Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 225
Stanworth [7] studied the optical spectra of a number of PbO-containing tellurite
glasses; however these were melted in ceramic (silica, alumina and zirconia) crucibles,
and therefore would probably have been contaminated. Feng et al. [8, 9] studied the
spectral properties of glasses of the system TeO2-Na2O-ZnO-GeO2-Y2O3-Er2O3. This
group added GeO2 to the ternary system TeO2-Na2O-ZnO [10] with the potential to
increase the viscosity at fibre drawing temperatures, and therefore inhibit crystallisation
[9]. Er2O3 was added for luminescence at 1.5 µm with potential for all-optical
amplification, and stability after work by Wang et al. [10]. Y2O3 was hoped to have a
similar stabilising effect to Er2O3 [9]. This work showed glass stability to increase with
GeO2 and Y2O3 addition [9].
The aim of synthesising bulk glasses in this study was a precursor to producing low
optical loss fibre. The position of the multiphonon edge is important for a wide mid-IR
transmission window. However, the tellurite glasses reported by Feng et al. [8, 9] were
found to contain significant absorption bands in the infrared due to hydroxyl groups, also
seen in this study in figs. (6.8) to (6.10). Reactive atmosphere processing (RAP) by this
group [8] (bubbling CCl4 through the melt) did reduce these bands, but not significantly
(see fig. (2.12)). It is interesting to note that the glasses prepared by Feng et al. exhibited
OH bands with an intensity of around 3 cm -1 (3000 dB.m -1 ) before RAP, and around 2
cm -1 (2000 dB.m -1 ) after RAP [8]. The GeO2 containing glass melted in this study
(MOD012) exhibited OH bands of around 0.8 cm -1 (800 dB.m -1 ) without RAP, and are
therefore relatively dry by comparison. The TeO2-ZnO-Na2O-PbO glasses melted in this
study were even dryer, with OH band intensities of around 0.55 cm -1 (550 dB.m -1 ).