TW202319809A - Display device with waveguide-based talbot illuminator - Google Patents

Abstract

A waveguide illuminator for illuminating a display panel includes an input waveguide, a waveguide splitter coupled to the input waveguide, and a waveguide array coupled to the waveguide splitter. The waveguide array includes an array of out-couplers out-coupling portions of the split light beam to form an array of out-coupled beam portions for illuminating a display panel. The out-coupled beam portions undergo optical interference and form a Talbot pattern of illumination correlated with pixel array of the display panel, enabling an optical throughput increase by centering individual Talbot peaks on the display panel pixels.

Description

Display device with waveguide-based Talbot illuminator

The present invention relates to luminaires, visual display devices and related components and modules. REFERENCE TO RELATED APPLICATIONS

This application claims U.S. Provisional Patent Application No. 63/222,224, filed July 15, 2021, entitled "Single Mode Backlight Illuminator," and U.S. Nonprovisional Patent Application No. 17/525,211, filed November 12, 2021 No., and said patent application is incorporated herein by reference in its entirety.

Visual displays provide information, including still images, video, data, etc., to a viewer. Visual displays have applications in diverse fields including entertainment, education, engineering, science, professional training, advertising, just to name a few. Some visual displays, such as televisions, display images to several users, and some visual display systems, such as near-eye displays (NEDs), are intended for individual users.

An artificial reality system typically includes a NED (eg, a headset or a pair of glasses) configured to present content to a user. Near-eye displays can display virtual objects or combine images of real and virtual objects, such as in virtual reality (VR), augmented reality (AR) or mixed reality (MR) applications . For example, in an AR system, a user can view an image of a virtual object (eg, a computer-generated image (CGI)) superimposed with the surrounding environment by observing a "compositor" component. The combiner of a wearable display is typically transparent to external light, but includes some light routing optics to direct display light into the user's field of view.

Since the display of an HMD or NED is typically worn on the user's head, a large, bulky, unbalanced and/or heavy display device would be cumbersome and uncomfortable for the user to wear. Head-mounted display devices thus benefit from a compact and efficient configuration, including efficient light sources and illuminators that provide illumination of the display panel, high-flux eye lenses, and other optical elements in the train of image-forming elements.

One aspect of the present invention relates to a display device comprising: a display panel including a pixel array on a display substrate; and a waveguide illuminator coupled to the display panel for illuminating the pixel array, the waveguide The illuminator includes: an illuminator substrate; a beam splitter, supported by the illuminator substrate, for splitting an input light beam into a plurality of sub-beams; a waveguide array, supported by the illuminator substrate and parallel to the pixel columns of the pixel array, wherein each waveguide in the array is configured to direct one of the plurality of sub-beams therein; and an outcoupling grating array coupled to the waveguide array; wherein the outcoupling grating array is along the The pixel array extends for outcoupling part of the sub-beams to propagate through the display substrate and form an array of Talbot peaks at the plane of the pixel array, wherein individual ones of the array of Talbot peaks The location of the Talbert peak corresponds to the location of individual pixels in the pixel array.

Another aspect of the invention relates to a method for coupling a display panel comprising an array of pixels to a waveguide illuminator comprising an outcoupling grating array coupled to the waveguide array, wherein the plurality of sub-beams of the input light beam are parallel to The column of the pixel array propagating in the waveguide, the method comprising: using the outcoupling grating array to outcouple the part of the sub-beam propagating in the waveguide array to pass through the substrate of the display panel towards the pixel array propagation; forming an array of Talbot peaks at the plane of the pixel array; and tuning the center wavelength of the light beam so that the positions of individual Talbot peaks in the array of Talbot peaks are within the pixel array at the center of the pixel.

Another aspect of the invention relates to 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: using a light source to provide a emit an input beam with a wide bandwidth; use a beam splitter to split the input beam into a plurality of sub-beams; make the plurality of sub-beams propagate in the waveguide parallel to the columns of the pixel array; use the out-coupling grating array to coupling a portion of the sub-beams propagating in the waveguide array to propagate through the substrate of the display panel towards the pixel array; and forming an array of Talbot peaks at the plane of the pixel array; wherein the Talbot The width of the Talbot peaks in the peak array depends on the emission bandwidth of the light source, wherein the width of the Talbot peaks is larger than the width of the pixels in the pixel array for overfilling The pixel apertures facilitate alignment of the waveguide illuminator to the display panel.

Although the teachings are described in connection with various specific examples and examples, the teachings are not intended to be limited to such specific examples. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of ordinary skill in the art. All statements herein reciting principles, aspects, and specific examples of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, ie, any elements developed that perform the same function, regardless of structure.

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

In a visual display comprising an array of pixels coupled to an illuminator, the efficiency of light utilization depends on the ratio of the geometric area occupied by the pixels to the total area of the display panel. For microdisplays typically used in near-eye and/or head-mounted displays, this ratio may be less than 50%. Efficient backlight utilization is further hindered by color filters on the display panel, which on average transmit no more than 30% of the incident light. Besides, polarization-based display panels (such as liquid crystal (LC) display panels) may have 50% polarization loss. All of these factors can significantly reduce the light utilization and overall socket efficiency of the display, which is undesirable.

According to the present invention, light utilization and wall plug efficiency of backlit displays can be improved by providing a waveguide illuminator that produces a peak distribution of optical power density at the display panel, where the individual peaks of optical power density are related to the display panel. Pixels overlap. In displays where the illuminators emit light of primary colors, such as red, green and blue, the color of the illumination light can be matched to a color filter, or the color filter can be omitted entirely. For polarization-based displays, the polarization of emitted light can be matched to a predefined input polarization state. Matching the spatial distribution, transmitted wavelength and/or transmitted polarization characteristics of the pixels of the display panel enables us to significantly improve 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, This results in a considerable improvement in display wall plug efficiency.

