Methods for transmitting signals of various types, data and control commands over fiber-optic communication lines began to be actively introduced in the last decade of the last century. However, for a long time they could not constitute serious competition (according to at least, in the TSB segment) coaxial cable and twisted pair. Despite such disadvantages as high resistance and capacitance, which significantly limits the signal transmission range, coaxial cable and twisted pair prevailed in security systems. Today the situation is beginning to change, and I would venture to say that these changes are fundamental. No in small systems Where video and control signals need to be transmitted over short distances, coaxial cable and twisted pair are still indispensable. In large and especially distributed systems There is practically no alternative to fiber optics.
The fact is that fiber optic equipment today has become much more affordable and the trend towards its further reduction in price is quite stable.
So fiber optics currently makes it possible to offer security systems customers not only a reliable, but also a cost-effective solution. Using a light beam to transmit a signal, a wide bandwidth allows you to transmit a high-quality signal over long distances without the use of amplifiers and repeaters.
The main advantages of using fiber optics are known to be:
– wider bandwidth (up to several gigahertz) than that of copper cable (up to 20 MHz);
– immunity to electrical interference, absence of “ground loops”;
– low losses during signal transmission, signal attenuation is about 0.2–2.5 dB/km (for coaxial cable RG59 – 30 dB/km for a 10 MHz signal);
– does not cause interference in neighboring copper or other fiber optic cables;
– long transmission range;
– increased security data transmission;
– good quality of the transmitted signal;
– fiber optic cable is miniature and lightweight.

Operating principle of a fiber optic line
Fiber optics is a technology that uses light as an information carrier, no matter what type of information. we're talking about: analog or digital. Typically, infrared light is used and the transmission medium is fiberglass.
Fiber optic equipment can be used to transmit analogue or digital signal various types.
In its simplest form, a fiber optic communication line consists of three components:
– a fiber-optic transmitter for converting the input electrical signal from a source (for example, a video camera) into a modulated light signal;
– a fiber optic line through which the light signal is transmitted to the receiver;
– a fiber-optic receiver that converts the signal into an electrical one, almost identical to the source signal.
The source of light distributed through optical cables is a light emitting diode (LED) (or semiconductor laser - LD). At the other end of the cable, a receiving detector converts the light signals into electrical signals. Fiber optics relies on a special effect - refraction at the maximum angle of incidence, when total reflection occurs. This phenomenon occurs when a ray of light leaves a dense medium and enters a less dense medium at a certain angle. The inner core (strand) of a fiber optic cable has a higher refractive index than the cladding. Therefore, a beam of light, passing through the internal core, cannot go beyond its limits due to the effect of total reflection (Fig. 1). Thus, the transported signal travels inside a closed medium, making its way from the signal source to its receiver.
The remaining elements of the cable only protect the fragile fiber from damage by the external environment of varying aggressiveness.

Introduction

Currently, the telecommunications industry is undergoing unprecedented changes associated with the transition from voice-based systems to data transmission systems, which is a consequence of the rapid development of Internet technologies and a variety of network applications. Therefore, one of the main requirements for transport networks for data transmission is the ability to quickly increase their capacity in accordance with the growth in traffic volumes.

Digital communication via optical cables, which is becoming increasingly relevant, is one of the main directions of scientific and technological progress.

The advantages of digital streams are their relatively easy computer processing, the ability to increase the signal-to-noise ratio and increase the information flow density.

The advantages of optical transmission systems over transmission systems operating over metal cables are:

Possibility of obtaining light guides with low attenuation and dispersion, which means increasing the communication range;

Wide bandwidth, i.e. large information capacity;

An optical cable does not have electrical conductivity or inductance, that is, the cables are not subject to electromagnetic influence;

Negligible crosstalk;

Low cost of optical cable material, its small diameter and weight;

High communication secrecy;

Possibility of system improvement while maintaining full compatibility with other transmission systems.

Linear paths of fiber-optic transmission systems are built as two-fiber single-band single-cable, single-fiber single-band single-cable, single-fiber multi-band single-cable (with wavelength division multiplexing).

