Method to improve display efficiency and uniformity of AR waveguide

A method of forming a design thickness distribution in an optical device, comprising:

• measuring a substrate thickness distribution of a substrate defined by a distance between a top surface of the substrate and a bottom surface of the substrate along a first length parallel to the top surface and a second length perpendicular to the first length;
• generating a phase map from the substrate thickness distribution across the bottom surface of the substrate;
• measuring a non-uniformity of pitch between adjacent optical device structures of a plurality of optical device structures disposed on the top surface of the substrate;
• generating an engineered phase profile by subtracting the phase map and the non-uniformity of pitch from a design phase map corresponding to a phase to be formed at each location of the optical device;
• converting the engineered phase profile to an engineered thickness distribution;
• and
• disposing an index-matched layer on the bottom surface of the substrate to have the engineered thickness distribution to form a design thickness distribution, wherein the design thickness distribution is defined by the engineered thickness distribution and the substrate thickness distribution, wherein the design thickness distribution varies along the first length and the second length.