Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 245
and θ = 20°. These glasses also transmitted to around 6 µm, whereas the tungsten-tellurite
glasses only transmitted to around 5.25 µm.
A suitable core / clad pair for a fluorotellurite multimode optical fibre operating at
632.8 nm would be MOF001 (25 mol. % ZnF2) as the clad (n2 = 1.887) and MOF005 (20
mol. % ZnF2) as the core (n1 = 1.914). Using equation (2.5), this gives NA = 0.32, and θ =
19°, an intermediate NA and acceptance angle compared to the oxide core / clad pairs
suggested above. Both glasses were relatively thermally stable on reheating, with a high
Tx-Tg (161°C for MOF001 and 153°C for MOF005). They also had similar glass
transition temperatures (237°C for MOF004 and 241°C for MOF005), and hence
probably minimal thermal expansion (TEC) mismatch (important for making strong fibre)
as the product TEC/Tg tends to be constant across a particular limited range of glass
compositions. These compositions also showed low intensity OH absorption bands at
2900 cm -1 (20 dB.m -1 ), and transmitted to around 6 µm. Therefore the fluorotellurite
glasses would probably be a better core / clad pair than the oxide glasses in terms of
thermal and optical properties.
6.5. References
[1] S. F. Dyke, A. J. Floyd, M. Sainsbury, and R. S. Theobald, Organic Spectroscopy
an Introduction. London: Longman, 1978.
[2] D. C. Harris and M. D. Bertolucci, Symmetry and spectroscopy: An introduction
to vibrational and electronic spectroscopy. New York: Dover, 1989.
[3] P. W. Atkins, Physical chemistry, 5th ed. Oxford: Oxford University Press, 1994.