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The development of technologies for continuous measurement of nitrogen forms in the soil is essential for optimizing the application of fertilizers in agriculture and preventing water-resource pollution. However, there is no effective commercial technology available for continuous monitoring of ammonium species in soil pore water. This work investigates an approach for real-time measurement of ammonium in soil water using near-infrared transmission spectroscopy and partial least squares regression (PLSR) for spectral analysis. The PLSR model was trained using soil pore water collected from various soils spiked with ammonium to achieve a wide concentration range. The monitoring approach was then validated through transport experiments in a soil column. The results demonstrated capabilities for real-time tracking of the temporal variation in soil ammonium concentration and potential utilization in agronomical or environmental sensing.

The evolution of communication system to the next generation e.g. B5G and 6G demands an ultra-reliable performance regardless of weather conditions. Such ultra-reliable system design will require that that the effects of short-term adverse weather events on communication system has to be modelled more accurately so that system design should be dynamically adaptive to such events. The performance of satellite link is severely affected by dynamic rain attenuation and thus an accurate and reliable modelling of performance parameters is essential for dynamic fade countermeasures especially above 10 GHz. In this work, we model the energy per bit to noise spectral density ratio ($E_b/N_0$) using Gaussian Mixture (GM) model during rainy events. The developed mathematical expression is used to accurately model the bit error rate (BER), outage probability and channel capacity of the link. The average BER, upper bound on BER and average ergodic capacity of an M-ary phase shift keying scheme (MPSK) using the GM model of $E_b/N_0$ is derived to evaluate the performance of the link under such short-term weather impairments. We then show the numerical results and analysis using the GM model of the measured $E_b/N_0$ data obtained with AMoS-7 satellite at a site located in Israel.

The progress in quantum computing would make the traditional encryption methods easier to hack and hence the next generation of communication networks should include various cross-layer solutions to ensure the cybersecurity of network. In this work, we propose a physical layer solution that rely on taking advantage from the inherent physical properties of the channel that marks its imprint on the propagation of the electromagnetic signal through the stochastic atmospheric channel. The proposed architecture would ensure the cybersecurity of a ground station against an MITM attack launched from an aerial platform (AP). As the signal traverses through the channel, various atmospheric effects including thermal noise and tropospheric scintillation fading causes rapid fluctuations in the received signal. The signal at the ground station from a satellite and an AP would traverse different spatial path over the dynamic atmosphere and hence will show different noise like rapid variations at the ground station. These noisy variations are extracted from the received signal using wavelet filtering technique and processed through a deep neural network based on long-short term memory network (LSTM) to identify whether the incoming signal belong to a legitimate satellite or a spoofing AP. We show that an accuracy of more than $98 \%$ is achieved in the considered scenario with the proposed network architecture as the altitude of AP changes for launching a machine-in-the-middle (MITM) attack in the line-of-sight direction.

The increasing demand in data rates and new emerging applications require that the future generation of satellite networks will be designed at sub-THz frequencies with ultra-broad bandwidth. At such frequencies, the satellite channel is impaired by the highly frequency dependent absorption of the signal by the gaseous atmospheric media besides the thermal noise from the sky, the ground, receiver circuit and molecular absorption noise thus, making it a highly frequency-selective channel. In this work, we derive a theoretical upper bound on the channel capacity of a LEO satellite communication link by optimizing the power spectral density (PSD) of the transmitted signal considering the physicla aspects of THz channel. We obtain a closed form expression of optimum transmitted signal PSD that maximizes the channel capacity of LEO satellite link as the elevation angle changes with the transmitted power held constant.

6G is already being planned and will employ much higher frequencies, leading to a revolutionary era in communication between people as well as things. It is well known that weather, especially rain, can cause increased attenuation of signal transmission for higher frequencies. The standard methods for evaluating the effect of rain on symbol error rate are based on long-term averaging. These methods are an inaccurate, which results with an inefficient system design. This is critical regarding bandwidth scarcity and energy consumption and requires a more significant margin of effort to cope with the imprecision. Recently we have developed a new and more precise method for calculating communication system performance in case of rain, using the probability density function of rain rate. For high rain rate (above 10mm/hr), for a typical set of parameters, our method shows the symbol error rate in this range to be higher by orders of magnitude than that found by ITU standard methods. Our model also indicates that sensing and measuring the rain rate probability is important in order to provide the required bit error rate to the users. To the best knowledge of the authors, this novel analysis is unique. It can constitute a more effi-cient performance metric for the new era of 6G communication and prevent disruption due to incorrect system design. Keywords: atmospheric propagation, communication system performance, attenuation, com-munication

