All-silica Based Multi-focus Fiber Metalens

We conducted numerical simulations of a multifocal fiber metalens utilizing an all-silica metasurface. This metasurface comprises cylindrical nanopillars with varying radii to achieve the desired phase distribution. The photonic crystal fibers employed in our study feature sufficiently large cores to accommodate the nanopillars effectively. The multifocal characteristics of the metalens are achieved through staggered arrangements of different media. Our proposed fiber metalens demonstrates the capability to generate three focal points with high focusing efficiency along the axial direction, each approaching the diffraction limit. Moreover, the metalens design enables broadband output, indicating promising applications in integrated optics and multifunctional nanodevices.