Microstructured optical fibres (i.e. fibres that contain holes) have assumed a high profile in recent years, and given rise to many novel optical devices. The problem of manufacturing such fibres by heating and then drawing a preform is considered for the particularly simple case of annular capillaries. A fluid-mechanics model is constructed using asymptotic analysis based on the small aspect ratio of the capillary. The leading-order equations are then examined in a number of asymptotic limits, many of which give valuable practical information about the control parameters that influence the drawing process. Finally, some comparisons with experiment are performed. For a limited set of experiments where the internal hole is pressurised, the theoretical predictions give qualitatively accurate results. For a much more detailed set of experiments carried out with a high-grade silica glass where no hole pressurisation is used, the relevant asymptotic solution to the governing equations is shown to give predictions that agree remarkably well with experiment.

/pdf/the-mathematical-modelling-of-capillary-drawing-for-holey-1vb2wk3rtd.pdf

The mathematical modelling of capillary drawing for holey fibre manufacture

The ability to produce small scale, crystalline silicon spheres is of significant technological and scientific importance, yet scalable methods for doing so have remained elusive. Here we demonstrate a silicon nanosphere fabrication process based on an optical fibre drawing technique. A silica-cladded silicon-core fibre with diameters down to 340 nm is continuously fed into a flame defining an axial thermal gradient and the continuous formation of spheres whose size is controlled by the feed speed is demonstrated. In particular, spheres of diameter o500 nm smaller than those produced under isothermal heating conditions are shown and analysed. A fibre with dual cores, p-type and n-type silicon, is drawn and processed into spheres. Spatially coherent break-up leads to the joining of the spheres into a bispherical silicon ‘p–n molecule’. The resulting device is measured to reveal a rectifying I–V curve consistent with the formation of a p–n junction.

/pdf/silicon-in-silica-spheres-via-axial-thermal-gradient-in-3dc75zkoil.pdf

Silicon-in-silica spheres via axial thermal gradient in-fibre capillary instabilities

This paper presents a study on drawing condition dependences of optical absorption at 630 nm and nonbridging oxygen hole centers (NBOHCs) in optical fibers drawn from low‐OH‐content synthetic silica glass. The intensity of the 630‐nm absorption is proportional to the NBOHC concentration, and the value of the oscillator strength for the NBOHC is 4.2×10−4, which nearly equals the theoretical values. These results confirm that the 630‐nm absorption is due to the NBOHCs in low‐OH‐content silica glass. Furthermore, the 630‐nm absorption increases with increasing drawing tension. This drawing tension dependence is explained by applying kinetics of the stress‐induced crack growth in metal to the formation of the NBOHCs in the drawing process.

Defect structure and formation mechanism of drawing‐induced absorption at 630 nm in silica optical fibers

Abstract The increasing fields of applications for modern optical fibers present great challenges to the material properties and the processing technology of fiber optics. This paper gives an overview of the capabilities and limitations of established vapor deposition fiber preform technologies, and discusses new techniques for improved and extended doping properties in fiber preparation. In addition, alternative fabrication technologies are discussed, such as a powder-based process (REPUSIL) and an optimized glass melting method to overcome the limits of conventional vapor deposition methods concerning the volume fabrication of rare earth (RE)-doped quartz and high silica glasses. The new preform technologies are complementary with respect to enhanced RE solubility, the adjustment of nonlinear fiber properties, and the possibility of hybrid fiber fabrication. The drawing technology is described based on the requirements of specialty fibers such as adjusted preform and fiber diameters, varying coating properties, and the microstructuring of fiber configurations as low as in the nanometer range.

https://www.degruyter.com/downloadpdf/j/aot.2014.3.issue-4/aot-2014-0010/aot-2014-0010.xml

Material and technology trends in fiber optics

We review the active and growing field of thermal processing of materials, with a particular emphasis on the linking of basic research with engineering aspects. In order to meet the challenges posed by new applications arising in electronics, telecommunications, aerospace, transportation, and other areas, extensive work has been done on the development of new materials and processing techniques in recent years. Among the materials that have seen intense interest and research activity over the last two decades are semiconductor and optical materials, composites, ceramics, biomarerials, advanced polymers, and specialized alloys. New processing techniques have been developed to improve product quality, reduce cost, and control material properties. However, it is necessary to couple research efforts directed at the fundamental mechanisms that govern materials processing with engineering issues that arise in the process, such as system design and optimisation, process feasibility, and selection of operating conditions to achieve desired product characteristics

R. B. Runk

Papers

Physical behavior of the neck-down region during furnace drawing of silica fibers (A)