Tellurite And Fluorotellurite Glasses For Active And Passive

2. Literature review; MDO 36
sharp signal launched into the fibre will spread out in space and time, resulting in a
distorted, noisy signal at the receiver. To overcome this, a very small core (of the order of
the wavelength of the light) can be used so only one mode propagates (single mode
fibre), or a complex refractive index profile (e.g. parabolic graded index fibres) can be
utilised, so essentially all modes propagate at the same speed [35].
2.4.1. Infrared (IR) fibre optics and potential applications
With the current interest in an efficient broadband, flat gain fibre optic amplifier and low-
loss infrared (IR) optical fibre, a number of ‘novel’ glass systems have received
considerable attention in the last 10 years, the three major groups include: chalcogenides
(anionic moiety in glass is sulphur, tellerium and / or selenium), fluorides and heavy
metal oxides (HMOs). Tellurite (TeO2) glasses, studied here, belong to the HMO group.
Advantages of tellurite glasses include [36]:
• reasonably wide transmission range, from visible to mid-IR (≈ 400 nm to 6 µm);
• good glass stability, strength and corrosion resistance;
• relatively low phonon energy for an oxide glass (≈ 800 cm -1 ) for amplification
applications;
• high refractive index (≈ 2) for non-linear applications; and
• ease of fabrication due to presence of oxide.