GB2405542A

GB2405542A - Multiple view directional display having display layer and parallax optic sandwiched between substrates.

Info

Publication number: GB2405542A
Application number: GB0320358A
Authority: GB
Inventors: Jonathan Mather; Diana Kean; Robert Winlow; Grant Bourhill; Akira Nakagawa
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2003-08-30
Filing date: 2003-08-30
Publication date: 2005-03-02
Also published as: CN1617014A; KR20050022955A; CN100576018C; JP2008020933A; KR100772758B1; CN101105579A; JP4999173B2; JP4471785B2; GB0320358D0; CN100406964C; KR100679189B1; JP2005078094A; KR20060134897A

Abstract

A multiple view display 58, for example for use in an autostereoscopic system or dual view display, comprises an image display layer or element 8 such as a liquid crystal display (LCD), plasma display or organic light-emitting device (OLED) sandwiched between first and second transparent substrates 6 and 7. A parallax optical device 13, such as a parallax barrier aperture array, may be disposed within or adjacent the image display element or the substrates. Colour filters 18 may be positioned in second substrate 7 and switching elements such as thin film transistors (TFTs) may be provided in substrate 6. A resin, plastics or glass spacer 20 may be present. A range of further embodiments are disclosed, including: providing the parallax barrier and colour filters in the same plane and substrate (Figures 6(c) and 6(d)); forming the parallax barrier elements in recesses below the filter elements (e.g. see 14, 16: Figures 9(a) and 9(b)), which may be triangular recesses - see Figure 12(a); and incorporating various types of lenticular lens arrays.

Description

A Multiple-View Directional Display The present invention relates to a

multiple-view directional display, which displays two or more images such that each image is visible from a different direction. Thus, two observers who view the display from different directions will see different images to one another. Such a display may be used as, for example, an autostereoscopic display device or a dual view display device.

For many years conventional display devices have been designed to be viewed by i multiple users simultaneously. The display properties of the display device are made- such that viewers can see the same good image quality from different angles with respect to the display. This is effective in applications where many users require the same information from the display - such as, for example, displays of departure information at airports and railway stations. However, there are many applications where it would be desirable for individual users to be able to see different information from the same display. For example, in a motor car the driver may wish to view satellite navigation data while a passenger may wish to view a film. These conflicting needs could be satisfied by providing two separate display devices, but this would take up extra space and would increase the cost. Furthermore, if two separate displays were used in this example it would be possible for the driver to see the passenger's display if the driver moved his or her head, which would be distracting for the driver. As a further example, each player in a computer game for two or more players may wish to view the game from his or her own perspective. This is currently done by each player viewing the game on a separate display screen so that each player sees their own unique perspective on individual screens. However, providing a separate display screen for each player takes up a lot of space and is costly, and is not practical for portable games.

To solve these problems, multiple-view directional displays have been developed. One application of a multiple-view directional display is as a 'dual-view display', which can simultaneously display two or more different images, with each image being visible only in a specific direction - so an observer viewing the display device from one direction will see one image whereas an observer viewing the display device from another, different direction will see a different image. A display that can show different images to two or more users provides a considerable saving in space and cost compared with use of two or more separate displays.

Examples of possible applications of multiple-view directional display devices have been given above, but there are many other applications. For example, they may be: used in aeroplanes where each passenger is provided with their own individual in-flight entertainment prograrnmes. Currently each passenger is provided with an individual display device, typically in the back of the seat in the row in front. Using a multiple i view directional display could provide considerable savings in cost, space and weights I since it would be possible for one display to serve two or more passengers while still allowing each passenger to select their own choice of film. i A further advantage of a multiple-view directional display is the ability to preclude the users from seeing each other's views. This is desirable in applications requiring security such as banking or sales transactions, for example using an automatic teller machine (ATM), as well as in the above example of computer games.

A further application of a multiple view directional display is in producing a three dimensional display. In normal vision, the two eyes of a human perceive views of the i world from different perspectives, owing to their different location within the head.

These two perspectives are then used by the brain to assess the distance to the various objects in a scene. In order to build a display which will effectively display a three dimensional image, it is necessary to recreate this situation and supply a so-called "stereoscopic pair" of images, one image to each eye of the observer.

Three dimensional displays are classified into two types depending on the method used to supply the different views to the eyes. A stereoscopic display typically displays both images of a stereoscopic image pair over a wide viewing area. Each of the views is encoded, for instance by colour, polarization state, or time of display. The user is required to wear a filter system of glasses that separate the views and let each eye see only the view that is intended for it.

An autostereoscopic display displays a right-eye view and a left-eye view in different directions, so that each view is visible only from respective defined regions of space.

The region of space in which an image is visible across the whole of the display active area is termed a "viewing window". If the observer is situated such that their left eye is in the viewing window for the left eye view of a stereoscopic pair and their right eye is in the viewing window for the right-eye image of the pair, then a correct view will be seen by each eye of the observer and a three-dimensional image will be perceived. An autostereoscopic display requires no viewing aids to be worn by the observer. i

An autostereoscopic display is similar in principle to a dual-view display. However, the two images displayed on an autostereoscopic display are the left-eye and right-eye images of a stereoscopic image pair, and so are not independent from one another.

Furthermore, the two images are displayed so as to be visible to a single observer, with one image being visible to each eye of the observer.

For a flat panel autostereoscopic display, the formation of the viewing windows is typically due to a combination of the picture element (or "pixel") structure of the image display unit of the autostereoscopic display and an optical element, generically termed a parallax optic. An example of a parallax optic is a parallax barrier, which is a screen with transmissive regions, often in the form of slits, separated by opaque regions. This screen can be set in front of or behind a spatial light modulator (SLM) having a two- dimensional array of picture elements to produce an autostereoscopic display.

Figure 1 is a plan view of a conventional multiple view directional device, in this case an autostereoscopic display. The directional display 1 consists of a spatial light modulator (SLM) 4 that constitutes an image display device, and a parallax barrier 5.

The SLM of Figure 1 is in the form of a liquid crystal display (LCD) device having an active matrix thin film transistor (TFT) substrate 6, a counter-substrate 7, and a liquid crystal layer 8 disposed between the substrate and the counter substrate. The SLM is provided with addressing electrodes (not shown) which define a plurality of independentlyaddressable picture elements, and is also provided with alignment layers (not shown) for aligning the liquid crystal layer. Viewing angle enhancement films 9 and linear polarisers 10 are provided on the outer surface of each substrate 6, 7.

Illumination 11 is supplied from a backlight (not shown).

The parallax barrier 5 comprises a substrate 12 with a parallax barrier aperture array 13 formed on its surface adjacent the SLM 4. The aperture array comprises vertically extending (that is, extending into the plane of the paper in Figure 1) transparent apertures 15 separated by opaque portions 14. An anti-reflection (AR) coating 16 is formed on the opposite surface of the parallax barrier substrate 12 (which forms the output surface of the display 1). i The pixels of the SLM 4 are arranged in rows and columns with the columns extending into the plane of the paper in Figure 1. The pixel pitch (the distance from the centre of one pixel to the centre of an adjacent pixel) in the row or horizontal direction being p. The width of the vertically-extending transmissive slits 15 of the aperture array 13 is 2w and the horizontal pitch of the transmissive slits 15 is b. The plane of the barrier aperture array 13 is spaced from the plane of the liquid crystal layer 8 by a distance s.

In use, the display device 1 forms a left-eye image and a right-eye image, and an observer who positions their head such that their left and right eyes are coincident with the left-eye viewing window 2 and the right-eye viewing window 3 respectively will see a three-dimensional image. The left and right viewing windows 2,3 are formed in a window plane 17 at the desired viewing distance from the display. The window plane is spaced from the plane of the aperture array 13 by a distance rO. The windows 2,3 are contiguous in the window plane and have a pitch e corresponding to the average separation between the two eyes of a human. The half angle to the centre of each window 10, 11 from the normal axis to the display normal is ocs.

