GB2408620A

GB2408620A - Transflective display

Info

Publication number: GB2408620A
Application number: GB0327788A
Authority: GB
Inventors: Marina Khazova; Grant Bourhill
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2003-11-29
Filing date: 2003-11-29
Publication date: 2005-06-01
Also published as: GB0327788D0

Abstract

A transflective display having reflective and transmissive display modes comprises a spatial light modulator such as a liquid crystal device (8). First and second volume reflection holograms (H1 and H2) are disposed behind the modulator (8) and have first and second reflective modes. The first reflective mode is responsive to a first type of illumination and provides a direct view reflective mode of the display. The second reflective mode responds to a different type of illumination and allows the display to be used with a projection attachment to provide an enlarged projected image. The transmissive mode of the display is not affected by the presence of the holograms (H1 and H2).

Description

TRANSFLECTIVE DISPLAY

The present invention relates to a transflective display. Such a display may be used in devices such as mobile or cellular telephones, personal digital assistants (PDA), personal game consoles and vehicle navigation and/or entertainment systems. The present invention also relates to such devices and to combinations of such devices with projection adaptors.

Known types of liquid crystal displays (LCDs) for such devices may operate in a variety of modes, such as a reflective mode, a transmissive mode or a transflective mode. A reflective mode LCD generally makes use of ambient light to display information and thus reduces the power consumption of such a device. A transflective LCD may operate in the reflective mode, again making use of ambient light for illumination, or in the transmissive mode if ambient illumination is insufficient. A backlight is required for the transmissive mode.

Figure 1 of the accompanying drawings illustrates a known type of transflective display, for example as disclosed in K. Fujimori et al, 'mew Colour Filter Structures for Transflective TFT-LCD", SID02 Digest, 53.3. The display is formed on and around an active matrix substrate 6 and a counter-substrate 7 carrying a plane electrode (not shown). Alignment layers (not shown) for a liquid crystal layer 8 are provided on the electrodes. A retardation film 9 and a polariser 10 are provided on the outer surface of the substrate 6, which is disposed above a backlighting system 11, which is energised in the transmissive mode of operation of the display.

The upper surface of the substrate 7 carries a colour filter arrangement 12, a retardation film 13 and a polariser 14.

Each pixel of the display is defined by an electrode 15, which has a transmissive area 16 and a reflective are a 17. The reflective area 17 of the electrode 15 is in the form of a metalised diffuse reflector, which reflects ambient light 18 modulated by the associated liquid crystal pixel, back through the same pixel.

The transmissive area 16 of the electrode 15 is, for example, made of indium tin oxide (ITO) and is transmissive to light from the backlighting system 11. Thus, for the transmissive mode, the backlighting system 11 is switched on and light passing through the transmissive area 16 is modulated by the associated liquid crystal pixel.

Transflective displays of this type provide images of reduced brightness, for a given illumination brightness, compared with displays which are arranged to operate only in the reflective mode or only in the transmissive mode. In particular, the area of each pixel of a transflective display is divided into two regions or areas 16, 17, only one of which functions in any particular mode of operation of the display whereas the other does not contribute any light to the image being displayed.

Figure 2 of the accompanying drawings illustrates an alternative arrangement of a known type of transflective display in which the electrode 15 is wholly transmissive throughout the area of each pixel and reflection is provided by a holographic reflective colour filter (RCF) arrangement 23. Both electrodes 15 and 24 are, for example, made of ITO. The simplified view of the display shown in Figure 2 also shows the liquid crystal (LC) layer 8 and the substrates 6 and 7 as illustrated in Figure 1. A display of this type is presently disclosed at http://www. dupont.com/holographics/displays.html.

The display shown in Figure 2 responds to collimated light, for example, from a distant light source, and the holographic reflector 23 redirects such light so as to function as an off-axis diffuser. The hologram 23 has substantially no effect on light from a backlight (not shown in Figure 2) so that substantially the whole area of each pixel modulates light in each of the transmissive and reflective modes.

