Optical device

Abstract

There is described an optical lens, comprising: a refractive index changing material layer; an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of the optical lens, at least some of the plurality of oval-shaped electrodes having a ratio of a major axis to a minor axis which changes as the major axis increases.

Description

[0001] OPTICAL DEVICE

[0002] The present application relates to a device comprising liquid crystal (LC) material controllable by electrical elements, an assembly comprising the device and at least one optical element, an apparatus comprising the device, a processor, a storage comprising instructions for controlling the device, and a method of operating such a 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] Fig. 1 shows a representation of an example of Fresnel groups of concentric conductor rings for a liquid crystal, LC, optical lens;

[0005] Fig. 2 shows a representation of an example of the radially innermost group of concentric conductor rings in Fig. 1 ;

[0006] Fig. 3 shows a cross-sectional example representation of a device including the Fresnel groups of conductor rings accordingto Fig. 1 ;

[0007] Fig. 4 shows a cross-sectional example representation of the passage of light beams through an LC layer of a device

[0008] Figs. 5(a) and 5(b) show a representation of how the eye pupil dictates what part of the lens focuses light for different viewing angle;

[0009] Figs. 6(a) and 6(b) show representations of an example of elliptically shaped Fresnel groups and elliptically shaped conductor rings respectively; Figs. 7(a) and 7(b) show a representation of an example lens with oval shaped Fresnel zones, and a plot of radial position against angular position for electrodes, respectively;

[0010] Fig. 8 shows a representation of an example of circuitry for generating voltages signals for Fresnel zones;

[0011] Fig. 9 shows a representation of an example of a headset incorporating a liquid crystal, adaptive optical lens;

[0012] Fig. 10 shows a representation of an example of a system for operating the headset of Fig. 9; and

[0013] Fig. 11 shows schematically a representation of an example apparatus.

[0014] There is disclosed an optical lens, comprising: a refractive index changing material layer; an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of the optical lens, at least some of the plurality of oval-shaped electrodes having a ratio of a major axis to a minor axis which changes as the major axis increases.

[0015] An oval-shaped electrode may have the shortest major axis length having a centre point coinciding with the optical axis of the lens.

[0016] An oval-shaped electrode may be circle-shaped.

[0017] The electrode layer may comprise a plurality of Fresnel zones, each Fresnel zone having a plurality of oval-shaped electrodes of increasing major axis length.

[0018] The innermost and outermost oval-shaped electrodes in each Fresnel zone may be connected across a different electrical potential in each Fresnel zone.

[0019] Each oval-shaped electrode in each Fresnel zone may be electrically connected to an adjacent oval-shaped electrode in the same Fresnel zone.

[0020] The optical device may further comprise a common electrode layer located in parallel to the electrode layer.

[0021] The refractive index changing material layer may be a liquid crystal layer. Each oval-shaped electrode may have a central point, the central point of at least one oval shaped electrode being offset from the focal axis of the optical device.

[0022] Each oval-shaped electrode may have a focii, the focii of at least one oval shaped electrode being offset from the focal axis of the optical device.

[0023] There is provided an assembly comprising: a refractive index changing material layer; an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of an optical lens, at least some of the plurality of oval-shaped electrodes having a ratio of a major axis to a minor axis which changes as the major axis increases; and at least one further optical element.

[0024] The at least one further optical element comprises at least one of: a waveguide, a luminance adjustment component, a lens, an image generation device, a reflectionreduction layer, or a protective layer.

[0025] Apparatus comprising: a refractive index changing material layer; an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of an optical lens, each of the plurality of oval-shaped electrodes having a ratio of a major axis to a minor axis which changes as the major axis increases; 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.

[0026] The may be 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.

[0027] The apparatus may further comprise 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.

[0028] The field of view of the eye may be a first field of view of a first eye, and the first lens may be configured to be positioned in the first field of view, in use, and the second lens may be configured to be positioned in a second field of view, of a second human eye of the human head, in use. The apparatus may be at least one of an augmented reality display device, a virtual reality display device or a mixed reality display device.

[0029] There is provided a method of operating a device comprising: a refractive index changing material layer; and an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of the optical lens, at least some of the plurality of ellipse-shaped electrodes having a ratio of the major axis to the minor axis which changes as major axis increases, the method comprising: selectively applying a potential difference across selected electrodes in order to control the refractive index of a portion of the underlying LC layer.

[0030] The electrode layer may comprise a plurality of Fresnel zones, each Fresnel zone having a plurality of oval-shaped electrodes of increasing major axis length.

