Fiber optical lines. Fiber optic communication lines

Not everyone still knows what fiber optic communication lines are. In optical communication lines, the light signal is transported within the fibers. An optical fiber communication system provides a connection for transmitting information between two points.

These components form the basis of any fiber optics, starting with a simple single-channel system. But there are also more complex systems that are professionally installed and installed by specialists from specialized companies who have professional equipment and a number of certificates from https://kabelnieseti.ru/services/volokonno-opticheskie-linii-svyazi/. The information transmitted is digital (in most cases), which makes the fiber optic system very versatile and relatively insensitive to harmonic distortion, for example. To understand what fiber optic communication lines are, let’s look at the basic concepts.

There are different modulation formats, that is, different methods of encoding information. For example, the simple non-return-to-0 (NRZ) format transmits successive bits by sending either high or low optical power signals, with no spaces between adjacent bits, and additional means for synchronization. In contrast, the return-zero (RZ) format easily self-synchronizes by returning to a rest state after each bit, but it requires higher optical transmission bandwidth for the same data rates.

In addition to hardware details and optical throughput related to modulation efficiency, transmission formats also vary in terms of their sensitivity to alternative noise and crosstalk.

FOCL signal transmitter

The transmitter converts the electronic input signal into a modulated light beam. Information can be encoded for example through:

optical power (intensity),
optical phase,
polarization;

Intensity modulation is the most common option. The optical wavelength is formed, as a rule, in one of the so-called telecommunication windows. A typical transmitter is based on a single-mode laser diode (usually a VCSEL or DFB), which can be either directly modulated by a DML current (= directly modulated laser) or by an external optical modulator.

Direct modulation is a simpler option and can operate at signal rates of up to 10 Gbps or even higher. However, the carrier density in the laser diode is varied and then adjusted to a particular instantaneous frequency so that the signal distorts in the form of frequency modulation. This makes the signal more sensitive to the effects of chromatic dispersion when transmitted over long distances. Thus, external modulation is usually preferred for the combination of high-speed data transmission (eg, 10 to 40 Gbit/s) with long transmission distances (many kilometers). The laser can operate continuously and signal distortion is kept to a minimum.

To achieve even higher-speed signaling in 1-channel systems, time division multiplexing can be used in systems with four 40 Gbit/s channels, each of which is used in a time-interleaved manner to achieve a total speed of 160 Gbit/s . But these are technologies of the future. To achieve high-speed data transmission with return-to-zero formats, it may be advantageous to use a pulsed source (eg, a laser emitting soliton pulses) in combination with an intensity modulator. This reduces the modulator's bandwidth requirements as the modulator's transmittance evolves between pulses.

To obtain high-speed data transmission, the transmitter must meet a number of requirements. It is important to achieve a high extinction ratio, low timing jitter, low intensity noise and a precisely controlled clock frequency. Of course, the data transmitter must operate stably and reliably with minimal operator intervention.

Optical fiber

Single-mode fibers are used for medium to long distance transmission, but the system can also be used with multimode fiber for short distances. In the latter case, mode-to-mode dispersion may limit the transmission range or speed. So-called full-duplex channels provide a connection for transmitting data in both directions.

Broadband fiber channels may contain fibers with amplifiers at certain points (lumped amplifiers) to prevent the power level from dropping to too low a level. Alternatively, a distributed amplifier can be used, implemented from the transmitting fiber itself, by injecting an additional high-power pump beam (usually at the receiver end).

Dispersion compensation (counteracting fiber chromatic dispersion effects) as well as signal regeneration can be used. The latter means that not only the power level, but also the signal quality (for example, pulse duration and time) are restored. This is achievable either by processing the optical signal itself, or by detecting the signal electronically, applying some optical signal processing, and retransmitting it. These are the basic principles of operation of fiber-optic communication lines.

What is a fiber optic receiver?

The receiver contains some type of fast photodetector, typically a photodiode, and suitable high-speed electronics to amplify the weak signal and extract digital data. Avalanche photodiodes can be used for particularly high sensitivity. The sensitivity of the receiver is limited by noise, usually of electronic origin. However, it should be noted that the optical signal itself is accompanied by optical noise, for example from an amplifier. Such optical noise introduces limitations that cannot be removed by any special receiver design.

Optics opens up great opportunities where high-speed communications with high throughput are required. This is a well-proven, understandable and convenient technology. In the Audio-Visual field, it opens up new perspectives and provides solutions not available through other methods. Optics has penetrated into all key areas - surveillance systems, control rooms and situation centers, military and medical facilities, and areas with extreme operating conditions. Fiber-optic lines provide a high degree of protection of confidential information and allow the transmission of uncompressed data such as high-resolution graphics and video with pixel accuracy. New standards and technologies of fiber-optic communication lines. Is fiber the future of SCS (structured cabling systems)? We are building an enterprise network.

Fiber optic (aka fiber optic) cable- this is a fundamentally different type of cable compared to the two types of electrical or copper cable considered. Information on it is transmitted not by an electrical signal, but by a light one. Its main element is transparent fiberglass, through which light travels over vast distances (up to tens of kilometers) with insignificant attenuation.

