FAST ELECTROACTIVE LENS SWITCHING SYSTEMS AND METHODS

A conventional liquid crystal lens switches on and off so slowly that a person can perceive the lens's gradual transition from high to low optical power. This makes a conventional liquid crystal lens unsuitable for focusing virtual images quickly in an augmented, mixed, or virtual reality system. Conversely, an inventive fast-switching electroactive lens system can switch so fast (e.g., in 35 milliseconds or less) that a person perceives its optical power to change instantaneously. The system accomplishes this fast switching with using an electroactive wave plate in series with slower liquid-crystal lenses. The wave place can be switched quickly between emitting vertically or horizontally polarized light. Each lens focuses either vertically or horizontally polarized light and transmits orthogonally polarized light. By switching between polarization states, the wave plate effectively turns one lens on and the other lens off much faster than either lens could be switched by itself.

BACKGROUND

An electroactive lens can be used to adjust the focus of a person's eye onto a digital image presented in an augmented or virtual reality display at a fixed virtual location from the eye but at various simulated distances. A typical electroactive lens is low in mass and volume and consumes little energy but does not switch optical power quickly. A typical thirty to forty millimeter wide electroactive lens takes a few hundred milliseconds to switch from one optical power to another optical power. This delay is discernable by the user and degrades the quality of the visual experience.

SUMMARY

An inventive electroactive lens system can (appear to) switch from one optical power to another in tens of milliseconds, or faster, rather than hundreds of milliseconds. It does this with a pair of electroactive lens elements (also called electroactive lenses), configured to operate on light in orthogonal polarization states (e.g., horizontal and vertical polarization states), and a dynamic polarization switcher that can switch light between those orthogonal polarization states in tens of milliseconds. For example, the first electroactive lens element may be configured to focus horizontally polarized light but not vertically polarized light, and the second electroactive lens element may be configured to focus vertically polarized light but not horizontally polarized light. Even if the electroactive lens elements turn on and off slowly, e.g., in hundreds of milliseconds, the polarization adjuster can switch the light between horizonal and vertical polarization states in tens of milliseconds. If the first and second electroactive lens elements have different optical powers, the polarization adjuster can effectively change the lens's optical power within tens of milliseconds by switching the light between horizonal and vertical polarization states quickly.

Although the optical power should be switched in tens of milliseconds or less, the time between switching events is rarely that brief. In practice, the time between switching events can be several seconds or more. The difference in the time it takes to switch an electroactive lens and the time between switching events can be exploited to increase the switching speed in a device with a fast polarization adjuster (also called a polarization orientation changer or variable retarder) and one or more slower focus-changing devices (electroactive or liquid-crystal lens elements). By combining a fast polarization-changing component with one or more slower focus-changing components (e.g., first and second electroactive lens elements), the polarization-changing component allows the optical power of only one focus-changing component to be “optically present” in the optical system at a time. While one focus-changing device is optically present, the other focus-changing components are not optically present, and vice versa. Since the polarization-changing component can switch incident light rapidly from one polarization orientation to the other, the system can rapidly switch from one focus-changing component to the other, with no moving parts. In a fast-changing electroactive lens system with only a single focus-changing element, the system can be rapidly switched from a “lens on” state to a “lens off” state rapidly. There is no limit to the number of focus-changing elements that can be used in a single electroactive lens system.

An inventive electroactive lens system may include a polarization changer, a first electroactive lens in optical communication with the polarization changer, and a second electroactive lens in optical communication with the polarization switcher and the first electroactive lens. The polarization changer is switchable between a first state in which the polarization changer switches a polarization of light between a first and second polarization states (e.g., orthogonal linear polarization states) and a second state in which the polarization changer transmits light in the first polarization state. The first electroactive lens is switchable between a first focusing state in which the first electroactive lens focuses light in the first polarization state and transmits light in the second polarization state and a first transmitting state in which the first electroactive lens transmits light in the first and second polarization states. And the second electroactive lens is switchable between a second focusing state in which the second electroactive lens transmits light in the first polarization state and focuses light in the second polarization state and a second transmitting state in which the second electroactive lens transmits light in the first and second polarization states.

