Patent Description:
Head mounted displays (HMDs) are devices worn on or about the head for the user to see information. The information seen can be either overlaid upon the images being observed in the real world (sometimes referred to as augmented reality), information presented that excludes the images of the real word (sometimes referred to as virtual reality), or combinations of these (sometimes referred to as virtual/augmented, or mixed reality).

Typically, the information-bearing images presented in today's HMDs are set to a single focus point. The most common focus point is infinity, or "far distance. " This allows the user to see the information images in focus simultaneously with distant real-world objects in the case of augmented reality applications and see only the information at a far distance in the case of virtual reality.

When the information-bearing images are presented to the user in the HMD at infinite focus, several problems arise. If the information-bearing images (also called virtual images) are set to far distance focus when using augmented reality, a user may wish to shift their gaze to an object that is nearer, for example, a hand-held item, which then causes the virtual images to appear out of focus. This could happen if the user looks at a hand-held tablet at normal reading distance. If the user's eyes can accommodate, they will change focus to bring the tablet into focus, but since the virtual images are set to far distance focus the virtual image will appear out of focus while the tablet image is in focus. In this case, it would be desirable if the virtual images could be refocused to the same distance as the tablet so that the virtual images and the tablet are in focus simultaneously.

Similar problems occur when displaying an information-bearing image with an HMD to view virtual reality. In order to create a realistic three-dimensional virtual image, the focus point of the virtual image should be varied so that the human eye changes its focus dynamically, thereby convincing the human brain that the image is nearer or farther away. If the information-bearing image remains at far distance focus only, and other means of simulating varying distance are used without varying focus distance, the effect is not as realistic as if the focus distance was also changed. It would be desirable if the virtual images could be refocused to varying distances dynamically to enhance the virtual reality experience. "<NPL>, discloses an augmented reality (AR) system involving the electrically tunable location of a projected image implemented using a liquid-crystal (LC) lens. <CIT> discloses an apparatus for a head mounted display which includes light bending optics to deliver display light from an image source to a near-to-eye emission surface for emitting the display light to an eye of a user within an eyebox. "<NPL>, discloses a polarized liquid crystal (LC) lens composed of a LC layers as a polarization switch and a liquid crystal and polymer composites lens (LCPC lens) with electrically switching (ES) mode and optically rewritten (ORW) mode. <CIT> discloses optical elements such as a vari-focal lens element, a vari-focal diffractive optical element and a variable declination prism usable as spectacle lens elements. <CIT> discloses an adjustable focusing electrically controllable electroactive lens.

Conventional lenses can be used to vary the focus of information-bearing images. But conventional lenses are constructed from glass and plastic, which are relatively heavy. In addition, conventional lenses generally must be moved with electro-mechanical actuators, such as electrical motors, to change focus. Actuators add more weight, bulk, and complexity. They may also consume relatively high amounts of electrical power, which could increase the weight, bulk, and cost of the power source.

An electro-active lens, such as a liquid-crystal lens, disposed between the eye and the image to be observed can also be used to vary the focus of the eye. Because the eye translates up and down as gaze changes, however, the electro-active lens should be much larger than the pupil of the eye. For example, a <NUM> pupil typically requires an optic that is approximately <NUM> wide to provide sufficient coverage in front of the eye to allow the typical gaze angle changes to occur. Because of limitations of optical path difference (OPD) changes that can be achieved with an electro-active lens, the electro-active lens is typically subject to optical compromises, such as layer stacking and phase wrapping, to achieve the required optical power at the desired optical sizes. These optical compromises usually increase power consumption and require higher speed switching, both of which translate to higher size, weight, and cost.

According to a first aspect disclosed herein, there is provided head-mounted display apparatus comprising: a display to emit light; a beam splitter, in optical communication with the display, to transmit a portion of the light emitted by the display; a transparent convex surface; a concave reflective surface, in optical communication with the beam splitter, to receive the portion of the light transmitted by the beam splitter and to reflect an image of the display to a wearer of the head-mounted display apparatus via the beam splitter; a liquid crystal layer sealed between the transparent convex surface and the concave reflective surface; and a first electrode layer, disposed on the transparent convex surface, and a second electrode layer, disposed on the concave reflective surface, to actuate the liquid crystal layer.

