Performance analysis of FSO links under turbulence-induced fading using robust beam engineering [Invited]

We report the performance of an engineered beam utilizing spatial and polarization diversity to make the beam robust against propagation over a turbulent channel. Additionally, we observe the modification in the irradiance fluctuation distributions of the received signal irradiance with the engineered beam compared to the Gaussian beam. We simulated the beam propagation over different turbulent channels using the multiple-phase screen split-step method to measure the irradiance fluctuation statistics. The measured probability distribution function is closely matched with the generalized Gamma distribution (GGD) over various turbulence regimes for the considered simulation model. Moreover, we measured irradiance fluctuations and the scintillation index and found that the turbulence-induced distortion experienced by the engineered beam is less than that experienced by Gaussian beam for different turbulence regimes. Furthermore, we used the GGD to derive analytical expressions for critical performance metrics, including average capacity, bit-error rate (BER), and outage probability. The study investigated free-space optical (FSO) systems that used both engineered and Gaussian beam transmissions, employing direct detection and heterodyne detection (HD) techniques across various turbulence regimes. Furthermore, we extend our study and measure the BER performance of the FSO system using an on–off keying (OOK) modulated signal over different turbulence regimes using Gaussian and engineered beams. In conclusion, the paper demonstrates the feasibility and advantages of employing engineered beams for FSO communications, particularly in scenarios characterized by medium-to-strong turbulence levels.