Patent Description:
Near-eye displays (NEDs) have been widely used in a variety of applications, such as video playback, gaming, and sports. NEDs have been used to realize virtual reality (VR), augmented reality (AR) or mixed reality (MR). AR or MR headsets display a virtual image overlapping with real-world images or see-through images. Pupil-expansion waveguide display systems with diffractive coupling structures are one of the most promising designs for AR/MR displays, potentially offering sun/eye-glasses form factors, a moderately large field of view (FOV), high transmittance and a large eye-box. A waveguide display system often includes a micro-display, collimator, and waveguide optics such as a waveguide combiner. The waveguide combiner integrates in-coupling and out-coupling elements that are often diffraction gratings, and a corresponding waveguide is referred to as a diffractive waveguide. Various diffraction gratings have been integrated into the waveguide, such as surface relief gratings obtained by nanofabrication or holographic gratings of various types.

<CIT> describes a waveguide configured for use with a near eye display (NED) device can include a light-transmissive substrate configured to propagate light rays through total internal reflection and a switchable diffractive optical element (DOE) on a surface of the substrate that is configured to input and/or output light rays to and/or from the substrate. The switchable DOE can include diffractive properties that vary across an area of the DOE. The switchable DOE includes a surface relief diffraction grating (SRG) a surface of the substrate, a layer of liquid crystal material in contact with the SRG, a layer of conducting material in contact with the liquid crystal material configured to apply the voltage to the liquid crystal material, and a layer of insulating material over the layer of conducting material.

According to the invention, there is provided an optical device according to claim <NUM>.

In some embodiments, a light field may correspond to a predetermined portion of a field of view (FOV) of a single-color image.

In some embodiments, a light field may correspond to a predetermined portion of a field of view (FOV) of a full-color image.

In some embodiments, a light field may correspond to a single-color image of a predetermined color.

In some embodiments, the switchable optically anisotropic material may include active liquid crystals (LCs).

In some embodiments, the at least one switchable diffractive optical element may be switchable between a diffraction state and a non-diffraction state via an external electric field applied to the at least one switchable diffractive optical element.

In some embodiments, the SRG may be one of a slanted grating and a non- slanted grating.

In some embodiments, the at least one switchable diffractive optical element may be a one-dimensional diffraction grating.

In some embodiments, the at least one waveguide may include M number of waveguides arranged to be stacked, M being a positive integer and M><NUM>, each of the M number of waveguides includes the at least one switchable diffractive optical element, during respective time periods, the at least one switchable diffractive optical elements included in the respective waveguides sequentially configured to be in a diffraction state to transmit respective light fields of the plurality of light fields, and during one time period, the at least one switchable diffractive optical element included in one of the M number of waveguides configured to be in the diffraction state to transmit a light field of the plurality of light fields, and the at least one switchable diffractive optical elements included in the remaining waveguides configured to be in a non-diffraction state.

In some embodiments, the at least one switchable diffractive optical element included in the respective waveguides may include N number of switchable diffraction gratings, N being a positive integer and N><NUM>.

It will appreciated that any features described herein as being suitable for incorporation into one or more aspects or embodiments of the present invention are intended to be generalizable across any and all aspects and embodiments of the present disclosure.

The following drawings are provided for illustrative purposes according to various disclosed embodiments and are not intended to limit the scope of the present disclosure.

Hereinafter, embodiments consistent with the disclosure will be described with reference to drawings, which are merely examples for illustrative purposes and are not intended to limit the scope of the disclosure. In the drawings, the shape and size may be exaggerated, distorted, or simplified for clarity. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts, and a detailed description thereof may be omitted. Further, in the present disclosure, the disclosed embodiments and the features of the disclosed embodiments may be combined under conditions without conflicts. The described embodiments are some but not all of the embodiments of the present disclosure. Based on the disclosed embodiments, persons of ordinary skill in the art may derive other embodiments consistent with the present disclosure, all of which are within the scope of the present disclosure.

The present disclosure provides an optical device. The optical device may include a light source assembly configured to generate an image light; and at least one waveguide configured to guide the image light to an eye-box of the optical device. The waveguide may include an in-coupling element and an out-coupling element, which are configured to transmit, via the waveguide, a plurality of light fields corresponding to the image light to the eye-box in a time-multiplexing manner. A light field may correspond to a predetermined portion of a field of view (FOV) of a single-color image, a predetermined portion of the FOV of a full-color image, or a single-color image of a predetermined color. At least one of the in-coupling element or the out-coupling element may include at least one switchable diffractive optical element. The switchable diffractive optical element may include a surface relief grating (SRG) filled with an active optically anisotropic material having a first principal refractive index along a groove direction of the SRG and a second principal refractive index along an in-plane direction perpendicular to the groove direction. One of the first and second principal refractive indices may substantially match a refractive index of the SRG, and the other may mismatch the refractive index of the SRG. The optically anisotropic material may include active or reorientable liquid crystals (LCs). The switchable diffractive optical element may be switchable between a diffraction state and a non-diffraction state due to reorientation of LCs in an external field, e.g., an electric field, a magnetic field, or a light, etc. The optical device may be a component of a near-eye display (NED).

The optically anisotropic material may be a uniaxial anisotropic material, whose refractive index ellipsoid has an axial symmetry with regard to its optic axis. noAN and neAN are principal refractive indices of the uniaxial anisotropic material. Nematic liquid crystals (LC) (except some exotic types like bend-core shaped) belong to the category of uniaxial anisotropic materials. Refractive index experienced by a light propagating in the nematic LC layer may be variable in a range between ordinary refractive index noAN and extraordinary refractive index neAN, depending on the angle α between the light polarization and optical axis of the optically anisotropic material. For example, the refractive index experienced by a light propagating in the nematic LC layer may be varied from noAN to neAN when the angle α changes from <NUM>° to <NUM>°.

The switchable diffractive optical element may be polarization selective, for example, the diffractive optical element may selectively diffract a linearly polarized light having a first polarization, and transmit a linearly polarized light having a second polarization with negligible diffraction. The diffraction efficiency of the linearly polarized light having the first polarization may be controllable by the external field. The diffraction efficiency of the linearly polarized light having the first polarization may be lower than a predetermined threshold, for example, about <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>%. In some embodiments, one of the first and second principal refractive indices may be the same as the refractive index of the SRG and, thus, the diffractive optical element may transmit the linearly polarized light having the second polarization without any diffraction.

<FIG> illustrates a schematic diagram of a near-eye display (NED) <NUM> according to an embodiment of the disclosure. In some embodiments, the NED <NUM> may be referred to as a head-mounted display (HMD). The NED <NUM> may present media to a user. Examples of media presented by the NED <NUM> include one or more images, video, audio, or some combination thereof. In some embodiments, audio is presented via an external device (e.g., speakers and/or headphones) that receives audio information from the NED <NUM>, a console (not shown), or both, and presents audio data based on the audio information. The NED <NUM> acts as a VR device, an AR device and/or a MR device, or some combination thereof. In some embodiments, when the NED <NUM> acts as an AR and/or MR device, portions of the NED <NUM> and its internal components may be at least partially transparent.

As shown in <FIG>, the NED <NUM> may include a frame <NUM> and a display <NUM>. Certain device(s) may be omitted, and other devices or components may also be included. The frame <NUM> may include any appropriate type of mounting structure to ensure the display <NUM> to be viewed as a NED by a user. The frame <NUM> may be coupled to one or more optical elements which together display media to users. In some embodiments, the frame <NUM> may represent a frame of eye-wear glasses. The display <NUM> is configured for users to see the content presented by the NED <NUM>. As discussed below in conjunction with <FIG>, the display <NUM> may include at least one display assembly (not shown) for directing image light to an eye of the user. In some embodiments, the at least one display assembly may be a projection system. For illustrative purposes, <FIG> shows the projection system may include a projector <NUM> that is coupled to the frame <NUM>.

<FIG> is a cross-section <NUM> of the NED <NUM> shown in <FIG> according to an embodiment of the disclosure. The display <NUM> may include at least one waveguide display assembly <NUM>. The waveguide display assembly <NUM> may include a waveguide or a stack of waveguides. An exit pupil <NUM> may be a location where an eye <NUM> is positioned in an eye-box region when the user wears the NED <NUM>. For purposes of illustration, <FIG> shows the cross section <NUM> associated with a single eye <NUM> and a single waveguide display assembly <NUM>, but in alternative embodiments not shown, another display assembly which is separate from the waveguide display assembly <NUM> shown in <FIG>, may provide image light to an eye-box located at an exit pupil of another eye of the user.

The waveguide display assembly <NUM>, as illustrated below in <FIG>, may be configured to direct the image light to an eye-box located at the exit pupil <NUM> of the eye <NUM>. The waveguide display assembly <NUM> may be composed of one or more materials (e.g., plastic, glass, etc.) with one or more refractive indices that effectively minimize the weight and widen the FOV of the NED <NUM>. In some embodiments, the waveguide display assembly <NUM> may be a component (e.g., the display <NUM>) of the NED <NUM>. In some embodiments, the waveguide display assembly <NUM> may be part of some other NED, or other system that directs display image light to a particular location. As shown in <FIG>, the waveguide display assembly <NUM> may be for one eye <NUM> of the user. The waveguide display assembly <NUM> for one eye may be separated or partially separated from the waveguide display assembly <NUM> for the other eye. In certain embodiments, a single waveguide display assembly <NUM> may be used for both eyes <NUM> of the user.

In some embodiments, the NED <NUM> may include one or more optical elements between the waveguide display assembly <NUM> and the eye <NUM>. The optical elements may act to, e.g., correct aberrations in image light emitted from the waveguide display assembly <NUM>, magnify image light emitted from the waveguide display assembly <NUM>, some other optical adjustment of image light emitted from the waveguide display assembly <NUM>, or some combination thereof. The example for optical elements may include an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, or any other suitable optical element that affects image light. In some embodiments, the NED <NUM> may include an adaptive dimming element <NUM>, which may dynamically adjust the transmittance of the real-world objects viewed through the NED <NUM>, thereby switching the NED <NUM> between a VR device and an AR device or between a VR device and a MR device. In some embodiments, along with switching between the AR/MR device and the VR device, the adaptive dimming element <NUM> may be used in the AR and/MR device to mitigate difference in brightness of real and virtual objects.

