TWI871845B - Improvements in or relating to augmented reality display units and augmented reality headsets comprising the same - Google Patents

Abstract

An augmented reality display unit for use in an augmented reality headset or the like comprising front and rear variable focusing power compression liquid lens assemblies (220, 230) in mutual optical alignment on an optical axis (O), a transparent waveguide display(240) interposed between the front and rear liquid lens assemblies (220, 230) and a selectively operable adjustment mechanism for simultaneously adjusting the focusing powers of the front and rear compression liquid lens assemblies (220, 230) in a mutually inverse manner; wherein each of the front and rear compression liquid lens assemblies (220, 230) stores elastic potential energy as its absolute focusing power is increased and releases elastic potential energy as its absolute focusing power is decreased; and wherein the adjustment mechanism is configured to couple the front and rear compression liquid lens assemblies (220, 230) together such that elastic potential energy released by one of the compression liquid lens assemblies when its absolute focusing power is decreased assists in driving the adjustment mechanism to increase the absolute focusing power of the other compression liquid lens assembly.

Description

Improvements to or related to augmented reality display units and augmented reality head mounted devices including the same

The invention relates to an augmented reality display unit of the type comprising front and rear variable focusing power lenses and an intercalated transparent waveguide display. The invention particularly relates to an augmented reality display unit comprising two variable focusing power compressible liquid lenses. The invention also includes an augmented reality head mounted device comprising at least one augmented reality display module according to the invention.

WO 99/061940 A1 discloses a compression type variable focus power liquid lens, in which a closed chamber with opposite walls (formed by a transparent wall member and an expandable film) is filled with a transparent liquid, and a member is provided for changing the interval between the transparent wall member and the expandable film to change the pressure of the transparent liquid in the chamber. A fixed focus rigid lens is arranged outside the chamber, adjacent to the transparent wall member.

WO2015/081313 A2 discloses a configuration for presenting virtual reality and augmented reality experience to a user. The system may include an image generation source, a light modulator, and a substrate, wherein the image generation source is used to provide one or more image data frames in a time-sequential manner, the light modulator is configured to transmit light associated with the one or more image data frames, and the substrate is used to direct image information to the user's eyes, wherein the substrate includes a plurality of reflectors, a first reflector of the plurality of reflectors is used to reflect the transmitted light associated with the first image data frame at a first angle to the user's eyes, and a second reflector is used to reflect the transmitted light associated with the second image data frame at a second angle to the user's eyes.

At the same time, WO2017/112958 A1 discloses a retinal light scanning engine (RLSE) for writing light corresponding to an image onto the user's retina. The light source of the retinal light scanning engine forms a single light spot on the retina at any single, discrete moment. In order to form a complete image, the RLSE uses a pattern to scan or write onto the retina to provide light to millions of such points corresponding to the image over a time period. The RLSE changes the density and color of the points drawn by the pattern by simultaneously controlling the power of different light sources and the movement of the optical scanner to display the desired content on the retina according to the pattern. In addition, the pattern can be optimized for writing images on the retina. In addition, multiple patterns can be used to increase or improve the field of view of the display.

US 2013/0300635 A1 discloses a method, apparatus, and computer program product for facilitating focus correction of displayed information. In the context of the method, a user's focal length is determined. The method may also determine at least one focus setting for one or more dynamic focus optical components of the display based on the focal length. The method may also cause the one or more dynamic focus optical components to be configured based on the at least one focus setting to present a representation of data on the display. The dynamic focus optical components can utilize techniques such as fluidics, optoelectronics, or any other dynamic focusing technology. For example, a fluidics-based dynamic focus component may include focusing elements whose focus setting or focus can be changed by fluid injection or reduction of the focusing elements.

One application of adjustable lenses is in the field of head-up displays (HUDs) and helmet mounted displays, as disclosed, for example, in EP 3091740 A1, in which a binocular display device comprises two eyepiece assemblies to be worn simultaneously by a user, with a corresponding eyepiece assembly at each eye, each eyepiece assembly comprising an outer optical component with positive optical power and an inner optical component with negative optical power, the outer optical component being arranged to receive external light from an external scene and for directing the result to a transparent waveguide display component of the device, the waveguide display component The device is a binocular display device for displaying a binocular image. The inner optical component is arranged to output substantially collimated display light, the inner optical component is arranged to receive both external light and the substantially collimated display light from the waveguide display component, and is used to add divergence to the received display light to produce a virtual focus that is substantially common to each eyepiece assembly, and output the result for display, so that in use, when viewed through the binocular display device, the image conveyed by the display light is superimposed on the external scene as a three-dimensional image. The device includes a controller unit configured to control the optical intensity of the two diverging lenses so that the virtual focus remains substantially common to each eyepiece assembly and the virtual focus can be changed in position.

US 2017/0293145 A1 discloses an augmented reality display system including a pair of variable focus lens elements sandwiching a waveguide stack. One of the lens elements is positioned between the waveguide stack and the user's eye to correct refractive errors in the focused light projected from the waveguide stack to the eye. The lens elements can also be configured to provide appropriate optical power to place the displayed virtual content on a desired depth plane. Another lens element is between the surrounding environment and the waveguide stack and is configured to provide optical power to compensate for aberrations in the ambient light transmitted through the waveguide stack in the lens element closest to the eye. In addition, the eye tracking system monitors the vergence of the user's eyes and automatically and continuously adjusts the optical power of the pair of lens elements based on the determined type of the eyes. In some embodiments, the variable focus lens elements may be adaptive optical elements. In some embodiments, the adaptive optical elements may include transmissive optical elements such as dynamic lenses (e.g., liquid crystal lenses, electro-active lenses, conventional refractive lenses with moving elements, lenses based on mechanical deformation, electro-wetting lenses, elastic lenses, or multiple fluids with different refractive indices).

Important considerations for an augmented reality display unit that includes two or more variable focus power lenses and an interpolated waveguide display include the size and weight of the unit, and the power consumption used to operate the variable focus power lenses.

An object of the present invention is to reduce the power requirements for an augmented reality display unit comprising two or more compressed variable focus power liquid lenses and an interpolated waveguide display.

Another object of the present invention is to reduce the size and/or weight of an augmented reality display unit that includes two or more compressed variable focus power liquid lenses and an interpolated waveguide display.

According to a first aspect of the invention, therefore, there is provided an augmented reality display unit for use in an augmented reality head mounted device or the like, the augmented reality display unit comprising front and rear variable focus power compression liquid lens assemblies optically aligned with each other on an optical axis, a transparent waveguide display inserted between the front and rear liquid lens assemblies, and a selectively operable adjustment mechanism for simultaneously adjusting the focus power of the front and rear compression liquid lens assemblies in a mutually inverse manner. Each of the front and rear compression liquid lens assemblies is configured to store elastic potential energy as its absolute focus power increases, and release the elastic potential energy as its absolute focus power decreases. Advantageously, the adjustment mechanism is configured to link actuation of the front and rear compression liquid lens assemblies so that the elastic potential released by one of the compression liquid lens assemblies as its absolute focusing power decreases assists in driving the adjustment mechanism to increase the absolute focusing power of the other compression liquid lens assembly.

As used herein, the "optical axis" of an augmented reality display unit refers to a straight line through the augmented reality display unit that introduces no net deviation in the direction of the light, i.e., no net prism. Generally, the augmented reality display unit will be configured so that in use, the user will look straight ahead through the augmented reality display unit along the optical axis. Each of the front and rear variable focus power compression liquid lens assemblies defines its own lens optical axis, which in each case is a straight line through the lens assembly that introduces no net deviation in the direction of the light. As will be described in more detail below, in some embodiments, the optical axis of the augmented reality display unit may be different from the optical axes of the lenses of the front and rear lens assemblies. As in a typical pair of corrective glasses or other eyewear having lenses, the optical axis of the augmented reality display unit may typically be positioned off-center, closer to a first nose region of the display unit (which is positioned alongside the user's nose in use) than a second temple region of the display unit (which is positioned alongside the user's temple in use).

Thus, in the absence of friction, a single adjustment mechanism for actuating the front and rear lens assemblies may require less work than an equivalent single adjustment mechanism for individually positively actuating one of the lens assemblies. To a first order (and in the absence of friction), quasi-static actuation of a linked pair of liquid lens assemblies according to the present invention would require approximately half the work required to actuate the individual liquid lens assemblies.

Suitably, each of the front and rear compression liquid lens assemblies may comprise a fluid-filled housing having a first wall formed by an expandable elastic membrane held under tension around its edges by a membrane retaining structure, a second substantially rigid wall formed by or supported on the inner surface of a transparent plate or hard lens having a fixed focusing power, and foldable side walls. The membrane may form an optical surface having a variable optical power. The adjustment mechanism may be arranged to displace the edge of the film toward or away from the second wall in a direction parallel to the optical axis for varying the fluid pressure within the housing, thereby causing the film to expand or contract in a direction parallel to the optical axis to vary the focusing power of the optical surface of the film. Each of the front and rear compression liquid lens assemblies defines an optical center located at a point where the film has a maximum expansion, the optical center being located on the optical axis of the lens assembly, which, as described above, may be the same as or different from the overall optical axis of the augmented reality display unit.

Suitably, the membrane retaining structure may comprise a circumferential support ring.

In some embodiments, the support ring may be circular. Suitably, the support ring may be rigid.

Alternatively, the support ring may be non-circular.

In some embodiments, particularly when the support ring is non-circular, the support ring may be resiliently bendable.

Suitably, the adjustment mechanism may be arranged to displace one or more regions of the edge of the film (e.g. where it is held by the support ring) in a direction parallel to the optical axis towards or away from the second wall. In the case where the film holding structure comprises a bendable support ring, this may result in bending of the support ring. In particular, the support ring may be bent in a direction substantially parallel to the optical axis. More specifically, the support ring may be bent in a plane substantially parallel to the optical axis and substantially parallel to a tangent to the support ring at the bending point.

In some embodiments, the edge of the film can be maintained (e.g., by the support ring) at a fixed distance from the second wall at one or more pivot points. The edge of the film is flexible between the pivot points. For example, the support ring is bendable between the pivot points.

In some embodiments, the actuation mechanism engages the film retaining structure (e.g., the support ring) at one or more actuation points such that operation of the actuation mechanism causes regional displacement of the film retaining structure toward or away from the second wall substantially parallel to the optical axis at the one or more actuation points.

Suitably, the adjustment mechanism may comprise a reciprocatable component operatively connected to the film holding structures (e.g. support rings) of the front and rear compression liquid lens assemblies for simultaneously shifting the film holding structures towards or away from their respective second walls in a direction substantially parallel to the optical axis and in mutually opposite directions, so that when the absolute focusing power of one of the compression liquid lens assemblies increases, the absolute focusing power of the other compression liquid lens assembly decreases, and vice versa.

For example, in some embodiments, the adjustment mechanism may include a reciprocating cam plate having one or more first cam surfaces and one or more second cam surfaces, the one or more first cam surfaces being arranged to engage one or more individual cam follower members at one or more actuation points on the film holding structure (e.g., a support ring) of the front compression liquid lens assembly, and the one or more second cam surfaces being arranged to engage one or more individual cam follower members at one or more actuation points on the film holding structure (e.g., a support ring) of the rear compression liquid lens assembly. One or more first cam surfaces and one or more second cam surfaces may be configured so that movement of the cam plate causes the membrane holding structures of the front and rear compression liquid lens assemblies to simultaneously shift in mutually opposite directions at their respective actuation points toward or away from their respective second walls in a direction generally parallel to the optical axis. In this way, as the absolute focusing power of one of the compression liquid lens assemblies increases, the absolute focusing power of the other compression liquid lens assembly may decrease, and vice versa.