The polarization switcher may comprise a liquid-crystal wave plate and may have a retardance of π/2 in the first state and a retardance of 0 in the second state. The polarization switcher can be configured to switch between the first state and the second state (i) faster than the first electroactive lens is configured to switch between the first focusing state and the first non-focusing state and (ii) faster than the second electroactive lens is configured to switch between the second focusing state and the second non-focusing state. For instance, the polarization switcher may switch between the first and second states within 100 milliseconds, 50 milliseconds, 35 milliseconds, 30 milliseconds, 25 milliseconds, 20 milliseconds, 15 milliseconds, 10 milliseconds, 5 milliseconds, or faster. Similarly, the first and second electroactive lenses may each be configured to switch between their respective focusing and non-focusing states in more than 100 milliseconds.

The polarization switcher and electroactive lenses may be integrated together, e.g., with no air gaps between components. For instance, the polarization switcher and first electroactive lens can share a first common substrate. Likewise, the first and second electroactive lenses can share a second common substrate.

This electroactive lens system can be used or operated by setting the polarization switcher to the first or second state; setting the first electroactive lens to the first focusing state or the first non-focusing state; setting the second electroactive lens to the second focusing state or the second non-focusing state; and sending the light through the polarization switcher, the first electroactive lens, and the second electroactive lens. If the polarization switcher is in the first state, the first electroactive lens is in the first focusing state, and the second electroactive lens is in the second non-focusing state, the second electroactive lens can be switched from the second non-focusing state to the second focusing state while the system transmits light in the first polarization state through the polarization switcher, focuses the light with the first electroactive lens, and transmits the light through the second electroactive lens without focusing the light by the second electroactive lens. After the second electroactive lens is switched from the second non-focusing state to the second focusing state, the polarization switcher can be switched from the first state to the second state, thereby causing the second electroactive lens to focus the light and causing the first electroactive lens to transmit the light without focusing the light. Switching the second electroactive lens from the second non-focusing state to the second focusing state and switching the polarization switcher from the first state to the second state may occur in response to a desired change in a position of a virtual image. Switching the second electroactive lens from the second non-focusing state to the second focusing state may take at least 100 milliseconds and switching the polarization switcher from the first state to the second state may take less than 100 milliseconds.

Another electroactive lens system includes a liquid-crystal wave plate in optical series with first and second liquid-crystal lenses. The liquid-crystal wave plate is switchable between a 0-wave retardance and a half-wave retardance within 35 milliseconds. The first liquid-crystal lens is switchable between a first state in which it focuses light in a first linear polarization state to a first focal plane and a second state in which it focuses light in the first linear polarization state to a second focal plane. The second liquid-crystal lens is switchable between a first state in which it focuses light in a second linear polarization state orthogonal to the first linear polarization state to a third focal plane and a second state in which it focuses light in the second linear polarization state to a fourth focal plane.

The liquid-crystal wave plate and the first liquid-crystal lens can share a first common substrate, and the first liquid-crystal lens and the second liquid-crystal lens can share a second common substrate. The first and second liquid-crystal lenses can transmit light in the second and first linear polarization states, respectively. The first liquid-crystal lens may take more than 35 milliseconds (e.g., 100 milliseconds or more) to switch before the first and second states.

This electroactive lens system may also include a display in optical communication with the liquid-crystal wave plate and configured to emit light in the first linear polarization state. And it may include a processor operably coupled to the liquid-crystal wave plate, the first liquid-crystal lens, the second liquid-crystal lens, and the display and configured to control a retardance of the liquid-crystal wave plate, the first liquid-crystal lens, the second liquid-crystal lens, and the display.

