UC Irvine

Optical fibers play a significant role in various practical applications from long-distance optical communication to fiber lasers. However, the fundamental challenges of optical fiber are that the properties of light being guided in the fiber is largely limited by the glass materials of the core and cladding, as well as by the guiding mechanism. In addition, the optical properties of the optical fibers are fixed after the fabrication process. These fundamental limitations significantly restrict further advancement of optical fiber applications. On the other hand, novel nanophotonic concepts, such as metasurfaces and zero-index photonics, provide new pathways for advanced functionalities and tunability. Metasurfaces are arrays of light resonator at subwavelength scale with designed size, shape, and orientation that induce abrupt changes of light. Zero-index materials are materials with vanishing permittivity possessing properties of strong light confinement, which enable efficient light manipulation at nanoscale. In this dissertation, I intend to integrate optical metasurfaces and zero-index photonics with optical fibers to develop a unique optical meta-fiber platform that not only allows guiding light in the long distance, but also manipulating it in the nanoscale. My dissertation demonstrates the feasibility of the meta-fiber platform in three sections, two of them on metasurface integration and one on zero-index-material integration. The first section demonstrates the focusing of the outgoing light from an optical fiber without an external lens, where I develop an ultrathin optical metalens directly patterned on the facet of a large mode area photonic crystal optical fiber operating at 1500-1630 µm. We experimentally characterized the performance of the fabricated metalens such as focal length (28 µm and 40 µm), full width at half maximum (2.40 µm and 3.65 µm) and operating efficiency (~16%). The second section is a proof-of-concept demonstration of fiber-integrated active metasurfaces, where I investigate a gate-tunable plasmonic color filter incorporating a metasurface heterostructure. The tunable metasurface is embedded with thin and active transparent conducting oxide layer to form a double metal-oxide-semiconductor configuration. The last section is the first experimental demonstration of nano-scale light guiding by an epsilon-near-zero (ENZ) hybrid fiber. The highly confined ENZ mode is excited internally on a side-polished optical fiber with controllable propagation (light-matter interaction) length. We also show the proof-of-concept tunability of the hybrid resonance by the external refractive index or the large nonlinearity of the ENZ thin-film. Our results indicate the accessibility of novel in-fiber devices with extended functionalities and potential applications for optical imaging, sensing, and communication technologies.