Patent Description:
An optical combiner comprising a waveguide and an outcoupling interface that folds a beam path is known from <CIT>.

Further details of polarization based beam folding lenses are known from <CIT>.

Further aspects of the invention are defined in the dependent claims.

The following describes example implementations of an optical combiner for use in a near-eye display system. The optical combiner uses a waveguide to convey light representative of display images from a micro-display or other display to a wearer's eye, and this conveyed display light can be combined at the optical combiner with scene light from the real-world scene of the near-eye display system to present combined display/scene imagery to a user. In at least one embodiment, the waveguide uses total internal reflection (TIR) to convey the display light from an incoupling interface facing the micro-display to an outcoupling interface that projects the combined display and scene light toward an expected position of the user's eye via an outcoupling interface. The outcoupling interface comprises a transparent pancake optic disposed between the proximal side of the waveguide and the expected position of the user's eye. This pancake lens employs a series of polarization-dependent layers, including a refractive beam-splitting convex lens, to fold the light path and reduce the dimensions of the near-eye optical system implementing the optical combiner. The refractive beam-splitting convex lens can be implemented as a plano-convex lens having one planar surface and an opposing convex surface or a bi-convex lens having two opposed convex surfaces.

Embodiments of the optical system including the refractive beam splitting convex lens typically produce lower optical aberration than conventional optical systems, which allows the user to resolve smaller display pixels and supports a larger eye box. The optical system also produces lower levels of spherical and chromatic aberration, astigmatism, and coma, and thus requires less computational effort to pre-process the display imagery to correct for such aberrations. The refractive portion of the refractive beam splitting convex lens balances the field curvature of the reflective portion, thereby reducing the overall field curvature produced by the optical system. Furthermore, the additional refractive power of the refractive beam splitting convex lens can be varied to enhance, optimize, or tune the optical performance of the optical system. As such, the outcoupling interface can be configured to provide any desired optical power, which in turn permits the use of a flat waveguide that provides no optical power, as well as providing for a large eye box due to the optical magnification occurring closer to the eye. Further, to mitigate world-side light leakage of reflected display light as a result of the optical path folding by the output interface, in at least some embodiment, the refractive beam-splitting convex lens is implemented using a light-absorbing material disposed on a world-facing side so as to provide an array or other pattern of partial mirrors, and thus provide for substantial absorption of light incident on the world-facing side of the lens, and thus reducing the amount of leaked display light.

<FIG> illustrates an example near-eye display system <NUM> employing an optical combiner <NUM> in accordance with at least one embodiment. The system <NUM> is implemented in an eyeglass form factor having an eyeglass frame <NUM> with eyeglass lenses <NUM>, <NUM> for a wearer's right eye and left eye, respectively. In the depicted embodiment, the optical combiner <NUM> is separate from the eyeglass lenses and instead overlies one of the eyeglass lenses (eyeglass lens <NUM> in this instance) such that an out-coupling interface (described in greater detail below with reference to <FIG>) of the optical combiner <NUM> faces the expected position of the corresponding eye of the wearer. The optical combiner <NUM> is mounted to the eyeglass frame <NUM> via a waveguide mount housing <NUM>, which also serves to house some or all of the electronic components (not illustrated in <FIG>) of the near-eye display system <NUM>, such as a display that generates augmented reality (AR) or (VR) imagery for display to the wearer via the optical combiner <NUM>, an incoupling optic to direct light from the display to an incoupling interface of the optical combiner <NUM>, one or more processors, wireless interfaces, batteries or other power sources, and the like. A number of these components are described in greater detail below.

<FIG> illustrates another example near-eye display system <NUM> employing an optical combiner <NUM> in accordance with at least one embodiment. As with the system <NUM> of <FIG>, the system <NUM> employs an eyeglass form factor with an eyeglass frame <NUM> having eyeglass lenses <NUM>, <NUM>. However, in contrast with the system <NUM>, the system <NUM> implements the optical combiner <NUM> using the eyeglass lens <NUM>. That is, the optical combiner <NUM> is integrated within the eyeglass lens <NUM>, and thus allowing the near-eye display system <NUM> to have a more traditional eyeglass appearance. In this implementation, a display housing (omitted from <FIG> for clarity of illustration) on, or within, the eyeglass frame <NUM> at the distal periphery of the eyeglass lens <NUM> contains a micro-display or other display to emit display light representative of AR or VR imagery and incoupling optic to direct the emitted display light to an incoupling interface of the optical combiner <NUM> in the lens <NUM>, whereupon the display light is propagated through the optical combiner <NUM>/eyeglass lens <NUM> toward an outcoupling interface <NUM> that is located in the eyeglass lens <NUM>/optical combiner <NUM> so as to be aligned with an expected position (or expected range of positions) of a corresponding eye of the wearer. In some embodiments, the eyeglass lens <NUM> likewise implements a corresponding optical combiner and outcoupling interface, and the system <NUM> employs corresponding display componentry in the same manner to provide for the display of AR or VR imagery to the other eye of the wearer as well.

