Analytical model of an ytterbium-erbium fiber saturating amplifier

Kinetics of the refractive index change in the core of active fibers, doped with Yb3+ and Er3+ ions, under pulsed optical pumping

“…As was shown in [16], when strong incoherent interaction is implemented, the excitation transfer rate c cr N Yb in phosphate fibers can be as high as 10 7 s -1 or more. This value can be reached in optical fibers with clusterization of rare earth ions when .…”

“…We assume also that the inversion changes only slightly for the time during which the pump pulse front passes through the active medium. On these assumptions, the system of rate equations in the subthreshold regime can be written as (see, for example, [16]) where and are the concentrations of ytter bium and erbium ions in the active medium.…”

“…The calculated phases at the end of the pump pulse were used for the pump powers below the threshold, and the calculated phases at the lasing onset were used for pumping above the threshold. The proportionality of the thermal and electronic contributions from erbium ions is due to the following: after reaching equilibrium, the thermal source power is proportional to the population of the metastable level of erbium ions: (16) A sharp increase in the contribution of ytterbium related electronic RICs is due to the inhomogeneous pump distribution along the active fiber length: at high pump powers, the erbium subsystem becomes almost completely inverted in some regions of the active medium; excitation is not transferred in these regions, as a result of which the population of the ytterbium metastable level increases and the contribu tion of Yb ions to the total RIC increases as well. The slope of the dependence for ytterbium related elec tronic RICs in this figure is 14.5 rad/W.…”