In this paper, we present a novel approach, enabling the measurement of nitrate concentrations in natural soil porewater containing natural soil dissolved organic carbon (DOC). The method is based on UV absorbance spectroscopy, combined with fluorescence spectroscopy, for simultaneous analysis of DOC and nitrate concentrations. The analytical procedure involves deduction of the absorption caused by the DOC from the total absorbance in the UV range that is attributed to both DOC and nitrate in the water solution. The analytical concept has been successfully tested in soil water samples obtained from five agricultural sites, as well as in water samples obtained from a commercial humus soil mixture. We believe that the new analytical concept can provide a scientific foundation for developing a sensor for real-time nitrate concentration measurements in agricultural soils. As such, it can play a significant role in reducing nitrate pollution in water resources, optimizing input application in agriculture, and decreasing food production costs.

Diffuse optical tomography (DOT) is a non-invasive method for detecting breast cancer; however, it struggles to produce high-quality images due to the complexity of scattered light and the limitations of traditional image reconstruction algorithms. These algorithms can be affected by boundary conditions and have a low imaging accuracy, a shallow imaging depth, a long computation time, and a high signal-to-noise ratio. However, machine learning can potentially improve the performance of DOT by being better equipped to solve inverse problems, perform regression, classify medical images, and reconstruct biomedical images. In this study, we utilized a machine learning model called “XGBoost” to detect tumors in inhomogeneous breasts and applied a post-processing technique based on genetic programming to improve accuracy. The proposed algorithm was tested using simulated DOT measurements from complex inhomogeneous breasts and evaluated using the cosine similarity metrics and root mean square error loss. The results showed that the use of XGBoost and genetic programming in DOT could lead to more accurate and non-invasive detection of tumors in inhomogeneous breasts compared to traditional methods, with the reconstructed breasts having an average cosine similarity of more than 0.97 ± 0.07 and average root mean square error of around 0.1270 ± 0.0031 compared to the ground truth.

Lack of real-time information on nutrient availability in cultivated soils inherently leads to excess application of fertilizers in agriculture. As a result, nitrate, which is a soluble, stable, and mobile component of fertilizers, leaches below the root zone through the unsaturated zone and eventually pollutes the groundwater and other related water resources. Rising nitrate concentration in aquifers is recognized as a worldwide environmental problem that contributes to water scarcity. The development of technologies for continuous in situ measurement of nitrate concentration in soils is essential for optimizing fertilizer application and preventing water resource pollution by nitrate. Here we present a conceptual approach for a monitoring system that enables in situ and continuous measurement of nitrate concentration in soil. The monitoring system is based on absorbance spectroscopy techniques for direct determination of nitrate concentration in soil porewater without pretreatment, such as filtration, dilution, or reagent supplementation. A new analytical procedure was developed to improve measurement accuracy while eliminating the typical measurement interference caused by soil dissolved organic carbon. The analytical procedure was tested at four field sites over 2 years and proved to be an effective tool for nitrate analysis when directly applied on untreated soil solution samples. A soil nitrate-monitoring apparatus, combining specially designed optical flow cells with soil porewater-sampling units, enabled, for the first time, real-time continuous measurement of nitrate concentration in soils. Real-time, high-resolution measurement of nitrate concentration in the soil has revealed the complex variations in soil nitrate concentrations in response to fertigation pattern. Such data are crucial for optimizing fertilizer application and reducing pollution potential of groundwater.

The capability to increase the robustness to scattering has become a crucial request for communication protocols and imaging systems. Here we perform a complete analysis regarding the spatial features and the polarization of structured beams propagating in different scattering media. We observe different behaviors for structured light scattered by a solution of polystyrene latex beads in water and by tissue-mimicking phantom. The reported study can help in establishing a framework for the application of structured light illumination in imaging and diagnostic.

Reconstructing objects behind scattering media is a challenging issue with applications in biomedical imaging, non-distractive testing, computer-assisted surgery, and autonomous vehicular systems. Such systems’ main challenge is the multiple scattering of the photons in the angular and spatial domain, which results in a blurred image. Previous works try to improve the reconstructing ability using deep learning algorithms, with some success. We enhance these methods by illuminating the set-up using several modes of vortex beams obtaining a series of time-gated images corresponding to each mode. The images are accurately reconstructed using a deep learning algorithm by analyzing the pattern captured in the camera. This study shows that using vortex beams instead of Gaussian beams enhances the deep learning algorithm’s image reconstruction ability in terms of the peak signal-to-noise ratio (PSNR) by ~ 2.5 dB and ~1 dB when low and high scattering scatterers are used respectively.

A deep-learning algorithm is employed to detect simulated anomalies inside compressed breasts using near-infrared light. Anomaly detection is improved by 55% after employing the algorithm according to the Dice similarity coefficient.

