Fig. 1. Cross-section of preform during the doping, showing two holes adjacent to the core with the dye and solvent fronts diffusing in from the holes (top). Plot of the position of the dye and solvents fronts as a function of time (bottom). The linear dependence indicates Case II diffusion. The dotted line indicates the position of the core radius.

Fig. 2. Fluorescence intensity as a function of radius to show uniform doping in the core.

Fig. 3. Cross section of a preform removed from the solution prior to the solvent fronts meeting in the core (left) and the same preform after heating (right).

Fig. 4. Optical loss measurements of a doped and undoped fibre, drawn from the same preform, indicating that the doping does not introduce losses other than those due to the absorption of the dye (the sharp increase at the short wavelength region of the graph).

Fig. 5. The absorption spectrum of the Rhodamine 6G dye as determined by measuring the loss spectrum of a doped fibre and subtracting from it the loss spectrum of an undoped fibre. Two fluorescence spectra are also shown for a very short fibre (few millimetres) and a longer fibre (approximately 2 m). The shift to the red in the longer fibre results from re-absorption of the fluorescence by the dye. The fluorescence measurements were taken by launching light from an Argon-ion laser (514 nm – this laser line has been removed from the graph) into the core of the fibre. For a concentration around 1 mmol/L the absorption peak reached approximately 20 dB/m.