RSoft Application Note: SOI Modulator

Tools Used: RSoft Products and Sentaurus TCAD

Silicon-based optical technologies are emerging as a promising candidate for high-speed devices that can offer significantly higher bandwidth with lower power consumption than conventional microelectronics. The SOI-based modulator is an essential building block for enabling future on-chip photonic networks.


  • SOI modulators are complicated devices, and for accurate simulation the relevant electronic, process, and optical physics must all be included.
  • Existing commercial simulation tools can be utilized for certain parts of the problem, but no one single tool offers an optimal simulation that incorporates all aspects of SOI modulator design.



SOI modulator layout

Refractive index perturbation at -5V
(with respect to 0V) 

Imported net doping profile (log scale). Acceptors are shown as negative numbers, donors positive


  • A mixed-level simulation solution utilizing the RSoft products to handle the optical part of the problem, and TCAD to handle the electronic & process part of the problem, offers a complete and rigorous SOI design solution.
  • Sentaurus TCAD SDevice is used to simulate the carrier distribution and corresponding index perturbation (as a function of applied electrode voltage) due to free-carrier effects.
  • RSoft’s optical mode solvers are then used to compute the modes and the effective index of the structure (as a function of the applied voltage).

Fundamental Mode at 0V (left) and -5V (right)


  • The perturbation to the mode effective index due to the applied voltage is accurately measured using the RSoft-TCAD interface.
  • Change in modal effective index, going from 0V to -5V, is 1.71e-4.