Optical interrogation of tissues is broadly considered in biomedical applications. Nevertheless, light scattering by tissue limits the resolution and accuracy achieved when investigating sub-surface tissue features. Light carrying optical angular momentum or complex polarization profiles, offers different propagation characteristics through scattering media compared to light with unstructured beam profiles. Here we discuss the behaviour of structured light scattered by tissue-mimicking phantoms. We study the spatial and the polarization profile of the scattered modes as a function of a range of optical parameters of the phantoms, with varying scattering and absorption coefficients and of different lengths. These results show the non-trivial trade-off between the advantages of structured light profiles and mode broadening, stimulating further investigations in this direction. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Coronary calcifications are an obstacle for successful percutaneous treatment of coronary artery disease patients. The optimal method for delineating calcifications extent is coronary optical coherence tomography (OCT). To identify calcification on OCT and subsequently tailor the appropriate treatment, requires expertise in both image acquisition and interpretation. Image acquisition consists from system calibration, blood clearance by a contrast agent along with synchronization of the pullback process. Accurate interpretation demands careful review by the operator of a segment of 50–75 mm of the coronary vessel at steps of 5–10 frames per mm accounting for 375–540 images in each OCT run, which is time consuming and necessitates some expertise in OCT analysis. In this paper we developed a new deep learning algorithm to assist the physician to identify and quantify coronary calcifications promptly, efficiently and accurately. Our algorithm achieves an accuracy of 0.9903 ± 0.009 over the test set at size of 1500 frames and even managed to find calcifications that were not recognized manually by the physician. For the best knowledge of the authors our algorithm achieves high accuracy which was never achieved in the past.

Diffuse optical tomography (DOT) is a non-invasive imaging technique utilizing multi-scattered light at visible and infrared wavelengths to detect anomalies in tissues. However, the DOT image reconstruction is based on solving the inverse problem, which requires massive calculations and time. In this article, for the first time, to the best of our knowledge, a simple, regression-based cascaded feed-forward deep learning neural network is derived to solve the inverse problem of DOT in compressed breast geometry. The predicted data is subsequently utilized to visualize the breast tissues and their anomalies. The dataset in this study is created using a Monte-Carlo algorithm, which simulates the light propagation in the compressed breast placed inside a parallel plate source-detector geometry (forward process). The simulated DL-DOT system's performance is evaluated using the Pearson correlation coefficient (R) and the Mean squared error (MSE) metrics. Although a comparatively smaller dataset (50 nos.) is used, our simulation results show that the developed feed-forward network algorithm to solve the inverse problem delivers an increment of ∼30% over the analytical solution approach, in terms of R. Furthermore, the proposed network's MSE outperforms that of the analytical solution's MSE by a large margin revealing the robustness of the network and the adaptability of the system for potential applications in medical settings.

A major challenge in use of the optical spectrum for communication and imaging applications is the scattering of light as it passes through diffuse media. Recent studies indicate that light beams with orbital angular momentum (OAM) can penetrate deeper through diffuse media than simple Gaussian beams. To the best knowledge of the authors, in this paper we describe for the first time an experiment examining transmission of OAM beams through biological tissue with thickness of up to a few centimeters, and for OAM modes reaching up to 20. Our results indicate that OAM beams do indeed show a higher transmittance relative to Gaussian beams, and that the greater the OAM, the higher the transmittance also up to 20, Our results extend measured results to highly multi scattering media and indicate that at 2.6 cm tissue thickness for OAM of order 20, we measure nearly 30% more power in comparison to a Gaussian beam. In addition, we develop a mathematical model describing the improved permeability. This work shows that OAM beams can be a valuable contribution to optical wireless communication (OWC) for medical implants, optical biological imaging, as well as recent innovative applications of medical diagnosis.

Discrete multi-tone (DMT) and optical orthogonal frequency division multiplexing (OFDM) modulations are well-known methods used to transmit high data rate information in visible light communication (VLC) applications over the illumination infrastructure. However, the use of these techniques in a multi-user environment requires effective subcarrier and power allocation design in order to achieve the maximum data rate offered by the spatial distribution of the transmitters and receiver as well as to minimize the efficiency reduction of the illumination system due to the communication. This could be achieved by minimizing the communication signal power in an appropriate way. In this paper, we propose a heuristic allocation algorithm that minimizes the system subcarrier transmitter power while keeping the required data rate and error bit rate. The numerical calculation was done for given parameters. The results indicate that transmitter power reduction of more than 10% in a most scenario is achieved in comparison to previous algorithms.