According to a second aspect disclosed herein, there is provided a method of displaying information on a head-mounted display apparatus comprising a liquid crystal layer sealed between a transparent convex surface and a concave reflective surface, the method comprising: displaying an information-bearing image to a wearer of the head-mounted display apparatus, via the head-mounted display apparatus, at a focus selected to match accommodation of the wearer, wherein displaying the information-bearing image comprises: generating the information-bearing image at a display of the head-mounted display apparatus; transmitting a portion of the information-bearing image from the display through a beam splitter, the transparent convex surface and the liquid crystal layer to the concave reflective surface; and reflecting the information-bearing image to the wearer via the concave reflective surface, the liquid crystal layer, the transparent convex surface and the beam splitter.

Embodiments of the present technology include a compact, efficient optical system that can work in tandem with an HMD to change the focus of the virtual images. In some implementations, this optical system is light weight, provides sufficient optical power to compensate for the accommodation range across a wide range of the population (e.g., about <NUM> Diopter to about <NUM> Diopters), and consumes very little power. It can also be implemented without any moving parts.

For instance, the present technology may be implemented as an HMD apparatus that includes a display, beam splitter in optical communication with the display, concave reflective surface in optical communication with the beam splitter, and a tunable lens disposed between the beam splitter and the concave reflective surface. The concave reflective surface could also be augmented with another focusing component, such as a Graded Refractive Index (GRIN) lens or Fresnel structure. In operation, the beam splitter transmits light emitted by the display. (The beam splitter may also transmit ambient light to a wearer of the HMD apparatus). The concave reflective surface receives the light emitted by the display and transmitted by the beam splitter and reflects an image of the display to the wearer via the beam splitter. And the tunable lens varies a focus of the image of the display reflected to the wearer.

In some cases, the display emits light polarized along an axis parallel to an optical axis of the liquid crystal layer, which may include nematic or bi-stable liquid crystal. Because the display emits polarized light, the liquid crystal layer may be implemented as just a single layer of nematic liquid crystal layer instead of the two nematic liquid crystal layers required by conventional devices. This reduces the device's size, weight, power consumption, cost, and complexity.

A head-mounted display apparatus according to the invention is specified in appended claim <NUM>. According to the claimed invention, the liquid crystal layer is disposed between the convex surface and the concave reflective surface. The concave reflective surface may form at least a portion of a ground plane in electrical communication with the liquid crystal layer. The HMD apparatus may also include a plurality of electrodes, disposed between the liquid crystal layer and the convex surface, to apply a voltage gradient to the liquid crystal layer so as to vary the variable refractive index of the liquid crystal layer.

Also described herein, not according to the claimed invention, is a tunable lens which comprises a liquid lens having a deformable curved membrane disposed in optical communication with the beam splitter. In these cases, the flexible membrane can define the concave reflective surface that changes shape as fluid is pumped into and out of a cavity defined at least in part of by the concave reflective surface.

The head-mounted display apparatus can include a controller, operably coupled to the tunable lens, to actuate the tunable lens in response to an input from the wearer. In addition, the controller can actuate the tunable lens in response to an image on the display.

The present invention may also be implemented as a method of displaying information on an HMD as specified in appended claim <NUM>. According to the claimed invention, the HMD displays an information-bearing image to a wearer of the HMD at a focus selected to match accommodation of the wearer. The HMD may generate the information-bearing image at a display, transmit the information-bearing image through an electro-active material disposed between a beam splitter and a concave reflective surface, and reflect the information-bearing image to the wearer via the concave reflective surface and the beam splitter. The HMD may actuate the electro-active material so as to change the focus of the information-bearing image. In some cases, the HMD actuates the electro-active material in response to a command from the wearer and/or in response to information in the information-bearing image. The HMD may also actuate the electro-active material in response to a signal from an accommodation sensor, which may measure inter-pupillary distance to determine the converging point of gaze of the eyes, sense the wavefront of incident light, measure pupil diameter and light level, etc..

Other embodiments of the present technology include a head-mounted display apparatus comprising a display, a beam splitter in optical communication with the display, a concave reflective surface in optical communication with the beam splitter, and a liquid crystal layer disposed between the convex surface and the concave reflective surface. In operation, the display emits polarized light. The beam splitter transmits a portion of the polarized light emitted by the display. The concave reflective surface receives the portion of the polarized light transmitted by the beam splitter and reflects an image of the display to a wearer of the head-mounted display apparatus via the beam splitter. And the liquid crystal layer varies a focus of the image of the display reflected to the wearer.

