Optical stack for directional display

Abstract

A privacy display comprises a spatial light modulator and a passive retarder arranged between first and second polarisers arranged in series with the spatial light modulator, On-axis light from the spatial light modulator is directed without loss, and off-axis light has reduced luminance. The visibility of the display to off-axis snoopers is reduced by means of luminance reduction over a wide polar field of view. Off-axis visibility of the display in an automotive vehicle can be reduced.

1 . A display device comprising:
 a spatial light modulator;   a display polariser arranged on a side of the spatial light modulator;   an additional polariser arranged on the same side of the spatial light modulator as the display polariser; and   at least two passive retarders arranged between the additional polariser and the display polariser, wherein the at least two passive retarders comprise:   a first passive retarder that has an optical axis with a component in the plane of the passive retarder and a component perpendicular to the plane of the first passive retarder; and   at least one further passive retarder that has an optical axis with a different orientation from the first passive retarder.   
     
     
         2 . A display device according to  claim 1 , wherein the additional polariser and the display polariser have electric vector transmission directions that are parallel. 
     
     
         3 . (canceled) 
     
     
         4 . A display device according to  claim 1 , wherein the at least one further passive retarder comprises a pair of passive retarders that have slow axes in the plane of the passive retarders that are crossed. 
     
     
         5 . A display device according to  claim 4 , wherein the pair of passive retarders have slow axes that extend at 45° and at 135°, respectively, with respect to an electric vector transmission direction that is parallel to the electric vector transmission of the display polariser. 
     
     
         6 - 8 . (canceled) 
     
     
         9 . A display device according to  claim 1 , wherein the at least one further passive retarder comprises a passive retarder having an optical axis perpendicular to the plane of the passive retarder. 
     
     
         10 - 13 . (canceled) 
     
     
         14 . A display device according to  claim 1 , wherein the component of the optical axis of the first passive retarder in the plane of the first passive retarder extends at 0°, with respect to an electric vector transmission direction that is parallel or perpendicular to the electric vector transmission of the display polariser. 
     
     
         15 . (canceled) 
     
     
         16 . A display device according to  claim 1 , further comprising at least one additional passive retarder and a further additional polariser, wherein the at least one additional passive retarder is arranged between the first mentioned additional polariser and the further additional polariser. 
     
     
         17 . A display device according to  claim 1 , wherein the spatial light modulator is a transmissive spatial light modulator and the display device further comprises a backlight arranged to output light. 
     
     
         18 . A display device according to  claim 17 , wherein the backlight provides a luminance at polar angles to the normal to the spatial light modulator greater than 45 degrees that is at most 10% of the luminance along the normal to the spatial light modulator, preferably at most 5% of the luminance along the normal to the spatial light modulator, and more preferably at most 2.5% of the luminance along the normal to the spatial light modulator. 
     
     
         19 . A display device according to  claim 17 , wherein the backlight comprises:
 an array of light sources;   a directional waveguide comprising:   an input end extending in a lateral direction along a side of the directional waveguide, the light sources being disposed along the input end and arranged to input input light into the waveguide; and   opposed first and second guide surfaces extending across the directional waveguide from the input end for guiding light input at the input end along the waveguide, the waveguide being arranged to deflect input light guided through the directional waveguide to exit through the first guide surface.   
     
     
         20 . A display device according to  claim 19 , wherein the backlight further comprises a light turning film and the directional waveguide is a collimating waveguide. 
     
     
         21 - 47 . (canceled) 
     
     
         48 . A display device according to  claim 17 , wherein the display polariser is an input polariser arranged on the input side of the spatial light modulator between the backlight and the spatial light modulator, and the additional polariser is arranged between the input polariser and the backlight. 
     
     
         49 . A display device according to  claim 48 , wherein the display device further comprises an output polariser arranged on the output side of the spatial light modulator. 
     
     
         50 . A display device according to  claim 1 , wherein the display polariser is an output polariser arranged on the output side of the spatial light modulator. 
     
     
         51 . A display device according to  claim 50 , wherein the display device further comprises an input polariser arranged on the input side of the spatial light modulator. 
     
     
         52 . A display device according to  claim 51 , further comprising a further additional polariser arranged on the input side of the spatial light modulator and at least one further passive retarder arranged between the at least one further additional polariser and the input polariser. 
     
     
         53 . A display device according to  claim 1 , wherein the spatial light modulator is an emissive spatial light modulator, and the display polariser is an output polariser arranged on the output side of the emissive spatial light modulator. 
     
     
         54 . A view angle control optical element for application to a display device comprising a spatial light modulator and a display polariser, the view angle control optical element comprising:
 a control polariser; and   at least two passive retarders for arrangement between the control polariser and the display polariser on application of the view angle control optical element to the display device, wherein the at least two passive retarders comprise:   a first passive retarder that has an optical axis with a component in the plane of the passive retarder and a component perpendicular to the plane of the first passive retarder; and   at least one further passive retarder that has an optical axis with a different orientation from the first passive retarder.   
     
     
         55 . A view angle control optical element according to  claim 54 , wherein the at least one further passive retarder comprises a pair of passive retarders that have slow axes in the plane of the passive retarders that are crossed. 
     
     
         56 . A view angle control optical element according to  claim 55 , wherein the pair of passive retarders have slow axes that extend at 45° and at 135°, respectively, with respect to an electric vector transmission direction that is parallel to the electric vector transmission of the control polariser. 
     
     
         57 . A view angle control optical element according to  claim 54 , wherein the at least one further passive retarder comprises a passive retarder having an optical axis perpendicular to the plane of the passive retarder. 
     
     
         58 . A view angle control optical element according to  claim 54 , wherein the component of the optical axis of the first passive retarder in the plane of the first passive retarder extends at 0°, with respect to an electric vector transmission direction that is parallel or perpendicular to the electric vector transmission of the control polariser. 
     
     
         59 . A view angle control optical element according to  claim 54 , further comprising at least one additional passive retarder and a further additional polariser, wherein the at least one additional passive retarder is arranged between the first mentioned additional polariser and the further additional polariser. 
     
     
         60 . A display device according to  claim 4 , wherein the pair of passive retarders are positively birefringent. 
     
     
         61 . A view angle control optical element according to  claim 55 , wherein the pair of passive retarders are positively birefringent.