Multiorder Harmonic Analysis of Time-Varying Media Using Time-Domain Simulation

This work puts forth a simple time-domain simulation technique, applicable to periodically space-time-modulated nanophotonic systems, whereby the electromagnetic fields associated with any harmonic order may be extracted in the time, space, and frequency domains. The technique uses existing time-domain simulation tools to run multiple simulations of the same system but with a progressive global phase shift between the source-and time-modulation signals. The fields associated with any desired harmonic order are obtained by particular linear combinations of the ensuing simulation results. To illustrate, the method is applied to the finite-difference time-domain simulation of a sinusoidally space-time-modulated surface conductivity and to a sinusoidally space-time-modulated coupled nanocavity system. The accuracy of the technique is confirmed by showing good agreement between numerical results and theoretical models. Until now, multiharmonic analysis could be done only with frequency-domain simulation methods.