The graph in Figure 2 compares the performance of a green holographic reflective filter with a metal diffuser reflector of the type illustrated in Figure 1. In this example, the display is illuminated with an angle of incidence of approximately +35 degrees. Whereas reflection of modulated light from the display increases progressively towards a peak at the specular reflection direction, the holographic reflector is designed so as to reflect and diffuse image light much nearer the on-axis viewing position, which is the normal viewing position for a display. Thus, a holographic reflector can be used to increase the image brightness for normal viewing in the reflective display mode, in addition to allowing the whole of the pixel area to be used.

Known types of holographic reflectors are disclosed in: US5,663,816; Tokumaru et al, "Holographic diffusive reflectors for reflective colour LCDs", SPE Proc., v3637, ppl96-203, 1998; and Ralli et al, "Imagix holographic diffusers for reflective liquid crystal displays", SID96, 44. 5L.

US5,629,806 discloses a display arrangement for providing private viewing and for displaying a relatively large image from a small direct view display. The arrangement comprises an image display, such as a cathode ray tube, electro- luminescent display or direct view back-lit transmissive LCD, together with focusing, conjugating and folding optics. The conjugating optics include a retro-reflector and a beam splitter.

Figure 3 of the accompanying drawings illustrates a known type of overhead projector of the reflection type for images fixed on transparencies. The projector comprises a light source including a condensing optic 1 for illuminating a transparency 2 carrying an image to be projected. The transparency 2 is disposed on a reflective Fresnel lens 3 with the axis of the lens 3 being laterally spaced from the axis of the condensing optic 1. The lens 3 images the light source at a projection lens 4, whose axis is also laterally spaced from the axis of the lens 3 and from the axis of the condensing optic 1. A folding mirror 5 directs light onto a projection screen (not shown) for displaying the projected image.

US5,970,418 discloses a wireless handset telephone including a virtual image display which reflects the image from a direct view display so that the virtual image is viewable while the telephone is held to the ear of a user. The display comprises a curved mirror, a partially reflective/transmissive optical element, the display and a rotating base.

US6,489,934 discloses a mobile or cellular telephone with a built-in optical projector. The optical projector is distinct from a direct view display of the telephone and comprises a high intensity lamp, a collimating lens, a transmissive LCD (which is distinct from the direct view LCD) and a projection lens.

US2002/0063855 discloses a small video projector which is functionally integrated into a device such as a mobile telephone or a personal digital assistant. The projector includes an internal light source, a microdisplay and a projection arrangement.

At the CeBIT2002 computer show in Hanover, Germany, Siemens AG disclosed a miniature daylight projector which may be connected to a mobile telephone with a suitable interface. The projector comprises a light source in the form of a light emitting diode array for illuminating a micro-display (distinct from the display of the mobile telephone) through a beam splitter. A projection lens projects the resulting image onto a suitable projection screen or surface.

JP2002-268005 discloses a portable projection display, which projects the image from a display element or its intermediate image on the eye of an observer.

JP2002-027060 discloses a mobile telephone including an overhead projection function. Information stored in a memory is displayed by a display panel. The displayed information is illuminated by an internal light source and reflected and projected through a magnifying lens onto a projection screen.

GB2360664 discloses a mobile telephone incorporating a projection arrangement and a projection screen, which may be stored or unfolded for use.

US6595648 discloses a projection display as illustrated in Figure 4 of the accompanying drawings. The display comprises a light source, comprising a lamp and collecting optics 20, 21, a condensing optic 1, a field stop 30 and a condensing optic 25, which forms an image 33 of the light source at a first reflecting surface of a turning prism 31. Light from the light source illuminates an LCD 10 provided with a volume reflection hologram 32 permanently attached to the rear surface of the LCD. The hologram 32 acts as a lens which forms an image 34 on a second reflecting surface of the turning prism 31. A projection lens 4 forms a final image 35 at a projection screen (not shown). The image 34 of the light source is laterally spaced from the image 33 of the light source. The hologram 32 thus functions as a reflector and off-axis lens.

Valliath et al, "Design of Hologram for Brightness Enhancement in Colour LCDs", SlD98 Digest 44.5 L, PP1139-1142, 1998 discloses the use of a transmission hologram for brightness enhancement of a front-illuminated reflective LCD. The hologram is permanently attached to a front surface of the LCD and, when suitably illuminated, directs light into a viewing region of the display.

