CN1748169A - Switchable display apparatus - Google Patents

Abstract

In one aspect, a display apparatus comprises: an emissive spatial light modulator comprising an array of pixels of organic electroluminescent material each arranged to output substantially polarised light; a switchable polariser being switchable between a first and a second polarisation mode in which the polariser passes light of respective polarisation components; and a birefringent lens positioned to receive light from the spatial light modulator. The birefringent lens is arranged to direct light of a first polarisation component into a first directional distribution and to direct light of a second polarisation component into a second directional distribution different from the first directional distribution, the birefringent lens and the switchable polariser being positioned in series. In another aspect, a display apparatus comprises: an emissive spatial light modulator comprising an array of pixels each arranged to output randomly polarised light; a birefringent lens positioned to receive light from the spatial light modulator arranged in a first mode of operation of the display apparatus to direct light of a first polarisation component into a first directional distribution and in a second mode of operation of the display apparatus to direct light of a second polarisation component into a second directional distribution different from the first directional distribution; a quarter waveplate; and a linear polariser. The quarter waveplate is arranged between the spatial light modulator and the birefringent lens and the linear polariser is arranged on the opposite side of the birefringent lens from the quarter waveplate.

Description

switchable display device

The invention relates to a device for image display.

Such devices may be used in autostereoscopic three-dimensional displays, switchable two-dimensional (2D)/three-dimensional (3D) autostereoscopic displays, or switchable high-brightness display systems. These systems can be used in computer monitors, communication handsets, digital cameras, notebook and desktop computers, gaming devices, automotive or other mobile display device applications, and telecommunication switching applications.

Display systems that use micro-optic components to enhance functionality include liquid crystal display (LCD) projectors, autostereoscopic 3D displays, and brightness enhancing reflective displays.

In each system, a micro-optical component, such as a microlens array, is aligned with at least one pixel of a spatial light modulator component. A rational system is shown in plan view in Figure 1. The backlight 2 produces the illumination 4 that enters the polarizer 6 of the LCD. Light passes through a thin film transistor (TFT) substrate 8 and is incident on a pixel layer 10 comprising individually controllable phase-modulating pixels 12-26. The pixels are arranged in rows and columns and include pixel apertures 28 and individual black masks 30 . The light then passes through an LCD countersubstrate 32 and a lens carrier substrate 36 on which a birefringent microlens array 38 is formed. Birefringent microlens array 38 includes isotropic lens microstructures 40 and birefringent material aligned with optical axis direction 42 . The output of the birefringent lens then passes through lens layer 44 and polarization changing means 46 .

Each birefringent lens of the lens array is cylindrical; the lens array 38 is a lenticular screen and the geometric axes of the lenses are outside the confines of the page. The pitch of the lenses in this example is set to be substantially twice the pitch of the pixels of the display, so that a two-view autostereoscopic display results.

In the first mode of operation, the polarization modifying device 46 is configured to transmit light in a polarization state parallel to the ordinary axis of the birefringent material of the microlens array. The ordinary refractive index of the material, such as a liquid crystal material, substantially matches the refractive index of the isotropic microstructures 40 . Therefore, the lens has no optical effect and the directional distribution of the output of the display does not change substantially. In this mode, the viewer will look at pixels 12-26 of the display with each eye and a 2D image will be generated.

In the second mode of operation, the polarization modifying means 46 is configured to transmit light in a polarization state parallel to the extraordinary axis of the birefringent lens array of the microlens array. The material (eg liquid crystal material) has an anomalous refractive index different from that of the isotropic microstructure 40, so the lens has an optical effect and the directional distribution of the display output is also changed. This directional distribution can be arranged as is known in the art so that the left eye of an observer correctly positioned in front of the display will see the left image corresponding to the light from the left image pixels 12, 16, 20, 24, and the right eye A right image corresponding to right image pixels 14, 18, 22, 26 will be seen. In this way, autostereoscopic displays that switch from 2D to 3D can be produced.

Lenticular arrays are particularly suitable for autostereoscopic displays because they combine high efficiency, small spot size functionality and the ability to be fabricated using well known lithographic processing techniques.

It is proposed to provide electrically switchable birefringent lenses for the purpose of directionally switching light, for example to switch a display between 2D and 3D modes of operation.

Electrically switchable birefringent liquid crystal microlenses are described on pages 48 to 58 of European Optical Society Topical Meetings Digest Series: 13, 15-16 May 1997 L.G. Commander et al "Electrode designs for tuneable microlenses".

