Two micron tellurite fibre lasers

Abstract

Glasses based on tellurium oxide (TeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) are well suited to act as host materials for fibre lasers emitting at wavelengths of 2 µm and greater, the spectral region in which optical absorption in silica fibres becomes significant. In particular, tellurite glass has a phonon energy of 600–800 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , significantly less than both silicates and germanates, which enables transmission of wavelengths as long as 5 µm. This low phonon energy also ensures that non-radiative recombination rates are low and the lifetime of excited states of rare earth (RE) dopants are long. Furthermore, tellurite glasses have high refractive indices which both enables high numerical aperture fibres to be fabricated and results in high absorption and emission cross-sections for RE dopants. These high cross-sections coupled with the high solubility of REs in tellurite glass allow lasing to be achieved using only short fibre lengths. Finally, tellurite glass is more stable thermally and chemically than fluoride glass, another fibre laser host material also transparent in this region.