Patent Grant
10359560
This disclosure generally relates to illumination of light modulation devices, and more specifically relates to light guides for providing large area illumination from localized light sources for use in 2D, 3D, and/or autostereoscopic display devices.
Spatially multiplexed autostereoscopic displays typically align a parallax component such as a lenticular screen or parallax barrier with an array of images arranged as at least first and second sets of pixels on a spatial light modulator, for example an LCD. The parallax component directs light from each of the sets of pixels into different respective directions to provide first and second viewing windows in front of the display. An observer with an eye placed in the first viewing window can see a first image with light from the first set of pixels; and with an eye placed in the second viewing window can see a second image, with light from the second set of pixels.
Such displays have reduced spatial resolution compared to the native resolution of the spatial light modulator and further, the structure of the viewing windows is determined by the pixel aperture shape and parallax component imaging function. Gaps between the pixels, for example for electrodes, typically produce non-uniform viewing windows. Undesirably such displays exhibit image flicker as an observer moves laterally with respect to the display and so limit the viewing freedom of the display. Such flicker can be reduced by defocusing the optical elements; however such defocusing results in increased levels of image cross talk and increases visual strain for an observer. Such flicker can be reduced by adjusting the shape of the pixel aperture, however such changes can reduce display brightness and can comprise addressing electronics in the spatial light modulator.
According to the present disclosure, a directional illumination apparatus may include an imaging directional backlight for directing light, an illuminator array for providing light to the imaging directional backlight. The imaging directional backlight may include a waveguide for guiding light. The waveguide may include a first light guiding surface and a second light guiding surface, opposite the first light guiding surface.
Display backlights in general employ waveguides and edge emitting sources. Certain imaging directional backlights have the additional capability of directing the illumination through a display panel into viewing windows. An imaging system may be formed between multiple sources and the respective window images. One example of an imaging directional backlight is an optical valve that may employ a folded optical system and hence may also be an example of a folded imaging directional backlight. Light may propagate substantially without loss in one direction through the optical valve while counter-propagating light may be extracted by reflection off tilted facets as described in U.S. Patent Publication No. 2012/0127573, which is herein incorporated by reference in its entirety.
Directional backlights provide illumination through a waveguide with directions within the waveguide imaged to viewing windows. Diverging light from light sources at the input end and propagating within the waveguide is provided with reduced divergence, and typically collimated, by a curved reflecting mirror at a reflecting end of the waveguide and is imaged towards a viewing window by means of curved light extraction features or a lens such as a Fresnel lens. For the on-axis viewing window, the collimated light is substantially parallel to the edges of a rectangular shaped waveguide and so light is output across the entire area of the waveguide towards the viewing window. For off-axis positions, the direction of the collimated light is not parallel to the edges of a rectangular waveguide but is inclined at a non-zero angle. Thus a non-illuminated (or void) outer portion (that may be triangular in shape) is formed between one edge of the collimated beam and the respective edge of the waveguide. Ideally, no light is directed to the respective viewing window from within the outer portion and the display will appear dark in this region. It would be desirable to reduce the appearance of the dark outer portions for off-axis viewing positions so that more of the area of the waveguide can be used to illuminate a spatial light modulator, advantageously reducing system size and cost.
In general with this and related imaging directional backlight systems, not all the backlight area may be useable due to vignetting at high angles. Modification of the system may overcome this limitation by introducing light into regions that are void. Such modified illumination apparatus embodiments may lead to increased brightness, local independent illumination and directional capabilities.
According to a first aspect of the present disclosure a directional waveguide may comprise: an input end; first and second opposed, laterally extending guide surfaces for guiding light along the waveguide; and a reflective end facing the input end for reflecting the input light back along the waveguide, the second guide surface being arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide being arranged to direct the output light into optical windows in output directions that are distributed in a lateral direction in dependence on the input position of the input light, wherein the reflective end is a Fresnel reflector comprising alternating reflective facets and draft facets, the reflective facets providing the Fresnel reflector with positive optical power laterally, and the ratio between (a) height of the input end between the first and second guide surfaces and (b) the height of the reflective end between the first and second guide surfaces has a profile across the lateral direction that is greatest at the optical axis of the Fresnel reflector and reduces towards each side of the optical axis. Said profile of said ratio may compensate for reduction with lateral position in the efficiency of reflection of light by the Fresnel reflector. The height of the input end between the first and second guide surfaces may have a profile across the lateral direction that is highest at the optical axis of the Fresnel reflector and reduces towards each side of the optical axis. Advantageously the spatial uniformity of the display in the lateral direction may be improved for on-axis and off-axis viewing positions in comparison to arrangements with a uniform ratio in the lateral direction.
The edge of the input end at the first guide surface may be straight and the edge of the input end at the second guide surface may be curved to provide said profile. The edges of the input end at the first guide surface and at the second guide surface may each be curved to provide said profile. The height of the reflective end between the first and second guide surfaces may have a profile that is flat. The first guide surface may be arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to direct light guided along the waveguide in directions allowing exit through the first guide surface as the output light and intermediate regions between the light extraction features that may be arranged to guide light along the waveguide. The second guide surface may have a stepped shape in which said light extraction features may be facets between the intermediate regions. The light extraction features may have positive optical power in the lateral direction.
Advantageously the tool can be conveniently formed to provide such curved first and second guide surfaces, providing low cost waveguides with appropriate shape.
Further according to a first aspect of the present disclosure, there is provided a directional waveguide comprising: an input end; first and second opposed, laterally extending guide surfaces for guiding light along the waveguide; and a reflective end facing the input end for reflecting the input light back along the waveguide, the second guide surface being arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide being arranged to direct the output light into optical windows in output directions that are distributed in a lateral direction in dependence on the input position of the input light, wherein the reflective end is a Fresnel reflector comprising alternating reflective facets and draft facets, the reflective facets providing the Fresnel reflector with positive optical power laterally, and the height of the input end between the first and second guide surfaces has a profile that is highest at the optical axis of the Fresnel reflector and reduces towards each side of the optical axis. Said profile of the height of the input end may compensate for reduction with lateral position in the efficiency of reflection of light by the Fresnel reflector. The edge of the input end at the first guide surface may be curved and the edge of the input end at the second guide surface may be straight to provide said profile.
According to a second aspect of the present disclosure a directional backlight may comprise: a directional waveguide according to the first aspect; and an array of input light sources arranged at different input positions in a lateral direction across the input end of the waveguide and arranged to input light into the waveguide.
According to a third aspect of the present disclosure a directional display device may comprise a directional backlight according to the second aspect; and a transmissive spatial light modulator arranged to receive the output light from the waveguide and to modulate it to display an image.
According to a fourth aspect of the present disclosure a directional display apparatus may comprise a directional display device according to the third aspect; and a control system arranged to control the light sources.
