Patent ID: 12204107

DETAILED DESCRIPTION

While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, 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, i.e., any elements developed that perform the same function, regardless of structure.

As used herein, the terms “first”, “second”, and so forth are not intended to imply sequential ordering, but rather are intended to distinguish one element from another, unless explicitly stated. Similarly, sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated. InFIGS.1A-1B,7A-7B, andFIGS.8and9, similar number refer to similar elements.

In a visual display including an array of pixels coupled to an illuminator, the efficiency of light utilization depends on a ratio of a geometrical area occupied by pixels to a total area of the display panel. For miniature displays often used in near-eye and/or head-mounted displays, the ratio can be lower than 50%. The efficient backlight utilization can be further hindered by color filters on the display panel, which on average transmit no more than 30% of incoming light. On top of that, there may exist a 50% polarization loss for polarization-based display panels such as liquid crystal (LC) display panels. All these factors considerably reduce the light utilization and overall wall plug efficiency of the display, which is undesirable.

In accordance with this disclosure, light utilization and wall plug efficiency of a backlit display may be improved by providing an illuminator a slab lightguide and a light-patterning structure, e.g. a phase mask, disposed downstream of the slab lightguide to concentrate the out-coupled wide light beam into an array of tightly focused light spots. In displays where the illuminator emits light of primary colors, e.g. red, green, and blue, the colors and locations of focused spots of illuminating light may be matched to that of the color filters of the display. Furthermore, upon such illumination with color-interleaved arrays of focused spots, the color filters may be omitted altogether. For polarization-based displays, the polarization of the emitted light may be matched to a pre-defined input polarization state. Matching the spatial distribution, transmission wavelength, and/or the transmitted polarization characteristics of the pixels of the display panel enables one to considerably improve the useful portion of display light that is not absorbed or reflected by the display panel on its way to the eyes of the viewer, and consequently to considerably improve the display's wall plug efficiency.

The phase mask, or another type of arrayed focusing element, may be configured to form an array of optical power density peaks from the array of light spots at a distance from the array of light spots due to Talbot effect. This enables the illuminating light to traverse a substrate of the display panel being illuminated while preserving the optical power density distribution in form of an array of peaks, which can be matched to individual pixels of the display panel. The phase mask and/or the illuminating multi-color light source may be configured to provide color-interleaved offset color channel sub-arrays matched to the color sub-pixel geometry of the display panel—an approach which may lead to very dense pixel pitches of a display panel, up to 2000 pixels per inch and higher.

In accordance with the present disclosure, there is provided an illuminator for a display panel. The illuminator comprises a slab of transparent material. The slab has first and second outer surfaces for propagating illuminating light in the slab by a series of internal reflections from the first and second outer surfaces. The illuminator further includes an out-coupling grating supported by the slab for out-coupling portions of the illuminating light from the slab at the first surface, and a focusing element for forming an array of light spots from the out-coupled illuminating light portions downstream of the focusing element for illuminating pixels of the display panel. The focusing element may be configured to form an array of optical power density peaks from the array of light spots at a distance from the array of light spots due to Talbot effect.

The focusing element may include a microlens array, e.g. an array of refractive microlenses, an array of diffractive microlenses, an array of liquid crystal microlenses, an array of Pancharatnam-Berry phase (PBP) microlenses, etc. More generally, the focusing element may include a phase mask, such as a liquid crystal (LC) layer with a spatially variable LC orientation, a patterned LC polymer, a nanostructure having a spatially varying height, etc.

In some embodiments, the illuminator includes multi-color light source for providing the illuminating light to the slab, the illuminating light comprising light of a plurality of color channels. Such illuminator may be configured to couple the light of different ones of the plurality of color channels at different angles into the slab. Light spots of the array of light spots form color-interleaved sub-arrays of light spots corresponding to the plurality of color channels. The focusing element may be configured to form color-interleaved sub-arrays of light spots, the color-interleaved sub-arrays corresponding to the light of the plurality of color channels. In some embodiments, the illuminator may include a light source for providing the illuminating light to the slab, and a tiltable reflector in an optical path between the light source and the slab, for varying an in-coupling angle of the illuminating light into the slab.

In accordance with the present disclosure, there is provided a display device comprising a display panel comprising a pixel array on a substrate, and an illuminator of this disclosure coupled to the display panel for illuminating the pixel array through the substrate. The illuminator may include: a slab of transparent material, the slab comprising first and second outer surfaces for propagating illuminating light in the slab by a series of internal reflections from the first and second surfaces; an out-coupling grating supported by the slab for out-coupling portions of the illuminating light from the slab at the first surface; and a light-patterning structure. The light-patterning structure comprises at least one of an amplitude mask or a phase mask for forming an array of light spots from the out-coupled illuminating light portions. In operation, light of the formed light spots propagates through the substrate and produces an array of optical power density peaks at the pixel array due to Talbot effect. The light patterning structure may include an array of refractive and/or diffractive microlenses, an array of Pancharatnam-Berry phase (PBP) microlenses, a patterned liquid crystal polymer, a nanostructure having a spatially varying height, etc.

