Field of view extension by image light redirection

Abstract

A near-eye display has an image projector coupled to a light guide for receiving and propagating image light provided by the image projector, the image light carrying an image to be displayed to a viewer. The field of view of the near-eye display may be expanded by providing a beam redirector downstream of the light guide for controllably redirecting the image light in coordination with the image projector displaying different field of view portions. To compensate for the redirection of the external light by the beam redirector, a second beam redirector may be disposed upstream of the first redirector and the light guide.

Description

Technical Field

[0001] The present disclosure relates to visual display devices and related components, modules and methods. Background Art

[0002] Visual displays provide information, including still images, video, data, etc., to one or more viewers. Visual displays have applications in a variety of fields, including entertainment, education, engineering, science, professional training, advertising, to name a few. Some visual displays (e.g., televisions) display images to multiple users at a time, while some visual display systems (e.g., near-eye displays (NEDs)) are intended for use by a single user.

[0003] Artificial reality systems typically include a NED (e.g., a headset or a pair of glasses) configured to present content to a user. A near-eye display can display virtual objects or combine images of real objects with images of virtual objects, as in virtual reality (VR) applications, augmented reality (AR) applications, or mixed reality (MR) applications. For example, in an AR system, a user can view images of virtual objects (e.g., computer-generated images (CGI)) superimposed with the surrounding environment by looking through a "combiner" component. The combiner of a wearable display is typically transparent to external light, but includes some light routing optics to direct the display light into the user's field of view.

[0004] Human vision has a fairly wide overall field of view (FOV). For AR / VR systems that simulate human vision, the operating field of view needs to be close to that of human vision. A direct approach to achieving a full visual FOV would require wide numerical aperture optics and a large pixel count, which would increase size and weight, complicate processing electronics, and increase the power requirements of the display. Because the display of a head-mounted display (HMD) or NED is typically worn on the user's head, a large, bulky, cumbersome, unbalanced and / or heavy display device with a heavy optoelectronic module and a heavy battery would be cumbersome and uncomfortable for the user to wear. Therefore, head-mounted display devices can benefit from a compact and efficient configuration that can extend the FOV to the limits of the natural FOV. Summary of the invention

[0005] According to a first aspect, a light guide assembly for a near-eye display is provided, the light guide assembly comprising a light guide body and a beam redirector, the light guide body being used to receive and propagate image light, the image light carrying an image in an angular domain to be displayed by the near-eye display, the light guide body comprising a coupling-out structure for coupling out spaced-apart portions of the image light; the beam redirector being located downstream of the light guide body for switchably redirecting portions of the image light coupled out by the coupling-out structure.

[0006] The beam redirector may include a Pancharatnam-Berry phase PBP grating. The PBP grating may be an active PBP grating including a liquid crystal LC layer that can be switched by applying an electric field to the LC layer. The beam redirector may also include a switchable polarization rotator located upstream of the PBP grating for switching the polarization of the image light portions between two mutually orthogonal polarization states.

[0007] The switchable polarization rotator may comprise a switchable wave plate.The switchable wave plate may comprise a liquid crystal.

[0008] The outcoupling structure may include an outcoupling grating. The outcoupling grating includes a polarization volume holographic PVH grating.

[0009] The outcoupling structure may include a plurality of tilted partial bulk reflectors.

[0010] According to a second aspect, a near-eye display NED is provided, which includes an image projector and a light guide component, the image projector being used to provide a first part and a second part of an image in an angular domain to be displayed by the near-eye display; according to the light guide component of the first aspect, the light guide component is located downstream of the image projector.

[0011] The NED may also include a controller operably coupled to the image projector and the first beam redirector.

[0012] The controller may be configured to: during a first time interval, cause the image projector to display the first portion of the image in the angular zone, and cause the first beam redirector to redirect the image light portions at a first angle; and during a subsequent second time interval, cause the image projector to display the second portion of the image in the angular zone, and cause the first beam redirector to redirect the image light portions at a different second angle. The first portion of the image may correspond to a first field of view FOV portion of the image. The second portion of the image may correspond to an adjacent second FOV portion of the image. The difference between the first angle and the second angle of the first beam redirector may cause the first FOV portion and the second FOV portion to partially overlap each other.

[0013] The NED may further include a second beam redirector located upstream of the light guide assembly in a path of the external light for controllably redirecting the external light to counteract redirection of the external light by the first beam redirector.

[0014] The controller may also be operably coupled to the second beam redirector. The controller may be configured to: during a first time interval, cause the image projector to display the first portion of the image in the angular zone and cause the first beam redirector to redirect the image light portions at a first angle; and during a subsequent second time interval, cause the image projector to display the second portion of the image in the angular zone and cause the first beam redirector to redirect the image light portions at a different second angle. The controller may be configured to cause the second beam redirector to counteract the redirection of the external light by the first beam redirector during both the first time interval and the second time interval.

[0015] According to a third aspect, a method for displaying an image to a user is provided, the method comprising: during a first time interval, causing an image projector to emit image light carrying a first portion of the image, and causing a first beam redirector to redirect the image light at a first angle; and during a subsequent second time interval, causing the image projector to emit image light carrying a different second portion of the image, and causing the first beam redirector to redirect the image light at a different second angle.

