Device for controlling transmittance of visible light

Abstract

There is disclosed a device comprising: a first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance for visible light of the first polarisation than for visible light of the second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmitting visible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation; the first cell comprising individually switchable pixel areas within a common switching area of the second cell.

Description

[0001] DEVICE FOR CONTROLLING TRANSMITTANCE OF VISIBLE LIGHT

[0002] The present application relates to a device for controlling transmittance of visible light, an assembly comprising the device and at least one optical element, an apparatus comprising the device, a processor, and a storage comprising instructions for controlling the device, and a method of operating such a device.

[0003] Some optical applications benefit from a capability to adjust transmittance of incident visible light between different areas of a viewing plane. One technique involves using a pixellated optical component exhibiting polarisation-dependent absorption characteristics, and employing two such pixellated optical components in optical series, one for each of two orthogonal polarisations, to together adjust the transmittance of unpolarised light.

[0004] The inventor for the present application has conceived a different approach.

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

[0006] Fig. 1 shows a representation of an example of elements of a dimmer device;

[0007] Fig. 2 shows another representation of an example of elements of a dimmer device;

[0008] Fig. 3 shows a representation of an example of electrodes of a dimmer device;

[0009] Fig. 4 shows a representation of an example headset incorporating a dimmer device;

[0010] Fig. 5 shows a representation of an example of a system for operating the headset of Fig. 4; and

[0011] Fig. 6 shows schematically an example of an apparatus.

[0012] There is provided a device comprising: a first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance for visible light of the first polarisation than for visible light of the second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmitting visible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation; the first cell comprising individually switchable pixel areas within a common switching area of the second cell.

[0013] The first cell may comprise an array of pixel electrodes within the common switching area of the second cell.

[0014] Only one of the first and second cells may comprise an array of independently addressable pixel electrodes.

[0015] The first cell may be a pixellated cell and the second cell being a global cell.

[0016] The first cell may comprise dye molecules electrically switchable between at least the first and second modes; and the second cell comprising dye molecules electrically switchable between at least the third and fourth modes.

[0017] The first and second cells may be a mixture of the dye molecules and liquid crystal material molecules, an orientation of the dye molecules being determined by an electrically switchable orientation of the liquid crystal molecules.

[0018] The first and second cells may be vertical alignment type liquid crystal cells.

[0019] The first and second cells may be electrically controlled birefringent type liquid crystal cells.

[0020] The device may further comprise: a first pair of film components in the first cell, either side of the mixture of dye molecules and liquid crystal material molecules, one film component supporting an array of individually addressable pixel electrodes on one side of the mixture, and the other film component supporting a common, blanket electrode on the other side of the mixture; and a second pair of film components in the second cell, either side of the mixture of dye molecules and liquid crystal material molecules, each film component supporting banket electrodes on either side of the mixture. There is provided an assembly comprising: a device comprising: a first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance forvisible light ofthe first polarisation than for visible light of the second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmitting visible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation, at least one further optical element.

[0021] The at least one further optical element may comprise at least one of: a waveguide, a luminance adjustment component, a lens, an image generation device, a reflectionreduction layer, or a protective layer.

[0022] There is disclosed an apparatus comprising: a first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance forvisible light ofthe first polarisation than forvisible light ofthe second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmitting visible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation, 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 switch the first cell between the first mode and the second mode, and to switch the second cell between the third mode and the fourth mode.

[0023] The apparatus may be configured to be mounted on a human head with the first and second cells positioned in a field of view of an eye of the human head.

[0024] The apparatus may comprise: a first lens comprising a first pair of the first and second cells, and a second lens comprising a second pair of the first and second cells. The field of view of the eye may be a first field of view of a first eye, the first lens may be configured to be positioned in the first field of view, in use, and the second lens may be positioned in a second field of view of a second eye of the human head, in use.

[0025] The apparatus may be at least one of: an augmented reality display device, a virtual reality display device, or a mixed reality display device.

[0026] There is disclosed a method of operating a device comprising: a first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance forvisible light ofthe first polarisation than for visible light of the second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmitting visible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation; the first cell comprising individually switchable pixel areas within a common switching area ofthe second cell, the method comprising: operating the first cell in the first mode for at least one of the pixel areas, and simultaneously operating the first cell in the second mode for at least one of the pixel areas.

[0027] The method may further comprise electrically switching dye molecules of the first cell between at least the first and second modes; and electrically switching dye molecules of the second cell between at least the third and fourth modes. 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.

[0028] Various other aspects are also described in the following detailed description and in the attached claims.