In some embodiments, the display includes a beam steering layer in an optical path downstream of the slab, for angularly steering the out-coupled illuminating light portions. The display device may include a multi-color light source for providing the illuminating light to the slab, the illuminating light comprising light of a plurality of color channels. The illuminator may be configured to couple the light of different ones of the plurality of color channels at different angles into the slab, such that light spots of the array of light spots form color-interleaved sub-arrays of the array of light spots, the color-interleaved sub-arrays corresponding to the light of the plurality of color channels. The light-patterning structure may be configured to form the color-interleaved sub-arrays of the array of light spots. The out-coupled illuminating light portions of the plurality of color channels formed into the color-interleaved sub-arrays of light spots may propagate in the substrate of the display panel and produce color-interleaved sub-arrays of the array of optical power density peaks at the pixel array. The color-interleaved sub-arrays of optical power density peaks at the pixel array may be different Talbot orders of the color-interleaved sub-arrays of the array of light spots. The color-interleaved sub-arrays of optical power density peaks may have a high spatial density of peaks, e.g. the color-interleaved sub-arrays of optical power density peaks may each have a density of at least 2000 peaks per inch.

The display device may include a tiltable reflector in an optical path between the multi-color light source and the slab for varying an in-coupling angle of the illuminating light into the slab. In such embodiments, the display device may further include a controller operably coupled to the multi-color light source and the tiltable reflector and configured to: tilt the tiltable reflector to a first tilt angle corresponding to a first color channel of the plurality of color channels; cause the multi-color light source to produce light of the first color channel; tilt the tiltable reflector to a first tilt angle corresponding to a second, different color channel of the plurality of color channels; and cause the multi-color light source to produce light of the second color channel. The first and second tilt angles may be selected to provide a same output angle of the illuminating light portions.

In accordance with the present disclosure, there is further provided a method for illuminating a display panel comprising a pixel array on a substrate. The method comprises propagating illuminating light in a slab of transparent material by a series of internal reflections from slab surfaces; out-coupling portions of the illuminating light from the slab at one of the slab surfaces using an out-coupling grating; spatially modulating the illuminating light portions in at least one of amplitude or phase to form an array of light spots from the out-coupled illuminating light portions; and propagating light of the formed light spots through the substrate to form an array of optical power density peaks at the pixel array due to Talbot effect.

In embodiments where the illuminating light comprises light of a plurality of color channels, the illuminating light portions may be spatially modulated to form color-interleaved sub-arrays of the array of light spots, the color-interleaved sub-arrays corresponding to the light of the plurality of color channels, whereby the array of optical power density peaks comprises color-interleaved sub-arrays of optical power density peaks at the pixel array. In some embodiments, the method may include angularly steering the out-coupled illuminating light portions using at least one of a tiltable reflector or a steering layer in an optical path between a source of the illuminating light and the pixel array. In embodiments where the display panel comprises a black grid, the out-coupled illuminating light portions may be steered in a spatially selective manner to provide a spatially-selective dimming of the display panel by redirecting the illuminating light portions to impinge onto the black grid instead of the pixel array.

Referring now toFIG.1A, an illuminator100for illuminating a display panel102includes a slab104of transparent material, e.g. a plano-parallel slab of glass, plastic, transparent oxide, transparent crystalline material, or another suitable material. The slab104includes first111and second112opposed outer surfaces for propagating illuminating light106in the slab104by a series of internal reflections from the first111and second112outer surfaces, as illustrated schematically with a zigzag dashed line. The illuminating light106may be emitted by a light source108and coupled into the slab104by an in-coupling grating110or by another suitable in-coupling structure such as a prism, etc. Portions114of the illuminating light106propagating in the slab104are out-coupled through the first surface111by an out-coupling grating116supported by the slab104. The out-coupled grating116may be a smooth and flat, continuous grating, and may be disposed in the slab104or on the slab104, as shown inFIG.1A. Thus, the slab104with its out-coupling grating116operates as a pupil-replicating lightguide providing multiple offset light portions114.

