Patent Description:
Various imaging systems, such as spatial-light-modulator (SLM) based projectors, microelectromechanical systems (MEMS) scanners, and fiber scanners, have been considered for providing imagewise modulated light in an augmented reality eyewear that includes an eyepiece. Despite significant progress, it has become increasingly difficult to reduce a size of the illumination system. Therefore a new scalable imaging architecture that allows further miniaturization is needed. <CIT> discloses a near-eye display including an image generator that generates angularly related beams over a range of angles for forming a virtual image and a waveguide that propagates the angularly related beams over a limited range of angles. An input aperture of the waveguide includes a plurality of controllable components that are selectively operable as diffractive optics for injecting subsets of the angularly related beams into the waveguide. An output aperture of the waveguide includes a plurality of controllable components that selectively operable as diffractive optics for ejecting corresponding subsets of the angularly related beams out of the waveguide toward an eyebox. A controller synchronizes operation of the controllable components of the output aperture with the propagation of different subsets of angularly related beams along the waveguide for ejecting the subsets of angularly related beams out of the waveguide for presenting the virtual image within the eyebox.

Optional features are defined in the dependent claims. Eyepieces and related methods are disclosed that employ a dynamic input coupling grating (ICG) to couple an input light beam into a waveguide and to controllably scan in the input light beam to form an image light field that is output from the waveguide to an eye of a viewer. In many embodiments, the intensity of the input light beam is modulated in conjunction with the scanning of the input light beam via the dynamic ICG to generate the image light field as a combination of time segments of the input light beam scanned to respective X and Y coordinate positions in the image light field. By using simultaneous modulation of the input light beam and corresponding scanning of the modulated input light beam, a simplified light source can be used that propagates the input light beam along a fixed one-dimensional propagation path, thereby allowing the light source to have reduced size relative to devices and approaches in which a two-dimensional light field is transmitted onto a non-dynamic input coupling grating.

According to some examples, eyepiece for projecting an image light field to an eye of a viewer includes a waveguide, a dynamic input coupling grating (ICG), a light source, a controller, and an exit pupil expander. The waveguide is configured to propagate light via internal reflection. The dynamic ICG is formed on a first lateral region of the waveguide. The light source is configured to generate a light beam transmitted to the dynamic ICG. The controller is coupled to the light source and the dynamic ICG,. The controller is configured to modulate an intensity of the light beam in a sequence of time slots. Each time slot of the sequence of time slots corresponds to a respective field angle of the image light field. The intensity of the light beam in each time slot of the sequence of time slots corresponds to an intensity of the image light field at the respective field angle. The controller is configured to control the dynamic ICG to, for each time slot of the sequence of time slots, diffract a respective portion of the light beam into the waveguide at a respective angle corresponding to the respective field angle. The exit pupil expander is coupled to a second lateral region of the waveguide and configured to direct each respective portion of the light beam out of the waveguide toward the eye of the viewer at the respective field angle, thereby projecting the image light field to the eye of the viewer.

According to a first aspect of the present invention, a method of projecting an image light field to an eye of a viewer is provided. The method includes modulating, by a controller, an intensity of a light beam in a sequence of time slots. Each time slot of the sequence of time slots corresponds to a respective field angle of the image light field. The intensity of the light beam in each time slot of the sequence of time slots corresponding to an intensity of the image light field at the respective field angle. The light beam is propagated onto a dynamic input coupling grating (ICG). The dynamic ICG is controlled, by a controller, to diffract a respective portion of the light beam into a waveguide at a respective angle corresponding to the respective field angle for each time slot of the sequence of time slots. Each respective portion of the light beam is directed out of the waveguide toward the eye at the respective field angle, thereby projecting the image light field to the eye of the viewer.

According to a second aspect of the present invention, an eyepiece for projecting an image light field to an eye of a viewer for forming an image of virtual content includes a waveguide configured to propagate light therein. The waveguide includes an input pupil. The eyepiece further includes a light source configured to deliver a light beam to be incident on the waveguide at the input pupil, and a controller coupled to the light source and configured to modulate an intensity of the light beam in a plurality of time slots. Each time slot corresponds to a respective field angle of the image. The intensity of the light beam in each time slot corresponds to an intensity of the image at the respective field angle. The eyepiece further includes a dynamic input coupling grating (ICG) formed on a first lateral region of the waveguide corresponding to the input pupil. The dynamic ICG is configured to, for each time slot, diffract a respective portion of the light beam into the waveguide at a respective total internal reflection (TIR) angle corresponding to a respective field angle, and scan the TIR angle from one time slot to a next time slot in accordance with modulation of the light beam. The eyepiece further includes an outcoupling diffractive optical element (DOE) coupled to a second lateral region of the waveguide and configured to diffract each respective portion of the light beam out of the waveguide toward the eye at the respective field angle, thereby projecting the light field to the eye of the viewer.

According to some examples, a method of projecting a light field to an eye of a viewer for viewing an image of virtual content includes providing a light beam incident on a dynamic input coupling grating (ICG). The dynamic ICG may include a surface acoustic wave (SAW) modulator. The SAW modulator may include a layer of a piezoelectric material and a transducer. The SAW modulator may be coupled to a first lateral region of a waveguide. The method may further include modulating an intensity of the light beam in a plurality of time slots corresponding to a plurality of field angles. The intensity of the light beam in each time slot may correspond to an intensity of the image at a respective field angle. The method may further include applying oscillating electric signals to the transducer at a plurality of frequencies in the plurality of time slots, thereby creating a respective sound wave in the layer of the piezoelectric material with a respective spatial period in the respective time slot, such that the dynamic ICG diffracts a respective portion the light beam into the waveguide at a respective total internal reflection (TIR) angle in the respective time slot. Each respective frequency may correspond to a respective time slot. The respective portion of the light beam may be propagated in the waveguide. The method may further include outcoupling, using a diffractive optical element (DOE) coupled to a second lateral region of the waveguide, each respective portion of the light beam propagating in the waveguide toward the eye at the respective field angle, thereby projecting the light field at the plurality of field angles to the eye for viewing the image of the virtual content.

