Nonvolatile linear resonant switching for neuromorphic photonics in a PCM-integrated silicon racetrack microresonator

Compact and energy-efficient optical switching elements are critical for scalable neuromorphic photonic systems and reconfigurable integrated photonics. Resonator-based devices integrated with phase-change materials (PCMs) offer strong light–matter interaction, nonvolatile programmability, and high transmission contrast. In this work, we investigate a PCM-integrated silicon racetrack microresonator as a geometry-optimized platform for nonvolatile linear resonant optical switching relevant to neuromorphic photonic architectures. A comparative material study is performed by integrating a fixed PCM segment at the waveguide–resonator coupling region and evaluating Sb2Se3, Sb2S3, and Ge2Sb2Te5 (GST) in both amorphous and crystalline states. Using static refractive-index models derived from experimentally reported optical constants, the materials are assessed based on transmission contrast, resonance modulation, and linewidth variation. Among the evaluated materials, GST exhibits the strongest state-dependent optical response and is selected for further optimization. An angular placement study positions a fixed-size GST segment at four locations around the racetrack resonator. Placement at the coupling region yields the highest transmission contrast, narrowest resonance linewidth, and largest modulation depth, indicating enhanced sensitivity to localized refractive-index perturbations. All results are obtained using three-dimensional finite-difference time-domain simulations under linear optical readout conditions. The findings establish geometry- and material-driven design guidelines for PCM-integrated racetrack resonators as nonvolatile optical switching primitives for neuromorphic photonic systems.