The out-coupled light portions114form a nearly-collimated light beam that impinges onto a focusing element118, whose function is to form an array of light spots120shown inFIG.1B. The array of light spots120is formed by focusing the out-coupled illuminating light portions114downstream of the focusing element118. In embodiments where a substrate122of the display panel102is thin enough, the light spots120may illuminate pixels124of the display panel102directly. In embodiments where the substrate122is too thick for the light spots120to be smaller than lateral size of the pixels124, the focusing element118may be configured to form an array of optical power density peaks128from the array of light spots120at a z-distance from the array of light spots120due to Talbot effect, which enables repetition of a peaky optical power density distribution at a distance from the array of light spots120for sufficiently spatially coherent light. Specifically, inFIG.1B, the array of optical power density peaks128illuminates the pixels124. Positions of individual optical power density peaks128are coordinated with positions of individual pixels124of the display panel102, e.g. with one optical power density peak128illuminating one pixel124. InFIGS.1A and1B, the display panel102is shown in a partial view. The display panel102may include other layers and substrates, which have been omitted inFIGS.1A and1Bfor brevity.

The Talbot effect that reproduces the optical power density distribution at a higher plane spaced apart from an original plane of a peaky optical power density distribution is illustrated inFIG.2. This figure shows a map200of optical power density through the substrate122of the display panel102, with horizontal axis (i.e. X-axis inFIG.2) representing a lateral coordinate on the focusing element118, and a vertical axis (i.e. Z-axis inFIG.2) representing the thickness dimension of the substrate122of the display panel102. The focusing element118is configured to form the array of light spots120at a small distance from the focusing element118, at a focal plane202disposed some 0.09 mm into the substrate122. The lateral (XY) optical power density distribution is repeated at a Talbot plane204, forming the array of optical power density peaks128at the Talbot plane204with a same pitch as at the focal plane202. The array of pixels124of the display panel102is disposed at the Talbot plane204. Such a configuration allows the efficiency of light utilization to be considerably increased due to most of the illuminating light106propagating through the pixels124without being absorbed by a black grid130between the pixels124(FIGS.1A and1B).

Non-limiting examples of the focusing element118will now be considered with reference toFIGS.3A to3F. Referring first toFIG.3A, a refractive microlens array318A may be used as the focusing element118of the illuminator100ofFIGS.1A and1B. The refractive microlens array318A ofFIG.3Aincludes many refractive microlenses300A disposed on a transparent substrate302A. The refractive microlens array318A may be made of e.g. a transparent isotropic material, e.g. injection molded from a suitable optical quality plastic. The refractive microlenses300A focus impinging light due to surface curvature, like regular refractive singlet lenses. The refractive microlenses300A may be disposed in a two-dimensional (2D) array with geometrical configuration and pitch corresponding to the geometrical configuration and pitch of the pixels124of the display panel102.

Referring toFIG.3B, a Pancharatnam-Berry phase (PBP) array318B may be used as the focusing element118of the illuminator100ofFIGS.1A and1B. The PBP microlens array318B ofFIG.3Bincludes an array of PBP LC microlenses300B formed in a liquid crystal (LC) layer. LC molecules304are disposed in XY plane at a varying in-plane orientation depending on the distance r from the lens center. The orientation angle ϕ(r) of the LC molecules304in the liquid crystal layer of each PBP LC microlens300B is given by

ϕ⁡(r)=π⁢r22⁢f0⁢λ0(1⁢a)

where f0is a desired focal length and λ0is wavelength. The optical phase delay in each PBP LC microlens300B is due to Pancharatnam-Berry phase, or geometrical phase effect. An optical retardation R of the liquid crystal layer having a thickness t is defined as R=tΔn, where Δn is the optical birefringence of the liquid crystal layer. At the optical retardation R of the LC layer of λ0/2, i.e. half wavelength, the accumulated phase delay P(r) due to the PBP effect can be expressed rather simply as P(r)=2ϕ(r), or, by taking into account Eq. (1a) above,

P⁡(r)=π⁢r2f0⁢λ0(1⁢b)

It is the quadratic dependence of the PBP P(r) on the radial coordinate r that results in the focusing, or defocusing, function of each PBP LC microlens300B. Each PBP LC microlens300B has the azimuthal angle ϕ continuously and smoothly varying across the surface of the LC layer. Accordingly, the mapping of the azimuthal angle to PBP, i.e. P(r)=2ϕ(r) when R=λ0/2, allows for a more drastic phase change without introducing discontinuities at a boundary of 2π modulo.

