A device, optical lens, headset and system comprising liquid crystal material controllable by electrical elements

Abstract

A device, comprising: at least one liquid crystal cell including groups of electrodes activatable in parallel to switch liquid crystal material into one or more configurations exhibiting co-operative refractive index distributions in respective zones of the liquid crystal material; the liquid crystal cell comprising one or more liquid crystal alignment layers that interface with the liquid crystal material; the one or more liquid crystal alignment layers being configured to act to induce respective first and second average molecular orientations in adjacent zones of the liquid crystal material; the first and second average molecular orientations being substantially orthogonal to one another.

Description

[0001] A DEVICE, OPTICAL LENS, HEADSET AND SYSTEM COMPRISING LIQUID CRYSTAL MATERIAL CONTROLLABLE BY ELECTRICAL ELEMENTS

[0002] The present invention relates to a device comprising liquid crystal (LC) material controllable by electrical elements, an adaptive optical lens comprising the device, a headset comprising one or more of the adaptive optical lenses, a system comprising the device and a driver chip, an assembly comprising the device and at least one optical element, and an apparatus comprising the device, a processor, a storage comprising instructions for controlling the device.

[0003] Some devices use the possibility to electrically vary one or more optical properties (such as refractive index) of LC material to achieve optical effects, such as optical focussing of incident light. Such devices may comprise groups of electrodes activatable in parallel to switch liquid crystal material into one or more configurations exhibiting co-operative refractive index distributions in respective zones of the liquid crystal material. These groups of electrodes may be referred to as Fresnel groups of electrodes because the respective zones of the liquid crystal material in which the groups of electrodes induce co-operative refractive index distributions correspond to the concentric annular sections of a Fresnel lens.

[0004] The inventor for the present application has worked on devising techniques to improve the optical performance of such devices.

[0005] Examples are described in detail herebelow, by way of example only, with reference to the accompanying drawings, in which:

[0006] Fig. 1 shows a representation of an example of Fresnel groups of concentric conductor rings for a liquid crystal optical lens according to some example example;

[0007] Fig. 2 shows a representation of an example for the radially innermost group of concentric conductor rings in Fig.1 , according to some examples;

[0008] Fig. 3 shows a cross-sectional representation of a device including the Fresnel groups of concentric conductor rings of Fig. 1, according to some examples examples; Fig. 4 shows a cross-sectional representation of a configuration of the liquid crystal material of a liquid crystal cell across a plurality of zones under the influence of the liquid crystal alignment layers of the cell without activation of the Fresnel groups of concentric electrodes, according to some example examples;

[0009] Fig. 5 shows a plan representation of an alignment pattern for a liquid crystal alignment layer of one cell according to some example examples;

[0010] Fig. 6 shows a cross-sectional representation of a configuration of the liquid crystal material across a plurality of zones when the Fresnel groups of concentric electrodes are activated in parallel by the application of a waveform in parallel across the Fresnel groups of concentric electrodes;

[0011] Fig. 7 shows a plan representation of the relative orientation of the liquid crystal alignment layers between two cells of a doublet;

[0012] Figs. 8 and 9 show a representation of a method for producing an alignment pattern in a liquid crystal alignment layer according to some examples;

[0013] Fig. 10 shows a representation of an example of a headset incorporating a liquid crystal, adaptive optical lens;

[0014] Fig. 11 shows a representation of an example of a system for operating the headset of Fig. 10; and

[0015] Fig. 12 shows schematically a representation of an example apparatus.

[0016] There is hereby provided a device, comprising: at least one liquid crystal cell including groups of electrodes activatable in parallel to switch liquid crystal material into one or more configurations exhibiting co-operative refractive index distributions in respective zones of the liquid crystal material; wherein the liquid crystal cell comprises one or more liquid crystal alignment layers that interface with the liquid crystal material; wherein the one or more liquid crystal alignment layers are configured to act to induce respective first and second average molecular orientations in adjacent zones of the liquid crystal material; wherein the first and second average molecular orientations are substantially orthogonal to one another. The respective zones may comprise a radial series of consecutive concentric zones comprising a first set of odd number zones in the series and a second set of even number zones in the series; and the one or more liquid crystal alignment layers may be configured to act to induce in the liquid crystal material in the first set of zones an average molecular orientation that is substantially orthogonal to an average molecular orientation that the one or more liquid crystal alignment layers act to induce in the liquid crystal material in the second set of zones.

[0017] The device may comprise at least one pair of the liquid crystal cells; the even number zones of a first liquid crystal cell of the pair may be substantially aligned with the even number zones of a second liquid crystal cell of the pair, and the odd number zones of the first liquid crystal cell may be substantially aligned with the odd number zones of the second liquid crystal cell; and the liquid crystal alignment layers of the pair of liquid crystal cells may be configured such that the one or more liquid crystal alignment layers of the first liquid crystal cell act to induce in the liquid crystal material in the first set of odd number zones of the first liquid crystal cell an average molecular orientation that is substantially orthogonal to an average molecular orientation that the one or more liquid crystal alignment layers of the second liquid crystal cell act to induce in the liquid crystal material in the first set of odd number zones of the second liquid crystal cell.

[0018] There is hereby provided an adaptive optical lens comprising a device as described above.

[0019] There is hereby provided a headset comprising an adaptive optical lens as described above.

[0020] The device may comprise electrical terminals electrically connected to the groups of electrodes in parallel.

[0021] There is hereby provided a system comprising a device as described above, and a driver chip connected to the electrical terminals.