The structure of fiber optic cable is very simple and is similar to the structure of a coaxial electrical cable (Fig. 1). Only instead of a central copper wire, thin (about 1 - 10 microns in diameter) glass fiber is used here, and instead of internal insulation, a glass or plastic shell is used, which does not allow light to escape beyond the fiberglass. In this case, we are talking about the mode of so-called total internal reflection of light from the boundary of two substances with different refractive indices (the glass shell has a much lower refractive index than the central fiber). There is usually no metal braiding on the cable, since shielding from external electromagnetic interference is not required. However, sometimes it is still used for mechanical protection from the environment (such a cable is sometimes called an armored cable; it can combine several fiber optic cables under one sheath).

Fiber optic cable has exceptional performance on noise immunity and secrecy of transmitted information. In principle, no external electromagnetic interference can distort the light signal, and the signal itself does not generate external electromagnetic radiation. It is almost impossible to connect to this type of cable for unauthorized network eavesdropping, since this would compromise the integrity of the cable. The theoretically possible bandwidth of such a cable reaches 1012 Hz, that is, 1000 GHz, which is incomparably higher than that of electrical cables. The cost of fiber optic cable is constantly falling and is now approximately the same as the cost of thin coaxial cable.

Typical signal attenuation in fiber optic cables at frequencies used in local networks ranges from 5 to 20 dB/km, which approximately corresponds to the performance of electrical cables at low frequencies. But in the case of a fiber-optic cable, as the frequency of the transmitted signal increases, the attenuation increases very slightly, and at high frequencies (especially above 200 MHz), its advantages over an electric cable are undeniable; it simply has no competitors.

Fiber-optic communication lines (FOCL) make it possible to transmit analog and digital signals over long distances, in some cases over tens of kilometers. They are also used over smaller, more "controllable" distances, such as inside buildings. Examples of solutions for building SCS (structured cabling systems) for building an enterprise network are here: Building an enterprise network: SCS construction diagram - Horizontal optics. , Building an enterprise network: SCS construction scheme - Centralized optical cable system. , Building an enterprise network: SCS construction scheme - Zone optical cable system.

The advantages of optics are well known: immunity to noise and interference, small diameter cables with huge bandwidth, resistance to hacking and interception of information, no need for repeaters and amplifiers, etc.
There were once problems with the termination of optical lines, but today they have been largely resolved, so working with this technology has become much easier. There are, however, a number of issues that must be considered solely in the context of the application areas. As with copper or radio transmission, the quality of fiber optic communication depends on how well the transmitter output signal and the receiver input stage are matched. Incorrect signal power specification results in increased transmission bit error rates; too much power and the receiver amplifier “oversaturates”; too little and a noise problem arises, as it begins to interfere with the useful signal. Here are the two most critical parameters of a fiber-optic line: the output power of the transmitter and transmission losses - attenuation in the optical cable that connects the transmitter and receiver.

There are two different types of fiber optic cable:

* multimode or multimode cable, cheaper, but of lower quality;
* single-mode cable, more expensive, but has better characteristics compared to the first one.

The type of cable will determine the number of propagation modes, or “paths,” that light travels within the cable.

Multimode cable, most commonly used in small industrial, residential and commercial projects, has the highest attenuation coefficient and only works over short distances. The older type of cable, 62.5/125 (these numbers characterize the inner/outer diameters of the fiber in microns), often called "OM1", has limited bandwidth and is used to transmit data at speeds up to 200 Mbps.
Recently, 50/125 “OM2” and “OM3” cables have been introduced, offering speeds of 1 Gbit/s over distances of up to 500 m and 10 Gbit/s over distances of up to 300 m.

Singlemode cable used in high-speed connections (above 10 Gbit/s) or over long distances (up to 30 km). For audio and video transmission, the most appropriate is to use “OM2” cables.
Rainer Steil, vice president of marketing for Extron Europe, notes that fiber optic lines have become more affordable and are increasingly being used for networking inside buildings, leading to an increase in the use of AV systems based on optical technologies. Steil says: “In terms of integration, fiber-optic lines already offer several key advantages today.
Compared to similar copper-cable infrastructure, optics allows the use of both analog and digital video signals simultaneously, providing a single system solution for working with existing as well as future video formats.
In addition, because The optics offer very high throughput, the same cable will work with higher resolutions in the future. FOCL easily adapts to new standards and formats emerging in the process of development of AV technologies.”

