This PDF file contains the front matter associated with SPIE Proceedings Volume 8874, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

In the conventional Kolmogorov model of turbulence the turbulent fluctuations of the index of refraction are assumed to be statistically homogeneous and isotropic, and there is a specific mathematical form for the power spectral density of the index of refraction fluctuations. Development of the turbulent theory of passive scalar transfer has shown that although the conventional Kolmogorov spectrum model with a 11/3 power-law index is generally correct near the ground (within the inertial subrange), it constitutes only one part of the more general behavior of passive scalar transfer in a turbulent flow. Hence, deviations from the conventional Kolmogorov model are possible. In this study we develop theoretical models for beam spot size, spatial coherence, and scintillation index that are valid in weak irradiance fluctuation regimes as well as in deep turbulence, or strong irradiance fluctuation regimes. These theoretical models are based on power-law index variations 3 <α< 4 in the spatial power spectrum model of atmospheric turbulence in addition to anisotropic conditions.

In this work we propose a numerical wave optics approach for simulating the propagation of a beam with spatially varying coherence properties. The concept involves the development of a random screen with spatially varying correlation (SVC) properties that is implemented in the source plane. Three scenarios with different SVC effects are presented and a large sequence of screen realizations is applied and the intensity results after propagation are averaged to yield the partially coherent result. This approach allows the propagation characteristics of a wide range of beam types to be evaluated. The simulation results demonstrate that beams with SVC properties can obtain unusual intensity distribution, which might not be achieved with more conventional beams such as the Gaussian Schell-model beam.

For the verification of Free Space Optics (FSO) systems it is common to determine optical power measured depending on illuminated area at a certain wavelength. In the context of this work a new measurement system was developed, which is able to measure not only the optical power but also the complete spectral distribution of the light beam. FSO is becoming more and more important, because of the high usable bandwidth (leading to high data-rates) in optics compared to radio frequency (RF).

The measurement system consists of a mechanical structure, where a collimator is mounted on. This collimator can be moved in two dimensions to enable the measurement of predefined points. It is connected with a spectrum analyzer using an optical fiber. A computer controls the position of the collimator and initiates the spectrum analyzer to record the spectral curves, the maximum peak of power, the 3dB bandwidth and the total power of spectrum. The obtained data covers a measurement area of 0.91 m by 0.77 m which can be surveyed at a high local resolution of 0.7 mm. Collimated beams in the range between 600 and 1750 nm are analyzed. The measurement results discussed in this contribution are shown on the example of light sources, used in at TU Graz developed FSO-systems.

A methodology is presented to infer the refractive-index structure function parameter and the structure parameters for temperature and humidity from numerical simulations of the turbulent atmospheric convective boundary layer (CBL). The method employs spatial and temporal averaging of multiple realizations of the CBL flow field reproduced by a large-eddy simulation (LES) of the atmosphere. The C_n² values yielded by LES-based approach agree fairly well with C_n² values predicted by the Monin-Obukhov similarity theory. In this respect, the C_n² retrieval from the LES data is promising for evaluating the vertical profile of C_n² throughout the entire CBL. Under the considered CBL conditions and for the selected optical wavelength of 0.55 μm the value of C_n² was found to be dominated by the C_T² contribution in the first few hundred meters above the surface, whereas the C_Tq contribution became significant aloft.

Recently, Ultraviolet communication is paid more and more attention, with its solar blind and Non-Line-of-Sight characteristic. However, it is hard to capture and recover the transmitted signal outdoor without synchronized signal. In this work, we integrate Universal Software Radio Peripheral (USRP) into UV communication system and employ GPS as synchronized signal. At receive side, photon counting and adaptive threshold method are used to recover original signal. Through experiments, we test path loss and BER of the system under di erent con guration geometries. Some results are compared to the previous proposed path loss and BER models.

High capacity directional wireless communications networks are an active research area because of their Gb/s or greater data rates over link lengths of many kilometers, providing fiber-like networks through the air. Their high data rates arise partly from their very high carrier frequencies (<60GHz for RF, and ~1550nm for free-space optical (FSO)) and partly because of their very narrow beamwidths. This second characteristic requires that transceivers be pointed precisely to their counterparts. In almost all cases this means that the transceiver aperture is mechanically pointed by a rotation stage, commonly known as a gimbal. How these platforms initially point at a target, acquire the signal, and then stay locked on the signal is known as pointing, acquisition, and tracking (PAT). Approaches for PAT in both RF and FSO have some similarities, but require overall divergent solutions, especially if the platforms are moving. This paper elaborates on the various considerations required for designing and implementing a successful PAT system for both directional RF and FSO systems. Approaches for GPS or beacon based pointing, types of acquisition scans, and the effects of platform vibration are analyzed. The acquisition time for a spiral scan of a given radius with an initial pointing error has been measured experimentally for a gimbal pointing system.

