NO20200867A1 - A Display Screen Adapted to Correct for Presbyopia - Google Patents

Description

A DISPLAY SCREEN ADAPTED TO CORRECT FOR PRESBYOPIA

The invention described herein relates to a display screen adapted to adjust for presbyopia. In particular, the invention relates to a display screen including correction means comprising a mirrored layer for rendering an image displayed on the screen clear to viewers suffering from long-sightedness.

In order to view objects both nearby and at a distance, a healthy eye adjusts the shape of the eye lens to focus light from an object onto the retina, which then stimulates neurons in the optic nerve for transmission of signals to the brain.

Light diverges as it travels away from a source, and the curvature of the wavefront is often referred to as the “vergence” of the light. This quantity reduces with distance from the source and is measured in Diopters (D). Vergence is negative for diverging light rays and positive for converging light rays, and can be defined by the equation where n is the refractive index of the material through which the light travels and r is the distance from a point source to the wavefront. The vergence 1mm from a light source for light travelling in air is therefore -1000D, while the vergence 0.5m from the same source is -2D. Where the distance from the source is infinite (parallel light rays) the vergence is 0D.

Figure 1 illustrates a healthy eye separately focusing parallel rays (left) and rays that are diverging from a nearby light source (right) onto the retina at the back of the eye. Where a nearby object is being viewed, as in the image on the right in figure 1, the lens thickens with a corresponding increase in power (accommodation). This way light is refracted to a greater extent by the lens of the eye and the diverging light rays can be focussed onto the retina. When reading text held near to 33cm away from the eye, for example, the vergence of the light travelling from a point on the page and reaching the eye is around -3D, and the lens of the eye needs to increase its refractive power by 3D as compared to a situation where distant objects are being viewed in order to properly focus the light.

With age, the lens of a person’s eye becomes gradually stiffer. This stiffening means that the muscles of the eye are not strong enough to adapt the lens sufficiently when viewing an object that is nearby. Light cannot be focussed as it should be on the retina, but instead is focussed slightly behind this causing the image of the object to appear blurry. This worsening of near vision with age is known as “presbyopia” which can affect, in particular, the experience of reading or viewing screens at close range and results in an inability to focus clearly on close objects which is progressively worsening. Correction can be achieved by way of reading glasses, progressive glasses, or contact lenses. These sit in front of the eye and do the job of the eye lens in that they help to refract light towards the principle axis of the lens so that it can be focussed onto the retina to produce a clear image.

In addition to being used in order to be able view books or papers clearly, reading glasses are now also commonly used when viewing electronic devices such as phones, laptops, and tablets. The use of such devices for reading has increased dramatically, and these play a central role in both our work lives and our leisure time. Clearly, any apparatus which is able to improve the comfort of the user of a device having a display screen will be of great benefit to many, and to an even greater extent as the speed and quality of devices with electronic screens continues to improve.

There are several different types of display screen currently used in electronic devices such as ipads<RTM>, televisions, mobile phones, tablets, etc. The choice of which type of screen to choose will depend on intended use and budget. In the case of a smartphones, for example, it is possible to choose between phones manufactured with LCD (liquid crystal display), LED (light emitting diode), OLED (organic light emitting diode), AMOLED (active matrix organic light emitting diode), TFT (thin film transistor), and IPS (in-plane switching) screens. These screens have in common the fact that they are made up of a large number of pixels, each including one or more red, green, and/or blue sub-pixels. The sub-pixels can be turned on and off separately and their brightness regulated by application of a current in order to control the overall appearance of the image displayed.

Many portable devices available on the market currently use an LCD (Liquid Crystal Display) screen to display images. Of the screen types mentioned above, all of LCD, TFT, and IPS screens use LCD technology. An LCD screen works by passing light through two polarising filters orientated at 90 degrees to each other with a layer of liquid crystal between. When electricity is applied to the liquid crystal layer, the crystals align which causes the polarisation of the light incident on the liquid crystal layer to be altered allowing it to pass through the second polarizing filter. Coloured filters represent the sub-pixels. When current to a region is switched off, the liquid crystal is not aligned and does not alter the polarisation of the light passing through.

The two oppositely polarising filters therefore together block the light and the subpixel appears dark. Transistors associated with each sub-pixel are capable of turning on and off very quickly to either supply or cut off electricity to the layer of liquid crystal in that sub-pixel. This allows light passing through any particular sub-pixel to be visible (current off) or invisible (current on). Backlighting panels in LCD screens often comprise a matrix of LED lights or side lighting which illuminates the rear of the screen.

LED, OLED, and AOLED, and micro-LED screens comprise an array of light emitting diodes each representing a sub-pixel. These are formed of a range of materials depending on the type of screen, and these materials emit one of red, blue, or green light when a current is passed through them. The colour contrast available from LED screens, and especially the newer OLED screens, is particularly good, and these can now be produced so as to be flexible and extremely thin. Plasma screens were commonly used in display devices, notably in televisions a number of years ago, but are less widely used at present.

