Laser communication with aliens. Laser communication systems

This week the results of a kind of lunar moon became known. laser communication. The test took place over 30 days under difficult conditions due to lunar dust. There was a special conductor who is located in this moment within the lunar orbit. This test showed that the communication system is fully operational despite the distance. It communicates as successfully as any radio signal from NASA.

This technology demonstrates the practical use of broadband lasers for interconnection and communications. This connection, or rather its loading, is performed much faster than a similar radio communication. This method allows you to receive a signal on Earth at a speed of 622 Mbit and send with 20 Mbit. This speed was recorded on October 20. It was transmitted from the Moon to Earth using a pulsed laser beam. This signal was received by a station in New Mexico, which is part of collaboration USA and Spain.

Lasers have big advantage in front of radio signals. They are the ones who have the greatest throughput. It is also important to transmit data using a specific coherent beam. This contributes to less energy consumption when transmitting signals over long distances.

Researchers at NASA claim that the program's test passed with great success. They did not expect this kind of results. The laser message was received and transmitted back into orbit even in the most difficult conditions. This confirms the theory that no matter what interference there is, the signal will arrive on Earth. Neither cosmic dust nor distance is an obstacle to the laser signal. Even at moments when the atmospheric layer increased, signal transmission was carried out without special problems, which indicates efficiency of this device. There was no trace of mistrust among the skeptics at NASA when even clouds did not become an obstacle to signal transmission.

Surprisingly, there was not a single error in the signal. The procedure is reminiscent of communication mobile phone. Moreover, it works without human intervention. The system can even lock itself when for a long time There is no signal coming from ground stations.

Laser data transmission systems are designed to organize one-way and duplex communication between objects within line of sight.
Free Space Optics - FSO technology, which includes atmospheric optical communication (AOLC) and wireless optical communication channel (BOX) is a way wireless transmission information in the short-wave part of the electromagnetic spectrum. It is based on the principle of transfer digital signal through the atmosphere (or outer space) by modulating radiation (infrared or visible) and its subsequent detection by an optical photodetector.
Current state of wireless optical communications allows you to create reliable communication channels at distances from 100 to 1500-2000 m in the atmosphere and up to 100,000 km in outer space, for example, for communication between satellites. Being alternative solution In relation to optical fiber, atmospheric optical data transmission lines (AODL) allow you to quickly create a wireless optical communication channel.

1. Atmospheric optical communication link

The rapid development of the telecommunications market requires high-speed data transmission lines. However, the gasket optical fiber implies a substantial investment, and in principle is not always possible.
A natural alternative in this case is microwave wireless communication lines, but the problem of quickly obtaining frequency permissions sharply limits the prospects for their use, especially in large cities.
Another way wireless communication are optical communication lines (laser or optical communication) using a point-to-point topology or point-to-multipoint access mode. Optical communication is carried out by transmitting information using electromagnetic waves optical range. An example of optical communication is the transmission of messages used in the past using bonfires or semaphore alphabet. In the 60s of the 20th century, lasers were created and it became possible to build broadband optical communication systems. The first atmospheric communication line (ALC) in Moscow appeared in the late 60s: it was launched phone line between the Moscow State University building on the Lenin Hills and Zubovskaya Square with a length of more than 5 km. Quality transmitted signal fully complied with the standards. In those same years, experiments with ALS were carried out in Leningrad, Gorky, Tbilisi and Yerevan. In general, the tests were successful, but at that time experts considered that they were bad weather make laser communication unreliable, and it was considered unpromising.
The use of signals with continuous (analog) modulation, which was used in those years, led to abnormal attenuation of the optical signal due to the influence of the atmosphere.
The modern widespread use of ALS in many countries around the world began in 1998, when inexpensive semiconductor lasers with a power of 100 mW or more were created, and the use digital processing signal made it possible to avoid abnormal signal attenuation and retransmit the information packet when an error is detected.
At the same time, the need for laser communications arose, as they began to develop rapidly information Technology. The number of subscribers requiring the provision of telecommunications services such as Internet, IP telephony, cable TV With a large number channels, computer networks etc. As a result, the “last mile” problem arose (connecting a broadband communication channel to end user). Laying new cable networks requires large capital investments, and in some cases, especially in dense urban areas, is very difficult or even impossible.
The optimal solution to the problem of the last section is to use wireless lines transfers.
The advantages of wireless communication lines are obvious: they are cost-effective (no need to dig trenches to lay cables and rent land); low operating costs; high throughput and quality digital communications; fast deployment and changing the network configuration; easy overcoming of obstacles - railways, rivers, mountains, etc.
Wireless communications in the radio spectrum are limited by congestion and scarcity frequency range, insufficient secrecy, susceptibility to interference, including intentional and from adjacent channels, increased power consumption. In addition, radio communications require lengthy approval and registration with the assignment of frequencies by the State Communications Supervision Authority of the Russian Federation, rent for the channel, and mandatory certification of radio equipment by the State Commission for Radio Frequencies. The use of laser means eliminates this difficult issue. This is due to the fact that, firstly, the radiation frequency laser systems communication goes beyond the range in which coordination is necessary (in Russia), secondly, by the lack of practical possibilities for their detection and identification as means of information exchange.
Basic properties of laser systems:
almost absolute security of the channel from unauthorized access and, as a consequence, high level noise immunity and noise immunity due to the possibility of concentrating the entire signal energy in angles of fractions of arc minutes (in laser space systems communications) up to tens of degrees (fully accessible indoor communication systems);
high information capacity of channels (up to tens of Gbit/s)
there are no delays in the transmission of information (ping<1ms) как у радиолиний
the absence of pronounced unmasking signs (mainly collateral electromagnetic radiation) and the possibility of additional camouflage, which makes it possible to hide not only the transmitted information, but also the very fact of information exchange.
In addition, many experts note the biological safety of these systems, since the average radiation power density in laser systems for various purposes is approximately 3–6 times less than the irradiation created by the Sun, as well as the simplicity of the principles of their construction and operation, and the relatively low cost compared to traditional means of transmitting information for a similar purpose.
Design:
The laser communication line consists of two identical stations installed opposite each other within line of sight (Fig. 1).

