12-channel LAN wavelength-division multiplexer with low random phase errors

In this paper, we demonstrate a 12-channel LAN wavelength division multiplexer with low random phase errors on a 300 nm-thick silicon nitride platform, based on Mach-Zehnder interferometers. We conducted a detailed analysis of the phase error contributors in the interferometers and implemented targeted structural optimizations that reduced the random phase error by approximately 70%. Ultimately, our device achieved an average insertion loss of -0.87 dB, crosstalk of -17 dB, and a 1-dB bandwidth of 2.3 nm (>50% channel spacing) without any calibration, as well as a fabrication tolerance of 22 pm/nm. Excellent reproducibility was observed both intra- and inter-chip. Benefiting from the low thermo-optic coefficient of silicon nitride, the device's temperature-dependent center wavelength shift is estimated to be nearly 11 pm/K. This work demonstrates the advantages and potential of silicon nitride-based passive devices, paving the way for high-capacity optical communications with increased channel counts.