Advantageously an array of optical windows can be formed, to provide a controllable directionality of optical output. The optical windows can be arranged to provide modes of operation that may be switched between (i) wide viewing angle mode that has similar spatial and angular uniformity to conventional non-imaging backlights, (ii) autostereoscopic 3D mode, (iii) privacy mode, (iv) dual view mode, (v) power savings mode, and (vi) efficient high luminance mode for outdoors operation.
According to a fifth aspect of the present disclosure a directional backlight may comprise: a waveguide comprising an input end; an array of input light sources arranged at different input positions in a lateral direction across the input end of the waveguide and arranged to input light into the waveguide, the waveguide further comprising first and second opposed, laterally extending guide surfaces for guiding light along the waveguide, side surfaces extending between the first and second guide surfaces, and a reflective end facing the input end for reflecting the input light back along the waveguide and having positive optical power laterally, the second guide surface being arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide being arranged to direct the output light into optical windows in output directions that are distributed in a lateral direction in dependence on the input position of the input light; and additional light sources arranged to direct additional light into the waveguide in a direction in which the additional light is reflected by the reflective end onto the opposite side surface and by the opposite side surface into a segment of the waveguide adjacent the opposite side surface extending from a corner between the reflective surface and the side surface.
Advantageously the spatial uniformity of the output of the backlight can be improved for off-axis viewing positions by means of filling of illumination voids.
The additional light sources may be disposed along at least a part of each side surface adjacent the input end, the additional light sources being arranged to direct additional light into the waveguide through one of the side surfaces.
Advantageously the efficiency of filling of illumination voids may be optimized, reducing power consumption while maintaining high spatial uniformity.
The additional light sources may be disposed along only said part of each side surface. Said part of each side surface along which the additional light sources are disposed may be at least 20% of the side surface. Said part of each side surface along which the additional light sources are disposed may be at most 80% of the side surface.
The device may further comprise a reflector element arranged along at least a part of each side surface adjacent the input end, the additional light sources may be disposed along the input end of the waveguide on each side of the array of input light sources, and may be arranged to direct additional light into the waveguide through the input end onto the reflector element, and the reflector element is arranged to reflect the additional light towards the reflective end so that the additional light is reflected by the reflective end onto the opposite side surface and by the opposite side surface into a segment of the waveguide adjacent the opposite side surface extending from a corner between the reflective surface and the side surface. The reflector element may be disposed along only said part of each side surface. Said part of each side surface along which the reflector element disposed may be at least 20% of the side surface.
Said part of each side surface along which the reflector element is disposed may be at most 80% of the side surface. Said reflector element may comprise an array of facets that are arranged to reflect light in a different direction from light rays of the additional light that are reflected from the side surface. The input end may have facets against which the additional light sources are disposed, which facets face the reflector element.
Advantageously a single light bar may be provided, reducing complexity of assembly and cost. Further hot spots in regions adjacent to the sides may be reduced.
The first guide surface may be arranged to guide light by total internal reflection and the second guide surface may comprise a plurality of light extraction features oriented to direct light guided along the waveguide in directions allowing exit through the first guide surface as the output light and intermediate regions between the light extraction features that are arranged to guide light along the waveguide. The second guide surface may have a stepped shape in which said light extraction features are facets between the intermediate regions. The light extraction features may have positive optical power in the lateral direction. The reflective end may be a Fresnel reflector comprising alternating reflective facets and draft facets, the reflective facets may provide the Fresnel reflector with positive optical power.
Advantageously the number of additional light sources provided may be minimized, reducing cost and complexity.
According to a sixth aspect of the present disclosure, a directional display device may comprise a directional backlight according to the fifth aspect; and a transmissive spatial light modulator arranged to receive the output light from the waveguide and to modulate it to display an image.
According to a seventh aspect of the present disclosure, a directional display apparatus may comprise said directional display device according to the sixth aspect and a control system arranged to control the light sources. Advantageously an array of optical windows can be formed, to provide a controllable directionality of optical output. The optical windows can be arranged to provide modes of operation that may be switched between (i) wide viewing angle mode that has similar spatial and angular uniformity to conventional non-imaging backlights, (ii) autostereoscopic 3D mode, (iii) privacy mode, (iv) dual view mode, (v) power savings mode, and (vi) efficient high luminance mode for outdoors operation.
The control system may be arranged to control input light sources selected to direct output light into desired optical windows, and may be further arranged to control at least one additional light source selected to provide additional light that is output from the directional backlight in the same output directions as the desired optical windows. The control system may be arranged, when a selected input light source is off-center of the array of input light surfaces, to control at least one additional light source that is on the opposite side of the directional backlight from the selected input light source.
Advantageously illumination voids that are not illuminated by at least a first light source may be illuminated by a second light source, achieving increased illumination uniformity, while achieving directional viewing.
According to an eighth aspect of the present disclosure a directional waveguide is provided comprising: an input end for receiving input light at different input positions in a lateral direction across the input end; first and second opposed guide surfaces for guiding input light along the waveguide; and a reflective end for reflecting input light back along the waveguide, wherein the second guide surface is arranged to deflect light reflected from the reflective end through the first guide surface as output light, and the waveguide is arranged to direct the output light into respective optical windows in output directions that are distributed laterally in dependence on the position of the input light, and further comprising a light blocking layer disposed across at least one of the first and second opposed guide surfaces adjacent the input end and arranged to absorb light incident thereon.
Said light blocking layer may be disposed across each of the first and second opposed guide surfaces adjacent the input end. The light blocking layer may comprise tape attached to said at least one of the first and second opposed guide surfaces. The light blocking layer may comprise paint on said at least one of the first and second opposed guide surfaces. The directional waveguide may be mounted to a mounting element, in which case the light blocking layer may be provided on the mounting element. The light blocking layer may extend along the entire extent of the input end.
According to a ninth aspect of the present disclosure a directional display device may comprising a directional backlight according to the eighth aspect; and a transmissive spatial light modulator arranged to receive the output light from the waveguide and to modulate it to display an image, the light blocking layer being arranged outside the area of the spatial light modulator.
Advantageously stray light near the input of the waveguide may be reduced. Further reflections at the input side may be reduced, so that cross talk is improved for modes of operation of the directional display device including autostereoscopic 3D and off-axis observers of a privacy display.
Any of the aspects of the present disclosure may be applied in any combination.
Embodiments herein may provide an autostereoscopic display that provides wide angle viewing which may allow for directional viewing and conventional 2D compatibility. The wide angle viewing mode may be for observer tracked autostereoscopic 3D display, observer tracked 2D display (for example for privacy or power saving applications), for wide viewing angle 2D display or for wide viewing angle stereoscopic 3D display. Further, embodiments may provide a controlled illuminator for the purposes of an efficient autostereoscopic display. Such components can be used in directional backlights, to provide directional displays including autostereoscopic displays. Additionally, embodiments may relate to a directional backlight apparatus and a directional display which may incorporate the directional backlight apparatus. Such an apparatus may be used for autostereoscopic displays, privacy displays, multi-user displays and other directional display applications that may achieve for example power savings operation and/or high luminance operation.
