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Space to Ground Optical Power Transmission
Abstract
Based on the fact that energy can be transmitted using photons, light sources such as lasers can be used to transport power. Solar radiation is thus a promising means of satisfying future energy demands. Space Power Satellites (SPSs) were demonstrated forty years ago, but only recently has this approach become feasible. A fully optical SPS eliminates the need for heavy, low efficiency photovoltaic cells as the first stage, so more energy can be obtained using very small and light structures. In this paper, the design of an SPS system is investigated. In addition, the effect of the turbulent atmospheric channel is examined.
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Lasers with high peak power pulses are commonly used in spaceflight missions for a wide range of applications, from LIDAR systems to optical communications. Due to the high optical power needed, the laser has to be located on the exterior of the satellite or coupled through a series of free space optics. This presents challenges for thermal management, radiation resistance, and mechanical design. Future applications will require multiple lasers located close together, which further complicates the design. Coupling the laser energy into a fiber optic cable allows the laser to be relocated to a more favorable position on the spacecraft. Typical fiber optic termination procedures are not sufficient for injection of these high-power laser pulses without catastrophic damage to the fiber endface. In the current study, we will review the causes of fiber damage during high-power injection and discuss our new manufacturing procedures that overcome these issues to permit fiber use with high reliability in these applications. We will also discuss the proper methods for launching the laser pulses into the fiber to avoid damage and how this is being implemented for current spaceflight missions.
The Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) is an international research initiative developed in response to the world-wide concern about the fate of tropical rain forest and about the global implications of the changes, which the Amazon region has been undergoing. As part of LBA, a full suite of aerosol, gas and meteorological measurements have been carried out near Manaus at Balbina. This report details the measurements of sub-micrometer aerosol particle size distributions and hygroscopic growth.
1] The number-size distribution and hygroscopic growth of submicrometer aerosol particles were measured in central Amazonia during the first Cooperative LBA Airborne Regional Experiment (CLAIRE) wet season experiment in March–April 1998. This was the first time ever that these types of measurements were performed in the Amazon rain forest. A Differential Mobility Particle Sizer (DMPS) was used to measure aerosol number-size distribution with diameters in the range 3–850 nm. The observed total number concentrations were frequently between 300 and 600 cm À3 with a mean value around 450 cm À3 . Two aerosol particle modes (Aitken and accumulation mode) were always present. The average particle concentrations for those two modes were 239 and 177 cm À3 , with geometric diameters of 68 and 151 nm, respectively. An ultrafine mode had a number concentration and a mean diameter of 92 cm À3 and 24 nm, respectively, and only occurred at 18% of the time, causing the size distribution to be trimodal instead of bimodal. The hygroscopic growth of aerosol particles was measured in situ with a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) at six dry particle diameters between 35 and 265 nm. In contrast to the bimodal hygroscopic behavior found in polluted continental environments, the hygroscopic properties of aerosol particles in the Amazon rain forest is essentially unimodal with average diameter growth factors of 1.16– 1.32 from dry to 90% relative humidity (RH). Aerosol soluble volume fractions were, in general, between 0.14 and 0.27, estimated by assuming that only ammonium hydrogen sulphate interacted with water vapour. aerosol particle size distribution and hygroscopic growth measured in the Amazon rain forest during the wet season, J. Geophys. Res., 107(D20), 8055, doi:10.1029/2000JD000203, 2002.
The main drawback of photovoltaic (PV) laser power converters based on GaAs material is the low output voltage, which is often insufficient to power electronic circuits directly. Aside from the use of a dc-dc converter in combination with a single PV converter, it is possible to boost the voltage by the monolithic serial interconnection of several converter segments on a single chip, often called multiple converters. Another novel approach introduced in this paper is a multijunction PV cell, where several subcells of the same material are stacked onto a substrate and interconnected by interband tunnel diodes. This paper explores a tandem GaAs-GaAs converter and compares the results with a 2-V multiple PV converter under monochromatic laser illumination. In addition, 4-V multiple PV converters with maximum monochromatic efficiencies (810 nm) of up to 50.1% at 51.6 W/cm<sup>2</sup> and 6-V converters are investigated. Thereby, the fabrication technology of the devices is outlined and the influence of inhomogeneous illumination on the performance of these energy converters is discussed.
Sub-microradian level laser beam pointing to an Earth-based receiver is required for deep space optical communications. This requires a beacon emanated from Earth towards the spacecraft. The beacon could be a laser or reflected sunlight from Earth. Earth image tracking in the visible is hampered by significant albedo variations and/or crescent Earth image yielding large central errors. Here, we report results of Earth-image tracking in the infrared (8 to 13 micron) region of the spectrum with the aim of substantially alleviating the two challenges mentioned earlier.