Modulating retro-reflectors (MRR) are beneficial for asymmetric free-space optics communication links. An MRR includes an optical retro-reflector and an electro-optic shutter. The main advantage of an MRR configuration is that it shifts most of the power, weight, and pointing requirements onto one end of the link. In this study an innovative device comprising of nanoparticle-embedded ferroelectric thin film is used as an MRR. The new modulator is mounted in front of a passive retro-reflector. In our study we calculated the link budget for lunar exploration scenario. The scenario includes a base station that communicates with several robots or astronauts. In our simulations, the base station illuminates a robot with a continuous-wave beam, i.e. an interrogating beam. The un-modulated beam strikes the MRR, which is located on the robot, and is passively reflected back to the base station carrying the data that has been modulated onto it by the MRR. In this scenario a robot and a base-station are 4km apart, with a clear line of sight. In addition, the innovative MRR is capable of achieving 12dB contrast ratio. Under these assumptions and using the nanoparticle-embedded ferroelectric MRR we calculated the required transmission power for a given bit-rate and BER.

Over the past several decades, free-space optical (FSO) systems have gained a specific place in the wireless technology area. The application of these systems is advantageous for high bandwidths, a license free band and quick installation. The main drawback of FSO systems is their dependence on the state of the atmosphere causing deterioration of the FSO systems availability. One of the atmospheric effects which has an essential impact on the performance of the FSO systems is atmospheric turbulence. Atmospheric turbulence leads to fluctuation of the optical intensity in the plane of the receiving aperture. It has been shown that to reduce the effect of atmospheric turbulence, uniform distribution of the optical intensity within the cross section of the beam in the plane of transmitting aperture (phenomenon of diffraction is neglected) and a suffciently large diameter of the circularly symmetric receiving aperture (to achieve aperture averaging effect) are needed. The main idea of our paper is the problem of beam shaping at the transmitter. In our contribution the technique of transformation of a Gaussian beam into a beam with uniform distribution of optical intensity is discussed. For the mentioned transformation we experimentally tested several shaping methods such as multi aperture beam integrators, diffractive diffusers, etc. Usage of laser sources with different degrees of coherence was considered.

The purpose of these techniques is to create an optical beam with uniform distribution of optical intensity on the transmitter output. In order to compare and evaluate the particular shaping techniques, a new Trans- formation Complex Quality (TCQ) parameter was defined. The TCQ parameter indicates the optimal shaping technique and also evaluates the quality of the resulting transformed beam with respect to its resistance towards atmospheric turbulence.

Obtaining accurate, precise and timely information about the local atmospheric turbulence and extinction conditions and aerosol/particulate content remains a difficult problem with incomplete solutions. It has important applications in areas such as optical and IR free-space communications, imaging systems performance, and the propagation of directed energy. The capability to utilize passive imaging data to extract parameters characterizing atmospheric turbulence and aerosol/particulate conditions would represent a valuable addition to the current piecemeal toolset for atmospheric sensing. Our research investigates an application of fundamental results from optical turbulence theory and aerosol extinction theory combined with recent advances in image-quality-metrics (IQM) and image-quality-assessment (IQA) methods. We have developed an algorithm which extracts important parameters used for characterizing atmospheric turbulence and extinction along the propagation channel, such as the refractive-index structure parameter C²_n , the Fried atmospheric coherence width r₀ , and the atmospheric extinction coefficient β_ext , from passive image data. We will analyze the algorithm performance using simulations based on modeling with turbulence modulation transfer functions. An experimental field campaign was organized and data were collected from passive imaging through turbulence of Siemens star resolution targets over several short littoral paths in Point Loma, San Diego, under conditions various turbulence intensities. We present initial results of the algorithm’s effectiveness using this field data and compare against measurements taken concurrently with other standard atmospheric characterization equipment. We also discuss some of the challenges encountered with the algorithm, tasks currently in progress, and approaches planned for improving the performance in the near future.

