Stacked devices

Abstract

There is disclosed a device, assembly, apparatus and method, including a stack comprising at least first and second support films stacked in a stack direction; the first support film supporting at least a first conductor track extending perpendicular to the stack direction, and the second support film supporting at least a second conductor track extending perpendicular to the stack direction; and an electrically conductive adhesive adhered to one or more faces of the stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least the first conductor track and the second conductor track.

Description

[0001] STACKED DEVICES

[0002] Examples of the subject matter described herein relate to a stacked device , to an assembly and apparatus comprising the stacked device, and to a method of producing such stacked device.

[0003] Preceding stacked devices comprise one or more externally addressable metal contacts, wherein corresponding contacts are connected in parallel to an electrical input.

[0004] The inventor for the present application has developed alternative techniques.

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

[0006] Fig. 1 is a representation of an example of a base half-cell for a first, base LC cell of a stack of cells;

[0007] Fig. 2 is a representation of an example of a base half-cell for a second LC cell of a stack of cells;

[0008] Fig. 3 is a representation of an example of a counter half-cell for both the first, base LC cell, and the second LC cell of a stack of cells;

[0009] Figs. 4 to 6 are representations of examples of cutting through the stack of cells;

[0010] Figs. 7 to 9 are representations of examples of individual components of the stack of cells after the cutting shown in Figs. 4 to 6;

[0011] Fig. 10 is a representation of the example of the stack of cells after cutting;

[0012] Fig. 11 is a representation of the example of the stack of cells with electrically conductive adhesive adhered to a cut face of the stack of cells;

[0013] Fig. 12 is another representation of the example of the stack of cells with electrically conductive adhesive adhered to a cut face of the stack of cells; Fig. 13 is a representation of an example of encapsulation and sealing of the stack of cells;

[0014] Figs. 14 to 16 are representations of examples of forming through holes in the individual components of the stack of cells;

[0015] Fig. 17 is a representation of an example of the stack of cells before forming the through holes;

[0016] Fig. 18 is a representation of an example of the stack of cells after forming the through holes;

[0017] Fig. 19 is a representation of an example of the stack of cells with adhesive adhered to the internal faces defining the through holes;

[0018] Fig. 20 is another representation of an example of the stack of cells with adhesive adhered to the internal faces defining the through holes;

[0019] Fig. 21 shows an example of a headset incorporating a liquid crystal, adaptive optical lens;

[0020] Fig. 22 shows a representation of an example of a system for operating the headset of Fig. 21; and

[0021] Fig. 23 shows schematically an example of apparatus.

[0022] There is provided a first device comprising: a stack comprising at least first and second support films stacked in a stack direction; the first support film supporting at least a first conductor track extending perpendicular to the stack direction, and the second support film supporting at least a second conductor track extending perpendicular to the stack direction; and an electrically conductive adhesive adhered to one or more faces of the stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least the first conductor track and the second conductor track.

[0023] There is provided a second device comprising: a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; and electrically conductive adhesive adhered to one or more faces of the liquid crystal cell stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between electrical circuitry for controlling one or more optical properties of the first layer of liquid crystal material, and electrical circuitry for controlling one or more optical properties of the second layer of liquid crystal material.

[0024] The stack of the first device may comprise a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films of the first and second support films; and the electrically conductive adhesive forms at least part of at least one electrical connection between at least one electrode for the first layer of liquid crystal material, and at least one electrode for the second layer of liquid crystal material.

[0025] The one or more faces of the liquid crystal cell stack of either the first or second device to which the electrically conductive adhesive adheres may comprise one or more internal faces defining one or more through holes extending through at least the one or more support films.

[0026] The one or more faces of the liquid crystal cell stack of the first or second device to which the electrically conductive adhesive adheres may comprise an external face coinciding with an outer edge of the one or more support films.