<FIG> illustrates a schematic diagram of a waveguide display assembly <NUM> according to an embodiment of the disclosure. The waveguide display assembly <NUM> may be implemented into NEDs for VR, AR or MR applications. As shown in <FIG>, the waveguide display assembly <NUM> may include a light source assembly <NUM>, a waveguide <NUM>, and a controller <NUM>. The light source assembly <NUM> may include a light source <NUM> and an optics system <NUM>. In some embodiments, the light source <NUM> may be a light source that generates coherent or partially coherent light. The light source <NUM> may include, e.g., a laser diode, a vertical cavity surface emitting laser, and/or a light emitting diode. In some embodiments, the light source <NUM> may be a display panel, such as a liquid crystal display (LCD) panel, an liquid-crystal-on-silicon (LCoS) display panel, an organic light-emitting diode (OLED) display panel, a micro light-emitting diode (micro-LED) display panel, a digital light processing (DLP) display panel, or some combination thereof. In some embodiments, the light source <NUM> may be a self-emissive panel, such as an OLED display panel or a micro-LED display panel. In some embodiments, the light source <NUM> may be a display panel that is illuminated by an external source, such as an LCD panel, an LCoS display panel, or a DLP display panel. Examples of an external sources may include a laser, an LED, an OLED, or some combination thereof. The optics system <NUM> may include one or more optical components that condition the light from the light source <NUM>. Conditioning light from the light source <NUM> may include, e.g., transmitting, attenuating, expanding, collimating, and/or adjusting orientation in accordance with instructions from the controller <NUM>.

The light source assembly <NUM> may generate an image light <NUM> and output the image light <NUM> to an in-coupling element <NUM> located at the waveguide <NUM>. The waveguide <NUM> may expanded image light <NUM> to an eye <NUM> of the user. The waveguide <NUM> may receive the image light <NUM> at one or more in-coupling elements <NUM> located at the waveguide <NUM>, and guide the received image light <NUM> to an out-coupling element <NUM> located at the waveguide <NUM>, such that the received input image light <NUM> is decoupled out of the waveguide <NUM> towards the eye <NUM> via the out-coupling element <NUM>. In some embodiments, the in-coupling element <NUM> may couple the image light <NUM> from the light source assembly <NUM> into the waveguide <NUM>. The waveguide <NUM> may include a first surface <NUM>-<NUM> facing the real-world and an opposing second surface <NUM>-<NUM> facing the eye <NUM>. In some embodiments, as shown in <FIG>, the in-coupling element <NUM> may be part of, or affixed to, the first surface <NUM>-<NUM> of the waveguide <NUM>. In some embodiments, the in-coupling element <NUM> may be part of, or affixed to, the second surface <NUM>-<NUM> of the waveguide <NUM>. In some embodiments, the in-coupling element <NUM> may include a surface relief grating, a volume hologram, a polarization grating, a polarization volume hologram, a metasurface grating, or other types of diffractive elements, or some combination thereof. In some embodiments, the in-coupling element <NUM> may include a diffraction grating, and a pitch of the diffraction grating may be chosen, such that the total internal reflection (TIR) occurs in the waveguide <NUM>, and the image light <NUM> may propagate internally in the waveguide <NUM> (e.g., by total internal reflection). The in-coupling element <NUM> is also referred to as an in-coupling grating.

The out-coupling element <NUM> may be part of, or affixed to, the first surface <NUM>-<NUM> or the second surface <NUM>-<NUM> of the waveguide <NUM>. In some embodiments, as shown in <FIG>, the out-coupling element <NUM> may be part of, or affixed to, the second surface <NUM>-<NUM> of the waveguide <NUM>. In some embodiments, the out-coupling element <NUM> may be part of, or affixed to, the first surface <NUM>-<NUM> of the waveguide <NUM>. In some embodiments, the out-coupling element <NUM> may include a surface relief grating, a volume hologram, a polarization grating, a polarization volume hologram, a metasurface grating, or other types of diffractive elements, or some combination thereof. In some embodiments, the out-coupling element <NUM> may include a diffraction grating, and the pitch of the diffraction grating may be configured to cause the incident image light <NUM> to exit the waveguide <NUM>, i.e., redirecting image light <NUM> so that the TIR no longer occurs. Such a grating is also referred to as an out-coupling grating.

The waveguide <NUM> may be composed of one or more materials that facilitate total internal reflection of the image light <NUM>. The waveguide <NUM> may be composed of, for example, plastic, glass, and/or polymers. The waveguide <NUM> may have a relatively small form factor. For example, the waveguide <NUM> may be approximately <NUM> wide along the x-dimension, <NUM> long along the y-dimension and <NUM>-<NUM> thick along the z-dimension. The controller <NUM> may control the operation scheme of the light source assembly <NUM>. In some embodiments, the waveguide <NUM> may output the expanded image light <NUM> to the eye <NUM> with a large field of view (FOV). For example, the expanded image light <NUM> may be provided to the eye <NUM> with a diagonal FOV (in x and y) of <NUM> degrees and or greater and/or <NUM> degrees and/or less. The waveguide <NUM> may be configured to provide an eye-box with a width of <NUM> or greater and/or equal to or less than <NUM>, and/or a height of <NUM> or greater and/or equal to or less than <NUM>. Using the waveguide display assembly <NUM>, the physical display and electronics may be moved to the side of the front rigid body and a fully unobstructed view of the real world may be achieved, therefore opening up the possibilities to true AR.

In some embodiments, the waveguide <NUM> may include additional gratings which redirect/fold and/or expand the pupil of the light source assembly <NUM>. For example, as shown in <FIG>, in a waveguide display assembly <NUM>, the waveguide <NUM> may further include a directing element <NUM> that redirects the received input image light <NUM> to the out-coupling element <NUM>, such that the received input image light <NUM> is decoupled out of the waveguide <NUM> via the out-coupling element <NUM>. The directing element <NUM> may be part of, or affixed to, the first side <NUM>-<NUM> of the waveguide <NUM>, and the out-coupling element <NUM> may be part of, or affixed to, the second side <NUM>-<NUM> of the waveguide <NUM>, such that the directing element <NUM> is arranged opposed to the out-coupling element <NUM>. In some embodiments, the directing element <NUM> and the out-coupling element <NUM> may be structurally similar. In some embodiments, the directing element <NUM> may include a surface relief grating, a volume hologram, a polarization grating, a polarization volume hologram, a metasurface grating, or other types of diffractive elements, or some combination thereof. In some embodiments, the directing element <NUM> may include a diffraction grating, and in this case the directing element <NUM> is also referred to as a folding grating. In some embodiments, multiple functions, e.g., redirecting/folding and/or expanding the pupil of the light source assembly <NUM> may be combined into a single grating, e.g. an out-coupling grating.

Referring to <FIG>, in some embodiments, the waveguide display assembly <NUM>/<NUM> may include a plurality of waveguides stacked together, where each waveguide <NUM> is designed to handle, e.g., some portion of the FOV and/or some portion of the color spectrum of the virtual image. In some embodiments, the waveguide display assembly <NUM>/<NUM> may include a plurality of source assemblies <NUM> and/or a plurality of waveguides <NUM>. Each of the source assemblies <NUM> may emit a monochromatic image light of a specific wavelength band corresponding to a primary color (e.g., red, green, or blue). The plurality of waveguides <NUM> may be stacked together to output an expanded image light <NUM> that is multi-colored, i.e., image light <NUM> of full colors. In some embodiments, each of the source assemblies <NUM> may emit full-color image lights corresponding to different portions of the FOV provided by the waveguide display assembly <NUM>/<NUM>. In some embodiments, the source assembly <NUM> may include a plurality of light sources <NUM>. Each of the light sources <NUM> may emit image lights of full colors. The full-color image lights emitted by different light sources <NUM> may correspond to different portions of the FOV provided by the waveguide display assembly <NUM>/<NUM>. For example, the source assembly <NUM> may include three light sources <NUM> emitting full-color image lights corresponding to a left portion, a center portion and a right portion of the FOV, respectively.

Referring to <FIG>, in the waveguide display assembly <NUM>/<NUM>, at least one of the in-coupling grating <NUM>, the out-coupling grating <NUM> or the directing grating <NUM> may include at least one switchable diffractive optical element in accordance with an embodiment of the present disclosure. In some embodiments, the switchable diffractive optical element may be switchable between a diffraction state (or an On-state) and a non-diffraction state (or an Off-state) by an external field.

<FIG> illustrate schematic diagrams of a grating <NUM> in a non-diffraction state and a diffraction state, respectively, according to an embodiment of the disclosure. As shown in <FIG>, the grating <NUM> may include a surface relief grating (SRG) <NUM> filled with an optically anisotropic material <NUM> consisting of elongated molecules. The SRG <NUM> may be a binary non-slanted grating. Molecules <NUM> of the optically anisotropic material <NUM> may be homogeneously aligned within the groove in the groove direction, for example, in the y-direction in <FIG>. The optically anisotropic material <NUM> may be uniaxial and have a first principal refractive index (e.g., neAN) in the groove direction (e.g., y-direction) of the SRG <NUM> and a second principal refractive index (e.g., noAN) along an in-plane direction (e.g., x-direction) perpendicular to the groove direction of the SRG <NUM>. The second principal refractive index (e.g., noAN) may substantially match a refractive index ng of the SRG <NUM>, and the first principal refractive index (e.g., neAN) may mismatch the refractive index ng of the SRG <NUM>.