Millimeter wave (mmWave) communication has raised increasing attentions from both academia and industry due to its exceptional advantages. Compared with existing wireless communication techniques, such as WiFi and 4G, mmWave communications adopt much higher carrier frequencies and thus come with advantages including huge bandwidth, narrow beam, high transmission quality, and strong detection ability. These advantages can well address difficult situations caused by recent popular applications using wireless technologies. For example, mmWave communications can significantly alleviate the skyrocketing traffic demand of wireless communication from video streaming. Meanwhile, mmWave communications have several natural disadvantages, e.g., severe signal attenuation, easily blocked by obstacles, and small coverage, due to its short wavelengths. Hence, the major challenge is how to overcome its shortcomings while fully utilizing its advantages. In this paper, we present a taxonomy based on the layered model and give an extensive review on mmWave communications. Specially, we divide existing efforts into four categories that investigate: physical layer, medium access control (MAC) layer, network layer, and cross layer optimization, respectively. First, we present an overview of some technical details in physical layer. Second, we summarize available literature in MAC layer that pertains to protocols and scheduling schemes. Third, we make an in-depth survey of related research work in network layer, providing brain storming and methodology for enhancing the capacity and coverage of mmWave networks. Fourth, we analyze available research work related to cross layer allocation/optimization for mmWave communications. Fifth, we make a review of mmWave applications to illustrate how mmWave technology can be employed to satisfy other services. At the end of each section described above, we point out the inadequacy of existing work and identify the future work. Sixth, we present some available resources for mmWave communications, including related books about mmWave, commonly used mmWave frequencies, existing protocols based on mmWave, and experimental platforms. Finally, we have a simple summary and point out several promising future research directions.

Data centers are crucial elements in modern information technology. In order to implement the next generation of data centers, new challenges must be overcome. These include reducing the energy consumption, increasing the data rates, reducing the communication latency, increasing the flexibility and scalability, and reducing the maintenance time and cost. One promising way for meeting these challenges is to employ multichannel optical wireless communication as part of the data center hybrid communication network. In this paper, we analyze three technologies that could be used in this context: MIMO (Multiple-in-Multipleout), multiplexing through orbital angular momentum of light, and direct modulation through the large number of modes associated with orbital angular momentum. Our results indicate that these technologies could provide an innovative and flexible means of meeting the challenges of the next generation of data centers.

True-time-delay devices could significantly contribute to improving the performance of many optical systems in applications such as sensing, ranging, communication and signal processing. Delay devices based on spiral optical waveguides are of special interest due to their small size and relatively low power attenuation. In this paper, we propose to fabricate spirals on both sides of a wafer, where the coupling between them is through a vertical interconnect. The novel through-wafer interconnect has a level of attenuation that compares competitively with that obtained with a conventional s-shaped interconnect between two interleaved spirals and considerably simplifies the waveguide design and fabrication.

Free space optical interconnections (FSOIs) are anticipated to become a prevalent technology for short-range high-speed communication. FSOIs use lasers in board-to-board and rack-to-rack communication to achieve improved performance in next generation servers and are expected to help meet the growing demand for massive amounts of inter-card data communication. An array of transmitters and receivers arranged to create an optical bus for inter-card and card-to-backplane communication could be the solution. However, both chip heating and cooling fans produce temperature gradients and hot air flow that results in air turbulence inside the server, which induces signal fading and, hence, influences the communication performance. In addition, the proximity between neighboring transmitters and receivers in the array leads to crosstalk in the received signal, which further contributes to signal degradation. In this Letter, the primary objective is to experimentally examine the off-axis crosstalk between links in the presence of turbulence inside a server chassis. The effects of geometrical and inter-chassis turbulence characteristics are investigated and first-and second-order statistics are derived.

Information Reconciliation (IR) in QKD is a fundamental step in ensuring Alice and Bob share identical set of bits (reconciled key). IR could be done by one-way or two-way channel coding using an auxiliary public authenticated channel to send parities to correct the actual labels so that the sample labels at Alice and Bob match. We assume that communication is performed through an Optical Wireless (OW) or Free Space Optics (FSO) channel, which effects the received signal by a stochastic fading due to jitter in pointing. The effect is that the received samples do not match with the transmitted ones, this is the reason why IR is necessary in such a system. In a previous work, we analyzed the system performance over FSO channel, uncovering the dependence between performance and system parameters such as fading variance or the telescope gain. In this paper we want to study the overall performance and try to obtain optimal values for the parameters that influence the sign error probability.