Single- or minority-mode waveguides (eg, 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 us to outcouple light at specific points on the waveguide and enables the incorporation of focusing outcouplers if desired. The narrow spectrum of laser illumination enables large color gamut displays. Furthermore, the single-mode waveguide can maintain polarization, which results in a highly polarized output from the backlight unit without the need for polarizers.

The Talbot effect can be used to generate peak illumination of display panels. One challenge associated with this approach is the alignment of the illuminator to the display panel, which is required to align the spots of the illumination pattern with the pixels of the display panel. The Talbert pattern with respect to the pixels of the display panel can be tuned using wavelength tuning of the light source. 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 invention, a display device is provided, which includes 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 splitting an input light beam into a plurality of sub-beams; a waveguide array, supported by the illuminator substrate and parallel to the A pixel column of a pixel array, wherein each waveguide in the array is configured to guide a sub-beam of the plurality of sub-beams therein; and an outcoupling grating array coupled to the waveguide array. The outcoupling grating array extends along the pixel array for outcoupling portions of the sub-beams to propagate through the display substrate and form an array of Talbot peaks at a plane of the pixel array. The positions of individual Talbot peaks in the array of Talbot peaks correspond to the positions of individual pixels in the pixel array.

A light source may be provided for generating the input beam and coupling the input beam to the beam splitter. The light source can be tuned in wavelength, and the position of individual Talbot peaks can be made to depend on the wavelength of the light source. The wavelength can be selected such that the Talbot peak is at the center of the pixel of the pixel array. The width of the Talbot peaks in the Talbot peak array usually depends on the emission bandwidth of the light source. In some embodiments, the width of the Talbot peak can be made larger than the width of the pixels in the pixel array for overfilling the voids of the pixels to facilitate alignment of the waveguide illuminator to the display panel.

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

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

The color selective reflector can be configured to provide different optical path lengths for light of different ones of the plurality of color channels. To this end, the color selective reflector may comprise a stack of dichroic reflectors configured to reflect said portion of said sub-beams outcoupled by the outcoupling grating array, Backpropagating through the illuminator substrate to illuminate onto the pixels of the pixel array. Alternatively or additionally, the beamsplitter may be configured to couple different ones of the plurality of color channels into different waveguides of the array of waveguides disposed at different depths within the illuminator substrate.

According to the invention there is provided a method for coupling a display panel comprising an array of pixels to a waveguide illuminator comprising an outcoupling grating array coupled to an array of waveguides, wherein sub-beams of an input light beam are parallel The columns of the pixel array propagate in the waveguide. The method includes: using the outcoupling grating array to outcouple a portion of the sub-beams propagating in the waveguide array to propagate towards the pixel array via a substrate of the display panel; at a plane of the pixel array forming an array of Talbot peaks; and tuning a central wavelength of the light beam so that individual Talbot peaks in the array of Talbot peaks are located at the centers of pixels in the pixel array. The method may further include: using a light source to provide the input light beam; and using a beam splitter coupled to the waveguide array to split the input light beam provided by the light source.

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

According to the invention there is further provided a method for coupling a display panel comprising an array of pixels to a waveguide illuminator comprising an array of outcoupling gratings coupled to an array of waveguides. The method includes: using a light source to provide an input light beam with an emission bandwidth; using a beam splitter to split the input light beam into a plurality of sub-beams; making the plurality of sub-beams parallel to the columns of the pixel array in the propagating in a waveguide; using the outcoupling grating array to outcouple a portion of the sub-beams propagating in the waveguide array to propagate towards the pixel array via a substrate of the display panel; at a plane of the pixel array Form a Talbot peak array.

The width of the Talbot peaks in an array of Talbot peaks may generally depend on the emission bandwidth of the light source. The width of the Talbot peak can be made larger than the width of the pixels in the pixel array for overfilling the voids of the pixels to facilitate alignment of the waveguide illuminator to the display panel.

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

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

Referring now to FIG. 1 , a waveguide illuminator 104 includes an illuminator substrate 101 supporting an input waveguide 106 for guiding an input light beam 108 . The input light beam 108 may be provided by a light source 110 (eg, a laser source). Herein, the term "waveguide" denotes a light-guiding structure that confines light propagation in two dimensions (eg, light rays) and guides light in a single transverse mode or in several transverse modes (eg, up to 12 propagating modes). The waveguides may be straight, curved, etc. One example of a waveguide is a ridge-type waveguide. The waveguide illuminator 104 may be implemented in a photonic integrated circuit (PIC).

A waveguide splitter 112 is coupled to the input waveguide 106 . The function of the waveguide beam splitter 112 is to split the input beam 108 into a plurality of sub-beams 114 . An array of waveguides 116 is coupled to waveguide splitter 112 for directing sub-beams 114 in waveguides 116 . The waveguides 116 are aligned parallel to each other as illustrated. Each waveguide 116 is configured to direct one of the sub-beams 114 from the waveguide splitter 112 to the end 129 of the waveguide 116 .

