This PDF file contains the front matter associated with SPIE Proceedings Volume 10408 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Lasercomm technology continues to be of interest for many applications both in the commercial and defense sectors because of its potential to provide high bandwidth communications that are secure without the need for RF spectrum management. Over the last decade, terrestrial Lasercomm development has progressed from initial experiments in the lab through field demonstrations in airborne and maritime environments. While these demonstrations have shown high capability levels, the complexity, size, weight, and power of the systems has slowed transition into fielded systems. This paper presents field test results of a recently developed maritime Lasercomm terminal and modem architecture with a compact form factor for enabling robust, 10-Gbps class data transport over highly scintillated links as found in terrestrial applications such as air-to-air, air-to-surface, and surface-to-surface links.

The image encryption and decryption technique using lens components and random phase screens has attracted a great deal of research interest in the past few years. In general, the optical encryption technique can translate a positive image into an image with nearly a white speckle pattern that is impossible to decrypt. However, with the right keys as conjugated random phase screens, the white noise speckle pattern can be decoded into the original image. We find that the fundamental ideas in image encryption can be borrowed and applied to carry out beam corrections through turbulent channels. Based on our detailed analysis, we show that by using two deformable mirrors arranged in similar fashions as in the image encryption technique, a large number of controllable phase and amplitude distribution patterns can be generated from a collimated Gaussian beam. Such a result can be further coupled with wavefront sensing techniques to achieve laser beam correction against turbulence distortions. In application, our approach leads to a new type of phase conjugation mirror that could be beneficial for directed energy systems.

As small and nanosatellites become increasingly relevant in the aerospace industry^{1, 2,} the need of efficient, lightweight and cost-effective networking solutions drives the need for the development of lightweight and low cost networking and communication terminals.

In this paper we propose the design and prototype results of a hybrid optical and radio communication architecture developed to fit the coarse pointing capabilities of nanosatellites, tested through a proxy flight experiment on stratospheric balloons. This system takes advantage of the higher data-rate offered by optical communication channels while relying on the more mature and stable technology of conventional radio systems for link negotiation and low-speed data exchange.

Such architecture allows the user to overcome the licensing requirements and scarce availability of high data-rate radio frequency channels in the commonly used bands.

Outlined are the architecture, development and test of the mentioned terminal, with focus on the communication part and supporting technologies, including the navigation algorithm, the developed fail-safe approach, and the evolution of the pointing system continuing previous work done in ³.

The system has been built with commercial-off-the-shelf components and demonstrated on a stratospheric balloon launch campaign.

The paper outlines the results of an in-flight demonstration, where the two platforms successfully established an optical link at stratospheric altitudes. The results are then analyzed and contextualized in plans of future work for nanosatellite implementations.

In this study, the characteristics of overwater non-line-of-sight (NLOS) ultraviolet (UV) communication channel which include scattering and turbulence effect are modeled using single scattering and Monte Carlo multiple scattering simulation. In addition, simulation results of turbulence effect and path loss at a short separation distance are reported and analyzed where, transmitting angles, along with airborne humidity and temperature were taken into considerations as key parameters which affect the distribution of the receiving signals. Overwater NLOS UV communication channel measurement test bed is proposed with field testing plan. These channel modeling results will be valuable for studying overwater NLOS UV communication performance and the development of unique overwater NLOS UV communication system.

Wireless communication systems that employ free-space optical links in place of radio/microwave technologies carry substantial benefits in terms of data throughput, network security and design efficiency. Along with these advantages comes the challenge of counteracting signal degradation caused by atmospheric turbulence in free-space environments. A fully coherent laser source experiences random phase delays along its traversing path in turbulent conditions forming a speckle pattern and lowering the received signal-to-noise ratio upon detection. Preliminary research has shown that receiver-side speckle contrast may be significantly reduced and signal-to-noise ratio increased accordingly through the use of a partially coherent light source. While dynamic diffusers and adaptive optics solutions have been proven effective, they also add expense and complexity to a system that relies on accessibility and robustness for successful implementation. A custom Hadamard diffractive matrix design is used to statically induce partial coherence in a transmitted beam to increase signal-to-noise ratio for experimental turbulence scenarios. Atmospheric phase screens are generated using an open-source software package and subsequently loaded into a spatial light modulator using nematic liquid crystals to modulate the phase.