[0027] Either the first or second device may further comprise sealant material adhered to the electrically conductive adhesive. The liquid crystal cell stack of either the first device or the second device may comprise first and second liquid crystal cells, the first cell comprising the first layer of liquid crystal material between first and second support films, and the second cell comprising the second layer of liquid crystal material between third and fourth support films; and wherein the electrically conductive adhesive adheres to at least one first conductive adhesive element that connects circuitry on opposing sides of the first and second support films; and wherein the electrically conductive adhesive adheres to at least one second conductive adhesive element that connects circuitry on opposing sides of the third and fourth support films; and creates an electrical connection between the first and second conductive adhesive elements.

[0028] The one or more faces of the liquid crystal cell stack of either the first device or the second device to which the electrically conductive adhesive adheres may comprise at least an internal face defining a through hole extending through the first to fourth support films and the first and second conductive elements.

[0029] The composition of the electrically conductive adhesive of either the first device or the second device may substantially match the composition of the first and second conductive adhesive elements.

[0030] The electrically conductive adhesive of either the first device or the second device may comprise a non-conductive adhesive material loaded with electrically conductive particles.

[0031] The first or second device may be operable as an adaptive optical lens.

[0032] The first or second device may be operable as an optical lens switchable between different optical powers.

[0033] There is provided a first assembly, comprising: a stack comprising at least first and second support films stacked in a stack direction; the first support film supporting at least a first conductor track extending perpendicular to the stack direction, and the second support film supporting at least a second conductor track extending perpendicular to the stack direction; an electrically conductive adhesive adhered to one or more faces of the stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least the first conductor track and the second conductor track; and at least one further optical element.

[0034] There is provided a second assembly comprising: a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; electrically conductive adhesive adhered to one or more faces of the liquid crystal cell stack substantially parallel to the stack direction, the electrically conductive adhesive forming at least part of at least one electrical connection between electrical circuitry for controlling one or more optical properties of the first layer of liquid crystal material, and electrical circuitry for controlling one or more optical properties of the second layer of liquid crystal material; and at least one further optical element.

[0035] The at least one further optical element of either the first assembly or the second assembly may comprise at least one of: a waveguide, a luminance adjustment component, a lens, an image generation device, a reflection-reduction layer, or a protective layer.

[0036] There is provided a first apparatus comprising: a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; electrically conductive adhesive adhered to one or more faces of the liquid crystal cell stack substantially parallel to the stack direction, the electrically conductive adhesive forming at least part of at least one electrical connection between electrical circuitry for controlling one or more optical properties of the first layer of liquid crystal material, and electrical circuitry for controlling one or more optical properties of the second layer of liquid crystal material; 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 first and second layers of liquid crystal material.

[0037] There is provided a second apparatus comprising: a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; an electrically conductive adhesive adhered to one or more faces of the liquid crystal cell stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least one electrode for the first layer of liquid crystal material, and at least one electrode for the second layer of liquid crystal material; 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 first and second layers of liquid crystal material.

[0038] The first or second apparatus may be configured to be mounted on a human head with the liquid crystal cell stack positioned in a field of view of an eye of the human head.

[0039] The first or second apparatus may further comprise: a first lens comprising a first one of the liquid crystal cell stack and a first one of the electrically conductive adhesive; and a second lens comprising a second one of the liquid crystal cell stack and a second one of the electrically conductive adhesive.

[0040] 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 eye of the human head, in use. The first or second apparatus may be at least one of: an augmented reality display device, a virtual reality display device or a mixed reality display device.

[0041] A first method comprises: providing a stack comprising at least first and second support films stacked in a stack direction; the first support film supporting at least a first conductor track extending perpendicular to the stack direction, and the second support film supporting at least a second conductor track extending perpendicular to the stack direction; and forming one or more layers of an electrically conductive adhesive in situ on one or more faces of the stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least the first conductor track and the second conductor track.

[0042] A second method comprises: providing a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; and forming one or more layers of at least one electrically conductive adhesive in situ on one or more faces of the liquid crystal cell stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between electrical circuitry for controlling one or more optical properties of the first layer of liquid crystal material, and electrical circuitry for controlling one or more optical properties of the second layer of liquid crystal material.