Invented more than a hundred years ago by Alexander Graham Bell, the technology of free-space optical communications, or lasercom, has finally reached the level of maturity required to meet a growing demand for operational multi-giga-bit-per-second data rate systems communicating to and from aircrafts and satellites. Putting the emphasis on near-earth links, including air, LEO, MEO, and GEO orbits, Near-Earth Laser Communications presents a summary of important free-space laser communication subsystem challenges and discusses potential ways to overcome them. This comprehensive reference provides up-to-date information on component and subsystem technologies, fundamental limitations, and approaches to reach those limits. It covers basic concepts and state-of-the-art technologies, emphasizing device technology, implementation techniques, and system trades. The authors discuss hardware technologies and their applications, and also explore ongoing research activities and those planned for the near future. The analytical aspects of laser communication have been covered to a great extent in several books. However, a detailed approach to system design and development, including trades on subsystem choices and implications of the hardware selection for satellite and aircraft telecommunications, is missing. Highlighting key design variations and critical differences between them, this book distills decades’ worth of experience into a practical resource on hardware technologies.
During the last years a new laser beam scanning system for heat treatment of metals with high power diode lasers was developed. The new external scanning optics is an optional tool, that can be used with common standard high power diode lasers (focal distance ≥ 300 mm). It works with high power diode lasers in the multi-kilowatt range up to 5 kilowatt laser power. The new system opens the door to a wide field of applications, that were not possible before. Heat treatment of metal surfaces with a track width of more than 50 mm at once is one of the capabilities.
Furthermore different approaches were gone to make the handling of the system more easier for the user. Real-time temperature control with cycle times in the range of microseconds ensures a reproducible hardening result even for complex 3D-shaped parts with difficult heat flow conditions. The latest status of the developments and examples are presented.
This book is intended for research scientists, engineers and students with an interest in the topic of free-space laser communications. It is intended as an all-inclusive source to serve the needs of those who require information about both basic concepts, as well as up-to-date advanced knowledge of the state-of-the-art in the technologies available today. This is the first book which provides in a comprehensive and tutorial manner, the fundamental principles and advances of free-space laser communications. Topics addressed include: atmospheric channel effects including available models, system design and performance, laser transmitter/ receiver designs for high performance photon-efficient systems, adaptive optics technology for atmospheric compensation, optical networks, coding techniques, and long wavelength free-space optical communications.
There are 71 chapters in the book and authors from Australia, Brazil, Canada, China, Hong Kong, Japan, Mexico, Taiwan and the United States. The chapters are arranged under seven sections, which include General Topics in Food Science and Technology; Food Processing and Engineering; Antioxidants in Foods; Nutrition and Food Science; Food Safety; Sensory Science of Foods; and Food Biotechnology. Many of the chapters are exceptional in the quality and depth of science and state-of-the-art instrumentation and techniques used in the experimentation. There is literally a gold mine of new information available in this book, not only for healthful foods for the Pacific Rim but for many other areas as well.
Base stations of the cellular system increase according to the increase of subscribers and transmission bit rate. Most of the places suitable for the base station were occupied by the existing systems. Therefore, sometimes, new base station must be installed at the places where power supply or transmission cable is not available. The proposed feeder system is applicable for such case. The RF signals are fed to the repeater through the air by optical beams. And electrical power is fed by the optical beam, too. This paper describes the design principle and experimental results of the proposed system. By using 4 cm diameter optical beams for RF transmission and 26cm diameter beam for power transmission, available forward link RF power at the repeater station is 10mW in the case that the distance between the base station and the repeater station is 40 m. If 48 cm diameter reflector is used for power transmission, 100 mW RF power will be available for the forward link.
Prospects of creation of components on new type fibers - photonic crystal fibers, possible areas of their application are considered. Comparative analysis PCF and standard quartz fibers is lead. Advantages and lacks of use PCF in electronic technique are allocated. The signal attenuation caused by a difference of connected fibers modes fields was estimated.
Abstract Wireless power,transmission,is an underdeveloped,field of study. There are many promising,applications for the ability to transport powerover,great distances and boundaries,without the need,for transmission,lines. Current technology,employs the use of microwaves,because,of the economic,and energy,efficiency that can be leveraged,by products already in production. There is some effort to develop new technology,that would accommodate,propagation,by electromagnetic waves in and around,the visual light spectrum; however,those technologies,are just emerging.
