Programmable simulator for beam propagation in turbulent atmosphere

Abstract

The study of light propagation though the atmosphere is crucial in different areas such as astronomy, free-space communications, remote sensing, etc. Since outdoors experiments are expensive and difficult to reproduce it is important to develop realistic numerical and experimental simulations. It has been demonstrated that spatial light modulators (SLMs) are well-suited for simulating different turbulent conditions in the laboratory. Here, we present a programmable experimental setup based on liquid crystal SLMs for simulation and analysis of the beam propagation through weak turbulent atmosphere. The simulator allows changing the propagation distances and atmospheric conditions without the need of moving optical elements. Its performance is tested for Gaussian and vortex beams.

A Simplified Model for Optical Systems with Random Phase Screens

“…Consider the case where the masks in Figure 2 a are RPSs, and we are interested in the output intensity for a coherent input. The output intensity measurement is the desired result in common optic systems with random media, such as biological and atmospheric light propagation applications [ 1 , 2 , 3 , 4 , 21 , 22 ]. A practical simulation example of this will be given in the next section.…”

“…An optical system with multiple arbitrary masks placed at arbitrary positions is the core scheme of a variety of optical systems. A scheme where the masks are random phase screens (RPSs) is an excellent model for the analysis, simulation, and interpretation of optical systems that involve optical scattering due to refractive index fluctuations [ 1 , 2 , 3 , 4 ]. RPS models were first introduced to represent the fading of radio waves due to fluctuations in the ionosphere layers, but were later found to be useful for modeling various other wave scattering phenomena, including optical scattering.…”

“…In Figure 1 a, a scheme of a paraxial optical system is illustrated, where there are sub paraxial systems, , and masks, , between them, while and denote the input field and output field, respectively. For example, in atmospheric propagation of light, the sub-systems might be free-space propagation combined with an optical scaling system where the masks are RPSs [ 4 , 6 ]. Figure 1 b is a specific case of Figure 1 a for two masks and three sub-systems, showing a paraxial system composed of intermittent lenses of focal length and free-space propagation sections of length with two masks in between.…”

“…The first order paraxial sub-systems between the masks in Figure 1 a might be any combination of beam propagation forms with ideal optical elements between the stages, such as ideal thin lenses, ideal graded-index fiber, etc. Such lenses and fibers are commonly used for scaling [ 4 ], imaging [ 10 ], and spatial filtering [ 5 ] between the RPSs in the system. For example, in Figure 1 b, is a free-space propagation section of length , is an ideal focal length system, and is an ideal focal length system with an additional free-space propagation section of length .…”

CNN-Based Phase Matching for the OAM Mode Selection in Turbulence Heterodyne Coherent Mitigation Links

“…In order to simulate real-time AT, random phase screens are adopted. The AT random phase screens are constructed by combining Fourier-transform and subharmonics method [29], [30]. And the Kolmogorov power spectrum is used to describe the atmospheric turbulence [12], [29] and [32].…”