[0043] In the first method, the stack may comprise a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films of the first and second support films; and the electrically conductive adhesive forms at least part of at least one electrical connection between at least one electrode for the first layer of liquid crystal material, and at least one electrode for the second layer of liquid crystal material.24. The method according to claim 22 or claim 23, wherein the one or more faces of the liquid crystal cell stack to on which the one or more layers of electrically conductive adhesive are formed in situ comprises at least an internal face defining a through hole extending through at least the one or more support films.

[0044] The one or more faces of the liquid crystal cell stack on which the one or more layers of electrically conductive adhesive are formed in situ in either the first method or the second method may comprise an external face coinciding with an outer edge of the one or more support films.

[0045] The first method or the second method may further comprise forming a layer of sealant material in situ on the electrically conductive adhesive.

[0046] The stack may comprise first and second liquid crystal cells according to either the first method or the second method, the first cell comprising the first layer of liquid crystal material between first and second support films, and the second cell comprising the second layer of liquid crystal material between third and fourth support films; and wherein the one or more layers of conductive adhesive may comprise a layer of conductive adhesive formed in situ on at least one first conductive adhesive element that connects circuitry on opposing sides of the first and second support films, and on at least one second conductive adhesive element that connects circuitry on opposing sides of the third and fourth support films, to create an electrical connection between the first and second conductive adhesive elements.

[0047] The face of the liquid crystal cell stack on which the one or more layers of electrically conductive adhesive are formed in situ according to either the first method or the second method may comprise at least an internal face defining a through hole extending through the first to fourth support films and the first and second conductive elements. The composition of the electrically conductive adhesive according to either the first method or the second method may substantially match the composition of the first and second conductive adhesive elements.

[0048] The electrically conductive adhesive according to either the first method or the second method may comprises a non-conductive adhesive material loaded with electrically conductive particles. The following description of examples is made in the context of a stacked device comprising a LC cell stack comprising two LC layers, but the same techniques are applicable to cell stacks comprising a higher number of LC layers, and to other kinds of stacked devices whose function does not involve controlling light using LC material, such as logic devices.

[0049] The following description of examples is made in the context of a LC cell stack for a LC lens for a headset such as an augmented reality (AR) headset, but the same techniques are applicable e.g. to other types of LC devices including a LC cell stack.

[0050] An example LC lens device comprises two LC cells: a first, base cell comprising a base half-cell A shown in Fig. 1 , and a counter half-cell B shown in Fig. 3; and a second auxiliary cell comprising a base half-cell C shown in Fig. 2 and a counter half-cell B shown in Fig. 3. Each LC cell contains a carefully controlled thickness (e.g. 15 microns) of LC material between its half-cells. Lateral spread of LC material within a cell is limited by a frame of adhesive 6 adhering the two halfcells together. In the drawings, this frame of adhesive 6 is dispensed onto the base half-cell A, C before bringing half-cells together; but the frame of adhesive 6 may alternatively be dispensed onto the counter half-cell B.

[0051] The base half-cell A of the base LC cell comprises a plastics (organic polymer) support film 2 (e.g. cellulose triacetate (TAC) film of thickness 40microns) supporting a patterned metal layer defining part of electrical circuitry for electrically controlling the refractive index of the LC material. The patterned metal layer defines ground contact 4a, active contact 4b, ground routing conductor 8a and active routing conductor 8b. The ground and active contacts 4a, 4b are electrically connected to respective conductor bumps of a driver chip 38 also supported by the support film 2. The routing conductors 8a and 8b contact parts of a conductive oxide (e.g. indium tin oxide ITO) electrode pattern in region 11. For example, the device may be a Fresnel-type lens, and the conductive oxide pattern may define concentric Fresnel sets of concentric ring electrodes, with the concentric ring electrodes being electrically linked in series within Fresnel sets by resistive links, and the Fresnel sets connected in parallel across routing conductors 8a and 8b. An electric potential difference across each concentric Fresnel set induces confocal refractive index patterns in the LC material. Examples of electrically driving the Fresnel sets of concentric ring electrodes are discussed further below. The routing conductors 8a, 8b also extend to regions in which electrically conductive adhesive paste (e.g. non-conductive adhesive paste loaded with electrically conductive particles) is dispensed onto the support film 2 outside of the non-conductive adhesive frame 6 to form conductive pads 10a, 10b. The routing conductors 8a, 8b make electrical contact with respective ones of the electrically conductive pads 10a, 10b.