The optical combiner <NUM> of system <NUM> of <FIG> and the optical combiner <NUM> of system <NUM> of <FIG> each operates to convey display light from a display to an eye of the user via one or more instances of total internal reflection (TIR) of the display light within the body of a waveguide of the optical combiner as the display light traverses from one end of the waveguide proximate to the display to the opposing end of the waveguide facing an eye of the wearer. The conveyed display light is then combined with scene light from the world-facing side of the waveguide for viewing by a user as a combination of the rendered or captured imagery represented by the display light and the real-world scene, or environment, viewed by the user through the lens of the system.

<FIG> illustrates a near-eye display system <NUM> in diagrammatic form, with the near-eye display system <NUM> representing, for example, either of the near-eye display systems <NUM> and <NUM> of <FIG>, respectively. The near-eye display system <NUM> includes an optical combiner <NUM>, an image source subsystem <NUM>, and a display panel <NUM>. The display panel <NUM> can include, for example, a micro-display (e.g., a display typically measuring under <NUM> diagonally, and in many cases, under <NUM> diagonally). Examples of the display panel <NUM> can include, for example, a liquid crystal display (LCD) panel, a light-emitting diode (LED) display, an organic LED (OLED) panel, a liquid crystal on silicon (LCoS) display, and the like. The image source subsystem <NUM> includes a computing system having one or more graphics processing units (GPUs) or other processors that operate to provide a sequence of display images <NUM> for display at the display panel <NUM>. Each display image <NUM> can represent any of a variety of visual content, such as symbols (e.g., navigational directional arrows), icons, text, captured or rendered imagery, video, and the like.

The optical combiner <NUM> includes an incoupling interface <NUM>, a waveguide prism <NUM>, and an outcoupling interface <NUM>. Display light <NUM> emitted by the display panel <NUM> when displaying the display image <NUM> is transmitted into the waveguide prism <NUM> via the incoupling interface <NUM>, whereupon the display light <NUM> is transmitted along the waveguide prism <NUM> via one or more TIRs to an outcoupling surface <NUM> that directs the display light <NUM> to the outcoupling interface <NUM>. In an embodiment, a linear polarizing (LP) layer <NUM> is disposed at the outcoupling surface <NUM> of the waveguide prism. The outcoupling interface <NUM> is a pancake optic with a plurality of polarization-dependent layers, and thus, through manipulation of the polarization state of the display light <NUM> via various polarization-dependent layers of the incoupling interface <NUM>, the waveguide prism <NUM>, and the outcoupling interface <NUM>, the optical path of the display light <NUM> is "folded" as it passes through the outcoupling interface <NUM> toward a viewer's eye <NUM>, thereby permitting a longer effective focal length relative to the thickness of the incoupling interface <NUM>.

Moreover, as described herein, in at least one embodiment, the outcoupling interface <NUM> includes a refractive beam-splitting convex lens (e.g., a convex partial mirror)(not shown in <FIG>) that serves both as a folding element to fold the optical path of the display light <NUM>, as well as a focusing element to introduce an optical power into the display light <NUM> as it traverses the outcoupling interface <NUM>. Concurrently, scene light <NUM> from a real-world scene <NUM> and incident on the world-facing side <NUM> of the waveguide prism <NUM> is transmitted through the waveguide prism <NUM> to the eye-facing side <NUM> and then through the outcoupling interface <NUM> toward the eye <NUM>. In some embodiments, because the scene light <NUM> does not have the particular polarity state that the waveguide prism <NUM> imparts on the display light <NUM>, the scene light <NUM> is not magnified, nor is its optical path extended via folding by the outcoupling interface <NUM> as it passes through the optical combiner <NUM> and thus, reaches the user's eye <NUM> relatively unaltered. That is, the scene light <NUM> experiences little to no distortion as it passes through the optical combiner <NUM>.