Referring toFIG.3C, a liquid crystal (LC) microlens array318C may be used as the focusing element118of the illuminator100ofFIGS.1A and1B. The LC microlens array318C ofFIG.3Cmay include an array of LC microlenses300C including round droplets (e.g. hemispherical droplets) of oriented LC molecules305immersed into an isotropic polymer substrate302C. The refractive index of the isotropic polymer substrate may be matched to an ordinary index of refraction of the LC fluid in the droplets. The LC molecules305may be oriented e.g. along X-axis as shown on a left-side portion ofFIG.3C. When illuminated with a light beam306linearly polarized along x-axis, the microlens300C will focus the light beam306due to the focusing property of a curved interface306between the LC droplets and the polymer substrate302C, the curved interface306having a non-zero refractive index step. When the LC molecules305become oriented along Z-axis, e.g. by applying an external electric field by means of applying a voltage to a pair of optional transparent electrodes314and315, the curved interface306has a zero refractive index step since the refractive index of the isotropic polymer substrate is matched to an ordinary index of refraction of the LC fluid. Accordingly, the light beam306will remain non-focused as illustrated on the right-side portion ofFIG.3C. It is noted that the switching property of the LC microlens array318C is optional, and LC molecules305may have a fixed orientation defined, for example, by a polymer network embedded into the LC droplets and defining a permanent orientation of the LC droplets.

Referring toFIG.3D, a diffractive microlens array318D may be used as the focusing element118of the illuminator100ofFIGS.1A and1B. Each diffractive microlens300D of the diffractive microlens array318D may include a plurality of concentric fringes or grooves309configured to diffract impinging light rays inwards to bring the rays to a focal point at a focal plane.

Turning toFIG.3E, a nanostructure318E may be used as the focusing element118of the illuminator100ofFIGS.1A and1B. The nanostructure318E ofFIG.1Eincludes an array of identical elements300E, which may be composed of an array of binary parallelepiped features of differing height. Only one such element300E is shown inFIG.3Efor brevity; other elements300E are presumed to be disposed in the rectangles formed by dashed lines312. Each element300E has a pre-defined spatially varying height distribution represented by nine elementary heights h1, h2, h3, h4, h5, h6, h7, h8, and h9in this example. The X-period and Y-period (FIG.3E) may be e.g. from 1 micrometer to 25 micrometers for example, and may be determined by a pitch of the display panel102being illuminated by the illuminator100(FIG.1A). For example, the X-period and Y-period may be equal to X- and Y-pixel pitch respectively of the display panel102. The operation of the nanostructure318E will be considered detail further below.

Referring now toFIG.3F, an amplitude mask318F is an example of an a light-patterning structure that may be used in place of the focusing element118of the illuminator100. The amplitude mask318F includes an array of openings300F that transmit impinging light. All the remaining light is blocked. The array of openings300F creates an initial optical power density distribution to be repeated in the substrate122of the display panel via Talbot effect, as illustrated above with reference toFIG.2. The amplitude mask318F would have to be disposed at the focal plane202instead of the bottom ofFIG.2, to form the array of light spots120by amplitude masking the impinging wide light beam. More generally, a light-patterning structure that may be used in place of the focusing element118may include any combination of the elements considered above with reference toFIGS.3A to3F, and may also include any type of patterned isotropic or anisotropic polymer, e.g. a patterned LC polymer.

For a color display panel, the illuminating light may include a multi-color light source that provides multi-color illuminating light to a pupil-replicating lightguide. The multi-color illuminating light may include light of a plurality of color channels, for example red, green, and blue channels. It would be beneficial to provide focused illuminating light to each color sub-pixel, a color channel of the focused illuminating light matching the color of the sub-pixel. In this manner, light losses due to absorption of light of a “wrong” color channel by a sub-pixel may be minimized, and display efficiency may be increased.

One way to provide an array of color-dispersed light spots to a display panel is to pre-tilt light beams of individual color channels impinging onto the pupil-replicating lightguide. Referring toFIG.4, the slab104is illuminated with a multi-color light beam406including light of red (R), green (G), and blue (B) color channels in-coupled by the in-coupling grating110into the slab104at slightly different in-coupling angles. The in-coupling angles are exaggerated inFIG.4for clarity. A light beam of the R color channel is shown with long-dash lines, a light beam of the G color channel is shown with solid lines, and a light beam of B color channel is shown with short-dash lines. The light beams of the R, G, B in-coupled color channels propagate in the slab104and are out-coupled by the out-coupling grating116at angles corresponding to the in-coupling angles of the R, G, B light beams into the slab104. Since the light beams of the R, G, B in-coupled color channels are out-coupled at different angles, the out-coupled light beams of the R, G, B color channels are focused by the focusing element118at offset locations forming color-interleaved sub-arrays of R, G, B light spots, each one of the color-interleaved sub-arrays of R, G, B light spots corresponding to light of a particular one of the plurality of R, G, B color channels.