Lack of real-time information on nutrient availability in cultivated soils inherently leads to excess application of fertilizers in agriculture. As a result, nitrate, which is a soluble, stable and mobile component of fertilizers, leaches below the root zone through the unsaturated zone and eventually pollutes the groundwater and other related water resources. Rising nitrate concentration in aquifers is recognized as a worldwide environmental problem that contributes to water scarcity. Accordingly, developing technologies for continuous in-situ measurement of nitrate concentration in the soils are essential for optimizing fertilizer application and preventing water resource pollution by nitrate. Here we present a conceptual approach for a monitoring system that enables in-situ and continuous measurement of nitrate concentration in soil. The monitoring system is based on absorbance spectroscopy techniques for direct determination of nitrate concentration in soil porewater without pretreatment, such as filtration, dilution, or reagent supplementation. A new analytical procedure was developed to improve measurement accuracy while eliminating the typical measurement interference caused by soil dissolved organic carbon. The analytical procedure was tested at four field sites over 2 years and proved to be an effective tool for nitrate analysis in untreated soil. A soil nitrate-monitoring apparatus, combining specially designed optical flow cells with soil porewater-sampling units, enabled for the first time, real-time continuous measurement of nitrate concentration in the soil. The system provided outstanding and explicit data revealing the complexities of the temporal variations in soil nitrate concentrations in response to irrigation cycles and fertilizer-application pattern. Such real-time measurements of soil nitrate levels are crucial for optimizing fertilizer application to increase agricultural yield while reducing the potential threat of groundwater contamination by down-leaching of nitrate from the soil.

In the last decade data-centers have become a crucial element in our society. As a result, in the coming years there will be increased threat from hackers, who could cause outage of the data-center, extract millions of account details, or steal financial and sensitive information. One way to reduce these threats is to divide the data-center into sub data-centers, and connect them by secure links which prevent access by unauthorized users. A possible technology to connect between the sub data-centers is optical wireless communication (OWC) or free space optics (FSO). An OWC link includes an optical receiver and laser transmitter. The transmitter transmits a light beam that carries information which propagates to the receiver. The light beam carrying the information propagates through the air. In order to increase the security and make the penetration and intrusion difficult quantum key distribution (QKD) is added to the link. By doing so the information exchange between the sub data-centers is encrypted. In this paper we review up to date literature in the field, propose an implementation scheme of an OWC network in sub data-centers, and discuss ways to hack the system.

The Internet of Things (IoT) is playing a growing role in society, and includes control over a range from household appliances to municipal power grids and nationwide assets. As a result, hackers from a national level down to low level criminals are looking to take advantage of important IoT infrastructures. These present an immediate target for cyber-terrorists as well as more mundane attacks by thieves and personal enemies, and it is imperative to devise defensive measures. In this work, we describe potential possible attacks on several IoT systems. As a result, vendors of the IoT infrastructure employ conventional encryption which is based on complexity to fight against hackers. However the emerging technology of quantum computing will make deciphering of the conventional encryption an easy task. This leads us to propose a scheme for use of QKD (quantum key distribution) which could be effective as a countermeasure. In this paper we will describe the feasibility study of weather effect design guidelines for a small, short range, mobile QKD system from drone to IoT on the ground.

In some emerging satellite applications, it is of paramount importance to accurately measure the distance between satellites in formations. Range measurement systems based on femtosecond lasers have been suggested as very precise solutions that could be incorporated into satellites. It would be fortuitous to exploit the same laser link for both the distance measurement and communication, thus achieving two functions with considerably reduced payload weight and size compared with that could be achieved if the two tasks were performed separately. In this letter, we propose to modulate the ranging femtosecond pulses to carry communication information. The proposed modulation is in the frequency domain, benefiting from the wideband property of femtosecond pulses. The method hinges on the special characteristics of the femtosecond pulse, which has a very broad frequency spectrum alongside its ultrashort time duration. We analyze the multiple-inverse-pulse-position modulation (MIPPM) method. The main idea of the MIPPM is the ON–OFF modulation of each spectral component, while each modulated symbol includes all spectral components and only few spectral components are in the OFF state at any given time. We analyzed the performance of the proposed system in terms of symbol error rate for a given set of parameters.

Security is an increasingly important issue in modern communication. We propose a concept for secure detection of vortex beams in free space optics (FSO). The transmitted signal is composed of a Gaussian beam together with a low powered vortex beam. For each vortex mode, we select the detectors with the maximum received power for the particular signal, depending on the spatial distribution probability of the signal beam. Eavesdroppers have no way of knowing which patterns are relevant for the transmitted signal. We perform a numerical calculation for maximal signal detection and security. Applications include l free space communication.