<FIG> illustrates a cross-section view of an implementation of the optical combiner <NUM> according to the claimed invention at, for example, line A-A of the optical combiner <NUM> of <FIG>. In the illustrated embodiment, display light <NUM> emitted by a display <NUM> is directed to incoupling interface <NUM> positioned at a distal end of waveguide prism <NUM>, wherein the incoupling interface <NUM> has disposed therein an LP layer <NUM> that serves to polarize the incoming display light <NUM> to a particular linear polarization state (e.g., a s-polarized state). The display light <NUM> is then conveyed to a proximal end of the waveguide prism <NUM> via three (or more) total internal reflections, such as the three TIRs illustrated in <FIG>. The outcoupling surface <NUM> of waveguide prism <NUM> is oriented at a non-zero angle relative to the world-facing surface <NUM> and the parallel eye-facing surface <NUM> of the waveguide prism <NUM> so as to reflect the display light <NUM> out of the waveguide prism <NUM> toward the outcoupling interface <NUM> disposed parallel to the eye-facing surface <NUM> at the proximal end of the waveguide prism <NUM>. In at least one embodiment, a polarized beam splitter (PBS) layer <NUM> is disposed at the outcoupling surface <NUM>. In an embodiment, the optical combiner <NUM> further includes a compensation prism <NUM> having a substantially similar index of refraction as the material of the waveguide prism <NUM> so that the optical combiner <NUM> effectively operates as a transparent "window" through which a user can view the real-world scene, thus facilitating the transmittance of scene light from the world-facing side <NUM> to a pupil <NUM> of a user's eye without introduction of aberrations, magnification, or other optical effects on the scene light.

As illustrated by expanded view <NUM>, the outcoupling interface <NUM> includes a pancake lens or similar optical element separated from the eye-facing surface <NUM> of the waveguide prism <NUM> via an air gap <NUM> or a low-index coating/adhesive. The outcoupling interface <NUM> has a plurality of layers or stages of polarization-dependent films or structures that operate to both fold the optical path of the light incident on the world-facing side of the outcoupling interface <NUM>, as well as to provide optical power to the display light <NUM> while imparting little or no optical power to the real-world scene light transmitted through the waveguide prism <NUM> and compensation prism <NUM>. In some embodiments, these layers include a first quarter-wave plate (QWP) layer <NUM> disposed opposite the air gap <NUM> from the eye-facing side <NUM> of the waveguide prism <NUM>, a refractive beam-splitting convex lens <NUM> implemented as, for example, a convex partially reflective mirror (e.g., a <NUM>/<NUM> mirror, an <NUM>/<NUM> mirror, a <NUM>/<NUM> mirror), a second QWP layer <NUM> disposed at the eye-facing side of a transparent sub-layer layer <NUM>, an advanced polarizing film (APF) layer <NUM>, and an LP layer <NUM>. In some embodiments, the refractive beam splitting convex lens <NUM> is implemented as a bi-convex lens having two opposed convex surfaces. To illustrate, the refractive beam-splitting convex lens <NUM> can be composed of two sub-layers <NUM>, <NUM> formed of glass or plastic, with sub-layer <NUM> having a convex profile on the surface facing the pupil <NUM> and the sub-layer <NUM> having a conforming, complementary concave profile on the surface facing the world, and with a half-silvered or other partial mirror layer <NUM> disposed therebetween. The two sub-layers <NUM>, <NUM>, in some embodiments, have different refractive indexes.

<FIG> illustrates an example optical path of a light ray <NUM> of the display light <NUM> as it travels within and out of the optical combiner <NUM> of <FIG>. As illustrated, light ray <NUM> interacts with the LP layer <NUM>, which in turn causes the light ray <NUM> to have a linear polarization state (e.g., x-linear polarized for purposes of this illustration), and the light ray <NUM> is conveyed through the waveguide prism <NUM> via the three illustrated TIRs <NUM>. Upon encountering the outcoupling surface <NUM>, the linear-polarized light ray <NUM> is reflected toward the eye-facing surface <NUM> and into the outcoupling interface <NUM>.