Considering that the share of costs for cable equipment makes up a significant part of the cost of communication, and prices for optical cable currently remain quite high, the task arises of increasing the efficiency of using the bandwidth of optical fiber by simultaneously transmitting a larger volume of information through it.

The purpose of the work is to consider in various ways increasing the throughput of optical fiber.

Principles of signal transmission over optical fiber and basic parameters of optical fibers

Principles of signal transmission over optical fiber

The use of optical fiber networks is based on the principle of propagation of light waves along optical fibers over long distances. In this case, electrical signals carrying information are converted into light pulses, which minimal distortion transmitted via fiber-optic communication lines (FOCL). Widespread similar systems received thanks to a number of advantages that fiber-optic lines have in comparison with transmission systems that use copper cables or radio lines as a transmission medium. The advantages of fiber-optic lines include a wide bandwidth due to the high carrier frequency - up to 10 14 Hz. This band makes it possible to transmit information flows at speeds of several terabits per second. An important advantage of fiber-optic lines are also such factors as low signal attenuation, which allows, using modern technologies, to build sections of optical systems of a hundred or more kilometers without repeaters, high noise immunity associated with the low susceptibility of optical fiber to electromagnetic interference, and much more.

Optical fibers are one of the main components of fiber-optic lines. They are a combination of materials having different optical and mechanical properties.

The outer part of the fiber is usually made of plastics or epoxy compositions that combine high mechanical strength and a high refractive index of light. This layer provides mechanical protection for the light guide and its resistance to external sources optical radiation.

The main part of the fiber consists of a core and a sheath. The core material is ultra-pure quartz glass, which is the main medium for transmitting optical signals. Confinement of the light pulse occurs due to the fact that the refractive index of the core material is greater than that of the cladding. Thus, with an optimally selected ratio of the refractive indices of the materials, the light beam is completely reflected into the core.

For transmission, light is introduced at a slight angle into the end of the optical fiber. The maximum angle of penetration of a light pulse into the fiber core b 0 is called the angular aperture of the optical fiber. The sine of the angular aperture is called the numerical aperture NA and is calculated by the formula:

From the above formula it follows that the numerical aperture of the optical fiber NA depends only on the refractive indices of the core and cladding - n 1 and n 2. In this case, the condition is always met: n 1 >n 2 (Figure 1).

Figure 1 - Light propagation in an optical fiber. Numerical aperture of the light guide.

If the angle of incidence of light b is greater than b 0, then the light beam is completely refracted and does not enter the optical fiber core (Fig. 2a). If the angle b is less than b 0, then reflection occurs from the boundary of the core materials on the shell, and the light beam propagates inside the core (Fig. 2b).

Figure 2 - Conditions for light propagation in optical fiber

The speed of light propagation in an optical fiber depends on the refractive index of the fiber core and is defined as:

where C is the speed of light in vacuum, n is the refractive index of the core.

Typical refractive indices of the core material are in the range of 1.45 - 1.55.

In order to transmit light along optical waveguides, a source of strictly coherent light is required. To increase the transmission range, the transmitter spectrum width should be as small as possible. Lasers are especially suitable for this purpose, which, thanks to the induced emission of light, make it possible to maintain a constant phase difference at the same wavelength. Due to the fact that the diameter of the fiber core is comparable to the wavelength of optical radiation, the phenomenon of interference occurs in the light guide. This can be proven by the fact that light propagates in the core glass only at certain angles, namely in directions in which the introduced light waves are amplified when superimposed. So-called constructive interference occurs. The allowed light waves that can propagate in an optical fiber are called modes (or natural waves). According to the types of propagation of light rays, optical fibers are divided into multimode, that is, using a number of light waves, and single-mode, in which only one light ray propagates. Several basic parameters are used to describe the processes of light propagation in optical fibers.

