A detailed analysis of the efficiency of four-wave mixing (FWM)
is performed for a closely spaced energy state quantum dash semiconductor
optical amplifier (SOA). The analysis takes into account the effect
of all discrete energy states, the gain dispersion of the quantum dash,
and the effect of doping on the FWM characteristics. Our analysis reveals
that large FWM efficiency can be obtained when the energy of the pump
signal is equal to the first excited state. We find that at low-applied current
doping the dashes by p-type concentration enhances the FWM efficiency.
While at high applied current, we find that doping the SOA with p-type
concentration slightly enhances the FWM efficiency of the ground state
and the first excited state and lowers the FWM efficiency of the higher excited
states. Also we find that doping the dashes by n-type concentration
slightly modifies the FWM efficiency spectrum.