Waveguide for head-up display, including reflective output coupling structure
A waveguide structure for a head up display in which a reflective output coupling structure is formed of a separate, but connected, component to a main waveguide. Light is coupled from the main waveguide to the output coupling structure by evanescent wave coupling. In a method of manufacture for such a waveguide the output coupling structure is attached to the main waveguide using an optical feedback technique.
1. An optical waveguide for a head up display, the waveguide comprising:
a waveguide body extending along its length from an input end to an output end and configured to guide light by total internal reflection from the input end to the output end;
an input coupling device at the input end of the waveguide body for coupling light into the waveguide body; and
an output coupling structure adhesively attached to a face of the waveguide body at the output end, wherein there is an air gap between the output coupling structure and a portion of the face of the waveguide body, the air gap being such that light is coupled from the air gap to the output coupling structure by evanescent wave coupling, wherein the output coupling structure has a length along the waveguide body that is less than half of the length of the waveguide body and includes a grating configured to direct light at a predetermined direction out of the optical waveguide by reflection, and wherein no grating structure is present on the face of the waveguide body adjacent to an entirety of the air gap.
2. The optical waveguide according to claim 1 , wherein the output coupling structure is a microstructure.
3. The optical waveguide according to claim 1 , wherein the grating is a saw-tooth grating.
4. The optical waveguide according to claim 1 , further comprising an optical coating on the face of the waveguide body in a region of the air gap.
5. The optical waveguide according to claim 1 , further comprising an optical coating on a face of the output coupling structure in a region of the air gap.
6. The optical waveguide according to claim 1 , wherein the output coupling structure comprises a UV curing material.
7. The optical waveguide according to claim 1 , wherein after being reflected by the output coupling structure, and before leaving the waveguide, the light passes through the waveguide body.
8. The optical waveguide according to claim 7 , wherein the light passes through the waveguide body substantially perpendicular to the face of the waveguide body to which the output coupling structure is attached.
9. The optical waveguide according to claim 1 , further comprising an adhesive, wherein the air gap is defined by a thickness of the adhesive.
10. A method of manufacturing a waveguide for a head up display, the method comprising:
providing a waveguide body having an input end at one end of length of the waveguide body and an output end at an opposite end of the length of the waveguide body; and
attaching, via an adhesive, an output coupling structure to a face of the waveguide body with an air gap between the output coupling structure and a portion of the face of the waveguide body, the air gap being such that light is coupled from the waveguide body to the output coupling structure by evanescent wave coupling, wherein the output coupling structure has a length along the waveguide body that is less than half of the length of the waveguide body and includes a grating configured to direct light at a predetermined direction out of the optical waveguide by reflection, and wherein no grating structure is present on the face of the waveguide body adjacent to an entirety of the air gap.
11. The method according to claim 10 , wherein attaching the output coupling structure to the face of the waveguide body includes using optical feedback to position the output coupling structure.
12. The method according to claim 10 , further comprising applying an optical coating on the face of the waveguide body and/or a face of the output coupling structure in a region of the air gap.
13. The method of manufacturing according to claim 10 , wherein the grating is a saw-tooth grating.
14. The method of manufacturing according to claim 10 , further comprising forming the output coupling structure from optically transmissive material, and wherein the output coupling structure is a microstructure, such that it does not interrupt the vision of a user of the head up display.
15. An optical waveguide for a head up display, the waveguide comprising:
a waveguide body extending along its length from an input end to an output end and configured to guide light by total internal reflection from the input end to the output end;
an input coupling device at the input end of the waveguide body for coupling light into the waveguide body, wherein the input coupling device includes a prism or a diffractive grating; and
an output coupling structure adhesively attached to a face of the waveguide body at the output end, wherein there is an air gap between the output coupling structure and a portion of the face of the waveguide body, the air gap being such that light is coupled from the region to the output coupling structure by evanescent wave coupling, wherein the output coupling structure has a length along the waveguide body that is less than half of the length of the waveguide body and includes a saw-tooth grating configured to reflect light at a predetermined direction out of the optical waveguide, and wherein no grating structure is present on the waveguide body anywhere on the portion of the face of the waveguide body adjacent to an entirety of the air gap.
16. The optical waveguide according to claim 15 , further comprising an optical coating bordering the air gap.
17. The optical waveguide according to claim 15 , further comprising an optical coating on an outward face of the output coupling structure.
18. The optical waveguide according to claim 15 , wherein the output coupling structure is a microstructure, such that it is small enough that it does not interrupt the vision of a user of the head up display.
19. The optical waveguide according to claim 15 , wherein after being reflected by the output coupling structure, and before leaving the waveguide, the light passes through the waveguide body.
20. The optical waveguide according to claim 15 , further comprising an adhesive, wherein the air gap is defined by a thickness of the adhesive.