DETAILED DESCRIPTION

A fast-switching electro-active lens system can change the focus of linearly polarized light from an object, for example, a display in an augmented reality headset, in periods of less than 35 milliseconds (e.g., 30, 25, 20, 15, 10, 5, or fewer milliseconds). It does this with a combination of fast-switching wave plates and slow-switching liquid crystal lenses. Each lens has two eigenaxes orthogonal to each other and to the lens's optical axis. Each lens focuses light polarized along one eigenaxis (the focusing eigenaxis) and transmitting light polarized along the other eigenaxis (the transmitting eigenaxis). The amount of focus, i.e., the optical power, along a lens's focusing eigenaxis depends on the liquid crystal thickness and applied voltage, among other things, and can be tuned continuously (e.g., between a —5 and +5 diopters) or switched among two or more discrete states (e.g., in 0.5 or 1.0 diopter increments between 0 and 5 diopters). Each lens can provide no (zero) optical power when it is off (when no voltage is applied) or can provide a non-zero optical power when it is off. Other ranges and values of optical power are also possible.

The lenses are aligned so that their optical axes are coincident but their eigenaxes are rotated by 90° with respect to each other—the first lens's focusing eigenaxis is parallel with the second lens's transmitting eigenaxis, and the first lens's transmitting eigenaxis is parallel with the second lens's focusing eigenaxis. The lenses optical axes are aligned coincident with the wave plate's optical axis, and the wave plate's eigenaxes are aligned with the lenses' eigenaxes. In other words, the wave plate and lenses have coincident surface normals and aligned eigenaxes when viewed along their surface normals (the fast-switching electroactive lens system's optical axis).

Because the lenses are aligned with 90°-rotated focusing and transmitting eigenaxes, when the system is illuminated by light that is linearly polarized along one of the system's eigenaxis, one lens focuses the light and other lens transmits the light. Transforming the polarization state of the incident light to the orthogonal linear polarization state (e.g., from horizontal to vertical or from +45° to −45° switches the lenses' operation. The wave plate changes state much faster than the lenses, allowing much quicker user-observable transitions from one optical power to the other than if a single lens were to provide all the optical adjustments. And if the transitions occur infrequently (e.g., at intervals greater than the lens switching time), then one lens can be switched between optical power levels while the other lens focuses light so that it is ready for the next transition.

Polarization States and Liquid Crystal Alignment Directions

FIGS. 1A, 1B, and 1Cshow symbols used in this disclosure to describe different linear polarization orientations or states. Symbol5inFIG. 1Aindicates that the direction of the linear polarization as if it were “going into and out of the flat plane of the figure.” Symbol10inFIG. 1Bindicates that the direction of the linear polarization is orthogonal to the direction indicated by symbol5. In this case, the direction of the linear polarization is “left and right across the flat plane of the figure.” Symbol15inFIG. 1Cindicates that the direction of the linear polarization is also orthogonal to the direction indicated by symbol5. The direction of the linear polarization indicate by symbol15is “up and down across the flat plane of the figure.”

FIGS. 2A, 2B and 2Cshow the symbols used in this disclosure to describe the orientation of the rub or alignment directions of the alignment layers used in the liquid-crystal focus changers (electroactive lenses). Symbol20inFIG. 2Aindicates that the direction of the rub direction as if it were “going into and out of the flat plane of the figure.” Symbol25inFIG. 2Bindicates that the direction of the rub direction is orthogonal to the direction indicated by symbol20, and in this case the direction of the rub direction is “left and right across the flat plane of the figure.” Symbol30inFIG. 2Cindicates that the rub direction is orthogonal to the directions indicated by symbols20and25, with the rub direction “up and down across the flat plane of the figure.” Each liquid-crystal lens typically has two alignment layers—one on either side of the liquid crystal material—whose rub directions may be parallel, anti-parallel, or orthogonal to each other. In some cases, only one alignment layer may be used for cost reduction. Using two alignment layers increases both the switching speed and the width of the field of view.

The symbols shown inFIGS. 1A-1C and 2A-2Cindicate relative directions. Different symbols can be used to indicate the same polarization state in different drawings if those drawings are from different perspectives. Similarly, the same symbol can be used to indicate the different polarization state in different drawings if those drawings are from different perspectives. For example, in a side or profile view of an optical component, symbol5may indicate a horizontal polarization state and symbol10may indicate a vertical polarization state. In an end-on view (i.e., a view along the optical axis) of the same optical component, symbol10may indicate the horizontal polarization state and symbol15may indicate the vertical polarization state.

