Free Space Optics

In this paper, the performance of a cooperative Decode-and-Forward (DF) relay network with adaptive M-ary Quadrature Amplitude Modulation (M-QAM) is analyzed. A five mode adaptive M-QAM scheme is employed, and the system performance is investigated for both fixed switching levels and for optimized switching levels with a target bit error rate (BER) constraint. Expressions for average BER, spectral efficiency, and outage probability are derived to investigate the performance of the cooperative system under independently and identically distributed (i.i.d.) Nakagami-m fading wireless environments. Adaptive M-QAM with optimized switching levels maintains the target BER constraint while fixed switching levels achieves a conservative BER, which is lower than the target.

The objective of the paper is to exhibit the significance of the LiFi-based data transmission using light. LiFi is deployed in numerous applications such as security, augmented reality, intelligent transport system etc. as typical indoor localization is essential and is being done with mobile robots. This research article proposes a short range, indoor design, light fidelity model and discusses the simulations conducted for the LiFi model and the model is analyzed for various aspects that uses different LED light sources with Line of Sight (LOS) and without Non-Light of Sight (NLOS), different room sizes, different modulation formats, and simulation is also performed with and without noise models. The LiFi proposed model is designed to transfer data wirelessly with a data rate of 10 Gbps. The proposed results obtained is validated with other pervious LiFi works. Simulations results of our proposed model outperform the other previous LiFi works when operating under ideal circumstances with and without noise.

Free Space Optical Communications (FSO) has become a magnet for a variety of applications in the communication field. Signal attenuation was highlighted in data transfer, particularly in the multimedia e.g. high-speed video camera network requires sufficient throughput. This paper focuses on finding an approach to improve the signal received through the use of bi-directional FSO multiple access channel with high transmission power to avoid signal attenuation in short distances over atmospheric turbulence channels. Comparison of the extracted results proved that the performance of the proposed system is effective to overcome these effects.

The main goal of these papers is to analyze the Free space optical system with the weather condition of Ankara, the capital city of turkey. Governmental meteorological data support the analysis of this study of wireless communication systems; where it provides real measurement values. The advantages of the FSO system are the simplicity and the cost of installation in comparison with fiber optic systems that use light amplified as a source for transmission. This system is used in short-range applications, which are between buildings in cities or between skyscrapers, and sometimes between ships, as well as very complex military situations. The laser generally is used as a signal transmitter because it has a special optical advantage that allows it to travel long distances. Telecommunications engineers normally prefer to use semiconductor lasers because of their special properties and their cost-effectiveness. The obstacles that face the FSO system are different weather conditions such as rain, fog, air molecules, and snow. This study will investigate the FSO using a semiconductor laser according to the weather conditions of Ankara and the distance traveled taking into account a good high-quality data transmission.

The modulation techniques covered include AM, FM, PM, ASK, FSK, PSK, and QAM. Furthermore, the article shed light on the enabling technology in telephony and internet connectivity, specifically in 3G, 4G, 5G, WiFi 5, and WiFi 6. It then concludes that as communication technology continues to evolve, staying updated with modulation techniques and enabling technologies will be essential for optimizing communication systems and ensuring reliable and high-quality information transmission.

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.

We propose an adaptive transmission technique for free space optical (FSO) systems, operating in atmospheric turbulence and employing subcarrier phase shift keying (S-PSK) intensity modulation. Exploiting the constant envelope characteristics of S-PSK, the proposed technique offers efficient utilization of the FSO channel capacity by adapting the modulation order of S-PSK, according to the instantaneous state of turbulence induced fading and a pre-defined bit error rate (BER) requirement. Novel expressions for the spectral efficiency and average BER of the proposed adaptive FSO system are presented and performance investigations under various turbulence conditions and target BER requirements are carried out. Numerical results indicate that significant spectral efficiency gains are offered without increasing the transmitted average optical power or sacrificing BER requirements, in moderate-to-strong turbulence conditions. Furthermore, the proposed variable rate transmission technique is applied to multiple input multiple output (MIMO) FSO systems, providing additional improvement in the achieved spectral efficiency as the number of the transmit and/or receive apertures increases.

Free Space Optics (FSO) shows a great alternative as the solution for last mile problem where fiber optics is unavailable due to deployment time and cost constraint.  However, the feasibility of using FSO system as communication link very much depends on local weather.  Since tropical region experiences heavy rainfall, rain with high intensity is expected to affect the FSO link severely. Few prediction models have been proposed by ITU-R based on France and Japan’s measurement. This paper has compared  rain attenuation predicted by  models and  data measured in Malaysia over Free Space Optical links for one year period. Prediction models are clearly unable to predict attenuation measured in tropical climate. ABSTRAK: Wayarles optik menjadi alternatif sebagai satu penyelesaian kepada masalah kesesakan terutama diakhir sesuatu talian dimana ianya tidak dapat diselesaikan dengan menggunakan gentian fiber akibat daripada kekangan masa pemasangan dan masalah kewangan.  Walaubagaimanapun, ...

