We report on the characteristics of an active fiber with core material made by sintering of Yb-doped silica powders as an alternative to a conventional modified chemical vapor deposition (MCVD) technique. This material provides the possibility to design very large and homogenously rare-earth doped active fiber cores. We have determined a fiber background attenuation of 20 dB/km and measured a slope efficiency of 80%. These values are comparable to established fibers made by MCVD technology.

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Diffusion of Ge and F was studied during drawing of silica optical fibres. Preforms were drawn using various draw conditions and fibres analysed using the etching and Atomic Force Microscope (AFM) technique. The results were confirmed by comparison with fibre Refractive Index Profiles (RIP). Both Ge and F were found to diffuse at high temperature, 2100 degrees C, and low draw speed, 10m/min. Diffusion simulations showed that most diffusion occurred in the neck-down region. The draw temperature and preform feed rate had a comparable effect on diffusion, whereas preform diameter did not significantly affect the diffusion.

The absorption specva of ZnS:Ni and ZnSe:Ni were measured at 100 K under hydrostatic pressure up to 10 GPa. Two kinds of optical transition were investigated: (i) the d-d transifions between crystal field levels of Ni2+ in the tetmhedrd field of the host lattice and (ii) a charge transfer band that occurs when an electron is Vansferred from the valence band to the Niz+ ion. The pressure dependence of the crystal field parameter Dy and of the Racah panmeter B were determined and B revised assignment of the d d transitions was obtained. The charge tnnsfer c m be considered as a deep-acceptor tmsition. In this w e the Ni acceptor level may be used JS an energy reference. which enabled us to determine the hydrostatic deformation potentid of the valence band.

We have determined the pressure dependence of the excitonic transition energy in lhin MOVPE ZnTe layers by measuring the absorption coefficient and the retractive index. Pressures up to 12GPa were applied in a diamond anvil cell. A special gasket technique was used to s u p p m the scattered light. The absorption coefficient was measured in l p m thick films at T = 115K and at T = 300K up to SOOOOcm-'.The spectra are dominated by a sharp excitonic slmcture. Its pressure dependence is evaluated using a model which allowed us to determine the rate of pressure-induced shift of the binding energy d E , / d P and the rate of change of lhe Rydterg energy dR:/dP. The refractive index n was measured on 2.4pm-thick films at T = 300K and a t T = 115K by observing the pressure shift of lhe interference extrema in the transparency region. The resulting refractive index was extrapolated to the frequency of the longitudinal optical phonon to obtain the constant 6 -. The Static dielectric constant 6,< was obtained using the LyddaneSachs-'Eller relation. Using this value and the determined effective masses at the applied pressures, we calculated the exciton binding energy. At the pressure P = 9.4GPa. a phase transition was observed. The obtained spectra far this phase were compared with a model describing indirect transitions in semiconductors. A further phase transition was observed at P = I0.9GPa.