Abstract
In 2021, as optical technologies continue to demonstrate their advantages in telecom and data-center networks, we are also witnessing the attractive and promising progress on free-space optical communications and new technologies for fiber optic communications. Therefore, in this last issue of the Optical Communications and Networks Series in 2021, we have selected three contributions that address the (i) intelligent reflecting surface-assisted free-space optical communications, (ii) routing techniques for elastic optical networks with space division multiplexing, and (iii) non-orthogonal frequency-division multiplexing in optical networks.