Tellurite And Fluorotellurite Glasses For Active And Passive

8. Fibre drawing; MDO 332
The data obtained was fitted to these models using least squares analysis, followed by the
iterative Solver function in Microsoft Excel, and parameters A, B, C and T0 were then
obtained. Initial values were used from the study by Braglia et al. [6].
8.1.2. Preform manufacture
Unstructured preforms (no cladding layer) were manufactured by casting around 30 g of
glass into the cylindrical brass (CB) mould described and pictured in section (3.3). Early
oxide structured preforms (core / clad) were manufactured using rotational casting [7]
equipment shown in fig. (8.1), however fibre drawing of these preforms was not
successful due to severe surface hydrolysis.
The glass preform was manufactured by the process shown in fig. (8.1a). The crucible
of molten core glass was put in either one of the crucible holder and the cladding glass in
the other, and the chamber evacuated (no additional heating is provided by the rotational
casting equipment). The preheated mould (≈ 250°C) was placed into the holder, and the
core glass was poured into the mould (1), which was then rotated horizontally and spun at
1000 rpm for 10 seconds (2) by which time it had cooled to around the mould
temperature (≈ Tg) and solidified into a tube of homogeneous thickness. The mould was
then rotated to its original vertical position and the cladding glass poured in (3). This
preform was then annealed for an hour at around Tg – 10°C and left to cool slowly to
room temperature. Fibres which result from preforms manufactured by this method
potentially have lower loss compared to fibre from preforms manufactured by the rod-in-