Optical stack for privacy display

Patent metadata

Field	Value
Publication number	US-11874576-B2
Application number	US-202217679337-A
Country	US
Kind code	B2
Filing date	Feb 24, 2022
Priority date	Jun 29, 2018
Publication date	Jan 16, 2024
Grant date	Jan 16, 2024

Abstract

A switchable privacy display apparatus comprises a polarised output spatial light modulator, and an additional polariser. A reflective polariser, switchable liquid crystal polar control retarder, passive polar control retarders and air gap are arranged between the display output polariser and additional polariser. The passive retarders are arranged to provide no phase difference to polarised light from the spatial light modulator for on-axis light; and simultaneously provide a non-zero phase difference for polarised light in off-axis directions. The polar control retarders are further arranged to achieve low reflectivity for light propagating through the air gap. A switchable privacy display that can be conveniently assembled at low cost can be provided with high contrast images for display users while maintaining high visual security level for off-axis snoopers.

First claim

The invention claimed is:

1. A display device comprising:
a spatial light modulator having an output side;
a display polariser arranged on the output side of the spatial light modulator, the display polariser being a linear polariser; and
a view angle control optical element comprising:
an additional polariser arranged on an output side of the display polariser, the additional polariser being a linear polariser; and
plural polar control retarders arranged between the additional polariser and the display polariser, wherein an air gap divides the plural polar control retarders into at least one air gap input retarder between the display polariser and the air gap and at least one air gap output retarder between the air gap and the additional polariser,
the at least one air gap input retarder being arranged to convert linearly polarised light passed by the display polariser into circularly polarised light,
the plural polar control retarders together being capable of simultaneously introducing no net, relative phase shift to orthogonal polarisation components of light passed by the display polariser along a first axis and introducing a net, relative phase shift to orthogonal polarisation components of light passed by the display polariser along a second axis inclined to the first axis.

2. A display device according to claim 1 , wherein the plural polar control retarders include at least one passive retarder.

3. A display device according to claim 2 , wherein the at least one passive retarder comprises two passive retarders which have optical axes in the plane of the two passive retarders that are crossed.

4. A display device according to claim 3 , wherein the two passive retarders have optical axes that extend at 45° and at 135°, respectively, with respect to an electric vector transmission direction that is parallel to an electric vector transmission direction of the display polariser.

5. A display device according to claim 3 , wherein the two passive retarders are both included in one of the at least one air gap output retarder or the at least one air gap input retarder.

6. A display device according to claim 5 , wherein
the two passive retarders introduce no net, relative phase shift to orthogonal polarisation components of light passed by the display polariser along the first axis, and
the at least one passive retarder comprises a further two passive retarders which have optical axes in the plane of the further two passive retarders that are crossed, the further two passive retarders being respectively included in the at least one air gap output retarder and the at least one air gap input retarder, the further two passive retarders introducing no net, relative phase shift to orthogonal polarisation components of light passed by the display polariser along the first axis, and the one of the further two passive retarders which is arranged in the at least one air gap input retarder being arranged to convert linearly polarised light passed by the display polariser into circularly polarised light.

7. A display device according to claim 5 , wherein
the two passive retarders introduce a net, relative phase shift to orthogonal polarisation components of light passed by the display polariser along the first axis, and
the at least one passive retarder comprises a further passive retarder included in the other of the at least one air gap output retarder or the at least one air gap input retarder, the further passive retarder introducing a relative phase shift to orthogonal polarisation components of light passed by the display polariser along the first axis that is equal and opposite to said net, relative phase shift introduced by the two passive retarders.

8. A display device according to claim 7 , wherein
one of the two passive retarders and the further passive retarder have optical axes in the plane of the one of the two passive retarders and the further passive retarder that are crossed, and
the other of the two passive retarders has a retardance for light of a wavelength of 550 nm that is equal to the retardance of said one of the two passive retarders minus the retardance of the further passive retarder.

9. A display device according to claim 7 , wherein
one of the two passive retarders and the further passive retarder have optical axes in the plane of the one of the two passive retarders and the further passive retarder that are aligned, and
the other of the two passive retarders has a retardance for light of a wavelength of 550 nm that is equal to the retardance of said one of the two passive retarders plus the retardance of the further passive retarder.

10. A display device according to claim 3 , wherein the plural polar control retarders include a switchable liquid crystal retarder comprising a layer of liquid crystal material, the switchable liquid crystal retarder being provided between the two passive retarders.

11. A display device according to claim 10 , further comprising a transparent electrode and a liquid crystal alignment layer formed on a side of each of the two passive retarders adjacent the switchable liquid crystal retarder.

12. A display device according to claim 11 , further comprising first and second substrates between which the switchable liquid crystal retarder is provided, the first and second substrates each comprising one of the two passive retarders.

13. A display device according to claim 3 , wherein
the two passive retarders are respectively included in the at least one air gap output retarder and the at least one air gap input retarder.

14. A display device according to claim 2 , wherein the at least one passive retarder comprises a passive retarder having an optical axis perpendicular to the plane of the passive retarder.

15. A display device according to claim 14 , wherein the passive retarder having an optical axis perpendicular to the plane of the passive retarder has a retardance for light of a wavelength of 550 nm in a range from −400 nm to −1000 nm or in a range from +500 nm to +1200 nm and preferably in a range from −750 nm to −850 nm or preferably in a range from +950 nm to +1050 nm.

16. A display device according to claim 1 , wherein the plural polar control retarders further comprise two passive retarders which have optical axes in the plane of the two passive retarders that are crossed, the two passive retarders being respectively included in the at least one air gap output retarder and the at least one air gap input retarder, the two passive retarders introducing no net, relative phase shift to orthogonal polarisation components of light passed by the display polariser along the first axis, and a one of the two passive retarders which is arranged in the at least one air gap input retarder being arranged to convert linearly polarised light passed by the display polariser into circularly polarised light.

17. A display device according to claim 10 , wherein a retardance of the at least one passive retarder is equal and opposite to a retardance of the switchable liquid crystal retarder.

18. A display device according to claim 1 , wherein the plural polar control retarders include a switchable liquid crystal retarder comprising a layer of liquid crystal material.

19. A display device according to claim 18 , wherein the switchable liquid crystal retarder comprises two surface alignment layers disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, each of the two surface alignment layers being arranged to provide homeotropic alignment in the adjacent liquid cryst

Assignees

• Reald Spark Llc

Inventors

• Woodgate Graham J
• Harrold Jonathan

Classifications

• G02F1/137 Primary

  characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering · CPC title

• G02B6/0038

  Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide · CPC title

• G02B6/0055

  Reflecting element, sheet or layer · CPC title

• G02F1/139

  based on orientation effects in which the liquid crystal remains transparent · CPC title

• G02F1/1323

  Arrangements for providing a switchable viewing angle · CPC title