Another recognized expert in the field is Jim Hayes, president of the Fiber Optic Association of America, which was founded in 1995 and promotes professionalism in the fiber optics field and has more than 27,000 qualified optical installation professionals. He says the following about the growing popularity of fiber-optic lines: “The benefit is the speed of installation and the low cost of components. The use of optics in telecommunications is growing, especially in Fiber-To-The-Home* (FTTH) systems. wireless enabled, and in the field of security (surveillance cameras).
The FTTH segment appears to be growing faster than other markets in all developed countries. Here in the USA, networks for traffic control, municipal services (administration, firefighters, police), and educational institutions (schools, libraries) are built on fiber optics.
The number of Internet users is growing - and we are rapidly building new data processing centers (DPCs), for the interconnection of which optical fiber is used. Indeed, when transmitting signals at a speed of 10 Gbit/s, the costs are similar to “copper” lines, but the optics consume significantly less energy. For many years, fiber and copper advocates have been battling each other for priority in corporate networks. Waste of time!
Today, WiFi connectivity has become so good that users of netbooks, laptops and iPhones have given preference to mobility. And now in corporate local networks, optics are used for switching with wireless access points.”
Indeed, the number of applications for optics is increasing, mainly due to the above-mentioned advantages over copper.
Optics has penetrated into all key areas - surveillance systems, control rooms and situation centers, military and medical facilities, and areas with extreme operating conditions. Reduced equipment costs have made it possible to use optical technology in traditionally copper-based areas - conference rooms and stadiums, retail and transportation hubs.
Extron's Rainer Steil comments: “Fiber optic equipment is widely used in healthcare settings, for example for switching local video signals in operating rooms. Optical signals have nothing to do with electricity, which is ideal for patient safety. FOCLs are also perfect for medical schools, where it is necessary to distribute video signals from several operating rooms to several classrooms so that students can watch the progress of the operation “live.”
Fiber optic technologies are also preferred by the military, since the transmitted data is difficult or even impossible to “read” from the outside.
Fiber-optic lines provide a high degree of protection of confidential information and allow the transmission of uncompressed data such as high-resolution graphics and video with pixel accuracy.
The ability to transmit over long distances makes optics ideal for Digital Signage systems in large shopping centers, where the length of cable lines can reach several kilometers. If for a twisted pair cable the distance is limited to 450 meters, then for optics 30 km is not the limit.”
When it comes to the use of fiber optics in the Audio-Visual industry, two main factors are driving progress. Firstly, this is the intensive development of IP-based audio and video transmission systems, which rely on high-bandwidth networks - fiber-optic lines are ideal for them.
Secondly, there is a widespread requirement to transmit HD video and HR computer images over distances greater than 15 meters - and this is the limit for HDMI transmission over copper.
There are cases when the video signal simply cannot be “distributed” over a copper cable and it is necessary to use optical fiber - such situations stimulate the development of new products. Byung Ho Park, vice president of marketing at Opticis, explains: “The UXGA 60 Hz data bandwidth and 24-bit color require a total speed of 5 Gbps, or 1.65 Gbps per color channel. HDTV has slightly lower bandwidth. Manufacturers are pushing the market, but the market is also pushing players to use higher quality images. There are certain applications that require displays capable of displaying 3-5 million pixels or 30-36-bit color depth. In turn, this will require a transmission speed of about 10 Gbit/s.”
Today, many manufacturers of switching equipment offer versions of video extenders (extenders) for working with optical lines. ATEN International, TRENDnet, Rextron, Gefen and others produce various models for a range of video and computer formats.
In this case, service data - HDCP** and EDID*** - can be transmitted using an additional optical line, and in some cases - via a separate copper cable connecting the transmitter and receiver.
As HD has become the standard for the broadcast market,“Other markets—installation markets, for example—have also begun to use copy protection for content in DVI and HDMI formats,” says Jim Giachetta, senior vice president of engineering at Multidyne. “Using our HDMI-ONE device, users can send a video signal from a DVD or Blu-ray player to a monitor or display located up to 1000 meters away. Previously, no multimode device supported HDCP copy protection.”

Those who work with fiber-optic lines should not forget about specific installation problems - cable termination. In this regard, many manufacturers produce both the connectors themselves and installation kits, which include specialized tools, as well as chemicals.
Meanwhile, any element of a fiber-optic line, be it an extension cord, a connector or a cable junction, must be checked for signal attenuation using an optical meter - this is necessary to assess the total power budget (power budget, the main calculated indicator of a fiber-optic line). Naturally, you can assemble fiber cable connectors manually, “on your knees,” but truly high quality and reliability are guaranteed only when using ready-made, factory-produced “cut” cables that have been subjected to thorough multi-stage testing.
Despite the enormous bandwidth of fiber-optic communication lines, many still have the desire to “cram” more information into one cable.
Here, development is going in two directions - spectral multiplexing (optical WDM), when several light rays with different wavelengths are sent into one light guide, and the other - serialization / deserialization of data (English SerDes), when parallel code is converted into serial and vice versa.
However, spectrum multiplexing equipment is expensive due to complex design and the use of miniature optical components, but does not increase transmission speed. The high-speed logic devices used in SerDes equipment also increase the cost of the project.
In addition, today equipment is produced that allows you to multiplex and demultiplex control data - USB or RS232/485 - from the total light flux. In this case, light streams can be sent along one cable in opposite directions, although the price of devices that perform these “tricks” usually exceeds the cost of an additional light guide for returning data.

Depending on the main area of application, fiber optic cables are divided into two main types:

Internal cable:
When installing fiber-optic lines in enclosed spaces, a fiber-optic cable with a dense buffer (to protect against rodents) is usually used. Used to build SCS as a trunk or horizontal cable. Supports data transmission over short and medium distances. Ideal for horizontal cabling.

External cable:
Fiber optic cable with a dense buffer, armored with steel tape, moisture resistant. It is used for external laying when creating a subsystem of external highways and connecting individual buildings. Can be installed in cable ducts. Suitable for direct installation in the ground.

External self-supporting fiber optic cable:
The fiber optic cable is self-supporting, with a steel cable. Used for external installation over long distances within telephone networks. Supports cable TV signal transmission as well as data transmission. Suitable for installation in cable ducts and overhead installations.

