A lens innovation from Canon is the Multi-layer Diffractive Optical Element (DO).
A single diffractive element is not suitable for lens use because it creates flare. However, Canon discovered that combining two diffractive elements in a single lens cancels out the flare. At the moment, the main advantage of the multi-diffractive element is that it reduces the length of telephoto lenses, a benefit mostly of interest initially to professional photographers travelling abroad on assignments.
The first DO lens was the EF 400mm f4 DO IS USM lens, introduced in 2001.
DO lenses are usually identified by a green line round the lens barrel, though Canon broke with this tradition when it introduced the RF 600mm f11 IS STM and RF 800mm f11 IS STM lenses in mid-2020.