Towards subdiffraction imaging with wire array metamaterial hyperlenses at MIR frequencies.

We describe the fabrication of metamaterial magnifying hyperlenses with subwavelength wire array structures for operation in the mid-infrared (around 3 µm). The metadevices are composed of approximately 500 tin wires embedded in soda-lime glass, where the metallic wires vary in diameter from 500 nm to 1.2 µm along the tapered structure. The modeling of the hyperlenses indicates that the expected overall losses for the high spatial frequency modes in such metadevices are between 20 dB to 45 dB, depending on the structural parameters selected, being promising candidates for far-field subdiffraction imaging in the mid-infrared. Initial far-field subdiffraction imaging attempts are described, and the problems encountered discussed.

All-plastic fiber-based pressure sensor.

We present a feasibility study and a prototype of an all-plastic fiber-based pressure sensor. The sensor is based on long period gratings inscribed for the first time to the best of our knowledge by a CO2 laser in polymethyl methacrylate (PMMA) microstructured fibers and coupled to a pod-like transducer that converts pressure to strain. The sensor prototype was characterized for pressures up to 150 mbars, and various parameters related to its construction were also characterized in order to enhance sensitivity. We consider this sensor in the context of future applications in endoscopic pressure sensors.

Holey fiber mode-selective couplers.

Directional mode coupling in an asymmetric holey fiber coupler is demonstrated both numerically and experimentally for the first time. The holey fiber mode couplers have interesting spectral characteristics and are also found to exhibit increased dimensional tolerances. Following a design based on numerical investigations, a dual-core polymer holey fiber coupler for LP(01) and LP(11) mode multiplexing was fabricated via a drilling and drawing technique. The measurements are compared with the simulation results.

Refractive index sensor based on a polymer fiber directional coupler for low index sensing.

We propose, numerically analyze and experimentally demonstrate a novel refractive index sensor specialized for low index sensing. The device is based on a directional coupler architecture implemented in a single microstructured polymer optical fiber incorporating two waveguides within it: a single-mode core and a satellite waveguide consisting of a hollow high-index ring. This hollow channel is filled with fluid and the refractive index of the fluid is detected through changes to the wavelength at which resonant coupling occurs between the two waveguides. The sensor design was optimized for both higher sensitivity and lower detection limit, with simulations and experiments demonstrating a sensitivity exceeding 1.4 × 10(3) nm per refractive index unit. Simulations indicate a detection limit of ~2 × 10(-6) refractive index units is achievable. We also numerically investigate the performance for refractive index changes localized at the surface of the holes, a case of particular importance for biosensing.

Multicore composite single-mode polymer fiber.

We study, fabricate and characterize an all-solid polymer composite waveguide consisting of a multicore fiber for single-mode operation down to the visible. The individual cores of the multicore structure are arranged such that they strongly interact, to form the composite core. The behavior and parameters of the multicore geometry are analyzed in order to achieve true single-mode operation. The composite core fiber is fabricated with off-the-shelf poly-methyl-methacrylate (PMMA) and Zeonex 480R polymers and characterized.

Stacked-and-drawn metamaterials with magnetic resonances in the terahertz range.

We present a novel method for producing drawn metamaterials containing slotted metallic cylinder resonators, possessing strong magnetic resonances in the terahertz range. The resulting structures are either spooled to produce a 2-dimensional metamaterial monolayer, or stacked to produce three-dimensional multi-layered metamaterials. We experimentally investigate the effects of the resonator size and number of metamaterial layers on transmittance, observing magnetic resonances between 0.1 and 0.4 THz, in good agreement with simulations. Such fibers promise future applications in mass-produced stacked or woven metamaterials.

Fluorescent response of dye-filled suspended-core microstructured polymer optical fiber.

Microstructured polymer optical fibers represent quite new technology that is still in the research and development stage. However, some advances and possible applications are available even now. One of these is the possibility of filling the fibers with various fluids to enhance or modify some of their characteristics. Filling fibers with fluorescent dyes is a good method to describe how the filled fiber behaves and to demonstrate sensing applications.

Bend loss in highly multimode fibres.

We investigate the bend loss of highly multimode air-clad microstructured polymer optical fibre which displays low bend loss for small bend radii. After repeated bending the loss approached a plateau, decreasing significantly after a characteristic length. The loss at a particular point depended on the configuration of the fibre preceding that point. A simple analytical model based on a transfer-matrix method is derived to explain this behaviour in terms of the power distribution amongst different mode groups. This model allows the effect of a particular fibre configuration to be predicted.

Opening up optical fibres.

A unique optical fibre design is presented in this work: a laterally accessible microstructured optical fibre, in which one of the cladding holes is open to the surrounding environment and the waveguide core exposed over long lengths of fibre. Such a fibre offers the opportunity of real-time chemical sensing and biosensing not previously possible with conventional microstructured optical fibres, as well as the ability to functionalize the core of the fibre without interference from the cladding. The fabrication of such a fibre using PMMA is presented, as well as experimental results demonstrating the use of the fibre as a evanescent wave absorption spectroscopy pH sensor using the indicator Bromothymol Blue.

Microstructured-core optical fibre for evanescent sensing applications.

The development of microstructured fibres offers the prospect of improved fibre sensing for low refractive index materials such as liquids and gases. A number of approaches are possible. Here we present a new approach to evanescent field sensing, in which both core and cladding are microstructured. The fibre was fabricated and tested, and simulations and experimental results are shown in the visible region to demonstrate the utility of this approach for sensing.

Fabricating metamaterials using the fiber drawing method.

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate (1). They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves (2). This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks (3), negative refractive index materials (4), and lenses that resolve objects below the diffraction limit (5). However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size (6-7). Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response (8). We combine the stack-and-draw technique used to produce microstructured polymer optical fiber (9) with the Taylor-wire process (10), using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 °C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.