Optical waveguide for head up display, and manufacturing method therefor
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. In a method of manufacture for such a waveguide the output coupling structure may be formed by depositing a material on a main waveguide, impressing the reflective structure into that material, and curing the material.
1. An optical waveguide for a head up display, the waveguide comprising:
a waveguide body extending 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, the waveguide body having optically flat and parallel outward-facing surfaces;
an input coupling device at the input end of the waveguide body for coupling light into the waveguide body; and
an output coupling structure attached to one of the outward-facing surfaces outside of the waveguide body at the output end, the output coupling structure distinct from the waveguide body, wherein the output coupling structure includes a reflective structure configured to direct light out of the optical waveguide by reflection,
wherein the output coupling structure includes a flat-topped saw-tooth grating to direct light out of the optical waveguide, the flat-topped saw-tooth grating having a flat top surface parallel to the outward-facing surfaces of the waveguide body.
2. The optical waveguide according to claim 1 , wherein the input coupling device includes a prism or a diffractive grating.
3. The optical waveguide according to claim 1 , wherein the saw-tooth grating is graded along a propagation axis of the waveguide body to provide varying reflectivity.
4. The optical waveguide according to claim 3 , wherein the saw-tooth grating is graded by varying the size, depth, or spacing of features of the grating along the propagation axis.
5. The optical waveguide according to claim 1 , further comprising an optical coating between the waveguide body and the output coupling structure.
6. The optical waveguide according to claim 1 , further comprising an optical coating on an exposed face of the output coupling structure.
7. The optical waveguide according to claim 1 , wherein the output coupling structure comprises a transmissive UV curing material.
8. A method of manufacturing a waveguide for a head up display, the method comprising:
providing a waveguide body having an input end, an output end, and optically flat and parallel outward-facing surfaces;
attaching an optically transmissive material to one of the outward-facing surfaces outside of the waveguide body at an output coupling region at the output end;
impressing into the optically transmissive material a reflective structure; and
curing the optically transmissive material to form an output coupling device.
9. The method according to claim 8 , wherein the curing comprises exposing the transmissive material to UV light.
10. The method according to claim 8 , wherein the optically transmissive material is attached in liquid or gel-like form.
11. The method according to claim 8 , further comprising applying an optical coating between the waveguide body and the optically transmissive material.
12. The method according to claim 8 , further comprising applying an optical coating to an exposed surface of the output coupling device.
13. The method according to claim 8 , wherein the output coupling structure includes a flat-topped saw-tooth grating, the flat-topped saw-tooth grating having a flat top surface parallel to the outward-facing surfaces of the waveguide body.
14. The method according to claim 8 , wherein the output coupling structure includes a saw-tooth grating, graded along a propagation axis of the waveguide body to provide varying reflectivity.
15. An optical waveguide for a head up display, the waveguide comprising:
a waveguide body extending 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, the waveguide body having optically flat and parallel outward-facing surfaces;
an input coupling device at the input end of the waveguide body for coupling light into the waveguide body; and
an output coupling structure attached to one of the outward-facing surfaces outside of the waveguide body at the output end, the output coupling structure distinct from the waveguide body, wherein the output coupling structure includes a reflective structure configured to direct light out of the optical waveguide by reflection; and
at least one of
an optical coating between the waveguide body and the output coupling structure, and
an optical coating on an exposed face of the output coupling structure.
16. The optical waveguide according to claim 15 , wherein the output coupling structure includes a flat-topped saw-tooth grating configured to reflect light out of the optical waveguide, the flat-topped saw-tooth grating having a flat top surface parallel to the outward-facing surfaces of the waveguide body.
17. The optical waveguide according to claim 15 , wherein the output coupling structure comprises a transmissive UV curing material.
18. The optical waveguide according to claim 16 , wherein the saw-tooth grating is graded along a propagation axis of the waveguide body to provide varying reflectivity.
19. The optical waveguide according to claim 18 , wherein the saw-tooth grating is graded by varying the size, depth, or spacing of features of the grating along the propagation axis.