Disclosed herein are metasurfaces formed on a substrate from a plurality of posts. The metasurfaces are configured to be optically active at one or more wavelengths and in certain embodiments are configured to form lenses having unexpectedly strong focusing power. In particular, the metasurfaces are formed from “low-contrast” materials, including CMOS-compatible materials such as silicon dioxide or silicon nitride. Accordingly, the disclosed metasurfaces are generally CMOS compatible and therefore embody a new paradigm in metasurface design and manufacturing.