Systems, devices, and methods for exit pupil expansion in a curved lens with embedded light guide
Systems, devices, and methods for for exit pupil expansion in a curved lens with embedded light guide are described. Exit pupil expansion in a curved lens may be achieved with a light guide comprising an outcoupler with minimized second order diffraction, where the outcoupler applies an optical power to outcoupled light.
1. A surface relief grating-based outcoupler comprising:
a set of ridges having:
a grating period;
a duty cycle; and
a modulation height,
wherein the duty cycle and the modulation height are varied as a function of propagation distance along the outcoupler and provide:
a second order diffraction efficiency for the outcoupler that is less than or equal to a first target value; and
a first order diffraction efficiency for the outcoupler that is sub-maximal and greater than or equal to a second target value.
2. The outcoupler of claim 1 wherein the grating period minimizes a variation of a diffraction efficiency of the outcoupler as a function of wavelength.
3. The outcoupler of claim 1 wherein the grating period is greater than or equal to half of a longest wavelength of light to be outcoupled by the outcoupler, and wherein the grating period is less than or equal to two times a shortest wavelength of light to be outcoupled by the outcoupler.
4. The outcoupler of claim 1 wherein the first target value is a minimum value for the second order diffraction efficiency of the outcoupler, and wherein the duty cycle and the modulation height provide a second order diffraction efficiency for the outcoupler that is equal to the first target value.
5. The outcoupler of claim 1 wherein the outcoupler is operative to outcouple a red wavelength of light, a green wavelength of light, and a blue wavelength of light, and wherein the duty cycle and the modulation height provide:
a second order diffraction efficiency for the outcoupler that is less than or equal to the first target value for each of the red wavelength of light, the green wavelength of light, and the blue wavelength of light; and
a first order diffraction efficiency for the outcoupler that is sub-maximal and greater than or equal to the second target value for each of the red wavelength of light, the green wavelength of light, and the blue wavelength of light.
6. The outcoupler of claim 5 wherein the red wavelength of light is about 640 nm, the green wavelength of light is about 520 nm, and the blue wavelength of light is about 450 nm, and wherein:
the grating period is in a range of 320 nm-900 nm;
the duty cycle is in a range selected from a group consisting of: 15%-30% and 65%-95%; and
the modulation height is in a range of 20 nm-100 nm.
7. The outcoupler of claim 6 wherein the grating period is in a range of 320 nm to 450 nm, the duty cycle is in a range of 67%-77%, and the modulation height is in a range of 50 nm-100 nm.
8. The outcoupler of claim 1 wherein the outcoupler is operative to provide an optical power to light outcoupled thereby, the optical power to compensate for a curvature of an eye-side surface of a lens into which the outcoupler is to be embedded.
9. A lightguide comprising:
a volume of optically transparent material;
an incoupler carried by the volume of optically transparent material; and
an outcoupler carried by the volume of optically transparent material, wherein the outcoupler comprises:
a set of ridges having:
a grating period;
a duty cycle; and
a modulation height, wherein the duty cycle and the modulation height are varied as a function of propagation distance along the outcoupler and provide:
a second order diffraction efficiency for the outcoupler that is less than or equal to a first target value; and
a first order diffraction efficiency for the outcoupler that is sub-maximal and greater than or equal to a second target value.
10. The lightguide of claim 9 wherein the grating period minimizes a variation of a diffraction efficiency of the outcoupler as a function of wavelength.
11. The lightguide of claim 9 wherein the first target value is a minimum value for the second order diffraction efficiency of the outcoupler, and wherein the duty cycle and the modulation height provide a second order diffraction efficiency for the outcoupler that is equal to the first target value.
12. The lightguide of claim 9 wherein the outcoupler is operative to outcouple a red wavelength of light, a green wavelength of light, and a blue wavelength of light, and wherein the duty cycle and the modulation height provide:
a second order diffraction efficiency for the outcoupler that is less than or equal to the first target value for each of the red wavelength of light, the green wavelength of light, and the blue wavelength of light; and
a first order diffraction efficiency for the outcoupler that is sub-maximal and greater than or equal to the second target value for each of the red wavelength of light, the green wavelength of light, and the blue wavelength of light.
13. The lightguide of claim 12 wherein the red wavelength of light is about 640 nm, the green wavelength of light is about 520 nm, and the blue wavelength of light is about 450 nm, and wherein:
the grating period is in a range of 320 nm-900 nm;
the duty cycle is in a range selected from a group consisting of: 15%-30% and 65%-95%; and
the modulation height is in a range of 20 nm-100 nm.
14. The lightguide of claim 9 wherein the outcoupler is operative to provide an optical power to light outcoupled thereby, the optical power to compensate for a curvature of an eye-side surface of a lens into which the lightguide is to be embedded.
15. An eyeglass lens comprising:
a curved lens; and
a lightguide embedded in the curved lens, wherein the lightguide comprises:
a volume of optically transparent material;
an incoupler carried by the volume of optically transparent material; and
an outcoupler carried by the volume of optically transparent material, wherein the outcoupler comprises:
a set of ridges having:
a grating period;
a duty cycle; and
a modulation height,
wherein the grating period, duty cycle, and the modulation height are varied as a function of propagation distance along the outcoupler and provide:
a second order diffraction efficiency for the outcoupler that is less than or equal to a first target value; and
a first order diffraction efficiency for the outcoupler that is sub-maximal and greater than or equal to a second target value.
16. The eyeglass lens of claim 15 wherein the grating period minimizes a variation of a diffraction efficiency of the outcoupler as a function of wavelength.
17. The eyeglass lens of claim 15 wherein the first target value is a minimum value for the second order diffraction efficiency of the outcoupler, and wherein the duty cycle and the modulation height provide a second order diffraction efficiency for the outcoupler that is equal to the first target value.
18. The eyeglass lens of claim 15 wherein the outcoupler is operative to outcouple a red wavelength of light, a green wavelength of light, and a blue wavelength of light, and wherein the duty cycle and the modulation height provides:
a second order diffraction efficiency for the outcoupler that is less than or equal to the first target value for each of the red wavelength of light, the green wavelength of light, and the blue wavelength of light; and
a first order diffraction efficiency for the outcoupler that is sub-maximal and greater than or equal to the second target value for each of the red wavelength of light, the green wavelength of light, and the blue wavelength of light.
19. The eyeglass lens of claim 18 wherein the red wavelength of light is about 640 nm, the green wavelength of light is about 520 nm, and the blue wavelength of light is about 450 nm, and wherein:
the grating period is in a range of 320 nm-900 nm;
the duty cycle is in a range selected from a group consisting of: 15%-30% and 65%-95%; and
the modulation height is in a range of 20 nm-100 nm.
20. The eyeglass lens of claim 15 wherein the curved lens includes an eye-side surface having a curvature, and wherein the outcoupler is operative to provide an optical power to light outcoupled thereby, the optical power to compensate for the curvature of the eye-side surface of the curved lens.