Efficient Adjoint Sensitivity Analysis Exploiting the FD-BPM

We propose a novel and simple approach for design sensitivity analysis using the beam propagation method (BPM). It exploits the adjoint variable technique to extract the response sensitivities with respect to all the design parameters, regardless of their number. The associated computational cost is less than that of an extra BPM simulation. The accuracy of the results are comparable to those obtained using the expensive central finite-difference approximations applied at the response level. Our approach is successfully illustrated through a number of examples.