Study of a novel free-space optical communication system with structured light beams

Since the advent of modern telecommunications, the necessity to exploit the same link to put in communication more users or to increase the amount of transmitted information has boosted the exploration of the different degrees of freedom of light, leading to the development of several division multiplexing techniques based on wavelength, time, polarization, phase/amplitude, and, more recently, space. Space division multiplexing (SDM) relies on structuring the intensity or phase distribution of electromagnetic waves over a set of non-interfering spatial configurations to be used as distinct information channels at the same frequency in combination with standard modulation formats, offering a way out to the impelling problem of networks saturation (optical crunch) and a wider alphabet of states for quantum protocols. That requires the choice of a suitable family of orthogonal beams and the design of specific devices, i.e., the multiplexer and the demultiplexer, realizing their superposition at the transmitter stage and separation at the receiver one. \\ In this thesis, a novel and innovative framework will be considered and investigated for SDM, based on the exploitation of a new type of beams characterized by multipole phases. The purpose of this work is the design and simulation of a free-space optical link based on multipole-phase division multiplexing. The generation (multiplexing), transmission, and sorting (demultiplexing) of multipole-phase beams will be analysed with both a theoretical and numerical approach, in order to engineer the design of efficient and compact all-optical devices for the manipulation and control of this new type of structured beams. This new spatial multiplexing technique provides an innovative and revolutionary solution in the scenario of free-space optical communication, from the optical up to the radio regimes, promising to solve the still-opened issues of previous techniques, as those based on orbital angular momentum, and offering an efficient and practical method for high-capacity transmission.