[0052] The counter half-cell B of the base LC cell comprises a plastics (organic polymer) support film 2 (e.g. TAC film of thickness 40microns) supporting a patterned metal layer defining another part of electrical circuitry for controlling the refractive index of the LC material of the base cell. The patterned metal layer defines a ground routing conductor 8e. The ground routing conductor 8e makes electrical contact with a counter electrode in active region 11. For example, the counter electrode may comprise a conductive oxide (e.g. ITO), or another transparent conductor such as e.g. metal mesh, nanowire, Poly(3,4-ethylenedioxythiophene) (PEDOT), carbon nanotubes (CNT). The ground routing conductor 8e also extends to a region in which conductive pad 10a (formed by dispensing electrically conductive adhesive paste) is located when the two-half cells are brought together to define the base cell. The routing conductor 8e makes electrical contact with the conductive pad 10a when the two half-cells are brought together to define the base cell. Within the base cell, the conductive pad 10a creates an electrical connection between ground routing conductor 8a of the base half-cell and ground routing conductor 8e of the counter half-cell B.

[0053] Counter half-cell B is sized such that it does not cover the driver chip 38 and electrical contacts 4a, 4b of the base cell when half-cell A and half-cell B are brought together to form the base cell.

[0054] The auxiliary cell comprises half-cell component C shown in Fig. 3 and another half-cell component B as shown in Fig. 2. Half-cell component B is described above. Half-cell component C is the same as half-cell component A of the base LC cell, except that it does not include electrical contacts 4a and 4b or the driver chip 38, and is sized such that it does not cover the driver chip 38 electrical contacts 4a, 4b of the base cell when the base cell and the auxiliary cell are brought together to form the cell stack. Within the auxiliary cell, the conductive pad 10c creates an electrical connection between ground routing conductor 8c of the base half-cell and ground routing conductor 8e of the counter half-cell.

[0055] The base and auxiliary cells are stacked in stack direction Y via an optical clear adhesive (OCA) 16 (e.g. thickness of about 25 microns). The cell stack is cut (by e.g. laser cutting) to define a face 14 parallel to the stack direction Y, at which the conductive pads 10a-10d are exposed. The cutting line X-X extends through the conductive pads 10a to 10d.

[0056] An encapsulation film 18 (e.g. thickness of about 50 microns) is laminated to one side of the cell stack perpendicular to the stack direction Y, as shown in Fig. 10.

[0057] Electrically conductive adhesive paste 20a, 20b (which may, for example, have the same composition as the electrically conductive adhesive paste used to form conductive pads 10a-10d, or may, for example, have a different composition that exhibits substantially the same post-curing rate of thermal expansion / contraction as the electrically conductive adhesive paste used to form conductive pads 10a- 10d) is applied to the cut face 14 and cured so as to (i) create an electrical connection between conductive pad 10a and conductive pad 10c, and (ii) create an electrical connection between conductive pad 10b and conductive pad 10d. The electrically conductive adhesive paste applied to the cut face thus creates electrical connections between (i) electrodes for the LC material for the base cell and (ii) electrodes for the LC material for the auxiliary cell.

