This PDF file contains the front matter associated with SPIE Proceedings Volume 9979 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Laser power delivery through atmospheric turbulence to photovoltaic (PV) cells, e.g., for remote powering of UAVs, has unique requirements on adaptive beam control. In contrast to directed energy applications or laser communications, where the goal is to concentrate as much power as possible on a target or a receiver aperture, respectively, efficient power conversion with PV cells requires a uniform irradiance over the PV converter area. To minimize the loss of optical energy, the beam shape and size should be matched to the area the PV converter. This should be realized even if the distances between the transmitter and the PV converter are varying over time. In this paper we present techniques for power beaming with adaptive fiber array transmitters. Control of piston, tip, and tilt phases within each sub-aperture allows for adaptive beam shaping and for mitigation of distortions caused by atmospheric-turbulence using light returning from an array of small retro-reflector interspersed with the PV cells as feedback signal for a stochastic parallel gradient descent (SPGD) controller. We will discuss several approaches to optimize the beam shape at the PV converter and present experimental results from proof-of-principle experiments on an atmospheric propagation path.

Beam spread and beam wandering are the most perceptible effects of atmospheric turbulence on propagating laser beams. The width of the mean irradiance profile is typically used to characterize the beam spread. This so-called Long- Term (LT) statistic allows for a relatively simple theoretical description. The LT beam size is not a very practical measure of the beam spread because its measurements are sensitive to the movements of the source and detector, and to the large-scale variations of the refractive index that are not associated with turbulence. The Short-Term (ST) beam spread is measured relative to the instantaneous position of the beam center and is free of these drawbacks, but has not been studied as thorough as the LT spread. We use a Markov approximation-based theoretical model for the ST beam irradiance that is valid for the wide range of turbulent conditions. Additional approximations are invoked to allow introduction of the isoplanatic ST Point Spread Function (PSF). Unlike the LT PSF, the ST PSF depends on the overall beam geometry. Adjustments of the initial beam width and focal distance make it possible to increase the contribution of the LT beam spread that is attributed to the beam wander and minimize the ST beam size at the observation plane for any given turbulence level. Analytical calculations of the optimal beam geometry are presented for the simple case of the coherent Gaussian beam, and Kolmogorov turbulence. We present the results of direct numerical simulation of beam wave propagation that confirm the existence of the optimal beam geometry.

Corruption of the wavefront, beam wondering and power density degradation at the receiving end are the effects typically observed at laser beam propagation through turbulent atmosphere. Compensation of these effects can be achieved if the reciprocal conditions for the propagating wave are satisfied along the propagation range. Practical realization of these conditions requires placing a localized beacon at the receiving end of the range and high-performance adaptive optics system (AOS). The key condition for an effective performance of AOS is a high value of the reciprocal component in the outgoing wave, since only this component is getting compensated after propagating turbulence perturbed path. The nonreciprocal components that is present in the wave directed toward the target is caused by three factors (detailed in this paper) that determine the partial restoration of the structure of the beacon beam. Thus solution of a complex problem of focusing the laser beam propagating through turbulent media can be achieved for the share of the outgoing wave that has a reciprocal component. This paper examines the ways and means that can be used in achieving the stated goal of effective laser power delivery on the distant image-resolved object.

We evaluate the accuracy of recently published, tractable yet approximate, analytic theory for describing the centroid-centered mean irradiance of beams propagated through atmospheric turbulence. Such theory, if accurate, is a highly desirable candidate for use in optical system performance calculations that perform active tracking.

Innovative technologies are needed to support and augment the development of various types of deformable mirrors (DM), such as Micro Electro Mechanical Systems (MEMS), segmented, bimorph and membrane types that are currently used in adaptive-optic (AO) systems. The paper discusses the results of initial studies that, could, potentially, be employed for full characterization of the dynamic behavior of adaptive optics mirrors. The experimental data were obtained from a typical bimorph mirror using both, a Shack-Hartman wavefront sensor (SHWFS) and an Imaging Laser Doppler Vibrometer (ILDV) developed exclusively by AS and T Inc. These two sensors were employed for quantitative measurement of both the spatial and temporal dynamics of the DM under broadband excitation via the piezo electric drive elements. The need to characterize the spatial and temporal dynamic response of current and future DM mirror designs is essential for optimizing their performance to a level adequate for high bandwidth AO systems, such as those employed for real-time compensation of wavefront perturbations.

