GB2321532A

GB2321532A - Multi-colour reflector device and display

Info

Publication number: GB2321532A
Application number: GB9701293A
Authority: GB
Inventors: Tomoaki Kuratate
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 1997-01-22
Filing date: 1997-01-22
Publication date: 1998-07-29
Also published as: GB9701293D0

Abstract

A reflector device has a stack of three reflective layers 100,102,108 each of which selectively reflects different a part of the spectrum of white light 106 to a different region. The respective regions may or may not overlap each other. The layers 100,102,108 may be reflective cholesteric liquid crystal materials, dichroic mirrors or reflective multi-layer interference structures. The layers 100,102,108 may be, planar, curved or formed from several curved surfaces in series (fig.11) and may be mutually inclined. The third layer 108 may be combined with either a black absorber layer (110, fig.5) or a panchromatic layer (112, fig.6). The incoming light may be focused by a plano-convex lens array (116,fig.13). The reflector device may be used in a display in conjunction with a spatial light modulator 104, such as a liquid crystal device, having pixels 104a-c, selectively illuminated by light from the regions.

Description

REFLECTOR DEVICE AND DISPLAY INCORPORATING SAME This invention relates to a reflector device and is more particularly, though not exclusively, concerned with a reflector device for use in a colour display for portable or other applications which require a bright, coloured display with a low power consumption.

In both reflective and transmissive (or backlit, i.e. lit from behind) displays, it is common to employ absorptive colour filters for providing the required colour display. In such colour filters, the desired colour is transmitted through the filter whilst the remainder of the light is absorbed. With transmissive displays, it is quite difficult to make bright colour displays having low power consumption in view of the fact that a high proportion of the electrically generated light is absorbed. With reflective displays, a lower power consumption is possible because the such displays rely on ambient light for illumination. However, it becomes difficult to provide a bright coloured reflective display with absorptive colour filters in view of the amount of light absorbed.

The use of a diffraction grating to split light into colours for a colour display has been proposed in, for example, US-A-4737448 wherein a plurality of small different reflective diffraction gratings all in the same plane are arranged so as to effect colour splitting by diffraction.

However, since the diffraction colour is strongly related to the angle of incident light, the viewing angle, and the directions of extent of the gratings, such reflectors are of limited use in displays. In practice, such colour-splitting gratings are restricted to displays where the optical part is fixed, for example projection-type displays. Such reflector devices are difficult to apply to direct view-type displays.

JP-A-61-210328 and JP-A-3-56922 disclose displays of the transparent type, i.e. displays in which the incident light beam passes through the display and exits the opposite side of the display in a direction which is substantially the same as the direction of the incident light beam. Thus, such displays are not of the reflective-type where management of split coloured beams is much more complicated. These references, however, disclose the use of dichroic mirrors to split the incident light beam into different coloured light beams.

It is an object of the present invention to provide a reflector device which is capable of being used in a wide range of different designs of display and which can enable a reflective bright coloured display to be achieved.

According to one aspect of the present invention, there is provided a reflector device comprising a plurality of optical layers including (i) a first reflective layer arranged to reflect a first part of the spectrum of light incident upon the device to at least one first region and to transmit a second part of the spectrum of the incident light; and (ii) a second reflective layer arranged to reflect, through the first reflective layer, to at least one second region distinct from said at least one first region, at least a proportion of the second part of the spectrum of the incident light transmitted through the first reflective layer.

Preferably, the second part of the spectrum of the incident light is substantially the whole of the remainder of the spectrum of the incident light not reflected by the first reflective layer.

The first and second reflective layers will normally be in a stacked relationship.

For certain applications, e.g. full colour displays, it is required for areas of the first and second regions not to overlap one another. However, for other applications, e.g. multi-colour displays, complete or partial overlap may occur so that, for example, the or each first region may be disposed wholly or partly within the or a respective one of the second regions.

The reflective device according to the present invention is applicable to pixellated displays. For pixellated displays, the first reflective layer is arranged to reflect said first part of the spectrum of the incident light to a plurality of discrete first regions whilst the second reflective layer is arranged to reflect at least a proportion of the second part of the spectrum of the incident light to a plurality of discrete second regions disposed adjacent to or at least partially overlapping respective first regions.

In embodiments where greater colour splitting is required, the second reflective layer may be arranged to transmit part or all of the light which is not reflected thereby, and a third reflective layer may be arranged to reflect at least a proportion of the light transmitted by the second reflective layer to at least one third region distinct from the first and second regions.

In a particularly convenient embodiment, a reflector device according to the present invention for use in a full colour display can be provided by arranging for each of the three reflective layers to reflect a respective one of the three primary colour regions of the spectrum, namely red, green and blue, and for at least the first and second reflective layers to transmit the remaining colour region(s).

It is within the scope of the present invention for that reflective layer which is disposed furthest away from the front of the reflective device to be a panchromatic reflective layer or to be selectively reflective, in which latter case a light absorbing layer may be provided behind the lastmentioned reflective layer.

The first reflective layer and any other reflective layer required to be both reflective and transmissive in certain spectrum bandwidths may be provided by a liquid crystal material or a liquid crystal polymer material that has a periodical molecular conformation in a liquid crystal phase, eg a so-called helical pitch structure (this structure is observed in cholesteric liquid crystal materials, chiral smectic C materials and chiral smectic CA materials, the latter being a sub-phase in smectic C having antiferromagnetic properties), a dichroic mirror or mirrors, a multi-layer interference structure or a grating layer or a hologram layer.

In the case where a helical liquid crystal layer is employed, it will be appreciated that the pitch of the helices can be set to reflect the selective wavelength range. For reflecting one part of the spectrum with maximum efficiency, two liquid crystal material layers having oppositehanded helical pitches are preferred as one selective reflection layer. In the case where a cholesteric liquid crystal layer is employed, the minimum thickness of such layer is typically about 6 ,um.