[0058] According to one example technique, uncured paste is applied to the cut face 14 by pressure-based dispensing of the paste through a nozzle, and the dispensed paste is cured by baking. According to one example technique, the electrically conductive adhesive paste used to form conductive pads 10a-10d is partially cured before applying the electrically conductive adhesive paste 20a / 20b to the cut face 14, and then subject to final curing after applying the electrically conductive adhesive paste 20a / 20b to the cut face 14, to ensure a better bond between the cured conductive pads 10a-10d, and cured conductive adhesive 20a / 20b at the cut face 14.

[0059] According to one example, a material based on a silver-loaded epoxy is used for the conductive pads 10a-1 Od and the conductive adhesive 20a / 20b at the cut face 14.

[0060] Another encapsulation film 22 is laminated to the other side of the cell stack (perpendicular to the stack direction Y). A flexible connector 26 is bonded to the base half-cell of the base cell of the cell stack for electrical connection of terminals on the flexible connector 26 to respective inputs of the driver chip 38 on the base half-cell A of the base cell. Sealant material 24 is then applied to complete the encapsulation of the cell stack. The sealant material 24 adheres to the electrically conductive adhesive material 20a, 20b adhered to cell stack face 14. A second example is illustrated by Figs. 14 to 20. The description of this second example also starts with half-cell component A illustrated in Fig. 1 , two half-cell components B as illustrated in Fig. 2, and a half-cell component C as illustrated in Fig. 3. Half-cell component A and a half-cell component B are pressed together to form the base LC cell, and half-cell component C and another half-cell component B are pressed together to form the auxiliary LC cell. The base and auxiliary cells are stacked in stack direction Y via an optical clear adhesive (OCA) 16 (e.g. thickness of about 25 microns).

[0061] Through holes 30a and 30b are then formed in the stack cell in a direction parallel to the stack direction Y. One through hole 30a creates an internal face 32a (extending parallel to the stack direction Y) at which conductive pads 10a and 10c, having a thickness in the stack direction of e.g. about 2 to 20 microns, are exposed. Another through hole creates an internal face 32b (also extending parallel to the stack direction Y) at which conductive pads 10b and 10d, having a thickness in the stack direction of e.g. about 2 to 20 microns, are exposed. The through holes are filled with electrically conductive adhesive paste 34a, 34b (which may, for example, have the same composition as the paste used to form conductive pads 10a-10d, or may, for example, have a different composition that exhibits substantially the same post-curing rate of thermal expansion / contraction as the electrically conductive adhesive paste used to form conductive pads 10a-1 Od). The electrically conductive adhesive paste 34a, 34b introduced into the through holes and cured to create: (a) an electrical connection between conductive pads 10a and 10c, thus creating an electrical connection between ground routing conductors 8a and 8e of the base cell and ground routing conductors 8c and 8e of the auxiliary cell; and (b) an electrical connection between conductive pads 10b and 10d, thus creating an electrical connection between the active routing conductor 8b of the base cell and the active routing conductor 8d of the auxiliary cell. The electrically conductive adhesive paste applied to the internal faces 32a, 32b thus creates electrical connections between (i) electrodes for the LC material for the base cell and (ii) electrodes for the LC material for the auxiliary cell.

[0062] According to one example technique, uncured paste is delivered into the through holes by e.g. pressure-based dispensing of the paste through a nozzle, and the paste delivered into the through holes is cured by baking. According to one example technique, the electrically conductive adhesive paste used to form conductive pads 10a-10d is partially cured before delivering the electrically conductive adhesive paste 34a / 34b into the through holes, and then subject to final curing after delivering the electrically conductive adhesive paste 34a / 34b into the through holes, to ensure a better bond between the cured conductive pads 10a-1 Od, and the cured conductive adhesive 34a / 34b in the through holes.

[0063] According to one example, a material based on a silver-loaded epoxy is used for the conductive pads 10a-1 Od and the conductive adhesive 34a / 34b in the through holes.

[0064] The cell stack may be encapsulated in the same way as the first example.

[0065] The cells may comprise additional elements such as, for example, spacers to assist with achieving a desired thickness of LC material.

[0066] The above-described techniques avoid the use of external connections to individually address the electrodes of each cell, which external connections could complicate the final module assembly and be unattractive for the final form factor of the device.