The pitch of the slits 15 in the parallax barrier 5 is chosen to be close to an integer multiple of the pixel pitch of the SLM 4 so that groups of columns of pixels are associated with a specific slit of the parallax barrier. Fig. 1 shows a display device in which two pixel columns of the Sl M 4 are associated with each transmissive slit 15 of the parallax harrier.

Figure 2 shows the angular zones of light created from an SLM 4 and parallax barrier 5 where the parallax barrier has a pitch of an exact integer multiple of the pixel column pitch. In this case, the angular zones coming from different locations across the display panel surface intermix and a pure zone of view for image 1 or image 2 (where 'image 1' and 'image 2' denote the two images displayed by the SLM 4) does not exist. In order to address this, the pitch of the parallax barrier is preferably reduced slightly so that it is slightly less than an integer multiple of the pixel column pitch. As a result, the angular zones converge at a pre-defined plane (the "window plane") in front of the display This effect is illustrated in Figure 3 of the accompanying drawings, which shows the- image zones created by an SLM 4 and a modified parallax barrier 5'. The viewing regions, when created in this way, are roughly kite-shaped in plan view.

Figure 4 is a plan view of another conventional multiple view directional display device 1'. This corresponds generally to the display device I of Figure 1, except that the parallax barrier 5 is placed behind the SLM 4, so that it is between the backlight and SLM 4. This device may have the advantages that the parallax barrier is less visible to an observer, and that the pixels of the display appear to be closer to the front of the device. Furthermore, although figures 1 and 4 each show a transmissive display device illuminated by a backlight, reflective devices that use ambient light (in bright conditions) are known. In the case of a transflective device, the rear parallax barrier of Figure 4 will absorb none of the ambient lighting. This is an advantage if the display has a 2D mode that uses reflected light.

In the display devices of figures 1 and 4, a parallax barrier is used as the parallax optic.

Other types of parallax optic are known. For example, lenticular lens arrays may be used to direct interlaced images in different directions, so as to form a stereoscopic image pair or to form two or more images, each seen in a different direction.

Holographic methods of image splitting are known, but in practice these methods suffer from viewing angle problems, pseudoscopic zones and a lack of easy control of the i mages.

Another type of parallax optic is a micropolariser display, which uses a polarised directional light source and patterned high precision micropolariser elements aligned with the pixels of the SLM. Such a display offers the potential for high window image quality, a compact device, and the ability to switch between a 2D display mode and a 3D display mode. The dominant requirement when using a micropolariser display as a parallax optic is the need to avoid parallax problems when the micropolariser elements are incorporated into the SLM. i

Where a colour display is required, each pixel of the SLM 4 is generally given a filter- associated with one of the three primary colours. By controlling groups of three pixels, each with a different colour filter, many visible colours may be produced. In an autostereoscopic display each of the stereoscopic image channels must contain sufficient of the colour filters for a balanced colour output. Many SLMs have the colour filters arranged in vertical columns, owing to ease of manufacture, so that all the pixels in a given column have the same colour filter associated with them. If a parallax optic is disposed on such an SLM with three pixel columns associated with each slit or Ienslet of the parallax optic, then each viewing region will see pixels of one colour only.

Care must be taken with the colour filter layout to avoid this situation. Further details of suitable colour filter layouts are given in EP-A-0 752 610.

The function of the parallax optic in a directional display device such as those shown in figures 1 and 4 is to restrict light transmitted through the pixels of the SLM 4 to certain output angles. This restriction defines the angle of view of each of the pixel columns behind a given element of the parallax optic (such as for example a transmissive slit).

The angular range of view of each pixel is determined by the pixel pitch p, the separation s between the plane of the pixels and the plane of the parallax optic, and the refractive index n of the material between the plane of the pixels and the plane of the parallax optic (which in the display of Figure 1 is the substrate 7). H Yamamoto et al. show, in "Optimum parameters and viewing areas of stereoscopic full-colour LED displays using parallax barrier", ILICE 'lrans. Electron., vol. E83-C, No. 10, pl632 (2000), that the angle of separation between images in an autostereoscopic display depends on the distance between the display pixels and the parallax barrier.

The half-angle or of Figure I or 4 is given by: sin = n sintarctan( 2P)) (1) One problem with many existing multiple view directional displays is that the angular i separation between the two images is too low. In principle, the angle 2x between viewing windows may be increased by increasing the pixel pitch p, decreasing the separation between the parallax optic and the pixels s, or by increasing the refractive index of the substrate n.

Co-pending UK patent application No. 0315171.9 describes a novel pixel structures for use with standard parallax barriers which provides a greater angular separation between the viewing windows of a multiple-view directional display. However, it would be desirable to be able to use a standard pixel structure in a multiple-view directional display.

Co-pending UK patent application Nos. 0306516.6 and 0315170.1 propose increasing the angle of separation between the viewing windows of a multiple-view directional display by increasing the effective pitch of the pixels.

JP-A-7 28 015 propose increasing the pixel pitch and therefore the angular separation between viewing windows of a multiple-view directional display by rotating the pixel configuration such that the colour sub pixels run horizontally rather than vertically.

This results in a threefold increase in pixel width and therefore roughly three times increase in viewing angle. This has the disadvantage that the pitch of the parallax barrier pitch must increase as the pixel pitch increases which, in turn, increases the visibility of the parallax barrier to an observer. The manufacture and driving of such a non- standard panel may not be cost effective. In addition there may be applications in which the increase in viewing angle needs to be greater than three times the standard configuration and in these cases simply rotating the pixels will not be sufficient. This is often the case with high resolution panels.

In general, however, the pixel pitch is typically defined by the required resolution specification of the display device and therefore cannot be changed.

It is not always practical or cost effective significantly to change the refractive index of the substrates, which are normally made of glass. i Other attempts at increasing the angular separation between the viewing windows of a multiple-view directional display device have attempted to reduce the separation between the parallax optic and the plane of the pixels of the SLM. However, this has been difficult as will be explained with respect to Figure 5, which is a schematic block view of the display device 1 of Figure 1 with an LCD as the SLM 4.

The LCD panel which forms the SLM 4 is made from two glass substrates. The substrate 6 carries TFT switching elements for addressing the pixels of the SLM, and is therefore known as a "TFT substrate". It will in general also carry other layers for, for example, aligning the liquid crystal layer 8 and allowing electrical switching of the liquid crystal layer. On the other substrate 7 (corresponding to the counter substrate of Figure 1) colour filters 18 are formed, together with other layers for, for example, aligning the liquid crystal layer. The counter substrate 7 is therefore generally known as a "colour filter substrate" or CF substrate. The LCD panel is formed by placing the colour filter substrate opposite to the TFT substrate, and sandwiching the liquid crystal layer 8 between the two substrates. In previous directional displays the parallax optic has been adhered to the completed LCD panel as shown in figure 5. The distance between the LCD pixels and the parallax optic is determined primarily by the thickness of the CF substrate of the LCD. Reducing the thickness of the CF substrate will reduce the distance between the LCD pixels and the parallax optic, but will make the substrate I correspondingly weaker. A realistic minimum for LC substrate thickness is about 0..5mm, but the pixel-to-parallax optic separation would still be too large for many applications if a parallax optic were adhered to a substrate of this thickness.

Japanese Patent No. 9-50 019 discloses a method for increasing the angular separation between the viewing windows of a multiple-view directional display device thereby to decrease viewing distance. This patent proposes reducing the thickness between the LC and barrier. This is done by constructing the stereoscopic LCD panel with the following order of components: LCD panel, parallax barrier, polariser. Previously the order had been: LCD panel, polariser, parallax barrier, as shown in Figure 1. This reduces the separation between the parallax barrier and the pixel plane by the thickness of the polariser, but this results in only a limited increase in the angular separation between the viewing windows of a multiple-view directional display device.

