From the concept of "light" to optical transmission of information - lionzage. More about optical data transmission technologies

An optical fiber consists of a central light conductor (core) - a glass fiber, surrounded by another layer of glass - a cladding, which has a lower refractive index than the core. While spreading through the core, the rays of light do not go beyond its limits, reflecting from the covering layer of the shell. In optical fiber, the light beam is usually generated by a semiconductor or diode laser. Depending on the distribution of the refractive index and the diameter of the core, optical fiber is divided into single-mode and multimode.

Market of fiber optic products in Russia

Story

Although fiber optics is a widely used and popular means of communication, the technology itself is simple and developed a long time ago. The experiment with changing the direction of a light beam by refraction was demonstrated by Daniel Colladon and Jacques Babinet back in 1840. A few years later, John Tyndall used this experiment in his public lectures in London, and already in 1870 he published a work on the nature of light. Practical use technology was found only in the twentieth century. In the 1920s, experimenters Clarence Hasnell and John Berd demonstrated the possibility of transmitting images through optical tubes. This principle was used by Heinrich Lamm for medical examination of patients. It wasn't until 1952 that Indian physicist Narinder Singh Kapany conducted a series of his own experiments that led to the invention of optical fiber. In fact, he created the very same bundle of glass threads, and the shell and core were made of fibers with different refractive indices. The shell actually served as a mirror, and the core was more transparent - this solved the problem of rapid dispersion. If previously the beam did not reach the end of the optical filament, and it was impossible to use such a means of transmission over long distances, now the problem has been solved. Narinder Kapani improved the technology by 1956. A bunch of flexible glass rods transmitted the image with virtually no loss or distortion.

The invention of fiber optics by Corning specialists in 1970, which made it possible to duplicate the telephone signal data transmission system over a copper wire over the same distance without repeaters, is considered to be a turning point in the history of the development of fiber optic technologies. The developers managed to create a conductor that is capable of maintaining at least one percent of the optical signal power at a distance of one kilometer. By today's standards, this is a rather modest achievement, but then, almost 40 years ago, - necessary condition in order to develop a new type of wired communication.

Initially, optical fiber was multiphase, that is, it could transmit hundreds of light phases at once. Moreover, the increased diameter of the fiber core made it possible to use inexpensive optical transmitters and connectors. Much later, they began to use higher-performance fiber, through which it was possible to transmit only one phase in the optical environment. With the introduction of single-phase fiber, signal integrity could be maintained over greater distances, which facilitated the transfer of considerable amounts of information.

The most popular fiber today is single-phase fiber with zero wavelength offset. Since 1983, it has been the industry's leading fiber optic product, proven to operate over tens of millions of kilometers.

Advantages of fiber optic communication

• The widebandwidth of optical signals due to the extremely high frequency carrier. This means that information can be transmitted over a fiber optic line at a speed of about 1 Tbit/s;
• Very low attenuation of the light signal in the fiber, which makes it possible to build fiber-optic communication lines up to 100 km or more in length without signal regeneration;
• Resistance to electromagnetic interference from surrounding copper cabling systems, electrical equipment (power lines, electric motors, etc.) and weather conditions;
• Protection against unauthorized access. Information transmitted over fiber-optic communication lines is practically impossible to intercept in a non-destructive manner;
• Electrical safety. Being, in fact, a dielectric, optical fiber increases the explosion and fire safety of the network, which is especially important in chemical and oil refineries, during maintenance technological processes increased risk;
• Durability of fiber-optic lines - service life of fiber optical lines connection is at least 25 years old.

Disadvantages of fiber optic communication

• The relatively high cost of active line elements that convert electrical signals into light and light into electrical signals;
• Relatively high cost of splicing optical fiber. This requires precision, and therefore expensive, technological equipment. As a result, if an optical cable breaks, the cost of restoring a fiber-optic line is higher than when working with copper cables.

Fiber Optic Line Elements

• Optical receiver

Optical receivers detect signals transmitted along a fiber optic cable and convert them into electrical signals, which then amplify and then restore their shape, as well as clock signals. Depending on the transmission speed and system specifics of the device, the data stream can be converted from serial to parallel.

• Optical transmitter

The optical transmitter in a fiber optic system converts the electrical data sequence supplied by the system components into an optical data stream. The transmitter consists of a parallel-serial converter with a clock synthesizer (which depends on system installation and bit rate), driver and optical signal source. Various optical sources can be used for optical transmission systems. For example, light-emitting diodes are often used in low-cost local networks for short distance communication. However, the wide spectral bandwidth and the inability to work in the wavelengths of the second and third optical windows do not allow the use of LEDs in telecommunication systems.

