Optical technologies supporting 5G/6G mobile networks

Intensively developed mobile systems and networks 5G and the planned 6G constitute one of the most important elements of modern telecommunications. The technologies of 5G/6G mobile systems and networks have become so demanding that they cannot be constructed and implemented without advanced optical and photonic technologies. Core networks (CN), backhaul (BH), midhaul (MH), fronthaul (FH) are the components that together constitute the networking realm of supporting 5G/6G mobile communications. Each of these components can be viewed as a service of an integrated X-haul/Crosshaul network, which can operate in a hybrid configuration based on DenseWavelength Division Multiplexing (DWDM); CoarseWavelength Division Multiplexing (CWDM); and optical transport network (OTN), Elastic Optical Network (EON), or passive optical network (PON) technologies. Moreover, 6G mobile networks will use not only optical fiber networks but also Light Fidelity (Li-Fi) optical wireless connectivity [15–17]. The increasing density of base stations operating at higher and higher radio frequencies will necessitate the introduction of Li-Fi, which will be dictated by the popularization of IoT services and the evolution of Industry 4.0 towards Industry 5.0. As the Radio Access Network (RAN) [20] domain of 5G/6G systems evolves towards Open Radio Access Networks (O-RANs), heterogeneous, multi-domain, and multi-operator optical networks will have to work coherently to ensure the efficient transport of highly diverse network traffic, as well as the extensive use of the computing and data-collecting cloud [23]. In many situations, only synchronous networks with all-optical links and very efficient management of optical resources will be able to meet these challenges. The search for optical and photonic solutions useful in 5G/6G networks concerns not only transmission systems but also systems supporting the operation of effective antenna array systems, which in the O-RAN architecture are most often connected in the Massive Multiple-Input Multiple-Output (mMIMO) or Fiber-to-the-Antenna (FTTA) configurations. In order to manage the shape of the radio beam, Fiber Bragg Grating (FBG)-based systems [26], optical delay lines, and multi-core fiber optics are used. Optical networks and systems are now widely available, but the optimal use of their capabilities and resources in terms of transmission and energy consumption leaves much to be desired. In order to dynamically manage these resources, it is necessary to introduce machine learning techniques and elements of artificial intelligence. It can be assumed that the intelligence of future universal optical networks will optimize and automate the planning of mobile networks and radio access. This Special Issue contains five contributions that primarily concern research in the area of optics and photonics used in telecommunications systems, without which 5G mobile systems cannot currently exist and 6G wireless radio and optical systems cannot be implemented in the future. In particular, two articles focus on passive optical networks, one on advanced optical modulations, one on optical path analysis in multi-layer optical networks, and one on solutions for efficient software/settings management during the monitoring of large numbers of optical converters. A more detailed description of these contributions is provided below.