For short links (< 1200 m), fog and low clouds are the primary concerns. For longer links, scintillation, heavy rain, and snow frequently become issues. To address these issues, long-term climate data are analyzed to determine the frequency of occurrence of low visibilities and low-cloud ceilings. To estimate availability at a site of interest, adjustments to airport climate data are made to accommodate differences in altitude, geography, and the effects of the urban heat island. In sum, communication via FSL is a feasible alternative to fiber optic cable when atmospheric conditions are considered and properly analyzed.
Polarization shift keying (PolSK) is a new modulation technique, it uses the state of polarization of an electromagnetic wave carrier as the information bearing parameter. This paper describes a modulation/demodulation method based on PolSK, and a high-speed laser communication system, and verifies its feasibility through theoretical analysis and computer simulation. Studies have shown that the based on the parameters of laser polarization modulation and demodulation techniques have unique advantages, such as in anti-atmospheric interference, higher data rate and lower bit error rate, greatly improving the reliability of communication. In addition to polymorphism modulation can be achieved by this modulation method, which has a data capacity. In the future, the PolSK modulation and differential demodulation method has a broad space for development and application prospects in the space laser communications.
The technology of laser communication was concerned by great nation in the world, because of its advantage of good security, building network conveniently, large communication capacity, smallness and portable, low power consumption and the other advantages. With the achievement of micro-arc order dynamic tracking technology, in order to develop its potentials and advantages further, high-rate and long distance became the new directions of the development of the laser communication.
The technology of laser communication combined some more mature technologies of high speed optical fiber communication technology, such as front optical amplification, wavelength division multiplexing, diversity reception and the all-optical network technology, which also brought new problems into the air light coupled into optical fiber. Because of the effects of the deviation of the alignment, vibration and atmosphere, it was difficult to achieve high efficiency of air light coupled into optical fiber for tiny diameter of core of the fiber.
Thus, big diameter of core of the fiber should be chosen. As the limit of the devices, the detective area of the detector of the high speed optoelectronic detector was difficult to achieve above 100Î¼m. Therefore, its necessary to optimize the diameter of fiber core and the detective area. At the same time, in order to lighten and lessen the optical platform and void some practical problems such as the high frequency interference and the moment of the wire-wound, its necessary to estimate and solve the loss of optical docking to optimize the high efficiency and speed received system of the atmospheric laser communication.
In the paper, the high-efficiency and high-speed receiver technology of atmospheric laser communication was analyzed, which was based on ideal and atmospheric condition. For which, the received system of the atmospheric laser communication and its main parameters were discussed and the effects of the atmospheric on the laser communication with high efficiency and velocity were analyzed. Besides, the factors were also discussed, which affected the space light coupling into the fiber and fiber docking coupling and the corresponding simulation results were given. The method was proposed, which was used to solve the problems of the atmospheric laser communication, and the results of the indoor fiber docking coupling were analyzed so that it was feasible and efficient.
The experiment of the maximum coupling efficiency about the atmosphere was carried out and the effects of the atmospheric on the experimental results were discussed. Modern lasers represent a massive improvement over lasers of the past, and the technology is advancing just as quickly now as it has been for the past decade. Optical fiber has demonstrated the ability to move hundreds of terabits of information per second. In addition, lasers are able to see through dense foliage, and can allow for space communication from distances measured in millions of miles. The capabilities of modern lasers almost are like science-fiction stories, and the technology involved is still improving
Statement of the Problem
This paper aims to identify the benefits of laser communication technology. The objective of these communication projects is to service personal communication users almost everywhere on Earth. The inter-satellite links in those projects use microwave radiation as the carrier. Free-space optical communication between satellites networked together can make possible high-speed communication between different places on Earth. Some advantages of an optical communication system over a microwave communication system in free space are: (1) smaller size and weight, (2) less transmitter power, (3) larger bandwidth, and (4) higher immunity to interference.
The pointing from one satellite to another is a complicated problem due to the large distance between the satellite, the narrow beam divergence angle, and vibration of the pointing system. Such vibration of the transmitted beam in the receiver plane decreases the average received signal, which increases the bit error rate. We review: (1) the present status of satellite networks, (2) developing efforts of optical satellite communication around the world, (3) performance results of vibration effects on different kinds of optical communication satellite networks, and (4) seven approaches to overcome the problems caused by transmitter pointing vibration
This paper aims to investigate the design and the benefits of using laser communication technology. Operation from a low earth orbit (LEO) platform (e.g., the International Space Station) would allow transmission of single photons and pairs of entangled photons to ground stations and hence permit quantum communication applications such as quantum cryptography on a global scale. Integration of a source generating entangled photon pairs and single-photon detection into existing optical terminal designs is feasible. Even more, major subunits of the classical terminals such as those for pointing, acquisition, and tracking as well as those providing the required electronic, thermal, and structural backbone can be adapted so as to meet the quantum communication terminal needs.
