Fluorogermanate glass with reduced content of OH-groups for infrared fiber optics

The hydroxyl (OH−) impurities in germanium oxide (GeO2)-based glasses cause a strong absorption band between 2.4 and 3.6 μm, which makes this region of the electromagnetic spectrum inaccessible for signal transmission. To eliminate the OH− absorption, PbF2 was employed by partially replacing the PbO content in the following compositions: 56GeO2−(31-x) PbO–9Na2O–4Ga2O3–xPbF2 (x = 0, 3, 6, 9, 15, 25, 31). The removal of OH- ions in relation to the concentration of PbF2 incorporated in the glass-forming liquid was systematically studied. Differential thermal analysis (DTA) and Fourier transform infrared (FTIR) spectroscopy were respectively used for the analysis of glass devitrification and optical properties. The results of FTIR suggest that over 99% OH− impurity was removed, as compared to glasses without a purification process. An optimized core/cladding glass pair was then selected and the rod-in-tube technique was used. Fiber drawing conditions were established using the measured viscosity data and the devitrification range. The low OH− absorption fiber has demonstrated the transmission window up to 4 μm with a loss of 2.34 dB/m at 1.49 μm.