Inverse Design of Plasmonic Structures with FDTD

Inverse design has greatly expanded nanophotonic devices and brought optimized performance. However, the use of inverse for plasmonic structures been challenging due to local field concentrations that can lead errors in gradient calculation when continuum adjoint method is used. On other hand, with discrete one achieve exact gradient. Historically version exclusively used a Finite Element model, applying Finite-Difference Time-Domain (FDTD) rarely attempted. Due popularity using FDTD simulating structures, we integrate present framework carry out density-based topology optimization. We demonstrate exactness block structure varying permittivity. Another challenge unique non-physical amplification caused by poorly chosen material interpolation destroy stable convergence To avoid this, adopt non-linear scheme solver. In addition, filtering-and-projection regularization incorporated ensure manufacturability designed structures. As an example this framework, successful reconstruction electric fields bowtie aperture presented.