The array of columns 119 of outcoupling gratings 120 is supported by the substrate 101 of the waveguide illuminator 104 . Each column 119 of outcoupling gratings 120 is coupled to the waveguides 116 of the waveguide array along the length of the waveguides 116 for outcoupling a portion 122 of one of the sub-beams 114 propagating in the waveguides 116 . Portions 122 outcoupled by all columns 119 of outcouplers 120 form a two-dimensional array of sub-beam portions 122 that are outcoupled from the waveguide array and exit to substrate 101 at an angle such as an acute or right angle. The X and Y pitches of the two-dimensional array of sub-beam portions 122 may, but need not, match the X and Y pitches 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 light beam 208 and split it into a plurality of sub-beams that propagate in individual waveguides. To split the light beam 208 into a plurality of sub-beams, the optical scheduling circuit 241 may include a binary tree of 1×2 waveguide splitters 244 coupled to each other by waveguides 245 . Other configurations of the optical scheduling circuit 241 are possible, e.g. it may be based on a tree structure of Mach-Zehnder interferometers, slab waveguide interferometers, etc. and may include different wavelengths (e.g. different color channels) The individual waveguide tree structure (waveguide tree) of the light source component under the wavelength).

PIC 234 further includes an array of waveguides 216 coupled to optical scheduling circuitry 241 for receiving sub-beams from optical scheduling circuitry 241 . The waveguides 216 are arranged parallel to each other to propagate the sub-beams therein. The PIC 234 further includes an array of outcoupling gratings 220 optically coupled to the waveguides 216 of the waveguide array for outcoupling portions of the sub-beams propagating in the waveguides 216 . As shown, outcoupling grating 220 is disposed parallel to the XY plane and performs the same or similar function as outcoupling grating 120 of waveguide illuminator 104 of FIG. 1 . The outcoupling grating 220 outcouples the sub-beam portions from the respective waveguides 216 to propagate through the substrate of the display panel, and due to the Talbert plane at the Talbot plane separated from the array of outcoupling gratings 220 The Burt effect forms an array of optical power density peaks, as will be explained in more detail below.

3A-3C illustrate possible implementations of the PIC 234 of FIG. 2 . Referring first to FIGS. 3A and 3B , a PIC illuminator 304 includes a substrate 306 and an array of waveguides 307 supported by the substrate 306 and arranged along an array of pixels of a display panel to be illuminated. In the PIC illuminator 304 shown in Figure 3A, the waveguides 307 include an array of "red waveguides" 307R for delivering light at red wavelengths, an array of "green waveguides" 307G for delivering light at green wavelengths, and an array of "blue waveguides" 307B for transporting light at blue wavelengths. Light 308 at different wavelengths can be generated by a multi-wavelength light source 310 and distributed among the different waveguides 307R, 307G and 307B by optical scheduling circuitry 319, which is part of the PIC. The function of the optical scheduling circuit 319 is to spread the light in the Y direction and reroute the light into the array of waveguides 307 . Optical scheduling circuit 319 may include a binary tree structure of optical splitters, similar to optical scheduling circuit 241 of FIG. 2 . A column of pixels of a display panel may be disposed across all waveguides 307R, 307G and 307B of the red, green and blue channels, respectively, which extend vertically in FIG. 3A. Columns of pixels are outlined in dashed rectangles 313 in FIG. 3A .

FIG. 3B is an enlarged view of three color channel waveguides under a single pixel 303 of a display panel. Each of the three color sub-pixels corresponds to one of the red (R), green (G) and blue (B) channels of the image, respectively. More than three color sub-pixels may be provided, for example in an RGGB scheme. 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 a corresponding grating array for each color channel. The gratings 312R, 312G, and 312B are chirpable for focusing the outcoupling light beam in a direction along the waveguide (ie, vertically in Figures 3A and 3B, ie, along the X-axis). Furthermore, the grating grooves can be curved to concentrate light in the horizontal direction in FIGS. 3A and 3B , ie along the Y-axis. In the example of FIG. 3C , gratings 312R, 312G, and 312B are formed in waveguides 307R, 307G, and 307B, respectively, but in some embodiments, grating arrays may be separately formed and optically coupled to the array of waveguides 307 .

To focus the outcoupled beams in the horizontal direction in FIG. 3B , a ID microlens 318 may be provided, as shown. Herein, the term "1D microlens" denotes a lens that focuses light primarily in one dimension, such as a cylindrical lens. An alternative to a 1D lens is to provide a 2D lens, ie a lens that focuses light in two orthogonal planes. 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 for propagation through through the corresponding sub-pixels 303R, 303G and 303B. The configuration of one white pixel 303 is shown in FIG. 3B. The white pixel configuration can be repeated for each white pixel of the display panel.

FIG. 4A illustrates a display device 400 using the waveguide illuminator 104 of FIG. 1 . The waveguide illuminator 204 of FIG. 2 and/or the PIC illuminator 304 of FIG. 3A may also be used. The display device 400 of FIG. 4A includes a display panel 402 illuminated by the 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 comprising a thin layer of LC fluid between a pair of substrates, one of which carries an array of electrodes defining transmissive LC pixels. A light source 110 provides an input beam 108 which is split by a beam splitter 112 into sub-beams propagating in waveguides 116 of the waveguide array, as explained above with reference to FIG. 1 . The outcoupling grating 120 outcouples a portion 122 of the sub-beam 114 from the waveguide illuminator 104 such that the outcoupled beam portion 122 propagates through the display substrate 408 and due to the The Talbot effect forms an array of optical power density peaks 422 at the array of pixels 406 (FIG. 4B). The location of the optical power density peak 422 ( FIG. 4 ) corresponds to the location of the pixel 406 , for example, the optical power density peak 422 may be at the center of the pixel 406 . Due to the optical power density peak 422 being at the center of the pixel 406, most of the illumination light travels through the pixel 406 and is not blocked by the opaque inter-pixel region 407, improving the overall light flux and thus wall plug efficiency of the display device 400. As shown, each pixel 406 may provide a peak 422 . In some embodiments, the distance between the peaks 422 may be equal to M times p , where P is the distance between pixel arrays, and M is an integer ≧1. For example, in an embodiment where a Talbot pattern is generated at several wavelengths of illumination light, each color subpixel in the pixel array may be provided with one peak 422 at the wavelength of a particular color channel, several subpixels Form an RGB pixel.