In order to provide the distinct first and second regions, a number of embodiments are possible. In one series of embodiments, each reflective layer is planar or curved and the reflective layers are mutually inclined.

In another series of embodiments, each reflective layer is formed of a plurality of curved or mutually inclined reflective regions.

In the case where each reflective layer is curved or comprises a plurality of curved reflective regions, the curvature may be such as to bring the reflected light to a focus or respective foci. Alternatively, a lens array may be arranged so that each lens brings light passing therethrough to a focus.

Also according to the present invention, there is provided a display comprising a reflector device according to the present invention, and a spatial light modulator comprising picture elements (pixels) which are arranged to be selectively illuminated by light from said first and second regions.

Preferably, the spatial light modulator is a liquid crystal device.

The display may further include a light guiding layer for guiding reflected light, e.g. for diffusing reflected light. Such light guiding layer may be provided by (i) a louvred layer; (ii) a layer having pin holes therein through which incident light can pass, preferably after concentration by lenses or (iii) a structured polymer layer which is capable of transmitting collimated or substantially collimated incident light without substantial optical modification, but which is capable of scattering the reflected light beams. A suitable structured polymer layer may be provided by a polymer film available from Sumitomo Chemical Limited, Japan under the Trade Mark LU MISTY.

Other features of the reflector device and display of the present invention will become apparent from the appended claims.

Embodiments of the present invention will now be described, by way of example, with reference to the accompany drawings, in which: Figures 1 to 20 are schematic illustrations of different designs of the reflector device according to the present invention, Figures 21 to 33 are schematic views of various embodiments of display according to the present invention, Figures 34 to 36 are schematic views of various embodiments of the light guiding layer forming part of a display device according to the present invention, Figure 37 is a schematic illustration of part of a display according to the present invention incorporating a light guiding layer of the type illustrated in Figure 34, Figures 38 and 39 are diagrammatic illustrations showing in more detail the arrangement of various reflective layers in a colour display, Figures 40 to 45 are views showing various alternative reflector structures in reflector devices according to the present invention, Figures 46 and 47 are schematic views showing alternative designs of display according to the present invention, Figure 48 is a schematic view of a display according to the present invention which is based on lenses and stacked flat selective reflectors and which is used for computer simulation purposes, Figure 49 is a diagram showing the calculated colour space for the display of Figure 48, Figure 50 is a schematic view of another display according to the present invention which is based on a stacked concave mirror structure and which is used for computer simulation, Figure 51 is a diagram showing the calculated colour space for the display of Figure 50, Figure 52 is a schematic iliustration of a further display configuration, and Figure 53 is a schematic illustrations of another design of reflector device according to the present invention.

Referring now to Figure 1 of the drawings, the reflector device comprises a plurality of stacked optical layers including a first selectively reflective layer 100, a second selectively reflective layer 102, incorporated into a display including a light modulating layer 104 having spaced first and second modulating portions 104a and 104b which may be individually controlled and which may be defined by an LCD display. In this embodiment, the first and second reflective layers 100 and 102 are mutually inclined such that the first reflective layer 100 is inclined in one direction relative to the direction (indicated by arrow 106) of incident white light, whilst the second reflective layer 102 is inclined in the opposite direction. The first reflective layer 100 is formed of one of the materials to be described hereinafter so that it is capable of reflecting the red component of the incident white light towards the first modulating region 104a. The material of which the first reflective layer 100 is formed is such that it transmits the remainder of the incident white light (i.e. complementary red or cyan, which corresponds to the green and the blue components). The second reflective layer 102 is formed of a material which is capable of reflecting the green component of the light transmitted through the first reflective layer 100, whilst transmitting the blue component of such light. The second reflective layer 102 is arranged to reflect the green component of the light through the first reflective layer 100 and towards the second modulating region 104b of the optical modulating layer 104.

It will therefore be understood that the reflected red and green components of the incident white light beam are completely separated from each other and directed to the respective modulating regions 1 04a and 104b wherein their intensity or other optical property can be modulated independently as desired. In this embodiment, the blue region of incident white light is not reflected.

In Figure 2, similar parts to those of Fig. 1 are accorded the same reference numerals. In this embodiment, however, the second reflective layer 102 is disposed perpendicular to the direction 106 of incident white light whilst the first reflective layer 100 is non-perpendicularly disposed with respect to direction 106. The resultant modulated reflected light beams (red and blue in this embodiment) are partially overlapping. Where there is no reflected beam overlap, independent blue colour modulation can be effected using the second modulating region 104b, whilst in the area of beam overlap, independent modulation of red and blue separately is not possible.

In Figure 3, a reflector device is shown in which mutually parallel, planar stacked first, second and third selectively reflective layers 100, 102 and 108, respectively, are provided. Such device is intended to be used in situations where a white light beam is incident upon the device in direction 106 which is non-perpendicularly disposed with respect to the planes of the reflective layers. In this particular embodiment, the reflector device is a full colour-type wherein the first reflective layer 100 reflects the blue component and transmits the green and red components, the second reflective layer 102 reflects the green component and transmits the red component, whilst the third reflective layer 108 reflects the red component of the incident light. The layers 100, 102 and 108 reflect the respective components of the incident white light beam along different optical paths. Any portion of the incident beam which may be transmitted fully through all three layers 100,102 and 108, as a result of a less than 100% efficiency of such layers, is unused.

In Figure 4, the first and second reflective layers 100 and 102 are the same as described with reference to Figure 3, whilst the third reflective layer 108 is a panchromatic reflective layer which reflects all of the light transmitted through the reflective layers 100 and 102. However, the light reflected off the third reflective layer 108 is mainly red.

In Figure 5, the reflective device is as described with reference to Figure 3, but a further black absorber layer 110 is provided under the third reflective layer 108 so as to absorb any small amount of light which is transmitted through all three layers 100, 102 and 108.