Fast Electroactive Lens Switching Systems

FIG. 3Ashows an exploded view of a fast switching lens system300that includes a polarization orientation changer (also called a polarization rotator, polarization adjuster, or variable retarder)40in optical communication with a first electroactive lens50and a second electroactive lens60. The polarization orientation changer40, first electroactive lens50, and second electroactive lens60are in optical series with each other or stacked together. The lens system300may utilize planar liquid crystal in all three components40,50, and60, for example, Merck MLC-2140. The first electroactive lens50has its alignment layer oriented orthogonal to the alignment layer of the second electroactive lens60. In this case, the first electroactive lens50has a horizontally oriented liquid-crystal rub direction25and the second electroactive lens60has a vertically oriented liquid-crystal rub direction30. Other rub directions are also possible (for example, ±45° rub directions), typically used if less-than-100% focusing is required (in other words, focus only a portion of the light while allowing the other portion to pass through unfocused).

Although the device300shown inFIG. 3Ais a preferred embodiment, additional polarization switchers may be added to add functional control options. For example, the device300inFIG. 3Acan switch quickly between the optical powers of lens50and lens60. If an additional polarization switcher is positioned between lens50and lens60, actuating both polarization switchers makes it possible to change the polarization state of the light propagating through the system so that both lenses50,60focus the light. More specifically, the first polarization switcher40can switch the light from the second polarization state10to the first polarization state15, and the second polarization switcher (not shown) can switch the light from the first polarization state15to the second polarization state10. Alternatively, both polarization switchers can be actuated so that neither lens50,60focuses the light even though one or both lenses are actuated to provide optical power or are being switched between states. This can be useful for providing more optical power than can be provided by a single lens.

In operation, linearly polarized light35from an object (e.g., a display or spatial light modulator in an augmented or virtual reality system) enters the polarization rotator40in a second polarization state (e.g., vertically polarized as shown by symbol10). If the polarization rotator40is in a first state (e.g., off), as shown inFIG. 3A, then it emits light45in a first polarization state, which may be rotated by 90° with respect to the second polarization state (e.g., horizontally polarized as shown by symbol15). If the polarization rotator40is in a second state (e.g., on), then it emits light45whose polarization state is the same as the polarization state as the input light35(horizontally polarized in this example).

The light45exiting the polarization adjuster40enters the first electroactive lens50, which focuses the light45to a first focal plane if the light45is in the first polarization state (e.g., vertically polarized) and the first electroactive lens50is in a first state (e.g., on). If the light45is in the first polarization state and the first electroactive lens50is in a second state (e.g., off), the first electroactive lens50focuses the light to a second focal plane. And if the light45is in the second polarization state (e.g., horizontally polarized), it passes through the first electroactive lens50without being focused by the first electroactive lens50.

Light55exiting the first electroactive lens50enters the second electroactive lens60, which, like the first electroactive lens50, is switchable between two states (e.g., on and off states). Unlike the first electroactive lens50, however, the second electroactive lens60acts only on light in the second polarization state (e.g., horizontally polarized). When the second electroactive lens60is in the first state, it focuses light in the second polarization state to a third focal plane. And when the second electroactive lens60is in the second polarization state, it focuses light in the second polarization state to a fourth focal plane. Light55in the first polarization state (e.g., vertically polarized) passes through the second electroactive lens60without being focused by the second electroactive lens60. Light65exits the second electroactive lens60and the system300.