The beam portions 122 formed in the array of Talbot peaks 422 are spatially modulated by the array of pixels 406 and propagate towards the eye lens 423 . The eye lens 423 collimates and redirects the light beam portion 122 towards the human eye window 424 of the display device 400 . The function of the eye lens 423 is to form an image in the angular domain at the human eye window 424 from the image in the linear domain displayed by the display panel 402 . Herein, the term "image" means an image in which individual pixels of the image are represented by coordinates of light beams having color and/or brightness, the coordinates indicating the color and/or brightness of those pixels. Thus, the term "image in the angular domain" means an image in which individual pixels of an image are represented by the beam angle of a light beam having color and/or brightness, which represents the color and/or brightness of those pixels.

FIG. 5 shows a Talbot fringe pattern 500 in the display substrate 408 ( FIG. 4A ) of the display panel 402 as an optical power density diagram. The horizontal direction in FIG. 5 is the thickness direction passing through the substrate of the display panel 402 . The Talbot fringe pattern 500 originates from a first plane 501 arranged parallel to the XY plane in FIG. 4A. The outcoupling grating 120 is arranged in the first plane 501 . Light propagates from left to right in FIG. 5 forming an array of optical power density peaks at various distances from the first plane 501 . The optical power density distribution at the first plane 501 is repeated at the second plane 502 spaced apart from the first plane 501 by a Talbot 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 the specific example where the array of outcoupling gratings 120 is disposed at the surface of the illuminator bonded to the display substrate 408, as shown in FIG. 4A, the Talbot pattern period (in the direction of the thickness of the display substrate 408) can be simply The ground is equal to the thickness of the substrate.

More generally, the distance D between the plane of the externally coupled grating and the plane of the pixel may comprise only a portion of a Talbert pattern, or several such patterns, according to equation (1) below

D ⁼ KT2 /( Nλ ), (1)

Where K and N are integers ≥ 1, and where λ is the wavelength of the light beam in the display substrate 408 . In equation (1) above, K is the number of repetitions of the Talbot pattern, and N defines sub-planes with higher spacing Talbot peaks. For example, at the intermediate plane 503 , which is spaced 0.25 mm from the first plane 501 and the second plane 502 , the spacing is doubled.

Turning to FIG. 6 , a Talbot pattern 600 of optical power density distribution inside the display substrate 408 is formed by optical interference between different portions of the beamlets 114 propagating in the waveguide 116 . Thus, the position of the optical power density peak 422 relative to the pixel 406 of the display panel 402 depends on the relative phase between the portions of the sub-beams 114 that are outcoupled by the outcoupling grating 120 . The relative phase is wavelength dependent; thus, the optical power density peak 422 can be shifted by tuning the wavelength of the sub-beam 114 . Providing a wavelength-tunable source (eg, a tunable laser) and tuning the wavelength allows us to center the optical power density peak 422 on the pixel 406 of the display panel 402 . When the wavelength of the light source 110 is tuned, the optical power density peak 422 shifts as indicated by arrow 630 .

The principle of wavelength tuning is further illustrated in FIG. 7 . Schematic 700 depicts the optical path of the outcoupled portion of sub-beam 114 . The first path pair is shown in solid lines. The first path pair produces 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 the sub-beam 114 in the corresponding medium.

The second path pair 702A, 702B is shown in dashed lines. The second path pair produces a local interference maximum 722 at the center location of the pixel 406 . The left path length 702A is equal to a′ and the right path length 702B is equal to b + c′ , where b is the distance between adjacent outcoupling gratings 120 . In this case, the condition for the local interference maximum can be written as

b + c' – a ' = nλ (3a)

By choosing the wavelength λ such that condition (3a) is satisfied, the local interference maximum 722 (ie, the Talbot optical power density peak 422 ) can be at the center of the pixel 406 . When c' = a' , as illustrated in Figure 7, condition (3a) reduces to

b = nλ (3b)

Adjusting the location of the local interference maxima 722 of the Talbot pattern 600 by tuning the wavelength of the light source 110 enables us to maximize the transmission of light emitted by the waveguide illuminator 104 through the display panel 102 when the display device 400 is assembled. This adjustment can be especially beneficial for micro display panels with small pixels on the order of microns and tight pixel pitches.

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

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

In operation, light beam 208 carries a first beam component 271 , a second beam component 272 and a third beam component 273 for carrying light at a first wavelength, a second wavelength and a third wavelength, respectively. For example, the first beam component 271 , the second beam component 272 and the third beam component 273 may be at red, green and blue wavelengths, respectively. The outcoupling grating 220 outcouples the light portion 212 carrying all beam components. The first beam component 271 is reflected by the first reflector 961 , wherein the remaining beam components 272 and 273 are transmitted therethrough. The second beam component 272 is reflected by the second reflector 962 , through which the third beam component 273 is transmitted. 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. The different distances can be chosen to compensate for the different distances to the Talbot plane for different wavelengths of light, as defined by equation (1) above, so that the peak Talbot patterns overlap at the pixel plane of the display panel . The color selective reflector 956 reflects portions of the sub-beams (i.e., beam components of different wavelengths or colors) outcoupled by the array of outcoupling gratings 220 for backpropagation through the illuminator substrate 954 to illuminate the display panel on the pixel.