[0022] There is hereby provided a method of operating the device as described above, comprising applying an electrical waveform across the electrical terminals. There is hereby provided a method, comprising: preparing a liquid crystal cell including groups of electrodes activatable in parallel to switch liquid crystal material of the cell into one or more configurations exhibiting co-operative refractive index distributions in respective zones of the liquid crystal material; wherein the zones comprise at least a first zone and a second zone adjacent to the first zone; wherein the method comprises: forming the groups of electrodes in situ on a support substrate; forming in situ on the support substrate one or more layers for processing into the one or more liquid crystal alignment layers; anisotropically processing the one or more layers in a first direction in a first region corresponding to at least the first zone of the liquid crystal material; and anisotropically processing the one or more layers in a second direction substantially orthogonal to the first direction in a second region corresponding to at least the second zone of the liquid crystal material.

[0023] The respective zones may comprise a radial series of concentric zones comprising a first set of odd number zones in the series and a second set of even number zones in the series, and the first region may correspond to the first set of odd number zones; and the second region may correspond to the second set of even number zones.

[0024] Anisotropically processing the one or more layers in a first direction in the first region and anisotropically processing the one or more layers in the second direction in the second region may comprise: covering the one or more layers in the second region; thereafter mechanically rubbing the one or more layers in the first direction; thereafter uncovering the one or more layers in the second region and covering the one or more layers in the first region; thereafter mechanically rubbing the one or more layers in the second direction; and thereafter uncovering the one or more layers in the first region.

[0025] Anisotropically processing the one or more layers in a first direction in the first region and anisotropically processing the one or more layers in the second direction in the second region may comprise: exposing the one or more layers selectively in the first region to light linearly polarised in a first polarisation direction; and exposing the one or more layers selectively in the second region to light linearly polarised in a second polarisation direction substantially orthogonal to the first polarisation direction. Anisotropically processing the one or more layers in a first direction in the first region and anisotropically processing the one or more layers in the second direction in the second region may comprise: covering the one or more layers in the second region; thereafter exposing the one or more layers in the first region to the light linearly polarised in the first polarisation direction; thereafter uncovering the one or more layers in the second region and covering the one or more layers in the first region; thereafter exposing the one or more layers in the second region to light linearly polarised in the second polarisation direction; and thereafter uncovering the one or more layers in the first region.

[0026] Some examples are described below for the example of a device to function as a LC lens for an augmented reality (AR) headset, but the techniques may also be applicable to other devices.

[0027] Fig. 1 shows a representation of an example of a radial series of Fresnel groups 20 of concentric conductor rings for a LC optical lens according to some examples. The example shown in Fig. 1 includes a radial series of five Fresnel groups A to E of concentric conductor rings, but other examples may include more or less Fresnel groups. The Fresnel groups A to E are connected in parallel to terminals 26, 28 located radially outwards of all five Fresnel groups 20 of concentric conductor rings via underlying bus conductors 22, 24. The bus conductors 22, 24 are at a level below the Fresnel groups 20 of concentric conductor rings 8 and connected to the Fresnel groups 20 of concentric conductor rings via through holes in an electrical insulator layer (not shown) formed between the bus conductors 22, 24 and the Fresnel groups 20 of concentric conductor rings. A driver chip 30 is connected to the terminals 26, 28 via pins 32, 34 of the driver chip 30, and to counter electrode terminal 29 (described below) via pin 35 of the driver chip.

[0028] Each Fresnel group 20 of concentric conductor rings comprises a plurality of concentric conductor rings electrically connected in series by conductor links. For example, a patterned conductor layer may define both the conductor links and the concentric conductor rings. For example, the patterned conductor layer may comprise a patterned metal oxide conductor layer such as e.g. a patterned indium-tin-oxide (ITO) layer. Fig. 2 shows a representation of an example of concentric conductor rings and conductor links for radially innermost group A of Fig. 1 . For simplicity of illustration, Fig. 2 shows only a small number of concentric conductor rings 8 electrically connected in series via conductor links 14, but a Fresnel group 20 may comprise much larger numbers of concentric rings 8. The radially innermost and outermost concentric conductors 8 of the Fresnel group A are connected to respective ones of the terminals 26, 28 via respective ones of the bus conductors 22, 24. The same is the case for all the other Fresnel groups 20 of concentric conductor rings.

[0029] Fig. 3 shows a cross-sectional representation of a device including the Fresnel groups 20 of concentric conductor rings of Fig. 1, according to some examples. The device comprises LC material 2 between two support components 4, 6. One of the support components 6 comprises a support film (e.g. flexible plastics (organic polymer) film) supporting the above-mentioned elements including: bus conductors 22, 24; concentric conductor rings 8 of the Fresnel conductor ring groups 20; conductive links 14; terminals 26, 28; and a terminal 29 connected to the counter conductor layer 10 described below.

[0030] The plastics support film also supports a LC alignment layer 18 layer 16. The LC alignment layer 18 interfaces with the LC material 2. The LC alignment layer 18 is discussed in more detail below.

[0031] The other of the two support components 6 also comprises a support film (e.g. flexible plastics (organic polymer) film) supporting a counter conductor (common conductor) layer 10 and a second LC alignment layer 18 between the counter conductor layer 10 and the LC material 2. The second LC alignment layer 18 also interfaces with the LC material 2, and co-operates with the first LC alignment layer 18 of opposing component 4. This second LC alignment layer 18 is also discussed in more detail below.

[0032] The Fresnel groups 20 of concentric conductor rings 20, and the concentric conductor rings 8 and conductor links 14 within the Fresnel groups 20, are configured such that an electrical potential difference applied across the terminals 26, 28 generates co-operative refractive index patterns in corresponding zones of the LC material 2, which co-operative refractive index patterns achieve an optical focussing effect for visible light incident on the LC material 2. The focal length may be adjusted by adjusting the size of the electrical potential difference across the terminals 26, 28.

