Plasmonic electro-optic modulators based on epsilon-near-zero materials: comparing the classical drift-diffusion and Schrödinger-Poisson coupling models.

We present the design, modeling, and optimization of high-performance plasmonic electro-optic modulators based on indium tin oxide (ITO), leveraging voltage-gated carrier density modulation. The carrier density is modeled using the classical drift-diffusion (CDD) and nonlinear Schrödinger-Poisson coupling (SPC) methods, with the latter providing precise carrier distribution profiles, particularly in epsilon-near-zero (ENZ) media like ITO. By combining the nanoscale field confinement of surface plasmon polaritons with the ENZ effect, our modulators, integrated with silicon waveguides and optimized for operation at  = 1550 nm, achieve a 3-dB bandwidth of 210 GHz, an insertion loss of 3 dB, and an extinction ratio of 5 dB for a device length of under 4 µm. These results highlight the critical trade-offs between high-speed modulator operation and low insertion loss extinction ratio, underscoring the necessity of precise carrier distribution modeling for ENZ materials in optoelectronic devices.