[0016] The first portion of the image may correspond to a first field of view (FOV) portion of the image. The second portion of the image may correspond to an adjacent second FOV portion of the image. The difference between the first angle and the second angle of the first beam redirector may cause the first FOV portion and the second FOV portion to partially overlap each other.

[0017] The method may also include controllably redirecting the external light to counteract the redirection of the external light by the first beam redirector using a second beam redirector, the second beam redirector being located upstream in the path of the external light relative to the first beam redirector. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Examples will now be described with reference to the accompanying drawings, in which:

[0019] Figure 1A is a side cross-sectional view of a near eye display (NED) having a light guide assembly including a beam redirector of the present disclosure;

[0020] Figure 1B It shows the use of Figure 1A Field of view (FOV) diagram showing the principle of FOV expansion using a beam redirector;

[0021] Figure 2A is available in Figure 1A A front view of a Pancharatnam-Berry phase (PBP) liquid crystal (LC) grating used in a beam redirector;

[0022] Figure 2B yes Figure 2A A magnified schematic diagram of LC molecules in the LC layer of the PBP LC grating;

[0023] Figure 3A It is in the OFF state Figure 2A , Figure 2B Active embodiment of the PBP LC grating;

[0024] Figure 3B It is an active PBP LC grating in the ON state;

[0025] Figure 4A and Figure 4B is a side cross-sectional view illustrating the operation of a beam redirector module including a switchable wave plate and a passive PBP LC grating;

[0026] Figure 4C and Figure 4D is a side cross-sectional view illustrating the operation of a beam redirector module including an active PBP LC grating;

[0027] Figure 5 yes Figure 1A A side cross-sectional view of a polarization volume hologram (PVH) / PBP embodiment of a light guide assembly;

[0028] Figure 6is a side cross-sectional view of a geometric waveguide having a beam redirector module including a binary stack of switchable PBP gratings;

[0029] Fig. 7A is a side cross-sectional view of a PVH that may be used in the light guide of the present disclosure;

[0030] Figure 7B It is shown Fig. 7A Illustration of the optical properties of PVH;

[0031] Figure 8 is a flow chart of a method for displaying an image to a user of the present disclosure;

[0032] Fig. 9 is an illustration of a wearable display of the present disclosure having the form factor of a pair of glasses; and

[0033] Fig.10 is a three-dimensional view of a head mounted display (HMD) of the present disclosure. DETAILED DESCRIPTION

[0034] Although the present teaching is described in conjunction with various examples, it is not intended that the present teaching be limited to such examples. On the contrary, as will be appreciated by those skilled in the art, the present teaching encompasses various alternatives and equivalents. All statements citing the principles, aspects and embodiments of the present disclosure and its specific examples herein are intended to encompass their structural equivalents and functional equivalents. In addition, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e. any element developed to perform the same function, regardless of the structure.

[0035] As used herein, unless explicitly stated, the terms "first" and "second", etc. are not intended to imply a sequential order but are intended to distinguish one element from another. Similarly, unless explicitly stated, the sequential order of method steps does not imply a sequential order in which they are performed. Figure 1A , Figure 5 as well as Figure 6 1 and 2. In the drawings, the same reference numerals denote the same elements.

[0036] According to the present disclosure, the field of view (FOV) of a near-eye display using a pupil-replicating light guide can be extended by providing a beam redirector downstream of the light guide, the beam redirector being used to controllably redirect image light coupled out of the light guide. Such a configuration allows different portions of the FOV to be displayed at different times, thereby extending the overall FOV by temporally sequencing different portions of the FOV.

[0037] According to the present disclosure, a light guide assembly for a near-eye display is provided. The light guide assembly includes: a light guide body for receiving and propagating image light, the image light carrying an image in an angular domain to be displayed by the near-eye display; and a beam redirector located downstream of the light guide body. The light guide body includes an outcoupling structure for outcoupling spaced-apart portions of the image light. The beam redirector is configured to switchably redirect the portions of the image light coupled out by the outcoupling structure.

[0038] In embodiments where the beam redirector comprises a Pancharatnam-Berry phase (PBP) grating, the PBP grating may be a passive PBP grating or an active PBP grating comprising a liquid crystal (LC) layer that can be switched by applying an electric field to the LC layer. The beam redirector may also include a switchable polarization rotator located upstream of the PBP grating for switching the polarization of the image light portion between two mutually orthogonal polarization states. The switchable polarization rotator may include a switchable wave plate that may be based on liquid crystal. In some embodiments, the outcoupling grating may include an outcoupling grating (e.g., a polarization volume hologram (PVH) grating) and / or a plurality of tilted partial volume reflectors.

[0039] According to the present invention, a near eye display (NED) is provided, the NED comprising: an image projector for providing a first portion and a second portion of an image in an angular domain displayed by the near eye display; and the above-mentioned light guide assembly. The NED may also include a controller operably coupled to the image projector and the beam redirector. The controller may be configured to operate as follows. During a first time interval, the controller may cause the image projector to display a first portion of the image in the angular domain, and cause the first beam redirector to redirect the image light portion at a first angle. During a subsequent second time interval, the controller may cause the image projector to display a second portion of the image in the angular domain, and cause the first beam redirector to redirect the image light portion at a different second angle.