A suburban ad-hoc network (SAHN) interconnects a cooperative group at broadband speed using wireless links. The nodes are stationary. A SAHN involves low installation and service costs for SAHN specific traffic. Some current routing solutions for mobile ad-hoc networks may be used in the SAHN after certain optimizations. Efficiency can be improved by using smart directional antennas. Neighboring nodes falling outside the transmission region of a directional antenna are less vulnerable to co-channel interference. Additionally, increased transmission range can be achieved by reducing noise, interference and multi-path fading. In this paper, we emphasize the interference reduction capability of directional antennas and investigate the routing performances using three antenna schemes; multiple fixed directional, multiple omnidirectional and single omnidirectional antennas. We present an estimate of the achievable performance in a SAHN through extensive simulations. We also discuss the impact of using omnidirectional antennas on routing performance where different networks, using overlapping frequency channels, exist within each other's transmission ranges.

We report on the performance characterization and issues associated with using Gigabit Ethernet (GigE) over a highly turbulent (G2 > lo-'') 1.3 km air-optic lasercom links. Commercial GigE hardware is a cost-effective and scalable physical layer standard that can be applied to air-optic communications. We demonstrate a simple GigE hardware interface to a singlemode fiber-coupled, 1550 nm, WDM air-optic transceiver. TCPAP serves as a robust and universal foundation protocol that has some tolerance of data loss due to atmospheric fading. Challenges include establishing and maintaining a connection with acceptable throughput under poor propagation conditions. The most usefil link performance diagnostic is shown to be scintillation index, where a value of 0.2 is the maximum permissible for adequate GigE throughput. Maximum GigE throughput observed was 49.7% of that obtained with a fiber jumper when scintillation index is 0.1. Shortcomings in conventional measurements such as bit error rate are apparent. Prospects for forward mor correction and other link enhancements will be discussed.

The main goal of these papers is to analyze the Free space optical system with the weather condition of Ankara, the capital city of turkey. Governmental meteorological data support the analysis of this study of wireless communication systems; where it provides real measurement values. The advantages of the FSO system are the simplicity and the cost of installation in comparison with fiber optic systems that use light amplified as a source for transmission. This system is used in short-range applications, which are between buildings in cities or between skyscrapers, and sometimes between ships, as well as very complex military situations. The laser generally is used as a signal transmitter because it has a special optical advantage that allows it to travel long distances. Telecommunications engineers normally prefer to use semiconductor lasers because of their special properties and their cost-effectiveness. The obstacles that face the FSO system are different weather conditions such as rain, fog, air molecules, and snow. This study will investigate the FSO using a semiconductor laser according to the weather conditions of Ankara and the distance traveled taking into account a good high-quality data transmission.

Modern communication systems adopt the principle of wireless communication as a basic choice in life in the city and nearby offices. Systems are often expensive and monopolized by governments and
regimes, so many researchers around the world are interested in finding systems that can be of a cheap nature, have good communication quality, and can send data at an acceptable to excellent rate. Free space optical system is one of those systems that unlicensed and cost-effective system. In this study we found the optimum wavelength for FSO system and apply it with the three main weather condition fog, rain and snow. FSO using many techniques like a LOS (line of sight) and multibeam sending data where voice, video communication and data is achieved with high data rate by bidirectional full duplex connectivity[1].
The 850 nm wavelength is very suitable for FSO system because of it’s reliable, high-performance, and inexpensive transmitter and detector components. Also, they are generally available and commonly used in today’s service provider networks and transmission equipment[6].

Computer-generated planar holograms are a powerful approach for designing planar lightwave circuits with unique properties. Digital planar holograms in particular can encode any optical transfer function with high customizability and is compatible with semiconductor lithography techniques and nanoimprint lithography. Here, we demonstrate that the integration of multiple holograms on a single device increases the overall spectral range of the spectrometer and offsets any performance decrement resulting from miniaturization. The validation of a high-resolution spectrometer-on-chip based on digital planar holograms shows performance comparable with that of a macrospectrometer. While maintaining the total device footprint below 2 cm 2 , the newly developed spectrometer achieved a spectral resolution of 0.15 nm in the red and near infrared range, over a 148 nm spectral range and 926 channels. This approach lays the groundwork for future on-chip spectroscopy and lab-on-chip sensing.

We theoretically study the performance of multiple-input multiple-output (MIMO) free-space optical (FSO) systems using subcarrier quadrature modulation (SC-QAM) signaling. The system average symbolerror rate (ASER) is derived taking into account the atmospheric turbulence effects on the MIMO/FSO channel, which is modeled by log-normal and the gamma-gamma distributions for weak and moderate-to-strong turbulence conditions. We quantitatively discuss the influence of index of refraction structure parameter, link distance, and different MIMO configurations on the system ASER. We also analytically derive and discuss the MIMO/FSO average (ergodic) channel capacity (ACC), which is expressed in terms of average spectral efficiency (ASE), under the impact of various channel conditions. Monte Carlo simulations are also performed to validate the mathematical analysis, and a good agreement between numerical and simulation results is confirmed.