Rice. 1. ALS design

The structure of all ALS stations is almost the same: interface module, modulator, laser, transmitter optical system, receiver optical system, demodulator and receiver interface module. The transmitter is an emitter based on a pulsed semiconductor laser diode (sometimes a regular LED). The receiver in most cases is based on a high-speed pin photodiode or an avalanche photodiode.
The transmitted data stream from the user equipment goes to the interface module and then to the emitter modulator. The signal is then converted by a highly efficient injection laser into infrared optical radiation, collimated by optics into a narrow beam and transmitted through the atmosphere to the receiver. At the opposite point, the received optical radiation is focused by a receiving lens onto the site of a highly sensitive high-speed photodetector (avalanche or pin photodiodes), where it is detected. After further amplification and processing, the signal is sent to the receiver interface, and from there to the user equipment. Similarly, in duplex mode, counter data flow occurs simultaneously and independently.
Since the laser beam is transmitted between communication points in the atmosphere, its distribution is highly dependent on weather conditions, the presence of smoke, dust and other air pollutants. However, despite these problems, atmospheric laser communication has proven to be quite reliable over distances of several kilometers and is especially promising for solving the “last mile” problem.
Let's consider the influence of the atmosphere on the quality of wireless infrared communications. The propagation of laser radiation in the atmosphere is accompanied by a number of phenomena of linear and nonlinear interaction of light with the medium. Based on purely qualitative characteristics, these phenomena can be divided into three main groups:
1. absorption (direct interaction of a photon beam with atmospheric molecules);
2. scattering by aerosols (dust, rain, snow, fog);
3. fluctuations of radiation due to atmospheric turbulence.

Laser beam communication through the atmosphere has now become a reality. It ensures the transmission of a large amount of information with high reliability over distances of up to 5 km and solves many difficult problems. Therefore, interest in this type of communication has recently increased.

¹Fluctuations (from Latin fluctuatio - fluctuation), random deviations of physical quantities from their average values.
²Internet source: http://laseritc.ru/?id=93

2. Wireless optical communication channel

Wireless optical communication channel (BOX) is a device that transmits data through the atmosphere. It is designed to create a data transmission channel of the Ethernet standard. BOXING consists of two identical transceivers (optical pipes) installed on both sides of the communication channel. Each unit consists of a transceiver module, a visor, an interface cable (5 m long), a guidance system, a bracket, a power supply and an access unit.
The transceiver module includes a transmitter of highly directional optical radiation in the IR range (consisting of an infrared semiconductor LED) and a receiver - a highly sensitive LED. LEDs operate at a wavelength of 0.87 microns. Several examples of domestic manufacturers of BOX systems and their characteristics are described in Table 1.
Table 1. Devices for creating optical communication channels

Figure 2 clearly shows BOX-10M.

Rice. 2. BOX-10M

Principle of operation:
Let's consider the process of data transmission using an optical channel (Fig. 3). The electrical signal from the Ethernet port travels through the interface cable to the transmitter, where the LED converts it into IR radiation, which passes through the beam splitter and is focused by the lens into a narrow beam. Having passed through the atmosphere, part of the radiation hits the lens of another transceiver, is focused and sent to the receiver by a beam splitter. The receiver converts IR radiation into an electrical signal, which is sent via an interface cable to the Ethernet port. The power supply powers the transmitter, receiver, display unit and lens anti-fog/ice prevention system.

Rice. 3. General operating principle of the BOX family device.

Transmission reliability is achieved primarily through correct guidance and energy reserves. With correct aiming, the energy reserve of the system should be fourfold for the BOX-10ML and BOX-10M models (in other words, by covering 4/5 of the objective lenses, we have a reliable 100% channel in good weather). The BOX-10MPD model has a 16-fold energy reserve. In this case, the availability of the channel throughout the year will be 99.7-99.9%. The higher the energy reserve of the system, the higher the reliability of the channel, which ideally reaches 99.99%.
In addition, reliable system operation is due to the CSMA/CD media access method used in Ethernet networks. Any collision - worsening weather conditions or the appearance of a short-term obstacle leads to retransmission of the packet at the physical level, but even if it happens that the collision will not be heard (this is possible, for example, in the BOX-10ML and BOX-10M models due to the fact that that the switching time from reception to transmission is, of course, equal to 4 μs) and the packet is lost, then higher-level protocols that work with a delivery guarantee will track this incident and the request will be repeated.
A connection through the atmosphere never gives a 100% guarantee of connection, so it is possible that, for example, in bad weather conditions (heavy snowfall, very dense fog, heavy rain, etc.) the channel will not work. But in this case, the cessation of communication will be temporary, and after conditions improve, the connection will be restored on its own. To reduce the likelihood of loss of communication due to weather conditions, it is necessary to install models with a larger operating distance, which increases the energy of the light flux and, as a result, the reliability of the system as a whole.
Another condition for reliable and stable operation of the system is the coincidence of the center of the geometric spot of illumination of the transmitter with the center of the receiver lens. Wind loads, as well as mechanical and seasonal vibrations of the support can remove the system from the light spot area, as a result of which the connection will disappear. The entire design of the systems and the size of the illumination spot from the transmitter are coordinated in such a way that the likelihood of loss of communication due to the above reasons is minimized. When pointing, the following geometric problem is solved: from the point obtained during rough pointing, it is required to move the system to the geometric center of the illumination spot from the light flux of the emitter, finally fixing the pointing system in this position. Using a standard guidance system, this problem is solved in 35 iterations.
Installation:
Transceivers can be installed on roof or wall surfaces. The BOX is mounted on a metal support, which allows you to adjust the angle of inclination horizontally and vertically (Fig. 4). The transceiver is connected through a special access unit; twisted pair category 5 (UTP) is usually used as connecting cables. On the optical channel side, the access unit is connected to the transceiver by an interface cable, which uses a regular twisted pair cable equipped with special connectors. On the other hand, the access unit connects to a computer or network device (router or switch).
The access unit and the transceiver power supply are always installed indoors next to each other. They can be mounted on the wall or placed in the same racks that are used for LAN equipment.
For reliable operation, the following recommendations must be taken into account:
buildings must be within line of sight (the beam must not encounter opaque obstacles along the entire path);
it is better if the device is located as high above the ground as possible and in a hard-to-reach place;
when installing the system, you should avoid orienting the transceivers in the east-west direction (this specific requirement is explained quite simply: the sun's rays at sunrise or sunset can block the radiation for several minutes, and the transmission will stop);
There should be no motors, compressors, etc. near the mounting point, since vibration can lead to the pipe shifting and breaking the connection.

