Microsoft patents thinner lens coating for mixed reality glasses

1. A near-eye mixed-reality optical system in which holographic images are mixed in with views of a real world, comprising: a see-through planar optical waveguide through which real-world images are viewable by a user of the mixed-reality optical system, the optical waveguide including a first planar side and a second planar side opposite the first planar side; a first diffractive optical element (DOE) disposed on a surface of one of the planar sides of the optical waveguide, the first DOE having an input region and configured as an in-coupling grating to in-couple, at the input region, one or more optical beams associated with holographic images from a holographic image source; a second DOE disposed on a surface of one of the planar sides of the optical waveguide and configured for pupil expansion of the one or more optical beams along a first direction; a third DOE disposed on a surface of one of the planar sides of the optical waveguide, the third DOE having an input and an output region and configured for pupil expansion of the one or more optical beams along a second direction, and further configured as an out-coupling grating to out-couple, as an output display from the output region to an eye of the user, the one or more optical beams having expanded pupil relative to the input; and a broadband reflector disposed on a planar side of the optical waveguide that is opposite the third DOE, the broadband reflector having a bandwidth including a range of visible wavelengths from 400 to 650 nm, wherein the broadband reflector reflects both wavelengths associated with holographic image light and wavelengths associated with the views of the real world, wherein the broadband reflector comprises a single-layer thin-film reflective coating disposed on a planar substrate, and wherein the substrate and optical waveguide are tightly coupled with a uniform gap to maintain parallelism between the plane of the substrate and the plane of the optical waveguide within a predetermined threshold.