According to a first aspect of the invention, there is provided a transflective display having reflective and transmissive display modes and comprising a spatial light modulator and first and second holographic reflectors disposed behind the modulator and having first and second reflective modes, respectively, which are different from each other.

The display may have a direct view reflective mode of operation when the first reflector operates in the first reflective mode.

The display may have a reflective mode of operation for projection when the second reflector operates in the second reflective mode.

The first reflector may be responsive to a first type of illumination to operate in the first reflective mode. The second reflector may be unresponsive the first type of illumination. The first type of illumination may be substantially collimated illumination incident on the first reflector at a predetermined angle. As an alternative, the first type of illumination may be illumination from a first light source position with respect to the first reflector.

The first reflector may perform reflection and diffusion in the first reflective mode. The first reflector, when in the first reflective mode, may diffuse incident light into a range of angles substantially excluding an angle of specular reflection.

The second reflector may be responsive to a second type of illumination to operate in the second reflective mode. The first reflector may be unresponsive to the second type of illumination. The second type of illumination may be illumination from a second light source position with respect to the second reflector.

The second reflector may act as a reflector and converging lens in the second reflective mode. The second reflector may act as an off-axis lens in the second reflective mode.

Each of the first and second reflectors may be a volume hologram. The first and second reflectors may comprise adjacent separate layers. As an alternative, the first and second reflectors may be formed in a single layer.

The first and second reflectors may be disposed adjacent the modulator to reflect modulated light from the modulator back through the modulator.

At least one of the first and second reflectors may be spatially continuous.

At least one of the first and second reflectors may be pixellated to form a plurality of groups of elements for reflecting respective different colour ranges.

The display may comprise a backlight for a transmissive mode with the first and second reflectors being disposed between the backlight and the modulator. The first and second reflectors may be substantially unresponsive to light from the backlight.

The modulator may be a liquid crystal display.

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

According to a third aspect of the invention, there is provided a combination of a device according to the second aspect of the invention and a projection adaptor for forming a projected enlarged image of an image displayed by the display.

The adaptor may comprise an illumination section, a projection section and a support arrangement supporting the illumination section and the projection section. The support arrangement may comprise alignment means for aligning the adapter with the display. The support arrangement may comprise a switch for switching off rear illumination of the display when the adapter is aligned with the display.

It is thus possible to provide a transflective display having two different reflective modes of operation in addition to a transmissive mode. For example, in addition to the direct view transmissive and reflective modes, it is possible to provide a mode which allows projection of the displayed image onto an external screen with magnification of the image size. It is therefore possible to increase the functionality of a device, such as a mobile or cellular telephone, a personal and digital assistant, a personal game console, or an in-vehicle navigation and/or entertainment system.

High brightness images can be achieved in all modes because substantially the whole area of each pixel of a pixallated spatial light modulator may be used to modulate the light, irrespective of the mode of operation. In a direct view reflective mode of operation, it is possible to achieve improved contrast of the image by separating the reflected image from specular reflection. In a projection mode, image brightness does not depend on image brightness in direct view modes because an external light source may be used for the projection mode.

By locating the holographic reflectors close to the active layer of the modulator, parallax effects can be reduced to an acceptable level. In the case of a liquid crystal device as the spatial light modulator, the holographic reflectors may be disposed substantially immediately adjacent the cell or even inside the cell so as to be substantially immediately adjacent the liquid crystal layer.