[0033] The LC alignment layers 18 are configured to induce different LC molecular orientations in different zones of the liquid crystal material 2 of the cell. With reference to Fig. 4 and Fig. 5, the LC alignment layers 18 of a cell are configured such that they act to induce, in the LC material in a zone in the region of any one Fresnel group 20, an average molecular orientation that is substantially orthogonal to the average molecular orientation that the LC alignment layers of the cell act to induce in the LC material in the zone(s) in the region of each adjacent Fresnel electrode group 20. For the example described above of a device comprising a radial series of five Fresnel groups 20 of concentric electrodes, the LC alignment layers 18 of a cell are configured such that they act to induce in the LC material 2 in the zones in the regions of electrode groups A, C and E an average molecular orientation that is substantially orthogonal to the average molecular orientation that the LC alignment layers 18 of the cell act to induce in the LC material in the zones in the regions of the electrodes groups B and D.

[0034] The average molecular orientation refers to the spatial and temporal average of the molecular orientation, and may also be referred to as the director of the liquid crystal material.

[0035] Fig. 6 shows a representation of the LC material when the radial series of groups 20 of concentric electrodes are activated in parallel by the application of an electrical potential difference (drive voltage) across terminals 26, 28, such that the concentric rings within a Fresnel group have increasingly smaller electric potentials radially across the group 20, relative to the electric potential at the counter electrode 10. According to one (DC drive) example of activating the concentric electrodes, the electric potential at the concentric electrodes is constant in terms of polarity over time relative to the electric potential at counter electrode 10. According to another (AC drive) example for activating the concentric electrodes, the electric potential at the concentric electrodes is alternated over time in terms of polarity relative to the electric potential at counter electrode 10, at a high switching frequency of e.g. about 60Hz or above. The AC drive example may help to better protect the molecules of the LC material. According to one example: synchronised AC voltage waveforms having relatively high and low amplitudes are applied to terminals 28 and 26 respectively; and a reference COM electric potential (e.g. OV) is applied to the third terminal 29 connected to the counter electrode 10. The sizes of the amplitudes of the synchronised AC voltage waveforms control the size of Rl distribution generated in the LC material and thus control the optical power (dioptres) of the device. In this simple example, three inputs (one input to counter electrode 10 (terminating in terminal 29) and two inputs to the two busbars (terminating in terminals 26, 28) are used), but other examples may include more busbars, and more respective inputs to those busbars via respective terminals.

[0036] In those parts of each zone A to E in which the electrical potential difference across the LC material 2 is low, the influence of the LC alignment layers 18 on the average molecular orientation of the LC material is at its strongest; and the influence of the LC alignment layers 18 on the average molecular orientation of LC material decreases with increasing electric potential across the LC material 2, i.e. decreases with increasing radial distance across the zone of the LC material in the region occupied by a group 20 of concentric electrodes. The orthogonal influence of the LC alignment layers 18 of the cell on the LC material in a zone in the region of one Fresnel electrode group 20 relative to the influence of the LC alignment layers 18 of the cell on the LC material in a zone in the region of an adjacent electrode group 20 may have the effect of reducing the influence of LC material in one zone (particularly the part of that zone where the electrical potential difference across the LC material is at its highest) on the LC material in an adjacent zone of the LC material (in the region of an adjacent electrode group 20), particularly a part of the adjacent zone where the electrical potential across the LC material is at its lowest. This can reduce the occurrence of defects (disinclination lines) when the device is activated by applying an electric potential in parallel across the Fresnel groups of electrodes.

[0037] The LC alignment layers 18 on opposite sides of the LC material are matching and aligned with each other in the assembled cell, so that they have a co-operative influence on the molecular orientation of the LC material 2 in each zone.

[0038] According to one example, a pair of the LC cells described above are combined as a doublet to provide the focussing effect for incident light of all polarisations. With reference to Figure 7, the two cells are aligned such that there is orthogonality between the two cells regarding the influence of the LC alignment layers 18 on LC average molecular orientation. For each zone (in the region of a respective Fresnel group 20 of concentric electrodes) the LC alignment layers 18 for one cell of the doublet act to direct the average molecular orientation of the LC material in a first direction, and the LC alignment layers 18 for the other cell of the doublet act to direct the average molecular orientation of the LC material in a second direction substantially orthogonal to the first direction. With reference to the description below of anisotropic processing for producing the LC alignment layers 18: for each pair of corresponding zones in the two cells, the anisotropic processing (e.g. mechanical rubbing in one direction or exposure to linearly polarised radiation) for one cell is orthogonal to the anisotropic processing for the other cell.

[0039] A method of producing the above-described LC alignment layers 18 according to some examples is described below, with reference to Fig.s 8 and 9. Fig.s 8 and 9 show a representation of processing a workpiece W starting from when the workpiece W comprises a substrate 60 (comprising a plastics (organic polymer) support film 60 and one or more components (not shown) formed in situ on the substrate) and a layer 62 formed in situ on the substrate 60 for processing in situ on the substrate 60 into a LC alignment layer 18. A mask 64 is formed on an upper surface of the workpiece W to cover layer 62 selectively in the region of every other Fresnel group 20 of concentric electrodes (e.g. odd-number regions wherein region#1 is the region of the most radially central Fresnel group 20) in the radial series of Fresnel groups 20 of concentric electrodes. The upper surface of the workpiece W is then subject to an anisotropic processing technique (such as e.g. mechanical rubbing in one direction or exposure to linearly polarised radiation (e.g. linearly polarised UV radiation) that gives anisotropic properties to the uncovered parts of layer 62. The mask 64 is then removed, and a new mask 66 is formed on the workpiece W to cover layer 62 selectively in the regions that were previously covered by mask 62 during the first anisotropic processing (e.g. formed on the workpiece W to cover layer 62 selectively in the regions of the even-number Fresnel groups 20 of concentric electrodes). The upper surface of the workpiece W is then subject to an anisotropic processing technique in a substantially orthogonal direction (such as e.g. mechanical rubbing in the orthogonal direction or exposure to linearly polarised radiation having an orthogonal polarisation) that gives to the newly uncovered parts of layer 62 anisotropic properties that are orthogonal to those anisotropic properties of the parts of layer now covered by mask 66. Finally, mask 66 is removed.