Based on analyzing the infrared laser transmitting characteristics in the atmosphere, the relationship between the atmospheric aerosol particles and the infrared laser is analyzed. Using Mie scatering theory, the scattering efficiency factor and the scattering phase function of atmospheric aerosol particles are simulated and calculated.At the same time, the scattering coefficient, forward scattering ratio and backward scattering ratio of atmospheric aerosol particles can be deduced. According to the simulation results, the scattering efficiency factor and the scattering phase function of atmospheric aerosol particles are calculated. The result proves that, as the radiuses increase, the scattering efficiency factor's swing of the atmospheric aerosol particles oscillates and decreases gradually, then approaches to 1.9. From the results of scattering phase function, it can find that the scattering of atmospheric aerosol particles is mainly a forward scattering. Therefore, by analyzing the scattering coefficient, forward scattering ratio and backward scattering ratio of atmospheric aerosol particles, it can prove the feasibility of correcting the aerosol particles' affect for the infrared laser transmitting characteristics in the atmosphere.
Wireless optical links are being increasingly deployed in a variety of indoor and outdoor applications. While it is known that fog and clouds produce the highest attenuation values on optical waves travelling through the Earth's atmosphere, it is shown here that other particulates as rain and snow might have a non-negligible effect, depending on the local climatology and on the quality of service requirements.
We highlight an electronic textbook available free of charge in PDF format at optics.byu.edu. The target audience is upper-division physics undergraduates.
Space-based solar power (SSP) generation is being touted as a solution to our ever-increasing energy consumption and dependence on fossil fuels. Satellites in Earth's orbit can capture solar energy through photovoltaic cells and transmit that power to ground based stations. Solar cells in orbit are not hindered by weather, clouds, or night. The energy generated by this process is clean and pollution-free. Although the concept of space-based solar power was initially proposed nearly 40 years ago, the level of technology in photovoltaics, power transmission, materials, and efficient satellite design has finally reached a level of maturity that makes solar power from space a feasible prospect. Furthermore, new strategies in methods for solar energy acquisition and transmission can lead to simplifications in design, reductions in cost and reduced risk. This paper proposes using a distributed array of small satellites to collect power from the Sun, as compared to the more traditional SSP design that consists of one monolithic satellite. This concept mitigates some of SSP's most troublesome historic constraints, such as the requirement for heavy lift launch vehicles and the need for significant assembly in space. Instead, a larger number of smaller satellites designed to collect solar energy are launched independently. A high frequency beam will be used to aggregate collected power into a series of transmission antennas, which beam the energy to Earth's surface at a lower frequency. Due to the smaller power expectations of each satellite and the relatively short distance of travel from low earth orbit, such satellites can be designed with smaller arrays. The inter-satellite rectenna devices can also be smaller and lighter in weight. Our paper suggests how SSP satellites can be designed small enough to fit within ESPA standards and therefore use rideshare to achieve orbit. Alternatively, larger versions could be launched on Falcon 9s or on Falcon 1s with booster stages. The only satellites that are constrained to a significant mass are the beam-down satellites, which still require significant transmission arrays to sufficiently focus the beams targeting corresponding ground stations. With robust design and inherent redundancy built-in, power generation and transmission will not be interrupted in the event of mishaps like space debris collision. Furthermore, the "plug and play" nature of this system significantly reduces the cost, complexity, and risk of upgrading the system. The distributed nature of smallsat clusters maximizes the use of economies of scale. This approach retains some problems of older designs and introduces additional ones. Mitigations will be explored further. For example, the distributed nature of the system requires very precise coordination between and among satellites and a mature attitude control and determination system. Such a design incorporates multiple beaming stages, which has the potential to reduce overall system efficiency. Although this design eliminates the need for space assembly, it retains the challenge of significant on-orbit deployment of solar and transmission arrays. Space power "beaming" is a three step process that involves: 1) conversion of dc power generated by solar cells on the satellite into an electromagnetic wave of suitable frequency, 2) transmission of that wave to power stations on ground, and 3) conversion of the radio waves back into dc power. A great deal of research has been done on the use of microwaves for this purpose. Various factors that affect efficient power generation and transmission will be analyzed in this paper. Based on relevant theory and performance and optimization models, the paper proposes solutions that will help make space-based solar power generation a practical and viable option for addressing the world's growing energy needs.
As lasers and photonic devices and systems become more important in electrical and information technologies, there is definitely a need to introduce this subject into the undergraduate curriculum of electrical engineering students as early as possible. Since most of the laser and electro-optical devices require extensive background in optics, this presents a problem for the electrical engineering textbook. Fundamental optics is not taught in the traditional electrical engineering curriculum. Many laser and electro-optic courses review some basic electromagnetic theory and move right into laser theory and device principles. Students often struggle to fill in the elementary optics background that is needed. This book is written to fill the gap in optics in standard laser textbooks by systematically presenting the relevant topics in optics that are important for laser science and devices.
