All-Fiber Synapse Based on Ge₂Sb₂Te₅ for Reconfigurable Logic Operations

Synapses are the key component in neuromorphic computing due to their abilities of signal memory, preprocessing and transmission. Synapses with nonvolatile and reconfigurable logic functions show high flexibility and strong calculating capacity when facing complex practical problems. We propose a nonvolatile all-fiber synapse (AFS) with reconfigurable logic functions. The functions are realized in an optical device where nonvolatile Ge<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>Sb<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>Te<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (GST)-integrated microfiber is placed on top of one arm of the fiber Mach-Zehnder interferometer. By using laser pulses, GST complex refractive index can be modulated through strong light-matter interactions and thermo-optic effects. This modifies the device transmission and subsequent the weight of AFS, enabling 10 dB modulation contrast. In addition, important synaptic functionalities, such as excitatory/inhibitory postsynaptic current (EPSC/IPSC), long-term potentiation/depression (LTP/LTD), spike amplitude-dependent plasticity (SADP), and spike number-dependent plasticity (SNDP) can be mimicked in such device. Remarkably, the reconfigurable logic functions such as AND, OR, NAND, NOR, and XOR can be also achieved in the single fiber-based device by controlling the phase of one arm of AFS and applying SADP, to obtain various on-demand responses to input optical signals. Overall, this work shows promising prospects for information processing in fiber communication networks.