The Optical Ground Station (OGS), installed in the Teide Observatory since 1995, was built as part of ESA efforts in the research field of satellite optical communications to test laser telecommunication terminals on board of satellites in Low Earth Orbit and Geostationary Orbit. As far as one side of the link is settled on the Earth, the laser beam (either on the uplink or on the downlink) has to bear with the atmospheric turbulence. Within the framework of designing an Adaptive Optics system to improve the performance of the Free-Space Optical Communications at the OGS, turbulence conditions regarding uplink and downlink have been simulated within the OOMAO (Object-Oriented Matlab Adaptive Optics) Toolbox as well as the possible utilization of a Laser Guide Star to measure the wavefront in this context. Simulations have been carried out by reducing available atmospheric profiles regarding both night-time and day-time measurements and by having into account possible seasonal changes. An AO proposal to reduce atmospheric aberrations and, therefore, ameliorate FSO links performance is presented and analysed in this paper

Quantum Cascade Lasers represent one of the most significant recent advances in solid state lasers. Their ability to generate mid-IR through THz wavelengths have found numerous application in IR Countermeasures and Remote Sensing for defence, security, and commercial application. In many practical defence and security applications, to achieve the required power levels, it may become desired to combine several beams to form a single focused beam. This paper examines both coherent and incoherent beam combining, and the effects imposed by atmospheric turbulence on the propagation of these combined beams. Here, beam centroid wander and beam spread are analyzed along with their eventual contribution to laser spot size to obtain energy/power on target at range for varying turbulence levels. Interestingly, it is found that there is little difference between the energy/power delivered to a target whether beams are coherently or incoherently combined. Additionally, it is found that there is a maximum intensity that can be propagated to a target that is independent of initial beam quality and size for km-type ranges and at moderate turbulence levels.

General anisotropy leads to different effects along the horizontal axis of a propagating beam than along the vertical axis. To better understand these effects, we developed theoretical models for beam diameter, mean intensity, and scintillation index of a Gaussian-beam wave. Two methods, valid in both weak and strong fluctuation regimes, are compared to determine beam diameter. Scintillation-index contours exhibit an elliptical shape corresponding to anisotropy while mean-intensity contours vary with path length and have no such obvious correspondence. The mean-intensity and scintillation-index analyses are based on weak-irradiance-fluctuation theory.

The growth of optical communication has created a need to correctly characterize the atmospheric channel. Atmospheric turbulence along a given channel can drastically affect optical communication signal quality. One means of characterizing atmospheric turbulence is through measurement of the refractive index structure parameter, Cn². When calculating Cn² from the scintillation index, σΙ²,the point aperture scintillation index is required. Direct measurement of the point aperture scintillation index is difficult at long ranges due to the light collecting abilities of small apertures. When aperture size is increased past the atmospheric correlation width, aperture averaging decreases the scintillation index below that of the point aperture scintillation index. While the aperture averaging factor can be calculated from theory, it does not often agree with experimental results. Direct measurement of the aperture averaging factor via the pupil plane irradiance covariance function allows conversion from the aperture averaged scintillation index to the point aperture scintillation index. Using a finite aperture, camera, and detector, the aperture averaged scintillation index and aperture averaging factor are measured in parallel and the point aperture scintillation index is calculated. A new instrument built by SSC Pacific was used to collect scintillation data at the Townes Institute Science and Technology Experimentation Facility (TISTEF). This new instrument’s data was then compared to BLS900 data. The results show that direct measurement of the aperture averaging factor is achievable using a camera and matches well with groundtruth instrumentation.

Unconventional wavefront sensing strategies are being developed to provide alternatives for measuring the wave-front deformation of a laser beam propagating through strong turbulence and/or along a horizontal path. In this paper we present a modified wavefront-sensorless (WFS) adaptive optical (AO) system where the well-known stochastic parallel gradient descent (SPGD) algorithm is extended with a-priori knowledge of the spatial and temporal statistics related to atmospheric turbulence. Here, a modal implementation of the correction algorithm allows us to exploit modal wavefront decomposition to decrease SPGD optimization complexity. We also propose an implementation of a modal decomposition based on Karhunen-Lo eve polynomials instead of the common Zernike polynomials. Appropriate calibration of the deformable mirror is also presented. Performance evaluation of this modified wavefront-sensorless AO system is carried out in a realistic simulated turbulence environment and the results are compared against the traditional, zonal SPGD algorithms.