In reflection modes of operation, by appropriately designing the holographic reflectors, the diffusion cone can be suitably controlled or selected. For example, the diffusion cone may be different in the vertical and horizontal directions.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure I is an exploded diagrammatic view of a known type of transflective display; Figure 2 illustrates diagrammatically another known type of transflective display and includes a graph comparing performance of such a display with that of a display of the type illustrated in Figure 1; Figure 3 is a crosssectional diagrammatic view of a known type of projection system; Figure 4 is a cross-sectional diagram illustrating another known type of projection system; Figure 5 is a diagram illustrating a transflective display constituting an embodiment of the invention; Figure 6 is a diagram illustrating a transmissive mode of the display of Figure 5; Figure 7 is a diagram illustrating a first reflective mode of the display of Figure 5; Figure 8 is a diagram illustrating a second reflective mode of the display of Figure 5; Figure 9 is a diagram illustrating alternative first reflective modes of the display of Figure 5; Figure 10 is a diagram further illustrating the alternative reflective mode; Figure 11 is a diagram illustrating a modification to the arrangement whose reflective mode is illustrated in Figure 9; and Figures 12 to 20 are cross-sectional diagrams illustrating a display of the type shown in Figure 5 in combination with various types of projection adapters.

Like reference numerals refer to like parts throughout the drawings.

Figure 5 illustrates diagrammatically a pixel of a transflective display, which differs from that shown in Figure I in that the electrode 15 is completely transmissive and two reflection holograms Hl and H2 are disposed behind the liquid crystal layer 8.

The holograms H I and H2 are volume reflection holograms which have substantially no effect on operation of the display in the transmissive mode but which have two different reflective modes according to the type of illumination from the front of the display. In the direct view transmission mode of the display illustrated in Figure 6, rear illumination illustrated at 40 from a suitable backlight (not shown) passes through the holograms Hl and H2 substantially without being altered. However, the whole of the area of the pixel modulates the light 40 to provide a brighter image than with the display of Figure 1.

In a first direct view reflective mode of operation of the display as illustrated in Figure 7, the hologram Hl acts as an off-axis diffuser when provided with overhead ambient illumination 41 incident on the display at an angle of, for example, +30 degrees. The light 41 passes through the liquid crystal layer 8 of each pixel and is modulated thereby. The hologram Hl reflects and diffuses the collimated illumination 41 mainly into an angular region or cone to permit on-axis viewing of the display. The viewing angle excludes the specular reflection angle so as to reduce glare and improve the image contrast of the display. The angular range or cone may be different in the horizontal and vertical planes or may be the same. The reflected and diffused light passes back through the liquid crystal layer 8 of the pixel for direct viewing.

The collimated illumination 41 may be provided by a distant light source or by a nearer suitably collimated light source. The whole of the area of the pixel modulates the illumination so as to provide a bright image of good contrast ratio. The angle of illumination is outside the angular acceptance range or cone for Bragg conditions for efficient diffraction in the hologram H2. Accordingly, the hologram H2 has substantially no effect on the operation in this direct view reflective mode.

Figure 8 illustrates a second reflective mode of operation of the display for use with a projection adaptor or attachment described hereinafter to provide a projection mode of operation for forming an enlarged image of the image displayed by the display.

The hologram H2 is arranged to act as an off-axis reflective holographic lens when illuminated by divergent light 42 from the illumination pupil 43 of the illumination section of the projection attachment. The divergent light 42 is modulated by the whole area of the pixel from a position which is angularly offset from the display axis in the negative direction, which is opposite the angular direction of illumination illustrated in Figure 7. Light modulated by the liquid crystal layer 8 of the pixel is reflected and 1 S imaged by the hologram H2 to form an image of the illumination source at a projection lens pupil 44 of a projection section of the projection attachment. The illumination pupil 43 and the projection lens pupil 44 are laterally offset with respect of each other and both pupils may be laterally offset from the display so that lines drawn from the pupils and intersecting the plane of the display orthogonally do not pass through the display surface of the display. The whole area of each pixel is used in this mode of operation so as to provide a relatively bright projection display in combination with the projection attachment. An external light source is used so that, for example, the projected image brightness does not depend on the brightness of a backlight for the transmissive mode of the display.

When the display is illuminated as shown in Figure 8, the angles of incidence from the illumination pupil 43 do not satisfy the Bragg conditions for the hologram Hi, which thus has substantially no effect on the operation of the display.

The transmission mode and the two reflective modes can operate substantially' independently of each other without mutual interaction. Thus, two or more of these modes may be used simultaneously. In particular, the transmissive mode may be used simultaneously with either or both of the reflective modes by switching on the backlight and by providing the appropriate front illumination. Each mode of operation is effectively activated when the appropriate type of illumination is provided and both modes may operate simultaneously without substantial interaction.