[0029] With reference to Figs. 1 to 3, a dimmer device according to some examples comprises two guest-host liquid crystal (LC) cells A and B in optical series. Fig. 1 shows guest-host cell A on a front side of the device, but alternatively guest-host cell B may be on the front side of the device. Each guest-host LC cell A and B comprises a respective volume 10, 12 of a mixture of liquid crystal molecules and dichroic (or negative dichroic) dye molecules contained between a respective pair of film components 2, 4 and 6, 8. The film components 2, 4, 6, 8 each comprise a respective support film (e.g. organic polymer / plastics film) 22, 24, 26, 28 supporting at least respective electrodes 14, 16, 18, 20 for switching the LC-dye mixture between at least two modes. The support films 22, 24, 26, 28 support other elements not shown in the drawings, such as electrical circuitry for addressing the electrodes 14, 16, 18, 20; and sealant / adhesive for bonding the film components of a cell together and laterally containing the LC / dye mixture. The support films 22, 24, 26, 28 may also support, for example, LC alignment layers (e.g. rubbed polyimide (PI) layers) interfacing the LC / dye mixture 10, 12; and spacers formed in situ on the support films 22, 24, 26, 28 to increase the uniformity of the thickness of the LC-dye mixture 10, 12 across the active area.

[0030] The dye molecules exhibit a change in orientation upon a change of orientation of the liquid crystal molecules. The degree of absorption ofvisible light by the dye molecules is dependent on the orientation of the dye molecules and the polarisation of the light. For positive dichroic dyes, more absorption is exhibited for light having an electric field which is parallel to the long axis of the dye molecules than for light having an electric field which is perpendicular to the long axis of the dye molecules; and the opposite is the case for negative dichroic dyes.

[0031] Cell A is electrically switchable between at least a transmission mode for transmission of visible light of both first and second orthogonal polarisations, and a dimming mode that exhibits a greater decrease (relative to the transmission mode) in transmittance for visible light of the first polarisation relative to the second polarisation. Cell B is electrically switchable between at least a transmission mode for transmission of visible light of both first and second orthogonal polarisations, and a dimming mode that exhibits a greater decrease (relative to the transmission mode) in transmittance for visible light of the second polarisation relative to the first polarisation.

[0032] Cell A is a pixellated cell, and cell B is a global cell. Cell A comprises an array of individually addressable pixel electrodes 14 on one side of the LC-dye mixture 10, and a common, blanket electrode 16 on the other side of the LC-dye mixture 10. The array of individually addressable pixel electrodes 14 permits changing of the transmittance (for visible light of a first polarisation) of the LC-dye mixture 10 for one or more pixel areas relative to one or more other pixel areas. Each of the pixel electrodes 14 of the array of pixel electrodes may be individually addressable through passive matrix circuitry or active matrix circuitry. According to another example, the pixels may be directly addressable through direct drive (segmented) circuitry (without any matrix), including a dedicated addressing conductor for each pixel. The electrical switching of a pixel area of cell A is achieved by changing an electric potential across the respective pixel electrode 14 and the common electrode.

[0033] Cell B comprises common, blanket electrodes 18, 20 on both sides of the LC-dye mixture 12. For cell B, there is no pixellation for the switching of transmittance (for visible light of the second polarisation) of the LC-dye mixture 12. The switching of cell B is restricted to switching for the whole of an area encompassing the entire array of pixel electrodes of cell A. The electrical switching of cell B is achieved by changing an electric potential across the electrodes 18, 20 of the cell on opposite sides of the LC-dye mixture of the cell.

[0034] According to one example, the decrease in transmittance (for visible light of the respective polarisation) is achieved for both cells A and B by the same change in electric potential across the LC-dye mixture 10, 12.

[0035] For example, both LC cells A and B may be vertical alignment (VA) type LC cells, and the decrease in transmittance may be achieved for both cells A and B by changing from a relatively small (e.g. zero) potential across the LC-dye mixture 10, 12 to a larger electric potential across the LC-dye mixture 10, 12.

[0036] Table 1 below shows total outputs for an individual pixel area for four combinations of electrical inputs for the two cells A and B.

[0037] Table 1

[0038] OFF refers to a substantially zero electric potential across the LC-dye mixture, and ON refers to a larger electric potential across the LC-dye mixture.

[0039] Alternatively, both cells A and B may be electrically controlled birefringent (ECB) type cells, and the decrease in transmittance may be achieved for both cells A and B by changing from a relatively large potential across the LC-dye mixture 10, 12 to a smaller electric potential (e.g., substantially zero) across the LC-dye mixture 10, 12.