The SRG <NUM> may be fabricated from an organic material, such as amorphous or liquid crystalline polymers, crosslinkable monomers including those having LC properties (reactive mesogens (RM)), or fabricated from an inorganic material, such as metals or oxides used for manufacturing of metasurfaces. The materials of the SRG <NUM> may be isotropic or anisotropic. In some embodiments, the SRG <NUM> may be nanofabricated from a resist material that is transparent or nearly transparent to a range of EM frequencies, such as the visible band. The resist material may be a form of thermoplastic, polymer, optically transparent photoresist, and so on. After set or cured, the resist material may provide an alignment of the optically anisotropic material <NUM> filled into the SRG <NUM>. That is, the SRG <NUM> may function as an alignment layer for the optically anisotropic material <NUM>. Various alignment patterns and features (e.g., sub <NUM>) may be formed using the nanofabrication techniques of the SRG <NUM>, which allows the creation of an alignment pattern of the optically anisotropic material <NUM> with high customizability. For example, the molecules of the optically anisotropic material <NUM> may be homeotropically or homogeneously or hybrid aligned within the grooves of the SRG <NUM>. In some embodiments, the molecules <NUM> of the optically anisotropic material <NUM> may be homeotropically or homogeneously aligned within the grooves of the SRG <NUM> by a stretch, a light (e.g., photoalignment), an electric field, a magnetic field, or any appropriate aligning methods.

The optically anisotropic material <NUM> may include active materials that are switchable by an external field. The active materials may include active or reorientable liquid crystals (LCs), or polymerizable liquid crystal (LC) precursors, or some combinations thereof. In some embodiments, the polymerizable LC precursors may include reactive mesogens (RMs) that are polymerizable LC materials. In some embodiments, the grating <NUM> may further include two opposite substrates that form a container of the SRG <NUM> and the optically anisotropic material <NUM>. In some embodiments, to enable an electrical switching of the grating <NUM>, each substrate may be provided with a transparent electrode, such as an indium tin oxide (ITO) electrode. In some embodiments, the alignment of the optically anisotropic material <NUM> may be provided by one or more alignment layers other than the SRG <NUM>, where the alignment layer may be disposed at the substrate. In some embodiments, the thickness of the optically anisotropic material <NUM> may be the same as a depth d of the SRG <NUM>. In some embodiments, the thickness of the optically anisotropic material <NUM> may be different from the depth of the SRG <NUM>, where the optically anisotropic material <NUM> disposed above the SRG <NUM> may be uniform and may not contribute to the diffraction.

The grating <NUM> may be sensitive to a linearly polarized incident light. As shown in <FIG>, for an incident light <NUM> polarized in the in-plane direction (e.g., x-direction) perpendicular to the groove direction of the SRG <NUM>, due to the substantial refractive index match between noAN and ng, the grating <NUM> may appear to be a substantially optically uniform plate for the incident light <NUM> with negligible diffraction. That is, the grating <NUM> may be in a non-diffraction state for the incident light <NUM> polarized in the in-plane direction (e.g., x-direction) perpendicular to the groove direction of the SRG <NUM>. In some embodiments, the second principal refractive index (e.g., noAN) may exactly match (or may be the same as) the refractive index ng of the SRG <NUM> and, thus, the incident light <NUM> may be transmitted through without any diffraction. That is, the diffraction effect of the grating <NUM> may be completely turned off.

As shown in <FIG>, for an incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>, due to the refractive index difference between neAN and ng, the light <NUM> may experience a periodic modulation of the refractive index in the grating <NUM> and become diffracted. That is, the grating <NUM> may be in a diffraction state for the incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>. The diffraction efficiency of the light <NUM> may be determined by the modulation of refractive index nm (i.e., the difference between the neAN and ng) provided by the grating <NUM>. The diffraction efficiency may be controllable by an externa field, e.g. an electric field, a magnetic field, or a light, etc..

<FIG> illustrate a schematic diagram of a grating <NUM> in a diffraction state and a non-diffraction state, respectively. The similarities between <FIG> and <FIG> are not repeated, while certain differences may be explained. As shown in <FIG>, molecules <NUM> of an optically anisotropic material <NUM> may be homogeneously aligned within the groove in the groove direction, for example, in the y-direction in <FIG>. The optically anisotropic material <NUM> may have a first principal refractive index (e.g., neAN) in a groove direction (e.g., y-direction) of the SRG <NUM> and a second principal refractive index (e.g., noAN) along an in-plane direction (e.g., x-direction) perpendicular to the groove direction of the SRG <NUM>. The second principal refractive index (e.g., noAN) may mismatch a refractive index ng of the SRG <NUM>, and the first principal refractive index (e.g., neAN) may substantially match the refractive index ng of the SRG <NUM>.

The grating <NUM> may be sensitive to a linearly polarized incident light. As shown in <FIG>, for an incident light <NUM> polarized in the in-plane direction (e.g., x-direction) perpendicular to the groove direction of an SRG <NUM>, due to the refractive index difference between noAN and ng, the light <NUM> may experience a periodic modulation of the refractive index in the grating <NUM> and, thus, get diffracted. That is, the grating <NUM> may be in a diffraction state for the incident light <NUM> polarized in the in-plane direction (e.g., x-direction) perpendicular to the groove direction of the SRG <NUM>. The diffraction efficiency of the light <NUM> may be determined by the modulation of refractive index nm (i.e., the difference between the noAN and ng) provided by the grating <NUM>.

As shown in <FIG>, for an incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>, due to the substantial refractive index match between neAN and ng, the grating <NUM> may appear to be a substantially optically uniform plate for the incident light <NUM> with negligible diffraction. That is, the grating <NUM> may be in a non-diffraction state for the incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>. In some embodiments, the first principal refractive index (e.g., neAN) may exactly match (or may be the same as) the refractive index ng of the SRG <NUM> and, thus, the incident light <NUM> may be transmitted through without any diffraction. That is, the diffraction effect of the grating <NUM> may be completely turned off.

<FIG> illustrate a schematic diagram of a grating <NUM> in a non-diffraction state and a diffraction state, respectively. The similarities between <FIG> and <FIG> are not repeated, while certain differences may be explained. Similar to the grating <NUM> in <FIG>, the grating <NUM> shown in <FIG> may include an SRG <NUM> filled with an optically anisotropic material <NUM>. Different from the binary non-slanted SRG <NUM> in <FIG>, the SRG <NUM> in <FIG> may be a binary slanted grating. The diffraction state and the non-diffraction state of the grating <NUM> in <FIG> may be referred to that of the grating <NUM> in <FIG>, and the details are not repeated here.

<FIG> show the diffractive optical element is an active grating that includes an SRG having a periodic rectangular profile, i.e., the cross-sectional profile of the grooves of the SRG has a periodic rectangular shape, which is for illustrative purposes and not intended to limit the scope of the present disclosure. In some embodiments, the fringes of the grating may be linear, i.e. the grating may be a one-dimensional grating. In some embodiments, the diffractive optical element may include a plurality of SRGs that are patterned and/or stacked. In some embodiments, the cross-sectional profile of the grooves of the SRG may be non-rectangular, for example, sinusoidal, triangular or saw-tooth, depending on the application scenarios. In some embodiments, the cross-sectional profile of the grooves of the SRG may be non-periodic, an exemplary diffractive optical element will be described in <FIG>. In some embodiments, the diffractive optical element may be configured with or without optical power. The disclosed diffractive optical elements may also realize almost the same optical functions as conventional refractive optics, such as lenses, prisms or aspheres, but may be much smaller and lighter.

<FIG> illustrates a schematic diagram of a switchable diffractive optical element <NUM>, according to another embodiment of the disclosure. As shown in <FIG>, the diffractive optical element <NUM> may include an SRG <NUM> filled with an optically anisotropic material <NUM>. Molecules <NUM> of the optically anisotropic material <NUM> may be homogeneously or homeotropically aligned within the groove, for example, homogeneously aligned in a groove direction (e.g., y-direction) of the SRG <NUM>. The optically anisotropic material <NUM> may have a first principal refractive index (e.g., an extraordinary refractive index neAN) in the groove direction (e.g., y-direction) of the SRG <NUM> and a second principal refractive index (e.g., an ordinary refractive index noAN) along an in-plane direction (e.g., x-direction) perpendicular to the groove direction. One of the first principal refractive index and the second principal refractive index may substantially match a refractive index ng of the SRG <NUM>, and the other may mismatch the refractive index ng of the SRG <NUM>. For discussion purposes, in the diffractive optical element <NUM>, the second principal refractive index (e.g., noAN) of the optically anisotropic material <NUM> may substantially match the refractive index ng of the SRG <NUM>, and the first principal refractive index (e.g., neAN) in the groove direction (e.g., y-direction) of the SRG <NUM> may mismatch the refractive index ng of the SRG <NUM>.

The cross-sectional profile of the grooves of the SRG <NUM> may have a non-periodic rectangular profile. In the in-plane direction (e.g., x-direction) perpendicular to the groove direction (e.g., y-direction) of the SRG <NUM>, the periodicity (wgroove + whill) of the SRG <NUM> may monotonically decrease from a center (c) to a periphery of the SRG <NUM>, through which a light focusing effect is achieved. For an incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>, due to the refractive index difference between neAN and ng, the light <NUM> may experience a periodic modulation of the refractive index in the diffractive optical element <NUM> and become diffracted. Through configuring the cross-sectional profile of the grooves of the SRG <NUM>, as well as, the refractive indices of the optically anisotropic material <NUM> and the SRG <NUM>, diffracted light beams <NUM> may be further focused. That is, the diffractive optical element <NUM> may function a cylindrical diffractive lens. The diffractive optical element <NUM> may also include other elements, such as substrates, electrodes for electrically switching, alignment layers, etc., and <FIG> merely shows a partial structure of the diffractive optical element <NUM>.