This work aims to study the improvement that has been achieved when replacing the traditional single-element (SE)receivers by imaging (IMG) receivers in line of sight (LOS) links, which can reduce the received ambient light noise, multipath distortion and co-channel interference. Also in non-directed non-LOS, the replacement of diffuse (DIF) transmitters by multi-beam (quasi-diffuse) (QDIF) transmitters has been studied such replacement leads to reduction in the path loss. This study first based on making validation to a previous approximate and exact analysis to LOS and non-LOS links, and then a parametric study to some parameters has been made to check their effect on the link performance. We quantify the performance of the LOS and NLOS links using two main parameters the reduction in the required transmitter power and high improvement in the signal to noise ratio (SNR).

Mixed-signal multidomain systems present a challenge for computer-aided design tools. Optical and electronic simulation tools are available as separate entities. However, to date, successful system-level cosimulation has not been implemented, leading to expensive refabrication. We present a unique system-level simulation tool for mixed electrooptical systems. We apply our tool Chatoyant to the simulation of an optical high-speed free-space interconnect system designed for 10-GHz speeds. The 10G free-space optical interconnect module has optical, optoelectronic, and microwave components and thus is an ideal vehicle to use as a test system. We demonstrate how Chatoyant, a mixed-signal multidomain simulator, has been used to evaluate end-to-end performance of this complex system, including the exploration of design tradeoffs and mechanical tolerancing.

We study nonlinear absorption in a series of ten polymethine dyes and two squarylium dyes using Z-scan, pump-probe and optical limiting experiments. Both picosecond and nanosecond characterization were performed at 532 nm, while Ž . picosecond measurements were performed using an optical parametric oscillator OPO from 440 to 650 nm. The photophysical parameters of these dyes including cross sections and excited-state lifetimes are presented both in solution in Ž . ethanol and in an elastopolymeric material, polyurethane acrylate PUA . We determine that the dominant nonlinearity in all Ž . these dyes is large excited-state absorption ESA , i.e. reverse saturable absorption. For several of the dyes we measure a relatively large ground-state absorption cross section, s , which effectively populates an excited state that possesses an 01 extremely large ESA cross section, s . The ratios of s rs are the largest we know of, up to 200 at 532 nm, and lead to 12 12 01 very low thresholds for optical limiting. However, the lifetimes of the excited state are of the order of 1 ns in ethanol, which is increased to up to 3 ns in PUA. This lifetime is less than optimum for sensor protection applications for Q-switched inputs, and intersystem crossing times for these molecules are extremely long, so that triplet states are not populated. These parameters show a significant improvement over those of the first set of this class of dyes studied and indicate that further improvement of the photophysical parameters may be possible. From these measurements, correlations between molecular structure and nonlinear properties are made. We propose a five-level, all-singlet state model, which includes reorientation processes in the first excited state. This includes a trans-cis conformational change that leads to the formation of a new state with a new molecular configuration which is also absorbing but can undergo a light-induced degradation at high inputs.

In this paper, the effect of atmospheric turbulence on bit error probability in free-space optical CDMA scheme with Sequence Inverse Keyed (SIK) optical correlator receiver is analyzed. Here Intensity Modulation scheme is considered for transmission. The turbulence induced fading is described by the newly introduced gamma-gamma pdf[1] as a tractable mathematical model for atmospheric turbulence. Results are evaluated with Gold and Kasami code & it is shown that Gold sequence can be used for more efficient transmission than Kasami sequence in an atmospheric turbulence channel.

This paper demonstrates an analytical approach on the bit error rate (BER) performance evaluation of a multi- carrier code division multiple access (MC-CDMA) communication link operating over terrestrial free space optical (FSO) channel considering effect of atmospheric turbulence The turbulence induced intensity fading is statistically modeled by Gamma-Gamma PDF (probability density function). Bit error rate performance improvement is proposed using photo detector spatial diversity with Equal Gain Combining (EGC) and Turbo Coding. Analysis is carried out with different bandwidth efficient phase shift keying (PSK) based sub-carrier intensity modulation (SIM) with direct detection. Numerical simulation results of proposed analytical model indicate that, sub-carrier intensity modulation scheme; number of receiver photo detectors, turbo coding parameter and link length should be optimally engineered for ensuring system reliability. It can be inferred from the simulation that, a reliabl...

The growing deployment and advanced development of high-speed train (HST) systems, coupled with the reliance on and demand for constant Internet connectivity anytime anywhere, have necessitated the imminent provisioning of broadband Internet services in HSTs. Ground-to-train free space optical (FSO) communications suffer from frequent handovers due to high mobility of HSTs, thus shortening the connection time between the train and ground, and greatly impacting passengers' user experience. To provision high-speed Internet services in HSTs, we propose the RotAting TranscEiver scheme (RATE) to mitigate the impact of handover processes with steerable FSO transceivers in a ground-to-train communications system. Owing to the rotating feature of the scheme, the on-roof transceiver of a train can maintain a reliable link with a base station (BS) for a longer time, and remarkably reduce the number of handover processes, thus provisioning higher data rates of the system. Meanwhile, since the separation distances between BSs are extended, the total number of BSs required to be deployed along the track is also reduced, thus reducing the deployment cost for service providers. Moreover, a new handover method is designed to mitigate the impact of each handover delay, especially on live streaming applications. Finally, the performance improvement of the proposed scheme is demonstrated via simulation results. Index Terms-FSO, handover, ground-to-train communications, high-speed train. H IGH-SPEED Internet connectivity is becoming an inte- gral and indispensable part in our daily lives. Broadband data services are expected to be provisioned in high-speed trains (HSTs). Thus, providing Internet access in HSTs is one of the main incentives for the railway operators to attract more passengers. Currently, radio frequency wireless technologies are used to provide Internet access to passengers [1-3]. However, owing to the limitation of radio wave bandwidth and interference [4], [5], the existing infrastructure based on radio frequency technology such as Wi-Fi/WiMAX can provide peak data rates of up to 54/75 Mbps theoretically, which drop to lower than 10 Mbps in real scenarios [6],

