Display with image light steering

A display device includes a directional illuminator providing a light beam, a display panel downstream of a directional illuminator, for receiving and spatially modulating the light beam, and a beam redirecting module downstream of the display panel, for variably redirecting the spatially modulated light beam. Steering the illuminating light by the beam redirecting module enables one to steer the exit pupil of the display device to match the user's eye location(s).

TECHNICAL FIELD

The present disclosure relates to optical devices, and in particular to visual displays and their components and modules.

BACKGROUND

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

An artificial reality system generally includes an NED, e.g. in form of a headset or a pair of glasses, configured to present artificial reality content to a user. The near-eye display may display virtual objects or combine images of real objects with virtual objects, as in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications. For example, in an AR system, a user may view both images of virtual objects (e.g., computer-generated images or CGIs) and the surrounding environment by seeing through a combiner component. The combiner component of a wearable display is typically transparent to external light, but includes some light routing optic to direct the display light into the user's field of view.

Compact and energy-efficient display devices are desired for head-mounted display systems. Because a display of HMD/NED is usually worn on the head of a user, a large, bulky, unbalanced, and/or heavy display device with a heavy battery would be cumbersome and uncomfortable for the user to wear. Compact display devices require compact and energy-efficient light sources, image projectors, lightguides, focusing optics, and so on.

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.1,2,8-10, and12, similar reference numerals denote similar elements.

A display device provides image light carrying an image for observation by a user. The image light may be spread over a large area including all possible locations of the display viewer(s). Spreading the image light over a broad area ensures that most of the light will be lost for the user. In accordance with this disclosure, the image light may be delivered specifically to the area of the user's eyes or even eye pupils, by causing the exit pupils of the display follow the eye pupils' position. To achieve the pupil steering function, a directional illuminator is used to illuminate a display panel. The display panel spatially modulates the illuminating light. The spatially modulated light is steered by a beam redirecting module disposed in an optical path downstream of the display panel. Such a configuration enables the image brightness improvement and/or energy savings due to not sending the image light to areas where it cannot be observed.

In accordance with the present disclosure, there is provided a display device comprising a directional illuminator for providing a light beam, a display panel downstream of the directional illuminator, for receiving and spatially modulating the light beam to provide a spatially modulated light beam carrying an image in linear domain, and a beam redirecting module downstream of the display panel, for variably redirecting the spatially modulated light beam. An ocular lens may be disposed downstream of the beam redirecting module, for forming an image in angular domain at an eyebox of the display device from the image in linear domain carried by the spatially modulated light beam and redirected by the beam redirecting module. An eye tracking system may be provided for determining a pupil position of a user's eye in the eyebox. A controller may be operably coupled to the eye tracking system and the beam redirecting module and configured to cause the beam redirecting module to redirect the spatially modulated light beam to match the eye pupil position in the eyebox. The directional illuminator may include at least one of a slab singlemode waveguide, a slab few-mode waveguide, or a pupil-replicating lightguide.

In some embodiments, the beam redirecting module comprises a stack of switchable gratings. Each switchable grating of the stack may be configured to redirect the spatially modulated light beam by a zero angle in a first state and a pre-determined non-zero angle in a second state. The pre-determined non-zero angles of different switchable gratings of the stack may be in a binary relationship to one another. The stack of switchable gratings may include e.g. a Pancharatnam-Berry phase (PBP) liquid crystal (LC) switchable grating. The stack of switchable gratings may further include a switchable polarization rotator disposed downstream of the PBP LC switchable grating, and a circular polarizer disposed downstream of the switchable polarization rotator.

In embodiments where the directional illuminator is configured for providing the light beam comprising light at first and second color channels, the PBP LC switchable gratings may include first and second PBP LC switchable gratings. The first PBP LC switchable grating may include a first LC layer having a first optical retardation substantially equal to an odd number of half wavelengths of the first color channel and an even number of half wavelengths of the second color channel. The second PBP LC switchable grating may include a second LC layer having a second optical retardation substantially equal to an odd number of half wavelengths of the second color channel and an even number of half wavelengths of the first color channel. More color channels may be provided. For example, the directional illuminator may be further configured for providing the light beam comprising light at a third color channel. The PBP LC switchable gratings may include a third PBP LC switchable grating comprising a third LC layer having a third optical retardation substantially equal to an odd number of half wavelengths of the third color channel, and an even number of half wavelengths of the first and second color channels.

