Sigmoid type neuromorphic activation function based on saturable absorption behavior of graphene/PMMA composite for intensity modulation of surface plasmon polariton signals

For an optical technology to be feasible as a substitution of electronics one for neuromorphic applications, it is required the waveguides in which are capable of confining and directing light signals in much smaller dimensions than the operating wavelength of the light, i.e., subwavelength optical components must be realized. Hybrid nature of surface plasmon polariton addresses the problem with the diffraction limit of regular photonic components. Here, the authors present a two-dimensional numerical simulation of a passive photonic element based on a saturable absorber material as a hardware base analogy to the biological activation function existed at the cell body of neurons. They demonstrate that at telecom wavelengths, a highly confined SPP mode can be modulated in a nonlinear fashion by considering the carrier dynamics of graphene/PMMA polymeric composite as a two-level system. The hardware base sigmoid type nonlinear activation function derived from this study further characterized; and the parameters which appeared to be effective on the performance of the structure, such as saturation intensity, modulation depth, and thickness of the synaptic part as a Fabry–Pérot structure, have been studied.