[0040] In embodiments where the first portion of the image corresponds to a first field of view (FOV) portion of the image and the second portion of the image corresponds to an adjacent second FOV portion of the image, the difference between the first angle and the second angle of the first beam redirector can cause the first FOV portion and the second FOV portion to partially overlap each other. In some embodiments, the NED may further include an additional beam redirector located upstream of the light guide assembly in the path of the external light for controllably redirecting the external light to offset redirection of the external light by the first beam redirector.

[0041] The controller may be configured to perform the following operations. During a first time interval, the controller may cause the image projector to display a first portion of an image in an angular domain and cause the first beam redirector to redirect the image light portion at a first angle. During a subsequent second time interval, the controller may cause the image projector to display a second portion of an image in an angular domain and cause the first beam redirector to redirect the image light portion at a different second angle. The controller may be configured to cause the additional (i.e., second) beam redirector to offset the redirection of external light by the first beam redirector during both the first time interval and the second time interval.

[0042] According to the present disclosure, a method for displaying an image to a user is also provided. The method includes the following: during a first time interval, causing an image projector to emit image light carrying a first portion of an image, and causing a first beam redirector to redirect the image light at a first angle; and during a subsequent second time interval, causing the image projector to emit image light carrying a different second portion of the image, and causing the first beam redirector to redirect the image light at a different second angle. The first portion of the image may correspond to a first field of view (FOV) portion of the image, and the second portion of the image may correspond to an adjacent second FOV portion of the image. The difference between the first angle and the second angle of the first beam redirector may be selected so that the first FOV portion and the second FOV portion partially overlap each other. The method may also include using a second beam redirector located upstream relative to the first beam redirector in the path of the external light to controllably redirect the external light to offset the redirection of the external light by the first beam redirector, thereby avoiding the splitting of the external image observed through the near eye display (NED).

[0043] Reference now Figure 1A , NED 170 includes a light guide assembly 100 optically coupled to an image projector 180. Light guide assembly 100 includes a light guide body 102, such as a flat plate or sheet of transparent material (including glass, plastic, metal oxides, inorganic crystals, etc.). Light guide body 102 can be configured to receive image light 108 from image projector 180. Image light 108 carries an image in the angular domain, i.e., an image where each pixel of the image is represented by a corresponding ray angle, in contrast to, for example, an image in the linear domain where each pixel (i.e., an element of the image being displayed) is represented by a corresponding ray coordinate.

[0044] For simplicity and generality, the image light 108 is shown as propagating in a straight line. In some embodiments, the light guide body 102 can propagate the image light 108 through a series of sawtooth reflections from its outer surface. The light guide body 102 has an outcoupling structure 104 for coupling out spaced-apart portions 106 of the image light 108 propagating within the light guide body 102. These portions 106 carry the image in the angular domain.

[0045] The beam redirector 110 is disposed downstream of the light guide body 102. The beam redirector 110 switchably redirects the image light segments 106, i.e., deflects all of the image light segments 106 by one of a set of predefined switchable angles. By having the image projector 180 display different FOV portions in a time-sequential manner, the overall FOV of the image conveyed by the image light 108 propagating in the light guide assembly 100 can be significantly extended.

[0046] For example, during a first time interval, the image light 108 may carry a first FOV portion, or in other words, a first portion of an image in an angular domain, and the beam redirector 110 may redirect the image light portion 106 by an angle of -α, as indicated by dashed line 111. During a subsequent second time interval, the image light 108 may carry a second FOV portion, such as an adjacent FOV portion, and the beam redirector 110 may redirect the image light portion 106 by an angle of +α, as indicated by dashed line 112. In this manner, the overall FOV may be extended by an angle of 2α. The coordination required for the operation of the image projector 180 and the beam redirector 110 may be provided by a controller 190, which is operably coupled to the image projector 180 and the beam redirector 110 and is configured to perform the above steps during the first time interval and during the second time interval.

[0047] The first FOV portion and the second FOV portion may have an overlap therebetween to avoid gaps in the overall FOV, or in other words, to avoid gaps in the image in the entire angular domain carried by the image light 108. Figure 1B It is shown in Figure 1B The first FOV portion 121 is shown partially overlapping the second FOV portion 122, making the overall FOV 120 almost twice that of either the first FOV portion 121 or the second FOV portion 122 alone. Such a configuration can double the overall field of view without increasing the complexity of the projector 180 and the angular bandwidth of the light guide body 102, and more generally expand the overall field of view several times, although at the expense of reducing the overall frame rate. The image projector 180 can be based on a microdisplay, and / or a 1D or 2D beam scanner that scans a collimated beam in one or two dimensions.

[0048] For augmented reality (AR) and similar applications in which the outside world remains at least partially visible to the NED wearer, the light guide assembly 100 / NED 170 may also include a second matching beam redirector 110' located on the opposite side of the light guide body 102 (i.e., on the far side or "world" side of the light guide body 102). The purpose of the matching beam redirector 110' is to compensate or counteract the shift that the beam redirector 110 would otherwise impose on the view of the outside world, which would cause the outside world to appear "doubled" or even divided into multiple overlapping images. The controller 190 can be configured to operate both beam redirectors 110, 110' in a coordinated manner so that one always compensates for the other.