A paraxial equation for electromagnetic wave propagation in a random medium is extended to include the depolarization effects in the narrow-angle, forward-scattering setting. A system of two coupled parabolic equations describes propagation of the polarized wave through random medium. In the Cartesian coordinate formulation the coupling term is related to the second mixed derivative of the refractive index. Closed-form parabolic equation for propagation of the coherence tensor is derived under a Markov random process propagation model. The scattering term in this equation includes a rank-four tensor that contains derivatives of the correlation function of the refractive index up to the fourth order. This equation can be also formulated as vector equations for generalized Stokes or lexicographic vectors. In contrast to the scalar case, these equations do not have an analytical solution. For a general partially coherent and partially polarized beam wave, this equation can be reduced to a system of ordinary differential equations allowing a simple numeric solution. For a special case of statistically homogeneous waves an analytical solution exists. In the Stokes vector formulation this solution is described by a range-dependent Mueller matrix. For isotropic random medium this Mueller matrix is diagonal and describes a pure non-uniform depolarizer. Statistics of the random medium is wrapped in a single parameter – depolarization length which is proportional to the fourth derivative of the covariance function at zero. For propagation through atmospheric turbulence estimates based on the perturbation solution support the common knowledge that the depolarization at the optical frequencies is negligible.

We suggest a technique for generation of optical vortex beams with a variable orbital angular momentum based on a fiber laser array. The technique uses the phase control of each single subbeam. Requirements for the number of subbeams and the spatial arrangement for the vortex beam generation are determined. The propagation dynamics of a vortex beam synthesized is compared with that of a continuous Laguerre–Gaussian beam in free space and in a turbulent atmosphere. Spectral properties of a beam synthesized, which is represented as a superposition of different azimuth modes, are determined during its free-space propagation. It is shown that energy and statistical parameters coincide for synthesized and continuous vortex beams when propagating through a turbulent medium. Probability density functions of the beam intensity fluctuations are well approximated to a gamma distribution in the cases where the scintillation index is lower than unity independently of the beam type and observation point position relative to the propagation axis.

In contrast to theory, speckle imaging has proven an effective tool for scene recovery over long horizontal paths where imaging distortions are highly anisoplanatic. One possible explanation for this efficacy is that the atmospheric bispectrum transfer function is less attenuated at higher spatial frequencies when the object is extended and not a pair of point sources, as examined by theory. In this work, I empirically evaluate the speckle, cross-spectrum, and bispectrum transfer functions by comparing these quantities as derived from both field and simulation data to a simulated diffraction-limited reference image. The empirical transfer function relationships are found by comparing turbulence quantities to those of their diffraction-limited counterparts.

Statistics of the random phase screens used for the modeling of beam propagation and imaging through the turbulent atmosphere is currently based on the Markov Approximation (MA) for wave propagation. This includes the phase structure functions of individual screens and the use of the statistically-independent screens for the multi-screen splitstep simulation of wave propagation. As the propagation modeling progresses to address the deep turbulence conditions, the increased number of phase screens is required to accurately describe the multiple scattering. This makes the MA a critical limitation, both because phase statistic of the thin turbulent layer does not follow MA, and because the closely space screens cannot be considered as statistically and functionally independent. A recently introduced Sparse-Spectrum (SS) model of statistically homogeneous random fields makes it possible to generate 3-D samples of refractive-index fluctuations with prescribed spectral density at a very reasonable computational cost. This leads to generation of samples of the phase screen sets that are free from the limitations of the MA. We investigated statistics of the individual phase screens and cross-correlations between the pairs of phase screens and found that the thickness Δz of the turbulent layer replaced by the phase screen is a new parameter defining the phase statistics in the non-Markov case. SS-based numerical algorithms for generation of the 3-D samples of the turbulent refractive index, and for the phase screen sets are presented. We also compare the split-step simulation results for the traditional MA and non-Markov screens.

