Observer-tracked privacy display
A display device comprising a spatial light modulator having a display polariser arranged on one side is provided with an additional polariser arranged on the same side as the display polariser and a polar control retarder between the additional polariser and the display polariser. The polar control retarder includes a liquid crystal retarder having two surface alignment layers disposed adjacent to a layer of liquid crystal material on opposite sides. The surface alignment layers provide alignment in the adjacent liquid crystal material with a twist. The out-of-plane orientation of the twisted layer of liquid crystal material is modified across at least one region of the display device to provide a transmission function in response to the measured location of an off-axis snooper, achieving increased size of polar region for which desired uniformity of security factor, or reduced distraction across the display to the driver in an automotive application is achieved.
1. A display apparatus comprising:
a display device comprising:
a spatial light modulator arranged to output spatially modulated light;
a display polariser arranged on a side of the spatial light modulator, the display polariser being a linear polariser; and
a view angle control arrangement comprising:
an additional polariser arranged on the same side of the spatial light modulator as the display polariser, the additional polariser being a linear polariser; and
at least one polar control retarder arranged between the display polariser and the additional polariser, wherein the at least one polar control retarder comprises a switchable liquid crystal retarder comprising a layer of liquid crystal material;
two surface alignment layers disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, the surface alignment layers each being arranged to provide homogenous alignment in the adjacent liquid crystal material, the liquid crystal material being provided with a twist; and
first and second electrode arrangements disposed on opposite sides of the layer of liquid crystal material and arranged to provide an electric field perpendicular to the layer of liquid crystal material,
wherein the display apparatus further comprises a control system arranged to control the spatial light modulator and to supply voltages to the first and second electrode arrangements for providing the electric field perpendicular to the layer of liquid crystal material, the control system being arranged to vary the voltages to the first and second electrode arrangements for controlling a direction of minimum light transmission of the view angle control arrangement.
2. A display apparatus according to claim 1 , wherein the display apparatus further comprises a viewer tracking system arranged to track the location of a viewer, wherein the control system is arranged to vary the voltages to the first and second electrode arrangements in response to the tracked location of the viewer.
3. A display apparatus according to claim 1 , wherein the control system is arranged to accept user input indicating a direction of minimum light transmission of the view angle control arrangement, and the control system is arranged to vary the voltages to the first and second electrode arrangements in response to the user input.
4. A display apparatus according to claim 1 , wherein components of the optical axis of the liquid crystal material in the plane of the layer of liquid crystal material have an average direction that is along the predetermined direction.
5. A display apparatus according to claim 1 , wherein the magnitude of the electric field perpendicular to the layer of liquid crystal material changes monotonically along a predetermined axis across at least part of the display device.
6. A display apparatus according to claim 5 , wherein the magnitude of the electric field changes monotonically along a predetermined axis across at least part of the display device so that directions of minimum light transmission of the view angle control arrangement from points of said at least part of the display device are directed towards a common off-axis point in front of the display device.
7. A display apparatus according to claim 1 , wherein the first electrode arrangement comprises a continuous electrode extending over the entirety of the layer of liquid crystal material, the continuous electrode having at least one contact disposed at each of opposite ends of the continuous electrode along the predetermined axis and arranged to supply respective voltages that create a voltage profile on the continuous electrode along the predetermined axis for providing the electric field perpendicular to the layer of liquid crystal material.
8. A display apparatus according to claim 7 , wherein at least one of the contacts comprises a conductive bar extending perpendicular to the predetermined axis.
9. A display apparatus according to claim 5 , wherein the first electrode arrangement comprises plural electrodes separated along the predetermined axis, the plural electrodes being arranged to supply different voltages that change monotonically along the predetermined axis.
10. A display apparatus according to claim 7 , wherein the second electrode arrangement is arranged to supply a common voltage.
11. A display apparatus according to claim 10 , wherein the second electrode arrangement comprises a continuous electrode extending over the entirety of the layer of liquid crystal material.
