Tellurite And Fluorotellurite Glasses For Active And Passive

2. Literature review; MDO 37
Non-silica based glass hosts typically exhibit higher rare-earth solubility, and lower
phonon energies, which results in longer excited state lifetimes of transitions in the glass.
Emission bands of rare-earths may also be shifted and broadened in these glasses,
compared to silica. Some novel glass groups have recently been investigated as Raman
amplifiers, such as tellurite glasses which exhibit Raman gain around 30 times that of
silica [37]. As well as amplification, infrared fibres find a number of other possible
applications in telecommunications such as switching and multiplexing [35].
The fundamental absorption bands for many organic groups lie beyond 2 µm
(attenuation in silica increases exponentially beyond 1.55 µm), therefore IR spectroscopic
sensing is a potential application for these materials. Fundamental frequencies of organic
groups will also be of much higher intensity than the overtone bands which silica can
transmit. Sensing of explosive materials, where the presence of an electric current may be
catastrophic, gives fibre optic sensors a distinct advantage [35]. Remote sensing ‘in the
field’ is another benefit of these devices, as spectroscopy can be carried out without
collecting samples which may degrade on transportation to a laboratory, or are toxic /
radioactive [38]. Fibre can be implanted in a medium, such as a resin or a biological
sample, and detect the chemical changes in the medium by spectroscopy of the
evanescent wave traveling in the cladding which interacts with the sample [35]. These
materials can be used for radiometric temperature sensing, and thermal imaging. Their
increased transmission range gives them a distinct advantage over silica, as very hot
sources, such as engine exhausts produce radiation in the 2 to 6 µm region (e.g. missile
countermeasures on a fighter jet [38]). Room temperature objects however emit further
into the infrared region: 8 to 12 µm [35]. Infrared fibres can also be used for scanning