SINGLE MODE FULL COLOR WAVEGUIDE COMBINER USING ASYMMETRIC TRANSMISSIVE AND REFLECTIVE DIFFRACTION GRATINGS

1 . An optical system comprising:

a waveguide substrate;

a diffractive coupler associated with the waveguide substrate, the diffractive coupler comprising at least two diffraction gratings;

wherein each of the diffraction gratings includes a first layer of grating elements and a second layer of grating elements, the first and second layers of grating elements being arranged in different planes, the first and second layers of grating elements having a same grating period associated with the respective diffraction grating, and the grating elements of the second layer having a lateral offset with respect to the grating elements of the first layer.

2 . The optical system of claim 1 , wherein the at least two diffraction gratings include a first diffraction grating (DG 2 ) overlaying the waveguide substrate and a second diffraction grating (DG 1 ) overlaying the first diffraction grating.

3 . The optical system of claim 1 , wherein:

the waveguide substrate has a first surface and a second surface substantially opposite the first surface; and

the at least two diffraction gratings are embedded in the waveguide substrate between the first surface and the second surface.

4 . The optical system of claim 1 , wherein:

the waveguide substrate has a first surface and a second surface substantially opposite the first surface;

and the at least two diffraction gratings include a first diffraction grating (DG 2 ) on the first surface and a second diffraction grating (DG 1 ) on the second surface.

5 . The optical system of claim 1 , wherein the at least two diffraction gratings have different associated grating periods.

6 . The optical system of claim 1 , wherein the at least two diffraction gratings have the same associated grating period.

7 . The optical system of claim 1 , wherein the waveguide substrate has a refractive index and grating elements of the at least two diffraction gratings have a refractive index greater than the refractive index of the waveguide substrate.

8 . The optical system of claim 1 , further comprising a phase-modifying layer between the first and second layers of grating elements of at least one of the diffraction gratings.

9 . The optical system of claim 1 , further comprising a stop layer between the first and second layers of grating elements of at least one of the diffraction gratings.

10 . The optical system of claim 1 , further comprising a stop layer between the waveguide substrate and at least one of the diffraction gratings.

11 . The optical system of claim 1 , wherein the grating elements of the at least two diffraction gratings have a substantially rectangular cross-section.

12 . The optical system of claim 1 , wherein a first diffraction grating of the at least two diffraction gratings is a transmissive diffraction grating and a second diffraction grating of the at least two diffraction gratings is a reflective diffraction grating.

13 . The optical system of claim 12 , further comprising a metallized surface over the second diffraction grating.

14 . The optical system of claim 1 , wherein the grating elements in any one of the layers of grating elements are not in contact with grating elements any other of the layers of grating elements.

15 . The optical system of claim 1 , wherein the coupler is asymmetric.

16 . A waveguide display comprising an image generator and an optical system, the optical system comprising:

a waveguide substrate;

a diffractive coupler associated with the waveguide substrate, the diffractive coupler comprising at least two diffraction gratings;

wherein each of the diffraction gratings includes a first layer of grating elements and a second layer of grating elements, the first and second layers of grating elements being arranged in different planes, the first and second layers of grating elements having a same grating period associated with the respective diffraction grating, and the grating elements of the second layer having a lateral offset with respect to the grating elements of the first layer.

17 . A method comprising generating an image and coupling the image into a waveguide, the waveguide comprising:

a waveguide substrate;

a diffractive coupler associated with the waveguide substrate, the diffractive coupler comprising at least two diffraction gratings;

wherein each of the diffraction gratings includes a first layer of grating elements and a second layer of grating elements, the first and second layers of grating elements being arranged in different planes, the first and second layers of grating elements having a same grating period associated with the respective diffraction grating, and the grating elements of the second layer having a lateral offset with respect to the grating elements of the first layer.

18 . The method of claim 17 , wherein the at least two diffraction gratings include a first diffraction grating overlaying the waveguide substrate and a second diffraction grating overlaying the first diffraction grating.

19 . The method of claim 17 , wherein:

the waveguide substrate has a first surface and a second surface substantially opposite the first surface; and

the at least two diffraction gratings are embedded in the waveguide substrate between the first surface and the second surface.

20 . The method of claim 17 , wherein:

the waveguide substrate has a first surface and a second surface substantially opposite the first surface;

and the at least two diffraction gratings include a first diffraction grating on the first surface and a second diffraction grating on the second surface.