Investigation of the deposition of porous layers by the MCVD method for the preparation of rare-earth doped cores of optical fibres

Investigation was carried out on core layer deposition by modified chemical vapour deposition (MCVD) process to fabricate rare earth (RE) doped preforms and fibres. The solution doping technique was adopted for incorporation of the RE and codopant such as Al2O3 into the core. The deposited cores composed of GeO2/P2O5/SiO2 glasses with GeO2 level in the range of 3-15 mol% and P2O5 up to 5 mol%. The soot layer was deposited inside the substrate tube both by forward and backward deposition methods. This basic difference in the process between the two modes of deposition produced significant variation in the RE incorporation, numerical aperture as well as core-clad dimensions, all of which contribute to the end fibre performance. The backward deposition method provided greater flexibility and control over the RE incorporation.