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We present the first experiment of intracavity pumping at 914nm of an Yb:S-FAP crystal emitting at 985nm on the three-level-laser transition. We obtained 250mW output power at 985nm for 9.7W incident pump power at 808nm.

In the scope of high rate submarine long haul transmissions, different kind of in line control systems are investigated.

We present an analytic model of polarization hole burning in Er3+ doped fibre amplifiers. The influence of both the pump and signal fields is examined. Optimum pump polarization is deduced for long-haul transmission systems.

The efficiency of unsaturated amplifiers scales as k = 1/σaτ, where σa is the absorption cross-section of the pump and τ is the lifetime of the metastable excited level. For μm direct pumping of praseodymium (DPP), k ≤ 2.5 10−29 m−2s−1’ which is to compare to 4. 10−26 m−2s−1 for 980 nm pumping of 1.55 μm erbium-doped fiber amplifiers (EDFA). This small value of k is both due to a short lifetime (non radiative decay is 30 times more efficient than radiative decay) and a weak absorption. The other consequence of the weak absorption is the use of cither long fibers or high praseodymium concentration. High NA monomode ZBLAN fibers are still lossy (0.05 to 1 dB/m) which reduces the gain of long fibers. Upper lasing level lifetime of praseodymium is quenched by cross-relaxations for praseodymium concentrations beyond 1000 ppm wt (ref. 1) which reduces the efficiency of these fibers. Optimization of direct pumping of praseodymium (DPP) results in a trade-off between fiber loss and 1G4 level lifetime.