Plasmonic enhanced electro-optic stub modulator on a SOI platform

Research Highlights▶ Investigated the performance of a metallised stub coupled to an SOI waveguide using Comsol Multiphysics. ▶ The subject of research is both timely and important because plasmonic modulators and waveguides have recently been realised, and this system is a promising candidate for integration of photonics with nano-scale electronics on a common platform (silicon-on-insulator), reducing device length considerably and enabling low power operation. ▶ Strong resonance in the stub could be achieved by varying stub dimensions (example, height and width). By incorporating this effect, the transmission of the system can be controlled by detuning the absorption coefficient (i.e. the imaginary part of the refractive index) of the material filling the stub. ▶ Our design exhibits high extinction ratios with acceptable insertion losses including the modifications in the design required to enable electrical drive of the proposed plasmonic stub structure.

The performance of a plasmonic enhanced stub modulator coupled to an underlying Si-waveguide was investigated using finite element simulations. The transmission of the system is controlled by changing the absorption coefficient of the material filling the stub, which modifies both the power transmitted by the stub itself and the field profile, and hence the coupling of this field into the single-mode output waveguide. An extinction ratio of 8.5 dB with an insertion loss of 8.5 dB can be achieved via electro-absorption derived from the quantum confined Stark effect (QCSE), assuming that the stub is filled with Ge/SiGe multiple quantum wells (MQWs) or Ge quantum dots (QDs) in a silicon matrix. The effect is of potential interest for application in electro-absorption modulators for integrated photonics, since the sub-wavelength dimensions of the device offer low power operation and high switching speeds.