If the first electroactive lens50and second electroactive lens60provide different optical power levels, the lens system300can be switched among a series of different optical power levels focal lengths by actuating the polarization switcher40, first electroactive lens50, and second electroactive lens60. For example, if the first electroactive lens50can be switched between optical power levels of 0.0 Diopters and 1.0 Diopters (first/on and second/off states, respectively) and the second electroactive lens50can be switched between optical power levels of 0.5 Diopters and 1.5 Diopters (first/on and second/off states, respectively), the lens system300can switched among optical power levels of 0.0, 0.5, 1.0, and 1.5 Diopters by actuating the polarization switcher40, first electroactive lens50, and second electroactive lens60. These optical power levels are just examples; other optical power levels are also possible, including optical power levels that are not evenly spaced, such as optical power levels selected to bring objects into focus at near, near-intermediate, intermediate, far-intermediate, and/or far planes.

The fast switching speed of the polarization adjuster40makes it possible for the lens system300to switch among these optical power levels quickly (e.g., within30ms or less) even though the first and second electroactive lenses50and60may switch slowly (e.g., in 100 ms or more). For instance, while the first electroactive lens50is on and the polarization adjuster40is off, the second electroactive lens60may be transitioned from one optical power to the other without affecting the light propagating through the lens system300. Once the second lens60has completed its transition, is ready, and is at the desired optical power, the polarization adjuster40switches states, causing the second electroactive lens60to focus the light while the first electroactive lens50no longer focuses the light even if the first electroactive lens50is still on.

FIG. 3Ashows the components in an exploded, perspective view, with gaps between the components. Although the lens system would work with gaps as shown inFIG. 3A, the lens system can also be made with the components next to each other and bonded or integrated together to eliminate reflections at the interfaces. For example, the first electroactive lens50can share a first substrate with the polarization orientation changer40and share a second substrate with the second electroactive lens60.

FIG. 3Bshows an integrated fast-switching electroactive lens system350. In this system350, substrates41and43, together with liquid crystal layer42, form the polarization adjuster40. Substrates43and46, together with liquid crystal layer44, form the first lens50. And substrates46and48, together with liquid crystal layer47, form the second lens60. Substrates43and46are shared by multiple components and so are coated on each side with separate alignment layers and independently actuated electrodes (not shown).

FIGS. 4A and 4Bshow side views of a cross section of the polarization adjuster40.FIG. 4Ashows the adjuster40in an unpowered or off (first) state, whileFIG. 4Bshows the adjuster40in a powered or on (second) state.

The polarization adjuster40is comprised of a first substrate72and a second substrate80, with planar liquid crystal (for example, Merck MLC-2140 nematic liquid crystal) sandwiched and sealed between the two substrates72and80. On the surface of lower substrate72is a transparent, electrically conductive coating75, also called an electrode (for example, indium tin oxide (ITO)). Atop this electrode75is a transparent alignment layer (for example, polyimide made from Nissan Sunever410polyimide varnish). The alignment layer is typically applied, cured, and then rubbed with a felt cloth along in the direction of the desired alignment orientation. (FIGS. 2A-2Cillustrate possible rubbing directions for the alignment layer.) Adjacent to electrode75is the liquid crystal. On the surface of upper substrate80is another electrically conductive coating (electrode)85, which can be made of the same material(s) that the first electrode75is made from.

FIG. 4Ashows a difference between the electrodes75and85: when the polarization adjuster40is off, the alignment layer on the first electrode75is configured to orient the adjacent liquid crystal molecules in the direction indicated by symbol25, whereas the alignment layer on the second electrode85is configured to orient the adjacent liquid crystal molecules in the direction indicated by symbol20. As a result of this configuration, the liquid crystal molecules are aligned at the first electrode75in orientation/direction25, aligned at the second electrode85in orientation/direction20, aligned in the middle of the liquid crystal layer in an orientation/direction midway between orientation25and orientation20, and gradually twisted closer to orientations25and20the closer the liquid crystal is to the first electrode75and second electrode85, respectively. This twisted configuration is indicated by the three symbols100inFIG. 4A. This twisting of liquid crystal molecules adjusts or changes the polarization direction of light105from polarization orientation10as it enters the polarization adjuster40to polarization orientation5as it exits the polarization adjuster40.