The availability of a cloud free line of sight (CFLOS) for a ground-space free space optical (FSO) link is strongly dependent on a satellite’s orbit and local cloud cover spatial and temporal statistics for all potential ground stations (GS) in the satellite’s field of regard. A diverse network of multiple GS at locations with minimal and uncorrelated cloud cover can be used to maximize the availability of a CFLOS to multiple satellite orbits. Historic cloud cover data for this availability study is extracted from the ERA-Interim database which is generated, updated, and maintained by the European Center for Medium-Range Weather Forecast (ECMWF). The database contains worldwide data in 6 hour time segments from 1970 to the present. For our analysis, cloud cover data, ground station locations, and satellite ephemerides are conjointly analyzed to determine ground-space link availabilities. The results of this analysis will be presented.

The Space Environment Research Centre (SERC) endeavors to demonstrate the ability to maneuver high area to mass ratio objects using ground based lasers. Lockheed Martin has been leading system performance modeling for this project that includes high power laser propagation through the atmosphere, target interactions and subsequent orbital maneuver of the object. This paper will describe the models used, model assumptions and performance estimates for laser maneuver demonstration.

Anyone who has driven through fog understands the detrimental effect scattering can have on your ability to see. When light interacts with a scattering center, in this case a fog droplet, it is scattered into a new direction, ultimately turning the world around you into a dull gray haze. In some fogs, visibility can be less than 100 meters. It would be possible to see through turbid media like fog if you can separate the scattered light from the unscattered, or ballistic, light; however, we must understand the light transport properties of the atmosphere to determine the optimum scheme. Here, we present an end-to-end simulation for polarized light transport through fog. Our approach can be summarized in three steps: compute the Mueller matrix for a single scattering interaction, ensemble average a distribution of sizes and shapes, and solve the light transport using a Monte Carlo simulation. For small spherical particles, such as fog, we use Mie theory to calculate the single scattering Mueller matrix, but this approach can be generalized to non-spherical particles using ray tracing for large particles or a T-matrix approach for smaller particles. Through this simulation, we are able to determine a backscattering Mueller matrix and a forward scattering Mueller matrix response function for the atmosphere as a function of position and detection angle.

For paraxial propagation of scalar waves classic electromagnetic theory definitions of transverse linear (TLM) and orbital angular (OAM) momenta of beam waves are simply related to the wave coherence function. This allows the extension of the TLM and OAM density concepts to the case of partially coherent waves. This is also makes possible to use the parabolic equations technique to describe TLM and OAM evolution on propagation. We show that both total TLM and OAM are conserved for the free space propagation, but not for propagation in inhomogeneous medium in general. Under Markov Approximation (MA), in the presence of the random statistically homogeneous medium the total TLM and OAM are conserved in average. Based on the MA parabolic equation for the fourth-order coherence function, we examine for evolution of the total OAM variance. Perturbation solution of this equation shows that the OAM fluctuations in general grow approximately linearly with the propagation path length. However, this growth appears to be slower for the beams with rotation-symmetric irradiance.

Theory presented in the companion paper [1] reveals that for paraxial propagation of scalar waves transverse linear momentum (TLM) and orbital angular momentum (OAM) of beam waves are simply related to the wave coherence function, and that the TLM and OAM densities can be measured by a conventional Shack-Hartman sensor, which is typically used for the phase measurements. Here we present the extension of this theory to the case of the OAM fluctuations of a spherical wave intercepted by a finite aperture. We report the OAM measurements derived from the data obtained by the Hartman Turbulence Sensor (HTS) during the field measurement campaign in 2009-10 and data produced by wave optics simulation of the HTS. We examine the statistics of the total OAM intercepted by the wave front sensor aperture and compare it to theoretical results. Modeling data supports the conservation of the mean OAM and relatively slow development of the OAM fluctuations predicted by the theory.