Suitably, the reciprocatable member may comprise a shaft ring having first and second opposite ends, the shaft ring being arranged in whole or in part to surround the waveguide display. The shaft ring may be arranged for reciprocating movement between the front and rear liquid compression lens assemblies in a direction substantially parallel to the optical axis. The first end of the shaft ring (or a part connected thereto) may be arranged to engage a film retaining structure (e.g. a support ring) of the front compression liquid lens assembly. At the same time, the second end of the shaft ring (or a part connected thereto) may be arranged to engage a film retaining structure (e.g. a support ring) of the rear compression liquid lens assembly.

In some embodiments, the front and rear compression liquid lens assemblies may be arranged so that their respective membranes and membrane retaining structures (e.g., support rings) face the shaft ring.

Suitably, the collar may be formed with at least one opening, the at least one hole being maintained in alignment with the waveguide display at all positions of the collar between the front and rear compression liquid lens assemblies.

In some embodiments, the second wall of the front compression liquid lens may be formed of or supported on a hard lens or plate having an optical outer surface having a focusing power in the range of about -1.0 to about 0 diopters, suitably 0 or -0.5 diopters. The optical surface of the film of the front compression liquid lens has a reference focusing power of about 0 to 1.0 diopters, suitably 0 or 0.5 diopters, and the reference focusing power is adjustable by an amount in the range of about 1.0 to 3.0 diopters, suitably 2.0 or 2.5 diopters. In some embodiments, the hard lens or plate of the front compression liquid lens may be formed on a reference curve, and the reference focusing power of the film of the front compression liquid lens should be adjusted accordingly.

Similarly, the second wall of the rear compression liquid lens may be formed of or supported on a hard lens having an optical outer surface having a focusing power in the range of about -1.0 to about -3.0 diopters, suitably -2.0 or -2.5 diopters. Suitably, the optical surface of the film of the rear compression liquid lens has a reference focusing power of about 0 to 1.0 diopters, suitably 0 or 0.5 diopters, and the reference focusing power is adjustable by an amount in the range of about 1.0 to 3.0 diopters, suitably 2.0 or 2.5 diopters. In some embodiments, the optical outer surface of the hard lens of the rear compression liquid lens may have a negative focusing power having an absolute value greater than the absolute value of the positive focusing power of the film of the rear liquid lens, so that the augmented reality display unit always has a constant net negative focusing power to correct the refractive error of the user. Therefore, in some embodiments, the optical outer surface of the hard lens of the rear compression lens may have a focusing power of up to about -9.0 diopters; more typically up to about -6.0 diopters.

Accordingly, in some embodiments, the net focusing power of the extended display unit can be maintained at approximately zero during the adjustment of the post-compression liquid lens. At the same time, in some embodiments, the net focusing power of the extended display unit can be maintained non-zero and approximately constant during the adjustment of the post-compression liquid lens.

In some embodiments, the second wall of the front compression liquid lens may be formed by or supported on a transparent plate or hard lens that is tilted at a first angle relative to the optical axis of the augmented reality display unit. Such tilting of the transparent plate or hard lens may introduce a first prism amount to light passing therethrough. The second wall of the rear compression liquid lens may similarly be formed by or supported on a transparent plate or hard lens that is tilted at a second angle relative to the optical axis, thereby introducing a second prism amount to light passing therethrough. The first and second prism amounts may be substantially equal and opposite to each other.

Therefore, in a second aspect of the present invention, there is provided an augmented reality display unit for use in an augmented reality head-mounted device or the like, comprising front and rear variable focus power compression liquid lens assemblies optically aligned with each other on an optical axis, a transparent waveguide display inserted between the front and rear liquid lens assemblies, and a selectively operable adjustment mechanism for adjusting the focus power of the front and rear compression liquid lens assemblies. Each of the front and rear compression liquid lens assemblies may include a fluid-filled housing having a first wall formed of an expandable elastic membrane held under tension around its edges by a surrounding membrane retaining structure, a second substantially rigid wall formed by or supported on the surface of a transparent plate or a hard lens having a fixed focusing power, and foldable side walls. In each of the front and rear compression liquid lens assemblies, the membrane may form an optical surface having a variable optical power. The adjustment mechanism may be arranged to displace the film holding structure parallel to the optical axis toward or away from the second wall to change the fluid pressure in the housing, thereby causing the film to expand or contract in a direction parallel to the optical axis to adjust the focusing power of the optical surface of the film. The second wall of the front compression liquid lens may be formed by a transparent plate or a hard lens inclined at a first angle to the optical axis or supported on the transparent plate or the hard lens to introduce a first prism into the light passing therethrough. The second wall of the post-compression liquid lens may be formed by or supported on a transparent plate or hard lens inclined at a second angle to the optical axis to introduce a second prism magnitude to the light passing therethrough. The first and second prism magnitudes are suitably substantially equal and opposite to each other.

As described above, the optical axis of the augmented reality display unit is the axis along which the user looks straight ahead through the augmented reality display unit. Suitably, the optical axis of the augmented reality display unit may be disposed in an eccentric position on each of the films, i.e., in an area closer to the edge of the film than other areas of the edge of the film. For example, for visual considerations, the optical axis may typically be disposed closer to the nose area of the edge of the film (which is arranged to be located at the nose of the side-by-side user during use) than the temple area of the edge of the film (which is arranged to be located at the temple of the side-by-side user during use).

Further, each of the front and rear compression liquid lens assemblies has an optical center located at the point where the film has the maximum expansion, and the optical center is located on the lens axis of the lens assembly. As mentioned above, the lens axis is a straight line passing through the lens assembly, which introduces no net deviation in the direction of the light, and as mentioned above, it can be the same or different from the overall optical axis of the augmented reality display unit.

In some embodiments, the front compression liquid lens assembly can be configured so that its membrane in its least expanded state has a curvature away from its second wall that is greater than the curvature of the second wall. At the same time, the rear compression liquid lens assembly can be configured so that its membrane in its least expanded state has a curvature away from its respective second wall that is less than the curvature of the second wall. Advantageously, the transparent plate or hard lens of the front compression liquid lens assembly can be tilted towards the first edge region of its associated membrane. Where the optical axis of the augmented reality display unit is located closer to a first edge region of the film than to other regions of the edge of the film, this has the effect of displacing the optical center of the front lens assembly away from the optical axis of the display unit toward the center of the film, thereby introducing a first prism amount. At the same time, the hard lens of the rear compression liquid lens assembly may be tilted away from a second edge region of its associated film. This has the effect of displacing the optical center of the rear lens assembly away from the optical axis of the display unit toward the center of the film, thereby introducing a second prism amount. The first and second edge regions of the films of the front and rear compression liquid lens assemblies may be aligned with each other. The first and second prisms are suitably equal and opposite so that there is no (or very little) net change in the direction of light travelling on the optical axis.

This arrangement advantageously allows the hard lens or plate of the front liquid lens assembly to be moved closer to its associated film (at least juxtaposed to the first edge region) to reduce the thickness of the front liquid lens assembly. Similarly, the arrangement can allow the hard lens of the rear liquid lens assembly to be moved closer to its associated film, thereby reducing the thickness of the rear liquid lens assembly. In both the front and rear lens assemblies, tilting the hard lens or plate allows the optical center of the lens assembly to be moved to (or closer to) the geometric center of the film. In some embodiments, the front and rear lens assemblies are shaped so that each film defines two mutually orthogonal axes, which are oriented to be substantially orthogonal to the optical axis; namely, a first major axis and a second minor axis, wherein the major axis is longer than the minor axis. Typically the lens assembly may be configured so that in use the major axis extends substantially horizontally, while the minor axis extends substantially vertically, although it will be understood that this depends on the shape of the eye defined by the lens assembly.

Therefore, when the front compression liquid lens assembly is configured as described above so that its film in its least expanded state is away from the curvature of its second wall greater than the curvature of the second wall, this arrangement allows the film to be compressed by approximately the same amount in the region of the edge of the film at opposite ends of the long axis in a direction parallel to the optical axis, which in turn allows the front lens assembly to be made as thin as possible on the optical axis because the front lens assembly obtains minimum gap conditions at both ends of this long axis.

Further, where the rear compression liquid lens assembly is configured as described above so that the film in its least expanded state is away from the curvature of its second wall greater than the curvature of the second wall, this arrangement allows the film to expand by approximately the same amount on the optical axis in the region of the edge of the film at the opposite end of the major axis, which in turn allows the rear lens assembly to be made as thin as possible on the optical axis. Because the minimum clearance condition for the front lens assembly is obtained at the center of the major axis between its two opposite ends. It will be understood that this consideration and the considerations of the previous paragraph are related to spherical film shapes, but similar considerations apply to elliptical (spherocylindrical) surfaces.

It will be appreciated that light emitted by the waveguide display component passes only through the rear lens assembly while the first and second prism quantities are suitably substantially equal and opposite to one another so that the net prism input to light passing through both the front and rear lens assemblies is zero or nearly zero. Suitably, therefore, the waveguide display may be configured to output light with a prism quantity equal to the first prism quantity.

As with the augmented reality display unit of the first aspect of the present invention, the film holding structure of the augmented reality display unit according to the second aspect may also include a film support ring, such as a bendable support ring. More generally, the features of the augmented reality display unit described in relation to either the first or second aspect of the present invention apply to both aspects and should be understood as such unless otherwise indicated to the contrary.

In another aspect of the present invention, there is provided an augmented reality head mounted device for a user, comprising at least one augmented reality display unit according to the first and/or second aspects of the present invention and at least one projector. The augmented reality display unit may be arranged on or in the head mounted device so that the augmented reality display unit is positioned in front of the user's eyes when the head mounted device is worn. The projector has an output which may be coupled to the waveguide display.

Suitably, the augmented reality head mounted device may comprise two augmented reality display units according to the first and/or second aspects of the invention. Suitably, each of the augmented reality display units may be positioned in or on the head mounted device such that each of the augmented reality display units is positioned in front of a respective eye of the user when the head mounted device is worn.

Background on the Augmented Reality Display Unit

Figures 1A to 1D include a series of schematic representations of an augmented reality display unit 10, which includes a front variable focus power compressible liquid lens assembly 20, a rear variable focus power compressible liquid lens assembly 30, and a transparent waveguide display 40 arranged between the front and rear compressible liquid lens assemblies 20, 30.

The front compressible liquid lens assembly 20 includes a plano-convex hard rear lens 22 having a planar rear optical surface 23 and a convex front surface 24. The front surface 24 of the rear lens 22 forms the rear wall of a fluid-filled housing 25 having a front wall formed by an optically transparent expandable film 26 held under tension around its edges by a peripheral support ring 21 serving as a film retaining structure. The housing further includes a foldable side wall 27 extending between the peripheral support ring and the front surface 24 of the rear lens 22 (best shown in FIGS. 1C and 1D), and the housing is filled with an optically transparent refractive fluid having a refractive index that is the same as or close to that of the rear lens 22.