In another type of switchable 2D-3D display disclosed in US-6069650 and WO-98/21620, switchable microlenses comprising a lenticular screen filled with liquid crystal material are used to vary the optical power of the lenticular screen .

Known organic electroluminescent displays may use reflective electrodes either in front of or behind the emissive portion of the pixels. The pixel aperture is divided into an emission portion and a gap portion, including the emission pixel aperture. For example, the vertical aperture ratio of the emission area may be limited by the required width of the gaps in the row electrodes. Electroluminescent displays can also use active matrix backplanes similar to those used in LCD displays. The result is again a reduction in the aperture ratio (emission area/total pixel area). Thus, such a panel is well suited for brightness enhancement as described in WO-03/015424. In this brightness enhancement, an array of microlenses is used to pass the image of the pixel into the pupil, or 'window' of the nominal viewing plane. In this window, the observer will see an increase in brightness proportional to the vertical aperture ratio of the panel. Outside the viewing window, the observer will see the gap between the pixels and the display, and the display has reduced brightness.

Emissive displays, such as inorganic and organic electroluminescent displays including polymers, and small molecule organic electroluminescent displays, typically produce unpolarized optical output. However, the directionally distributed optical switching system may rely on polarization switching to enable the display to be reconfigured between a first mode and a second mode, eg the first mode may be Lambertian and the second mode may be an autostereoscopic 3D window. Therefore, when a non-polarized display is combined with a polarization distribution optical switching system, the non-polarized display will exhibit a loss of polarization.

It is known in the art to use circular polarizers to avoid reflections from these electrode layers where the emission is essentially randomly polarized. Circular polarizers are used to cancel the reflection of external light from the electrodes, and usually include a linear polarizer and a quarter-wave plate. For example, it may be desirable to apply such a circular polarizer to a display device having a lens capable of changing the directional distribution of output light to produce a 3D autostereoscopic effect or an enhanced brightness effect. However, in the case where the lens is a switched birefringent lens for allowing changes made by a lens that operates depending on the polarization of the light passing through the display, it is not undocumented how to operate a circular polarizer that also depends on the polarization of the light Self-explanatory.

In one form according to the first aspect of the invention there is provided a display device comprising:

an emitting spatial light modulator comprising an array of pixels of organic electroluminescent material, each pixel arranged to output substantially polarized light;

a switchable polarizer switchable between a first polarization mode and a second polarization mode, wherein the polarizer passes light of each polarization component in the first polarization mode and the second polarization mode;

a birefringent lens arranged to receive light from the spatial light modulator, arranged to direct light of a first polarization component into a first directional distribution and to direct light of a second polarization component into a second directional distribution different from the first directional distribution , the birefringent lens and the switchable polarizer are arranged in series.

Polarized light from the spatial light modulator passes through the switchable polarizer and the birefringent lens (in whatever order). The modes of the polarizers effectively select light corresponding to one or the other of the first or second polarization components for output from the display device. Thus, switching of the mode of the polarizer causes the light output from the display device to switch between the first and second directional distribution.

In many implemented embodiments, the birefringent lens has substantially no effect on light of the second polarization component, such that the second directional distribution is the same as the directional distribution of light input to the birefringent lens. This allows the device to switch between two modes: in one mode, the birefringent lens has no effect, and in another mode, the birefringent lens changes the directional distribution of the display device.

It is therefore a first aspect of the present invention to provide high optical efficiency in emissive displays by aligning the output polarization of the polarized emissive display with the input polarization state of the directionally distributed optical switching system. This polarization orientation can be achieved by uniaxially oriented chromophores of the emissive material in the emissive pixels of the display. The alignment direction of the principal axis of the polarized output can be set to coordinate with the alignment direction of the birefringent material in the birefringent lens.

In this way, highly efficient emission direction distribution optically switched displays can be realized. Such displays have additional advantages over LCDs, such as not requiring a backlight, and thus can be made thinner and lighter, which is very important for mobile applications.

In another form according to the first aspect of the invention there is provided an optical device comprising:

An emissive display light direction switching device comprising: an emissive spatial light modulator comprising an array of emissive pixel regions, each emissive pixel region having a substantially polarized optical output;

a switchable polarizer switchable between a first polarization mode through which light of the first polarization component passes and a second polarization mode through which light of the second polarization component passes; and

a birefringent lens such that in operation the birefringent lens introduces a first polarization component substantially into a first directional distribution and a second polarization component substantially into a second directional distribution different from the first directional distribution;

The switchable polarizer and the birefringent lens are arranged in series and are arranged such that when input light comprising or decomposable into a first polarization component and a second polarization component is input to the device, when the switchable polarizer is set to the second When the polarizer is set to the second polarization mode, the light output by the device is basically the first polarization component and is basically introduced into the first direction distribution, and when the polarizer is set to the second polarization mode, the light output by the device is basically The second polarization component is also introduced substantially into the second directional distribution.

