Patent Description:
An augmented reality device allows the user to view the real world with a virtual image superimposed upon a view of the real world. In a typical augmented reality device, a beam splitter or beam combiner brings together light from the real world and light from a display. The light from the display appears as the virtual image.

Beam splitters and beam combiners are only partial reflectors of light. That is, they transmit and reflect incident light. If a beam splitter has two input ports-one for the light from the real world and one for the light from display-and two output ports, it will send some light from each input port through each output port. This attribute allows light from the real world and the display to be combined at a ratio set by the beam-splitting ratio (e.g., <NUM>/<NUM>).

Unfortunately, this attribute also causes problems when the ambient light level fluctuates. If the ambient light from the real world is much brighter than the light from the display, it may be difficult to see the virtual image. One solution to this problem is to increase the brightness of the display (the virtual image source). Unfortunately, increasing the display brightness leads to undesired increases in the size, weight, power consumption, and/or cost of the augmented reality device.

<CIT> discloses an eyepiece for a head wearable display which includes a light guide component for guiding display light received at a peripheral location offset from a viewing region and emitting the display light along an eye-ward direction in the viewing region.

<CIT> discloses apparatus, devices, and methods to provide a modified-transmissivity zone on a projection surface used to generate a virtual image superimposed onto a real-world view.

<CIT> discloses an electronic display device including a display unit for displaying an image and a light controller disposed in front of the display unit. The light controller includes a polarizing switch for controlling a polarizing direction using an electrical signal, and a pattern polarizer for controlling light transmission in cooperation with the polarizing switch.

<CIT> discloses a see through display which includes a variably transmissive element positioned between a real world view and an eye of a user, and a generated display optical system for generating a displayed information image superimposed over the real world view in the visual field of the user.

<CIT> discloses a heads-up display including ambient light control,.

<CIT> discloses a see-through display system including a narrowband light source configured to emit light within a first spectral band, a polarized image producing stage configured to polarize the light emitted by the narrowband light source and to produce a polarized image, and a see-through optical system configured to receive the polarized image from the polarized image producing stage and to transfer the polarized image to a display output.

<CIT> discloses a see-through head mounted display with liquid crystal module for adjusting brightness ration of combined images.

The present technology provides a solution to the problem of bright ambient light washing out the virtual image in an augmented reality device. By utilizing an electro-active beam splitter whose reflect/transmit ratio can be varied or switched on and off rapidly, more light from the virtual image source can be reflected toward the eye while the amount of light coming from the real world may be reduced, increasing the ratio of virtual image light to real world image light, making the virtual image appear brighter when in bright ambient light conditions. For example, the splitting ratio of the variable beam splitter combiner may be continuously adjustable to balance the light from the real world and virtual image sources based on the ambient light level. If the real-world light is twice as bright as the virtual image light, the beam splitter could be adjusted to transmit <NUM>% of the real-world light and reflect <NUM>% of the virtual image light, restoring visibility balance.

The variable beam splitter/combiner may switch from full transmission of real-world light to full reflection of virtual image light more quickly than the user can perceive the switching (i.e., faster than the flicker fusion threshold). While the beam splitter is switching above this threshold, the user observes the images from the real world and the virtual world as one. In this mode, the balance of light intensity may be adjusted by adjusting the duty cycle, or the ratio of the amount of time being in reflect mode versus transmit mode. For example, <NUM> milliseconds of transmit mode and <NUM> milliseconds of reflect mode cause a real-world scene that is in reality twice as bright as the virtual image appear to be appear equally bright as the virtual image.

An example of this type of variable beam splitter can be used in an augmented reality device that also includes a display, a controller, and a photodetector operably coupled to the controller. In operation, the photodetector senses an ambient light level. The variable beam splitter, which is operably coupled to the controller and in optical communication with the display, reflects light from the display and transmits ambient light to a user's eye in a proportion determined by the controller based on the ambient light level.