Embodiments herein may provide an autostereoscopic display with large area and thin structure. Further, as will be described, the optical valves of the present disclosure may achieve thin optical components with large back working distances. Such components can be used in directional backlights, to provide directional displays including autostereoscopic displays. Further, embodiments may provide a controlled illuminator for the purposes of an efficient autostereoscopic display.
Embodiments of the present disclosure may be used in a variety of optical systems. The embodiment may include or work with a variety of projectors, projection systems, optical components, displays, microdisplays, computer systems, processors, self-contained projector systems, visual and/or audiovisual systems and electrical and/or optical devices. Aspects of the present disclosure may be used with practically any apparatus related to optical and electrical devices, optical systems, presentation systems or any apparatus that may contain any type of optical system. Accordingly, embodiments of the present disclosure may be employed in optical systems, devices used in visual and/or optical presentations, visual peripherals and so on and in a number of computing environments.
Before proceeding to the disclosed embodiments in detail, it should be understood that the disclosure is not limited in its application or creation to the details of the particular arrangements shown, because the disclosure is capable of other embodiments. Moreover, aspects of the disclosure may be set forth in different combinations and arrangements to define embodiments unique in their own right. Also, the terminology used herein is for the purpose of description and not of limitation.
Directional backlights offer control over the illumination emanating from substantially the entire output surface controlled typically through modulation of independent LED light sources arranged at the input aperture side of an optical waveguide. Controlling the emitted light directional distribution can achieve single person viewing for a security function, where the display can only be seen by a single viewer from a limited range of angles; high electrical efficiency, where illumination is primarily provided over a small angular directional distribution; alternating left and right eye viewing for time sequential stereoscopic and autostereoscopic display; and low cost.
These and other advantages and features of the present disclosure will become apparent to those of ordinary skill in the art upon reading this disclosure in its entirety.
Embodiments are illustrated by way of example in the accompanying FIGURES, in which like reference numbers indicate similar parts, and in which:
Time multiplexed autostereoscopic displays can advantageously improve the spatial resolution of autostereoscopic display by directing light from all of the pixels of a spatial light modulator to a first viewing window in a first time slot, and all of the pixels to a second viewing window in a second time slot. Thus an observer with eyes arranged to receive light in first and second viewing windows will see a full resolution image across the whole of the display over multiple time slots. Time multiplexed displays can advantageously achieve directional illumination by directing an illuminator array through a substantially transparent time multiplexed spatial light modulator using directional optical elements, wherein the directional optical elements substantially form an image of the illuminator array in the window plane.
The uniformity of the viewing windows may be advantageously independent of the arrangement of pixels in the spatial light modulator. Advantageously, such displays can provide observer tracking displays which have low flicker, with low levels of cross talk for a moving observer.
To achieve high uniformity in the window plane, it is desirable to provide an array of illumination elements that have a high spatial uniformity. The illuminator elements of the time sequential illumination system may be provided, for example, by pixels of a spatial light modulator with size approximately 100 micrometers in combination with a lens array. However, such pixels suffer from similar difficulties as for spatially multiplexed displays. Further, such devices may have low efficiency and higher cost, requiring additional display components.
High window plane uniformity can be conveniently achieved with macroscopic illuminators, for example, an array of LEDs in combination with homogenizing and diffusing optical elements that are typically of size 1 mm or greater. However, the increased size of the illuminator elements means that the size of the directional optical elements increases proportionately. For example, a 16 mm wide illuminator imaged to a 65 mm wide viewing window may require a 200 mm back working distance. Thus, the increased thickness of the optical elements can prevent useful application, for example, to mobile displays, or large area displays.
Addressing the aforementioned shortcomings, optical valves as described in commonly-owned U.S. patent application Ser. No. 13/300,293 (U.S. Patent Publication No. 2012/0127573), herein incorporated by reference in its entirety, advantageously can be arranged in combination with fast switching transmissive spatial light modulators to achieve time multiplexed autostereoscopic illumination in a thin package while providing high resolution images with flicker free observer tracking and low levels of cross talk. Described is a one dimensional array of viewing positions, or windows, that can display different images in a first, typically horizontal, direction, but contain the same images when moving in a second, typically vertical, direction.
Conventional non-imaging display backlights commonly employ optical waveguides and have edge illumination from light sources such as LEDs. However, it should be appreciated that there are many fundamental differences in the function, design, structure, and operation between such conventional non-imaging display backlights and the imaging directional backlights discussed in the present disclosure.
Generally, for example, in accordance with the present disclosure, imaging directional backlights are arranged to direct the illumination from multiple light sources through a display panel to respective multiple viewing windows in at least one axis. Each viewing window is substantially formed as an image in at least one axis of a light source by the imaging system of the imaging directional backlight. An imaging system may be formed between multiple light sources and the respective window images. In this manner, the light from each of the multiple light sources is substantially not visible for an observer's eye outside of the respective viewing window.
In contradistinction, conventional non-imaging backlights or light guiding plates (LGPs) are used for illumination of 2D displays. See. e.g., Kälil Käläntär et al., Backlight Unit With Double Surface Light Emission, J. Soc. Inf. Display, Vol. 12, Issue 4, pp. 379-387 (December 2004). Non-imaging backlights are typically arranged to direct the illumination from multiple light sources through a display panel into a substantially common viewing zone for each of the multiple light sources to achieve wide viewing angle and high display uniformity. Thus non-imaging backlights do not form viewing windows. In this manner, the light from each of the multiple light sources may be visible for an observer's eye at substantially all positions across the viewing zone. Such conventional non-imaging backlights may have some directionality, for example, to increase screen gain compared to Lambertian illumination, which may be provided by brightness enhancement films such as BEF™ from 3M. However, such directionality may be substantially the same for each of the respective light sources. Thus, for these reasons and others that should be apparent to persons of ordinary skill, conventional non-imaging backlights are different to imaging directional backlights. Edge lit non-imaging backlight illumination structures may be used in liquid crystal display systems such as those seen in 2D Laptops, Monitors and TVs. Light propagates from the edge of a lossy waveguide which may include sparse features; typically local indentations in the surface of the guide which cause light to be lost regardless of the propagation direction of the light.
As used herein, an optical valve is an optical structure that may be a type of light guiding structure or device referred to as, for example, a light valve, an optical valve directional backlight, and a valve directional backlight (“v-DBL”). In the present disclosure, optical valve is different to a spatial light modulator (even though spatial light modulators may be sometimes generally referred to as a “light valve” in the art). One example of an imaging directional backlight is an optical valve that may employ a folded optical system. Light may propagate substantially without loss in one direction through the optical valve, may be incident on an imaging reflector, and may counter-propagate such that the light may be extracted by reflection off tilted light extraction features, and directed to viewing windows as described in U.S. patent application Ser. No. 13/300,293 (U.S. Pat. Publ. No. 2012/0127573), which is herein incorporated by reference in its entirety.