In Figure 6, the reflector device is similar to that of Figure 5 except that, in this case, the black absorber layer 110 is replaced by a panchromatic reflective layer 112, and the third reflective layer 108 is replaced by an absorption-type colour filter 109 that, at least, transmits the red component and absorbs both the blue and green components or either the blue or the green component In Figure 7, the reflector device is a multi-colour type device wherein first reflective layer 100 is arranged to reflect the red component of the incident white light beam and to transmit the blue and green components, namely cyan (complementary red). The second reflective layer 102 in this embodiment is a panchromatic reflector layer which reflects all of the light transmitted through the first reflective layer 100.

Thus, the second reflective layer 102 reflects cyan. The layers 100 and 102 are arranged to reflect the respective coloured beams along different optical paths.

In Figure 8, a similar arrangement to that of Figure 7 is provided, except that the first reflective layer 100 is arranged to reflect green and to transmit magenta (complementary green), whilst the second reflective layer 102 is arranged to reflect the red component and to transmit the remainder of the light beam which has been transmitted through the first reflective layer 100.

In Figure 9, the arrangement is similar to that of Figure 8 except that black absorber layer 110 is additionally provided under the second reflective layer 102.

In Figure 10, the first reflective layer 100 reflects the green component and transmits the complementary green component, whilst the second reflective layer 102 reflects the red component and absorbs the blue component of the incident white light beam. Panchromatic reflector layer 112 is provided under the layer 102 to reflect any remaining light which may be transmitted through the layer 102.

Figures 11 to 20 and also Figure 53 illustrate examples of ways of concentrating discrete colour components. In these Figures, for convenience, the concentration of light reflected only by the first reflective layer 100 is illustrated, whilst the remainder of the incident light is only shown as being transmitted through such layer 100. In practice, however, the device will have at least one further reflective layer which will be arranged in a similar manner to the illustrated reflective layer. It is possible to configure several optical components as lens arrays in common.

In Figure 11, only part of the reflector device is illustrated wherein the first reflective layer 100 comprises an array of concave reflector regions 100a. In this embodiment, the reflector regions 100a are of paraboloidal shape so as to bring the incident beam which is a parallel white light beam passing in the direction of arrows 106 to respective foci 114 which lie in a common plane extending perpendicularly with respect to the direction 106. The reflective layer 100, in this embodiment, reflects the red component of the incident white light beam and transmits cyan (complementary red) to the second reflective layer 102 (not illustrated in Figure 11).

In Figure 12, the first reflective layer 100 is similar to that of Figure 11.

However, in this embodiment, an optical layer comprising a pianoconvex lens array 11 6 is provided in front of the first reflective layer 100.

The lens array 116 has individual lenses aligned with respective ones of the concave reflective regions 100a of the layer 100. Each lens serves to cause a parallel white light beam (not shown) incident upon the lens array 11 6 to become slightly convergent (see arrows 118) during passage towards the respective concave reflective region 100a. The colour component reflected off the region 100a is brought to focus 114 in a plane lying between the layer 100 and the lens array 116.

In the alternative embodiment shown in Figure 53, the focus 114 lies on the opposite side of the lens array 116 to the region 1 00a. As the reflected light beam diverges from each focus 114, it passes through the lens array 116 which decreases the divergence of the reflected beam somewhat to provide a more concentrated beam of reflected light through each lens of the lens array 116. The complementary light beam transmitted through each concave reflective region 100a is also slightly convergent and passes to the second reflective layer 102 (also not shown).

In Figure 13, an arrangement similar to that of Figure 12 is provided, except that the first reflective layer 100 is planar rather than being formed of a plurality of concave reflective regions 100a, and the lens array 116 is optically stronger so as to cause the incident white light beam 118 transmitted through the lens array 116 to be rather more convergent. The convergent white light beam 118 passing through each lens of the lens array 116 is incident upon the respective region of the first reflective layer 100 and a colour component thereof is reflected back as a convergent beam through focus 114 whilst the remainder of the beam which has been transmitted through the reflective layer 100 is brought to a focus 120 lying between the first reflective layer 100 and the second reflective layer 102 (not illustrated).

In Figure 14, the arrangement is similar to that of Figure 11, except that reflective regions 100a of the first reflective layer 100 are not of plain paraboloidal shape as in the embodiment of Figure 11, but are of asymmetric concave shape having a focal axis which is not aligned with the direction 106 but which is inclined with respect thereto so that the focus 114 is laterally displaced from that illustrated in Figure 11. The second layer 102 is not illustrated in Figure 14.

In Figure 15, a similar arrangement to that of Figure 14 is provided, except that lens array 11 6 is also provided. In this embodiment, the light reflected off each region 100a passes through the respective focus 114 where it is diffused so that it passes through more than one of the overlying lenses of the lens array 116 as diffused light. Either before or after being reflected by the second reflective layer 102 (not illustrated in Figure 15), light which is transmitted through each region 100a is brought to a focus (not shown in Figure 15) which is not coincident with focus 114 and reflected light that exits from this device is always diffused. It is possible to arrange the light beams reflected from either or both reflective layers 100 and 102 towards the lenses of the lens array 116 so as to produce the most effective diffusion of light.

In Figure 16, an arrangement similar to that of Figure 13 is provided, but in this case the first reflective layer 100 is formed by a plurality of planar reflective regions 100a which are inclined with respect to the optical axis of the respective lens of the lens array 116. In this embodiment, the colour component which has been reflected from each region 1 00a passes through focus 114 and the reflected light which exits from this device becomes diffused light. Either before (as illustrated in Figure 16) or after being reflected by the second reflective layer 102 (not illustrated in Figure 15), light which is transmitted through each region 100a is brought to focus 120 which is not coincident with focus 114 and eventually passes through the lens array 116 as diffused light. It is possible to arrange the light beams reflected from either or both reflective layers 100 and 102 towards the lenses of the lens array 116 so as to produce the most effective diffusion of light, whilst the remainder of light is completely through a region of the associated lens so that the direction of the reflected array is slightly inclined with respect to the incident parallel white light beam (not shown in Figure 16).

