Theoretical realization of single-mode fiber integrated metalens for beam collimating.

Optical fiber facet has rapidly emerged as a powerful light-coupling platform for integrating metasurfaces with miniaturized footprint and multifarious functionalities, through direct lithographic patterning or decal transfer. However, the fiber integrated metasurfaces investigated so far have been usually limited to high refractive index (RI) materials, thus leading to severe impedance mismatch at the fiber/metasurface interface and low efficiency. Here we report a single-mode fiber (SMF) integrated metalens based on low-RI material. We theoretically show that the highly divergent beam at the cleaved SMF is fully collimated by the metalens consisting of elliptical nanoposts with uniform height but varied width and length. The spatial wavefront of the transmitted light at the end facet of the light waveguide is properly modulated by the metasurface while maintaining an efficiency beyond 95% in the simulation. This study demonstrates a roadmap to design highly efficient SMF integrated metasurface based on low-RI material and may find applications in biomedical and optical imaging.