The holograms H1 and H2 may be in the form of continuous elements disposed behind and adjacent the liquid crystal layer 8 of the display. The use of such continuous or uniform holograms removes the need for the holograms to be aligned with the pixel structure of the spatial light modulator of the display. Also, although the spatial light modulator is described herein as being a liquid crystal device, other types of transmissive spatial light modulators may alternatively by used.

In an alternative arrangement, the holograms H1 and H2 may be pixellated. The hologram pixels may be arranged to reflect different primary colours or colour ranges so as to replace or augment the colour filtering provided by a colour filter such as that illustrated at 12 in Figure 1. For example, the pixels of the holograms H1 and H2 may be arranged as triplets associated with corresponding triplets of pixels of the spatial light modulator to provide red, green and blue pixels. Such an arrangement requires that the pixel structure of the holograms H1 and H2 is appropriately aligned with the pixel structure of the modulator during manufacture.

In order to reduce or minimise parallax errors, it is desirable to reduce the separation between the light-modulating layer of the spatial light modulator and the holograms H1 and H2. The holograms H1 and H2 may be disposed inside the light modulating layer or may form part of a substrate of the spatial light modulator.

The volume reflection holograms H1 and H2 may be formed in any suitable way for providing the desired optical properties. Techniques for forming such holograms are well-known and will not be described further. The holograms may be formed as two separate layers which may subsequently be attached to each other and to a substrate of the spatial light modulator. Altematively, both holograms may be formed in a single layer, for example by spatial multiplexing, so that manufacture of the display is simplified by the need to handle one less layer.

Figure 9 illustrates at 46 the direct view reflective mode illustrated in Figure 7 in which illumination is by collimated light from a distant light source. Alternatively, as illustrated at 47, the direct view reflective mode may be illuminated by a more closely positioned source 45 of illumination, which provides divergent illumination of the display. The illumination source 45 may be an ambient illumination source or may be a specially provided auxiliary illuminator. The viewer may have to align the display manually so as to provide correct illumination from the illuminator 45. Alternatively, the illuminator 45 may be provided with means for fixing it relative to the display or a device containing the display in the correct position.

Operation in the direct view reflective mode is illustrated in Figure 10. The volume reflection hologram HI receives the divergent illumination 48 from the relatively closely positioned light source 45 and is arranged to act as a collimating lens, a reflector and a diffuser. In particular, the reflection hologram HI is arranged to reflect and diffuse the divergent light with uniform reflection and diffusion angular ranges across the display irrespective of the angle of incidence of light from the light source 45.

Figure 11 illustrates an arrangement of the type shown at 47 in Figure 9 but with a beam shaping and polarization conversion optical system 50 provided between the light source 45 and the display. The system 50 transforms a round or elliptical profile of light emitted by the light source 45 to a rectangular shape and homogenises the intensity distribution. A uniformly illuminated image with reduced light wastage is provided. Also, the unpolarised light from the light source 45 is converted to light of the substantially single uniform polarization required by a liquid crystal display acting as a spatial light modulator. In particular, such a system passes light of the desired polarization and converts light of other polarizations substantially to the desired polarization so as to improve the efficiency of use of light from the light source 45 and so as to reduce the wastage of light incident on the liquid crystal device. This results in a brighter image for a given light source intensity.

Figure 12 illustrates a display 55 of the type described hereinbefore with reference to Figures 5 to 11 provided in a device. Only the display 55 is shown in relation to a clip-on projection attachment 60 for use during the reflective projection mode of the display. Some or all of the elements of a projection system, other than the display 55, are provided on or in the attachment 60, which forms a supporting arrangement for mounting these elements and for allowing the attachment to be detachably attached to the device containing the display 55. The supporting arrangement may comprise alignment means for accurately positioning the arrangement with respect to the display 55.