The front compressible liquid lens assembly 20 thus forms an integral, variable focus power lens having a front optical surface provided by the expandable membrane 26 and a rear optical surface provided by the rear surface 23 of the rear lens 22. The focus power of the front compressible liquid lens assembly 20 is determined by the focus power of the rear surface 23 of the rear lens 22 (zero in this example because its rear surface 23 is flat) and the focus power (variable) of the membrane 26. In this example, the focus power of the membrane 26 is variable between 0 and +2.5 diopters, so that the front compressible liquid lens assembly also has a variable focus power in the range of 0 to +2.5 diopters, but this range is given purely for illustrative purposes and may be wider or narrower in other examples.

An appropriate adjustment mechanism (not shown) is provided for displacing the peripheral support ring which surrounds the edge of the membrane 26 to maintain the membrane towards the front surface 24 of the rear lens 22. The foldable sidewalls 27 allow the support ring to be moved towards the rear lens 22 to increase the pressure of the refractive fluid within the housing 25, thereby causing the membrane 26 to expand forwardly, increasing the focusing power of the membrane 26. The membrane 26 is shown in its most expanded state in FIG. 1A.

The front compressible liquid lens assembly 20 exists in a relatively high potential energy state due to the membrane 26 in its most expanded state and the increased fluid pressure in the housing 25. Operating the adjustment mechanism to cause or allow the support ring to move forward away from the front surface 24 of the rear lens 22 reduces the pressure of the fluid in the housing 25 and allows the membrane 26 to relax and become less expanded (as shown in Figures 1B-1D, where the focusing power of the membrane 26 gradually decreases). As the membrane 26 becomes less expanded and the fluid pressure in the housing 25 decreases, the front compressible liquid lens assembly 20 releases potential energy. In Figure 1D, the membrane 26 is shown in a less expanded state (in which it is almost flat), so that the front compressible liquid lens assembly 20 has a small positive focusing power of (for example) about +0.5 diopters. In its minimum expanded state, the front compressible liquid lens assembly 20 is in a relatively low potential energy state.

The rear compressible liquid lens assembly 30 is constructed in a manner similar to that of the front compressible liquid lens assembly 20, wherein the rear lens assembly 30 includes a hard rear lens 32, a pre-tensioned optically transparent expandable film 36, and a foldable sidewall 37. The film 36 and the foldable sidewall 37 form a fluid-filled housing 35 having a convex front surface 34 of the rear lens 32. Similar to the front lens assembly 20, the housing 35 of the rear lens assembly 30 is filled with a refractive fluid having a refractive index that is the same or substantially the same as the refractive index of the rear lens 32.

As shown in FIGS. 1A-1D , a transparent waveguide display 40 is coupled to a projector, as described in more detail below.

Unlike rear lens 22 of front lens assembly 20, rear lens 32 of rear lens assembly 30 has a concave rear surface 33 having negative focusing power. In this example, rear surface 33 has a focusing power of -2.5 diopters. Similar to front lens assembly 20, membrane 36 of rear lens assembly is held around its edges by a peripheral support ring 31 that can be shifted toward and away from rear lens 32 by an adjustment mechanism to change the focusing power of membrane 36. Membrane 36 of rear lens assembly 30 has zero focusing power in its minimum expanded state (as shown in FIG. 1A ) because it is substantially flat, while membrane 36 has an optical power of approximately +2.5 diopters in its maximum expanded state. Thus, similar to the front lens assembly 20, the rear lens assembly 30 also forms an overall variable focus power lens having a net focus power determined by the variable focus power of the membrane 36 and the fixed focus power of the rear surface 33 of the rear lens 32. The focus power of the rear lens assembly 30 can therefore be adjusted within a range of -2.5 to zero diopters, but again, in other examples this range can be wider or narrower depending on how the rear lens assembly 30 is configured, and similarly the focus power of the rear surface 33 of the rear lens 32 can be varied.

However, as will become apparent below, the rear lens assembly 30 should be capable of adjustment over a range of negative refractive powers (including zero), while the front lens assembly 20 should be capable of adjustment over a concentric range of positive refractive powers (including zero).

As mentioned above, the transparent waveguide display 40 is coupled to a projector (not shown) for receiving light that conveys an image to be displayed to the user. The light is transmitted along the waveguide and emitted as collimated light directed toward the user's eyes (indicated by the letter E in Figures 1A to 1D) in a manner known to those skilled in the art of virtual and augmented reality display devices. Because the light emitted by the waveguide display 40 is collimated, the image conveyed by the light will be perceived by the user as being at infinity. In order to create a virtual image at an image plane closer than infinity, the focusing power of the rear lens assembly 30 can be adjusted to a negative diopter. The greater the (negative) power of the rear lens assembly 30, the closer the virtual image will appear to the user. 1A-1D show a virtual image of a bee (represented by the letter V) in the image plane at increasing distances from the user as the focusing power of the rear lens assembly 30 is increased from about -2.5 diopters to about -0.5 diopters (by gradually increasing the curvature of the film 36).

In order for the user's vision of real objects in his or her field of vision (such as, for example, foxgloves represented by the letter R in FIGS. 1A-1D ) to be unaffected by the focusing power of the rear lens assembly 30, the focusing power of the front lens assembly 20 is adjusted in an inverse manner. As the focusing power of the rear lens assembly 30 is made more negative, the focusing power of the front lens assembly 30 is made more positive to an equal (or approximately equal) and opposite degree. Thus, in FIG. 1A , the rear lens assembly 30 has a net focusing power of approximately −2.5 diopters and the front lens assembly 20 has a net focusing power of approximately +2.5 diopters, with the film 26 in its maximum expansion state as described above. At the same time, as the net focusing power of the rear lens assembly 30 decreases (e.g., about -0.5 diopters as shown in FIG. 1D ), the net focusing power of the front lens assembly 20 remains approximately equal and opposite (e.g., about +0.5 diopters), with the membrane 26 in a less expanded state. In this way, the image plane of the virtual bee V or other images conveyed by light emitted from the waveguide display 40 can be adjusted as desired, while the user continues to perceive the real foxglove R (and any other real objects in his or her field of vision) at their actual distance.

The adjustment mechanism is configured to operate the front and rear lens assemblies 20, 30 simultaneously in an opposing manner so that the focusing powers of the front and rear lens assemblies 20, 30 remain approximately equal and opposite, regardless of the focusing power of the rear lens assembly 30. This is particularly useful when two augmented reality display units of the type shown in Figures 1A-1D are used to form a stereoscopic image in a binocular manner, in which the virtual objects are displayed with a degree of parallax corresponding to the virtual distance from the user. In order to avoid vergence-accommodation conflict (VAC), the image planes of the virtual objects can be manipulated by the two augmented reality display units to coincide with the degree of parallax of the virtual objects so that the user approaches and adapts to the same image plane.

Example 1 : Augmented Reality Display Unit

2-4 show an augmented reality display unit 100 according to a first embodiment of the present invention. Broadly speaking, the augmented reality display unit 100 has an arrangement similar to the augmented reality display unit described above with reference to FIGS. 1A-1D , including a front variable focus power compressible liquid lens assembly 120, a rear variable focus power compressible liquid lens assembly 130, and a transparent waveguide display 140 in the middle.

One difference from the augmented reality display unit of Figures 1A to 1D (which can be immediately seen from the inspection of Figure 4) is that in the augmented reality display unit 100 in this embodiment, the front compressible liquid lens assembly 120 is arranged in the opposite direction to the front compressible liquid lens assembly 20 of Figures 1A to 1D, and has an expandable film 126 disposed behind the optically transparent hard front plate 122 so that the film 126 faces the transparent waveguide display 140, while in Figures 1A to 1D, the film 26 is disposed in front of the hard rear lens 22 and faces the opposite direction of the transparent waveguide display 40. However, the orientation of the front (or rear) compressible liquid lens assembly 120 (or 130) is not a necessary feature of the present invention, and those skilled in the art will be able to readily adapt the components of the augmented reality display unit 100 and their arrangement to orient the front and rear compressible liquid lens assemblies 120, 130 as desired according to the end use of the display unit 100. It is important that the front and rear compressible liquid lens assemblies 120, 130 should be operated as concentric variable focus power lenses, as described above in connection with Figures 1A to 1D and described in more detail below.

As best shown in FIG. 4 , the augmented reality display unit 100 thus includes a circular, optically transparent hard front plate 122 having planar rear and front surfaces 123, 124, respectively, such that the hard front plate 122 has substantially no intrinsic focusing power, although in other embodiments the hard front plate 122 may be replaced by a hard front lens having a fixed focusing power of up to about +4.0 diopters (typically up to about +1.0 diopters or +2.0 diopters). The rear surface 123 of the front plate 122 forms a hard front wall of a fluid-filled housing 125 filled with a substantially incompressible, optically transparent refractive fluid 128.

A foldable side wall 127 with an annular cross section extends circumferentially around the housing 125 (as shown in FIG. 4 ) and is bonded to the rear surface 123 of the front plate 122 or the front end thereof facing the rear surface 123 of the front plate 122. The foldable side wall 127 is also bonded to the front surface of the circular expandable film 126 or the rear end thereof facing the front surface, surrounding the film 126. The rear surface of the film 126 is bonded to the annular front end 152 of the oscillating cylindrical shaft ring 150, which extends rearward from the front compressible liquid lens assembly 120. The membrane 126 is thus clamped between the foldable side wall 127 and the cylindrical shaft ring 150 and is pre-tensioned to a linear tension of at least 180 N/m (as described in WO 2017/055787 A2, the contents of which are hereby incorporated by reference).

The oscillation shaft ring 150 is mounted for oscillation back and forth on the optical axis O of the augmented reality display unit 100 (as shown in Figures 5A-5C), and is basically composed of a cylindrical wall that surrounds and defines a cylindrical recess 155 in the augmented reality display unit 100. The cylindrical wall has an outer surface 157 to which is attached a component (not shown) that is configured to engage a selectively operable linear actuator for driving the shaft ring 150 rearwardly and forwardly along the optical axis O between the front and rear lens assemblies 120, 130. For example, the component may include a tooth that is configured to engage a corresponding pinion that is arranged to be driven by an electric motor or the like (not shown).

The transparent waveguide display 140 is received in a cylindrical recess 155 behind the front compressible liquid lens assembly 120. The cylindrical wall is provided with a window 158 (as best shown in Figures 2 and 4) for coupling the waveguide display 140 to a projector (schematically represented at 160). As shown in Figure 2, the waveguide display 140 is arranged generally orthogonal to the optical axis O.

The rear end 153 of the collar 150 is bonded to the front of the expandable membrane 136 of the rear compressible liquid lens assembly 130, which is disposed behind the waveguide display 140. The expandable membrane 136 forms the front wall of the fluid-filled housing 135, which is filled with a substantially incompressible, optically transparent refractive fluid 138. The outer shell 135 is surrounded by a foldable side wall 137 having an annular cross-section, which is bonded to the rear of the film 136 or the front end toward the rear of the film 136, so that the expandable film 136 is clamped between the rear end 153 of the shaft ring 150 and the front end of the foldable side wall 137, and is located at the front surface 134 of the hard rear lens 132 or the rear end toward the front surface 134 of the hard rear lens 132, and the hard rear lens 132 also has a rear surface 133.

Unlike the hard front plate 122 which is planar, the hard rear lens 132 is a concave-convex lens in which the front surface 134 is convex and the rear surface 133 is concave, such that the rear surface 133 has a fixed negative focusing power of about -2.0 diopters. Those skilled in the art will appreciate that the curvature of the rear surface 133 of the rear lens 132 shown in Figures 2, 4, and 5A to 5C is much greater than -2.0 diopters (more negative than that), and the curvature of the rear surface 133 in these figures is exaggerated for illustrative purposes. The curvatures of the films 126 and 136 shown in these figures are similarly schematic. In other embodiments, the focusing power of the rear surface 133 of the rear lens 132 can be in the range of about -1.0 to about -3.0 diopters.

