Directional display apparatus

Patent metadata

Field	Value
Publication number	US-2021341799-A1
Application number	US-202117243993-A
Country	US
Kind code	A1
Filing date	Apr 29, 2021
Priority date	Apr 30, 2020
Publication date	Nov 4, 2021
Grant date	—

Abstract

A switchable privacy display comprises a spatial light modulator (SLM), a first switchable liquid crystal (LC) retarder and first passive retarder between a first pair of polarisers and a second switchable LC retarder and second passive retarder between a second pair of polarisers. The first switchable LC retarder comprises a homeotropic alignment layer and a homogeneous alignment layer. The second switchable LC crystal retarder comprises two homeotropic alignment layers or two homogeneous alignment layers. In landscape or portrait privacy mode, on-axis light from the SLM is directed without loss, whereas off-axis light has reduced luminance to reduce visibility to off-axis snoopers. Display reflectivity may be reduced for on-axis reflections of ambient light, while reflectivity may be increased for off-axis light to achieve increased visual security. In public mode, the LC retardance is adjusted so that off-axis luminance and reflectivity are unmodified. The display may switch between day-time and night-time operation.

First claim

1 . A display device comprising:
a spatial light modulator; a display polariser arranged on a side of the spatial light modulator, the display polariser being a linear polariser; a first additional polariser arranged on the same side of the spatial light modulator as the display polariser, the first additional polariser being a linear polariser; at least one first polar control retarder arranged between the first additional polariser and the display polariser, a second additional polariser, the second additional polariser being a linear polariser; and at least one second polar control retarder, wherein either:
the second additional polariser is arranged on the same side of the spatial light modulator as the first additional polariser outside the first additional polariser, and the at least one second polar control retarder is arranged between the first additional polariser and the second additional polariser; or
the display device further comprises a backlight arranged to output light, the spatial light modulator comprises a transmissive spatial light modulator arranged to receive output light from the backlight, said display polariser is an input display polariser arranged on the input side of the spatial light modulator, and the display device further comprises an output display polariser arranged on the output side of the spatial light modulator, the second additional polariser is arranged on the output side of the spatial light modulator, and the at least one second polar control retarder is arranged between the second additional polariser and the output display polariser,
wherein: each of the at least one first polar control retarder and the at least one second polar control retarder comprises a respective switchable liquid crystal retarder comprising a layer of liquid crystal material and two surface alignment layers disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, in respect of one of the at least one first polar control retarder and the at least one second polar control retarder, one of the surface alignment layers is arranged to provide homogenous alignment in the adjacent liquid crystal material and the other of the surface alignment layers is arranged to provide homeotropic alignment in the adjacent liquid crystal material, and in respect of the other of the at least one first polar control retarder and the at least one second polar control retarder, both of the surface alignment layers are arranged to provide homogenous alignment in the adjacent liquid crystal material or both of the surface alignment layers are arranged to provide homeotropic alignment in the adjacent liquid crystal material.

2 . A display device according to claim 1 , wherein the switchable liquid crystal retarder of said one of the at least one first polar control retarder and the at least one second polar control retarder has a retardance for light of a wavelength of 550 nm having a first retardance value in a range from 700 nm to 2500 nm, preferably in a range from 850 nm to 1800 nm.

3 . A display device according to claim 1 , wherein said one of the at least one first polar control retarder and the at least one second polar control retarder further comprises at least one passive compensation retarder.

4 . A display device according to claim 3 , wherein the at least one passive compensation retarder of said one of the at least one first polar control retarder and the at least one second polar control retarder is arranged on the same side of the switchable liquid crystal retarder as the surface alignment layers that is arranged to provide homeotropic alignment in the adjacent liquid crystal material.

5 . A display device according to claim 3 , wherein the at least one passive compensation retarder of said one of the at least one first polar control retarder and the at least one second polar control retarder comprises a passive uniaxial retarder having its optical axis perpendicular to the plane of the retarder.

6 . A display device according to claim 5 , wherein the passive uniaxial retarder has a retardance for light of a wavelength of 550 nm in a range from −400 nm to −2100 nm, preferably in a range from −700 nm to −1700 nm.

7 . A display device according to claim 1 , wherein
the display device further comprises a reflective polariser, the reflective polariser being a linear polariser, and either:
said display polariser is an output display polariser arranged on the output side of the spatial light modulator, the second additional polariser is arranged on the same side of the spatial light modulator as the first additional polariser outside the first additional polariser, the at least one second polar control retarder is arranged between the first additional polariser and the second additional polariser, and the reflective polariser is arranged between the first additional polariser and the at least one second polar control retarder; or
the display device further comprises a backlight arranged to output light, the spatial light modulator comprises a transmissive spatial light modulator arranged to receive output light from the backlight, said display polariser is an input display polariser arranged on the input side of the spatial light modulator, and the display device further comprises an output display polariser arranged on the output side of the spatial light modulator, the second additional polariser is arranged on the output side of the spatial light modulator, the at least one second polar control retarder is arranged between the second additional polariser and the output display polariser, and the reflective polariser is arranged between the output display polariser and the at least one second polar control retarder.

8 . A display device according to claim 7 , wherein said one of the at least one first polar control retarder and the at least one second polar control retarder is the at least one second polar control retarder and said other of the at least one first polar control retarder and the at least one second polar control retarder is the at least one first polar control retarder.

9 . A display device according to claim 1 , wherein the switchable liquid crystal retarder of said one of the at least one first polar control retarder and the at least one second polar control retarder has a retardance for light of a wavelength of 550 nm having a first retardance value and the switchable liquid crystal retarder of said other pf the at least one first polar control retarder and the at least one second polar control retarder has a retardance for light of a wavelength of 550 nm having a second retardance value, the first retardance value being greater than the second retardance value.

10 . A display device according to claim 9 , wherein the magnitude of the difference between half the first retardance value and the second retardance value is at most 400 nm.

11 . A display device according to claim 9 , wherein
in respect of said other of the at least one first polar control retarder and the at least one second polar control retarder, both of the surface alignment layers are arranged to provide homogenous alignment in the adjacent liquid crystal material which has a retardance for light of a wavelength of 550 nm in a range from 450 nm to 900 nm, preferably in a range from 550 nm to 800 nm, and said other of the at least one first polar control retarder and the at least one second polar control retarder further comprises a pair of passive uniaxial retarders having optical axes in the plane of the retarders that are crossed and each having a retardance for light of a wavelength of 550 nm in a range from 250 nm to 800 nm, preferably in a range from 400 nm to 625 n

Assignees

• Reald Spark Llc

Inventors

• Woodgate Graham J
• Robinson Michael G
• Ramsey Robert A

Classifications

• G02B2207/123

  Optical louvre elements, e.g. for directional light blocking · CPC title

• G02F1/1323

  Arrangements for providing a switchable viewing angle · CPC title

• G02F1/133536

  Reflective polarizers (G02F1/13362 takes precedence) · CPC title

• G02F1/0136

  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation (G02F1/0353 takes precedence) · CPC title

• G02B30/31

  involving active parallax barriers (involving directional light or back-light sources G02B30/33) · CPC title