• Preamplifier

The amplifier converts the asymmetric current from the photodiode sensor into an asymmetric voltage, which is amplified and converted into a differential signal.

• Data synchronization and recovery chip

This chip must restore the clock signals from the received data stream and their clocking. The phase-locked loop circuitry required for clock recovery is also fully integrated into the clock chip and does not require external control clock pulses.

• Serial to parallel code conversion block

• Parallel-to-serial converter

• Laser shaper

Its main task is to supply bias current and modulating current to directly modulate the laser diode.

• Optical cable, consisting of optical fibers located under a common protective sheath.

Singlemode fiber

If the fiber diameter and wavelength are small enough, a single beam will propagate through the fiber. In general, the very fact of selecting the core diameter for the single-mode signal propagation mode speaks about the particularity of each individual fiber design option. That is, single-mode refers to the characteristics of the fiber relative to the specific frequency of the wave used. The propagation of only one beam allows you to get rid of intermode dispersion, and therefore single-mode fibers are orders of magnitude more productive. On this moment a core with an outer diameter of about 8 microns is used. As with multimode fibers, both step and gradient material distribution densities are used.

The second option is more productive. Single-mode technology is thinner, more expensive and is currently used in telecommunications. Optical fiber is used in fiber-optic communication lines, which are superior to electronic communications in that they allow lossless, high-speed transmission of digital data over vast distances. Fiber optic lines can either form a new network or serve to combine existing networks - sections of optical fiber highways, connected physically at the light guide level, or logically at the level of data transfer protocols. Data transmission speeds over fiber-optic lines can be measured in hundreds of gigabits per second. The standard is already being finalized to allow data transmission at a speed of 100 Gbit/s, and the 10 Gbit Ethernet standard has been used in modern telecommunications structures for several years.

Multimode fiber

In a multimode optical fiber, a large number of modes—rays introduced into the fiber at different angles—can propagate simultaneously. Multimode OF has a relatively large core diameter (standard values ​​50 and 62.5 μm) and, accordingly, a large numerical aperture. The larger core diameter of multimode fiber simplifies the coupling of optical radiation into the fiber, and the more relaxed tolerance requirements for multimode fiber reduce the cost of optical transceivers. Thus, multimode fiber predominates in short-range local and home networks.

The main disadvantage of multimode optical fiber is the presence of intermode dispersion, which arises due to the fact that different modes follow different optical paths in the fiber. To reduce the influence of this phenomenon, a multimode fiber with a graded refractive index was developed, due to which the modes in the fiber propagate along parabolic trajectories, and the difference in their optical paths, and, consequently, the intermodal dispersion, is significantly less. However, no matter how balanced gradient multimode fibers are, their throughput cannot be compared to single-mode technologies.

Fiber Optic Transceivers

To transmit data over optical channels, the signals must be converted from electrical to optical, transmitted over a communications link, and then converted back to electrical at the receiver. These transformations occur in the transceiver device, which contains electronic components along with optical components.

Widely used in transmission technology, the time division multiplexer allows the transmission speed to be increased to 10 Gb/s. Modern high-speed fiber optic systems offer the following transmission speed standards.

SONET standard	SDH standard	Transmission speed
OC 1	-	51.84 Mb/sec
OC 3	STM 1	155.52 Mb/s
OC 12	STM 4	622.08 Mb/sec
OC 48	STM 16	2.4883 Gb/sec
OC 192	STM 64	9.9533 Gb/sec

New methods of multiplexing wavelength division or wavelength division multiplexing make it possible to increase data transmission density. To achieve this, multiple multiplexed streams of information are sent over a single fiber optic channel using each stream's transmission at a different wavelength. The electronic components in the WDM receiver and transmitter are different from those used in a time division system.

Application of fiber optic communication lines

Optical fiber is actively used to build city, regional and federal communication networks, as well as to install connecting lines between city automatic telephone exchanges. This is due to the speed, reliability and high capacity of fiber networks. Also, through the use of fiber optic channels, there are cable television, remote video surveillance, video conferences and video broadcasts, telemetry and others Information Systems. In the future, it is planned to use the conversion of speech signals into optical signals in fiber-optic networks.

Fiber optic cables are used for high-speed data transmission in a variety of industries, especially telecommunications. But what exactly is fiber optic cable? How does he work? How is it designed? In this article we will try to provide answers to all these questions.

What are fiber optic cables?

In general, fiber optic cables are not much different from other types of cables. Except that they use light (photons) rather than energy (electrons) to transmit data. Fiber optic transmission is a general term for the transmission of information in the form of light.

How are fiber optic cables constructed?

The fiber optic cable is based on a core consisting of quartz glass or plastic fiber. It is this core that serves as the main conductor of light inside the cable. Between the cable core and its sheath there is another layer called the “boundary layer”. It serves to reflect light. The refractive index directly affects the transmission speed of the light beam.

