Fiber-optic multi-band transmission (MBT) aims at exploiting the low-loss spectral windows of single-mode fibers (SMFs) for data transport, expanding by ~11 times the available bandwidth of C-band line systems and by ~5 times C+L-band line systems'. MBT offers a high potential for cost-efficient throughput upgrades of optical networks, even in absence of available dark-fibers, as it utilizes more efficiently the existing infrastructures. This represents the main advantage compared to approaches such as multi-mode/-core fibers or spatial division multiplexing. Furthermore, the industrial trend is clear: the first commercial C+L-band systems are entering the market and research has moved toward the neighboring S-band. This article discusses the potential and challenges of MBT covering the ITU-T optical bands O -> L. MBT performance is assessed by addressing the generalized SNR (GSNR) including both the linear and nonlinear fiber propagation effects. Nonlinear fiber propagation is taken into account by computing the generated nonlinear interference by using the generalized Gaussian-noise (GGN) model, which includes the interaction of nonlinear fiber propagation with stimulated Raman scattering (SRS), and in general considers wavelength-dependent fiber parameters. For linear effects, we hypothesize typical components' figures and discussion on components' limitations, such as transceivers', amplifiers' and filters' are not part of this work. We focus on assessing the transmission throughput that is realistic to achieve by using feasible multi-band components without specific optimizations and implementation discussion. So, results are meant to address the potential throughput scaling by turning-on excess fiber transmission bands. As transmission fiber, we focus exclusively on the ITU-T G.652.D, since it is the most widely deployed fiber type worldwide and the mostly suitable to multi-band transmission, thanks to its ultra-wide low-loss single-mode high-dispersion spectral region. Similar analyses could be carried out for other single-mode fiber types. We estimate a total single-fiber throughput of 450 Tb/s over a distance of 50 km and 220 Tb/s over regional distances of 600 km: ~10 times and 8 times more than C-band transmission respectively and ~2.5 times more than full C+L.

In the evolution of optical networks, enhancement of spectral efficiency (SE) enhancement has been the most cost-efficient and thus the main driver for capacity enhancementincrease for decades. As a result, the development of optical transport systems has been focused on the $C$ -and $L$ -bands, where silica optical fiber exhibits the lowest attenuation, and erbium-doped fiber amplifiers provide an efficient solution forto compensatinge for the optical loss. With a gradual maturity in the SE growth, however, the extension of the optical bandwidth beyond the $C$ $+$ $L$ -band is expected to play a significant role in the future capacity upgrades of optical networks and, thus, attracting increasing research interests. In this article, we discuss the merits and challenges of ultrawideband optical transport systems and networks beyond conventional bands.

This paper reports on a field trial in a robotic manufacturing cell. Channel measurements and transmission experiments were conducted, assisting the development of a light-emitting diode-based optical wireless communication (OWC) system tailored for the needs of industrial wireless applications. These are moderate data rates, reliability, and low latency. Since dedicated radio spectrum is hardly available, the usage of light is an interesting alternative. Due to its spatial confinement, OWC links provide enhanced security and are difficult to jam from outside a building—a particularly interesting property for industrial applications. We performed broadband distributed $8\times 6$ multiple-input multiple-output (MIMO) channel measurements in a manufacturing cell. Results confirm that the signal-to-noise ratio is sufficient if a line-of-sight (LOS) is available and bandwidth is limited to a few megahertz. However, small movements and rotations may lead to sudden fades of 10–20 dB, when an LOS is blocked. To improve reliability, antenna diversity concepts are applied. Results show that for reliable communication, MIMO diversity schemes are indispensable as it increases the probability of a free LOS significantly. Based on these insights, we suggest an OWC design tailored to industrial wireless applications.

In this invited contribution, we discuss technology options for bandwidth-variable transceivers which are key components for the realization of flexible software-defined optical networking. Bandwidth-variable transceivers enable the software-controlled adaptation of physical layer parameters such as transmitted bit rate, spectral efficiency and transparent reach according to the traffic demands at hand. In particular, we focus on recent advances in four-dimensional modulation formats and in modulation format transparent data-aided digital signal processing. It is argued that four-dimensional modulation formats present an attractive complement to conventional polarization-multiplexed formats in the context of bandwidth-variable transceivers, where they enable a smooth transition with respect to spectral efficiency while requiring marginal additional hardware effort. Results of numerical simulations and experiments supporting this statement are presented. For the cost-efficient hardware implementation of bandwidth-variable transceivers supporting several polarization-multiplexed and four-dimensional modulation formats, digital signal processing algorithms are required which operate format transparent and consume little hardware resources. We discuss data-aided signal processing as one possible option, in particular with respect to carrier frequency recovery and channel estimation in combination with frequency domain equalization.

We experimentally demonstrate the use of data-aided digital signal processing for format-flexible coherent reception of different 28-GBd PDM and 4D modulated signals in WDM transmission experiments over up to 7680 km SSMF by using the same resource-efficient digital signal processing algorithms for the equalization of all formats. Stable and regular performance in the nonlinear transmission regime is confirmed.

A successful migration from current C-band based optical networks to a multiband scenario primarily depends on the development of solutions that can reliably measure physical properties of optical links over broad spectral transmission windows. Additionally, these solutions must be capable of delivering wavelength-dependent and spatially-resolved indicators that can empower network operators to identify faults before they lead to severe service disruptions. Recently, the exploitation of receiver based digital signal processing as a tool for optical performance monitoring has gained tremendous popularity. One successful example is the so-called in-situ power profile estimator, which can reconstruct the per-channel longitudinal power profile along the optical fiber link solely processing the received signal samples. In this work, we propose a novel application for the in-situ power profile estimator by harnessing it on multiple wavelengths to accurately estimate the spectral gain profile of C+L-band in-line Erbium-doped fiber amplifiers deployed in a 280-km single mode fiber link. Furthermore, we show how this scheme can be efficiently used to detect amplification-related anomalies, such as gain tilt and narrowband gain compression. In our measurements, we achieved a sub-dB estimation accuracy by comparing the proposed gain extraction approach with the back-to-back characterization obtained from an optical spectrum analyzer.