Waveguide structure
An optical waveguide device for use in a head up display. The waveguide device provides pupil expansion in two dimensions. The waveguide device comprises a primary waveguide and a secondary waveguide, the secondary waveguide being positioned on a face of the primary waveguide. The secondary waveguide has a diffraction grating on a face opposite to the face which contacts the primary waveguide. The diffraction grating diffracts light into more than one diffraction order. Rays diffracted into a non-zero order are trapped in the secondary waveguide by total internal reflection.
1 . An optical waveguide system to be used in a head-up display, the optical waveguide system comprising:
a first optical waveguide and a second optical waveguide assembled such that inner faces and outer faces of each of the first optical waveguide and the second optical waveguide are substantially parallel to one another, the first optical waveguide having a first diffraction grating coupled thereto and the second optical waveguide having a second diffraction grating coupled thereto, the first diffraction grating and the second diffraction grating being arranged in directions such that the gratings are not at right angles to each other, the first diffraction grating and the second diffraction grating further being arranged to partially overlap each other such that an input region of the first optical waveguide is arranged such that light projected into the first optical waveguide within an input-angle range substantially strikes the first diffraction grating without passing through the second diffraction grating, an area of the partial overlap between the first diffraction grating and the second diffraction grating being further arranged such that the first diffraction grating diffracts a portion of light trapped in the first optical waveguide to an angle at which the diffracted light propagates out of the first optical waveguide to strike the second diffraction grating, the second diffraction grating being configured to diffract a portion of light trapped in the second optical waveguide to an angle at which the diffracted light is to propagate out of the second optical waveguide to re-enter the first optical waveguide and strike the first diffraction grating.
2 . The optical waveguide system of claim 1 , wherein at least one of an output region of the first optical waveguide and the second optical waveguide is arranged such that light trapped in at least one of the first optical waveguide and the second optical waveguide by total internal reflection that strikes at least one of the first diffraction grating and the second diffraction grating is to be diffracted into the input angle range to exit the optical waveguide system to an exit pupil substantially without striking the other of the first diffraction grating and the second diffraction grating.
3 . The optical waveguide system of claim 1 , wherein at least one of the first diffraction gratings and the second diffraction grating is configured to diffract reflectively.
4 . The optical waveguide system of claim 1 , wherein at least one of the first diffraction grating and the second diffraction grating is configured to diffract in transmission.
5 . The optical waveguide system of claim 1 , wherein at least one of the first diffraction grating and the second diffraction grating is coated with a reflective coating to preferentially reflect light that is not trapped by total internal reflection.
6 . The optical waveguide system of claim 1 , wherein at least one of the first diffraction grating and the second diffraction grating comprise overlapping layers of profiled material that are configured to combine to produce a phase profile.
7 . The optical waveguide system of claim 6 , wherein the overlapping layers are arranged to approximate a blazed grating shape.
8 . The optical waveguide system of claim 6 , wherein the overlapping layers are formed as a rectangular profiled material.
9 . An optical waveguide system, comprising:
a first optical waveguide and a second optical waveguide arranged substantially parallel to one another, the first optical waveguide having a first diffraction grating and the second optical waveguide having a second diffraction grating, the first diffraction grating and the second diffraction gratings being arranged in directions such that the gratings are not at right angles to each other, the first diffraction grating and the second diffraction grating further being arranged to partially overlap each other, the optical waveguide system configured such that light projected into the first optical waveguide within an input-angle range substantially strikes the first diffraction grating without passing through the second diffraction grating, an area of overlap between the first diffraction grating and the second diffraction grating being arranged such that the first diffraction grating diffracts a portion of light trapped in the first optical waveguide to an angle at which the diffracted light propagates out of the first optical waveguide to strike the second diffraction grating, the second diffraction grating being configured to diffract a portion of light trapped in the second optical waveguide to an angle at which the diffracted light is to propagate out of the second optical waveguide to re-enter the first optical waveguide and strike the first diffraction grating.
10 . The optical waveguide system of claim 9 , wherein at least one of an output region of the first optical waveguide and the second optical waveguide is arranged such that light trapped in at least one of the first optical waveguide and the second optical waveguide by total internal reflection that strikes at least one of the first diffraction grating and the second diffraction grating is to be diffracted into the input angle range to exit the optical waveguide system to an exit pupil substantially without striking the other of the first diffraction grating and the second diffraction grating.
11 . The optical waveguide system of claim 9 , wherein light trapped in at least one of the first optical waveguide and the second optical waveguide that strikes at least one of the first diffraction grating and the second diffraction grating is to be diffracted to exit the optical waveguide system via an exit pupil without further striking the other of the first diffraction grating and the second diffraction grating.
12 . The optical waveguide system of claim 9 , wherein an output region of the first optical waveguide is configured to be oriented in a direction of propagation of light in the first optical waveguide with respect to an input region of the first optical waveguide.
13 . The optical waveguide system of claim 9 , wherein at least one of the first diffraction gratings and the second diffraction grating is configured to diffract reflectively.
14 . The optical waveguide system of claim 9 , wherein at least one of the first diffraction grating and the second diffraction grating is configured to diffract in transmission.
15 . The optical waveguide system of claim 9 , wherein at least one of the first diffraction grating and the second diffraction grating is coated with a reflective coating to preferentially reflect light that is not trapped by total internal reflection.
16 . The optical waveguide system of claim 9 , wherein at least one of the first diffraction grating and the second diffraction grating comprise overlapping layers of profiled material that are configured to combine to produce a phase profile.
17 . The optical waveguide system of claim 16 , wherein the overlapping layers are arranged to approximate a blazed grating shape.
18 . A head-up display, comprising:
a projector configured to project light, and
an optical waveguide system configured to receive the light from the projector, the optical waveguide system comprising:
a first optical waveguide and a second optical waveguide arranged substantially parallel to one another, the first optical waveguide having a first diffraction grating and the second optical waveguide having a second diffraction grating, the first diffraction grating and the second diffraction gratings being arranged in directions such that the gratings are not at right angles to each other, the first diffraction grating and the second diffraction grating further being arranged to partially overlap each other, the optical waveguide system configured such that light projected into the first optical waveguide within an input-angle range substantially strikes the first diffraction grating without passing through the second diffraction grating, an area of overlap between the first diffraction grating and the second diffraction grating being arranged such that the first diffraction grating diffracts a portion of light trapped in the first optical waveguide to an angle at which the diffracted light propagates out of the first optical waveguide to strike the second diffraction grating, the second diffraction grating being configured to diffract a portion of light trapped in the second optical waveguide to an angle at which the diffracted light is to propagate out of the second optical waveguide to re-enter the first optical waveguide and strike the first diffraction grating.
19 . The head-up display of claim 18 , wherein first optical waveguide and the second optical waveguide are separated by an airgap.