Rice. 4. Guidance system diagram

Connection types:
Figure 5 shows the possible types of BOX connections.

Rice. 5. Types of BOX connections

In various sources there are a large number of names of equipment for wireless data transmission in the infrared wavelength range. Abroad, this class of systems is usually called FSO - Free Space Optics; in the post-Soviet space, there are a number of designations for wireless optical communication systems. As a basis, you should take the abbreviation BOX - wireless optical communication channel, as reflected in the certificate of the Communication system (CCS).

Active research into microwaves began in the mid-20th century. American physicist Charles Townes decided to increase the intensity of the microwave beam. Having excited the ammonia molecules to high energy levels through heat or electrical stimulation, the scientist then passed a weak microwave beam through them. The result was a powerful microwave amplifier, which Townes called a “maser” in 1953. In 1958, Townes and Arthur Schawlow took the next step: instead of using microwaves, they tried to amplify visible light. Based on these experiments, Maiman created the first laser in 1960.

The creation of the laser made it possible to solve a wide range of problems that contributed to significant developments in science and technology. Which made it possible at the end of the 20th and beginning of the 21st centuries to obtain such developments as: fiber-optic communication lines, medical lasers, laser processing of materials (heat treatment, welding, cutting, engraving, etc.), laser guidance and target designation, laser printers, barcode readers and much more. All these inventions have greatly simplified the life of an ordinary person and allowed the development of new technical solutions.

This article will answer the following questions:

1) What is wireless laser communication? How was it accomplished?

2) What are the conditions for using laser communications in space?

3) What equipment is needed to implement laser communication?

Definition of wireless laser communication, methods of its implementation.

Wireless laser communication is a type of optical communication that uses electromagnetic waves in the optical range (light) transmitted through the atmosphere or vacuum.

Laser communication between two objects is carried out only through a point-to-point connection. The technology is based on data transmission using modulated radiation in the infrared part of the spectrum through the atmosphere. The transmitter is a powerful semiconductor laser diode. The information enters the transceiver module, in which it is encoded with various noise-resistant codes, modulated by an optical laser emitter and focused by the optical system of the transmitter into a narrow collimated laser beam and transmitted into the atmosphere.

At the receiving end, the optical system focuses the optical signal onto a highly sensitive photodiode (or avalanche photodiode), which converts the optical beam into an electrical signal. Moreover, the higher the frequency (up to 1.5 GHz), the greater the volume of transmitted information. The signal is then demodulated and converted into output interface signals.

The wavelength in most implemented systems varies between 700-950 nm or 1550 nm, depending on the laser diode used.

From the above it follows that the key instrument elements for laser communication are a semiconductor laser diode and a highly sensitive photodiode (avalanche photodiode). Let's look at the principle of their operation in a little more detail.

Laser diode is a semiconductor laser built on the basis of a diode. Its work is based on the appearance of population inversion in the region of the pn junction upon injection of charge carriers. An example of a modern laser diode is provided in Figure 1.

Avalanche photodiodes are highly sensitive semiconductor devices that convert light into an electrical signal due to the photoelectric effect. They can be considered as photodetectors that provide internal amplification through the avalanche multiplication effect. From a functional point of view, they are solid-state analogs of photomultipliers. Avalanche photodiodes have greater sensitivity compared to other semiconductor photodetectors, which allows them to be used for recording low light powers (≲ 1 nW). An example of a modern avalanche photodiode is provided in Figure 2.

Conditions for using laser communications in space.

One of the promising areas for the development of space communication systems are systems based on transmitting information via a laser channel, since these systems can provide greater throughput, with lower power consumption, overall dimensions and weight of transceiver equipment than currently used radio communication systems.

Potentially, space laser communication systems can provide extremely high speed information flow - from 10-100 Mbit/s to 1-10 Gbit/s and higher.

However, there are a number of technical problems that need to be solved in order to implement laser communication channels between the spacecraft (SC) and the Earth:

• high accuracy of guidance and mutual tracking is required at distances from half a thousand to tens of thousands of kilometers and when carriers move at cosmic speeds.
• The principles of receiving and transmitting information via a laser channel are becoming significantly more complicated.
• Optical-electronic equipment is becoming more complex: precision optics, precision mechanics, semiconductor and fiber lasers, highly sensitive receivers.

Experiments on the implementation of space laser communications

Both Russia and the United States of America are conducting experiments on the implementation of laser communication systems for transmitting large amounts of information.

RF Laser Communication System (SLS)

In 2013, the first Russian experiment was carried out to transmit information using laser systems from Earth to the Russian segment of the International Space Station (RS ISS) and back.

