Recent advances and future directions in high-capacity optical fiber communication networks for 5G, 6G and Beyond

The rapid expansion of digital services, including cloud computing, artificial intelligence (AI), the Internet of Things (IoT), smart city applications, autonomous technologies, and emerging sixth-generation (6G) wireless systems, has placed unprecedented demands on communication networks. To support these growing requirements, optical fiber communication has become the foundation of modern telecommunications, offering high bandwidth capacity, low transmission loss, resistance to electromagnetic interference, and reliable long-distance connectivity. Over the past decade, significant progress has been achieved through the development of coherent optical transmission, wavelength division multiplexing (WDM), space division multiplexing (SDM), software-defined networking (SDN), machine learning-based network management, and all-optical networking architectures. These innovations have contributed to substantial improvements in network capacity, efficiency, flexibility, and operational performance. However, several challenges continue to influence the evolution of optical communication systems, including latency constraints, fiber nonlinearities, increasing energy demands, network management complexity, and scalability limitations. This review examines recent developments in optical fiber communication technologies, discusses current approaches to performance optimization and intelligent network management, and highlights emerging research directions that are expected to influence the design and operation of future communication networks.