According to some embodiments of the present disclosure, an eyepiece includes a waveguide and a dynamic input coupling grating (ICG) coupled to the waveguide. The dynamic ICG is configured to scan a fixed input laser beam into a range of two-dimensional TIR angles in the waveguide. By modulating the laser beam intensity in a sequence of time slots as a function of image point locations in a field of view, which is synchronized with the scanning of the dynamic ICG, a viewer may see a full image field display. This imaging paradigm may eliminate the need for an external projector, and therefore may afford a compact, lightweight eyewear. Such an eyewear may be used, for example, in an augmented reality system or other wearable display and computing products.

A diffraction grating is an optical component that deflects light by an angle that is dependent on the wavelength of light and the angle of incidence on the grating. A diffraction grating may have a periodic structure with a period that is on the order of the wavelength of light with which the diffraction grating is to be used. The periodic structure can be a surface relief profile or a volume modulation of the index of refraction of a transparent material. The operation of a diffraction grating may be governed by the grating equation: <MAT> where θm is the angle of a light beam exiting the diffraction grating (diffraction angle) relative to a vector normal to the surface of the grating; λ is the wavelength; m is an integer valued parameter known as the diffraction "order"; d is the period of the grating; and θi is the angle of incidence of an input light beam relative to the vector normal to the surface of the grating.

Gratings may also be blazed, i.e., given a particular periodic profile so as to concentrate the light they diffract into a particular "order" specified by a particular value of the order parameter m. Gratings may be reflective in which case light departs the grating on the same side that light is incident on the grating, or transmissive in which case light exits primarily on a side of the grating opposite from which the light is incident.

<FIG> is a perspective view of a pair of augmented reality glasses <NUM> according to some embodiments. The glasses <NUM> include a frame <NUM> including a left arm <NUM> and a right arm <NUM> connected by a front piece <NUM>. The front piece <NUM> supports a left eyepiece <NUM> and a right eyepiece <NUM>. Referring in particular to the right eyepiece <NUM> for the purpose of discussion, the right eyepiece <NUM> includes a right stack of a plurality of waveguides <NUM>. The right stack of waveguides <NUM> is transparent so that a person wearing the glasses <NUM> can see the real world while wearing the augmented reality glasses <NUM> and virtual content can be superimposed and displayed in context with the real world. As illustrated in <FIG> a right front waveguide <NUM> included in the right stack waveguides <NUM> includes a right front selectively actuable in-coupling grating <NUM>, a right front orthogonal pupil expander <NUM>, and a right front exit pupil expander <NUM>. As discussed in <CIT>, entitled "Planar Waveguide Apparatus with Diffraction element(s) and System Employing Same," the exit pupil expander <NUM> can be designed to impart different field curvature corresponding to different virtual source light to exiting light. Similarly, the left eyepiece <NUM> includes a left stack of waveguides <NUM> including a left front waveguide <NUM>. As illustrated in <FIG>, the left front waveguide includes a left-front selectively actuable in-coupling grating <NUM>, a left-side orthogonal pupil expander <NUM>, and a left-side exit pupil expander <NUM>. The left eyepiece <NUM> is also transparent. A left-side source of imagewise modulated light <NUM> and a right-side source of imagewise modulated light <NUM> are supported respectively inboard of the left arm <NUM> and the right arm <NUM> of the frame <NUM> and are selectively optically coupled, respectively to the left stack of waveguides <NUM> and the right stack of waveguides <NUM>.

<FIG> shows an exemplary augmented reality system <NUM> that may be operable to render virtual content (e.g., virtual objects, virtual tools, and other virtual constructs, for instance applications, features, characters, text, digits, and other symbols) in a field of view of a user <NUM>, and may include a head-mounted wearable display device <NUM> and a computing device <NUM>. The head-mounted wearable display device <NUM> may include a pair of augmented reality glasses <NUM> similar to that illustrated in <FIG>. The computing device <NUM> may include components (e.g., processing components, power components, memory, etc.) that perform a multitude of processing tasks to present the relevant virtual content to the user <NUM>.

The computing device <NUM> may be operatively and/or communicatively coupled to the head-mounted wearable display device <NUM> by way of connection <NUM> (e.g., wired lead connection, wireless connection, etc.). The computing device <NUM> may be removably attached to the hip <NUM> of the user <NUM> in a belt-coupling style configuration. In other examples, the computing device <NUM> may be removably attached to another portion of the body of the user <NUM>, attached to or located within a garment or other accessory (e.g., frame, hat or helmet, etc.) worn by the user <NUM>, or positioned in another location within the environment of the user <NUM>.

