Interesting Canon patent to reduce flare in difrractive optical elements. Let’s start with the abstract:
Basically, this means that an aluminium coating is applied to diffractive lens elements, in order to reduce light scattering. The aluminium layer is applied with an angle (you see it in the pictures), and is then partially oxidised so that the aluminium coating becomes transparent. According to the patents claim, flare is massively reduced (up to eight times).
Some more “patentish language”: