Polarization fields for dynamic light field display

• US 20130176704A1
• Filed: 11/29/2012
• Published: 07/11/2013
• Est. Priority Date: 11/29/2011
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Lanman, Douglas, Hirsch, Matthew, Heidrich, Wolfgang, Raskar, Ramesh, Wetzstein, Gordon
• Granted Patent: US 8,651,678 B2
• Time in Patent Office: Days
• US Class Current: 362/19
• CPC Class Codes: F21V 9/14 for producing polarised light
• CPC Class Codes: G02B 30/10 using integral imaging methods
• CPC Class Codes: G09G 2300/023 Display panel composed of stacked panels
• CPC Class Codes: G09G 2300/0447 for multi-domain technique to improve the viewing angle in a liquid crystal display, such as multi-vertical alignment [MVA]
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 3/003 to produce spatial visual effects
• CPC Class Codes: H04N 13/32 using arrays of controllable light sources; using moving apertures or moving light sources
• CPC Class Codes: H04N 13/324 Colour aspects

Abstract

In exemplary implementations of this invention, a flat screen device displays a 3D scene. The 3D display may be viewed by a person who is not wearing any special glasses. The flat screen device displays dynamically changing 3D imagery, with a refresh rate so fast that the device may be used for 3D movies or for interactive, 3D display. The flat screen device comprises a stack of LCD layers with two crossed polarization filters, one filter at each end of the stack. One or more processors control the voltage at each pixel of each LCD layer, in order to control the polarization state rotation induced in light at that pixel. The processor employs an algorithm that models each LCD layer as a spatially-controllable polarization rotator, rather than a conventional spatial light modulator that directly attenuates light. Color display is achieved using field sequential color illumination with monochromatic LCDs.

Claims

1. A method comprising, in combination:

(a) using an illumination source to provide light that is transmitted through at least (i) a stack of polarization rotators and (ii) a polarizer; and

(b) using one or more processors

(i) to perform an optimization calculation to compute a set of polarization state rotations induced in the light at respective pixels of the polarization rotators; and

(ii) to output control signals to control the polarization state rotations induced in the light at the respective pixels;

wherein

(I) each of the polarization rotators is a layer in the stack,

(II) the polarizer is optically in front of the stack,

(III) each of the polarization rotators comprises a spatially addressable device, the device being configured to dynamically vary per pixel polarization state rotations induced in the light, and

(IV) for each respective light ray in a set of light rays, the optimization calculation includes computing a summation of changes to polarization state rotation of the respective light ray that occur as the respective light ray travels through the stack of polarization rotators.

2. The method of claim 1, wherein the optimization calculation includes computing, according to Malus'"'"' law, an intensity of the respective light ray, the intensity being as of when the respective light ray emerges from the polarizer.

3. The method of claim 2, wherein (a) Malus'"'"' law includes a term that is a square of a sinusoidal function;

(c) the sinusoidal function has an argument;

(c) the optimization calculation includes solving for the argument, using an approximation based on only a single period of the sinusoidal function.

4. The method of claim 1, wherein for a least one pair of adjacent polarization rotators in the stack, no polarizer is positioned between the pair.

5. The method of claim 1, wherein the optimization calculation does not perform operations on values that are indicative of per pixel attenuation of the light and that are for pixels in a polarization rotator other than the front polarization rotator in the stack.

6. The method of claim 1, wherein each of the polarization rotators comprises a layer of liquid crystal.

7. The method of claim 1, wherein each of the polarization rotators is monochromatic and the illumination source is a strobe backlight configured to sequentially illuminate the polarization rotators with varying colors of light.

8. The method of claim 1, wherein each of the polarization rotators, respectively, is configured to dynamically vary voltage applied at the respective pixels in order to control polarization state rotation induced in the light at the respective pixels.

9. The method of claim 1, wherein the optimization calculation is a constrained linear least squares optimization calculation.

10. The method of claim 1, wherein the one or more processors are configured to employ a SART technique when performing the optimization calculation.

11. The method of claim 1, wherein the set of polarization state rotations, which is computed by the optimization calculation, minimizes error between a light field transmitted from the polarizer and a light field that would be created by a target 3D scene.

12. The method of claim 1, wherein light emerging from the polarizer produces an automultiscopic display.

13. Apparatus comprising, in combination:

a stack of polarization rotators, each of the polarization rotators being a layer in the stack;

a polarizer, the polarizer being optically in front of the stack;

an illumination source, the illumination source being configured to provide light that is transmitted through at least the stack and the polarizer; and

one or more processors;

wherein

(a) the one or more processors are configured

(i) to perform an optimization calculation to compute a set of polarization state rotations induced in the light at respective pixels of the polarization rotators, and

(ii) to output control signals to control the polarization state rotations induced in the light at the respective pixels,

(b) each of the polarization rotators comprises a spatially addressable device, the device being configured to dynamically vary per pixel polarization state rotations induced in the light, and

(c) for each respective light ray in a set of light rays, the optimization calculation includes computing a summation of changes to polarization state rotation of the respective light ray that occur as the respective light ray travels through the stack of polarization rotators.

14. The apparatus of claim 13, wherein the optimization calculation includes computing, according to Malus'"'"' law, an intensity of the respective light ray, the intensity being as of when the respective light ray emerges from the polarizer.

15. The apparatus of claim 14, wherein (a) Malus'"'"' law includes a term that is a square of a sinusoidal function;

(c) the sinusoidal function has an argument;

(c) the optimization calculation includes solving for the argument, using an approximation based on only a single period of the sinusoidal function.

16. The apparatus of claim 13, wherein for a least one pair of adjacent polarization rotators in the stack, no polarizer is positioned between the pair.

17. The apparatus of claim 13, wherein the optimization calculation does not perform operations on values that are indicative of per pixel attenuation of the light and that are for pixels in a polarization rotator other than the front polarization rotator in the stack.

18. The apparatus of claim 13, wherein the set of polarization state rotations, which is computed by the optimization calculation, minimizes error between a light field transmitted from the polarizer and a light field that would be created by a target 3D scene.

19. The apparatus of claim 13, wherein each of the polarization rotators is monochromatic and the illumination source is a strobe backlight configured to sequentially illuminate the polarization rotators with varying colors of light.

20. The apparatus of claim 13, wherein the optimization calculation is a linear optimization calculation and the one or more processors are configured to employ a SART technique when performing the linear optimization calculation.