3D nanoprinting of high-numerical aperture multilevel metalenses.

We present the development and evaluation of metalenses fabricated with the two-photon polymerization-based 3D nanoprinting technology. In our design, we investigated a periodic lattice of multilevel nanopillars, based on the natural ellipsoidal shape of the 3D voxel in the fabrication process. By creating nanopillars with various heights, we can tune the effective refractive index of the metasurface in order to modulate the phase profile of an incoming light beam. We therefore push the fast and flexible two-photon polymerization technique to its limits in terms of dimensions in view of creating high performance metalenses. To demonstrate the optical performance of these metalenses, we also created their refractive and diffractive counterparts with the same fabrication technology to allow for a direct performance comparison. Moreover, we show that these metalenses can be fabricated on the tip of standard telecom single-mode optical fibers for the effective collimation of their output light beam.