This study introduces a high-performance silicon-based optical modulator that utilizes a germanium-antimony-telluride (GST) nanolayer within an elliptical cylindrical waveguide structure. By exploiting the phase-change dynamics of GST and engineered hybrid \(\text{e}\text{H}{\text{E}}_{11}\) and \(\text{o}\text{H}{\text{E}}_{11}\) mode confinement, the device achieves an ultralow insertion loss of 0.15 dB, a remarkably high extinction ratio of 30.28 dB at a wavelength of 1550 nm for the fundamental \(\text{e}\text{H}{\text{E}}_{11}\) mode. The elliptical geometry enhances light-matter interaction through anisotropic mode confinement while improving thermal management, enabling a data bit rate of \(13.33\text{ Mb/s}\) via sub- \(\:200\text{ ns}\) dual-voltage electrothermal actuation (4 V for crystallization, 10 V for amorphization). The switch maintains high energy efficiency, consuming \({E}_{\text{SET}}=12.227\text{}\text{ nJ}\) and \({E}_{\text{RESET}}=5.015\text{ nJ}\) calculated across the entire device volume. Multiphysics simulations validate the design: the tuned GST thickness ( \(40\pm\:10\text{ nm}\) ) balances the switching speed and optical contrast, while gold electrodes enable localized Joule heating with minimal optical loss ( \(0.1\:{\text{dB/}}\mu {\text{m}} \) ). These advancements position the proposed modulator as a promising candidate for high-speed optical interconnects and programmable photonic circuits, addressing the critical demands for low-loss, high-contrast, and robust integrated photonics.