Another way to provide an array of color-dispersed light spots to a display panel is to configure the focusing element118to focus light of different color channels at laterally offset locations. Referring for a non-limiting illustrative example toFIGS.5A,5B, and5C, and with further reference toFIG.3E, an embodiment of the nanostructure318E includes a lateral distribution500of height, i.e. a local thickness variation along X-axis as illustrated. The thickness variation is repeated for every pixel of the nanostructure318E, only one period of such variation being shown inFIG.5A. Since wavelengths of R, G, and B color channels are different, the lateral distribution500will translate into different lateral distributions of optical retardation in waves of corresponding colors. InFIG.5A, such lateral distributions of optical retardation are shown in units of phase. A R color channel optical retardation distribution500R is different from a G color channel optical retardation distribution500G and is different from a B color channel optical retardation distribution500B.

FIG.5Bshows simulation results of focusing of the light of G, R, and B color channels by the nanostructure318E with the lateral distribution500of height. InFIG.5B, the simulation results are shown as spatial intensity maps (heat maps)510G for G color channel,510R for R color channel, and510B for B color channel. One can see that the three focal spots are clearly separated from one another along X-axis. The nanostructure318E may be configured to match the focused color spots positions with positions of the G, R, and B color sub-pixels of a display panel. This is illustrated inFIG.5C, which is a graph of lateral optical power density or intensity distribution for light of different color channels. The locations of green520G, red520R, and blue520B sub-pixels are denoted with dashed rectangles. Lateral distributions of optical power density of the light of G (530G), R (530R), and B (530B) color channels are matched to the green520G, red520R, and blue520B sub-pixel positions.

A z-position ZTof a Talbot order N can be determined from the following equation:

ZT=Na2λ,(2)

where a is the length of a Talbot period and λ is wavelength of light.FIG.6Aillustrates the wavelength dependence of z-positions (along the substrate thickness dimension) of different Talbot orders. One can see that the z-positions ZTof different color channels are different for a same order. To make sure that the color-interleaved sub-arrays of optical power density peaks are at the same Z-distance in the plane of the pixel array, different Talbot orders of different color channels may be used. For example, a straight line650denotes the z-distance of 9 millimeters. At this distance, an order651may be used for blue light at the wavelength of 0.47 micrometer, an order652may be used for green light at the wavelength of 0.53 micrometer, and an order653may be used for red light at the wavelength of 0.65 micrometer. A partial or fractional Talbot order may be used for the red light at the wavelength of 0.63 micrometer. The color-interleaved sub-arrays of the array of light spots of all color channels will be at the same distance of 9 mm from the array of light spots formed by the illuminator's focusing element.

The formation of fractional Talbot orders and planes is illustrated inFIG.6Bfor illuminating light of a single color channel.FIG.6Bis an optical power density distribution600shown in a XZ plane view. A microlens array618focuses illuminating light portions out-coupled from a pupil-replicating lightguide at a focal plane602inside a substrate of a display panel being illuminated, forming an array of light spots620. Intermediate or fractional-order Talbot planes form e.g. at623,624,625as illustrated. The distribution of optical power density at the focal plane602is repeated at a first-order Talbot plane604, which coincides with a pixel plane of the display panel. An array of optical power density peaks628is formed at openings in black matrix (BM) of the display panel, as illustrated. This enables a more efficient light utilization, since less light is being blocked by the black matrix.

Referring now toFIGS.7A and7B, a display device750includes a display panel702(FIG.7A) optically coupled to the illuminator100ofFIGS.1A and1Band separated from the illuminator100by a spacer or air gap752. The display panel702ofFIG.7Ais a transmissive LC panel including in sequence an optional polarization element754, a thin film transistor (TFT) substrate722with optional cleanup color filters755, a twisted nematic (TN) LC fluid layer756including LC molecules757, a backplane substrate758supporting a black matrix (BM) layer760, an analyzing polarizer762, and virtual reality (VR) optics/ocular lens764. Other configurations of the transmissive LC panel are of course possible; the configuration of the display panel702is only meant as an illustrative non-limiting example.

The operation of the illuminator100of the display device950has been explained above with reference toFIGS.1A and1B. Briefly, the light source108emits the light beam106, which is coupled into the slab104, propagating in zigzag pattern by a series of reflections e.g. total internal reflections (TIRs) from the top and bottom surfaces of the slab106. Portions of the light beam106are out-coupled by the out-coupling grating116. A microlens array618, corresponding to the focusing element118of the illuminator100ofFIGS.1A and1B, focuses the light beam portions as explained above with reference toFIG.6B, forming the Talbot optical power density distribution600throughout the display panel702. For clarity of the picture, the optical power density distribution600is shown offset to the right as schematically indicated with arrows770. The spacer or air gap752is selected or tuned during manufacturing and calibration to make sure that the first-order Talbot plane604coincides with the BM layer760, to maximize the optical throughput of the display panel702.

