Simulating atmospheric turbulence using a bubble model for free space optical communication links

Free space optical (FSO) communication has emerged as a viable technology for broadband wireless applications. FSO technology offers the potential of high bandwidth capacity over unlicensed optical wavelengths. On long-range FSO links, atmospheric turbulence causes intensity fluctuations, which degrades links performance. Optical signals propagating through the atmosphere are subject to random fluctuations in phase and amplitude. These fluctuations are caused by random temperature distributions in the atmosphere, which manifests themselves as a random index of refraction changes along the propagation path. In addition, experimenting on a free space optical communication system is rather tedious and difficult. The interference of plentiful elements affects the result and causes the experimental outcomes to have bigger error variance margins than they are supposed to have. Especially when we go into the stronger turbulence regimes the simulation and analysis of the turbulence induced beams require delicate attention. For all these purposes, we propose a new geometrical model to assess the effects of turbulence on laser beam propagation. The atmosphere along the laser beam propagation path will be modeled as a spatial distribution of spherical bubbles with refractive index discontinuity statistically distributed according to various models. For each statistical representation of the atmosphere, the path of rays will be analyzed using geometrical optics. These Monte Carlo techniques will assess the phase of the beam as well as the aperture averaging effects at the receiver. An effective turbulence index C_n^2 can be determined by correlating beam wander behavior with the path length. The Monte Carlo analysis will be compared with the predictions of wave theory as well as with empirical results.