<FIG> illustrates the optical path of the light ray <NUM> as it traverses the outcoupling interface <NUM> of <FIG>. For purposes of illustration, an exploded cross-section view <NUM> of the outcoupling interface <NUM> with each layer separated from the adjacent layer(s) is depicted. For purposes of this example, the light ray <NUM> enters the outcoupling interface <NUM> from the waveguide prism <NUM> in an x-linear polarization state. The QWP layer <NUM> converts the linearly polarized light ray <NUM> into a light ray <NUM>-<NUM> having a first circular polarization. For example, the QWP layer <NUM> can convert the light ray <NUM> from a linear polarization in the y-direction to the light ray <NUM>-<NUM> that is right-hand circularly polarized (RCP). The refractive beam-splitting convex lens <NUM> transmits and refracts a portion of the circularly polarized light ray <NUM>-<NUM> as light ray <NUM>-<NUM>, which is transmitted to the QWP layer <NUM>, which converts the circularly polarized light ray <NUM>-<NUM> to a linearly polarized light ray <NUM>-<NUM>. For example, the QWP layer <NUM> can convert the RCP light ray <NUM>-<NUM> into a light ray <NUM>-<NUM> that is linearly polarized in the x-direction. In this example, the APF layer <NUM> (e.g., a polarization-dependent beam splitter) reflects x-linear polarized light, and thus the light ray <NUM>-<NUM> is reflected by the AFP layer <NUM> as light ray <NUM>-<NUM> and converted to a circularly polarized light ray <NUM>-<NUM> as it passes through the QWP layer <NUM>. For example, the light ray <NUM>-<NUM> can be converted to RCP. The light ray <NUM>-<NUM> is reflected by the refractive beam-splitting convex lens <NUM> as light ray <NUM>-<NUM>, with this reflection introducing optical power as well as reversing or changing the circular polarization state of the light ray <NUM>-<NUM>, e.g., reflection converts the light ray <NUM>-<NUM> to a left-hand circularly polarized (LCP) light ray <NUM>-<NUM>. The QWP layer <NUM> converts the circularly polarized light ray <NUM>-<NUM> into a linearly polarized light ray <NUM>-<NUM>. For example, the LCP state of the light ray <NUM>-<NUM> is converted into linear polarization of the light ray <NUM>-<NUM> in the y-direction. The AFP layer <NUM> and the LP layer <NUM> then transmit the resulting linearly polarized light ray <NUM>-<NUM> toward the user's eye.

<FIG> illustrates a cross-section view <NUM> of an implementation of the optical combiner <NUM> (referred to herein as "optical combiner <NUM>") at, for example, line A-A of the optical combiner <NUM> of <FIG>. In the illustrated embodiment, display light <NUM> emitted by a display <NUM> is directed to an incoupling interface of a distal end of a waveguide prism <NUM> via an incoupling interface (omitted from <FIG> for purposes of clarity), wherein the incoupling interface has disposed thereon a linear polarizing (LP) layer <NUM> that serves to polarize the incoming display light <NUM> to a particular linear polarization state. The display light <NUM> then is conveyed to a proximal end of the waveguide prism <NUM> via two total internal reflections. An outcoupling surface <NUM> of waveguide prism <NUM>, which is disposed at a non-zero angle (e.g., <NUM> degrees) relative to the world-facing surface <NUM> and the parallel eye-facing surface <NUM> of the waveguide prism <NUM> so as to reflect the display light <NUM> out of the waveguide prism <NUM> toward an outcoupling interface <NUM> disposed parallel to the eye-facing surface <NUM> at the proximal end of the waveguide prism <NUM>. In at least one embodiment, both an APF layer <NUM> and an LP layer <NUM> are disposed at the outcoupling surface <NUM>. The optical combiner <NUM> further can include a compensation prism <NUM> having a substantially similar index as the material of the waveguide prism <NUM>.

The outcoupling interface <NUM> includes a pancake lens or similar optical element separated from the eye-facing surface <NUM> of the waveguide prism <NUM> and has one or more layers or stages of polarization-dependent films or structures that operate to both fold the optical path of the light incident on the world-facing side of the outcoupling interface, including a refractive beam-splitting convex lens <NUM> to provide optical power to the display light <NUM> while imparting little or no optical power to the real-world scene light transmitted through the waveguide prism <NUM> and compensation prism <NUM>.

<FIG> illustrates a cross-section view <NUM> of an implementation of the optical combiner <NUM> (referred to herein as "optical combiner <NUM>") at, for example, line A-A of the optical combiner <NUM> of <FIG>. As with the other implementations described above, the optical combiner <NUM> includes an outcoupling interface <NUM> having a pancake lens or similar optical element with a plurality of layers or stages of polarization-dependent films or structures that operate to both fold the optical path of the light incident on the world-facing side of the outcoupling interface <NUM>. The outcoupling interface <NUM> includes a refractive beam-splitting convex lens <NUM>, as similarly described above, as well as to provide optical power to display light <NUM> conveyed from a display <NUM> at the distal end of a waveguide prism <NUM> using a single TIR while imparting little or no optical power to the real-world scene light transmitted through the waveguide prism <NUM> and compensation prism <NUM>.