Methods for transmitting signals of various types, data and control commands over fiber-optic communication lines began to be actively introduced in the last decade of the last century. However, for a long time they could not seriously compete (at least in the TSB segment) with coaxial cable and twisted pair. Despite such disadvantages as high resistance and capacitance, which significantly limits signal transmission range, coaxial cable and twisted pair prevailed in security systems. Today the situation is beginning to change, and I would venture to say that these changes are fundamental. No, in small systems where video and control signals need to be transmitted over short distances, coaxial cable and twisted pair are still indispensable. In large and especially distributed systems, optical fiber has practically no alternative.
The fact is that fiber optic equipment today has become much more affordable and the trend towards its further reduction in price is quite stable.
So fiber optics currently makes it possible to offer security systems customers not only a reliable, but also a cost-effective solution. Using a light beam to transmit a signal, a wide bandwidth allows you to transmit a high-quality signal over long distances without the use of amplifiers and repeaters.
The main advantages of using fiber optics are known to be:
– wider bandwidth (up to several gigahertz) than that of copper cable (up to 20 MHz);
– immunity to electrical interference, absence of “ground loops”;
– low losses during signal transmission, signal attenuation is about 0.2–2.5 dB/km (for RG59 coaxial cable – 30 dB/km for a 10 MHz signal);
– does not cause interference in neighboring copper or other fiber optic cables;
– long transmission range;
– increased security of data transmission;
– good quality of the transmitted signal;
– fiber optic cable is miniature and lightweight.

Operating principle of a fiber optic line
Fiber optics is a technology that uses light as an information carrier, and it does not matter what type of information we are talking about: analog or digital. Typically, infrared light is used and the transmission medium is fiberglass.
Fiber optic equipment can be used to transmit various types of analog or digital signals.
In its simplest form, a fiber optic communication line consists of three components:
– a fiber-optic transmitter for converting the input electrical signal from a source (for example, a video camera) into a modulated light signal;
– a fiber optic line through which the light signal is transmitted to the receiver;
– a fiber-optic receiver that converts the signal into an electrical one, almost identical to the source signal.
The source of light distributed through optical cables is a light emitting diode (LED) (or semiconductor laser - LD). At the other end of the cable, a receiving detector converts the light signals into electrical signals. Fiber optics relies on a special effect - refraction at the maximum angle of incidence, when total reflection occurs. This phenomenon occurs when a ray of light leaves a dense medium and enters a less dense medium at a certain angle. The inner core (strand) of a fiber optic cable has a higher refractive index than the cladding. Therefore, a beam of light, passing through the internal core, cannot go beyond its limits due to the effect of total reflection (Fig. 1). Thus, the transported signal travels inside a closed medium, making its way from the signal source to its receiver.
The remaining elements of the cable only protect the fragile fiber from damage by the external environment of varying aggressiveness.

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Rice. 1 Fiber optics are based on the effect of total reflection

Physical parameters of optical fibers
All common types of fibers are characterized by two the most important parameters: attenuation and dispersion.
There are mode and material dispersions - signal distortions caused by the peculiarities of the propagation of light waves in the medium.
Material dispersion is caused by waves of different lengths traveling with at different speeds, which is due to the characteristics of the physical structure of the fiber. This effect is especially noticeable when using single-mode fiber. Reducing the source radiation bandwidth and choosing the optimal wavelength leads to a decrease in material dispersion.
Mode dispersion occurs in multimode fiber due to the difference in path lengths traversed by rays of different modes. Its reduction is caused by a decrease in the diameter of the fiber core, a reduction in the number of modes, and the use of fiber with a gradient profile.
The signal attenuation in a fiber optic cable depends on the properties of the material and on external influences. Attenuation characterizes the loss of power of a transmitted signal over a given distance, and is measured in dB/km, where decibel is the logarithmic expression of the ratio of the power leaving the source P1 to the power entering the receiver P2, dB = 10*log(P1/P2). A loss of 3 dB means that half the power is lost. A loss of 10 dB means that only 1/10 of the source power reaches the receiver, a loss of 90%. Fiber optic lines can typically operate normally with a loss of 30 dB (receiving only 1/1000th of the power).
There are two fundamentally different physical mechanisms that cause this effect. Absorption losses. Associated with the transformation of one type of energy into another. Electromagnetic wave a certain length causes in some chemical elements a change in electron orbits, which, in turn, leads to heating of the fiber. Naturally, the process of wave absorption is less, the shorter its length and the purer the fiber material.
Scattering losses. The reason for the decrease in signal power in this case means the output of the part luminous flux from the waveguide. This is due to inhomogeneities in the refractive index of materials. And as the wavelength decreases, scattering losses increase.

