Method to obtain the initial value for the inverse design in nanophotonics based on a time-reversal technique

In the inverse design of nanophotonic devices, mathematical optimization methods are generally used to perform local optimization in the design region to obtain the physical structure that meets design expectations. These methods usually produce good structures. However, due to the lack of physical considerations, most of the inverse design methods for nanophotonic devices use random initial topology as the initialization for optimization, which will inevitably cause a waste of computing resources. In this Letter, we propose a method based on a time-reversal technique to quickly determine the induced source of the physical structure in the design region and, thus, obtain the initial topological structure of the nanophotonic devices. For a nanophotonic 90°-bend waveguide and 90°-bend power splitter waveguide, numerical examples show that the initial topology obtained by our method not only has good initial performance, but also can be used as a reasonable initialization for inverse design.