[0067] According to one (DC drive) example of activating the above-mentioned Fresnel sets of concentric ring electrodes, the electric potential at the Fresnel sets of concentric ring electrodes is constant in terms of polarity over time relative to the electric potential at the opposing counter electrode on the opposite side of the LC layer . According to another (AC drive) example for activating the concentric ring electrodes, the electric potential at the Fresnel sets of concentric electrodes is alternated over time in terms of polarity relative to the electric potential at the opposing counter electrode, 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.

[0068] The above-described examples include only two contacts 4a, 4b electrically connected to the driver chip 38, but other examples may include more than two contacts electrically connected to the driver chip 38. According to one example, the ground contact 4b is replaced by two contacts electrically connected to respective conductor bumps of the driver chip 38; and the ground routing conductor 8a is replaced by two routing conductors terminating in respective ones of the contacts. Two of the three routing conductors function as active routing conductors for applying an electric potential difference in parallel across the Fresnel sets of concentric ring electrodes; and the third of the routing conductor functions as a ground routing conductor for controlling the electric potential at the ITO counter electrode on the opposite side of the LC layer. With this increased number of contacts and routing conductors, the operation of driving the lenses may, for example, comprise applying synchronised AC voltage waveforms having relatively high and low amplitudes to respective ones of the two active routing conductors, and applying a reference COM electric potential (e.g. OV) to the third routing conductor connected to the ITO counter electrode. 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.

[0069] In other examples, more contacts and more routing conductors may be used.

[0070] 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).

[0071] 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.

[0072] 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. 21 . The headset 40 comprises a support frame 42 supporting optical components arranged in optical series in front of the user eye. The optical components include: (i) a pull lens 52, a waveguide 50 and a push lens 48 for presenting a virtual object to the user; (ii) a front window / lens 44; and (iii) a variable dimmer device 46 between (ii) the front window / lens 44 and (i) the optical components for presenting a virtual object to the user.

[0073] At least one optical component such as one or more of the optical components shown in Fig. 21 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. 21 , such an assembly includes a stack of liquid crystal cells according to examples herein. In the example of Fig. 21 , 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. 21 only shows the optical components for one half of the headset, but a matching set of optical components is also provided for the other half of the headset.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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 vergenceaccommodation conflict).

[0078] In Fig. 21, 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. 21, 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.

[0079] 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, with 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). 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). Variable 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, variable 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.

[0080] Although not shown in Fig. 21 , 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.

[0081] In the example of Fig. 21, 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.

[0082] 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 Fig. 21 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. 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.

[0083] Fig. 21 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. 21, 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.

[0084] With reference to Fig. 22, a system according to some examples comprises a processor operating on the basis of computer program code stored in memory 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. .. Although not shown in Fig. 22, 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. 21. 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. 23. 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.

[0085] Based on inputs fed into the processor from one or more sensors sensing the movement of the user's eyes and / or based on the content being displayed by the waveguides 50, the processor controls the adaptive lens driver chip 38 to control the electrical inputs to the contacts / routing conductors 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).

[0086] 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 80 to achieve the optical focussing power (Dioptres) required to achieve the abovedescribed 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.

[0087] Fig, 23 illustrates schematically hardware architecture of apparatus 60 according to further examples. The apparatus 60 comprises at least one liquid crystal cell stack in accordance with examples herein. In Fig. 23, 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. 23, the apparatus 60 is an AR headsetfor displaying a virtual image to a wearer of the headset, and may be similar to or the same as the headset 40 of Fig. 21. In other examples, though, apparatus including a similar hardware architecture to the apparatus 60 of Fig. 23 may be configured for a different purpose, may include additional components and / or may omit at least one of the components illustrated in Fig. 23.

[0088] The apparatus 60 of Fig. 23 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.

[0089] 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. 21 ), 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. 21, 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.

[0090] In Fig. 23, 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.

[0091] 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. 23.

