Planar, polarization insensitive, optical elements to control refraction of transmitted light in free space are disclosed. In one aspect, an optical element includes a substrate having a planar surface, and a polarization insensitive, high contrast, sub-wavelength grating composed of posts that extend from the planar surface. The grating has at least one region. Within each region, cross-sectional dimensions of the posts and/or lattice arrangement of the posts are nonperiodically varied to control refraction of light transmitted through the optical element.