Data centers (DCs) are intrinsic to emerging technologies which require to store and process massive amounts of versatile data through large-scale networks of computing and storage units. Conventional wired DC networks (DCNs) with static links and finite network interfaces suffer from cabling cost and complexity as scalability increases, lack the flexibility to handle the dynamic and large volume of traffic outbursts (i.e., hotspots), and have limited bisection bandwidths mainly due to the switching speeds. Therefore, optical wireless DCNs have recently attracted attention by their capability to augment the inherent restrictions of wired DCNs. In addition to the reduced cost of wiring, wireless communication can provide a flexible topology to overcome oversubscriptions and hotspots. Moreover, it is possible to adapt the link capacities in accordance with the quality of service demands of different services and flow classes. Furthermore, wireless communication can also make it possible to eliminate switches by establishing direct links among the servers. In this paper, we first present potential state- of-art optical wireless technologies. Second, practical challenges of design and provisioning of optical wireless communications in real-life DCNs are outlined along with a survey of recent advances and implementations. Finally, we motivate researchers with the exciting prospects of optical wireless DCNs including physical and virtual topology design, interference management, multiple access techniques, traffic management and grooming, and flow classification.