  The replacement of bulk refractive optical elements with diffractive planar
components enables the miniaturization of optical systems. However, diffractive
optics suffers from large chromatic aberrations due to the dispersion of the
phase accumulated by light during propagation. We show that this limitation can
be overcome with an engineered wavelength-dependent phase shift imparted by a
metasurface and demonstrate a design that deflects three wavelengths without
dispersion. A planar lens without chromatic aberrations at three wavelengths is
also presented. Our design is based on low-loss dielectric resonators which
introduce a dense spectrum of optical modes to enable dispersive phase
compensation. The suppression of chromatic aberrations in metasurface-based
planar photonics will find applications in lightweight collimators for
displays, and chromatically-corrected imaging systems.