Next is the core shell itself, which also acts as a conductor of light rays, but has a lower reflection index than core . The shell is covered by the next layer, called the “buffer”. Its function is to prevent moisture from forming inside the core and shell.
And finally, the final layer is the outer covering of the cable, which protects the cable from mechanical damage.

How do fiber optic cables transmit light rays?

To transmit data over optical fiber, the incoming electrical signal is converted into a light pulse using a special electro-optical converter. After this, the light beam begins to move along the cables. At the final point of its route, the beam enters an optoelectronic converter, where it is converted into electronic signals.
Different types of fiber optic cables have different core diameters. Cores with larger diameters can transmit more rays. Fiber optic cables can be bent, but you must ensure that the cable is not bent too much as this may interfere with the transmission of light rays within the cable.

What are the types of fiber optic cables?

There are several types of fiber optic cables. Let's look at them all.

Multi-mode fibers with step-index profile (Multimode Step Index Cables)

Multimode stepped index cables are the simplest fiber optic cables. They consist of a glass core that has a constant reflectance index. This type of cable allows you to simultaneously transmit several beams, which are reflected with different intensities and transmitted along a zigzag path. However, the reflectance index remains constant.
Due to the fact that rays are refracted many times under different angles, the data transfer speed decreases. Cables of this type provide throughput up to 100 MHz and allow you to transmit signals over a distance of up to 1 kilometer.The core diameters of cables of this type are usually: 100, 120 or 400 µm.
Multi-mode fibers with graded index (Graded Index Multimode Cables).

Same as the previous cable type, this cable allows you to simultaneously transmit many signals, however, the signals inside the optical fiber are not refracted in a zigzag, but along a parabolic path, which allows you to significantly increase the data transfer speed. The disadvantages of these cables include their higher cost. Cables of this type are usually used to build high-speed data transmission networks.
Core diameters: 50 µm, 62.5 µm, 85 µm, 100 µm, 125 µm, 140 µm.

Single-mode fibers (Single mode cables)

Single-mode fiber optic cables have a very small core diameter and can only carry one signal at a time. The absence of refractions has a positive effect on the speed and distance of data transmission. Single-mode cables are quite expensive, but provide excellent throughput and data transmission range, up to 100 (Gbit/s) km.

What are the benefits of using fiber optic cables?
Compared to conventional cables, fiber optics provides the following advantages:
Resistance to radio interference and voltage surges
Increased level of durability
High-speed data transmission over long distances
Electromagnetic Interference Immunity
Compatible with other cable types

In data transmission networks, a fiber optic cable provides a number of advantages: it is not affected by electromagnetic interference, transmits a signal at a very high speed over long distances without repeaters, etc. In order to combine a fiber optic cable with an existing network equipment connected by copper wires, converters are required, such as fiber optic converters from ADFweb.

LLC "Krona", St. Petersburg

A little about the terms

A converter is a converter. It is not very clear why the English word converter has replaced its Russian equivalent. However, for quite some time now in technology, various devices have received this name, the only similarity between which is the conversion function. Why converters are not called converters, why a foreign word has taken root, only the Russian language knows.

Advantages of fiber optic cable

In data transmission networks built on the basis of Ethernet technologies, the signal can be transmitted via both copper and fiber optic wires, only in the first case this is carried out using electricity, and in the second - using light. Light not only allows you to transmit information to longer distance With higher speed, but also gives the optical fiber absolute immunity to any type of electromagnetic interference.

Traditional copper wires are susceptible to external electromagnetic interference, which distorts the signal. But there are many sources capable of generating this interference! Therefore, to ensure that the electronics do not freeze or fail, the data bus must be carefully separated from the power bus.

In addition, the signal passing through copper wires fades quite quickly, so repeaters are needed, or, to use the tracing term again, repeaters - devices that update it. Repeaters have to be placed quite close to each other - approximately every hundred meters. If we take into account the distances that it can cover industrial network, it becomes clear that many such devices are required.

Fiber optics provide a fast, simple, reliable connection while allowing for absolute electrical and galvanic isolation. Therefore, when using an optical cable, there is no need to separate the data bus from the power bus, and in addition, there is no danger that the entire network of devices will be damaged if one node fails (for example, when struck by lightning). All network components, when connected via an optical cable, are completely isolated from each other, so if one of the network nodes is electrically damaged, this damage does not spread to the remaining nodes. And finally, it is much easier to diagnose the state of the network and instantly localize its faulty component.

Fiber optic cable can be used for different types of networks; it allows you to connect nodes over very long distances. And in addition, optical fiber has much greater “bandwidth” than a copper core, in other words, a much larger amount of information can be transmitted via a fiber-optic cable per unit of time, which plays a significant role on the scale of an industrial enterprise.