[0040] For example, layer 62 may be a polyimide layer formed in situ on support film 60, and the anisotropic processing may comprise unidirectional mechanical rubbing.

[0041] The liquid crystal device described above may, for example, function as or be used within a switchable lens device or a beam steering device. For example, a device may be or comprise an adaptive optical lens comprising a liquid crystal device according to any of the examples herein. Such a device may be or comprise a headset, which may be referred to as a head-mounted display (HMD).

[0042] The liquid crystal device described above is useful in a wide range of applications, including ophthalmic lenses (such as spectacle lenses), virtual reality (VR), mixed reality (MR) and augmented reality (AR) headsets; optical projectors; photographic devices; and communication devices.

[0043] The LC optical lens device may be used for the push lens and / or the pull lens or a combined push / pull lens of an augmented reality (AR) headset such as e.g. that shown in Fig. 10.

[0044] The headset 40 comprises a support frame 42 supporting optical components arranged in optical series in front of the user eye.

[0045] At least one optical component such as one or more of the optical components shown in Fig. 10 may be considered to correspond to or be part of an assembly, which may be considered to be a display stack, comprising at least one liquid crystal cell according to examples herein. In examples, such as that of Fig. 10, such an assembly includes a stack of liquid crystal cells according to examples herein. In the example of Fig. 10, the push lens 48a includes at least one stack of liquid crystal cells, the pull lens 48b includes at least one stack of liquid crystal cells, and the assembly includes the push lens 48a, the waveguide 50, the pull lens 48b, the variable dimmer device 46, which is an example of a luminance adjustment component, and the front window / lens 44. Liquid crystal cells of a stack may be aligned along a common optical axis. In some cases, though, optical axes of at least two of the liquid crystal cells of a stack may be offset from each other in a direction parallel to a plane of a radial electrode pattern of at least one of the liquid crystal cells, provided that light traversing the assembly traverses the liquid crystal cells of the stack. Fig. 10 only shows the optical components for one half of the headset for clarity of representation, but a matching set of optical components is also provided for the other half of the headset.

[0046] The waveguides 50 of the headset respectively display left-and right perspectives of one or more virtual reality objects, by which the user perceives the one or more virtual reality objects as 3D objects. Alternatively, other mechanisms may be employed to display the left / right perspectives of the one or more virtual reality objects, such as e.g. laser projection.

[0047] The degree to which the user's left and right eyes need to rotate relative to each other such that the left and right perspectives of a virtual reality object are simultaneously directed onto the foveas (which are the parts of the retina responsible for sharp central vision necessary for activities for which visual detail is of primary importance) of respective left and right eyes of the user determines the distance at which the user perceives the virtual reality object to be. This mechanism is referred to as vergence.

[0048] The LC optical lens device described above may be used as an adaptive lens device to control the location at which the user's eyes perceive the left / right perspectives of a displayed virtual reality object in focus (i.e. not blurred), which location may be referred to as a focal plane. In other words, the LC optical lens device described above may be used as an adaptive lens device to control the degree to which the lenses in the user's eyes need to adapt to perceive the left and right perspectives of the virtual reality object in focus (i.e. not blurred). This adaptation mechanism of the lenses in the user's eyes is known as accommodation.

[0049] The LC optical lens device described above may be used to produce optical images (real or virtual) of the left / right perspectives of a virtual reality object substantially at the distance from the user's eyes at which the user perceives the virtual reality object to be located through the vergence mechanism discussed above. This may allow the user to perceive a focussed 3D image of the virtual reality object without disrupting the vergenceaccommodation reflex, by which the focussing action of the lenses in the user's eyes (accommodation) is unconsciously linked to the above-mentioned rotation of the left and right eyes relative to each other (vergence). In other words, the LC optical lens device may be used to avoid or reduce the strain on the user's eyes that can arise from a conflict between the vergence and accommodation mechanisms (referred to as the vergenceaccommodation conflict). For example, the LC optical lens device may be switchable between a positive focal power and a negative focal power.

[0050] Hence, a liquid crystal device according to examples herein may provide a lower complexity and / or higher quality system to actively adjust focus to compensate for focal differences between a virtual object and a real-world environment visible to a user of a headset through the optical components mounted in front of each eye. This for example allows the perceived and actual image depth to be brought together in a consistent manner, improving user comfort.

[0051] In Fig. 10, the headset 40 permits transmission of light from a real-world environment around the headset 40 at least partly through the optical components and into the user's eyes. In this example, the optical components are at least partly transparent. On a bright day, the luminance of the environment may be significantly higher outdoors than indoors, such as around 100 times higher. This can lead to a virtual object appearing washed out and difficult to see when the user operates the headset outdoors, unless the luminance of the light transmitted from the environment to the user is appropriately controlled. In Fig. 10, the variable dimmer device 46 controls the amount of light transmitted through the optical components and towards the eyes, e.g. so as to reduce the luminance of light from the environment transmitted towards the user in bright conditions, and may be used to provide ambient dimming to dim ambient light transmitted through the headset 40.

[0052] The variable dimmer device 46 may provide so-called global dimming, in which the luminance of the light from the environment is adjusted by substantially the same amount within an extent of a plane of the variable dimmer device 46 facing the user (e.g. to reduce the luminance of the light by substantially the same amount across an entire surface area of the variable dimmer device 46). In other words, global dimming can allow the luminance of the light transmitted through the variable dimmer device 46 to be controlled in a substantially spatially uniform manner (e.g. so as to provide a substantially spatially uniform reduction in the luminance across a field of view of the user).