Preferably, one or more of the following optional features are present.

The emissive material can be a polymeric electroluminescent material or a small molecule electroluminescent material.

Basically polarized output can be:

linear polarization;

essentially the same direction for all pixels;

Achieved by uniaxially oriented chromophores; and/or

Aligned parallel to the geometric optical axis of the birefringent lens.

Clear polarizers can be used. It may be located between pixels and other optical components of an emissive display. The clear polarizer may have a transmission axis substantially parallel to the main axis of output polarization of the emissive display.

The display device according to the first aspect of the present invention may comprise any of the features of the display device disclosed in WO-03/015424, which is incorporated herein by reference, the display device comprising the rights of WO-03/015424 All of the features in the claims mutated to the display device having an emitting spatial light modulator comprising an array of pixels of an organic electrotropic material arranged to each output substantially polarized light. The advantages of the display device disclosed in WO-03/015424 apply equally to the present invention.

In one form according to the second aspect of the invention there is provided a display device comprising:

a transmitting spatial light modulator comprising an array of pixels each arranged to output substantially randomly polarized light;

a birefringent lens arranged to receive light by the spatial light modulator, arranged to direct light of a first polarization component into a first directional distribution in a first mode of operation of the display device, and in a second mode of operation of the display device directing light of the second polarization component into a second directional distribution different from the first directional distribution;

quarter-wave plate, and

linear polarizer,

Wherein, the quarter-wave plate is arranged between the spatial light modulator and the birefringent lens, and the quarter-wave plate is arranged on a side of the birefringent lens opposite to the linear polarizer.

A quarter-wave plate combined with a linear polarizer was used as a circular polarizer to reduce reflections in the well-known manner mentioned above. This effect is realized in display devices with birefringent lenses that allow the directional distribution of the output light to be changed, this change being called switching. The inventors have realized that the element placement of the circular polarizer, i.e. the quarter wave plate and the linear polarizer on opposite sides of the birefringent lens, still allows the effect of the birefringent lens to be appropriate in both modes of operation of the birefringent lens. switching and proper operation of the circular polarizer, although both effects are polarization-dependent.

Moreover, the positioning of these elements achieves the following important advantages: First, compared to the conceptual possibility of placing the circular polarizer as a whole between the spatial light modulator and the birefringent lens, only a quarter wave A sheet may be located therebetween. As a result, the distance between the spatial light modulator and the birefringent lens can be minimized. This is an important advantage. The minimization of the spacing achieved by the present invention is in directional mode, for example in the case of lenses that provide enhanced brightness effects, since the viewing freedom of the display is determined by the spacing between the lens and the pixel plane and the vertical extent of the pixels of the display. Optimizing the viewing freedom of the monitor. Conversely, minimizing this distance does not improve viewing freedom in standard 2D displays.

Another advantage is related to losses. Non-polarized emissive displays are less expensive and easier to manufacture than polarized emissive displays. However, the use of a birefringent lens to provide a switchable change in the directional distribution reduces the nominal output by 50% when used in conjunction with a non-polarized emissive display due to the effect of polarization control. Similarly, a linear polarizer with a circular polarizer reduces the nominal output by 50% when used with a non-polarized emissive display without a birefringent lens. However, the arrangement of the first aspect of the invention allows circular polarizer and switchable birefringent lens to be realized with a total loss of only 50%, ie the individual losses of circular polarizer and switchable birefringent lens do not accumulate. This is an important advantage that allows the merging of two features without a corresponding increase in loss.

In another form according to the second aspect of the invention there is provided a emission direction display comprising:

a substantially randomly polarized output emitting spatial light modulator comprising an array of pixels;

passive birefringent lens;

Polarization rotation device;

quarter wave plate;

linear polarizer;

Among them, the quarter-wave plate is located between the pixel array and the passive birefringent lens.

In another form according to the second aspect of the invention there is provided an emission directional display comprising:

a substantially randomly polarized output emitting spatial light modulator comprising an array of pixels;

Active birefringent lenses;

quarter wave plate;

linear polarizer;

Among them, the quarter-wave plate is located between the pixel array and the active birefringent lens.