[0049] exist Figure 1A In the illustrated embodiment, the beam redirection module 110 may be based on one or more Pancharatnam-Berry phase (PBP) gratings, such as PBP liquid crystal (LC) gratings. Figure 2A , the PBP LC grating 200 includes LC molecules 202 in a thin LC layer 204. The LC molecules 202 are arranged in the XY plane with different in-plane orientations (i.e., rotated about the Z axis) according to the X coordinate. The orientation angle φ(x) of the LC molecules 202 in the PBP LC grating 200 is given by:

[0050] φ(x) = πx / T = πx sinθ / λ o (1)

[0051] Where T is the pitch of the grating 200 and θ is the diffraction angle given by:

[0052] θ = sin -1 (λ o / T ) (2)

[0053] Azimuth φ Figure 2B The θ is shown to vary continuously with a constant period T on the surface of the LC layer 204 . Figure 2A The optical phase delay P in the PBP LC grating 200 is due to the PBP effect, and the optical delay R in the LC layer 204 is λ o / 2, that is, when the optical delay R is half a wavelength, the PBP effect is quite simply expressed as P(x) = 2φ(x). When R = λ0 / 2, the cumulative phase delay P(r) caused by the PBP effect is:

[0054] P(x) = 2φ(x) = 2πx sinθ / λ o (3)

[0055] The PBP LC grating 200 can be a passive device or an active device. The passive version of the PBP LC grating 200 can be preceded by an active wave plate or polarization rotator for switching the polarization of the incident light. In an active PBP LC device, the orientation of the LC molecules can be controlled by an electric field applied to the LC layer 204. In a normal (non-driven) state, the orientation of the LC molecules 202 is determined by an alignment layer that has been irradiated with polarized light (usually ultraviolet (UV) light), so that the LC molecules 202 are aligned according to the polarization direction of the UV light used to cure the alignment layer. For example, a UV light pattern for obtaining a desired spatial distribution of polarization can be generated by using optical interference. In a driven state, the LC molecules 202 are oriented almost perpendicular to the Z axis.

[0056] The operation of active PBP LC devices is Figure 3A and Figure 3B First refer to Figure 3A , the LC molecules 300 are aligned in-plane (i.e., in the XY plane as shown) to provide the desired PBP effect, such as redirecting light or refocusing light. When an electric field is applied to the LC layer, the LC molecules 300 of the positive LC material will preferably align along the electric field lines, so that the molecules are aligned as shown in FIG. Figure 3B The orientation shown is out of plane or along the Z axis, thereby eliminating or at least significantly reducing the PBP effect. Note that negative LC materials may also be used, where the LC molecules are preferably oriented perpendicular to the electric field lines, in which case the effect of the applied electric field is opposite.

[0057] The optical performance of the beam redirector based on PBP LC grating is FIG. 4A to FIG. 4D Shown in. Figure 4A and Figure 4BThe operation of a beam redirector module based on a switchable half-wave plate or polarization rotator 410 (e.g., a switchable half-wave plate based on LC, or a polarization rotator based on a twisted nematic (TN) LC cell or a mixed twisted nematic (MTN) LC cell with a twist angle other than 90 degrees) and a passive PBP LC grating 415 downstream of the switchable half-wave plate 410 is shown. The switchable polarization rotator 410 switches the polarization of the incident light between two mutually orthogonal polarizations. For example, when the switchable polarization rotator 410 is in the off state, the light beam 400 incident on the PBP LC grating 415 is right-circular polarized (RCP). As shown, the passive PBP LC grating 415 diffracts the RCP light beam 400 upward. When the switchable polarization rotator 410 is in the on state, the light beam 400 incident on the PBP LC grating 415 is left-circular polarized (LCP). The passive PBP LC grating 415 diffracts the RCP light beam 400 downward. Therefore, Figure 4A The beam redirection module has a switchable beam redirection property, ie the light beam 400 can be switched between two predefined redirection angles.

[0058] The optical performance of beam redirector modules based on one or more active PBP LC gratings is Figure 4C and Figure 4D In Figure 4C , the active PBP LC grating 420 is in the off state so that its LC molecules are mainly arranged in-plane. When the incident light beam 400 is left circularly polarized (LCP), the active PBP LC grating 420 redirects the light beam 400 upward, and the light beam becomes right circularly polarized (RCP). The deflected RCP light beam 400 is shown with a solid line. When the incident light beam 400 is right circularly polarized (RCP), the active PBP LC 420 redirects the light beam 400 downward, and the light beam becomes left circularly polarized (LCP). The deflected LCP light beam 400 is shown with a dotted line. Applying a voltage to the active PBP LC grating 420 will be as follows Figure 4D The LC molecules are realigned as shown. Therefore, the beam 400 retains its original direction regardless of whether it is LCP or RCP. Thus, the active PBP LC grating 420 has a switchable beam steering or redirection property.