The book covers optics quite well, probably because of the fact that the earlier version of the text had the title `Optics'. From geometric optics to wave optics, interference to diffraction, basic theory to optical instruments, and polarization to coherence, the authors give a balanced discussion of optical phenomena and their mathematical formulation. The mathematics has been kept at an elementary level.
The modern parts that include lasers and various photonic and electro-optic devices are a bit too sketchy in comparison with the optics part (chapters 1 to 14). Descriptions of laser systems, nonlinear optics, fiber amplifiers and ultrashort pulse lasers, to name just a few, are either too brief or totally lacking.
Color photographs are excellent features throughout the book. Solutions to numerical examples and problems will definitely help students using the book for self-study.
In conclusion, this is a self-contained book for an undergraduate text on lasers and photonics that does not require instructors and/or students to search for supplemental topics in optics.
Chi H Lee
Cellular wireless networks have consistently relied upon Radio Frequency (RF) channels to provide connectivity between users and base stations. RF channels have also provided, in large part, connectivity within the Radio Access Network (RAN) and the Core Network (CN) for the purpose of connecting mobile users to the Public Switched Telephone Networks (PSTN) and Internet. However, other methods may be necessary in order to provide the faster data rates required by many new and emerging applications. This paper provides a comprehensive overview of the potential role for Free Space Optical (FSO) communications within next generation cellular networks. The argument is made that the increasing number of base stations, as well as the advanced topologies supported by next generation cellular networks, pave the way for a growing reliance upon FSO communications, with a view to support the high bandwidth applications offered to mobile users.
The use of wireless power transmission in Space Solar Power (SSP) activities creates significant policy issues regarding the beam right-of-way. There will not be a single beam, there may well be hundreds of beams for economical systems. Are some or all of these power beams to be afforded priorities of space for unobstructed power delivery, or must the beaming systems be designed to be capable of detecting any and all potential beam interceptions and appropriately responding? The repeated interruptions for guaranteed safety of transit for freely moving air and space traffic are of great consequence. The safety issues are critical, but the implications for equipment transient protection, energy storage system costs and the quality of power delivery service are also significant for wireless power transmission economics. A scenario of precursor wireless power transmission developments leading up to and including SSP applications will be used to frame and to discuss the beamed power technology implications and policy issues.
The optical coherent wave propagation is affected by the atmosphere in many ways. Several theoretical models for propagation of light through the atmosphere are well known. To predict link availability in different climate zones it is necessary to do field tests for data acquisition. Therefore reliability- and availability-tests on free space optics (FSO)-systems have been done at the Department of Communications and Wave Propagation (by the research-group "OptiKom"). There have been obtained evaluation results for commercial available and also for self-developed optical point-to-point and point-to-multipoint FSO-systems. Test data at 155 Mbps (STM-1) were transmitted from one FSO-unit to a distant (2.7 km) FSO-unit. The received data were sent back (loop) to the first unit. The primary interest in this long-time investigation was the time of link failure, because it turned out that BERs be low in general, less than 10<sup>-8</sup> at very bad weather conditions in winter and less than 10<sup>-12</sup> at clear sky. In a second measurement campaign the influence of turbulences in the air was investigated. The measurements clearly show variations in the fluctuation of the incoming optical power during a day. In principle there are two periods with strong variations, during the day and during the night, and two periods of rather stable air, these are around sunset and sunrise. The power variations have the highest amplitude and show the fastest changes at noon and they are less distinct and show slower changes in the night. As a medium value power variations of 4 dB over the distance of 2.7 km were measured in summer. The duration of fades/scintillations was in the order of 4 to 60 milliseconds at daytime and about 10 to 150 ms in the night.
In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received light signal, impairing link performance. We describe several communication techniques to mitigate turbulence-induced intensity fluctuations, i.e., signal fading. These techniques are applicable in the regime in which the receiver aperture is smaller than the correlation length of fading and the observation interval is shorter than the correlation time of fading. We assume that the receiver has no knowledge of the instantaneous fading state. When the receiver knows only the marginal statistics of the fading, a symbol-by-symbol ML detector can be used to improve detection performance. If the receiver has knowledge of the joint temporal statistics of the fading, maximum-likelihood sequence detection (MLSD) can be employed, yielding a further performance improvement, but at the cost of very high complexity. Spatial diversity reception with multiple receivers can also be used to overcome turbulence-induced fading. We describe the use of ML detection in spatial diversity reception to reduce the diversity gain penalty caused by correlation between the fading at different receivers.
Refractive Index of Atmospheric Aerosols
- M Jonasz
M. Jonasz, Refractive Index of Atmospheric Aerosols, http://www.tpdsci.com/tpc/RIAtmAer.php, 2006.
Free Space Laser Communications: Principles and Advances
Field Guide to Atmospheric Optics