The variable beam splitter comprises two liquid crystal layers, at least one liquid crystal layer sandwiched between a pair of substrates. For example, the variable beam splitter includes at least two liquid crystal layers: a first cholesteric liquid crystal layer having a first chirality; and a second cholesteric liquid crystal layer, parallel to and in optical communication with the first cholesteric liquid crystal layer, having a second chirality opposite the first chirality. It may also include a polarizer structure in optical communication with the liquid crystal layer(s). This polarizer structure has adjacent polarizing and non-polarizing sections, each of which has a width and a height on the order of microns in size.

The controller may switch the variable beam splitter between a first splitting ratio and a second splitting ratio at a rate faster than a flicker fusion threshold of the user and a duty cycle selected to provide the proportion determined by the processor based on the ambient light level. The controller can change the duty cycle based on a change in the ambient light level sensed by the photodetector.

An alternative augmented reality device comprises a display, a controller, an ambient light sensor operably coupled to the controller, and a variable transmissive-reflective (transflective) device operably coupled to the controller and in optical communication with the display. Again, the ambient light sensor detects the ambient light level. And the variable transflective device reflects light from the display and transmits ambient light to a user's eye in a proportion determined by the controller based on the ambient light level.

The transflective device may include transmissive and reflective sections. The transmissive section reflects some of the light from the display and transmits some of the ambient light to the user's eye in the proportion determined by the processor based on the ambient light level. The reflective section, which is next to the transmissive section, reflects some of the light from the display to the user's eye and to blocks some ambient light. The transmissive section may include a liquid crystal layer or an electrochromic layer.

The controller can switch the variable transflective device between a first splitting ratio and a second splitting ratio at a rate faster than a flicker fusion threshold of the user and a duty cycle selected to provide the proportion determined by the processor based on the ambient light level. The controller can also change the duty cycle based on a change in the ambient light level sensed by the ambient light sensor.

All combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are part of the inventive subject matter disclosed herein. The terminology used herein that also may appear in any disclosure incorporated by reference 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).

<FIG> shows an augmented reality (AR) device <NUM> with a beam splitter/combiner <NUM> that combines light 101a originating from the virtual image source <NUM>, such as a miniature liquid-crystal display (LCD), with ambient light 102a from the real world (real object) <NUM>. The beam splitter <NUM> typically transmits about <NUM>% of the ambient light 102a and reflects about <NUM>% of the display light 101a toward the user's eye <NUM> as shown in <FIG>. To the user, this combined light 103a appears as a virtual image superimposed on the real world object <NUM>. The remaining ambient light 102a and display light 101a propagates out the other port of the beam splitter <NUM> (not shown).

The AR device <NUM> also includes a variable electro-active attenuator <NUM> between the beam splitter <NUM> and the real world object <NUM>. This attenuator <NUM> is coupled to a processor or controller <NUM>, which is also coupled to the display <NUM> and to a photodetector <NUM>. In operation, the photodetector <NUM> senses incident ambient light 102a. The photodetector <NUM> produces an electrical signal, such as a photocurrent, that represents the intensity or irradiance of incident ambient light 102a. The controller <NUM> receives this electrical signal and uses it to change the brightness of the display <NUM> and/or the transmittance of the attenuator <NUM>.

For example, if the user is wearing the AR device <NUM> in bright sunlight, the photodetector <NUM> may detect the bright ambient light 102a, and the controller <NUM> may increase the brightness of the display <NUM> and/or decrease the transmittance of the attenuator <NUM>. If the attenuator <NUM> has a transmittance that is variable (e.g., continuously variable or stepwise variable) between <NUM>% transmissive (only the environment is visible) and <NUM>% transmissive (only the virtual image is visible), the controller <NUM> may set the transmittance to an intermediate value (e.g., <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or any other value between <NUM>% and <NUM>%). , such as <NUM>%.