[0031] The method may selectively apply a potential difference comprising applying a respective potential difference across an innermost and an outermost oval electrodes of each Fresnel zone.

[0032] The method may electrically connect each adjacent oval electrode of each Fresnel zone.

[0033] In the above, many different aspects have been described. It should be appreciated that further aspects may be provided by the combination of any two or more of the aspects described above.

[0034] Various other aspects are also described in the following detailed description and in the attached claims.

[0035] To achieve liquid crystal, LC, lenses with aperture diameters attractive in for example the augment reality / virtual reality (AR / VR) space (aperture diameters >25mm) while keeping optical powers relevant (>0.5D) and switching speeds low (ideally below 0.5s), segmented phase profile lenses with a set of Fresnel resets along the optical path difference (OPD) profile are used.

[0036] Fig. 1 shows an example representation of a radial series of Fresnel zones 20 of concentric conductor rings for an LC optical lens. The example shown in Fig. 1 includes a radial series of five Fresnel zones A to E of concentric conductor rings, but other examples may include more or less Fresnel groups. Each Fresnel zone includes a plurality of concentric electrodes.

[0037] The Fresnel zones 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. In Fig. 1 only the connection for the first Fresnel zone A is shown via underlying bus conductors 22, 24 for ease of illustration. Typically the innermost and outermost electrodes of each Fresnel zone are connected to respective ones of the bus conductors. In this way an electric potential is applied to each Fresnel zone via bus conductors.

[0038] 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 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 via pin 35 of the driver chip.

[0039] The electrodes, or concentric conductor rings, of each Fresnel zone 20 comprise a plurality of concentric conductor rings electrically connected in series by conductor links. A patterned conductor layer may define both the conductor links and the concentric conductor rings. The patterned conductor layer may comprise a patterned metal oxide conductor layer such as e.g. a patterned indium-tin-oxide (ITO) layer.

[0040] Fig. 2 shows an example representation of concentric conductor rings and conductor links for Fresnel group or zone A of Fig. 1 . For simplicity of illustration, Fig. 2 shows only a small number of concentric conductor rings 8 of Fresnel zone A of Fig. 1 , electrically connected in series via conductor links 14, but a Fresnel zone 20 may comprise much larger numbers of concentric rings 8. The radially innermost and outermost concentric conductors 8 of Fresnel A are connected to respective ones of the terminals 26, 28 by respective ones of the bus conductors 22, 24. Each other Fresnel zone 20 of concentric conductor rings may be configured in a similar manner to Fresnel zone A. The positioning of the conductor links 14 is an illustrative example. Fig. 3 shows an example cross-sectional representation of a device including the Fresnel groups 20 of concentric conductor rings of Fig. 1. The device comprises LC material 2 between two support components 4, 6, such as plastic substrates. It will be appreciated that a device includes multiple layers for its operation. For simplicity, not all required layers are shown in Fig. 3, and only those layers which are helpful for an understanding of the invention are illustrated and / or described.

[0041] 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; and terminals 26, 28; and a terminal 29 connected to the counter conductor layer 10 described below. The concentric rings 8 are shown in Fig. 3, but other elements are not shown for simplicity of the drawing. A first LC alignment layer (not shown) is provided on the substrate formed by the plastics support film 6, which interfaces with the LC material 2.

[0042] The other of the support components 4 also comprises a support film (e.g. flexible plastics (organic polymer) film) supporting a counter conductor or electrode (common conductor) layer 10. A second LC alignment layer (not shown) is provided on the substrate formed by the plastics support film 4. The first and second alignment layers formed on the substrates 4 and 6 , and may co-

[0043] The Fresnel zones 20 of concentric conductor rings 20, and the concentric conductor rings 8 and conductor links 14 within the Fresnel zones 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 example for visible light or other wavelengths outside the visible region, 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. Control may be achieved in each Fresnel zone independent of the other Fresnel zones.

[0044] The LC layer 2 is typically formed of nematic liquid crystal molecules, that are anisotropic molecules that collectively produce optical birefringence. Depending on the average molecular orientation (director) light that passes through the liquid crystal will experience a different refractive index. By producing a controlled gradient in refractive index across a liquid crystal cell, the behaviour of an ordinary refractive lens can be emulated. This is how also a static GRIN (gradient-refractive index) lens functions. However, since the liquid crystal molecules are actuated by an electric field, a liquid crystal lens allows the optical power to be continuously tuned.

