Plasmonic Modulators for Near-Infrared Photonics on a Silicon-on-Insulator Platform

A CMOS compatible interference-based Mach-Zehnder modulator with each arm comprising a metal-insulator-silicon-insulator-metal structure and a simpler, single-arm variant is considered for electro-optic and electroabsorption modulation, respectively, using finite-element electromagnetic simulations. In the calculation of electron density profiles in bias-induced accumulation layers, the size-quantization effects at oxide-silicon interfaces are considered. These are then used to find the complex refractive index profiles across the structure, in its biased and unbiased states, and eventually the modulator insertion loss and extinction ratio, as they depend on various structural parameters. Furthermore, an alternative modulator, comprising a metalized stub filled with SiGe/Ge multiple quantum wells or quantum dots in a silicon matrix, coupled to a dielectric waveguide structure is also investigated using 3-D finite-element simulations. The principle behind its modulation is the change of electromagnetic field profile after the stub, relative to the incoming mode, which happens when the absorption of the stub material varies. This affects the field coupling into a single-mode output waveguide, resulting in a controllable transmission.