A switching between a diffraction state and a non-diffraction state of an active diffractive optical element (e.g., an active grating) in accordance with an embodiment of the present disclosure will be explained in the following with the accompanying <FIG> and <FIG>. In some embodiments, an active diffractive optical element in accordance with an embodiment of the present disclosure may be switchable between a non-diffraction state and a diffraction state by applying an electric field to the active LC materials, due to an electric-field-induced reorientation of the LCs filled into the SRG. In some embodiments, the active diffractive optical element may be switchable between a non-diffraction state and a diffraction state by applying a light to the active LC materials, due to a photo-induced reorientation of the LCs filled into the SRG. In some embodiments, the active diffractive optical element may be switchable between a non-diffraction state and a diffraction state by applying a magnetic field to the active LC materials, due to a magnetic-field-induced reorientation of the LCs filled into the SRG. Further, in the diffraction state, the diffraction efficiency of a light incident onto the active diffractive optical element may be continuously changeable via continuously varying the applied electric field or light or magnetic field. That is, the active diffractive optical element may be configured to provide different diffraction efficiency to an incident light, thereby satisfying different application scenarios. In some embodiments, at least one of the electrodes of the active diffractive optical element may include pixelated electrodes. A light incident onto the active diffractive optical element may irradiate one or more pixelated electrodes, and the diffraction efficiency of the light may spatially vary by applying different voltages to the different pixelated electrodes. For discussion purposes, a grating filled with active LCs is used as example to explain the switching of the disclosed diffractive optical elements in <FIG> and <FIG>.

<FIG> illustrate a schematic diagram of switching a diffractive optical element <NUM>, according to an embodiment of the disclosure. For discussion purposes, the diffractive optical element <NUM> may be a grating <NUM>. As shown in <FIG>, the grating <NUM> may include upper and lower substrates <NUM> arranged opposite to each other. Each substrate <NUM> may be provided with a transparent electrode at an inner surface of the substrate <NUM> for applying an electric field to the grating <NUM>, such as an ITO electrode (not drawn). The grating <NUM> may include an SRG <NUM> bonded to or formed on the lower substrate <NUM> and an optical anisotropic material <NUM> filled into grooves of the SRG <NUM>. The optical anisotropic material <NUM> may include active anisotropic materials, such as active LCs having positive or negative dielectric anisotropy. The optically anisotropic material <NUM> may have a first principal refractive index (e.g., neAN) in the groove direction (e.g., y-direction) of the SRG <NUM> and a second principal refractive index (e.g., noAN) along an in-plane direction (e.g., x-direction) perpendicular to the groove direction of the SRG <NUM>.

For discussion purposes, in <FIG>, the optical anisotropic material <NUM> may include active LCs having positive anisotropy, such as nematic liquid crystals (NLCs). LC molecules <NUM> may be homogeneously aligned within the groove in the groove direction, for example, y-direction. The second principal refractive index (e.g., noAN) may substantially match a refractive index ng of the SRG <NUM>, and the first principal refractive index (e.g., neAN) may mismatch the refractive index ng of the SRG <NUM>. In a voltage-off state, as shown in <FIG>, for an incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>, due to the refractive index difference between neAN and ng, the light <NUM> may experience a periodic modulation of the refractive index when propagating through the grating <NUM> and, thus, get diffracted. That is, the grating <NUM> may be in a diffraction state (or On-state) for the incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>.

In some embodiments, at the voltage-off state (or more generally, when applied voltage is lower than a threshold voltage to reorient the LC molecules <NUM>), the modulation of refractive index nm (i.e., the difference between neAN and ng) provided by the grating <NUM> to the light <NUM> may be the largest as compared to other voltage-on states. Accordingly, the diffraction efficiency of the light <NUM> may be the highest. In a voltage-on state, as shown in <FIG>, an electric field (e.g., along a z-direction) may be generated between the two opposite substrates <NUM>. When the applied voltage is gradually increased to be higher than the threshold hold voltage, the LC molecules <NUM> having positive dielectric anisotropy may trend to be reoriented along the electric field. As the applied voltage changes, for the incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>, the modulation of refractive index nm (i.e., the difference between neAN and ng) provided by the grating <NUM> may change accordingly, which in turn changes the diffraction efficiency provided by the grating <NUM> to the incident light <NUM>. Further, in the diffraction state, the diffraction efficiency provided by the grating <NUM> to the incident light <NUM> may be continuously adjustable via continuously varying the applied voltage. That is, the grating <NUM> may provide different diffraction efficiency to the light <NUM>, thereby satisfying different application scenarios. In some embodiments, at least one of the electrodes of the grating <NUM> may include a plurality of pixelated electrodes. The light <NUM> may irradiate one or more pixelated electrodes, and the diffraction efficiency of the light <NUM> may spatially vary by applying different voltages to the different pixelated electrodes.

In the voltage-on state where the applied voltage is sufficiently high, as shown in <FIG>, the LC molecules <NUM> having the positive dielectric anisotropy may be reoriented to be parallel to the electric field direction (e.g., z-direction). For the incident light <NUM> polarized in the groove direction of the SRG <NUM>, due to the substantial refractive index match between noAN and ng, the grating <NUM> may appear to be a substantially optically uniform plate for the incident light <NUM>. That is, the grating <NUM> may be in a non-diffraction state (or Off-state) for the incident light <NUM> polarized in the groove direction of the SRG <NUM>. In some embodiments, the second principal refractive index (e.g., noAN) may exactly match (or may be the same as) the refractive index ng of the SRG <NUM> and, thus, the light <NUM> may be transmitted through the grating <NUM> without any diffraction. That is, the diffraction effect of the grating <NUM> may be completely turned off for the incident light <NUM>.

<FIG> illustrate a schematic diagram of switching a diffractive optical element <NUM>, according to another embodiment of the disclosure. The similarities between <FIG> and <FIG> may be not repeated, while certain differences may be explained. Different from the active LCs <NUM> having the positive dielectric anisotropy filled into the SRG <NUM> shown in <FIG>, an SRG <NUM> in <FIG> may be filled with active LCs <NUM> having negative dielectric anisotropy. LC molecules <NUM> may be homeotropically aligned within the groove of the SRG <NUM> in an out-of-plane direction perpendicular to a substrate <NUM>, for example, the z-direction in <FIG>. The second principal refractive index (e.g., noAN) of the LCs <NUM> may substantially match a refractive index ng of the SRG <NUM>, and the first principal refractive index (e.g., neAN) of the LCs <NUM> may mismatch the refractive index ng of the SRG <NUM>.

In a voltage-off state where the applied voltage is zero (or more generally, the applied voltage is lower than the threshold voltage to reorient the LC molecules <NUM>), as shown in <FIG>, the LC molecules <NUM> having negative dielectric anisotropy may be homeotropically aligned within the groove, for example, in the z-direction. For an incident light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>, due to the substantial refractive index match between noAN and ng, the grating <NUM> may appear to be a substantially optically uniform plate for the light <NUM>. That is, the grating <NUM> may be in a non-diffraction state for the light <NUM> polarized in the groove direction of the SRG <NUM>. In some embodiments, the second principal refractive index (e.g., noAN) of the LCs <NUM> may substantially match the refractive index ng of the SRG <NUM>, and the light <NUM> may be transmitted through the grating <NUM> with negligible diffraction. In some embodiments, the second principal refractive index (e.g., noAN) of the LCs <NUM> may be the same as the refractive index ng of the SRG <NUM> and, thus, the light <NUM> may be transmitted through without any diffraction. That is, the diffraction effect of the grating <NUM> may be completely turned off for the light <NUM> polarized in the groove direction of the SRG <NUM>.

In a voltage-on state, as shown in <FIG>, an electric field may be generated between the electrodes at two opposite substrates <NUM>, and the LC molecules <NUM> having negative dielectric anisotropy may be reoriented by the electric field from a vertical (homeotropic) state to a horizontal (planar) state. The long axes of the LC molecules <NUM> may tend to be perpendicular to the electric field direction (e.g., z-direction) and parallel to the groove direction (e.g., y-direction) of the SRG <NUM> when the applied voltage is sufficiently high. The light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM> may experience a periodic modulation of the refractive index in the grating <NUM> and, thus, get diffracted due to the refractive index difference between neAN and ng. That is, the grating <NUM> may be in a diffraction state for the light <NUM> polarized in the groove direction (e.g., y-direction) of the SRG <NUM>. Referring to <FIG> and <FIG>, when the grating is at a voltage-off state, the grating may be in a diffraction state or a non-diffraction state, similarly, when the grating is at a voltage-on state, the grating may be in a diffraction state or a non-diffraction state, depending on the configuration of the grating and the polarization of the incident light.

Active gratings in accordance with an embodiment of the present disclosure may enable time-multiplexing of a plurality of different light fields (e.g., portions of FOV, images in various colors, etc.) delivered by one or more waveguides. FOV in waveguides is often limited by the angular bandwidth of gratings, as well as the angular limitation of waveguides that is mainly determined by refractive index of the waveguides. One method to expand FOV is splitting of the FOV in several portions and delivering the portions by different gratings or sets of gratings. To avoid crosstalk between the gratings, the light fields corresponding to different parts of FOV may be desired to be delivered in different time frames, e.g., by using time-multiplexing approach. In the following, exemplary waveguide architectures corresponding to a "symmetrical" case where the FOV is not rotated after translation through the waveguide are explained. This case may also correspond to compensation of optical dispersion caused by separate gratings in the waveguide, through which a broadband light source may be allowed to be used as a light source coupled to the waveguide. For example, mutual compensation of the dispersion caused by the in-coupling and outcoupling gratings may be achieved in the two-grating waveguides. Mathematical expression describing this regime is <MAT>, where ki is a grating vector of the i-th grating, n is the number of gratings on the way of light in a waveguide. That is, a vector sum of the grating vectors of the gratings which direct each portion of light in a waveguide may be substantially equal to zero. Active gratings in accordance with an embodiment of the present disclosure may allow expanding FOV by time-multiplexing different portions of FOV that is split and delivered by different pairs of active gratings arranged in different ways, such as in a way of tiling gratings at a common waveguide, or a way of stacking gratings at a common waveguide or different waveguides. Similar principles may be used to deliver images in different colors.

