Computing the causal impulse responses of passive photonic integrated circuits by extrapolation

Accurate time-domain simulation is crucial for designing large and complex photonic integrated circuits (PICs). Passive devices and circuits, such as Mach-Zehnder interferometers and all kinds of wavelength filters, play important roles in PICs, with their input and output characteristics typically described using S-parameters. However, their practical application in the time domain is limited by the fact that they are usually band-limited. Applying the inverse fast Fourier transform (IFFT) directly to these band-limited S-parameters can result in impulse responses that violate causality significantly. To address this issue, this paper proposes a novel method for extrapolating S-parameters of photonic circuits in order to obtain causal and accurate impulse responses.