Light emitted from the front of the screen, which in the case of most devices will be located no further than a meter or so from the viewer during use, is focussed by the eye onto the retina. For a presbyopic viewer using a device with a traditional screen, reading glasses may be required in order to view the display clearly because of the need to bend light from the nearby pixels further than the lens is capable of doing in order to focus properly.

According to a first aspect of the present invention, there is provided a display screen comprising: a mirrored layer made up of an array of concave mirror segments; and a light source centered at the focal point of each mirror segment in the array and configured to emit light towards the mirrored layer so that light from each of the sources can be reflected from the mirrored layer towards a viewer as a collimated beam.

When the mirror surface is included in the screen, the light forming the image travels from the front of the screen to the viewer as parallel rather than diverging rays.

Focusing by the lens of the eye onto the retina is therefore possible for a person suffering from presbyopia, which means that the screen can be viewed at close range without reading glasses. Reference to a collimated beam refers to the fact that light rays travelling from region of the pixel and reflected from the mirror are substantially parallel to one another. A concave mirror segment refers to a mirrored region which is shaped as all, or more usually part, of a concave surface. The mirror segment may therefore represent a section taken from a larger concave surface such as a parabolic or spherical surface. The section can be shaped so as to form any part of the larger surface (including or not including the vertex). The focal point referred to is the focal point of the theoretical larger concave mirror surface of which the section forms a part. The use of mirrors presents a further advantage in that no chromatic aberration occurs. Where refraction occurs, as it does when light passes through a lens (commonly used in visual systems such as glasses or contact lenses), the angle of refraction depends on the wavelength of the light. White light can therefore be split into the various component colours causing a disturbing visual effect.

In embodiments, the light sources each comprise one pixel of a pixel array. The mirrored layer includes as many mirror segments as pixels in the display screen.

In embodiments, the display screen is an LED, LCD, or plasma screen.

In embodiments, the display screen is an LCD screen and each pixel comprises a light source configured to emit light towards the mirrored layer through a liquid crystal layer.

In embodiments, the screen is configured such that light reflected from the mirror passes through a liquid crystal layer as it travels towards the front of the screen. Here, the light passing through the liquid crystal layer and cross-polarizers has already been collimated by the mirrored surface.

In embodiments, the mirror segments are parabolic mirror segments. A parabolic surface has a single focal point for parallel beams, which is ideal for the present purposes.

In embodiments, the mirror segments are spherical mirror segments.

In embodiments, the parabolic mirror segments each represent a part of a circular paraboloid that is centered on the vertex.

In embodiments, the parabolic mirror segments each represent a part of a circular paraboloid that is offset from the vertex. Pixels in this case need not be located directly in line between the mirror segments and the viewer which can help to reduce the effect of the shadow of the pixels or light source located in front of the mirrored layer.

In embodiments, the mirror segments do not include the vertex of the paraboloid.

In embodiments, the mirror segments form an array of segments which touch adjacent mirror segments along all sides such that the mirrored surface is continuous. This configuration is especially advantageous in terms of providing a compact screen since the entirety of the mirrored layer can be used to reflect light as parallel rays towards the front of the screen.

In embodiments, the width of each pixel is between 5µm and 20µm and the diameter of each mirror segment is between 50µm and 200µm. The diameter refers to the width of the mirror segment as viewed from above when the display screen is placed on a horizontal surface (as shown in figures 3A-3C). The mirror segments may appear circular. If the mirror segments are hexagonal, semi-circular, square, or of any other shape, then the diameter will refer to the largest width across the mirror segment when viewed from above. In embodiments, the width of each pixel is around 10 µm and the diameter of each mirror segment making up the mirrored surface is around 70µm.

According to a second aspect of the present invention, there is provided a device including the display screen of the first aspect.

In embodiments, the device is one of a mobile phone, a tablet, a PC, and a laptop.

The invention will be described in more detail with reference to the figures in which:

Figure 1 illustrates an eye focussing light from a distant object (left) and from a nearby object (right);

Figure 2A shows a pixel and parabolic mirror collimating light from the pixel within a display screen;

Figure 2B shows some parameters associated with the parabolic surface;

Figure 2C illustrates some example measurements for a parabolic mirror segment; Figure 3A illustrates a pixel and mirror in an embodiment where each pixel has associated its own separate circular mirror segment;

Figure 3B illustrates an embodiment where the mirrored layer is continuous and the mirror segments appear hexagonal when viewed from above;

Figure 3C illustrates an embodiment including mirror segments that appear circular when viewed from above and which are separated so that the layer is not continuous;

Figure 4 illustrates spherical aberration occurring for a spherical mirror in comparison with a parabolic reflector surface;

