SPECTROSCOPIC PROPERTIES OF RARE EARTH METAL ION DOPED TELLURIUM OXIDE GLASSES AND FIBRES

摘要

The tellurium oxide (TeO_2) glasses are unique for their exceptionally large solubility for rare-earth metal ions. The paper discusses various structural, thermal, and spectroscopic properties, essential for fibre and waveguide design. Low-loss fibre fabrication requires an understanding of a relationship between the glass structure, thermal properties, e.j the glass transition, crystallisation, and melting temperatures, and the viscous relaxation. We discuss the properties of tellurium oxide glasses modified by the addition of sodium and zinc oxides, and their vibrational properties are characterised by Raman and infrared spectroscopy. The Raman spectra of these glasses show a range of structural units, namely TeO_3, TeO_(3+δ), and TeO_4. The processes of tellurite glass preform and fibre fabrication are described in detail. The spectroscopic properties of rare-earth metal ion dopants (Er~(3+), Tm~(3+), and Nd~(3+)) are specially discussed for designing broadband fibre and waveguide amplifiers, covering nearly 400 nm wavelength for both coarse (C-) and dense (D-) wavelength division multiplexing (WDM) systems. We demonstrate the usefulness of such fibres in designing ultra-short fibre waveguide amplifiers, which are capable of yielding large gain, e.g. in Er~(3+)-ion doped tellurite fibres larger than 30 dB internal (or relative) gain in the small-signal regime is possible in the C-band region.