We discuss the design of an acousto-optic cell based free space optical communication link where the data beam is made secure through chaos encryption. Using external signal modulation of the diffracted light from a hybrid acousto-optic cell chaos (or directly via incorporation in the sound-cell driver's bias voltage) encryption of data is possible. We have shown numerically that decryption of the encoded data is possible by using an identical acousto-optic system in the receiver.

The papers included in this volume were part of the technical conference cited on the cover and title page. Papers were selected and subject to review by the editors and conference program committee. Some conference presentations may not be available for publication. The papers published in these proceedings reflect the work and thoughts of the authors and are published herein as submitted. The publisher is not responsible for the validity of the information or for any outcomes resulting from reliance thereon. Please use the following format to cite material from this book: Author(s), "Title of Paper," in Atmospheric Propagation V, edited by G.

In this paper, we summarize progress in free space laser propagation research at the U.S. Naval Research Laboratory, specifically in the context of propagating and detecting signals through the atmosphere in a maritime environment. Transmission through the atmosphere over large bodies of water presents different challenges than transmission through the atmosphere over land. Our paper reports some of these findings as well as progress in our collaborative efforts to mitigate turbulence to enhance our data links.

In this paper, we report the results of a recent demonstration in which a Multiple Quantum Well retromodulator array was used as a low power, lightweight means to provide optical tagging of a remotely located object. A laser diode integrated on a tracker/pointing system scanned without cueing for a modulated retroreflected beam. The retroreflected energy was received and the embedded code demodulated for tagging identification. Ranges were on the order of 40 meters using an array of 1/2 cm MQW devices. Data were transferred at a rate of one mega chip per second over the link. Device power requirements were on the order of several milliwatts. TABLE OF CONTENTS 1. INTRODUCTION 2. RETROMODULATORS AND MQW DEVICES 3. FIELD TEST 4. RESULTS 5. SUMMARY 6. REFERENCES Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

In this paper, we describe progress in the development of the NRL Multiple Quantum Well modulating retroreflector including a description of recent demonstrations of an infrared data link between a small rotary-wing unmanned airborne vehicle and a ground based laser interrogator using the NRL multiple quantum well modulating retro-reflector. Modulating retro-reflector systems couple an optical retro-reflector, such as a corner-cube, and an electro-optic shutter to allow two-way optical communications using a laser, telescope and pointer-tracker on only one platform. The NRL modulating retroreflector uses a semiconductor based multiple quantum well shutter capable of modulation rates up to 10 Mbps, depending on link characteristics. The technology enables the use of near-infrared frequencies, which is well known to provide covert communications immune to frequency allocation problems. The multiple quantum well modulating retro-reflector has the added advantage of being compact, lightweight, covert, and requires very low power. Up to an order of magnitude in onboard power can be saved using a small array of these devices instead of the Radio Frequency equivalent. In the described demonstration, a Mbps optical link to a unmanned aerial vehicle in flight at a range of 100-200 feet is shown. Near real-time compressed video is also demonstrated at the Mbps level.

Free space optics (FSO) can provide high data rates with efficient use of power. However, small platforms may not be able to support the payload requirements of a conventional FSO terminal. An alternative FSO terminal uses a modulating retro-reflector (MRR). MRRs shift most of the power, weight, and pointing requirements to one end of the link. With a MRR configuration, it is possible to establish a two-way FSO link using a single laser transmitter. The MRR terminal of these systems can be small, lightweight, and low power. The MRR maintains the small beam divergence of a conventional optical communications link, but gains the loose pointing advantage of an RF link, reducing the pointing requirements. Communication needs in space present many asymmetric scenarios in which a MRR architecture could be beneficial. This paper describes some of the current capabilities and limitations of MRR systems, as well as applications to space links. An evaluation of the radiation tolerance of modulators is presented.

Based on the wavelet transformation and adaptive Wiener Filtering, a new method was presented by the authors to perform the synchronization and detection of the binary data from the Free-Space Optical (FSO) signal . It was shown in that the Haar wavelet with a fixed scale is an excellent choice for this purpose. The output of the filter is zero-mean and is closely related to the derivative of the binary data. In this effort an analysis of the work in [1] is presented to obtain the probability of bit error using a Bayesian ternary hypotheses testing. The analysis also results in determining optimum thresholds for the detection of binary data.

Photoreceiver array configurations for enhancing the sensitivities of free space optical terminals down to the quantum limits are described. Small format arrays at 1550nm have been implemented and shown to improve sensitivity by 1.8 dB. The concept of large format arrays based on optically preamplified photoreceivers in a summed configuration for is elucidated and shown to be capable of sensitivities as low as -53 dBm at 2.5 Gbps bit rate and 10 -9 BER for (8 X 8) arrays.