The present invention provides a multiple view directional display having an image display element and a parallax optic; wherein the image display element comprises: a first substrate; a second substrate; and an image display layer sandwiched between the first substrate and the second substrate; and wherein the parallax optic is disposed within the image display element l Putting the parallax optic within the image display element puts the parallax optic closer to the image display layer, thereby reducing the separation s of equation (1) and increasing the angular separation between two viewing windows produced by the display device. It is not necessary to reduce the thickness of one of the substrates of the image display element, so that the structural strength of the image display element is not affected.

The parallax optic may be disposed between the first substrate and the second substrate.

This is a convenient way of placing the parallax optic close to the image display layer. i Alternatively, the parallax optic may be disposed within one of the first substrates or the second substrate. This is another method of enabling the parallax optic to be placed closer to the image display layer without reducing the thickness of the substrates of the l image display element.

The parallax optic and one of a colour filter array and an array of switching elements may be disposed over a first principal surface of the first substrate.

The parallax optic may be disposed on the first principal surface of the first substrate and the colour filter array or array of switching elements may be disposed over the parallax optic. Alternatively, the colour filter array or array of switching elements may be disposed on the first principal surface of the first substrate and the parallax optic may be disposed over the colour filter array or the or array of switching elements. i

The display may further comprise a transparent spacer layer disposed between the parallax optic and the colour filter array or array of switching elements The display may further comprise another parallax optic disposed between the parallax optic and the colour filter array or array of switching elements.

The parallax optic may comprise a plurality of parallax elements, with each parallax element being disposed in a respective recess in the principal surface of the substrate.

Each parallax element may be disposed on a bottom face of a respective recess.

A light-transmissive layer may be disposed over a principal surface of the substrate; a plurality of recesses may be defined in the lighttransmissive layer; and the parallax optic may comprise a plurality of parallax elements, each parallax element being disposed in a respective recess in the light-transmissive layer.

The cross-section of a recess, parallel to the surface of the sul:istrate, may decrease with depth.

Each parallax element may substantially fill a respective recess.

One of a colour filter array and an array of switching elements may be disposed over a first principal surface of the first substrate and the parallax optic may be disposed over a second principal surface of the first substrate and.

The parallax optic may comprise a plurality of parallax elements, each parallax element being disposed in a respective recess in the second principal surface of the substrate.

The parallax optic may be a parallax barrier, or a lenticular lens array.

The parallax optic may be disableable, and it may be addressable.

A second aspect of the present invention provides a dual-view display device i comprising a multiple-view directional display device as defined above.

A third aspect of the present invention provides an auto-stereoscopic display device comprising a multiple-view directional display device as defined above.

A fourth aspect of the present invention provides a parallax optic comprising: a light- transmissive substrate; and a plurality of parallax elements, each parallax element being disposed in a respective recess in a surface of the substrate.

The cross-section of a recess, parallel to the surface of the substrate, may decrease with depth.

Each parallax element may substantially fill a respective recess.

Preferred embodiments of the present invention will now be described by way of illustrative example with reference to the accompanying figures in which: Figure I is a schematic plan view of a conventional autostereoscopic display device; Figure 2 is a schematic illustration of viewing windows provided by a conventional multiple-view display device; Figure 3 is a schematic plan view of viewing windows produced by another conventional multiple-view directional display device; Figure 4 is a schematic plan view of another conventional auto-stereoscopic display device; Figure 5 is a schematic plan view showing the principle components of a conventional multiple-view directional display device; Figures 6(a) and 6(b) illustrate a display according to a first embodiment of the present invention; Figures 6(c) and 6(d) illustrate a display according to a further embodiment of the present invention; Figures 7(a) and 7(b) illustrate a display according to a further embodiment of the i present invention; Figures 8(a) and 8(b) illustrate a display according to a further embodiment of the present invention; Figures 9(a) and 9(b) illustrate a display according to a further embodiment of the present invention; Figures lO(a) and lO(b) illustrate a display according to a further embodiment of the present invention; Figures ll(a) and ll(b) illustrate a display according to a further embodiment of the present invention; Figure 12(a) and 12(b) illustrate a display according to a further embodiment of the present invention; Figure 13(a) and 13(b) illustrate a display according to a further embodiment of the present invention; Figures 14(a) and 14(b) illustrate a display according to a further embodiment of the present invention; Figures 15(a) and 15(b) illustrate a display according to a further embodiment of the present invention; Figures 15(c) and 15(d) illustrate colour filter substrates of displays according to further embodiments of the invention; Figures 16(a) and 16(b) illustrate a display according to a further embodiment of the present invention; Figures 17(a) and 17(b) illustrate a display according to a further embodiment of the present invention; Figures 18(a) and 18(b) illustrate a display according to a further embodiment of the present invention; Figures 19(a) and 19(b) illustrate a display according to a further embodiment of the present invention; Figures 20(a) and 20(b) illustrate a display according to a further embodiment of the present invention; Figures 20(c) and 20(d) illustrate colour filter substrates of displays according to further embodiments of the invention; Figures 21(a) and 21(b) illustrate a display according to a further embodiment of the i present invention; Figures 21(c) and 21(d) illustrate colour filter substrates of displays according to further! embodiments of the invention; Figure 22 illustrates a display according to a further embodiment of the present! invention; Figure 23 illustrates a display according to a further embodiment of the present invention; Figure 24 illustrates a display according to a further embodiment of the present invention; and Figure 25 illustrates a display according to a further embodiment of the present invention; Like reference numerals denote like components throughout the drawings.

Figure 6(b) is a schematic plan view of a multiple-view directional display according to a first embodiment of the present invention. The display device 58 comprises a first transparent substrate 6 and a second transparent substrate 7, with an image display layer 8 disposed between the first substrate 6 and the second substrate 7. An array of colour I filters 18 is provided on the second substrate 7, and the second substrate will therefore be referred to as a colour filter substrate.

The first substrate 6 is provided with pixel electrodes (not shown) for defining an array of pixels in the image display layer 8, and is also provided with switching elements (not shown) such as thin film transistors (TFTs) for selectively addressing the pixel electrodes. The substrate 6 will be referred to as a 'TFT substrate'.

The image display layer 8 is, in this example, a liquid crystal layer 8. The invention is not limited to this, however, and any transmissive image display layer may be used.

Moreover, where the display is used in a "front barrier mode", with the parallax optic disposed between the image display layer and an observer, the display layer may alternatively be an emissive display layer such as a plasma display or an organic light- emitting device (OLED) layer. i The display 58 is assembled such that the colour filters 18 are each substantially opposite a respective pixel of the image display layer 8. Other components such as alignment layers may be disposed on the surfaces of the substrate 6, 7 adjacent to the image display layer, and a counter electrode or electrodes may also be disposed on the CF substrate 7; these components are conventional, and will not be described further.

Furthermore, the display 58 may comprise further components suchpolarisers, viewing-angle enhancement films, anti-reflection films etc., disposed outside the image display element; these components are also conventional and will not be described further.

The colour filter substrate 7 is shown in more detail in figure 6(a). The colour filter substrate 7 comprises a base substrate 19 made of a lighttransmissive material such as glass. A parallax barrier aperture array 13 is disposed on one principle surface of the base substrate 19. In the embodiment of figure 6(a) the parallax barrier aperture array 13 is formed by depositing opaque strips 14 on the surface of the base substrate, thereby defining transmissive slits 15 between the opaque strips.

A spacer layer 20, in this embodiment formed of light-transmissive resin is provided over the parallax barrier aperture array 13. Finally, the colour filters 18 are disposed on the upper surface of the spacer layer 20.

In this embodiment, the parallax barrier aperture array 13 is separated from the pixels of the liquid crystal layer 8 by the thickness of the resin spacer layer 20. The resin layer can be made very thin, so that the separation s of equation (1) is small leading to a large angular separation of the viewing windows. Although the resin layer 20 is shown as a single layer, in practice it may be necessary to deposit two or more separate resin layers in order to obtain a spacer layer having the desired thickness. For example, the layer 20 may have a thickness of 50 microns and may comprise polyethylene perephthalate. i

Figures 6(d) is a schematic plan views of display 21 according to a further embodiment of the present invention, and Figure 6(c) shows the counter substrate of this display.

