Using multi-microchannel capillaries for determination of the zeta potential of a microfluidic channel

Theoretical Investigation of the Capacity of Space Division Multiplexing with Multimode Step-Index Air-Clad Silica Optical Fibers

We studied the effect of mode coupling on the space division multiplexing (SDM) capabilities of multimode step-index (SI) air-clad silica optical fibers by numerically solving the power flow equation. Mode coupling considerably reduces the length of these fibers at which space division multiplexing may be achieved with minimal crosstalk between neighboring optical channels, according to the findings. Up to 120 m and 30 m, respectively, the two and three spatially multiplexed channels in the investigated multimode step-index silica optical fibers can be used with low crosstalk. When building a space division multiplexing-based optical fiber transmission system, such characterization of optical fibers should be taken into account.

Percolation Diffusion into Self-Assembled Mesoporous Silica Microfibres

Percolation diffusion into long (11.5 cm) self-assembled, ordered mesoporous microfibres is studied using optical transmission and laser ablation inductive coupled mass spectrometry (LA-ICP-MS). Optical transmission based diffusion studies reveal rapid penetration (<5 s, D > 80 μm²∙s^-¹) of Rhodamine B with very little percolation of larger molecules such as zinc tetraphenylporphyrin (ZnTPP) observed under similar loading conditions. The failure of ZnTPP to enter the microfibre was confirmed, in higher resolution, using LA-ICP-MS. In the latter case, LA-ICP-MS was used to determine the diffusion of zinc acetate dihydrate, D~3 × 10^-4 nm²∙s^-1. The large differences between the molecules are accounted for by proposing ordered solvent and structure assisted accelerated diffusion of the Rhodamine B based on its hydrophilicity relative to the zinc compounds. The broader implications and applications for filtration, molecular sieves and a range of devices and uses are described.

Evanescent-field spectroscopy using structured optical fibers: detection of charge-transfer at the porphyrin-silica interface

The fabrication of porphyrin thin films derived from dichloro[5,10,15,20-tetra(heptyl)porphyrinato]tin(IV) [Cl-Sn(THP)-Cl] in the holes of photonic crystal fibers over 90 cm in length is described. Evanescent field spectroscopy (EFS) is used to investigate the interfacial properties of the films, with the high surface optical intensity and the long path length combining to produce significant absorption. By comparison with results obtained for similar films formed from Cl-Sn(THP)-Cl inside fused-silica cuvettes and on glass slides, the film is shown to be chemisorbed as a surface Si-O-Sn(THP)-X (X = Cl or OH) species. In addition to the usual porphyrin Q and Soret bands, new absorptions in the in-fiber films are observed by EFS at 445 nm and between 660-930 nm. The 660-930 nm band is interpreted as a porphyrin to silicon charge-transfer transition and postulated to arise following chemisorption at mechanical-strain induced defect sites on the silica surface. Such defect sites are caused by the optical fiber production process and are less prevalent on other glass surfaces. EFS within optical fibers therefore offers new ways for understanding interface phenomena such as surface adsorbates on glass. Such understanding will benefit all devices that exploit interface phenomena, both in optical fibers and other integrated waveguide forms. They may be directly exploited to create ultrasensitive molecular detectors and could yield novel photonic devices.

Focused ion beam processing and engineering of devices in self-assembled supramolecular structures

Self-assembled supramolecular structures such as optical wires, films and 2D slabs offer a new generation of electronic and optical devices. In particular, self-assembled porphyrin devices, including those integrated onto silica and silicon platforms, open new opportunities in photonic applications spanning molecular biosensing, photovoltaics and telecommunications. All reports to date, however, largely highlight the potential but have not established a clear pathway to the actual implementation of more complex device prototypes. In this paper, we propose and demonstrate the use of a focused ion beam (FIB) to process and fabricate devices in porphyrin-based supramolecular structures. These self-assembled structures have an initial root mean squared (rms) values for surface roughness of < 0.5 nm as measured by atomic force microscopy. Under appropriate FIB processing and cutting conditions, the rms value for surface roughness falls to < 0.4 nm, comparable with some of the best optical flatnesses obtained within, for example, structured optical fibres and integrated optical waveguides. The milling rate of the porphyrin structures was estimated to be approximately 70% of that of silica. The versatility of a FIB as a tool for rapid processing and fabricating 1D and 2D photonic waveguide structures within supramolecular self-assembled platforms is demonstrated by fabricating a 2D coupler, setting the groundwork for true optical device engineering and integration using these new organic systems.

Micromachining structured optical fibers using focused ion beam milling

A focused ion beam is used to mill side holes in air-silica structured fibers. By way of example, side holes are introduced in two types of air-structured fiber, (1) a photonic crystal four-ring fiber and (2) a six-hole single-ring step-index structured fiber.

Water-soluble porphyrin detection in a pure-silica photonic crystal fiber

Aqueous solutions of the water-soluble porphyrin 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinatomanganese(III) acetate were inserted into the holes of a photonic crystal fiber, and the porphyrin absorption bands were identified. Results were obtained for three concentrations. The porphyrins in water show no surface interactions with the silica walls of the capillary channels. We discuss the implications for future hybrid electronic and photonic fiber devices.

Impact of water and ice 1h formation in a photonic crystal fiber grating

The impact of ice 1h formation inside the holes of a photonic crystal fiber Bragg grating was analyzed and discussed. As a result of the ice's expansion, a broadening of the grating spectrum was observed that corresponds to internal microbending of the fiber and after some temperature cycling leads to failure of the fiber. An analytical model with which to estimate the internal compression forces is proposed, and the calculated values are found to be in agreement with reported data.