Controlling reflection in LCD devices

• US 8,593,598 B2
• Filed: 05/09/2011
• Issued: 11/26/2013
• Est. Priority Date: 05/09/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Chen, Cheng, Zhong, John Z.
• Primary Examiner(s): Briggs, Nathanael R
• Application Number:
  US13/103,757
• Publication Number:
  US 20120287378A1
• Time in Patent Office: 932 Days
• Field of Search: 349/114, 349/96
• US Class Current: 349/114
• CPC Class Codes: G02F 1/133509 Filters, e.g. light shielding masks
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605
• CPC Class Codes: G02F 2203/09 transflective

Abstract

Systems and methods are provided for controlling the light reflected from a display panel. In one embodiment, a prism mirror and a diffuse reflector are positioned between the bottom polarizer and the liquid crystal layer of a pixel to control the polarization of reflected light transmitted through the display panel. The diffuse reflector diffuses light towards the prism mirror, and the prism mirror affects the polarization of the light. When the pixel is on, the liquid crystals of the liquid crystal layer may shift the polarization of the reflected light such that it can be transmitted through the top polarizer. When the pixel is off, the liquid crystals may not substantially shift the polarization of the reflected light, and the reflected light may be polarized to be absorbed by the top polarizer. Accordingly, reflected light is substantially transmitted through the pixel when the pixel is on, and substantially absorbed by the top polarizer when the pixel is off.

Claims

1. A display device comprising:

a plurality of pixels, wherein each pixel comprises;

a top polarizer configured to pass light having a first polarization and absorb light not having the first polarization;

a liquid crystal layer disposed beneath the top polarizer; and

a transflective layer disposed beneath the liquid crystal layer,

wherein the transflective layer comprises a prism mirror and a diffuse reflector disposed directly adjacent to the prism mirror on a common plane of the transflective layer, wherein the diffuse reflector is configured to direct light towards the prism mirror and the prism mirror is configured such that light reflected from the prism mirror has a second polarization.

2. The display device of claim 1, wherein the liquid crystal ayer comprises liquid crystal molecules configured to shift a polarization of light when a respective pixel is activated and not shift a polarization of light when the respective pixel is deactivated.

3. The display device of claim 1, wherein the liquid crystal layer is configured to shift a polarization of light having the first polarization to produce light having the second polarization while light having the first polarization propagates from the top polarizer through the liquid crystal layer and towards the transflective layer, if the pixel is activated.

4. The display device of claim 3, wherein the liquid crystal layer is configured to shift a polarization of light having the second polarization to produce light having the first polarization while light having the second polarization propagates from the prism mirror through the liquid crystal layer and towards the top polarizer, if the pixel is activated.

5. The display device of claim 1, wherein the liquid crystal layer is configured to transmit light having the first polarization without substantially changing a polarization of light having the first polarization while light having the first polarization propagates from the top polarizer through the liquid crystal layer and towards the transflective layer, if the pixel is deactivated.

6. The display device of claim 5, wherein the prism mirror is configured to change a polarization of light having the first polarization, such that light having the second polarization is reflected from the prism mirror.

7. The display device of claim 6, wherein the liquid crystal layer is configured to transmit light having the second polarization without substantially changing a polarization of light having the second polarization while light having the second polarization propagates from the prism mirror through the liquid crystal layer and towards the top polarizer, if the pixel is deactivated.

8. The display device of claim 7, wherein the top polarizer is configured to substantially absorb light having the second polarization while the light propagates to the top polarizer from the liquid crystal layer.

9. The display device of claim 1, wherein the prism mirror comprises mirrors angled such that light impinging the mirrors impinge incident to Brewster'"'"'s angle.

10. The display device of claim 1, wherein the transflective layer comprises a transflective substrate configured to transmit light through the transflective substrate and reflect light from the transflective substrate, wherein the diffuse reflector and the prism mirror are disposed directly over or substantially in-plane with the transflective substrate.

