High Q-factor ring resonator nested in Mach–Zehnder interferometer based on Ge₂Sb₂Te₅ phase change material for realization of synapses in optical neural networks

Abstract In this study, a novel optical neuromorphic photonic crystal structure, using a silicon triangular rod-type lattice and germanium-antimony-telluride phase-change material (GST-PCM), is proposed for use as an optical neural network synapse. This structure includes ring resonators, cavities, and a Mach–Zehnder interferometer, which are specifically designed to improve the transmission with a high Q-factor. GST-PCM is the active material that enables precise modulation of the optical properties of the structure through controlled phase transitions. Finite-difference time-domain (FDTD) simulations show that phase changes induced by changes in the crystallinity of GST-PCM allow for precise tuning of the transmission modulation from 0 to 90% at a wavelength of 1550 nm. A key innovation of this work is the use of a photonic crystal platform, which significantly reduces the footprint of the structure compared to previous works and conventional silicon photonic designs. This study highlights the significant potential of the proposed structure for applications in optical memory and information-processing systems, offering a promising pathway for the development of optical synapses in optical neural networks.