
360 Optical Fiber Communication Systems with MATLAB
®
and Simulink
®
Models
Stage 3
(Figure 9.6)
Stage 4
(Figure 9.7)
The
coherence of pump sources and signals implies that the incident photon and the stim-
ulated
one have the same frequency, phase, propagation direction, and polarization [15, 16].
The optical gain is achieved when the population inversion reaches a sufciency high level
at which the absorption from the ground state is considerably reduced. This can be readily
achieved with available pump lasers because the metastable state exists in Er
3+
thus rendering
the population inversion possible. In addition, the photon lifetime from the ...