  Neuromorphic photonics that aims to process and store information
simultaneously like human brains has emerged as a promising alternative for the
next generation intelligent computing systems. The implementation of hardware
emulating the basic functionality of neurons and synapses is the fundamental
work in this field. However, previously proposed optical neurons implemented
with SOA-MZIs, modulators, lasers or phase change materials are all dependent
on active devices and quite difficult for integration. Meanwhile, although the
nonlinearity in nanocavities has long been of interest, the previous theories
are intended for specific situations, e.g., self-pulsation in microrings, and
there is still a lack of systematic studies in the excitability behavior of the
nanocavities including the silicon photonic crystal cavities. Here, we report
for the first time a universal coupled mode theory model for all side-coupled
passive microresonators. Attributed to the nonlinear excitability, the passive
microresonator can function as a new type of all-optical spiking neuron. We
demonstrate the microresonator-based neuron can exhibit the three most
important characteristics of spiking neurons: excitability threshold,
refractory period and cascadability behavior, paving the way to realize
all-optical spiking neural networks.

Optics