Erbium and ytterbium doped phosphotellurite glasses for lasers and optical amplifiers

Abstract

The luminescence from rare earth ions offer ample prospect for fabrication of laser and amplifier. Erbium (Er) doped tellurite glasses provide broad C+L band (1535-1610nm) amplification suitable for wavelength division multiplexed (WDM) optical communication networks. Tellurite glasses are important because of their high emission cross-section, higher gain bandwidth, wide range of transparency and higher nonlinear refractive index comparing to many other glasses. However, tellurite based glasses have some drawbacks such as low glass transition temperature (Tg) and low phonon energy. The multiphonon relaxation rate of the Er3+ ions from 4I11/2 (pump level) to 4I13/2 level (lasing level) is less due to low phonon energy of the tellurite glass, thus making the 980nm pumping of Er3+ ions from 4I15/2 (ground state) to 4I11/2 transition less efficient. To increase the phonon energy of the tellurite based glasses, approaches like addition of tungsten oxide and borate are reported. In the present thesis work, phosphate has been used as an additive in the tellurite host in order to address the issue of low phonon energy as well as low glass transition temperature. Phosphotellurite (PT) glasses have attracted the attention of many researchers in the past due to the interesting structural properties that results from mixed network formers viz., tellurite and phosphate. Neodymium doped PT glasses have been studied for laser applications and PT glasses containing heavy metal oxides have been reported for ultra broadband fibre Raman amplifiers..