[0053] The variable dimmer device 46 may also or alternatively provide local dimming, in which the variable dimmer device 46 is adjustable to control the luminance of the light transmitted from the environment on an area-by-area basis (where an area may correspond to a single pixel or a plurality of pixels). Local dimming may involve adjusting the luminance across less than all of the surface area of the variable dimmer device 46, such as within a sub-area which is smaller than the surface area of the variable dimmer device 46. In other cases, though, local dimming may involve adjusting the luminance across the entire surface area of the variable dimmer device 46 but by different amounts in at least two portions of the surface area.

[0054] Although not shown in Fig. 10, it is to be appreciated that the headset 40 may be configured to obtain luminance data, e.g. from a light sensor of the headset 40, indicative of the luminance of the light within the environment of the headset 40. For example, if a first side 49a of the headset 40 is configured to face the user, with the headset 40 mounted on the head of the user, the headset 40 may include a light sensor to detect the luminance of light at a second side 49b of the headset 40, opposite to the first side 49a. The variable dimmer device 46 may be controlled at least partly based on the luminance data, so as to adjust the luminance of light transmitted from the second side of the headset 40 towards the user, to improve the visibility of the virtual object displayed to the user by the headset 40.

[0055] In the example of Fig. 10, a first lens comprising at least one liquid crystal cell stack of the examples herein (the push lens 48a) is located between the waveguide 50 and the eye, with the headset 40 in use. Light representative of the virtual object is generated and transmitted to the waveguide 50, which directs the light through the push lens 48a and into the eye. The push lens 48a has a focusing effect to focus the light representative of the virtual object so that the object appears in focus to the user. For example, the virtual object may be generated so that it is in focus at a focal plane of infinity. The push lens 48a may then bring the virtual object into focus at a focal plane which is closer to the user than infinity, to allow the user to focus on the virtual object more comfortably. The focal plane at which the virtual object is to be brought into focus, and hence the focusing power to be applied by the push lens 48a, may be determined based on eye tracking data, e.g. obtained by a suitable sensor as discussed further below, which is indicative of a direction in which the eye of the user is looking.

[0056] Prior to use of the headset 40, the external environment may appear in focus to the user. However, in the absence of the pull lens 48b, light from the external environment would be at least partly transmitted through the waveguide 50 and through the push lens 48a and would therefore be subject to the focusing effect provided by the push lens 48a. This would distort the external environment as viewed by the user through the headset 40. To compensate for the distortion introduced by the push lens 48a, the headset 40 of Filg. 10 includes a second lens (the pull lens 48b) positioned at an opposite side of the waveguide 50 to the push lens 48a. The pull lens 48b applies an appropriate focusing effect to light from the environment traversing the pull lens 48b to at least partially compensate for or otherwise reduce the focusing effect introduced by the push lens 48a. For example, the push and pull lenses 48a, 48b may provide opposite focusing effects to each other, e.g. with substantially equal magnitudes but opposite signs. As an example, one of the push and pull lenses 48a, 48b may provide a positive focusing power and the other one of the push and pull lenses 48a, 48b may provide a negative focusing power, which may be substantially equal in magnitude.

[0057] In examples at least one lens of examples herein (such as at least one of the push lens 48a and the pull lens 48b, and in some cases both the push and pull lenses 48a, 48b) each includes a so-called doublet of liquid crystal cells according to examples herein. A doublet is a stack of two liquid crystal cells. The focusing effect of a liquid crystal-based lens may depend on the polarization of the light incident on the lens. Rather than using a separate polarizer component, using a doublet such as this may provide an appropriate focusing effect with improved light transmission; in some examples this is achieved by positioning one liquid crystal cell of the doublet orthogonal to the other liquid crystal cell of the doublet, with respect to the respective orientation of polarization that each liquid crystal cell is configured to modify light for.

[0058] Fig. 10 shows an example of a push lens 48a and a pull lens 48b in combination with various other optical components. It is to be appreciated that a liquid crystal cell in accordance with examples herein can be used in combination with different optical component(s) than those shown in Fig. 10, to provide further flexibility in functionality. This may further reduce the size and / or weight of apparatus including the liquid crystal cell and / or improve optical performance of the apparatus. For example, an assembly, such as a display stack, including a liquid crystal cell in accordance with examples herein may include a reflection-reduction layer (such as an anti-reflection (AR) coating), which may be laminated to another optical component of the assembly, such as the front window / lens 44, and / or a protective layer (such as a hard coat) to protect the assembly from damage, e.g. due to abrasion, and / or wear due to exposure to environmental conditions.

[0059] In examples, the liquid crystal device comprises electrical terminals electrically connected to the busbars. The electrical terminals for example allow a potential difference to be applied across the busbars, and thus across each set of concentric rings. As explained above, the electrical potential applied to an electrical terminal can be controlled by a suitable control system.

[0060] With reference to Fig. 11, a system 55 according to some examples comprises a processor operating on the basis of computer program code stored in a memory 52 to control an image generation driver chip 53 to cause an image generation system to generate images of left / right perspectives of one or more virtual reality objects, by which the user may perceive 3D images of the virtual reality objects, and display the images via the waveguide 50.

[0061] Although not shown in Fig. 11 , it is to be appreciated that there may be two waveguides: one to display an image of a left perspective of a virtual reality object to a left eye and another to display an image of a right perspective of a virtual reality object to a right eye, as discussed furtherwith reference to Fig. 11 . There mayfurther be two image generation systems: one to generate the image of the left perspective of the virtual reality object and another to generate the image of the right perspective of the virtual reality object (although in some cases a single image generation system may generate both images or an image generation system may generate a single image to be displayed to both eyes). An image generation system is discussed further below with reference to Fig. 12. Inputs from sensors feed into the processor to enable the processor to control positions at which the virtual reality objects are displayed by the waveguides 50, for seamless overlay of the one or more virtual reality objects into the user's view of the user's real environment.

