Tellurite And Fluorotellurite Glasses For Active And Passive

2. Literature review; MDO 33
depolymerisation will occur with addition, as was shown with ZnO [22], although it will
not be as significant as with Na2O addition.
Nazabal et al. [30, 31] showed for the TeO2-ZnO-ZnF2 system, that ZnF2 addition
increases the amount of [TeO3] in the glass at the expense of [TeO4] via [TeO3+1], much
like ZnO and to a lesser extent than Na2O.
2.4. The impact of fibreoptics
The transmission of light along a curved dielectric cylinder was the subject of a
spectacular lecture demonstration by John Tyndall in 1854 [32]. His light pipe was a
stream of water emerging from a hole in the side of a tank which contained a bright light.
The light followed the stream by total internal reflection at the surface of the water. Light
pipes made of flexible bundles of glass are now used to illuminate internal organs in
surgical operations in the endoscope which also transmits the image back to the surgeon.
As already introduced in chapter 1, the overwhelming use of glass fibres is, however, to
transmit modulated light over large distances at high speeds with low loss for
communications, first shown by van Heel in 1954 [33]. Unlike coaxial cable, optical fibre
loss does not depend on frequency in the 10 MHz to 1 GHz region [34].
Electrical communication cables and radio have largely been replaced by optical fibre
in long-distance terrestrial communications. Hundreds of thousands of kilometres of fibre
optic cables are now in use, carrying light modulated at high frequencies, providing the
large communication bandwidths needed for television and data transmission. The
techniques which made this possible include the manufacture of glass with very low