Image blurring and resolution degradation due to aero-optical effects around a hemispherical turret were studied experimentally in-flight using AAOL-T program at subsonic and transonic speeds. A target board consisted of spoke patterns and three-bar groups with various sizes was used to quantify the image blurring. Aero-optical effects and related image blurring were measured simultaneously using synchronized high-speed cameras. Instantaneous wavefronts were used to compute point-spread functions and modulation transfer functions. It was demonstrated that point-spread functions were mostly axisymmetric over a wide range of viewing angles and could be faithfully approximated by the Gaussian ones. Image degradation was found to primarily dependent on the overall level of aero-optical distortions, expressed in waves, and less on spatial statistical properties of the wavefronts. Simulations of image resolution degradation using realistic aero-optical wavefront spectrum were shown to agree with experimentally-obtained results. Presented results and analysis provide means of estimating the image resolution degradation from statistics of the nearfield aero-optical distortions.

We present our findings from a modeling and simulation effort in which we analyzed the imaging performance of a turreted laser beam director/telescope on a transonic aircraft platform. We used real wavefront sensor (WFS) data collected by the Airborne Aero-Optics Laboratory-Transonic (AAOL-T) test platform at Mach 0.8. Using these WFS data, we quantified the imaging point spread function (PSF) for a variety of line-of-sight (LOS) angles. The LOS angle values sweep from forward-looking angles, through the shock wave to backward-looking angles, imaging through the turbulent wake. Our simulation results show Strehl ratios from 4% to 50% with substantial scattering of energy out to many times larger than the diffraction-limited core. For each LOS angle, we analyzed the imaging modulation transfer function (MTF) which showed a rapid reduction of contrast for low-to-mid range spatial frequencies. We reaffirm that practical limits to usable spatial frequencies require higher imaging signal to noise ratio in the presence of aero-optical disturbances at high Mach number. The presented MTF analysis speaks to the degradation of image-contrast-based tracking algorithms that rely on an illuminator laser propagating through aero-optical aberrations. In conclusion, we discuss the AAOL-T imaging flight test campaigns and the anticipated imaging performance of AAOL-T turret.

Large temperature gradients are a known source of strong atmospheric turbulence conditions. Often times these areas of strong turbulence conditions are also accompanied by conditions that make it difficult to conduct long term optical atmospheric tests. The Shuttle Landing Facility (SLF) at the Kennedy Space Center (KSC) provides a prime testing environment that is capable of generating strong atmospheric turbulence yet is also easily accessible for well instrumented testing. The Shuttle Landing Facility features a 5000 m long and 91 m wide concrete runway that provides ample space for measurements of atmospheric turbulence as well as the opportunity for large temperature gradients to form as the sun heats the surface. We present the results of a large aperture LED scintillometer, a triple aperture laser scintillometer, and a thermal probe system that were used to calculate a path averaged and a point calculation of C_n². In addition, we present the results of the Plenoptic Sensor that was used to calculate a path averaged C_n² value. These measurements were conducted over a multi-day continuous test with supporting atmospheric and weather data provided by the University of Central Florida.

An accurate model and parameterization of aerosol concentration is needed to predict the performance of electro-optical imaging systems. Current models have been shown to vary widely in their ability to accurately predict aerosol size distributions and subsequent scattering properties of the atmosphere. One of the more prevalent methods for modeling particle size spectra consists of fitting a modified gamma function to measurement data, however this limits the distribution to a single mode. Machine learning models have been shown to predict complex multimodal aerosol particle size spectra. Here we establish an empirical model for predicting aerosol size spectra using machine learning techniques. This is accomplished through measurements of aerosols size distributions over the course of eight months. The machine learning models are shown to extend the functionality of Advanced Navy Aerosol Model (ANAM), developed to model the size distribution of aerosols in the maritime environment.

Local meteorological conditions drive variability of vertical extinction profiles over both short and long timescales. Wind speed and relative humidity, in particular, are associated with production modes for maritime aerosols. We model climatological variability of profiles based upon surface layer historical measurements of meteorological parameters using the International Comprehensive Ocean Atmosphere Data Set (ICOADS). We have generated a database of profiles using a unique methodology, optimizing computational time by computing profiles over a mesh of relative humidity and wind speed. The profiles are weighted and sorted based upon ICOADS data for a region in southern California coastal waters. Climatological vertical extinction profiles based on this methodology are computed using the aerosol model LEEDR and compared with a new database of space-based LIDAR profiles from the CALIOP instrument aboard NASA’s CALIPSO satellite. We also compare Aerosol Optical Depth (AOD) among CALIOP, LEEDR, and the Aerosol Robotic Network (AERONET), a network of ground-based sun photometers. We discuss agreement and discrepancies among the three datasets.