Over the last few years, there has been an exponential increase in the amount of communication network traffic, where the data center (DC) is a major building block of this network. However current DCs face various problems in the light of current demands, such as high power consumption, low scalability and low flexibility. It is necessary to build a new high speed data center which could support this exponential growth. One of the technologies that could scale up the performance of the data center is free space optical (FSO) communication. FSO communication could provide an adaptive, flexible and dynamic network that could meet the performance requirements of future DCs. However, no one has characterized the optical communication channel in DC. In DC there is an HVAC system that causes non-homogeneous changes in temperature and air velocity that can affect the performance of the optical signal. In this work, we demonstrate that by using deep learning algorithms for channel estimation and signal detection, without knowledge of the channel model, we can improve the signal detection and increase the performance of the optical communication in DC environment.

In the last decade data centers have become a crucial element in modern human society. However, to keep pace with internet data rate growth, new technologies supporting data center should develop. Integration of optical wireless communication (OWC) in data centers is one of the proposed technologies as augmented technology to the fiber network. One implementation of the OWC technology is deployment of optical wireless transceiver on top of the existing cable/fiber network as extension to the top of rack (TOR) switch; in this way, a dynamic and flexible network is created. Optical wireless communication could reduce energy consumption, increase the data rate, reduce the communication latency, increase flexibility and scalability, and reduce maintenance time and cost, in comparison to extra fiber network deployment. In this paper we review up to date literature in the field, propose an implementation scheme of OWC network, discuss ways to reduce energy consumption by parallel link communication and report preliminary measurement result of university data center environment.

Optical wireless communication (OWC) systems provide many advantages over radio frequency (RF) wireless technologies in some scenarios, including significantly higher data rates and a large amount of available license-free frequency spectrum. Recently, OWC has also been proposed in fifth generation 5G standard as a tool to augment capacity due to RF spectrum crunching challenges. Various forms of OWC can be used to augment RF capacity at both access and backhaul/fronthaul levels. Despite the major advantages and various application areas, the widespread deployment of OWC is delayed by several challenges, such as the demand to maintain strict line-of-sight alignment between transmitter and receiver in long range outdoor applications; the need to combat attenuation due to adverse weather conditions such as fog, cloud, and turbulence; to modulate light emitting diodes at high frequencies without distortion at indoor visible light communication (VLC) applications and retaining power levels within the eye safety limits for laser transmitters and comfortable illumination levels for LED transmitters.

Due to copyright restrictions, the access to the full text of this article is only available via subscription. New data services and applications are emerging continuously and enhancing the mobile broadband experience. The ability to cope with these varied and sophisticated services and applications will be a key success factor for the highly demanding future network infrastructure. One such technology that could help address the problem would be optical wireless communications (OWC), which presents a growing research interest in the last few years for indoor and outdoor applications. This paper is an overview of the OWC systems focusing on visible light communications, free space optics, transcutaneous OWC, underwater OWC, and optical scattering communications. European Commission ; National Key Basic Research Program of China ; National Natural Science Foundation of China ; Shenzhen Peacock Plan

The growing demand for high interconnection speed in next-generation computers is driving the technology shift for communication from the electronic to the optic domain. One of the favored interconnection technologies for this task is the free-space optical interconnect (FSOI). FSOI technology uses laser links between computer components and provides a lower bound on propagation delay due to the low index of refraction of air, when compared with the indexes common in waveguide technologies. FSOIs based on dc-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) may provide excellent data throughput in intensity modulation/direct detection systems. However, the main drawback limiting the implementation of FSOIs is the inevitable tradeoff between interconnection density and the crosstalk level, resulting from the diffraction effect and from optical misalignment. The purpose of this paper is to promote improved interconnection density of such FSOIs by use of inherent DCO-OFDM resource allocation capabilities. The crosstalk-resulted interference was formulated as joint multilink bit-and-power allocation optimization. The theoretical analysis reveals general guidelines for dense FSOI. Further, a reduced-complexity numerical suboptimal algorithm for joint multilink bit-and-power allocation was proposed. The simulation results show that the proposed suboptimal algorithm outcome is close to the theoretical optimal performance.

Confining light to nanoscale dimensions has become possible with surface plasmons. However, active control of plasmonic responses remains a hurdle for building plasmonic optical devices. In this letter, we analytically derive a model describing the gap between the local surface plasmon (LSP) modes of a spherical nanoparticle in anisotropic media as a function of applied external electric field. Anisotropic ferroelectric materials exhibit birefringence that can be controlled through the electro-optic effect. Hence, the splitting of LSP frequencies in ferroelectrics embedded with nanoparticles can be controlled. In other words, by applying an external voltage a transition between the anisotropic and the isotropic phases can be achieved. As a result, the gap created by anisotropy can be tuned by the applied voltage. We derive and provide an explanation to the required field intensity according to the coercive field of ferroelectric materials. This simple approach is the basis for a method to actively tune the amplitude and the polarizability of light. The method can be considered for photonic applications, such as optical switches and biomedical sensors.