Math modeling of a low-data-rate optical communication system is presented and compared with recent testing results over ranges up to 100 m in an indoor tunnel at Kennedy Space Center. Additional modeling of outdoor testing results at longer ranges in the open atmosphere is also presented. The system modeled is the Army’s Multiple Integrated Laser Engagement System (MILES) that has been used as a tactical training system since the early 1980s. The objective of the current modeling and testing is to obtain target hit zone profiles for the M16A2/M4 rifles and establish a data baseline for MILES that will aid in its upgrade using more recently developed lasers and detectors.

Free space laser communications provides wide bandwidth and high security capabilities to cellular backhaul network in order to successfully accomplish data communication between cell sites and NOC (Network Operation Center). For this application, an optical receiver is a critical component and needs to be designed to operate in sunlight and other ambient noise environments while providing reliable data transmission. In this paper, a method of Free Space Laser Communication along with a differential optical receiver is presented for the backhaul solution of 5G networks that provides high capacity, reliability, less deployment cost, and long distance reach. At the receiver, two photo diodes are cross coupled. The effect is that the net output power is close to zero. The laser signal is then transmitted only into one of the receivers. With all other signals being cancelled out, the laser signal is an overwhelmingly dominant signal. In the proposed configuration, two signals generating photo-receptors are arranged such that when they are opposed to one another, the effect is a cancellation, if and only if the both photo-receptors receive the same amount of input.

Laser based radio communication system, i.e. OptoRadio, using Orthogonal M-ary PSK Modulation scheme is presented in this paper. In this scheme, when a block of data needs to be transmitted, the corresponding block of biorthogonal code is transmitted by means of multi-phase shift keying. At the receiver, two photo diodes are cross coupled. The effect is that the net output power due to ambient light is close to zero. The laser signal is then transmitted only into one of the receivers. With all other signals being cancelled out, the laser signal is an overwhelmingly dominant signal. The detailed design, bit error correction capabilities, and bandwidth efficiency are presented to illustrate the concept.

For over a century and Mr. Guglielmo Marconi invention, systems using radio waves have controlled over wireless telecommunication solutions; from Amplitude Modulation (AM) radio products to satellite communications for instance. But beyond an increasingly negative opinion face to radio waves and radio spectrum availability more and more reduced; there is an unprecedented opportunity with LED installation in displays and lighting to provide optical wireless communication solutions. As a result, technologically mature solutions are already commercially available for services such as Location Based Services (LBS), broadcast diffusion or Intelligent Transport Services (ITS). Pending finalization of the standard review process IEEE 802.15.7 r1, our paper presents the results of the European collaborative project named "ACEMIND". It offers an indoor bilateral optical wireless communication prototype having the following characteristics: use of the existing electrical infrastructure, through judicious combination with Light Fidelity (LiFi), Power Line Communication (PLC) and Ethernet to reduce the implementation cost. We propose a bilateral optical wireless communication even when the light is switched off by using Visible Light Communication (VLC) and Infra-Red Communication (IRC) combined to a remote optical switch. Dimensionally optimized LiFi module is presented in order to offer the possibility for integration inside a laptop. Finally, there is operational mechanism implementation such as OFDM/DMT to increase throughput. After the introduction, we will present the results of a market study from Orange Labs customers about their opinion on LiFi components. Then we will detail the LiFi prototype, from the physical layer aspect to MAC layer before concluding on commercial development prospects.

The raised cosine waveform is a common efficient waveform to control the bandwidth reduction of a communications signal at the cost of controlled Inter Symbol Interference (ISI) with relatively large Peak to Average Power Ratio (PAPR). Reducing the PAPR has been addressed extensively in the literature using methods such as the clipping and coding the data among others. In this paper, we reduce the PAPR by windowing the raised cosine waveform to minimize contributions to PAPR with minimal spectral growth. We simulate the modified raised cosine to determine the reduction in PAPR for various Quadrature Amplitude Modulation (QAM) orders and excess bandwidths.