In Figure 17, the first reflective layer 100 is formed of a plurality of regular polygonal mirror regions 100a which serve to concentrate the reflected light beam symmetrically of each mirror region 100a, whilst the complementary colour light beam transmitted through the layer 100 passes to the second reflective layer 102 (not shown in Figure 17).

In Figure 18, each polygonal mirror region 100a is asymmetrically disposed so as to concentrate reflective light to an offset region as compared with Figure 17. The second layer 102 is not illustrated in Figure 18.

In Figure 19, a similar arrangement to that of Figure 17 is provided with the addition of lens array 116 which serves to provide a further concentration of the colour component reflected from each region 100a.

In this embodiment, a separate lens in the lens array 116 is provided for each facet of each polygonal mirror region 100a. The second layer 102 is not illustrated in Figure 19.

In Figure 20, an arrangement similar to that of Figure 19 is provided, but with the asymmetric polygonal mirror arrangement of Figure 18.

In Figure 21, there is shown a display including a reflector device having first, second and third reflective layers 100, 102, and 108 which, in this embodiment, are mutually inclined with the first reflective layer 100 being disposed perpendicularly with respect to the optical axis of lens array 116. The display is a full colour display with, in this embodiment, the layers 100, 102 and 108 selectively reflecting red, green and blue, respectively.

In this embodiment, optical modulating layer 104 is provided between the lens array 116 and the first reflective layer 100. In this case, the optical modulating layer 104 is an active, pixellated liquid crystal device with individually addressable pixels 104 arranged in groups G1, G2, G3, etc of three pixels 104a, 104b and 104c, with each group G being associated with one of the lenses of the lens array 116. Each pixel 104a, 104b and 104c can modulate at least a certain part of the spectrum of the reflected light which it receives from the respective reflective layer 100, 102 and 108. As each reflected light colour from each pixel group G illuminates a different part of the lens associated with that group G, each such light colour is diffused in a different direction. In practice, the display of Figure 21 will use light guiding devices which are described later.

In Figure 21, the first reflective layer 100 is completely planar and the arrangement is such that the red component of light reflected therefrom is arranged to be incident upon the pixels 104a of the pixel groups G.

The second and third reflective layers 102 and 108 are formed with individual regions 102a and 106a mutually oppositely inclined with respect to the optical axis of the respective lens of the lens array 116 so that the colour component reflected from layer 102 in use is incident upon the pixels 104b of the pixel groups G, whilst the colour component reflected from layer 108 is incident upon the pixels 104c of the pixel groups G. It will therefore be appreciated that, by appropriate control of the individually addressable pixels 104, light of the appropriate colour can either be transmitted through the respective pixels 104a, 104b or 104c or prevented from being transmitted depending upon the state of the pixel.

In Figure 21, the pixels 104 of group G1 are all light transmitting so that red light is transmitted through pixel 104a, green light is transmitted through pixel 104b and blue light is transmitted through pixel 104c, all of which pass through the lens associated with the pixel group G1 so as to produce the appearance of white light. As Figure 21 shows, each of the reflected light beams passing through the pixels 104a, 104b and 104c illuminates a different part of the lens array 116 so that these light beams exit the lens array 116 in different directions. In practice, the light guiding devices which will be used to convert the diffuse direction so as to make the device into a display.

In the next pixel group G2, only the pixel 104b is light transmitting so that the reflected green component is transmitted therethrough and viewed, whilst only the red component is transmitted and viewed in the pixel group G3. In the pixel group G4, only the blue component is transmitted, whilst none of the light is transmitted through the pixel group G5 so as to give a black appearance to that lens.

Whenever the direction of exit of each reflected colour beam from the surface of the lens array 116 is different, in the practical device the size and structure of each lens of the lens array 116 are so small that a person viewing the display will not find it possible to discern the separate colours which pass through such lens; and that after passage through the light guiding devices for adjusting the final exit light direction and scattering properties, it is possible to discern the final light beam which exits from the lens as a certain colour which is dependent upon the intensities of the separated and reflected coloured beams passing through that lens.

In Figure 22, a dual colour display is provided as opposed to the full colour display of Figure 21. In this embodiment, the first reflective layer 100 is planar and arranged in the same way as layer 100 in the embodiment of Figure 21 to reflect light through the pixels 104a of pixel groups G. The second reflective layer 102 is formed of a number of regions associated with each lens of the lens array 116 such that mutually oppositely inclined portions 102a and 102b are provided for reflecting light which has been transmitted through the first reflective layer 100 back through such layer and towards the respective pixels 104b and 104c, respectively, of the pixel groups G. The second reflective layer 102 may be a panchromatic reflective coating so that the reflected light consists of the complementary colour to that reflected by the layer 100. Alternatively, it may be a selective reflective layer so that it reflects only a part of the complementary colour transmitted through the layer 100.

In Figure 23, a reiatively simple dual colour display is provided where the second reflective layer 102 is planar and may be either a panchromatic reflector or a selective reflector. However, in both cases, reflection occurs in a way in which the light reflected therefrom passes through the first reflective layer 100 and towards all three pixels 104a, 104b and 104c of each pixel group G. It will be seen that a number of coloured states can be discerned, but that this combination does not permit solely the colour component reflected by the first reflective layer 100 to the pixels 104a of the pixel groups G to be transmitted.

