The increasing fields of applications for modern optical fibers present great challenges to the material properties and the processing technology of fiber optics. This paper gives an overview of the capabilities and limitations of established vapor deposition fiber preform technologies, and discusses new techniques for improved and extended doping properties in fiber preparation. In addition, alternative fabrication technologies are discussed, such as a powder-based process (REPUSIL) and an optimized glass melting method to overcome the limits of conventional vapor deposition methods concerning the volume fabrication of rare earth (RE)-doped quartz and high silica glasses. The new preform technologies are complementary with respect to enhanced RE solubility, the adjustment of nonlinear fiber properties, and the possibility of hybrid fiber fabrication. The drawing technology is described based on the requirements of specialty fibers such as adjusted preform and fiber diameters, varying coating properties, and the microstructuring of fiber configurations as low as in the nanometer range.

The MgB 2 -based material high-pressure synthesized at 2 GPa and 800 o C for 1 h from Mg and B (taken in the stoichiometry ratio of MgB 2 ) with addition of 2-10 wt% of Ti demonstrated the critical current density (j c ) higher than 100 kA/cm 2 at 33 K in 0 T field and at 20 K up to 3 T. At 20 K the critical current density higher than 10 kA/cm 2 was observed up to 5 T field. In the magnetic field up to 2 T high-pressure synthesized MgB 2 (with 10 % of Ti) at 20 K behaves in the same manner as Nb 3 Sn at 4.2 K.In XRD patterns of magnesium diboride with the Ti added, we observed no evidence of titanium diboride or unreacted titanium and only one compound with titanium was identified, namely, titanium dihydride TiH 2 (or more strictly TiH 1.924 ). The sample with the highest critical current density and irreversible field in the temperature range of 25-10 K contained some amount of pure Mg that was rather homogeneously dispersed in the material.The critical currents and irreversible fields of magnesium diboride synthesized at high pressure with Ti added are higher than those in the case where Ta has been added.

The actual limitations for the trapped field in YBa2Cu3O7−δ (YBCO) monoliths are discussed. The influence of the sample geometry and of the critical current density on the trapped field is investigated by numerical calculations. The field dependence of the critical current density strongly influences the trapped field. A nonlinear relationship between the sample size, the critical current density and the resulting trapped field is derived. The maximum achievable trapped field in YBCO at 77 K is found to be around 2.5 T. This limit is obtained for reasonable geometries and high but realistic critical current densities. Such high fields have not been reached experimentally so far, due to non-optimized flux pinning and material inhomogeneities. These inhomogeneities can be directly assessed by the magnetoscan technique, and their influence is discussed. Significant differences between the a- and the c-growth sectors were found. Limitations due to cracks and non-superconducting inclusions (e.g. 211 particles) are estimated and found to be candidates for variations of Jc on a millimetre length scale, as observed in experiments.

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Y-Ba-Cu-O melt processed samples were prepared from mixtures of powders (starting average particle size ranging from to ) with and 1 wt% or 1 wt% . The resulting microstructure of the samples was composed of network and low concentration regions with size and morphology correlating with the starting powder size independently of the holding time in the melted state. The 211 particle size was smaller for Ce doped samples than for Pt doped samples. The differences in porosity of Pt and Ce doped samples were related to the changes in the interfacial energy of the constituent phases.