[0059] In some embodiments, active PBP LC gratings can be combined with switchable wave plates and / or passive PBP LC gratings. Furthermore, PBP grating-based redirectors can be assembled in binary stacks to achieve several switchable beam deflection angles. As a non-limiting example, a stack of two PBP gratings can provide 4 switching angles, a stack of three PBP gratings can provide 8 switching angles, and so on. Fig. 7A and Figure 7B Consider further the PVH grating.

[0060] Reference now Figure 5 , the light guide assembly 500 is similar to Figure 1A The light guide assembly 100 is similar to and includes similar elements. Figure 5 The light guide assembly 500 includes a light guide body 502 having an incoupling grating 503 for coupling image light 508 (e.g., a scanned beam from a 2D beam scanner 580) into the light guide body 502. The light guide body 502 also includes an outcoupling grating, which in this example is a polarization volume hologram (PVH) grating 504, which is used to couple out a portion 506 of the image light 508 from the light guide body 102. The light guide assembly 500 and the 2D beam scanner 580 are components of a near eye display (NED) 570. The NED 570 may also include a controller 590 that operates the beam scanner / image projector and one or more beam redirectors to display different FOV portions in a time sequential manner.

[0061] In operation, the PVH grating 504 couples out only light of one polarization handedness, in this example, a right circularly polarized (RCP) image light portion 506. The light guide assembly 500 also includes a beam redirector module 510 disposed downstream of the light guide body 502, which is used to controllably redirect the image light portion 506. In the illustrated embodiment, the beam redirector module 510 includes a switchable half-wave plate (sHWP) 511 that switches the polarization of the image light portion 506 between RCP light and an oppositely polarized left circularly polarized (LCP). As shown, the beam redirector module 510 also includes a PBP grating 512 that redirects the image light portion 506 to the left (for LCP light) and the right (for RCP light), enabling the FOV portion to be switched, thereby enabling the image light portion 506 to be switched as described above with reference to FIG. Figure 1A and Figure 1B In some embodiments, the sHWP 511 may include a switchable LC cell (e.g., a TN or MTN cell for switching between LCP and RCP), and a retarder stack for improving broadband / off-axis performance of polarization switching.

[0062] For augmented reality (AR) and similar applications of the NED 570 in which the outside world remains at least partially visible to the user of the NED 570, the light guide assembly 500 may include a matching beam redirector 510' located on the opposite side of the light guide body 502 (i.e., on the far side or "world" side of the light guide body 502). The purpose of the matched beam redirector 510' is to compensate, offset or cancel the shift that the beam redirector 110 would otherwise impose on the external light 508', which would cause the external scene to appear "doubled". In the illustrated embodiment, the matched beam redirector 510' includes a matched PBP grating 512' that separates the external light into LCP light and PRC light that propagate at opposite angles to the direction of the incident external light 508', as shown. The matched PBP grating 512' is followed by a matched switchable half-wave plate (sHWP) 511', which switches the polarization of the external light 508' from RCP to LCP and from LCP to RCP synchronously with the switchable half-wave plate (sHWP) 511 disposed on the inner side (near side) of the waveguide body 503. The controller 590 can be operably coupled to the 2D scanner 580 and the two redirector modules 510, 510', and is configured so that the matched beam redirector 510' cancels the redirection of the external light 508' by the main beam redirector 510 at any time.

[0063] Go to Figure 6 , the light guide assembly 600 is similar to Figure 1A The light guide assembly 100 is similar to and includes similar elements. Figure 6The light guide assembly 600 includes a geometric waveguide 602 coupled to a beam redirector module 610. The geometric waveguide 602 has an incoupling region 603 for incoupling image light 608 to propagate in the geometric waveguide 602 by a series of zigzag reflections (typically total internal reflections) from opposing surfaces 641 and 642 of the geometric waveguide. The geometric waveguide 602 also includes a plurality of parallel translucent slanted body reflectors 604 for outcoupling a portion 606 of the image light 608 to propagate through the beam redirector module 610. In the illustrated embodiment, the beam redirector module 610 includes a stack of redirectors 650, each capable of redirecting the image light portion 606 at one of two predetermined angles. The angles of different redirectors 650 can be in a binary relationship to each other, for example, the angle of each next redirector 650 can be twice the angle of the previous redirector, thereby enabling redirection through a plurality of switchable angles. The binary redirector may be used in any of the light guide assemblies considered herein, not just in light guide assemblies that include geometric waveguides. In the most basic configuration, the beam redirector module 610 may include only one redirector that switches between two predefined deflection angles, which allows for a nearly 2x FOV expansion. The parallel tilted body reflector 604 may be, for example, a partial body reflector based on a dielectric coating.

[0064] Non-limiting examples of PVH gratings that may be used in the light guide assemblies of the present disclosure will now be presented. Fig. 7A , you can use PVH Grating 700 as Figure 1A The outcoupling structure 104 and Figure 5 The out-coupling structure 504 is provided. Fig. 7A The PVH grating 700 includes an LC layer 704 defined by opposite parallel top and bottom surfaces 705, 706. The LC layer 704 may include an LC fluid containing rod-shaped LC molecules 707 having positive dielectric anisotropy, i.e., nematic LC molecules. A chiral dopant may be added to the LC fluid such that the LC molecules in the LC fluid self-organize into a periodic spiral configuration including a spiral structure 708 extending between the parallel top and bottom surfaces 705, 706 of the LC layer 704. This configuration of the LC molecules 707 is referred to herein as a cholesteric configuration, which includes a plurality of spiral periods p, such as at least two, at least five, at least ten, at least twenty, or at least fifty spiral periods p between the parallel top and bottom surfaces 705, 706 of the LC layer 704.

