Short-cavity EDFA: The theoretical analyses of the short OGC-EYDFA
can be efficiently done by using a laser rate-equation model that we have
recently proposed to describe the device from a laser point of view [5].
Solving the rate-equation, we have found that overshoot after channel
drop increases as the square root of cavity length. Therefore short fibre
E(Y)DFA or EDWAwill outperform standard EDFA [4]. In addition, the
power overshoot increases as pump power is reduced, i.e. as the laser
operates closer to the threshold level. The intrinsic stability of the short
OGC-EDFAwill thus result in an extra benefit as little extra pump power
is required to stabilise laser action [6]. We will use the parameter x, the
ratio between used pump power and laser threshold power, to evaluate
the extra pump power. In fact the laser threshold power also almost
corresponds to not-clamped OA operation. Working close to the laser
threshold will also generate lower lasing power that will have negligible
impact on the optimum inversion profile along the active fibre (laser
saturates usually one end of output coupler). As a consequence no noisefigure
degradation is observed [8].