  Time, polarization, and wavelength multiplexing schemes have been used to
satisfy the growing need of transmission capacity. Using space as a new
dimension for communication systems has been recently suggested as a versatile
technique to address future bandwidth issues. We review the potentials of
harnessing the space as an additional degree of freedom for communication
applications including free space optics, optical fiber installation,
underwater wireless optical links, on-chip interconnects, data center indoor
connections, radio frequency and acoustic communications. We focus on the
orbital angular momentum (OAM) modes and equally identify the challenges
related to each of the applications of spatial modes and the particular OAM
modes in communication. We further discuss the perspectives of this emerging
technology. Finally, we provide the open research directions and we discuss the
practical deployment of OAM communication links for different applications.