Figure 5 is a ray diagram showing the path of light rays travelling from the focal point of a parabolic mirror segment and of light rays travelling from a point on an extended pixel which is located above the focal point;

Figure 6 shows a parabolic mirror segment including the vertex at its center and an off-center parabolic mirror segment;

Figures 7A shows a plan view of part of a mirrored layer comprising an array of parabolic mirror segments including the vertex and placed adjacent on another;

Figure 7B shows a side view of part of a mirrored layer comprising an array of parabolic mirror segments including the vertex and placed such that there are no gaps between segments;

Figure 7C shows a side view of part of a mirrored layer including an array of off-axis parabolic mirror segments;

Figure 8 illustrates part of an LED screen in incorporating a mirrored layer;

Figure 9 illustrates part of an LCD screen incorporating a mirrored layer;

Figure 10 shows a ray diagram in an embodiment where the distance from which light appears to diverge is controlled;

Figure 11 illustrates an embodiment wherein mirror segments partially overlap; and

Figure 12 illustrates an embodiment wherein ring shaped parabolic or spherical mirror segments are used to reflect light that travels in a forward direction.

Each pixel within a display screen may be formed of a number of sub-pixels. In most cases a pixel is made up of one green, one red, and one blue sub-pixel each of which is controlled separately by its own transistor. The colour that each pixel appears can then be controlled by adjusting the amount of red, green, and blue light emitted. In some screens, different combinations of sub-pixels and sub-pixel groups including different colour combinations are used. The PinTile arrangement in some AMOLED screens includes pixels which each contain two colours of LED, green and red or green and blue. The particular arrangement of sub-pixels on a screen is the subject of many patent applications but will not be discussed further here. The concept described below of including a mirrored surface within a display screen to provide light form the display as a collimated beam to the user can be applied to all arrangements of pixel and sub-pixel (such as a Bayer pattern where each group of four adjacent sub-pixels includes two green, one blue, and one red sub-pixel). Each mirror segment may be configured to reflect light from a single pixel, and even from a single sub-pixel in some embodiments.

The display screen described below comprises a mirrored layer located towards the back of the screen which reflects light from the pixels or light source as a collimated beam through the front of the screen to the viewer. The mirrored layer may be formed as an array of parabolic surfaces, wherein light which will form the image travels from the focal point of each of the parabolic mirror segments before being reflected in a direction perpendicular to the screen surface towards the eye of the viewer. Spherical mirror segments or other concave mirror segments can be used in place of parabolic mirror segments in any of the examples described herein, however these suffer from spherical aberration (as illustrated in figure 4) and are therefore less preferable. There may be some divergence in the beam reflecting from the mirror. This can be due to the shape of the mirror being adapted so that it is not precisely parabolic, defects in the mirror shaping, or the pixel size being such that it extends away from the focal point some distance.

As shown in figure 2A, each pixel 2 including the red, green, and blue sub-pixels may be located at the focal point F of one of the parabolic mirror segments. In the example shown, the parabolic mirror segment 4 represents a region of a “paraboloid of revolution” or circular paraboloid that includes the vertex V at its center. In place of a parabolic mirror a spherical mirror section or another concave mirror section can be used, however spherical aberration is observed for spherical mirrors and so parabolic mirror segments are preferred. Figure 2A is intended to illustrate some characteristics of the parabolic surface. In a cross-section the surface appears as line y<2>=2px in the 2D plane, where the focal point of the parabola is at p=x. The parabola can also be characterised in that the distance from the focal point to the surface of the parabola at a point is equal to the distance from the same point to a line x=c where c is a constant. Figure 2C illustrates the size of one of the parabolic mirror segments in an example. The radius of the mirror segment (viewed from above) may be between 20µm and 50µm, more preferably between 30µm and 40µm, and most preferably around 36µm. The distance from the focal point to the surface of the parabola, which defines the size of the parabola, may be between 10µm and 40µm, more preferably between 20µm and 30µm, and most preferably around 25µm.

Figures 3A to 3C show the position of a plurality of pixels 2 and mirror segments 4 configured as an array and viewed from the front. In the example illustrated in figure 3A, the pixels and mirror segments in this example are configured as in figure 2. The mirror segment surfaces, and the light emitted by the pixels and reflected by the mirrors, are visible in a ring around each pixel. Because of the small size of the pixels, the fact that some of the light is blocked in the centre of each mirror by the pixel itself should not be readily discernible to the viewer of the screen. Pixels are located at the focal point of the mirror such that the light rays reflected from the mirror are substantially parallel. A viewer with presbyopia is able to focus the light onto their retina without the aid of reading glasses to view the screen clearly, even at close range.