Also described herein is a head-mounted display apparatus comprising a display, a beam splitter in optical communication with the display, a liquid lens in optical communication with the beam splitter, and a mirror in optical communication with the liquid lens and the beam splitter. In operation, the beam splitter transmits light emitted by the display. The liquid lens provides a variable optical power. And the mirror receives the light emitted by the display and transmitted by the beam splitter via the liquid lens and reflects an image of the display to a wearer of the head-mounted display apparatus via the liquid lens.

It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the subject matter disclosed herein In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein should be accorded a meaning most consistent with the particular concepts disclosed herein.

The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and/or structurally similar elements).

A birdbath with a dynamic focusing element, such as an electro-active lens concave mirror, allows dynamic change of focus of the virtual image for compensating for accommodation or enhancing the illusion of depth. It also provides for the ability to compensate for refractive errors of the user, eliminating the need for the user to wear corrective lenses, such as glasses, between an HMD device and the eye when using the HMD. Such a birdbath system allows the dynamic changing of focus of the virtual image displayed by the HMD with low power consumption and no moving (mechanical) parts.

Applications for inventive HMD devices include, but are not limited to: map guidance while driving without having to look away from the road, performing surgery while being provided vital signs data within the same field of view, utilizing repair and service manuals with virtual instructive diagrams overlaid upon the actual object being repaired or serviced, improving situational awareness of military and law enforcement personnel by allowing additional tactical information being provided to them while simultaneously keeping "eyes on target," and more.

<FIG> shows a conventional "birdbath" optic <NUM> for use with a head-mounted display (HMD). It includes a mini display or other display source <NUM>, an optic block <NUM>, a beam splitter <NUM>, and a concave mirror <NUM>. An information-bearing image from the mini display or other display source <NUM> enters into an optic block <NUM> (in this case it is solid but could be air), and encounters a beam splitter <NUM>. The beam splitter <NUM> directs a portion of the light away from the eye and allows a portion of the light to continue its journey to a mirror <NUM>. The mirror <NUM> in this example is a curved concave mirror that reflects an incident light ray <NUM> at an angle, causing the light ray <NUM> to converge to a focus. The light ray <NUM> encounters beam splitter <NUM> again, which reflects the converging light rays <NUM> toward the eye <NUM>.

Because the mirror <NUM> is concave, the wavefront approaching the eye is also concave, or "pre-focused," allowing the optics of the eye (i.e., the cornea and crystalline lens), to focus an image on the retina with the eye fairly close to the device. If the mirror <NUM> was flat, a corrective optic would be required in front of the eye to assist the eye to bring the image into focus, but the curvature of mirror <NUM> eliminates the need for a corrective optic. However, the eye should be at a predetermined distance from the device in order for the image to come in to focus without accommodation. Typical predetermined distances are <NUM>-<NUM>. At these distances, people feel comfortable with the device in front of their eyes.

<FIG> shows a birdbath optic <NUM> that is similar to the device <NUM> in <FIG>, except that it includes a concave mirror <NUM> with a shorter radius of curvature than the concave mirror <NUM> shown in <FIG>. The mirror's shorter radius of curvature results in the eye <NUM> having to be closer to the device <NUM> in order for the image to come into focus without accommodation or corrective optics. That is, <FIG> shows that altering the curvature of the concave mirror <NUM> in a birdbath <NUM> alters the focus of the virtual images provided by the birdbath <NUM> by changing the convergence angle of light rays <NUM> and <NUM>.

A dynamic focus birdbath includes a tunable lens, such as an electro-active lens or liquid lens, combined with a mirror and integrated inside of the birdbath system. Placing a lens with an adjustable focal length between the display and concave mirror in the birdbath (e.g., over mirror <NUM> in <FIG> or mirror <NUM> in <FIG>) makes it possible to vary the power of the concave mirror and the focus of the virtual image without moving parts. This brings at least the following improvements to the overall system.

First, by combining the mirror with a tunable lens, the focus of the information-bearing image that the user sees through the dynamic focus birdbath optic may be adjusted without affecting the focus of the real world image that the user also sees through the dynamic focus birdbath optic. This can be very helpful for people with accommodation remaining in their eyes.

Second, because the tunable lens works with the mirror such that the light passes through the lens on the way toward the mirror, and then again after it has been reflected, the lens retards the light twice, effectively doubling the its optical power range. This reduces power consumption, device complexity, and light scattering.

