Study on mechanism of sidewall roughness scattering in slot optical waveguides by FDTD simulation

Abstract The slot optical waveguide is different from the conventional solid-core optical waveguide in both structure and features and has many unique and important applications. However, serious sidewall roughness scattering (SRS) loss limits the performance of the devices based on it. So far, the mechanism of the SRS in the slot waveguide is still not clear, and it seems not reasonable to analyze it directly by the Bragg diffraction condition. In this paper, through finite-difference time-domain simulation, we demonstrate that the regimes of the SRS and backscattering in the slot waveguide are the same as those of the solid-core waveguide, and the conditions of the diffraction radiation caused by the outer and the inner sidewalls are the same. The rationality of these conclusions are explained by taking the slot waveguide as a whole. The scattering regimes revealed and verified in this paper will benefit the suppression of the SRS loss and the utilization of the slot waveguide.