Light projecting method and device

1. A waveguide, comprising: a first surface and a second surface, wherein:

the first surface comprises a first plurality of grating structures;

the first surface other than the first plurality of grating structures comprises a first reflective layer;

the second surface comprises a second reflective layer;

the waveguide is configured to guide an in-coupled light beam to undergo reflections between the first reflective layer and the second reflective layer;

the first plurality of grating structures are configured to disrupt the reflections to cause at least a portion of the in-coupled light beam to couple out of the waveguide and project from the first surface, the portion of the in-coupled light beam coupled out of the waveguide forming out-coupled light beams; and

the out-coupled light beams converge from the first surface to form an upright cone of light on top of the first plurality of grating structures.

2. The waveguide of claim 1 , wherein:

the out-coupled light beams diverge to form an inverted cone of light above the upright cone of light.

3. The waveguide of claim 1 , wherein:

the first surface is in an x-y plane comprising an x-direction and a y-direction perpendicular to each other;

the in-coupled light beam propagates inside the waveguide substantially along the x-direction of the x-y plane;

the out-coupled light beams propagate substantially along a z-direction normal to the x-y plane;

the first plurality of grating structures are each associated with a grating depth and a duty cycle; and

the first plurality of grating structures at different x-direction positions have at least one of different grating depths or different grating duty cycles.

4. The waveguide of claim 1 , wherein:

the first surface is in an x-y plane comprising an x-direction and a y-direction perpendicular to each other;

the in-coupled light beam propagates inside the waveguide substantially along the x-direction of the x-y plane;

the out-coupled light beams propagate substantially along a z-direction normal to the x-y plane;

the first plurality of grating structures are each associated with an orientation in the x-y plane with respect to the z-direction; and

the first plurality of grating structures at different y-direction positions have different orientations.

5. The waveguide of claim 1 , wherein:

the waveguide is a planar waveguide;

the first surface and the second surface are parallel to each other and are the largest surfaces of the planar waveguide; and

the out-coupled light beams couple out of the waveguide from the first surface.

6. The waveguide of claim 1 , wherein:

the waveguide is a planar waveguide;

the first surface and the second surface are parallel to each other and are the largest surfaces of the planar waveguide;

the first plurality of grating structures comprise volumetric gratings between the first surface and the second surface; and

the out-coupled light beams couple out of the waveguide from the first surface.

7. The waveguide of claim 1 , further comprising an elongated third surface, wherein:

a light source couples light into the waveguide via the third surface to form the in-coupled light beam; and

the light from the light source is collimated into a line shape corresponding to the elongated third surface.

8. The waveguide of claim 1 , further comprising a fourth surface, wherein:

a remainder of the in-coupled light beam undergoing the reflections reaches the fourth surface; and

the fourth surface comprises a light-absorbing material layer for absorbing the remainder of the in-coupled light beam.

9. The waveguide of claim 1 , further comprising a second plurality of grating structures on at least one of the first surface or the second surface, wherein:

a light source couples light into the waveguide via the second plurality of grating structures to form the in-coupled light beam.

10. A light projecting system, comprising:

a waveguide comprising a first surface and a second surface, wherein:

the first surface comprises a first plurality of grating structures,

the first surface other than the first plurality of grating structures comprises a first reflective layer, and

the second surface comprises a second reflective layer; and

a light source coupling light into the waveguide to form an in-coupled light beam, wherein:

the waveguide is configured to guide the in-coupled light beam to undergo reflections between the first reflective layer and the second reflective layer,

the first plurality of grating structures are configured to disrupt the reflections to cause at least a portion of the in-coupled light beam to couple out of the waveguide and project from the first surface, the portion of the in-coupled light beam coupled out of the waveguide forming out-coupled light beams, and

the out-coupled light beams converge from the first surface to form an upright cone of light on top of the first plurality of grating structures.

11. The light projecting system of claim 10 , wherein:

the out-coupled light beams diverge to form an inverted cone of light above the upright cone of light.

12. The light projecting system of claim 10 , wherein:

the first surface is in an x-y plane comprising an x-direction and a y-direction perpendicular to each other;

the in-coupled light beam propagates inside the waveguide substantially along the x-direction of the x-y plane;

the out-coupled light beams propagate substantially along a z-direction normal to the x-y plane;

the first plurality of grating structures are each associated with a grating depth and a duty cycle; and

the first plurality of grating structures at different x-direction positions have at least one of different grating depths or different grating duty cycles.

13. The light projecting system of claim 10 , wherein:

the first surface is in an x-y plane comprising an x-direction and a y-direction perpendicular to each other;

the in-coupled light beam propagates inside the waveguide substantially along the x-direction of the x-y plane;

the out-coupled light beams propagate substantially along a z-direction normal to the x-y plane;

the first plurality of grating structures are each associated with an orientation in the x-y plane with respect to the z-direction; and

the first plurality of grating structures at different y-direction positions have different orientations.

14. The light projecting system of claim 10 , wherein:

the waveguide is a planar waveguide;

the first surface and the second surface are parallel to each other and are the largest surfaces of the planar waveguide; and

the out-coupled light beams couple out of the waveguide from the first surface.

15. The light projecting system of claim 10 , wherein:

the waveguide is a planar waveguide;

the first surface and the second surface are parallel to each other and are the largest surfaces of the planar waveguide;

the first plurality of grating structures comprise volumetric gratings between the first surface and the second surface; and

the out-coupled light beams couple out of the waveguide from the first surface.

16. The light projecting system of claim 10 , wherein:

the waveguide further comprises an elongated third surface;

the light source couples the light into the waveguide via the third surface to form the in-coupled light beam; and

the light from the light source is collimated into a line shape corresponding to the elongated third surface.

17. The light projecting system of claim 10 , wherein:

the waveguide further comprises a fourth surface;

a remainder of the in-coupled light beam undergoing the reflections reaches the fourth surface; and

the fourth surface comprises a light-absorbing material layer for absorbing the remainder of the in-coupled light beam.

18. The light projecting system of claim 10 , wherein:

the waveguide further comprises a second plurality of grating structures on at least one of the first surface or the second surface; and

the light source couples the light into the waveguide via the second plurality of grating structures to form the in-coupled light beam.