[0065] The boundary LC molecules 707b at the top surface 705 of the LC layer 704 may be oriented at an angle to the top surface 705. The boundary LC molecules 707b may have spatially varying azimuth angles, for example, the azimuth angles vary linearly along an X-axis parallel to the top surface 705, such as Fig. 7A As shown. To this end, an alignment layer 712 can be provided at the top surface 705 of the LC layer 704. The alignment layer 712 can be configured to provide a desired orientation pattern of the boundary LC molecules 707b, such as a linear dependence of the azimuth angle on the X coordinate. A UV light pattern with a spatially varying polarization direction can be selected to match the desired orientation pattern of the boundary LC molecules 707b at the top surface 705 and / or the bottom surface 706 of the LC layer 704. When the alignment layer 712 is coated with a cholesteric LC fluid, the boundary LC molecules 707b are oriented along the photopolymer chains of the alignment layer 712, thereby adopting a desired surface orientation pattern. As shown, adjacent LC molecules adopt a spiral pattern extending from the top surface 705 of the LC layer 704 to the bottom surface 706.

[0066] The boundary LC molecules 707b define the relative phase of a helical structure 708 having a helical period p. The helical structure 708 forms a volume grating comprising helical stripes 714 tilted at an angle φ, such as Fig. 7A As shown. The steepness of the tilt angle φ depends on the rate of change of the azimuth angle of the boundary LC molecules 707b at the top surface 705 and the top surface 705. Therefore, the tilt angle φ is determined by the surface alignment pattern of the boundary LC molecules 707b at the alignment layer 712. The volume grating has a period Λ along the X axis. x and Λ along the Y axis y In some embodiments, the periodic helical structure 708 of the LC molecules 707 may be polymer-stabilized by mixing a stabilizing polymer into the LC fluid and curing (polymerizing) the stabilizing compound.

[0067] The spiral nature of the fringes 714 of the volume grating causes the PVH grating 700 to preferentially respond to light having a particular handedness of polarization (e.g., left circular polarization or right circular polarization), while being substantially unresponsive to light of the opposite polarization handedness. Thus, the spiral fringes 714 render the PVH grating 700 polarization selective, causing the PVH grating 700 to diffract light having only a single circular polarization handedness. This is particularly useful in Figure 7B It is shown in Figure 7BA light beam 720 is shown incident on the PVH grating 700. The light beam 720 includes a left circularly polarized (LCP) beam component 721 and a right circularly polarized (RCP) beam component 722. The LCP beam component 721 propagates through the PVH grating 700 substantially without diffraction. As used herein, the term "substantially without diffraction" means that even though a small portion of the beam (in this case, the LCP beam component 721) may diffract, the portion of the diffracted light energy is so small that it does not affect the intended performance of the PVH grating 700. The RCP beam component 722 of the light beam 720 undergoes diffraction, thereby producing a diffracted beam 722'.

[0068] The polarization selectivity of the PVH grating 700 is due to the fact that the effective refractive index of the grating depends on the relationship between the handedness or chirality of the incident light beam and the handedness or chirality of the fringes 714 of the grating. The performance of the PVH grating 700 can be switched by changing the handedness of the incident light. The PVH grating 700 can also be made tunable by applying a voltage to the LC layer 704, which distorts or eliminates the above-mentioned spiral structure. It should also be noted that the sensitivity of the PVH 700 to right circularly polarized light is only as an illustrative example. When the handedness of the spiral fringes 714 is reversed, the PVH 700 can be made sensitive to left circularly polarized light. Therefore, the operation of the PVH 700 can be controlled by controlling the polarization state of the incident light beam 720. In addition, in some embodiments, the PVH 700 can be made tunable by applying an electric field on the LC layer 704, which eliminates the periodic spiral structure 708.

[0069] Go to Figure 8 And further reference Figure 1A A method 800 for displaying an image to a user includes: enabling an image projector (e.g., Figure 1A The image projector 180 of the NED 170 transmits ( Figure 8 ; 802) carries image light of a first portion of an image and causes a first beam redirector (e.g., beam redirector 110 ( Figure 1A )) at a first angle (e.g., Figure 1A The method 800 further includes causing the image projector to emit (806) image light carrying a different second portion of the image, and causing the first beam redirector to emit (807) image light at a different second angle (e.g., Figure 1AThe image light is redirected (808) at an angle of +α in the image. The emission 806 and redirection 808 of the image light carrying the second portion of the image is performed during a second time interval following the first time interval. The subsequent second time interval may immediately follow the first time interval or, if desired, may be separated from the first time interval by an idle period. One of the first angle or the second angle may be a zero angle.

