Experimental and numerical study of interlock requirements for high-power EYDFAs

In this work, we studied the interlock requirements in a seed failure scenario for Er³⁺:Yb³⁺ doped fiber amplifiers (EYDFAs) pumped with high intensities in the MWcm^-2 range at 9XX nm. We fed a time-dependent FEM-tool with the data from backwards directed amplified spontaneous emission (ASE) transients of different commercially available core-pumped single-mode fibers. In the FEM-tool, the Er³⁺:Yb³⁺ system is defined as a bi-directional energy transfer process and described by the corresponding rate equations. The power evolution of the pump, seed, and ASE signal is computed by differential equations taking into account the transient population densities of the relevant energy levels. With the model, we computed the temporal evolution of the corresponding energy levels after a seeder failure to take place within tens to hundreds of µs and calculated the associated gain. The fibers under test provide a critical total gain of 30 dB after ∼ 80 µs within the Yb³⁺ band and after ∼300 µs within the Er³⁺ band. This time decreases with increasing pump power and doping concentration. The results can be extrapolated to high-power cladding-pumped EYDFAs to meet the challenging requirements of engineering-level systems.