<FIG> is a schematic edge-on view of the right eyepiece <NUM> illustrated in <FIG>. Note that the placement of the in-coupling grating <NUM>, the orthogonal pupil expander <NUM> and the exit pupil expander <NUM> is altered in <FIG> relative to the placement shown in <FIG> for the purpose of illustration. Although not shown, the structure of the left eyepiece <NUM> is a mirror image of the structure of the right eyepiece <NUM>. As illustrated in <FIG>, in addition to the right front waveguide <NUM>, the right stack of the plurality of waveguides <NUM> of the right eyepiece <NUM> includes a right second waveguide <NUM> disposed behind the right front waveguide <NUM>, a right third waveguide <NUM> disposed behind the right second waveguide <NUM>, a right fourth waveguide <NUM> disposed behind the right third waveguide <NUM>, a right fifth waveguide <NUM> disposed behind the right fourth waveguide <NUM>, and a right back waveguide <NUM> disposed behind the right fifth waveguide <NUM>. Each of the second through fifth waveguides <NUM>, <NUM>, <NUM>, <NUM> and back waveguide <NUM> has respectively a second through sixth incoupling grating 118b, 118c, 118d, 118e, 118f The in-coupling gratings 118a, 118b, 118c, 118d, 118e, 118f can be designed, for example, to have a grating pitch and profile (e.g., blazed profile) to deflect imagewise modulated light that is incident perpendicularly to an angle above the critical angle for the waveguides <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The second through fifth waveguides <NUM>, <NUM>, <NUM>, <NUM> and back waveguide <NUM> also each include one of an additional set of orthogonal pupil expanders <NUM>, and one of an additional set of exit pupil expanders <NUM>.

The right-side source of imagewise modulated light <NUM> suitably outputs imagewise modulated light for different color channels and for different virtual object depths during separate time subframe periods. A particular sequence of color channels and depth planes can be repeated periodically at a video frame rate. The stack of six waveguides <NUM> can include two sets of three waveguides, wherein each of the two sets includes a red, a green and a blue color (RGB color) channel waveguide, and each of the two sets emits light with one of two virtual object distances which are determined by the field curvature of the emitted light. Light exiting from the front of the right eyepiece <NUM> is directed backward, passing to an eye position <NUM>.

<FIG> shows an imaging system <NUM> that may be used for projecting an image light field to an observer's eye <NUM> through an eyepiece <NUM>. The imaging system <NUM> may include a spatial-light-modulator (SLM) <NUM>. The SLM <NUM> may include, for example, a liquid crystal on silicon (LCOS) display, a digital light processing (DLP) chip, or the like. An illumination source (not shown), such as light-emitting diodes (LEDs), lasers, and the like, may provide a (quasi) collimated light illumination <NUM> to be incident on the SLM <NUM>. The SLM <NUM> may spatially modulate the illumination <NUM> to form a two-dimensional (2D) image of virtual content by controlling an amount of transmitted (or reflected) light incidence on each pixel. The imaging system <NUM> may further include a projection lens <NUM>. The SLM <NUM> may be positioned at a back focal plane of the projection lens <NUM>. Light transmitted by a respective pixel P at position (xP, yP) may be transformed by the eyepiece <NUM>.

The beam incident on an in-coupling grade (ICG) <NUM> of the eyepiece <NUM>, which couples a portion of the incident light into a waveguide <NUM> as a total internal refraction (TIR) beam at a respective propagation direction (θP,TIR, ϕP,TIR). Each TIR beam is replicated into multiple TIR beams in the waveguide <NUM>, all with the same propagation direction. An exit pupil expander (EPE) <NUM> couples the TIR beams out of the eyepiece <NUM> as multiple output beams, all at the same propagation direction (θP, ϕP) toward the observer's eye <NUM>. The beam replication allows the observer to view the image from an effectively larger exit pupil, hence the term exit pupil expander. A pupil of the observer's eye <NUM> collects a number of these beams, which will then be focused by the eye lens into a specific position on the retina (xP', yP'). Thus, the light transmitted by a respective pixel P at a position (xP, yP) may be transformed by the eyepiece <NUM> into a beam of parallel rays that propagates at a respective direction (θP, ϕP). For clarity, the second coordinate yP and the second angle ϕP are suppressed in <FIG> and subsequent figures.

Various imaging systems, such as spatial-light-modulator (SLM) based projectors, microelectromechanical systems (MEMS) scanners, and fiber scanners, have been considered for providing imagewise modulated light in an augmented reality eyewear that includes an eyepiece, such as the eyepiece <NUM> illustrated in <FIG>. Despite significant progress, it has become increasingly difficult to reduce the size of the projector. For example, a typical size of an SLM-based project may be about <NUM>, excluding the illumination module; a typical size of a fiber scanner may be about <NUM>, excluding the illumination module; and a typical size of a MEMS scanner may be about <NUM>, excluding the illumination module.

As described above, there may be a one-to-one correspondence between each pixel position (xP, yP) on the SLM <NUM> (or other types of 2D scanner, such as a fiber scanner), a respective propagation direction θP, ϕP) in free space, a respective TIR propagation direction (θP,TIR, ϕP,TIR) inside the waveguide <NUM>, and a respective image position (xP', yP') at the retina of the observer's eye <NUM>. According to some embodiments of the present disclosure, the TIR propagation direction (θP,TIR, ϕP,TIR) may be generated directly in an eyepiece and may be scanned for all points in the image field. This new imaging paradigm may eliminate the need for the external imaging system <NUM>, and therefore may enable the construction of a very compact eyewear.