FIG. 4Bshows the polarization adjuster40with a voltage supply110applying an electric field potential to the first electrode75while the opposite electric field potential is applied to the second electrode85. The applied voltage may be an alternating current (AC) signal, such as a sine or square wave. When power is applied, the liquid crystal molecules reorient from orientation100to orientation115as shown inFIG. 4B. In this state, the polarization orientation10of the light105entering the polarization adjuster is the same as the polarization orientation10of the light105as it exits the polarization adjuster. In other words, applying the voltage to the electrodes75and85changes the polarization adjuster's retardance from π/2 to 0. The polarization adjuster40does not change the light's direction of propagation.

Other configurations of the polarization adjuster are also possible. For instance, the alignment layers can have parallel or anti-parallel rub directions instead of crossed or orthogonal rub directions as inFIGS. 4A and 4B. With parallel or anti-parallel rub directions, the polarization adjuster does not change the polarization state of incident light when it is off (i.e., when no voltage is applied across the liquid crystal by the electrodes); its nominal retardance is0. Instead, the polarization adjuster changes the polarization state of incident light when it is on (i.e., when a voltage is applied across the liquid crystal by the electrodes), for example, by changing horizontally polarized light or vertically polarized light for a retardance change of π/2.

The polarization adjuster's design parameters, including the liquid crystal material and liquid crystal thickness, may be selected to increase the switching speed. The formulas below give an example design set to achieve fast switching speed and high optical efficiency. Several example turn-off times are shown (indicating that a preferred liquid crystal thickness of either 2.4 μm or 5.3 μm), however, the turn-on times may be reduced by using higher-than-needed switching voltages. The liquid crystal used in the preferred embodiment is HAE614752 made by Jiangsu Hecheng Display Technology Co. Ltd. of China. Other liquid crystals may be used as well, for example, MLC2136 made by Merck Chemicals of Germany.

For a twisted nematic liquid crystal cell placed between two polarizers aligned parallel and perpendicular to the respective surface molecular directors, the transmission is:

where u=πdΔn/θλ, θ is the liquid crystal twist angle, d is the cell thickness, Δn is the refractive index anisotropy of the liquid crystal material, and λ is the transmission wavelength. For a twisted nematic liquid crystal cell between parallel polarizers (i.e., θ=π/2), the transmission becomes:

where x=dΔn/λ. The transmission minima for this expression occur for x=√{square root over (m2−1/4)}, where m is a positive integer. The first minimum occurs for x=0.87, which corresponds to Δn=0.2, λ=550 nm and d=2.4 μm.

A polarization switcher that provides a half wave of retardance (i.e., θ=π/2), should have a liquid crystal layer whose thickness meets the criteria for minimum transmission using the equation given above. For a liquid crystal layer with Δn=0.2, λ=550 nm, a viscosity of 100 mPa, and K=10 pN, the liquid crystal layer thickness should 2.4 μm or 5.3 μm for a switching time of 6 ms or 29 ms, respectively. These switching times are short enough for the polarization switcher to change state (e.g., turn on or off) without a lag perceptible by a person.

Operation of a Fast-Switching Electroactive Lens System

FIGS. 5-7illustrate operation of a fast-switching electroactive lens system500with a polarization adjuster120, a first electroactive (liquid crystal) lens125, and a second electroactive (liquid crystal) lens130in optical series with each other. The first electroactive lens125has alignment layers rubbed in orientation30and the second electroactive lens130has alignment layers rubbed in orthogonal orientation20. AlthoughFIGS. 5-7show gaps between the components, the components can be touching each other and bonded together or otherwise integrated to form a single unit just like the system350inFIG. 3B. The fast-switching electroactive lens system500focuses and/or transmits polarized light emitted a display520, such as a transparent organic light-emitting diode (OLED) display in an augmented reality system. The fast-switching electroactive lens system500and display520are operably coupled to a processor510, which can control the polarization adjuster120, first electroactive lens125, and second electroactive lens130in response to the content (video imagery) shown on the display520.