The carbonaceous particles are the main source of the light absorption in atmospheric aerosol. Different from the case in tissue-like turbid media, the light absorption in atmospheric environments can be described as an inherent attribute on scatterers rather than an interstitial propagation effect. In this paper, we simulated the optical absorption due to carbonaceous scatterers and analyzed the influence of various parameters on their polarization properties, such as the imaginary part refractive index, the size and shape. Also we compare these results with our previous research work on absorption effect in ambient medium. For the single scattering, the polarization scattering angular distribution implies the potential of distinguishing different carbonaceous particles with different structural and absorption parameters. In the other hand, for the week scattering case of suspension system, using the backward Mueller matrix polar decomposition method, we can find out that the additional absorption effect on carbonaceous particles can enhance their depolarization and moreover produce more diattenuation and linear retardance for those anisotropic particles. The subsequent experiments of standard samples show a good agreement with simulation results. The paper further studies the phase function of single scattering and the distribution of scattering numbers, which can explain these unique polarization scattering phenomena. We hope these fundamental results can help to investigate how to identify the carbonaceous particles and characterize their optical features from the atmospheric hybrid suspension system.

The Laser Communication Relay Demonstration is NASA’s multi-year demonstration of laser communication to a geosynchronous satellite. We are currently assembling the optical system for the first of the two baseline ground stations. The optical system consists of an adaptive optics system, the transmit system and a camera for target acquisition. The adaptive optics system is responsible for compensating the downlink beam for atmospheric turbulence and coupling it into the modem’s single mode fiber. The adaptive optics system is a woofer/tweeter design, with one deformable mirror correcting for low spatial frequencies with large amplitude and a second deformable mirror correcting for high spatial frequencies with small amplitude. The system uses a Shack- Hartmann wavefront sensor. The transmit system relays four beacon beams and one communication laser to the telescope for propagation to the space terminal. Both the uplink and downlink beams are centered at 1.55 microns. We present an overview of the design of the system as well as performance predictions including time series of coupling efficiency and expected uplink beam quality.

Active satellites have the ability to maneuver to avoid collision with other space objects. Unfortunately the majority of objects in space are debris objects that do not have the ability to maneuver. In the future the population of debris objects will grow and the probability of collision will increase. This paper will provide details on plans to use a ground based laser with uplink adaptive optics compensation to apply photon pressure to debris objects and maneuver them out of harm’s way. This work is ongoing at the Space Environment Research Centre at Mt. Stromlo Australia with collaborative efforts from Lockheed Martin, Electro-Optics Systems Inc. and the Australian National University.

Satellite tracking and imaging is conducted by the ANU Research School of Astronomy and Astrophysics (RSAA) and Electro-Optic Systems at Mount Stromlo as part of the Space Environment Management Cooperative Research Centre to support debris tracking. To optimally design adaptive optics systems for those applications, it is important to know the atmospheric profile, i.e. how the turbulence is distributed as a function altitude. We have designed a new stereo-SCIDAR instrument1 to conduct a site characterisation campaign at Mount Stromlo site. This paper summarises our current progress: specifications, design choices and post-processing techniques. In particular, we compare two different post-processing algorithms for stereo-SCIDAR, using simulated data cubes. One of the codes is implemented by the RSAA, the other by the Centre for Advanced Instrumentation, University of Durham. The comparison shows that the current implementations of both codes produce decent results. However, we can see potential for further improvements.

In this work we present a practical, experimental analysis of the effects of adaptive optics compensation on the performance of free-space coherent optical receivers. In order to fulfill this objective, we have developed a laboratory test bed for simulating atmospheric turbulence using Kolmogorov statistics; we have implemented a digital-signal-processing-based phase shift keying heterodyne coherent receiver; and we have integrated a compact module operating a low-cost adaptive optics system that applies modal and zonal wavefront correction. We have checked our experimental results against previously reported analytical models describing the performance of coherent receivers using atmospheric compensation techniques.