<FIG> illustrates schematically an eyepiece <NUM>, according to some embodiments. The eyepiece <NUM> includes a waveguide <NUM>, a two-dimensional (2D) dynamic ICG <NUM> coupled to a first lateral region of the waveguide <NUM>, and a diffractive optical element (DOE) <NUM> (such as an orthogonal pupil expander OPE, and/or exit pupil expander EPE) coupled to a second lateral region of the waveguide <NUM>. An input light beam <NUM> with a fixed propagation direction (e.g., normal to the waveguide <NUM>, <IMG> = <NUM>) is incident on the dynamic ICG <NUM>. The input light beam <NUM> may be intensity modulated in one or more time slots such that, for each time slot, the intensity of the input light beam <NUM> corresponds to the relative brightness of a respective image point P in an image field (the image point P may be analogous to a pixel (xP, yP) on the SLM <NUM> illustrated in <FIG>).

<FIG> illustrates schematically the action of the dynamic ICG <NUM>, according to some embodiments. The dynamic ICG <NUM> is configured to diffractively couple the input light beam <NUM> into the waveguide <NUM> as a TIR beam. As illustrated in <FIG>, a TIR angle of a diffracted light beam <NUM> may be dynamically varied from one time slot to another time slot synchronously with the modulation of input light beam <NUM>, such that the TIR angle (<IMG>, <IMG>) for each time slot corresponds to the respective image field P. Thus, by scanning the TIR angle (<IMG>, <IMG>) in a range of TIR angles in the one or more slots, the entire image field may be scanned.

Referring again to <FIG>, for a respective TIR angle (<IMG>, <IMG>) in a respective time slot, the EPE <NUM> couples the TIR beams out of the eyepiece <NUM> at a corresponding propagation directions (θP, ϕP) toward the observer's eye <NUM>. The pupil of the observer's eye <NUM> collects the output beams, which are then focused by the eye lens into a specific position on the retina (xP', yP'). As the TIR angle (<IMG>, <IMG>) is scanned by the dynamic ICG <NUM> in the range of TIR angles in the one or more time slots, the propagation direction (θP, ϕP) of the output beams is scanned correspondingly, thereby covering the entire image field. (Note, for clarity, only one propagation direction (θP, ϕP) is shown in <FIG>.

Therefore, as described above, the dynamic ICG <NUM> integrates the function of an ICG with the function of a scanner in a single device, thereby eliminating the need for a separate imaging system <NUM> as illustrated in <FIG>. As such, the eyewear may be made with significantly reduced size and weight as compared to a conventional eyewear. In some embodiments, the dynamic ICG <NUM> may have no moving parts, unlike a fiber scanner or a MEMS scanner, for example. An eyepiece incorporating a dynamic ICG <NUM> may afford other advantages. For example, higher brightness and lower power consumption may be realized, as there are less optical components that can cause additional loss.

In some embodiments, simultaneous color may be used. In these embodiments, red (R), green (G), and blue (B) information may be simultaneously present as colinear R, G, B beams from R, G, B lasers, respectively. As the three colinear R, G, B beams are scanned across an image field, an amount of each color at any point (pixel) may be controlled by modulating independently, but simultaneously, the three lasers. In contrast, sequential color may be used if a single LCOS is shared to generate R, G, B images, one color at a time.

<FIG> illustrates schematically a compact eyewear, according to some embodiments. The compact eyewear may include an eyepiece (e.g., similar to the eyepiece <NUM>) that includes a dynamic ICG (e.g., similar to the dynamic ICG <NUM>). A compact light source module mounted on the eyewear may provide an input light beam incident on the dynamic ICG at a fixed propagation direction. In some embodiments, the compact light source module may emit collimated light. In some embodiments, the compact light source module may emit light that has a narrow spectrum / beam spread. In some embodiments, the compact light source module may include one or more lasers. For example, the compact light source module may include a red laser, a blue laser, and a green laser. In some embodiments, the compact light source module may be in a head-mounted wearable display device (e.g., similar to the head-mounted wearable display device <NUM> illustrated in <FIG>). In some embodiments, the compact light source module may include one or more LEDs. For example, the one or more LEDs may be one or more superluminescent LEDs (SLEDs). In some embodiments, a controller may be used to operate the compact light source module, for example move the compact light source module and/or to modulate the compact light source module. The controller may be used to load an image into one or more light beams.

<FIG> illustrates schematically a compact eyewear, according to some embodiments. Here, a separate light source package may provide an input light beam via an optical fiber. In some embodiments, the compact light source module may be in a beltpack (e.g., in the computing device <NUM> illustrated in <FIG>) and may be delivered to a head-mounted wearable display device via a fiber. Since the operation of the dynamic ICG may be polarization independent, the input light beam can be unpolarized. Therefore, efficient fiber transport may be realized by using a non-polarization-maintaining optical fiber.

<FIG> illustrates schematically a one-dimensional dynamic ICG based on a surface acoustic wave (SAW) modulator, according to some embodiments. A SAW modulator uses an acousto-optic effect to diffract light using sound waves (for example, at radio-frequency). A transducer (e.g., a piezoelectric transducer) is attached to a substrate of the SAW modulator. An oscillating electric signal may drive the transducer to vibrate, which may create an acoustic wave that propagates on the surface of the substrate. This acoustic wave (which may be referred to as a surface acoustic wave, or SAW) may cause deformation of the surface and form a diffraction grating. The substrate may include a material that exhibits the piezoelectric effect, such as fused silica, lithium niobate, lithium tantalite, lanthanum gallium silicate, arsenic trisulfide, tellurium dioxide, tellurite glass, lead silicate, or the like. The substrate can include a material that exhibits the piezoelectric effect as originally fabricated, or a material that exhibits the piezoelectric effect can be deposited onto the substrate. For each pixel, a certain diffraction grating in 2D is created having a particular grating pitch that will diffract light in a particular direction. Changing the diffraction grating by changing the grating pitch will result in a change in the direction.

