Improvement of input power dynamic range for 20 Gbit/s optical WDM switch nodes using an integrated Michelson wavelength converter

The implementation of photonic wavelength-division multiplexing (WDM) switch nodes with wavelength converters allows for higher throughput and easier management, as well as wavelength reuse. Furthermore, semiconductor optical amplifiers (SOAs) are attractive for space switching in the nodes because they offer short switching times, compensate for loss and, very importantly, have the high on-off ratios of 40-50 dB that are required to overcome crosstalk induced penalty. One disadvantage of the SOA gates is their limited input power dynamic range and, thus, limited cascadability caused by noise and gain saturation. We show that even at a high bit-rate of 20 Gbit/s the latter imperfection can be compensated by the extinction ratio enhancing capability of interferometric wavelength converters (IWCs). Consequently, the input power dynamic range for switch blocks using IWCs together with SOA gates can be improved compared to switch blocks without IWCs. This is especially important at high bit rates where the cascadability of the SOA gates decreases. Here, more than 15 dB improvement of the input power dynamic range is achieved at 20 Gbit/s using a high-speed Michelson interferometer wavelength converter after the SOA gate compared to the SOA gate alone.