Current transmissometer designs can be physically bulky, electronically complex, and susceptible to background light; ultimately limiting performance. We describe a novel transmissometer design based upon a modulated LED source and an AC-coupled receiver to improve upon the aforementioned shortcomings. The design aims to reduce both complexity and SWAP through the use of a high frequency modulation technique, while ultimately improving SNR and measurement range over a variety of atmospheric conditions. The instrument is a dynamic atmosphere and range transmissometer (DART). First we discuss the theory associated with our technique; particularly addressing how the effects of atmospheric turbulence are handled. Next, we describe the radiometry and calibration procedures for the transmitter and the receiver. We describe the instrument hardware and how the DART was built and tested in the laboratory. Finally, we discuss the field experiment to test the DART against a commercial unit over a 700m coastal path in San Diego. The processed data are compared with concurrent measurements from the Optec LPV-3 commercial transmissometer. Transmission data from the DART tracks the commercial instrument very well over varying atmospheric conditions.

Shack-Hartmann sensors have been widely applied in wavefront sensing. However, they are limited to measuring slightly distorted wavefronts whose local tilt doesn’t surpass the numerical aperture of its micro-lens array and cross talk of incident waves on the mrcro-lens array should be strictly avoided. In medium to strong turbulence cases of optic communication, where large jitter in angle of arrival and local interference caused by break-up of beam are common phenomena, Shack-Hartmann sensors no longer serve as effective tools in revealing distortions in a signal wave. Our design of a modified Plenoptic Camera shows great potential in observing and extracting useful information from severely disturbed wavefronts. Furthermore, by separating complex interference patterns into several minor interference cases, it may also be capable of telling regional phase difference of coherently illuminated objects.

We propose the use of multifractal detrended fluctuation analysis (MF-DFA) to measure the influence of atmospheric turbulence on the chaotic dynamics of a HeNe laser. Fit ranges for MF-DFA are obtained with goodness of linear fit (GoLF) criterion. The chaotic behavior is generated by means of a simple interferometric setup with a feedback to the cavity of the gas laser. Such dynamics have been studied in the past and modeled as a function of the feedback level. Different intensities of isotropic turbulence have been generated with a turbulator device, allowing a structure constant for the index of refraction of air adjustable by means of a temperature difference parameter in the unit. Considering the recent interest in message encryption with this kind of setups, the study of atmospheric turbulence effects plays a key role in the field of secure laser communication through the atmosphere. In principle, different intensities of turbulence may be interpreted as different levels of white noise on the original chaotic series. These results can be of utility for performance optimization in chaotic free-space laser communication systems.

In recent years the need for high data rate underwater wireless communication (WC) has increased. Nowadays, the conventional technology for underwater communication is acoustic. However, the maximum data rate that acoustic technology can provide is a few kilobits per second. On the other hand, emerging applications such as underwater imaging, networks of sensors and swarms of underwater vehicles require much faster data rates. As a result, underwater optical WC, which can provide much higher data rates, has been proposed as an alternative means of communication. In addition to high data rates, affordable communication systems become an important feature in the development requirements. The outcome of these requirements is a new system design based on off-the-shelf components such as blue and green light emitting diodes (LEDs). This is due to the fact that LEDs offer solutions characterized by low cost, high efficiency, reliability and compactness. However, there are some challenges to be met when incorporating LEDs as part of the optical transmitter, such as low modulation rates and non linearity. In this paper, we review the main challenges facing the incorporation of LEDs as an integral part of underwater WC systems and propose some techniques to mitigate the LED limitations in order to achieve high data rate communication

Underwater communication has mainly been driven by the Navy under specific circumstances and challenges. Currently used here are conventional technologies using acoustic transmission, which can only realize data rates up to several kilobits. From the perspective of the operators of a submarine there is a logical prioritization towards covert operation combined with an evolution in data rates. The use of unmanned underwater vehicles (UUVs) in submarine operation enhances the capabilities of submarine missions. The fibre optic link however hampers the submarine’s movements underwater and does not provide the anticipated communication “at speed and depth”. Cassidian Optronics has developed and patented a special optical method¹, wherein these difficulties can be overcome by means of an “optical GPS” . The report describes the underlying process and thereby gives an outlook on the possibilities opened up.

The importance and using of power LED diodes increases. White power LED diodes cover a wide spectral range and they are usable in many applications. These LED diodes work in optical systems, the original spectrum of a white power LED diode can be changed by using all kinds of optical elements. This article describes a pursuit of the most faithful recovery of the original spectrum of a white power LED diode. The evaluative criterion is the value of the Correlated Color Temperature of the original white power LED diode compared with the value of the Correlated Color Temperature of the recovered spectrum. This recovery can be used in communication engineering.