Third, when implemented as a liquid crystal optic combined with a concave mirror inside of the birdbath optic and used with a display engine that emits a polarized output, only a single layer of nematic liquid crystal or other polarization sensitive material is needed, reducing complexity, cost, power consumption, and light loss. Conversely, if the dynamic compensating liquid crystal optics were arranged in a single-pass geometry, each compensating element might require two layers of liquid crystal (one for each polarization state) because the incident ambient light is not necessarily polarized. A device with two separate compensating lenses has up to four liquid crystal layers, with each compensating lens having two orthogonally aligned layers of nematic liquid crystal. Each compensating lens has two orthogonally aligned liquid crystal layers because nematic liquid crystal can alter one polarization state at a time. To act on unpolarized light, a beam splitter or pair of polarizers in the compensating lens resolves the unpolarized light into orthogonal polarization states that can be modulated by the nematic liquid crystal layers. This ensures both that light in both polarization states is altered simultaneously. In contrast, a birdbath optic with an electro-active concave mirror could be implemented with a single liquid crystal layer that focuses polarized light coming from the display engine and is not required to focus unpolarized light coming from the real world.

<FIG> shows in cross section an exemplary construction of a variable-focus birdbath optic <NUM> with a liquid crystal based, dynamically adjustable concave mirror <NUM>. Like the birdbaths shown in <FIG> and <FIG>, the birdbath optic <NUM> in <FIG> includes a display <NUM> and an optic block <NUM> that defines a beam splitter <NUM> and a transparent convex surface <NUM>. Unlike the conventional birdbath optics, however, the birdbath optic <NUM> includes several layers sandwiched between the transparent convex surface <NUM> and a concave reflective layer <NUM>. Together, these layers form the liquid crystal based, dynamically adjustable concave mirror <NUM>.

As shown in <FIG>, the transparent convex surface <NUM> is coated with a layer <NUM> of (substantially) transparent electrically conductive material, such as a <NUM> thick layer of indium tin oxide (ITO). Layer <NUM> is an alignment layer, such as rubbed polyimide. Layer <NUM> is a layer of liquid crystal material, for example, a <NUM>-micron thick layer of Merck MLC-<NUM>. Layer <NUM> is another alignment layer, which could also be rubbed polyimide.

Layer <NUM> includes electrically conductive and insulating materials patterned to form electrodes for actuating the liquid crystal material. For example, layer <NUM> may be patterned into a series of concentric conductive rings, e.g., as described in greater detail below with respect to <FIG>. Layer <NUM> could also include electrodes patterned in different shapes, including orthogonally positioned and stacked linear electrodes that individually produce cylinder optical power and in combination produce spherical power. Layer <NUM> could also be patterned to form individually addressable pixelated areas (pixels), each of which acts individually to produce piston-only retardation. These pixels can be actuated collectively to produce spherical, cylindrical, or arbitrary wavefront shapes.

The concave reflective layer <NUM> forms a reflective surface and can be made of or include aluminum or another suitable reflective material. Surface <NUM> is an end cap that traps layers <NUM> through <NUM> between surfaces <NUM> and <NUM>. At the periphery of each of the layers described above is a sealing material (not shown), such as Norland <NUM> or another adhesive, to prevent the liquid crystal from escaping or leaking out.

Each layer sandwiched between the transparent convex surface <NUM> and the concave reflective layer <NUM> can have a uniform thickness or a thickness that varies with distance from the optical axis of the liquid crystal based, dynamically adjustable concave mirror <NUM>. In other words, the transparent convex surface <NUM> and the concave reflective layer <NUM> can have the same radius of curvature or different radii of curvature. In a dynamically adjustable concave mirror <NUM> with a single electrode configured for a positive optical power, for example, the liquid crystal layer <NUM> may be thicker at the center of the dynamically adjustable concave mirror <NUM> and thinner at the edges of the dynamically adjustable concave mirror <NUM>. The liquid crystal layer <NUM> may include nematic, cholesteric, or other bi-stable liquid crystal material. In this case, the concave reflective layer <NUM> has a smaller radius of curvature than the transparent convex surface <NUM>. For a lens with negative optical power the reverse would be the case, i.e., the liquid crystal layer <NUM> is thinner in the center and thicker at the edges.