Additionally, as used herein, a stepped waveguide imaging directional backlight may be at least one of an optical valve. A stepped waveguide is a waveguide for an imaging directional backlight comprising a waveguide for guiding light, further comprising: a first light guiding surface; and a second light guiding surface, opposite the first light guiding surface, further comprising a plurality of light guiding features interspersed with a plurality of extraction features arranged as steps.
In operation, light may propagate within an exemplary optical valve in a first direction from an input side to a reflective side and may be transmitted substantially without loss. Light may be reflected at the reflective side and propagates in a second direction substantially opposite the first direction. As the light propagates in the second direction, the light may be incident on light extraction features, which are operable to redirect the light outside the optical valve. Stated differently, the optical valve generally allows light to propagate in the first direction and may allow light to be extracted while propagating in the second direction.
The optical valve may achieve time sequential directional illumination of large display areas. Additionally, optical elements may be employed that are thinner than the back working distance of the optical elements to direct light from macroscopic illuminators to a window plane. Such displays may use an array of light extraction features arranged to extract light counter propagating in a substantially parallel waveguide.
Thin imaging directional backlight implementations for use with LCDs have been proposed and demonstrated by 3M, for example U.S. Pat. No. 7,528,893; by Microsoft, for example U.S. Pat. No. 7,970,246 which may be referred to herein as a “wedge type directional backlight;” by RealD, for example U.S. patent application Ser. No. 13/300,293 (U.S. Patent Publication No. 2012/0127573) which may be referred to herein as an “optical valve” or “optical valve directional backlight,” all of which are herein incorporated by reference in their entirety.
The present disclosure provides stepped waveguide imaging directional backlights in which light may reflect back and forth between the internal faces of, for example, a stepped waveguide which may include a first side and a first set of features. As the light travels along the length of the stepped waveguide, the light may not substantially change angle of incidence with respect to the first side and first set of surfaces and so may not reach the critical angle of the medium at these internal faces. Light extraction may be advantageously achieved by a second set of surfaces (the step “risers”) that are inclined to the first set of surfaces (the step “treads”). Note that the second set of surfaces may not be part of the light guiding operation of the stepped waveguide, but may be arranged to provide light extraction from the structure. By contrast, a wedge type imaging directional backlight may allow light to guide within a wedge profiled waveguide having continuous internal surfaces. The optical valve is thus not a wedge type imaging directional backlight.
Further, in
The waveguide 1 has first and second, opposed guide surfaces extending between the input end 2 and the reflective end 4 for guiding light forwards and back along the waveguide 1. The second guide surface has a plurality of light extraction features 12 facing the reflective end 4 and arranged to reflect at least some of the light guided back through the waveguide 1 from the reflective end from different input positions across the input end in different directions through the first guide surface that are dependent on the input position.
In this example, the light extraction features 12 are reflective facets, although other reflective features could be used. The light extraction features 12 do not guide light through the waveguide, whereas the intermediate regions of the second guide surface intermediate the light extraction features 12 guide light without extracting it. Those regions of the second guide surface are planar and may extend parallel to the first guide surface, or at a relatively low inclination. The light extraction features 12 extend laterally to those regions so that the second guide surface has a stepped shape which may include the light extraction features 12 and intermediate regions. The light extraction features 12 are oriented to reflect light from the light sources, after reflection from the reflective end 4, through the first guide surface.
The light extraction features 12 are arranged to direct input light from different input positions in the lateral direction across the input end in different directions relative to the first guide surface that are dependent on the input position. As the illumination elements 15a-15n are arranged at different input positions, the light from respective illumination elements 15a-15n is reflected in those different directions. In this manner, each of the illumination elements 15a-15n directs light into a respective optical window in output directions distributed in the lateral direction in dependence on the input positions. The lateral direction across the input end 2 in which the input positions are distributed corresponds with regard to the output light to a lateral direction to the normal to the first guide surface. The lateral directions as defined at the input end 2 and with regard to the output light remain parallel in this embodiment where the deflections at the reflective end 4 and the first guide surface are generally orthogonal to the lateral direction. Under the control of a control system, the illuminator elements 15a-15n may be selectively operated to direct light into a selectable optical window. The optical windows may be used individually or in groups as viewing windows.
The SLM 48 extends across the waveguide and modulates the light output therefrom. Although the SLM 48 may a liquid crystal display (LCD), this is merely by way of example and other spatial light modulators or displays may be used including LCOS, DLP devices, and so forth, as this illuminator may work in reflection. In this example, the SLM 48 is disposed across the first guide surface of the waveguide and modulates the light output through the first guide surface after reflection from the light extraction features 12.
The operation of a directional display device that may provide a one dimensional array of viewing windows is illustrated in front view in
Continuing the discussion of
In some embodiments with uncoated extraction features 12, reflection may be reduced when total internal reflection (TIR) fails, squeezing the xz angular profile and shifting off normal. However, in other embodiments having silver coated or metallized extraction features, the increased angular spread and central normal direction may be preserved. Continuing the description of the embodiment with silver coated extraction features, in the xz plane, light may exit the stepped waveguide 1 approximately collimated and may be directed off normal in proportion to the y-position of the respective illuminator element 15a-15n in illuminator array 15 from the input edge center. Having independent illuminator elements 15a-15n along the input edge 2 then enables light to exit from the entire first light directing side 6 and propagate at different external angles, as illustrated in
Illuminating a spatial light modulator (SLM) 48 such as a fast liquid crystal display (LCD) panel with such a device may achieve autostereoscopic 3D as shown in top view or yz-plane viewed from the illuminator array 15 end in
The reflective end 4 may have positive optical power in the lateral direction across the waveguide. In embodiments in which typically the reflective end 4 has positive optical power, the optical axis may be defined with reference to the shape of the reflective end 4, for example being a line that passes through the center of curvature of the reflective end 4 and coincides with the axis of reflective symmetry of the end 4 about the x-axis. In the case that the reflecting surface 4 is flat, the optical axis may be similarly defined with respect to other components having optical power, for example the light extraction features 12 if they are curved, or the Fresnel lens 62 described below. The optical axis 238 is typically coincident with the mechanical axis of the waveguide 1. In the present embodiments that typically comprise a substantially cylindrical reflecting surface at end 4, the optical axis 238 is a line that passes through the center of curvature of the surface at end 4 and coincides with the axis of reflective symmetry of the side 4 about the x-axis. The optical axis 238 is typically coincident with the mechanical axis of the waveguide 1. The cylindrical reflecting surface at end 4 may typically comprise a spherical profile to optimize performance for on-axis and off-axis viewing positions. Other profiles may be used.
Continuing the discussion of
Advantageously, the arrangement illustrated in
A further wedge type directional backlight is generally discussed by U.S. Pat. No. 7,660,047 which is herein incorporated by reference in its entirety. The wedge type directional backlight and optical valve further process light beams in different ways. In the wedge type waveguide, light input at an appropriate angle will output at a defined position on a major surface, but light rays will exit at substantially the same angle and substantially parallel to the major surface. By comparison, light input to a stepped waveguide of an optical valve at a certain angle may output from points across the first side, with output angle determined by input angle. Advantageously, the stepped waveguide of the optical valve may not require further light redirection films to extract light towards an observer and angular non-uniformities of input may not provide non-uniformities across the display surface.
