  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.