In a dynamically adjustable concave mirror <NUM> with multiple electrodes, the liquid crystal layer <NUM> may be thicker at the center of the dynamically adjustable concave mirror <NUM> and thinner at the edges of the dynamically adjustable concave mirror <NUM> to bias the optical power to having more plus power. For example, instead of being capable of adjusting from zero to <NUM> Diopters in infinite steps, it may then be designed to adjust from zero to one diopter in one discrete jump, then adjust from <NUM> to <NUM> Diopters in infinite steps. In this case, the concave reflective layer <NUM> has a smaller radius of curvature than the transparent convex surface <NUM>. Reversal of this configuration, i.e., with an electro-active element that is thinner in the center than the edges, would bias the lens toward having more negative optical power.

The radii of curvature of the concave reflective layer <NUM> and the transparent convex surface <NUM> also depend on the desired focal length of the dynamically adjustable concave mirror <NUM>. As well understood in the art of optics, the focal length of a concave mirror is given by: <MAT> where s<NUM> is the object distance from the mirror, s<NUM> is the image distance from the mirror, R is the mirror's radius of curvature, and f is the mirror's focal length. Generally speaking, the radii of curvature of the concave reflective layer <NUM> and the transparent convex surface <NUM> may be selected according to this formula such that the object distance can be anywhere from <NUM> to infinity and the image distance can be anywhere from <NUM> to infinity. When adding a dynamic liquid crystal lens to a curved mirror, the curved mirror's new, adjusted focal length can be calculated by adding or subtracting to the resultant focal length the influence of the liquid crystal's effect upon the light rays travel toward and away from the mirror. For example, if the fixed mirror produces <NUM> Diopters of optical power (i.e., a focal length of <NUM>), and the liquid crystal lens adds two Diopters of plus optical power (i.e., a focal length of <NUM>), the new focal length is <NUM> Diopters (i.e., a focal length of <NUM>).

<FIG> shows a birdbath optic <NUM> a pair of crossed liquid crystal lenses 311a and 311b (collectively, liquid crystal lenses <NUM>) that provide variable cylindrical power along orthogonal axes. Each liquid crystal lens <NUM> includes a corresponding liquid crystal layer 385a/385b sandwiched between a corresponding pair of alignment layers 380a/380b and 390a/390b. And each liquid crystal layer 385a/385b may include nematic liquid crystal material or cholesteric or other bi-stable liquid crystal material. A common ground plane <NUM> is disposed between the alignments layers 390a/390b. Each liquid crystal lens <NUM> also includes a set of linear electrodes 375a/37b. As shown in <FIG>, these sets of linear electrodes 375a/375b are crossed. In this example, linear electrodes 375a are arrayed parallel to the y axis and linear electrodes 375b are arrayed parallel to the z axis. Generally, the linear electrodes can be arrayed in any pair of orthogonal directions in a plane perpendicular to the birdbath optic's optical axis (the x axis in <FIG>).

Together, the crossed, dynamically adjustable lenses <NUM> provide cylindrical optical powers that can be adjusted independently by applying an appropriate waveform to the electrodes. The optical powers may be chosen to produce a net spherical optical power or to produce a desired amount of astigmatism, e.g., to compensate for astigmatism in the user's eye or elsewhere in the optical train.

Those of skill in the art will readily appreciate that the birdbath optic <NUM> can include more or fewer components. For example, the liquid crystal based, dynamically adjustable concave mirror <NUM> may include more or fewer layers, including an additional layers of liquid crystal and electrodes. The layers may also be arranged in different orders. And the entrance and exit windows of birdbath optic <NUM> may be coated with polarizing filters to reduce glare, anti-reflection coatings, and/or scratch coatings.

Those of skill in the art will also appreciate that the variable optical power provided by the electro-active lenses shown in <FIG> and <FIG> can be provided instead or in addition by other types of devices. For instance, an electro-active lens may include a reflective Fresnel lens, e.g., as disclosed in <CIT>. Likewise, the liquid crystal portion of each electro-active lens may be implemented as s graded-index (GRIN) liquid crystal lens, diffractive liquid crystal lens, liquid crystal lens with floating electrodes, variable liquid crystal thickness lens, varied alignment layer strength liquid crystal lens, varied polymer network density liquid crystal lens, or varied photoalignment exposure liquid crystal lens. If implemented as a GRIN lens, the electro-active lens may have powering electrodes variably spaced away from the liquid crystal, a high dielectric constant insulation layer and hole patterned electrodes, a thick insulation layer and hole patterned electrodes, a high resistance conductive layer, or hole and ring-based electrodes. The electro-active lens may also be implemented as a blue phase polarization insensitive lens, a dark conglomerate phase polarization insensitive lens, a twisted nematic (TN) liquid crystal transmission-based Fresnel zone plate, or a spatial light modulator (SLM) adaptive optics system.