The front plate 122 and the rear lens 132 may be made of the same or different materials, but are generally made or formed of a self-hardening, optically transparent material (of the type commonly used in making ophthalmic lenses).

The foldable side walls 127, 137 of the front and rear liquid lens assemblies 120, 130 may also be made from the same or different materials. In the present embodiment, both are made from an optically transparent, flexible thermoplastic polyurethane (e.g., Tuftane® ^, available from Permali Gloucester Ltd, Gloucester, UK). The foldable side walls 127, 137 are bonded to the front plate 122 and rear lens 132, respectively, using a suitable adhesive, such as, for example, epoxy (e.g., ^Delo® MF643 UV-curing epoxy adhesive) or other means known in the art, such as ultrasonic welding.

The films 126, 136 of the front and rear lens assemblies 120, 130 can be made from the same or different materials, but in this embodiment they are both made from a thermoplastic polyurethane sheet having a thickness of about 220 μm (e.g., Elastollan ^® 1185A10, which can be purchased from BASF). Other suitable materials can be used for the films 126, 136 (and other components of the front and rear lens assemblies 120, 130), as disclosed in WO 2017/055787 A2.

The foldable side walls 127, 137 are bonded to the films 126, 136, respectively, using a light-curable adhesive (e.g., Delo® MF643 UV-curable epoxy adhesive), which is also used to bond the films 126, 136 to the front and rear ends 152, 153 of the hub 150. Again, other suitable alternative adhesives and bonding methods are known and available to those skilled in the art.

The refractive fluids 128, 138 used to fill the housings 125, 135 of the front and rear liquid lens assemblies 120, 130, respectively, may be the same or different from each other. Conveniently, the refractive fluids 128, 138 are the same as each other, especially where the same material is used to form the expandable membranes 126, 136 of the front and rear liquid lens assemblies 120, 130.

The refracting fluids 128, 138 should be colorless and have a refractive index of at least about 1.5. Suitably, the refractive index of each refracting fluid 128, 138 should match its respective film 126, 136 so that the interface between the film 126, 136 and the associated fluid 128, 138 is substantially imperceptible to the user. The refracting fluids should have low toxicity and low volatility; they should be inert and not exhibit phase changes above about -10°C or below about 100°C. The fluids 128, 138 should be stable at elevated temperatures of at least about 80°C and exhibit low microbial growth. In some embodiments, the fluids 128, 138 may have a density of about 1 g/ ^cm3 . A variety of suitable fluids are available to those skilled in the art, including silicone oils and silicones (such as, for example, phenylsiloxanes). A preferred fluid is pentaphenyltrimethyltrisiloxane.

In this embodiment, the films 126, 136 are both formed from polyether polyurethane (e.g. ^Elastollan® 1185) and the two fluids 128, 138 are both phenyl siloxanes, such as pentaphenyl trimethyl trisiloxane. The refractive index of the film material and the fluid is suitably the same or substantially the same and is at least 1.5.

The augmented reality display unit 100 is designed to be mounted in a suitable frame or other structure that maintains the front plate 122 and the rear lens 132 at a fixed distance from each other while allowing the shaft ring 150 to oscillate between the state a shown in FIG. 5A and the state c shown in FIG. 5C on the optical axis O between the front plate 122 and the rear lens 132. It will be understood that when the shaft ring 150 is moved forward on the optical axis O, the foldable side wall 127 of the front compressible liquid lens assembly 120 is gradually compressed between the shaft ring 150 and the front plate 122, which is held fixed by the frame or other structure as mentioned above, as shown in FIGS. 5B and 5C. This compression of the fluid-filled housing 125 of the front lens assembly 120 causes an increase in the pressure of the fluid 128 within the housing 125, causing the expandable membrane 126 to expand rearwardly, with the curvature of the membrane increasing as the pressure within the housing 125 increases. Since the membrane 126 is round, it expands spherically or nearly spherically to form the optical lens surface.

In a similar manner, when the shaft ring 150 is moved rearward on the optical axis O, the foldable sidewall 137 of the rear liquid lens assembly 130 is compressed between the shaft ring 150 and the hard rear lens 132, which, as mentioned above, is also held fixed in a frame or other structure, thereby causing the membrane 136 of the rear lens assembly 130 to expand forwardly, with the curvature of the membrane increasing as the pressure in the fluid-filled housing 135 of the rear lens assembly 130 increases, as shown in Figures 5B and 5A. Like the membrane 126 of the front lens assembly 120, the membrane 136 (which is round) also expands spherically or nearly spherically to form an optical lens surface.

It will also be understood that when the shaft ring 150 is moved forward, the foldable side wall 137 of the rear lens assembly 130 is extended, allowing the membrane 136 of the rear lens assembly 130 to relax and reduce the pressure within the housing 135 (as shown in Figures 5B and 5C), while moving the shaft ring 150 backward allows the membrane 126 of the front lens assembly 122 to relax and the pressure within the housing 125 to be reduced, as shown in Figures 5B and 5A.

In this way, the actuation of the front and rear compressible liquid lens assemblies 120, 130 is coupled by the oscillating shaft ring 150, so that as the curvature of the film 126 of the front liquid lens assembly 120 gradually increases, the curvature of the film 136 of the rear liquid lens assembly 130 gradually decreases, and vice versa. Accordingly, when the potential energy stored in the front compressible liquid lens assembly 120 increases, the potential energy stored in the rear compressible liquid lens assembly 130 is released, and vice versa.

As mentioned above, the films 126, 136 of the front and rear lens assemblies 120, 130 are pre-tensioned to a linear tension of at least about 180 N/m, respectively. When the oscillating shaft ring 150 is disposed in the intermediate state (state b) between the front and rear lens assemblies 120, 130 (as shown in FIGS. 2, 4, and 5B), the front and rear films 126, 136 each have a curvature of about +1.0 diopters, and the two films 126, 136 expand inwardly toward the waveguide display 140. Since the front plate 122 has no (or almost no) focusing power, and the rear surface 133 of the rear lens 132 has a focusing power of about -2.0 diopters, the net focusing power of the augmented reality display unit 100 is zero or substantially zero. However, a net focusing power of approximately -1.0 diopter is applied to light emitted rearwardly from the waveguide display 140, which light only passes through the rear lens assembly 130. In this way, the focusing power of the rear lens assembly 130 can be used to change the apparent focal plane of the image conveyed by the light emitted from the waveguide display 140, as described above with respect to FIGS. 1A-1D.

If it is desired to bring the apparent focal plane of the image conveyed by the light emitted from the waveguide display 140 closer to the user, the shaft ring 150 can be driven forward (as shown in Figure 5C) to reduce the curvature of the film 136 of the rear lens assembly 130 until it is planar or nearly planar, so that the net focusing power of the rear lens assembly 130 is approximately -2.0 diopters (state c). As described above, moving the shaft ring 150 forward on the optical axis O increases the curvature of the film 126 of the front lens assembly 120, and in the maximum expansion state c (as shown in FIG. 5C ), the film 126 of the front lens assembly 120 has a focusing power of approximately +2.0 diopters, so that the net focusing power of the augmented reality display unit 100 is maintained at zero or close to zero, so that the light passing through the entire unit 100 from the outside is generally not affected by the front and rear lens assemblies 120 and 130.

It will also be noted from FIG. 5C that the maximum focusing power of the front film 126 is limited by the gap between the rear surface 123 of the front plate and the front end 152 of the shaft ring 150, while the minimum thickness of the rear lens assembly 130 is limited by the gap between the rear film 136 and the front surface 134 of the hard rear lens 132 on the optical axis O (i.e., at the optical center of the rear lens 132).

In this embodiment, the front and rear films 126, 136 each have a baseline focusing power of about 0 diopters and a maximum focusing power of about +2.0 diopters. However, it will be understood that in other embodiments, each of the front and rear films 126, 136 may (regardless) have a baseline focusing power of up to about +1.0 diopters and may be adjusted in the range of about 1.0 to about 3.0 diopters.

If it is desired to move the apparent focal plane of the image conveyed by the light emitted from the waveguide display 140 away from the user toward infinity, the oscillating shaft ring 150 can be moved rearwardly (as shown in FIG. 5A ) to compress the foldable side wall 137 of the rear lens assembly 130, increasing the focusing power of the film 136 to a maximum focusing power of approximately +2.0 diopters (state a), negating the negative focusing power of the rear surface 133 of the rear lens 132. As the shaft ring 150 moves backward along the optical axis O, the foldable side wall 127 of the front lens assembly 120 extends, reducing the curvature of the film 126 of the front lens assembly and reducing its focusing power to the minimum focusing power of about 0 diopter in state a, so that the net focusing power of the augmented reality display unit 100 is maintained at about 0 diopter.

The components of the augmented reality display unit 100, including the hub 150, are dimensioned so that the separation between the waveguide display 140 and the front and rear films 126, 136, respectively, is sufficient to accommodate the films 126, 130 in their fully expanded states a and c (as shown in FIGS. 5A and 5C) without impacting the waveguide display 140. Further, the components of the unit 100 as described above are configured and arranged so that the front and rear films 126, 136 operate as a concentric pair whose individual focusing powers sum to a total focusing power of approximately +2.0 diopters (regardless of the actual position of the hub 150 between the front and rear assemblies 120, 130) to negate the fixed focusing power of -2.0 diopters of the rear surface 133 of the hard rear lens 132.

Advantageously, in accordance with the present invention, the front and rear compressible liquid lens assemblies 120, 130 are coupled together by an oscillating shaft ring 150 so that when one of the lens assemblies 120, 130 is compressed to increase the focusing power of its film 126, 136, the other lens assembly 130, 120 is expanded to reduce the focusing power of its film 136, 126, so that the front and rear lens assemblies 120, 130 operate as a concentric pair. The potential energy released from one lens assembly 120, 130 that is expanded when the shaft ring 150 is moved is utilized as work to drive the shaft ring 150 to compress the other compressed lens assembly 130, 120. Therefore, coupling the front and rear compressible liquid lens assemblies 120, 130 together using the shaft ring 150 facilitates moving the shaft ring 150 back and forth between the front and rear lens assemblies 120, 130, thereby reducing the energy requirements of the power supply for the actuator of the type mentioned above for actively driving the shaft ring 150. In this way, an augmented reality head mounted device or other device incorporating one or more augmented reality display units 100 according to the present invention can be made smaller and/or lighter, with a smaller power supply.

In the augmented reality display unit 100 shown in FIGS. 2-4 , the optical axis O passes through the geometric center of each of the front and rear lens assemblies 120, 130. However, in some augmented reality display units, the optical axis O may be positioned non-centrally relative to the front and rear lens assemblies 120, 130. It is well known that the optical axis of an ophthalmic lens is often located off-center of the lens to ensure that the lens is properly centered for a given user (i.e., so that the optical center of the lens is properly aligned with the center point of the user). Advantageously, an augmented reality display unit having front and rear compressible liquid lens assemblies in accordance with the present invention can be configured to optimize the thickness and weight of the unit, particularly when the optical axis is located off-center relative to the front and rear lens assemblies, as described below.

