Optical Fiber Meta-Tips Based on Partial-Phase Control

Abstract

Lab-on-fiber technology is deemed pivotal in many fields due to the advantages offered by the mature optical fiber technology. Therefore, the development of optical components integrated into optical fibers is crucial. The ability to integrate metasurfaces into optical fibers has led to a greater number of degrees of freedom that might be used to realize all-in-fiber optical components. Here we explore the potential of plasmonic MSs based on a partial coverage of the phase range, introduced by Hail, but so far essentially unexplored. Exploiting this paradigm, we realize a beam splitter and a focusing lens at the tip of a single mode fiber operating in the near infrared. We show that partial-phase MSs, unlike their standard plasmonic counterparts, enable the generation of two beams, the ordinary and the anomalous one, that have the same polarization state and delivered power, allowing efficiencies of up to ∼30% to be achieved. Furthermore, we demonstrate that it is possible to focus light a few micrometers from the tip without the need of a beam expander. The realized meta-lens has a numerical aperture of 0.71 and a focusing efficiency of 20%, the highest efficiency achieved so far with a flat lens on a fiber tip.