Optical fiber meta-tips based on holey metasurface for wavefront manipulation.

Optical fibers are of great technological importance due to their unique features such as flexible handling, strong light confinement, and efficient light transportation over large distances, representing a key element in a multitude of applications in modern optics, including fiber communications, analog computing, optical trapping, sensing, and imaging. The integration of optical metasurfaces (MSs) on the tip of an optical fiber is able to enormously expand the fiber functionalities, by endowing a simple optical fiber with extraordinary capabilities of light manipulation. Furthermore, properly designed MSs are able to replace traditional bulky optical components, with the great advantage of reducing the size of the devices. In 2017 we realized the first optical fiber meta-tip (OFMT) for wavefront modulation, based on plasmonic antennas which were able to span the entire $2\pi$ phase range on the cross-polarized transmission coefficient, suffering however low efficiency. Here we go a step ahead and realize OFMTs based on aperture antennas in a gold layer, spanning a partial phase range, which are able to steer and focus the outcoming light beam with higher efficiency.