[0070] Still refer to Figure 8 And now further reference Figure 1B , the first part of the image may correspond to the first FOV part of the image, e.g. Figure 1B The first FOV portion 121 of the image, and the second portion of the image may correspond to the second FOV portion of the image, e.g. Figure 1B The difference between the first angle and the second angle of the first beam redirector can cause the first FOV portion and the second FOV portion to partially overlap each other, such as Figure 1B As shown and referenced in Figure 1B Since the image displayed to the user is located in the angular domain, the FOV portions 121, 122 of the overall FOV 120 are the portions where the image is displayed.

[0071] In some embodiments, method 800 may further include: using a second beam redirector (e.g., Figure 1A The method 800 includes controlling a first beam redirector 110' to controllably redirect (810) external light to counteract the redirection of the external light by the first beam redirector, the second beam redirector being upstream in the path of the external light relative to the first beam redirector. The second beam redirector is used during both time intervals. The method 800 may be implemented in a controller 190 of the NED 170. The first angle or the second angle may be zero, but not both. The first angle and the second angle are different from each other.

[0072] Reference now Fig. 9 , the augmented reality (AR) NED 900 may include any of the light guide components disclosed herein for expanding the FOV of the artificially generated image. Fig. 9The AR near-eye display 900 includes a frame 901 that supports, for each eye, a light engine or image projector 930 for providing an image beam carrying an image in an angular domain, a pupil replicating light guide 906, including any of the light guide assemblies disclosed herein, for providing multiple offset portions of the image beam to spread the image in the angular domain over an eyebox 912, and a plurality of eyebox illuminators 910, which are shown as black dots, with clear apertures around the pupil replicating light guide 906 spread over a surface facing the eyebox 912. An eye tracking camera 904 may be provided for each eyebox 912.

[0073] The purpose of the eye tracking camera 904 is to determine the position and / or orientation of the user's eyes. The eye zone illuminator 910 illuminates the eye at the corresponding eye zone 912, thereby allowing the eye tracking camera 904 to obtain an image of the eye, as well as provide a reference reflection, i.e., a glint. The glint can be used as a reference point in the collected eye image, thereby facilitating the determination of the eye gaze direction by determining the position of the eye pupil image relative to the glint position. In order to avoid the light of the eye zone illuminator 910 distracting the user's attention, the eye zone illuminator 910 can be made to emit light that is invisible to the user. For example, infrared light can be used to illuminate the eye zone 912.

[0074] Go to Fig.10 , HMD 1000 is an example of an AR / VR wearable display system that surrounds the user's face to immerse the user in an AR / VR environment to a greater extent. HMD 1000 can generate completely virtual 3D images. HMD 1000 may include a front body 1002 and a band 1004 that can be fixed around the user's head. The front body 1002 is configured to be set in front of the user's eyes in a reliable and comfortable manner. The display system 1080 can be set in the front body 1002 for presenting AR / VR images to the user. The display system 1080 may include any of the light guide assemblies disclosed herein. The side 1006 of the front body 1002 may be opaque or transparent.

[0075] In some embodiments, the front body 1002 includes a locator 1008, an inertial measurement unit (IMU) 1010 for tracking the acceleration of the HMD 1000, and a position sensor 1012 for tracking the position of the HMD 1000. The IMU 1010 is an electronic device that generates data indicating the position of the HMD 1000 based on measurement signals received from one or more position sensors 1012, which generate one or more measurement signals in response to the movement of the HMD 1000. Examples of the position sensor 1012 include one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects movement, a type of sensor used for error correction of the IMU 1010, or some combination thereof. The position sensor 1012 can be located outside the IMU 1010, inside the IMU 1010, or some combination thereof.

[0076] The localizer 1008 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 1000. The information generated by the IMU 1010 and the position sensor 1012 can be compared with the position and orientation obtained by tracking the localizer 1008 to improve the tracking accuracy of the position and orientation of the HMD 1000. When the user moves and turns in 3D space, accurate position and orientation are important for presenting an appropriate virtual scene to the user.

[0077] The HMD 1000 may also include a depth camera assembly (DCA) 1011 that collects data describing depth information of a local area surrounding part or all of the HMD 1000. The depth information may be compared with information from the IMU 1010 to more accurately determine the position and orientation of the HMD 1000 in 3D space.

[0078] The HMD 1000 may also include an eye tracking system 1014 for determining the orientation and position of the user's eyes in real time. The acquired position and orientation of the eyes also allow the HMD 1000 to determine the user's gaze direction and adjust the image generated by the display system 1080 accordingly. The determined gaze direction and convergence angle can be used to adjust the display system 1080 to reduce convergence adjustment conflicts. As disclosed herein, direction and convergence can also be used for exit pupil steering of the display. In addition, the determined convergence and gaze angles can be used to interact with the user, highlight objects, bring objects to the foreground, create additional objects or pointers, etc. An audio system may also be provided, including, for example, a set of small speakers built into the front body 1002.

