Laser communication

(2008) Lakshmi, Kumar. 2008 International Conference on Computer and Communication Engineering. Read by researchers in: 50% Materials Science, 50% Engineering. Laser communication links in space are attractive alternatives to present-day microwave links. This ...

This paper analyses the possibility of exploiting a small spacecrafts constellation around Mars to ensure a complete and continuous coverage of the planet, for the purpose of supporting future human and robotic operations and taking advantage of optical transmission techniques. The study foresees such a communications mission to be implemented at least after 2020 and a high data-rate requirement is imposed for the return of huge scientific data from massive robotic exploration or to allow video transmissions from a possible human outpost.In addition, the set-up of a communication constellation around Mars would give the opportunity of exploiting this multi-platform infrastructure to perform network science, that would largely increase our knowledge of the planet.The paper covers all technical aspects of a feasibility study performed for the primary communications mission. Results are presented for the system trade-offs, including communication architecture, constellation configuration and transfer strategy, and the mission analysis optimization, performed through the application of a multi-objective genetic algorithm to two models of increasing difficulty for the low-thrust trajectory definition.The resulting communication architecture is quite complex and includes six 530 kg spacecrafts on two different orbital planes, plus one redundant unit per plane, that ensure complete coverage of the planet’s surface; communications between the satellites and Earth are achieved through optical links, that allow lower mass and power consumption with respect to traditional radio-frequency technology, while inter-satellite links and spacecrafts-to-Mars connections are ensured by radio transmissions. The resulting data-rates for Earth–Mars uplink and downlink, satellite-to-satellite and satellite-to-surface are respectively 13.7 Mbps, 10.2 Mbps, 4.8 Mbps and 4.3 Mbps, in worst-case.Two electric propulsion modules are foreseen, to be placed on a C3∼0 escape orbit with two Zenith Sea Launch rockets in March 2021 and carrying four satellites each. After the entrance in Mars sphere of influence, the single spacecrafts separate and spiral-down with Hall effect thrusters until they reach the final operational orbits in April 2025, at 17,030 km of altitude and 37 deg of inclination. The preliminary design includes 105 kg and 577 W of mass and power margin for each satellite, that can be allocated for scientific payloads.The main challenges of the proposed design are represented by the optical technology development and the connected strict pointing constraints satisfaction, as well as by the Martian constellation operations management.This mission study has therefore shown the possibility of deploying an effective communication infrastructure in Mars orbit employing a small amount of the resources needed for the human exploration programme, additionally providing the chance of performing important scientific research either from orbit or with a network of small rovers carried on-board and deployed on the surface.

Free-space laser communication has been demonstrated with application potential in many areas such as line-of-sight communications, satellite communications and the last mile solution in a fiber optics networking. Both 0.8 and 1.5 micron wavelengths are currently used in state-of-the-art free space laser communication systems; unfortunately the system performance is imposed by atmospheric turbulence. To reduce the atmospheric effect in free-space laser communication systems, several techniques have been used, such as adaptive optics, aperture averaging and multiple transmitters; however, significant improvement has not been achieved. Theoretically, the seeing effect may be released using a longer wavelength. In this paper, we present a 3.5 micron free-space laser communication system model and its system performance evaluation. A 3.5 micron propagation model based on MODTRAN simulation results in different weather patterns is presented first, and a propagation link budget system model is described after that. The propagation channel performance evaluation results are presented by means of bit error rate versus various propagation distances.

Laser communications systems offer a significant advantage over traditional radio frequency systems due to the shorter wavelength of laser light. Data can be sent at higher rates for less power with proportionally smaller transmitters and receivers. A laser communications system has never been demonstrated in a moon to Earth link at MBps data rates This paper presents a model of a laser downlink from the moon, developed to rapidly explore various system architectures. Modeling and analysis shows that the target data rates of above 2 Mb/s are possible with 300 mW of transmitter power using a 3.5 mm aperture, a 1.5 m receiver diameter and a minimum gimbal resolution (maximum step size) of 78 μrad. 19.89 Mb/s data rates are possible using a 1 cm transmit aperture but with a much stricter minimum gimbal resolution (maximum step size) of 27 μrad.

The optical communication arena has perceived a surge in its usage and promising future recently. In this tempest for excellence, getting a versatile and efficient mode of optical transmission is inevitable. Following this, our idea contributes a vital stride forward by proposing a new modulation technique based on the polarizers' intricate working. Due to their complicated quantum results of the three-polarizer paradox, Polarizers are still unique in their practical usage in different fields.

The new scheme uses the source's optical intensity and wavelength as the varying parameter for message data encoding, which can also be termed the merger of the amplitude modulation and the chromatic shifting, accomplished by Polarizer's specific orientation and externally modulating it. The rotation of the Polarizers into known orientation yields an inexorably predicted intensity backed by Physics equations. The output into quantized intensity levels serves our purpose of communication, where we try to translate the binary values into Optical intensity levels essential for communication. The study includes the requirements and performance of different components essential for transmission and reception.