There will now be described some waveguides, directional backlights and directional display devices that are based on and incorporate the structures of
The reflective end 4 converges the reflected light. Fresnel lens 62 may be arranged to cooperate with reflective end 4 to achieve viewing windows at a viewing plane. Transmissive spatial light modulator 48 may be arranged to receive the light from the directional backlight. The image displayed on the SLM 48 may be presented in synchronization with the illumination of the light sources of the array 15.
The control system may comprise a sensor system arranged to detect the position of the observer 99 relative to the display device 100. The sensor system comprises a position sensor 406, such as a camera arranged to determine the position of an observer 408; and a head position measurement system 404 that may for example comprise a computer vision image processing system. The position sensor 406 may comprise known sensors including those comprising cameras and image processing units arranged to detect the position of observer faces. Position sensor 406 may further comprise a stereo sensor arranged to improve the measure of longitudinal position compared to a monoscopic camera. Alternatively position sensor 406 may comprise measurement of eye spacing to give a measure of required placement of respective arrays of viewing windows from tiles of the directional display.
The control system may further comprise an illumination controller and an image controller 403 that are both supplied with the detected position of the observer supplied from the head position measurement system 404.
The illumination controller comprises an LED controller 402 arranged to determine which light sources of array 15 should be switched to direct light to respective eyes of observer 408 in cooperation with waveguide 1; and an LED driver 400 arranged to control the operation of light sources of light source array 15 by means of drive lines 407. The illumination controller 74 selects the illuminator elements 15 to be operated in dependence on the position of the observer detected by the head position measurement system 72, so that the viewing windows 26 into which light is directed are in positions corresponding to the left and right eyes of the observer 99. In this manner, the lateral output directionality of the waveguide 1 corresponds with the observer position.
The image controller 403 is arranged to control the SLM 48 to display images. To provide an autostereoscopic display, the image controller 403 and the illumination controller may operate as follows. The image controller 403 controls the SLM 48 to display temporally multiplexed left and right eye images and the LED controller 402 operates the light sources 15 to direct light into viewing windows in positions corresponding to the left and right eyes of an observer synchronously with the display of left and right eye images. In this manner, an autostereoscopic effect is achieved using a time division multiplexing technique. In one example, a single viewing window may be illuminated by operation of light source 409 (which may comprise one or more LEDs) by means of drive line 410 wherein other drive lines are not driven as described elsewhere.
The head position measurement system 404 detects the position of an observer relative to the display device 100. The LED controller 402 selects the light sources 15 to be operated in dependence on the position of the observer detected by the head position measurement system 404, so that the viewing windows into which light is directed are in positions corresponding to the left and right eyes of the observer. In this manner, the output directionality of the waveguide 1 may be achieved to correspond with the viewer position so that a first image may be directed to the observer's right eye in a first phase and directed to the observer's left eye in a second phase.
Thus a first guide surface may be arranged to guide light by total internal reflection and the second guide surface may be substantially planar and inclined at an angle to direct light in directions that break that total internal reflection for outputting light through the first guide surface, and the display device may further comprise a deflection element extending across the first guide surface of the waveguide for deflecting light towards the normal to the first guide surface.
The continuous curve to the mirror end 4 increases the footprint of the waveguide in comparison to conventional scattering waveguides, increasing bezel size. It would be desirable to reduce the bezel of the waveguide 1 while maintaining lateral uniformity of profile 208.
In the present embodiments, the uniformity profile 208 across the line 202 represents the spatial uniformity across the waveguide 1. This is separate to the angular uniformity across the array of optical windows. Desirably a backlight is arranged to provide high spatial uniformity, typically greater than 70% across the display area. However, the same backlight may provide angular uniformity in wide angle mode that may be greater than 20% across a +/−45 degrees angular range. In Privacy, 3D, high efficiency and outdoors operation modes, the angular uniformity may be greater than 2% across a +/−45 degrees. Thus spatial and angular uniformity are different properties. The present embodiments are arranged to provide desirable spatial uniformity for directional backlight with controllable angular uniformity in a lateral direction.
Thus a directional waveguide 1 comprising: an input end 2; first and second opposed, laterally extending guide surfaces 6, 8 for guiding light along the waveguide 1; and a reflective end 4 facing the input end 2 for reflecting the input light back along the waveguide 1, the second guide surface 8 being arranged to deflect the reflected input light through the first guide surface 6 as output light, and the waveguide 1 being arranged to direct the output light into optical windows 26 in output directions that are distributed in a lateral direction (y-axis) in dependence on the input position of the input light.
where θi is the incident angle and θf is the facet 220 angle. Thus for a central light source 15 the efficiency reduces with lateral position 206.
It would be desirable to achieve high lateral uniformity with the small bezel size achieved by a Fresnel reflector.
Relative Geometric Efficiency=(1−b/m)/(1−B/M) eqn. 2
Height difference may arise from regions 10 that are not typically not parallel to side 6. Further height difference 225 is provided by steps 12 of the stepped waveguide. Desirably the step height may be at least 0.5 micrometers, preferably at least 1.0 micrometers and more preferably at least 1.5 micrometers to minimize facet rounding during tooling and molding of the waveguide 1. To minimize Moiré visibility the pitch of the facets 12 may be desirably less than 500 micrometers, more preferably less than 350 micrometers and most preferably less than 200 micrometers. Thus the range of height difference 225 may be determined by fabrication and image appearance characteristics of the light guide.
It would be desirable to control the lateral geometric efficiency to compensate for the Fresnel reflector efficiency roll-off shown in
t(y)=t0−δ*y2 eqn. 3
where t0 is the thickness of the input aperture aligned with the optical axis 199 which may be for example 0.7 mm and δ is the variation parameter which may be for example 0.000008 mm−1. The height of the input end 2 between the first and second guide surfaces 6,8 thus has a profile that is highest at the optical axis 199 of the Fresnel reflector and reduces towards each side of the optical axis 199.
Advantageously the output from waveguide 1 may be provided with a substantially uniform profile 208 while maintaining the small footprint of the Fresnel reflector end 4.
In the above embodiments, the height of the reflective end 4 between the first and second guide surfaces 6, 8 has a profile across the lateral direction that may be flat.
The first guide surface 6 is arranged to guide light by total internal reflection and the second guide surface 8 comprises a plurality of light extraction features 12 oriented to direct light guided along the waveguide 1 in directions allowing exit through the first guide surface 6 as the output light and intermediate regions 10 between the light extraction features 12 that are arranged to guide light along the waveguide 1. The second guide surface 8 has a stepped shape in which said light extraction features are facets 12 between the intermediate regions 10.
The light extraction features 12 may have positive optical power in the lateral direction (y-axis).