To achieve the power levels necessary for directed energy applications with fiber or slab lasers, it is necessary to combine multiple lasers into a single beam director. Here we compare the performance of incoherent and coherent beam combining strategies and address three important issues that should be considered before a beam combining architecture is implemented. First, we consider the difficulty in phase locking high-power fiber and slab lasers. The large linewidths of high-power fiber and slab lasers induce random phase fluctuations occurring on sub-nanosecond time scales. To coherently combine these high-power lasers can involve rapid and precise phase control to compensate for these fluctuations. Even with a master oscillator - multiple power amplifier system, the coherence length of the beams to be combined is very short necessitating continuous precise control of optical path lengths. Second, we consider the dephasing effects of atmospheric turbulence. We find that in moderate to strong turbulence conditions and kilometer propagation distances, coherent combining at the transmitter plane has negligible impact on the energy delivered to a target. Finally, we consider the multifaceted task of coherent combining at the target plane. This is effectively an adaptive optics situation in which the distortions caused by atmospheric turbulence are partially compensated for.

Adaptive optics relies on the accuracy and speed of a wavefront sensor in order to provide quick corrections to distortions in the optical system. In weaker cases of atmospheric turbulence often encountered in astronomical fields, a traditional Shack-Hartmann sensor has proved to be very effective. However, in cases of stronger atmospheric turbulence often encountered near the surface of the Earth, atmospheric turbulence no longer solely causes small tilts in the wavefront. Instead, lasers passing through strong or “deep” atmospheric turbulence encounter beam breakup, which results in interference effects and discontinuities in the incoming wavefront. In these situations, a Shack-Hartmann sensor can no longer effectively determine the shape of the incoming wavefront. We propose a wavefront reconstruction and correction algorithm based around the plenoptic sensor. The plenoptic sensor’s design allows it to match and exceed the wavefront sensing capabilities of a Shack-Hartmann sensor for our application. Novel wavefront reconstruction algorithms can take advantage of the plenoptic sensor to provide a rapid wavefront reconstruction necessary for real time turbulence. To test the integrity of the plenoptic sensor and its reconstruction algorithms, we use artificially generated turbulence in a lab scale environment to simulate the structure and speed of outdoor atmospheric turbulence. By analyzing the performance of our system with and without the closed-loop plenoptic sensor adaptive optics system, we can show that the plenoptic sensor is effective in mitigating real time lab generated atmospheric turbulence.

The Kolmogorov’s theory has been used to explain physical phenomena like the vertical turbulence in atmosphere, others recent works have made new advances and have improved K41 theory. In addition, this theory has been applied to studying different issues associated to measure atmospheric effects, and have special interest to find answers in optics to questions as e.g. at ground level, Could it find edges of two or more close objects, from a distant observer? (Classic resolution problem). Although this subject is still open, we did a model using the statistics of the centroid and the diameter of the laser beam propagated under horizontal turbulence at ground level until the object plane. The goal is to measure efficiently the turbulence effects in the long horizontal path propagation of electromagnetic wave. Natural movement of laser beam within the cavity needs be subtracted from the total transversal displacement in order to obtain a best approach. This simple proposed method is used to find the actual statistics of the centroid and beam diameter on the object plane where the turbulence introduces an additional transversal shift. And it has been tested for different values of horizontal distances under non-controlled environment in a synchronized acquisition scheme. Finally, we show test results in open very strong turbulence with high controlled temperature. This paper presents the implemented tests mainly into laboratory and discuss issues to resolve.