In accordance with the present disclosure, there is provided a display device comprising a light source for providing a light beam, a pupil-replicating lightguide downstream of the light source, for expanding the light beam to provide an expanded light beam, a display panel downstream of the pupil-replicating lightguide, for receiving and spatially modulating the expanded light beam to provide a spatially modulated light beam carrying an image in linear domain, and a beam redirecting module downstream of the display panel, for variably redirecting the spatially modulated light beam. An ocular lens may be disposed downstream of the beam redirecting module, for forming an image in angular domain at an eyebox of the display device from the image in linear domain carried by the spatially modulated light beam. An eye tracking system may be provided for determining a display user's eye pupil position in the eyebox. A controller may be operably coupled to the eye tracking system and the beam redirecting module and configured to cause the beam redirecting module to redirect the spatially modulated light beam to match the eye pupil position in the eyebox. The beam redirecting module may include a stack of switchable gratings, e.g. PBP LC switchable gratings. The PBP LC switchable gratings may include an LC layer between parallel substrates configured for applying an electric field across the LC layer. LC molecules of the LC layer may be oriented substantially parallel to the substrates in absence of the electric field, and substantially perpendicular to the substrates in presence of the electric field.

In accordance with the present disclosure, there is further provided a method for displaying an image to a user. The method includes providing a light beam, receiving and spatially modulating the light beam to provide a spatially modulated light beam carrying an image in linear domain, and using a beam redirecting module to variably redirect the spatially modulated light beam towards an eye of the user. The method may include forming, by an ocular lens, an image in angular domain from the image in linear domain carried by the spatially modulated light beam and redirected by the beam redirecting module. The method may further include determining a display user's eye pupil position in an eyebox and causing the beam redirecting module to redirect the spatially modulated light beam to match the eye pupil position in the eyebox. Using the beam redirecting module may include switching at least one switchable grating of a stack of switchable gratings.

An illustrative general configuration of a display device with exit pupil steering is illustrated inFIG.1. A display device130includes a directional illuminator100providing an illuminating light beam114. Herein, the term “directional illuminator” denotes an illuminator that provides a directed light beam as opposed to a diffused light beam obtained by passing a light beam through a diffuser such as milky glass, for example. The directed light beam may be a parallel light beam or a light beam with a well-defined divergence or convergence. Illustrative examples of directional illuminators will be provided further below.

A display panel118is disposed in an optical path downstream of the directional illuminator100. The display panel may include an array of light valves such as a liquid crystal array, for example. The display panel118receives and spatially modulates the light beam114in amplitude and/or phase, providing a spatially modulated light beam115carrying an image in linear domain. Herein, the term “image in linear domain” means an image where different coordinates of light rays carrying the image correspond to different pixels of the image, as opposed to the term “image in angular domain”, which means an image where different angles of light rays carrying the image correspond to the different pixels. In this context, the term “pixel” means an element of the displayed image.

A beam redirecting module150is disposed downstream of the display panel118. The function of the beam redirecting module150is to variably redirect the spatially modulated light beam115to match location of an eye134of the user, or in some embodiments to match a specific location of a pupil135of the eye134. InFIG.1, three such locations are shown, “A”, “B”, and “C”. The beam redirecting module150is capable to redirect the spatially modulated light beam115to any of the locations “A”, “B”, or “C”, or any locations in between if desired. It is noted that the locations “A”, “B”, and “C” are generally in a three-dimensional space downstream of the beam redirecting module150.

Turning toFIG.2, a multimode directional illuminator200may be used as the directional illuminator100in the display device130ofFIG.1. The directional illuminator200ofFIG.2includes a pupil-replicating lightguide206configured to receive a light beam204from a light source202. The pupil-replicating lightguide206includes opposed first211and second212surfaces running parallel to one another. The light beam204is in-coupled into the pupil-replicating lightguide206by an in-coupler208to propagate in the pupil-replicating lightguide206by a series of zigzag reflections, e.g. total internal reflections or TIRs from the opposed first211and second212surfaces, i.e. parallel to Y-axis in downward direction inFIG.2. The output light beam of the multimode directional illuminator200, also termed expanded light beam, includes parallel beam portions214offset along Y-axis, which are out-coupled from the pupil-replicating lightguide206by an out-coupler216. More than one grating216may be provided. The in-coupler208and/or the out-coupler216may include diffraction gratings, for example. The pitch of the diffraction gratings may be selected so as to provide the required angular deflection of the light beam for the light beam in-coupling and out-coupling. The gratings may include surface relief gratings, refractive transmissive gratings, volume Bragg gratings, volume hologram gratings, polarization hologram gratings, etc. The gratings may be polarization selective to only diffract light in a particular polarization state, such as linear polarization of a certain orientation or a circular polarization of a certain handedness, for example.