Advantages of fiber optic communication lines:

Transmitting information via fiber-optic lines has a number of advantages over transmission via copper cable. The rapid implementation of Vols in information networks is a consequence of the advantages arising from the characteristics of signal propagation in optical fiber.
Wide bandwidth - due to the extremely high carrier frequency of 1014 Hz. This makes it possible to transmit information flows of several terabits per second over one optical fiber. High bandwidth is one of the most important advantages of optical fiber over copper or any other information transmission medium.
Low attenuation of the light signal in the fiber. Industrial optical fiber currently produced by domestic and foreign manufacturers has an attenuation of 0.2-0.3 dB at a wavelength of 1.55 microns per kilometer. Low attenuation and low dispersion make it possible to build sections of lines without relaying with a length of up to 100 km or more.
The low noise level in the fiber optic cable allows you to increase the bandwidth by transmitting various modulations of signals with low code redundancy.
High noise immunity. Because the fiber is made of a dielectric material, it is immune to electromagnetic interference from surrounding copper cabling systems and electrical equipment that can induce electromagnetic radiation (power lines, electric motors, etc.). Multi-fiber cables also avoid the electromagnetic crosstalk problem associated with multi-pair copper cables.
Low weight and volume. Fiber optic cables (FOC) have less weight and volume compared to copper cables for the same bandwidth. For example, a 900-pair telephone cable with a diameter of 7.5 cm can be replaced by a single fiber with a diameter of 0.1 cm. If the fiber is “dressed” in many protective sheaths and covered with steel tape armor, the diameter of such a fiber optic cable will be 1.5 cm, which several times smaller than the telephone cable in question.
High security against unauthorized access. Since the FOC practically does not emit in the radio range, it is difficult to overhear the information transmitted over it without disrupting the reception and transmission. Monitoring systems (continuous monitoring) of the integrity of the optical communication line, using the high sensitivity properties of the fiber, can instantly turn off the “hacked” communication channel and sound an alarm. Sensor systems that use the interference effects of propagated light signals (both through different fibers and different polarizations) have a very high sensitivity to vibrations and small pressure differences. Such systems are especially necessary when creating communication lines in government, banking and some other special services that have increased requirements for data protection.
Galvanic isolation of network elements. This advantage of optical fiber lies in its insulating property. Fiber helps avoid electrical ground loops that can occur when two non-isolated network devices connected by copper cable have ground connections at different points in the building, such as on different floors. This may result in a large potential difference, which can damage network equipment. For fiber this problem simply does not exist.
Explosion and fire safety. Due to the absence of sparking, optical fiber increases network security at chemical and oil refineries, and when servicing high-risk technological processes.
Cost-effectiveness of fiber-optic communication lines. The fiber is made from quartz, which is based on silicon dioxide, a widespread and therefore inexpensive material, unlike copper. Currently, the cost of fiber relative to a copper pair is 2:5. At the same time, FOC allows you to transmit signals over much longer distances without relaying. The number of repeaters on long lines is reduced when using FOC. When using soliton transmission systems, ranges of 4000 km have been achieved without regeneration (that is, only using optical amplifiers at intermediate nodes) at transmission rates above 10 Gbit/s.
Long service life. Over time, the fiber experiences degradation. This means that the attenuation in the installed cable gradually increases. However, thanks to the perfection of modern technologies for the production of optical fibers, this process is significantly slowed down, and the service life of the FOC is approximately 25 years. During this time, several generations/standards of transceiver systems may change.
Remote power supply. In some cases, remote power supply to an information network node is required. Optical fiber is not capable of performing the functions of a power cable. However, in these cases, a mixed cable can be used when, along with optical fibers, the cable is equipped with a copper conductive element. This cable is widely used both in Russia and abroad.

However, fiber optic cable also has some disadvantages:

The most important of them is the high complexity of installation (micron precision is required when installing connectors; the attenuation in the connector greatly depends on the accuracy of fiberglass chopping and the degree of its polishing). To install connectors, welding or gluing is used using a special gel that has the same refractive index of light as fiberglass. In any case, this requires highly qualified personnel and special tools. Therefore, most often, fiber optic cable is sold in the form of pre-cut pieces of different lengths, at both ends of which the required type of connectors are already installed. It should be remembered that poor installation of the connector sharply reduces the permissible cable length, determined by attenuation.
We must also remember that the use of fiber optic cable requires special optical receivers and transmitters that convert light signals into electrical signals and vice versa, which sometimes significantly increases the cost of the network as a whole.
Fiber optic cables allow for signal branching (special passive splitters (couplers) for 2-8 channels are produced for this), but, as a rule, they are used to transmit data only in one direction between one transmitter and one receiver. After all, any branching inevitably greatly weakens the light signal, and if there are many branches, then the light may simply not reach the end of the network. In addition, the splitter also has internal losses, so that the total signal power at the output is less than the input power.
Fiber optic cable is less durable and flexible than electrical cable. The typical allowable bend radius is about 10 - 20 cm, with smaller bend radii the central fiber may break. Does not tolerate cable and mechanical stretching, as well as crushing influences.
The fiber optic cable is also sensitive to ionizing radiation, which reduces the transparency of the glass fiber, that is, increases the attenuation of the signal. Sudden changes in temperature also have a negative impact on it, and the fiberglass can crack.
Fiber optic cable is used only in networks with a star and ring topology. There are no coordination or grounding problems in this case. The cable provides ideal galvanic isolation of network computers. In the future, this type of cable is likely to replace electrical cables, or at least greatly displace them.