Only the differences between this embodiment and the previous embodiment will be described.

In this embodiment, the parallax barrier aperture array 13 and the colour filters 18 are both disposed on a first principal surface of the base substrate 19 of the colour filter substrate 7'. The spacer layer 20, again formed of resin, is then disposed over the parallax barrier aperture array 13 and the array of colour filters. Again, the parallax barrier aperture array 13 is separated from the pixels in the liquid crystal layer 8 by the thickness of the resin layer 20, and this can be made small. Providing the parallax barrier and colour filters in the same plane simplifies the manufacture of the display; Figure 7(b) is a plan view of a display 22 according to a further embodiment of the present invention, and Figure 7(a) shows the colour filter substrate of the display 22.

Only the differences between this embodiment and the first embodiment will be described.

In the embodiment of figures 7(a) and 7(b) the parallax barrier aperture array 13 is deposited on a principal surface of the base substrate 19. A spacer layer 20 is placed over the parallax barrier aperture array 13 and the array of colour filters is disposed over the spacer layer 20. In this embodiment, the spacer layer 20 is a glass spacer layer rather than a resin spacer layer. The glass spacer layer is adhered to the parallax barrier, and may be etched in situ to a desired thickness.

Figure 8(b) is a schematic plan-view of a display 23 according to a further embodiment of the present invention, and Figure 8(a) shows the CF substrate of this display. The display 23 of this embodiment corresponds generally to the display of figure 6(b), and only the differences between the embodiments will be described. in the display 23, the spacer layer 20 between the parallax barrier aperture array and the alTay of colour filters 18 is a layer of a plastics material. The layer of plastics material is adhered to the i parallax barrier aperture array 13 by a suitable method such as lamination or gluing.- The plastics material 20 may alternatively be printed over the parallax barrier aperture arTay.

Figure 9(b) is a schematic plan view of a multiple view directional display 24 according to a further embodiment of the present invention, and Figure 9(a) shows the CF substrate 25 of the display. The display 24 again comprises a TFT substrate 6, a colour filter substrate 25, and a liquid crystal layer or other image display layer 8 disposed between the TFT substrate 6 and the colour filter substrate 25.

Figure 9(a) shows the colour filter substrate 25 of the display. As can be seen from the figure, a plurality of recesses 26 is formed in a first principal surface of a base substrate 19. The base substrate l9 may be formed of any suitable light- transmissive material such as, for example, glass, plastic, or glass- reinforced plastic. The recesses 26 may be formed by any suitable process such as, for example, an etching or cutting process. The recesses 26 are preferably in the form of slots that extend across the entire vertical height of the base substrate 19 - that is, they extend into the plane of the paper in Figure 9(a). The recesses 26 preferably have substantially the same depth and width as one another.

A parallax barrier aperture array is defined in the substrate 19 by depositing an opaque material into each recess 26 so that it covers at least the bottom face of each recess. The opaque material thereby defines opaque strips 14 of a parallax barrier aperture array, and lighttransmissive regions are defined between the opaque strips 14.

The opaque material that forms the opaque regions of the parallax barrier aperture array may be any suitable opaque material, and may be deposited by any suitable method.

For example, an opaque resin may be deposited in the recesses 26 using a spinning process.

Once the opaque material has been deposited, the recesses are then filled with a light- i transmissive material in order to planarise the surface of the base substrate 19. For- example, a light-transmissive resin may be deposited in the recesses 26 using a spinning process.

Once the surface of the substrate 19 has been made flat, an array of colour filters 18 may be deposited over the substrate 19 to complete the colour filter substrate 25.

In this embodiment, the separation between the parallax barrier aperture array and the liquid crystal layer is approximately equal to the depth d of the recesses 26. The depth d of the recesses can be made small, for example 50 microns, so that a large angular separation between viewing windows can be obtained.

Figure 10(b) shows a display 27 according to a further embodiment of the present invention. The display 27 again comprises a TFT substrate 6, a colour filter substrate 25', and a liquid crystal layer (or other image display layer) 8 disposed between the TFT substrate 6 and the colour filter substrate 25'. This embodiment corresponds generally to the embodiment of figure 9(a) and 9(b) , and only the differences between the two embodiments will be described.

Figure 10(a) is a schematic plan view of the colour filter substrate 25' of the display 27.

In this embodiment, the colour filters 18 are deposited on a first principal surface of the base substrate 19. Recesses 26 are defined in a second principal surface of the base substrate 19, for example using an etching or cutting technique. An opaque material is then deposited in the recesses, to form the opaque strips 14 of a parallax barrier aperture array. If desired, the recesses may then be filled with a lighttransmissive material in order to planarise the second principal surface of the base substrate 19. As in the previous embodiment, any suitable material may be deposited as the opaque material, and may be deposited by any suitable technique. In one preferred embodiment, an opaque resin is deposited into the recesses 26 using a spinning technique.

Compared to the conventional display of figure 5, the separation between the parallax barrier and the liquid crystal layer is reduced by the depth of the recesses, for example i microns, so that the angular separation between viewing windows is therefore- increased. Since the thickness of the base substrate is reduced only where the recesses are present, the structural strength of the base substrate may be greater than if the entire substrate had been made with a reduced thickness.

Figure 11(b) is a schematic plan view of a multiple-view directional display 28 according to a further embodiment of the present invention. This display again consists of a TFT substrate 6, a colour filter substrate 29, and a liquid crystal layer 8 or other image display layer disposed between the TOT substrate 6 and the colour filter substrate 29.

The colour filter substrate 29 is shown in figure 11(a). As can be seen, the colour filter substrate 29 is generally similar to the colour filter substrate 7 of figure 6(a), except that it is provided with two parallax barriers 13, 13'. The colour filter substrate 29 comprises a base substrate 19 which is made of any suitable light-transmissive material such as, for example, glass. A first parallax barrier aperture array 13 is disposed over a first surface of the base substrate. The parallax barrier aperture array may be formed by, for example, depositing stripes 14 of an opaque material over the substrate to form the opaque portions 14 of a parallax barrier aperture array 13.

A first light-transmissive spacer layer 20 is then deposited over the surface of the substrate 19 on which the parallax barrier aperture array is formed. The first spacer layer may be formed of, for example, a lighttransmissive resin, glass, or a transparent plastics material as in the embodiments of figures 6(a), 7(a) and 8(a) described above.

A second parallax barrier aperture array 13' is disposed over the upper surface of the first spacer layer 20. This second parallax barrier aperture array may again be provided by depositing opaque material over the spacer layer 20 in order to form opaque portions 14' of the second parallax barrier aperture array.

A second spacer layer 20' is provided over the second parallax barrier aperture array. i The second spacer layer may again be any suitable lighttransmissive material such as a- l light-transmissive resin, a glass layer, glass, or a light-transmissive plastics material.

The colour filters 18 are deposited over the upper surface of the second spacer layer 20'.

This embodiment is not limited to the provision of two parallax barriers on the colour filter substrate. In principle, three or more parallax barrier aperture arrays could be l provided over the substrate 19, with each pair of adjacent parallax barrier aperture arrays being separated by a respective spacer layer.

In the embodiment of figure I l(a), it is not necessary for the two spacer layers 20, 20' to be formed of the same material. The two spacer layers may be made of different l materials - thus, as an example, the first spacer layer 20 could be a glass layer whereas the second spacer layer 20' could be a light-transmissive resin layer.

In another embodiment (not illustrated), the colour filter substrate is provided with two! parallax barrier aperture arrays, one disposed on each side of the base substrate l9. In this embodiment, a first parallax barrier array would be formed on one principal surface of the base substrate 19 and the filters 18 would be provided over the first parallax barrier aperture array with a light-transmissive spacer layer being interposed between the first parallax barrier aperture array and the colour filters 18 as in figure 6(a), 7(a), or 8(a). A second parallax barrier aperture array would be formed on the second principal surface of the base substrate 19, and this would be overlaid by a light-transmissive layer.