A model for predicting the radiometry for a resolved laser beam due to scattering in the maritime atmosphere, has been developed by the Electro-Optics group in the Atmospheric Propagation Branch at SPAWAR Systems Center, Pacific. The model predicts the power received at a sensor using local meteorological measurements of the current atmospheric conditions. Field experiments conducted in San Diego, CA were used to validate the predictions of the model. Radiometric calibrations of a CCD camera provided power measurements of a resolved laser to be taken from various senor-laser beam orientations. The performance of the laser scattering model is assessed from the field measurements.

Recent works indicate that both MFBD and speckle imaging methods are e ective in recovering images of scenes from sets of turbulence-degraded imagery acquired over long horizontal paths. In this work, a prototype scene estimate, generated using speckle-imaging methods, is used in place of the multi-frame ensemble average, to initialize the iterative MFBD algorithm. Available performance improvements are described quantitatively by examining the improvement in Mean Squared Error (MSE) compared to a di raction-limited image. When speckle image estimates initialize the MFBD algorithm residual MSE is reduced by 16% on average compared the case where the multi-frame average is used as a starting point. Similarly, residual MSE is reduced another 8% beyond what is available using speckle imaging method alone when the number of iterations is not constrained. We also nd that the variation in reconstruction MSE is reduced signi cantly using only a limited number of iterations when subject to low to moderated image degradation compared to speckle imaging alone.

Atmospheric turbulence can cause significant degradation to video over long horizontal paths. The refractive index fluctuations along the path from scene to camera lead to blur, varying across the frame and from frame to frame. Computationally inexpensive methods model this effect with an MTF blur function; however this technique neglects anisoplanatic effects. Wave optics techniques have been developed taking into account anisoplanatism, but ignoring scintillation, and spatial and temporal effects. Since long horizontal paths over varied surfaces (e.g. water to land or vice versa) will encounter varying turbulence strength along the path, the turbulence strength should be defined independently at each phase screen. Also important, turbulence strength can vary over short time scales (<1s), so a physically accurate simulation must allow time-dependent phase screens. We will present results of a wave optics simulation technique that includes these spatial and temporal variations.

The results will provide validation for turbulence removal algorithms.

Active systems and raster scans are the most popular methods for achieving the pointing accuracy required to form an optical link. With advances in vision system technology, a potential extension to current methods of alignment is to use cameras to control coarse and/or fine pointing acquisition and tracking to establish covert optical communication links. The narrow beam width of an optical link requires very accurate pointing capabilities that are not achievable by low-resolution cameras. This paper focuses on analyzing the feasibility for a vision system to establish a covert optical link between two terminals.

Modern free-space optical (FSO) communication systems in many aspects overcome wire or radio communications. They offer a license-free operation and a large bandwidth. Operation of outdoor FSO links struggles with many atmospheric phenomena that deteriorate phase and amplitude of the transmitted optical beam. Thanks to the recent advancing development, these effects are more or less well understood and described. Goal driven research increased the link availability.

Besides increasing the availability of data links it is necessary to focus on the accuracy and reliability of testing optical links. Research of the data optical links is focused on the transmission of a large amount of data whereas the testing FSO link is designed to achieve maximal resolution and sensitivity thus improving accuracy and repeatability of the atmospheric effects measurement. Given the fact that testing links are located in the measured media, they are themselves influenced by it. Phenomena such as the condensation on transceiver windows (rain, frost) and the deviation of the optical beam path caused by the wind are referred to as non-standard effects. Non-standard effects never occur independently; therefore we must always verify the cross-sensitivity of the testing link.

In the paper we respond to an increasing number of articles dealing with influence of the atmosphere on the link but ignoring the cross-sensitivity of the testing link on other variables than tested. In conclusion, we carry out qualitative and quantitative analysis of self-identified non-standard effects.