Electro-optical (EO) and infrared (IR) signals propagating through the atmosphere exhibit intensity fluctuations caused by atmospheric turbulence, a phenomenon known as scintillation. Scintillation is directly related to the refractive index structure parameter Cn2 defined as the refractive index structure function scaled to for the turbulence inertial subrange. Quantifying Cn2 is essential to evaluate and predict scintillation effects on EO/IR systems. Meanwhile, aerosols in the lower atmosphere absorb and scatter EO/IR energy, resulting in attenuation, aliasing, and blurring. We will present initial results on Cn2 and aerosol variability in the coastal zone using simultaneous measurements from a Twin Otter research aircraft, two instrumented ocean vessels [R/V John Martin and a rigid hull inflatable boat (RHIB)] , and a coastal land site. All measurements were taken as part of the Coastal Electro-Optical PropagaTion eXperiment (CEOPTeX) conducted in April/May 2016 offshore of Moss Landing, CA. Aerosol concentration, scattering, and absorption were obtained from the research aircraft in the atmospheric boundary layer. Cn2 was derived from measurements of temperature and humidity sampled at 20 Hz from all platforms/site. Two level Cn2 measurements were also taken when the R/V John Martin and the RHIB were co-located. We will discuss the spatial/temporal variability of the measured quantities, and the difference between the Cn2 at the coastal region and those predicted by surface layer similarity theory and the measured bulk quantities.

Our ability to generate an accurate vertical profile characterizing the atmosphere from the surface to a point above the boundary layer top is quite rudimentary. The region from a land or sea surface to an altitude of 3000 meters is dynamic and particularly important to the performance of many active optical systems. Accurate and agile instruments are necessary to provide measurements in various conditions, and models are needed to provide the framework and predictive capability necessary for system design and optimization. We introduce some of the path characterization instruments and describe the first work to calibrate and validate them. Along with a verification of measurement accuracy, the tests must also establish each instruments performance envelope.

Measurement of these profiles in the field is a problem, and we will present a discussion of recent field test activity to address this issue. The Comprehensive Atmospheric Boundary Layer Extinction/Turbulence Resolution Analysis eXperiment (CABLE/TRAX) was conducted late June 2017. There were two distinct objectives for the experiment: 1) a comparison test of various scintillometers and transmissometers on a homogeneous horizontal path; 2) a vertical profile experiment. In this paper we discuss only the vertical profiling effort, and we describe the instruments that generated data for vertical profiles of absorption, scattering, and turbulence. These three profiles are the core requirements for an accurate assessment of laser beam propagation.

Atmospheric turbulence impacts on the propagation of electro-optical radiation. Typical manifestations of optical turbulence are scintillation (intensity fluctuations), beam wander and (for laser systems) reduction of beam quality. For longer propagation channels, it is important to characterize the vertical and horizontal distribution (inhomogeneity) of the optical turbulence. In the framework of the First European South African Transmission ExpeRiment (FESTER) optical turbulence was measured between June 2015 and February 2016 over a 1.8 km over-water link over False Bay. The link ran from the Institute of Maritime Technology (IMT) at Simons Town to the lighthouse at Roman Rock Island. Three Boundary layer scintillometers (BLS900) allowed assessing the vertical distribution of optical turbulence at three different heights between 5 and 12 m above the water surface. The expected decrease with C_n² with height is not always found. These results are analyzed in terms of the meteorological scenario, and a comparison is made with a fourth optical link providing optical turbulence data over a 8.69 km path from IMT to St. James, roughly perpendicular to the three 1.8 km paths.

This paper compares in-situ and path-averaged measurements of the electro-optical transmission, with emphasis on aerosol effects. The in-situ sensors consisted of optical particle counters (OPC), the path-averaged data was provided by a 7-wavelength transmissometer (MSRT) and scintillometers (BLS). Data were collected at two sites: a homogeneous test site in Northern Germany, and over the inhomogeneous False Bay near Cape Town, South Africa. A retrieval algorithm was developed to infer characteristics of the aerosol size distribution (Junge approximation) from the MSRT data. A comparison of the various sensors suggests that the optical particle counters are over optimistic in their estimate of the transmission. For the homogeneous test site, in-situ and path-averaged sensors yield similar results. For the inhomogeneous test site, sensors may react differently or temporally separated to meteorological events such as a change in wind speed and/or direction.