Figure 12 illustrates the attachment 60 as comprising part of an illumination section illustrated as a condensing lens 61 for cooperating with an internal or external light source. Light from the lens 61 forms an image of the light source at the illumination pupil 43 substantially at one reflective face of beam steering optics 62 illustrated as a reflective prism. The light from the illumination section illuminates the display 55 from the correct position for the volume reflection hologram H2 to act as a reflector and off-axis converging lens as described hereinbefore. The hologram H2 images the light source image at the pupil 44 of a projection lens 63 of a projection section of the attachment 60. The image is formed at a second reflective surface of the optics 62. The projection lens 63 projects the enlarged image of the image displayed by the display 55 onto a screen 64, which may be part of the attachment 60 or may be separate therefrom.

Figure 13 illustrates a projection attachment 60 which differs from that shown in Figure 12 in that the beam steering optics 62 comprise a mirror and the attachment includes an illumination source 65 in the form of a light emitter and parabolic mirror together with beam shaping and polarization conversion optics 50. The optics 50 perform substantially the same function as that shown in Figure 11 and described herein before. In the specific arrangement illustrated in Figure 13, the collecting optics form an image of the illumination source above and off-centre with respect to the display 55.

The reflection hologram H2 within the display 55 forms an image above the display 55 and laterally displaced from the entrance pupil.

In order to increase the brightness of the projected image, various measures may be taken. For example, the projection screen 64 may have a gain, for example, of 3 to 5.

To increase efficiency of light utilization, the spectral response of the holograms HI and H2 may be designed to match the spectral characteristics of the illumination source 65 and/or the spectral transmission of colour filters within the display 55. For example, the spectral characteristics of the illumination source 65 and the spectral response of the holograms may be designed to match the transmission of the colour filters within the display 55.

The projection attachment 60 shown in Figure 14 differs from that shown in Figure 13 in that an example of the beam shaping and polarisation conversion optics 50 is illustrated in more detail. The optics 50 comprise matching microlens arrays 67 and 68, a polarisation beam splitter 69 and an array of /2 waveplate retarder elements 70.

The optics 50 supply output light 71 of substantially uniform singlelinear polarisation suitable for illuminating the display 55. Also, the optics 50 convert the beam such that it has the same shape as the display 55 and is of substantially uniform intensity transverse to the direction of propagation.

Figure 15 illustrates a projection attachment 60 which differs from that shown in Figure 14 in that the beam shaping and polarisation conversion optics 50 are of the type disclosed in EP1197766, the contents of which are incorporation herein by reference.

Light from the illumination source 65 is incident on a polarisation beam splitter 69, comprising wedges of isotropic and anisotropic material for directing orthogonal polarizations in different directions. The microlens arrays 67 and 68 homogenise the light from the beam splitter 69 and focus light of different polarizations on different regions of the patterned half wave retarder 70.

Figure 16 illustrates a projection attachment 60 which differs from that shown in Figure 14 in that the beam shaping and polarisation conversion optics are replaced by a polarisation recovery light pipe 72. A light pipe of this type is available from OCLI, Inc. and will not therefore be described further.

Figure 17 illustrates an alternative arrangement, in which the illumination source comprises an array of red (R), green (G), and blue (B) light emitting diodes (LEDs).

In this case, each LED is provided with a transmission-type homogeniser in the form of an array 73. Such homogenizers are designed to improve the uniformity and to reshape the illumination profile and may also be used to assist in matching the angular characteristics of the individual LEDs. Such homogenizers may be embodied as diffractive or refractive optical elements.

Figure 18 illustrates an arrangement which differs from that shown in Figure 13 in that the beam steering optics 62 comprise a further reflector for bending the illumination light path within the attachment 60. Such an arrangement allows a more compact design to be achieved.

Figure 19 illustrates an attachment 60 which differs from that shown in Figure 18 in respect of the illumination source and the beam shaping and polarization and conversion optics. In particular, the illumination source 65 comprises an array of LEDs of the type illustrated in Figure 17. Also, the optics 62 comprise an array of reflection homogenizers or an array of transmission homogenisers of the type shown in Figure 17 provided with a rear mirror. Such an arrangement allows a very compact attachment 60 to be provided.