Preferably, one or more of the following optional features are present.

The emitting material can be a polymer electroluminescent material or a small molecule electroluminescent material.

The geometric optical axis of the lens may be aligned with the pixels of the spatial light modulator.

Pixels can be arranged in rows and columns.

The birefringent lens and the switching arrangement therefor according to the second aspect of the invention may comprise any of the features of the corresponding parts of the display device published in WO-03/015424, including the features in the claims of WO-03/015424, WO-03/015424 is incorporated herein by reference.

According to both aspects of the invention, the lenticular array can be used to change the orientation distribution of the display device in one or two modes to achieve various effects, including but not limited to providing: 3D autostereoscopic display; increased brightness; or multiple The user displays the system.

Therefore, this device can be used for:

an autostereoscopic display device which advantageously provides a full color 3D autostereoscopic display image viewable by the naked eye in one mode of operation and a full resolution 2D image in a second mode of operation;

a switchable, high-brightness display system exhibiting substantially non-directional brightness performance in a first mode and substantially directional brightness performance in a second mode; or

a multi-observer display device which, conveniently in one mode of operation, provides one moving full-color 2D image to one observer and at least a second different 2D image to at least a second observer, and In the second mode of operation, all observers see the full resolution 2D image.

Advantageously, by applying enhanced brightness performance to organic electroluminescent displays, the lifetime of the displays can be extended. Brightness enhancement can be used to achieve a desired brightness level for a reduced electrical drive load of the pixels of the display. A reduction in the electrically driven load of the pixels can be used to extend the lifetime of materials used in the display.

Embodiments of the invention described hereinafter may provide the following advantages alone or in combination;

Switchable orientation display devices using emissive displays can be constructed with high optical efficiency;

The device allows efficient switching between high-resolution, high-brightness 2D modes and high-brightness 3D modes;

The device allows efficient switching between standard brightness 2D mode and increased brightness 2D mode, effectively increasing the optical aperture of the display;

The device can be manufactured at low cost;

Optimizing optical crosstalk in 3D mode;

The use of emissive displays allows fabrication of thin devices without the use of backlight components;

The parts can be manufactured using known techniques;

The displays are operable in a wide range of operating environments.

Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows one type of switchable 2D-3D autostereoscopic display device using a liquid crystal display;

Figure 2 shows another type of switchable 2D-3D autostereoscopic display device using a polarized emissive display;

Figure 3 shows another type of switchable 2D-3D autostereoscopic display device using a polarized emissive display;

Figure 4 shows another type of switchable 2D-3D autostereoscopic display device using a polarized emissive display;

Figure 5 shows one type of display device with switchable brightness enhancement using a polarized emissive display;

Figure 6 shows a device including a quarter wave plate to eliminate front reflections from electrodes in a randomly polarized emitting OEL display;

Figure 7 shows the process used for OEL panel structure to allow short viewing distance while maintaining structural stability;

Figure 8 shows a display incorporating an active birefringent lens and a quarter-wave plate;

Figure 9 shows the arrangement of the optical axes of the quarter wave plate in the embodiment of Figure 6;

The various embodiments described hereinafter share some common figures. In short, common figures and common reference numerals will be used, and descriptions thereof will not be repeated for each embodiment.

Figure 2 shows a first embodiment of the invention. An array of pixels 50 is formed on display substrate 48 to make up a spatial light modulator. Substrate 48 may include a series of arrays of addressable thin film transistors and electrodes so that each pixel may be individually addressed using electrical signals. The thin film transistor may be inorganic or may be implemented with organic materials. On the other hand, pixels can be addressed by an active addressing scheme in which addressing transistors need not be present on the pixels.

Each of the pixels 50 includes an emissive region in which the emissive material including the chromophores is uniaxially aligned such that the polarization of the emission is substantially linear and in substantially the same direction throughout the pixel. Preferably, each pixel is arranged to have substantially the same polarization direction.

The emissive material of the pixel 50 can be any organic electroluminescent material, such as a polymeric electroluminescent material or a small molecule electroluminescent material. The emissive material may be arranged to generate polarized emissions by aligning the molecules of the emissive material using any suitable technique. For example, the emissive material may be the material disclosed in the following article: Adv. Mater. -contact Photoalignment Layer", A.E.A.Contoret, S.R.Farrar, P.O.Jackson, S.M.Khan, L.May, M.O'Neill, J.E.Nicholls, S.M.Kelly, and G.J.Richards, which demonstrates that 11: Polarization efficiency of 1.