A beam of light ("In") incident on the diffraction grating formed by the SAW may be diffracted, either in a transmission geometry or a reflection geometry (e.g., on a metallized surface). <FIG> illustrates a SAW modulator in a transmission geometry. As illustrated, various diffraction orders (e.g., -<NUM>, <NUM>, +<NUM> orders) may result. The period of the diffraction grating may depend on the frequency of the driving electric signal. Diffraction angles (e.g., in the first order diffraction) depend on the period of the diffraction grating. Therefore, by modulating the frequency of the driving electric signal, the diffracted light may scan a range of angles.

The SAW modulator described above may be extended to a two-dimensional (2D) case. <FIG> illustrates schematically a 2D SAW modulator in a transmission geometry, according to some embodiments. A first transducer for the X-axis motion and a second transducer for the Y-axis motion are attached to a substrate. A first oscillating electric signal RF (RF)x may drive the first transducer to vibrate along the X-axis, and a second oscillating electric signal RF (RF)y may drive the second transducer to vibrate along the Y-axis, together which may create a 2D SAW that propagates on the surface of the substrate. The 2D SAW may cause deformation of the surface of the substrate and form a 2D diffraction grating. An incident light beam may be diffracted by the diffraction grating (for clarity, only the main diffraction order, for example, a first order, is shown in <FIG>). By scanning the frequencies of the driving electric signals (RF)x and (RF)y along the X-axis and the Y-axis, respectively, the diffracted light may scan a range of 2D angles (θ, ϕ), for example in an x-y pattern (raster scan), or in a spiraling pattern.

In some embodiments, multiple driving frequencies may be superimposed on each other. For example, one or more electric signals may be combined as a composite driving signal along the X-axis, where each respective electric signal corresponds a respective frequency. In this manner, a group of pixels (or an entire line of pixels) along the X-axis may be simultaneously addressed. In some embodiments, the acoustic wave may be modulated by a superposition of RF signals. In some embodiments, two gratings may be superimposed and light may be diffracted according to the diffraction characteristics (e.g., pitch and/or amplitude) of each of the two gratings. For example, if there is a first grating and a second grating and the first grating and the second grating are superimposed, then light incident thereon will be diffracted and split in directions determined by both a first pitch of the first grating and a second pitch of the second grating, and have amplitudes related to a first amplitude of the first grating and a second amplitude of the second grating. A frequency of a first RF signal may determine the first pitch of the first grating and an amplitude the first RF signal may determine an amplitude of the first grating. Similarly, a frequency of a second RF signal may determine the second pitch of the second grating and an amplitude of the second RF signal may determine an amplitude of the second grating. In some embodiments, multiple gratings may be superimposed and light diffracted off the multiple gratings may follow all the multiple gratings.

It may be noted that the grating amplitude may depend on the electric power delivered to the one or more transducer. Therefore, in some embodiments, image intensity modulation may also be performed by the SAW modulator by modulating the electric power of the driving electric signal, in addition to modulating the frequency of the driving electric signal.

It may also be noted that the constantly changing diffraction gratings as a result of the frequency/amplitude modulation may help reduce coherent artifacts that a static grating may produce. For example, coherent artifacts produced by a static grating may manifest as a light-dark variations across an image field. The constantly changing diffraction gratings may produce "sliding" light-dark variations that may be less noticeable as the eye integrates the light in a response time window.

In some embodiments, the SAW modulator may be formed on a surface of a waveguide, as illustrated in <FIG>. For example, a layer of piezoelectric material, such as lithium niobate, and one or more transducers may be attached to the surface of the waveguide. In some embodiments, the SAW modulator may be formed below the surface of the waveguide. For example, a layer of piezoelectric material may be embedded in the waveguide, and one or more transducers may be coupled to the layer of piezoelectric material. In some embodiments, the SAW modulator may be an integral part of the waveguide. For example, the waveguide may include a piezoelectric material, such as lithium niobate. One or more transducers may be formed on a first lateral region of the surface of the waveguide for generating SAWs in the first lateral region of the surface.

It should be understood that, although a SAW modulator is discussed above as an example of a dynamic ICG, other types of analog scanning technologies may also be used for the dynamic ICG.

<FIG> illustrates schematically a 2D dynamic ICG in an eyepiece in a transmission geometry, according to some embodiments. The eyepiece includes a waveguide that has a first surface and a second surface opposite the first surface. The 2D dynamic ICG is coupled to the first surface of the waveguide. Note that this configuration is similar to that illustrated in <FIG> and <FIG>. An intensity-modulated input light beam is normally incident on the 2D dynamic ICG. As described above with reference to <FIG>, the 2D dynamic ICG is modulated synchronously with the intensity modulation of the input light beam, such that one or more corresponding diffracted light beams in the transmission geometry with a range of propagation angles (θ, ϕ) are propagated in the waveguide. Each propagation angle (θ, ϕ) corresponds to a respective image field P. It should be understood that, although the 2D dynamic ICG is illustrated as positioned above the first surface of the waveguide, this is not required. In some embodiments, the 2D dynamic ICG may be imbedded in the waveguide or may be an integral part of the waveguide.

