Effective Single-Frequency Source Spectra in Broadband Time-Domain Electromagnetic Simulation of Time-Varying Materials

An advantage of time-domain electromagnetic simulation tools is that an entire spectrum can be obtained in a single simulation run by using a broadband initial condition and Fourier transformation of the ensuing time sequences. However, when the simulation involves time-varying materials, the system is no longer time-invariant, and Fourier techniques must be reconsidered to obtain desired results. Most theoretical and many experimental conditions assume a single-frequency or narrowband source excitation, which minimizes the unintended effects of frequency mixing. However, performing many single-frequency time-domain simulations would be needed to construct an entire spectrum in this way, which would become computationally impractical. This work shows how a few finite-difference time-domain (FDTD) simulations can be used with broadband initial conditions to obtain scattering spectra in time-modulated resonator systems that effectively correspond to a single-frequency source spectrum. The approach involves running FDTD simulations in which the phase between the modulating signal and the source signal is deliberately changed and then averaging the spectra from the simulations. Using only six simulations, the source frequencies up to (plus or minus) five times the modulating frequency can be canceled out, which provides good agreement with theoretical predictions over a broad range of parameter values.

Automated summary

Time-domain electromagnetic simulation tools have the advantage of obtaining the entire spectrum in a single simulation run using broadband initial conditions and Fourier transformation. However, when dealing with time-varying materials, Fourier techniques need to be reconsidered. This study demonstrates how a few finite-difference time-domain simulations can be used with broadband initial conditions to obtain scattering spectra in time-modulated resonator systems.