Adjoint sensitivity technique for FDTD methods on structured grids

In this paper, we propose an adjoint-based approach to design sensitivity analysis with time-domain methods using fixed structured grids, which do not change during the optimization. It is simple to implement with existing algorithms such as the FDTD technique. It produces the response and its gradient in the design parameter space with two simulations regardless of the number of design parameters. The proposed method is validated by a number of waveguide examples analyzed by a finite-difference algorithm based on the time-dependent 2D E-field wave equation.