<FIG> illustrates schematically a 2D dynamic ICG in an eyepiece in a reflection geometry, according to some embodiments. The eyepiece includes a waveguide that has a first surface and a second surface opposite the first surface. The 2D dynamic ICG is coupled the second surface of the waveguide. An intensity-modulated input light beam passes through the waveguide and is normally incident on the 2D dynamic ICG. The 2D dynamic ICG is modulated synchronously with the intensity modulation of the input light beam, such that one or more corresponding diffracted light beams in the reflection geometry with a range of propagation angles (θ, ϕ) are propagated in the waveguide. Each propagation angle (θ, ϕ) corresponds to a respective image field P. It should be understood that, although the 2D dynamic ICG is illustrated as positioned below the second surface of the waveguide, this is not required. In some embodiments, the 2D dynamic ICG may be imbedded in the waveguide or may be an integral part of the waveguide.

<FIG> illustrates schematically an eyepiece that includes two one-dimensional (1D) dynamic ICGs cascaded with respect to each other, according to some embodiments. The eyepiece includes a waveguide that has a first surface and a second surface opposite the first surface. A first 1D dynamic ICG is coupled to the second surface of the waveguide. A second 1D dynamic ICG is coupled to the first surface of the waveguide. An intensity-modulated input light beam passes through the waveguide and is normally incident on the first 1D dynamic ICG.

The first 1D dynamic ICG is modulated synchronously with the intensity modulation of the input light beam, such that one or more corresponding diffracted light beams in the reflection geometry with a range of propagation angles θ are propagated in the waveguide. The left and right arrows under the first 1D dynamic ICG illustrated in <FIG> indicate that input light beams are dispersed into one or more propagation angles θ in the plane of the paper.

The light beams diffracted by the first 1D dynamic ICG with a range of propagation angles θ are incident on the second 1D dynamic ICG. The second 1D dynamic ICG is modulated synchronously with the intensity modulation of the input light beam, such that one or more corresponding diffracted light beams in the reflection geometry with a range of propagation angles ϕ are propagated in the waveguide. The dot and the cross above the second 1D dynamic ICG illustrated in <FIG> indicate that the light beams are dispersed into one or more propagation angles ϕ in the plane perpendicular to the paper. In some embodiments, because the input light beam is diffracted twice (by the first 1D dynamic ICG followed by the second 1D dynamic ICG), the coupling efficiency may not be as high as in the cases with a single 2D dynamic ICG as illustrated in <FIG> (the effective diffraction efficiency may be approximately η<NUM>, where η is the diffraction efficiency of a single ICG).

In some cases, it may be desirable to have the input light beam incident on the dynamic ICG at a bias angle θbias. <FIG> illustrates schematically an eyepiece where the input light beam is incident on a dynamic ICG at a bias angle θbias with respect to a normal of the surface of the dynamic ICG, according to some embodiments. Diffracted light beams in a range of dynamically modulated angles (θ, ϕ) in the transmission mode are propagated in the waveguide. The angular bias can be done in any direction, either in θ or ϕ, or a combination thereof (although only shown for θ in <FIG> for purposes of clarity).

A bias angle θbias may be desirable in some cases in order to facilitate propagation in the waveguide via total internal reflection (TIR). For example, depending on the possible grating vectors that can be generated by the dynamic ICG, the range of propagation angles (θ, φ) of the diffracted light beams generated from a normal incident input light beam may not meet the TIR condition of the waveguide. In such cases, a bias angle θbias of the input light beam may provide an extra "kick" needed for making the range of propagation angles (θ, φ) meet the TIR condition of the waveguide (as discussed in further detail below with reference to <FIG>).

<FIG> illustrates schematically an eyepiece that includes a static diffraction grating coupled to the first surface of a waveguide. The input light beam is normally incident on the static diffraction grating, and is diffracted by the static diffraction grating at a bias angle θ'bias. The diffracted light beam is then incident on the dynamic ICG at the bias angle θ'bias, and is diffracted by the dynamic ICG into a range of dynamically modulated angles (θ, φ) in the reflection mode. In this embodiments, because the input light beam is diffracted twice (by the static diffraction grating followed by the dynamic ICG), the coupling efficiency may not be as high as the case illustrated in <FIG>.

In some cases, the modulation range of a dynamic ICG may not be large enough to cover a full field of view (FOV). In some embodiments, multiple input light beams may be used to increase the image field of view. <FIG> illustrates schematically a configuration where two input light beams ("IN1" and "IN2") are used. The eyepiece may include a static ICG coupled to a first surface of a waveguide, and a dynamic ICG coupled to a second surface of the waveguide. A first input light beam "IN1" is incident on the static ICG at a first bias angle θ<NUM>,bias, and is diffracted by the static ICG at a first diffraction angle. The first input light beam "IN1" diffracted by the static ICG is subsequently diffracted by the dynamic ICG into a first range of dynamically modulated total internal reflection (TIR) angles Δθ<NUM>,TIR. A second input light beam "IN2" is incident on the static ICG at a second bias angle θ<NUM>,bias, and is diffracted by the static ICG at a second diffraction angle. The second input light beam "IN2" diffracted by the static ICG is subsequently diffracted by the dynamic ICG into a second range of dynamically modulated TIR angles Δθ<NUM>,TIR. The total range of TIR angles ΔθTIR may be the sum of the first range of dynamically modulated TIR angles Δθ<NUM>,TIR and the second range of dynamically modulated TIR angles Δθ<NUM>,TIR. Therefore, a larger field of view compared to the case of a single input light beam may be achieved. For example, the first TIR angles θ<NUM>,TIR may range from <NUM>° to <NUM>° (i.e., Δθ<NUM>,TIR = <NUM>°), and the second TIR angles θ<NUM>,TIR may range from <NUM>° to <NUM>° (i.e., Δθ<NUM>,TIR = <NUM>°). Thus, the total range of TIR angles ΔθTIR may be <NUM>°.

