Single-step initialization of a 16-channel silicon nitride DWDM demultiplexer using a physics-informed digital twin

We demonstrate a clear-box, single-step initialization framework for photonic integrated circuits (PICs) applied to an O-band 16-channel silicon nitride (SiN) dense wavelength-division multiplexing (DWDM) demultiplexer based on a Mach-Zehnder interferometer (MZI) lattice structure. A physics-informed digital twin of the PIC based on a compact set of measured transmission spectra enabled inference of the effective and group indices, per-arm phase offsets, and thermal response including crosstalk. After model calibration, the digital twin was used to generate a heater-voltage vector that initialized the PIC by a single application of the computed settings. We experimentally show that the initialized device recovered flat-top passbands with bandwidth and ripple close to the design. Moreover, the digital twin predicted the chip response with a mean MSE of 11.8 dB² over 30 randomly generated heater settings. We also evaluated reusing the fitted effective thermal parameters on three other dies from the same wafer.