The light source108may be a multi-color light source for providing the illuminating light to the slab, the illuminating light comprising light of a plurality of color channels. As was explained above with reference toFIG.4, the illuminator100may be configured to couple the light of different ones of the plurality of color channels at different angles into the slab104, such that light spots of the array of light spots form color-interleaved sub-arrays corresponding to the light of the plurality of color channels of the multi-color light source. Alternatively or in addition, the focusing element118may be configured to form the color-interleaved sub-arrays of the array of light spots. This optional feature of the illuminator100was described above with reference toFIGS.5A,5B, and5C. The out-coupled illuminating light portions of the plurality of color channels formed into the color-interleaved sub-arrays of light spots propagate through the spacer or air gap752, the polarization element754, and the TFT substrate722of the display panel702and produce color-interleaved sub-arrays of the array of optical power density peaks at a pixelated plane of the display panel702, for example at the BM layer760. The color-interleaved sub-arrays of optical power density peaks at the pixel array/BM layer760may be different Talbot orders of the color-interleaved sub-arrays. This has been explained above with reference toFIG.6A.

The configuration of the illuminator100and the configuration of the display device750shown inFIGS.1A,1B, andFIGS.7A,7Benable very dense pitches of color-interleaved sub-arrays of illuminating light, the smallest pitch being limited by the accuracy of collimated color channel beam pointing. In some embodiments, a density of at least 2000 optical power density peaks per inch may be achieved, enabling ultra compact display panel e.g. for near-eye display applications with pixel densities of 2000 pixels per inch or higher.

A tight pitch of optical power density peaks and associated small size of color sub-pixels of the illuminated display panel may require a very fine adjustment of the lateral position of the optical power density peaks relative to the color sub-pixels of the display panel, to maximize the optical throughput of a display panel. The adjustment may be performed in a variety of ways. For example, referring toFIG.8, an illuminator800is similar to the illuminator100ofFIGS.1A and1B, and includes similar elements. The illuminator800ofFIG.8includes a slab804of transparent material, an in-coupling grating810and an out-coupling grating816supported by the slab804. The in-coupling grating810is a polarization volume hologram (PVH) grating that diffracts circularly polarized light of a first handedness while transmitting through a circularly polarized light of a second, opposite handedness.

In operation, a light source808emits a light beam806that is circularly polarized at the second handedness. The light beam806propagates through the PVH in-coupling grating810and the slab804and impinges onto a microelectromechanical system (MEMS) reflector840including a tiltable mirror842supported by a MEMS substrate850. The light beam806is reflected by the tiltable mirror842and impinges again onto the PVH in-coupling grating810. Since handedness of a circularly polarized light reverses upon reflection, the reflected light beam806is diffracted by the PVH in-coupling grating810, which in-couples the light beam806into the slab804to propagate in the slab804by a series of internal reflections from opposed outer surfaces of the slab804, as illustrated with a solid zigzag arrow.

Out-coupled portions814of the light beam806are focused by a focusing element818, in this embodiment a microlens array. It is to be noted that the out-coupled portions814originate from an out-coupled wide beam that is broken into individual portions or sub-beams by microlenses819of the focusing element818, not necessarily by the X-period of zigzag reflections. The individual portions are focused into light spots820, similarly to the illuminator100ofFIGS.1A and1B. The array of light spots820is converted into an array of optical power density peaks828by Talbot effect in an optical stack including a substrate822of the display panel being illuminated, as explained above with reference toFIGS.7A and7B.

The illuminator800ofFIG.8further includes a controller880operably coupled to the light source808and the MEMS reflector840. The controller880is configured to tilt the tiltable mirror842by a controllable angle to make the array of optical power density peaks828coincide with the array of pixels124defined by the black grid or black matrix130. For example, initially the controller880may tilt the out-coupled portions814to shifted positions814′ shown with dashed lines. At the shifted positions814′, the light spots820are shifted from a nominal position. The shifted light spots820cause the array of optical power density peaks828to also be shifted to positions828′ shown with dashed lines, and no light passes through the black grid130. The controller880may tune the angle of tilt of the tiltable mirror842to bring the array of optical power density peaks828to the positions overlapping with the pixels124, and the light passes through the pixels124. Herein the term “pixels” also includes color sub-pixels of a color display panel.

A tiltable reflector is one example of a steering element of the illuminating light beam. More generally, one or more beam steering layers may be provided in an optical stack of a display device. Referring for a non-limiting example toFIG.9, a display device950is similar to the display device750ofFIG.7A, and includes similar elements. The display device950ofFIG.9includes the illuminator800ofFIG.8having the MEMS reflector840, for adjusting the lateral position (XY plane position) of the arrays of optical power density peaks in the plane of the BM layer760. For embodiments where the light source808is a color light source emitting light beams of a plurality of color channels, the MEMS reflector840(or another suitable tiltable reflector) may adjust the lateral position (XY plane position) of the color-interleaved sub-arrays of optical power density peaks in the plane of the BM layer760.

