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Title: Tellurite and fluorotellurite glasses for active and passive fibreoptic waveguides
Author: O'Donnell, Matthew David
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2004
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Glasses systems based on TeO2-ZnO-Na2O (TZN), TeO2-WO3, and TeO2-Na2O-ZnF2 are reported here, with a number of other components added (PbO, GeO2, Nb2O5, Bi2O3, Er2O3, Yb2O3, PbF2, and ErF3). Glass formation was shown for the first time, to this author's knowledge, in the ternary system (90-x)TeO2-10Na2O-xZnF2 for x = 5 to 30 mol. %. Glass stability (Tx-Tg) was found to increase with ZnF2 addition, reaching a plateau of around 161oC at x = 25 mol. %. This could be due to competition of various phases to crystallise (NaZnF3 and Zn2Te3O8) as the eutectic is approached, with fluoride addition. These glasses are the most stable ZnF2 containing tellurite compositions reported to date, to the author's knowledge. As-received ZnF2 batch material was shown to contain a significant proportion of Zn(OH)F, identified by XRD. The as-received ZnF2 was fluorinated with (NH4)HF2, which produced a substantially more phase pure powder, with oxygen levels reduced from around 13.2 to 3.1 at. % from XPS spectra. By calculation from the O1s XPS peaks, the proportion of Zn(OH)F was reduced in the powders from 39.7 to 9.4 mol. %. A number of absorption bands in the infrared were identified by FTIR for the TeO2 -ZnO-Na2O glasses due to intrinsic lattice vibrations (visible in a 0.2 mm sample), and extrinsic impurity absorption, including: free OH (around 3.0 microns, 3300 cm-1), weakly hydrogen-bonded OH (around 3.3 microns, 3060 cm-1), and strongly hydrogen-bonded OH (around 4.8 microns, 2090 cm-1). For the series (90-x)TeO2-10Na2O-xZnF2, mol. %, x = 5 to 30 mol. % melted for 2 hours as bulk glasses, OH bands at 2900 cm-1 were reduced in intensity with ZnF2 addition due to self drying of the melt, from around 0.12 cm-1 (120 dB.m-1) for x = 5 mol. %, to around 0.02 cm-1 (20 dB.m-1) for x > 15 mol. %. Melting time also had a significant effect on drying of this series, with the loss at 2900 cm-1 reduced by two orders of magnitude when increased from 1 hour (around 705 cm-1, 705 dB.m-1) to 2 hours (0.01 cm-1, 10 dB.m-1). Refractive index of the series (90-x)TeO2-10Na2O-xZnF2, mol. %, x = 5 to 30 mol. % decreased linearly with ZnF2 addition, from 2.02 (x = 5 mol. %) to 1.85 (x = 30 mol. %), as the fluoride and zinc are less polarisable than oxygen and tellurium. Cohen-Grest viscosity modelling was used to predict the fibre drawing temperature (around 330oC, corresponding to a viscosity of 10^4.5 Pa.s), and fragility of the fluorotellurite core / clad pair (20 / 25 mol. % ZnF2), occurring at least 60oC < Tx. Fragility of these glasses was predicted to lie between oxide tellurite glasses (stronger) and fluorozirconate glasses (more fragile). Increasing melting time and fluorination resulted in a significant decrease in OH bands in the 700 nm to 2.5 micron region for unstructured 70TeO2-10Na2O-20ZnF2 mol. % fibre, from around 40 to 4 dB.m-1 at 2.5 microns as melting time was increased from 3 to 10 hours. Fibre optical loss for the 10 hour melt was relatively flat (around 5 dB.m-1) over the entire 700 nm to 2.5 micron region.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA1501 Applied optics. Phonics