[0045] In a LC lens arrangement including a Fresnel region or zone electrode arrangement, each segment (Fresnel zone) spans a number of waves of path difference, and in each zone a ring electrode network builds up the voltage profile that will result in the desired GRIN profile.

[0046] In realisations of such tuneable LC lenses, the refractive index gradient is designed for normal incidence illumination. However, due to the anisotropy of the liquid crystal molecules, the accumulated optical path length (phase) is quite different depending on the angle of incidence. As illustrated in Fig. 4, light beams 15, 19 from opposite angles from the surface normal will travel through the LC molecules with two different angles, and therefore experience different refractive indices than light beam 17 incident at the surface normal, which results in different lens behaviour for different incident beams of light, and poor imaging performance.

[0047] This can be addressed by stackingtwo identical lenses, but with the LC alignment direction in a reversed direction, effectively creating a dual-stack rotationally symmetric system around the optical axis. However, this simultaneously doubles the number of LC cells required, increases the haze, and makes alignment and assembly more challenging.

[0048] In an example the tuneable LC lens may be used in a near-eye device, for example in an AR / VR system, and the human eye pupil will serve as the aperture of the system. The pupil aperture is displaced by approximately 27 mm from the LC lens, being the sum of the average human vertex distance of 14 mm and the average eye’s centre of rotation being 13 mm behind the corneal vertex. When a small pupil is displaced from the lens, only specific portions of the lens will contribute to the imaging at specific field angles. This is illustrated in Fig. 5(a), shown as the human eye rotates through angles 0°, 10°, 20°, and 30° from an axis normal to the surface of the lens. More specifically, for a pupil diameter of 5 mm, the acceptance cone of angles and the average angle for each radial position is around 10° on the lens. This is illustrated with respect to Fig. 5(b).

[0049] The preceding paragraph with reference to Figs. 5(a) and 5(b) sets out an example scenario, and an example application. In general the techniques described may be applied to any LC lens application, for example any LC lens application with a stop / pupil separated from the LC lens.

[0050] With the phase profile typically used to design LC lenses then the response for a single layer for different angles may be deficient because of the problem discussed with reference to Fig 4. Figs. 5(a) and 5(b) show that only certain parts of the lens are responsible for focusing light from certain gaze angles, and this allows a lens design where LC molecule orientation presents the correct phase profile for all parts of the lens in a single layer.

[0051] The off-axis issues the LC molecule anisotropy causes are addressed by departing from the radially symmetric lens design as shown in the exemplary arrangement of Fig. 1 . An electrode structure is presented which will generate an electric field in which molecules will orient to produce the optical path difference that will make the light focus correctly for only the specific cone of rays that are allowed through the eye’s pupil at a particular gaze angle.

[0052] Instead of designing the lens for the idealised normal-incidence case, the accumulated optical path is simulated for different liquid crystal configurations. The configuration is selected that for each position of the lens, for the average acceptance angle at that lens position, generates the adequate phase difference for aberration-free lensing. Using an optical model, a point-by-point optimisation of the LC molecular orientation and by extension the spatially varying electric field is performed, to find the non-rotationally symmetric solution which allows the lens to function well even for off- axis objects.

[0053] This optical model consists of multiple components. The first thing needed is to relate applied voltage to the liquid crystal molecule orientation (director profile). This can be achieved either via commercially available simulation software or analytical models. Once a voltage-dependent director profile is obtained, the optical path difference (OPD) through the LC cell for different angles need be calculated. An analytical approach to solving angled optical propagation in birefringent materials is the Extended Jones matrix model. This allows an OPD to be calculated for each angle of incidence and applied voltage. When these components are in place, an optimisation can be performed thatfor each point on the LC lens will inform what volage should be applied to achieve the targeted OPD for the lens that is being designed. In the final stage of the optimisation algorithm, the electrode pattern to generate the angle-corrected voltage profile is calculated while making sure that design rules are followed.

[0054] When this lens optimisation scheme is applied to an LC lens in the eyeglass formfactor placed in front of a smaller physical aperture (emulatingthe human eye pupil) the electrode pattern the model converges to consists of a set of nested oval shapes.

[0055] Each Fresnel group or zone, and each electrode ring within each Fresnel group or zone, is an oval shape. In an example, the oval shape is an elliptical shape, and further examples are described based on this example of an elliptical shape. An oval shape is non-circular.

[0056] The shape of each electrode preferably adjusts gradually when moving out radially from the optical axis of the lens. In an example implementation, the further an electrode ring is from the optical axis, the greater the change in shape, for at least some some directions, at at least some radial distance, and under at least some design considerations. Within each Fresnel group or zone, each electrode ring shape may change gradually the further away from the optical axis the electrode ring is.