So, to summarize what has been said, the advantages of connecting using an optical cable include:

Immunity to electromagnetic and electrostatic interference;

High speed of information reception/transmission;

Connecting subscribers over a long distance;

Security and functionality.

It is impossible to say that fiber optic cable always and in every way outperforms copper cable. Copper cable has its advantages. For example, it is cheaper and not as fragile as fiber optics. Nevertheless, there are a number of industrial areas where the use of fiber optic cable is fully justified:

Oil and gas complex;

Power plants, including nuclear;

Telecommunications;

Remote control and monitoring systems;

Medicine.

All this has led to the fact that today many enterprises are switching to fiber optic infrastructure. In this case, very often a device is required that allows you to combine fiber optic cable with existing network equipment adapted for copper infrastructure.

In order to convert existing networks to fiber optics, converters have been developed that allow you to connect devices with RS, Ethernet and other outputs to fiber optic cables. Converters make it possible to forward existing networks/buses (LAN/Ethernet, CAN, serial ports RS‑232, RS‑485) through fiber optic cables, guaranteeing their reliability and functionality. Moreover, these networks can be forwarded through the same connection at the same time. It is possible to use the network topology with any combination of fiber optic cables, both single-mode and multimode.

Fiber optic converters from ADFweb

The KRONA company presents ADFweb fiber optic converters of two types: “economical” and “advanced”.

The economy series converters, HD67072, HD67074 and HD67075, allow you to connect devices with RS or USB ports via multimode fiber optic cable over four different network topologies:

Point To Point (direct connection, point to point): one device is connected directly to another using a fiber optic cable;

Single Loop (ring): several devices are connected by a fiber optic cable in series with a loopback, that is, connecting the first to the last;

Double Loop: Multiple devices are connected in series using two pairs of fiber optic cables. In this case, the connections are looped into double ring. This connection is extremely reliable;

Multi-Drop (in-line): Multiple devices are connected in series with two fiber optic cables. In this case, there is no need to loop the connection.

Rice. HD67702 converter from ADFweb

The advanced series converters, HD67701 and HD67702, allow connection via both multimode and single-mode cables. They allow you to connect devices with Ethernet, CAN, RS-232 or RS-485 ports using the same four network topologies listed above.

The advanced series, of course, will cost more, partly due to the use of single-mode cable. Multimode fiber has a wider core diameter, which causes the light wave to travel through it at a slower speed and attenuate faster. In single-mode fiber, the core diameter is so small (8 microns) that only one beam generated by the laser propagates through it along a single path - the mode. Thanks to this, the signal speed is extremely high (from 10 Gb), and its attenuation rate is only 0.5 dB/km. This cable is more expensive because it is created using more complex technologies, but in large enterprises these costs are justified.

Additionally, advanced series devices have the following capabilities:

Have distributed input/output;

Create a map for linking outputs to inputs;

Provides reading of input/output status via standard Modbus commands.

Advanced series converters provide access to diagnostic data through standard Modbus registers, which allows them to be easily integrated with existing control systems (for example, connected to a SCADA system).

An important advantage of the HD67701 and HD67702 series converters is that with their help, up to 6 existing networks can be “forwarded” over one optical fiber cable at the same time, including 4 serial networks (for example, Modbus RTU), one CAN network(for example, CANopen) and one Ethernet network(e.g. PROFINET or Modbus TCP).

It is possible to combine these converters with input/output modules, which contain 4 discrete inputs and outputs. Thanks to these modules, it is possible to route dry contacts through a fiber optic cable over long distances.

Innovative is the ability to create a map for binding inputs to outputs: one input is connected to several outputs. Thus, using two blocks of input and output signals, between which a fiber-optic cable is laid, “by pressing a button” you turn on several pumps that are located 50 km from this button.

1. General concepts electromagnetic radiation
2. The concept of "Light"

A. Story
b. General information
V. Development
4. Conclusion

1. General concepts of electromagnetic radiation.
Electromagnetic radiation is the movement of disturbances electromagnetic field in space. There are invisible and visible electromagnetic radiation. Electromagnetic radiation is generated by moving electrical charges, and propagates in all directions and in almost all environments. They are transferred without attenuation over long distances.

Electromagnetic radiation is divided into:
. radio waves (starting from ultra-long ones);
. infrared radiation;
. visible light;
. ultraviolet radiation;
. X-rays and hard (gamma radiation).

The electromagnetic scale (spectrum) is the totality of all frequency ranges of electromagnetic radiation. The following quantities are used as spectral characteristics:
. Wavelength;
. Oscillation frequency;
. Photon energy.

