Optically Readable Waveguide-Integrated Electrochromic Artificial Synaptic Device for Photonic Neuromorphic Systems

Despite advances in numerous artificial synaptic devices, the search for a new functionalized synaptic device remains the subject of rigorous investigation for constructing neuromorphic systems. Optical readout functionality in artificial synapses is interesting as on-chip photonic integration technology could increase bandwidth and signal transmission, stop signal interference, reduce power loss, and provide degrees of freedom that complete the photonic neuromorphic system using light rather than electrons. Here, a waveguide-integrated electrochromic artificial synaptic device in which the electrolyte-gated electrical synaptic signal is read by optical means is demonstrated. The optically readable electrochromic synaptic device successfully imitates essential synaptic functions, such as short- and long-term plasticity, excitatory and inhibitory postsynaptic potentiation, and paired-pulse facilitation. In addition, randomly accessible nonvolatile multilevel optical memories are also demonstrated based on electrolyte ion dynamics that enable electrical switching of the transparency of the electrochromic material in a nonvolatile manner. This optically readable artificial synapse approach based on photonic integration circuit technologies provides insight into an exact reading of the emulation of the biological synapse in an optical manner and is a key step toward the implementation of non-conventional photonic neuromorphic systems with tunable bio-inspired synaptic functions.