Optical fiber transmission distances. Optical Fiber Bandwidth Fiber Optic Communication Speed

over one physical fiber-optic cable. This increase in cable capacitance is achieved based on a fundamental principle of physics. It consists in the fact that light rays with different wavelengths do not interact with each other. The basic idea of ​​WDM systems is to use multiple wavelengths (or frequencies) to transmit a separate data stream on each one. Thanks to this, it was possible to increase the channel bandwidth per fiber by 16-160 times [16]. The multiplexing circuit is shown in Fig. 3.13. At the channel input, the signals are combined into one common fiber using a prism. At the output, these signals are separated using a similar prism. The number of fibers at the input and output can reach 32 or more (instead of prisms, miniature mirrors have recently been used, where wavelength scanning is used).

Rice. 3.13.

This is achieved using several components. First, the transmitted data must be sent on a specific carrier wavelength. Usually wave multiplexing WDM is carried out in the transparency window of 1530-1560 nm, where minimal signal attenuation up to 0.2 dB/km. Typically, fiber optic systems use 3 wavelengths - 850, 1310 and 1550 nm. If the input signal is optical and transmitted at one of these wavelengths, it must be converted to transmit at the WDM transparency window wavelength. When there are multiple independent input signals, each must be converted to transmit at a different wavelength within that range. These signals are then combined using an optical system such that most of the power of all signals is transmitted over a single optical fiber. At the other end of the line, the light signals are divided using a splitter 5 a device designed to split a signal into several parts.(another lens system) into several channels. Each of these channels passes through filters that separate only one of the wavelengths. Ultimately, each of the separated wavelengths reaches its own receiver, which converts it into its original form (optical at wavelengths 850, 1310 and 1550 nm or copper).

There are two types of WDM systems providing coarse-grained (CWDM) multiplexing with large carrier spacing or dense (DWDM) wavelength scale division. CWDM systems typically provide transmission of 8 to 16 wavelengths in 20 nm increments, from 1310 to 1630 nm. DWDM systems operate at up to 144 wavelengths, typically in sub-2 nm increments over roughly the same wavelength range. WDM (CWDM or DWDM) is typically used in one of two applications.

The first and most important thing is to increase the amount of information transmitted via optical fiber. In this case, a large number of data streams are transmitted over a small number of optical cables. This makes it possible to significantly increase the throughput of the optical cable. So, at a speed of 10 Gbit/s per channel total throughput each fiber will be 1.25 Tbit/s (that is, 12,500,000,000,000 bits per second). Of course, in most cases this level of speeds is not required; a common task is to transmit multiple Gigabit Ethernet streams over a single pair of fibers when there are no additional pairs available. In many cases, laying a new optical cable is too expensive or simply impossible. Then the use of WDM technology becomes the only option to increase throughput.

The second application of WDM appeared relatively recently, when an increasing number of customers began to use high-speed communication channels. In this case, the telecom operator provides customers with offices in different parts of the city with wavelengths in their cable for organizing point-to-point channels. For example, a large company that has two buildings in different parts of the city may set the task of merging them. To solve this problem, the operator can deploy a network. When using WDM, the operator does not need to worry about which protocol or technology is used by customers, which allows for more flexible service delivery. The use of WDM in subscriber access networks will be discussed further.

Devices for organizing WDM are passive, i.e. do not require power supply. However, many of them require a constant temperature. To do this, temperature control devices are installed, and they require a remote power supply. Then a mixed cable is used, which, along with optical fibers, contains copper conductors. To ensure attenuation standards when transmitting information via optical cables, signal regenerators and amplifiers are used.

When transmitting a single optical signal (see Fig. 3.13 a), each regenerator converts the optical signal into an electrical one, adjusts the timing parameters, extracts the transmitted information and, as a result, controls the laser transmitter to regenerate the signal and convert the optical signal into electrical signal requires high costs because it uses very expensive components (lasers and ultra-high-speed electronics).

imOptical transmission systems: a) with linear regeneration; b) DWDM composite signal with one wavelength division section; c) DWDM composite signal with an optical amplifier for serially inputting information into an optical cable for transmitting it through the next section.

