Processing and characterization of core–clad tellurite glass preforms and fibers fabricated by rotational casting

We report results on the processing and characterization of tellurite-based glass preforms (core and cladding bulk glasses) and fibers within the TeO2–Bi2O3–ZnO glass system. The core–clad fiber has been drawn from a core–clad preform prepared via rotational casting. Using Cu as a tracer to assess interface quality between the core and clad layers, we show excellent cladding layer thickness uniformity across lengths of up to 40 mm in a 65 mm long perform. No measurable diffusion of Cu between the core and the clad has been observed, within the accuracy of measurement, indicating good stability and interface quality during casting of melted glass. Micro-Raman spectroscopy has been used to identify subtle post-draw structural modification induced in the preform following the fiber drawing. These changes have been attributed to modification to the bulk glass’ thermal history upon drawing and small scale molecular orientation of chain units within the tellurite glass matrix produced during the fiber drawing process. The resulting fiber was found to have an index step of (0.009 ± 0.002) between the fiber core and clad composition at 632 nm and propagation losses of (3.2 ± 0.1) dB/m at 632 nm and (2.1 ± 0.1) dB/m at 1.5 μm. The primary source of loss in the near-IR (NIR) is associated with residual hydroxyl (OH−) groups in the bulk preform which remain in the glass fiber.