Atmospheric propagation emulator for free space optical applications: design and performances

Abstract

Free space optics propagation through the atmosphere experiences wavefront phase deformation, beam distortion, and aberrations due to the refraction index variations fluctuation along the optical path . Many studies have been done to analyse the atmospheric layers and understand their effects on beam quality. Different applications need to tackle the atmospheric effect like satellite to ground optical communication, astronomy, beam sensing, and power beaming where the atmospheric effect leads to beam wandering that result on beam mis-pointing and power loss at the receiver/target. This paper covers the design of an atmospheric turbulence generator and its characterization and capabilities to create different atmospheric turbulent strength levels. Temperature variation, wind speed/direction, and humidity effects are considered and monitored to emulate different turbulences regimes (corresponding to different spatial coherence levels) that will impact a Gaussian wavefront beam with different turbulence strengths. The turbulence emulator has various apertures for the incoming beam, outcoming beam, ambient air flow, and tuneable temperature air flow. The mixture of these two airflows results in high-speed refractive index fluctuations. A 1064 nm collimated optical beam is used to characterize the turbulence generator and illustrate the impact of the environmental condition on the outcoming optical beam.