Figures 3B and 3C illustrate reflecting layers comprising mirror segments which are configured slightly differently. In figure 3B, mirror segments appear hexagonal when viewed from above and the mirrored layer is continuous, meaning that for mirror segments not at the edge of the mirrored layer these are surrounded by and touching adjacent mirror segments along all sides. Each point on the mirrored surface represents part of a concave (usually parabolic) surface. In figure 3C an example is illustrated where mirror segments appear circular when viewed from above and are spaced slightly apart from adjacent mirror segments. The section of the screen between mirror segments may be flat, for example.

The configuration of mirror segments shown in figures 2A-C and 3A-C will be suitable for use in plasma screens, LCD, and LED screens in particular, but can be used with any type of screen formed from a plurality of pixels. The pixels are turned so that light is emitted towards the back of the screen rather than the front as usual, and a plurality of small mirror segments are placed behind each pixel to reflect collimated light back towards the front of the screen. In some cases, all surfaces of the pixel except for the one facing the mirror may be coated or covered with an opaque or mirrored material in order to prevent light from the pixel from travelling directly through the front of the screen without travelling first towards the mirrored layer to be reflected as a collimated beam. This may not be necessary for some pixel types if light is only emitted only towards the mirrored layer. The front surface of the screen may also be covered by an anti-reflective layer.

In the example shown in figures 2A and 3A-C, the mirrored layer comprising the parabolic (or other concave) mirror segments 4 will need to be placed within the electronic display screen such that the light emitting part of each pixel can be located at the focal point of one of the mirror segments 4. This may mean that electrodes or polarizing filters and other elements of the screen as well as the light emitting material also need to be located at or near to the focal point of a mirror segment. Reference to a component, such as a light source or a pixel, being placed at the focal point means that at least a part of the component is located at the focal point. The component will obviously have a defined size and so cannot be located at the focal point in its entirety. If the component is described as being centered at the focal point, then its geometric centre will coincide with the focal point. In the case of a pixel, the light emitting portion of the pixel will generally be centered at the focal point of its associated parabolic or spherical mirror surface but will extend away from this a small distance.

A parabolic mirror (shaped as a section of a paraboloid of revolution or a circular paraboloid) has a single focal point for all rays travelling parallel to the optical axis. This is in contrast to a spherical mirror which has a different focal point for parallel rays near to and far from the optical axis. This means that spherical aberration is not an issue in the case of parabolic mirrors. Figure 4 illustrates the mechanism resulting in spherical aberration for a large spherical mirror, where light hitting the mirror as parallel rays is focused not to a single point but at points along a short length of the optical axis. Because of the small size of the mirrors used in the display screen of the present invention, the spherical segment may approximate a parabolic section at the vertex and so the difference between the two shapes in terms of clarity of the image achievable may not be too great.

Obviously, the relative sizes of the mirrors and the pixels will be important in terms both of the resolution achievable with the screen and the clarity of the image. The pixel has a defined volume and so will extend a small way from the focal point in all directions. If the pixel is centered at the focal point, then light from the edges of the pixel will not travel in a direction parallel to the optical axis after hitting the mirror but will have a small vergence at the position of the eye of the viewer. The smaller the height and width of the pixel, the smaller an effect this will have. Generally, minimising pixel size is desirable.

Pixels can also be shaped to adjust for the above effects. Pixels can be cone-shaped or frustoconical, for example, with the peak of the cone or the flat top of the frustoconical pixel orientated such that it is located nearest to the mirror. The peak of a cone shaped pixel can be situated at the focal point in which case the rest of the pixel will be located behind the focal point. This may be preferable to the effect when the pixel is aligned with the focal point, and the size and shape of the cone can be adjusted to give the best results for any particular selection of mirror segment size and shape. In general, for any pixel, the size and shape of the pixel and the size and curvature of the mirror can be tailored such that the light leaving the display screen is as close to a collimated beam as possible. Optionally, additional lenses located the front of the display screen can be used to correct for any divergence the light. A lens may be associated with each mirror segment and may form part of a transparent substrate in which the pixels and electronics required for the screen are embedded, as described in more detail below.

It is possible using current techniques to produce optical components including mirrors, pixels, and optical fibres on the micron-scale. Electronic components can also be manufactured to be transparent at optical wavelengths. Micro reflectors or micromirrors for use in the mirrored layer can be formed by chemical etching of a material such as silicon to form an array of very small parabolic surfaces (off-axis or including the vertex of the parabola) prior to coating these surfaces with a reflective material such as aluminium to form the mirror segments. The same technique can be used to produce an array of spherical mirror segments. Coatings can be applied to form the reflective surfaces by processes such as vapour deposition. Other types of etching can be used (plasma etching, for example) or the mirror layers can be built up in a different way such as by nanoimprinting. These techniques are known in the art and will not be covered further here.