Referring to FIG. 10, waveguide illuminator 1004 is similar to waveguide illuminator 104 of FIG. 1, includes similar components, and may be implemented as a PIC. The waveguide illuminator 1004 of FIG. 10 further includes a first inward coupler 1041 for coupling the light of the first light source 1051, the second light source 1052 and the third light source 1053 (such as a laser source) into the waveguide illuminator 1004, The second in-coupler 1042 and the third in-coupler 1043 are, for example, edge in-couplers. The first light source 1051, the second light source 1052, and the third light source 1053 can respectively emit light 1061, 1062, and 1063 of the first color channel, the second color channel, and the third color channel, such as red light of the red channel and green light of the green channel. Blue light of light and blue channel.

The wavelength multiplexer 1070 is coupled to the first inward coupler 1041, the second inward coupler 1042 and the third inward coupler 1043, for combining the first color channel, the second color channel and the third inward coupler 1043 The light 1061 , 1062 and 1063 of the three color channels are respectively combined into the input beam 108 and the input beam 108 is coupled into the input waveguide 106 . The abbreviation "CWM" in Figure 10 means a "coarse" wavelength multiplexer with wavelengths separated by 20nm or more. The waveguide beam splitter 1012 is a specific example of the waveguide beam splitter 112 of the waveguide illuminator 104 in FIG. 1 . The waveguide splitter 1012 of FIG. 10 includes a 1× N splitter 1072 for splitting the input light beam 108 into N portions 1008, where N is an integer, each of which propagates in one of the N output waveguides 1016 . 1xN beamsplitter 1072 may comprise, for example, an array of 1x2 beamsplitters arranged in a binary tree structure as in waveguide illuminator 204 of FIG. 2 . N sections 1008 may all have the same optical power.

The waveguide splitter 1012 further includes N wavelength demultiplexers 1074, each coupled to a specific one of the N output waveguides 1016 for separating the first color channel, the second color channel, and the third color channel, respectively. Lights 1061, 1062, and 1063 are coupled to different waveguides 116 in the waveguide array 1080 and propagate light of different color channels therein. Different waveguides can be placed at different depths within the illuminator substrate to ensure that the Talbot planes of the light 1061, 1062 and 1063 of the first, second and third color channels are in the plane of the pixel array of the display panel Overlap. In other words, the different depths of the waveguides in the waveguide array 1080 can be selected such that the Talbot peaks of the light of the different color channels are focused at the pixel plane.

Turning to FIG. 11 , with further reference to FIGS. 1 , 4A, and 4B , a method for coupling a display panel (eg, display panel 402 of FIG. 4A ) to a waveguide illuminator (eg, the waveguide illuminator of FIGS. 1 and 4A ) is presented. 104) of method 1100. Optional steps of method 1100 are indicated by dashed rectangles. The method 1100 of FIG. 11 may include providing ( 1102 ) an input light beam using a light source, such as the light source 110 of FIG. 4A . The light source 110 can be a monochromatic or polychromatic light source. Method 1100 may include splitting an input light beam provided by light source 110 using a beam splitter (eg, beam splitter 112 coupled to waveguide array 116 ) ( 1104 ). Method 1100 includes using an array of outcoupling gratings, such as outcoupling grating 120 ( FIG. 4A ), to outcouple ( 1108 ) portions of sub-beams propagating in an array of waveguides toward pixel array 406 via substrate 408 of display panel 402 . spread. An array of Talbot peaks (eg, Talbert peaks 422 in FIG. 4B ) is formed ( 1110 ) at the plane of pixel array 406 . The center wavelength of light beam 108 provided by light source 108 is tuned (1112) so that the location of individual Talbot peaks 422 in the array of Talbot peaks are centered on pixels 406 in the pixel array.

In the embodiment where light source 110 is a polychromatic light source that generates an input light beam carrying light from a plurality of color channels, method 1100 may include coupling (1105) a plurality of color channels of the plurality of color channels to a waveguide array using a beam splitter In individual waveguides therein, light for each of the plurality of color channels is then guided (1106) in each waveguide in the array of waveguides. A color selective reflector (eg, color selective reflector 956 of FIG. 9 ) may be used in the optical path between the outcoupling grating array and the display panel (FIG. 11; 1109) to target one of the plurality of color channels Light of different color channels provides different optical path lengths, as explained above with reference to FIG. 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 ). 1200. Method 1200 includes using a light source to provide (1202) an input beam of light having a sufficiently wide emission bandwidth. A beam splitter (eg, beam splitter 112 in FIG. 1 or beam splitter 1012 in FIG. 10 ) is used to split ( FIG. 12 ; 1204 ) the input beam into a plurality of sub-beams. The plurality of sub-beams is propagated in the waveguide parallel to the columns of the pixel array (1206). Portions of the sub-beams propagating in the waveguide array are outcoupled ( 1208 ) using an outcoupling grating array to propagate through the substrate of the display panel towards the pixel array, as illustrated for example in FIG. 4A . Method 1200 further includes forming ( 1210 ) an array of Talbert peaks at the plane of the pixel array, as illustrated, for example, in FIG. 4B . The width of the Talbot peaks in the Talbot peak array depends on the emission bandwidth of the light source. To facilitate the alignment of the waveguide illuminator to the display panel, the bandwidth should be wide enough such that the width of the Talbot peak is greater than the width of the pixels in the pixel array for overfilling the voids of the pixels, as explained above and in Fig. 8 explained.