The spectrum is divided into the following sections:
. Low frequency vibrations;
. Radio waves;
. Infrared radiation;
. Visible radiation (light);
. Ultraviolet radiation;
. X-ray radiation;
. Gamma radiation.
Electromagnetic waves are widely used nowadays in radio and electrical engineering, modern devices. Radio waves are used for radio communications, television, and radar. Infrared radiation is used in ovens, heaters and all heating and drying devices. Ultraviolet radiation is used for disinfection of premises, studies and research of atoms and molecules. Widely used in forensics to find biological traces. X-rays are used in medicine to diagnose diseases and to treat certain diseases.

2. The concept of "Light".
Light is visible electromagnetic radiation emitted by a heated or excited substance. But the adjacent broad spectrum regions: ultraviolet and infrared radiation are also mistaken for light. Visible wavelengths range from 380 to 780 nanometers. Light is studied by a branch of physics called optics. Light can be considered either as an electromagnetic wave, the speed of propagation in a vacuum of which is constant, or as a stream of photons - particles with a certain energy, momentum, intrinsic angular momentum and zero mass.
Light has all the properties of electromagnetic waves:
. Reflection;
. Refraction;
. Interference;
. Diffraction;
. Polarization.
Light can exert pressure on a substance, be absorbed by the medium, and cause the photoelectric effect. Light deviates from a straight direction. It has a final speed of propagation in a vacuum of 300,000 km/s, and in the medium the speed decreases. In addition to the drop in speed, light begins to refract and can begin to split into the light spectrum under certain circumstances. This is explained by the phenomenon of interference. It is the interference of light that explains the color soap bubbles and thin oil films on water. Light waves are partially reflected from the surface of a thin film, partially transmitted into it, and we observe a rainbow pattern on the surface.
Diffraction of light is the deviation of a light wave from linear propagation. This can be clearly seen when in a room curtained with dark, thick curtains, make a small hole in the curtain, the light will come out like a cone, the top of which will be in our hole. We can observe the refraction of light by placing a spoon in a glass of water. It will be divided at the border between air and water.
We observe the world around us only because humans can perceive the visible spectrum of electromagnetic waves. This occurs due to the fact that special receptors located in the retina of the eye can react to light radiation. And we can distinguish visual images: color, shape, size, distance to an object and much more. Human vision has a number of properties:
. Light sensitivity;
. Sharpness;
. Field of view;
. Binocularity;
. Contrast and adaptation.