The diagram shown in Fig. 3.13 b, transmits a composite WDM signal. In this case, at each regenerator section the composite signal is split into separate signals. Next, individual conversion to electrical form and individual regeneration take place. It is more preferable to use optical amplifiers that can amplify the signal at all wavelengths that make up the WDM signal. An optical amplifier based on an erbium-doped fiber (Erbium-Doped Fiber Amplifier - EDFA) is a piece of EDFA-type optical fiber and a semiconductor laser diode as a “pumping” source. The amplifier takes the attenuated signal and generates a high-power signal into an erbium-doped optical cable. When exposed to a powerful signal, the erbium atoms are excited and generate photons in the same phase and direction as the sent signal. The result is an amplification effect. Such amplifiers can be designed for all wavelength ranges. The use of amplifiers reduces the need to use regenerators, as shown in Fig. 3.13 b. In this case, there is a limitation on the number of amplifiers installed in series. However, the installation of amplifiers makes it possible to increase the distance between regenerators and the associated optics-electronics conversion to hundreds and thousands of kilometers.

Brief summary

• Transmitting information via fiber-optic cable has a number of advantages over transmission via copper cable: wide bandwidth, low attenuation of the light signal in the fiber, low noise level, immunity from electromagnetic interference, low weight and volume, high security from unauthorized access, galvanic isolation network elements, fire safety, reduction of requirements for linear cable structures, efficiency, long service life.
• A fiber optic cable contains three main elements: braid, jacket, and core.
• The core - a fiber light-conducting element is surrounded by a shell, which has a lower refractive index of light. This causes most of the light rays in the core to be reflected into the core.
• The maximum angle at which total internal reflection is ensured for light radiation introduced into the fiber is called numerical aperture.
• When building networks, multicore cables can be used.
• Optical fibers that allow rays to travel through multiple paths to the receiver are called multimode.
• Delayed rays lead to the expansion of transmitted pulses. This phenomenon is called dispersion. The amount of this expansion is directly proportional to the pulse width and inversely proportional to the transmission speed.
• The throughput of an optical cable, which is characterized by the bandwidth factor (BDF - Bandwidth Distance Factor).
• Fibers that exhibit a jump in refractive index at the cladding-core interface are called step-index fibers.
• Fibers with a changing refractive index according to the above law are called gradient and have a broadband coefficient two orders of magnitude greater than stepped fibers.
• Attenuation is measured in dB/km and is determined by the loss due to absorption or scattering of radiation in an optical fiber. Absorption losses depend on the transparency of the material from which the fiber is made. Scattering losses depend on the refractive inhomogeneity of the material.
• Chromatic dispersion occurs when the light signal consists of different wavelengths. Chromatic dispersion is one of the bandwidth-limiting mechanisms of fiber optic cables that impairs the propagation of signal pulses that consist of different colors of transmitted light (signal incoherence).
• Chromatic dispersion consists of material and waveguide components and occurs during propagation in both single-mode and multimode fiber.
• The material component reflects the properties of the dependence of the refractive index of the fiber on the wavelength. The expression for the dispersion of a single-mode fiber includes a characteristic of the material, namely, the dependence of the indicator on the wavelength. This component is determined by the rate (differential) of increase or decrease of the refractive index depending on the wavelength. As the wavelength increases, this indicator can be positive (the refractive index increases) or negative (the refractive index decreases).
• Wave dispersion is determined by the propagation time of the signal depending on the wavelength. It is always positive (the propagation time only increases with increasing wavelength).
• At a certain wavelength (approximately for a stepped single-mode fiber), mutual compensation of material and wave dispersions occurs, and the resulting dispersion becomes zero. The wavelength at which this occurs is called the zero-dispersion wavelength. Usually a certain range of wavelengths is specified, within which it can vary for that particular fiber.
• It has been established that for a certain signal shape it has the least dispersion. Such impulses are called solitons.
• There are two types of devices that convert an electrical signal into light - LEDs and laser diodes. LEDs (LED-Light-Emitting Diode) generate incoherent radiation (the signal contains components of several wavelengths). The principle of LED radiation allows modulation only by radiation intensity. The emission power of LEDs can reach several tens of microwatts.
• The laser diode provides coherent radiation. Its beam has a narrower spectrum compared to an LED. The principle of radiation from laser diodes allows the use of modulation according to the parameters of the light wave, for example frequency.
• Laser diodes have a more complex design and higher electrical loads compared to LEDs, but they are inferior to the latter in reliability. ease of use and cost.
• In conventional photodiodes, a current is generated depending on the intensity of the incident radiation; they are distinguished by good linearity and stability of operation, short response time, but they do not provide amplification of the photocurrent.
• Phototransistors They have high sensitivity and good gain, but due to the large barrier capacitance they have a long response time, that is, the frequency characteristics are worse than those of diodes.
• p-i-n are more sensitive than LEDs. Their barrier capacitance is small, which ensures good frequency characteristics (cutoff frequency - up to 1 GHz).
• Avalanche diodes are characterized by high sensitivity, high gain and high speed, however, their use is hampered by complexity, high cost, high operating voltages, the need to stabilize voltages and temperatures, and operation only in weak signal amplification mode.
• Some of the critical areas of fiber systems are the fiber splices and connectors. Light loss in the connector is 10-20%. For comparison: welding fibers leads to losses of no more than 1-2%.
• A cross designed for optical cable is a high-density cross, i.e. the number of connected pairs per unit area exceeds previous systems (for example, digital compaction systems).
• Wave Division Multiplexing -

