Geometrical optics analysis of atmospheric turbulence

Abstract

2D phase screen methods have been frequently applied to estimate atmospheric turbulence in free space optic communication and imaging systems. In situations where turbulence is "strong" enough to cause severe discontinuity of the wavefront (small Fried coherence length), the transmitted optic signal behaves more like "rays" rather than "waves". However, to achieve accurate simulation results through ray modeling requires both a high density of rays and a large number of eddies. Moreover, their complicated interactions require significant computational resources. Thus, we introduce a 3D ray model based on simple characteristics of turbulent eddies regardless of their particular geometry. The observed breakup of a beam wave into patches at a receiver and the theoretical description indicates that rays passing through the same sequence of turbulent eddies show "group" behavior whose wavefront can still be regarded as continuous. Thus, in our approach, we have divided the curved trajectory of rays into finite line segments and intuitively related their redirections to the refractive property of large turbulent eddies. As a result, our proposed treatment gives a quick and effective high-density ray simulation of a turbulent channel which only requires knowledge of the magnitude of the refractive index deviations. And our method points out a potential correction in reducing equivalent C n 2 by applying adaptive optics. This treatment also shows the possibility of extending 2D phase screen simulations into more general 3D treatments.

Phase and amplitude wave front sensing and reconstruction with a modified plenoptic camera

“…Unlike normal cameras whose image is an integral of a plenoptic function over angular space 6 , the plenoptic camera divide its high resolution into a 4D space, which is made up of 2D spatial and 2D angular information sets of the incident light field . The goal of adaptive optics in correcting the beam is to confine a complex wavefront sensed by the modified plenoptic camera at target site to as few block images as possible and to eliminate interference patterns within those block images.…”