Systems and methods for optical imaging based on diffraction gratings

1. A device, comprising:

a light guide configured to receive incident light from a light source;

a cover layer with a sensing surface configured to receive an input object to be sensed; and

a set of photodetectors;

wherein the light guide includes a plurality of diffraction gratings configured to diffract the incident light as diffracted light, wherein the diffracted light exits the light guide and travels towards the sensing surface, the diffracted light is reflected from the sensing surface as reflected light, and the reflected light is sensed by the set of photodetectors to form an image of the input object;

wherein the plurality of diffraction gratings includes at least one grating structure within each diffraction grating of the plurality of diffraction gratings; and

wherein, for each diffraction rating of the plurality of diffraction gratings, a length of the at least one grating structure in the diffraction grating increases in proportion to a distance of the diffraction grating from the light source.

2. The device of claim 1 , wherein the diffracted light travels towards the sensing surface at an angle that causes the diffracted light that is incident on a portion of the input object to be partially transmitted through the input object and causes the diffracted light that is not incident on a portion of the input object to be reflected from the sensing surface.

3. The device of claim 1 , wherein each diffraction grating in the plurality of diffraction gratings comprises two or more grating structures.

4. The device of claim 3 ,

wherein the plurality of diffraction gratings includes a first diffraction grating and a second diffraction grating;

wherein each grating structure in the first diffraction grating has a first length;

wherein each grating structure in the second diffraction grating has a second length;

wherein the second diffraction grating is located a greater distance away from the light source than the first diffraction grating; and

wherein the second length is greater than the first length.

5. The device of claim 3 , wherein the two or more grating structures comprise grooves or bumps formed on the light guide.

6. The device of claim 5 , wherein the grooves or bumps are formed by chemical etching, embossing, molding, stamping, or printing.

7. The device of claim 1 , further comprising:

a display layer comprising a set of display pixels.

8. The device of claim 7 , wherein the light guide is disposed between the display layer and the cover layer.

9. The device of claim 7 , wherein the display layer is disposed between the light guide and the cover layer.

10. The device of claim 7 , wherein the set of photodetectors is disposed between the light guide and the display layer.

11. The device of claim 1 , wherein the light guide comprises a film that is disposed on the cover layer.

12. The device of claim 1 , wherein the light source is configured to emit incident light of one or more wavelengths, and the plurality of diffraction gratings are configured to diffract the incident light based on the one or more wavelengths.

13. A light guide, comprising:

a substrate; and

a plurality of diffraction gratings;

wherein:

the substrate is configured to receive incident light from a light source;

the plurality of diffraction gratings is configured to diffract the incident light as diffracted light, wherein the diffracted light exits the light guide and travels towards a sensing surface configured to receive an input object to be sensed;

the plurality of diffraction gratings includes at least one grating structure within each diffraction grating of the plurality of diffraction gratings; and

for each diffraction grating of the plurality of diffraction gratings, a length of the at least one grating structure in the diffraction grating increases in proportion to a distance of the diffraction grating from the light source.

14. The light guide of claim 13 ,

wherein each diffraction grating in the plurality of diffraction gratings comprises two or more grating structures;

wherein the plurality of diffraction gratings includes a first diffraction grating and a second diffraction grating;

wherein each grating structure in the first diffraction grating has a first length;

wherein each grating structure in the second diffraction grating has a second length;

wherein the second diffraction grating is located a greater distance away from the light source than the first diffraction grating; and

wherein the second length is greater than the first length.

15. The light guide of claim 14 , wherein the grooves or bumps are formed by chemical etching, embossing, molding, stamping, or printing.

16. The light guide of claim 13 , wherein the substrate comprises a film and the plurality of diffraction gratings is formed on the film.

17. The light guide of claim 13 , wherein the light guide is disposed between a display layer that comprises a set of display pixels and the sensing surface.

18. The light guide of claim 13 , wherein a display layer that comprises a set of display pixels is disposed between the light guide and the sensing surface.

19. The light guide of claim 13 , wherein the light guide is disposed within a display layer of an electronic device that comprises a set of display pixels.

20. A method for performing optical sensing, the method comprising:

receiving light from a light source into a light guide;

diffracting the light using a plurality of diffraction gratings to cause diffracted light to exit the light guide, where the diffracted light is reflected from a sensing surface as reflected light; and

detecting the reflected light using one or more photodetectors to form an image of an input object placed on the sensing surface;

wherein the diffracted light travels towards the sensing surface at an angle that causes the diffracted light that is incident on a portion of the input object to be partially transmitted through the input object and causes the diffracted light that is not incident on a portion of the input object to be reflected from the sensing surface;

wherein the plurality of diffraction gratings includes at least one grating structure within each diffraction grating of the plurality of diffraction gratings; and

wherein, for each diffraction grating of the plurality of diffraction gratings, a length of the at least one grating structure in the diffraction grating increases in proportion to a distance of the diffraction grating from the light source.