<FIG> illustrates a schematic diagram of a waveguide <NUM>, and <FIG> illustrate an operation scheme of the waveguide <NUM> in <FIG> to deliver different portions of FOV in a time-multiplexing manner. The waveguide <NUM> may be an embodiment of the waveguide <NUM> in <FIG>. As shown in <FIG>, the waveguide <NUM> may be configured to receive an image light from the light source assembly <NUM> via an in-coupling grating <NUM> and guide the image light towards the eye <NUM> via an out-coupling grating <NUM>. At least one of the in-coupling grating <NUM> and the out-coupling grating <NUM> may be any one of the disclosed active gratings. The in-coupling grating <NUM> and the out-coupling grating <NUM> each may include a plurality of subgratings where neighboring subgratings may be partially overlapped to get a continuous FOV. Exemplary overlapping configurations of the subgratings will be explained in the following with the accompanying <FIG>.

Referring to <FIG>, the subgratings of the in-coupling grating <NUM> may be one-to-one corresponding to the subgratings of the out-coupling grating <NUM>. The number of subgratings of the respective gratings may be corresponding to the number of portions of FOV that is split. The subgratings in the in-coupling grating <NUM> and the out-coupling grating <NUM> may be disposed at a first surface <NUM>-<NUM> and/or a second surface <NUM>-<NUM> of the waveguide <NUM>. The subgratings of the in-coupling grating <NUM> may be disposed at the same surface or different surfaces of the waveguide <NUM>. The subgratings of the out-coupling grating <NUM> may be disposed at the same surface or different surfaces of the waveguide <NUM>. In some embodiments, the subgrating may have a 1D grating patterning to tile the FOV in one-dimension. In some embodiments, the subgrating may have a 2D grating patterning to tile the FOV in two-dimension.

For discussion purposes, the in-coupling grating <NUM> and the out-coupling grating <NUM> may be disposed at a second surface 1000_2 and a first surface 1000_1 of the waveguide <NUM>, respectively, and both the in-coupling grating <NUM> and the out-coupling grating <NUM> may be the disclosed switchable gratings. The in-coupling grating <NUM> may include three subgratings: a first in-coupling subgrating 1005_1, a second in-coupling subgrating 1005_2, and a third in-coupling subgrating 1005_3. The out-coupling grating <NUM> may include three subgratings: a first out-coupling subgrating 1010_1, a second out-coupling subgrating 1010_2, and a third out-coupling subgrating 1010_3, which are one-to-one corresponding to the first in-coupling subgrating 1005_1, the second in-coupling subgrating 1005_2, and the third in-coupling subgrating 1005_3.

The light source assembly <NUM> may emit an image light from a light source (e.g., a display) towards the in-coupling grating <NUM>. The image light may include rays corresponding to different portions of the FOV of the display. For example, as shown in <FIG>, an angular range encompassed by rays <NUM> of the image light may correspond to a left portion of the FOV of the display, and an angular range encompassed by rays <NUM> of the image light may correspond to a center portion of the FOV of the display, and an angular range encompassed by rays <NUM> of the image light may correspond to a right portion of the FOV of the display. In some embodiments, the image light may be a linearly polarized light. In some embodiments, the image light may be other than a linearly polarized light, and optical elements (e.g., a linear polarizer, or a quarter-wave plate, etc.. ) may be arranged between the light source assembly <NUM> and the waveguide <NUM> to convert the image light emitted from the light source assembly <NUM> to be a linearly polarized image light to be incident onto the in-coupling grating <NUM>.

A display frame of the display in the light source assembly <NUM> may be divided in three subframes for sequential transmission of rays corresponding to different portions of the FOV of the display, thereby realizing sequential transmission of different portions of the FOV of the display. At a <NUM>st subframe, referring to <FIG> and <FIG>, the first in-coupling subgrating 1005_1 and the first out-coupling subgrating 1010_1 may be switched to a diffraction state (or an ON state), while the remaining subgratings may be all switched to a non-diffraction state (or an OFF state). Thus, the rays in the angular range encompassed by the rays <NUM> may be coupled into a TIR path in the waveguide <NUM> via the first in-coupling subgrating 1005_1, and decoupled out of the waveguide <NUM> via the first out-coupling subgrating 1010_1 into an angular range encompassed by rays <NUM>' to be viewed by the eye <NUM>, while the rays in the angular range compassed by the rays <NUM> and the rays in the angular range compassed by the rays <NUM> may be not coupled into the waveguide <NUM>. The angular range encompassed by the rays <NUM>' may correspond to the left portion of the FOV.

At a <NUM>nd subframe, referring to <FIG> and <FIG>, the second in-coupling subgrating 1005_2 and the second out-coupling subgrating 1010_2 may be switched to a diffraction state (or an ON state), while the remaining subgratings may be all switched to a non-diffraction state (or an OFF state). Thus, the rays in the angular range compassed by the rays <NUM> may be coupled into a TIR path in the waveguide <NUM> via the second in-coupling subgrating 1005_2, and decoupled out of the waveguide <NUM> via the second out-coupling subgrating 1010_2 into an angular range encompassed by rays <NUM>' to be viewed by the eye <NUM>, while the rays in the angular range compassed by the rays <NUM> and the rays in the angular range compassed by the rays <NUM> may be not coupled into the waveguide <NUM>. The angular range encompassed by the rays <NUM>' may correspond to the central portion of the FOV.

At a <NUM>rd subframe, referring to <FIG> and <FIG>, the third in-coupling subgrating 1005_3 and the third out-coupling subgrating 1010_3 may be switched to a diffraction state (or an ON state), while the remaining subgratings may be all switched to a non-diffraction state (or an OFF state). Thus, the rays in the angular range compassed by the rays <NUM> may be coupled into a TIR path in the waveguide <NUM> via the third in-coupling subgrating 1005_3, and decoupled out of the waveguide <NUM> via the third out-coupling subgrating 1010_3 into an angular range of rays <NUM>' to be viewed by the eye <NUM>, while the rays in the angular range compassed by the rays <NUM> and the rays in the angular range compassed by the rays <NUM> may be not coupled into the waveguide <NUM>. The angular range encompassed by the rays <NUM>' may correspond to the right portion of the FOV.

Thus, through sequentially switching the pair of the first in-coupling subgrating 1005_1 and the first out-coupling subgrating 1010_1, the pair of the second in-coupling subgrating 1005_2 and the second out-coupling subgrating 1010_2, and the pair of the third in-coupling subgrating 1005_3 and the third out-coupling subgrating 1010_3 to a diffraction state, a sequential transmitting of different portions of the FOV in a common waveguide may be realized by tiling the FOV. Further, switching of the subgratings in different subframes may eliminate crosstalk caused by the spatial overlapping between the neighboring subgratings. In some embodiments, the in-coupling grating <NUM> and the out-coupling grating <NUM> each may include two subgratings that are optimized for sequentially transmitting the right and left portions of the FOV of the display.

It is to be noted that, <FIG> shows a single light source assembly <NUM> emitting image lights corresponding to the entire FOV, which is for illustrative purposes and is not intended to limit the scope of the present disclosure. In some embodiments, a plurality of light source assemblies may be used, each of which emit image lights corresponding to a portion of the entire FOV provided by the waveguide display assembly. For example, three light source assemblies may be used, which emit image lights corresponding to a left portion, a center portion and a right portion of the entire FOV, respectively. In some embodiments, the emitted image lights corresponding to the left portion and the center portion of the entire FOV may be partially overlapped, and the image lights corresponding to the right portion and the center portion of the entire FOV may be partially overlapped, such that a continuous FOV may be introduced into the waveguide from the in-coupling element <NUM>.

It is to be noted that, <FIG> shows both the in-coupling grating <NUM> and the out-coupling grating <NUM> include a plurality of disclosed switchable gratings, which is for illustrative purposes and is not intended to limit the scope of the present disclosure. In some embodiments, one of the in-coupling grating <NUM> and the out-coupling grating <NUM> may include a plurality of disclosed switchable gratings, while the other may include one or more non-switchable gratings. For example, different portions of the FOV may be introduced into the waveguide from the non-switchable in-coupling grating <NUM>. The out-coupling grating <NUM> may include three out-coupling subgratings, and a display frame may include three sub-frames. During each subframe, one subgrating may be switched to the diffraction state to decouple the image lights corresponding to a predetermined portion of the FOV out of the waveguide <NUM>, while the remain subgratings may be switched to the non-diffraction state to suppress the crosstalk.

<FIG> illustrate schematic diagrams of overlapping configurations of the in-coupling subgratings included in the waveguide <NUM> in <FIG>. In some embodiments, one or more in-coupling subgratings may be disposed at different planes, such that neighboring in-coupling subgratings may be partially overlapped. The space around the in-coupling subgratings may be filled with an index-matching material. In one embodiment, as shown in <FIG>, each of the in-coupling subgratings 1005_1, 1005_2 and 1005_3 may be disposed at a different plane, such that the neighboring in-coupling subgratings may be partially overlapped. A space around the in-coupling subgratings may be filled with an index-matching material <NUM>, such that light reflections may be suppressed in the space. In one embodiment, as shown in <FIG>, the first in-coupling subgrating 1005_1 and the third in-coupling subgrating 1005_3 may be disposed at the same plane, while the second in-coupling subgrating 1005_2 may be disposed at a different plane, such that the neighboring in-coupling subgratings may be partially overlapped. The overlapping configurations of the out-coupling subgratings included in the waveguide <NUM> in <FIG> may be similar to that of the in-coupling subgratings, and the details are not repeated here.

