Photonic integrated devices for exploiting the orbital angular momentum of light in optical communications

In general, OAM can be regarded as an additional degree of freedom of a light beam or even of a single photon, to be added to the standard ones ordinarily exploited in current photonic technologies. In many respects OAM resembles polarization, with which it shares many features. However, while polarization is characterized by two orthogonal basis states, OAM is defined in an unbounded space (a Hilbert space in the case of photons). Therefore, it is in principle possible to encode a much larger amount of information in the OAM space than in the polarization space, e.g., achieving a greater channel capacity. This property makes OAM highly attractive for future optical communication systems. Specifically, OAM states could be used as a different dimension to create an additional set of data carriers in a Space Division Multiplexing (SDM) system. Moreover, OAM multiplexing does not rely on the wavelength or polarization, indicating that OAM could be used in addition to Wavelength Division Multiplexing (WDM) and Polarization Division Multiplexing (PDM) techniques to boost system capacity. This paper will discuss the potential applications of OAM of light in optical communication systems, and highlight recent advances in CMOS-compatible silicon photonic integrated device technology for OAM generation, manipulation, and (de)multiplexing.