The birdbath optic <NUM> shown in <FIG> also includes other elements absent from conventional birdbath displays, namely, an electronics assembly <NUM> with a controller <NUM> and an optional antenna <NUM>. This electronic assembly <NUM> may be mounted inside a housing <NUM>, shown as part of an HMD <NUM> in <FIG>, that can also contain the display source <NUM> as well as a power supply and any other electronics. For instance, the housing <NUM> may also hold a sensor <NUM> that detects ambient light levels, movement, range, or any other parameter that can be used to actuate the birdbath optic <NUM> and/or the display source <NUM>.

In operation, the controller <NUM> controls the focus of the information-bearing image (virtual image) by varying the voltage applied to the liquid crystal layer <NUM> via the electrodes (described below with respect to <FIG>). The variation can be binary (e.g., near or far), stepped through a range of positions (e.g., infinite focus, focus at <NUM> meters, focus at <NUM> meter, focus at <NUM>, focus at <NUM>, etc.), or continuously variable over a particular range (e.g., infinite focus to <NUM>) depending on the electrodes, controller <NUM>, and user interface for controlling the focus.

In some cases, the controller <NUM> changes the focus of the information-bearing image in response to a signal received by the antenna <NUM>, e.g., from a separate device used by the wearer to control the birdbath optic <NUM>. For instance, the wearer may transmit a wireless control signal (e.g., a Bluetooth or Wifi signal) to the controller <NUM> from a smart phone, smart watch, fob-style controller, or other suitable device.

The wearer may also adjust the focus of the information-bearing image by pressing a button or swiping an area <NUM> on the temple or frame of the head-mounted display <NUM> to which the birdbath optic <NUM> is attached. Touching the button once or swiping the area <NUM> in a first direction may bring the focus closer, and touching the button twice or swiping the area in a second direction may move the focus farther away.

The controller <NUM> may also vary the focus of the information-bearing image based on the information-bearing image itself. In these cases, the controller <NUM> may also be operably coupled to and control the display <NUM> and/or be operably coupled to and receive control signals from a processor (not shown) that controls the display <NUM>. If the display <NUM> shows information intended to be seen at near focus, such as information about products on the shelf in the grocery store, the controller <NUM> may automatically cause the information-bearing image to appear at near focus. Similarly, if the display <NUM> shows information intended to be seen at infinite focus, such as information about the next exit on a highway, the controller <NUM> may automatically cause the information-bearing image to appear at infinite focus. Note that the wearer may indirectly control the focus of the information-bearing image by viewing different types of information via the birdbath optic <NUM>.

The controller <NUM> may also respond to anatomical triggering. For instance, it may sense accommodation based on signals from photodetectors (e.g., sensor <NUM> in <FIG>) that sense ambient light level levels and/or pupil diameter. It may also sense the position or orientation of the wearer's head based on signals from an accelerometer and/or a gyroscope. If the controller <NUM> senses that the wearer is looking down based on the accelerometer and/or gyroscope signals, it may bring the information-bearing image to near focus. And if the controller <NUM> senses that the wearer is looking up based on the accelerometer and/or gyroscope signals, it may bring the information-bearing image to infinite focus. The controller <NUM> may also be configured to vary the focus of the information-bearing image based on electrical detection of nervous impulses or brain waves.

<FIG> and <FIG> illustrate the electrode layer <NUM> in greater detail. <FIG> shows an end-on view of layer <NUM> as it may be positioned upon reflective layer <NUM>, which is positioned upon end cap <NUM>. The point of view illustrated in <FIG> is that of looking at the end cap into its concave surface. Comprising part of the electrode layer <NUM>, a series of concentric electrodes <NUM> made from an electrically conductive but optically transparent material are patterned onto layer <NUM>. On top of the electrodes <NUM> is an electrically insulating layer (not shown) that covers the electrodes and the gaps between them. Holes <NUM> patterned into the insulating layer expose a small area of each of the electrodes <NUM> as shown in <FIG>. The insulating layer can be silicon dioxide, which is typically <NUM> thick, or any other electrically insulating, substantially transparent material that can be processed using electronics lithography.

<FIG> shows a series of seven bus lines <NUM> connecting seven holes <NUM> (labeled in <FIG>) to seven electrical connection pads <NUM>. With this configuration, electrical power can be applied to each pad <NUM>, and the current flows to the corresponding electrode <NUM> without short circuiting as the bus line <NUM> passes over top of the other electrodes <NUM>. The bus lines <NUM> and pads <NUM> can be formed from nickel or another suitable conductive material, e.g., sputtered to a thickness of about <NUM>.