<FIG> illustrate schematic diagrams of time-multiplexing of different portions of FOV delivered by a stack of waveguides. <FIG> illustrates a schematic diagram of a stack <NUM> of waveguides, and <FIG> illustrate an operation scheme of the stack <NUM> in <FIG> to deliver different portions of FOV in a time-multiplexing manner. The stack <NUM> of waveguides may be an embodiment of the waveguide <NUM> in <FIG>. The similarities between <FIG> and <FIG> are not explained, while certain differences may be explained. As shown in <FIG>, the stack <NUM> may include a plurality of waveguides stacked together, for example, three waveguides <NUM>, <NUM> and <NUM>. The waveguide <NUM> may include an in-coupling grating <NUM> and an out-coupling grating <NUM>, the waveguide <NUM> may include an in-coupling grating <NUM> and an out-coupling grating <NUM>, and the waveguide <NUM> may include an in-coupling grating <NUM> and an out-coupling grating <NUM>. To ensure that a wave guiding can take place in each waveguide, the three waveguides <NUM>, <NUM> and <NUM> may be separated by air gaps. In some embodiments, the air gaps between the waveguides <NUM>, <NUM> and <NUM> may be filled with a material (e.g., a liquid glue) having a refractive index lower than that of the waveguides. At least one of the in-coupling gratings and the out-coupling gratings may include any one of the disclosed switchable gratings. The in-coupling gratings and the out-coupling gratings may be disposed at a first surface and/or a second surface of the respective waveguides. For discussion purposes, in <FIG>, all the in-coupling gratings and the out-coupling gratings in the stack <NUM> may be the disclosed switchable gratings, and disposed at the second surface of the respective waveguides.

The light source assembly <NUM> may emit an image light from a light source (e.g., a display) towards the stack <NUM>, where the image light may include rays corresponding to different portions of the FOV of the display. For example, in <FIG>, an angular range encompassed by rays <NUM> may correspond to a left portion of the FOV of the display, an angular range encompassed by rays <NUM> correspond to a center portion of the FOV of the display, and an angular range encompassed by rays <NUM> may correspond to a right portion of the FOV of the display. The image light emitted from the light source assembly <NUM> may be a linearly polarized light or converted to a linearly polarized light by some optical elements arranged between the light source assembly <NUM> and the stack <NUM>.

A display frame may be divided in three subframes for sequential transmission of the rays corresponding to different portions of the FOV. At a <NUM>st subframe, referring to <FIG>, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be switched to a diffraction state (or an ON state), while the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM>, as well as, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be switched to a non-diffraction state (or an OFF state). Thus, the rays in the angular range encompassed by the rays <NUM> may be coupled into a TIR path in the waveguide <NUM> via the in-coupling grating <NUM>, and decoupled out of the waveguide <NUM> via the out-coupling grating <NUM> into an angular range encompassed by rays <NUM>' to be viewed by the eye <NUM>, while the rays in the angular range encompassed by the rays <NUM> and the rays in the angular range encompassed by the rays <NUM> may be not coupled into any of the waveguides <NUM>, <NUM> and <NUM>. The angular range encompassed by the rays <NUM>' may correspond to the left portion of the FOV. That is, the left portion of the FOV may be replicated at the eye-box located at the exit pupil of the eye <NUM>.

At a <NUM>nd subframe, referring to <FIG> and <FIG>, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be switched to a diffraction state (or an ON state), while the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM>, as well as, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be all switched to a non-diffraction state (or an OFF state). Thus, the rays in the angular range encompassed by the rays <NUM> may be coupled into a TIR path in the waveguide <NUM> via the in-coupling grating <NUM>, and decoupled out of the waveguide <NUM> via the out-coupling grating <NUM> into an angular range encompassed by rays <NUM>' to be viewed by the eye <NUM>, while the rays in the angular range encompassed by the rays <NUM> and the rays in the angular range encompassed by the rays <NUM> may be not coupled into any of the waveguides <NUM>, <NUM> and <NUM>. The angular range encompassed by the rays <NUM>' may correspond to the central portion of the FOV. That is, the central portion of the FOV may be replicated at the eye-box located at the exit pupil of the eye <NUM>.

At a <NUM>rd subframe, referring to <FIG> and <FIG>, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be switched to a diffraction state (or an ON state), while the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM>, as well as, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be all switched to a non-diffraction state (or an OFF state). Thus, only the rays in the angular range encompassed by the rays <NUM> may be coupled into a TIR path in the waveguide <NUM> via the in-coupling grating <NUM>, and decoupled out of the waveguide <NUM> via the out-coupling grating <NUM> into an angular range encompassed by the rays <NUM>' to be viewed by the eye <NUM>, while the rays in the angular range encompassed by the rays <NUM> and the rays in the angular range encompassed by the rays <NUM> may be not coupled into any of the waveguides <NUM>, <NUM> and <NUM>. The angular range encompassed by the rays <NUM>' may correspond to the right portion of the FOV. That is, the right portion of the FOV may be replicated at the eye-box located at the exit pupil of the eye <NUM>.

Thus, through sequentially switching the pairs of the in-coupling grating and the out-coupling grating at the respective waveguides in the stack <NUM> to a diffraction state while switching the remaining in-coupling gratings and out-coupling gratings in the stack <NUM> to a non-diffraction state, a sequential transmitting of the left, central and right portions of the FOV may be realized. The in-coupling gratings and out-coupling gratings in the stack <NUM> may be designed, such that the left, central, and right portions of FOV may be transmitted partially overlapped to provide a continuous FOV delivered by entire frame. Further, switching of the pairs of the in-coupling grating and the out-coupling grating at the respective waveguides in different subframes may eliminate crosstalk caused by the spatial overlapping between different portions of FOV. In some embodiments, the FOV may be divided in two portions, for example, left and right portions, and the same principle may be used for separate transmission of two portions of FOV.

In some embodiments, not according to the claimed invention, instead of disposing the in-coupling gratings and the out-coupling gratings at the respective waveguides in the stack <NUM>, the in-coupling gratings <NUM>, <NUM>, and <NUM> may be stacked and attached to a common (e.g., a single) waveguide, and the out-coupling gratings <NUM>, <NUM>, and <NUM> may be stacked and attached to the common waveguide, as <FIG> shows. <FIG> illustrate a schematic diagram of a waveguide <NUM> of delivering different portions of FOV in a time-multiplexing manner, according to another embodiment of the disclosure. The similarities between <FIG> and <FIG> are not repeated, while certain differences may be explained. As shown in <FIG>, a plurality of in-coupling gratings <NUM>, <NUM> and <NUM> may be disposed at a first surface or a second surface of the waveguide <NUM>, and a plurality of out-coupling gratings <NUM>, <NUM> and <NUM> may be disposed at the first surface or the second surface of the waveguide <NUM>. The plurality of in-coupling gratings <NUM>, <NUM> and <NUM> and the plurality of out-coupling gratings <NUM>, <NUM> and <NUM> may be disposed at the same surface or different surfaces of the waveguide <NUM>. The operation scheme of the in-coupling gratings <NUM>, <NUM> and <NUM> and the out-coupling gratings <NUM>, <NUM> and <NUM> to realize a time-sequential transmitting of the left, central and right portions of the FOV may be similar to that shown in <FIG>, and the details are not repeated here.

<FIG> illustrates a schematic diagram of a stack <NUM> of waveguides, according to another embodiment of the disclosure, and <FIG> illustrates an operation scheme of the stack <NUM> of waveguides in <FIG> to deliver single-color images of different colors in a time-multiplexing manner. The stack <NUM> of waveguides may be similar to the stack <NUM> of waveguides in <FIG>, and the details are not repeated here. The stack <NUM> of waveguides may receive image lights from a plurality of source assemblies, for example, three source assemblies <NUM>, <NUM> and <NUM>. Each source assembly may emit a monochromatic image light of a specific wavelength band corresponding to a primary color (e.g., red, green, or blue). For example, the source assemblies <NUM>, <NUM> and <NUM> may emit a monochromatic image light <NUM>, <NUM> and <NUM> of a specific wavelength band corresponding to a first primary color (e.g., red), a second primary color (e.g., green) and a third primary color (e.g., blue), respectively. The source assemblies <NUM>, <NUM> and <NUM> may be configured to sequentially emit the corresponding image lights in accordance with instructions from a controller. The image lights emitted from the source assemblies <NUM>, <NUM> and <NUM> each may be a linearly polarized light or converted to a linearly polarized light by some optical elements arranged between the source assemblies and the stack <NUM>.

The waveguide <NUM> may include an in-coupling grating <NUM> and an out-coupling grating <NUM> both designed for a wavelength band corresponding to the first primary color (e.g., red), the waveguide <NUM> may include an in-coupling grating <NUM> and an out-coupling grating <NUM> both designed for a wavelength band corresponding to the second primary color (e.g., green), and the waveguide <NUM> may include an in-coupling grating <NUM> and an out-coupling grating <NUM> both designed for a wavelength band corresponding to the third primary color (e.g., blue). At least one of the in-coupling gratings <NUM>, <NUM> and <NUM> and the out-coupling gratings <NUM>, <NUM> and <NUM> may include any one of the disclosed polarization sensitive switchable gratings. For discussion purposes, all the coupling gratings <NUM>, <NUM> and <NUM> and the out-coupling gratings <NUM>, <NUM> and <NUM> may be the disclosed polarization sensitive switchable gratings.

A display frame may be divided in three subframes for sequential transmission of the image lights <NUM>, <NUM> and <NUM>. At a <NUM>st subframe, referring to <FIG>, the image light <NUM> (e.g., red light) may be emitted by the source assembly <NUM> towards the stack <NUM>, and the image light <NUM> (e.g., green light) and <NUM> (e.g., blue light) may not be emitted from the corresponding source assemblies. The in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be switched to a diffraction state (or an ON state), while the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM>, as well as, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be all switched to a non-diffraction state (or an OFF state). Thus, the image light <NUM> (e.g., red light) may be coupled into a TIR path in the waveguide <NUM> via the in-coupling grating <NUM>, and decoupled out of the waveguide <NUM> via the out-coupling grating <NUM> into an image light <NUM>' (e.g., red light) to be viewed by the eye <NUM>. That is, a single-color image (e.g. red color image) may be viewed by the eye <NUM>.