Referring toFIG.3A, a Pancharatnam-Berry phase (PBP) liquid crystal (LC) switchable grating300may be used as a building block of the beam redirecting module150of the display device130ofFIG.1. The PBP LC switchable grating300includes LC molecules302in an LC layer304. The LC molecules302are disposed in XY plane at a varying in-plane orientation depending on the X coordinate. The orientation angle ϕ(x) of the LC molecules302in the PBP LC switchable grating300is given by
ϕ(x)=πx/T=πxsin θ/λo(1)

where λois the wavelength of impinging light, T is a pitch of the PBP LC switchable grating300, and θ is a diffraction angle given by
θ=sin−1(λo/T)  (2)

The azimuthal angle ϕ varies continuously across the surface of an LC layer304parallel to XY plane as illustrated inFIG.3B. The variation has a constant period equal to T. The optical phase delay P in the PBP LC grating300ofFIG.3Ais due to the PBP effect, which manifests P(x)=2ϕ(x) when the optical retardation R of the LC layer304is equal to λ□/2.

FIGS.4A and4Billustrate the operation of the PBP LC switchable grating300ofFIG.3A. The PBP LC switchable grating300includes the LC layer304(FIG.3A) disposed between parallel substrates configured for applying an electric field across the LC layer304. The LC molecules302are oriented substantially parallel to the substrates in absence of the electric field, and substantially perpendicular to the substrates in presence of the electric field.

InFIG.4A, of the PBP LC switchable grating300is in OFF state, such that its LC molecules302are disposed predominantly parallel to the substrate plane, that is, parallel to XY plane inFIG.4A. When an incoming light beam415is left-circular polarized (LCP), the PBP LC switchable grating300redirects the light beam415upwards by a pre-determined non-zero angle, and the beam415becomes right-circular polarized (RCP). The RCP deflected beam415is shown with solid lines. When the incoming light beam415is right-circular polarized (RCP), the PBP LC switchable grating300redirects the beam415downwards by a pre-determined non-zero angle, and the beam415becomes left-circular polarized (LCP). The LCP deflected beam415is shown with dashed lines. Applying a voltage V to the PBP LC switchable grating300reorients the LC molecules along Z-axis, perpendicular to the substrate plane, as shown inFIG.4B. At this orientation of the LC molecules302, the PBP structure is erased, and the light beam415retains its original direction, whether it is LCP or RCP. Thus, the active PBP LC grating400has a variable beam steering property.

In accordance with this disclosure, the above described active PBP LC gratings may be used to construct a beam deflection element switchable between three beam deflection angles. Referring toFIG.5, a beam deflection element500includes the PBP LC switchable grating300ofFIGS.3A and4A-4B, an LC switchable half-wave plate502functioning as a switchable polarization rotator, and a left-circular polarizer503, arranged in a stack. In this example, the PBP LC switchable grating300includes a positive LC material, i.e. an LC material showing positive dielectric anisotropy, although a negative LC material could also be used. The input light may be not polarized, i.e. the input light may include both LCP and RCP light. When the PBP LC switchable grating300is in “ON” state, i.e. when the electric field is applied, the PBP structure is erased, thus the PBP LC switchable grating300does not deflect the light beam; as denoted at511, no overall beam deflection occurs. When the PBP LC switchable grating300is in “OFF” state, i.e. when the electric field is not applied, the PBP LC orientation is present, providing the deflection of the light beam by the angle α for LCP light and −α for RCP light. When the switchable half-wave waveplate502is in OFF state, i.e. when the electric field is not applied, the half-wave retardation is present, as denoted at512. As a result, the RCP light at the deflection angle −α becomes LCP light, which is passed through the left-circular polarizer503. Thus, the beam deflection element500deflects the light beam by the angle of −α. When the switchable half-wave waveplate502is in ON state, i.e. when the electric field is applied, the half-wave retardation is erased, and the LCP light remains L-polarized, as denoted at513. Thus, the beam deflection element500deflects the light beam by the angle α.