Figure 12(a) and 12(b) show a further embodiment of the present invention. Figure 12(b) is a schematic plan view of a multiple-view directional display 30 according to this embodiment of the present invention. The display device again comprises a lkl substrate 6, a colour filter substrate 31, and a liquid crystal layer 8 or other image display layer disposed between the TFT substrate 6 and the colour filter substrate 31. i

Figure 12(a) is a schematic plan view of the colour filter substrate 31 of this embodiment of the invention. The colour filter substrate 31 comprises a base substrate 19 which may be made of any suitable light-transmissive material. A plurality of recesses 26 are defined in one surface of the substrate 19, by any suitable process such as etching or cutting. When the substrate 31 is seen in front view, the recesses 26 appear as parallel strips that run from top to bottom of the base substrate 19.

As shown in figure 12(a), in this embodiment the width of a recess, parallel to the surface of the substrate 19, decreases with distance into the substrate. In the embodiment of figure 12(a) the recesses 26 have a triangular cross-section, but the recesses are not limited to this specific cross-section.

A parallax barrier aperture array 13 is formed by depositing an opaque (or reflective) material (or both) into the recesses 26 so as to form opaque portions 14 of the parallax barrier aperture array. The opaque material preferably substantially fills the recesses 26, so as to planarise the upper surface of the base substrate 19. In a preferred embodiment, the opaque material is an opaque resin that is deposited in the recesses 26 by a spinning process - however, in principle, any opaque material may be used.

A light-transmissive spacer layer 20 is deposited over the upper face of the base substrate 19. As described above, this may be a lighttransmissive resin layer, a glass layer, a layer of light-transmissive plastics material, etc. The spacer layer may be adhered to the substrate 1'3 in any suitable manucr.

Finally, the colour filters 18 are deposited on the upper surface of the spacer layer 20 to form the colour filter substrate 31.

In this embodiment, the parallax barrier has a three-dimensional profile, since the opaque elements 14 of the parallax barrier aperture array extend over a finite depth, for example 50 microns, into the substrate. The parallax barrier acts in a similar way to a conventional parallax barrier, such as the parallax barrier of figure 6(a). However, owing to the three-dimensional structure of the parallax barrier, light that is incident on j the parallax barrier at high angles to the normal to the plane of the substrate 19 is- blocked whereas such rays would be transmitted by a conventional parallax barrier of the type shown in figure 6(a). This may be beneficial in preventing secondary windows.

In the colour filter substrate of figure 12(a), the depth of the recesses may be varied over the substrate 19, in order to vary the depths of the opaque portions of the parallax barrier. Doing this would mean that the cut-off angle, relative to the normal to the plane of the substrate, at which light rays are blocked would vary across the display device.

Figure 13(a) shows a further colour filter substrate 31' of the present invention, and figure 13(b) shows the colour filter substrate of 13(a) incorporated in a display 30'.

These embodiments are generally similar to the embodiments of figures 12(a) and 12(b) respectively, and only the differences will be described here.

In the colour filter substrate 31' of figure 13(a), the recesses 26 are not formed in the base substrate 19. Instead, a light-transmissive spacer layer 32 is provided over the base substrate 19, and the recesses 26 are formed in the spacer layer 32. The spacer layer 32 may be of any suitable material such as, for example, light-transmissive resin, glass, or a light-transmissive plastics material. The recesses 26 may be formed in the spacer layer 32 by any suitable methoci, such as cutting or etching.

An opaque material is deposited in the recesses 26 in the spacer layer 32 to form the opaque portions 14 of a parallax barrier aperture array, as described in connection with figure 12(a) above. Finally, a second spacer layer 20 is deposited over the first spacer layer 32, and colour filters 18 are formed over the upper surface of the second spacer layer 20.

In the embodiments described above, the parallax optic has been constituted by a parallax barrier aperture array. The present invention is not, however, limited to this particular form of parallax optic, but may be employed with other types of parallax optic.

Figures 14(a) and 14(b) illustrate a further embodiment of the present invention, in which the parallax optic is formed by a lenticular lens array.

Figure 14 (h) is a schematic plan view of a multiple-view directional display according to this embodiment of the present invention. The display 33 again comprises a TFT substrate 6, a colour filter substrate 34, and a liquid crystal layer or other image display layer 8 disposed between the colour filter substrate 34 and the TFT substrate 6.

Figure 14(a) shows the colour filter substrate 34 of the display device 33. The colour filter substrate 34 comprises a light-transmissive substrate 19 having an upper surface which is profiled so as to form a lenticular lens array 35. The substrate 19 may be formed in any suitable manner such as, for example, by moulding a light-transmissive plastics material using a suitable mould to provide the lenticular lens array 35 on one surface of the substrate 19. As an alternative, the lens array 35 may be formed by pressing a glass substrate.

A spacer layer 20 is deposited over the lenticular lens array 35. The spacer layer is light-transmissive, and is preferably formed of a resin or plastics material so that the lower surface of the spacer layer can follow the profile of the lenticular lens array 35.

Colour filters 18 are deposited on the upper surface of spacer layer 20, which is preferably flat.

In this embodiment, the separation between the parallax optic (the lenticular lens array 35) and the liquid crystal layer 8 is equal to the thickness of the spacer layer 2O, which must be at least thick enough to planarise the lenses. The spacer layer 20 may be made thin, so that a large angular separation between viewing windows can be obtained.

Figures 15(a) and 15(b) show a further embodiment of the present invention. This embodiment is generally similar to the embodiment of figures 14(a) and 14(b), and only the differences will be described.

In figures 14(a) and 14(b) the lenticular lens array 35 is integral with the base substrate 19, and is obtained by suitably profiling the upper surface of the base substrate 19. In the embodiment of figures 15(a) and lS(b), however, the lenticular lens array 35' is not integral with the base substrate 19. Instead, the base substrate l9 has a substantially flat upper surface, and the lenticular lens array 35' is deposited on the upper surface of the base substrate 19. This may be done by any suitable technique. For example, a layer of light-transmissive resin or light-transmissive plastics material may be deposited over the upper surface of the base substrate 19, and this layer may be pattered to form the lenticular lens array 35'.

Figure 15(c) illustrates a CF substrate 34'' which differs from the substrate 34' of Figure lS(a) in that the lenticular lens array 34'' is "double-sided". In other words, whereas the lenticules of the array 35'are piano-convex, the lenticules of the array 35'' are convexo-convex. Although such an arrangement is more difficult to manufacture because recesses have to be formed in the substrate l9, optical performance is improved. For example, a display using the substrate 34'' of Figure 15(c) has a smaller crosstalk region and wider freedom of viewer movement.

Figure lS(d) illustrates another modified CF substrate 34''', which differs trom the substrate 34'' of Figure lS(c) in that the lenticules of the array 34''' are spaced apart and are separated by black mask regions 35 ''. In Fact, any embodiment using a lens array as the parallax optic may similarly have the individual lenses or lens elements separated by black mask regions which are non-transmissive to visible light.

The f-number of the lenticular lens array is required to be very low, which makes the array difficult to manufacture. By decreasing the diameter of each lens of the array and keeping the pitch constant (by filling the gaps between the lenses with light-absorbing material or light-reflecting material or both), the f-number of the lenses may be increased. Such an arrangement improves performance, for example in terms of providing a smaller crosstalk region and larger freedom of viewer position. ; Figures 16(a) and 16(b) show a further embodiment of the present invention. Figure 16(b) is a schematic plan view through a multiple-view directional display 37 of this embodiment, and figure 16(a) is a schematic plan view of the colour filter substrate 36.

This embodiment is generally similar to the embodiment of figure 6(a) and 6(b), and only the differences will be described here.