In some embodiments, the light source may include a polychromatic light source for providing an input light beam comprising light of a plurality of color channels. Optical splitter 112 may couple multiple color channels of the plurality of color channels into individual waveguides 116 in the array of waveguides. In these embodiments, method 1200 can also include using a color selective reflector (eg, color selective reflector 956 of FIG. 9 ) in the optical path between the outcoupling grating array and the display panel to target the complex Light from different ones of the color channels provides different optical path lengths (dashed rectangle at 1209). Alternatively, light of different color channels may be coupled into different waveguides in a waveguide array, as in, for example, waveguide illuminator 1004 of FIG. 10 . For these embodiments, the waveguides carrying the light of the different color channels can be placed at different depths within the substrate of the illuminator to achieve the same goal of providing different optical path lengths for the light of different ones of the plurality of color channels .

Turning to FIG. 13, a virtual reality (VR) near-eye display 1300 includes a frame 1301 supporting, for each eye: a light source 1302; a waveguide illuminator 1306 operably coupled to the light source 1302 and including the Either of the waveguide illuminators; (the light source can be built into the luminaire); a display panel 1318 comprising an array of display pixels where the position of the outcoupling grating in the waveguide illuminator 1306 is tuned to the polarization of the display panel 1318 positional coordination of pixels; and an eye 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 observation at the human eye window 1326 . A plurality of eye window illuminators 1362 , shown as black dots, may be placed on the side of waveguide illuminator 1306 facing eye window 1326 . An eye-tracking camera 1342 may be provided for each eye window 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 window illuminator 1362 illuminates the eye corresponding to the eye window 1326 so that the eye tracking camera 1342 obtains an image of the eye and provides a reference reflection, ie, a flash. The flash of light can serve as a reference point in capturing the image of the eye, thereby facilitating eye gaze direction determination by determining the position of the eye pupil image relative to the flash image. In order to avoid distracting the user's attention by the light of the eye window illuminator 1362, the eye window illuminator can be made to emit light that is invisible to the user. For example, infrared light may be used to illuminate the window 1326 of the human eye.

Turning to FIG. 14 , HMD 1400 is an example of an AR/VR wearable display system that encloses the user's face for maximum immersion in the AR/VR environment. HMD 1400 can produce completely virtual 3D images. The HMD 1400 can include a front body 1402 and a strap 1404 that can be fastened 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 can be disposed in the front body 1402 to present AR/VR images to the user. Display system 1480 may include any of the display devices and illuminators disclosed herein. The sides 1406 of the front body 1402 may be opaque or transparent.

In some embodiments, the front body 1402 includes a positioner 1408 and an inertial measurement unit (IMU) 1410 for tracking the acceleration of the HMD 1400 and a position sensor 1412 for tracking the position of the 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 of position sensors 1412 that generate a position in response to motion of HMD 1400. or multiple 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 to detect motion, error correction for IMU 1410 A type of sensor, or some combination thereof. Position sensor 1412 may be located external to IMU 1410, internal to IMU 1410, or some combination of external and internal.

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 can be compared with the position and orientation obtained by tracking locator 1408 to improve the tracking accuracy of the position and orientation of HMD 1400 . As the user moves and turns in 3D space, accurate position and orientation are critical to presenting the user with an appropriate virtual scene.

HMD 1400 may further include a depth camera assembly (DCA) 1411 that captures data describing depth information surrounding some or all of the localized areas in HMD 1400 . The depth information may be compared with information from the IMU 1410 for better accuracy in determining the position and orientation of the HMD 1400 in 3D space.

The HMD 1400 may further include an eye tracking system 1414 for determining the orientation and position of the user's eyes in real time. The obtained position and orientation of the eyes also allows the HMD 1400 to determine the direction of the user's gaze and adjust the image generated by the display system 1480 accordingly. The determined gaze direction and vergence angle can be used to adjust the display system 1480 to reduce vergence accommodation conflicts. Direction and vergence may also be used for exit pupil steering of displays as disclosed herein. In addition, the determined vergence and gaze angle can be used to interact with the user, highlight objects, bring objects to the foreground, generate additional objects or indicators, and the like. An audio system including, for example, a set of small speakers built into the front body 1402 may also be provided.

Embodiments of the present invention may include an artificial reality system, or may be implemented in conjunction with an artificial reality system. The artificial reality system adjusts sensory information about the external world obtained through sensing in a certain way before presenting it to the user, such as visual information, audio, contact (somatosensory) information, acceleration, balance, etc. As non-limiting examples, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), composite reality, or some combination thereof and/or derivatives. Artificial reality content may include fully generated content or generated content combined with captured (eg, real world) content. Artificial reality content may include video, audio, physical or tactile feedback, or some combination thereof. Any of this content may be presented in a single channel or in multiple channels, such as in stereoscopic video which produces a three-dimensional effect to the viewer. Additionally, in some embodiments, AR may also be used in conjunction with applications, such as those used to create content in AR and/or otherwise used in AR (e.g., to perform activities in AR), products, accessories, services or a combination thereof. Artificial reality systems that provide artificial reality content can be implemented on a variety of platforms, including wearable displays such as HMDs connected to a host computer system, standalone HMDs, near-eye displays with a form factor of glasses, mobile devices or computing systems, Or any other hardware platform capable of delivering artificial reality content to one or more viewers.