FIG6 schematically depicts a front compressible liquid lens assembly 220 for use in an augmented reality display unit according to the present invention. The front lens assembly 220 has a rigid plate or lens 222 of fixed focus power, a foldable sidewall 227, and an expandable film 226 maintained under tension around its edge 229, which define a housing 225 filled with a refractive fluid 228. The foldable sidewall 227 is compressible between states A and B (as shown in FIG6), wherein the film 226 is expanded to a maximum and a minimum, respectively, away from the rigid plate or lens 222. The rigid plate or lens 222 has a first surface 223 inside a cavity 225 and a second surface 224 outside the cavity. The augmented reality display unit has an optical axis O, which is located at the center relative to the lens assembly 220. As described above with respect to FIG. 5C, the maximum expansion state (state A) of the film 226 is limited by the gap between the first surface 223 of the hard lens or plate 222 and the edge 229 of the film 226.

FIG. 7 schematically shows a rear compressible liquid lens assembly 230 for use with the front lens assembly 220 in an augmented reality display unit according to the present invention. The rear lens assembly 230 includes a hard lens 232, a foldable sidewall 237, and an expandable membrane 236 maintained under tension around its edge 239. The hard lens 232 has a first inner surface 233 and a second outer surface 234, which is concave so that the second surface 234 has a negative fixed focusing power. The first surface 233 of the hard lens 232 and the membrane 236 and the foldable sidewall 237 define a housing 235, which is filled with a refractive fluid 238. Like the foldable sidewall 227 of the front lens assembly 220, the foldable sidewall 237 of the rear lens assembly 230 is compressible between states A and B (as shown in FIG. 7). In state A, the membrane 236 is maximally expanded and has a curvature that substantially corresponds to the curvature of the second surface 234 of the hard lens 232, such that the net focusing power of the rear lens assembly 230 is close to zero. In its minimum expanded state B, the membrane 236 has substantially no focusing power, such that the net focusing power of the rear lens assembly 230 is substantially equal to the focusing power of the second surface 234 of the hard lens 232. As described above with respect to FIG. 5C , the minimum thickness of the rear lens assembly 230 is governed by the minimum gap condition between the first surface 233 of the hard lens 232 and the film 236 on the optical axis O in state B. In FIG. 7 , the optical axis O of the augmented reality display unit passes through the center of the rear lens assembly 230 .

As shown in FIG. 8 , the augmented reality display unit is modified by arranging its optical axis O toward a first region of the edge of the film 226 eccentrically. According to the present invention, the thickness of the front lens assembly 220 can be reduced by tilting the hard plate or lens 222 relative to the optical axis O toward the first region R1 of the edge of the film 226. In this way, the hard plate or lens 222 is arranged closer to the edge of the film 229 adjacent to the first region R1 without negatively affecting the minimum gap condition between the edge 229 of the film 226 and the first surface 223 of the hard lens or plate 222. In turn, this allows the front lens assembly 220 to be filled with a reduced amount of refractive fluid 228.

The effect of tilting the hard lens or plate 222 relative to the optical axis O as described above is to introduce a prism into the light passing through the front lens assembly 220. This can be negated by introducing a substantially equal and opposite prism into the rear compressible liquid lens assembly 230 (as shown in Figures 9A-9C). The rear lens assembly 230 (modified so that the optical axis O of the augmented reality display unit is eccentric) is shown in Figure 9A. The optical axis O is closer to the edge 239 of the film 236 than other areas of the edge 239. The region R2 of the edge of the film 236 of the rear lens assembly 230 corresponds to and is aligned with the region R1 of the edge 229 of the film 226 of the front lens assembly 220.

In FIG. 9B , the hard lens 232 is tilted relative to the optical axis O to move the hard lens 232 away from the region R2 of the edge 239 of the film 236. The hard lens 232 is tilted by an amount that is approximately equal and opposite to the amount of tilt of the hard lens or plate 222 of the front lens assembly 220 so that the prism it introduces into the rear lens assembly 230 is approximately equal and opposite to the prism created by tilting the hard lens or plate 222 of the front lens assembly 220 in the front lens assembly. Since the minimum thickness of the rear lens assembly 230 is governed by the minimum gap condition between the film 236 and the first surface 233 of the hard lens 232 on the optical axis O (as described above), by tilting the hard lens 232 away from the film 236, the spacing between the hard lens 232 and the film 236 can be reduced (compared to the unmodified lens assembly shown in Figure 9C), thereby further reducing the thickness of the augmented reality display unit and the amount of fluid 238 required to fill the outer shell 235 of the rear lens assembly 230.

It will be appreciated that, as shown in FIG. 10 , while light passing through both the front and rear lens assemblies 220, 230 will have zero or substantially zero net prism (although the optical axis will be “kinked”), light emitted by the waveguide display 240 interposed between the front and rear lens assemblies 220, 230 will only be affected by the rear lens assembly 230. The waveguide display 240 (or a projector arranged to input light into the waveguide display 240) must therefore be configured to impart a prism to the light emitted by the waveguide display 240 toward the user that is substantially equal and opposite to the prism produced by tilting the hard lens 232 of the rear lens assembly 230.

In a variation of the augmented reality display unit 100 of this example, one or more of the optical components including the hard front plate 122, the hard rear lens 132, and the waveguide display 140 can be manufactured on a base curve in a manner well known to those skilled in the art. Where the hard front plate 122 is replaced by such an optical element, the range of curvature of the expandable film 126 should be adjusted accordingly. For example, in some embodiments, the hard front plate 122 can be replaced by a hard front lens having zero or nearly zero inherent focusing power but manufactured on a positive base curve, so that the front surface of the hard front lens has a positive curvature (e.g., about +1 diopter), while the rear surface of the hard front lens has an opposite and approximately equal negative curvature (e.g., about -1 diopter). In such a case, the focusing power of the front film 126 should range from about -1 diopter to about +1 diopter, rather than 0 to +2 diopter.

Example 2 : Augmented reality headsets

FIG. 11 illustrates an augmented reality head mounted device 30 of a user. The head mounted device 30 resembles a pair of glasses having a frame 32, a nose bridge 35, and left and right temples 36, 37, respectively, the frame having left and right eye-wire portions 33, 34, respectively. Each of the left and right eye-wire portions 33, 34 defines a non-circular opening 38, 39 shaped and sized to accommodate a respective augmented reality display unit 300 according to the present invention. The display units 300 for the left and right eye-wire portions 33, 34 are similar to each other, but have reflection symmetry with respect to a longitudinal section of the user. The working parts of the left hand display unit 300 are illustrated in Figures 12A, 12B, 13A, 13B, 14A, 14B, and 15A, 15B, but the following description is equally applicable to the right hand display unit 300. In other embodiments, the augmented reality head mounted device can be implemented in the form of goggles or a visor, which can optionally integrate a helmet in the form of a head-up display or a helmet mounted display. As described in detail below, the augmented reality display unit 300 incorporated into the head mounted device 30 implements one or more of the same inventive concepts as described above in connection with Example 1.

As best seen in FIGS. 14A and 14B , the augmented reality display unit 300 includes a front variable focus power compressible liquid lens assembly 320, a rear variable focus power compressible liquid lens assembly 330, and an interposed optically transparent waveguide display 340. The display unit 300 thus has a similar architecture to the display units 10 and 100 described above, and operates in substantially the same manner. One significant difference between the display unit 300 of this example and the display unit 100 of Example 1 (most evident from FIGS. 12A and 12B ) is that in this embodiment each of the front and rear lens assemblies 320, 330 has a non-circular optical surface. Non-circular compressible liquid lens assemblies are described in WO 2013/144533 A2, WO 2013/144592 A1, WO 2013/143630 A1, WO 2014/125262 A2, WO 2015/044260 A1, UK Patent Application No. 1800933.2 and UK Patent Application No. 1801905.9, the contents of which are hereby incorporated by reference.

In addition to the components shown in the figures, the augmented reality display unit 300 also includes a suitable housing (not shown) to accommodate and retain the operating components as described below.

Each of the front and rear liquid lens assemblies 320, 330 includes a respective substantially rectangular hard rear lens 322, 332 having a fixed focusing power. In the present embodiment, each of the front and rear lenses 322, 332 includes a concave-convex lens having a concave rear surface 323, 333 and a convex front surface 324, 334, the concave-convex lens being made from any suitable optically transparent hard material known in the art of manufacturing ophthalmic lenses. The front and rear lenses 322, 332 have similar non-circular shapes to each other, and the front and rear lenses are aligned with each other, with their optical centers being disposed on the optical axis z of the display unit 300. The front and rear lenses 322, 332 are each mounted in a fixed position within the housing of the unit 300. Although the lenses 322, 332 are generally rectangular in the present embodiment, the present invention can be extended to a number of other eye shapes for use in conventional eyewear types, such as Aviator, butterfly, cat eye, flat top, pincushion rectangular, rectangular, square, or Wayfarer-type shapes.

A waveguide display 340 is also mounted in a fixed position within the housing of the unit 300 between the front and rear lens assemblies 320, 330.

As will be observed from FIGS. 14A and 14B , the rear surface 333 of the rear lens 332 has a greater curvature than the rear surface 323 of the front lens 322. In this embodiment, the rear surface 333 of the rear lens 332 has a focusing power of approximately -2.5 diopters, while the rear surface 323 of the front lens 322 has a focusing power of approximately -0.5 diopters. More generally, the focusing power of the rear surface 333 of the rear lens 332 may be in the range of approximately -1.0 to approximately -3.0 diopters, while the focusing power of the rear surface 323 of the front lens 322 may be in the range of approximately 0 to approximately -1.0 diopters.

The front surface 324, 334 of each of the front and rear lenses 322, 332 carries a disc-shaped container 370, 380 (or "bag"), which includes a rear wall 372, 382 and an integrally foldable peripheral side wall 373, 383, the shape of which corresponds to the shape of the front surface 324, 334 of the respective lens 322, 332, and the foldable peripheral side wall extends forward from the rear wall 372, 382 and terminates in a peripheral protrusion 375, 385. In this embodiment, each disc-shaped container 370, 380 is made of optically transparent, flexible thermoplastic polyurethane (for example ^Tuftane® , which can be purchased from Permali Gloucester Ltd of Gloucester, UK) and the rear and side walls 372, 373; 382, 383 are about 50 µm thick, but other transparent materials (especially transparent elastomers) can be used and the thickness adjusted accordingly.

The rear wall 372, 382 of each dish-shaped container 370, 380 is continuously bonded to the front surface 324, 334 of the corresponding hard lens 322, 332 by a transparent pressure sensitive adhesive (PSA), such as, for example, 3M® 8211. In this embodiment, a layer of PSA with a thickness of about 25 µm is used, but this can be changed as desired.

The peripheral protrusion 375, 385 of each disc-shaped container 370, 380 is bonded to a respective expandable film 326, 336 having a non-circular shape, which is similar to the shape of the front and rear lenses 322, 332. Each film 326, 336 is formed from a piece of thermoplastic polyurethane (e.g., Elastollan ^® 1185A10, which can be purchased from BASF) and has a thickness of about 220 μm. Other suitable materials can be used for the films 326, 336 (and other components of the display unit 300), such as those disclosed by WO 2017/055787 A2.

Each of the membranes 326, 336 is held under tension around its circumference by a respective resiliently flexible support ring 377, 387. As described in more detail below, each of the membranes 326, 336 forms the front optical surface of a respective liquid lens assembly 320, 330, such that the net effective focusing power of each lens assembly 320, 330 is determined by the curvature of the membrane 326, 336 and the fixed focusing power of the rear surface 323, 333 of the associated hard lens 322, 332.