[0092] 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. 23, 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. 21 . 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. 21) 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.

[0093] In the example of Fig. 23, 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.

[0094] 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.

[0095] In some examples, apparatus, such as the apparatus 60 of Fig. 23, 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.

[0096] 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).

[0097] 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. 22, 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).

[0098] 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. 23, 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.

[0099] 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.

[0100] 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.

[0101] 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. The apparatus 60 of Fig. 23 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.

[0102] 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.

[0103] 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.

[0104] 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: a stack comprising at least first and second support films stacked in a stack direction; the first support film supporting at least a first conductor track extending perpendicular to the stack direction, and the second support film supporting at least a second conductor track extending perpendicular to the stack direction; and an electrically conductive adhesive adhered to one or more faces of the stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least the first conductor track and the second conductor track.

2. A device comprising: a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; and electrically conductive adhesive adhered to one or more faces of the liquid crystal cell stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between electrical circuitry for controlling one or more optical properties of the first layer of liquid crystal material, and electrical circuitry for controlling one or more optical properties of the second layer of liquid crystal material.

3. The device according to claim 1 , wherein the stack comprises a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films of the first and second support films; andthe electrically conductive adhesive forms at least part of at least one electrical connection between at least one electrode for the first layer of liquid crystal material, and at least one electrode for the second layer of liquid crystal material.

4. The device according to claim 2 or claim 3, wherein the one or more faces of the liquid crystal cell stack to which the electrically conductive adhesive adheres comprises one or more internal faces defining one or more through holes extending through at least the one or more support films.

5. The device according to claim 2 or claim 3, wherein the one or more faces of the liquid crystal cell stack to which the electrically conductive adhesive adheres comprises an external face coinciding with an outer edge of the one or more support films.

6. The device according to claim 5, further comprising sealant material adhered to the electrically conductive adhesive.

7. The device according to claim 2, wherein the liquid crystal cell stack comprises first and second liquid crystal cells, the first cell comprising the first layer of liquid crystal material between first and second support films, and the second cell comprising the second layer of liquid crystal material between third and fourth support films; and wherein the electrically conductive adhesive adheres to at least one first conductive adhesive element that connects circuitry on opposing sides of the first and second support films; and wherein the electrically conductive adhesive adheres to at least one second conductive adhesive element that connects circuitry on opposing sides of the third and fourth support films; and creates an electrical connection between the first and second conductive adhesive elements.

8. The device according to claim 7, wherein the one or more faces of the liquid crystal cell stack to which the electrically conductive adhesive adheres comprisesat least an internal face defining a through hole extending through the first to fourth support films and the first and second conductive elements.

9. The device according to claim 7 or claim 8, wherein the composition of the electrically conductive adhesive substantially matches the composition of the first and second conductive adhesive elements.

10. The device according to any preceding claim, wherein the electrically conductive adhesive comprises a non-conductive adhesive material loaded with electrically conductive particles.11 . The device according to any preceding claim, operable either as an adaptive optical lens or as an optical lens switchable between different optical powers.

12. An assembly, comprising: a stack comprising at least first and second support films stacked in a stack direction; the first support film supporting at least a first conductor track extending perpendicular to the stack direction, and the second support film supporting at least a second conductor track extending perpendicular to the stack direction; an electrically conductive adhesive adhered to one or more faces of the stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least the first conductor track and the second conductor track; and at least one further optical element.

13. An assembly comprising: a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films;electrically conductive adhesive adhered to one or more faces of the liquid crystal cell stack substantially parallel to the stack direction, the electrically conductive adhesive forming at least part of at least one electrical connection between electrical circuitry for controlling one or more optical properties of the first layer of liquid crystal material, and electrical circuitry for controlling one or more optical properties of the second layer of liquid crystal material; and at least one further optical element.