In the embodiment of figures 16(a) and 16(b), the positions of the parallax barrier aperture array 13 and the colour filters 18 are interchanged compared to their positions in the embodiment of figures 6(a) and 6(b). That is, the colour filters 18 are deposited on a principal surface of the light-transmissive base substrate 19. A spacer layer 20 is deposited over the colour filters 18, and the parallax optic is formed over the upper surface of the spacer layer 20. In the embodiment shown in figures 16(a) and 16(b) a parallax barrier aperture array 13 forms the parallax optic, but this embodiment is not limited to this particular type of parallax optic. The spacer layer 20 may be a light- transmissive resin layer, a glass layer, a light-transmissive layer of plastics material, etc. In the embodiment of figures 16(a) and 16(b) the parallax barrier array 13 is disposed substantially adjacent to the liquid crystal layer 8. A large angular separation between different viewing windows can therefore be obtained.

Figures 17(a) and 17(b) illustrate a display 38 according to a further embodiment of the present invention. In this embodiment, the parallax optic is constituted by a reactive mesogen parallax barrier. This embodiment corresponds generally to the embodiment of figure 6(a) and 6(b) , and only the differences will be described here.

The RM parallax barrier in this embodiment is formed by strips 40 of a reactive mesogen material disposed over the upper surface of the lighttransmissive base substrate 19. A polariser 41 is provided over the upper surface of the base substrate including over the strips 40 of RM material. The strips 40 of RM material and the i polariser 41 form a RM parallax barrier 42. The operation of a RM parallax barrier is- explained in detail in EP A 0 829 744.

A spacer layer 20 is deposited over the upper surface of the RM parallax barrier 42.

Colour filters 18 are deposited on the upper surface of the spacer layer 20. As in previous embodiments, the spacer layer 20 may be, for example, a light transmissive resin layer, a glass layer, a light-transmissive plastic layer, etc. The base substrate 19 may be a glass substrate, a plastics substrate, a glass-reinforced plastics substrate, etc. In the multiple-view directional display 38 of this embodiment, the separation between the parallax barrier 42 and the liquid crystal layer 8 is again approximately equal to the thickness of the spacer layer 20. The spacer layer may be made thin, so that good angular separation between different viewing windows can be achieved.

This embodiment has the further advantage that the RM parallax barrier is an active parallax barrier, and may be switched (using suitable addressing means, not shown) to put the strips of RM material 40 in a transparent state so that the parallax barrier is disabled or "switched off'. If the parallax barrier 42 is disabled, the display device will act as a conventional 2-dimensional or single view display device. Thus, this embodiment provides a display that is operable in either a 2-D display mode or a 3-D or multiple view display mode, and that can provide good angular separation between adjacent viewing windows when operating in the 3-D or multiple view display mode.

Figure 18(b) illustrates a display 38' according to a further embodiment of the present invention, and Figure 18(a) is a schematic sectional view of the colour filter substrate 39' of the display. The display 38' of this embodiment corresponds essentially to the embodiment of figures 17(a) and 17(b) except that the spacer layer 20 is omitted and the colour filters 18 are disposed directly on the upper surface of the polariser 42. All other features of the display 38' of figure 18(b) correspond to those of the display 38 of figure 17(b) and so will not be described further here.

Figures 19(a) and 19(b) show a further embodiment of the present invention. In this i embodiment, the colour filter substrate 44 of the multiple-view directional display 43 is- provided with an active parallax barrier 46. Figure 19(b) is a schematic plan view through the display device 43 and figure 19(a) is a schematic sectional view of the colour filter substrate 44.

The active parallax barrier 46 is formed by a plurality of regions 47 of a material whose optical properties are switchable disposed on the surface of the base substrate 19. The regions 47 may be in the form of strips that extend into the plane of the paper in Figure 19(a). The active parallax barrier is formed by the regions 47 in combination with another layer 45 disposed over the regions 47 which may be a linear polariser or a transparent spacer layer depending on the material used for the active strips 47.

In a preferred embodiment the regions 47 are regions of a liquid crystal material and the layer 45 is a linear polariser. As is well known, a liquid crystal material may be addressed so as to either rotate or not rotate the plane of polarisation of linearly polarised light passing through it. Preferably, the regions 47 of liquid crystal material can be switched between a state in which it rotates the plane of polarisation ol linearly polarised light by 90 and a state in which it does not rotate the plane of polarization of linearly polariscd light. Thus, the regions 47 of liquid crystal material may be addressed so that light passing through the regions 47 is either transmitted by the linear polariser 45 (in which case the regions 47 define transmissive regions) or is blocked by the linear polariser 45 (in which case the regions 47 define opaque regions).

The display 43 is required to be illuminated from the colour filter substrate side by polarised light, either from a light source that emits polarised light or from a polariser disposed in front of a light source. Alternatively, it may be illuminated from the TFT side, in which case a further polariser (not shown) must be disposed beyond the colour filter substrate.

If light that does not pass through the regions 47 of switchable optical properties (i.e., that passes through a gap between adjacent active regions) is passed by the polariser 45, a parallax barrier is formed when light that passes through the regions 47 is blocked by the polariser; in this case, a 3-D or multiple view display mode is obtained. If theregions 47 are switched so that light that passes through a region 47 is transmitted by the polariser 45, then no barrier exists and a 2-D or single view display mode is obtained.

It would in principle also be possible to arrange the transmission direction of the polariser 45 and the polarisation direction of the incident light such that light passing through the gaps between the regions 47 of liquid crystal material is blocked by the polariser 45. In this case a parallax barrier is formed when the regions 47 rotate the plane of polarisation of incident light so that it can pass through the polariser 45.

However, when the regions 47 were switched so that light passing through the strips 47 is blocked by the polariser 45, a dark display would be produced as all light would be blocked by the polariser.

The regions of active material 47 are not limited to liquid crystal material. Any material that can be addressed to alter its opticalproperties can in principle be used. For example, a polymer-dispersed liquid crystal material may be used as the material of the active parallax barrier. As is weld-known, a PDLC consists of droplets of liquid crystal material dispersed through a polymer matrix. The refractive index of the liquid crystal droplets can be varied, and the PDLC will transmit light if the refractive index of the liquid crystal droplets is the same as the refractive index of the polymer matrix.

However, if the liquid crystal material is switched so that its refractive index is different from the refractive index of the polymer matrix, light passing through the PDLC is scattered.

Another suitable material for the active parallax barrier is a dichroic guest-host material.

This embodiment allows the parallax barrier to be switched on and off, thereby allowing either a 3-D (or multiple view) or a 2-D display mode to be selected. Furthermore, it is possible to arrange the active parallax barrier 46 so that the configuration of transmissive and opaque areas can be altered. For example, the active parallax barrier 46 may be switched so that the opaque regions of the barrier move from one position to- another. This effectively causes the barrier to be translated across the area of the display device, and this would alter the position of the viewing windows. Thus, in this embodiment, it is possible to control the position of the viewing windows by suitably addressing the active parallax barrier 46. This embodiment would be particularly useful when combined with an observer tracking device which tracks the observer of the display, as the position of the viewing windows could be controlled on the basis of the position of the observer as determined by the observer-tracking device.

It should be noted that, in this embodiment, the polariser 45 is contained within a liquid crystal display element. The polariser 45 must therefore be able to withstand the harsh processing conditions that occur during manufacture of a liquid crystal panel.

Conventional polarisers used on the outside of a liquid crystal display may well not stand the processing conditions, and so cannot be used. This has the possible disadvantage that it may be necessary to use a polariser having a lower contrast ratio than conventional polarisers used outside a liquid crystal panel. If this is the case, the polariser 45 can be oriented so that its poor contrast ratio affects either the contrast ratio of the parallax barrier or the contrast ratio of the pixels of the liquid crystal layer 8.

Where the layer 45 is a spacer layer, it may be treated so that it aligns liquid crystal material, for example of the regions 47, with a particular alignment direction and pre-tilt angle. For example, the spacer layer may be coated with a polyimide layer (not shown) and rubbed and/or exposed to ultraviolet light in a conventional photo-alignment process.