The SLS space experiment was carried out with the aim of testing and demonstrating Russian technology and equipment for receiving and transmitting information via a space laser communication line.

The objectives of the experiment are:

• testing, under conditions of space flight on the ISS RS, the main technological and design solutions incorporated into the standard equipment of the intersatellite laser information transmission system;
• development of technology for receiving and transmitting information using a laser communication line;
• study of the possibility and operating conditions of laser communication lines “on board the spacecraft – ground station” under different atmospheric conditions.

The experiment is planned to be carried out in two stages.

At the first stage, a system for receiving and transmitting information flows along the lines “on board the RS ISS–Earth” (3, 125, 622 Mbit/s) and “Earth–on board the RS ISS” (3 Mbit/s) is being developed.

At the second stage, it is planned to develop a high-precision guidance system and an information transmission system along the line “on board the ISS RS – relay satellite.”

The laser communication system at the first stage of the SLS experiment includes two main subsystems:

• on-board laser communication terminal (BTLS), installed on the Russian segment of the International Space Station (Figure 3);
• ground laser terminal (GLT) installed at the Arkhyz optical observation station in the North Caucasus (Figure 4).

Objects of study at stage 1 of FE:

• on-board laser communication terminal equipment (BTLN);
• ground laser communication terminal (GLT) equipment;
• atmospheric radiation propagation channel.

Figure 4. Ground laser terminal: astro pavilion with optical-mechanical unit and alignment telescope

Laser communication system (LCS) - stage 2.

The second stage of the experiment will be carried out after the successful completion of the first stage and the readiness of a specialized spacecraft of the “Luch” type on the GEO with an on-board terminal of the inter-satellite laser information transmission system. Unfortunately, information about whether the second stage was carried out or not could not be found in open sources. Perhaps the results of the experiment were classified, or the second stage was never carried out. The information transfer scheme is shown in Figure 5.

Project OPALS USA

Almost simultaneously, the American space agency NASA begins deploying the OPALS (Optical Payload for Lasercomm Science) laser system.

“OPALS represents the first experimental site for the development of laser space communications technologies, and the International Space Station will serve as a test site for OPALS,” said Michael Kokorowski, OPALS project manager and a member of NASA's Jet Propulsion Laboratory (JPL). Jet Propulsion Laboratory, JPL) - "Future laser communications systems that will be developed based on OPALS technologies will be able to exchange large volumes of information, eliminating the bottleneck that in some cases is holding back scientific research and commercial enterprises."

The OPALS system is a sealed container containing electronics connected via an optical cable to a laser transmitting and receiving device (Figure 6). This device includes a laser collimator and a tracking camera mounted on a moving platform. The OPALS installation will be sent to the ISS aboard the Dragon spacecraft, which will launch into space in December this year. Once delivered, the container and transmitter will be installed outside the station and a 90-day field testing program for the system will begin.

Operating principle of OPALS:

From Earth, specialists from the Optical Communications Telescope Laboratory will send a beam of laser light towards the space station, which will act as a beacon. The equipment of the OPALS system, having caught this signal, using special drives, will aim its transmitter at a ground-based telescope, which will serve as a receiver, and transmit a response signal. If there is no interference on the path of propagation of laser light beams, a communication channel will be established and the transmission of video and telemetric information will begin, which will last about 100 seconds for the first time.

European Data Relay System abbreviated EDRS.

The European Data Relay System (EDRS) is a project planned by the European Space Agency to create a constellation of modern geostationary satellites that will transmit information between satellites, spacecraft, unmanned aerial vehicles (UAVs) and ground stations, providing faster transmission than traditional methods. data speed, even in conditions of natural and man-made disasters.

EDRS will use the new Laser Communication Terminal (LCT) laser communication technology. The laser terminal will allow transmitting information at a speed of 1.8 Gbit/s. LCT technology will enable EDRS satellites to transmit and receive about 50 terabytes of data per day in almost real time.

The first EDRS communications satellite is scheduled to launch into geostationary orbit in early 2016 from the Baikonur Cosmodrome on a Russian Proton launch vehicle. Once in geosynchronous orbit over Europe, the satellite will carry laser communications links between the four Copernicus Earth observation program Sentinel-1 and Sentinel-2 satellites, unmanned aerial vehicles, and ground stations in Europe , Africa, Latin America, the Middle East and the northeast coast of the United States.

A second, similar satellite will be launched in 2017, and the launch of a third satellite is planned for 2020. Together, these three satellites will be able to cover the entire planet with laser communications.

Prospects for the development of laser communications in space.

Advantages of laser communication compared to radio communication:

• transmission of information over long distances
• high transmission speed
• compactness and lightness of data transmission equipment
• energy efficiency

Disadvantages of laser communication:

• the need for precise pointing of receiving and transmitting devices
• atmospheric problems (cloudiness, dust, etc.)

Laser communications make it possible to transmit data over much greater distances compared to radio communications; the transmission speed, due to the high concentration of energy and a much higher carrier frequency (by orders of magnitude), is also higher. Energy efficiency, low weight and compactness are also several times or orders of magnitude better. Difficulties in the form of the need for precise guidance of receiving and transmitting devices can be solved with modern technical means. In addition, ground-based receiving devices can be located in areas of the Earth where the number of cloudy days is minimal.

In addition to the problems presented above, there is another problem - the divergence and attenuation of the laser beam when passing through the atmosphere. The problem is especially aggravated when the beam passes through layers with different densities. When passing through the interface between media, a light beam, including a laser beam, experiences particularly strong refractions, scattering and attenuation. In this case, we can observe a kind of light spot resulting precisely from passing such an interface between the media. There are several such boundaries in the Earth's atmosphere - at an altitude of about 2 km (active weather atmospheric layer), at an altitude of approximately 10 km, and at an altitude of approximately 80-100 km, i.e. already at the boundary of space. The heights of the layers are given for mid-latitudes in the summer. For other latitudes and other seasons, the heights and the very number of interfaces between the media may differ greatly from those described.