12. A display apparatus according to claim 1 , wherein the magnitude of the electric field is uniform across the entirety of the display device.
13. A display apparatus according to claim 12 , wherein each of the first electrode arrangement and the second electrode arrangement comprises a continuous electrode extending over the entirety of the layer of liquid crystal material.
14. A display apparatus according to claim 1 , wherein the surface alignment layers are each arranged to provide homogenous alignment in the adjacent liquid crystal material, the surface alignment layers having an in-plane component in the plane of the layer of liquid crystal material having an angle that changes monotonically along a predetermined axis across at least part of the display device.
15. A display apparatus according to claim 1 , wherein the switchable liquid crystal retarder has a retardance for light of a wavelength of 550 nm in a range from 300 nm to 1500 nm, preferably in a range from 400 nm to 1200 nm.
16. A display apparatus according to claim 1 , wherein the twist is in a range from 60° to 120°, preferably in a range from 70° to 90°.
17. A display apparatus according to claim 1 , wherein the electric vector transmission direction of the additional polariser is oriented at a non-zero angle with respect to the electric vector transmission direction of the display polariser.
18. A display apparatus according to claim 17 , wherein the non-zero angle is the same as the twist.
19. A display apparatus according to claim 1 , wherein
the surface alignment layer closest to the display polariser has a pretilt having a pretilt direction with a component in the plane of the layer of liquid crystal material that is parallel or perpendicular to an electric vector transmission direction of the display polarisers, and
the surface alignment layer closest to the additional polariser has a pretilt having a pretilt direction with a component in the plane of the layer of liquid crystal material that is parallel or perpendicular to an electric vector transmission direction of the additional polariser.
20. A display apparatus according to claim 1 , wherein the at least one polar control retarder further comprises at least one passive retarder.
21. A display apparatus according to claim 20 , wherein the at least one passive retarder is an A-plate with a retardance for light of a wavelength of 550 nm in a range of 250 nm to 300 nm.
22. A display apparatus according to claim 1 , wherein the liquid crystal material has a positive dielectric anisotropy.
23. A display apparatus according to claim 1 , wherein the display device is curved with a concave curvature as viewed from the output side.
24. A display apparatus according to claim 1 , wherein said display polariser is an output display polariser arranged on the output side of the spatial light modulator.
25. A display apparatus according to claim 24 , wherein there is not a reflective polariser arranged between the output display polariser and the at least one polar control retarder.
26. A display apparatus according to claim 24 , further comprising a reflective polariser arranged between the output polariser and the at least one polar control retarder, the reflective polariser being a linear polariser arranged to pass the same linearly polarised polarisation component as the output polariser.
27. A display apparatus according to claim 24 , wherein the spatial light modulator comprises an emissive spatial light modulator arranged to emit the spatially modulated light.
28. A display apparatus according to claim 24 , wherein the spatial light modulator comprises a transmissive spatial light modulator and the display device further comprises a backlight arranged to illuminate the spatial light modulator.
29. A display apparatus according to claim 1 , wherein the spatial light modulator comprises a transmissive spatial light modulator, the display device further comprises a backlight arranged to illuminate the spatial light modulator, and said display polariser is an input display polariser arranged on the input side of the spatial light modulator.
30. A display apparatus according to claim 29 , further comprising:
an output display polariser arranged on the output side of the spatial light modulator;
a further additional polariser arranged on the output side of the spatial light modulator, the further additional polariser being a linear polariser; and
at least one further polar control retarder arranged between the further additional polariser and the output display polariser.
31. A display apparatus according to claim 30 , wherein
the at least one further polar control retarder comprises a switchable liquid crystal retarder comprising a layer of liquid crystal material, and
the display device further comprises first and second electrode arrangements disposed on opposite sides of the layer of liquid crystal material, wherein the first and second electrode arrangements are arranged to provide an electric field perpendicular to the layer of liquid crystal material, wherein the magnitude of the electric field changes monotonically along a predetermined axis across at least part of the display device.
