Impact of in-band crosstalk signals with different duty-cycles in M-QAM optical coherent receivers

Optical coherent technology leads to the coexistence of signals with different modulation formats and different bit rates in optical networks. Due to this coexistence, several in-band crosstalk scenarios are possible. In this work, the impact of in-band crosstalk due to M-QAM interferers on the performance of PDM-QPSK and PDM-16-QAM coherent receivers at a bit rate of 100 Gbps is studied. The influence of the duty-cycle, time misalignment and phase difference between interferers and selected signal on the receiver performance is also assessed. We show that the QPSK signal with a duty-cycle of 33% is, generally, the most tolerant selected signal to in-band crosstalk and the less detrimental interferer to the coherent receiver performance. Additionally, we show that the time misalignment has a strong influence on the in-band crosstalk impact, when the duty-cycles of the interferers or selected signal are low.