In Figure 24, the incident light which has been rendered convergent by passage through the lenses of the lens array 116 is not brought to a focus at the plane of the reflector 102 as in the embodiment of Figure 23, but is incident upon the p

The light guiding layer 140 may take any of the forms to be described hereinafter with reference to Figs 34 to 36.

In Figure 26, a similar arrangement to that of Figure 25 is provided except that the positions of the layers 104 and 140 have been reversed.

In Figure 27, lens array 116 is provided in the place of light guiding layer 140 in an arrangement similar to that illustrated in Figure 25.

In Figure 28, the positions of the lens array 116 and the modulating layer in the form of liquid crystal display 104 have been reversed as compared with that shown in Figure 27.

In Figure 29, the display includes both a lens array 116 and a light guiding layer 140 which are disposed respectively above and below the LCD layer 104.

In Figure 30, the arrangement is such that both the lens array 116 and the light guiding layer 140 are provided above the LCD layer 104.

In Figure 31, the light guiding layer 140 is provided over the LCD layer 104, whilst the lens array 116 is disposed between the LCD layer 104 and the first reflective layer 100 of the reflector device.

In Figure 32, both the light guiding layer 140 and the lens array 116 are provided between the LCD layer 104 and the first reflective layer 100 of the reflector device, with the lens array 116 being disposed under the light guiding layer 140.

In Figure 33, the arrangement is similar to that of Figure 32 except that the order of the lens array 116 and the light guiding layer 140 is reversed. In a modification (not shown), the positions of the layers 104 and 140 are reversed from the positions illustrated in Figure 33.

In Figure 34, there is shown one embodiment of light guiding layer 140.

In this embodiment, the layer 140 is a louvre-type arrangement where a series of horizontally spaced light-impermeable louvres 140a are disposed. The gaps 140b between the louvres 140a define light transmissive regions which are either constituted by voids or by optically clear material. The side surfaces of the louvres 140a (i.e. those surfaces between which the light transmissive regions 140b are defined) have a surface coating thereon which has a light modifying function. For example, the surface coating may provide for light scattering. In this regard, a magnesium oxide scattering coating may be provided or the surface coating may define a multiplicity of microprisms serving to cause a controlled complex scattering reflection of light which is incident upon such coating. Alternatively, the coating may simply be a mirror coating to provide for relatively simple reflection off the sides of the louvres 140a. As a further alternative, the coating may be a fluorescent dye which is capable of converting incident light in the invisible region of the spectrum to light in the visible region.

In all the above cases, the louvre-type arrangement is such that a collimated or substantially collimated incident light beam can pass through the light transmissive regions 140b substantially unmodified, whilst the light beams which have been reflected from the reflective layers of the reflector device are directed such that at least some of such reflected light is incident upon the surface coating on the sides of the louvres 140a and so is modified/guided in any desired manner, and most preferably to increase the angle of scatter so as to improve the viewing angle.

In Figure 35, the light guiding layer 140 is formed of a structured polymer sheet such as that sold by Sumitomo Chemical Limited, Japan under the Trade Mark LUMISTY. Such a film is capable of transmitting collimated or substantially collimated incident light perpendicular to the plane of the sheet in a way in which it is substantially unaltered optically. However, such sheet is capable of inducing scatter of the reflected light beams which are non-perpendicularly disposed with respect to the plane of the sheet.

In Figure 36, the light guiding layer 140 is defined by a scattering plate with a multiplicity of laterally-spaced pinholes 140c therethrough. The arrangement of the pinholes 140c corresponds to the unit light illuminating area that corresponds either to the unit light modulating pixel 104 or to the unit colour modulating area represented by pixel group G. The incident light beam (arrow A) is arranged to be focussed directly in the pinholes 140c by means of a lens array (not shown) and diffuses. So as to combine this kind of selective transmitting/scattering device with a reflector device according to the present invention, another lens array is required to direct reflected light from the reflector device along a different path to most of the incident light which is directed through the pinholes 140c, the arrangement being such that the reflected light beams (arrow B) are not focussed in the pinholes 140c and are scattered as illustrated in Figure 36.

In Figure 37, the display partly shown therein illustrates the effect produced by use of a louvre-type light guiding layer 140 of the type illustrated in Figure 34. In this embodiment, the sides of the louvres 140a are coated with microprisms 140d. Reflective layer 100 is provided by mutually inclined mirror regions 100a and 100b which are illustrated as being planar in Figure 37, but which may be curved. The mirror region 100b receives an incident light beam via one of the lenses of the lens array 116, said incident light beam being slightly convergent and passing substantially perpendicularly through one of the light transmission regions 140b. Such light beam is reflected by the mirror region 100b towards the microprisms 140d coating a louvre 140a associated with an adjacent light transmission region 140b which lies above the mirror region 100a, so as to cause scattering as illustrated.

The mirror region 100a serves to reflect light through the overlying adjacent light transmissive area 140b of the layer 140 in a symmetrical way. In this device configuration, the mirror region 100a may not only be a planar mirror (as illustrated), it may alternatively be a convex mirror, a concave mirror, or a scattering reflector; whenever the reflected light is diverged, the divergence of the reflected light beam is smaller that the illuminated regions 140d and 140b of the light guiding layer 140.

In Figure 38, there is shown a more practical embodiment of full colour display device where the first, second third reflective layers 100, 102 and 108 are all formed by respective concave reflecting regions serving to focus the reflected light the respective pixels 104a, 104b, 104c of pixel groups G1, G2, G3, etc. of pixellated, active liquid crystal display layer 104. The liquid crystal display layer 104 may be a black-and-white type LCD layer or a pixellated coloured LCD layer wherein the red, green and blue colour components are controlled independently at each pixel in a manner known per se in the art. As can be seen in Figure 38, the concave regions of the various reflective layers 100, 102 and 108 are mutually displaced laterally of each other. Light guiding layer 140 is provided over the liquid crystal display layer 104 and may be of any of the types previously described. An optically clear layer 150 is provided between the LCD layer 104 and the first reflective layer 100 to act as a spacer layer.