A directional waveguide 1 may be arranged wherein the height of the input end 2 between the first and second guide surfaces 6, 8 has a profile 205 across the lateral direction that is flat. The height of the reflective end 2 between the first and second guide surfaces 6,8 may have a profile 205 across the lateral direction that is lowest at the optical axis 199 of the Fresnel reflector and increases towards each side of the optical axis 199.
A directional backlight may comprise: a directional waveguide 1 arranged to achieve small footprint and high lateral uniformity for central light sources of array 15, as described herein; and an array 15 of input light sources 15a-n arranged at different input positions in a lateral direction across the input end 2 of the waveguide 1 and arranged to input light into the waveguide 1. As shown in
It may further be desirable in manufacture to adjust the shape of the reflective end to increase yield and/or device uniformity.
As shown in
Similarly the additional light sources 19a-n may be arranged to direct additional light into the waveguide 1 through one of the side surfaces 24 in a direction in which the additional light is reflected by the reflective end 4 onto the opposite side surface 222 and by the opposite side surface 22 into a segment of the waveguide 1 adjacent the opposite side surface 22 extending from a corner between the reflective surface 4 and the side surface 22.
Region 305 between lines 301, 303 is illuminated by light source 15. Advantageously void A, 300 may be filled in a controllable manner by adjustment of the flux from the light sources 17, for a wide range of viewing positions. Further the angular illumination profile of the output windows may be controlled to provide a wide angle mode of similar or better performance compared to conventional waveguides 1.
As illustrated in
It would be desirable to reduce cost and complexity by minimizing the number of light sources 17, 19 on the sides 22, 24 of the waveguide 1.
The additional light sources 17a-n, 19a-n may be disposed along at least a part 877, 879 of each side surface 22, 24 adjacent the input end 2, the additional light sources 17a-n, 19a-n being arranged to direct additional light into the waveguide 1 through one of the side surfaces 22, 24.
Typically it is desirable to provide void A, 300 filling for optical windows 26 that are up to approximately 45 degrees off-axis in a lateral direction. At much higher angles, general diffusion and stray light in the waveguide 1 and diffuser elements may be provided to achieve void A, 300 filling and window 26 provision. Such a window direction requires the uppermost light source 17n to create a ray 307 that has an angle θ to the side 24 that may be approximately 30 degrees inside the waveguide in the x-y plane. In an illustrative embodiment, a waveguide 1 with 16:9 aspect ratio may be provided with an edge facet 220 facet angle θef of approximately 20 degrees. The angle θl is given by:
θl=θ+2·θef eqn. 5
To continue the illustrative embodiment θl may be 70 degrees. The relative size of the region of the side 22 that is free of light sources 17a-n may then be determined as
Δ=W/(L·tan(θl)) eqn. 6
Where W is the waveguide 1 width (in y direction) and L is its height (in x direction). Thus for the 16:9 arrangement of waveguide 1, Δ=65% and the light sources 17 are required for 35% of the height of the waveguide 1 from the input side. When θ=θc then the light exits the waveguide parallel to the surface 6. Thus the minimum Δ is approximately 25%.
Thus said part 877, 879 of each side surface along which the additional light sources are disposed is at least 20% of the side surface from the input end 2 and preferably at least 40% of the side surface. Said part 877, 879 of each side surface along which the additional light sources are disposed is at most 80% of the side surface from the input end 2 and preferably at most 60% of the side surface.
Advantageously void A may be filled and the number of light sources 17, 19 may be reduced, minimizing cost and optimizing uniformity. In operation, light sources 17, 19 are arranged to provide illumination for off-axis optical windows in wide angle operation. Advantageously, the flux provided by such LEDs may be minimized due to the relatively low illumination levels at high angles compared to the on-axis LEDs of array 15.
It would be desirable to provide filling of Void B, 332 to optimize uniformity in an efficient manner.
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The included angle θi between facets 326, 328 may be for example 130 degrees at positions across the width of the input side 2. Such an angle conveniently minimizes retroreflection of light into the waveguide, minimizing stray light artifacts in the uniformity of the output.
Advantageously, light can be provided to the opposite end of the Fresnel mirror with respect to the displacement of the light source, and Void B, 322 may be filled, increasing uniformity. It would be desirable to control the amount of light that is directed towards Void B, 322.
Advantageously the filling of Void B may be controlled for a wide range of optical window positions in the lateral direction. Both angular profile uniformity and image uniformity from a given angular direction may be achieved.
It would be desirable to provide off-axis filling of illumination voids with light sources that are arranged in a single lightbar with the primary light sources that are arranged to provide on-axis illumination.
The reflector element 824 may be disposed along only said part 874 of each side surface 24, similarly the reflector element 822 may be disposed along only said part of each side surface 22. Said part 872, 874 of each side surface along which the reflector element is disposed is at least 20% of the side surface and preferably at least 40% of the side surface. Said part 872, 874 of each side surface 22, 24 along which the reflector element 822, 824 is disposed is at most 80% of the side surface and preferably at most 60% of the side surface.
The input end 2 may have facets 328 against which the additional light sources 815a-n are disposed, which facets 326 face the reflector element 822, 824.
Light sources 815a-c are arranged on draft facets 328 of the input side 2. For convenience of illustration, outer light sources are not shown on the left hand outer region of the input side but would be present on both sides.
In operation, light from sources 815a-c is directed through facets 328 towards side 24. Reflector 824, such as ESR™ from 3M corporation may be arranged adjacent to side 24 to reflect light from sources 815a-c towards reflective end 4. After reflection from end 4, light may be incident on side 22 and reflected to provide filling of illumination voids as described elsewhere herein. Alternatively the sides 22, 24 may be metallized.
Advantageously light sources 815a-c may be arranged on the same lightbar as sources 15a-n, reducing complexity and cost. Further, light sources 17a-n and 19a-n may be removed, reducing complexity and cost. Further illumination hotspots scatter in the waveguide 1 near the input region of light from light sources 17a-n and 19a-n may be reduced, improving uniformity.
In other words, reflector 824 may comprise a plane surface as shown in further detail in
It would be desirable to reduce the number of connections to the LEDs of the array while maintaining control of angular and spatial uniformity across the waveguide output.
As shown in
In privacy operation, light rays 264 returning to the input side 2 may undesirably provide unwanted illumination at high angle optical windows.
It would be desirable to match the profiles in the near and far corners of the Fresnel reflector using the interlaced P and S type structures as described above.
It would be desirable to reduce the number of light sources on the input side 2 to reduced cost and physical size of the backlight unit while maintaining desirable uniformity by means of void filling.
The input facets 326, 328 provide angular redirection of input light to increase high lateral uniformity. During thermal cycling, the dimensions of the waveguide 1 may alter, and so lights sources 15a-n may vary in relative location with respect to the waveguide 1 in x and y directions, reducing efficiency and creating hotspots. It would be desirable to reduce degradations of uniformity due to thermal cycling, while maintaining lateral uniformity and minimizing reflection of light in privacy operation for off-axis positions on the input side 2.