14. The assembly of claim 12 or claim 13, 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.

15. Apparatus comprising: a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; electrically conductive adhesive adhered to one or more faces of the liquid crystal cell stack substantially parallel to the stack direction, the electrically conductive adhesive forming at least part of at least one electrical connection between electrical circuitry for controlling one or more optical properties of the first layer of liquid crystal material, and electrical circuitry for controlling one or more optical properties of the second layer of liquid crystal material; 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 first and second layers of liquid crystal material.

16. Apparatus comprising:a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; an electrically conductive adhesive adhered to one or more faces of the liquid crystal cell stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least one electrode for the first layer of liquid crystal material, and at least one electrode for the second layer of liquid crystal material; 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 first and second layers of liquid crystal material.

17. The apparatus according to claim 15 or claim 16, wherein the apparatus is configured to be mounted on a human head with the liquid crystal cell stack positioned in a field of view of an eye of the human head.

18. The apparatus according to claim 17, comprising: a first lens comprising a first one of the liquid crystal cell stack and a first one of the electrically conductive adhesive; and a second lens comprising a second one of the liquid crystal cell stack and a second one of the electrically conductive adhesive.

19. The apparatus according to claim 18, 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 eye of the human head, in use.

20. The apparatus according to any one of claims 15 to 19, wherein the apparatus is at least one of: an augmented reality display device, a virtual reality display device or a mixed reality display device.

21. A method comprising: providing a stack comprising at least first and second support films stacked in a stack direction; the first support film supporting at least a first conductor track extending perpendicular to the stack direction, and the second support film supporting at least a second conductor track extending perpendicular to the stack direction; and forming one or more layers of an electrically conductive adhesive in situ on one or more faces of the stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between at least the first conductor track and the second conductor track.

22. A method comprising: providing a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films; and forming one or more layers of at least one electrically conductive adhesive in situ on one or more faces of the liquid crystal cell stack substantially parallel to the stack direction; the electrically conductive adhesive forming at least part of at least one electrical connection between electrical circuitry for controlling one or more optical properties of the first layer of liquid crystal material, and electrical circuitry for controlling one or more optical properties of the second layer of liquid crystal material.

23. The method according to claim 21 : wherein the stack comprises a liquid crystal cell stack comprising at least first and second layers of liquid crystal material stacked in a stack direction via one or more support films of the first and second support films; and the electrically conductive adhesive forms at least part of at least one electrical connection between at least one electrode for the first layer of liquid crystal material, and at least one electrode for the second layer of liquid crystal material.

24. The method according to claim 22 or claim 23, wherein the one or more faces of the liquid crystal cell stack to on which the one or more layers of electrically conductive adhesive are formed in situ comprises at least an internal face defining a through hole extending through at least the one or more support films.

25. The method according to claim 24, wherein the one or more faces of the liquid crystal cell stack on which the one or more layers of electrically conductive adhesive are formed in situ comprises an external face coinciding with an outer edge of the one or more support films.

26. The method according to claim 25, further comprising forming a layer of sealant material in situ on the electrically conductive adhesive.

27. The method according to claim 22, wherein the stack comprises first and second liquid crystal cells, the first cell comprising the first layer of liquid crystal material between first and second support films, and the second cell comprising the second layer of liquid crystal material between third and fourth support films; and wherein the one or more layers of conductive adhesive comprise a layer of conductive adhesive formed in situ on at least one first conductive adhesive element that connects circuitry on opposing sides of the first and second support films, and on at least one second conductive adhesive element that connectscircuitry on opposing sides of the third and fourth support films, to create an electrical connection between the first and second conductive adhesive elements.

28. The method according to claim l, wherein the face of the liquid crystal cell stack on which the one or more layers of electrically conductive adhesive are formed in situ comprises at least an internal face defining a through hole extending through the first to fourth support films and the first and second conductive elements.

29. The method according to claim 27 or claim 28, wherein the composition of the electrically conductive adhesive substantially matches the composition of the first and second conductive adhesive elements.

30. The method according to any of claims 21 to 29, wherein the electrically conductive adhesive comprises a non-conductive adhesive material loaded with electrically conductive particles.

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