[0062] Based on inputs fed into the processor 51 from one or more sensors 54 sensing the movement of the user's eyes and / or based on the content being displayed by the waveguides 50, the processor 51 controls the adaptive lens driver chip 38 to achieve the optical focussing power (Dioptres) required to achieve the above-described generation of optical images of the display output of the waveguides at a distance from the user's eyes at which the virtual content that the user is determined to be looking at (e.g. through tracking of the user's eyes) is intended to be perceived by the user (through the vergence mechanism described above). A driver chip is an example of a controller, which may be implemented in hardware, e.g. via suitably configured circuitry. In some cases, a driver chip may include or be considered to implement at least one processor.

[0063] Fig. 12 illustrates schematically hardware architecture of an apparatus 60 according to further examples. The apparatus 60 comprises at least one liquid crystal cell stack in accordance with examples herein. In Fig. 12, the apparatus 60 is configured to be mounted on human head, e.g. a head of a user, with a liquid crystal cell stack positioned in a field of view of an eye of the head, in use. In the example of Fig. 12, the apparatus 60 is an AR headset for displaying a virtual image to a wearer of the headset, and may be similar to or the same as the headset 40 of Fig. 10. In other examples, though, apparatus including a similar hardware architecture to the apparatus 60 of Fig. 12 may be configured for a different purpose, may include additional components and / or may omit at least one of the components illustrated in Fig. 12. The apparatus 60 of Fig. 12 includes an optical system 62, an image generation system 64, at least one processor 66, storage 68, at least one sensor 70, a user input / output interface 72, a communications system 74 and at least one further hardware system 76. Components of the apparatus 60 are connected to each other via at least one bus 78, which may be or include any suitable interface or bus for transferring data between the illustrate components.

[0064] The optical system 62 includes a first assembly and a second assembly, which in this example are a first display stack 62a and a second display stack 62b, respectively. The first display stack 62a comprises a first set of optical components, e.g. arranged as a stack of layers. The apparatus 60 is configured to permit at least partial transmission of light from an external environment through the first display stack 62a and towards a first eye of the user, with the apparatus 60 in use and mounted on the head. In other words, where the apparatus 60 has a first side configured to face the user, in use (e.g. the first side 49a of Fig. 10), the first display stack 62a is arranged for directing light from the second side towards the first eye (in this case, through the first display stack 62a). The first display stack 62a in this case includes the optical components shown in Fig. 10, i.e. the push lens 48a, the waveguide 50, the pull lens 48b (where the push and pull lenses 48a, 48b are each an example of a liquid crystal device according to examples herein), the variable dimmer device 46 and the front window / lens 44. The push lens 48a and / or the pull lens 48b of the first display stack 62a may be considered to be a first lens comprising a first at least one of the liquid crystal cell stacks according to examples herein. The first lens is configured to be positioned in a first field of view of a first eye, e.g. the first eye of a user, in use.

[0065] In Fig. 12, the second display stack 62b comprises a second set of optical components, which in this example is the same as the first set of optical components but configured to transmit light towards a second eye of the user, with the apparatus 60 in use. In other words, the second display stack 62b is arranged to direct light from the second side of the apparatus 60 towards the second eye. Hence, in this example, the push lens and / or the pull lens of the second display stack 62b may be considered to be a second lens comprising a second at least one of the liquid crystal cell stacks according to examples herein. The second lens is configured to be positioned in a second field of view of a second eye, e.g. the second eye of the user, in use. It is to be appreciated that the first lens may be visible to solely the first eye or to both the first and second eye, in use, and the second lens may be visible to solely the second eye or to both the first and second eye, in use.

[0066] A spatial arrangement of elements of the second display stack 62b in at least one layer of the stack may mirror the spatial arrangement of corresponding elements of the first display stack 62a in the corresponding layer of the stack of the first optical arrangement 62a as reflected in a sagittal plane of the apparatus 60 (which may be referred to as a longitudinal plane of the apparatus 60, and e.g. separates left and right sides of the apparatus, with the apparatus in use). In other cases, though, the first and second display stacks 62a, 62b may have a different structure from each other. It is to be appreciated that the optical system 62 may include further components, e.g. further optical components, not shown in Fig. 12.

[0067] The apparatus 60 also includes an image generation system 64 to generate an image of a virtual object to be displayed to the user of the apparatus 60 so that the virtual object appears to the user to be overlaid on top of the external environment, which is at least partly visible to the user through the optical system 62. The image generation system 64 may be or include a display device to generate an image (e.g. of a virtual object) for display by the apparatus 60 to the user. The display device may be a liquid crystal display (LCD) device, a light emitting diode (LED) display device such as an organic light emitting diode (OLED) display device, an electroluminescent (EL) display device and so forth. In the example of Fig. 12, the image generation system 64 is in optical communication with the optical system 62. For example, the image generation system 64 may be housed by the support frame 42 if the apparatus 60 is in the form of the headset 40 of Fig. 10. Light generated by the image generation system 62 representing the virtual object may be transmitted to the optical system (e.g. to a waveguide such as the waveguide 50 shown in Fig. 10) either directly (e.g. without traversing another optical component) or via at least one further optical component. In some cases, the image generation system may include two display devices, a first one for the first eye and a second one for the second eye, e.g. if it is desired to display a first image to the first eye and a second image to the second eye. In other examples, a single display device may be used to generate an image to be displayed to both the first and second eyes.

[0068] In the example of Fig. 12, the image generation system 64 is shown as a separate system from the optical system 62. In other examples, though, the image generation system may form part of the optical system. For example, an assembly, such as a display stack, of the optical system may include an image generation system, such as a display device.

[0069] The at least one processor 66 of the apparatus 60 may be a single processor or a plurality of processors of one or more types. Components of the at least one processor 66 may be implemented using suitably programmed hardware, e.g. in the form of circuitry. The at least one processor 66 may include a central processing unit (CPU), a graphics processing unit (GPU) and / or a neural processing unit (NPU), which may be referred to as a neural network accelerator.