In alternative embodiments, the colour filters may be disposed on the TFT substrate 6 or between the active parallax barrier 46 and the substrate 19.

Figure 20(b) shows a display 48 according to a further embodiment of the present invention, and Figure 20(a) shows the colour filter substrate 49 of the display. This embodiment corresponds generally to the embodiment of Figure 6(a)-6(b) except that in I this embodiment, the colour filter substrate 49 of the multiple-view directional display- 48 again comprises an active parallax optic 35''. In this embodiment the active parallax optic 35'' is an active lenticular lens array. The lenticular lens array can be switched between a mode in which it has substantially no tensing effect (so that no parallax optic exists) and a mode in which it has a tensing effect (so that a parallax optic is formed) .

The lenticular lens array 35'' may be addressed by suitable addressing means (not shown).

For example, the lenticules of the lenticular lens array may be made of a liquid crystal material that is addressed by electrodes (not shown) disposed on opposite sides of the lenticules. The liquid crystal material is chosen so that, for some applied voltage across the lens array, its refractive index is as close as possible to the refractive index of the base substrate 19. When the appropriate voltage is applied between the electrodes provided on opposite sides of a lenticule, the refractive index of the liquid crystal material of that lenticule therefore closely matches the refractive index of the spacer layer 20, and the lenticule has substantially no tensing effect. By varying the applied voltage, however, the liquid crystal material of the lenticule may be changed so that its refractive index is made different to the refractive index of the substrate 19. The lenticule therefore acts as a lens, and so forms an element of a parallax optic.

The lenticules 50 of the active lenticular lens array may be arranged as graded refractive (GRIN), or they be arranged as Fresnel lenses.

Figure 20(c) illustrates a substrate 49 which differs from that shown in Figure 20(a) in that the glass substrate 19 is recessed to accommodate the active lenticular lens array 35''. In this arrangement, the refractive index of the active array should substantially match that of the substrate 19 in the single view or non-directional mode of operation.

Figure 20(d) illustrates a substrate 49 in which the lenses of the active array 35'' are convexo-convex to provide improved performance, such as a smaller crosstalk region and a greater freedom of movement of the viewer. In this case, in the single view mode of operation, the refractive index of the array 35'' should substantially match the I refractive indices of the substrate 19 and the spacer 20.

Figure 21(b) shows a display 48' according to a further embodiment of the present invention, and Figure 21(a) shows the colour filter substrate 49' of the display 48'. This embodiment is generally similar to the embodiment of figures 20(a) and 20(b), and only the differences will be described here.

The multiple-view directional display 48' of figure 21(b) has a colour filter substrate 49' that incorporates an active lenticular lens array 35". In this embodiment, however, switching of the lens array is achieved in a different way. In this embodiment, the lenticules 50 are made of liquid crystal material. However, the microscopic structure of the liquid crystal material is fixed, and the liquid crystal material is not addressed in operation of the device.

The switching of the lens array in this embodiment is achieved by making use of the fact that the refractive index of a liquid crystal material is generally dependent on the polarisation state of the light passing through it. The liquid crystal material of the lenticules 50 is chosen such that, for light of one polarization state, the refractive index of the liquid crystal material is substantially the same as the refractive index of the spacer layer 20. Thus the liquid crystal material has substantially no tensing effect on light of this polarization state. However, for another polarization state, in particular for a polarization state orthogonal to the first polarization state, the refractive index of the liquid crystal material will not match the refractive index of the layer 20 so that the liquid crystal material has a tensing effect for light of the second polarisation state.

The liquid crystal lenticules 50 are switched on or off by changing the po]arisation state of light entering the display 48. This may be done by providing a polarisation switch 51 that can change the polarization state of light passing through a selected portion of the polarization switch 51, for example by selecting one of two orthogonal linear polarizations. The polarization switch 51 may be constituted by, for example, a liquid crystal cell and is followed by a polaiser 51'.

Figure 21(c) illustrates another substrate 49' in which the glass substrate 19 is recessed so as to accommodate the array 35''. In this case, one of the refractive indices of the material of the array 35'' must substantially match the refractive index of the glass substrate 19 so as to provide a single view mode of operation.

Figure 21(d) illustrates another form of the colour filter substrate 49' in which both the spacer 20 and the glass substrate 19 have recesses to accommodate the lens array 35'', which is convexo-convex. In this case, one of the refractive indices of the material of the array 35'' is required substantially to match the refractive indices of the spacer 20 and the glass substrate 19 in order to provide a non-directional or single view mode of operation.

Figure 22 is a schematic sectional view of a multiple-view directional display 52 according to a further embodiment of the present invention. This is in many ways similar to the display 58 of figure 6(b), except that a plurality of prisms 53 are provided on the external surface of the base substrate 19 of the colour filter substrate 7. In figure 22 the prisms 53 are shown as having a triangular cross-section. The prisms 53 work in combination with the parallax barrier 13 provided inside the display device. In use, the device is illuminated by a light provided behind the TFT substrate 6, so that the base substrate 19 of the colour filter substrate 7 forms the exit lace of the display device.

The prism structure varies the angle of separation between the left and right images induced by the parallax barrier.

In the embodiment of figure 22, the prisms are arranged so that they reduce the angle of separation between the viewing windows of different images.

Although the prisms are shown as having a triangular cross-section in figure 22, this embodiment is not limited to prisms having a triangular cross-section. In principle, any prism structure that reduces the angle of separation between two viewing windows may be used. Furthermore, where prisms having a triangular cross-section are used, it is not necessary for the prisms to have a cross-section that is an equilateral triangle. In fact 7 any symmetrical or asymmetrical convergent or divergent element may be used, fort example to suit any application of the display.

The embodiment of figure 22 may be of use in, for example, an autostereoscopic display device where the angular separation between the viewing windows of the lett- eye image and the right-eye image is required to provide a separation between the left- eye and right-eye windows that is equal to the distance between the two eyes of a human at the desired viewing distance of the display.

Figure 23 shows a display 52' according to a further embodiment of the present invention. This display 52' corresponds generally to the display of figure 22, except that the prisms 53 provided on the surface of the base substrate 19 are intended to increase the angle of separation between the two viewing windows.

Figure 24 illustrates a multiple-view directional display 59 according to a further embodiment of the present invention. The display 59 of this embodiment corresponds generally to the display device 20 of figure 6(b), except that it further comprises switchable means 54 for varying the angle between two viewing windows produced by the device. The switchable means 54 may be switched between a state in which it has substantially no effect on the angular separation between two viewing windows and another state in which it will increase or decrease the angular separation between two viewing windows. In this embodiment the switchable means 54 comprises a plurality of light-transmissive prisms 53 mounted on the external surface of the base substrate 19 of the colour filter substrate. An active layer 55 is disposed over the prisms 53 so as to planarise the prisms. The active layer is contained by a transparent plate 56. The prisms and the transparent plate may be formed of glass, transparent resin, transparent plastics material, etc. The active layer 55 may comprise, for example, a liquid crystal layer. The liquid crystal layer is selected such that, when no electric field is applied across the liquid crystal material, the refractive index of the liquid crystal material matches the refractive index of the prisms 53. In this state, the prisms have substantially no effect on the angular separation between two viewing windows produced by the device 54. i The switchable means 54 further comprises electrodes (not shown) that allow an electric field to be applied across the liquid crystal layer 55. By applying a voltage across the electrodes, and thereby applying an electric field across the liquid crystal layer, it is possible to vary the refractive index of the liquid crystal material so that it becomes different from the refractive index of the prisms 53. Light passing through the interface between a prism and the liquid crystal layer therefore undergoes refraction. In consequence, the angular separation between two viewing windows formed by the display device is altered by the prisms 53. This allows the display 59 to switch, tor example, between a dual-view display mode and an autostereoscopic display mode.