Figure 5 illustrates a ray diagram including a light source and a parabolic mirror surface. In the image on the left, the light rays emanate from the focal point and are reflected as a collimated beam. In the image on the right, the light rays emanate from a point at the edge of a pixel that is oriented perpendicular to the optical axis, and so travel from a point slightly above the optical axis and the focal point of the mirror segment. Rays travelling towards the viewer from the upper edge of the pixel do not travel exactly parallel to the optical axis but are diverging and an inverted image of the pixel is formed. The fact that the image is inverted will not affect the viewing experience given that the image is that of a single pixel. In order to help to prevent light which does not travel parallel to the optical axes of the mirrors from reaching the eye, blanking walls or baffles can be provided between the mirrors in some embodiments.

As an example of the size and resolution of a typical screen, the Apple iPad mini 2-5 generation has a screen size of 200mm (height) with a resolution of 2048 x 1536 and an aspect ratio of 3:4. The pixel density of the screen is 326 pixels per inch (128 pixels per cm) and the pixel size is 77.9 microns. The total number of pixels is 3,145,728. The size of the mirrors required to achieve a good resolution is therefore very small, however it is possible using current techniques in the field of micro-optics to achieve this. The many parabolic surfaces will together form a larger mirrored layer in front of which an array of pixels is located. The smaller the pixels the more light will be able to reflect from the mirrors and back around each pixel towards the viewer. Pixels having sizes down to 5 microns across can be produced for use in glasses to provide a micro-display and this type of micron-scale pixel is suitable for use in the adapted screen described herein.

The mirrored layer may be continuous, so that each concave surface touches every adjacent concave surface along its whole perimeter. The concave surfaces may be parabolic as described above. The layer may comprise a sheet of silicon or another suitable material which is shaped (for example by etching or 3D printing) to include many small concave indents and then is coated with a reflective layer. If there is no gap between adjacent concave surfaces then these may be joined along straight lines to form a series of squares or hexagons as viewed from above, for example. Figure 3B depicts an example where parabolic mirror segments are touching and the edge of each mirror segment is hexagonal when viewed from above. The mirrored layer in this case can be referred to as continuous because all regions of the layer form part of one of the parabolic (or other concave) segments.

The mirrored surface may alternatively be formed of a number of (for example) circular mirror segments placed adjacent to one another. These adjacent mirrors may be touching as shown in figure 3A or may be spaced apart slightly as shown in figure 3C. In both cases there will be gaps between the parabolic surfaces, which may be flat. A dense distribution for the mirror segments is preferred because of associated improvements in resolution of the screen. Including a continuous surface for the mirror may simplify the process of manufacture and will minimise light leakage.

Pixel widths in typical display screens are between 2µm and 300µm, and in standard screens pixel size is usually above around 50µm. The mirror segments within the mirrored layer and associated with each pixel should have a width that is between 2 and 20 times the pixel width, so between 4µm and 6000µm. Preferably, for an array of pixels of 10µm size, the diameter of each mirror segment will be between 20µm and 2000µm, more preferably between 50µm and 500µm, and most preferably around 100µm. Separation between adjacent pixels will be 10 times the width of the pixel this case. The size of each mirror segment relative to the pixel size can be reduced if the pixel is offset from the center of the parabolic mirror surface (off-axis parabolic surfaces used).

For mirrors of 200µm size a pixel density of 50 px/cm is possible. If

pixels and mirrors are made smaller, or the width of each mirror segment relative to the associated pixel is reduced, then this can be improved upon so that the resolution of the screens including the mirrored surface will be comparable to that of screens which are currently on the market. If the width of the pixels used is 5µm, for example, and the mirror diameter or width (depending on the shape of the section of the paraboloid used for each mirror segment) is 50µm then a pixel density of 200 px/cm is achievable.

A circular parabolic surface, also termed a paraboloid of revolution, includes a vertex at the point where the axis of symmetry intersects the paraboloid and where the curvature of the parabolic surface is greatest. In some examples of the mirrored surface in the display screen described above, each parabolic segment of the surface (usually one segment associated with each pixel) will have the vertex at its center, meaning that the pixel will need to be located directly in front of the parabolic mirror section, coincident with the focal point of the mirror, in order to reflect light parallel to the optical axis and towards the viewer.

An alternative option is to form the mirrored surface from a plurality of parabolic mirrors which are off-axis, or which form sections of the paraboloid not including the vertex. The pixel associated with any particular parabolic mirror segment does not then need to be located directly in front of the center of the mirror but can be slightly off-center and still form a beam of parallel rays. Figure 6 illustrates the location of a pixel at the focal point in front of an off-axis parabolic mirror section and shows sections of a circular parabolic which are on-axis and off-axis. Pixels still need to be located at the focal point of the parabolic mirror surface including the segment, however this focal point is not now located directly in a line between the mirror segment and the viewer.

If an array of off-axis mirror segments is used to form the mirrored surface, these will need to be angled relative to the front surface of the screen in order to reflect the light towards the user as a parallel beam. It is conceivable that the mirror sections associated with each pixel can be angled differently and/or can be sections taken from different parts of a parabolic surface so that the focal point of the mirror section and thus the position of the pixels in front of each mirror segment can be tailored to minimise any shadow of the pixels in front of the associated mirror segment or adjacent mirror segments. The shadow produced by the individual pixels may not affect the image too much given their size.

