  The rapid growth of brain-inspired computing coupled with the inefficiencies
in the CMOS implementations of neuromrphic systems has led to intense
exploration of efficient hardware implementations of the functional units of
the brain, namely, neurons and synapses. However, efforts have largely been
invested in implementations in the electrical domain with potential limitations
of switching speed, packing density of large integrated systems and
interconnect losses. As an alternative, neuromorphic engineering in the
photonic domain has recently gained attention. In this work, we demonstrate a
purely photonic operation of an Integrate-and-Fire Spiking neuron, based on the
phase change dynamics of Ge$_2$Sb$_2$Te$_5$ (GST) embedded on top of a
microring resonator, which alleviates the energy constraints of PCMs in
electrical domain. We also show that such a neuron can be potentially
integrated with on-chip synapses into an all-Photonic Spiking Neural network
inferencing framework which promises to be ultrafast and can potentially offer
a large operating bandwidth.