If the attenuator <NUM> has only two settings-e.g., <NUM>% or <NUM>% transmissive-then the controller <NUM> may cause the attenuator <NUM> to switch between those settings at a duty cycle selected to decrease the relative brightness of the ambient light 102a. This duty cycle may range between <NUM>% and <NUM>% (e.g., <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or any other value or range of values between <NUM>% and <NUM>%). For example, the attenuator <NUM> may switch between settings at a duty cycle of <NUM>% to reduce the apparent brightness of the ambient light 102a by about <NUM>%. Increasing the duty cycle (i.e., increasing the portion of the period during which the attenuator <NUM> blocks the ambient light 102a) reduces the intensity of ambient light 102a perceived by the user. If the attenuator <NUM> has more than two settings-e.g., <NUM>%, <NUM>%, or <NUM>% transmissive-then the controller <NUM> may switch among the settings in a more complicated fashion.

The attenuator <NUM> switches between settings at a rate faster than the flicker fusion rate or flicker fusion threshold, which is the frequency at which an intermittent light stimulus appears to be completely steady to the average human, so that the switching is imperceptible to the user. Practically, the attenuator <NUM> may switch between settings at rate of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or higher.

<FIG> shows a variable beam splitter <NUM> that can be used instead of the beam splitter <NUM> and variable electro-active attenuator <NUM> in the AR device <NUM> of <FIG>. The variable beam splitter <NUM> has one or more cholesteric liquid crystal layers <NUM> sandwiched between a pair of transparent substrates 307a and 307b. The cholesteric liquid crystals in the cholesteric liquid crystal layer(s) <NUM> are liquid crystals with a right- or left-handed helical structure. Due to this structure of the liquid crystal, Bragg reflection takes place when the pitch of the liquid crystal helix is of the order of the wavelength of light. The reflection band is specified by the pitch length and the birefringence of the liquid crystal. Reflection occurs for light polarized in the same configuration as the liquid crystal helix structure (i.e., right- or left-hand circularly polarized light for right- and left-handed helixes).

A high birefringence liquid crystal material can reflect light over a wavelength band covering the visible spectrum. Alternatively, several layers of cholesteric liquid crystal with different pitch lengths can reflect light over the entire visible wavelength band, with each layer reflecting a certain wavelength sub-band in the visible spectrum. By ensuring the reflection bands in each layer cover the visible spectrum, the layers together reflect light over the entire visible spectrum.

A standard cholesteric liquid crystal layer reflects approximately <NUM>% and reflects approximately <NUM>% of incident unpolarized light due to the polarization-sensitive nature of the cholesteric liquid crystal material. Two cholesteric liquid crystal layers with opposite chirality (e.g., a layer with right-handed helixes and a layer with left-handed helixes) can reflect <NUM>% of incident unpolarized light. If the helix is unwound, then there is <NUM>% transmission, with the liquid crystal becoming vertically aligned. Winding and unwinding the helix structure modifies the reflectance.

Using one or more pairs cholesteric liquid crystal layers <NUM> with opposite chiralities in the variable beam splitter <NUM> in <FIG> makes it possible to vary the variable beam splitter's splitting ratio. (The layers <NUM> may be a single pair of broadband layers or one or more pairs of narrowband layers, depending on the desired wavelength range. ) By varying the amount of time that the pair(s) of cholesteric liquid crystal layers <NUM> spend in the reflective and transmissive states, the ratio of light from the environment and the virtual image can be controlled. For example, if the layers <NUM> are in the reflective state <NUM>% of the time and in the transmissive state <NUM>% of the time, then the user's eye <NUM> will sense the display light reflected by the variable beam splitter <NUM> for three times as long as it senses the ambient light transmitted by the variable beam splitter <NUM>. Adjusting this ratio weights the apparent brightness of the ambient light with respect to the brightness of the virtual image.

As mentioned briefly above, a cholesteric liquid crystal, also called a chiral nematic liquid crystal, is a nematic liquid crystal configuration where the liquid crystal director forms a chiral twisted or helical structure. In some configurations, the liquid crystal system is able to act as a Bragg reflector, and liquid crystal reflects light polarized in the same configuration as the chiral pitch. To meet the Bragg condition for reflected polarized light, the liquid crystal's pitch should be on the order of the wavelength (e.g., about <NUM> to about <NUM> for visible light). The peak of the Bragg reflection at a wavelength of λ<NUM> is defined as: <MAT> where P is the pitch of the liquid crystal structure and nav is the average refractive index of the liquid crystal. For a liquid crystal with an ordinary refractive index of <NUM> and an extraordinary refractive index of <NUM>, the liquid crystal pitch should be <NUM> for reflection at <NUM> (the peak response of human vision). The scope of this invention can include liquid crystals with a range of birefringence and pitch lengths, whereby all wavelengths of light in the visible spectrum are reflected depending upon the configuration.

