▎ 摘　　要

Phase change materials like vanadium dioxide (VO2) have recently gained particular attention to realize effective optical modulators. In this paper, we propose a high-performance optical modulator based on VO2. The structure is constructed by a stack of two graphene sheets spaced by a VO2 layer that are all grown over a silicon waveguide. The input light propagating along the modulating region of the waveguide can interact with the VO2 at the top and side of the structure. When an external voltage is applied across the graphene sheets, the VO2 changes to the metallic phase and the modulator is set at the off state. Most of the previously reported VO2-based modulators are polarization sensitive and suffer from high polarization diversity. When such modulators are integrated into a fiber-based optical system containing light with random polarization, the modulation efficiency is profoundly degraded. In our proposed modulator, the structure is optimized to achieve a polarization-insensitive response with an off-state propagation loss of & SIM;14 dB/mu m. The TE (TM) insertion loss is also calculated to be as low as 2.25 dB/mu m (3.22 dB/mu m), so that an extinction ratio of as high as & SIM;11.5 dB/mu m is obtained. In addition, the required low modulating voltage of 1.12 V and reasonable modulation speed of 390 MHz together with the low energy consumption of 2.1 fJ/bit could make our proposed modulator a good candidate for photonic integrated systems.