The scope of the invention is not limited by the particular embodiments described herein. Indeed, various other embodiments and modifications, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description and drawings. Accordingly, such other embodiments and modifications are intended to be within the scope of this invention. Additionally, while the invention has been described herein in the context of particular implementations in particular environments for specific purposes, those skilled in the art will recognize that its validity is not limited thereto and that the present invention may be presented Beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full scope and spirit of the invention as described herein.

101: Illuminator substrate 104: Waveguide illuminator 106: Input waveguide 108: Input beam 110: Light source 112: Waveguide beam splitter 114: Sub-beam 116: Waveguide 119: Column 120: Outcoupling grating/outcoupler 122: Part 129: Terminal 204: Waveguide Illuminator 208: Input Beam 210: Light Source 212: Optical Section 216: Waveguide 220: Outcoupling Grating 234: PIC 241: Optical Scheduling Circuit 244: 1×2 Waveguide Splitter 245: Waveguide 271: PI First beam component 272: second beam component 273: third beam component 303: pixel 303B: subpixel 303G: subpixel 303R: subpixel 304: PIC illuminator 306: substrate 307: waveguide 307B: blue waveguide 307G: green waveguide 307R: red waveguide 308: light 310: multi-wavelength light source 312B: grating 312G: grating 312R: grating 313: dotted line rectangle 318: 1D microlens 319: optical scheduling circuit 400: display device 402: display panel 406: pixel 407: between pixels Region 408: Display Substrate 422: Optical Power Density Peak 423: Eye Lens 424: Human Eye Window 500: Talbot Stripe Pattern 501: First Plane 502: Second Plane 503: Middle Plane 600: Talbot Pattern 630: Arrow 700: Schematic 701A: Left Path Length 701B: Right Path Length 702A: Left Path Length 702B: Second Path 721: Local Interference Max 722: Local Interference Max 800: Schematic 802: Optical Path 822: Talber Extra Peak 904: Waveguide Illuminator 908: Substrate 952: Core Layer 954: Illuminator Substrate 956: Color Selective Reflector 961: First Reflector 962: Second Reflector 963: Third Reflector 964: Reflector Substrate 1004 : waveguide illuminator 1008: part 1012: waveguide splitter 1016: output waveguide 1041: first in-coupler 1042: second in-coupler 1043: third in-coupler 1051: first light source 1052: second light source 1053: third light source 1061: light 1062: light 1063: light 1070: wavelength multiplexer 1072: 1× N optical splitter 1074: wavelength demultiplexer 1080: waveguide array 1100: method 1102: step 1104: step 1105: step 1106: Step 1108: Step 1109: Step 1110: Step 1112: Step 1200: Method 1202: Step 1204: Step 1206: Step 1208: Step 1209: Step 1210: Step 1300: Virtual Reality (VR) Near Eye Display 1301: Frame 1302 : Light Source 1306: Waveguide Illuminator 1318: Display Panel 1326: Human Eye Window 1332: Eye Lens 1342: Eye Tracking Camera 1362: Human Eye Window Illuminator 1400: HMD 1402: Front Body 1404: Strip 1406: Side 1408: Positioning 1410: Inertial Measurement Unit 1411: Depth Camera Assembly 1412: Position Sensor 1414: Eye Tracking System 1480: Display System

Illustrative embodiments will now be described in conjunction with the drawings, in which:

[Fig. 1] is a schematic plan view of the waveguide illuminator of the present invention;

[Fig. 2] is a schematic plan view of a specific example of the illuminator in Fig. 1;

[FIG. 3A] is a schematic top view of the polychromatic waveguide illuminator of the present invention with surface relief gratings on the ridge waveguide;

[FIG. 3B] is a schematic top view of a portion of the polychromatic waveguide illuminator of FIG. 3A superimposed on a single RGB pixel of the display panel;

[FIG. 3C] is a three-dimensional schematic diagram of the ridge waveguide of the polychromatic waveguide illuminator of FIG. 3A;

[FIG. 4A] is a schematic cross-sectional view of a display device of the present invention;

[ FIG. 4B ] is an enlarged cross-sectional view of a pixel array of the display device of FIG. 4A superimposed with a peak Talbert optical power density distribution of illumination light at the pixel array;

[ FIG. 5 ] is a calculated Talbert diagram of the optical power density distribution through the thickness of the display panel substrate of the display device of FIG. 4A ;

[ FIG. 6 ] is a side cross-sectional view of the display device of FIG. 4A showing a Talbot pattern showing optical power density inside the substrate;

[FIG. 7] is a schematic diagram of the cross-sectional view of FIG. 6, illustrating the principle of wavelength tuning of the Talbert peak position;

[ FIG. 8 ] is a schematic diagram of the cross-sectional view of FIG. 6 , which illustrates the principle of overfilling pixel voids overfilled with broadband illumination light;

[ FIG. 9 ] is a cross-sectional exploded view of a specific example of a waveguide illuminator with a built-in dichroic mirror;

[FIG. 10] is a schematic diagram of a multi-color embodiment of the waveguide illuminator of FIG. 4A;

[ FIG. 11 ] is a flowchart of a method for coupling a waveguide illuminator to a display panel by wavelength tuning;

[ FIG. 12 ] is a flowchart of a method for coupling a waveguide illuminator to a display panel by pixel aperture overfilling;

[ Fig. 13 ] is a view of an augmented reality (augmented reality; AR) display of the present invention having the appearance size of a pair of glasses; and

[ FIG. 14 ] is a three-dimensional view of a head-mounted display (HMD) of the present invention.