Each of the support rings 377, 387 is made from a stainless steel sheet and has a thickness of about 0.55 mm, but more typically each ring may have a thickness in the range of about 0.50-0.60 mm, or may include a stack of two or more ring elements instead of a single ring. Each film 326, 336 is bonded to a respective support ring 377, 387 by a light-curable adhesive (e.g., Delo® MF643 UV-curing epoxy adhesive) or other means and is maintained at a linear tension of about 200 Nm ^-1 .

The peripheral protrusions 375, 385 of each disc-shaped container 370, 380 are bonded to the peripheral areas 327, 337 of the respective films 326, 336 by using a suitable adhesive (e.g., Delo® MF643 UV-curing epoxy adhesive) or other means, such as (e.g.,) ultrasonic welding, laser welding, and the like, so that each film 326, 336 is sandwiched between the protrusions 375, 385 of the respective disc-shaped containers 370, 380 and the corresponding support rings 377, 387.

Each of the support rings 377, 387 can be moved toward or away from the respective hard lens 322, 332, and the side walls 373, 383 of the associated dish-shaped containers 370, 380, respectively, fold over themselves or extend to allow such movement.

In other embodiments of the invention, more than one support ring 377, 387 may be used in one or both of the front and rear lens assemblies 320, 330. For example, the membrane 326, 336 may be sandwiched between two similar support rings, as described, for example, in WO 2013/144533 A1. In this embodiment, only one ring is shown for simplicity.

Each of the support rings 377, 387 is formed to have a plurality of integral, spaced-apart, outwardly protruding tabs, including active tabs 378, 388 and passive tabs 379, 389, as described in more detail below. In Figures 12A and 12B, only the active tabs 378 and passive tabs 379 of the support ring 377 of the front lens assembly 320 can be seen.

The active tabs 379, 389 of the front and rear lens assemblies 320, 330 engage in corresponding elevator tracks formed in an arcuate cam plate 390 mounted within the housing toward the relatively short left temple 301 of the unit 300 (the right temple of the unit 300 is shown in the right hand). Cam plate 390 is constrained within the housing to slide along a curved path y that is orthogonal to optical axis z and follows the curvature of adjacent regions of the front and rear lens assemblies 320, 330 (as best seen in Figures 12A and 12B) between a first position shown in Figures 12A, 13A, 14A and 15A and a second position shown in Figures 12B, 13B, 14B and 15B. The active tab 379 of the front lens assembly 320 engages a front series of elevator tracks 391, while the active tab 389 of the rear lens assembly 330 engages a rear series of elevator tracks 392. As best seen in Figures 13A, 13B and 19, the front and rear series of elevator tracks 391, 392 are configured to be mirror images relative to each other in a plane that is orthogonal to the optical axis z and intersects the cam plate 390 between the front and rear series of elevator tracks 391, 392, so that reciprocating movement of the cam plate along path y causes the active tab 379 of the front lens assembly 320 and the active tab 389 of the rear lens assembly 330 to move in opposite directions parallel to the z- axis.

The number and location of active tabs 379, 389 of the front and rear lens assemblies 320, 330 vary depending on the shape of the lens assemblies 320, 330 and the accuracy required for shaping the membranes 326, 336 into spherical optical surfaces. In this embodiment, there are three active tabs 379, 389 on the foot side of the lens assemblies 320, 330 for each of the front and rear lens assemblies 320, 330. In other embodiments, there may be more or fewer tabs 379, 389 as desired.

As best shown in Figures 12A and 12B, the passive tabs 378, 388 of the front and rear lens assemblies 320, 330 are disposed at spaced locations on the relatively longer upper and lower sides 302, 303 of each support ring 377, 387, and on the relatively shorter nose side 304 located opposite to the temple side 301. The passive tabs 378, 388 are coupled to the housing (not shown) of the display unit 300 to hold the support rings 377, 387 at the passive tabs 378, 388 at a fixed position relative to the housing. Each of the support rings 377, 387 is held parallel to the z- axis by its passive tabs 378, 388 at a fixed distance from the front surface 324, 334 of the associated hard lens 322, 332. Since the support rings 377, 387 are bendable, they are free to bend between the passive tabs 378, 388 toward or away from the hard lens 322, 332. As described in more detail below, the passive tabs 378, 388 are located at individual points on each support ring 377, 387 where the neutral circle NC (whose center is at the optical center OC of the film 326, 336) passes over the edge of the film 326, 336 (or close to that point). In this embodiment, the passive tabs 378, 388 are therefore approximately equidistant from the optical center. In this embodiment, the eye shape has been selected for good example of illustration. In particular, the temple side 304 of each support ring 377, 387 is on a radius from the optical center OC so that the entire temple side 304 of each support ring 377, 387 remains generally planar in all actuated states, as described below.

The rear wall 372, 382 and side walls 373, 383 of each dish-shaped container 370, 380 thus form with the associated film 326, 336 a respective housing having an internal cavity 325, 335. The cavity 325, 335 of each housing is filled with a substantially incompressible, optically transparent, refractive fluid 328, 338. The fluid 328, 338 should be colorless and have a refractive index of at least about 1.5. Suitably, the refractive index of each film 326, 336 and the associated fluid 328, 338 should be matched so that the interface between the film 326, 336 and the corresponding fluid 328, 338 is substantially imperceptible to the user. The fluid 328, 338 should have low toxicity and low volatility; it should be inert and not exhibit phase changes above about -10°C or below about 100°C. The fluid 328, 338 should be stable at elevated temperatures of at least about 80°C and exhibit low microbial growth. In some embodiments, the fluid 328, 338 may have a density of about 1 g/ ^cm3 . A variety of suitable fluids are available to those skilled in the art, including silicone oils and silicones (such as, for example, phenylsiloxanes). A preferred fluid is pentaphenyltrimethyltrisiloxane.

In this embodiment, each of the films 326, 336 is formed from a polyether polyurethane (e.g., ^Elastollan® 1185) and each of the fluids 328, 338 is a phenyl siloxane, such as pentaphenyltrimethyltrisiloxane. The refractive index of the film material and the fluid is suitably the same or substantially the same and is at least 1.5.

Suitable methods for assembling the front and rear lens assemblies 320, 330 while placing the films 326, 336 under tension as described above are disclosed in WO 2017/055787 A2.

In this embodiment, the internal cavities 325, 335 of the front and rear lens assemblies 320, 330 are filled with refractive fluids 328, 338 so that each of the front and rear films 326, 336 has a minimum curvature of about 0.5 diopters. In other embodiments, the cavities 325, 335 can be filled so that the films 326, 336 have other reference curvatures. Suitable reference curvatures are in the range of about 0 to 1.0 diopters. The reference curvatures for the front and rear films 326, 336 can be the same or different from each other.

As described above, the cam plate 390 is operable to move the active tabs 378, 388 on the support rings 377, 387 forwardly and rearwardly within the housing, away from and toward their corresponding hard lenses 322, 332, respectively. As best shown in Figures 16 and 17, the outer surface of the cam plate 390 carries short teeth 395 that engage a pinion 401, which is arranged to be driven by a bidirectional electric motor 400 through a gear box 402. In this embodiment, a rotary position encoder 403 is also provided to provide an input signal to control the electronic components (not shown) related to the position of the cam plate 390 between the first and second positions of the cam plate 390 as described above. Operating the electric motor 400 thus causes movement of the gear 395 along its curved path, as described above.

In the first position illustrated in Figures 12A, 13A, 14A and 15A, the membrane 326 of the front lens assembly 320 is disposed in its minimum expanded state, having a curvature of approximately 0.5 diopters as mentioned above, as best shown in Figure 14A. The active tabs 378 on the support ring 377 of the front lens assembly 320 are disposed toward the front end of the front series of elevator tracks 391, as best shown in Figure 13A. The pressure of the fluid 328 within the interior cavity 325 is at a minimum state, and the front lens assembly 320 is in a minimum potential condition. The net focusing power of the front lens assembly 320 is therefore approximately zero diopters because the focusing power of the film 326 (which is approximately +0.5 diopters) negates the focusing power of the rear surface 323 of the hard lens 322 (which is approximately -0.5 diopters).

At the same time, the active tabs 388 on the support ring 387 of the rear lens assembly 330 are positioned at the rear end of the rear series of elevator tracks 392, causing the fluid-filled housing of the rear lens assembly 330 to be compressed, particularly in an area toward its foot side 301. The compressible side walls 383 of the dish-shaped container 380 of the rear lens assembly 330 can collapse by folding over itself (as best seen in FIG. 14A), allowing the support ring 387 to move toward the front surface 334 of the hard lens 332, particularly at the foot side 301. The pressure of the fluid 338 in the inner cavity 335 of the rear lens assembly 330 is in a maximum condition, and the film 336 is in a state with a maximum curvature (approximately +2.5 diopters). In this state, the rear lens assembly 330 is in a maximum potential condition. Like the front lens assembly 320, the net focusing power of the rear lens assembly 330 is also approximately zero diopters, and the focusing power of the film 336 (+2.5 diopters) negates the focusing power of the rear surface 333 of the hard lens 332 (approximately -2.5 diopters).

With the cam plate 390 in the first position, the net focusing power of both the front and rear lens assemblies 320, 330 is therefore approximately zero diopter, and the combined focusing power of the entire display unit 300 is also approximately zero diopter.

When the electric motor 400 is operated to drive the cam plate 390 toward its second position (as shown in Figures 12B, 13B, 14B, and 15B), the first and second series of lifter tracks 391, 392 move across the active tabs 378, 388 of the front and rear support rings 377, 387 to drive the active tab 378 of the front lens assembly 320 rearward toward the corresponding hard lens 322, while causing or allowing the active tab 388 on the rear support ring 387 to move forward away from the individual hard lens 332. As cam plate 390 thus gradually moves from its first position toward its second position, the fluid-filled housing of front lens assembly 320 is compressed (particularly toward its temple side 301) while the fluid-filled housing of rear lens assembly 330 is decompressed. Compression of front lens assembly 320 causes fluid pressure within interior cavity 328 to increase, causing membrane 326 to expand forwardly, with the curvature gradually increasing to a maximum curvature of approximately +2.5 diopters when cam plate 390 is in the second position (as best shown in FIG. 14B ). At the same time, the decompression of the rear lens assembly 330 reduces the pressure of the fluid 338 in the cavity 335 of the rear lens assembly 330, causing or allowing the membrane 336 of the rear lens assembly 330 to relax toward its minimum expanded state of +0.5 diopters.

In this position, the active tab 378 on the front support ring 377 is positioned at the rear end of the first series of elevator tracks 391, while the active tab 388 on the rear support ring 387 is positioned at the front end of the second series of elevator tracks 392; the front lens assembly 320 is then in a relatively high energy condition, while the rear lens assembly 330 is in a relatively low energy condition.

In this position, the net focusing power of the front lens assembly 320 is about +2 diopters, while the net focusing power of the rear lens assembly 330 is about -2 diopters. Accordingly, the composite focusing power of the entire display unit 300 is maintained at about zero diopters, but the light emitted from the waveguide display 340 (which only passes through the rear lens assembly 330) is subjected to a focusing power of about -2 diopters, causing the virtual focal plane of the image carried by the light emitted from the waveguide display 340 to move toward the user, as described above with respect to FIGS. 1A to 1D.