The range of reflected wavelengths (Δλ) is determined by the birefringence of the liquid crystal (Δn) and the pitch, and is governed by the equation: <MAT> For a liquid crystal with an ordinary refractive index of <NUM>, an extraordinary refractive index of <NUM>, a liquid crystal pitch of <NUM>, the range of reflected light wavelengths is <NUM>. For broadband reflectance in the visible spectrum (e.g., from about <NUM> to about <NUM>), the wavelength range should be <NUM>.

Increasing the birefringence of the liquid crystal or the pitch increases the reflectance wavelength range. Similarly, broadband reflectance can be achieved by stacking together several liquid crystal layers with different peak reflectance wavelengths and shorter wavelength ranges.

The number of pitches in the liquid crystal device for high reflectance at the peak wavelength depends upon the birefringence of the liquid crystal. In the case of a high birefringence liquid crystal (e.g., Δn = <NUM>), <NUM>% and higher reflectance can be achieved with four pitches. Reducing the number of pitches for a given reflectance allows a thinner liquid crystal device to be used.

A chiral nematic liquid crystal can be switched using an electric field across the liquid crystal layer. Switching winds and unwinds the liquid crystal's chiral structure. A helical liquid crystal can be in a homeotropic or planar orientation depending upon the liquid crystal dielectric properties and electric field direction. The electric field turns off the reflective properties of the liquid crystal, causing the liquid crystal device (e.g., the variable beam splitter <NUM> in <FIG>) to switch between reflective and transmissive states. The liquid crystal's response time increases with the thickness of the liquid crystal layer, so reducing the number of pitches and hence using a thinner liquid crystal layer increases the liquid crystal's switching speed and reduces the liquid crystal's response time.

In operation, the variable beam splitter <NUM> in <FIG> can be coupled to and actuated by the controller <NUM> in <FIG> as described above with respect to the variable electro-active attenuator <NUM>. More specifically, the controller <NUM> may switch the cholesteric layers <NUM> between the transmissive and reflective states at a rate equal to or faster than the flicker fusion threshold and at a duty cycle that depends on the photosensor's measurement of the ambient light level.

<FIG> shows an alternative variable beam splitter <NUM> that can be used instead of the beam splitter <NUM> and variable electro-active attenuator <NUM> in the AR device <NUM> of <FIG>. It includes a first cholesteric liquid crystal layer <NUM> on one input port to modulate the intensity of the display light 101a and a second cholesteric liquid crystal layer <NUM> on the other input port to modulate the intensity of the ambient light 102a. The first and second cholesteric liquid crystal layers <NUM>, <NUM> independently control the amount of light entering the beam splitter <NUM> from the environment and the display <NUM> according to commands from the controller <NUM> based on the light level readings by the photodetector <NUM>. The controller <NUM> can optimize the visibility of the virtual image by varying the attenuation ratio provided by the cholesteric liquid crystal devices <NUM>, <NUM>. For example, the controller <NUM> may drive the cholesteric liquid crystal layers <NUM> and <NUM> so that they pulse on and off at a rate faster than the flicker fusion rate and at a duty cycle selected to provide the desired visibility for the virtual image.

<FIG> show liquid crystal and electrochromic devices that can be used as variable attenuators in the AR device <NUM> and the variable beam splitter <NUM> of <FIG>.