Thus, when entering the Earth’s atmosphere, a laser beam, which had previously calmly traveled millions of kilometers without any losses (except perhaps a slight defocusing), loses the lion’s share of its power within some unfortunate tens of kilometers. However, we can turn this fact, bad at first glance, to our advantage. Since this fact allows us to do without any serious aiming of the beam at the receiver. Because as such a receiver, or rather a primary receiver, we can use precisely these very boundaries between layers and media. We can point the telescope at the resulting spot of light and read information from it. Of course, this will significantly increase the amount of interference and reduce the data transfer rate. And it will make it completely impossible during the daytime. But this will make it possible to reduce the cost of the spacecraft by saving on the guidance system. This is especially true for satellites in non-stationary orbits, as well as for spacecraft for deep space research.

At the moment, if we consider the Earth-spacecraft and spacecraft-Earth communications, the optimal solution is the synergy of laser and radio communications. It is quite convenient and promising to transmit data from the spacecraft to the Earth using laser communications, and from the Earth to the spacecraft using radio communications. This is due to the fact that the laser receiving module is a rather bulky system (most often a telescope) that captures laser radiation and converts it into electrical signals, which are then amplified using known methods and converted into useful information. Such a system is not easy to install on a spacecraft, since most often the requirements are compactness and low weight. At the same time, the laser signal transmitter is small in size and weight compared to antennas for transmitting radio signals.

Alexander Lobinsky

In the last issue of SR we experimented with a new method of presenting news “with discussions and comments” and it seems that our readers liked the initiative. This time, the material published on the well-known news portal ZDNet on laser communication systems again comes under scrutiny. And a specialist from the Belarusian company Belana shares his thoughts on this topic with you.

publication on ZDNet:

Lasers solve the bandwidth problem

Carriers and equipment makers have been testing high-speed data technology for enterprises for months, called "lasers in open space" or "optical wireless communications", which until recently remained the subject of theoretical debate, research and pilot projects.
Terabeam and FSONA Communications plan to introduce the first commercial products and services based on this technology in the near future. "It's already clear that it's ready for widespread use," says independent telecom industry analyst Jeff Kagan. “It’s time to offer it to the market and see how it turns out. It’s clear that it won’t be without problems. But if it works, we can count on huge success.”

Lasers of the invisible optical range are harmless to the human eye and make it possible to provide high-speed access to the Internet and corporate networks through a beam passing through an office window.
The technology provides faster performance than existing wireless networks and is cheaper than fiber optic communications, which require cables to be laid across streets. Lasers have the potential to solve an important problem facing the telecommunications industry.

While large nationwide networks already exist, the construction and modernization of intracity networks is just beginning. Therefore, enterprises often have to wait months before they are provided with Internet access or communication with a remote office. However, the success of laser technology is by no means guaranteed. First, the laser beam is affected by dense fog, which can interfere with propagation and reduce communication reliability. In addition, analysts say laser communications will face challenges such as market skepticism and limited applications compared to fixed-line radio and direct fiber optic links.

dangerous competitor

Still, executives at companies working with laser technology believe it is ready to compete with alternative means of data transmission. "We feel like it's time to go public," says Terabeam CEO Dan Hesse, who left a high-paying job at AT&T Wireless to lead the laser company. Terabeam offers data speeds of up to 1 Gbps in Seattle and is preparing to launch a major marketing campaign in the coming month. Terabeam serves two local clients - digital advertising agency Avenue A and Simpson Investment - with a third to join in the coming days. By the end of the year, it is planned to begin selling services in five more US cities. “Other technologies require lengthy permitting and cabling.

We can send an optical signal directly through the window, which is usually transmitted through thick cables. We see our technology as an extension of fiber optics," says Hesse.
The company's strategy is different in that it plans to operate both as a service provider and as a manufacturer of laser equipment. AT&T followed the same strategy in its early years, when it operated as both a carrier and a manufacturer of telephone equipment. Tera-beam has signed an agreement to jointly develop hardware with Lucent Technologies. Lucent owns a 30% stake in Terabeam Labs, a hardware joint venture whose executives dream of spinning off to become its own company in a few years. FSONA plans to announce the first laser products for telecom operators next week.
In April, the company will begin selling its SONAbeam 155-2 laser system, capable of transmitting data at 155 Mbps over distances of up to 2 km, priced at $20,000 for transmitting and receiving equipment. "We will be releasing the first mass-market optical cable-free communications product," says FSONA chief engineer Stephen Mecherle. “It should become a touchstone for this technology.”
FSONA recently tripled its production capacity by opening a new building in Vancouver with an area of ​​approximately 27 thousand square meters. m.
Planning to expand further, the company held preliminary negotiations with potential overseas partners. This year it intends to release a cheaper version of the 155 Mbit/s laser system, operating over shorter distances, as well as a system with a throughput of 622 Mbit/s.

Many analysts praise the technology's merits, but are unsure of its reliability. FSONA estimates the uptime rate to be 99%, which is not good enough by telecom industry standards. But the company intends to offer additional backup systems to increase reliability to 99.9%.
Terabeam executives believe their network can provide uptime 99.9% of the time, which adds up to about one day of downtime per year.
The capabilities of laser technology and its reliability were enough to interest Lucent. Avenue A has also been pleased with Terabeam's service so far, especially with how quickly the company has received it compared to the wait times to connect to phone company services and other network services such as WorldCom and Sprint. "You have to wait forever for channels," says Avenue A CIO Jamie Marra. - “When you hear about the 90-day period, you will no longer want to contact these service providers.” Avenue A turned to Terabeam instead. “It was only three weeks from the time we asked, ‘What can you offer?’ to the installation of the equipment,” says Marra. - "We received service quickly and at a price comparable to telephone company prices."
Terabeam and FSONA are not alone in their pursuit of the telecommunications market. Other laser communications service providers include AirFiber, which has signed agreements with Nortel Networks, Optical Access (the solutions of this company were discussed in detail in the previous issue of CP - editor's note) and LightPointe Communications.