[0040] Table 2 below shows total outputs for an individual pixel area for four combinations of electrical inputs for the two cells A and B.

[0041] Table 2

[0042] Again, OFF refers to a substantially zero electric potential across the LC-dye mixture, and ON refers to a larger electric potential across the LC-dye mixture.

[0043] For example, total transmittance values of about 18.5%, 44% and 65% have been achieved in a test device for the dark / dark, dark / clear and clear / clear combinations, respectively.

[0044] As will be discussed below, the dimmer device may form part of an augmented reality (AR) headset. Having the global cell B in the dark mode may be useful when the headset is used in bright outdoor conditions. Cell A pixels in areas in which a virtual object is presented to the user of the headset by a light engine are then in dark mode, and cell A pixels in areas where no virtual object is presented to the user by the light engine are then in clear mode. Having the global cell B in the clear mode may be useful when the AR headset is used in intermediate illuminated conditions or in indoor dim conditions. Cell A pixels in areas in which a virtual object is presented to the user of the headset by a light engine may then be in dark mode or clear mode depending on whether the light engine needs assistance from the dimmer device to clearly present a virtual object to the user against the real background.

[0045] According to one example, the global cell B in the dark mode exhibits a greater decrease in transmittance for visible light of a vertical polarisation than for visible light of a horizontal polarisation, and pixellated cell A in the dark mode exhibits a greater decrease in transmittance for visible light of a horizontal polarisation than that for visible light of a vertical polarisation. Operating cell B in the dark mode and operating pixels of cell A in the clear mode then provides the same kind of glare-reducing effect, for those pixel areas, as polarised sunglasses.

[0046] The above description refers to switching between two modes (a maximum transmission mode and a minimum transmission mode), but the technique may be expanded to switching one or both of the two cells A and B between more than two modes, including an intermediate transmission mode between the maximum transmission mode and the minimum transmission mode.

[0047] Compared to the approach of providing two pixellated cells in optical series, the above-described dimmer device requires less stringent alignment processes for its assembly. Additionally, for the example of a pixellated cell type comprising a black matrix (such as active matrix type pixellated cells), reducing the number of pixellated cells from two to one can provide a dimmer device exhibiting less parallax.

[0048] The dimmer device described above may, for example, be used within a liquid crystal device, such as 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 including a dimmer 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). A liquid crystal device including the dimmer 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.

[0049] The dimmer device may be used for an augmented reality (AR) headset such as e.g. that shown in Fig. 4. Fig. 4 shows a representation of a AR headset incorporating the dimmer device described above.

[0050] The headset 40 comprises a support frame 42 supporting optical components arranged in optical series in front of the user eye.

[0051] At least one optical component such as one or more of the optical components shown in Fig. 4 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. 4, such an assembly includes a stack of liquid crystal cells according to examples herein. In the example of Fig. 4, 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.

[0052] Liquid crystal cells of a stack may be aligned along a common optical axis. In some cases, though, optical axes of at least two ofthe 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. 4 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The LC optical lens device described above may be used to produce optical images (real or virtual) of the left / right perspectives of a virtual reality object substantially at the distance from the user's eyes at which the user perceives the virtual reality object to be located through the vergence mechanism discussed above. This may allow the user to perceive a focussed 3D image of the virtual reality object without disrupting the vergenceaccommodation reflex, by which the focussing action of the lenses in the user's eyes (accommodation) is unconsciously linked to the above-mentioned rotation of the left and right eyes relative to each other (vergence). In other words, the LC optical lens device may be used to avoid or reduce the strain on the user's eyes that can arise from a conflict between the vergence and accommodation mechanisms (referred to as the vergenceaccommodation conflict).

[0057] 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.

[0058] In Fig. 4, 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. 4, 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.

[0059] 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).

[0060] 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, local dimming may involve adjusting the luminance across the entire surface area of the local dimmer device 46 but by different amounts in at least two portions of the surface area.

[0061] Although not shown in Fig. 4, 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.

[0062] In the example of Fig. 4, 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.

[0063] 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. 4 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.

[0064] 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.

[0065] Fig. 4 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. 4, 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.

[0066] With reference to Fig. 5, a system 55 according to some examples comprises a processor 51 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 I eft / 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.

[0067] Although not shown in Fig. 5, 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. 5. 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. 6. 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.

[0068] 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.

[0069] Fig. 6 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. 6, 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. 6, 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. 4. In other examples, though, apparatus including a similar hardware architecture to the apparatus 60 of Fig. 6 may be configured for a different purpose, may include additional components and / or may omit at least one of the components illustrated in Fig. 6.

