Optical transitions of rare earth ions for amplifiers: how the local structure works in glass

Abstract

Several properties of 4f optical transitions of rare earth ions in glasses utilized as optical amplifiers for telecommunications are discussed. For the Er 3+: 1.55 μm transition, the role of Judd–Ofelt Ω 6 parameters is presented. With compositional change in structure of aluminosilicate glasses, the changes of the radiative cross section, quantum efficiency, and flatness, is observed, which are especially important for the amplifiers in the wavelength-division-multiplexing (WDM) network system. Moreover, the energy level structures and resultant spectral properties of Pr 3+, Nd 3+ and Dy 3+ ions, all of which are 1.3 μm-active ions, are compared. The hypersensitivity of Dy 3+ transitions appears especially in chalcogenide glasses, where the non-radiative loss due to multiphonon emissions is minimized. Compositional variations of the branching ratio and radiative cross sections, and their dependence on the Ω 2 parameters, which are affected by the asymmetry of the rare earth ion sites, are discussed.