It is also possible to use optical waveguides such as optical fibres to direct light from a pixel to the focal point of each parabolic mirror segment. This may help to concentrate the pixel light in a smaller area closer to a point source which will reduce the effect of having a pixel of extended size. This will also allow the mirrored layer to be placed at the front of the screen with other components (such as the electrodes, semiconductor layers, emissive layers, pixels, or liquid crystal layers depending on the type of screen) located behind the mirrored layer. At present, the diameter of optical fibres is larger than that the smallest achievable pixel width so this may not be the best option at present in terms of maximising resolution, however the size of the optical fibres available in the future will likely be reduced.

The display screen, then, includes a layer of mirror segments which are located adjacent one another, with or without gaps between, to together form a larger continuous mirrored layer. This mirrored layer is incorporated into the screen to reflect light from the plurality of pixels ,or from a plurality of light sources, as a collimated beam of parallel rays towards the viewer. The mirror segments will usually be sections of a paraboloid, either with the vertex in their center or off-axis (in which case they may be angled with respect to the screen surface to reflect the light towards the viewer).

In order to properly locate the light source (which may be a pixel), both the mirror segments and the light sources can be coupled to or located within a transparent material layer or substrate. This method can be used to provide accurate positioning of the light sources in relation to the mirrored layer for all embodiments described herein. Light rays reflected from the mirrored layer and passing through the transparent layer and out of the front of the screen will be substantially parallel to one another and perpendicular to the front surface of the screen, so that no or very little refraction will occur at this interface. The focal length of the concave mirror segments should not be affected by the refractive index of the material in which it is located so the pixels can be orientated as for a case where a transparent substrate is not used. The transparent layer can in any case be selected as a material having a refractive index that similar to that of air, but this need not necessarily be the case.

Where a transparent substrate is used, the back surface of the substrate itself can be shaped to form the mirrored layer, for example by etching or printing to create an array of indents which appear concave when viewed from the front of the screen. This shaped layer can be provided with a reflective coating over at least the parts of the surface comprising the concave mirror segments and preferably over the whole shaped back surface of the transparent substrate, thus forming the mirrored layer. Pixels and associated electronics can be fixed in position at the focal point of each mirror segment and within the transparent substrate. This can be achieved during formation of the substrate layer, for example within a mould, or pixels can be sandwiched between two transparent layers to form the substrate layer. The front surface of the transparent substrate can form the front of the screen and thus may be provided with anti-reflective coatings and may be flat. The front surface of the transparent substrate can optionally also be shaped to form an array of correcting lenses, or correcting lenses can be coupled to the front of the transparent substrate layer. These correcting lenses can each correspond to one of the mirror segments in the mirrored layer in order to compensate for any light propagating through the front of the screen in a direction which is not perpendicular to the screen surface (i.e. light which is not effectively collimated).

Minimising the light loss is desirable and so the materials forming the screen can be chosen so that reflection does not occur at the boundaries. One or more antireflective layers could be used to achieve this. The light source can be held at the focal point by some other means than the transparent substrate, however light should be able to pass from the mirror and around the source to exit the display screen at the front. The source will form a shadow in front of the mirror if the focal point, and hence the light source, is positioned directly between the mirror segment and viewer, however because of the small size of the combined components making up each light source this will in most cases not be too big of an issue in terms of display quality. In one example, the light sources are fixed as an array to the back of a transparent screen, which is then placed on top of the mirrored layer. Light hits the mirror and travels back as a collimated beam through the transparent material of the screen. Because the light enters and exits the screen at a normal to its surface, refraction by the screen of the outgoing light is not an issue.

In some examples, additional means such as a layer of one-way glass can be included to prevent light hitting the front of the screen from entering the screen and reflecting back from the mirrored surface towards the viewer.

Figure 7A-7C illustrate some different configurations of the mirrored layer 6 comprising an array of parabolic mirror segments. Figure 7A is a plan view of a mirrored layer including parabolic indentations coated with a reflective surface to form the mirror segments. In this case segments do not contact each other along their entire perimeter but do touch adjacent mirror segments. Figures 7B and 7C illustrate side views of a part of a mirror surface made up of parabolic mirror segments 4 including the vertices V of the circular paraboloids from which the segments 4 are taken (figure 7B) and off-axis parabolic surfaces (figure 7C).

LED screens comprise layers of n-type and p-type semiconducting material sandwiched together between positive and negative electrodes. Applying a current between the electrodes causes recombination to occur within the semiconducting material resulting in the emission of photons. The choice of emissive material allows the colour to be controlled. OLED screens work similarly, but comprise an emissive layer containing organic molecules and a conductive layer between the two electrode layers. Again, application of a current between the positive and negative electrodes result in emission due to recombination occurring within the emissive layer.