In the embodiment of Figure 39, a similar arrangement to that of Figure 38 is provided, except that the curved regions of the various reflective layers 100, 102 and 108 are not focussed within the pixels 104a, 104b and 104c but are focussed on points which are either in the light guiding layer 140 or in the clear layer 150 and which are positioned under the respective pixels 104a to 104c in regions where the reflected light from the layers 100, 102 and 108 are separated. Additionally, light guiding layer 140 is provided between the optically clear layer 150 and the LCD layer 104. By way of example, light in the blue region of the visible spectrum may be reflected at the interface between the clear layer 150 and the first reflective layer 100, light in the green region of the visible spectrum may be reflected at the interface between the reflective layers 100 and 102, whilst light in the red region of the visible spectrum may be reflected at the interface between the reflective layers 102 and 108.

In Figure 40, the reflector device illustrated therein is produced by forming the reflective layers 100, 102 and 108 and the optically clear layer 150 on directly on top of the next in a stack. Each of the layers 100, 102 and 108 is formed of a cholesteric liquid crystal polymer whose cholesteric pitch has been adjusted to the selective wavelength range to be reflected. For maximum efficiency, each layer 100, 102 and 108 consists of both right handed and left handed helical structured cholesteric liquid crystal materials. The minimum thickness of each cholesteric layer is 6,us.

In Figure 41, the layers 100, 102 and 108 are formed of similar cholesteric liquid crystal polymers, but in this case optically clear polymer layers 150 are interleaved between layers 100, 102 and 108 as well as being provided above the layer 100.

In Figure 42, the reflective layers 100, 102 and 108 are separately formed in a respective film in which the respective reflective layer is sandwiched between an optically clear layer 150, and then the resultant films are stacked together to form the reflector device.

In Figure 43, the reflective layers 100, 102 and 108 of the reflector device are defined by respective holographic layers which are stacked together. Each holographic layer has a structure which effects selective colour reflection, and each reflected colour beam has multiple foci respectively associated with the pixels 104a, 104b or 104c for that colour.

In Figure 44, the reflective layers 100, 102 and 108 are formed by transmissive diffraction grating layers that selectively reflect the required colour and transmit the remainder. Each diffraction grating has a different phase and/or amplitude to the other gratings, and these gratings are stacked together to form the reflector device.

In Figure 45, the arrangement is similar to that of Figure 42 wherein selectively reflective films are formed and stacked together to form the layers 100, 102 and 108. However, in this case, the layers 100, 102 and 108 are not sandwiched between respective optically clear layers 150 but are provided as the bottom layer of the respective films.

In Figure 46, the display illustrated therein employs polygonal dichroic mirrors as the selectively reflective layers 100, 102 and 108 (see also Figure 18) and a light guiding layer 140 of the type described hereinabove in relation to Figures 34 and 37.

In this embodiment, liquid crystal display layer 104 is a pixellated colour LCD arranged in groups G1, G2 etc of individually controllable full colour-transmitting pixels 104a, 104b and 104c, ie they can be controlled so as to transmit red, blue or green or any combination thereof. Each cell 104 is aligned with a respective one of the light transmitting regions 140b of the light guiding layer 140. Such regions 140b are aligned with respective facets of arrays of polygonal dichroic mirrors defining the regions of the reflective layers 100, 102 and 108.

Each region 140b receives a respective one of the red, green and blue regions of the spectrum reflected from the respective dichroic mirror facets which lie under the relevant pixel group G1, G2 etc. Thus, proceeding from the left hand side of the light guiding layer 140 to the right hand side, the first region 140b receives reflected red light from those three mirror facets of the layer 100 which lie under pixel group G1; the second region 140b receives reflected green light from those mirror facets of the second reflective layer 102 which lie under the pixel group G1; whilst the third region 140b of the light guiding layer 140 receives the reflected blue light from those mirror facets of the third reflective layer 108 which lie under the pixel group G1. This sequence is repeated for the next group, and so on.

The LCD display layer 104 can be appropriately controlled to obtain the required light output from the various pixels groups G. In the particular embodiment shown, proceeding from the left hand side of Figure 46, the first pixels 104a, 104b and 104c of the pixel group G1 are fully transmissive, thereby enabling all three reflected colours to be transmitted via the light guiding layer 140 so that pixel group G1 appears to be in the white state. In the next pixel group G2, the pixel 104a thereof is also fully transmittive and so allows transmission of the reflected red light from the underlying first reflective region 100 via the associated light transmitting region 140b of the light guiding layer 140.

However, the next pixel 104b of group G2 is controlled so as to allow only transmission of red and blue light, thus preventing reflected green light from passing through. Likewise, the next pixel 104c of group G2 is controlled to prevent passage of blue light, thereby preventing reflected blue light from the underlying regions of the third reflective layer 108 from being transmitted. The net result of these last three pixels is that an overall red colour is perceived for group G2 since the green and blue regions in such group have not been transmitted through the liquid crystal display layer 104.

In Fig. 47, the arrangement illustrated therein is similar to that of Figure 46 except that, in the place of a full colour type LCD layer 104, a black/white LCD layer 104 is employed wherein each pixel 104a, 104b and 104c is either in the white (or light transmitting) state or is in the black (or dark) state. In Figure 47, all three pixels 104a - 104c of group G1 and the pixel 104a of group G2 are shown in the white state, whilst the two pixels 104b and 104c of group G2 are shown in the dark state.

Thus, the pixel group G1 gives the appearance of having a white colour state, whilst the pixel group G2 gives the appearance of a red colour state, although with reduced intensity red as compared with the full colour arrangement of Figure 46 in view of the fact that red light is only reflected from one of the mirror facets of the layer 100 underlying pixel group G2.

