Optical Beamforming Networks for Millimeter-Wave Wireless Communications

With the rapid data growth driven by smart phone, high-definition television and virtual reality/augmented reality devices and so on, the launched 5G and upcoming 6G wireless communications tend to utilize millimeter wave (mmWave) to achieve broad bandwidth. In order to compensate for the high propagation loss in mmWave wireless communications and track the moving users, beamforming and beamsteering are indispensable enabling technologies. These have promising potential to be realized through the use of optical beamforming networks (OBFNs) that have a wider bandwidth and smaller size, lower power consumption, and lower loss compared to those of their electric counterparts. In this paper, we systematically review various OBFN architectures using true time delays and optical phase shifters, as well as discuss performances of different architectures, scalable technologies that promote the advancement of OBFNs, and the application potentials of OBFNs. Two-dimensional OBFNs with discrete components or integrated optical devices have been elaborated, in addition to one-dimensional architectures. Moreover, the state-of-the-art technologies relative to reducing the size, loss and nonlinearity of OBFNs have also been discussed here.