[0070] The apparatus 60 of Fig. 6 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.

[0071] 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. 4), 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. X, 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.

[0072] In Fig. 6, 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.

[0073] 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. 6.

[0074] 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. 6, 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. 4. 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. 4) 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.

[0075] In the example of Fig. 6, 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.

[0076] 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.

[0077] In some examples, apparatus, such as the apparatus 60 of Fig. 6, includes driving circuitry connected to at least one electrical connection connected to the electrode patterns of the liquid crystal cell stack to apply a potential difference across one or more electrode sets of the liquid crystal cells of the liquid crystal cell stack. The potential difference applied (such as a magnitude and / ortiming of the potential difference applied) may be determined by the at least one processor 66 and / or by the driving circuitry, such as by a controller implemented by at least a portion of the driving circuitry, based on the instructions stored in the storage.

[0078] 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).

[0079] 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. 5, 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).

[0080] 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. 6, 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.

[0081] 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.

[0082] 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.

[0083] 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. 6includes 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.

[0084] 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.

[0085] Further examples relate to a method of operating a device according to any of the examples herein.

[0086] 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.

[0087] 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.

[0088] 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 first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance for visible light of the first polarisation than for visible light of the second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmitting visible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation; the first cell comprising individually switchable pixel areas within a common switching area of the second cell.

2. The device according to claim 1, the first cell comprising an array of pixel electrodes within the common switching area of the second cell.

3. The device according to claim 1, only one of the first and second cells comprising an array of independently addressable pixel electrodes.

4. The device according to claim 1 , the first cell being a pixellated cell and the second cell being a global cell.

5. The device according to any preceding claim, the first cell comprising dye molecules electrically switchable between at least the first and second modes; and the second cell comprising dye molecules electrically switchable between at least the third and fourth modes.

6. The device according to any preceding claim, the first and second cells comprising a mixture of the dye molecules and liquid crystal material molecules, an orientation of the dye molecules being determined by an electrically switchable orientation of the liquid crystal molecules.

7. The device according to claim 6, the first and second cells being vertical alignment type liquid crystal cells.

8. The device according to claim 6, the first and second cells being electrically controlled birefringent type liquid crystal cells.

9. The device according to any one of claims 5 to 8, further comprising: a first pair of film components in the first cell, either side of the mixture of dye molecules and liquid crystal material molecules, one film component supporting an array of individually addressable pixel electrodes on one side of the mixture, and the other film component supporting a common, blanket electrode on the other side of the mixture; and a second pair of film components in the second cell, either side of the mixture of dye molecules and liquid crystal material molecules, each film component supporting banket electrodes on either side of the mixture.

10. An assembly comprising: a device comprising: a first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance for visible light of the first polarisation than for visible light of the second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmittingvisible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation, at least one further optical element.

11. The assembly of claim 10, in which 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.

12. Apparatus comprising: a first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance for visible light of the first polarisation than for visible light of the second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmittingvisible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation, 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 switch the first cell between the first mode and the second mode, and to switch the second cell between the third mode and the fourth mode.

13. The apparatus according to claim 12 configured to be mounted on a human head with the first and second cells positioned in a field of view of an eye of the human head.

14. The apparatus according to claim 13 comprising: a first lens comprising a first pair of the first and second cells, and a second lens comprising a second pair of the first and second cells.

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

16. The apparatus according to anyone of claims 12 to 15, wherein the apparatus is at least one of: an augmented reality display device, a virtual reality display device, or a mixed reality display device.

17. A method of operating a device comprising: a first cell electrically switchable between at least a first mode transmitting visible light of first and second orthogonal polarisations; and a second mode exhibiting, relative to the first mode, a greater decrease in transmittance for visible light of the first polarisation than for visible light of the second polarisation; and a second cell in optical series with the first cell, wherein the second cell is electrically switchable between a third mode transmitting visible light of the first and second polarisations, and a fourth mode exhibiting, relative to the third mode, a greater decrease in transmittance for visible light of the second polarisation than for visible light of the first polarisation; the first cell comprising individually switchable pixel areas within a common switching area of the second cell, the method comprising: operating the first cell in the first mode for at least one of the pixel areas, and simultaneously operating the first cell in the second mode for at least one of the pixel areas.

18. The method according to claim 17, further comprising electrically switching dye molecules of the first cell between at least the first and second modes; and electrically switching dye molecules of the second cell between at least the third and fourth modes.

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