Preparation of Optical Fiber

As many other processes the outside vapour phase oxidation(OVPO) is used to prepare both the step and the graded index fiber. The SiCl4 and GeCl4 in the gaseous stage are mixed Oxygen to obtain pure SiO2 as given by the following reactions.

SiCl4+2H2O=SiO2+(HCl)
i.e,vapour +gas=solid+gas


GeCl4+O2=Geo2+2Cl2
i.e,vapour+gas=solid+gas

The mixture of Sio2 and GeO2 is then passed through a burner so that a layer of this mixtur is deposited on a cool rotaing mandrel.

The burner is moved back and forth over the lenght of the mandrel dto deposit approximately 200 layer sothe mixture.The amount of GeO2 is not changed untl the core calddding interface is reached to prepare a step index fiber,whereas it is gradulally changed at the completion of each travers of the burner for preparing a graded index fibre. In this process ,SiO2 is the base material and GeO2 is the dopant.

The compounds such as P2O5 and F can also be used as dopants.After depositing the required number of layers, the mandrel is remover and the central hole is collapsed.The resulted shape of the mixture is called the preform. It is possible to draw a biber of lenght around 10km eith 120 micro meter cor in diameter.
The mixture from which the fiber is prepared is usually denoted by single symbol such as GeO2-SiO2 in this case, which is read as SiO2(Silica glass) dopped with Ge2.