Dispersion-compensated meta-holograms based on detour phase
  Subwavelength structured surfaces, known as metasurfaces, hold promise for future compact and optically thin devices with versatile functionalities. Here, by revisiting the concept of detour phase at the basis of the first computer generated holograms we have designed high-performance transmissive dielectric meta-holograms with new functionalities. In one class of such devices wavelength- independent phase masks have been generated by compensating the inherent dispersion of the detour phase with that of the subwavelength structures. This leads to broadband operation from the visible to the near infrared with efficiency as high as 75% in the 1000 to 1400 nm range. We have also shown that we can fully control the effective focal length of the imaging optical system by incorporating a lens-like function in the meta-hologram. In a second class of devices we have incorporated in the phase map a geometric phase to achieve for the first time chiral imaging: the projection of different images depends on the handedness of the reference beam. The compactness, lightweight and ability to produce images even at large angles of our devices have significant potential for important emerging applications such as wearable optics. 
Mohammadreza Khorasaninejad, Antonio Ambrosio, Pritpal Kanhaiya, and   Federico Capasso
physics.optics