All of these companies could pose a serious threat to fixed-line radio and gigabit Ethernet service providers. With the ability to shine a laser beam directly through a window, service providers can avoid purchasing expensive radio frequency licenses and negotiating with property owners about roof access rights. "This level of competitive freedom may well make Teligent, Winstar and other landline radio service providers nervous," says Pat Brogan, associate director at research firm The Precursor Group.
This opinion is shared by other analysts. Laser network technology, they say, could become popular if these early applications prove reliable and appeal to customers. "If this technology works as promised, it may be a hit," Kagan says. “With high data transfer rates, short installation times, and no need to bother with permissions, this is quite possible.”
Corey Grice, ZDNet

Discussion of the article: opinion of a Velana specialist

“The idea of ​​transmitting information using a laser beam is by no means new. In the late 80s, while still a schoolboy, I myself saw an experimental installation at BSUIR (then MRTI), in which a laser beam was used to transmit voice. Attempts to use similar systems (t .n. "atmospheric laser") for data transmission have been going on for as long as data transmission networks have existed. The results of numerous experiments, some of which even resulted in the release of commercial products, turned out to be very controversial.
Some argue that “atmospheric” technology is very promising, but requires improvement, others say that it is a waste of time and money. Here is a typical example of a skeptical attitude: “Yeah... Very cool. The channel has fallen.
Possible reasons: the wind is driving the leaves, there is smog in the yard (a KRAZ drove under the window), rain, snow, the cleaning lady hasn’t washed the window for a long time, a suicide bomber flying outside the window crossed the beam :), a poster was hung on the street, birds are flying. Excellent, reliable connection, nothing to add. Please lay the cable for me.

Besides, “invisible optical lasers are harmless to the human eye” is nonsense. The fact that the eye cones do not respond to radiation below a certain frequency does not mean that the tissues of the eye do not absorb radiation.
On the contrary, invisible radiation is dangerous because some time passes before a person feels that something is wrong. You can easily lose your eyes. As for the settings, at a distance of 100 meters (10,000 cm), an angular disturbance of 10/10,000 = 0.001 rad is sufficient to deflect the beam by 10 cm. I can’t quite imagine how to ensure such stability.”
In principle, the presented opinion is not devoid of logic, just like the optimistic one presented in the article under discussion.
Let's try to figure it out, though. The fact that wireless optical systems have not yet received mass acceptance (the absence of the need to lay expensive fiber-optic lines makes them very attractive economically) is explained by a number of reasons. Let's try to analyze them.

1. The technology under consideration is effective only when transmitting data over long distances. At short distances (tens of meters), non-directional infrared technology is used, and very effectively. The laser system is an order of magnitude inferior to it both in cost and flexibility. At long distances, laser technology encounters difficulties with the data transmission medium - the atmosphere, which, unfortunately, is not always transparent, especially in urban environments. Overcoming this problem is to increase the laser power.
A few years ago, this solution led to the creation of devices that consumed a lot of energy, cost a lot of money and looked like turbolaser guns from Star Wars. Today this problem has been largely solved, as new types of compact, powerful and inexpensive laser emitters have been invented.

2. The beam can be interrupted by all sorts of moving objects, such as birds, low-flying airplanes, leaves, drops, etc. At the dawn of network technologies, even a short-term interruption of the beam caused a break in the data transmission channel, which contributed to the awarding of the title “extremely unstable” to laser communications. At dawn, but not today.
Since then, entire series of link layer protocols have been developed, designed for wireless communications and capable of automatically restoring the channel after a short-term interruption. And the continuity of data flows is ensured by higher-level protocols (for example TCP/IP).
Thus, the myth about the instability of laser communication can be refuted today.

3. The laser communication system is difficult to set up. Indeed, with a beam diameter of several millimeters (or even fractions of a millimeter), vibrations of the light spot with an amplitude of several centimeters can seriously complicate the entire procedure of pointing at the receiver. This is one of the most serious technical problems in atmospheric laser communication today. True, recently reports have begun to appear about the development of highly sensitive optical sensors operating in narrow spectral ranges, which makes it possible to create relatively cheap panels with an area of ​​several tens of square centimeters, insensitive to daylight illumination, and therefore allowing for stable beam reception.

I doubt that atmospheric laser communication technology will be cheap enough to be used at home any time soon (and not everyone lives in high-rise buildings where line of sight can be provided).
However, this technology can become a worthy competitor to fixed radio communications in corporate data networks. With approximately the same cost of equipment, laser technology will not require painful (and very expensive) procedures for isolating radio frequency channels, carrying out work on high-altitude installation of heavy and bulky equipment and, as mentioned earlier, turns out to be less harmful to the health of others.

Today it is impossible to imagine our life without computers and networks based on them. Humanity is on the threshold of a new world in which a single information space will be created. In this world, communications will no longer be hampered by physical boundaries, time or distance.

Nowadays there are a huge number of networks all over the world that perform various functions and solve many different problems. Sooner or later, there always comes a time when the network capacity is exhausted and new communication lines need to be laid. This is relatively easy to do inside a building, but difficulties begin when connecting two adjacent buildings. Special permits, approvals, licenses to carry out work are required, as well as the fulfillment of a number of complex technical requirements and the satisfaction of considerable financial requests from organizations managing land or sewerage. As a rule, it immediately becomes clear that the shortest path between two buildings is not a straight line. And it is not at all necessary that the length of this path will be comparable to the distance between these buildings.