In order to include a mirrored layer in a display screen in a case where pixels are located directly in front of the mirror segments, gaps between pixels or in some cases between sub-pixels must be present in order to allow reflected light to pass from the back to the front of the screen around each of the pixels. Each pixel within the screen must be small enough and the pixels spaced far enough apart for this to be possible. Compared to traditional display screens and depending on the pixel spacing, therefore, light emitting materials may need to be distributed across the screen a bit differently in order to accommodate the mirrored layer. The light emitting portions of the pixels should also emit light only towards the mirror. This can be achieved by a layer of opaque material covering the back of the emissive regions. This may be simplified if a transparent material is used to support the pixels in a spaced apart configuration.

In the case of an LCD screen, light also needs to travel back towards the mirrored layer to be reflected towards the front of the screen. Rather than emitting light as in an LED screen or plasma screen, materials within the LCD screen block or transmit light using a set of oppositely orientated polarizers depending on whether current is provide to the sub-pixel or not. The LCD screen is usually backlit. Where a mirrored layer is to be incorporated within an LCD screen, the array of mirror segments may be incorporated behind the pixels including the backlight source as for the LED and plasma screens above so that light passes through the polarizing and liquid crystal layers before hitting the mirror or may be situated at the rear of the screen directly behind the source of the backlighting so that the light reflects from the mirror before passing through the polarizing and liquid crystal layers as a collimated beam.

In the former case each pixel will include a source of light which emits in a backwards direction through the various layers of the pixel (polarizing filters, colour filters, and liquid crystal layer) to the mirror segment behind. The light will then reflect back around the pixel to the front of the screen. The light sources associated with each of the pixels will need to emit light only in a backwards direction away from the front surface of the screen, and this can be achieved fairly easily by including opaque material to block any light from the source from travelling toward the front of the screen directly. As for the LED and plasma screens, at least the majority of the portion of the screen in front of the mirror segments and surrounding each pixel will need to be transparent (or empty) in order to allow light reflected from the mirror to pass through the various layers.

In the latter case, small LED lights or another source of light can be located at the focal point of each mirror so that light passing through the polarizing and liquid crystal layers of the LCD screen, which sit in front of the mirrored layer, has already been reflected by the mirror and is already collimated. This is shown in figure 9 and is described below. The backlighting mechanism in this example therefore has the mirrored layer incorporated, which makes it fairly simple to manufacture and to integrate into existing LCD screens. This also means that the size of the mirrors is not limited by the size of the pixels within the screen. Again, light emitted by the source should travel only in the direction of the associated mirror segment and additional material such as an opaque covering or screen in front of each light source may be required in order to achieve this. Here, the light sources should not sit directly in line between the mirror segment and the pixel so that the shadow of the light source covers the entire area of the pixel. This can be achieved in several ways. For example, the pixel can be offset from the light source so that each pixel is located to the side of the light source rather than in its shadow or off-axis parabolic segments can be used. Alternatively, the pixel width can be configured such that it is larger than the components making up the light source so that light can reflect from the mirror and pass through the various layers forming the pixel even if some of the light is blocked by the shadow of the light source itself. Again, components can be accurately located within a transparent substrate to ensure that the distance between the pixel and mirror segment is constant. In this embodiment, the number of light sources and hence the number of mirror segments need not necessarily correspond to the number of pixels. A single light source and mirror segment could provide a collimated beam spanning a larger area of the screen comprising a group of pixels, for example.

Figure 8 shows a cross section through an LED screen which incorporates a mirrored layer 6. The mirrored layer 6 sits behind each of the two electrode layers and the semiconductor layers (or conductive and organic molecule layers in the case of an OLED screen) which form a plurality of pixels 18. The emissive regions are located at the focal point of each of the parabolic mirror segments 4. A transparent substrate 20 can be used as described above to position the mirror segments and pixel layers correctly while allowing light to pass around the pixels after reflection from the mirrored layer 6. A similar configuration can be used for a plasma screen. The transparent substrate may completely surround all of the components of the screen in which case positioning of the various components can be well controlled.

Figure 9 illustrates an LCD screen incorporating a mirrored layer 6. The backlight array is configured such that the LEDs or other light sources 16 are located at the focal points of each of the parabolic mirror segments 4. The collimated light then passes through the polarizing layers 12 and the liquid crystal layer 10 which are configured as in a normal LCD screen as part of a plurality of coloured sub-pixels.

As explained above, for any of the screen types, light can be directed towards an offaxis parabolic mirror surface from in front and slightly to the side to reduce the effect of the shadow produced by the pixel itself. This is possible for LED, plasma, and LCD screens, among others.