101: Illuminator substrate

104: Waveguide illuminator

106: Input waveguide

108: Input beam

110: light source

112: waveguide splitter

114: sub-beam

116: waveguide

119: column

120: Outcoupling grating / outcoupler

122: part

129: end

Claims (20)

A display device comprising: a display panel comprising an array of pixels on a display substrate; and A waveguide illuminator coupled to the display panel for illuminating the pixel array, the waveguide illuminator comprising: illuminator substrate; a beam splitter, supported by the illuminator substrate, for splitting the input light beam into a plurality of sub-beams; an array of waveguides supported by the illuminator substrate parallel to the columns of pixels of the pixel array, wherein each waveguide in the array is configured to guide a sub-beam of the plurality of sub-beams therein; and an outcoupling grating array coupled to the waveguide array; wherein the outcoupling grating array extends along the pixel array for outcoupling part of the sub-beams to propagate through the display substrate and form an array of Talbot peaks at the plane of the pixel array, wherein The positions of individual Talbot peaks in the array of Talbot peaks correspond to the positions of individual pixels in the pixel array. The display device according to claim 1, further comprising a light source for providing the input light beam to the beam splitter. The display device of claim 2, wherein the light source is tunable in wavelength; wherein in operation said position of said individual Talbot peak depends on the wavelength of the light source, wherein the wavelength is selected such that said Talbot peak is centered on a pixel in the pixel array . The display device as claimed in claim 2, wherein the light source has an emission bandwidth; Wherein in operation, the width of the Talbot peak in the Talbot peak array depends on the emission bandwidth of the light source, wherein the width of the Talbot peak is larger than that in the pixel array The width of the pixel is used to overfill the aperture of the pixel to facilitate the alignment of the waveguide illuminator to the display panel. The display device according to claim 2, wherein the light source is a polychromatic light source for providing the input beam of light comprising a plurality of color channels. The display device of claim 5, wherein the beam splitter is configured to couple a plurality of color channels of the plurality of color channels to individual waveguides in the waveguide array, wherein each waveguide in the waveguide array is configured to The light of each of the plurality of color channels is directed therein. The display device of claim 6, wherein the waveguide illuminator further comprises a color selective reflector in the optical path between the outcoupling grating array and the substrate of the display panel, wherein the color selective reflector passes through configured to provide different optical path lengths for the light of different ones of the plurality of color channels. The display device of claim 7, wherein the color selective reflector comprises a stack of dichroic reflectors configured to reflect the portion of the sub-beams outcoupled by the outcoupling grating array to Backpropagation passes through the illuminator substrate to illuminate onto the pixels of the pixel array. The display device of claim 5, wherein the beam splitter is configured to couple different color channels of the plurality of color channels to different waveguides of the waveguide array, wherein the different waveguides are disposed in different waveguides of the illuminator substrate. depth. The display device of claim 1, wherein the waveguide array comprises ridge waveguides, and wherein the gratings in the outcoupling grating array are formed in the ridge waveguides in the waveguide array. A method for coupling a display panel comprising an array of pixels to a waveguide illuminator comprising an array of outcoupling gratings coupled to an array of waveguides, wherein a plurality of sub-beams of an input light beam are parallel to the columns of the array of pixels in said Propagated in a waveguide, the method involves: using the outcoupling grating array to outcouple a portion of the sub-beams propagating in the waveguide array to propagate through the substrate of the display panel towards the pixel array; forming an array of Talbot peaks at the plane of the pixel array; and The center wavelength of the beam is tuned so that the positions of individual Talbot peaks in the array of Talbot peaks are at the center positions of pixels in the pixel array. The method of claim 11, further comprising using a light source to provide the input light beam. The method of claim 12, further comprising splitting the input light beam provided by the light source using a beam splitter coupled to the waveguide array. The method of claim 11, further comprising using a polychromatic light source to provide the input light beam comprising light of a plurality of color channels. The method of claim 14, further comprising: using a beam splitter to couple color channels of the plurality of color channels into individual waveguides of the array of waveguides; and The light of each of the plurality of color channels is guided in each waveguide in the array of waveguides. The method of claim 15, further comprising using a color selective reflector in the optical path between the outcoupling grating array and the display panel to provide the light for different color channels of the plurality of color channels Different optical path lengths. The method of claim 14, further comprising: Different ones of the plurality of color channels are coupled into different waveguides in the array of waveguides using a beam splitter, wherein the different waveguides are disposed at different depths within the substrate of the illuminator. A method for coupling a display panel comprising an array of pixels to a waveguide illuminator comprising an array of outcoupling gratings coupled to a waveguide array, the method comprising: 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; propagating the plurality of sub-beams in the waveguide parallel to the columns of the pixel array; using the outcoupling grating array to outcouple a portion of the sub-beams propagating in the waveguide array to propagate through the substrate of the display panel towards the pixel array; and forming an array of Talbot peaks at the plane of the pixel array; Wherein the width of the Talbot peak in the Talbot peak array depends on the emission bandwidth of the light source, wherein the width of the Talbot peak is greater than the width of a pixel in the pixel array for overfilling the voids of the pixels to facilitate alignment of the waveguide illuminator to the display panel. The method of claim 18, wherein: the light source is a polychromatic light source providing the input light beam comprising light of a plurality of color channels; the optical splitter couples color channels of the plurality of color channels into individual waveguides of the array of waveguides; and The method further includes using a color selective reflector in an optical path between the outcoupling grating array and the display panel to provide different optical path lengths for the light of different ones of the plurality of color channels. The method of claim 18, wherein: the light source is a polychromatic light source providing the input light beam comprising light of a plurality of color channels; the optical splitter couples different ones of the plurality of color channels into individual waveguides in the waveguide array; and The different waveguides are disposed at different depths within the substrate of the illuminator.

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