Another cover substrate 52 is attached to the pixels. The substrate 52 may incorporate a barrier layer and a contrast enhancing black mask layer.

An optional polarizer 54 may be attached to the substrate 52 . Alternatively, the polarizing material may be incorporated at or close to the pixel plane, such as on the inner surface of the substrate 52 .

For example, one known polarized organic electroluminescent display has a polarization ratio of 11:1. Combined with a typical polarizer with a polarization efficiency of 45%, the total flux of the light source would be 82.5%, compared to 45% for an unpolarized light source incorporating a clean-up polarizer.

An optional substrate 56 is attached to the polarizer 54 and has birefringent microlenses formed on its surface. The birefringent microlens incorporates a surface relief structure, such as a lenticular surface relief structure. Surface relief structures can be formed at the interface of birefringent and isotropic materials. A birefringent microlens combines a birefringent material having an orientation direction 42 with an isotropic material 40 . For example, a birefringent microlens includes an aligned liquid crystal material, such as a nematic liquid crystal, sandwiched between a uniformly aligned layer and a surface of an isotropic material on the substrate 56 . Vertical alignment layers may also be used. The birefringent material may be a UV-treated liquid crystal material, such as a reactive mesogen liquid crystal. The relative orientation of the liquid crystal material on the two surfaces of the birefringent lens may be parallel, antiparallel or there may be a twist between the two surfaces such that the incident polarization is rotated in the birefringent lens before encountering the surface relief structure. The refractive index and dispersion of an isotropic material are substantially the same as either of the refractive index and dispersion of a birefringent material. Examples of birefringent materials useful in the present invention are described in WO-03/015,424, which is incorporated herein by reference.

In the following birefringent microlenses, the polarization switching unit is formed on the substrate 41 . The switch is used to switch the polarization transmitted through the final linear output polarizer 66 and may comprise a layer of nematic liquid crystal material 60 sandwiched between a transparent ITO electrode and an alignment layer 58 . To switch the output polarization from the switching cell, a voltage 62 is applied across the liquid crystal cell.

The device of Figure 2 operates in the following manner. Emissive displays produce an output polarization that is substantially linear. The output polarization from the polarized emitting pixel array 50 is canceled by a linear polarizer 54 having a transmission direction parallel to the main axis of the polarization direction of the emissive material. This polarization state is oriented at 45 degrees to the orientation of the liquid crystal material in the birefringent lens 42 so that it can be resolved by the lens into two orthogonal components. The polarization switching material 60 in the first state is oriented such that the polarization state transmitted through the output polarizer 66 is parallel to the normal index of refraction of the liquid crystal material in the birefringent lens 42 . This index of refraction substantially matches that of the isotropic material 40, so there is essentially no lensing effect, although there may be a small amount of residual optical effect to the extent that it is impossible to obtain an exact index match. The display then has substantially the same directional distribution as the optical output from the pixel plane.

In the second mode, the switch 62 adjusts the material 60 so that the transmitted polarization through the polarizer 66 causes an anomalous index of refraction of the birefringent material 42, and thus there is an index step across the isotropic material of the lens surface, and The lens has an optical function. This causes a change in the directional distribution of the optical output. The lenses are arranged to produce an image of the pixel plane on the window plane.

In this specification, the direction of the optical axis of a birefringent material (dominant direction, or extraordinary axis direction) will be referred to as a birefringent optical axis. This is not to be confused with the conventionally defined optical axis of a lens in geometric optics.

The orientation of the liquid crystals in the lens can be set parallel across the thickness of the cell. The lens surfaces may be oriented parallel to the geometric lens axis of the cylindrical lens. On the other hand, the birefringent optical axis will be arranged to rotate through the cell so that the polarization orientation direction of the emissive display and canceling polarizer is at a different angle to the geometric lens axis. This is advantageous, for example, to relax manufacturing tolerances in the production of polarized emitting devices, or to improve the viewing angle of the device if there is a viewing angle limitation due to polarized emitting conditions.

The lenses are arranged in a column direction with a pitch that is substantially (but not exactly) twice the column pitch of the pixels of the display. If the user places their eyes in the plane of the window, alternating columns of pixels of the panel are seen and a stereoscopic image is observed. The optical output is described in WO-03/015424.

Alternatively, the lenses may be arranged in a row of cylindrical lenses with a pitch substantially (but not exactly) equal to the display row pitch. If the aperture ratio of the pixel in the vertical direction is less than 100%, then in the directional mode of operation the lens will create an area from which the display will have areas of lower brightness due to the lens focusing from the center of the pixel Separated higher brightness.

