Canon has their DO (Diffractive Optics) technology[1] which I think only ever made it into a 70-300[2].

Mirror lenses have been around for a long time. They fold the length of larger telephotos into about a third with some trade-offs in speed and image quality.

[1] https://global.canon/en/v-square/34.html [2] https://www.usa.canon.com/internet/portal/us/home/products/d...