There is a growing need for accurate, high-resolution intersatellite ranging, for instance for gravitational mapping, which has led to extensive research on optical methods that can augment or replace existing spaceborne microwave techniques. In this letter, we outline a top-level design concept for intersatellite ranging based on measurements using a homodyne Mach–Zehnder interferometer housed on one satellite. The phase degradation in the reference arm of the interferometer on the local satellite is maintained at a minimal level to yield useful interference with the measuring arm that traverses hundreds of kilometers to the remote satellite and back. In this preliminary study, the feasibility of the concept in terms of link budget and noise level is validated. Ranging resolution is expected to be similar to the current heterodyne state-of-the-art.

In recent years, an increasing number of data center networks (DCNs) have been built to provide various cloud applications. Major challenges in the design of next generation DC networks include reduction of the energy consumption, high flexibility and scalability, high data rates, minimum latency and high cyber security. Use of optical wireless communication (OWC) to augment the DC network could help to confront some of these challenges. In this paper we present an OWC multi channels communication method that could lead to significant energy reduction of the communication equipment. The method is to convert a high speed serial data stream to many slower and parallel streams and vies versa at the receiver. We implement this concept of multi channels using optical orthogonal frequency division multiplexing (O-OFDM) method. In our scheme, we use asymmetrically clipped optical OFDM (ACO-OFDM). Our results show that the realization of multi channels OFDM (ACO-OFDM) methods reduces the total energy consumption exponentially, as the number of channels transmitted through them rises.

A data center (DC) is a facility either physical or virtual, for running applications, searching, storage, management and dissemination of information known as cloud computing, which consume a huge amount of energy. A DC includes thousands of servers, communication and storage equipment and a support system including an air conditioning system, security, monitoring equipment and electricity regulator units. Data center operators face the challenges of meeting exponentially increasing demands for network bandwidth without unreasonable increases in operation and infrastructure cost. In order to meet the requirements of moderate increase in operation and infrastructure cost technology, a revolution is required. One way to overcome the shortcomings of traditional static (wired) data center architectures is use of a hybrid network based on fiber and optical wireless communication (OWC) or free space optics (FSO). The OWC link could be deployed on top of the existing cable/fiber network layer, so that live migration could be done easily and dynamically. In that case the network topology is flexible and adapts quickly to changes in traffic, heat distribution, power consumption and characteristics of the applications. In addition, OWC could provide an easy way to maintain and scale up data centers. As a result total cost of ownership could be reduced and the return on investment could be increased. In this talk we will review the main OWC technologies applicable for data centers, indicate how energy could be saved using OWC multichannel communication and discuss the issue of OWC pointing accuracy for data center scenario.

Data centers are a key building block in the rapidly growing area of internet technology. A typical data center has tens of thousands of servers, and communication between them must be flexible and robust. Vortex light beams have orbital angular momentum and can provide a useful and flexible method for optical wireless communication in data centers. Vortex beams can be generated with orbital angular momentum but independent of polarization, and used in a multiplexed system. We propose a multiplexing vortex system to increase the communication capacity using optical wireless communication for data center networks. We then evaluate performance. This paper is intended for use as an engineering guideline for design of vortex multiplexing in data center applications.

Data centers collect and process information with a capacity that has been increasing from year to year at an almost exponential pace, while many datacenter applications are provided at no cost. This faces datacenter operators with the challenges of meeting exponentially increasing demands for network bandwidth without unreasonable increases in operation and infrastructure cost. In order to meet the requirements of moderate increase in operation and infrastructure cost new technologies are desired. Optical wireless technology could a) reduce the power consumption, b) increase the flexibility and scalability and c) reduce the network overload.. The OWC link could be deployed on top of the existing cable/fiber network layer, such that live migration could be done easily and dynamically and network topology is flexible and adapts quickly to changes in traffic, heat distribution, power consumption and characteristics of the applications. In addition, OWC could provide an easy way to maintains and scale up data centers which would reduce total cost of ownership and increase the return on investment. In this talk we will review the main OWC technologies, algorithms concepts and configurations which improve the performance of next generation data centers.

This research comprises an end-to-end experimental comparison of the bit-rates and bit error-rates of four major adaptive bit-and-power allocation algorithms for dc biased optical orthogonal frequency-division multiplexing. The comparison includes studying different channel conditions and different numbers of subcarriers. The experimental results show that all the methods compared display similar performance without significant superiority of a single method, even though in theory some difference is expected. Our analysis of the experimental data showed that the main reason for the uniformity in performance is the high variance in the channel estimation, especially at higher frequency subcarriers.