The device of Figure 2 has a nominal 50% brightness because the polarization state input to the lens is resolved into two orthogonal components parallel and orthogonal to the birefringent optical axis of the birefringent microlens, respectively.

A device capable of displaying a full brightness mode of operation is shown in FIG. 3 . Compared with Fig. 2, the positions of the polarization switch and the birefringent microlens array are reversed. The output polarization from the polarization emitting display and canceling polarizer 54 is incident on polarization switching mechanisms 60 , 58 , 62 . In the first mode, no polarization switching occurs so that the polarization incident on the birefringent lens array 42 is parallel to the ordinary component of the refractive index at the lens surface, and since the refractive index matches the isotropic material 40, essentially Can't see the lens. The light passes through a final substrate 68 which may include, for example, an anti-reflective film. Therefore, the light has substantially the same directional distribution as the emitting panel.

In a second mode of operation, the polarization switch rotates the polarization from the panel so that the polarization is parallel to the birefringent optical axis of the birefringent microlens and the lens is optically functional.

In this configuration, all light energy passes through the correct lens axis, so there is essentially no loss in the system.

This construction has an increased viewing distance due to the thickness of the additional layers. The thickness can be reduced by removing the substrate 64 and using a processed liquid crystal material for the birefringent lens, as shown in FIG. 4 . An optional substrate 70 is formed on polarizer 54 with ITO and alignment layer 58 formed on the opposite surface of the optional substrate. Birefringent microlenses and isotropic materials can be formed on a substrate 68 with an ITO coating. The birefringent microlens array 42 may be fabricated using a UV-treated material, such as reactive mesogen, and an alignment layer 74 may be formed on its surface. A switchable polarization modulating material, such as a nematic liquid crystal material 60 , can be sandwiched between the microlens alignment layer 42 and the ITO and alignment layer 58 . Alternatively, an ITO coating 72 may be formed on the surface of the UV-treated birefringent microlens 42 bonded to the alignment layer 74 . Voltage is applied to the ITO coating through a power source 62 .

In this way, the separation between the lens and the pixel plane will be reduced. This is very advantageous for devices with small pixel sizes. Substrate 70 may also be removed so that layer 58 is formed over, for example, polarizer 54 .

Figure 5 shows a switchable enhanced brightness display device using a polarized emissive display.

As shown in FIG. 5 , polarized emissive pixels in pixel plane 50 may include emissive regions 80 and gaps 82 between emissive pixels. The gap region may include, for example, electrodes or addressing transistors. The lenses may be arranged relative to the row direction of the display. The pitch of the lenses is set to be substantially equal to the pitch of the pixels in the row direction. The remainder of the elements of the display may be constructed and operated as shown in FIG. 4 . In the first mode of operation, the lenses are configured to have no optical function, so that light from the emission area is substantially not altered by the lenses of the cylindrical lens array. In a second mode of operation, the lenses are configured to have an optical function such that each pixel is imaged by the respective lens to a window plane at a nominal distance from the display. If a viewer places their eyes on the image of the pixels of the window plane, the display has an increased brightness compared to the unaltered display. If the viewer places their eyes at the gaps between the images, the display has a reduced brightness compared to the unaltered display. In this way, the brightness of the display can advantageously be increased in case the aperture ratio of the pixels is less than 100% in the first direction.

Another embodiment of the first aspect of the invention may be formed as a display device as disclosed in WO-03/015424, which is hereby incorporated by reference, but where the spatial light modulator disclosed therein uses an emitting Instead of a spatial light modulator, the transmitting spatial light modulator comprises an array of pixels of organic electroluminescent material each arranged to output substantially polarized light, as described above. Therefore, the disclosure of WO-03/015424 applies equally to the present invention, except for replacing the spatial light modulator.

Figure 6 shows a cross-section of a brightness-enhancing display device with a non-polarized display.

The display device includes an array of pixels 50 formed on a display substrate 48 to form a spatial light modulator having the same structure as in the emissive display device described above except that it outputs substantially randomly polarized light and layout. Therefore, the emitting material of the pixel 50 can be any organic electroluminescent material, such as a polymeric electroluminescent material or a small molecule electroluminescent material. On the other hand, the array of pixels 50 and substrate 48 may be replaced by any other type of emitting spatial light modulator comprising an array of pixels arranged to output randomly polarized light.

