Analysis of competing mechanisms in transitions between excited states in Er-doped integrated waveguides

A new procedure for determining the prevalence of either excited-state absorption (ESA) or nonradiative cooperative energy transfer between erbium ions in transitions between excited states in Er-doped integrated waveguides is presented. These transitions are currently very attractive for the development of upconversion lasers. The procedure is based on the analysis of the dependence on the transition-originating mechanisms of the modulation transfer from the pump to the excited levels' population. The accuracy and validity range of the method are studied numerically using ordinary integrated structures. By using this procedure, the ratio of the contributions of the two competing mechanisms to the /sup 4/I/sub 13/2/ /spl rArr/ /sup 4/I/sub 9/2/ transition is determined from fluorescence measurements on a Er,Ti:LiNbO/sub 3/ sample excited by a 1480-nm pump. Moreover, new values of the excited-state pump-absorption cross section from level /sup 4/I/sub 13/2/, /spl sigma//sub 24/ (/spl ap/1480 nm) = 0.8 /spl times/ 10/sup -26/ m/sup 2/, and of the parameter associated with nonradiative cooperative energy transfer between Er/sup 3+/ ions, C/sub 22/ = 3 /spl times/ 10/sup -24/ m/sup 3/ s/spl middot//sup -1/, are reported.