It will be appreciated that when the cam plate 390 is disposed in an intermediate position between its first and second positions, the front and rear films 326, 336 each have a curvature between 0.5 and 2.5 diopters. The front and rear lens assemblies 320, 330 are configured so that at each position of the cam plate 390, the combined focusing power of the front and rear films 326, 336 is always approximately equal to the inverse of the combined focusing power of the rear surfaces 323, 333 of the hard lenses 322, 332. In this way, the front and rear lens assemblies 320, 330 are configured to operate as a concentric pair so that the net focusing power of the entire display unit 300 is maintained at approximately zero, while allowing the net focusing power of the rear lens assembly 330 applied to the light emitted by the waveguide display 340 to gradually vary between 0 and -2 diopters.

In this example, therefore, the net focus power of the display unit 300 remains approximately zero as the distance to the virtual image plane changes asymptotically from about 50 cm to infinity. While this is adequate for a user with perfect vision, those skilled in the art will appreciate the need for a display unit with a constant, non-zero net focus power for users with refractive errors. For example, a myopic user may require a display unit 300 in which the rear surface 333 of the rear hard lens 332 has a focusing power of approximately -4.75 D and the rear surface 323 of the front hard lens 322 has a focusing power of -0.5 D, while the focusing power of each film 326, 336 varies between approximately +0.5 D and approximately +2.5 D (as described above), so that the net composite focusing power of the display unit 300 will remain approximately -2.25 D. Other requirements (including astigmatism correction) will also be apparent to those skilled in the art. Note that any refractive error correction should be placed on the rear lens assembly 330 so that the error correction is applied to both the virtual image and the real world view.

As mentioned above, the front and rear films 326, 336 in this embodiment should expand spherically or nearly spherically. It will be understood by those skilled in the art that each of the front and rear lens assemblies 320, 330 is compressed as described above, and there will be a "neutral circle" NC for each assembly 320, 330.

The neutral circle NC of the front lens assembly 320 is shown in Figures 12A and 12B, but similar considerations apply to the rear lens assembly 330. For a given volume of refractive fluid 328, the neutral circle NC has a constant diameter and a constant distance from the back wall 272 of the dished container 270 (which is bonded to the hard lens 322), regardless of the expansion of the film 326 and the corresponding focusing power of the lens assembly 320. The neutral circle is defined by the intersection of a plane and the film 326, so that the volume of fluid 328 enclosed by the plane and the film 326 is equal to that above and below the plane. In other words, as the membrane 326 expands forwardly due to moving the cam plate 390 toward its second position (as described above), the volume of fluid 328 displaced from the surrounding area 351 of the cavity 325 outside the neutral circle NC (as shown in Figures 12A and 12B) is equal to the volume of fluid displaced into the inner area 352 of the cavity 325 within the neutral circle NC.

It can be seen that after actuating each of the front and rear lens assemblies 320, 330 to deform the membrane 326, 336 spherically or nearly spherically, the distance between the edge of the membrane 326, 336 and the rear wall 372, 382 of the corresponding disc-shaped container 370, 380 should be maintained substantially constant. Accordingly, the passive tabs 379, 389 on the front and rear support rings 377, 387 should be placed at (or close to) the position where the neutral circle NC intersects the edge of the membrane 326, 336, as mentioned above.

Suitably, the cam plate 390 is made from a strong, rigid material, such as, for example, steel. As illustrated in FIG. 19 , each of the lifter tracks 391 , 392 is advantageously provided with a liner 393 made from a low friction material, such as, for example, PTFE, to facilitate sliding of the active tabs 378, 388 within the lifter tracks 391 , 392. Alternatively, the entire cam 390 may be coated with such a low friction material. Alternatively (or additionally), the active tabs 378, 388 may be coated with such a low friction material. In another embodiment, the active tabs 378, 388 on the front and rear support rings 377, 387 may be replaced by short shafts 478, 488, respectively, which protrude outwardly from the support rings 377, 387, as shown in Figure 21. Each short shaft 478, 488 carries a small rotating wheel 479, 489, which is received in a respective one of the elevator tracks 391, 392, as shown in Figure 20. The small rotating wheels 479, 489 are also responsible for facilitating their movement within the elevator tracks 391, 392.

As mentioned above, when the cam plate 390 is disposed in its first position, the film 326 of the front lens assembly 320 is disposed in a relatively low energy state, while the film 336 of the rear lens assembly 330 is disposed in a relatively high energy state. As the cam plate 390 is moved (after operation of the electric motor 400) toward its second position, the front film 326 gradually becomes more expanded, storing more potential energy, while the rear film 336 gradually relaxes, releasing potential energy. It will be appreciated that by operation of the cam plate 390, which links the front and rear lens assemblies 320, 330, the potential energy stored in the rear lens assembly 330 is released in the form of work to assist the electric motor 400 in driving the cam plate toward its second position, in which progressively more potential energy is stored in the front film 326.

Thus, when the cam plate 390 is disposed in its second position, the film 326 of the front lens assembly 320 is disposed in a relatively high energy state, while the film 336 of the rear lens assembly 330 is disposed in a relatively low energy state. As the cam plate 390 moves in the opposite direction, after operating the electric motor 400, the front film 326 relaxes, releasing potential energy, while the rear film 336 becomes progressively more expanded, storing potential energy, and energy is released from the front lens assembly 320 in the form of work to assist the electric motor 400 in driving the cam plate 390 back toward its first position, in which more potential energy is stored in the rear film 336.

For the first order case, in the absence of friction, the work required for quasi-static actuation of the front and rear lens assemblies 320, 330 is half the work required to individually actuate the front or rear lens assemblies 320, 330. The use of low friction materials on the active tabs 378, 388 or on the runner assemblies 478, 479; 488, 489 can be used to reduce friction in the elevator track of the cam plate 390, allowing as much energy as possible to be released from one of the lens assemblies 320, 330 as it relaxes to expand as work in accordance with the present invention to facilitate actuation of the other lens assembly 330, 320 as it expands.

FIG. 19 shows the cam plate 390 in an intermediate position between the first and second positions. As shown, the active tabs 378, 388 tend to push the cam plate 319 on the actuator track forward in a direction parallel to the z- axis. N1 and N2 respectively show the normal forces of the active tabs 378, 388 on the cam plate 390, while arrows Y1 and Y2 are the forces caused by the active tabs 378, 388 in the y -direction. It will be appreciated that in either direction of movement of the cam plate 390, the active tabs 378, 388 in one of the first or second series of lifter tracks 391, 392 will assist movement of the cam plate 390, while the active tabs 388, 378 in the other of the second or first series of lifter tracks 392, 391 will resist such movement (as long as the friction between the active tabs 378, 388 and the lifter tracks 391, 392 is low). In the absence of friction, a single cam plate 390 for actuating both the front and rear lens assemblies 320, 330 requires less work than an equivalent single cam for positive actuation of a single lens. For the cam plate 390 to move from the first position to the second position (for example), the elastic position of the rear lens assembly 330 that is released from actuation can assist in actuating the front lens assembly 320 .

E: User's eye N1, N2: Normal force O: Optical axis R: Foxglove R1, R2: Region V: Bee Y1, Y2: Arrow OC: Optical center NC: Neutral circle 20: Front variable focus power compressible liquid lens assembly 21: Peripheral support ring 22: Hard rear lens 23: Rear optical surface 24: Front surface 25: Housing 26: Expandable membrane 27: Foldable sidewalls 30: Rear variable focus power compressible liquid lens assembly/head-mounted device 31: Peripheral support ring 32: Hard rear lens/frame 33: Concave rear surface/left eyeline part 34: convex front surface/right eyeline part 35: shell/nose bridge 36: expandable film/left temple 37: foldable side wall/right temple 38: non-circular opening 39: non-circular opening 40: waveguide display 100: augmented reality display unit 120: front variable focus power compressible liquid lens assembly 122: hard front plate 123: rear surface 124: front surface 125: shell 126: expandable film 127: foldable side wall 128: fluid 130: rear variable focus power compressible liquid lens assembly 132: Hard rear lens 133: Rear surface 134: Front surface 135: Housing 136: Expandable membrane 137: Foldable sidewalls 138: Fluid 140: Waveguide display 150: Shaft ring 152: Front end 153: Rear end 155: Cylindrical groove 157: External surface 158: Window 160: Projector 220: Front liquid lens assembly 222: Hard lens 223: First (inner) surface 224: Second (external) surface 225: Housing/cavity 226: Expandable elastic membrane 227: Foldable sidewalls 228: Fluid 229: edge 230: rear liquid lens assembly 232: hard lens 233: first (inner) surface 234: second (outer) surface 235: housing 236: expandable elastic membrane 237: foldable sidewall 238: fluid 239: edge 240: transparent waveguide display 300: display unit 301: foot side 302: upper side 303: lower side 304: nose side 320: front variable focus power compressible liquid lens assembly 322: hard lens 323: rear surface 324: front surface 325: cavity 326: front film 327: surrounding area 328: refractive fluid 330: rear variable focus power compressible liquid lens assembly 332: hard lens 333: rear surface 334: front surface 335: cavity 336: rear film 337: surrounding area 338: refractive fluid 340: waveguide display 351: surrounding area 352: inner area 370: dish-shaped container 372: rear wall 373: side wall 375: protrusion 377: support ring 378: active tab 379: passive tab 380: dish-shaped container 382: rear wall 383: side wall 385: protrusion 387: support ring 388: active tab 389: passive tab 390: cam plate 391: lifter track 392: lifter track 393: pad 395: short gear 400: electric motor 401: small gear 402: transmission box 403: rotary position encoder 478: short shaft 479: small wheel 488: short shaft 489: small wheel

The following is a description by way of example only, with reference to the accompanying drawings of embodiments of various aspects of the present invention.

In the diagram:

FIG. 1A-1D is a series of schematic representations of an augmented reality display unit including front and rear variable focus power compressible liquid lens assemblies and an interpolated waveguide display. The augmented reality display unit is shown in cross section to illustrate the adjustment of the front and rear compressible liquid lens assemblies with concentric pairs so that their net focus power is zero. In each of FIG. 1A-1D, a virtual object (a bee) is displayed in different virtual image planes according to the focus power of the rear compressible liquid lens assembly, while a real object (foxglove) is displayed in its real image plane.

FIG. 2 is a plan view of an augmented reality display unit according to the first embodiment of the present invention. The augmented reality display unit includes front and rear variable focus power compressible liquid lens assemblies, each having a circular front and rear optical outer surface, one of the front and rear optical outer surfaces having a fixed focus power provided by the surface of a hard lens, and the other having a variable focus power provided by the surface of an expandable film. The augmented display unit also includes an interpolated waveguide display. The front and rear optical outer surfaces of both the front and rear compressible liquid lens assemblies and the waveguide display are represented by dotted lines.

FIG. 3 is a front elevation view of the augmented reality display unit of FIG. 2.

FIG. 4 is a perspective view from the front and to one side of the augmented reality display unit of FIGS. 2 and 3 , wherein the augmented reality display unit is shown in cross section along the straight line B-B of FIG. 3 .

5A-5C are a series of cross-sectional views of the augmented reality display unit of FIGS. 2-4 along line A-A of FIG. 3. In each of FIGS. 5A-5C, the expandable membranes of the front and rear compressible liquid lens assemblies are shown in different actuation states that combine to produce the same net focusing power.

FIG. 6 is a schematic representation of a type of front compressible liquid lens assembly included in the augmented reality display unit of FIGS. 2 to 5 , wherein the front compressible liquid lens assembly has an optical axis located at the center.

FIG. 7 is a schematic representation of a type of rear compressible liquid lens assembly included in the augmented reality display unit of FIGS. 2 to 5, wherein the rear compressible liquid lens assembly has an optical axis located at the center.