Of course, everyone knows a wireless solution based on various radio equipment (radio modems, small-channel radio relay lines, microwave digital transmitters). But the number of difficulties does not decrease. The airwaves are oversaturated and obtaining permission to use radio equipment is very difficult, and sometimes even impossible. And the throughput of this equipment significantly depends on its cost.

We propose to use a new, economical type of wireless communication that has emerged quite recently - laser communication. This technology received the greatest development in the USA, where it was developed. Laser communications provides a cost-effective solution to the problem of reliable, high-speed short-range communications (1.2 km) that can arise when connecting telecommunications systems from different buildings. Its use will allow for the integration of local networks with global ones, the integration of local networks remote from each other, and also to meet the needs of digital telephony. Laser communication supports all interfaces necessary for these purposes - from RS-232 to ATM.

How does communication work?

Laser communication allows for point-to-point connections with information transfer rates of up to 155 Mbit/s. In computer and telephone networks, laser communication ensures the exchange of information in full duplex mode. For applications that do not require high transmission rates (for example, video and control signals in process and closed-circuit television systems), a special, cost-effective half-duplex solution is available. When it is necessary to combine not only computer but also telephone networks, models of laser devices with a built-in multiplexer can be used to simultaneously transmit LAN traffic and digital group telephony streams (E1/ICM30).

Laser devices can transmit any network stream that is delivered to them using optical fiber or copper cable in the forward and reverse directions. The transmitter converts electrical signals into modulated laser radiation in the infrared range with a wavelength of 820 nm and a power of up to 40 mW. Laser communication uses the atmosphere as a propagation medium. The laser beam then hits a receiver that has maximum sensitivity within the wavelength range of the radiation. The receiver converts laser radiation into signals from the electrical or optical interface used. This is how communication is carried out using laser systems.

Families, models and their features

In this section, we would like to introduce you to the three families of the most popular laser systems in the USA - LOO, OmniBeam 2000 and OmniBeam 4000 (Table 1). The LOO family is basic and allows data and voice communications up to 1000 m. The OmniBeam 2000 family has similar capabilities, but operates over a longer distance (up to 1200 m) and can transmit video images and a combination of data and voice. The OmniBeam 4000 family can provide high-speed data transfer: from 34 to 52 Mbit/s over distances up to 1200 m and from 100 to 155 Mbit/s up to 1000 m. There are other families of laser systems on the market, but they either cover shorter distances, or support fewer protocols.

Table 1.

Each family includes a set of models that support different communication protocols (Table 2). The LOO family includes economical models that provide transmission distances of up to 200 m (the letter "S" at the end of the name).

Table 2.

An undoubted advantage of laser communication devices is their compatibility with most telecommunications equipment for various purposes (hubs, routers, repeaters, bridges, multiplexers and PBXs).

Installation of laser systems

An important stage in creating a system is its installation. The actual switching on takes a negligible amount of time compared to the installation and configuration of laser equipment, which takes several hours if performed by well-trained and equipped specialists. At the same time, the quality of operation of the system itself will depend on the quality of these operations. Therefore, before presenting typical inclusion options, we would like to pay some attention to these issues.

When placed outdoors, transceivers can be installed on roof or wall surfaces. The laser is mounted on a special rigid support, usually metal, which is attached to the wall of the building. The support also provides the ability to adjust the angle of inclination and azimuth of the beam.

In this case, for ease of installation and maintenance of the system, its connection is made through distribution boxes (RK). The connecting cables are usually fiber optic for data transmission circuits and copper cable for power and control circuits. If the equipment does not have an optical data interface, then it is possible to use a model with an electrical interface or an external optical modem.

The power supply unit (PSU) of the transceiver is always installed indoors and can be mounted on a wall or in a rack that is used for LAN equipment or structured cabling systems. A condition monitor can also be installed nearby, which serves to remotely monitor the functioning of transceivers of the OB2000 and OB4000 families. Its use allows for diagnostics of the laser channel, indication of the signal magnitude, as well as looping the signal to check it.

When installing laser transceivers internally, it is necessary to remember that the power of laser radiation decreases when passing through glass (at least 4% on each glass). Another problem is water droplets running down the outside of the glass when it rains. They act as lenses and can cause beam scattering. To reduce this effect, it is recommended to install the equipment near the top of the glass.

To ensure high-quality communication, it is necessary to take into account some basic requirements.

The most important of them, without which communication will be impossible, is that buildings must be within line of sight, and there should be no opaque obstacles in the path of beam propagation. In addition, since the laser beam in the receiver area has a diameter of 2 m, it is necessary that the transceivers are located above pedestrians and traffic at a height of at least 5 m. This is due to ensuring safety regulations. Transport is also a source of gases and dust, which affect the reliability and quality of transmission. The beam must not be projected in close proximity to or cross power lines. It is necessary to take into account the possible growth of trees, the movement of their crowns during gusts of wind, as well as the influence of precipitation and possible disruptions due to flying birds.

The correct choice of transceiver guarantees stable operation of the channel in the entire range of climatic conditions in Russia. For example, a larger beam diameter reduces the likelihood of precipitation-related failures.

Laser equipment is not a source of electromagnetic radiation (EMR). However, if placed near devices with EMR, the laser's electronics will pick up this radiation, which can cause a change in the signal in both the receiver and transmitter. This will affect the quality of communication, so it is not recommended to place laser equipment near EMR sources such as powerful radio stations, antennas, etc.

When installing a laser, it is advisable to avoid oriented laser transceivers in the east-west direction, since several days a year the sun's rays can block the laser radiation for several minutes, and transmission will become impossible, even with special optical filters in the receiver. Knowing how the sun moves across the sky in a specific area, you can easily solve this problem.