InFIG. 5, the polarization adjuster120is in an off state, as are the electroactive lenses125and130. Light entering polarization adjuster120in polarization orientation5and exits in orientation15(i.e., it is changed from one linear polarization state to an orthogonal linear polarization state). In this example, if polarization adjuster120and lens125are in the electrically off state and lens130is switched to the electrically on state, no optical focusing takes place because the orientation of the rub direction of lens130is orthogonal to the polarization state of the light entering the lens130. Put differently, if the first electroactive lens125has no optical power in the off state, and the second electroactive lens130does not act upon the light in polarization orientation15, the system500does not focus incident light.

FIG. 6shows polarization adjuster120still in the electrically off state and the first and second electroactive lenses125and130in the electrically on state. In this configuration, the first electroactive lens125has optical power thanks to a voltage that actuates its liquid crystal material, changing its refractive index distribution. Because the polarization of light entering the first electroactive lens125matches the orientation of the first electroactive lens's rub direction30, the first electroactive lens125focuses the incident light. The second electroactive lens130, however, does not focus light, regardless of its setting, because its rub direction20is orthogonal to the polarization orientation15of the light.

FIG. 7shows the polarization adjuster120, first electroactive lens125, and second electroactive lens130in the electrically on state (i.e., with voltages applied to their liquid crystal layers). In this condition, the polarization adjuster120does not transform the polarization state of the incident light; instead, the polarization adjuster120transmits the incident light in polarization orientation5. This means that the light emerging from polarization adjuster120is no longer polarized in the same orientation of the rub direction30of the first electroactive lens125but is now polarized in the same orientation of the rub direction20of the second electroactive lens130. As a result, the second electroactive lens130focuses the incident light but the first electroactive lens125does not. If the second electroactive lens130has a higher optical power (shorter focal length) in the on state than the first electroactive lens125, as shownFIG. 7, this change in the polarization state changes the optical power (focal length) of the lens system500even though the states of the first and second electroactive lenses125and130did not change.

Viewing a Video with a Fast-Switching Electroactive Lens System

FIG. 8illustrates a process by which a fast-switching electroactive lens system like the systems inFIGS. 3 and 5-7can be used to adjust the focus of virtual images appearing in a video or other dynamic environment presented via an augmented, mixed, or virtual reality system. In the following example, the electroactive lens system includes a polarization-changing component (or polarization changer) that can switch between states A (e.g., π/2 retardance) and B (e.g., 0 retardance) in 35 milliseconds and two focus-changing components (electroactive lenses or focus changers, lenses A and B) that can switch states in about350milliseconds each. The electroactive lens system is used in an augmented/virtual reality system that shows a video clip of eight seconds duration. Displaying the video clip involves changing the focus every two seconds, with the focus change occurring in 35 milliseconds as apparent to the viewer.

This example video clip begins with the digital image at far distance. At the two-second mark, the digital image's simulated distance changes from far distance to far-intermediate as shown in the bottom trace inFIG. 8. At the four-second mark, the simulated distance changes from far-intermediate to near. At the six-second mark, the simulated distance changes from near to intermediate. And at the eight-second mark, the simulated distance changes back to far distance from intermediate.

For purposes of this example, the simulated distances for far, far intermediate, intermediate, and near are 6 meters, 2 meters, 1 meter, and 0.5 meters, respectively. To view images at these distances, the electroactive lens system provides net perceptible optical powers, in the same order, of zero diopters, a half diopter, one diopter, and two diopters of optical power, respectively. In this example, lenses A and B are each switchable among at least a subset of these optical powers, with lens A switchable between a zero-diopter state and a two-diopter state and lens B switchable among a zero-diopter state, a half-diopter state, and a one-diopter state.

In this example, when the polarization changer is in state A, lens A is optically present and lens B is not. When polarization changer is in state B, lens A is not optically present and lens B is present. That is, lens A focuses light transmitted by the polarization changer is in state A but not when the polarization changer is in state B, and lens B focuses light transmitted by the polarization changer is in state B but not when the polarization changer is in state A. A lens that is not focusing light, either because the lens is not actuated or because the incident light is the polarization state that isn't focused by the lens, provides an optical power of zero diopters.

