An efficient modal analysis in nano-resonators

Accurate spectral and modal analysis of nano-resonators is critical for the design of high-performance nanophotonic and plasmonic devices. Conventional numerical methods, such as the finite element method (FEM) and finite-difference timedomain (FDTD) technique, demand substantial computational resources for electromagnetic analysis, posing significant challenges for rapid device optimization. In this work, we present a generalized quasi-normal mode (QNM) framework applicable to arbitrary resonator geometries, including heterostructures, with unrestricted material composition. Upon determining the QNMs of a nano-resonator, their excitation coefficients under specific incident waves can be computed efficiently. The complete electromagnetic response can then be reconstructed with negligible computational overhead. Benchmarking against traditional FEM simulations demonstrates that the QNM-based spectral reconstruction achieves a computational speedup exceeding 90% while maintaining approximately 1% relative error. This approach establishes a rigorous connection between structural geometry, material properties, and optical response, offering a powerful tool for inverse design and real-time performance prediction in nanophotonics.