In accordance with an aspect of this disclosure, the beam redirecting module150of the display device130ofFIG.1may include a stack of the beam deflection elements500ofFIG.5with different magnitudes of deflection. The magnitudes of deflection may be in a binary relationship to one another. Referring toFIG.6for a non-limiting illustrative example, a binary stack600of switchable deflection elements includes a first switchable deflection element601providing switchable deflection between angles of −α, 0, +α; a second switchable deflection element602providing switchable deflection between angles of −2α, 0, +2α; a third switchable deflection element603providing switchable deflection between angles of −4α, 0, +4α, and a fourth switchable deflection element604providing switchable deflection between angles of −8α, 0, +8α. Together, the switchable deflection elements601-604of the stack600may deviate a light beam606by an angular range from −15α to 15α by switching ON and OFF corresponding PBP LC gratings and waveplates.

PBP LC devices may exhibit a wavelength dependence of performance. It follows from Eqs. (1) and (2) that a PBP LC grating having an LC director profile ϕ(r) will exhibit a deflecting angle θ directly proportional to wavelength λ0. If such a grating were used to redirect light of a color display, which typically has three primary color channels, only one color channel would be redirected properly.

To make sure that all three color channels are redirected correctly, a stack of three PBP LC gratings may be used, one for each color channel. By way of a non-limiting example, referring toFIG.7A, a switchable PBP LC device700is a combination of three switchable PBP LC stacks600ofFIG.6: G stack701for green color, B stack702for blue color, and R stack703for red color. InFIG.7A, a green beam component711(solid lines) of a beam706is redirected by the G stack701only; a blue beam component712(short-dash lines) is focused by the B stack702only; and a red beam component713(long-dash lines) is focused by the R stack703only. To provide zero optical power at wavelengths of the other color channels, the R, G, B PBP LC grating and waveplate thicknesses are selected such that their optical retardation at both other wavelengths is integer number of waves, or even number of half wavelengths, resulting in zero PBP and no LCP/RCP polarization transformation and, accordingly, zero deflection angle at the other two color channels. To provide the beam deflecting power at the R, G, B channel wavelengths, the R, G, B PBP LC grating and waveplate thicknesses are selected such that their optical retardation at their own wavelengths is an odd number of half wavelengths, resulting in a non-zero PBP and LCP/RCP polarization transformation and, accordingly, a non-zero optical power of the R, G, B gratings. This technique may be used to make the PBP LC gratings operate with at least two channels. For two color channels, the PBP LC switchable gratings may include first and second PBP LC switchable gratings. The first PBP LC switchable grating may include a first LC layer having a first optical retardation substantially equal to: an odd number of half wavelengths of the first color channel; and an even number of half wavelengths of the second color channel. The second PBP LC switchable grating may include a second LC layer having a second optical retardation substantially equal to: an odd number of half wavelengths of the second color channel; and an even number of half wavelengths of the first color channel. In a similar manner, for three color channels, the PBP LC switchable gratings may further include a third PBP LC switchable grating having a third LC layer having a third optical retardation substantially equal to: an odd number of half wavelengths of the third color channel; and an even number of half wavelengths of the first and second color channels.

Referring toFIG.7B, all three stacks701-603are in “ON” state, and as a result, the beam deflecting power of the switchable LC PBP device700is zero, i.e. the beam706retains original direction of propagation. It is to be noted that, even though one voltage V is shown to be applied to the stack of the PBP LC stacks701-603for simplicity, in actual implementation different sets of voltages are typically applied to different PBP LC stacks701-703. It is also to be understood that the term “achromatic” is used herein to indicate a reduced dependence of performance of PBP LC devices on wavelength, and the achromaticity may be incomplete due to intra-channel wavelength dependence of optical retardation.

The above examples of PBP LC switchable gratings considered the light beam deflection only in one plane. To achieve a light beam deflection in two orthogonal planes, two PBP LC gratings, or two stacks of such gratings may be disposed at 90 degrees clocking angle w.r.t. each other. For example, for each PBP LC switchable grating300(FIG.3A) with the azimuthal angle ϕ1varying along X-axis, ϕ1=ϕ(x), the stack may include a PBP LC switchable grating300with the azimuthal angle ϕ2varying along Y-axis, ϕ2=ϕ(y).

Referring toFIG.8, a transmissive near-eye display (NED) device830is a an embodiment of the display device130ofFIG.1. The transmissive NED830ofFIG.8uses the transmissive display panel118, the multimode directional illuminator200ofFIG.2, and the achromatic switchable PBP LC device700ofFIGS.7A and7Bas the beam redirecting device. Other types of directional illuminators and beam redirecting devices may be used as well. The display device830also includes an ocular lens832and an eye-tracking system838.

