A special case of SDM is the utilization of orthogonal spatially overlapping and co-propagating spatial modes, known as mode-division multiplexing. One approach that has recently attracted wide interest is to use the spatial property of an EM wave, such that different spatial waves are multiplexed (i.e. Meeting future bandwidth demands may require new forms of data channel multiplexing. This can be achieved by using various properties of the electromagnetic (EM) wave, including time, wavelength and polarization, such that multiple data streams can be efficiently multiplexed and demultiplexed using appropriate device technologies. In the past, the capacity of a communication system can be dramatically increased by multiplexing and simultaneously transmitting multiple independent data streams. However, as the demand for data increases, there is a keen interest in increasing the data capacity of such communication systems. This article is part of the themed issue вЂOptical orbital angular momentumвЂ™.ДЇree-space communication links are important in many data transfer applications, and they can use either optical or radio-frequency (RF) waves. atmospheric turbulence and crosstalk) as well as potential techniques to mitigate such degrading effects. We discuss different technical challenges (e.g. In this review paper, we highlight recent advances in the use of OAM multiplexing for high-capacity free-space optical and millimetre-wave communications. Over the past few years, progress has been made in understanding the advantages and limitations of using multiplexed OAM beams for communication systems. As a result, the total capacity and spectral efficiency of the communication system can be multiplied by a factor equal to the number of transmitted OAM modes. In such a system, multiple OAM beams each carrying an independent data stream are multiplexed at the transmitter, propagate through a common medium and are demultiplexed at the receiver. A potential modal basis set to achieve MDM is to use orbital angular momentum (OAM) of EM waves. A subset of SDM is mode division multiplexing (MDM), in which multiple orthogonal beams each on a different mode can be multiplexed. One technique uses the spatial domain of an electromagnetic (EM) wave, and space division multiplexing (SDM) has become increasingly important for increased transmission capacity and spectral efficiency of a communication system.

There is a continuing growth in the demand for data bandwidth, and the multiplexing of multiple independent data streams has the potential to provide the needed data capacity.

Freespace optical communication