It should be appreciated that two or more of the configurations illustrated in <FIG>, <FIG>, <FIG>, and <FIG> may be combined, according to some embodiments.

In some embodiments, full RGB colors may be implemented using a stack of three waveguides (e.g., as illustrated in <FIG>), each waveguide configured for one of the RGB colors. The colors may be separated using a split pupil configuration or an in-line configuration, as described in <CIT>.

Assuming a speed of a SAW is vs and a RF driving frequency is f, the SAW grating period Λs may then be expressed as, <MAT>.

Consider a 1D transmission dynamic ICG with input angle of incidence θin, as illustrated in <FIG>. Assume that the RF frequencies supported by the modulator ranges from fmin to fmax. Assume further that first-order diffraction propagates via TIR inside the waveguide (with index of refraction ng) over the operational RF frequency range (otherwise an angular bias may be used, as discussed below with reference to <FIG>). <FIG> shows the k-vector diagram for the first-order diffraction based on transverse momentum conservation. The k-vector diagram may be represented by the following equation: <MAT> where K is the dynamic grating vector with magnitude <NUM>π/Λs. From Eq. (<NUM>), the Bragg-Snell equation follows: <MAT>.

As a numerical example, assume θin = <NUM>° (normal incidence), λ = <NUM>, n = <NUM>, vs = <NUM>/s, fmin = <NUM>, and fmax = <NUM>. Using Eq. (<NUM>), one may find that θTIR(fmin) = <NUM>° (above <NUM>° critical angle) and θTIR(fmax) = <NUM>°. Using a <NUM> pitch EPE, the TIR beams can be coupled out to span an angular field of view (FOV) of Δθ = <NUM>° (i.e., ±<NUM>°).

Assuming a length of the dynamic grating to be D, using a Fourier transform lens with a focal length of F, a spot size at a transform plane may be expressed as d = <NUM>Fλ/D. With a FOV of ⊗ <IMG>, an image size would be 2F tan(⊗ <IMG>/<NUM>). Therefore, the number of resolution spots across a scanned image may be expressed as, <MAT>.

Assuming the length of the dynamic grating D = <NUM>, using ⊗<IMG>= <NUM>° and <IMG> = <NUM> from Example <NUM>, the number of resolution spots may be <NUM> (which corresponds to <NUM> arcmin angular resolution).

A minimum pixel time may be the time the SAW goes across the grating length D. A more conservative value for the pixel time Tpixel that accounts for the transient may be assumed to be about three times this ratio, <MAT>.

For vs = <NUM>/s and D = <NUM>, according to Eq. (<NUM>), the pixel time would be Tpixel = <NUM>.

<FIG> shows a k-vector diagram of a 2D dynamic ICG for a normal incident input beam. For the purpose of illustration, a 2D dynamic ICG with two orthogonal eigenmodes propagating in the + and - directions is considered. Shaded region <NUM> in the k-space represents all grating vectors K with magnitude 2π/Λs that can be generated by the 2D dynamic ICG. The shaded region <NUM> may be referred herein as the dynamic grating region. The subscripts "min" and "max" correspond to the minimum and maximum RF frequencies, respectively. In some embodiments, broadband transducers may be used to achieve a larger dynamic grating region <NUM>, thus a wider FOV.

To show the propagation inside the eyepiece waveguide, it may be useful to overlay the above diagram with the waveguide TIR diagram, as illustrated in <FIG>. The annular region <NUM> bounded by the two circles <NUM> and <NUM> represent the k space where TIR can occur in the waveguide. The overlap of the dynamic grating region <NUM> (i.e., the shaded region) and the TIR annular region <NUM> represents the k space where the diffracted light beams generated by the 2D dynamic ICG may propagate in the waveguide via TIR.

An angular bias can be applied to improve the TIR region utilization, as illustrated in <FIG>. For example, notice a larger shaded region <NUM> in <FIG> as compared to the shaded region <NUM> shown in <FIG>.

For relatively small dynamic grating vectors, the dynamic grating region may reside outside the TIR region <NUM>. In such cases, an angular bias may be used to shift the dynamic grating region <NUM> to the TIR region <NUM>, as illustrated in <FIG>. As described above, the bias may be introduced by using a specific external incident angle (as illustrated in <FIG>), or by using a static grating (as illustrated in <FIG>).

In summary, the concept of a very compact eyewear using a dynamic ICG is presented. A dynamic ICG may be configured to scan a fixed input laser beam into a range of two dimensional TIR angles in an eyepiece. By modulating the laser beam intensity as a function of the image point location, an observer may see a full image field. This new imaging paradigm may eliminate the need for an external projector and therefore may enable the construction of a very compact eyewear.

<FIG> is a flowchart illustrating a method <NUM> of projecting a light field to an eye of a viewer for viewing an image of virtual content, according to some embodiments. Any suitable components, assemblies, and approaches can be used to accomplish the method <NUM> including, but not limited to, any suitable components, assemblies, and approaches described herein.

The method <NUM> may include, at <NUM>, providing a light beam incident on a dynamic input coupling grating (ICG). The dynamic ICG may include a surface acoustic wave (SAW) modulator. The SAW modulator may include a layer of a piezoelectric material and a transducer. The SAW modulator may be coupled to a first lateral region of a waveguide.

