Tunable optical materials are indispensable elements in modern optoelectronics, especially in integrated photonics circuits where precise control over the effective refractive index is essential for diverse applications. Two-dimensional materials like Transition Metal Dichalcogenides (TMDs) and graphene exhibit remarkable optical responses to external stimuli. However, achieving distinctive modulation across a broad spectrum while enabling precise phase control at low signal loss within a compact footprint remains an ongoing challenge. In this work, we unveil the robust electro-refractive response of multilayer ferroionic two-dimensional CuCrP2S6 (CCPS) in the near-infrared wavelength range. By integrating CuCrP2S6 into SiPh microring resonators (MRR), we enhance light-matter interaction and measurement sensitivity to minute phase and absorption variations. Results show that electrically driven Cu ions can tune the effective refractive index on the order of 2.8 x10-3 RIU (refractive index unit) while preserving extinction ratios and resonance linewidth. Notably, these devices exhibit low optical losses of 2.7 dB/cm and excellent modulation efficiency of 0.25 V.cm with a consistent blue shift in the resonance wavelengths among all devices. These results outperform earlier findings on phase shifter based on TMDs. Consequently, CCPS integration endows characteristics akin to those of high-index active dielectric materials. Moreover, we showcase the electro-optic tuning sensitivity to light polarization, opening avenues for versatile light manipulation. The dual optoelectronic and ionotronic capabilities of the two-terminal CCPS devices hold vast potential, spanning applications such as phased arrays, optical switching, and neuromorphic systems in light-sensitive artificial synapses.