FIG. 8 is a schematic representation of a front compressible liquid lens assembly for use in an augmented reality display unit of the present invention, wherein the optical axis is eccentric and the hard lens is tilted relative to the optical axis.

Figures 9A-9C are a series of schematic representations of a rear compressible liquid lens assembly used in an augmented reality display unit of the present invention, wherein the optical axis is eccentric. In Figure 9A, the hard lens of the rear compressible liquid lens assembly is shown in an untilted position; in Figure 9B, the hard lens of the rear compressible liquid lens assembly is tilted relative to the optical axis; in Figure 9C, the hard lens of the rear compressible liquid lens assembly is tilted relative to the optical axis and moved closer to the expandable film.

FIG. 10 is a schematic diagram of an augmented reality display unit according to the present invention, wherein the hard lenses of the front and rear compressible liquid lens assemblies are tilted relative to the optical axis so that the amount of prism introduced by each is equal and opposite, and the waveguide display is configured to apply a prism amount to the light output from the waveguide display that is equal and opposite to the amount of prism introduced by the hard lens of the tilted rear compressible liquid lens assembly.

Figure 11 is a schematic perspective view of an augmented reality head-mounted device (worn by a user) according to the second embodiment of the present invention.

Fig. 12A is a front view of a left-side non-circular augmented reality display unit according to the present invention, which is included in the augmented reality head-mounted device of Fig. 11. The left-side augmented reality display unit includes an adjustment mechanism, which is shown (in Fig. 12A) in a first position.

FIG. 12B is another front elevation view of the augmented reality display unit of FIG. 12A , with the adjustment mechanism shown in a second position.

FIG. 13A is a left elevation view of the augmented reality display unit of FIGS. 12A and 12B , with the adjustment mechanism shown in a first position.

FIG. 13B is another left elevation view of the augmented reality display unit of FIGS. 12A , 12B , and 13A , with the adjustment mechanism shown in a second position.

Fig. 14A is a cross-sectional view of the augmented reality display unit of Figs. 12A, 12B, 13A, and 13B taken on line A-A shown in Fig. 12A. Fig. 14A shows the front and rear compressible liquid lens assemblies and the intercalated waveguide display forming part of the augmented reality display unit.

FIG. 14B is a cross-sectional view of the augmented reality display unit of FIGS. 12A, 12B, 13A, 13B, and 14A taken along the line B-B shown in FIG. 12B.

Figure 15A is a perspective view from the front and to the right side of a section of the augmented reality display unit of Figures 12A, 12B, 13A, 13B, 14A, and 14B on the straight line C-C in Figure 12A, showing the adjustment mechanism in the first position.

Figure 15B is a perspective view from the front and to the right side of a section of the augmented reality display unit of Figures 12A, 12B, 13A, 13B, 14A, 14B, and 15A on the straight line D-D in Figure 12B, showing the adjustment mechanism in the second position.

FIG. 16 is a perspective view from the left rear of a cam plate having an external toothed portion, which forms part of the adjustment mechanism of the left side augmented reality display unit of FIGS. 12A, 12B, 13A, 13B, 14A, 14B, 15A and 15B.

Figure 17 is a bottom view of the cam plate and electric motor (also forming part of the adjustment mechanism) of Figure 16, showing the mutual engagement of the gear portion and the small gear arranged to be driven by the electric motor.

FIG. 18 is a perspective view of the electric motor shown in FIG. 17.

FIG. 19 is a left elevation view of the cam plate of FIG. 16 , including an enlarged view of a portion of the cam plate showing two lifter cam tracks.

FIG. 20 is a side elevation view of an alternative cam plate for use in an adjustment mechanism for an augmented reality display unit according to the present invention.

FIG. 21 is an exploded perspective view from the left rear of the cam plate of FIG. 20 , showing its engagement with the cam followers (in the form of rollers) on the front and rear compressible liquid lens assemblies of the augmented reality display module.

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

E: User's eyes

R: Foxglove

V: Bee

20: Front variable focus power compressible liquid lens assembly

22: Hard rear lens

23: Rear optical surface

24: Front surface

25: Shell

26: Expandable film

32: Hard rear lens/frame

36: Expandable film/left temple

40: Waveguide display

Claims (23)

An augmented reality display unit for use in an augmented reality head mounted device, comprising a front compression liquid lens assembly and a rear compression liquid lens assembly arranged on an optical axis in optical alignment with each other, a transparent waveguide display inserted between the front compression liquid lens assembly and the rear compression liquid lens assembly, and a selectively operable adjustment mechanism for adjusting the focusing power of the front compression liquid lens assembly and the rear compression liquid lens assembly simultaneously in a mutually opposite manner; wherein the Each of the front compression liquid lens assembly and the rear compression liquid lens assembly comprises a fluid-filled housing having a first wall, a second wall and a foldable side wall formed by an expandable elastic film, the expandable elastic film being held under tension around its edges by a film retaining structure, the second wall being substantially rigid and formed by or supported on an inner surface of a transparent plate or a hard lens having a fixed focusing power; wherein the expandable elastic film forms a first wall having a second wall and a foldable side wall; The selectively operable adjustment mechanism is arranged to displace the film holding structure parallel to the optical axis toward the second wall or away from the second wall to increase or decrease the pressure of the fluid in the housing, thereby causing the expandable elastic film to expand or contract parallel to the optical axis to change the focusing power of the optical surface of the expandable elastic film, wherein each of the front compression liquid lens assembly and the rear compression liquid lens assembly stores elastic potential energy when its absolute focusing power increases. and releases elastic potential energy when its absolute focusing power decreases; and wherein the selectively operable adjustment mechanism is configured to couple the front compression liquid lens assembly and the rear compression liquid lens assembly together, so that the elastic potential energy released by one of the front compression liquid lens assembly and the rear compression liquid lens assembly when its absolute focusing power decreases assists in driving the selectively operable adjustment mechanism to increase the absolute focusing power of the other of the front compression liquid lens assembly or the rear compression liquid lens assembly. An augmented reality display unit as described in claim 1, wherein the film retaining structure includes a peripheral support ring. An augmented reality display unit as described in claim 2, wherein the surrounding support ring is circular. An augmented reality display unit as described in claim 3, wherein the surrounding support ring is rigid. An augmented reality display unit as described in claim 2, wherein the peripheral support ring is non-circular. An augmented reality display unit as described in claim 5, wherein the surrounding support ring is elastically bendable. An augmented reality display unit as described in claim 6, wherein the selectively operable adjustment mechanism is arranged to displace one or more regions of the peripheral support ring parallel to the optical axis toward the second wall or away from the second wall, resulting in bending of the peripheral support ring. An augmented reality display unit as described in claim 7, wherein the peripheral support ring is maintained at a fixed distance from the second wall at one or more pivot points, and the peripheral support ring is bendable between the pivot points. An augmented reality display unit as described in claim 1, wherein the film holding structure is maintained at a fixed distance from the second wall at one or more pivot points. An augmented reality display unit as described in claim 1, wherein the selectively operable adjustment mechanism engages the film holding structure at one or more actuation points, so that operation of the selectively operable adjustment mechanism causes the edge of the expandable elastic film to be regionally displaced toward or away from the second wall parallel to the optical axis at the one or more actuation points. An augmented reality display unit as described in claim 1, wherein the selectively operable adjustment mechanism comprises a reciprocating structural member, the reciprocating structural member is operatively connected to the film holding structures of the front compression liquid lens assembly and the rear compression liquid lens assembly, and is used to simultaneously displace the film holding structures toward or away from their respective second walls in a mutually opposite manner parallel to the optical axis, so that when the absolute focusing power of one of the compression liquid lens assemblies increases, the absolute focusing power of the other compression liquid lens assembly decreases, and vice versa. An augmented reality display unit as described in claim 11, wherein the selectively operable adjustment mechanism includes a reciprocating cam plate having one or more first cam surfaces and one or more second cam surfaces, the one or more first cam surfaces being arranged to engage one or more individual cam follower members at one or more actuation points on the film holding structure of the front compression liquid lens assembly, and the one or more second cam surfaces being arranged to engage one or more actuation points on the film holding structure of the rear compression liquid lens assembly. One or more individual cam follower components at the actuation points; the one or more first cam surfaces and the one or more second cam surfaces are configured so that the movement of the cam plate causes the film holding structures of the front compression liquid lens assembly and the rear compression liquid lens assembly to simultaneously shift in a mutually opposite manner parallel to the optical axis toward or away from their respective second walls at their respective actuation points, so that as the absolute focusing power of one of the compression liquid lens assemblies increases, the absolute focusing power of the other compression liquid lens assembly decreases, and vice versa. An augmented reality display unit as described in claim 12, wherein the reciprocating structural member comprises a shaft ring having first and second opposite ends, the shaft ring being disposed around the transparent waveguide display and arranged for reciprocating movement parallel to the optical axis between the front compression liquid lens assembly and the rear compression liquid lens assembly, the first end of the shaft ring or at least one component connected thereto being arranged to engage the film retaining structure of the front compression liquid lens assembly, and the second end of the shaft ring or at least one component connected thereto being arranged to engage the film retaining structure of the rear compression liquid lens assembly. An augmented reality display unit as described in claim 13, wherein the front compression liquid lens assembly and the rear compression liquid lens assembly are arranged so that their respective expandable elastic films and film retaining structures face the shaft ring. An augmented reality display unit as claimed in claim 13, wherein the shaft ring is formed to have at least one opening, and the at least one opening is maintained aligned with the transparent waveguide display at all positions of the shaft ring between the front compression liquid lens assembly and the rear compression liquid lens assembly. An augmented reality display unit as claimed in claim 1, wherein the second wall of the front compression liquid lens assembly is formed by or supported on a hard lens having an optical outer surface, the optical outer surface having a focusing power in the range of about -1.0 to about 0 diopters. An augmented reality display unit as described in claim 16, wherein the optical surface of the expandable elastic film of the front compression liquid lens assembly has a baseline focusing power of about 0 to 1.0 diopters, and the baseline focusing power can be adjusted within a range of about 1.0 to 3.0 diopters. An augmented reality display unit as claimed in claim 1, wherein the second wall of the rear compression liquid lens assembly is formed by or supported on a hard lens having an optical outer surface having a focusing power in the range of about -1.0 to about -3.0 diopters. An augmented reality display unit as described in claim 18, wherein the optical surface of the expandable elastic film of the rear compression liquid lens assembly has a baseline focusing power of about 0 to 1.0 diopters, and the baseline focusing power can be adjusted within a range of about 1.0 to 3.0 diopters. An augmented reality display unit as described in claim 1, wherein the net focusing power of the augmented display unit is maintained at approximately zero during adjustment of the rear compression liquid lens assembly. An augmented reality display unit as claimed in claim 1, wherein during adjustment of the post-compression liquid lens assembly, such as to correct for a user's refractive error, the net focusing power of the augmented display unit remains non-zero and substantially constant. An augmented reality head mounted device for a user, comprising at least one augmented reality display unit as described in claim 1 and at least one projector, wherein the augmented reality display unit is arranged to be positioned in front of the user's eyes when the head mounted device is worn, and the projector has an output coupled to the transparent waveguide display. An augmented reality head mounted device as claimed in claim 22, comprising two augmented reality display units as claimed in claim 1, wherein each of the augmented reality display units is arranged to be positioned in front of a respective one of the user's eyes when the head mounted device is worn.