Rice. 2 Optical fiber transparency windows

In theory best performance overall attenuation can be achieved at the intersection of the absorption and dissipation curves. The reality is somewhat more complex and is related to the chemical composition of the environment. In quartz fibers (SiO2), silicon and oxygen are active at a certain wavelength and significantly degrade the transparency of the material in two vicinities.
As a result, three transparency windows are formed (Fig. 2), within which attenuation has the smallest value. The most common wavelengths are:
0.85 µm;
1.3 µm;
1.55 microns.
At analog transmission The most commonly used wavelengths are 850 and 1310 microns.
It is for these ranges that special heterolasers have been developed, on which modern FOCLs (fiber-optic communication systems) are based.
Currently, optical fiber with this characteristic is already considered obsolete. Quite a long time ago, the production of optical fiber of the AllWave ZWP (zero water peak) type was developed, in which hydroxyl ions in the composition of quartz glass are eliminated. Such glass no longer has a window, but an opening in the range from 1300 to 1600 nm.
All transparency windows lie in the infrared range, i.e. the light transmitted through the fiber optic link is not visible to the eye. It is worth noting that radiation visible to the eye can be introduced into a standard optical fiber. For this, they use either small blocks present in some reflectometers, or even a slightly modified Chinese laser pointer. With the help of such devices you can find fractures in cords. Where the optical fiber is broken, a bright glow will be visible. Such light quickly attenuates in the fiber, so it can only be used over short distances (no more than 1 km).

Analogue transmission

The simplest video transmitters use amplitude modulation (AM): the intensity of the emitted light changes in proportion to changes in the amplitude of the video signal. To obtain a more stable result, increase the signal transmission distance, achieve best ratio signal/noise frequency modulation (FM) is applied.
Amplitude modulation (AM) is a type of modulation in which the variable parameter of the carrier signal is its amplitude. The intensity of the emitted light changes in proportion to the change in the amplitude of the video signal. Since it is quite difficult to control the radiation intensity at a high level, even small changes in it introduce significant distortions into the transmitted signal.
Frequency modulation (FM) is a type of analog modulation in which an information signal controls the frequency of light pulses. Compared with amplitude modulation the amplitude remains constant.
The analog method is used to transmit video and audio signals, control signals, 10/100M Ethernet, and monitoring the status of contacts.
It should be noted that analog devices are not the best choice for transmitting video or audio information. Transmitting and receiving it via fiber optic lines using analog equipment can be quite difficult. In addition, the price differences between analog and similar digital equipment insignificant.
Equipment of this type is present in the assortment of many market players; readers will be able to familiarize themselves with some models in the review part of the article.

S732DV (GE Security, Fiber Option)
A set of analog transceivers is designed to transmit video and data over 1 single-mode or multimode optical fiber over a distance of up to 60 km. Distinctive features of the device are a wide range of operating temperatures (from -40 C to +75 C), Plug-and-Play technologies, CWDM, SMARTSä diagnostics, which allows testing the system in real time. The equipment comes with a 5-year warranty.

DE7400 (GE Security, EtherNAVä IFS line)

The series of 2-port transceivers are designed to transmit and receive data at speeds of 10/100/1000 Mbps over multimode, single-mode fiber optics or Cat 5 electrical cable. The DE7400 features increased climate protection for operation in extreme temperatures (-40 C to +85 C). Standard function is the actuation of contacts to initiate a remote alarm in case of loss optical communications. The RJ-45 connector has LED indicators power status and data transfer speed. It also supports RSTP, QoS/CoS, IGMP, VLAN, SNMP protocols. Supports IEEE 802.3 standards, which makes possible connection any devices for organizing local networks. The equipment comes with a lifetime warranty.
The IFS equipment line includes equipment with different configurations of ports.

