We experimentally assess the impact of different band drops on the performance of $\mathbf{S}+\mathbf{C}+\mathbf{L}$ multi-band optical transmission systems. We also present the digital twin of our experiment that quantifies the different noise contributions affecting the system performance in detail. Our results highlight how the L band is largely affected due to the lack of ISRS-induced power transfer when the S band is missing.

Recent advances in multi-band amplification support ultra-wideband (UWB) systems as a suitable solution to cope with the increasing fiber communications traffic demand. The combination of UWB with spectral-efficient modulation formats can significantly increase in the total throughput of wavelength division multiplexed (WDM) transmission systems. In this work, we demonstrate a 240×70 Gbaud PCS-256QAM WDM transmission using an optical bandwidth of 150 nm across the S, C and L bands. We combine doped-fiber amplifiers, semiconductor optical amplifiers (SOA) and backward distributed Raman amplification to achieve 200.5 Tbit/s of total generalized mutual information (GMI) throughput over two 100 km pure-silica-core fibers (PSCFs). We also present the digital twin of this experiment, providing the impact of wavelength-dependent impairments on the system performance. Our results demonstrate the feasibility of high-throughput multi-span UWB transmission.

We experimentally assess the impact of different band drops on the performance of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{S}+\mathbf{C}+\mathbf{L}$</tex> multi-band optical transmission systems. We also present the digital twin of our experiment that quantifies the different noise contributions affecting the system performance in detail. Our results highlight how the L band is largely affected due to the lack of ISRS-induced power transfer when the S band is missing.

We experimentally observe the signal-to-noise ratio (SNR) degradation of previously established services induced by loading new services in a network, and we mitigate this degradation by periodic power re-optimization via two different strategies: (1) a static strategy based on end-of-life parameters and (2) a dynamic strategy based on real-time monitoring to the current state of the network. We use a mesh network testbed of four nodes and five links with commercial equipment only. We observe up to 3.4 dB SNR degradation on the previously established services due to the loading of new services. Then we demonstrate an improvement of up to 3.2 dB in the network margin achieved by applying our proposed power re-optimization strategy.

The tight channel filtering imposed by long cascades of reconfigurable optical add-drop multiplexers (ROADMs) represents, nowadays, one of the major performance-limiting aspects for optically-routed coherent optical fiber systems. This makes it vital to perform a ROADM-aware optimization of the network performance at the physical layer. In particular, the use of different modulation options is known to have a strong impact on the extent of the filtering-induced penalties. In that regard, a long debate between single- and multi-carrier modulation has been taking place during the last few years, sometimes leading to apparently contradictory results. Following the open scientific discussion on this topic, in this work, we investigate by simulation and experimentally the wavelength selective switch (WSS) filtering tolerance of single-carrier (SC) and digital subcarrier multiplexing (DSCM) signals. In order to promote a fair comparison, both modulation options are carefully designed to minimize the ROADM-filtering penalties, namely resorting to the use of entropy loading together with baud rate optimization. After some preliminary numerical assessment, a comprehensive set of experiments are carried out for the transmission of 21-WDM 95–105 Gbaud SC and DSCM signals over a 2040 km straight line of fiber with regularly spaced WSSs. In general, our results allow to conclude that the two modulation options yield similar performance if the overall baud rate is optimized for each filtering scenario, keeping the baud rate at $\pm$ 5% of the optimized value.

Using accurate ISRS GN modeling and the fast-converging ASE-NL optimization algorithm, we demonstrate 6.2 Tbit/s throughput improvement in a 2-span ultra-wide-band system thanks to the use of the predicted total and per channel power.

We demonstrate 158.4 Tb/s GMI throughput over 120km field-deployed SMF multiplexing 6THz-bandwidth S, C and L lumped amplifiers and optimizing channel power pre-emphasis and constellation entropy to maximize fiber capacity.

