Embodiments of the present disclosure generally relate to methods for forming a waveguide. Methods may include measuring a waveguide substrate, the waveguide having a substrate thickness distribution; and depositing an index-matched layer onto a surface of the waveguide, the index-matched layer having a first surface disposed on the waveguide substrate and a second surface opposing the first surface, wherein the index-matched layer is disposed only over a portion of the waveguide substrate, and a device slope of a second surface of the index-matched layer is substantially the same as the waveguide slope of the first surface of the waveguide.