Inverse Design and Optical Performance of Cascaded Wavelength Division Multiplexers

The problem of direct inverse optimization of multi-output wavelength division multiplexers (WDMs) on silicon is that these WDMS often exhibit inter-channel crosstalk, making reliable designs difficult to achieve. A cascaded WDM design on a silicon photonics platform is implemented using an inverse design approach. The key idea is to avoid the instability of direct multi-output optimization by sequentially combining several two-output units, thereby realizing a single-input three-output device within a small footprint. Full-wave FDTD simulations show that the first stage achieves effective wavelength separation with high transmission. After cascading two stages, three target wavelengths (1450 nm, 1500 nm, and 1550 nm) are successfully routed to different output ports, with a minimum transmission exceeding 0.71 and inter-channel crosstalk below −9.97 dB, within a total device footprint of 17.745 μm2. These results indicate that cascaded inverse design offers a stable and practical solution for multi-channel WDM design on silicon.