[0070] In some examples, apparatus, such as the apparatus 60 of Fig. 12, includes driving circuitry connected to at least one electrical connection connected to the electrode patterns of the liquid crystal cell stack to apply a potential difference across one or more electrode sets of the liquid crystal cells of the liquid crystal cell stack. The potential difference applied (such as a magnitude and / ortiming of the potential difference applied) may be determined by the at least one processor 66 and / or by the driving circuitry, such as by a controller implemented by at least a portion of the driving circuitry, based on the instructions stored in the storage.

[0071] If the potential difference is determined by the driving circuitry, the determination of the potential difference may be instigated by instructions received from the at least one processor, such as instructions indicative that a virtual object is to be displayed and that one or more electrode sets are thus to be activated so that the virtual object appears in focus to the user. In this way, the driving circuitry may be agnostic to the at least one processor from which the instructions are received. In other words, the operation of the driving circuitry may for example be independent of the at least one processor used to control the driving circuitry, such that the same effect can be achieved irrespective of the at least one processor coupled to the driving circuitry (provided the at least one processor provides an appropriate indication to the driving circuitry to cause the driving circuitry to determine a suitable potential difference).

[0072] The potential difference may be applied to the electrical connection(s) by at least one driver of the driving circuitry, such as the adaptive lens driver chip 38 of Fig. 11 , which is an example of a driver. Application of a potential difference by the at least one driver may be considered to amount to so-called "driving" of the electrode pattern(s), via the electrical connection(s). The driving circuitry may be in the form of at least one system- on-a-chip (SoC).

[0073] The storage 68 may be or include computer-useable volatile and / or non-volatile memory. The storage 68 may comprise random access memory (RAM) and / or read-only memory (ROM). The storage 68 may be removable or non-removable from the apparatus 60. The storage 68 stores instructions for controlling the apparatus 60 in accordance with examples herein, e.g. to activate one or more electrode sets of the liquid crystal cells of the liquid crystal cell stack. Activation of an electrode set for example refers to applying a potential difference between at least two connectors connected to the electrode set. The instructions may be in the form of computer-readable and / or executable instructions, e.g. computer program instructions. Although the storage 68 is shown as a separate component to the at least one processor 66 in Fig. 12, in some cases the storage 68 may be or include internal storage of the at least one processor 66, in which cases the at least one processor 66 and the storage 68 may be at least partly integrated into the same system or component.

[0074] The at least one sensor 70 in this example is configured to obtain eye tracking data of the apparatus, in use, which for example indicates a direction in which at least one eye of the user is looking, as the skilled person will appreciate. Eye tracking data may be obtained for each eye, or the eye tracking data may be obtained for a single eye or for a combination of both eyes of the user. Suitable sensors for obtaining eye tracking data include a camera 70a for obtaining images of at least one eye of the user, an inertial measurement unit (IMU) 70b for determining an orientation of the apparatus 60 and at least one position sensor 70c such as a global positioning system (GPS) sensor to determine a location of the apparatus 60. As the skilled person will appreciate, an IMU 70b may include at least one accelerator or gyroscope for use in determining the orientation of the apparatus 60. The focusing effect of the at least one liquid crystal cell may be controlled based on the eye tracking data, e.g. so as to reduce user eye strain as described further above.

[0075] The apparatus 60 also includes a user input / output interface 72 via which a user can interact with the apparatus 60 to control aspects of the apparatus 60. For example, the user input / output interface 72 may be or include an input device such as a button, a touchscreen, a slider, a controller or any other suitable device for communicating user requests to the apparatus 60 to control the apparatus 60.

[0076] The apparatus 60 includes a communications system 74 for receiving data from a remote system, e.g. via a suitable telecommunications network, such as a wireless network, or via some other type of network or connection. The communications system 74 may include an input / output interface, such as a Bluetooth connector, a universal serial bus (USB) connector or a network connector, for receiving the data from the remote system.

[0077] The apparatus 60 of Fig. 12 includes at least one further hardware system 76 such as a power source, e.g. a battery, for providing electrical power to the electrical components of the apparatus 60.

[0078] Some examples have been described above for the example of an optical focussing device, but the same techniques have application in other areas such as e.g. beam steering optics.

[0079] Further examples relate to a method of operating a liquid crystal device according to any of the examples herein.

[0080] The term "substantially" used herein may be considered to mean that two elements that are "substantially" the same are: the same within manufacturing tolerances, the same within measurement uncertainties and / or are within 5% of each other. Examples herein refer to a liquid crystal (LC) material. A liquid crystal material is an example of a material with a switchable refractive index, or a refractive index changing material.

[0081] The described device, assembly and apparatus has use in example implementations other than tuneable lens and optical components. Other example implementations include, but are not limited to: image generation systems, read only memory, network connections, USB, Bluetooth systems etc., methods of powering and associated techniques. In addition to any modifications explicitly mentioned above, it will be evident to a person skilled in the art that various other modifications of the described examples may be made within the scope of the invention.

[0082] Some examples have been described above for the example of an optical focussing device, but the same techniques have application in other areas such as e.g. beam steering optics.

[0083] In addition to any modifications explicitly mentioned above, it will be evident to a person skilled in the art that various other modifications of the described example may be made within the scope of the invention.

[0084] The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features.

Claims

CLAIMS1. A device, comprising: at least one liquid crystal cell including groups of electrodes activatable in parallel to switch liquid crystal material into one or more configurations exhibiting co-operative refractive index distributions in respective zones of the liquid crystal material; the liquid crystal cell comprising one or more liquid crystal alignment layers that interface with the liquid crystal material; the one or more liquid crystal alignment layers being configured to act to induce respective first and second average molecular orientations in adjacent zones of the liquid crystal material; the first and second average molecular orientations being substantially orthogonal to one another.