To change the focus of the electro-active concave mirror, a voltage potential is applied to each of the electrodes in a gradient fashion, with the opposite side of the circuit connected to the ground plane (layer <NUM>). An exemplary voltage profile may be <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> volts, from the center to the outside electrode respectively. This voltage profile adds optical power to the reflective surface. Reversing the sequence of the voltages (for example, <NUM>, <NUM>, <NUM><NUM>, <NUM>, <NUM> and <NUM> volts, from the center to the outside electrode, respectively) reduces the total optical power of the lens. This allows the user to make the virtual image appear closer (using positive optical power) or farther away (using negative optical power).

In this exemplary embodiment, the patterned electrodes are at layer <NUM> and the ground plane is layer <NUM>. However, by reversing the two such that the ground plane is at layer <NUM>, layer <NUM> may be combined with reflective layer <NUM> and serve as both the optically reflective surface and the electrical ground plane, reducing complexity and cost.

In this exemplary embodiment, there are seven electrodes. Depending on the design, using more electrodes may produce a higher quality optical result. For example, a typical, high quality design may utilize one hundred or more electrodes in a lens with a diameter of <NUM> across. Likewise, <FIG> show circular electrodes, but other shapes could be used, including linear electrodes configured to produce two cylinder lenses placed orthogonal to each other to provide spherical optical power with variable astigmatism.

The dynamically adjustable concave mirror <NUM> illustrated in <FIG> includes multiple electrodes that can create a gradient in the index of refraction of a liquid crystal layer. This gradient focuses light incident on the liquid crystal layer. Those of ordinary skill in the art will readily appreciate that other techniques can be used to vary the optical power of a concave mirror. For instance, a dynamically adjustable concave mirror may include a layer of electro-optic polymer or crystal whose refractive index changes in response to an applied stress, strain, or electromagnetic field.

Alternatively, in an exemplary device not according to the invention, the reflective surface may be formed on a flexible membrane that, together with the convex surface of the birdbath, defines a sealed cavity. Pumping index-matching fluid into the sealed cavity causes the membrane to bulge, changing the focal length of the dynamically adjustable concave mirror. Withdrawing the fluid from the cavity relieves the bulge, returning the focal length to its original value. The flexible membrane can also be actuated electro-statically, piezo-mechanically, thermally, or using any other suitable technique.

<FIG> and <FIG> illustrate a birdbath <NUM> with a membrane-based dynamic focusing mirror <NUM>. The membrane-based dynamic focusing mirror <NUM> includes a deformable curved membrane <NUM> disposed opposite a transparent, rigid wall <NUM>. The curved membrane <NUM> is reflective or coated in a reflective coating to reflect incident light towards the transparent, rigid wall <NUM>. Together, the curved membrane <NUM> and the transparent, rigid wall <NUM> define a cavity <NUM> that is in fluid communication with a fluid reservoir <NUM> via an aperture <NUM> and a fluidic channel <NUM>. The membrane-based dynamic focusing mirror <NUM> also includes a pump <NUM> that is coupled to the fluid reservoir <NUM> (and could alternatively be coupled to another portion of the fluid path). And the birdbath <NUM> includes a controller <NUM> that controls the pump <NUM>.

In operation, the controller <NUM> actuates the pump <NUM> in response to signals from the antenna <NUM>, sensor <NUM>, switch (e.g., user-activated area ) <NUM>, etc. The pump <NUM> responds to the actuation signal from the controller <NUM> by pumping transparent fluid <NUM> between the fluid reservoir <NUM> and the cavity <NUM>. For example, the pump <NUM> may force fluid <NUM> into the cavity <NUM>, thereby causing the curved membrane <NUM> to move away from the transparent, rigid wall <NUM> as shown in <FIG>. This reduces the focusing mirror's radius of curvature and increases its optical power. Similarly, the pump <NUM> may also force fluid <NUM> out of the cavity <NUM>, thereby causing the curved membrane <NUM> to move towards from the transparent, rigid wall <NUM> as shown in <FIG>. This increases the focusing mirror's radius of curvature and decreases its optical power. The exact change in optical power depends on the amount and pressure of the fluid in the cavity <NUM> and can be controlled in a continuous (analog) or stepped (digital) fashion by the controller <NUM>.