The directional illuminator200illuminates the display panel118with the light beam portions214obtained from the light beam204emitted by the light source202and coupled into the pupil-replicating lightguide206, which outputs the light beam portions214as explained above. An ocular lens832is coupled to the display panel118for converting an image in linear domain displayed by the display panel118into an image in angular domain for observation by a user's eye834placed at an eyebox836. The display panel118operates in transmission in this example.

An eye tracking system838is configured to determine a position/orientation of the eye834, and/or the position of the pupil835of the eye834. A controller840is operably coupled to the switchable PBP LC device700and the eye tracking system838and configured to tune the out-coupling angle of light beam portions214for a converging beam817focused by the ocular lens832to match the eye pupil835position. For example, when the eye834shifts to a new position shown with dashed lines at834A, the eye tracking system838determines the new position, reports the new position to the controller840, which then tunes the switchable PBP LC device700to provide deflected light beam portions214A that are focused by the ocular lens832to provide a focused beam817A converging on the new position834A. Such a configuration enables the NED830to only send image light where the eye pupils are located, providing power savings and/or increasing perceived brightness of the observed image. In other words, the NED830enables steering of the exit pupil of the display to match the current eye pupil position.

A reflective configuration of a display device is possible with a reflective display panel such as, for example, a reflective liquid crystal on silicon (LCoS) display panel. LCoS display panels combine a possibility of miniaturization with the convenience of disposing the driving circuitry on the reflective silicon substrate of the LC array. Referring toFIG.9, a reflective NED930is similar to the transmissive NED830ofFIG.8, but uses a polarized light source902and a reflective display panel918instead of the transmissive display panel118. The reflective NED930includes a pupil-replicating lightguide906having an in-coupling grating908and an out-coupling polarization-selective grating916. A polarized light beam904emitted by the polarized light source902is coupled into the pupil-replicating lightguide906by the in-coupling grating908, out-coupled by the out-coupling polarization-selective grating916as polarized light beam portions914. The polarized light beam portions914are directed to the reflective display panel918, propagate back through the pupil-replicating lightguide906, through the switchable PBP LC device700, and towards the ocular lens832, forming a converging beam917at the eyebox836.

The propagation of the light beam portions914is illustrated more precisely inFIG.10. The polarized portions914of the light beam904guided by the pupil-replicating lightguide906are out-coupled by the polarization-selective grating916at a linear polarization perpendicular to the plane ofFIG.10, i.e. parallel to X-axis. The polarized light beam portions914propagate towards the reflective display panel918, e.g. an LCoS reflective display panel, which reflects the light beam portions914to propagate back towards the pupil-replicating lightguide906with a spatially variant polarization state. The light beam portions914at a linear polarization state in plane ofFIG.10, that is, parallel to Y-axis, propagate freely through the polarization-selective grating916, while the light beam portions914at the initial polarization state, that is, perpendicular to the plane ofFIG.5or parallel to X-axis, are deviated (diffracted) by the polarization-selective grating916away from the optical path. As a result, the polarized beam portions914propagated through the polarization-selective grating916(from left to right inFIG.5, i.e. in the direction of Z-axis) are modulated in amplitude providing an image in linear domain. The beam portions914can then be redirected by the switchable PBP LC device700or, more generally, the beam redirecting module150.

Referring now toFIG.11, a singlemode directional illuminator1100can be used as the directional illuminator100of the display device130ofFIG.1or, for example, instead of the directional illuminator200of the display device830ofFIG.8. The singlemode directional illuminator1100includes a slab waveguide1101, typically a singlemode or a few-mode slab waveguide, and a light source1102providing a light beam1110, which is in-coupled into the slab waveguide1101using a suitable coupler, e.g. a lens-based coupler, not shown. The slab waveguide1101includes a substrate1104, a (slab) core layer1106on the substrate1104, and a cladding layer1108over the core layer1106. Thickness of the cladding layer1108may change, i.e. may vary spatially, in a direction of the light1110propagation in the core layer1106, that is, along Y-axis inFIG.11. The light1110propagates in Y-direction inFIG.11, and the thickness (measured in Z-direction) gradually decreases in going along the Y-direction, i.e. bottom to top inFIG.11.

A light extractor1112, e.g. a thin prism, is disposed on the top cladding layer1108. The light extractor11212has a refractive index nexthigher than an effective refractive index neffof a mode of propagation of the light1110in the slab waveguide1101, and the cladding layer1108is thin enough for evanescent out-coupling of the light1110from the core layer1106into the light extractor1112. By way of illustration, the thickness of the cladding layer1108may be between 0.3 and 3 micrometers, or even between 0.1 micrometer and 5 micrometers in some embodiments.