Referring now to Figure 48, the display illustrated therein is used for computer simulation and is based on stacked pianar reflective layers 100, 102 and 108, light modulating layer 104 and an array 160 of tilted lenses through each of which light is concentrated towards respective focus 162 so as to pass through the light modulating layer 104 and reach to selectively reflective layers 100, 102 and 108. In this computer simulation, the characteristics of the various layers etc are as set out in Table 1 below.

TABLE 1

Light Incident angle 20.5 deg divergence 0.05 deg type D65 (CIE definition) Lens Array 160 Position (Depth) 1640 ,um Focal length 3802 pm Diameter 485.5 ,um Lens tilt 20.5 deg Modulating Layer 104 Position (Depth) 0.0 lim Thickness 10 vm First Layer 100 Position (Depth) -786pm Thickness 10 m Second Layer 102 Position (Depth) -856 m Thickness 10 Hm Third Layer 108 Position (Depth) -926 m Thickness 10 Hm [The position (0.0 m) represents the centre of each pixel group G in the modulating layer 104 in the direction of layer stacking. The reflectivity and transmittance of each layer 100, 102 and 108 is assumed to be 90%.

The reflectivity and transmittance of each layer 100, 102 and 108 is assumed to be 90%. The reflective spectrum band of each layer is from 400nm to 500nm for the first layer 100, from 500nm to 600nm for the second layer 102, and from 650nm to 750nm for the third layer 108.

Without adjusting the reflective spectrum band width, the white coloured state in this experiment is not a pure white colour.

The calculated colour space for this computer simulation is given by the shaded area in Figure 49.

Referring now to Figure 50, there is illustrated another display configuration for computer simulation. In this case, the display is based on stacked reflective layers 100, 102 and 108 having concave reflective regions and a collimated beam of incident white light. The characteristics of the various layers etc are as illustrated in Table 2 below.

TABLE 2

Light Incident angle 0.0 deg divergence 2.0 deg type D65 (CIE definition) Modulating Position(Depth) 0 m Layer 104 Thickness 10 m Pixel Group 500,11m Width (0.0 pm,-250 pm) - (0.0 pm, 250 pm) First Layer 100 Position(Depth) -200.0,um Thickness 108.6 pm Focus position (0.0 pm + 180.0 m) Reflectivity 90% Transmittance 90% Second Layer Position(Depth) -350.0 pm 102 Thickness 64.2 pm Focus position (0.0 pm, 0.0 pm) Reflectivity 90% Transmittance 90%

Third Layer Position(Depth) 400.0,um 108 Thickness 126.1 jim Focus position (0.0,us, -180.0,um) Reflectivity 90% Transmittance 90% [The position (0.0,um) corresponds to the centre of each pixel group Gin the modulating layer 104. The reflectivity and transmittance of each layer 100, 102, 108a is assumed as 900/o. The reflective spectrum band of each layer is from 400nm to 500nm for the first layer 100, from 500nm to 600nm for the second layer 102, and from 650nm to 750nm for the third layer 108. Without adjusting the reflective spectrum band width, the white coloured state in this experiment is not a pure white colour.

The calculated colour space for the above described display is shown by the shaded area in Figure 51.

Referring now to Figure 52, there is shown a further display used for computer simulation which is a dual-colour arrangement rather than a full-colour arrangement as in the devices of Figures 48 and 50. In this display, a planar dichroic mirror is used for the first reflective layer 100 whilst a panchromatic mirror is used for the second reflective layer 102.

Light guiding layer 140 is provided between lens array 116 and light modulating layer 104 and is of the type described in more detail in Figure 35 above since it uses a LUMISTY film. For the purposes of this simulation, a respective optically clear glass spacer layer 150 is provided between the layers 104 and 140, between the layers 104 and 100, and between the layers 100 and 102. The characteristics of the various layers etc are as set out in Table 3 below.

TABLE 3

Light Incident angle 10 deg divergence 1 deg type D65 (CIE Definition) Lens Array 116 Position (Depth) 4 mm Lens pitch 9 mm Focus length 9 mm Lens tilt 0.0 deg Modulating layer 104 Position (Depth) 0.0pm Focus 10 cm First Layer 100 Position (Depth) -5 mm Tilt 0.0 deg Second layer 102 Position (Depth) -12 mm Tilt 0.0 deg [The position (0.0,um) corresponds to the centre position of each pixel group G in the modulating layer in the direction of layer stacking] Table 4 below gives the experimental results for the above-described display both with and without the LUMISTY film forming the light guiding layer 140.

TABLE 4

Without LUMISTY film With LUMISTY film Green Clearly recognised. A little bit dim (Reflected colour at 1st layer 100) Strongly viewing angle dependence Magenta Colour Clearly recognised A little bit dim (Inverse colour of Green Reflected colour at 2nd layer 102) Viewing angle dependence Strong Weak Quality Quite sharp in each The display colour reflected coloured is recognised as light path uniform colour in unit area Virtual image recognition visible invisible In all of the above described embodiments, it will be understood that the various selectively reflective layers 100, 102 and 108 cause the colour components reflected therefrom in use to be directed towards distinct first, second and third regions, respectively, in that functional optical layer of the display which lies immediately above the first reflective layer 100. The identity of that optical layer in which the first, second and third regions are provided depends upon the particular design of the display concerned, and may be the lens array layer 116, the light modulating layer 104 or the light guiding layer 140.

The reflective display of the present invention is considered to be compatible with current transmissive-type displays and it is therefore considered that current LCD technology for controlling display colour can be employed with the displays of the present invention.

It is within the scope of the present invention for additional functional optical layers to be provided such as polarisers or waveplates. For example, such functional optical layers may be provided as intermediate layers between the reflective layers of the reflector device.

In the accompanying drawings, the various pixels have only been depicted as a one-dimensional array. In practice, a two-dimensional array will be provided as in conventional displays.

