Processing of Optical Fibres

The inside process is similar to the outside process, however the substrate is now a tube and pure or doped Si02 is deposited in the interior of the tube [181]. It is also possible to use plasma-enhanced CVD [315]. In this case, the quality of the final product is much better than compared to those obtained using the outside process. 

The processing steps that follow to produce an optical fibre are the collapse of the preform to close the inner opening (if present) and the drawing of the fibres. 

The double crucible method to draw optical fibres uses two crucibles positioned into each other. The inner crucible contains the glass material from which the core is drawn whereas the outer crucible holds the melt for the 

This method also allows for the formation of multi-filaments which are drawn from crucibles with many nozzles. Geometrical arrangements up to 100 fibres are quite common [181]. If three crucibles are stacked into each other, it is possible to produce multi-layer fibres [10,276]. 

A modified crucible technique allows the preparation of gradient index optical fibres [276,301]. In this technique, a larger distance between the nozzles of inside and outside crucible is used, so that the glass leaving the inner crucible flows through the melt of the outer crucible. During this time, ion diffusion occurs to form a parabolic index profile. An ion diffusion process can also be initiated during an additional thermal treatment step. 

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Suah F.B.M., Ahmad M., Taib M.N., Applications of artificial neural network on signal processing of optical fibre pH sensor based on bromophenol blue doped with sol-gel film, Sens. Actuat B 2003 90 182-188. 

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