Prospects for the development of fiber optic lines:

With the growing demands of new network applications, the use of fiber optic technologies in structured cabling systems is becoming increasingly important. What are the advantages and features of using optical technologies in the horizontal cable subsystem, as well as at user workplaces?
Having analyzed changes in network technologies over the past 5 years, it is easy to see that copper SCS standards have lagged behind the “network arms” race. Without having time to install SCS of the third category, enterprises had to switch to the fifth, now to the sixth, and the use of the seventh category is just around the corner.
Obviously, the development of network technologies will not stop there: gigabit per workplace will soon become a de facto standard, and subsequently de jure, and for LANs (local area networks) of a large or even medium-sized enterprise, 10 Gbit/s Etnernet will not be uncommon.
Therefore, it is very important to use a cabling system that would easily cope with the increasing speeds of network applications for at least 10 years - this is the minimum service life of SCS defined by international standards.
Moreover, when changing standards for LAN protocols, it is necessary to avoid re-laying new cables, which previously caused significant costs for the operation of SCS and is simply not acceptable in the future.
Only one transmission medium in SCS satisfies these requirements - optics. Optical cables have been used in telecommunications networks for more than 25 years, and recently they have also found widespread use in cable television and LANs.
In LANs, they are mainly used to build backbone cable channels between buildings and in the buildings themselves , while ensuring high data transfer speeds between segments of these networks. However, the development of modern network technologies is actualizing the use of optical fiber as the main medium for connecting users directly.

New standards and technologies for fiber-optic communication lines:

In recent years, several technologies and products have appeared on the market that make it much easier and cheaper to use fiber optics in a horizontal cabling system and connect it to user workstations.

Among these new solutions, first of all, I would like to highlight optical connectors with a small form factor - SFFC (small-form-factor connectors), planar laser diodes with a vertical cavity - VCSEL (vertical cavity surface-emitting lasers) and new generation optical multimode fibers.

It should be noted that the recently approved type of multimode optical fiber OM-3 has a bandwidth of more than 2000 MHz/km at a laser wavelength of 850 nm. This type of fiber provides serial transmission of 10 Gigabit Ethernet protocol data streams over a distance of 300 m. The use of new types of multimode optical fiber and 850-nanometer VCSEL lasers ensures the lowest cost of implementing 10 Gigabit Ethernet solutions.

The development of new standards for fiber optic connectors has made fiber optic systems a serious competitor to copper solutions. Traditionally, fiber optic systems required twice as many connectors and patch cords as copper systems—telecommunications locations required a much larger footprint to accommodate optical equipment, both passive and active.

Small form factor optical connectors, recently introduced by a number of manufacturers, provide twice the port density of previous solutions because each small form factor connector contains two optical fibers instead of just one.

At the same time, the sizes of both optical passive elements - cross-connects, etc., and active network equipment are reduced, which allows four times to reduce installation costs (compared to traditional optical solutions).

It should be noted that the American standardization bodies EIA and TIA in 1998 decided not to regulate the use of any specific type of small form factor optical connectors, which led to the appearance on the market of six types of competing solutions in this area: MT-RJ, LC, VF-45, Opti-Jack, LX.5 and SCDC. There are also new developments today.

The most popular miniature connector is the MT-RJ type connector, which has a single polymer tip with two optical fibers inside. Its design was designed by a consortium of companies led by AMP Netconnect based on the Japanese-developed MT multi-fiber connector. AMP Netconnect has today provided more than 30 licenses for the production of this type of MT-RJ connector.

The MT-RJ connector owes much of its success to its external design, which is similar to that of the 8-pin modular copper RJ-45 connector. The performance of the MT-RJ connector has improved markedly in recent years - AMP Netconnect offers MT-RJ connectors with keys that prevent erroneous or unauthorized connection to the cable system. In addition, a number of companies are developing single-mode versions of the MT-RJ connector.

The company's LC connectors are in fairly high demand in the optical cable solutions market Avaya(http://www.avaya.com). The design of this connector is based on the use of a ceramic tip with a diameter reduced to 1.25 mm and a plastic housing with an external lever-type latch for fixation in the socket of the connecting socket.

The connector is available in both simplex and duplex versions. The main advantage of the LC connector is the low average loss and its standard deviation, which is only 0.1 dB. This value ensures stable operation of the cable system as a whole. Installation of the LC fork follows a standard epoxy bonding and polishing procedure. Today, the connectors have found their use among manufacturers of 10 Gbit/s transceivers.

Corning Cable Systems (http://www.corning.com/cablesystems) produces both LC and MT-RJ connectors. In her opinion, the SCS industry has made its choice in favor of MT-RJ and LC connectors. The company recently released the first single-mode MT-RJ connector and UniCam versions of the MT-RJ and LC connectors, which feature short installation time. At the same time, to install UniCam-type connectors, there is no need to use epoxy glue and poly

The intensive development of the telecommunications industry, driven by the need to transmit increasingly large volumes of information, has led to the need to improve communication networks, including subscriber access networks. Today we can observe the stage of convergence of communication networks. In convergent networks, unified multiservice networks focused on packet traffic are used to provide various types of services. Providing high-quality broadband services requires the provider to have a high-speed subscriber access network.