Ultrawide-bandwidth (UWB) optical amplification covering C+L bands over 102 nm is implemented by using a seamless semiconductor optical amplifier (SOA) as a high-power booster with a maximum output power of 24.4 dBm as well as a hybrid scheme of pre-amplification, which combines backward distributed Raman pumping with SOA. In order to provide understanding of the transmission performance of SOA, we perform a thorough SOA characterization. By applying different total input powers, we have measured the output spectrum shape and power. In addition, the dependence of the gain on the driving current is also shown. The SOA noise figure is also analyzed for the case of a single channel input. Using the characterized SOA and employing real-time transponders, supporting two different modulation formats: 400 Gb/s PDM-16QAM and 200 Gb/s PDM-QPSK, a total real-time throughput of 59.2 Tb/s has been achieved over an unrepeated transmission span of 201.6 km-long pure silica core fiber (PSCF). Three different configurations of the output power of SOA booster are compared, which demonstrates an improvement of 17% in total throughput when increasing the SOA output power from 21 dBm to 24.4 dBm. Our results show the advantages and benefits of high-power SOA boosters for UWB amplification.

SOA nonlinearity tolerance is experimentally demonstrated for 68 Gbaud single-carrier/8-carrier PCS-64QAM systems. 1.4 dB additional output power is obtained with a 256 blocklength ESS, at the similar optimal SNR and rate loss of long blocklength CCDM.

We compare S+C+L link power optimization based on the fast and simple heuristic balance of linear and nonlinear noises versus more complex ML-based techniques to estimate optimum per-band line amplifier settings for system capacity maximization. © 2021 The Author(s)

We experimentally assess the use of super-symbol (SUP) transmission with different distribution matching methods in a 100 GBd PCS-256QAM digital subcarrier multiplexing system. We achieve 0.1 dB SNR improvement after 900 km, a gain which comes almost for free due to the low complexity of SUP.

We demonstrate that, in an actual network, maximizing the transmission spectral efficiency requires not only to take into account transceiver impairments, but also to consider WSS filtering and flex-grid specifications. In a WDM transmission experiment over a 10-span link covering $\sim 38$ nm, we study achievable rate, bitrate and spectral efficiency for different symbol rates of 62.5, 75, 87.5, 100 and 112.5Gbaud with corresponding channel spacings of 75, 87.5, 100, 112.5, 125GHz, therefore accounting for few GHz bandguard required for potential WSS filtering effect, as well as being compatible with flex-grid configuration. While maximum achievable information rate per transceiver (wavelength) is achieved for the lowest symbol rate, and operating at larger symbol rate maximizes the bitrate per wavelength, to maximize overall fiber spectral efficiency (and therefore, capacity), operation at intermediate symbol rates, from 75 to 100Gbaud in our study, is required as a trade-off between the penalties from transceiver impairments and WSS filtering.

We experimentally compare the WSS filtering tolerance of single-carrier (SC) and digital sub-carrier multiplexing (DSCM) at 95–105 Gbaud. Whereas DSCM tends to be advantageous when using excessive baudrates, the two modulation options yield similar performance if the baudrate is optimized.

We demonstrate a network automation framework called AI-Light able to: create a digital twin based on the monitoring, perform an SNR-based optimization by leveraging the digital twin and, push the optimized configuration into the network.

We propose an experimental method to tune SOA model parameters that yields good prediction abilities of nonlinear distortions induced on PCS-QAM signals. We show that reducing SOA nonlinearities is achieved by a trade-off between a high $P_{\text{sat}}$ and a low $\alpha_{H}$ . © 2021 The Author(s)

We demonstrate a record of 200.5 Tb/s total GMI throughput on two 100 km PSCF spans employing 240×70 GBd CS-256QAM signals by using S+C+L discrete amplification covering 150 nm-wide bandwidth jointly with backward distributed Raman pumping.

We demonstrate a 63.2-Tb/s throughput in a 5-span 440-km SSMF link employing real-time 400G 16QAM transponders and fully discrete C- and L-band amplifiers with a total amplification bandwidth approaching 100nm.

Transmission of C-band 40×800 Gbit/s signals using 125 Gbaud PCS-64QAM is demonstrated by performing power allocation optimization at the input of 3 OMSs along a 15-span link (>20 dB loss each) with EDFA-only amplification.

We predict the per-channel OSNR of optical links with up to 23 EDFAs via a machine learning model based on learned noise figures from experimental data. For a 20 span link, the error margin to cover 99% of cases is less than 0.35 dB.