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 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 diffraction grating comprises an array of grooves running parallel to one another and meandering in a plane of the first diffraction grating 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.
2. The optical waveguide of claim 1 , wherein the grooves are spaced apart at a first grating pitch, wherein an amplitude of meander of the grooves is no greater than the first grating pitch.
3. The optical waveguide of claim 2 , wherein the amplitude of meander is spatially varying.
4. The optical waveguide of claim 1 , wherein the grooves are meandering in a periodic pattern.
5. The optical waveguide of claim 4 , wherein a period of the periodic pattern is greater than 2 mm.
6. The optical waveguide of claim 5 , wherein the period of the periodic pattern is greater than 2 mm and an amplitude of meander of the grooves is no greater than 500 nm.
7. The optical waveguide of claim 1 , wherein the grooves are meandering in a pseudo-random pattern.
8. The optical waveguide of claim 1 , wherein the first diffraction grating comprises a surface-relief diffraction grating.
9. The optical waveguide of claim 8 , wherein the grooves of the surface relief diffraction grating have a spatially varying fill factor for providing the spatial variation of optical phase of the portions of the optical beam diffracted by the first diffraction grating.
10. The optical waveguide of claim 1 , wherein the spatial variation of optical phase is no greater than 2π.
11. 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.
12. The optical waveguide of claim 11 , wherein the second diffraction grating is laterally offset from the first diffraction grating in a direction of diffraction of the portions of the optical beam on the first diffraction grating.
13. The optical waveguide of claim 11 , wherein the second diffraction grating is disposed opposite the first 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.
14. The optical waveguide of claim 1 , further comprising an input coupler for coupling the optical beam into the optical waveguide.
15. An optics block for a near-eye display, the optics block comprising the waveguide of claim 14 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.
16. 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 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 diffraction grating comprises an array of grooves running parallel to one another and meandering in a plane of the first diffraction grating 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.
17. The method of claim 16 , wherein the grooves are spaced apart at a first grating pitch, wherein an amplitude of meander of the grooves is no greater than the first grating pitch.
18. The method of claim 16 , wherein the grooves of the first diffraction grating have a spatially varying duty cycle for providing the spatial variation of optical phase of the portions of the optical beam diffracted by the first diffraction grating.