In the embodiments illustrated in Figure 17 and 19, the differently coloured LEDs may be illuminated simultaneously or time-sequentially with red, green and blue colour component images being likewise displayed timesequentially and in synchronism by the display 55. Time-sequential colour systems are known and will not be described further.

Figure 20 illustrates a projection attachment 60 which differs from that shown in Figure 13 in that a clean-up polariser 75 is disposed between the projection optics 63 and the display 55. The light reflected from the display 55 is generally polarised and the polariser 75 is oriented so as to pass light of this polarization and to attenuate or reject light of other polarizations. Thus, any light from a source other than the image displayed by the display 55 directed towards the projection optics 63 is attenuated or extinguished and the contrast ratio of the projection display is improved. For convenience and compactness, the polariser 75 is disposed adjacent the entrance pupil of the projection optics 63.

As an alternative, the polariser 75 may be disposed downstream of the projection optics 63. For example, the polariser may be in the form of a reflective polariser, such as a Moxtek wire grid polariser, and may be combined in the beam steering optics 62 as a single polarising and reflecting element. s

Claims

CLAIMS: 1. A transflective display having reflective and transmissive

display modes and comprising a spatial light modulator and first and second holographic reflectors disposed behind the modulator and having first and second reflective modes, respectively, which are different from each other.
2. A display as claimed in claim 1, having a direct view reflective mode of operation when the first reflector operates in the first reflective mode.
3. A display as claimed in claim 1 or 2, having a reflective mode of operation for projection when the second reflector operates in the second reflective mode.
4. A display as claimed in any one of the preceding claims, in which the first reflector is responsive to a first type of illumination to operate in the first reflective mode.
5. A display as claimed in claim 4, in which the second reflector is unresponsive to the first type of illumination.
6. A display as claimed in claim 4 or 5, in which the first type of illumination is substantially collimated illumination incident on the first reflector at a predetermined angle.
7. A display as claimed in claim 4 or 5, in which the first type of illumination is illumination from a first light source position with respect to the first reflector.
8. A display as claimed in any one of the preceding claims, in which the first reflector performs reflection and diffusion in the first reflective mode.
9. A display as claimed in claim 8, in which the first reflector, when in the first reflective mode, diffuses incident light into a range of angles substantially excluding an angle of specular reflection.
10. A display as claimed in any one of the preceding claims, in which the second reflector is responsive to a second type of illumination to operate in the second reflective mode.
11. A display as claimed in claim 10, in which the first reflector is unresponsive to the second type of illumination.
12. A display as claimed in claim 10 or 11, in which the second type of illumination is illumination from a second light source position with respect to the second reflector.
13. A display as claimed in any one of the preceding claims, in which the second reflector acts as a reflector and converging lens in the second reflective mode.
14. A display as claimed in claim 13, in which the second reflector acts as an off- axis lens in the second reflective mode.
15. A display as claimed in any one of the preceding claims, in which each of the first and second reflectors is a volume hologram.
16. A display as claimed in claim 15, in which the first and second reflectors comprise adjacent separate layers.
17. A display as claimed in claim 15, in which the first and second reflectors are formed in a single layer.
18. A display as claimed in any one of the preceding claims, in which the first and second reflectors are disposed adjacent the modulator to reflect modulated light from the modulator back through the modulator.
19. A display as claimed in any one of the preceding claims, in which at least one of the first and second reflectors is spatially continuous.
20. A display as claimed in any one of claims I to 18, in which at least one of the first and second reflectors is pixellated to form a plurality of groups of elements for reflecting respective different colour ranges.
21. A display as claimed in any one of the preceding claims, comprising a backlight for a transmissive mode with the first and second reflectors being disposed between the backlight and the modulator.
22. A display as claimed in claim 21, in which the first and second reflectors are substantially unresponsive to light from the backlight.
23. A display as claimed in any one of the preceding claims, in which the modulator is a liquid crystal display.
24. A device including a display as claimed in any one of the preceding claims.
25. A combination of a device as claimed in claim 24 and a projection adaptor for forming a projected enlarged image of an image displayed by the display.
26. A combination as claimed in claim 25, in which the adaptor comprises an illumination section, a projection section and a support arrangement supporting the illumination section and the projection section.