Lifetime quenching in Yb-doped fibres

Abstract

We have discovered that in ytterbium-doped silica fibres the excited state lifetime of a fraction of the Yb ions can be quenched to a very small value, leading to a strong unbleachable loss. This unexpected behaviour seems to be caused by some, yet unidentified, impurity or structural defect. It is of considerable relevance for various Yb doped lasers and amplifiers including Er:Yb codoped fibres as used in telecommunication amplifiers although it should also be emphasized that fibres can be produced that are free from the quenching effect.

Experimentally verified modeling of erbium-ytterbium co-doped DFB fiber lasers

“…The fiber with lower Yb concentration ( m ) exhibited an unsaturable loss 2 3 m (13 dB/m), whereas in the fiber with large Yb concentration ( m ), this value was as large as 30 m (130 dB/m). The unsaturable loss phenomenon in Yb-only-doped media has been reported previously [10], [27], [28]. Although the exact mechanism behind this absorption has not yet been explained, the overall effect appears to be due to lifetime quenching of a portion of Yb ions.…”

“…Around this wavelength, the Yb absorption is largest, which leads to the maximum energy transfer from pump to signal over the shortest length. The total pump absorption coefficient by both Yb and Er ions is given by (10) where is the overlap coefficient between the pump power distribution and the active medium cross section. stands for any constant background loss at the pump wavelength.…”

“…An extremely small lifetime causes the excited state ions to return to ground state very quickly through some nonradiative relaxation. Since this cycle is completed very fast, absorption due to the quenched ions appears to be an unsaturable loss in addition to normal Yb saturable absorption [10].…”

“…In addition to the basic absorption and emission transitions of a quasi-three-level system, there is energy transfer between Er and Yb ions, in both directions; the excited state absorption (ESA) of both pump and signal is possible; cooperative upconversion for ions at various excited states is allowed, which may be a two-, three-, or many-ion interaction; and the relaxation of excited ions can be through phonon emission as well as spontaneous emission, such as at green light wavelengths. Also lifetime quenching of Yb ions has been reported [10]. Therefore, the full description of the medium would include many linear and nonlinear equations.…”

Spectroscopic excitation and quenching processes in rare-earth-ion-doped AI203 and their impact on amplifier and laser performance

“…5.1 show the pump absorption versus launched pump power of the waveguide with an Er A number of authors [109][110][111][112][113] have attributed a similar behavior observed in other host materials to a fast quenching process. In our samples, such a process can be induced by, e.g., fast static ETU due to active ion pairs or clusters, energy transfer to undesired impurities, or trapping of excitation energy by host material defects, such as voids.…”