Because the vergence of the light can be controlled by the introduction of a mirrored screen, the distance at which objects displayed by the screen appear to the viewer can also potentially be controlled in order to produce what appears as a 3D image on the screen. The user views light from the pixels as if it is travelling from a point some distance away, meaning that the image in the display screen also seems to be located at a distance.

Our brain generally interprets distance using differences in the appearance of an object seen with each eye. An object nearby appears in a different position relative to the background due to the angle of light travelling from that object to each eye. Other factors play a part in distance determination too, though, and we use various clues (the position of shadows and so on) in order to perceive distance. We can also judge distance based on the adjustment of the focus of the eye required to view near and far objects. Light coming towards the eye as parallel rays may therefore appear to be coming from an object at a distance. Mirror segments within a mirrored layer such as those described above can therefore be used to cause at least some areas of the screen to appear to be located at a distance by collimating light coming from these regions. Other regions of the screen can be treated differently as explained below to cause these parts to appear to be closer to the viewer.

Figure 10 illustrates a possible mechanism for controlling the apparent distance to pixels in an image. The screen may include a number of pixels 22b-d displaced from the focal point of each parabolic mirror segment 4 as well as a pixel 22a located at the focal point. Light travelling from pixels 22b-d in front of the focal point crosses and appears to diverge from a point closer to the eye. The light from that region of the image will therefore appear clear in a particular focal plane. By controlling which of the pixels in front of each parabolic section emit light at any particular time, the apparent distance to parts of the image can be controlled. Because the distance of the region producing light to the mirror is controlled, the vergence of the light at the eye can be correspondingly controlled. The eye will need to refocus to view different parts of the image, which will give an interesting visual effect.

Figure 11 shows an embodiment where parabolic mirror segments within the mirrored layer overlap so that each pixel sits behind an adjacent mirror segment to provide a more compact configuration. Spherical or other concave mirror segment could be used in the same configuration, or a combination of parabolic and spherical mirror segments. The pixel then sits at the focal point of its associated mirror segment and behind the adjacent mirror segment. The parabolic section used to form each segment represents an area of the parabola with the vertex at its edge. Each mirror segment may appear as a semi-circle from above so that the whole mirrored layer has a fish scale pattern. This overlapping configuration can be used in any of the examples described above.

In the example shown in figure 12, light from the pixels located at the focal point (F) travels forwards and is reflected as a collimated beam from a ring-shaped mirror which represents a section of the parabolic surface not including the vertex. The thickness of the reflecting layer is minimal. Light from the pixel may also travel directly out through the front of the screen or may be prevented from doing so by a masking means of some sort. In the former case not all of the light travelling to the viewer through the front of the screen will be collimated but a proportion of it will, and the total amount of light reaching the viewer will be higher. Ring shaped segments of spherical mirrors can also be used here. The centre portion of the mirror is cut-out so that the mirror segment appears as a ring from above. The ring need not necessarily be circular but can be hexagonal, for example, in order to fit together with adjacent segments as described with reference to figure 3B. The ring can also be square, rectangular, or any other shape wherein the portion of the mirror including the vertex is cut-out and the pixel is located in the centre of this cut-out when viewed from above.

Claims (13)

Claims

1. A display screen comprising: a mirrored layer made up of an array of concave mirror segments; and a light source centered at the focal point of each mirror segment in the array and configured to emit light towards the mirrored layer so that light from each of the sources can be reflected from the mirrored layer and towards a viewer as a collimated beam.

2. A display according to claim 1, wherein the light sources each comprise one pixel of a pixel array.

3. A display according to any of claims 1 and 2, wherein the display screen is an LED, LCD, or plasma screen.

4. A display according to any of claims 1 to 3, wherein the display screen is an LCD screen, each pixel comprises a light source configured to emit light towards the mirrored layer, and the screen is configured such that light reflected from the mirror passes through a liquid crystal layer as it travels towards the front of the screen.

5. A display according to any of claims 1 to 4, wherein the mirror segments are parabolic mirror segments or spherical mirror segments.

6. A display according to claim 5, wherein the mirror segments are parabolic mirror segments each representing a part of a circular paraboloid that is centered on the vertex.

7. A display according to claim 5, wherein the mirror segments are parabolic mirror segments each representing a part of a circular paraboloid that is offset from the vertex.

8. A display according to claim 7, wherein the mirror segments do not include the vertex of the paraboloid.

9. A display according to any of claims 1 to 8, wherein the mirror segments form an array of segments which touch adjacent mirror segments along all sides such that the mirrored surface is continuous.

10. A display according to claim 2, wherein the width of each pixel is between 5µm and 20µm and the diameter of each mirror segment is between 50µm and 200µm.

11. A display according to claim 10, wherein the width of each pixel is around 10 µm and the diameter of each mirror segment making up the mirrored surface is around 70µm.

12. A device including the display screen according to any of claims 1 to 11.

13. A device according to claim 12, wherein the device is one of a mobile phone, a tablet, a laptop, or a PC.