Waveguide grating with spatial variation of optical phase
An optical waveguide is disclosed. The optical waveguide includes a plate of transparent material comprising opposed first and second surfaces for guiding an optical beam between the surfaces by at least one of reflection or diffraction. A diffraction grating is disposed at the first surface for spreading the optical beam by diffracting portions thereof into a non-zero diffraction order to propagate inside the plate. The first diffraction grating includes an array of parallel grooves structured to provide a spatial variation of optical phase of the portions of the optical beam diffracted by the first diffraction grating into the non-zero diffraction order.
1. An optical waveguide comprising:
a plate of transparent material comprising opposed first and second surfaces for guiding an optical beam therebetween by at least one of reflection or diffraction; and
a first surface-relief diffraction grating at the first surface for spreading the optical beam by diffracting portions thereof into a non-zero diffraction order to propagate inside the plate;
wherein the first surface-relief diffraction grating comprises an array of grooves running parallel to one another and having a spatially varying fill factor to provide a spatial variation of optical phase of the portions of the optical beam diffracted by the first surface-relief diffraction grating into the non-zero diffraction order, to reduce optical interference between the diffracted portions of the optical beam.
2. The optical waveguide of claim 1 , wherein the grooves of the first surface-relief diffraction grating have a spatially varying width to provide the spatially varying fill factor.
3. The optical waveguide of claim 1 , wherein the grooves of the first surface-relief diffraction grating have a spatially varying thickness.
4. The optical waveguide of claim 3 , wherein the grooves of the first surface-relief diffraction grating have a spatially varying width to provide the spatially varying fill factor.
5. The optical waveguide of claim 1 , wherein the fill factor is varying in a periodic pattern.
6. The optical waveguide of claim 5 , wherein a period of the periodic pattern is greater than 2 mm.
7. The optical waveguide of claim 5 , wherein the period of the periodic pattern is greater than 2 mm, and wherein the fill factor is varying in a sinusoidal pattern.
8. The optical waveguide of claim 1 , wherein the fill factor is varying in a pseudo-random pattern.
9. The optical waveguide of claim 1 , wherein the spatial variation of optical phase is no greater than 27c.
10. The optical waveguide of claim 1 , further comprising a second diffraction grating at the second surface for outputting the optical beam by diffracting portions thereof to propagate out of the plate.
11. The optical waveguide of claim 10 , wherein the second diffraction grating is laterally offset from the first surface-relief diffraction grating in a direction of diffraction of the portions of the optical beam on the first surface-relief diffraction grating.
12. The optical waveguide of claim 10 , wherein the second diffraction grating is disposed opposite the first surface-relief diffraction grating and comprises an array of grooves running parallel to one another and structured to provide a spatial variation of optical phase of the portions of the optical beam diffracted by the second diffraction grating.
13. The optical waveguide of claim 1 , further comprising an input coupler for coupling the optical beam into the optical waveguide.
14. An optics block for a near-eye display, the optics block comprising the waveguide of claim 13 and an image source optically coupled to the input coupler for providing the optical beam thereto, wherein in operation, the optical beam carries an image to be displayed by the near-eye display.
15. The optics block of claim 14 , wherein the grooves of the first surface-relief diffraction grating have a spatially varying width to provide the spatially varying fill factor.
16. The optics block of claim 14 , further comprising a second diffraction grating at the second surface of the plate of transparent material, wherein the second diffraction grating is configured for outputting the optical beam by diffracting portions thereof to propagate out of the plate.
17. A method for reducing a spatial variation of throughput of an optical waveguide comprising a plate of transparent material having opposed first and second surfaces for guiding an optical beam therebetween by at least one of reflection or diffraction, the method comprising:
providing a first surface-relief diffraction grating at the first surface of the plate, for spreading the optical beam by diffracting portions thereof into a non-zero diffraction order to propagate inside the plate;
wherein the first surface-relief diffraction grating comprises an array of grooves running parallel to one another and having a spatially varying fill factor to provide a spatial variation of optical phase of the portions of the optical beam diffracted by the first surface-relief diffraction grating into the non-zero diffraction order, to reduce optical interference between the diffracted portions of the optical beam.
18. The method of claim 17 , wherein the grooves of the first surface-relief diffraction grating have a spatially varying width to provide the spatially varying fill factor.
19. The method of claim 18 , wherein the fill factor is varying in a periodic pattern.
20. The method of claim 17 , wherein the fill factor is varying in a pseudo-random pattern.