Transient adjoint sensitivity analysis exploiting FDTD

We present an accurate technique for efficiently estimating the gradient of time-varying responses at each time step. Using only one extra simulation, the sensitivities of a transient field response with respect to all the system parameters are evaluated regardless of their number at all time steps. A step function excitation is used to generate the adjoint fields. Our approach is validated through a waveguide filter example modeled with the FDTD method. We show that the estimated sensitivities with respect to the dimensions and material properties of waveguide discontinuities match those obtained using the time-intensive central finite difference (CFD) approximation.