5.2 DIFFERENCE IN TRAVEL TIME LIMITS

COMMUNICATION LINE CAPACITY

The optimistic forecasts about the enormous capacity of optical cables and communications mentioned in § 4.1 are based on the consideration that the bandwidth of the transmitted signal should always be somewhat less than the carrier frequency itself.

The carrying capacity of glass fiber is not unlimited.

To transmit a telephone conversation as a sequence of pulses, it is necessary to transmit a large number (specifically 64,000) binary characters per second (64,000 bps or 64 kbps). To convert the continuously varying microphone current into a binary signal, it must first be reproduced using pulses. The amplitude values ​​found will now be represented as a binary number and sent as binary signals between two pulse bursts. On the receiver side, the same inverse conversion follows. To transmit a signal with higher quality, it is necessary to distinguish at least 256 amplitude values ​​of the microphone current. Therefore, an eight-code system (8 binary characters per code word) is required for each pulse value. To transmit one moving television picture, a transmission rate of 80 million bits per second (80 Mbps) is required.

As bandwidth line - whether made of copper or glass - the highest speed of signal transmission through this line, measured in bits per second (bit is a binary digit), is accepted.

A unit of binary information can be roughly converted into a corresponding frequency bandwidth, as is commonly done in analogue transmission technology to indicate the characteristics of signals or cables. Since transmitting information at 2 bps theoretically requires a bandwidth of at least 1 Hz (practically around 1.6 Hz), we can approximate the signal transmission rate or bandwidth in bits per second and the corresponding bandwidth in hertz .

Let's take a binary encoded telephone signal as an example. Each single signal in this sequence (a single pulse of current or light) must be no longer than 1/64000 s so as not to interfere with subsequent signals. The capacity of a line is fundamentally higher, the shorter the pulses can be transmitted over it.

In the same way, there are limits for the light guide. The principle of its operation was previously mentioned: light propagates in a zigzag manner in the light-conducting core due to total internal reflection from the walls, the outer side of which is adjacent to a medium with a low refractive index - the cladding. This total reflection is subject to one condition. The angle between the light beam and the optical axis of the light guide must be no more than the maximum angle of total internal reflection. It is determined by the ratio of the refractive indices in the core and in the cladding :

One might favor a fiber with a larger refractive index difference, since it can obviously accept and transmit more light from a source with a larger angle of emission. This advantage would be truly decisive if the requirements were only for the highest possible throughput of the optical fiber.

5.3 FIBER CAPACITY

It is different in single-mode (monomode) and multimode fibers (more in single-mode fibers due to their rod thickness). The time dispersion of the elements of the output signal caused by different path lengths in the light guide and, as a consequence, the dissipation of part of the energy at the output of the light guide is called mode dispersion. Unfortunately, this is not the only reason for bandwidth limitation. It is also necessary to add the so-called material dispersion. It consists in the fact that the refractive index of the light guide rod depends on the wavelength. Long-wavelength red rays are deflected less than short-wavelength blue rays. This effect would not be significant for light communication technology if the sources used emitted light of only one wavelength. Unfortunately, this does not happen. Although the spectral width of a semiconductor laser is relatively narrow, it emits light over a range of wavelengths several nanometers wide. The light-emitting diode is significantly superior in this regard - by approximately 30 - 40 nm. Limiting this band is impossible without loss of energy. It is these different spectral components of the radiation that pass through the light guide at different speeds
, which, of course, leads to pulse broadening and limits the throughput of the fiber.

