Small signal gain and saturation intensity of a Yb:Silica fiber MOPA system

In this work, the small signal gain (γ0) and signal saturation power (Psat) of a continuous wave (CW) single-frequency ytterbium-doped (YD) double-clad (DC) fiber master oscillator power amplifier (MOPA) array has been determined in the optimum length. At first, we have obtained output versus input signal powers in the amplifier, using the coupled steady-state rate equations for the various end diode pumping such as co/counter propagation and bidirectional modes. On the other hand, the steady-state amplification relation was employed at a presumed γ0 and Psat as initial guess, to generate output signals. Then, using the least square method (LSM), those input/output signal powers were fitted by the best regression curve obtained from the amplification relation to determine the converged γ0 and Psat values. The analytical formulae for γ0 and Psat were derived using the rate equations as well.