Optical system having an improved signal-to-noise ratio of eye-tracking

1. A system, comprising:

a polarizer;

a grating structure configured to diffract a first input light as a first output light toward the polarizer; and

at least one substrate coupled to the grating structure, a surface of the at least one substrate configured to reflect a second input light as a substantially s-polarized light toward the polarizer,

wherein the first input light and the second input light are incident onto the grating structure and the at least one substrate, respectively, from a side where the polarizer is located, and

wherein the polarizer is configured to transmit the first output light diffracted by the grating structure and block the substantially s-polarized light reflected by the surface of the at least one substrate.

2. The system of claim 1 , further comprising:

an optical sensor disposed facing the grating structure and configured to receive the first output light that is diffracted by the grating structure and transmitted through the polarizer.

3. The system of claim 1 ,

wherein the substantially s-polarized light reflected by the surface of the at least one substrate and the first output light diffracted by the grating structure have different polarizations.

4. The system of claim 1 , wherein the grating structure includes a polarization volume hologram (“PVH”) layer.

5. The system of claim 4 , wherein the grating structure including the PVH layer is configured to diffract a polarized light having a first predetermined handedness, and to transmit a polarized light having second predetermined handedness that is opposite to the first predetermined handedness.

6. The system of claim 5 , further comprising a waveplate disposed between the grating structure and the polarizer.

7. The system of claim 6 , wherein the waveplate is a quarter-wave plate for an infrared spectrum.

8. An optical system, comprising:

at least one substrate;

a grating structure coupled to the at least one substrate, the grating structure configured to diffract a first light having an incidence angle within a predetermined range; and

a polarizer configured to transmit the first light diffracted by the grating structure and block a second light reflected by a surface of the at least one substrate,

wherein the grating structure is a polarization volume hologram (“PVH”) grating,

wherein the at least one substrate includes a first substrate and a second substrate arranged opposite to the first substrate,

wherein the first substrate and the second substrate are disposed at opposing first and second sides of the PVH grating to sandwich the PVH grating, and

a quarter-wave plate disposed between the PVH grating and the first substrate.

9. The system of claim 1 , wherein the grating structure is a volume Bragg grating (“VBG”).

10. The system of claim 1 , wherein the first input light has an incidence angle within a first predetermined range of 0 degree to 35 degrees.

11. The system of claim 1 , further comprising a light source configured to emit an infrared light, wherein the first input light and the second input light are both infrared light.

12. An eye-tracking system, comprising:

a light source configured to emit a light to illuminate an eye of a user;

a polarizer;

a grating structure disposed facing the eye and configured to diffract a first input light reflected from the eye as a first output light toward the polarizer; and

at least one substrate coupled to the grating structure, a surface of the at least one substrate configured to reflect a second input light reflected from the eye as a substantially s-polarized light toward the polarizer,

wherein the first input light and the second input light are incident onto the grating structure and the at least one substrate, respectively, from a side where the polarizer is located, and

wherein the polarizer is configured to transmit the first output light diffracted by the grating structure, and to block the substantially s-polarized light reflected by the surface of the at least one substrate; and

an optical sensor configured to receive the first output light transmitted through the polarizer and generate an image of the eye based on the received first output light.

13. The eye-tracking system of claim 12 , wherein the first output light diffracted by the grating structure and the substantially s-polarized light reflected by the surface of the at least one substrate have different polarizations.

14. The eye-tracking system of claim 12 , wherein the grating structure includes a polarization volume hologram (“PVH”) layer configured to diffract a polarized light having a first predetermined handedness, and to transmit a polarized light having a second predetermined handedness that is opposite to the first predetermined handedness.

15. The eye-tracking system of claim 14 , further comprising a quarter-wave plate for an infrared spectrum disposed between the grating structure and the polarizer.

16. The eye-tracking system of claim 12 , wherein the grating structure is a volume Bragg grating (“VBG”).

17. The system of claim 1 , wherein the second input light has an incidence angle within a second predetermined range of 45° to 75° in air.

18. The system of claim 1 , wherein the first input light is incident onto the grating structure from air, and the second input light is incident onto the at least one substrate from air.

19. The system of claim 8 , wherein the first light is incident onto the grating structure from air, and the second light is incident onto the surface of the at least one substrate from air at an incidence angle in a range of 45° to 75° in air.