Atmospheric turbulence causes severe performance degradation in free space optical communication links. However, by using a reliable low bandwidth wireline or radio frequency link in parallel, the performance of such links can be improved significantly. This is achieved by using error correction codes at the transmitter, and decoding the received data jointly over the two links at the receiver. Our work describes the feasibility study of such a hybrid link. It is observed that a 10% use of the wireline link can result in more than 8 dB performance gain in the optical link.

The Solar Hidden Photon Search (SHIPS) is a joint astroparticle project of the Hamburger Sternwarte and DESY. The main target is to detect the solar emission of a new species of particles, so called Hidden Photons (HPs). Due to kinetic mixing, photons and HPs can convert into each other as they propagate. A small number of solar HPs -originating from photon → HP oscillations in the interior of the Sun -can be converted into photons in a long vacuum pipe pointing to the Sun -the SHIPS helioscope.

The melting duration and molten depth are key information for Laser-Assisted Direct Imprinting, which raises the issue of the melting & solidification induced by excimer-pulse-laser shining through unilaterally transparent binary materials. Based on the matured laser-annealing analysis, the thermal-contact resistance is taken into account to simulate and predict the melting behavior for this process. The result in this study indicates the laser-annealing case as well as the perfect-contact case provide the upper-bound and the lower-bound values for the physical quantities involved in this process even without the detail information of the changing of thermal-contact resistance during process.

The use of LEDs for illumination and simultaneous communication becomes more and more interesting and it goes hand in hand with the increasing deployment of LEDs to peoples homes and industrial buildings. Modulation of this kind of light sources is difficult because of high voltage and of current demands. Since the LED configurations and the values of current and voltage are different, the universal modulator suggested by the research team of the Department of Telecommunications should be able to operate even under various circumstances. The objective of this paper is to present a design of a simple and universal current modulator for LED lighting modulation for the frequencies of around 1 MHz. The modulator should allow the initial testing of different types of High Power LEDs and different photodetector configurations and circuits in diffusively based Free-Space-Optical networks. Also, in the experimental part, the results obtained in the testing were compared with some different types of LED light sources.

The use of LEDs for illumination and simultaneous communication becomes more and more interesting and it goes hand in hand with the increasing deployment of LEDs to peoples homes and industrial buildings. Modulation of this kind of light sources is difficult because of high voltage and of current demands. Since the LED configurations and the values of current and voltage are different, the universal modulator suggested by the research team of the Department of Telecommunications should be able to operate even under various circumstances. The objective of this paper is to present a design of a simple and universal current modulator for LED lighting modulation for the frequencies of around 1 MHz. The modulator should allow the initial testing of different types of High Power LEDs and different photodetector configurations and circuits in diffusively based Free-Space-Optical networks. Also, in the experimental part, the results obtained in the testing were compared with some different types of LED light sources.

Free-Space Optics (FSO) is a high-speed communication technology that provides speed and bandwidth comparable to optical fiber. In terms of deployment time and cost, FSO is superior to optical fiber. However, variable weather conditions, such as rain, that impact the signal are one of the primary obstacles to FSO, as the signal is transmitted through the atmosphere. But, rainy weather substantially affects the efficacy of FSO links, resulting in diminished transmission quality and potential signal loss. The purpose of this research is to evaluate the performance of an FSO connection while considering the impairments induced by precipitation for the proposed data capacity. In light of these challenges and the benefits of FSO, this study proposed a hybrid multiplexing technique-based system that achieves data throughput of 0.344Tbps per WDM channel by combining coherent optical orthogonal frequency division multiplexing (CO-OFDM), polarization division multiplexing (PDM), and Wavelength division multiplexing (WDM). A quadrature amplitude modulation (4-QAM) scheme has also been used to achieve a total capacity of 1.38 Tbits/s and spectral efficiency of 3.4bps/HZ for four distinct WDM channels. Under situations of clear weather, light rain, medium rain, and heavy rain, the proposed system has been capable of supporting transmissions of up to 66.99 km, 5.049 km, 3.60 km, and 2.0498 km, respectively. The results show that the greatest link range could be achieved under the most difficult channel circumstances while maintaining a minimum acceptable bit error rate (BER) of log (BER) ≤-2.42, which has been accomplished by using pre-and post-optical amplification between FSO channels.

To efficiently support the fast-growing demand for transmission capacity, optical packet-switched systems seem to be strong candidates as they allow fast dynamic allocation ofWDM channels combined with a high degree of statistical resource sharing. In this work, we propose the architecture of an optical packet switching node, equipped with a shared fiber delay line buffer, for all-optical switching of IP traffic flows. Some traffic simulations results of node operation are also presented.

An optical architecture is described that offers the maximum interconnectivity afforded by light. The switch is described conceptually, and specific implementations are detailed for a prototype and for a large-scale version that supports more than 10 million channels, each of which carries data at rates of 10 Gbit/s or more. Results for a prototype are presented. Implementation issues, including off-axis propagation and filter angular sensitivity, are addressed. The architecture supports a new generation of parallel routers, and the switch is strictly nonblocking if color switching is not required. Modest levels of color switching, i.e., wavelength changing, can be supported by the architecture with little change by use of an optical foreplane. If full color switching is required, an optical backplane compatible with the architecture is used. Both opaque (optical-electronic-optical) and transparent (mirror array) versions of the switch are described. The architecture can support very low-cost switches for two reasons: (1) The underlying components can utilize wafer-based technologies, and (2) a single alignment can align hundreds or even thousands of channels at once.