Recently published Sparse-Spectrum (SS) model of the phase front perturbations by atmospheric turbulence¹ is based on the trigonometric series with discrete random spectral support. SS model offers substantial computational savings, while preserving the wide range of scales typically associated with turbulence perturbations. We present an improved version of the SS model that accurately reproduces the power-law spectral density of the phase fluctuations in the arbitrary wide spectral band. SS model offers an ample flexibility in the choice of the probability distributions of the components wave vectors. The number of spectral components and the degree of probability distributions overlapping are the primary factors affecting the SS phase statistics. We use the Monte-Carlo model to examine the statistics of the SS phase samples for four basic versions of the SS model. We also present the calculations of the practically important long-exposure Strehl numbers. Non-overlapping SS model with log-uniform partition emerges as the most appropriate for the atmospheric turbulence representation. However, it is possible that the other model types can be used for optical propagation through different turbulent flows, such as air flows around domes and turrets, jets engine plumes, etc.

Atmospheric turbulence has a significant impact on the quality of a laser beam propagating through the atmosphere over long distances. Turbulence causes intensity scintillation and beam wander from propagation through turbulent eddies of varying sizes and refractive index. This can severely impair the operation of target designation and Free-Space Optical (FSO) communications systems. In addition, experimenting on an FSO communication system is rather tedious and difficult. The interferences of plentiful elements affect the result and cause 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. We propose a new geometrical model to assess the phase shift of a laser beam propagating through turbulence. The atmosphere along the laser beam propagation path will be modeled as a spatial distribution of spherical bubbles with refractive index discontinuity calculated from a Gaussian distribution with the mean value being the index of air. 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 shift as a summation of the phases that arrive at the same point at the receiver. Accordingly, there would be dark and bright spots at the receiver that give an idea regarding the intensity pattern without having to solve the wave equation. The Monte Carlo analysis will be compared with the predictions of wave theory.

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_n² by applying adaptive optics. This treatment also shows the possibility of extending 2D phase screen simulations into more general 3D treatments.

Ways of calculating phase shifts between laser beams propagating through atmospheric turbulence can give us insight towards the understanding of spatial diversity in Free-Space Optical (FSO) links. We propose a new geometrical model to estimate phase shifts between rays as the laser beam propagates through a simulated turbulent media. Turbulence is simulated by filling the propagation path with spherical bubbles of varying sizes and refractive index discontinuities statistically distributed according to various models. The level of turbulence is increased by elongating the range and/or increasing the number of bubbles that the rays interact with along their path. For each statistical representation of the atmosphere, the trajectories of two parallel rays separated by a particular distance are analyzed and computed simultaneously using geometrical optics. The three-dimensional geometry of the spheres is taken into account in the propagation of the rays. The bubble model is used to calculate the correlation between the two rays as their separation distance changes. The total distance traveled by each ray as both rays travel to the target is computed. The difference in the path length traveled will yield the phase difference between the rays. The mean square phase difference is taken to be the phase structure function which in the literature, for a pair of collimated parallel pencil thin rays, obeys a five-third law assuming weak turbulence. All simulation results will be compared with the predictions of wave theory.

We have been investigating the dynamics of molecular systems as analogies for directional wireless networks. This has provided significant insight into reconfigurations of mobile wireless networks using directional point-to-point links (e.g. free-space optics or radio frequency). In this effort, we conceptualize the network as a giant molecule comprised of atoms that exert forces (attraction and repulsion) that stretch and relax the corresponding links. We monitor second-order variations of a potential energy function to gain an improved understanding of the large dimensionality of the optimized reconfiguration for network topology management. Ultimately, we envision this approach will allow for the prediction of two distinct events: 1) localized link failures and 2) catastrophic network events such as a partition. Our results show the detection of localized link failures and the availability for resource allocation more than one minute ahead of the failure (due to known events such as range and antenna blockage) with <80% accuracy.

In this paper, we consider the problem of precoder design for an optical intensity modulation (IM) system with multiple redgreen- blue (RGB) light emitting diodes (LEDs) as transmitters and imaging lens with color filters as receivers. The purpose of using a precoder is to optimally allocate power for each LED based on the current channel condition to minimize the detection error rate. To achieve the goal, an non-convex optimization problem due to a nonconvex constraint is formulated first taking into account several crucial lighting constraints, such as flicker-free, color rendering index (CRI), and luminous efficacy rate (LER) as well as the average optical intensity constraint and non-negative transmitter-side signal constraint. By manipulations we transform the problem into a semi-definite programming (SDP) and by approximation we relaxed the non-convex constraint into a convex one. The resulting convex problem is iteratively solved by CVX, an add-in to MATLAB, which jointly optimizes the precoder and DC-biases driving each LED. We assume that M-PAM signal constellation is used as input to the precoder and an MMSE receiver is applied to recover the input signals in this paper, while our method is not restrict to the specific choice.