32. A display apparatus according to claim 1 , further comprising:
a further additional polariser arranged on the same side of the spatial light modulator as the additional polariser outside the additional polariser, the further additional polariser being a linear polariser; and
at least one further polar control retarder arranged between the additional polariser and the further additional polariser.
33. A display apparatus according to claim 32 , wherein
the at least one further polar control retarder comprises a switchable liquid crystal retarder comprising a layer of liquid crystal material, and
the display device further comprises first and second electrode arrangements disposed on opposite sides of the layer of liquid crystal material, wherein the first and second electrode arrangements are arranged to provide an electric field perpendicular to the layer of liquid crystal material, wherein the magnitude of the electric field changes monotonically along a predetermined axis across at least part of the display device.
34. A display apparatus according to claim 1 , wherein the backlight comprises:
at least one first light source arranged to provide input light;
at least one second light source arranged to provide input light in an opposite direction from the at least one first light source;
a waveguide arrangement comprising at least one waveguide, the waveguide arrangement being arranged to receive the input light from the at least one first light source and the at least one second light source and to cause light from the at least one first light source and the at least one second light source to exit from the waveguide arrangement by breaking total internal reflection; and
an optical turning film component comprising:
an input surface arranged to receive the light exiting from a waveguide through a light guiding surface of the waveguide by breaking total internal reflection, the input surface extending across the plane; and
an output surface facing the input surface, wherein the input surface comprises an array of prismatic elements.
35. A display apparatus according to claim 34 , wherein the waveguide arrangement comprises:
a waveguide extending across a plane and comprising:
first and second opposed light guiding surfaces arranged to guide light along the optical waveguide, the second light guiding surface being arranged to guide light by total internal reflection, and
first and second input ends arranged between the first and second light guiding surfaces and extending in a lateral direction between the first and second light guiding surfaces;
wherein the at least one first light source is arranged to input light into the waveguide through the first input end and the at least one second light source is arranged to input light into the waveguide through the second input end, and
the waveguide is arranged to cause light from the at least one first light source and the at least one second light source to exit from the waveguide through one of the first and second light guiding surfaces by breaking total internal reflection.
36. A display apparatus according to claim 34 , wherein the waveguide arrangement comprises:
a first waveguide extending across a plane and comprising
first and second opposed light guiding surfaces arranged to guide light along the optical waveguide, the second light guiding surface being arranged to guide light by total internal reflection; and
a first input end arranged between the first and second light guiding surfaces and extending in a lateral direction between the first and second light guiding surfaces;
wherein the at least one first light source is arranged to input light into the first waveguide through the first input end, and the first waveguide is arranged to cause light from the at least one first light source to exit from the first waveguide through one of the first and second light guiding surface by breaking total internal reflection;
a second waveguide extending across the plane arranged in series with the first waveguide and comprising
first and second opposed light guiding surfaces arranged to guide light along the optical waveguide, the second light guiding surface being arranged to guide light by total internal reflection, and
a second input end arranged between the first and second light guiding surfaces and extending in a lateral direction between the first and second light guiding surfaces;
wherein the at least one second light source is arranged to input light into the second waveguide through the second input end, and the second waveguide is arranged to cause light from the at least one second light source to exit from the second waveguide through one of the first and second light guiding surfaces by breaking total internal reflection, and
wherein the first and second waveguides are oriented so that at least one first light source and at least one second light source input light into the first and second waveguides in opposite directions.
37. A display apparatus according to claim 1 , comprising plural, tiled display devices.
38. A display apparatus according to claim 37 , wherein the magnitude of the electric field across at least part of the display device is different in different display devices.
39. A display apparatus according to claim 37 , wherein the profile of the change in the magnitude of the electric field monotonically along a predetermined axis across at least part of the display device is different in different display devices.
40. A display apparatus according to claim 39 , wherein the directions of minimum light transmission of the view angle control arrangement from points of said at least part of each of the display devices are directed towards a common off-axis point in front of the display apparatus.