Simulations Of Orbital Angular Momentum(OAM) Optical Communications Based On Multi-input Multi-output(MIMO) Technology

With the development of morden science and technology, there is an increasing demand on the communication transmission capacity. For the traditional optical communication technology, the communication capacity has reached its theory limit. Different dimensions of electromagnetic waves such as frequency, polarization, amplitude and phase have been well developed, while the space dimension has not yet been effectively exploited. Optical communication employing orbital angular momentum(OAM) could be an alternative way to facilitate efficient usage of space dimension. Optical communications using multiple OAM mode multiplexing can further increase the transmission capacity, but the orthogonality of different OAM modes might be broken in practical communication links, resulting in mode crosstalk between different OAM modes. Multi-input multi-output(MIMO) equalization technology could provide an effective approach to reduce the influence of mode crosstalk. In this thesis, OAM mode multiplexing transmission is studied by employing the MIMO equalization technique as follows.(1) The MIMO equalization algorithm is improved. By improving the error function of equalizer, independent equalizations of the amplitude and phase of a light beam are implemented. By adding the coherence function between different equalizers, the convergence of different equalizers to the same objective signal is solved.(2) Fractional order OAM mode multiplexing transmission system is simulated. Dense space-division multiplexing of fractional order OAM modes is proposed. The fractional order OAM mode multiplexing transmission is studied considering the relatively large mode crosstalk induced by the atmospheric turbulence. MIMO equalization technology is employed to relieve the influence of the mode crosstalk and improve the performance of the communication systems.(3) Bessel beam OAM mode multiplexing transmission system is simulated. The self-reconfiguration property of the Bessel beam is calculated. The performance of different kinds of OAM beams in atmospheric turbulence is compared with each other. The obtained results indicate that Bessl beams carrying OAM feature advantageous in free-space optical communications. Finally, the communication performance of different transmission systems employing different kinds of OAM beams is improved by exploiting MIMO equalization technology.