Figure 1

Schematics of optical beam refractions with phase gradient in the incidence plane.
(a) At air-glass interface is along z-axis normal to the surface and radii of circles of equifrequency contour are different in air and glass. (b) At phase-discontinuity metasurface
is along x-axis tangential to the surface and the net refraction after passing through the glass substrate is described by circle of equifrequency contour in air with an additional momentum from
.