Optical microcavity surface roughness modelling
Date
2025
Authors
Qin, Heming
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Abstract
Surface roughness at the sidewalls and top surfaces of whispering-gallery mode (WGM) microdisk cavities causes scattering loss that degrades the cavity quality factor. This thesis presents a three-dimensional full-wave electromagnetic modeling framework implemented in COMSOL Multiphysics to analyze the impact of surface roughness on WGM microcavity performance. A statistical roughness generation methodology produces Gaussian-distributed surface profiles with controlled root-mean-square height and correlation length. The simulation results reveal systematic trends in quality factor degradation with increasing surface roughness, showing more than three orders of magnitude reduction for moderate roughness levels. The scattering field extraction formalism is also implemented, allowing detailed analysis of roughness-induced scattering. Comparison with established semi-analytical models demonstrates that the three-dimensional full-wave approach captures comprehensive surface scattering interactions from all cavity surfaces, while semi-analytical models typically focus on specific dominant scattering sources such as disk-edge roughness. The results provide actionable guidance for microcavity fabrication optimization and establish a foundation for predictive modeling of surface-scattering effects in high-Q optical devices.
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Keywords
WGM resonators, Surface roughness scattering, Quality factor