In the atmosphere, black carbon aggregates interact with both organic and inorganic matter. In many studies they are modeled using different, less complex, geometries. However, some common simplification might lead to many inaccuracies in the following light scattering simulations. The goal of this study was to compare the spectral behavior of different, commonly used soot particle models. For light scattering simulations, in the visible spectrum, the ADDA algorithm was used. The results prove that the relative extinction error δC_ext, in some cases, can be unexpectedly large. Therefore, before starting excessive simulations, it is important to know what error might occur.

We evaluate the piston-removed anisoplanatic error for smaller apertures imaging over long horizontal paths. Previous works have shown that the piston and tilt compensated anisoplanatic error saturates to values less than one squared radian. Under these conditions the definition of the isoplanatic angle is unclear. These works focused on nadir pointing telescope systems with aperture sizes between five meters and one half meter. We directly extend this work to horizontal imaging scenarios with aperture sizes smaller than one half meter. We assume turbulence is constant along the imaging path and that the ratio of the aperture size to the atmospheric coherence length is on the order of unity.

It is well known that passive image correction of turbulence distortions often involves using geometry-dependent deconvolution algorithms. On the other hand, active imaging techniques using adaptive optic correction should use the distorted wavefront information for guidance. Our work shows that a hybrid hardware-software approach is possible to obtain accurate and highly detailed images through turbulent media. The processing algorithm also takes much fewer iteration steps in comparison with conventional image processing algorithms. In our proposed approach, a plenoptic sensor is used as a wavefront sensor to guide post-stage image correction on a high-definition zoomable camera. Conversely, we show that given the ground truth of the highly detailed image and the plenoptic imaging result, we can generate an accurate prediction of the blurred image on a traditional zoomable camera. Similarly, the ground truth combined with the blurred image from the zoomable camera would provide the wavefront conditions. In application, our hybrid approach can be used as an effective way to conduct object recognition in a turbulent environment where the target has been significantly distorted or is even unrecognizable.

When the flight with an optical window is flying in a high speed, the temperature and the refractive index of the air around it will be changed because of the friction, and this will make the image on the detector blurring and shifting, which will degrade the detecting precision greatly. This paper chooses a typical kind of model for the research. Ansys is used in order to gain the temperature field around the hood in real size instead of an assumptive and approximate model. So the refractive index of the air could be worked out. On this basis, the offset and the blur of the image could be figured out using the ray tracing method. Considering of the characters of the grid points distribution and the huge amount of data exported from Ansys, self-adaptive step length tracing method and interpolation method are used in order to shorten the run time and guarantee computational precision at the same time instead of the adaptive variable step method and complicated gradient algorithm. In this study, 3D simulation and programming results under different flight conditions are discussed. The results clearly show the relationship between the image quality and the flight altitude, wavelength and focal length.

For many years, acoustic systems have been used as the primary method for underwater communication; however, the data transfer rate of such systems is low because sound propagates slowly through water. A higher throughput can be achieved using visible light to transmit data underwater. The first issue with this approach is that there is generally a large loss of the light signal due to scattering and absorption in water, even though there is an optimal wavelength for transmission in the blue or green wavelengths of the visible spectrum. The second issue is that a simple communication system, consisting only of a highly directional source/transmitter and small optical detector/receiver, has a very narrow field of view. The goal of this project is to improve an optical, underwater communication system by increasing the effective field of view of the receiving optics.

To this end, we make two changes to the simple system: (1) An optical dome was added near the receiver. An array of lenses is placed radially on the surface of the dome, reminiscent of the compound eye of an insect. The lenses make the source and detector planes conjugate, and each lens adds a new region of the source plane to the instrument's total field of view. (2) The receiver was expanded to include multiple photodiodes. With these two changes, the receiver has much more tolerance to misalignments (in position and angle) of the transmitter.

