Measurement-based building-block behavioral modeling of passive photonic circuits from magnitude-only responses

Accurate frequency-domain characterization is essential for reliable modeling of photonic integrated circuits (PICs). In practice, PIC measurements are often performed using a tunable laser and an optical power meter, providing only magnitude responses and no phase information, which hinders the construction of physically consistent frequency- and time-domain models. This paper presents a robust approach that directly constructs rational models from magnitude-only frequency responses, ensuring that the resulting models share the same magnitude response as the PIC under study. Unlike existing methods based on magnitude-squared fitting and spectral factorization, which are frequently degraded by imaginary-axis zeros, the proposed method synthesizes a minimum-phase realization by explicitly handling these zeros. The synthesized phase is not the true physical phase; however, it is consistent with the Kramers–Kronig relations corresponding to the given magnitude response, thereby enabling the direct use of standard S -parameter approximation techniques to generate rational behavioral models. The resulting models can be applied to modulated signal transmission simulations in wavelength-division multiplexed (WDM) telecommunication scenarios.