  There has been a recent surge of interest in the implementation of linear
operations such as matrix multipications using photonic integrated circuit
technology. However, these approaches require an efficient and flexible way to
perform nonlinear operations in the photonic domain. We have fabricated an
optoelectronic nonlinear device--a laser neuron--that uses excitable laser
dynamics to achieve biologically-inspired spiking behavior. We demonstrate
functionality with simultaneous excitation, inhibition, and summation across
multiple wavelengths. We also demonstrate cascadability and compatibility with
a wavelength multiplexing protocol, both essential for larger scale system
integration. Laser neurons represent an important class of optoelectronic
nonlinear processors that can complement both the enormous bandwidth density
and energy efficiency of photonic computing operations.