2. The device according to claim 1, the respective zones comprising a radial series of consecutive concentric zones comprising a first set of odd number zones in the series and a second set of even number zones in the series; the one or more liquid crystal alignment layers being configured to act to induce in the liquid crystal material in the first set of zones an average molecular orientation that is substantially orthogonal to an average molecular orientation that the one or more liquid crystal alignment layers act to induce in the liquid crystal material in the second set of zones.

3. The device according to claim 2, comprising at least one pair of the liquid crystal cells; the even number zones of a first liquid crystal cell of the pair being substantially aligned with the even number zones of a second liquid crystal cell of the pair, and the odd number zones of the first liquid crystal cell are substantially aligned with the odd number zones of the second liquid crystal cell; and the liquid crystal alignment layers of the pair of liquid crystal cells being configured such that the one or more liquid crystal alignment layers of the first liquid crystal cell act to induce in the liquid crystal material in the first set of odd number zones of the first liquid crystal cell an average molecular orientation that is substantially orthogonal to an average molecular orientation that the one or more liquid crystal alignment layers of the second liquid crystal cell act to induce in the liquid crystal material in the first set of odd number zones of the second liquid crystal cell.

4. An adaptive optical lens comprising a device according to any of claims 1 to 3.

5. A headset comprising an adaptive optical lens according to claim 4.

6. The device according to any of claims 1 to 3, comprising electrical terminals electrically connected to the groups of electrodes in parallel.

7. A system comprising a device according to claim 6, and a driver chip connected to the electrical terminals.

8. A method of operating the device according to claim 6, comprising applying an electrical waveform across the electrical terminals.

9. An assembly comprising: at least one liquid crystal cell including groups of electrodes activatable in parallel to switch liquid crystal material into one or more configurations exhibiting co-operative refractive index distributions in respective zones of the liquid crystal material; the liquid crystal cell comprising one or more liquid crystal alignment layers that interface with the liquid crystal material; the one or more liquid crystal alignment layers being configured to act to induce respective first and second average molecular orientations in adjacent zones of the liquid crystal material; the first and second average molecular orientations being substantially orthogonal to one another, and comprising at least one further optical element..

10. The assembly of claim 9, the at least one further optical element comprising at least one of: a waveguide, a luminance adjustment component, a lens, an image generation device, a reflection-reduction layer, or a protective layer.

11. Apparatus comprising: at least one liquid crystal cell including groups of electrodes activatable in parallel to switch liquid crystal material into one or more configurations exhibiting co-operative refractive index distributions in respective zones of the liquid crystal material; the liquid crystal cell comprising one or more liquid crystal alignment layers that interface with the liquid crystal material; the one or more liquid crystal alignment layers being configuredto act to induce respective first and second average molecular orientations in adjacent zones of the liquid crystal material; the first and second average molecular orientations being substantially orthogonal to one another, the apparatus further comprising: at least one processor; and at least one storage comprising instructions, the instructions configured to, with the at least one processor, cause the apparatus to control one or more properties of the LC layer.

12. The apparatus of claim 11, configured to be mounted on a human head with the optical device cell stack positioned in a field of view of an eye of the human head.

13. The apparatus of claim 12 further comprising a first lens comprising a first one of the LC layer and first electrode and a second lens comprising a second one of the LC layer and first electrode.

14. The apparatus of claim 13 the field of view of the eye being a first field of view of a first eye, and the first lens being configured to be positioned in the first field of view, in use, and the second lens is configured to be positioned in a second field of view, of a second human eye of the human head, in use.

15. The apparatus according to any one of claims 11 to 14, the apparatus being at least one of an augmented reality display device, a virtual reality display device or a mixed reality display device.

16. A method, comprising: preparing a liquid crystal cell including groups of electrodes activatable in parallel to switch liquid crystal material of the cell into one or more configurations exhibiting cooperative refractive index distributions in respective zones of the liquid crystal material; the zones comprising at least a first zone and a second zone adjacent to the first zone; the method comprises: forming the groups of electrodes in situ on a support substrate; forming in situ on the support substrate one or more layers for processing into the one or more liquid crystal alignment layers; anisotropically processing the one or more layersin a first direction in a first region corresponding to at least the first zone of the liquid crystal material; and anisotropically processing the one or more layers in a second direction substantially orthogonal to the first direction in a second region corresponding to at least the second zone of the liquid crystal material.

17. The method according to claim 16, the respective zones comprise a radial series of concentric zones comprising a first set of odd number zones in the series and a second set of even number zones in the series, and the first region corresponding to the first set of odd number zones; and the second region corresponds to the second set of even number zones.

18. The method according to claim 16 or claim 17, anisotropically processing the one or more layers in a first direction in the first region and anisotropically processing the one or more layers in the second direction in the second region comprises: covering the one or more layers in the second region; thereafter mechanically rubbing the one or more layers in the first direction; thereafter uncovering the one or more layers in the second region and covering the one or more layers in the first region; thereafter mechanically rubbing the one or more layers in the second direction; and thereafter uncovering the one or more layers in the first region.

19. The method according to claim 16 or claim 17, anisotropically processing the one or more layers in a first direction in the first region and anisotropically processing the one or more layers in the second direction in the second region comprises: exposing the one or more layers selectively in the first region to light linearly polarised in a first polarisation direction; and exposing the one or more layers selectively in the second region to light linearly polarised in a second polarisation direction substantially orthogonal to the first polarisation direction.

20. The method according to claim 19, anisotropically processing the one or more layers in a first direction in the first region and anisotropically processing the one or more layers in the second direction in the second region comprises: covering the one or more layers in the second region; thereafter exposing the one or more layers in the first region to the light linearly polarised in the first polarisation direction; thereafter uncovering theone or more layers in the second region and covering the one or more layers in the first region; thereafter exposing the one or more layers in the second region to light linearly polarised in the second polarisation direction; and thereafter uncovering the one or more layers in the first region.T1

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