[0057] The change in shape is to accentuate the ellipticalshape the furtherthe electrode is from the optical axis.

[0058] The electrode ring closest to the optical axis may be circular, but the electrode ring closest to the optical axis may be of an elliptical shape.

[0059] The central point or focii position of each electrode may adjust gradually when moving out radially from the optical axis of the lens. The further an electrode ring is from the optical axis, the further the central point or focii of the electrode may be from the optical axis, for at least some directions, at at least some radial distance, and under at least some design considerations. The ring widths and spacing are preferably as small as possible, as allowed by the lithographic exposure tool. An example is a 5um gap and a 5um electrode width. These dimensions could be smaller if tools allow.

[0060] Fig. 6(a) shows an example representation of a radial series of Fresnel groups or zones 20 of conductor rings for a LC optical lens. The example shown in Fig. 6(a) includes a radial series of three Fresnel groups or zones A to C of conductor rings for ease of explanation, but other examples may include more or less Fresnel groups. Each Fresnel group or zone includes a plurality of electrodes (not shown).

[0061] Reference numeral 80 denotes the optical axis of the lens, which extends through the page.

[0062] An elliptical ring 82 is defined around the optical axis 80, and generally denotes the outer region of Fresnel zone A. The dashed line 83 denotes a concentric ring around the optical axis, and is for illustrative purposes only. The dashed line 83 shows the variation provided by the elliptical ring 82, defining Fresnel zone A.

[0063] An elliptical ring 86 is defined around the optical axis 80, and generally denotes the outer region of a Fresnel zone B. The inner region of Fresnel zone B substantially aligns with the outer region of Fresnel zone A. The dashed line 84 denotes a concentric ring around the optical axis, and is for illustrative purposes only. The dashed line 84 shows the variation provided by the elliptical ring 82, defining Fresnel zone B.

[0064] An elliptical ring 90 is defined around the optical axis 80, and generally denotes the outer region of Fresnel zone C. The inner region of Fresnel zone C substantially aligns with the outer region of Fresnel zone B. The dashed line 88 denotes a concentric ring around the optical axis, and is for illustrative purposes only. The dashed line 84 shows the variation provided by the elliptical ring 82, defining Fresnel zone B.

[0065] From the example representation of Fig. 6(a), it can be seen that each Fresnel zone is defined by elliptical rings rather than circular rings. From the example representation of Fig. 6(a), it can be seen that for each Fresnel zone moving away from the optical axis of the lens, the elliptical shape may become more accentuated. Fig. 6(b) illustrates a selection of electrodes within a Fresnel zone, such as Fresnel zone A. Electrodes 104, 112, and 108 are three electrodes having shapes which, in this example, become more accentuated the further the electrode is from the optical axis. Only for illustrative example, the dashed lines 106, 114 and 110 represent concentric circle electrodes which the elliptical electrodes replace. Fig. 6(b) thus illustrates that within each Fresnel zone the shapes of successive electrodes may become more accentuated the further the distance from the optical axis. The outer electrode elliptical shape of a Fresnel zone may be more accentuated than an inner electrode elliptical shape. Fig. 6(b) represents an illustrative example, and other configurations are possible. Some adjacent electrodes, within a Fresnel zone or of adjacent Fresnel zones, may have the shape for example.

[0066] Fig. 6(b) also shows three central points generally denoted by reference numeral 116. This is to illustrate that the central points of the elliptical electrodes may change the further the distance from the optical axis, as well as the elliptical shape. The three dots illustrated may be the nominal central points of the respective electrodes 104, 108, 112. In alternatives, one or more different electrode shapes may have a common central point.

[0067] From the example representation of Fig. 6(b), it can be seen that for some electrodes moving away from the optical axis of the lens, the centre point of the elliptical shape may become more offset from the optical axis of the lens.

[0068] The elliptical shape of an electrode may become more accentuated by the ratio of the major access length to the minor axis length successively increasing, or successively decreasing, for each successive Fresnel zone.

[0069] In general, there is described a lens having electrodes that start close to radially symmetric in the centre and become increasingly elliptical and potentially offset from the centre further from the optical axis.

