Optical device
Optical devices and methods for expanding input light and outputting the expanded light include a waveguide and an input optical element to receive light incident on a first side of the waveguide. The input optical element includes an input reflective surface to reflect the received light into the waveguide. An intermediate diffractive optical element receives light in the waveguide from a first direction, and provides an expansion of the received light in a second direction perpendicular to the first direction. An output optical element includes an output reflective surface to reflect the expanded light out of the waveguide towards a viewer. The waveguide guides light along an optical path from the input optical element to the intermediate diffractive optical element and from the intermediate diffractive optical element to the output optical element.
1. An optical device for expanding input light and outputting the expanded light, the optical device comprising:
a waveguide;
an input optical element configured to receive light incident on a first side of the waveguide and comprising a curved, smooth, continuous input reflective surface configured to reflect the received light into the waveguide;
an intermediate diffractive optical element configured to receive light in the waveguide from a first direction, and provide an expansion of the received light in a second direction perpendicular to the first direction; and
an output optical element comprising a curved, smooth, continuous output reflective surface configured to reflect the expanded light out of the waveguide towards a viewer,
wherein the waveguide is configured to guide light along an optical path from the input optical element to the intermediate diffractive optical element and from the intermediate diffractive optical element to the output optical element.
2. An optical device according to claim 1 , wherein the output optical element is configured to reflect light out of the waveguide through the first side.
3. An optical device according to claim 1 , wherein the input optical element is configured to reflect light into the waveguide with a range of angles relative to a plane of the waveguide, such that the received light is expanded by a first expansion factor parallel to its direction of motion within the waveguide.
4. An optical device according to claim 3 , wherein the intermediate diffractive optical element is configured to expand the received light in the second direction by second expansion factor that is a predetermined multiple of the first expansion factor.
5. An optical device according to claim 1 , wherein the intermediate diffractive optical element comprises a first grating oriented at a third angle to light received from the input optical element to provide a first diffraction and a second diffraction within the intermediate diffractive optical element in order to couple light towards the output optical element, wherein the first diffraction couples light from the input optical element towards the first grating at a fourth angle so that the second diffraction is provided at a plurality of spaced positions in the intermediate diffractive optical element thereby providing expansion of light, wherein the second diffraction couples light towards the output optical element.
6. An optical device according to claim 5 , wherein the intermediate diffractive optical element further comprises a second grating oriented at a fifth angle to light received from the input optical element to provide a third diffraction and a fourth diffraction within the intermediate diffractive optical element in order to couple light towards the output optical element, wherein the third diffraction couples light from the input optical element towards the second grating at a fourth angle so that the fourth diffraction is provided at a plurality of spaced positions in the intermediate diffractive optical element thereby providing one-dimensional expansion of light, wherein the fourth diffraction couples light towards the output optical element.
7. An optical device according to claim 6 , wherein the first angle and the third angle are substantially equal and opposite.
8. An optical device according to claim 7 , wherein the first angle is +(45+Δ)° and the third angle is−(45+Δ)°, where Δ is non-zero.
9. An optical device according to claim 6 , wherein the first and second gratings are physically spaced apart on the waveguide.
10. An optical device according to claim 6 , wherein the first and second gratings are at least partially overlaid on one another in the waveguide as a pair of crossed gratings.
11. An optical device according to claim 10 , wherein the first and second gratings are provided on opposing surfaces of the waveguide.
12. An optical device according to claim 10 , wherein the first and second gratings are provided in substantially a same plane in the waveguide.
13. An optical device according to claim 10 , wherein the first and second gratings are provided using a photonic crystal.
14. An optical system comprising:
a projector arranged to project light; and
an optical device for expanding input light and outputting the expanded light, the optical device comprising:
a waveguide;
an input optical element configured to receive light from the projector incident on a first side of the waveguide, and including a curved, smooth, continuous input reflective surface configured to reflect the received light into the waveguide;
an intermediate diffractive optical element configured to receive light in the waveguide from a first direction, and provide an expansion of the received light in a second direction perpendicular to the first direction; and
an output optical element including a curved, smooth, continuous output reflective surface configured to reflect the expanded light out of the waveguide towards a viewer,
the waveguide configured to guide light along an optical path from the input optical element to the intermediate diffractive optical element and from the intermediate diffractive optical element to the output optical element.
15. An optical system according to claim 14 , wherein the projector is configured to project light across an angular field of view of the input optical element.
16. A method, comprising:
projecting light towards a first side of a waveguide;
reflecting received light from the projector incident on the first side into the waveguide through an input optical element comprising a curved, smooth, continuous input reflective surface;
receiving light in the waveguide from a first direction at an intermediate diffractive optical element;
expanding the received light in a second direction perpendicular to the first direction through the intermediate diffractive optical element;
reflecting expanded light from the intermediate diffractive optical element out of the waveguide towards a viewer through an output optical element comprising a curved, smooth, continuous output reflective surface; and
guiding light along an optical path from the input optical element to the intermediate diffractive optical element and from the intermediate diffractive optical element to the output optical element through the waveguide.
17. The method of claim 16 , wherein projecting light comprises projecting light across an angular field of view of the input optical element.
18. The method of claim 16 , wherein reflecting expanded light from the intermediate diffractive optical element out of the waveguide towards a viewer through the output optical element comprises reflecting the expanded light from an output reflective surface of the output optical element.
19. The method of claim 16 , wherein the reflecting expanded light from the intermediate diffractive optical element out of the waveguide towards a viewer through the output optical element comprises reflecting light out of the waveguide through the first side.
20. The method of claim 16 , wherein expanding the received light in the second direction perpendicular to the first direction through the intermediate diffractive optical element comprising expanding the received light in the second direction by second expansion factor that is a predetermined multiple of a first expansion factor associated with expansion parallel to a direction of motion of the received light within the waveguide.