Richard Lwin

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.

Drawn metamaterials with plasmonic response at terahertz frequencies

Electromagnetic metamaterials attract much attention since they can be engineered to exhibit optical properties not found in nature. Their fabrication, however, is challenging, especially in volume. We introduce drawing as a means of fabricating metamaterials, thus demonstrating a terahertz metamaterial. We codraw polymethyl-methacrylate and indium, producing several meters of metamaterial with wire diameters down to ∼10 μm, and lattice constants of ∼100 μm. We experimentally characterize the transmission properties of different samples, observing high-pass filtering between 0.3–0.4 THz, in good agreement with simulations.

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.

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.

A loss-based, magnetic field sensor implemented in a ferrofluid infiltrated microstructured polymer optical fiber

We report an in-fiber magnetic field sensor based on magneto-driven optical loss effects, while being implemented in a ferrofluid infiltrated microstructured polymer optical fiber. We demonstrate that magnetic field flux changes up to 2000 gauss can be detected when the magnetic field is applied perpendicular to the fiber axis. In addition, the sensor exhibits high polarization sensitivity for the interrogated wavelengths, providing the possibility of both field flux and direction measurements. The underlying physical and guidance mechanisms of this sensing transduction are further investigated using spectrophotometric, light scattering measurements, and numerical simulations, suggesting photonic Hall effect as the dominant physical, transducing mechanism.

Microstructured Polymer Optical Fibres: New Opportunities and Challenges

ABSTRACT Microstructured polymer optical fibres [mPOF] were first developed in 2001, and have attracted attention in part because the range of fabrication techniques possible with polymers has allowed novel structures to be made that cannot be made simply in other materials. Their material properties also offer attractive possibilities as polymers can contain a much larger variety of dopants than glass. In this article, we review progress on some of the major challenges of this technology: particularly the need to reduce fibre losses, and report on some recent developments including the fabrication of the first hollow core mPOF. Some initial investigations into changing the material properties are reviewed.

Fabrication of microstructured optical fibers-part II: numerical modeling of steady-state draw process

By combining theoretical, numerical, and experimental analyses, this paper examines the continuous draw process that underpins the fabrication of microstructured optical fibers (MOFs) with the aim of quantifying the impact of material properties and drawing conditions on the hole structure in the finished fiber. First, by treating the continuous draw process as a steady-state isothermal extensional flow of a Newtonian material, three-dimensional (3-D) modeling clearly demonstrates how a combination of force effects can lead to dramatic hole deformation in the neck-down region-i) surface tension contributing to hole size collapse (particularly if the fiber contains small holes and is drawn slowly over a long distance), while ii) viscous effects are the major contributor to hole shape changes (particularly in cases where different size holes are in close proximity within the overall structure). Then the central role of the neck-down region in hole deformation is examined via nonisothermal numerical analysis. Results indicate that the shape of the neck-down region is highly sensitive to the viscosity profile and thus to temperature gradients. Finally, it is shown that predicted hole deformations agree well with experimental measurements made in drawing polymethylmethacrylate MOFs.

Fiber-drawn double split ring resonators in the terahertz range

We present a novel method for producing metamaterials based on double split ring resonators with a magnetic resonance at terahertz (THz) frequencies. The resonators were made by fiber drawing, a scalable method capable of producing large volumes of metamaterials, demonstrating that this technique can be extended to complex meta-atoms. The observed resonances occur at larger wavelengths relative to the resonator size, compared to single split ring resonators, and are in good agreement with simulations.

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.

Beyond the bandwidth-length product: Graded index microstructured polymer optical fiber

Large core multimode polymer fibers for high data rate transmission are an important growth area. The conventional approach to reducing the intermodal dispersion in such fibers is to use a graded index (GI) profile. More recently, microstructures rather than differences in chemical composition have been used to produce the GI structure. We compare the bandwidth performance of two GI microstructured fibers to a conventional GI fiber made from the same material. The microstructured fibers not only show excellent bandwidth performance but also their bandwidth has an unconventional length dependence: no additional pulse broadening beyond a characteristic length.