Fiber optics is increasingly being used as a transmission medium for wired subscriber access networks. Optical cables, unlike electrical ones, have a number of advantages: high throughput, low signal attenuation, high immunity from external electromagnetic interference, small size and weight. Among optical access technologies, the most popular group of technologies is FTTx. FTTx technologies are divided according to network construction into active optical networks AON and passive optical networks PON. The main difference between these technologies is that a passive optical network, unlike an active one, does not require power supply for intermediate nodes of the subscriber line. As a result, a passive optical network will be more reliable and cheaper to operate. Other important advantages are the low cost of network construction and the possibility of its gradual expansion. Such advantages will allow expanding the existing network and attracting new subscribers. Thus, PON technology is of particular interest in terms of expanding the scope of broadband networks.

Optical access networks have various construction options. The “star” topology with point-to-point connections (P2P, point-to-point) involves connecting each subscriber with a separate fiber to the access node. The “star” topology is used when subscribers are densely located in the area of the telephone exchange. This topology is characterized by a minimum number of optical splitters and a single installation location. The obvious disadvantage of this topology is the presence of a large number of fibers and optical transmitters. The advantages of this topology: ease of maintenance, operational measurements and detection of line fault locations. This topology is characterized by high reliability, since the break of one of the fibers will not affect the operation of the entire network.

The “tree” type topology is used when subscribers are located in different locations. The optimal distribution of power between different branches is decided by selecting the division coefficients of optical splitters. The tree topology is flexible in terms of potential development and expansion of the subscriber base. Depending on the need for power supply for intermediate nodes, topologies are distinguished between “tree with active nodes” and “tree with passive nodes”. Each topology has its own advantages and disadvantages.
When using a “tree with active nodes” topology, each subscriber is connected to a switch, which in turn is connected by fiber to the access node. The switch is active equipment, that is, it requires power. If there is no power supply, subscribers connected to the switch will lose access to the network. However, this solution fits well within the Ethernet standard and is relatively cheap.

A passive optical tree topology with point-to-multipoint connections (P2MP) uses a backbone fiber that is divided between all subscribers using a passive splitter. Each user connects to the splitter using a separate fiber. An entire segment of the tree architecture, which covers dozens of subscribers, can be connected to one access node port. The intermediate nodes are equipped with completely passive splitters that do not require power supply or maintenance. The advantages of the PON architecture include the absence of the need for power supply at intermediate nodes, high network scalability, and saving on fibers and optical transmitters in the central node. Network scalability allows you to connect as many new subscribers as the optical power budget allows.

Operating principle of PON network

The basis of PON technology is the point-to-multipoint P2MP logical structure. An entire fiber-optic segment of a tree-like architecture, covering many subscribers, can be connected to one port of the central node. At the intermediate nodes of the tree, intermediate passive elements - splitters - are installed. Splitters are designed to divide the power of an optical signal in a given ratio.

Purpose of the circuit blocks:

The central OLT node is a network device that is located in the access node, receives data from the backbone networks via SNI interfaces and forms a downstream flow to subscribers along the PON tree.
The ONT subscriber node is a network device that is located on the subscriber side, receives and transmits data to the OLT at wavelengths of 1550 nm and 1310 nm, respectively, converts the data and transmits it to subscribers via UNI interfaces.
A splitter is a passive optical multiport network that distributes the flow of optical radiation in one direction and combines this flow in the opposite direction.

The main idea of the PON architecture is to use just one transceiver module in the central OLT node to transmit data to and receive data from multiple ONT subscriber nodes.

The number of ONT subscriber nodes connected to one OLT transceiver module depends on the power budget and the maximum speed of the transceiver equipment. For forward (outgoing) flow transmission from OLT to ONT, a wavelength of 1550 nm is used. When transmitting reverse (upstream) data streams from subscriber nodes from ONT to OLT, a wavelength of 1310 nm is used. WDM multiplexers built into OLT and ONT equipment separate upstream and downstream streams.

WDM is wavelength division multiplexing. This technology allows you to combine several information channels over one optical fiber. In this case, each channel has its own frequency. WDM technology is based on the fact that when light is transmitted at different wavelengths, their mutual interference does not occur in the fiber. Each wavelength represents one optical channel in the fiber. The outgoing stream is broadcast - it is transmitted to all subscribers connected to the OLT. Each ONT subscriber node reads the address fields in order to select the information intended for it from the general flow. Subscriber nodes transmit at the same wavelength and, in order to avoid signal intersections, they use the TDMA time division multiple access method. Each ONT has its own individual data transmission schedule, taking into account latency adjustments. The TDMA MAC protocol solves this problem.

An ONT optical terminal is installed directly at the subscriber's premises, which is also a home access gateway. When using a unified optical transport terminal ONT, the configuration of the transport component is not tied to services. Thus, subsequent service configuration will be carried out on the home access gateway.