The display device950may further include a beam steering layer in an optical path downstream of the slab804, for angularly steering the out-coupled illuminating light portions. For example, a reflective beam steering layer902may be provided in configurations where the out-coupling grating816out-couples portions of illuminating light downwards, not upwards. In such embodiments, the out-coupling grating816may be a PVH grating configured to out-couple the portions of the light beam106at a circular polarization of e.g. a first handedness while propagation the portions of the light beam of the second handedness reflected by the reflective beam steering layer902.

In some embodiments, a beam steering layer904may be provided downstream of the focusing element118. In such embodiments, the array of optical power density peaks828(FIG.8) may be steered relative to the array of light spots820. Alternatively or in addition, a beam steering layer906may be provided downstream of the display panel702, for the purpose of steering the output light beam at the eyebox of the display device950. The beam steering by the MEMS reflector840and the beam steering layer(s)902,904,906, as the case may be, is controlled by the controller880(FIG.9).

In some embodiments, the beam steering by a beam steering layer may be spatially selective. For this, the beam steering layer may be pixelated. Individual areas or pixels of the beam steering layer may be controlled independently. The beam steering layer may include e.g. a switchable diffraction gratings, switchable PBP gratings and/or PBP lenses, etc.

When operating with a color light source emitting light of a plurality of color channels, the beam steering layers902,904, and906based on switchable gratings will exhibit a wavelength dependence of steering angle. This is illustrated inFIG.10Awhere the R, G, and B out-coupled light beam portions are diffracted by a switchable grating1004at different angles. To compensate for the angular dispersion of the diffraction angle of the switchable grating1004, the R, G, and B beams may be in-coupled into the slab804at different angles, such that the out-coupled light beam portions of the R, G, and B beams are at different angles as illustrated inFIG.10B. The pre-compensation of the beam angle enables the R, G, and B light beam portions to be steered by a switchable grating1004at a same angle. In another embodiment, the R, G, and B beams are in-coupled into the slab804in a time-sequential manner, and the MEMS reflector840(or another suitable tiltable reflector) is tilted at an angle to provide the out-coupled beam angle pre-compensation illustrated inFIG.10B.

In embodiments where a steering layer of the illuminator is pixelated, a spatially-selective dimming of the illuminating light is possible. Turning for a non-limiting example toFIGS.11A,11B, and11C, a segment1104of the switchable grating1004ofFIGS.10A and10Bsteers R, G, and B sub-beams that provide respective optical power density peaks at R, G, and B sub-pixels surrounded by the black grid130. InFIG.11A, the segment1104is tuned to center the optical power density peaks at the R, G, and B pixels. InFIG.11B, the segment1104is tuned to shift the optical power density peaks off center of the R, G, and B sub-pixels to impinge onto the black grid130, causing local dimming. Furthermore inFIG.11C, the segment1104is tuned to shift the optical power density peaks to a next one of the R, G, and B sub-pixels to cause local dimming by absorption in a color filter element of the respective R, G, and B sub-pixels.

Referring now toFIG.12, a method1200for illuminating a display panel including a pixel array on a substrate includes propagating (1202) illuminating light in a slab of transparent material. The illuminating light is propagated by a series of internal reflections, such as total internal reflections (TIRs), from opposed outer surfaces of the slab. Portions of the illuminating light are out-coupled (1204) from the slab at one of the slab's outer surfaces using an out-coupling grating. The out-coupling grating may be disposed on or within the slab, and may be a continuous straight diffraction grating such as a surface-relief grating, a PVH grating, etc. The illuminating light portions are spatially modulated (1206) in at least one of amplitude or phase to form an array of light spots from the out-coupled illuminating light portions. The spatially modulating element may include a microlens array, e.g. an array of diffractive, PBP, refractive microlenses, or more generally by a phase and/or amplitude mask as disclosed herein. Light of the formed light spots is propagated (1208) through the substrate to form an array of optical power density peaks at the pixel array due to Talbot effect, as explained above with reference toFIGS.2,6B, and7B.

In embodiments where the illuminating light comprises light of a plurality of color channels, the step1206of spatially modulating the illuminating light is performed so as to form color-interleaved sub-arrays (in both X and Y directions) of the array of light spots. The color-interleaved sub-arrays correspond to the light of the plurality of color channels. For example, if the illuminating light includes R, G, and B color channels, the color-interleaved sub-arrays include red, green, and blue interleaved light spots. Light of the arrays of light spots propagates in the substrate of the display panel, forming color-interleaved sub-arrays of optical power density peaks at the pixel array, as explained above with reference toFIGS.4,5A-5C, andFIG.6A. In such embodiments, the out-coupled illuminating light portions may be angularly steered (1210) using at least one of a tiltable reflector or a steering layer disposed in an optical path between a source of the illuminating light and the pixel array, as explained above with reference toFIG.9.