<FIG> shows a liquid crystal device <NUM> with a liquid crystal layer <NUM> sandwiched between alignment layers <NUM>, transparent electrodes <NUM>, orthogonal or parallel polarizers <NUM>, and substrates <NUM>. The liquid crystal layer <NUM> can take the form of a twisted nematic, super twisted nematic, planar aligned, or vertically aligned nematic structure. By applying a voltage across the liquid crystal layer <NUM> with the electrodes <NUM>, or using in-plane switching, the optical transmission for incident unpolarized light can be varied between <NUM>% to <NUM>%.

<FIG> shows a polarizer array <NUM> that can used in place of either or both of the regular polarizers <NUM> in the liquid crystal device <NUM> of <FIG>. The polarizer array <NUM> has a checkerboard arrangement of polarizers <NUM> and clear (non-polarizing) sections <NUM>. (Other arrangements are also possible. ) The polarizers <NUM> and clear sections <NUM> are too small (e.g., about <NUM> microns wide by <NUM> microns high) to be resolved by an observer. The polarizer array <NUM> can be formed by ablating sections of a thin sheet of polarizer to yield clear sections <NUM> or by printing polarizing sections <NUM> on a clear substrate.

Interleaving or alternating the clear sections <NUM> with the polarizers <NUM> increases the overall transmission of the polarizer array <NUM> compared to that of a conventional polarizer when used in a liquid crystal element. For example, if half of the liquid crystal element area contains polarizers <NUM>, and the other half is clear (clear section <NUM>), then the liquid crystal will have a <NUM>% transmission in the off state. By varying the liquid crystal orientation in the polarization-sensitive areas, the liquid crystal element's total transmission can be reduced to <NUM>%. There is hence a compromise between maximum light transmission and transmission range in this system.

<FIG> shows two views of a liquid crystal element <NUM> that includes dichroic dye <NUM> mixed into liquid crystal material <NUM> between a pair of substrates <NUM>. In this case, the dichroic dye <NUM> absorbs light of a certain polarization, either parallel or perpendicular to the long molecular axis of the dye <NUM>. The liquid crystal <NUM> can be aligned either parallel (left) or perpendicular (right) to the substrates <NUM>, with the dye <NUM> following the orientation of the liquid crystal <NUM>. For example, in the parallel alignment state (left), light polarized parallel to the direction of the molecular axis of the dye is absorbed, and there is <NUM>% transmission through the liquid crystal element <NUM>. When the liquid crystal <NUM> is aligned in a perpendicular state (right), the dye molecules <NUM> are oriented perpendicular to the substrates <NUM>. In this case the molecular axis of the dye <NUM> is no longer aligned with the polarization of light, and there is <NUM>% transmission. The liquid crystal <NUM> and dye <NUM> can be switched between perpendicular and parallel states with in-plane electrodes (not shown) to provide <NUM>% transmission in the off state and <NUM>% transmission in the on state or vice versa, depending on the relaxed orientation of the liquid crystal <NUM> and dye <NUM>.

<FIG> shows a transmissive electrochromic (EC) device <NUM> with an electrolyte layer <NUM> sandwiched between a cathodic electrochromic layer <NUM> and an anodic electrochromic layer <NUM>, which in turn are between transparent electrodes <NUM> and substrates <NUM>. This EC device <NUM> can be used to control the light intensity from the environment or display source in an AR device. Applying a voltage to the EC device <NUM> causes the electrochromic layers <NUM> and <NUM> to undergo certain redox reactions and change color. The overall transmission (color) of the EC device <NUM> changes, e.g., from a transparent (clear) state to dark color state and vice versa. This effect can be used to control the ambient light transmitted to or through a beam splitter in an AR device.

<FIG> shows a combined EC/liquid crystal device <NUM>. It includes an electrochromic device <NUM> and a liquid crystal <NUM> in optical series between a pair of clear substrates <NUM>. These substrates <NUM> may replace or augment the outer substrates in the electrochromic device <NUM> and liquid crystal device <NUM>.

