disclosure is not limited by the specific embodiments described herein. Indeed, various other embodiments and modifications in addition to those described herein will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Accordingly, such other embodiments and modifications are intended to be within the scope of this disclosure. Furthermore, although the present disclosure has been described herein in the context of specific implementations in specific environments for specific purposes, those of ordinary skill in the art will recognize that the applicability of the present disclosure is not so limited, and that the present disclosure Disclosure may be advantageously practiced in any number of circumstances for any number of purposes. Accordingly, the following appended claims are to be construed in light of the full breadth of the present disclosure as described herein.

Claims (20)

1. A display device, including: A display panel including a pixel array on a display substrate; and A waveguide illuminator, the waveguide illuminator is coupled to the display panel, the waveguide illuminator is used to illuminate the pixel array, the waveguide illuminator includes: illuminator substrate; a beam splitter supported by the illuminator substrate, the beam splitter configured to divide an input beam into a plurality of sub-beams; An array of waveguides, each waveguide being supported by the illuminator substrate and extending parallel to a row of pixels of the pixel array, wherein each waveguide in the array is configured to direct one of the plurality of beamlets in the waveguide a sub-beam of a coupling-out grating array, the coupling-out grating array being coupled to the waveguide array; Wherein, the coupling grating array extends along the pixel array to couple portions of the plurality of sub-beams to propagate through the display substrate and form a Taber peak at a plane of the pixel array. Array, wherein the position of each Taber peak in the Taber peak array corresponds to the position of each pixel in the pixel array. 2. The display device of claim 1, further comprising a light source for providing the input beam to the beam splitter. 3. The display device of claim 2, wherein the light source is tunable in wavelength; wherein, in operation, the position of each Taber peak depends on a wavelength of the light source, wherein the wavelength is selected such that the Taber peak is centered on a pixel in the pixel array. 4. The display device according to claim 2 or 3, wherein the light source has an emission bandwidth; Wherein, during operation, the width of the Taber peak in the Taber peak array depends on the emission bandwidth of the light source, wherein the width of the Taber peak is greater than the width of the Taber peak in the pixel array. The width of a pixel is such that it overfills the aperture of the pixel, thereby facilitating alignment of the waveguide illuminator with the display panel. 5. A display device according to any one of claims 2 to 4, wherein the light source is a polychromatic light source for providing the input beam comprising light of a plurality of color channels. 6. The display device of claim 5, wherein the beam splitter is configured to couple a plurality of the plurality of color channels into respective waveguides of the waveguide array, wherein the Each waveguide in the array of waveguides is configured to guide light in the waveguide for each of the plurality of color channels. 7. The display device of claim 6, wherein the waveguide illuminator further comprises a color selective reflector located between the outcoupling grating array and the substrate of the display panel in the optical path, wherein the color selective reflector is configured to provide different optical path lengths for the light of different color channels in the plurality of color channels. 8. The display device of claim 7, wherein the color-selective reflector comprises a stack of dichroic reflectors configured to be coupled by the outcoupling grating array. The portions of the outcoupled plurality of beamlets are reflected to propagate back through the illuminator substrate to illuminate pixels in the pixel array. 9. The display device of claim 5, wherein the beam splitter is configured to couple different color channels of the plurality of color channels into different waveguides in the waveguide array, wherein the The different waveguides are disposed at different depths within the illuminator substrate. 10. A display device according to any preceding claim, wherein the waveguide array includes a ridge waveguide, wherein gratings in the array of coupling-out gratings are formed in the ridge waveguides in the array of waveguides. . 11. A method for coupling a display panel comprising an array of pixels to a waveguide illuminator, the waveguide illuminator comprising an array of coupling gratings coupled to the array of waveguides, in the array of waveguides, A plurality of beamlets of an input beam are propagated in waveguides parallel to rows of the pixel array, the method comprising: using the outcoupling grating array to couple portions of the plurality of beamlets propagating in the waveguide array through a substrate of the display panel toward the pixel array; forming a Taber array at the plane of the pixel array; and The central wavelength of the light beam is tuned so that the position of each Taber peak in the Taber peak array is centered on the pixel in the pixel array. 12. The method of claim 11, further comprising using a light source to provide the input beam. 13. The method of claim 12, further comprising splitting the input beam provided by the light source using a beam splitter coupled to the waveguide array. 14. The method of claim 11, further comprising using a polychromatic light source for the input beam comprising light of multiple color channels. 15. The method of claim 14, further comprising: coupling a plurality of the plurality of color channels into respective waveguides in the array of waveguides using a beam splitter; and Light is directed for each of the plurality of color channels in each waveguide of the array of waveguides. 16. The method of claim 15, further comprising using a color-selective reflector in a light path between the coupling-out grating array and the display panel to provide light for different ones of the plurality of color channels. Available in different optical path lengths. 17. The method of claim 14, further comprising: Coupling different ones of the plurality of color channels into different waveguides in the waveguide array using a beam splitter, wherein the different waveguides are disposed at different depths within the substrate of the illuminator . 18. A method for coupling a display panel comprising an array of pixels to a waveguide illuminator comprising an array of outcoupling gratings coupled to the waveguide array, the method comprising: Use a light source to provide an input beam with an emission bandwidth; using a beam splitter to split the input beam into a plurality of sub-beams; causing the plurality of beamlets to propagate in respective waveguides parallel to rows of the pixel array; using the outcoupling grating array to couple portions of the plurality of beamlets propagating in the waveguide array through a substrate of the display panel toward the pixel array; and forming a Taber peak array at the plane of the pixel array; Wherein, the width of the Taber peak in the Taber peak array depends on the emission bandwidth of the light source, and the width of the Taber peak is greater than the width of the pixels in the pixel array, so as to pass The apertures of the pixels are filled thereby facilitating alignment of the waveguide illuminator with the display panel. 19. The method of claim 18, wherein: the light source is a polychromatic light source providing the input beam comprising light of a plurality of color channels; the beam splitter couples a plurality of the plurality of color channels into respective waveguides in the waveguide array; and The method also includes using a color-selective reflector in the optical path between the coupling-out grating array and the display panel to provide different optical path lengths for light in different color channels of the plurality of color channels. 20. The method of claim 18, wherein: the light source is a polychromatic light source providing the input beam comprising light of a plurality of color channels; the beam splitter couples different color channels of the plurality of color channels into different waveguides in the waveguide array; and The different waveguides are disposed at different depths within the substrate of the illuminator.