Accurate sensitivity analysis of photonic devices exploiting the finite-difference time-domain cavity adjoint variable method.

For what is believed to be the first time, the central adjoint variable method (CAVM) is applied to the sensitivity analysis of photonic devices using the finite-difference time-domain (FDTD) technique. The FDTD-CAVM technique obtains accurate sensitivities of any desired response with respect to the different design parameters. Our technique requires only one extra FDTD simulation to extract the sensitivities with respect to all the design parameters regardless of their number. Cost-free sensitivities of the power reflectivity are also derived without any additional simulation. The results show a very good agreement between the CAVM sensitivities and those obtained using the expensive central finite difference approximation.