The propagation and split of the filamentation of femtosecond pulses in air have been paid much attention since last a few years. However, most research works are performed with few considerations of the turbulence effects of atmosphere due to the difficulties of utilizing analytical solutions and experiment conditions. In this work, we will attempt to introduce a kind of numerical simulation method to analyze the transmission features of femtosecond laser pulses in air or in the turbulent air, namely, it is called multi-phase screen method (MPSM) which use phase screen to simulate atmospheric turbulence. In this presentation, the main laser parameters are as follows: 85 fs pulse-width, 0.8cm radius of the beam, the two kinds of 160GW and 1.0 TW peak-power operating at 800 nm. Then utilizing the structure of Vortex soliton to control the filamentation is proposed. In our cases, four Gaussian pulses with a difference of π/2 in the phase of each adjacent beam as a ring to control the filamentation by utilizing its characteristics of the vortex soliton. Some results show that the coupling and interaction among four Gaussian pulses cause the rotational transfer of the energy of the four beams. Finally, we obtain the transmission features of the beams propagating in the turbulent air with different intensities by the MPSM.

The laser time transfer link is under construction for the European Space Agency for its application in the experiment Atomic Clock Ensemble in Space. We have developed and tested the photon counting detector optimized for operation in space for this project. In this paper are reported the main characteristics which changed after the irradiation by proton and gamma ionizing radiation. The resulting change of the detection delay with temperature is typically below 500 fs/K. The detector has been approved for application in the European Laser Timing experiment, the flight module is under manufacturing now.

Free-Space Optical (FSO) communications is a vital area of research due to its important advantages of providing a very large bandwidth and relatively low cost of implementation. One of the inherent limitations on the quality of an FSO communication link is the degradation of the received beam due to atmospheric turbulence. This paper is concerned with prototyping a wavelet-based algorithm to remove or reduce the effect of the scintillation noise and other unwanted signal on an FSO link that uses analog frequency modulation. The applicability of these concepts will be demonstrated by providing a real-time prototype using reconfigurable hardware, namely Field Programmable Gate Arrays (FPGA), and high-level design tools such as System Generator for DSP from Xilinx. Our proposed prototype was realized on the Virtex-6 FPGA ML605 board using the XC6VLX240T-1FFG1156 device.

Phase-space optics has its advantage over the research of laser beam propagating through atmospheric turbulence channel due to its special joint space-spatial frequency representation, which can be used to describe the property of optical signals between variables that form a Fourier transform pair. In this paper, we introduce the effect of atmospheric turbulence in terms of matrix into the phase-space analysis of laser beam propagation through turbulence. The far field optical intensity in the channel will be given in terms of phase-space representation and the phase-space distribution of received optical intensity can be plotted. It may be a new method analyzing optical scintillation under the turbulent condition.

Atmospheric turbulence influences the wave-front, and reduces homodyne detection efficiency and bit error rate in the Satellite-to-Ground Laser Communication. Free-space differential interference structure based on differential phase shift keying (DPSK) is applied in the optical signal receiver. The free-space Mach-Zehnder delay interferometer without lens is suited for differential delay which is equal to the one bit period. Differential information is obtained by the subtraction of the two successive wave-front phases when made to interfere. Differential distance at the interference receiver is varied with transmission rate from satellite to ground. And through the receiving telescope, the spot size of incident signal light within the interference became small than before, which influences the interference efficiency of the two unequal branches. So that, it is significant for increasing homodyne efficiency to determine the optical signal rate and choose the magnification of receiving telescope. In this paper, the effect of the spot size of incident light and transmission data rate on homodyne detection efficiency is analysed. By the simulation result of efficiency in different spot size and transmission date of incident light, the homodyne efficiency will be predicted in the given data rate and light spot size on the basis of experiment setup. And application condition of free-space differential structure at DPSK differential receiver is proposed.

We investigate the random phase fluctuations of coherent laser propagate through the turbulent atmosphere, and introduce a model of its impact on optical heterodyne reception free space coherent laser optical communication (FSO) system. A polarization based shearing interferometer is used to detect the distorted laser wave-front and reconstruct the wave-front after propagate through a 1Km near-ground atmospheric channel. Further, the heterodyne efficiency of the heterodyne reception system would be given under special consideration of the mismatch between the signal field and the local oscillator. By analyzing the heterodyne efficiency data and the real-time atmospheric coherence length data, a mathematical model of the effects of atmospheric turbulence on FSO system performance is given.