Depth-varying light fields for three dimensional sensing

1. A method for imaging, comprising:

defining a first optical constraint such that application of the first optical constraint to a beam of light splits the beam into a pattern of multiple spots;

defining a second optical constraint such that application of the second optical constraint to the beam of light causes the beam to form a spot having a shape characteristic that changes in a predefined manner as a function of a distance along an axis of the beam;

designing a first filter to implement the first optical constraint and a second filter, different from the first filter, to implement the second optical constraint;

creating at least one optical element as a superposition of the first and second filters; and

directing a beam of light through the at least one optical element so as to project the pattern onto a surface such that the multiple spots in the pattern have the shape characteristic.

2. The method according to claim 1 , wherein the at least one optical element comprises a first optical element, comprising the first filter, for splitting the beam into the pattern and a second optical element, comprising the second filter, for applying the shape characteristic.

3. The method according to claim 2 , wherein the pattern comprises a speckle pattern.

4. The method according to claim 3 , wherein the first optical element comprises a diffuser.

5. The method according to claim 1 , wherein the at least one optical element comprises a diffractive optical element (DOE).

6. The method according to claim 5 , wherein the DOE comprises at least one zone plate for imparting an elongate shape to the spots.

7. The method according to claim 6 , wherein the at least one zone plate comprises a plurality of superposed zone plates, having different, respective periods and angular orientations so as to cause the elongate shape of the spots to rotate as a function of the distance.

8. The method according to claim 1 , wherein the at least one optical element comprises a refractive optical element.

9. The method according to claim 1 , wherein the pattern defined by the first optical constraint has a duty cycle that is no greater than ¼.

10. The method according to claim 1 , wherein the pattern defines respective positions of the spots such that the positions are uncorrelated.

11. The method according to claim 1 , wherein the second optical constraint causes the spot to have an elongate shape, which rotates as a function of the distance.

12. The method according to claim 1 , wherein the second optical constraint causes the spot to have an annular shape.

13. The method according to claim 1 , and comprising capturing an image of the spots on the surface, and processing the image so as to determine the distance of the surface from the at least one optical element.

14. Apparatus for imaging, comprising:

at least one optical element, which is designed as a superposition of different, first and second filters, which respectively implement first and second optical constraints, such that application of the first optical constraint to a beam of light splits the beam into a pattern of multiple spots, and application of the second optical constraint to the beam of light causes the beam to form a spot having a shape characteristic that changes in a predefined manner as a function of a distance along an axis of the beam; and

a light source, which is configured to direct a beam of light through the at least one optical element so as to project the pattern onto a surface such that the multiple spots in the pattern have the shape characteristic.

15. The apparatus according to claim 14 , wherein the at least one optical element comprises a first optical element, comprising the first filter, for splitting the beam into the pattern and a second optical element, comprising the second filter, for applying the shape characteristic.

16. The apparatus according to claim 15 , wherein the pattern comprises a speckle pattern.

17. The apparatus according to claim 16 , wherein the first optical element comprises a diffuser.

18. The apparatus according to claim 14 , wherein the at least one optical element comprises a diffractive optical element (DOE).

19. The apparatus according to claim 18 , wherein the DOE comprises at least one zone plate for imparting an elongate shape to the spots.

20. The apparatus according to claim 19 , wherein the at least one zone plate comprises a plurality of superposed zone plates, having different, respective periods and angular orientations so as to cause the elongate shape of the spots to rotate as a function of the distance.

21. The apparatus according to claim 14 , wherein the at least one optical element comprises a refractive optical element.

22. The apparatus according to claim 14 , wherein the pattern defined by the first optical constraint has a duty cycle that is no greater than ¼.

23. The apparatus according to claim 14 , wherein the pattern defines respective positions of the spots such that the positions are uncorrelated.

24. The apparatus according to claim 14 , wherein the second optical constraint causes the spot to have an elongate shape, which rotates as a function of the distance.

25. The apparatus according to claim 14 , wherein the second optical constraint causes the spot to have an annular shape.

26. The apparatus according to claim 14 , and comprising an imaging assembly, which is configured to capture an image of the spots on the surface, and an image processor, which is coupled to process the image so as to determine the distance of the surface from the at least one optical element.

27. A method for imaging, comprising:

defining a target pattern of multiple spots as a convolution of at least first and second patterns of different types;

superposing at least first and second filters, which are designed to create the first and second patterns, respectively; and

directing a beam of light through the superposed filters so as to project the target pattern onto a surface.

28. The method according to claim 27 , wherein superposing at least the first and second filters comprises providing a first optical element comprising the first filter and a second optical element comprising the second filter.

29. The method according to claim 27 , wherein at least one of the first and second filters comprises a diffractive optical element.

30. The method according to claim 27 , wherein at least one of the first and second filters comprises multiple micro-lenses.

31. The method according to claim 27 , and comprising capturing an image of the spots on the surface, and processing the image so as to construct a three-dimensional map of the surface.

32. Apparatus for imaging, comprising:

a first filter and a second filter, which are together configured to create, by superposition of the first and second filters, a target pattern of multiple spots, which is a convolution of a first pattern created by the first filter and a second pattern, of a different type from the first pattern, created by the second filter; and

a light source, which is configured to direct a beam of light through the first and second filters in superposition so as to project the target pattern onto a surface.

33. The apparatus according to claim 32 , and comprising a first optical element comprising the first filter and a second optical element comprising the second filter.

34. The apparatus according to claim 32 , wherein at least one of the first and second filters comprises a diffractive optical element.

35. The apparatus according to claim 32 , wherein at least one of the first and second filters comprises multiple micro-lenses.

36. The apparatus according to claim 32 , and comprising an imaging assembly, which is configured to capture an image of the spots on the surface, and an image processor, which is coupled to process the image so as to construct a three-dimensional map of the surface.