11. A method of controlling a polarization of light propagating in a pixel in a display device, the method comprising:

polarizing external light at a top polarizer of the pixel such that light polarized in a first polarization propagates from the top polarizer towards a liquid crystal layer of the pixel;

when the pixel is in an off state, reflecting the light polarized in the first polarization off a prism mirror beneath the liquid crystal layer as light polarized in a second polarization and absorbing the light polarized in the second polarization at the top polarizer; and

when the pixel is in an on state, shifting the polarization of the light polarized in the first polarization at the liquid crystal layer to produce light polarized in the second polarization, reflecting the light polarized in the second polarization from the prism mirror, shifting the light polarized in the second polarization reflected from the prism mirror to produce light polarized in the first polarization, and transmitting the light polarized in the first polarization out of the top polarizer of the pixel.

12. The method of claim 11, comprising reflecting the light polarized in the first polarization or the light polarized in the second polarization from a diffuse reflector disposed adjacent to the prism mirror and beneath the liquid crystal layer, towards the prism mirror.

13. The method of claim 11, comprising absorbing internal light from an internal light source at the top polarizer when the pixel is in the off state and transmitting the internal light through the top polarizer when the pixel is in the on state.

14. A transflective display device comprising a transflective layer, wherein the transflective layer comprises:

a transflective substrate configured to transmit light through the transflective substrate and reflect light from the transflective substrate; and

a prism mirror disposed on the transflective substrate or disposed substantially in-plane with the transflective substrate, wherein the prism mirror is configured such that light impinging the prism mirror is substantially reflected as light having an s-polarization; and

a diffuse reflector material disposed over the transflective substrate or disposed in-plane with the transflective substrate and directly adjacent to the prism mirror, wherein the diffuse reflector material is configured to reflect light towards the prism mirror.

15. The transflective display device of claim 14, comprising:

a liquid crystal layer disposed over the transflective layer, wherein the liquid crystal layer is configured to shift a polarization of light from the s-polarization to a p-polarization or from the p-polarization to the s-polarization when a pixel comprising the transflective layer is activated, and configured to not substantially change a polarization of light when the pixel is not activated;

a color filter within a black mask disposed over the liquid crystal layer; and

a top polarizer disposed over the color filter with the black mask, wherein the top polarizer is configured to transmit light having the p-polarization and absorb light not having the p-polarization.

16. The transflective display device of claim 15, wherein the color filter comprises holes, wherein external light can transmit through the top polarizer and through the color filter or through a hole in the color filter, through the liquid crystal layer, and towards reflective material in the transflective layer.

17. The transflective display device of claim 15, wherein the black mask comprises one or more holes, wherein external light can transmit through the top polarizer and through the one or more holes in the black mask, through the liquid crystal layer, and towards reflective material in the transflective layer.

18. The transflective display device of claim 15, further comprising:

a bottom polarizer disposed beneath the transflective layer; and

a backlight disposed beneath the bottom polarizer, wherein the backlight is configured to emit internal light towards the bottom polarizer, and wherein the bottom polarizer is configured to polarize the internal light to a s-polarization.

19. A method of controlling reflections over a pixel in a display device, the method comprising:

reflecting light impinged on a prism mirror in a transflective layer in the pixel as light polarized in a s-polarization;

absorbing the light polarized in s-polarization at a top polarizer of the pixel;

shifting a polarization of the light polarized in the s-polarization to produce light polarized in a p-polarization at a liquid crystal layer disposed below the top polarizer and above the transflective layer, while the light polarized in the s-polarization propagates from the prism mirror through the liquid crystal layer, and while the pixel is in an on state; and

transmitting the light polarized in the p-polarization out of the top polarizer of the pixel while the pixel is in the on state.

20. The method of claim 19, comprising polarizing external light at a top polarizer of the pixel to the p-polarization, such light polarized in the p-polarization propagates from the top polarizer towards the liquid crystal layer.

21. The method of claim 20, comprising shifting a polarization of the light polarized in the p-polarization to produce light polarized in the s-polarization at the liquid crystal layer while the light polarized in the p-polarization propagates from the top polarizer through the liquid crystal layer, and while the pixel is in the on state.