Tellurite And Fluorotellurite Glasses For Active And Passive

1. Introduction; MDO 3
distance systems operate at 1.3 and 1.55 µm using InGaAsP sources, where losses and
pulse dispersion are lowered. 1.55 µm operation can incorporate all optical amplifiers;
erbium doped fibre amplifiers (EDFAs), with erbium (III) - Er +3 , doped into the silica
glass [2]. These are fast, and the signal no longer has to be transduced to electronics for
amplification (hence all optical). EDFAs can transmit data at 2.4 Gbit.s -1 over a distance
of 21,000 km [8], with efficiencies around 50,000 Gbit.km.s -1 [9], without the need for a
repeater, and performance of these devices has since increased further due to wavelength
division multiplexing (WDM) [6]. WDM currently allows the simultaneous transmission
of around 100 different wavelengths along one fibre, to increase signal capacity, and is at
present limited by the flatness of gain of the EDFA.
1.2. The role of novel glass compositions
Novel glass compositions made from constituents other than SiO2, such as fluorides,
chalcogenides, and heavy-metal oxides, are more optically flexible than silica, having a
wide range of transparent windows, linear and non-linear refractive indices, and lower
phonon energies, for more efficient rare-earth luminescence [10]. This lower phonon
energy than silica, results in substantially increased rare-earth lifetimes in the glass host
(and possibly shifted and broadened emission bands), as de-population of excited states is
statistically less likely by non-radiative processes. Rare-earth solubility is often higher in
novel glass hosts [11]. These are important considerations for developing the next
generation of low loss broadband, flat gain fibre amplifiers.