Enhanced coupling strength grating having a cover layer

A grating, comprising:

• a substrate;
• a core disposed on the substrate, wherein the core has an index of refraction (ncore);
• one or more ridges and one or more grooves formed on the core, wherein the one or more grooves are adjacent to, or between the one or more ridges, wherein the ridges and grooves form a grating;
• a liner layer disposed on at least a portion of a grating cycle, wherein the liner layer has a liner thickness of between 5 and 50 nm and an index of refraction (nliner);
• an amorphous or crystalline cover layer disposed on the liner layer, wherein the cover layer has a cover thickness of between 100 and 300 nm, and an index of refraction (ncover);
• a superstrate or air layer disposed above the cover layer;
• wherein a first material selected for the core and ridges and a second material selected for the liner layer are selected to provide a first difference in the index of refraction between the first material (ncore) and second material (nliner) that is sufficient to provide a contrast therebetween;
• and
• wherein a third material is selected for the amorphous or crystalline cover layer to provide a second difference in the index of refraction between the second material (nliner) and the third material (ncover), and the third material is not the same as the first material.