The extreme ultraviolet (EUV) reflectance of amorphous tetrahedrally coordinated carbon films (ta-C) prepared by filtered cathodic vacuum arc was measured in the 30-188-nm range at near normal incidence. The measured reflectance of films grown with average ion energies in the ~70-140-eV range was significantly larger than the reflectance of a C film grown with average ion energy of ~20 eV and of C films deposited by sputtering or evaporation. The difference is attributed to a large proportion of sp 3 atom bonding in the ta-C film. This high reflectance is obtained for films deposited onto room-temperature substrates. The reflectance of ta-C films is higher than the standard singlelayer coating materials in the EUV spectral range below 130 nm. A selfconsistent set of optical constants of ta-C films was obtained with the Kramers-Krönig analysis using ellipsometry measurements in the 190-950 nm range and the EUV reflectance measurements. These optical constants allowed calculating the EUV reflectance of ta-C films at grazing incidence for applications such as free electron laser mirrors.

This paper proposes a method to extend the depth range of integral imaging systems by representing three-dimensional (3D) images in both virtual-real and real-real forms. The approach combines two integral imaging systems using a transmission-type retroreflector and a beam splitter (BS). The transmission-type retroreflector relays the integrated images from one display to form a real full-color 3D aerial images while preserving the resolution at extended depths. The BS combines the second integral imaging system across various depth ranges, providing additional real or virtual 3D images. The proposed method enhances the applicability of integral imaging systems in mixed-reality environments without requiring complex equipment.

The modern communications technology is a positive case for disaster risk reduction, since they to it provides critical information to realize risk assessment. In this study, we present an innovative technique is characterized by an aerial platform as a robust method to monitor disaster area. Traffic Surveillance System (TSS), based on Detection and Early Warning (DEW) units, is used to monitor the roads in preventing accidents at the same time finding what causes the accidents. This is done by implementing some image vision protocols as that of Gaussian. This paper will discuss about the cameravideo-surveillance capabilities of tracking across different and varied road environments including detection of moving vehicles. The programming method used will be the functional programming of OpenCV which could be operated under Linux OS. The bit error rate (BER) also was evaluated among multiple platform links in mobile environments. We adopted multi-level deployment besides low aggregate throughput delivered to all remote-sensing terminals in order to accommodate the reliability of data transmission from the last mile.

The performance of free space optical (FSO) communication is affected by various phenomena such as absorption, scattering, and turbulence. For FSO uplink, the major factors that degrade the performance are "turbulence-induced scintillation and beam wander effect." The effect of scintillation causes fluctuations in the received irradiance and the beam wander effect leads to the displacement of the beam centroid significantly. In this letter, variance in the optical irradiance due to turbulence-induced beam wander effect has been determined experimentally for different operating wavelengths and turbulent conditions in an optical turbulence generator (OTG) chamber.

In this paper, we theoretically analyze the performance of multiple-input multiple-output (MIMO) free-space optical (FSO) systems. The MIMO/FSO average channel capacity (ACC), which is expressed in terms of average spectral efficiency (ASE) is derived taking into account the atmospheric turbulence effects on the MIMO/FSO channel. They are modeled by log-normal and the gamma-gamma distributions for the cases of weak-to-strong turbulence conditions. We quantitatively discuss the influence of turbulence strength, link distance, and different MIMO configurations on the system ASE. Numerical and computer simulation results are presented in order to verify the validity of the mathematical analysis.

The channel capacity of terahertz (THz) wireless communications can be increased by multiplexing multiple orthogonal data-carrying orbital-angular-momentum (OAM) beams. In THz links using OAM multiplexing (e.g., Laguerre-Gaussian LG ℓ,p beams with p = 0), the system performance might degrade due to limited receiver aperture size and multipath effects. A limited-size aperture can truncate the received beam profile along the radial direction. In addition, due to beam divergence, part of the beam might interact with reflectors in the environment, causing the signal to reflect and interfere at the receiver with the directly propagating part of the beam; this is known as the multipath effect. In this paper, we simulate and analyze the impact of both effects on the equality of the THz OAM link by considering a full two-dimensional (2-D) LG modal set. The simulation results show (i) a limitedsize receiver aperture can induce power loss and modal power coupling mainly to LG modes with the same ℓ but p > 0 for directly propagated OAM beams; (ii) the multipath effect can induce modal power coupling across multiple 2-D LG modes, which leads to inter-channel coupling among the different channels in an OAM multiplexed link; (iii) the interference between the reflected and direct beams can induce intra-channel coupling between the received signals from the reflected and direct beams; and (iv) beams with a higher OAM order (e.g., from ± 1 to ± 5) or a lower carrier frequency (e.g., from 0.1 to 1 THz) experience larger intra-and inter-channel coupling. The intra-and inter-channel coupling in an OAM-multiplexed THz link can degrade the signal-to-noise ratio (SNR) and induce SNR penalty when compared to a single-channel system. Structured electromagnetic (EM) waves have gained much interest partially due to their unique spatial beam structures with tailored amplitude and phasefronts 1,2 . One type of structured EM wave is orbital-angular-momentum (OAM) . A beam carrying OAM has a unique spatial structure, such that the amplitude has a ring-like doughnut profile and the phasefront "twists" in a helical fashion as it propagates. OAM beams are a subset of the complete Laguerre Gaussian (LG ℓ, p ) modal basis set, which has two modal indices: (i) ℓ represents the number of 2π phase shifts in the azimuthal direction, which is the OAM order, and (ii) p + 1 represents the number of concentric intensity rings . OAM beams with different OAM orders are orthogonal to each other. This orthogonality between different OAM modes could enable the data-multiplexing technique of mode-division multiplexing (MDM), which is a subset of space-division multiplexing (SDM) . In this approach, multiple independent data-carrying OAM beams can be efficiently multiplexed at the transmitter, spatially co-propagate through the same medium, and

