Development of rare-earth doped fibres for amplifiers in WDM systems

Rare-earth (Er, Yb, Nd etc.) doped alumino-germano-silicate preforms and fibres with extensive variation in rare-earth (RE) concentration, composition, and proportion of codopants as well as waveguide parameters were fabricated by the modified chemical vapour deposition (MCVD) process in combination with the solution-doping and sol-gel methods. The fibres were characterised for evaluation of the optical properties including refractive index profile, numerical aperture, spectral attenuation, cut-off wavelength, concentration and distribution of the RE, Giles parameters and also the optical gain. The fabricated fibres had Er ion concentrations varying between 100 and 1000 ppm and numerical apertures in the range 0.17-0.24. Some of the fibres are suitable for use in C-band optical amplifiers.