Optical Fibres Revisited

A history of the use of single- and multimode fibres in optic fibres is provided. Wavelength division multiplex is introduced, The same fibre can carry hundreds of wavelength bands. The longest stretch of optical fibre line is about 10,000 km. The greatest capacity achieved has been in the petabit/s range for a single cable with 32 cores, each one having 16 wavelength channels capable of carrying 680 Gb/s each. The ‘last mile’ problem still has not been solved in Britain. The relative advantages of satellites and optical fibres are discussed. Fibres working on different physical principles, e.g. holey fibres, have also been invented.

Elliptical pore regularisation of the inverse problem for microstructured optical fibre fabrication

A mathematical model is presented describing the deformation, under the combined effects of surface tension and draw tension, of an array of channels in the drawing of a broad class of slender viscous fibres. The process is relevant to the fabrication of microstructured optical fibres, also known as MOFs or holey fibres, where the pattern of channels in the fibre plays a crucial role in guiding light along it. Our model makes use of two asymptotic approximations, that the fibre is slender and that the cross-section of the fibre is a circular disc with well-separated elliptical channels that are not too close to the outer boundary. The latter assumption allows us to make use of a suitably generalised ‘elliptical pore model (EPM)’ introduced previously by one of the authors (Crowdy, J. Fluid Mech., vol. 501, 2004, pp. 251–277) to quantify the axial variation of the geometry during a steady-state draw. The accuracy of the elliptical pore model as an approximation is tested by comparison with full numerical simulations. Our model provides a fast and accurate reduction of the full free-boundary problem to a coupled system of nonlinear ordinary differential equations. More significantly, it also allows a regularisation of an important ill-posed inverse problem in MOF fabrication: how to find the initial preform geometry and the experimental parameters required to draw MOFs with desired cross-plane geometries.

Detecting phase transitions in supercritical mixtures: an enabling tool for greener chemical reactions

Detecting phase transitions in high-pressure CO 2 and supercritical fluids was first attempted in the nineteenth century. By contrast, Green Chemistry, the design and implementation of cleaner methods of manufacturing and processing chemicals, is barely 20 years old. Now, the use of CO 2 as an environmentally more acceptable replacement for traditional solvents for greener chemical reactions is creating the need for new, more rapid methods for elucidating high-pressure phase behaviour. This paper describes the advantages and limitations of a number of approaches, developed in Nottingham, to meet this need, including acoustic measurements, shear-mode quartz sensors, the fibre-optic reflectometer, the use of holey fibres, attenuated total reflectance infrared spectroscopy and pressure drop measurements.