In a fiber with a step index profile, mode dispersion predominates due to the large difference in travel times between the axial and boundary rays. In a gradient fiber with an optimal refractive index profile, both dispersions become approximately equal. In contrast, in monomode fiber, mode dispersion is not important and only material dispersion determines the transmission performance.

And the third factor influencing the quality of transmission is waveguide dispersion. It occurs only in monomode fibers, namely because the only mode capable of propagation has a propagation speed that depends on the wavelength.

An analysis of the causes and influence of material dispersion on transmission characteristics allowed us to draw conclusions that are of exceptional interest for practice and have a decisive influence on the further development of light-guide technology. First of all, it turned out that the pulse broadening caused by material dispersion is largely determined by the microstructure of the wavelength dependence of the refractive index of a given light-conducting material. If there is a section on the graph of such a dependence where the curve tends to zero, then at this wavelength one can expect minimal pulse broadening and neglect the influence of material dispersion.

Indeed, such a point can be found on the refractive index profile curves, for example, for quartz glass at
. This means that if among the narrowband light sources there are those for which the material dispersion is zero, then, accordingly, the throughput takes on a maximum value.

Based on the material dispersion values, it is possible to calculate the pulse broadening for different wavelengths and from this the transmission speed for the laser (spectral width about 2 nm) and for the light-emitting diode (spectral width about 40 nm). Even for a light-emitting diode in this wavelength region, transmission rates in excess of 1 Gbit/s per km can be expected. For lasers, a value of 1.4 Gbit/s per 1 km was experimentally obtained! It is clear that this region of wavelengths of zero dispersion of the optical fiber is of great interest.

The transmission characteristics just mentioned are real and indicate the technical possibilities that exist in simple multimode fibers and have not yet been exhausted today. We must not forget, however, that such high transmission rates can only be achieved by ensuring optimal parameters of the light-emitting diode for a certain wavelength, which create worse transmission conditions for other wavelengths. In addition, it is necessary to maintain very small tolerances when manufacturing the light guide to ensure the required refractive index profile, which undoubtedly increases the cost of the light guide.

The above considerations are also interesting and important: in any case, a fiber with maximum throughput cannot be created. For most areas, the throughput of the fiber is sufficient. In this case, it turns out to be possible to use simpler electrical connectors and obtain greater efficiency when connecting, etc.

5.4 OPTICAL CABLES, THEIR DESIGNS AND PROPERTIES

A single two-wire circuit, a single coaxial pair, are a rare phenomenon in electrical communication technology. Typically, an electrical cable consists of several pairs. General armor protects them from various types of environmental influences - damage by rodents, humidity and mechanical influences.

A light guide, like an electrical conductor, in addition to being used as a single conductor of light, is included in an optical cable, and is subject to requirements similar to those for electrical cables.

However, electrical conductors and optical fibers are so different that it would be surprising if electrical and optical cables did not differ from each other in design, installation methods, laying and operation. At the same time, there is many years of experience in the mechanical protection of thin conductors (copper wires tenths of a millimeter thick are used quite widely), which can be used to protect sensitive glass fibers.

When it comes to the difference between light guides and copper conductors, it is necessary to name the main property that has not yet been named at all: the absolute insensitivity of the light guide with respect to interference from electrical And magnetic fields. Here it could be said that shielding electrical cables to protect them from external electromagnetic interference is absolutely unnecessary in optical cables.

The main role is played, of course, by the material itself - glass, which now acts as a substitute for the valuable non-ferrous metal - copper. This substitute material results in a large economic gain. The world's copper reserves are constantly depleting, and prices are rising. According to some forecasts, by the end of the century, the onshore deposits known today will be exhausted. The main material for glass optical fibers, quartz sand, is available in large quantities. In communications technology, several kilograms of copper can be replaced by 1 g of high-purity glass, if the same cable capacity is taken as a basis.

This ratio leads to another advantage: optical cables easier electrical. This is especially noticeable in high-bandwidth cables due to the small diameter of the light guide. It is clear that both of these properties are an immediate advantage in many applications.