The switchable means 54 may allow the angular separation between two viewing windows to be controlled continuously by continually varying the electric field applied across the liquid crystal layer. This allows the angular separation between two viewing windows to be tuned to suit a particular use of the display device 54. This embodiment is particularly useful if information about the longitudinal separation between the display and an observer is available, for example from an observer tracking device - in an autostereoscopic display mode the switchable means 54 may control the angular separation between the left-eye and right-eye viewing windows so that the lateral separation at the observer is kept equal to the separation between the two eyes ot a human.

Figure 25 shows a multiple-view directional display 57 according to a further embodiment of the present invention. This display 57 is generally similar to the display - 54 of figure 24, and only the differences will be described here.

In the display 57 of figure 25, the switchable means 54 for varying the angular separation between two viewing windows formed by the display comprises prisms 53 disposed on the external surface of the substrate 19 of the colour filter substrate 7. A liquid crystal-layer 55 is placed over the prisms 53, but, in contrast to the embodiment of figure 24, the microscopic structure of the liquid crystal layer is fixed. No means for i addressing the liquid crystal layer 55 are therefore required.

The refractive index of the liquid crystal layer 55 is dependent on the state of polarisation of light passing through the liquid crystal layer. The liquid crystal layer is chosen such that its refractive index, for one polarisation state, is substantially equal to the polarisation state of the prisms 53. In this case, light passing through the prisms undergoes substantially no refraction.

For light of another polarisation state, for example a polarisation state orthogonal to the first polarisation state, however, the refractive index of the liquid crystal material 55 is not equal to the refractive index of the prisms 53. For light of this second polarisation state, therefore, refraction occurs at the interface between the prisms and the liquid crystal layer 55, leading to a variation in the angular separation between two viewing windows formed by the display 57.

The refraction effect in this embodiment may be switched on or off by suitably selecting the polarisation state of light entering of leaving the panel. This may be done by providing a polarisation switch 51 and a polariser 51' between the light source and the observer. In figure 25 the polarisation switch 51 and the polariser 51' arc disposed between the display device and an observer, hut they could alternatively be provided between the light source and the display device. The polarisation switch may be, for example, a liquid crystal cell.

The embodiments of Figures 24 and 25 may be effected using a prism structure that tends to increase the angular separation between viewing windows, as in figure 23.

Embodiments of the invention have been described above with reference to specific types of parallax optics. The embodiments are not, however, limited to the specific types of parallax optic shown, and may be used with other types of parallax optic.

The present invention allows a substrate on which a parallax optic is mounted to be used as a substrate of an image display element such as, for example, a liquid crystal display i element. This has the advantage that the alignment of the parallax optic and the pixels- 1 of the display element is carried out during manufacture of the display element. This allows the alignment to be carried out more precisely compared to the conventional case where an external parallax optic is aligned with a complete liquid crystal display element (as in figure 1). Furthermore, eliminating the step of gluing or otherwise adhering a parallax optic to a completed image display element makes the] manufacturing process quicker and cheaper.

In the embodiments described above the parallax optic has been disposed on the same substrate as the colour filters. It would alternatively be possible to dispose the parallax optics on the TFT substrate 6 of the display and, for every embodiment described above i with a parallax optic provided on the colour filter substrate, there is a corresponding embodiment in which a parallax optic is provided on the TFT substrate. In such modified embodiments, an array of switching elements such as an array of I l s and the elements of the parallax optics would be disposed over a base substrate of the TFT substrate, possibly with a spacer layer interposed between the parallax optic and the thin film transistors. The separation between the parallax barrier and the image display layer would again be substantially the thickness ol the spacer layer (assuming that the spacer layer was disposed over the parallax optic). Moreover, in the embodiments of Figures; 22 to 25, the prisms 53 may be disposed on the TFT substrate.

Furthermore, in some liquid crystal panels the colour flitters are disposed on the same substrate as the thin film transistors. the invention may then be applied to such a device. For example, a light- transrnissive spacer layer (for example a resin, glass or plastics spacer layer) may be disposed over the TFTs (or other switching elements) and the colour filters, and the parallax optic may be disposed over the spacer layer.

The embodiments of the invention, with the exception of those shown in figures 22-25, may be used as either a rear barrier device (as in Figure 4) or as a front barrier device (as in Figure 1).

Where a device of the present invention in which the parallax optic is a parallax barrier is used in the rear-barrier mode of Figure 4, it is preferable if the parallax barriers elements are reflective on the side facing the back light. Light from the back light that is incident on the opaque regions of the barrier will then be reflected, and can be rereflected from the back light so that it may pass through the parallax barrier and thus through the display device. This would increase the brightness of the display. The surface of the parallax barrier elements facing away from the backlight is preferably absorbing, to prevent crosstalk.

The invention has been described above with reference to an image display element that comprises a liquid crystal layer. The invention is not, however, limited to this particular image display element and any suitable image display element may be used. As an example, an OLED (organic light-emitting device) image display element may be used.

Claims

CLAIMS: 1. A multiple view directional display having an image display

element and a parallax optic; wherein the image display element comprises: a first substrate; a second substrate; and an image display layer sandwiched between the first substrate and the second substrate; and wherein the parallax optic is disposed within the image display element.
2. A display as claimed in claim 1 wherein the parallax optic is disposed between the first substrate and the second substrate.
3. A display as claimed in claim 1 wherein the parallax optic is disposed within one of the first substrate or the second substrate.
4. A display as claimed in claim 2 wherein the parallax optic and one of a colour filter array and an array of switching elements are disposed over a principal surface of the first substrate.
5. A display as claimed in claim 4 wherein the parallax optic is disposed on the first principal surface of the first substrate and the colour filter array or array of switching elements is disposed over the parallax optic.
6. A display as claimed in claim 4 wherein the co]our filter array or array of switching elements is disposed on the first principal surface of the first substrate and the parallax optic is disposed over the colour filter array or the array of switching elements.
7. A display as claimed in claim 5 or 6 and further comprising a transparent spacer layer disposed between the parallax optic and the colour filter array or array of switching elements
8. A display as claimed in claim 5, 6 or 7 and further comprising another parallax optic disposed between the parallax optic and the colour filter array or array of switching elements.
9. A display as claimed in claim 4 wherein the parallax optic comprises a plurality of parallax elements, each parallax element being disposed in a respective recess in the principal surface of the substrate.
10. A display as claimed in claim 9 wherein each parallax element is disposed on a i bottom face of a respective recess.
11. A display as claimed in claim 4 wherein: a light-transmissive layer is disposed over a principal surface of the substrate; a plurality of recesses are defined in the light- transmissive layer; and the parallax optic comprises a plurality of parallax elements, each parallax element being disposed in a respective recess in the light-transmissive layer.
12. A display as claimed in claim 9 or 11 wherein the cross-section of a recess, parallel to the surface of the substrate, decreases with depth.
13. A display as claimed in claim 12 wherein each parallax element substantially fills a respective recess.
14. A display as claimed in claim 3 wherein one of a colour filter array and an array of switching elements is disposed over a first principal surface of the first substrate and the parallax optic is disposed over a second principal surface of the first substrate.
15. A display as claimed in claim 14 wherein the parallax optic comprises a plurality of parallax elements, each parallax element being disposed in a respective recess in the second principal surface of the substrate.
16. A display as claimed in any preceding claim wherein the parallax optic is a parallax barrier.
17. A display as claimed in any preceding claims wherein the parallax optic is lenticular lens array.
18. A display as claimed in any preceding claim wherein the parallax optic is disableable.
19. A display as claimed in any preceding claim wherein the parallax optic is- addressable.
20. A dual-view display comprising a multiple-view directional display as defined in any preceding claim.
21. An autostereoscopic display comprising a multiple-view directional display as defined in any of claims I to 19.
22. A parallax optic comprising: a light-transmissive substrate; and a plurality of parallax elements, each parallax element being disposed in a respective recess in a surface of the substrate.
23. A parallax optic as claimed in claim 21 wherein the cross-section of a recess, parallel to the surface of the substrate, decreases with depth.
24. A parallax optic as claimed in claim 22 wherein each parallax clement substantially fills a respective recess.