<FIG> illustrates a cross-section view <NUM> of an implementation of the optical combiner <NUM> (referred to herein as "optical combiner <NUM>") at, for example, line A-A of the optical combiner <NUM> of <FIG>. As with the other implementations described above, the optical combiner <NUM> includes an outcoupling interface <NUM> having a pancake lens or similar optical element with a plurality of layers or stages of polarization-dependent films or structures that operate to both fold the optical path of the light incident on the world-facing side of the outcoupling interface <NUM>, including a refractive beam-splitting convex lens <NUM> as similarly described above, as well as to provide optical power to display light <NUM> conveyed from a display <NUM> at the distal end of a curved waveguide prism <NUM> using multiple TIRs, and with the curved waveguide prism <NUM> also imparting optical power to, or implementing a prescription for, the real-world scene light transmitted through the non-planar waveguide prism <NUM>.

<FIG> illustrates a cross-section view <NUM> of an optical combiner <NUM> having an outcoupling interface <NUM> with a refractive beam-splitting convex lens <NUM>, as represented in the embodiments described above, wherein some of the display light <NUM> from display <NUM> passing from the waveguide prism <NUM> into the outcoupling interface <NUM> is reflected back into, and through the waveguide prism <NUM>. This results in the emission of display light from the optical combiner <NUM> as world-side light leakage <NUM> that may be seen by observers looking at the user wearing a near-eye display system as the display imagery represented by the display light <NUM> superimposed over the user's eyes. <FIG> illustrates an example near-eye display system <NUM>, including an optical combiner such as optical combiner <NUM>, exhibiting this distracting world-side light leakage <NUM>.

<FIG> illustrates a cross-section view <NUM> of an implementation of an optical combiner <NUM>, to reduce the amount of world-side light leakage. The optical combiner <NUM> includes an outcoupling interface <NUM> with a refractive beam-splitting convex lens <NUM> as similarly described above, the world-facing side <NUM> of the refractive beam-splitting convex lens <NUM> partially coated with a light-absorbing material <NUM> (e.g., a black material) in a pattern that provides apertures <NUM> between portions of the light-absorbing material <NUM>, thus forming an array of light-absorbing features <NUM> in the refractive beam-splitting convex lens <NUM>. As such, any light incident in a non-aperture region of the eye-facing side of the lens <NUM> will be substantially absorbed by the light-absorbing material <NUM>, and thus the amount of world-side light leakage exhibited by the optical combiner <NUM> is significantly reduced.

<FIG> illustrates an example of an array of partial mirrors on a refractive beam-splitting convex lens <NUM>, such as outcoupling interface <NUM> of <FIG>, having an array of light-absorbing features <NUM> formed from circular pieces of light-absorbing material <NUM> positioned on the world-facing side of the refractive beam-splitting convex lens <NUM>. Although an array of circular light-absorbing features <NUM> is illustrated, other patterns can be implemented to provide for an array of light-absorbing features <NUM> forming apertures with substantially uniform illumination across the lens <NUM>, such as a checkerboard aperture pattern, a striped aperture pattern, a concentric aperture pattern, and the like.

Claim 1:
An optical combiner comprising:
a waveguide prism (<NUM>) configured to convey display light, from a display panel, from a proximal end of the waveguide prism to a distal end of the waveguide prism via total internal reflection; and
an outcoupling interface (<NUM>) disposed at an eye-facing surface (<NUM>) of the waveguide prism at the distal end of the waveguide prism, the outcoupling interface having a plurality of polarization-dependent layers including a refractive beam-splitting convex lens (<NUM>),
characterized in that
the plurality of polarization-dependent layers comprises:
a first quarter-wave plate -QWP- layer (<NUM>) disposed between the waveguide prism and the refractive beam-splitting convex lens;
a second QWP layer (<NUM>) disposed at an eye-facing surface of the refractive beam-splitting convex lens;
an advanced polarizing film -APF- layer (<NUM>) disposed on the second QWP layer; and
a linear polarizing layer (<NUM>) disposed on the APF layer.