Over the recent few years, optical wireless communication (OWC) has attracted significant attention in both academia and the research community. Contrary to radio frequency (RF) systems, the spatial confinement of the optical beams makes the OWC system a potential system offering higher data rates and secured communication. OWC systems and applications in several areas, such as terrestrial outdoor (free-space optical (FSO) communication), indoor and outdoor visible light communication (VLC), etc. For the terrestrial outdoor FSO systems, spatial diversity techniques are employed over FSO links to enhance the diversity and overall performance. To this end, the spatial diversity techniques corresponding to the state-of-the-art are repetition coding (RC), transmit laser selection (TLS), and orthogonal space-time block codes. Note that, TLS is the optimal transmission scheme in the FSO systems. In this dissertation, we name the conventional TLS scheme as a single TLS (STLS) scheme. However, the performance of the conventional STLS scheme is highly dependent on the feedback errors. On the other side, the outdoor VLC finds applications in vehicle-to-vehicle (V2V) communications, infrastructure-to-vehicle (I2V) communications, etc. Emphasizing the state-of-the-art corresponding to the outdoor V2V-VLC systems, there is a lack of comprehensive modeling and performance investigation under the adverse challenges of the outdoor VLC environment. Moreover, to address the challenges of the next-generation-based outdoor intelligent transportation systems (ITSs), an indoor testbed design for an outdoor I2V-VLC system is still missing.

In order to enhance the diversity and overall performance of the terrestrial outdoor FSO systems, the study begins by proposing two novel TLS schemes. We call the proposed schemes as two TLS (TTLS) and modified error-tolerant weighting scheme iii (METWS). Note that, the conventional STLS scheme gives optimal performance under a perfect feedback scenario. However, its performance degrades significantly under an imperfect feedback scenario. To this end, the two proposed schemes overcome the practical limitations of the conventional STLS scheme. Moreover, we analyze the performance of the two proposed schemes for both perfect and imperfect channel state information (CSI)-based communication scenarios. Further, different performance metrics, such as bit error rate (BER), diversity gain, etc., are thoroughly analyzed. Furthermore, to gain more insights, the performance of the two proposed schemes is also compared with the conventional STLS and RC schemes.

We then investigate the diversity-multiplexing tradeoff (DMT) for the OWC systems. To this end, we mainly focus on the indoor VLC and outdoor FSO systems. For the DMT investigation of the indoor VLC system, we consider the random radial movement of the end-user in the proposed system model. The optimal DMT for both the single-input single-output (SISO) and multiple-input multiple-output (MIMO) VLC systems are analyzed. Novel analytical expressions for the probability distribution function (PDF), outage probability, and outage diversity order for the SISO-VLC and MIMO-VLC systems are derived. Moreover, we extend our study to the outdoor FSO system. For the first time in literature, a limited feedback-based DMT is investigated for the FSO system under different transmission scenarios. To this end, we consider a MIMO-FSO setup and investigate the DMT for single-rate and adaptive-rate trans mission scenarios.

Further, we venture into the area of vehicular VLC and comprehensively explore the area of vehicular VLC. To this end, contrary to the state-of-the-art, we emphasize comprehensive modeling of the V2V-VLC system under the practical challenges of an outdoor VLC environment. For the first time, we model the vehicle's mobility as random with a specific PDF. Therefore, we emphasize a more realistic approach to model the vehicle's mobility. Moreover, a novel channel model that incorporates the joint impact of the outdoor V2V-VLC random path loss and atmospheric turbulence (AT) is emphasized. Further, different performance metrics are analytically examined, such as path loss, outage probability, average BER (ABER), diversity order, discrete-input continuous-output memoryless channel (DCMC) capacity, etc., under different weather conditions.

We also extend our work on vehicular VLC by proposing a shadowing/blocking-based V2V-VLC model. In a line-of-sight (LOS) VLC system, the communication link is exposed to temporary shadowing due to physical obstructions by vehicles in the same lane or nearby parked vehicles. Since VLC is highly dependent on the LOS, proposing and analyzing a V2V-VLC model under a shadowing-based transmission scenario is of extreme importance. The performance of the proposed V2V-VLC model is analyzed with the DMT metric. Moreover, to minimize the path loss at the receiver (Rx), a novel hemispherical optical concentrator-based Rx structure (offering an omnidirectional gain) is also proposed. Some striking insights are envisioned for the proposed work.