An overview is given of the First European – South African Transmission ExpeRiment (FESTER), which took place in South Africa, over the False Bay area, centered around Simon’s Town. The experiment lasted from April 2015 through February 2016 and involved continuous observations as well as periodic observations that took place during four Intensive Observation Periods (IOPs) of 2 weeks each, which were spread over the year. The continuous observations aimed at a characterization of the electro-optical propagation environment, and included standard meteorology, aerosol, refraction and turbulence measurements. The periodic observations aimed at assessing the performance of electro-optical sensors in VIS / SWIR / MWIR and LWIR wavebands by following a boat sailing outbound and inbound tracks. In addition, dynamic aspects of electro-optical signatures, i.e., the changes induced by variations in the environment and/or target orientation, were studied. The present paper provides an overview of the trial, and presents a few first results.

Optical turbulence for over-water conditions was investigated in a long-term experiment over False Bay near Cape Town, South Africa. A sonic anemometer and two boundary-layer scintillometers were deployed to access in-situ turbulence as well as the integrated turbulence over two 1.8 and 8.7 km paths. Statistical analysis reveals spatial temporal variations of the turbulence conditions over False Bay, which might be related to differences in the atmospheric conditions and/or the surface (water) temperatures. An analysis in terms of mechanical and thermal forcing reveals that the latter factor is more dominant in determining the turbulence strength.

We present some preliminary results and discussion of our ongoing effort to develop a prototype volumetric atmospheric optical refraction simulator which uses 3D nonlinear ray-tracing and state-of-art physics-based rendering techniques. The tool will allow simulation of optical curved-ray propagation through nonlinear refractivity gradient profiles in volumetric atmospheric participating media, and the generation of radiometrically accurate images of the resulting atmospheric refraction phenomena, including inferior and superior mirages, over-the-horizon viewing conditions, looming and sinking, towering and stooping of distant objects. The ability to accurately model and predict atmospheric optical refraction conditions and phenomena is important in both defense and commercial applications. Our nonlinear refractive ray-trace method is currently CPU-parallelized and is well-suited for GPU compute implementation.

Most models that predict the infrared signature of an object are based on steady-state equilibrium conditions and do not model the dynamic nature of the real world. To gain more understanding of the dynamic infrared signatures of an object, several outdoor experiments were performed, using a CUBI and a small vessel as an object. Dynamic changes were (intentionally) made to the object, while the temperatures of the facets, the meteorological parameters, and the infrared signature were being monitored. The influence of environmental parameters on the dynamic infrared signature of an object is discussed in this paper. A first attempt to model the decrease in object temperature is made.

For more than a decade, Defence Research and Development Canada (DRDC) has been developing a Library of computer models for the calculations of atmospheric effects on EO-IR sensor performances. The Library, called EOSPEC-LIB (EO-IR Sensor PErformance Computation LIBrary) has been designed as a complement to MODTRAN, the radiative transfer code developed by the Air Force Research Laboratory and Spectral Science Inc. in the USA. The Library comprises modules for the definition of the atmospheric conditions, including aerosols, and provides modules for the calculation of turbulence and fine refraction effects. SMART (Suite for Multi-resolution Atmospheric Radiative Transfer), a key component of EOSPEC, allows one to perform fast computations of transmittances and radiances using MODTRAN through a wide-band correlated-k computational approach. In its most recent version, EOSPEC includes a MODTRAN toolbox whose functions help generate in a format compatible to MODTRAN 5 and 6 atmospheric and aerosol profiles, user-defined refracted optical paths and inputs for configuring the MODTRAN sea radiance (BRDF) model. The paper gives an overall description of the EOSPEC features and capacities. EOSPEC provides augmented capabilities for computations in the lower atmosphere, and for computations in maritime environments.

An accurate model and parameterization of fog is needed to increase the reliability and usefulness of electro-optical systems in all relevant environments. Current models vary widely in their ability to accurately predict the size distribution and subsequent optical properties of fog. The Advanced Navy Aerosol Model (ANAM), developed to model the distribution of aerosols in the maritime environment, does not currently include a model for fog. One of the more prevalent methods for modeling particle size spectra consists of fitting a modified gamma function to fog measurement data. This limits the fog distribution to a single mode. Here we establish an empirical model for predicting complicated multimodal fog droplet size spectra using machine learning techniques. This is accomplished through careful measurements of fog in a controlled laboratory environment and measuring fog particle size distributions during outdoor fog events.