The method <NUM> may further include, at <NUM>, modulating an intensity of the light beam in one or more time slots corresponding to one or more field angles. The intensity of the light beam in each time slot corresponds to an intensity of the image at a respective field angle. The method <NUM> may further include, at <NUM>, applying oscillating electric signals to the transducer at one or more frequencies in the plurality of time slots. Each respective frequency corresponds to a respective time slot. Therefore, a respective sound wave is created in the layer of the piezoelectric material with a respective spatial period in the respective time slot, such that the dynamic ICG diffracts a respective portion the light beam into the waveguide at a respective total internal reflection (TIR) angle in the respective time slot. The respective portion of the light beam propagates in the waveguide.

The method <NUM> may further include, at <NUM>, outcoupling, using a diffractive optical element (DOE) coupled to a second lateral region of the waveguide, each respective portion of the light beam propagating in the waveguide toward the eye at the respective field angle. Therefore, the light field at the one or more field angles is projected to the eye for viewing the image of the virtual content.

It should be appreciated that the specific acts illustrated in <FIG> provide a particular method of projecting a light field to an eye of a viewer for viewing an image of virtual content, according to some embodiments. Other sequences of acts may also be performed according to some embodiments. For example, some embodiments may perform the acts outlined above in a different order. Moreover, the individual acts illustrated in <FIG> may include multiple sub-acts that may be performed in various sequences as appropriate to the individual act. Furthermore, additional acts may be added or removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

<FIG> is a flowchart illustrating a method <NUM> of projecting an image light field to an eye of a viewer, according to some embodiments. Any suitable components, assemblies, and approaches can be used to accomplish the method <NUM> including, but not limited to, any suitable components, assemblies, and approaches described herein.

The method <NUM> includes, at <NUM>, modulating, by a controller, an intensity of a light beam in a sequence of time slots. Each time slot of the sequence of time slots corresponds to a respective field angle of the image light field. The intensity of the light beam in each time slot of the sequence of time slots corresponds to an intensity of the image light field at the respective field angle.

The method <NUM> includes, at <NUM>, propagating the light beam onto a dynamic input coupling grating (ICG). In many embodiments, the light beam is propagated to the dynamic ICG on a fixed optical path without any transverse scanning of the light beam or variation in the light beam transverse to the fixed optical path. In many embodiments, the light beam is propagated to a fixed point on the ICG. Accordingly, a light source used to generate and transmit the light beam onto the dynamic ICG can have a reduced size relative to light sources configured for two-dimensional scanning of the light beam or two-dimensional variation in the light beam transverse to the propagation direction of the light beam.

The method <NUM> includes, at <NUM>, controlling the dynamic ICG, by the controller, to diffract a respective portion of the light beam into a waveguide at a respective angle corresponding to the respective field angle for each time slot of the sequence of time slots. In many embodiments, the controller controls the modulation of the intensity of the light beam in conjunction with control of the dynamic ICG so as to effect two-dimensional scanning of the light beam to form the image light field projected to the eye of the viewer.

The method <NUM> includes, at <NUM>, directing each respective portion of the light beam out of the waveguide toward the eye at the respective field angle, thereby projecting the image light field to the eye of the viewer. Therefore, the image light field at the one or more field angles is projected to the eye of the viewer. The method <NUM> can be used to project the image light field to the eye of the viewer in any suitable application including, but not limited to, superimposing the image light field on an external image viewed by the eye of the viewer.

It should be appreciated that the specific acts illustrated in <FIG> provide a particular method of projecting an image light field to an eye of a viewer, according to some embodiments. Other sequences of acts may also be performed according to some embodiments. For example, some embodiments may perform the acts outlined above in a different order. Moreover, the individual acts illustrated in <FIG> may include multiple sub-acts that may be performed in various sequences as appropriate to the individual act. Furthermore, additional acts may be added or removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the purview of this application and scope of the appended claims.

In some embodiments, full RGB colors may be implemented using a stack of three waveguides (e.g., as illustrated in <FIG>), each waveguide configured for one of the RGB colors. The colors may be separated using a split pupil configuration or an in-line configuration, as described in <CIT>, the content of which is incorporated herein by reference.

Assuming a length of the dynamic grating to be D, using a Fourier transform lens with a focal length of F, a spot size at a transform plane may be expressed as d = <NUM>Fλ/D. With a FOV of ⊗<IMG>, an image size would be <NUM>F tan(⊗<IMG>/<NUM>). Therefore, the number of resolution spots across a scanned image may be expressed as, <MAT>.

Claim 1:
A method (<NUM>) of projecting an image light field to an eye (<NUM>) of a viewer, the method comprising:
modulating (<NUM>), by a controller, an intensity of a light beam (<NUM>) in a sequence of time slots, each time slot of the sequence of time slots corresponding to a respective field angle of the image light field, the intensity of the light beam (<NUM>) in each time slot of the sequence of time slots corresponding to an intensity of the image light field at the respective field angle;
propagating (<NUM>) the light beam (<NUM>) onto a dynamic input coupling grating, ICG, (<NUM>);
controlling (<NUM>) the dynamic ICG (<NUM>), by the controller, to diffract a respective portion of the light beam (<NUM>) into a waveguide (<NUM>) at a respective angle corresponding to the respective field angle for each time slot of the sequence of time slots; and
directing (<NUM>) each respective portion of the light beam (<NUM>) out of the waveguide (<NUM>) toward the eye (<NUM>) at the respective field angle, thereby projecting the image light field to the eye (<NUM>) of the viewer.