Receiver/transmitter OVT/OVR-1 (“BIK-Inform”)
The OVT/OVR-1 series equipment (receiver/transmitter) is designed for transmitting analog video signals in real time in video surveillance systems at industrial and extended facilities. The device allows you to transmit high-quality color and b/w video signals over multimode optical fiber over a distance of up to 5 km in the frequency band 25 Hz - 10 MHz with a signal-to-noise ratio of at least 5 dB. The equipment is characterized by high noise immunity. There is a built-in test signal generator, AGC systems (automatic level adjustment based on the clock signal level), low current consumption - no more than 85 mA for the transmitter and 75 mA for the receiver. Compact dimensions allow devices to be placed both in DIN-rail mounting cabinets and in small junction boxes. No hardware required additional settings and can be operated in a temperature range from -40 °C to +50 °C.

SFS10-100/W-80 (SF&T)

The kit, consisting of two analog transceivers, is designed to organize 1 Ethernet 10/100M data channel over 1 single-mode optical fiber. This device, the latest in the SFS10-100/W-xx series, allows you to increase the signal transmission distance to 80 km. Operating modes: duplex and half-duplex.
Thanks to support for IEEE 802.3 10 Base-T/100Base-Tx/100Base-Fx standards, it is possible to connect most IP devices used to organize local networks, as well as to build video surveillance systems.
Wide operating temperature range (from -10 to +70 °C), Plug-and-play support, no need for additional settings or use of attenuators, as well as compact dimensions(165 x 144 x 33 mm) make installation of devices as fast and convenient as possible. The modular design allows the SFS10-100/W-80 to be used as individual modules and rack-mounted.
All SF&T equipment comes with a 3-year warranty.

SVP-11T/12R
SVP-13T/14R (“Special Video Project”)
The devices are designed to transmit signals in television surveillance systems over distances of up to 6–12 km. Transmitter and receiver sets provide transmission of one composite video signal over a multimode optical cable at wavelengths of 850 and 1310 nm.
Video signal resolution – 570 TVL, signal-to-noise ratio at maximum range – no worse than 50 dB, frequency band: 50 Hz – 8 MHz. System automatic adjustment gain constantly maintains a video signal swing of 1 V at the output. Light signaling indicates the presence or absence of a video signal. The devices have small dimensions, low power consumption, and are equipped with wall mounting elements.
The devices are protected from power reversal - if turned on incorrectly, they do not fail. They operate in plug and play mode - no setup or adjustment is required during installation.
Signal receivers are also available in a housing designed for installation in standard 19” racks.

SVP-21T
SVP-22T (“Special Video Project”)

Fiber optic video transmitters SVP-21T and SVP-22T are designed to work with outdoor television surveillance cameras. The sealed casing is equipped with sealed leads and has a weather protection rating of IP66. Operating temperature from -35 to +50 °C. The signal is transmitted over long distances: up to 6–12 km.
Transmitters SVP-21T and SVP-22T, complete with receivers SVP-12R, SVP-14R, SVP-12-2Rack, SVP-14-2Rack, provide transmission of one composite video signal over a multimode optical cable at wavelengths of 850 and 1310 nm. Devices are supplied with mains power supply alternating current with a voltage of 220 V or 24 V. They operate in plug and play mode - no configuration or adjustment is required during installation. The automatic gain control system in the receivers constantly maintains a video signal swing of 1 V at the output.
The pressurized housing has free space for cross-connecting cables of other equipment. dimensions: 200 x 150 x 55 mm.

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 the new kind wired connection.

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

• Broadband optical signals due to extremely high carrier frequency. This means that information can be transmitted over a fiber optic line at a speed of about 1 Tbit/s;
• Very low attenuation light signal in fiber, which allows you 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 communication lines - the service life of fiber-optic communication lines is at least 25 years.

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 baud rate and system specifics of the device, the data stream may be converted from sequential type in 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 area networks for short-distance communications. 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 communication high speed broadcast digital data over vast distances. Fiber optic lines can form both new network, and serve to unite already existing networks- sections of optical fiber trunks, connected physically at the fiber 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, it can propagate simultaneously big number modes - rays introduced into the fiber at different angles. 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, they throughput cannot be compared with 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 optical at the receiver. electric type. 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. Electronic components in the WDM receiver and transmitter are different compared to 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 TV, remote video surveillance, video conferencing and video broadcasting, 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.

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 existing network equipment connected by copper wires, converters are required, for example 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 greater 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 networks different types, it allows you to connect nodes over a very large distance. 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 a 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(e.g. 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.