Finally, it is necessary to point out the factor of galvanic isolation of the transmitter and receiver. In an optical system, they are electrically completely isolated from each other, and many of the problems associated with grounding and potential removal that hitherto arose when connecting electrical cables are no longer valid.

Along with these useful parameters, it is necessary, of course, to name others in which optical fibers are inferior to copper and which the cable designer must take into account.

This is first of all sensitivity unprotected fiber to water vapor. This critical property was very quickly discovered, but a countermeasure was also discovered: directly coating the light guide with a protective film several micrometers thick directly during the fiber drawing process.

This protective sheath, mainly composed of polymer, completely protects the light guide. It also increases the mechanical strength of the light guide and its elasticity. In addition, consistency of parameters is ensured under unfavorable environmental conditions; without a protective shell, they decline within a few hours or days.

Mechanical tensile strength for fiber is quite high and matches the strength of steel. However, glass is fragile; the fiber cannot withstand bends with a small radius and breaks. But this drawback is also relative: fiberglass, equipped with the aforementioned thin protective layer, can easily be wrapped around a finger, and some varieties can even be wrapped around a thin pencil. Given this typical property of glass, it is of course necessary to take protective measures in cases where several optical fibers are combined in one cable, which will subsequently bend and twist. This happens during winding on the drum and during laying. The cable design must be such as to eliminate mechanical overloads of the light guide. But not only fiber destruction is dangerous, but also microbending. They occur when light-conducting fibers lie on a rough surface under tensile force, and can cause additional light loss. This phenomenon can be observed in a demonstration experiment when visible light, for example from a He-Ne laser, is supplied to a light-conducting fiber wound tightly, turn to turn, on a drum. The entire drum emits a bright red light, indicating light loss caused by microbending.

To reduce the mechanical stress on the fibers, a number of solutions have been tried. Individual conductors are laid freely in the cross-section of the cable; During the cable manufacturing process, make sure that the fibers are slightly longer than the cable. The figure shows a layer-concentric design; it is used very often. In this case, the light guides lie freely in thin flexible tubes or porous insulation is applied to them.

When hesitating ambient temperature The mechanical forces that act on the light guide significantly depend on the design of the cable. The only weak point seems to be the cladding of the step-index fibers. Its refractive index, which is only slightly less than the refractive index of the core, can in unfavorable cases increase at low temperatures, which will violate the conditions of total internal reflection and, accordingly, additional radiation losses will appear.

Optical fibers...operation fiber-optical lines communications on air lines power transmission...

Setting up laboratory work for the course fiber-optical systems communications

Abstract >> Industry, production

I.I.. Fiber-optical lines communications. -M.: Radio and connection, 1990 –224 p. MM. Butusov, S.M. Wernick, S.L. Balkin and others. Fiber-optical transmission systems. -M.: Radio and connection ...

Fiber-optical sensors

Abstract >> Communications and communications

Information. There are so-called coherent fiber-optical lines communications, where only single-mode is suitable... in coherent lines communications impractical, which predetermined the use in such lines single-mode only optical fibers. Against, ...

Modernization of the zonal network of the Samara region based on fiber-optic lines gears

Thesis >> Communications and communications

IN AND. Ivanova. – M.: Radio and Connection, 1994. – 224 p. Construction and technical operation fiber-optical lines communications/ V.A. Andreev, V.A. Burdin, B.V. Popov...

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 for 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 terminating 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 optical fiber.
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.

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. At least without significant work effort and financial costs.

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 inherent in 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, 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 laid 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 fiber optic fiber optic fiber 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 communication 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

Optical data transmission technologies have become a breakthrough in the field of telecommunications and data networks that require high transmission speeds. Over the past few years, research has led to the emergence of systems that are capable of transmitting data at speeds of 10 Gb/s and higher. One of the main advantages of optical cable is its ability to transmit high-speed optical signals over long distances. This article is devoted to optical cable, the principles on which it operates, as well as the main blocks of data transmission systems over optical fiber.

Fiber optic technology simply uses light to transmit data. The use of optical cable began around 1970, when it was possible to reduce the cost of producing optical cable and the associated costs.