Results and Discussion
Common uses for lasers in sensing include determining precise location information that radar and traditional sighting systems for kinetic weapons like rifles and missiles cannot provide. When using lasers with a weapon system theyre a complement to kinetic systems, explains Michael Rinn, vice president of the Boeing Co. Directed Energy Systems segment in Albuquerque, N.M. Lasers offer an advantage of cost-per-shot, precision ranging, and precision pointing, Rinn continues. From three, four, or five kilometers away a laser can focus on a moving target precisely. Radar and gun systems are nowhere near the kinds of ranges were demonstrating. Of course, lasers arent a replacement for any system, but they serve to compliment systems by providing additional information. Light detection and ranging (LIDAR) is one of the primary ways lasers can sense objects and movement. LIDAR can create images by bouncing lasers off a target.
Narrow-beam lasers enable LIDAR to detect images where other sensors could not, such as finding objects in heavy foliage or finding exact distances, heights, chemical compounds, and atmospheric composition. LIDAR not only provides this information, but also can render still images in three dimensions. Given sufficient processing power, lasers also can render moving images that look like videos. Scientists have used LIDAR to guide unmanned aerial vehicles (UAVs), including an AH-6 unmanned Little Bird light helicopter gunship, through areas with obstacles. LIDAR provides the precision necessary for autonomous piloting, a hot commodity at a time when UAVs require at least one operator.
The AH-6 is a military version of the MD 500 light helicopter. As with any advancing technology ” especially one that involves as much computation as laser technology does ” the size of laser systems has shrunk to sizes that were unimaginable when they were first introduced. Were seeing leaps and bounds in the technology, says Boeings Rinn. Sizes have gone down from racks to credit-card size; youre seeing a lot of transformation in the industry. Early-model laser systems were big, awkward, and used too much power to make them practical for vehicles. Todays lasers, however, can fit in small boxes and can be parts of UAV payloads, fixed-site perimeter-security systems, helicopters, and ground vehicles.
Laser sensing does have a weakness, when compared to other kinds of sensors. Heavy rain, really bad weather conditions, and sandstorms, cause problems for lasers, explains Boeings Rinn. Adverse weather conditions prevent laser light from reaching its target. Even heat waves can distort the laser beam and lead to inaccurate or lost data. Fortunately, there is a way around atmospheric issues with lasers. The answer to this problem is an atmospheric-compensation sensor that uses a low-power beam before correcting itself.
The now-discontinued Airborne Laser (ABL) program, for example, sent out a low-power laser before firing its powerful chemical laser. The low-power laser measured atmospheric distortion between the aircraft and its target, and used that information to calibrate the laser weapon to put the most energy possible on target. Atmospheric compensation enables the use of lasers even in harsh environments that would render uncorrected laser sensors useless. Atmospheric compensation does not allow lasers to function in particularly bad conditions, however. Atmospheric distortion happens when air currents or pollution bends light, and is the phenomenon that makes the stars at night appear to twinkle
. Lasers for communications
Fiber-optic cable has seen huge improvements in the past decade. With potential data rates that reach data rates of terabits per second, lasers can move vast quantities of data more securely than other forms of communications. Lasers are impervious to electromagnetic interference (EMI), do not emit stray signals like RF energy does, and fiber lasers are substantially lighter than copper cable. Fiber-optic cable Is lighter, faster, smaller has no EMI and doesnt cause sparks, explains John Lee, vice president of marketing at optical fiber specialist Timbercon Inc. in Lake Oswego, Ore. War fighters today have a huge appetite for data, if we dont have the type of bandwidth fiber provides we wont be giving our war fighters everything we can. Lasers also have been used in communications without optical fiber. Laser communication is a very specific application ” satellite-to-satellite, terrestrial-to-satellite, terrestrial-to-airplane ” are very high bandwidth applications that lasers can do.
Boeings Rinn says. Lasers can be used for communication without any cables to communicate from huge distances, particularly in space. This practice, called free-space optical communications, uses laser beams that travel through the air, or through outer space, instead through optical fiber, and is generating substantial industry excitement for its potential in broadband data communications. The NASA Jet Propulsion Laboratory (JPL) in Pasadena, Calif., in fact, has created its own free-space optical communications research group. More information on the NASA group is online at Free-space optical communications send lasers operating at wavelengths not visible to the human eye to receivers for high-bandwidth line-of-sight communications. The benefit of free-space optical communication over radio signals is clear.
Free-space optical communication does not experience interference from radio waves and is nearly impossible for an enemy to intercept or disrupt. Free-space optical communication is particularly applicable to inter-satellite communications because it is relatively interference-free, offers better connections than RF signals, and travels for longer ranges. Lasers provide high-bandwidth communications links between satellites, deep-space probes, and orbiting telescopes using lasers, lenses, and mirrors, these connections allow for fast communication with receivers and transmitters. Some space-based free-space optical communications links operate reliably millions of miles apart.