In operation, the angle 1654 may be for example 55° to best cooperate with the angle of the rear reflector (not shown). Thus the luminance may be decreased with respect to the surface normal direction and cone 1657 may be directed away from the surface normal direction, reducing the luminance in the normal direction.
It may be desirable to increase the overall vertical diffusion angle and luminance in the normal direction angle, that is the width and distribution of the light cone 1653.
The separation of the LEDs 15a-n and 19a-n may advantageously be non-uniform. The diffusion properties of elements in the backlight may be angularly dependent, thus higher separations may be provided at higher angular input positions. Further, higher lumens per millimeters can desirably be provided in the central region of the waveguide 1.
Advantageously the number of LEDs and the number of addressable channels of the control system may be reduced, reducing cost while maintaining angular and spatial uniformity performance.
Advantageously such an arrangement reduces the number of connections from 64 to 16, advantageously reducing size and cost of the control circuit.
Light in the waveguide that is reflected from LED elements after reflection from the Fresnel reflector undesirably can increase the level of stray light and reduce the stray light performance of the display. It would be desirable to reduce stray light levels in privacy mode of operation.
A further origin of spatial non-uniformity arises from stray light scatter in the vicinity of the sides 2, 4, 22, 24 of the waveguide 1. Further the waveguide is desirably attached to the remainder of the backlight and spatial light modulator 48 to provide mechanical ruggedness.
As will be further described herein with reference to
LED 15 may be provided on a support substrate 2500 such as a flexible printed circuit board, FPC 2500 that may have a white, black or other colour upper layer 2502.
A directional waveguide may thus comprise an input end 2 for receiving input light at different input positions in a lateral direction across the input end 2; first and second opposed guide surfaces 6,8 for guiding input light 2511 along the waveguide 1; and a reflective end 4 for reflecting input light back along the waveguide 1, wherein the second guide surface 8 is arranged to deflect light reflected from the reflective end 4 through the first guide surface 6 as output light, and the waveguide 1 is arranged to direct the output light into respective optical windows 26 in output directions that are distributed laterally in dependence on the position of the input light.
In operation stray light from aperture 2504 of light source 15a of light source array 15 may create undesirable image streaks. Stray light may arise for example from manufacturing defects, parting lines, inadequate surface quality and light source misalignment to the input side 2.
Reflections from input side 2 of light that has reflected from reflective end 4 of waveguide 1 may further provide undesirable cross talk that degrades privacy and autostereoscopic performance. It would be desirable to reduce light streaks and stray light.
The directional waveguide may further comprising a light blocking layers 2510 disposed across the first and second opposed guide surfaces 6, 8 adjacent the input end 2 and arranged to absorb light 2511 incident thereon.
The light blocking layers 2510 may comprise an absorbing layer 2509 and an adhesive layer 2512 arranged to provide optical coupling between the waveguide 1 and absorbing layer 2509. The absorbing layer 2509 may be black tape for example so that the light blocking layer comprises tape attached to the first and second opposed guide surfaces 6, 8.
The light blocking layers 2510 may be arranged outside of the active area 2302 of the spatial light modulator 48 (the area 2302 of the spatial light modulator 48 where image pixels are arranged), between the boundary 2300 and in the input side 2. The light blocking layers 2510 may be arranged to absorb some of the light from the input side 2, enabling some light to pass without blocking.
Although in this example the light blocking layers 2510 are disposed across each of the first and second opposed guide surfaces 6, 8, as an alternative a light blocking layer 2510 may be disposed across only one of the first and second opposed guide surfaces 6, 8.
Thus a directional display device may comprise a directional backlight 1, 15 and a transmissive spatial light modulator 48 arranged to receive the output light from the waveguide 1 and to modulate it to display an image, the light blocking layer 2510 being arranged outside the active area 2302 of the spatial light modulator.
Scatter from regions 2513 near the input side may create light rays 2511 that can be extracted to cause image streaks 2. Such unwanted light may be absorbed in the absorbing layer 2510. Advantageously light streaks near the input can be reduced by absorbing layer 2510.
Further adhesive layer 2514 may be provided to achieve attachment of the waveguide 1 and light blocking layer to a printed circuit such as a flexible printed circuit (FPC) 2500. The absorbing layer 2510 may further provide attachment to FPC 2500 to improve mechanical stability of the assembled unit.
Said light blocking layer 2510 may be disposed on each or either of the first and second opposed guide surfaces 6, 8 adjacent the input end 2. The waveguide 1 can be attached to the polarizer 2210 to further improve mechanical stability.
Advantageously, assembly of the unit may be less complicated than the embodiment of
In addition to reducing stray light directly from the input end, the present embodiments also reduce unwanted light rays 2517 from reflective end 4 that may be further reflected by light source 15 or input side 2. Such rays 2517 provide undesirable cross talk and streak artefacts that may degrade autostereoscopic and privacy modes of operation. Such unwanted light may be partially absorbed in the light blocking layer 2510. Such light is incident on light blocking layer 2510 in both forwards and backwards directions (+x and −x directions), and so may be incident on the light blocking layer 2510 twice in comparison to the directly injected light from side 2 which sees the light blocking layer 2510 once. Thus cross talk is preferentially reduced in comparison to directly input light.
Advantageously cross talk may be reduced, and improved off-axis image quality achieved for privacy mode and reduced left to right eye cross talk for autostereoscopic mode.
If a light blocking layer is provided, for example as described above with reference to any of
Black tape 2509 may be replaced by reflective tape so that stray light rays are prevented from directing to the observer through the spatial light modulator, but light rays are directed into the waveguide 1. The reflective tape may for example by ESR™ from 3M.
Advantageously stray light may be controlled while maintaining efficiency of coupling into the waveguide 1.
It would be desirable to provide automatic control of image uniformity to compensate light source degradation mechanisms.
U.S. Patent Application Publication No. 2014/0009508, entitled “Controlling light sources of a directional backlight,” filed May 17, 2013 , which is herein incorporated by reference in its entirety, generally describes a luminance calibration apparatus and method wherein photodetectors are arranged at the input side 2 of directional waveguide 1, for example as part of the lightbar comprising the array 15 and electrical connections. It would be desirable to reduce the cost and complexity of the photodetector and control apparatus.
Light rays 1210 from illuminator element 1216 are directed to reflective end 4, reflected and directed back towards the input end 2. Some of the light from source 1216 will be extracted by means of light extraction features 12, while some of the light will be incident on at least a portion of the input end 2. Sensor elements that may include 1400, 1402 may be arranged as described above.
Measured signals from sensors 1400, 1402 may be passed to illumination controller 1274 which drives illuminator elements of array 15 using an illuminator element driver 1233 which may be a current driver with grey level control to drive lines 1244 to provide drive signals to the array of illuminator elements. The illumination controller 1274 calibrates the drive signals supplied to the illuminator elements 15n in response the measured signals representing the sensed light, as follows.
