Multipass Performance of a Chip-Enhanced WSS for Nyquist-WDM Sub-Band Switching

We investigate the performance of a chip-enhanced wavelength selective switch (EWSS) in multipass add/drop experiments. The demonstrated EWSS device uses a ring-assisted Mach-Zehnder interferometer chip as a wavelength interleaver, to preprocess the incoming super channel before launch into a commercial wavelength selective switch. We show that a 4% guardband, quadrature-phase-shift-keying encoded Nyquist wavelength division multiplexing super channel can successfully pass through seven EWSS nodes. We further investigate the number of reachable nodes with varied guardbands, showing that a modest increase in guardband can translate to a significant increase in the number of reachable EWSS nodes.