Methods and Apparatus for Light Field Projection

• US 20140300869A1
• Filed: 04/09/2014
• Published: 10/09/2014
• Est. Priority Date: 04/09/2013
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Hirsch, Matthew, Wetzstein, Gordon, Raskar, Ramesh, Lee, Vincent
• Granted Patent: US 9,405,124 B2
• Time in Patent Office: Days
• US Class Current: 353/7
• CPC Class Codes: G02B 3/0068 arranged in a single integral body or plate, e.g. laminates or hybrid structures with other optical elements G02B5/1885, G02B17/002, G02B30/27 take precedence
• CPC Class Codes: G02B 30/27 involving lenticular arrays
• CPC Class Codes: G03B 21/00 Projectors or projection-type viewers; Accessories therefor devices for changing pictures G03B23/00
• CPC Class Codes: H04N 13/305 using lenticular lenses, e.g. arrangements of cylindrical lenses
• CPC Class Codes: H04N 13/307 using fly-eye lenses, e.g. arrangements of circular lenses
• CPC Class Codes: H04N 13/363 using image projection screens volumetric display H04N13/388
• CPC Class Codes: H04N 5/7416 involving the use of a spatial light modulator, e.g. a light valve, controlled by a video signal

Abstract

In exemplary implementations of this invention, light from a light field projector is transmitted through an angle-expanding screen to create a glasses-free, 3D display. The display can be horizontal-only parallax or full parallax. In the former case, a vertical diffuser may positioned in the optical stack. The angle-expanding screen may comprise two planar arrays of optical elements (e.g., lenslets or lenticules) separated from each other by the sum of their focal distances. Alternatively, a light field projector may project light rays through a focusing lens onto a diffuse, transmissive screen. In this alternative approach, the light field projector may comprise two spatial light modulators (SLMs). A focused image of the first SLM, and a slightly blurred image of the second SLM, are optically combined on the diffuser, creating a combined image that has a higher spatial resolution and a higher dynamic range than either of two SLMs.

Claims

1. A method that comprises using a light field projector to project a set of light rays onto a screen, wherein:

(a) each respective light ray, out of the set of light rays, enters a first side of the screen at an entrance angle and exits a second, different side of the screen at an exit angle; and

(b) over an interval of the entrance angles, which interval does not include the angle zero, the magnitude of the exit angle of each respective light ray is greater than the magnitude of the entrance angle of the respective light ray;

angles in each case being defined relative to a direction that is perpendicular to the screen.

2. The method of claim 1, wherein the light rays create an automultiscopic display.

3. The method of claim 2, wherein the automultiscopic display exhibits parallax in only a first dimension.

4. The method of claim 3, wherein a diffuser that is positioned before or after the screen diffuses light, such that a light ray impacting the diffuser is spread only in a plane that is perpendicular to the first dimension.

5. The method of claim 2, wherein the display exhibits parallax in two different directions, the two different directions being perpendicular to each other.

6. The method of claim 1, wherein:

(a) the screen comprises a first planar array of optical elements and a second planar array of optical elements;

(b) the optical elements in each case are lenslets or lenticules;

(c) a plane located between the first and second planar arrays is conjugate to optical elements of the first planar array and to optical elements of the second planar array.

7. The method of claim 1, wherein the screen comprises a first planar array of lenticules and a second planar array of lenticules.

8. The method of claim 1, wherein the screen comprises a first planar array of lenslets and a second planar array of lenslets.

9. The method of claim 1, wherein, within the light field projector, light is transmitted through or reflected from two or more spatial light modulators that each display time-varying spatial light modulation patterns.

10. The method of claim 1, wherein the light field projector includes a coded aperture.

11. The method of claim 1, wherein, over the interval of entrance angles, the exit angles of the respective light rays map to the entrance angles of the respective light rays according to a linear function.

13. The system of claim 1, wherein the light field projector is configured to project an automultiscopic display on or through the screen.

12. A system comprising, in combination

(a) a screen, and

(b) a light field projector for projecting light onto the screen,

wherein the screen is configured such that, over a range of entrance angles, for each light ray that enters a first side of the screen at a non-zero entrance angle and exits a second, different side of the screen at an exit angle:

(1) the entrance angle has a first magnitude;

(2) the exit angle has a second magnitude; and

(3) the second magnitude is larger than the first magnitude;

angles being defined relative to a direction that is perpendicular to the screen.

14. A method comprising using a light field projector to project light rays through a focusing lens onto a diffusive screen, which screen is either transmissive or reflective.

15. The method of claim 14, wherein the light field projector comprises a first spatial light modulator and a second light modulator.

16. The method of claim 15, wherein:

(a) the first spatial light modulator displays a first spatial light attenuation pattern;

(b) the second spatial light modulator displays a second spatial light attenuation pattern;

(c) an image projected on the screen comprises a product of the first and second patterns; and

(d) the image has a higher spatial resolution than the first spatial light modulator and a higher spatial resolution than the second light modulator.

17. The method of claim 16, wherein the image has a higher dynamic range than the first spatial light modulator and a higher dynamic range than the second light modulator.

18. A system comprising, in combination:

(a) a diffusive screen, which screen is either transmissive or reflective;

(b) a focusing lens; and

(c) a light field projector for projecting light through the focusing lens onto the screen.

19. The system of claim 18, wherein:

(a) the light field projector includes a first spatial light modulator and a second spatial light modulator; and

(b) the projector is configured such that, during the projecting

(i) the first spatial light modulator displays a first spatial light attenuation pattern;

(ii) the second spatial light modulator displays a second spatial light attenuation pattern;

(iii) an image projected on the screen comprises a product of the first and second patterns; and

(iv) the image has a higher spatial resolution than the first spatial light modulator and a higher spatial resolution than the second light modulator.

20. The system of claim 19, wherein the image has a higher dynamic range than the first spatial light modulator and a higher dynamic range than the second light modulator.