Photonic implementation of the synaptic depression functions based on a vertical-cavity semiconductor optical amplifier

Based on typical Fabry-Pérot (F-P) analysis approach, we numerically simulate the output characteristics of a vertical-cavity semiconductor optical amplifier (VCSOA) under optical pulse injection. The results demonstrate that the VCSOA can be utilized as a photonic synapse to mimic biological synapses with depression-related functions. First, adopting a pair of optical pulse injection to stimulate the VCSOA, the paired-pulse depression (PPD) at sub-nanosecond scale can be observed. Thisbehaviorisanalogoustothat in biological synapses, but its characteristic relaxation time is much faster above 8 orders of magnitude than those of biological synapses. Next, adopting continuous optical pulse injection to stimulate the VCSOA, the inhibitory behaviors of the photonic synapse are further investigated. Through varying the bias current and injection pulse power, the inhibitory behaviors can be controlled, and the synaptic weight (SW) of the photonic synapse is decreased with the enhancement of the inhibitory behaviors. Meanwhile, some characteristics of the VCSOA in biological synapses such as spiking-duration-dependent plasticity (SDDP), spiking-rate-dependent plasticity (SRDP), and spiking-number-dependent plasticity (SNDP), are demonstrated. Finally, the potential of the VCSOA-based photonic synapse as a low-pass filter (LPF) is preliminarily demonstrated.