The reflective layers of the reflector device of the present invention can be very thin, with the result that the restricted viewing angle problem associated with thicker display structures is reduced.

Claims

1. A reflector device comprising a plurality of optical layers; said optical layers including (i) a first reflective layer arranged to reflect a first part of the spectrum of incident light to at least one first region and to transmit a second part of the spectrum of the incident light; and (ii) a second reflective layer arranged to reflect, through the first reflective layer, to at least one second region distinct from said at least one first region, at least a proportion of the second part of the spectrum of the incident light transmitted through the first reflective layer.

2. A reflector device as claimed in Claim 1, wherein the first reflective layer is arranged to transmit substantially the whole of the remainder of the incident light not reflected by such layer.

3. A reflector device as claimed in Claim 1 or 2, having a plane wherein the first and second regions do not overlap one another.

4. A reflector device as claimed in Claim 1 or 2, wherein the first and second regions are mutually overlapping.

5. A reflector device as claimed in any preceding Claim, wherein the first reflective layer is arranged to reflect said first part of the spectrum of the incident light to a plurality of discrete first regions whilst the second reflective layer is arranged to reflect at least a proportion of the second part of the spectrum of the incident light to a plurality of discrete second regions disposed adjacent to or at least partially overlapping respective first regions.

6. A reflector device as claimed in Claim 1, wherein the second reflective layer is arranged to transmit part or all of the light which is not reflected thereby, and the optical layers include a third reflective layer arranged to reflect at least a proportion of the light transmitted by the second reflective layer to at least one third region distinct from the first and second regions.

7. A reflector device as claimed in Claim 6, wherein each of the three reflective layers is arranged to reflect a respective one of the three primary colour components of the visible spectrum.

8. A reflector device as claimed in any preceding Claim, wherein that reflective layer which is disposed furthest away from the front of the reflector device is a panchromatic reflective layer.

9. A reflector device as claimed in any one of Claims 1 to 7, wherein that reflective layer which is disposed furthest away from the front of the reflector device is selectively reflective.

10. A reflector device as claimed in Claim 9, wherein a light absorbing layer may be provided behind that reflective layer which is disposed furthest away from the front of the reflector device.

11. A reflector device as claimed in any preceding Claim, wherein the first reflective layer is defined by one or more selectively reflective cholesteric liquid crystal materials, one or more selectively reflective dichroic mirrors, or one or more selectively reflective multi-layer interference structures.

12. A reflector device as claimed in any preceding Claim, wherein each of the reflective layers is planar or curved and the reflective layers are mutually inclined.

1 3. A reflector device as claimed in any preceding Claim, wherein at least one of the reflective layers is formed of a plurality of curved or mutually inclined reflective regions.

14. A reflector device as claimed in any preceding Claim, wherein at least one of the reflective layers is curved or comprises a plurality of curved reflective regions.

15. A reflector device as claimed in Claim 14, wherein the curvature is such as to bring at least a part of the reflected light to a focus or a respective focus.

16. A reflector device as claimed in any preceding Claim, wherein means are provided for bringing the reflected light to a multiplicity of non-coincident foci.

1 7. A display comprising a reflector device as claimed in any preceding Claim, and a spatial light modulator comprising picture elements (pixels) which are arranged to be selectively illuminated by light from said first and second regions.

18. A display as claimed in Claim 17, wherein the spatial light modulator has a function that modulates transmittance, reflectivity or a scattering property of at least a part of the spectrum of the reflected light which illuminates the spatial light modulator in use.

19. A display as claimed in Claim 17 or 18, wherein the spatial light modulator is a liquid crystal device having pixels and a control for individually controlling the pixels so as to modulate at least a part of the spectrum of the reflected light which is incident on the pixels in use.

20. A display as claimed in claim 19, wherein the pixels of the liquid crystal device are arranged so that, in use, some pixels receive red light selectively reflected from the reflector device, other pixels receive green light selectively reflected from the reflector device and further pixels receive blue light selectively reflected from the reflector device, whereby the display acts as a full colour display device.

21. A display as claimed in Claim 17, 18, 19 or 20, further including a light guiding layer arranged to guide light reflected by said reflective layers.

22. A display as claimed in Claim 21, wherein the light guiding layer is arranged to control diffusion of the reflected light.

23. A display as claimed inany one of Claims 1 7 to 22, further including a lens array which is arranged to receive reflected light from said reflective layers.

24. A display as claimed in any one of Claims 1 7 to 23, further including a lens array which is arranged to receive the incident light and to redirect such incident light towards the reflective layers.

25. A display as claimed in any one of Claims 17 to 21, further including a lens array which is arranged to receive the incident light and direct such incident light towards the reflective layers, and also to receive the reflected light from the latter.

26. A display as claimed in claim 19, wherein the pixels of the liquid crystal device are arranged in groups, and each reflective layer is arranged to reflect a different colour component towards a respective pixel of each pixel group of the liquid crystal device.

27. A display as claimed in claim 19, further including a lens array which is arranged to receive reflected light from said reflective layers, and wherein (a) the liquid crystal display device is disposed between the lens array and the reflective layers; (b) each pixel group of the liquid crystal display device is associated with a respective lens of said lens array; and (c) each lens of the lens array is arranged to receive the reflected light which passes through the associated pixel group of the liquid crystal display device.

28. A display as claimed in Claim 17, substantially as hereinbefore described with reference to the accompanying drawings.

28. A display as claimed in claim 19 when appended to Claim 7, wherein each pixel group of the liquid crystal display device consists of three pixels, and each of three said pixels in a group is associated with a different one of said three reflective layers which are arranged so as to reflect light only towards the associated pixel in each group.

27. A reflector device as claimed in Claim 1, substantially as hereinbefore described with reference to the accompanying drawings.