Weight adjustable photonic synapse by nonlinear gain in a vertical cavity semiconductor optical amplifier

In this paper, we report a high-speed and tunable photonic synaptic element based on a vertical cavity semiconductor optical amplifier (VCSOA) operating with short (150 ps-long) and low-energy (mu W peak power) light pulses. By exploiting nonlinear gain properties of VCSOAs when subject to external optical injection, our system permits full weight tunability of sub-ns input light pulses, just by varying the VCSOA's applied bias current. Not only is the VCSOA-based synapse able to adjust the strength of incoming optical pulses, but it can also provide gain (applied weight factors > 1). Moreover, we show that this simple approach permits dynamical weight tuning at high-speed (ns rates) with up to an 11.6-bit precision. These results are realized with commercially sourced, inexpensive vertical cavity surface emitting lasers, operating at the key telecom wavelengths of 1300 and 1550 nm and hence making our approach compatible with optical network and data center technologies. This VCSOA-based system, therefore, offers a hardware friendly, low-energy, and high-speed solution for photonic synaptic links with high potential for use in future neuromorphic photonic systems.