  We experimentally demonstrate that networks of identical photonic spiking
neurons based on coupled degenerate parametric oscillators can show various
chimera states, in which, depending on their local synchronization and
desynchronization, different kinds of spiking dynamics can develop in a
self-organized manner. Even when only a static interaction is implemented,
through synchronized inputs from connected neurons, the spiking mode of
photonic neurons can be spontaneously and adaptively changed between the
Class-I and Class-II modes classified by A. L. Hodgkin. This spontaneous
spiking-mode shift induces a significant change in the spiking frequency
despite the all neurons having the same natural spiking frequency, which
encourages the generation of chimera states. Controllability and self-organized
flexibility of the spiking modes in the present system allow us to create an
experimental platform to explore the nature of chimera states in neuromorphic
spiking neural networks.