Using an optical cable

Fiber optic cables are used in a wide range of applications, from medical sensing to high-speed defense data networks. Data transmission is carried out using optical transmitters that transmit high-speed signals to special optical receivers. In this case, digital signals are converted into optical signals and vice versa. The data transfer speed via optical cable reaches 10 Gb/s.

Today, there are two types of optical cable: single-mode (SM) and multi-mode (MM). Recently, statements have increasingly been heard that multimode is more promising, providing more than a hundred times superior performance relative to single-mode optical cable.

The most active use of optical cable occurs in the telecommunications industry. Initially, telephone companies used optical cable to carry large volumes of voice traffic between telephone central offices. Since the 1980s, telephone companies have begun deploying optical networks everywhere.

The throughput of an optical cable is its most important and significant characteristic. The greater the bandwidth, the higher the transmission speed and the greater the traffic. Copper has very limited bandwidth and severe limitations on cable length, making copper pair less suitable for transmitting high-speed signals over long distances.

Using an optical cable provides the following advantages:

• High bandwidth for voice or video transmission.
• Optical fibers can carry thousands of times more information than copper wire. For example, just one strand of fiber can carry all of America's telephone conversations during rush hour.
• Optical cable is approximately 10 times lighter than copper.
• Low losses. The higher the signal frequency, the greater the losses in the copper pair. Signal loss in an optical cable is the same at all frequencies, with the exception of ultra-high frequencies.
• Reliability - Optical cable is more reliable and has a longer lifespan than copper cable.
• Security - optical fibers do not emit electromagnetic fields and are insensitive to interference.

Physical mechanism for transmitting optical signals

In modern applications, optical cables are divided into multimode (MM) and single mode (SM), but both are based on the same principles. Signal transmission through an optical cable is possible due to a phenomenon called total internal reflection. This makes it possible to transmit optical signals at high speed over long distances.

Single-mode optical cable or multimode?

SM and MM cables differ in size, which in turn affects the signal passing through the fiber. SM cables use a core fiber thickness of 8 to 10 microns, which allows only one wavelength to be transmitted. MM cables, on the other hand, use a thicker core fiber of approximately 50-60 microns, which allows multiple wavelengths to be transmitted simultaneously. SM cables have less attenuation, which makes it possible to use them over long distances. MM cable allows you to transfer more data. That. MM cable is usually used over short distances where data needs to be transferred at high speeds, such as in data storage systems.

Building Blocks of Fiber Optic Systems

A typical fiber optic system design consists of a transmitter, an optical cable, and a receiver. The transmitter converts digital electrical signals into optical ones, which are then transmitted via an optical cable, providing high transmission speeds and independence from electromagnetic interference.
An optical cable consists of an optical fiber and two connectors at the ends, usually ST, SC, or FC, depending on the configuration of the receiver and transmitter.

An optical fiber consists of a central fiber several microns thick, a cladding that provides complete optical reflection of the signal, and an outer braid that provides protection and identification of the optical cable.

Thus, the construction and operation of fiber-optic systems is hardware-oriented for signal transmission over long distances. Often the task is set exactly this way: using an optical cable to transmit a high-speed signal over a long distance with low attenuation at an acceptable level of financial costs.

Optical cable design

consists of several elements. An optical cable consists of several elements: a core, a cladding and an outer covering. An optical cable is based on a core through which light signals are transmitted. The core is based on silicon and germanium. The sheath surrounding the core of the optical cable is made of silicon and has a refractive index slightly lower than the central core. The refractive index is the ratio of the speed of light in a vacuum to the speed of light in a material. The speed of light in a vacuum is 300,000,000 meters per second. The higher the refractive index, the lower the speed of light in the material. For example, the refractive index of light in clean air is 1, which means the speed of light in air is 300,000 km/s. The refractive index in glass is 1.5, which means the speed of light in glass is 200,000 km/s.

Several layers of buffer sheathing protect the central core. The protection serves to reduce physical stress on the cable, such as stretching, bending, etc. The outer braid protects against external influences, such as environmental ones (temperature, humidity, aggressive environment).

SC connectors are most often used to connect optical cables. The SC connector provides the highest packaging density. System administrators must consider the characteristics of the optical cable and active equipment to select the appropriate connector type.

