Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 235
Comparison of infrared spectra of oxide tellurite glasses with a view to the manufacture
of low optical loss mid-infrared fibre
Glasses in the ternary system TeO2-ZnO-Na2O exhibited transmission to around 1667
cm -1 (6 µm) with OH absorption bands of around 0.6 cm -1 (600 dB.m -1 ) in intensity. The
addition of a few mol. % GeO2, PbO, or varying the ZnO content of these glasses did not
dramatically alter the multiphonon edge, or intensity of the OH bands. The OH bands in
the tungsten-tellurite glasses were less intense than the TeO2-ZnO-Na2O glasses, at
around 0.2 cm -1 (200 dB.m -1 ). However, these glasses did not transmit as far into the
infrared, and addition of tungsten significantly shifted the multiphonon edge to higher
wavenumbers: 5 mol. % WO3 1862 cm -1 (5.37 µm), 7.5 mol. % WO3 1905 cm -1 (5.25
µm), and 25 mol. % WO3 1946 cm -1 (5.14 µm). For low loss fibre in the 2 to 5 µm
region, the tungsten-tellurite glasses would be more suitable than the TeO2-ZnO-Na2O
glasses, due to the lower intensity OH bands seen, although reflection losses would be
higher due to higher refractive indices. Because of the refractory nature of the compounds
in the tungsten-tellurite glasses (WO3 and Nb2O5), fibre pulled from these materials
would have better environmental durability than the TeO2-ZnO-Na2O based glasses.
However, processing such as fibre drawing would have to be carried out at higher
temperatures as the fibre drawing viscosity (≈ 10 4.5 Pa.s) would occur at higher
temperatures for the tungsten-tellurite glasses compared to the TeO2-ZnO-Na2O glass. If
transmission is required to 6 µm, the TeO2-ZnO-Na2O based glasses would be more
suitable, and have the advantage of altering the refractive index for a core / clad pair with