In operation, the light1110propagates in the core layer1106in Y-direction, as shown with a gray arrow. Portions1116of the light1110are out-coupled into the light extractor1112as the light1110propagates in the core layer1106. Angle θ (relative to the waveguide normal) at which the portions1116are out-coupled depends only on the ratio of the effective refractive index neffof the waveguide mode to the refractive index nextof the extractor1112:
θ=asin(neff/next)  (3)

Eq. (3) follows from the law of momentum conversion applied to light. The rate of light tunneling is controlled by the thickness of the cladding layer1108.

The thickness of the cladding layer1108may decrease in the direction of the light1110propagation (i.e. along Y-axis), so as to offset depleting optical power level of the light1110as portions1116are evanescently out-coupled, and thereby increase spatial uniformity of collimated light1114out-coupled from the core layer1106through the top cladding layer1108and into the light extractor1112. The wedging may be achieved, by low-resolution greytone etching techniques. There may be an AR coating between the cladding layer1108and the light extractor1112. The AR coating may be applied to either top of the cladding1108, the bottom of the light extractor1112, or both, depending on the refractive index of the light extractor1112, the cladding layer1108, and the bonding material used.

In the embodiment shown, the light extractor1112is a thin prism, e.g. thinner than 1 mm, having first1121and second1122faces forming a small acute angle. The second face1122may include a reflector, e.g. metal or dielectric reflector, for reflecting the light portions1116out-coupled by the prism to propagate back through the slab waveguide1101at an angle close to normal angle. For example, for 0.95 mm tall light extractor212, the angle may be about 26 degrees; it may be as low as within 15 degrees of the normal angle for some materials. The reflector at the second face1122may be polarization-selective in some embodiments. In applications where a wider beam is needed, a thicker prism may be used. The prism's height may still remain less than one half of the beam diameter in that case. The second face1122may be polished to a radius of curvature, so that the reflector has an optical (i.e. focusing or defocusing) power. It is noted that the term “prism”, as used herein, includes prisms with curved outer faces.

Turning toFIG.12, an augmented reality (AR) near-eye display1200includes a frame1201supporting, for each eye: a light source1202; a pupil-replicating lightguide1206for guiding the light beam inside and out-coupling portions of the light beam as disclosed herein; a display panel1218illuminated by the light beam portions out-coupled from the pupil-replicating lightguide1206for spatially modulating the light beam portions; a beam redirecting module1250for redirecting the spatially modulated beam portions; an ocular lens1232for converting an image in linear domain displayed by the display panel1218into an image in angular domain at an eyebox1236as disclosed herein; an eye-tracking camera1238; and a plurality of eyebox illuminators1262, shown as black dots. The eyebox illuminators1262may be supported by ocular lens1232for illuminating an eyebox1236.

The purpose of the eye-tracking cameras1238is to determine position and/or orientation of both eyes of the user to enable steering the output image light to the locations of the user's eyes as disclosed herein. The illuminators1262illuminate the eyes at the corresponding eyeboxes1236, to enable the eye-tracking cameras1238to 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 illuminators1262, the light illuminating the eyeboxes1236may be made invisible to the user. For example, infrared light may be used to illuminate the eyeboxes1236.

Referring now toFIG.13with further reference toFIGS.1,2, and8, a method1300for displaying an image to a user includes providing (1302) a light beam, e.g. the light beam204emitted by the light source202(FIG.2), receiving and spatially modulating (FIG.13;1304) the light beam to provide a spatially modulated light beam (e.g. the modulated light beam115inFIG.1) carrying an image in linear domain, and using a beam redirecting module such as the beam redirecting module150or the switchable PBP LC device700, to variably redirect (FIG.13;1306) the spatially modulated light beam towards an eye of the user.

The method300may further include forming (1307), by an ocular lens such as the ocular lens832shown inFIG.8, an image in angular domain from the image in linear domain carried by the spatially modulated light beam and redirected by the beam redirecting module. Further optional steps of the method300may include determining (1305) a user's eye pupil position in the eyebox before the redirection (1306) of the spatially modulated light beam to match the eye pupil position in the eyebox. Using the beam redirecting module may include switching at least one switchable grating (e.g. the PBP LC grating300ofFIG.3) of a stack of switchable gratings (e.g. the stack600ofFIG.6).

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.