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Photonic Crystal Fibers (PCF) based on special glasses with a high optical nonlinearity are of high interest for
applications. High optical nonlinearity can be achieved by a large concentration of heavy elements in the fiber core. The
dispersion characteristics can be tailored by an adapted microstructured cladding design. We have investigated two
different fiber types based on highly germanium doped silica and on lanthanum silicate glass. The properties of these
fiber types will be discussed and compared.
Highly germanium doped PCFs with a Ge concentration of up to 36 mol% in the central rod have been prepared by a
stack-and-draw technique from a silica capillary arrangement. Due to their compatibility with all-silica fibers, system
integration is easily possible by low-loss splicing techniques. Microstructured fibers based on alternative La2O3-Al2O3-SiO2-BaO-B2O3 glasses allow to further increase the optical nonlinearity compared to MCVD based high silica glasses.
However, the application of such fibers is often limited by their transmission properties due to imperfect purity and
homogeneity. We have achieved best fiber loss results of 1.2 dB/m at 1200 nm wavelength with glasses with a
lanthanum oxide concentration of about 16 mol% and a moderate boron concentration. Other limiting factors caused by
the thermochemical properties of the prepared glasses (such as low glass transition temperature, high thermal expansion
coefficient, limited crystallization stability) can be partially overcome by modifications of the material composition, by
suitable surface processing of preform components and by optimized drawing conditions.
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