The array of pixels 50 has a vertical aperture ratio of less than 100%, and emits light toward quarter wave plate 84 . When the light is substantially randomly polarized, the first and second resolved line components having substantially the same intensity are incident on the lens array 42 . The first resolved linear polarization component parallel to the optical axis of the birefringent material can cause a phase step at the lens surface so light from the pixel aperture is directed towards the window at the nominal viewing position. The decomposed components normal to the optical axis of the birefringent material cause a rate match at the refractive surface and therefore essentially produce no lens function. The light then passes through switchable polarization rotators 58-62. In the off state, the first resolved linear polarization state is rotated and canceled by the output polarizer 66 , while the second resolved linear polarization state is rotated and transmitted through the output polarizer 66 . When an electric field is applied to layer 60, this state is not rotated, so the first polarization state is transmitted and the second state is absorbed. Therefore, the display operates in legacy mode.

In the first mode of operation, light incident from an external light source 86 in front of the display is polarized by polarizer 66 and rotated by rotators 58-62 so that no phase jump is caused on lenses 42,40. The light then passes through wave plate 84 to become circularly polarized. Figure 9 shows in more detail the coordination of the orientation of the optical axis of the quarter wave plate with that of the birefringent lens. For ease of operation, the optical path of the light from the external light source 86 is expanded and shown for the directional mode of the device of FIG. 6 . Incident light from light source 86 has a polarization direction 93 from polarizer 66 having a polarized transmission direction 92 . The light passes through a polarization switch (not shown) so that the polarization state 94 passes through the substrate 41 . Polarization state 97 is incident on the birefringent optical axis of birefringent lens 42 . In this example, the orientation of the birefringent lenses is antiparallel, so that an orientation direction 98 on the substrate 56 is created and a polarization direction 99 in the substrate 56 is created. The optical axis direction 100 of the quarter wave plate 84 is set at 45 degrees to the direction 98, forming the orientation of the birefringent material at the birefringent lens surface closest to the quarter wave plate. The quarter wave plate produces a substantially circular polarization state 101 . Light is reflected from pixel plane 50 in circular polarization state 102 and causes quarter wave plate axis 100 to give polarization state output 104 . Therefore, a quarter wave plate is used to output the polarization state at 90 degrees from direction 99 on the reflected path. Such polarization states 106, 108 are orthogonal to the directions 96, 98 of the birefringent optical axes of the lens. In a polarization switch, the polarization state is not rotated, so polarization state 110 passes through substrate 64 and is incident on polarizer 66 which substantially absorbs it.

In reflections from the electrodes of the pixel plane 50 a phase shift occurs. The light then passes through a wave plate 84 from behind to produce a linear polarization orthogonal to the input, causing a phase jump across the lens surface. The polarization states are again rotated by rotators 58 - 62 and canceled by input polarizer 66 . In the switched state, the same phase shift occurs in the reflector, so the reflection is again canceled by the quarter-wave plate and polarizer combination. Thus, the front reflection from the reflector is canceled while maintaining the switchable brightness enhancement or autostereoscopic display functionality.

Such an externally polarized embodiment has the advantage of reduced visibility of the lens in external ambient light. An external light source incident on the front of the display passes through the input polarizer, undergoes Fresnel reflection on lenses and other surfaces with phase hopping (e.g. from reflective coatings such as ITO), and then passes behind the output polarizer . Thus, the external polarizer absorbs a proportion of the light traveling in each direction, thus reducing reflections from the lens, which advantageously increases display contrast.

The viewing freedom of a display in boosted brightness mode or the nominal viewing distance in 3D mode is determined by the distance between the pixel and the lens plane. It is desirable to minimize the thickness of the additional layer between these two surfaces. Quarter wave plate 84 may be a thin wave plate, such as a coated, oriented, processable liquid crystal layer. An example of such a material is RM257 available from Merck Ltd. which can be UV treated after a suitable alignment layer has been oriented. Typically this layer will be less than two microns thick. Multiple layers can increase the spectral efficiency of a quarter wave plate, which is well known in the art.

For example, the substrate 56 may be a thin glass microplate (Schott A.G.) or be removed using a liquid crystal material by processing in the lens 42 . In order to ensure the structural stability of the encapsulation layer counter-substrate 52, the OEL device can be assembled together with the lens at an appropriate position.

This assembly process is depicted in FIG. 7 . On the side of the substrate 41 having the ITO layer 58 there is an isotropic lens structure 40 formed on the second surface by a known method such as UV casting or embossing. The surface may be coated with an alignment layer, such as polyimide, or may have a diffractive alignment layer structure formed thereon. The diffractive layer structure can be formed by a controlled tool embossing the surface relief structure, thus requiring a separate embossing step.

