Interaction analysis: coherent vs. legacy transmission data systems for ITU grid spacing

Coherent high-speed optical systems have played a very significant role in the world of data transmission in the last 15 years, and transmission speeds from 1.2 Tb/s to 1.6 Tb/s per lambda are expected to enter the market very soon. Historically, legacy high-speed 10 Gb/s data transmission systems have used the simplest On-Off Keying (OOK) modulation scheme. Since data transmission systems have been gradually moving to coherent transmissions with advanced modulation schemes, the coexistence of slower signals using OOK modulation can have a significant impact on coherent data signals via the nonlinear effect of Cross-Phase Modulation (CPM). In this paper, we evaluate the Bit Error Rate (BER) and Optical Signal-to-Noise Ratio (OSNR) for legacy 10 Gb/s data signals transmitted together with high-speed coherent 200 Gb/s data signals for fiber distances ranging from 100 km to 800 km. This scenario is rather suitable for National Research and Educational Network (NREN) operators, where slow OOK and high-speed coherent data signals are transmitted on the predefined International Telecommunication Union (ITU) channel spacing, usually 100 GHz.