Array luminous flux distribution controller 1224 may include for example a stored reference grey level profile 1230 from front of screen measurements that may be provided at the time of manufacture. This enables the control system to output scaled luminous fluxes that have a predetermined distribution across the array of light sources, for example to vary the scaled luminous fluxes as described above.
Data from sensors 1400, 1402 may be supplied for example to calibration measurement system 1222 that may provide data to a look up table 1226 within the luminous flux distribution controller 1224. Further selection of luminous intensity distribution (for example to select between luminous intensity distributions 1266, 1272, 1274, 1276, 1294) may be provided by selection controller 1228. Selection controller may have user input or an automatic input that is determined by sensing of display viewing conditions. For example the number of viewers, the room brightness, display orientation, the image quality settings and/or the power savings mode settings may be used to vary the selected distribution.
In device manufacture, the output of the sensors 1400, 1402 in response to each of the light sources of the array 15 may be compared to the signal from a camera or detector placed in the window plane of the display. This achieves an initial calibration or referencing of the internal sensors with respect to light in the window plane. Such calibration may be stored in a look up table or similar.
In operation of a calibration mode, a single illuminator element of the array 15 is illuminated and sensors 1400, 1402 may measure a signal for the said illuminator element. The said illuminator element is extinguished and the next source of the array operated and a measurement taken. The output of the array of measurements is compared with a factory calibration so that the output luminous intensity for the given luminous flux distribution can be interpolated. The appropriate luminous flux distribution for the required luminous intensity distribution is then derived by the controller 1224 and the illuminator element controller 1233 appropriately configured to achieve the desired luminous flux distribution.
Advantageously the light from the whole array 15 may be measured by a combination of sensors 1400, 1402 and a desired luminous intensity distribution may be achieved.
The sensor system may be arranged with the waveguide 1 during the fabrication of the display for characterization purposes and removed after completion of product fabrication. Preferably the sensor system may be arranged with the waveguide 1 during normal operation. The in-field calibration phase may be applied during display switch-on. The spatial light modulator may be arranged with a black image during calibration to remove visibility to the user of the calibration phase. The calibration phase may be repeated on a daily, weekly or monthly basis for example to compensated for ageing artefacts as shown in
It would be desirable to further reduce the cost and complexity of the LED ageing compensation system by eliminating the photodetection and control system.
Spatial light modulator 48 may comprise a liquid crystal display that may comprise an input polarizer 2210, TFT glass substrate 2212, liquid crystal layer 2214, color filter glass substrate 2216 and output polarizer 2218. Red pixels 2220, green pixels 2222 and blue pixels 2224 may be arranged in an array at the liquid crystal layer 2214. White, yellow, additional green or other color pixels (not shown) may be further arranged in the liquid crystal layer to increase transmission efficiency, color gamut or perceived image resolution.
In the embodiment of
As described in U.S. Provisional Patent Application No. 62/167,203, to which this application claims priority, a directional display device may comprise a waveguide 1301 that further comprises a reflective end 1304 that is elongated in a lateral direction (y-axis), the first and second guide surfaces 6,8 extending from laterally extending edges of the reflective end 1304, the waveguide 1301 further comprising side surfaces 1322, 1324 extending between the first and second guide surfaces 6,8, and wherein the light sources include an array 1317 of light sources 1317a-n arranged along a side surface 1322 to provide said input light through that side surface 1322, and the reflective end 1304, comprises first and second facets 1327, 1329 alternating with each other in the lateral direction, the first facets 1327 being reflective and forming reflective facets of a Fresnel reflector having positive optical power in the lateral direction, the second facets 1329 forming draft facets of the Fresnel reflector, the Fresnel reflector 1304 having an optical axis 1287 that is inclined towards the side surface 1322 in a direction in which the Fresnel reflector 1304 deflects input light from the array of light sources 1317 into the waveguide 1301. Thus angle 1277 is non-zero. Similarly the second facets 1329 may be reflective and form reflective facets of a Fresnel reflector having positive optical power in the lateral direction, the Fresnel reflector 1304 having an optical axis 1289 that is inclined towards the side surface 1324 in a direction in which the Fresnel reflector 1304 deflects input light from the array of light sources 1319 into the waveguide 1301.
Illustrative light ray 1363 from source 1317a may be arranged to provide optical window 1326a and light ray 1365 from source 1317b may be arranged to provide optical window 1326b. Other layers such as diffusers, prismatic reflection films, retarders and spatial light modulators may be arranged in series with the waveguide 1301 in a similar manner to that described for waveguide 1 in the arrangement of
Advantageously a thin backlight with low bezel size may be achieved. Such an arrangement has light sources that are not arranged on the long sides of the waveguide 1301 and thus may have small form factor. Further light sources 1317 and 1319 may be arranged with overlapping optical windows, and thus display luminance may be increased.
It would be further desirable to achieve uniform illumination of a waveguide with a narrow bezel along the edges of the waveguide in wide angle mode of operation. The embodiments described elsewhere herein may be applied to either the long side light source array input of
The embodiments related to stepped waveguide directional backlights may be applied with changes as necessary to the wedge directional backlight as described herein.
As may be used herein, the terms “substantially” and “approximately” provide an industry-accepted tolerance for its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from zero percent to ten percent and corresponds to, but is not limited to, component values, angles, et cetera. Such relativity between items ranges between approximately zero percent to ten percent.
Also incorporated by reference herein in their entireties are U.S. Patent Publication Nos. 2013/0307831, 2013/0335821, and 2013/0307946.
While various embodiments in accordance with the principles disclosed herein have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with any claims and their equivalents issuing from this disclosure. Furthermore, the above advantages and features are provided in described embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages.
Additionally, the section headings herein are provided for consistency with the suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the embodiment(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Technical Field,” the claims should not be limited by the language chosen under this heading to describe the so-called field. Further, a description of a technology in the “Background” is not to be construed as an admission that certain technology is prior art to any embodiment(s) in this disclosure. Neither is the “Summary” to be considered as a characterization of the embodiment(s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple embodiments may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the embodiment(s), and their equivalents, that are protected thereby. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.
This application claims priority to U.S. Provisional Patent Application No. 62/146,648, entitled “Wide Angle Imaging Directional Backlights” filed Apr. 13, 2015, U.S. Provisional Patent Application No. 62/154,932, entitled “Wide Angle Imaging Directional Backlights” filed Apr. 30, 2015, U.S. Provisional Patent Application No. 62/167,185, entitled “Wide Angle Imaging Directional Backlights” filed May 27, 2015, U.S. Provisional Patent Application No. 62/255,248, entitled “Wide Angle Imaging Directional Backlights” filed Nov. 13, 2015, and U.S. Provisional Patent Application No. 62/167,203, entitled “Wide Angle Imaging Directional Backlights” filed May 27, 2015, all of which are herein incorporated by reference in their entirety.
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| 20160299281 A1 | Oct 2016 | US |
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| 62255248 | Nov 2015 | US |
