Full-color waveguide combiner with embedded metagrating

An optical method comprising:

• providing light having at least first and second colors at an input region of a waveguide, wherein the waveguide includes a first surface and a second surface substantially opposite the first surface, and wherein the input region includes a reflective diffractive in-coupler in the waveguide between the first and second surfaces and a first transmissive diffractive in-coupler in the waveguide between the reflective diffractive in-coupler and the second surface, wherein a spacing between the reflective diffractive in-coupler and the first transmissive diffractive in-coupler is no greater than 400 nm;
• coupling light of the first color into the waveguide using the reflective diffractive in-coupler;
• and
• coupling light of the second color into the waveguide using the first transmissive diffractive in-coupler.

A method of manufacturing an optical system, the method comprising:

• forming a first diffraction grating on a first waveguide substrate layer;
• forming a second diffraction grating on a second waveguide substrate layer;
• and
• combining the first and second waveguide substrate layers into a combined waveguide with the first and second diffraction gratings on the interior of the combined waveguide, wherein a spacing between the first diffraction grating and the second diffraction grating in the combined waveguide is no greater than 400 nm.