At a <NUM>nd subframe, referring to <FIG> and <FIG>, the image light <NUM> (e.g., green light) may be emitted by the source assembly <NUM> towards the stack <NUM>, and the image light <NUM> (e.g., red light) and <NUM> (e.g., blue light) may be not emitted from the corresponding source assemblies. The in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be switched to a diffraction state (or an ON state), while the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM>, as well as, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be all switched to a non-diffraction state (or an OFF state). Thus, the image light <NUM> (e.g., green light) may be coupled into a TIR path in the waveguide <NUM> via the in-coupling grating <NUM>, and decoupled out of the waveguide <NUM> via the out-coupling grating <NUM> into an image light <NUM>' (e.g., green light) to be viewed by the eye <NUM>. That is, a single-color image (e.g. green color image) may be viewed by the eye <NUM>.

At a <NUM>rd subframe, referring to <FIG> and <FIG>, the image light <NUM> (e.g., blue light) may be emitted by the source assembly <NUM> towards the stack <NUM>, and the image light <NUM> (e.g., red light) and <NUM> (e.g., green light) may be not emitted from the corresponding source assemblies. The in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be switched to a diffraction state (or an ON state), while the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM>, as well as, the in-coupling grating <NUM> and the out-coupling grating <NUM> at the waveguide <NUM> may be all switched to a non-diffraction state (or an OFF state). Thus, the image light <NUM> (e.g., blue light) may be coupled into a TIR path in the waveguide <NUM> via the in-coupling grating <NUM>, and decoupled out of the waveguide <NUM> via the out-coupling grating <NUM> into an image light <NUM>' (e.g., blue light) to be viewed by the eye <NUM>. That is, a single-color image (e.g. blue color image) may be viewed by the eye <NUM>.

Thus, through sequentially emitting the monochromatic image lights <NUM>, <NUM> and <NUM>, and sequentially switching the corresponding pairs of the in-coupling grating and the out-coupling grating to a diffraction state, a sequential transmitting of image lights in different colors (e.g., red, green, blue) may be realized. That is, a sequential transmitting of single-color images in different colors may be realized. A final image may be viewed by the eye <NUM> as a polychromatic image. Further, a time-multiplexing that is realized by using the disclosed switchable gratings may eliminate crosstalk in the stack <NUM> and, thus, improve the image performance of the waveguide display assembly including the stack <NUM>. In some embodiments, the source assemblies <NUM>, <NUM> and <NUM> may remain emitting the respective image lights even when the corresponding pairs of the in-coupling grating and the out-coupling grating is switched to a non-diffraction state, through which the control may be simplified, while the power consumption may be increased.

In some embodiments, not according to the claimed invention, instead of disposing the in-coupling gratings and the out-coupling gratings at the respective waveguides in the stack <NUM>, the in-coupling gratings <NUM>, <NUM>, and <NUM> may be stacked and attached to a common (e.g., a single) waveguide, and the out-coupling gratings <NUM>, <NUM>, and <NUM> may be stacked and attached to the common waveguide, and a similar structure may be referred to FIG. The stack of the in-coupling gratings and the stack of the out-coupling gratings each may be disposed at the first surface or the second surface of the common waveguide. The operation scheme of the in-coupling gratings <NUM>, <NUM>, and <NUM> and the out-coupling gratings <NUM>, <NUM>, and <NUM> to realize a time-sequential transmitting of the image lights in different colors may be similar to that shown in <FIG>, and the details are not repeated here.

The embodiments in <FIG> may be effective for monochromatic image light. For the color images, the image light of different colors may be spatially and/or temporally multiplexed. The number of waveguides in the stack may be reduced to two. For separate transmission of colors, one waveguide may be configured for red/green and the other for the green/blue colors.

It is to be noted that, <FIG> shows the in-coupling gratings and the out-coupling grating each is the disclosed switchable gratings, which is for illustrative purposes and is not intended to limit the scope of the present disclosure. In some embodiments, the in-coupling gratings each may be the disclosed switchable grating, while the out-coupling gratings each may be a non-switchable grating. In some embodiments, the out-coupling gratings each may be the disclosed switchable grating, while the in-coupling gratings each may be a non-switchable grating. For example, RGB colors may be introduced from separate projectors by non-switchable in-coupling gratings. A display frame may include three subframes. In each subframe, only the projector emitting one of the RGB colors may be turned on and the out-coupling grating corresponding to the one of the RGB colors may be configured to be at the diffraction state to deliver the image light of the one of the RGB colors, while the remaining projectors may be turned off and the remaining out-coupling gratings may be configured to be at the non-diffraction state to suppress the crosstalk.

The present disclosure also provides a method for a waveguide display assembly to deliver a plurality of light fields of an image light emitted from a light source assembly in a time-multiplexing manner. The method may include during a first time period, in-coupling, by a first in-coupling grating, a first plurality of image lights corresponding to a first light field of a plurality of light fields into a first waveguide via diffraction, and decoupling, by a first out-coupling grating, the first plurality of image lights out of the first waveguide towards an eye-box of the optical device via the diffraction. The method may include during a second time period, in-coupling, by a second in-coupling grating, a second plurality of image lights corresponding to a second light field of the plurality of light fields into a second waveguide via diffraction, and decoupling, by a second out-coupling grating, the second plurality of image lights out of the second waveguide towards an eye-box of the optical device via the diffraction. A light field may correspond to a predetermined portion of a field of view (FOV) of a single-color image, a predetermined portion of the FOV of a full-color image, or a single-color image of a predetermined color. The method may further include during a third time period, in-coupling, by a third in-coupling grating, a third plurality of image lights corresponding to a third light field of the plurality of light fields into a third waveguide via diffraction, and decoupling, by a third out-coupling grating, the third plurality of image lights out of the third waveguide towards an eye-box of the optical device via the diffraction.

For discussion purposes, <FIG> illustrates a flow chart <NUM> of a method of a waveguide display assembly for delivering different portions of FOV in a time-multiplexing manner, according to an embodiment of the disclosure. The waveguide display assembly may be an embodiment of the waveguide display assemblies <NUM> and <NUM> in <FIG>. The waveguide display assembly may include at least one disclosed switchable diffractive optical element.

As shown in <FIG>, the method may include: during a first time period, in-coupling, by a first in-coupling element, a first plurality of rays emitted from a light source assembly into a first waveguide via diffraction, and decoupling, by a first out-coupling element, the first plurality of rays out of the first waveguide into a first angular range of rays towards an eye-box via diffraction (S1310). An angular range of the first plurality of rays emitted from the light source assembly may correspond to a first portion of a FOV provided by the light source assembly. The first angular range of the rays decoupled out of the first waveguide may correspond to the first portion of the FOV provided by the light source assembly.

The method may further include: during a second time period, in-coupling, by a second in-coupling element, a second plurality of rays emitted from the light source assembly into a second waveguide via diffraction, and decoupling, by a second out-coupling element, the second plurality of rays out of the second waveguide into a second angular range of rays towards an eye-box via diffraction (S1320). An angular range of the second plurality of rays emitted from the light source assembly may correspond to a second portion of the FOV provided by the light source assembly. The second angular range of the rays decoupled out of the second waveguide may correspond to the second portion of the FOV provided by the light source assembly.

In some embodiments, the light source assembly may include a source that is a display, the first time period and the second time period may be a first sub-frame and a second sub-frame of a display frame of the display, respectively. In some embodiments, the first and second waveguides may be a same waveguide (referred to as a common waveguide), where the common waveguide may have a first surface facing the light source assembly and an opposing second surface. In some embodiments, the first and second in-coupling elements may be tiled at the first or second surface of the common waveguide, and the first and second out-coupling elements may be tiled at the first or second surface of the common waveguide. In some embodiments, not according to the claimed invention, the first and second in-coupling elements may be stacked and attached to the first or second surface of the common waveguide, and the first and second out-coupling elements may be stacked and attached to the first or second surface of the common waveguide.

In some embodiments, the first and second waveguides may be individual waveguides that are separated by a low index material, where each waveguide may have a first surface facing the light source assembly and an opposing second surface. The in-coupling elements of the respective waveguides may be disposed at the first or second surface of the respective waveguides, and the out-coupling elements of the respective waveguides may be disposed at the first or second surface of the respective waveguides.

In some embodiments, the method may further include: during a third time period, in-coupling, by a third in-coupling element, a third plurality of rays emitted from the light source assembly into a third waveguide via diffraction, and decoupling, by a third out-coupling element, the third plurality of rays out of the third waveguide into a third angular range of rays towards an eye-box via diffraction. An angular range of the third plurality of rays emitted from the light source assembly may correspond to a third portion of the FOV provided by the light source assembly. The third angular range of the rays decoupled out of the third waveguide may correspond to the third portion of the FOV provided by the light source assembly.

For discussion purposes, <FIG> illustrates a flow chart <NUM> of a method of a waveguide display assembly for delivering single-color images of different colors in a time-multiplexing manner, according to an embodiment of the disclosure. The waveguide display assembly may be an embodiment of the waveguide display assemblies <NUM> and <NUM> in <FIG>. The waveguide display assembly may include at least one disclosed switchable diffractive optical element.

As shown in <FIG>, the method may include: during a first time period, in-coupling, by a first in-coupling element, an image light of a first color emitted from a first light source assembly into a first waveguide via diffraction, and decoupling, by a first out-coupling element, the image light of the first color out of the first waveguide towards an eye-box via diffraction (S1410). The method may include: during a second time period, in-coupling, by a second in-coupling element, an image light of a second color emitted from a second light source assembly into a second waveguide via diffraction, and decoupling, by a second out-coupling element, the image light of the second color out of the second waveguide towards the eye-box via diffraction (S1420).

