The present invention discloses a process for making
rare earth (RE) doped optical fibre by using RE
oxide coated
silica nanoparticles as the precursor materia, more particularly the method of the present invention involves preparation of stable dispersions (
sol) of RE
oxide coated
silica nanoparticles at ambient temperature and applying a thin
coating on the inner surface of
silica glass tube following
dip coating technique or any other conventional methods, of the said silica
sol containing suitable dopants selected from Ge, Al, P, etc., the coated tubes were further processed into optical preforms by following MCVD technique and fiberised in desired configuration, the novelty lies in eliminating the step of the formation of porous
soot layer at high temperature by CVD process inside a fused
silica glass tube for formation of the core and also in the elemination of the incorporation of the
rare earth ions into the porous
soot layer following the solution
doping technique or other conventional methods, the direct addition of RE oxides in the
sol eliminates the formation of microcrystalites and clusters of
rare earth ions and prevents change in composition including variation of RE concentration in the core which results in increase in the reproducibility and reliability of the process to a great extent, further the addition of Ge(OET)4 at ambient temperature in the silica sol reduces the quantity of GeCl4 which is required at high temperature to achieve the desired
Numerical Aperture.