At the start of the video, the polarization changer is in state A, lens A is at zero diopters because it is off, and lens B is also at zero diopters because it is off and because the polarization changer is in state A. The net perceptible optical power of the electroactive lens system is zero diopters.

Shortly after the video clip begins, for example, at the one-second mark, a processor coupled to or integrated in the electroactive lens instructs lens B to switch optical power from zero diopters to one-half diopter. While lens B changes focus, the viewer cannot see any optical effects occurring in lens B because the polarization changer has rendered lens B not optically present (the polarization changer is still in state A). Lens B has a full second to complete its change to the new optical power, far more time than required. At the two-second mark in the video clip, the polarization changer switches states from state A to state B, causing lens B to be optically present, causing the net perceptible optical power of the system to change from zero diopters to one-half diopter in 35 milliseconds.

Shortly after the two-second mark has passed, for example, at the three-second mark, the processor instructs lens A to switch optical power from zero to two diopters. While lens A changes focus, the viewer cannot see any optical effects in lens A occurring because the polarization changer has rendered lens A not optically present (the polarization changer is still in state B, so the net perceptible optical power of the electroactive lens system remains at one-half diopter). Lens A has a full second to complete its change to the new optical power, far more time than required. At the four-second mark in the video clip, the polarization changer switches states again, causing lens A to be optically present and lens B not to be optically present, resulting in the net perceptible optical power of the system changing from one-half diopters to two diopters in 35 milliseconds.

Shortly after the four-second mark has passed, for example, at the five-second mark, the processor instructs lens B to switch optical power from one-half diopter to one diopter. While in the transition state of change, the user cannot see any optical effects occurring because the polarization changer has rendered lens B not optically present. Lens B has a full second to complete its change to the new optical power, far more time than required. At the six-second point in the video clip the polarization changer switches states, resulting in the net perceptible optical power of the system changing from two diopters to one diopter in 35 milliseconds.

Shortly after the six-second mark has passed, for example, at the seven-second point, lens A is instructed to switch optical power from one diopter to zero diopters. While lens A changes focus again, the viewer cannot see any optical effects occurring in lens A because the polarization changer has rendered lens A not optically present (the polarization changer is still in state B). Lens A has a full second to complete its change to the new optical power, far more time than required. At the eight-second mark in the video clip, the polarization changer switches states again, causing lens A to be optically present and lens B to be optically absent (not present), resulting in the net perceptible optical power of the system changing from two diopters to zero diopters in 35 milliseconds.

This sequence may be modified and repeated as desired, tied to and coordinated by signals from the controller or processor presenting the digital images.

Although the lenses may take hundreds of milliseconds to change focus, the viewer observes each focus change occurring within 35 millisecond.

The video output can be prepared beforehand and can be programmed/controlled to be coordinated with the electroactive lens components to reduce the viewer's perception of focus-switching time. However, in some cases, video imagery may not be pre-prepared and cannot be used to control the switching in this pre-programmed manner. Instead, the electroactive lens operates in an on-demand switching mode controlled by the viewer with a switch or other command device. In these cases, a similar strategy may be employed where the polarization changer changes state from one state to another state can be delayed until the focus-changing time period has completed, resulting in the user seeing a 35-millisecond optical switching period and a 350-millisecond lag between the switching command and the execution, which may be more desirable than having the user experience a 350 millisecond change-of-focus duration.

In another embodiment, a single electroactive lens may be used with a polarization rotator. Using two tunable lenses allows an almost infinite combination of fast switching configurations from one optical power to another, for example, from one diopter to two diopters to one-half diopter to one diopter and to one-half diopter, etc., while using a single lens allows for fast switching between zero and another optical power, then back to zero diopters, then to another optical power, then zero diopters, etc.

Although the system functions when randomly polarized light enters the system, for example, non-polarized emission from a non-polarized OLED display, it works best with polarized light. Non-polarized or randomly polarized light can be polarized with a polarizer filter located at the light entry point of the system, or by using display technology that emits polarized light, such as LED displays or polarized OLED displays.

CONCLUSION

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.