We report a hollow-core photonic crystal fiber that is engineered so as to strongly suppress higher-order modes, i.e., to provide robust LP₀₁ single-mode guidance in all the wavelength ranges where the fiber guides with low loss. Encircling the core is a single ring of nontouching glass elements whose modes are tailored to ensure resonant phase-matched coupling to higher-order core modes. We show that the resulting modal filtering effect depends on only one dimensionless shape parameter, akin to the well-known d/Λ parameter for endlessly single-mode solid-core PCF. Fabricated fibers show higher-order mode losses some ∼100 higher than for the LP₀₁ mode, with LP₀₁ losses <0.2  dB/m in the near-infrared and a spectral flatness ∼1  dB over a >110  THz bandwidth.

We report a novel splicing-based pressure-assisted melt-filling technique for creating metallic nanowires in hollow channels in microstructured silica fibers. Wires with diameters as small as 120 nm (typical aspect ration 50:1) could be realized at a filling pressure of 300 bar. As an example we investigate a conventional single-mode step-index fiber with a parallel gold nanowire (wire diameter 510 nm) running next to the core. Optical transmission spectra show dips at wavelengths where guided surface plasmon modes on the nanowire phase match to the glass core mode. By monitoring the side-scattered light at narrow breaks in the nanowire, the loss could be estimated. Values as low as 0.7 dB/mm were measured at resonance, corresponding to those of an ultra-long-range eigenmode of the glass-core/nanowire system. By thermal treatment the hollow channel could be collapsed controllably, permitting creation of a conical gold nanowire, the optical properties of which could be monitored by side-scattering. The reproducibility of the technique and the high optical quality of the wires suggest applications in fields such as nonlinear plasmonics, near-field scanning optical microscope tips, cylindrical polarizers, optical sensing and telecommunications.

We report a hybrid chalcogenide-silica photonic crystal fiber made by pressure-assisted melt-filling of molten glass. Photonic bandgap guidance is obtained at a silica core placed centrally in a hexagonal array of continuous centimeters-long chalcogenide strands with diameters of 1.45 μm. In the passbands of the cladding, when the transmission through the silica core is very weak, the chalcogenide strands light up with distinct modal patterns corresponding to Mie resonances. In the spectral regions between these passbands, strong bandgap guidance is observed, where the silica core transmission loss is 60 dB/cm lower. The pressure-assisted fabrication approach opens up new ways of integrating sophisticated glass-based devices into optical fiber circuitry with potential applications in supercontinuum generation, magneto-optics, wavelength selective devices, and rare-earth-doped amplifiers with high gain per unit length.

We present a simple refractive index sensor based on a step-index fiber with a hollow micro-channel running parallel to its core. This channel becomes waveguiding when filled with a liquid of index greater than silica, causing sharp dips to appear in the transmission spectrum at wavelengths where the glass-core mode phase-matches to a mode of the liquid-core. The sensitivity of the dip-wavelengths to changes in liquid refractive index is quantified and the results used to study the dynamic flow characteristics of fluids in narrow channels. Potential applications of this fiber microstructure include measuring the optical properties of liquids, refractive index sensing, biophotonics and studies of fluid dynamics on the nanoscale.

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