3. Application of light in optical fiber.
A. Story
Light is widely used in technology, but has received particular development these days in fiber optic networks. The history of transmitting data over a distance using light and transparent materials began in 1934. Norman French proposed converting the voice into light signals and transfer it along glass rods. A few years later, Swiss physicist Jean-Daniel Colladon conducted an experiment with the transmission of light through a “parabolic liquid flow,” that is, water.
Optical fiber of the modern type was invented in 1954. This was done by two English physicists Narinder Singh Kapani, Harold Hopkins and the Dutch researcher Abraham Van Heel. They announced their inventions at the same time, so all three are considered the founders of this technology. By the way, optical fiber was called optical fiber two years after its invention.
The first fiber optic cables had high light loss. Lawrence Curtis managed to reduce losses in the late 50s. After laser technology was discovered in 1962, fiber optics received another boost in development.
b. General information
Fiber-optic communication is a type of wired telecommunication that uses electromagnetic radiation of the optical (near-infrared) range as an information signal carrier, and fiber-optic cables as guide systems. Thanks to the high carrier frequency and wide multiplexing capabilities, the throughput of fiber-optic lines is many times higher than the throughput of all other communication systems and can be measured in terabits per second. But let's return from history to modern times. Today, fiber optic cable is the most... quick way data transmission. This is not surprising. Light acts as a carrier of information, and it, as is known, has the most high speed movement in the Universe (300 thousand kilometers per second). Low attenuation of light in optical fiber allows the use of fiber-optic communications over significant distances without the use of amplifiers. Fiber optic communications are free from electromagnetic interference and difficult to access for unauthorized use—it is technically extremely difficult to surreptitiously intercept a signal transmitted over an optical cable. When compared with other methods of information transmission, the order of magnitude TB/s is simply unattainable. Another advantage of such technologies is transmission reliability. Fiber optic transmission does not have the disadvantages of electrical or radio signal transmission. There is no interference that can damage the signal, and there is no need to license the use of the radio frequency. However, not many people imagine how information is transferred over optical fiber in general, and even more so are not familiar with specific implementations of technologies. First, let's look at how information is transmitted over optical fiber in general. An optical fiber is a waveguide through which electromagnetic waves with a wavelength of about a thousand nanometers (10-9 m) propagate. This is the area infrared radiation, invisible to the human eye. And the main idea is that with a certain selection of the fiber material and its diameter, a situation arises when for some wavelengths this medium becomes almost transparent and even when it hits the boundary between the fiber and the external environment, most of the energy is reflected back into the fiber. This ensures that radiation passes through the fiber without much loss, and the main task is to receive this radiation at the other end of the fiber. Of course, for so much brief description hides the enormous and difficult work of many people. Do not think that such material is easy to create or that this effect is obvious. On the contrary, it should be treated as a great discovery, since today it provides a better way of transmitting information. You need to understand that the waveguide material is a unique development and the quality of data transmission and the level of interference depend on its properties; The waveguide insulation is designed to ensure that the outward energy output is minimal. Specifically speaking about a technology called “multiplexing,” this means that you transmit multiple wavelengths at the same time. They do not interact with each other, and when receiving or transmitting information, interference effects (superposition of one wave on another) are insignificant, since they manifest themselves most strongly at multiple wavelengths. Right here we're talking about about using close frequencies (frequency is inversely proportional to wavelength, so it doesn’t matter what you talk about). A device called a multiplexer is a device for encoding or decoding information into waveforms and back.
V. Development
Smoothly moving on to the development trends of this technology, we certainly will not discover America if we say that DWDM is the most promising optical data transmission technology. This can be associated to a greater extent with the rapid growth of Internet traffic, the growth rates of which are approaching thousands of percent. The main starting points in development will be an increase in the maximum transmission length without optical signal amplification and the implementation of a larger number of channels (wavelengths) in one fiber. Today's systems provide transmission of 40 wavelengths, corresponding to a 100-gigahertz frequency grid. Devices with a 50-GHz network supporting up to 80 channels are next in line to enter the market, which corresponds to the transmission of terabit streams over a single fiber. And today you can already hear statements from laboratories of development companies such as Lucent Technologies or Nortel Networks about the imminent creation of 25-GHz systems.
However, despite such rapid development of engineering and research, market indicators make their own adjustments. The past year has been marked by a serious decline in the optical market, as evidenced by the significant drop in Nortel Networks' share price (29% in one day of trading) after it announced difficulties in selling its products. Other manufacturers found themselves in a similar situation.
At the same time, while Western markets are experiencing some saturation, Eastern markets are just beginning to unfold. The most striking example is the Chinese market, where a dozen national-scale operators are racing to build backbone networks. One cannot help but envy the Chinese - they will now build houses only in close proximity to the fiber optic cable. China's Ministry of Industry and Information Technology recently issued a circular to this effect. In addition, according to this new policy, in order to maintain healthy competition, connection services must be provided to subscribers by several providers at once. True, the connection speed is not specified in any way.
Such a policy is of course beneficial for Chinese operators. In 2012, China Unicom (Hong Kong) Ltd (China's second largest telecommunications company) provided connectivity to 10 million Chinese households on its FTTH networks. And according to Economic Information Daily, approximately 40 million more will join them in 2015. The Chinese government regulation comes into force on April 1, 2013. Meanwhile, in the United States, Google's initiative called "Google Fiber" is being discussed. The bottom line is that Google is going to offer FTTH connections at speeds of 1 gigabit per second to the end consumer. Previously, 1 Gbps speeds were used only in some scientific, government and military institutions. And now we are talking about a nationwide network with such communication speeds. As a pilot version, Google fiber began to be implemented in Kansas. And although work in this direction continues, wait for the emergence of a nationwide fiber optic Google network it will take a long time. Goldman Sachs estimates the cost of this project at more than $140 billion.
Let me remind you that a lot of fiber-optic networks have already been built in the United States. The most famous example is Verizon, which has been building its own fiber optic infrastructure for many years and has already spent $15 billion on it, providing connectivity to approximately 15 million homes. But Verizon offers speeds of 50 Mbps, which can only be increased to 100 Mbps for now. And if “they” have practically resolved the issues of building backbone networks, then in our country, sad as it may be, there is simply no need for thick channels for transmitting our own traffic.
Today on Russian market There are two main competing areas for high-speed Internet connections - home fiber optic networks and ADSL connections.
Home networks are a specific type of "dedicated connection" that provides connectivity home computer to the network via a fiber optic cable, which the provider connects to each apartment. ADSL technology, in turn, refers to a type of broadband connection that operates on the principle of a telephone modem, converting analog telephone line into a high-speed transmission channel using special technology. Thus, the main difference between the two competing technologies is technological.
However, the exhibition “Departmental and corporate networks Communications" revealed the huge interest of domestic telecom operators in new technologies, including DWDM. And if such monsters as Transtelecom or Rostelecom already have state-scale transport networks, then the current energy sector is just beginning to build them. So, despite all the troubles, optics are the future. And DWDM will play a significant role here. The cost of using fiber optic technology is decreasing, making this service competitive compared to traditional services. Fiber optic data transmission technology will continue to evolve until an alternative is found. Of the future competitors, only a quantum network is seen, but this technology is still in its infancy and is not yet afraid of optical fiber.
As for the disadvantages, there is only one - the high cost of equipment and tools for installing fiber optics. The cable itself costs tens of times less than transmitters, receivers and signal amplifiers. In addition, special inverters are used to solder cables, some of which cost as much as an expensive car.

