Experimental demonstration of robust nanophotonic devices optimized by topological inverse design with energy constraint

In this paper,we present the experimental results for integrated photonic devices optimized with an energyconstrained inverse design method.When this constraint is applied,optimizations are directed to solutions that contain the optical field inside the waveguide core medium,leading to more robust designs with relatively larger minimum feature size.We optimize three components:a mode converter(MC),a 1310 nm/1550 nm wavelength duplexer,and a three-channel C-band wavelength demultiplexer for coarse wavelength division multiplexing(CWDM)application with 50 nm channel spacing.The energy constraint leads to nearly binarized structures without applying independent binarization stage.It also reduces the appearance of small features.In the MC,well-binarized design,improved insertion loss,and cross talk are obtained as a result.Furthermore,the proposed constraint improves the robustness to fabrication imperfections as shown in the duplexer design.With energy constraint optimization,the corresponding spectrum shifts for the duplexer under±10 nm dimensional variations are reduced from 105 nm to 55 nm and from 72 nm to 60 nm for the 1310 nm and 1550 nm channel,respectively.In the CWDM demultiplexer,robustness toward±10 nm fabrication error is improved by a factor of 2.The introduction of the energy constraint into topological optimization demonstrates computational gain with better-performing designs.