Inter-satellite communications links can send and receive data that are exponentially larger than RF signals can provide, while using less power. NASAs own project, the Laser Communications Relay Demonstration, seeks to prove the long-term viability of free-space optical communication and increase current inter-satellite data rates by as much as a hundred times greater than current RF communication allows. The Laser Communications Relay Demonstration will be holding preliminary design review in 2013, with ground testing starting in 2014. The project will then fly as a commercial satellite payload in 2016.
Future laser technology
Laser technology has yet to mature, and many enhancements are left to be made. Everything lasers can do currently is still improving at a rapid rate and new techniques to improve lasers are still in the works. One such new technique is beam combining, which blends several laser streams into one high-power beam. There are a lot of people chasing combining laser beams, says Boeings Rinn. Theres a lot of research and technology growth going on there. Researchers are taking three approaches to combine laser beams: spectral beam combining, coherent beam combining and polarization beam combining. Each approach has its own uses, benefits, and downsides. The goal of beam combining is to increase laser power and brightness to enable long-distance communications and laser weapons.
Beam combining techniques
Polarization beam combining blends two linearly polarized laser beams ” one vertically polarized and the other horizontally polarized. These beams move to a thin-film polarizer so that one is reflected and the other transmitted, forcing both beams to propagate in the same direction. This creates an unpolarized beam with almost the same optical power as the two input beams combined, and with the same beam quality. Brightness similarly increases. Polarized beam combining does not scale power, however, because the unpolarized output cannot go through the same process. It is expected that beam-combined laser systems will in the near future reach output power levels of tens to hundreds of kilowatts, Paschotta says. Possible applications of such systems are in the military sector in the context of anti-missile and other directed energy laser weapons. There are also possibilities for long-distance free-space optical communication and laser-based manufacturing.
In the free-space laser communication there is sometimes a strong need for reduction of the diffraction spot size in the far field. In this paper, instead of the usage of the larger size aperture lens in the free-space laser communication system, we introduce diffractive superresolution technology to design and fabricate a cheap pure-phase plate for realizing the smaller spot size than the usual Airy spot size, which can decrease the weight and size of the emitting lens. We have calculated 2, 3, 4, 5 circulation zones for optimizing the highest energy compression (Strehl ratio) with the constraint of the First zero ratio value G=0.8.
Numerical results show that the 2- or 3-circular zone pure-phase plate can yield the highest Strehl ratio (Sâ‰ˆ0.59) with the constraint of G=0.8, but the 4, 5 circular zone binary phase (0,Ï€) plates are calculated to yield the result ofSâ‰ˆ0.57 with G=0.8. We have fabricated 2- and 3-circular zone binary phase plate with binary optics technology. Finally, we have established an experimental system for simulation of the free-space laser communication to verify the advantage of the superresolution phase plate. Detailed experiments are presented. Factories use sensors to guarantee product quality. The advent of cell phones and constant communications with satellites has raised demands for better communications. The transoceanic fiber cables that sit at the bottom of the ocean, coupled with data demands that almost double yearly thanks to the explosion of streaming video has also led to more and more research being performed on optimizing optical communications and optics in general.
Foremost, I would like to express my sincere gratitude to my Teacher Madam Marlita delos Santos for the continuous support of my study, for his patience, motivation, enthusiasm, and immense knowledge. His guidance helped me in all the time.I could not have imagined having a better advisor and mentor for my study.
Besides my Teacher, I would like to thank the rest of my teachers in Lope de Vega National High School for their encouragement, insightful comments, and hard questions.
My sincere thanks also goes to my parent for their support and undying love to me so I can finish the secondary learning and I may able to achieve my dreams and ambitions.
I thank my fellow Classmates, school mates, and friends for the stimulating discussions, for the sleepless nights we were working together before deadlines, and for all the fun we have had in the last four years.
Last but not the least; I would like to thank God for his Guidance and Love for me and the World.
1. Journal of Optical Networking, Vol. 4, Issue 9, pp. 549-560 (2005) 2. http://dx.doi.org/10.1364/JON.4.00
3. http://www.opticsinfobase.org/jocn/abstract.cfm?URI=jon-4-9-5490549 4. http://lasers.jpl.nasa.gov.
5. M. Pfennigbauer, M. Aspelmeyer, W. Leeb, G. Baister, T. Dreischer, T. Jennewein, G. Neckamm, J. Perdigues, H. Weinfurter, and A. Zeilinger, Satellite-based quantum communication terminal employing state-of-the-art technology, J. Opt. Netw. 4, 549-560 (2005)