4. Conclusion.
In our time of information technology, the state has begun to pay special attention to the process of informatization of society. This process could not but affect such an aspect of public life as education. Today more and more budget funds is spent on raising the level of technical equipment in schools to improve the information education of young people. These improvements also affect the quality of the Internet connection in educational institutions. And the most progressive and fastest way to connect to the Internet is fiber optic systems. Their introduction into education will make it possible to achieve a huge leap in the information education of students and schoolchildren, which in the future will make it possible to train excellent specialists in the field of international Internet systems that will raise our country to greater heights. high level development in the world. In parallel with this, the development of telecommunications will help educate people capable of maintaining the stability and security of our Internet resources.
From my point of view, the study of the problem posed has a great future and I expect to continue working on this topic as a student. I believe that by studying modern technologies By participating in various levels of research and conferences, you can become a competitive specialist.

Literature:
1) Great Russian Encyclopedia.
2) "White Paper" newspaper.
3) Magazine "ComputerPress No. 1 2001."
4) Kudryashov Yu. B., Perov Yu. F. Rubin A. B. Radiation biophysics: radio frequency and microwave electromagnetic radiation.
5) Listvin A.V., Listvin V.N., Shvyrkov D.V. Optical fibers for communication lines. M.: LESARart, 2003.
6) Alcatel-Lucent report for SEPTEMBER 28, 2009.
7) Soviet encyclopedia.
8) Tarasov K.I. Spectral devices.

There are not many articles on Habré devoted to optical communication line technologies. More recently, there have been articles on high-power DWDM systems, and a short article on the application of a CWDM system. I will try to supplement these materials and tell you briefly about all the most common and accessible ways in Russia of using the resource of fiber-optic communication lines in data transmission networks and - just a little - cable television.

Start. Properties of standard single-mode G.652 fiber

The most common single-mode optical fiber is SMF G.652 different modifications. It's almost certain that if you have a fiber optic line, it's made of G.652 fiber. It has a number of important characteristics that you need to keep in mind.
Specific (also called kilometric) attenuation - that is, the attenuation of one kilometer of fiber - depends on the wavelength of the radiation.

Wikipedia tells us the following distribution:

In real life, the picture is now better, in particular, the specific attenuation in the 1310 nm window is usually within 0.35 dB/km, in the 1550 nm window it is about 0.22-0.25 dB/km, and the so-called “water peak” in the region of 1400-1450 nm is not present in modern fibers so strongly expressed or absent altogether.

Nevertheless, we must keep in mind this picture and the very presence of this dependence.

Historically, the range of wavelengths that an optical fiber carries is divided into the following ranges:

O - 1260…1360
E - 1360…1460
S - 1460…1530
C - 1530…1565
L - 1565…1625
U - 1625…1675
(I quote from the same Wikipedia article).

To a reasonable approximation, the fiber properties within each range can be considered approximately the same. The water peak usually occurs at the long-wave end of the E-band. We will also keep in mind that the specific (kilometer) attenuation in the O-band is approximately one and a half times higher than in the S- and C-bands, the specific chromatic dispersion, on the contrary, has a zero minimum at a wavelength of 1310 nm and non-zero in C -range.

The simplest compaction systems - bidirectional transmission along a single fiber

Initially, a duplex fiber-optic communication line required two fibers to operate: one fiber transmitted information in one direction, and the other fiber transmitted information in the other direction. This is convenient in its obviousness, but rather wasteful in relation to the use of the resource of the laid cable.

Therefore, as soon as technology began to allow, solutions began to appear for transmitting information in both directions over one fiber. Titles similar decisions- “single-fiber transceivers”, “WDM”, “bi-directional”.

The most common options use wavelengths of 1310 and 1550 nm, respectively from the O- and C-band. “In the wild,” transceivers for these wavelengths are found for lines up to 60 km. More “long-range” options are made for other combinations - 1490/1550, 1510/1570 and similar options using transparency windows with lower specific attenuation than in the O-band.

In addition to the above pairs of wavelengths, it is possible to find a combination of 1310/1490 nm - it is used if, simultaneously with data, a cable television signal at a wavelength of 1550 nm is transmitted along the same fiber; or 1270/1330nm - it is used to transmit 10 Gbit/s streams.