[0070] In general, an ellipse has a major axis and a minor axis. In order for the elliptical shape to become more accentuated further away from the optical axis of the lens, the ratio of the length of the major axis to the length of the minor axis increase or decreases the furtherthe distance from the focal point. In general, an ellipse has a central point or focii. The position of the central point orfoci may become more offsetfrom the position of the opticalaxisthefurtherthe ellipse is from the optical axis. As the shape becomes more accentuated, the elliptical central point or foci may become more offset from the optical axis.

[0071] There is thus described a lens in which the electrodes of Fresnel zones are provided with an oval shape, with the oval shape of each electrode being a solution to the optical optimisation model discussed above. This means the oval shape of electrodes may become more accentuated the further the electrode is from the optical axis of the lens. This means a foci or central point of each oval shape becomes further offset from the optical axis of the lens the further the electrode is from the optical axis of the lens. Thus the design of the lens is such that an optimal electrode design is provided accordingto the viewing angle of incidence, as per Fig. 5(a).

[0072] Fig. 7(a) illustrates for completeness an exemplary arrangement of a lens showing a plurality of Fresnel zones, each of oval shape, and in this example arrangement the oval shape being modified the further the shape is from a focal axis.

[0073] Fig. 7(b) shows a lens a plot of radial electrode position against angular position for the oval electrodes in the lens of Fig. 7(a). This illustrates that as the electrode distance from the optical axis increases, the angular position of the oval electrode increases in this example.

[0074] Figs. 7(a) and 7(b) illustrate an example of electrode position for 6V equipotential lines for a select number of Fresnel zones. These calculations show a sample design of a 0.5D lens separated by 27mm from a 3mm aperture and based on a 20um thick LC cell with a pretilt of 3°. Fig. 7(a) displays the radial plot of the oval electrode tracks, whereas Fig. 7(b) show a linear graph of the non-radial-symmetric shape of the electrodes.

[0075] Each Fresnel zone has a potential difference applied across its innermost and outermost electrode rings, to control the electrical potentials within that Fresnel zone. As noted above, for example, in Fresnel zone A this potential difference is applied using bus conductors 22 and 24. As also noted above, within each Fresnel zone the electrodes are electrically interconnected. An alternative arrangement in Fig. 7(b) may be an example voltage of 4V, for a 0.5D

[0076] LC lens with cell gap of 14 pm and a diameter of 30mm.

[0077] The oval shape of the electrodes in Fig. 7(a) will vary when any of these stated parameters change, as well as separation between lens and eye pupil, LC properties, etc. changes.

[0078] Each ring in Fig. 7(b) is associated with the radial position of this voltage in every Fresnel zone of the LC lens. Because of how the LC director profile changes with applied voltage and viewing angle, the network results in the inner ring is extending upwards, while outer rings are extending downwards. This accounts for the modified refractive index environment that the average pencil of rays through each part of the lens experiences.

[0079] Fig. 8 shows a lens controller 121 including at least a processor 122 and a memory 124, and connected to control a Fresnel zone controller 126. The Fresnel zone controller 126 is controlled to generate pairs of signalsl 30a to 130e to each of Fresnel zones A to E, respectively denoted 128a to 128e. These pairs of differential signals will be applied to the innermost and outermost electrodes of the Fresnel zone.

[0080] 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).

[0081] 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.

[0082] The LC optical lens device may be used forthe push lens and / orthe pull lens or a combined push / pull lens of an augmented reality (AR) headset such as e.g. that shown in Fig. 9. The headset 40 comprises a support frame 42 supporting optical components arranged in optical series in front of the user eye.

[0083] At least one optical component such as one or more of the optical components shown in Fig. 9 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. 9, such an assembly includes a stack of liquid crystal cells according to examples herein. In the example of Fig. 9, 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.

[0084] 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. 9 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.

[0085] 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.

[0086] 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. 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.

[0087] 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 vergence-accommodation 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 vergence-accommodation conflict). For example, the LC optical lens device may be switchable between a positive focal power and a negative focal power.

[0088] 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.

[0089] In Fig. 9, 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. 9, 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.

[0090] 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).

[0091] 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.

[0092] Although not shown in Fig. 9, it is to be appreciated that the headset 40 may be configured to obtain luminance data, e.g. from a light sensorof 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.

[0093] In the example of Fig. 9, 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 powerto be applied bythe push lens48a, 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.

[0094] 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 bythe 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 lens48b) 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.

[0095] 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.

[0096] Fig. 9 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. 9, 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.

[0097] 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. With reference to Fig. 10, 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.

[0098] Although not shown in Fig. 10, 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 further with reference to Fig. 10. There may further 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. 11. 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.

[0099] 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.