When building an optical network, a two-stage optical signal division scheme is used. A splitter with a division ratio of 1:2 is installed on the station side. At the entrance of the house, a splitter with a division ratio of 1:32 is installed in the optical distribution cabinet, which ensures the distribution of the optical signal among the subscribers of the residential building. It is worth noting that houses with a small number of subscribers use other optical signal distribution schemes:

1:4 – first level, 1:16 – second level
1:8 – first level, 1:8 – second level

Passive optical network technologies enable the convergence of various services. When using PON, it is possible to provide Internet access, telephony, and television services. The provision of comprehensive services is implemented using subscriber equipment. To organize access to NGN services, a hybrid service model is used, shown in the figure.

A PPPoE session is initiated on the subscriber's equipment (PC). ONT is configured in bridge operating mode. The BRAS broadband remote access router terminates the PPPoE session. To organize Internet access, each virtual PPPoE adapter on the subscriber's equipment is assigned its own public IP address, which is routed on the Internet.

To organize Triple Play services, three virtual private VLANs are organized. Internet access traffic is transmitted within the first VLAN. The second VLAN carries traffic for IPTV and VoD services. The third VLAN organizes the transmission of analogue and IP telephony services. The ONT subscriber terminal compares the port identifier through which the subscriber equipment is connected and the identifier corresponding to the VLAN.

An analog telephone is connected via the FXS port, which emulates an extension of the PBX interface. To prevent broadcast relaying of multicast traffic, the IGMP snooping process is enabled on OLT equipment. IPTV and VOD access gateways, as well as a flexible Softswitch, provide access to television and telephony services, respectively.

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Fiber optic communication lines

(FOCL), optical communication lines in which information is transmitted using fiber-optic elements. A fiber-optic line consists of transmitting and receiving optical modules, fiber-optic cables and fiber-optic connectors. Optical fiber is the most perfect medium for transmitting large flows of information over long distances. It is made from silica-based quartz, a common and inexpensive material, unlike the copper used in conventional wires. The optical fiber is very compact and lightweight, its diameter is only approx. 100 microns. Fiber light guides are optical fiber bundles, glued or sintered at the ends, protected by an opaque sheath and having ends with a polished surface. Glass fiber is a dielectric, therefore, during the construction of fiber-optic communication systems, individual optical fibers do not need to be isolated from each other. The durability of optical fiber is up to 25.

When creating fiber-optic communication lines, highly reliable electronic elements are needed that convert electrical signals into light and light into electrical signals, as well as optical connectors with low optical losses. Therefore, the installation of such lines requires expensive equipment. However, the advantages of using fiber-optic communication lines are so great that, despite the listed disadvantages of optical fibers, these communication lines are increasingly used to transmit information. The data transfer speed can be increased by transmitting information in two directions at once, since light waves can propagate in one optical fiber independently of each other. This makes it possible to double the capacity of the optical communication channel.

Fiber-optic communication lines are resistant to electromagnetic interference, and those transmitted through light guides are protected from unauthorized access. It is impossible to connect to such communication lines without violating the integrity of the line. Signal transmission over optical fiber was first carried out in 1975. Nowadays, long-distance optical communication systems over distances of many thousands of kilometers are rapidly developing. Transatlantic communication lines USA - Europe, Pacific line USA - Hawaiian Islands - Japan are successfully operated. Work is underway to complete the construction of a global fiber-optic communication line Japan - Singapore - India - Saudi Arabia - Egypt - Italy. In Russia, TransTeleCom has created a fiber-optic communication network with a length of more than 36,000 km. It is duplicated by satellite communication channels. In the end 2001 A unified backbone digital communication network was created. It provides long-distance and international telephone services, Internet, and cable television in 56 of the 89 regions of Russia, where 85–90% of the population lives.

Encyclopedia "Technology". - M.: Rosman. 2006 .

See what “fiber-optic communication lines” are in other dictionaries:

A fiber-optic communication line (FOCL) is a fiber-optic system consisting of passive and active elements designed to transmit an optical signal via a fiber-optic cable. Contents 1 Elements of fiber-optic communication lines 2 Installation ... ... Wikipedia

fiber optic communication system- - [E.S. Alekseev, A.A. Myachev. English-Russian explanatory dictionary on computer systems engineering. Moscow 1993] fiber-optic communication system Transmission of modulated or unmodulated optical energy through a fiber-optic medium, ... ...

RD 45.047-99: Fiber-optic transmission lines on the backbone and intra-zonal primary networks of the VSS of Russia. Technical operation. Guiding technical material- Terminology RD 45.047 99: Fiber optic transmission lines on the backbone and intra-zonal primary networks of the VSS of Russia. Technical operation. Guiding technical material: 3.1.18 “EMERGENCY” quality parameters exceeded the limits... ... Dictionary-reference book of terms of normative and technical documentation

fiber optic cable- A cable containing one or more optical fibers and intended for data transmission. fiber optic cable [Luginsky Ya. N. et al. English-Russian dictionary of electrical engineering and... ... Technical Translator's Guide

fiber optic adapter- A passive device used to connect optical plugs and connect optical fibers. [SN RK 3.02 17 2011] fiber optical adapter A component of switching equipment designed for positioning and connecting two... ... Technical Translator's Guide

fiber optic line- A set of fiber optic segments and repeaters that, when connected, form a transmission path. [Source] Topics: optical communication lines EN fiber optic link ... Technical Translator's Guide

fiber optic attenuator- A component installed in a fiber optic transmission system to reduce the power of the optical signal. Often used to limit the optical power received by the photodetector to the sensitivity limits of the optical... ... Technical Translator's Guide

