Science http://doi.org/2mn (2015)

Reducing the dimensions of lenses can prove useful for a plethora of applications. Most lenses however, especially when reduced in size and thickness, suffer from large chromatic aberrations due to the wavelength dependence of their focal distance. Although such behaviour can be corrected, it requires additional optical elements, increasing the complexity and the size of the system as a whole. Now, Francesco Aieta and colleagues have demonstrated a flat lens design based on metasurfaces. Such arrays of low-loss dielectric resonators allow continuous control of the phase profile, making it possible not only to correct the aberrations that degrade the performance of conventional lenses, but also to achieve broadband operation. The team managed to overcome the wavelength dependence, demonstrating the same focal length for red, blue and green light — the primary colours used in display applications — as well as deflection of these three different wavelengths by the same angle. This approach is an important step towards the implementation of flat optics in conventional applications.