Low-Loss Silicon 2 × 4λ Multiplexers Composed of On-Chip Polarization-Splitter-Rotator and 2 × 2 and 2 × 1 Mach-Zehnder Filters for 400GbE

2×4λ Si-photonics multiplexers for 400GbE composed of Mach-Zehnder filters and a polarization-splitter-rotator are proposed and experimentally demonstrated for the first time. Relative spectral position of two filters is locked by using 2×2 and 2×1 configurations.