Tellurite And Fluorotellurite Glasses For Active And Passive

2. Literature review; MDO 38
near field spectroscopy, by etching a tip on the end of the fibre (e.g. sub-cellular
spectroscopy) [38].
Laser power delivery in the infrared is also another possible usage for these materials.
Welding and surgical lasers are the two main applications in this field. The use of optical
fibre to deliver the beam would significantly reduce the size of current systems [35].
Surgical lasers operate at the resonant frequencies of organic groups present in tissue,
such as OH (2.94 µm), or for cleaner incisions, proteins (6.45 µm) [38]. Surgical fibres
must lack toxicity, have relatively low loss at the laser wavelengths (< 1 dB.m -1 ), be
resistant to damage from high laser power, and possess a small bend radius to enable easy
manipulation [35].
2.4.2. Optical loss mechanisms
Attenuation in an optical fibre can be categorised by absorption or scattering losses. The
source of these losses can be either intrinsic to the material, or extrinsic, and in theory the
latter reduced significantly, or eliminated with careful processing. The multiphonon and
electronic absorption edges are intrinsic to the constituent atoms / ions present in the
glass, and can be shifted with composition.
Transition metals, such as Fe, Cr, Mo, and Co, exhibit absorption bands in the near-IR,
but contribute to attenuation less than the scattering component, in parts per billion
concentration (loss depends on valence, and coordination of ions in the glass host).
However, OH contributes significantly to loss, even at parts per billion levels [39], and is
much more difficult to eliminate from the glass.