[0079] Embodiments of the present disclosure may include an artificial reality system or be implemented in conjunction with the artificial reality system. The artificial reality system adjusts the sensory information about the outside world obtained through the senses in some way (e.g., visual information, audio, touch (body) information, acceleration, balance, etc.), and then presents it to the user. As a non-limiting example, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and / or derivative thereof. Artificial reality content may include fully generated content, or generated content combined with collected (e.g., real-world) content. Artificial reality content may include video, audio, somatic or tactile feedback, or some combination thereof. Any of these contents may be presented in a single channel or in multiple channels (e.g., in a stereoscopic video that produces a three-dimensional effect to the viewer). In addition, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, which are used, for example, to create content in artificial reality and / or otherwise used in artificial reality (e.g., performing activities in artificial reality). Artificial reality systems that provide artificial reality content can be implemented on a variety of platforms, including wearable displays (e.g., HMDs connected to a host computer system), standalone HMDs, near-eye displays with eyeglass form factors, mobile devices or computing systems, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0080] The scope of the present disclosure is not limited by the specific embodiments described herein. In fact, in addition to the embodiments and modifications described herein, various other embodiments and modifications will be apparent to those of ordinary skill in the art according to the foregoing description and accompanying drawings. Therefore, such other embodiments and modifications are intended to fall within the scope of the present disclosure. In addition, although the present disclosure has been described herein in the context of a specific embodiment in a specific environment for a specific purpose, those of ordinary skill in the art will recognize that the usefulness of the present disclosure is not limited thereto, and the present disclosure can be beneficially implemented in any number of environments for any number of purposes. Therefore, the claims set forth should be interpreted according to the full scope and spirit of the present disclosure as described herein.

Claims

1. A light guide assembly for a near-eye display, the light guide assembly comprising: a light guide body for receiving and propagating image light carrying an image in an angular domain to be displayed by the near-eye display, the light guide body including an outcoupling structure for outcoupling spaced-apart portions of the image light; as well as A beam redirector is located downstream of the light guide body for switchably redirecting the image light portion coupled out by the outcoupling structure.

2. The light guide assembly according to claim 1, wherein: The beam redirector comprises a Pancharatnam-Berry phase PBP grating.

3. The light guide assembly according to claim 2, wherein: The PBP grating is an active PBP grating comprising a liquid crystal LC layer which can be switched by applying an electric field to the LC layer.

4. The light guide assembly according to claim 2 or 3, wherein: The beam redirector further comprises a switchable polarization rotator located upstream of the PBP grating for switching the polarization of the image light portion between two mutually orthogonal polarization states.

5. The light guide assembly according to claim 4, wherein: The switchable polarization rotator comprises a switchable wave plate; Preferably, the switchable wave plate comprises liquid crystal.

6. A light guide assembly according to any preceding claim, wherein: The outcoupling structure comprises an outcoupling grating; Preferably, the outcoupling grating comprises a polarization volume holographic PVH grating.

7. A light guide assembly according to any preceding claim, wherein: The outcoupling structure includes a plurality of inclined segment reflectors.

8. A near-eye display (NED), comprising: an image projector for providing a first portion and a second portion of an image in an angular region to be displayed by the near-eye display; as well as A light guide assembly as claimed in any preceding claim, located downstream of the image projector.

9. The NED of claim 8, further comprising a controller operably coupled to the image projector and the first beam redirector, and configured to: causing the image projector to display the first portion of the image in the angular region and causing the first beam redirector to redirect the image light portion at a first angle during a first time interval; and During a subsequent second time interval, the image projector is caused to display the second portion of the image in the angular region and the first beam redirector is caused to redirect the image light portion at a second, different angle.

10. The NED of claim 9, wherein: The first portion of the image corresponds to a first field of view (FOV) portion of the image; the second portion of the image corresponds to an adjacent second FOV portion of the image; and A difference between the first angle and the second angle of the first beam redirector causes the first FOV portion and the second FOV portion to partially overlap each other.

11. The NED of claim 8, further comprising a second beam redirector located upstream of the light guide assembly in a path of external light for controllably redirecting the external light to counteract redirection of the external light by the first beam redirector.

12. The NED of claim 11, further comprising a controller operably coupled to the image projector, the first beam redirector, and the second beam redirector, and configured to: causing the image projector to display the first portion of the image in the angular region and causing the first beam redirector to redirect the image light portion at a first angle during a first time interval; and during a subsequent second time interval, causing the image projector to display the second portion of the image in the angular region and causing the first beam redirector to redirect the image light portion at a second, different angle; in, The controller is configured to cause the second beam redirector to counteract the redirection of the external light by the first beam redirector during both the first time interval and the second time interval.

13. A method for displaying an image to a user, the method comprising: causing the image projector to emit image light carrying a first portion of the image and causing the first beam redirector to redirect the image light at a first angle during a first time interval; as well as During a subsequent second time interval, the image projector is caused to emit image light carrying a second, different portion of the image, and the first beam redirector is caused to redirect the image light at a second, different angle.

14. The method according to claim 13, wherein: The first portion of the image corresponds to a first field of view (FOV) portion of the image; the second portion of the image corresponds to an adjacent second FOV portion of the image; and A difference between the first angle and the second angle of the first beam redirector causes the first FOV portion and the second FOV portion to partially overlap each other.

15. The method according to claim 13 or 14 further comprises using a second beam redirector to controllably redirect external light to offset redirection of the external light by the first beam redirector, the second beam redirector being located upstream relative to the first beam redirector in the path of the external light.

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