In some embodiments, the first and second light source assemblies may be individual light source assemblies. Each of the first and second light source assemblies may include a source that is a display, and the first time period and the second time period may be a first sub-frame and a second sub-frame of a display frame of the display, respectively. In some embodiments, the first and second light source assemblies may be a same common light source assembly, which is controlled to sequentially emit the image light of the first color and the image light of the second color. In some embodiments, the image light of the first color and the image light of the second color may be monochromatic lights at wavelength bands corresponding to different primary colors. The first and second waveguides may be individual waveguides that are separated by a low index material. Each waveguide may have a first surface facing the light source assembly and an opposing second surface. The in-coupling elements of the respective waveguides may be disposed at the first or second surface of the respective waveguides, and the out-coupling elements of the respective waveguides may be disposed at the first or second surface of the respective waveguides.

In some embodiments, the method may further include: during a third time period, in-coupling, by a third in-coupling element, an image light of a third color emitted from a third light source assembly into a third waveguide via diffraction, and decoupling, by a third out-coupling element, the image light of the third color out of the third waveguide towards the eye-box via diffraction.

It is to be noted that, the disclosed methods for spatial- and/or time-multiplexing of different colors and/or different portions of FOV based on the disclosed switchable gratings may be combined to deliver full-color images with wide FOV, all of which are within the scope of the present disclosure. For example, the waveguide stack <NUM> or in <FIG> or the waveguide <NUM> in <FIG> may also be used for transmitting full-color images with large FOV, where the one or more waveguides are configured to deliver full-color images with different portions of FOV in a time-multiplexing manner. To realize the transmitting of full-color images with large FOV via the waveguides in a time-multiplexing manner, each of the in-coupling gratings and the out-coupling gratings in each waveguide may include a plurality of subgratings for delivering different colors (e.g., red, green, and blue colors) corresponding to different portions of the FOV.

For example, to sequentially deliver full-color image lights corresponding to predetermined portions of the FOV in a time-multiplexing manner via the waveguide stack <NUM> in <FIG> or the waveguide <NUM> in <FIG>, each of the in-coupling gratings <NUM>, <NUM> and <NUM> in <FIG> or <NUM>, <NUM>, <NUM> in <FIG> may include a plurality of switchable in-coupling subgratings, and each of the out-coupling gratings <NUM>, <NUM> and <NUM> in <FIG> or <NUM>, <NUM>, <NUM> in <FIG> may include a plurality of switchable out-coupling subgratings. The in-coupling gratings <NUM>, <NUM> and <NUM> in <FIG> or <NUM>, <NUM>, <NUM> in <FIG> may be an in-coupling grating stack, and the out-coupling gratings <NUM>, <NUM> and <NUM> in <FIG> or <NUM>, <NUM>, <NUM> in <FIG> may be an out-coupling grating stack. Provided that X number of subgratings are designed for delivering FOV and Y number of subgratings are designed for delivering single-color images forming a full-color image (e.g., RGB colors), the total amount of subgratings included in each of the in-coupling and out-coupling grating stacks may be X*Y, where X and Y are positive integers and X≥<NUM> and Y≥<NUM>. For example, each of the in-coupling gratings <NUM>, <NUM> and <NUM> in <FIG> or <NUM>, <NUM>, <NUM> in <FIG> serving for delivering <NUM>/<NUM> portion of FOV (X=<NUM>) may be split in <NUM> subgratings (Y=<NUM>) to deliver a corresponding portion of FOV in red, green and blue colors. For the same purpose, the out-coupling gratings <NUM>, <NUM> and <NUM> in <FIG> or <NUM>, <NUM>, <NUM> in <FIG> serving for delivering <NUM>/<NUM> portion of FOV (X=<NUM>) may be split in <NUM> subgratings (Y=<NUM>) to deliver a corresponding portion of FOV in red (R), green (G) and blue (B) colors. The total amount of the in-coupling subgratings may be equal to the total amount of the out-coupling subgratings and may be designed as X*Y=<NUM>*<NUM>=<NUM>. In some embodiments, the corresponding subgratings from the in-coupling and out-coupling grating stacks may be activated in separate subframes (e.g., <NUM> subframes) to suppress the crosstalk.

In each subframe, one pair of switchable in-coupling and out-coupling subgratings may be configured to be in the diffraction state to transmit a single-color image corresponding to a predetermined portion of the FOV to the eye, while the remaining pairs of the in-coupling subgratings and out-coupling subgratings may be configured to be in the non-diffraction state. Thus, during the entire display frame, single-color images corresponding to different portions of the FOV may be sequentially transmitted to the eye in the time-multiplexing manner. For example, a single-color image of red color corresponding to the left portion of FOV, a single-color image of green color corresponding to the left portion of FOV, a single-color image of blue color corresponding to the left portion of FOV, a single-color image of red color corresponding to the center portion of FOV, a single-color image of green color corresponding to the center portion of FOV, a single-color image of blue color corresponding to the center portion of FOV, a single-color image of red color corresponding to the right portion of FOV, a single-color image of green color corresponding to the right portion of FOV, and a single-color image of blue color corresponding to the right portion of FOV may be sequentially transmitted to the eye in the time-multiplexing manner. In some embodiments, the number of subframes may be reduced provided some subgratings in the waveguide stack <NUM> (for example for different colors) or the waveguide <NUM> are highly selective so that a crosstalk between them may be negligible.

Similarly, the waveguide <NUM> in <FIG> may also be used for transmitting full-color images with large FOV, where the waveguide <NUM> is configured to deliver full-color images with different portions of FOV in a time-multiplexing manner. To realize the transmitting of full-color images with large FOV via the waveguides in a time-multiplexing manner, each of the in-coupling sub-gratings 1005_1, 1005_2 and 1005_3 may further include a plurality of in-coupling tertiary gratings and each of the out-coupling sub-gratings 1010_1, 1010_2 and 1010_3 may further include a plurality of out-coupling tertiary gratings for delivering different colors (e.g., red, green, and blue colors). The respective tertiary gratings may be stacked or tiled at a surface of the waveguide <NUM>, and the details are not repeated here. The number of the in-coupling tertiary gratings and out-coupling tertiary gratings may be determined in a same way as that of the in-coupling subgratings and out-coupling subgratings included in the waveguide stack <NUM> in <FIG>, and the details are not repeated here. The operation scheme of the pairs of switchable in-coupling and out-coupling tertiary gratings in the waveguide <NUM> may be similar to that of the pairs of switchable in-coupling and out-coupling subgratings in the waveguide stack <NUM> in <FIG>, and the details are not repeated here.

In the above discussion, to sequentially deliver full-color image lights corresponding to predetermined portions of the FOV in a time-multiplexing manner, each in-coupling grating may include three switchable in-coupling subgratings, and each out-coupling grating may include three switchable out-coupling subgratings, which is for illustrative purposes, and is not intended to limit the scope of the present disclosure. In some embodiments, to multiplex colors and tile FOVs at the same time, each in-coupling grating (sub-grating) may include N number of in-coupling subgratings (tertiary gratings), and each out-coupling grating (sub-grating) may include N number of out-coupling subgratings (tertiary gratings), N is a positive integer and N≥<NUM>. In some embodiments, N≥<NUM>. That is, an in-coupling subgrating (tertiary grating) and a corresponding out-coupling subgrating (tertiary grating) may form a pair, a disclosed waveguide or waveguide stack may include N pairs. During respective time periods, respective pairs of the N pairs may be sequentially configured to be in the diffraction state to transmit respective light fields of a plurality of light fields, and the remaining pairs of the N pairs may be configured to be in the non-diffraction state. The plurality of light fields may correspond to single-color images of different colors, different portions of FOV of single-color images or different portions of FOV of full-color images.

Further, the disclosed methods and disclosed waveguide display assemblies for spatial- and/or time-multiplexing of different colors and/or different portions of FOV may also be realized by other switchable gratings, such as geometric phase gratings based on active LCs, metasurface/LC gratings etc., all of which are within the scope of the present disclosure.

The foregoing description of the embodiments of the disclosure have been presented for the purpose of illustration. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

Some portions of this description describe the embodiments of the disclosure in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules, without loss of generality. The described operations and their associated modules may be embodied in software, firmware, hardware, or any combinations thereof.

Embodiments of the disclosure may also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, and/or it may comprise a general-purpose computing device selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a non-transitory, tangible computer readable storage medium, or any type of media suitable for storing electronic instructions, which may be coupled to a computer system bus. Furthermore, any computing systems referred to in the specification may include a single processor or may be architectures employing multiple processor designs for increased computing capability.

Claim 1:
An optical device, comprising:
a light source assembly (<NUM>) configured to generate an image light; and
at least one waveguide (<NUM>) including an in-coupling element (<NUM>) and an out-coupling element (<NUM>) configured to transmit, via the at least one waveguide, a plurality of light fields of the image light to an eye-box of the optical device, in a time-multiplexing manner,
wherein at least one of the in-coupling element or the out-coupling element comprises N switchable diffraction gratings (1005_1, 1005_2, 1005_3), N being a positive integer and N≥<NUM>, and wherein each switchable diffractive optical element comprises:
a surface relief grating, SRG, (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) filled with a switchable optically anisotropic material (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a first principal refractive index along a groove direction of the SRG and a second principal refractive index along an in-plane direction perpendicular to the groove direction, one of the first and second principal refractive indices substantially matching a refractive index of the SRG, and the other mismatching the refractive index of the SRG, and
wherein:
during respective time periods, the N number of switchable diffraction gratings sequentially configured to be in a diffraction state to transmit respective light fields of the plurality of light fields, and
during one time period, one of the N number of switchable diffraction gratings configured to be in the diffraction state to transmit a light field of the plurality of light fields and the remaining switchable diffraction gratings configured to be in a non-diffraction state;
characterised in that
the switchable diffraction gratings are partially overlapped with each other at a surface (<NUM>-<NUM>, <NUM>-<NUM>) of the waveguide.