In embodiments where the display panel comprises a black grid, the out-coupled illuminating light portions are steered (1212) in a spatially selective manner to provide a spatially-selective dimming of the display panel by redirecting the illuminating light portions to impinge onto the black grid instead of the pixel array, as explained above with reference toFIGS.11A-11C.

Referring toFIG.13, a virtual reality (VR) near-eye display1300includes a frame1301supporting, for each eye: an illuminator1330including any of the waveguide illuminators disclosed herein; a display panel1310including an array of display pixels; and an ocular lens1320for converting the image in linear domain generated by the display panel1310into an image in angular domain for direct observation at an eyebox1312. A plurality of eyebox illuminators1306, shown as black dots, may be placed around the display panel1310on a surface that faces the eyebox1312. An eye-tracking camera1304may be provided for each eyebox1312.

The purpose of the eye-tracking cameras1304is to determine position and/or orientation of both eyes of the user. The eyebox illuminators1306illuminate the eyes at the corresponding eyeboxes1312, allowing the eye-tracking cameras1304to obtain the images of the eyes, as well as to provide reference reflections i.e. glints. The glints may function as reference points in the captured eye image, facilitating the eye gazing direction determination by determining position of the eye pupil images relative to the glints images. To avoid distracting the user with the light of the eyebox illuminators1306, the latter may be made to emit light invisible to the user. For example, infrared light may be used to illuminate the eyeboxes1312.

Turning toFIG.14, an HMD1400is an example of an AR/VR wearable display system which encloses the user's face, for a greater degree of immersion into the AR/VR environment. The HMD1400may generate the entirely virtual 3D imagery. The HMD1400may include a front body1402and a band1404that can be secured around the user's head. The front body1402is configured for placement in front of eyes of a user in a reliable and comfortable manner. A display system1480may be disposed in the front body1402for presenting AR/VR imagery to the user. The display system1480may include any of the display devices and illuminators disclosed herein. Sides1406of the front body1402may be opaque or transparent.

In some embodiments, the front body1402includes locators1408and an inertial measurement unit (IMU)1410for tracking acceleration of the HMD1400, and position sensors1412for tracking position of the HMD1400. The IMU1410is an electronic device that generates data indicating a position of the HMD1400based on measurement signals received from one or more of position sensors1412, which generate one or more measurement signals in response to motion of the HMD1400. Examples of position sensors1412include: 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 IMU1410, or some combination thereof. The position sensors1412may be located external to the IMU1410, internal to the IMU1410, or some combination thereof.

The locators1408are traced by an external imaging device of a virtual reality system, such that the virtual reality system can track the location and orientation of the entire HMD1400. Information generated by the IMU1410and the position sensors1412may be compared with the position and orientation obtained by tracking the locators1408, for improved tracking accuracy of position and orientation of the HMD1400. Accurate position and orientation is important for presenting appropriate virtual scenery to the user as the latter moves and turns in 3D space.

The HMD1400may further include a depth camera assembly (DCA)1411, which captures data describing depth information of a local area surrounding some or all of the HMD1400. The depth information may be compared with the information from the IMU1410, for better accuracy of determination of position and orientation of the HMD1400in 3D space.

The HMD1400may further include an eye tracking system1414for determining orientation and position of user's eyes in real time. The obtained position and orientation of the eyes also allows the HMD1400to determine the gaze direction of the user and to adjust the image generated by the display system1480accordingly. The determined gaze direction and vergence angle may be used to adjust the display system1480to reduce the vergence-accommodation conflict. The direction and vergence may also be used for displays' exit pupil steering as disclosed herein. Furthermore, the determined vergence and gaze angles may be used for interaction with the user, highlighting objects, bringing objects to the foreground, creating additional objects or pointers, etc. An audio system may also be provided including e.g. a set of small speakers built into the front body1402.

Embodiments of the present disclosure may include, or be implemented in conjunction with, an artificial reality system. An artificial reality system adjusts sensory information about outside world obtained through the senses such as visual information, audio, touch (somatosensation) information, acceleration, balance, etc., in some manner before presentation to a user. By way of non-limiting examples, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include entirely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, somatic or haptic feedback, or some combination thereof. Any of this content may be presented in a single channel or in multiple channels, such as in a stereo 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 to, for example, create content in artificial reality and/or are otherwise used in (e.g., perform activities in) artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a wearable display such as an HMD connected to a host computer system, a standalone HMD, a near-eye display having a form factor of eyeglasses, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various 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. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be 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 breadth and spirit of the present disclosure as described herein.