ITO-based electro-optical modulator integrated in silicon-on-insulator waveguide using surface plasmon interference

In this paper, an innovative integrated Si photonic modulator based on electrically refractive index-tunable indium-tin-oxide (ITO) material is presented. The key component of the device consists of a thin Au layer embedded in a Si waveguide and a thin layer of ITO deposited on the Au layer through an adhesive HfO₂ layer. Light coupled into the transverse-magnetic mode of the Si waveguide generates two surface plasmon modes propagating simultaneously at the Au-HfO₂ interface and at the Au-Si interface. These waves recombine and interfere at the end of the Au layer. The modulation mechanism is activated by electrically tuning the free carrier concentration of the ITO layer, which changes the ITO refractive index, causing a difference in the group index between the two interfering modes. This complementary-metal-oxide-semiconductor-compatible integration of electro-optical modulation into a commercially available silicon-on-insulator platform provides great potential toward compact and efficient photonic integrated circuits for next-generation data communication.