<FIG> shows an AR device <NUM> with an electro-active trans-reflective (transflective) device <NUM> for controlling the ratio of light originating from the real world object <NUM> to the light originating from the virtual image source <NUM>. The transflective electro-active device <NUM> is coupled to a controller <NUM> and has a variable transmissive section <NUM> next to a reflective section <NUM>. The reflective section <NUM> reflects light 101a from the virtual image source <NUM> to the user's eye <NUM>. The reflective section <NUM> may have a fixed or electrically tunable reflectivity. If fixed, the reflectivity may be less than <NUM>% so that virtual image formed by the light 101a from the virtual image source <NUM> appears superimposed over at least part of the real-world object <NUM> or scene. If variable, the reflectivity may be adjusted to a level or switched at a duty cycle selected by the controller <NUM> based on the ambient light level measured by the photodetector <NUM> to make the virtual image appear dimmer or brighter with respect to the real-world scene.

The variable transmissive section <NUM> of the transflective device <NUM> controls the intensity of light 102a from a real-world object <NUM> that reaches the user's eye <NUM>. The controller <NUM> sets the transmissivity of the variable transmissive section <NUM> based on the ambient light level measured by the photodetector <NUM>. For example, the controller <NUM> may set the variable transmissive section's transmissivity to a given level (e.g., any level between <NUM>% and <NUM>%) to make the virtual image appear dimmer or brighter with respect to the real-world scene. If the variable transmissive section's transmissivity is switched among two discrete levels (e.g., a "clear" state and a "dark" state), the controller <NUM> may switch the variable transmissive section's transmissivity between those levels at a duty cycle selected to make the virtual image appear dimmer or brighter with respect to the real-world scene.

<FIG> and <FIG> show transflective electrochromic and liquid crystal devices, respectively, suitable for use in the transflective AR device <NUM> of <FIG>. As shown in <FIG>, the transflective electrochromic device <NUM> has one side with an electrolyte layer <NUM> sandwiched between a cathodic electrochromic layer <NUM> and an anodic electrochromic layer <NUM>, which in turn are between transparent electrodes <NUM> and substrates <NUM>. A fixed reflector <NUM> between the substrates <NUM> occupies the other side of the transflective electrochromic device <NUM>. Applying a voltage to the electrochromic device <NUM> causes the electrochromic layers <NUM> and <NUM> to undergo certain redox reactions and change color. The overall transmission (color) of one side of the electrochromic device <NUM> changes, e.g., from a transparent (clear) state to dark color state and vice versa. This effect can be used to control the ambient light transmitted in an AR device.

As shown in <FIG>, the transflective liquid crystal device <NUM> includes a liquid crystal layer <NUM> sandwiched on one side between alignment layers <NUM>, transparent electrodes <NUM>, orthogonal or parallel polarizers <NUM> (e.g., like the polarizer structure <NUM> in <FIG>), and substrates <NUM>. On the other side of the transflective liquid crystal device <NUM>, a reflector <NUM> displaces at least a portion of the liquid crystal <NUM>, one alignment layer <NUM>, and one transparent electrode <NUM>. Again, the liquid crystal layer <NUM> can take the form of a twisted nematic, super twisted nematic, planar aligned, or vertically aligned nematic structure. By applying a voltage across the liquid crystal layer <NUM> with the electrodes <NUM>, or using in-plane switching, the optical transmission for incident unpolarized light can be varied continuously, e.g., between <NUM>% and <NUM>%.

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. Those skilled in the art will recognize or be able to ascertain, using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. 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 and equivalents thereto, 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.

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:
An augmented reality device (<NUM>) comprising:
a display (<NUM>);
a controller (<NUM>);
a photodetector (<NUM>), operably coupled to the controller, to sense an ambient light level; and
a variable beam splitter (<NUM>), operably coupled to the controller and in optical communication with the display, to reflect light (101a) from the display and to transmit ambient light (102a) to a user's eye in a proportion determined by the controller based on the ambient light level, characterized by the variable beam splitter comprising:
a first liquid crystal layer (<NUM>) to adjust an intensity of the light from the display coupled to a first input port of the variable beam splitter; and
a second liquid crystal layer (<NUM>) to adjust an intensity of ambient light coupled to a second input port of the variable beam splitter independent of the intensity of the light from the display.