FIG. 7 b shows a layer 42 of processable liquid crystal material formed on the surface of the lens 40 . The orientation of the lens surface is fixed by an orientation layer on the isotropic lens. The orientation of the opposite surface can be fixed by an orientation layer on a second substrate (not shown), by diffractive structures on a plane shim, or can be a relaxed orientation state of the liquid crystal material (i.e., in the material no fixed orientation). If a second substrate is used, the second substrate can be removed after the lens is cured so that the overall thickness of the device is reduced.

Figure 7c shows the attachment of the wave plate. The wave plate may be a coated wave plate, such as a processable liquid crystal polymer, or it may be a laminated layer. Alternatively, this layer can be attached to the display counter-substrate 52 .

Figure 7d shows the attachment to the display counter substrate 52. This resulting counter substrate is then attached to the OEL emitting substrate to provide the package as shown in Figure 7e. In case the color filters are fixed to the counter substrate, this will be applied to the flat glass 52 or to the assembled composite substrate.

Figure 7f shows the final fixation of the switch unit to the assembled device.

In another embodiment of the invention, the polarization rotator and the passive birefringent lens can be replaced by an active lens, the cross-section of which is shown in FIG. 8 . Emitting pixel plane 50 passes light through quarter wave plate 84 and onto an active lens comprising transparent electrodes 92 , 94 and liquid crystal layer 88 . The surface relief lens 90 has a refractive index substantially equal to the ordinary refractive index of the liquid crystal layer 88 . In the first mode, no field is applied to the element, and the lens is oriented such that there is a phase jump at the lens surface, giving the lens functionality. The lenses are arranged to create viewing windows. In the second mode, a field is applied between the electrodes 92, 94 so that the liquid crystal material 88 reorients and index matching occurs at the lens surface. Light incident from ambient light sources is de-functionalized by the combination of quarter wave plate 84 and polarizer 66 as previously described.

Claims (7)

1. A display device, comprising: a transmitting spatial light modulator comprising an array of pixels each arranged to output substantially randomly polarized light; a birefringent lens arranged to receive light by the spatial light modulator, arranged to direct light of a first polarization component into a first directional distribution in a first mode of operation of the display device, and in a second mode of operation of the display device directing light of the second polarization component into a second directional distribution different from the first directional distribution; quarter-wave plate; and linear polarizer, Wherein, the quarter-wave plate is arranged between the spatial light modulator and the birefringent lens, and the linear polarizer is arranged on a side of the birefringent lens opposite to the quarter-wave plate. 2. The display device according to claim 1, wherein, the birefringent lens is a passive birefringent lens arranged to direct light of a first polarization component into said first directional distribution and light of a second polarization component into said second directional distribution, and The display device also includes a switchable polarization rotator disposed between the birefringent lens and the linear polarizer, the switchable polarization rotator being switchable between a first mode and a second mode, wherein in the first mode In the first mode, the incident light of the first polarization component is output with a polarization that allows it to pass through a linear polarizer, and in the second mode, the incident light of the second polarization component has a polarization that allows it to pass through a linear polarizer. polarization is output. 3. The display device of claim 1, wherein the birefringent lens is an active birefringent lens switchable between a first mode and a second mode, wherein, in the first mode, a Light polarized by a linear polarizer is directed into said first directional distribution, and in a second mode light having a polarization which allows it to pass through the linear polarizer is directed into said second directional distribution. 4. A display device as claimed in any one of the preceding claims, wherein the pixels of the spatial light modulator comprise an organic electroluminescent material. 5. A display device as claimed in any one of the preceding claims, wherein the optical axis of the wave plate is oriented to be substantially birefringent with the birefringent optical axis of the lens on the surface of the lens closest to the wave plate The material is oriented at 45 degrees. 6. A display device, comprising: an emitting spatial light modulator comprising an array of pixels of organic electroluminescent material, each pixel arranged to output substantially polarized light; a switchable polarizer switchable between a first polarization mode and a second polarization mode, wherein the polarizer passes light of each polarization component in the first polarization mode and the second polarization mode; a birefringent lens arranged to receive light from the spatial light modulator, arranged to direct light of a first polarization component into a first directional distribution and to direct light of a second polarization component into a second directional distribution different from the first directional distribution , the birefringent lens and the switchable polarizer are arranged in series. 7. A display device as claimed in any one of the preceding claims, wherein the second directional distribution is the same as the input distribution such that the birefringent lens has substantially no optical effect.

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