[0100] Fig. 11 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. 11 , 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. 11 , 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. 9. In other examples, though, apparatus including a similar hardware architecture to the apparatus 60 of Fig. 11 may be configured for a different purpose, may include additional components and / or may omit at least one of the components illustrated in Fig. 11 .

[0101] The apparatus 60 of Fig. 11 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.

[0102] 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. 9), 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. 9, 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. In Fig. 11 , 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.

[0103] 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. 11 .

[0104] 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. 11 , 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. 9. 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. 9) 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.

[0105] In the example of Fig. 11 , 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.

[0106] 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.

[0107] In some examples, apparatus, such as the apparatus 60 of Fig. 11 , 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 / or timing 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.

[0108] 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).

[0109] 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. 10, 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).

[0110] 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. 11 , 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] The apparatus 60 of Fig. 11 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.

[0115] 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.

[0116] Further examples relate to a method of operating a liquid crystal device according to any of the examples herein. 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.

[0117] Examples herein refer to a liquid crystal (LC) material. A liquid crystal material is an example of a material with a switchable refractive index, ora refractive index changing material.

[0118] 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 embodiment examples may be made within the scope of the invention.

[0119] 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 embodiment may be made within the scope of the invention.

[0120] 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. An optical lens, comprising: a refractive index changing material layer; an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of the optical lens, at least some of the plurality of oval-shaped electrodes having a ratio of a major axis to a minor axis which changes as the major axis increases.

2. The optical lens of claim 1 , an oval-shaped electrode having the shortest major axis length having a centre point coinciding with the optical axis of the lens.

3. The optical lens of claim 1 or claim 2, an oval-shaped electrode having the shortest major axis length being circle-shaped.

4. The optical lens of any one of claims 1 to 3, the electrode layer comprising a plurality of Fresnel zones, each Fresnel zone having a plurality of oval-shaped electrodes of increasing major axis length.

5. The optical lens of claim 4, the innermost and outermost oval-shaped electrodes in each Fresnel zone being connected across a different electrical potential in each Fresnel zone.

6. The optical lens of claim 4 or claim 5, each oval-shaped electrode in each Fresnel zone being electrically connected to an adjacent oval-shaped electrode in the same Fresnel zone.

7. The optical device of any one of claims 1 to 6 further comprising a common electrode layer located in parallel to the electrode layer.

8. The optical device of any one of claims 1 to 7, the refractive index changing material layer being a liquid crystal layer.

9. The optical device of any one of claims 1 to 8, each oval-shaped electrode having a central point, the central point of at least one oval shaped electrode being offset from the focal axis of the optical device.2610. The optical device of any one of claims 1 to 9, each oval-shaped electrode having focii, the focii of at least one oval shaped electrode being offset from the focal axis of the optical device.

11. An assembly comprising: a refractive index changing material layer; an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of an optical lens, at least some of the plurality of oval-shaped electrodes having having a ratio of a major axis to a minor axis which changes as the major axis increases; and at least one further optical element.

12. The assembly of claim 11 , wherein the at least one further optical element comprises at least one of: a waveguide, a luminance adjustment component, a lens, an image generation device, a reflection-reduction layer, or a protective layer.

13. Apparatus comprising: a refractive index changing material layer; an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of an optical lens, each of the plurality of oval-shaped electrodes having a ratio of a major axis to a minor axis which changes as the major axis increases; 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.

14. The apparatus of claim 13, 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.

15. The apparatus of claim 14 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.

16. The apparatus of claim 15 wherein the field of view of the eye is a first field of view of a first eye, and the first lens is 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.

17. The apparatus according to any one of claims 13 to 16, the apparatus being at least one of an augmented reality display device, a virtual reality display device or a mixed reality display device.

18. A method of operating a device comprising: a refractive index changing material layer; and an electrode layer, comprising a plurality of oval-shaped electrodes of increasing major axis length spaced about an optical axis of the optical lens, at least some of the plurality of ellipse-shaped electrodes having a ratio of the major axis to the minor axis which changes as major axis increases, the method comprising: selectively applying a potential difference across selected electrodes in order to control the refractive index of a portion of the underlying LC layer.

19. The method of claim 18, the electrode layer comprising a plurality of Fresnel zones, each Fresnel zone having a plurality of oval-shaped electrodes of increasing major axis length.

20. The method of claim 19, selectively applying a potential difference comprising applying a respective potential difference across an innermost and an outermost oval electrodes of each Fresnel zone.21 . The method of claim 20, electrically connecting each adjacent oval electrode of each Fresnel zone.

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