TeO2-ZnO-La2O3 tellurite glass system investigation for mid-infrared robust optical fibers manufacturing

TeO2-ZnO-La2O3 (TZL) ternary glasses were investigated in order to manufacture step-index optical fibers with low optical losses in the near- and mid-infrared ranges and superior mechanical properties. To identify appropriate TZL glass compositions for optical fibers manufacturing, the whole vitreous domain of the ternary diagram was explored by characterizing bulk samples from thermal and optical point of view. Investigations were focused on understanding how the refractive index evolves as a function of the composition. For this, several parameters were analyzed such as density, molar volume, oxygen packing density, molar refractivity, polarizability and optical basicity. Finally, thermal and structural studies such as DSC and X-Ray diffraction allowed to select the most promising core and cladding glasses combination (in terms of stability against crystallization), in order to draw optical fibers. Step-index optical fibers were then successfully fabricated. Optical losses of these first TZL fibers were measured, giving minimum attenuations of 1.25 dB/m at 2.15 µm and less than 2 dB/m up to 2.75 µm and compared to well-known TeO2-ZnO-Na2O (TZN) glass fibers. Finally, first mechanical tests were performed as microhardness and tensile strength measurements with the aim of demonstrating the improvement in workability and resistance of the TZL fibers compared to TZN fibers.