Those of skill in the art will readily appreciate that a birdbath optic that can focus to compensate for accommodation can be implemented with many types of liquid-based lenses in addition to the pump-based fluidic shown in <FIG> and <FIG>. For instance, it can be implemented with an electro-wetting lens that uses oil, saline, and/or other fluids to provide a variable optical power. And it can be implemented with an electronically controlled shape distorting capsule lens.

<FIG> illustrate real and virtual images as seen, by a wearer whose eyes accommodate, through a head-mounted display with a birdbath optic that includes a dynamically adjustable concave mirror like those shown in <FIG>, <FIG>, and <FIG>. <FIG> shows a view of what the wearer sees when looking through the birdbath optic at objects 805a at or near infinite focus. The objects 805a at infinite focus appear sharply in focus, whereas closer objects, such as the wine bottle 801a at bottom left, appear blurry or fuzzy. Because the wearer's eyes are focused on the far objects 805a, the dynamically adjustable concave mirror is set to produce virtual images 803a (here, object labels) at infinite focus that also appear sharply in focus.

<FIG> shows a view of what the wearer sees when looking through the birdbath optic at near objects without a change in the focus of the virtual images. In this case, the wine bottle 801b and other objects in the foreground appear sharply in focus, whereas objects 805b in the background appear blurry or out of focus. Because the wearer's eyes accommodate, any information-bearing images 803b at infinite focus also appear blurry or out of focus. (As mentioned above, a conventional birdbath optics cannot account for accommodation, so the information-bearing images that it displays may appear out of focus to a wearer whose focus changes.

<FIG> shows a view of what the wearer sees when looking through the birdbath optic at near objects with a change in the focus of the virtual images. Again, the wine bottle 801c and other objects in the foreground appear sharply in focus, and objects 805c in the background appear blurry or out of focus. In this case, however, the birdbath optic focus is selected to generate the information-bearing images 803c at near focus so that they also appear sharply in focus. This selection may be made by the user via an actuator on or coupled to the birdbath optic or a remote control, such as a smart phone, smart watch, or purpose-built device. The birdbath optic may also automatically adjust the focus in response to a signal from the display controller, possibly based on the information being displayed, or in response to detection of an anatomical cue, such as a change in pupil diameter absent a change in ambient light level.

While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

The above-described embodiments can be implemented in any of numerous ways. For example, embodiments of designing and making the technology disclosed herein may be implemented using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.

Further, it should be appreciated that a computer may be embodied in any of a number of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer. Additionally, a computer may be embedded in a device not generally regarded as a computer but with suitable processing capabilities, including a Personal Digital Assistant (PDA), a smart phone or any other suitable portable or fixed electronic device.

Such computers may be interconnected by one or more networks in any suitable form, including a local area network or a wide area network, such as an enterprise network, and intelligent network (IN) or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks.

The various methods or processes (e.g., of designing and making technology disclosed above) outlined herein may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.

In this respect, various inventive concepts may be embodied as a computer readable storage medium (or multiple computer readable storage media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other non-transitory medium or tangible computer storage medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the invention discussed above. The computer readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present invention as discussed above.

The terms "program" or "software" are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of embodiments as discussed above. Additionally, it should be appreciated that according to one aspect, one or more computer programs that when executed perform methods of the present invention need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present invention.

Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

Claim 1:
A head-mounted display apparatus (<NUM>, <NUM>) comprising:
a display (<NUM>) to emit light; an optic block (<NUM>) that defines a beam splitter (<NUM>) and a transparent convex surface (<NUM>) in optical communication with the display (<NUM>) to transmit a portion of the light emitted by the display (<NUM>);
a concave reflective surface (<NUM>), in optical communication with the beam splitter (<NUM>, <NUM>), to receive the portion of the light transmitted by the beam splitter (<NUM>, <NUM>) and to reflect an image of the display (<NUM>) to a wearer of the head-mounted display apparatus (<NUM>, <NUM>) via the beam splitter (<NUM>, <NUM>);
a liquid crystal layer (<NUM>) sealed between the transparent convex surface (<NUM>) and the concave reflective surface (<NUM>) to vary a focus of the image of the display reflected to the wearer; and
a first electrode layer (<NUM>), disposed on the transparent convex surface (<NUM>), and a second electrode layer (<NUM>), disposed on the concave reflective surface (<NUM>), to actuate the liquid crystal layer (<NUM>).