A design study and advantages of meta-Alvarez lenses

We study the aberrations of a meta-Alvarez lens introduced by an air gap between the two elements. We find that four aberrations change with the air gap thickness: Spherical, Tetrafoil, Coma, and Trefoil. These aberrations grow linearly with the air gap thickness; hence as the air gap increases, the image quality degrades. These results reveal an important benefit of using metalens for Alvarez systems: The flat profile of metalens enables minimal separation between the two lenses, hence potentially better imaging performance than refractive Alvarez lens.