Intelligent transport systems have become the major technology for increasing road safety and traffic efficiency, as well as for reducing the number of road casualties. Radio frequency and optical wireless communication technologies have been proposed as a means for establishing communication between vehicular and road infrastructure, such as traffic lights, billboards and road infrastructures and for providing inter-vehicular communication. These technologies provide one-way or two-way short-range to medium-range wireless communication links that are specifically designed for the automotive sphere. The technology that is analysed in this paper is optical wireless communication. This technology modulates optical data on top of the illumination in the traffic lights and in the automotive lighting and detects the information using fast imaging sensors. Using knowledge of the amplitudes of the signal and the noise in each pixel, we tune adaptively and separately the gain of each individual pixel in the imaging sensor for communication signals. Tuning the gain is based on the mathematical model derived in this research. Comparison is made between the adaptive model and the standard model. From the mathematical analysis and the results of the comparison, it is clear that this model significantly improves communication system performance. In our numerical calculation for a given set of parameters, the signal-to-noise ratio of the standard system and the adaptive system changes from more than 7×10-4 to more than 7 and less than 2×10-3 to more than 30 for a change in transmitter power from 10 to 100watts respectively. Copyright © 2014 John Wiley & Sons, Ltd.

In recent years, several space systems consisting of multiple satellites flying in close formation have been proposed for various purposes such as interferometric synthetic aperture radar measurement (TerraSAR-X and the TanDEM-X), detecting extra-solar earth-like planets (Terrestrial Planet Finder-TPF and Darwin), and demonstrating distributed space systems (DARPA F6 project). Another important purpose, which is the concern of this paper, is for improving radio frequency communication to mobile terrestrial and maritime subscribers. In this case, radio frequency signals from several satellites coherently combine such that the received/transmit signal strength is increased proportionally with the number of satellites in the formation. This increase in signal strength allows to enhance the communication data rate and/or to reduce energy consumption and the antenna size of terrestrial mobile users' equipment. However, a coherent combination of signals without aligning the phases of the individual communication signals interrupts the communication and outage link between the satellites and the user. The accuracy of the phase estimation is a function of the inter-satellite laser ranging system performance. This paper derives an outage probability model of a coherent combination communication system as a function of the pointing vibration and jitter statistics of an inter-satellite laser ranging system tool. The coherent combination probability model, which could be used to improve the communication to mobile subscribers in air, sea and ground is the main importance of this work.

In this paper, the free-space optics (FSO) quantum backscatter communication (QBC), inspired by the quantum illumination concept, is described. In this method, the transmitter generates entangled photon pairs. The signal photon is transmitted in the direction of the modulated retro reflector (MRR) or the tag antenna, and the idler photon is moved to the receiver. The MRR communicates by modulating the received photon and retro-reflecting it back to the receiver. QBC could provide performance improvement in comparison to conventional backscatter communications. In this work, a mathematical model of the FSO QBC systems is derived. In an FSO system, the pointing direction jitter is a stochastic process that reduces the communication performance. In this paper, optimization of FSO QBC performance is proposed to minimize the error probability. This could be done by adapting the telescope gain to jitter a standard deviation amplitude.

Data Center (DC) servers consume a huge amount of energy. However, a part of this energy (cooling and information technology devices) can be saved by shutting down racks containing idle servers. This can be achieved by rerouting workloads from partially loaded racks, and thus allowing additional racks to switch into idle mode. Workload rerouting requires additional wired links or by optical wireless communication (OWC) links, which can be deployed on top the existing network. In comparison to classic wired infrastructure, OWC deployment and maintenance is faster and simpler, and it offers dynamic configuration of the network. Moreover, OWC can be used to augment the performance of virtualization techniques, which allow load balancing. In this paper we developed a mathematical model and an optimization algorithm along with numerical simulations, which evaluate the energy consumption in DCs. Results show that for a uniform distributed load between 24–100% and a 100% deployment of OWC links, 33% of the IT and cooling energy consumed can be saved.

Data Centers (DC) consume an enormous amount of energy, now accounting for about 1.5% of US electrical usage. However, part of this energy (server operation and cooling) can be saved by turning off idle servers. This can be achieved by rerouting workloads from partially loaded servers, and thus allowing additional idle servers to shut down. Workload rerouting could be done by optical wireless communication (OWC) links, which can be deployed on top the existing cable/fiber network. In comparison to classic wired infrastructure, OWC deployment and maintenance is faster and simpler, and it offers dynamic configuration of the network. In this paper we derive a stochastic model of data center energy reduction using optical wireless links as a function of the data center load. Our results indicate that for typical data center energy reduction of more than 5% could be achieved for given set of parameters.