Tellurite And Fluorotellurite Glasses For Active And Passive

8. Fibre drawing; MDO 367
8.3.4. Optical loss of fluorotellurite fibre
Fig. (8.16) shows the optical loss of fibre of composition MOF005 (70TeO2-10Na2O-
20ZnF2 mol. %) with various melting times (3, 4, 5 and 10 hours). After 3 hours of
melting, the fibre exhibited a minimum loss at around 6000 cm -1 (1.67 µm) of around 5
dB.m -1 . From this minimum, the loss increased in the infrared to over 35 dB.m -1 at
around 4200 cm -1 (2.38 µm). The loss also increased into the visible region (beyond
14000 cm -1 → 714 nm) to over 20 dB.m -1 , likely to be due to scattering (proportional to
1
4
λ ). After 4 hours of melting, the fibre showed minimum loss at around 6000 cm-1 (1.67
µm) of about 2.5 dB.m -1 . From this minimum, the loss increased into the infrared to over
12 dB.m -1 at around 4200 cm -1 (2.38 µm). The loss also increased into the visible region
(beyond 14000 cm -1 → 714 nm) to over 10 dB.m -1 , again likely to be due to scattering.
For the glass melted for 5 hours the minimum loss of around 3 dB.m -1 occurred at around
4000 cm -1 (2.5 µm) and increased to over 15 dB.m -1 into the visible region. The glass
melted for 10 hours showed a minimum loss of around 4 dB.m -1 at around 4000 cm -1 (2.5
µm) and stayed at 5 dB.m -1 or below over the entire 700 nm to 2.5 µm region [9]. It is
interesting to note, the fibre made using fluorinated ZnF2 (5 and 10 hr. melts) does not
exhibit the intense band around 2.5 µm attributed to the first overtone of strongly
hydrogen bonded OH in the glass. This is to be expected, as fluorination and longer
melting times will significantly reduce the amount of OH in the glass, resulting in few
nearest neighbours for remaining OH groups to H-bond to.