Two versions of the optical dome (with 6" and 8" diameters) were designed using PTC’s Creo CAD software and modeled using Synopsys' CODE V optical design software. A series of these transparent hemispherical domes, with both design diameters, were manufactured using a 5-axis mill. The prototype was then retrofitted with lenses and compared with the computer-generated model to demonstrate the effectiveness of this solution. This work shows that the dome design improves the optical field of view of the underwater communication system considerably. Furthermore, with the experimental test results, a geometric optimization model was derived providing insights to the design performance limits.

In the field of satellite communication, space laser communication technology is famous for its high communication rate, good confidentiality, small size, low power consumption and so on. The design of coherent optical communication detection device based on modified balanced optical phase-locked loop (OPLL) is presented in the paper. It combined by local oscillator beam, modulator, voltage controlled oscillator, signal beam, optical filter, 180 degree hybrid, balanced detector, loop filter and signal receiver. Local oscillator beam and voltage controlled oscillator trace the phase variation of signal beam simultaneously. That taking the advantage of voltage controlled oscillator which responses sensitively and tunable local oscillator laser source with large tuning range can trace the phase variation of signal beam rapidly and achieve phase locking. The demand of the phase deviation is very low, and the system is easy to adjust. When the transmitter transmits the binary phase shift keying (BPSK) signal, the receiver can demodulate the baseband signal quickly, which has important significance for the free space coherent laser communication.

The method to realize the integration of laser communication and ranging is proposed in this paper. In the transmitter of two places, the ranging codes with uniqueness, good autocorrelation and cross-correlation properties are embed in the communication data and the encoded with the communication data to realize serial communication. And then the encoded data are modulated and send to each other, which can realize high speed two one-way laser communication. At the receiver, we can get the received ranging code after the demodulation, decoding and clock recovery. The received ranging codes and the local ranging codes do the autocorrelation to get a roughly range, while the phase difference between the local clock and the recovery clock to achieve the precision of the distance.

In this study, a special class of nonuniformly correlated beams with radially symmetric coherence distributions, called radial partially coherent beams (RPCBs), is numerically studied. By spatially modulating uniformly correlated phase screens used for generating conventional Gaussian Schell-model beams, RPCBs with arbitrary distributions of degree of coherence are produced. RPCBs whose degree of coherence decreases from the beam center along the radial direction were found to self-focus in free-space propagation, leading to augmented optical intensity near the beam center. Meanwhile, the scintillation mitigation ability of RPCBs remains significant. By means of wave optics simulation, propagation properties of RPCBs in anisotropic non-Kolmogorov turbulence are analyzed. Simulation results show that, under certain conditions RPCBs are still able to deliver improved performance in anisotropic non-Kolmogorov turbulence. Moreover, due to the elliptical far-field irradiance pattern caused by anisotropy, a matched elliptic receiving aperture can further reduce the turbulence-induced scintillation.

This paper proposes a new method for variable rate DPSK in the satellite-to-ground laser communication. Compared to the general method, this method doesn’t need to change the original communication rate, reduces the complexity of the system. In theory, SNR can improve above 3 dB when rate into half. We construct a simplified experimental apparatus to verify the effectiveness of the proposed method. The experimental devices and results are presented. Offline processing results are very similar to theory, is superior to the traditional means. The further study about doppler effect and clock synchronization is being conducted.

Laser beam's acquisition, pointing and tracking are crucial technologies of free space optical communication. Fine tracking system is an important component of APT (acquisition, pointing and tracking) system. Traditional fine tracking system use CCD or quadrant detector as the position detector of signal light. In order to simplify the system and improve accuracy, we propose a fine tracking system based on fiber nutation which don’t need a position detector and theoretically prove that the system is feasible. Meanwhile corresponding fine track system was built, experiment on position detection of the fine tracking system is done.

Performance of satellite laser communications between GEO and LEO satellites can be influenced by background light noise appeared in the field of view due to sunlight or planets and some comets. Such influences should be studied on the ground testing platform before the space application. In this paper, we introduce a simulator that can simulate the real case of background light noise in space environment during the data talking via laser beam between two lonely satellites. This simulator can not only simulate the effect of multi-wavelength spectrum, but also the effects of adjustable angles of field-of-view, large range of adjustable optical power and adjustable deflection speeds of light noise in space environment. We integrate these functions into a device with small and compact size for easily mobile use. Software control function is also achieved via personal computer to adjust these functions arbitrarily. Keywords: