The 5G fronthaul optical modules are the basic building block of the 5G network and WDM solutions are desired. Application code of MWDM has just been defined in ITU SG15 in December 2021 and are currently under intense study, naming draft recommendation G.owdm2. We organized the investigation and evaluation of MWDM optical modules from different vendors. Key parameters of optical/electrical interface have been tested and analyzed, including wavelength deviation, 20dB bandwidth, total mean output power, optical sensitivity, optical path penalty, eye diagram, power consumption as well as DDM function. Current commercial 25G MWDM optical modules are demonstrated capable to support transmission in O band covering almost all scenarios of 5G fronthaul.
To support high-quality network plan, reliable operation and efficient service provisioning, the quality of transmission estimation (QoT-E) tool, which predicts the penalty of transmission impairments, is highly required. Among these channel impairments, non-linear-interference noise (NLIN) in high-speed, large-capacity and long-reach transmission systems with advanced modulation formats and powerful digital signal processing (DSP) algorithms is complex and difficult to be accurately estimated, thus an precise and practical model of NLIN is desperately desired as one of the key components for QoT-E. Nowadays, 400Gb/s/ch combined with multi-band transmission has become a research hotspot achieving larger capacity without deploying new fibers. However, in this multi-band scenario, the interaction of NLIN with the stimulated Raman scattering (SRS) must be properly considered. In this paper, an equivalent attenuation coefficient assisted enhanced Gaussian noise (EGN) model which considers the impact of SRS on the nonlinear interference in C+L band, is proposed and experimentally verified. The real-time experiments of 400Gb/s/ch transmission system in 11-THz C+L band over 14x75 km G.652 and 14x100 km G.654E fiber links are carried out using coherent transponders modulated with 91.6 GBaud digital sub-carrier multiplexing (DSCM) based probabilistic constellation shaping (PCS) 16QAM format, achieving a net spectral efficiency of 4 bit/s/Hz. The experimental results show that the maximum deviation of NLI induced OSNR penalty at different frequencies across the whole C+L band is found to be less than 0.22 dB. This work could potentially provide an effective and accurate tool for QoT-E estimation in broadband C+L or even multiband systems, paving the way for intelligent management and control of high-capacity and flexible optical networks.
An accurate and practical model of non-linear-interference noise (NLIN) is the key enabler for the quality of transmission (QoT) estimation tool, which predicts the penalty of transmission impairments. For next generation 400G/800G coherent transponders, probabilistic constellation shaping (PCS) and digital sub-carrier multiplexing (DSCM) are used to provide better transmission performance and finer data rate adaptability. However, to the best of our knowledge, there is little information so far about how to evaluate the penalty of NLIN in 400G/800G systems with PCS and DSCM, as traditional Gaussian noise (GN) or enhanced GN (EGN) model can not deal with such a problem directly. In this paper, we propose a modified EGN model to take into account the impact of PCS and DSCM on 400G/800G transmission system by performing simulations and experiments. To fully validate the accuracy of our model, a set of real-time experiments of 400G and 800G transmission system within 100/112.5GHz channel spacing, using 95GBaud commercial coherent modules. The 400G real-time transmission platform includes 10 spans of 75km G.652 fiber and all EDFA amplification is used, while the 800G link is limited to 5 spans G.652 fiber due to its higher OSNR requirement. The experiment result shows that the maximum estimation deviation of non-linearity induced OSNR penalty for the modified EGN model is about 0.3 dB under different transmission scenarios. We believe our work could potentially provide an effective and accurate tool for QoT estimation, paving the way for future physical-layer-aware management and control of high-capacity and flexible optical networks.
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