Moreover, it is compatible with the conventional optical sources in the visible region, such as LASER or LED. Implementing further advancements in the field of encoding techniques can increase the efficiency of transmission significantly, as well. The Graphical interface backs the modulation scheme for user-friendliness along with the numerous transmission options it provides. We proceed further to detailed applicability of the photoelectric effect and design an Optical Intensity receiver using LDR on the receiver side, enabling proper decoding of the transmitted message.

The development of a high data-rate communications electronic subsystem for future application in free-space, direct-detection laser communications is described. The dual channel subsystem uses quaternary pulse position modulation (GPPM) and operates at a throughput of 650 megabits per second. Transmitting functions described include source data multiplexing, channel data multiplexing, and QPPM symbol encoding. Implementation of a prototype version in discrete gallium arsenide logic, radiofrequency components, and microstrip circuitry is presented.

An introductory paper to laser communications technology along with their pros and cons and the challenges they will face while deployed on a ship. Their ground to space and intersatellite usage is also covered. Finally, experimental results that have taken place in US are presented.

This paper shows the impact of atmospheric turbulence-induced fading on the symbol decision position in the on-off keying (OOK) and the binary phase shift keying (BPSK) subcarrier intensity modulated (SIM) laser communication link. Weak turbulence is simulated in the laboratory using a chamber equipped with heating elements and fans. We have shown that in atmospheric turbulence, it is advantageous to employ modulation schemes such as pulse time and subcarrier intensity modulations that do not directly impress data on the optical irradiance as is the case with the OOK. For the OOK-modulated laser communication system, atmospheric turbulence imposes complexity on the symbol decision subsystem and by extension places a limit on the achievable bit error rate (BER) performance.

The advantages of laser communications including high bandwidth, resistance to jamming and secure links have made it a key technology for current and future C4ISR capabilities. Laser Communications between space/air/ground/sea-based assets may require multiple links. One advantage of this redundancy is that the signal is more likely to reach the intended receiver even if the environmental conditions are poor for

Abstract-Mobile free-space Laser communications is the next frontier for net-centric connectivity, as bandwidth, spectrum and security issues drive its adoption as an adjunct to RF communications. However, key technology challenges must be addressed and mission ...

Several NASA missions, like LISA, Lator, Maxim, any Grace follow-on mission, and others, utilize laser interferometer to measure changes in distances between the various spacecraft. These laser interferometers are usually interferometers with substantial arm length differences and require sophisticated phase measurement capabilities to reach their limit which is often set by shot noise or laser frequency noise. In many cases the measurement system is also required to synchronize and stabilize the clocks on each S/C and perform ranging measurements to retrieve the absolute distance between the S/C. In addition to this, the S/C also need to communicate directly with each other to exchange status information or exchange other data. Each of these tasks can usually be performed by customized individual systems, but it is much more desirable to combine all these tasks with the main interferometry to reduce mass and energy consumption. Such a multi-task system has to show that its various ...

Pulse position modulation (PPM) provides a means of using high peak power lasers for transmitting communications signals from planetary spacecraft to earth-based receiving stations. Large aperture (approximately 10 m diameter) telescopes will be used to collect and focus the laser communications signal originating from a deep space transmitter on to a PPM receiver. Large area (1 - 3 mm diameter)

This paper presents an experimental free space optical (FSO) communication system combined with a redundant radio frequency (RF) communication link that provides high availability and continuous communication even in adverse weather conditions. The experimental hybrid ...

Weyl’s Gauge Principle of 1929 has been used to show that a five-dimensional gauge field wherein the fifth dimension is conserved in the same mathematical sense as the conservation of mass embeds a four-dimensional hyper surface into the five dimensional manifold. The equations specifying the geometry of the embedded hyper surface are similar in form to Einstein’s field equations of his General Theory of Relativity. These field equations become Einstein’s field equations when one takes the fifth dimension to be mass density. This means the predictions of Einstein’s General Theory may be achieved in two different ways. One by using Einstein’s method and the other by using a five dimensional manifold of space, time and mass density while restricting mass to be conserved. The five dimensional gauge fields associated with these phenomena are converted into a four dimensional curved hyper surface by the conservation of mass. The mathematical equivalence of the two methods provides the ju...

We present an overview of an air-to-ground laser communications demonstration performed at MIT Lincoln Laboratory. Error-free communication at 2.5 Gb/s was demonstrated along a 25-km slant path between a 1-in transmit aperture on an aircraft at 12 kft altitude and ground terminal with 4 separate 1-cm receivers. Power fluctuations from turbulence-induced scintillation are mitigated in the spatial domain by use

Optical communication has become the order of the day due to its very high bandwidth, low noise and reduced number of repeaters. Optical communication systems use an optical fiber to carry the modulated light from one point to other. In other words the optical fibers only replace the electrical wires. In addition, optical computer solves the problem of slowness and heat buildup associated with electronic computers. The present global research aims at fibreless optical communication, something similar to wireless electronic communication. With the transparent medium for light propagation and clear line of sight for communication fibreless optical link is possible for terrestrial and satellite laser communication with proper beam steering system. This paper describes a beam steering technique of a propagating laser beam, which is essential for Free-Space Optical Communication (FSOC) and FSOC to Single Mode Fiber (SMF) coupling. The displacement (tilt) of the arrived laser beam is meas...