We present our progress in the production of ytterbium (Yb) doped optical fibers fabricated by two variants of the
granulated aluminophosphosilicate method. We show advantages and disadvantages of mixing rare earth and
aluminophosphosilicate granulated oxides directly (variant 1) or by using the sol-gel method to produce doped granulate
material (variant 2). For both methods we studied the effects of varying the dopant concentrations and of introducing
iterative melting and milling procedures. In particular, the sol-gel based method eases the inclusion of P2O5 and thus, in
combination with Al2O3, higher dopant concentration of Yb and Er are possible. Sintering the sol-gel material at high
temperature eliminated bubbles in the core. We fabricated optical fibers that, piecewise, between individual strong
scatterers, exhibited attenuation losses as low as 0.35dB/m.
For our comparative study we determined volume percentage and distribution of chemical elements in the fabricated
fiber glasses by the analytical technique of Energy-Dispersive X-ray, Electro Probe Microanalysis and the degree of
crystallization by X-Ray Diffraction analysis. Furthermore we measured fluctuations of the refractive index profile and
scattering losses of the fiber core.
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