Simulating particle influence on silicon nitride strip waveguide single-mode parameters

Detecting and classifying particles over a wide range of types and sizes is essential for precise air quality determination. In this study the use of optical waveguide-based particle detection is examined using finite element method (FEM) based simulations. The simulation model assumes a silicon nitride strip waveguide and is built up in 3D using the Comsol Multiphysics platform. The waveguide geometry parameters were varied to identify suitable geometries for single-mode wave guidance of the fundamental quasi-TE and quasi-TM modes. The geometries with their according effective wave indices are reported. Furthermore, the intensity and phase changes of the single-mode wave introduced by the presence of a particle are analyzed und the underlying physical effects are discussed for spherical particles of radii from 50 to 500 nm. The results show non-linear and non-monotonic behavior and give substantial input to understand basic particle interaction with waveguide structures. Furthermore, they provide helpful knowledge for designing waveguide-based particle detectors.