IoT and AI-related services and applications are becoming more common and it is expected that cyber-physical systems will enrich our daily lives in the near future. In such a situation, a huge amount of data is exchanged throughout the world in a real time fashion, which will increasingly push the need for optical network evolution. Considering these trends, intensive efforts on research and development have recently been dedicated to realize All-Photonics Network (APN) that is a key element of Innovative Optical and Wireless Network (IOWN). For materializing APN vision, one of the fundamental challenges is to expand network capacity in a highly cost- and energy-efficient manner. Meanwhile, many detailed studies have greatly improved the performance of multi-band optical networks. Thanks to such efforts, multi-band networking has been becoming feasible as a promising capacity-scaling solution, which can be a key enabler for APN. This paper reviews the recent advances in the multi-band optical network from various aspects. Specifically, we take a quick look at the studies enabling multi-band transmission in terms of devices design of transceiver and amplifier, quality-of-transmission estimation, and launch power optimization. Then, we focus on progress in optical switch technology, optical node configuration, path provisioning, and network analysis, aiming to deploy multi-band networks nationwide. We also refer to several emerging technologies, which include our efforts related to wavelength-selective band switching technology. This paper gives an opportunity to understand the trends and potential of multi-band optical networking.