Finally, as a part of the next-generation-based ITSs, we also develop an indoor testbed for an outdoor I2V-VLC system. For the first time in literature, we experimentally demonstrate the communication between the traffic light acting as the transmitter (Tx) and the camera (i.e., the Rx) under different realistic I2V-VLC scenarios in a controlled indoor environment. Moreover, all the experimental findings are demonstrated for different exposure times of the camera for the first time, which is a very critical parameter when using a camera-based Rx. Further, different performance metrics are experimentally examined, such as BER, peak signal-to-noise ratio (PSNR), and capacity. Furthermore, LOS blockage-based communication scenarios are also experimentally analyzed.

a lot of trouble nishing my Ph.D. program. Most signicantly, I owe my parents for encouraging me to pursue a Ph.D., for consistently being there for me through every stage, and for being able to relate to me no matter what. I am grateful to have a supportive supervisor and considerate parents. I feel blessed for their unwavering attention and care.

This paper deals with phase gratings working in the paraxial domain. The profile of the optimum-efficiency beam multiplier with an arbitrary number of output diffraction orders is derived in an analytic form by exploiting methods from the calculus of variation. The output beams may be equiintense or with arbitrary distribution of power. Numerical examples are given for different values of the number of output beams.

in this paper we analyze the effect of environmental conditions on a 632.8 nm free space optical (FSO) communication link. Three different environmental conditions were considered; clear, rain and dust. Furthermore, both dark and light conditions were taking into consideration. The rainy and dust conditions were artificially fabricated in our lab. Results show that in general the 632.8 nm optical signal is heavily attenuated in free space environment. Additionally, rain and dust have much higher attenuation compared to clear conditions. Results also show that optical pulses are heavily distorted even for very small distances for all three environmental conditions. Thus, higher optical power is required to achieve high data rates for moderate distances.

The use of optical spatial modulation (OSM), which has been recently emerged as a power and bandwidth efficient pulsed modulation technique for indoor optical wireless communication, is proposed as a simple, low-complexity means of achieving spatial diversity in coherent free space optical (FSO) communication systems. In doing so, this paper makes several novel contributions as follows. It presents a generic analytical framework for obtaining the Average Bit Error Probability (ABEP) of uncoded OSM with coherent detection in the presence of turbulence-induced fading. Although the framework is general enough to accommodate any type of models based on turbulence scattering, the focus in this paper is the H-K distribution. Although this distribution represents a very general scattering model valid over a wide range of atmospheric conditions, it is has not been considered in the past in conjunction with FSO systems possibly because of its mathematical complexity. The proposed analytical framework yields exact performance evaluation results for MIMO systems with two transmit and an arbitrary number of receive apertures. In addition, tight upper bounds are derived for the error probability for OSM systems with an arbitrary number of transmit apertures as well as for convolutionally encoded signals. The performance of OSM is compared to that of well established coherent FSO schemes, employing spatial diversity at the transmitter or the receiver only. Specifically, it is shown that OSM can offer comparable performance with conventional coherent FSO schemes while outperforming the latter in terms of spectral efficiency and hardware complexity. Various numerical performance evaluation results are also presented and compared with equivalent results obtained by Monte Carlo simulations which verify the accuracy of the derived analytical expressions.

The Free Space Optics (FSO) is a high-speed connectivity system that has the same advantages of speed and bandwidth as that of optic fiber. In comparison to optic fiber, FSO is the preferred choice when it comes to cost and deployment period. However, one of the main challenges with FSO is the changing weather conditions that affect the signal since the transmitted signal is radiated through the atmosphere. This investigation focuses on examining the variables that influence the reduction of visibility at different wavelengths: 750nm, 780nm, 850nm, and 1550nm. The locations of interest concerning visibility and rain data are Pretoria, Upington, Bloemfontein, and Cape Town in the Republic of South Africa. Results indicate that fog attenuates the signal more when compared to rain. Furthermore, signals transmitted at 1550nm will attenuate the signal less when compared to the other wavelengths of interest.

Tissue handling systems position ex-vivo samples to a required accuracy that depends on the features to be imaged. For example, to resolve cellular structure, micron pixel spacing is needed. 3D tissue scanning at cellular resolution allows for more complete histology to be obtained and more accurate diagnosis to be made. However, accurate positioning of a light beam on the sample is a significant challenge, especially when fine spacing between scan steps is desired or large, inconsistently shaped samples need to be imaged. Optical coherence tomography (OCT) is an application where accurate positioning systems are required to reap the full benefit of the technology. By simultaneously manipulating the light beam position and sample location, a 3D image is reconstructed from a series of depth profiles produced. To automate image acquisition, a fully integrated and synchronised system is necessary. A tissue handling and light delivery system for free-space optical devices is described. Performance characteristics such as resolution, uncertainty, and repeatability are evaluated for novel hardware configurations of OCT. Typical scanning patterns with associated synchronisation requirements are discussed.