Conventional optical fiber has excellent performance in guiding light, which has been widely employed for long-distance optical communication. Although the optical fiber is efficient for transmitting light, its functionality is limited by the dielectric properties of the core’s and cladding’s materials (e.g. Ge-doped-silica and silica glasses). The spot size of the transmitted light is diverging and restricted by the diffraction limit of the dielectric core, and the numerical aperture is determined by the refractive index of the fiber materials. However, the novel technology of metasurfaces is opening the door to a variety of optical fiber innovations. Here, we report an ultrathin optical metalens directly patterned on the facet of a photonic crystal optical fiber that enables light focusing in the telecommunication regime. In-fiber metalenses with focal lengths of 28 μm and 40 μm at a wavelength of 1550 nm are demonstrated with maximum enhanced optical intensity as large as 234%. The ultrathin optical fiber metalens may find novel applications in optical imaging, sensing, and fiber laser designs.

We demonstrate in-fiber polarization-dependent optical filter by nanopatterning an asymmetric metallic metasurface array on the end-facet of polarization-maintaining photonic-crystal fibers. The asymmetric cross-typed nanoslit metasurface arrays are fabricated on the core of the optical fiber using the focused ion beam milling technique. Highly polarization- and wavelength-dependent transmission with transmission efficiency of ∼70% in the telecommunication wavelength was observed by launching two orthogonal linear-polarization states of light into the fiber. Full-wave electromagnetic simulations are in good agreement with the experimental results. These advanced meta-structured optical fibers can potentially be used as novel ultracompact in-fiber filters, splitters, and polarization converters.

We present a study of optical modulation by the effect of temperature-induced insulator-to-metal phase transition of vanadium dioxide ( V O 2 ) nanocrystals deposited in an antiresonance hollow-core fiber (AR-HCF). We fabricate such a V O 2 -coated fiber by embedding alkylsilane functionalized V O 2 nanocrystals into the air holes of an AR-HCF. With this fiber, we achieve an optical loss modulation of ∼ 60 % at a temperature above ∼ 53 ∘ C over an ultrabroad spectral range that encompasses the S + C + L band.

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