ABSTRACT
Wavelengths within the gain band of the semiconductor optical amplifier (SOA) will deplete the carrier concentration while shorter wavelengths can pump it for the opposite effect. Due to the gain depletion property of the SOA, the spike output is inverted. The temporal integration block consists of an SOA with a gain sampling mechanism. The working principle of an SOA integrator is based on the decrease in carrier density induced by an optical pulse launched to the SOA, and the exponential recovery behavior of the carrier density in the presence of a pumping current. Gain sampling is used as the means of converting SOA carrier density to pulse intensity. To control the firing of neurons, the pulses representing the change in carrier density are then launched to an optical thresholder. Since both the SOA and the mode-locked laser are integratable devices, the ability to integrate the feedforward neuron depends crucially on shrinking the thresholder into a small footprint.