- (FOCL), Fiber-optic communication line (FOCL) is a fiber-optical system consisting of passive and active elements, designed to transmit information in the optical (usually near-infrared) range. Contents 1 ... Wikipedia

Check information. It is necessary to check the accuracy of the facts and reliability of the information presented in this article. There should be an explanation on the talk page... Wikipedia

A technique for transmitting information from one place to another in the form of electrical signals sent through wires, cables, fiber optic lines, or without any guide lines at all. Directional transmission through wires is usually carried out from one... ... Collier's Encyclopedia

Books

Fiber-optic communication lines and their protection from external influences, Sokolov S.. Basic information is given on the physical foundations, structure and application of optical fibers, principles and technology of optical signal transmission, construction and operation of fiber-optic...

We are being asked more and more questions about the implementation, principles of operation of this network, and so on.

Therefore, in the near future we will publish a series of articles about PON technology, examining these nuances in more detail. And let's start with the basics: what is it, what are PON networks good for, and why do Ukrainian suppliers mainly offer GEPON equipment, and not GPON or EPON?

What is PON technology?

Optical fiber provides the ability to transmit large volumes of data at high speeds, including data that requires signal stability, such as voice and video. And this is good. But optical cable is expensive, and providing a separate fiber for each subscriber is an prohibitive expense for most providers. And that's bad. Moreover, many subscribers do not use the full potential of the dedicated optical fiber, and most of it is “idle.”

Therefore, PON technology was developed to make the most efficient and economical use of the capabilities of the fiber optic network. The main advantage of Passive optical network is organization of connecting several dozen subscribers to the network via ONE optical fiber. This is implemented by separating the transmission of packets in time (TDM and TDMA protocols), as well as separating the reception and transmission of data in different wavelength ranges.

Types of PON. What to choose: GEPON or GPON?

About the progenitors of modern PON technologies APON and BPON- There’s no point in even talking anymore. The low supported speed, coupled with the rather high cost of deploying a network based on them, is the reason for their becoming a thing of the past. The same applies EPON with its 100 Mb/sec.

The Ukrainian provider has to choose between GEPON And GPON. Despite similar names and high speed, these are different standards. The picture below illustrates this: if in GEPON data packets are transmitted without any special changes, then in GPON this is more complicated, with double “packing” into GEM and GTC frames. In addition, GPON uses ATM cells, which GEPON does not.

GPON supports speeds of 2.5 Gbps, offers efficient transmission of TDMA traffic and has several other advantages. But all of them are canceled out by the cost of the equipment (much higher than in GEPON) and its more complex configuration. Only a small segment of providers serving large serious clients or building huge extensive networks can afford such a network.

Most Ukrainian telecommunications companies choose GEPON:

the bandwidth of such a network meets standard modern requirements (1 Gbit);
equipment for GEPON is cheaper than for GPON and easier to configure;
In terms of the number of connected subscribers per 1 OLT port (64) and the maximum network radius (20 km), GEPON is not inferior to GPON.

There is also 10GEPON technology, which promises speeds of 10 Gbit, but its development is still underway (since 2009).

Where can I extend PON (GEPON)?

Networks based on PON technology are universal. They can be used even in conditions where it is unprofitable or impossible to organize a regular fiber-optic FTTH network or forward Wi-Fi links.

Let's take, for example, a standard fiber-based network, when a separate fiber is allocated for each subscriber. We have already discussed above that this is disadvantageous due to the cost of the cable itself. Add to this an indispensable attribute of such a network - active equipment. Necessary:

Buy switches and install it in each access point, plus provide a more powerful switch for aggregation. The price of switches (even the most unassuming ones) for several dozen subscribers starts somewhere from $400.
Equip with SFP modules(they usually do not come with switches), media converters, etc.
Somewhere post, and this “somewhere” should be a warm, dry room.
Protect from vandals and thieves(installation locking cabinet or box).
Take care of your power supply and about backup power (or UPS), in case of a power outage.
Provide configuration, monitoring and maintenance all active equipment.

And if in the conditions of urban development this is all at least somehow feasible, then in the private sector it is unlikely.

An excellent solution for the private sector is Wi-Fi networks. But here, too, there may be stumbling blocks: densely “populated” ether, lack of line of sight, and the like, when GEPON becomes the solution.

And cable TV to boot

Connecting the Internet using PON technology, in addition to saving on the cost of optical fiber, has many advantages:

The purchase of active equipment is reduced to a minimum. In fact, you only need to purchase one headend - OLT and user terminals-modems (ONU). Moreover, the price of the latter can be compensated by the subscriber in the cost of connection.

Configuration and administration will only be required for OLT.

Throughout the entire length of GEPON, only passive elements are used - splitters, which do not require a power supply or a heated room.

PON makes efficient use of network bandwidth. Since it is general, when one or more subscribers are inactive and the load on the channel is reduced speed increases for everyone. It also drops proportionally, but there are enough bandwidth resources even with the heaviest load. If we divide gigabit into 64 connected subscribers (maximum), then each it turns out minimum 16 Mbit!

And an additional bonus - based on GEPON, you can provide cable television to subscribers using the same network infrastructure. TV data transmission is carried out on a different wavelength.