In this paper we introduce the use of Karhunen-Loève functions as a basis set to decompose atmospheric phase aberrations in a digital holographic wavefront sensor (HWS). We show that the intermodal crosstalk when using Karhunen-Loève functions is reduced in comparison to the Zernike decomposition. Additionally, the sensor’s response showed an improved linearity and better robustness to scintillation. Intermodal crosstalk remains a significant problem for this sensor but operation of an adaptive optics system based on HWS is less challenging when using Karhunen-Loève functions instead of Zernike polynomials.

There are many techniques to achieve basic wavefront sensing tasks in the weak atmospheric turbulence regime. However, in strong and deep turbulence situations, the complexity of a propagating wavefront increases significantly. Typically, beam breakup will happen and various portions of the beam will randomly interfere with each other. Consequently, some conventional techniques for wavefront sensing turn out to be inaccurate and misleading. For example, a Shack-Hartmann sensor will be confused by multi-spot/zero-spot result in some cells. The curvature sensor will be affected by random interference patterns for both the image acquired before the focal plane and the image acquired after the focal plane. We propose the use of a plenoptic sensor to solve complex wavefront sensing problems. In fact, our results show that even for multiple beams (their wavelengths can be the same) passing through the same turbulent channel, the plenoptic sensor can reconstruct the turbulence-induced distortion accurately. In this paper, we will demonstrate the plenoptic mapping principle to analyze and reconstruct the complex wavefront of a distorted laser beam.

A plenoptic sensor can be used to improve the image formation process in a conventional camera. Through this process, the conventional image is mapped to an image array that represents the image’s photon paths along different angular directions. Therefore, it can be used to resolve imaging problems where severe distortion happens. Especially for objects observed at moderate range (10m to 200m) through turbulent water, the image can be twisted to be entirely unrecognizable and correction algorithms need to be applied. In this paper, we show how to use a plenoptic sensor to recover an unknown object in line of sight through significant water turbulence distortion. In general, our approach can be applied to both atmospheric turbulence and water turbulence conditions.

In this article the author’s team deals with using Wavelength Division Multiplexing (WDM) for Free Space Optical (FSO) Communications. In FSO communication occurs due to the influence of atmospheric effect (attenuation, and fluctuation of the received power signal, influence turbulence) and the WDM channel suffers from interchannel crosstalk. There is considered only the one direction. The behavior FSO link was tested for one or eight channels. Here we will be dealing with modulation schemes OOK (On-Off keying), QAM (Quadrature Amplitude Modulation) and Subcarrier Intensity Modulation (SIM) based on a BPSK (Binary Phase Shift Keying). Simulation software OptiSystem 14 was used for tasting. For simulation some parameters were set according to real FSO link such as the datarate 1.25 Gbps, link range 1.4 km. Simulated FSO link used wavelength of 1550 nm with 0.8 nm spacing. There is obtained the influence of crosstalk and modulation format for the BER, depending on the amount of turbulence in the propagation medium.

There are several parameters of the atmospheric environment which have an effect on the optical wireless connection. Effects like fog, snow or rain are ones of the effects which appears tendentiously and which are bound by season, geographic location, etc. One of the effects that appear with various intensity for the whole time is airflow. The airflow changes the local refractive index of the air and areas with lower or higher refractive index form. The light going through these areas refracts and due to the optical intensity scintillates on the detector of the receiver. The airflow forms on the basis of two effects in the atmosphere. The first is wind cut and flowing over barriers. The other is thermal flow when warm air rises to the higher layers of the atmosphere. The heart of this article is creation such an environment that will form airflow and the refractive index will scintillate. For the experiment, we used special laboratory box with high-speed ventilators and heating units to simulate atmospheric turbulence. We monitor the impact of ventilator arrangement and air temperature on the scintillation of the gas laser with wavelength 633 nm/15 mW. In the experiment, there is watched the difference in behavior between real measurement and flow simulation with the same peripheral conditions of the airflow in the area of 500 x 500 cm.