Vibration can cause the laser transceiver to shift. To avoid this, it is not recommended to install laser systems near motors, compressors, etc.

Picture 1.
Placement and connection of laser transceivers.

Several typical inclusion methods

Laser communication will help solve the problem of short-range communication in point-to-point connections. As examples, let's look at several typical options or methods of inclusion. So, you have a central office (CO) and a branch (F), each of which has a computer network.

Figure 2 shows a variant of organizing a communication channel for the case in which it is necessary to combine the F and DSO, using Ethernet as the network protocol, and coaxial cable (thick or thin) as the physical medium. In the CO there is a LAN server, and in F there are computers that need to be connected to this server. With laser systems such as the LOO-28/LOO-28S or OB2000E models, you can easily solve this problem. The bridge is installed in the central center, and the repeater in F. If the bridge or repeater has an optical interface, then an optical minimodem is not required. Laser transceivers are connected via dual fiber optics. The LOO-28S model will allow you to communicate at a distance of up to 213 m, and the LOO-28 - up to 1000 m with a “confident” reception angle of 3 mrad. The OB2000E model covers a distance of up to 1200 m with a “confident” reception angle of 5 mrad. All these models operate in full duplex mode and provide a transfer speed of 10 Mbit/s.

Figure 2.
Connecting a remote Ethernet LAN segment using a coaxial cable.

A similar option for combining two Ethernet networks using twisted pair cable (10BaseT) as a physical medium is shown in Figure 3. Its difference is that instead of a bridge and a repeater, concentrators (hubs) are used that have the required number of 10BaseT connectors and one AUI interface or FOIRL for connecting laser transceivers. In this case, it is necessary to install a LOO-38 or LOO-38S laser transceiver, which provides the required transmission speed in full duplex mode. The LOO-38 model can support communication distances up to 1000 m, and the LOO-38S model can communicate up to 213 m.

Figure 3.
Connecting a remote Ethernet LAN segment based on twisted pair.

Figure 4 shows a variant of combined data transmission between two LANs (Ethernet) and a group digital stream E1 (PCM30) between two PBXs (in the CO and F). To solve this problem, the OB2846 model is suitable, which provides data and voice transmission at a speed of 12 (10+2) Mbit/s over a distance of up to 1200 m. The LAN is connected to the transceiver using dual optical fiber through a standard SMA connector, and telephone traffic is transmitted via 75 Ohm coaxial cable via BNC connector. It should be noted that multiplexing of data and speech streams does not require additional equipment and is performed by transceivers without reducing the throughput of each of them separately.

Figure 4.
Integration of computer and telephone networks.

An option for high-speed data transfer between two LANs (LAN "A" in the central center and LAN "B" in the F) using ATM switches and laser transceivers is presented in Figure 5. The OB4000 model will solve the problem of high-speed short-range communication in an optimal way. You will have the opportunity to transmit E3, OC1, SONET1 and ATM52 streams at the required speeds over a distance of up to 1200 m, and 100 Base-VG or VG ANYLAN (802.12), 100 Base-FX or Fast Ethernet (802.3), FDDI, TAXI 100/ 140, OC3, SONET3 and ATM155 with the required speeds - over a distance of up to 1000 m. The transmitted data is delivered to the laser transceiver using a standard dual optical fiber connected via an SMA connector.

Figure 5.
Consolidation of high-speed telecommunication networks.

The examples given do not exhaust all possible applications of laser equipment.

Which is more profitable?

Let's try to determine the place of laser communication among other wired and wireless solutions, briefly assessing their advantages and disadvantages (Table 3).

Table 3.

Let's start with the well-known ordinary copper cable. Some of its characteristics make it possible to almost accurately calculate the parameters of the created communication channel. For such a channel, it does not matter what the direction of transmission is and whether objects are in direct visibility; there is no need to think about the influence of precipitation and many other factors. However, the quality and transmission speed provided by this cable leave much to be desired. The bit error rate (BER) is on the order of 1E-7 or higher, which is significantly higher than that of fiber optics or wireless communications. Copper cables are a low-speed communication link, so before installing new cables, consider whether they are worth using. If you already have a cable, then you should think about how to increase its capacity using HDSL technology. However, it should be taken into account that it may not provide the required quality of communication due to the unsatisfactory condition of the cable lines.

Fiber optic cables have significant advantages over copper cables. High throughput and transmission quality (BER)

Nowadays, radio communications are widely used, especially radio relay lines and radio modems. They also have their own set of advantages and disadvantages. Existing radio technologies will provide you with higher quality (BER) when creating a data transmission channel

Laser communication - quickly and efficiently, reliably and effectively solves the problem of short-range communication between two buildings located at a distance of up to 1200 m and in direct visibility. Without these conditions being met, laser communication is impossible. Its undoubted advantages are:

• "transparency" for most network protocols (Ethernet, Token Ring, Sonet/OC, ATM, FDDI, etc.);
• high data transfer speed (up to 155 Mbit/s today, up to 1 Gbit/s for equipment announced by manufacturers);
• high quality of communication with BER=1E-10...1E-9;
• connecting network traffic to the laser transceiver using cable and/or fiber optic interface devices;
• no need to obtain permission to use;
• relatively low cost of laser equipment compared to radio systems.

Laser transceivers, due to the low power of their radiation, do not pose a health hazard. It should be noted that although the beam is safe, the birds see it and try to avoid it, which significantly reduces the likelihood of failures. If the transmitted information is delivered to and from the laser transceiver via a standard multimode fiber optic cable, then data transmission is guaranteed without radio waves and electromagnetic radiation. This not only ensures that there is no impact on equipment operating nearby, but also makes unauthorized access to information impossible (it can only be obtained by approaching the transceiver directly).