Leakage Suppression in Fiber-Based WDM SOA–MZI Switches by Wavelength-Resolved SOP Trimming

Wavelength-dependent inter-arm polarization mis-match accumulated after the semiconductor optical amplifiers (SOAs) can reduce the recombination contrast of fiber-based wavelength-division-multiplexed (WDM) SOA-Mach-Zehnder interferometer (SOA-MZI) switches, causing residual wavelength leakage. This letter experimentally demonstrates a dense wave-length-division multiplexing (DWDM)-assisted, post-SOA, pre-combiner wavelength-resolved polarization-trimming method in a two-wavelength2× 2prototype. After the SOAs, the two data wavelengths are demultiplexed, independently polarization-adjusted in both interferometer arms, and remultiplexed before final recombination. A polarizing-beam-splitter (PBS) projection sweep enables repeatable tuning, while an all-polarization-maintaining DWDM reference, arm-power monitoring, and control-only measurements assess alternative causes of the improvement. In separately held Cross and Bar states with 10 Gbps non-return-to-zero on-off-keying (NRZ-OOK) signals, the intra-port wave-length contrast increases from 20.99-22.47 to 27.50-29.18 dB; the passive reference yields 19.46-20.55 dB. The corresponding Q-factor-estimated bit error rates (BERs) range from3.47× 10 ⁻¹²to7.97× 10 ⁻¹².