Data and cable multiplexing

Since I touched on the topic of CTV, I’ll tell you a little more about it.

To deliver a cable television signal from the headend to an apartment building, optics are now also used. It uses either a wavelength of 1310 nm - here there is minimal chromatic dispersion, that is, signal distortion; or a wavelength of 1550 nm - here there is a minimum specific attenuation and it is possible to use pure optical amplification using EDFA. If there is a need to deliver both a data stream (Internet) and a CATV signal to one home at the same time, you need to either use two separate fibers or a simple passive device - an FWDM filter.

This is a reversible device (that is, the same device is used for both multiplexing and demultiplexing of streams) with three outputs: for CATV, a single-fiber transceiver and a common output (see diagram). In this way, you can build a PON or Ethernet network using wavelengths 1310/1490 for data transmission, and 1550 nm for CATV.

CWDM and DWDM

theslim has already briefly talked about CWDM compaction. On my own behalf, I will only add that the channels for receiving and transmitting data indicated in the article are purely arbitrary; the multiplexer does not care at all which direction the signal goes in each channel; and optical receivers are broadband, they respond to radiation of any wavelength. From important points that must be kept in mind when designing a CWDM line is the difference in specific attenuation in the fiber on different channels (see the first section of this article), as well as the difference in the attenuation introduced by the multiplexer itself. The multiplexer is made of series-connected filters, and if for the first channel in the chain the attenuation can be less than one decibel, then for the last it will be closer to four (these values ​​are given for a 1x16 multiplexer, for 16 wavelengths). It is also useful to remember that no one prohibits building two-fiber CWDM lines by simply combining two pairs of multiplexers into one functional block.
In addition, I note that it is quite possible to allocate part of the frequency resource for CATV, transmitting up to seven duplex data streams over one fiber simultaneously with analog television.

A DWDM system is fundamentally no different from a CWDM system, but - as they say - “the devil is in the details.” If the channel pitch in CWDM is 20 nm, then for DWDM it is much narrower and is measured in gigahertz (the most common option now is 100 GHz, or about 0.8 nm; the aging option with a 200 GHz band is also possible, and more modern ones are gradually spreading - 50 and 25 GHz). The DWDM frequency range lies in the C- and L-band, with 40 channels at 100 GHz each. This implies several important properties DWDM systems.

Firstly, they are significantly more expensive than CWDM. Their use requires lasers with strict wavelength tolerances and multiplexers of very high selectivity.

Secondly, the ranges used lie in the working areas of EDFA optical amplifiers. This makes it possible to build long lines with purely optical amplification without the need for optoelectronic signal conversion. It is this property that has led many, when they hear the word “DWDM,” to immediately imagine the complex systems of telecom market monsters, although such equipment can be used in simpler systems.
And thirdly, attenuation in the C- and L-bands is minimal across the entire transparency window of the optical fiber, which makes it possible to build lines of greater length even without amplifiers than when using CWDM.

DWDM multiplexers are just as passive devices as CWDM multiplexers. For up to 16 channels they are also made up of individual filters and are fairly simple devices. However, multiplexers for a larger number of channels are made using Arrayed Wavelength Grating technology, which is extremely sensitive to temperature changes. Therefore, such multiplexers are produced either with electronic circuit thermal stabilization (Thermal AWG), or using special ways automatic compensation that does not require energy (Athermal AWG). This makes such multiplexers more expensive and more difficult to operate.

Practical Limitations in Fiber Optic Communications

Finally, I'll talk a little about the limitations that you have to deal with when organizing optical communications.

As comrade saul quite rightly noted, the first limitation is the optical budget.
I will add some clarifications to it.

If we are talking about two-fiber communication lines, it is enough to calculate the optical budget for one wavelength - the one at which the transmission will be carried out.

As soon as we have wave multiplexing (especially in the case of single-fiber transceivers or CWDM systems), we immediately need to remember about the unevenness of the specific attenuation of the fiber at different wavelengths and about the attenuation introduced by multiplexers.

If we are building a system with intermediate branches on OADM, do not forget to calculate the attenuation on OADM. By the way, it differs for the end-to-end channel and output wavelengths.

Don't forget to leave a few decibels of operational reserve.

The second thing you have to deal with is chromatic dispersion. It really becomes relevant for 10 Gbit/s lines, and generally speaking, the equipment manufacturer thinks about it first of all. By the way, it is dispersion that gives physical meaning mention of kilometers in the marketing names of transceivers. It is simply useful for the operating specialist to understand that there is such a property of the fiber and that in addition to signal attenuation in the fiber, dispersion also spoils the picture. Add tags