Gain optimization in switches based on semiconductor opticalamplifiers

The distribution of unsaturated gains that minimizes the noise figure of a three-stage optical switch based on semiconductor-optical-amplifier (SOA) gates is found. Gain saturation under both unidirectional (isolators inserted) and bidirectional (no isolators) propagation of spontaneous emission noise is analyzed, and a noise figure penalty associated with the absence of isolators is determined. Determination of the optimal set of pump currents is a nonlinear optimization problem, while determination of the optimum set of saturated gains is a linear optimization problem. The latter solution is found analytically, while the former solution requires a nonlinear optimization approach. The results are extended to the case of a sequence of N SOA's