Types of optical cable

Single-mode optical cable has a very small core, typically 8-10 microns, which allows light signals to be transmitted without repeaters over distances of up to 80 km, depending on the type of equipment. SC optical cable has enormous information potential due to the fact that it has virtually unlimited bandwidth.

Multimode can transmit multiple light waves and has a thicker core measuring around 50 or 62.5 microns. Due to dispersion, multimode optical cable has higher attenuation.

Optics

Any optical system consists of three components: the transmitter, the middle (fiber cable) and the receiver. The transmitter converts electrical signals into light and sends it along the fiber. The receiver receives the light signal and converts it into electrical
signal. There are two types of transmitters: laser diode or LED.

The output power of a transmitter indicates the amount of energy emitted in a specific time slice. The higher the power, the longer the signal transmission distance. The transmitter has the ability to change the baud rate to meet the system's bandwidth needs. The range of wavelengths emitted by the signal source is in the spectral width.

Transceivers are sensitive to environmental conditions. The laser diode requires stable voltage and temperature. LEDs are less sensitive to environmental fluctuations. Laser diodes are more expensive. LED optical sources have a shorter lifetime, but are easier to install and more economical.

Conclusion

Although the development of the use of optical cable began in the telecommunications environment, today it is already commonplace. Many companies and industries have taken advantage of fiber optic systems to increase their productivity. One of the challenges some businesses face is how to connect existing equipment and infrastructure to a fiber optic system without expensive upgrades. Using media converters that allow you to connect conventional network channels based on copper twisted pair and optical fiber, it is possible to connect almost any network equipment. Media converters are designed to ease the transition to using optical cable, minimizing the cost of troubleshooting problems that arise.

Attention! Copying and reprinting information from this site is prohibited without the written consent of the administration.

For simple, low-cost fiber optic systems, distances between repeaters of up to 5 km are possible. Repeater distances of up to 300 km are now readily available for high quality commercial systems. Systems (without repeaters) have been developed for distances of up to 400 km. In laboratory conditions

Distances close to 1000 km have been achieved, but they are not yet available on the market. One European company has announced that it is currently developing a fiber optic cable that can be laid along the earth's equator and, without any repeaters, it will be possible to transmit a signal from one end to the other! How is this possible? With a slightly radioactive shell, incoming low-energy photons excite electrons in the shell, which in turn emit higher-energy photons. This creates some form of auto-amplification. The following chapters will explain the terms used to the reader.

In the 4 Mbps twisted pair cable market, repeater distances of up to 2.4 km are available. For coaxial cables at speeds less than 1 Mbit/s, distances of up to 25 km between repeaters are possible.

].2.5. Size and Weight Fiber Optic

Compared to all other transmission cables, fiber optic cables are very small in diameter and extremely lightweight. A four-core fiber optic cable weighs approximately 240 kg/km, while a *36-core fiber optic cable weighs only approximately 3 kg more. Because they are smaller in size than traditional cables of the same capacity, they are typically easier to install in existing environments, and installation time and cost are generally lower because they are lightweight and easier to work with.

Traditional cable can weigh from 800 kg/km for 36 twisted pair cable to 5 t/km for high quality large diameter coaxial cable.

1.2.6. Use in flammable gas environments Fiber optics

Multi-mode fibers that work with LED light sources are suitable for use in flammable areas. Until recently, it was believed that all types of fibers were suitable for use in flammable areas; however, research has shown that certain fiber systems with high-powered light sources (lasers) can raise the temperature of the metal surface they shine on to the point of ignition of flammable gases, and can also cause sparks under certain conditions.

Unless traditional cable-based communication systems are very strictly designed and adhere to certain internal safety standards, they are not suitable for use in flammable areas. Conventional cables, even those carrying low currents, can create sparks or arcs between themselves unless current limiting means are used in the transmission circuits.

Electromagnetic waves involve a combination of electric and magnetic fields. Let's consider an electric charge. It creates an electric field around itself. If a charge moves, it creates a magnetic field. It was theoretically shown and...

Here, the transmitter and receiver establish an initial synchronization, then continuously transmit data, maintaining it throughout the transmission session. This is achieved through special data coding schemes, such as Manchester coding (Manchester...

Here, the transmitter and receiver operate independently and exchange a synchronizing bit pattern at the beginning of each message chip (frame). There is no fixed relationship between one message frame and the next. This is similar to...