Fiber Optics Communication System -- A Brief
Overview
Part I
Fiber optic communication which was invented in the early 197...
where private Internet users can already obtain affordable
Internet connections with data rates of 100 Mbit/s – well above...
Further advancement was made in 1880 by Alexander Graham
Bell. He invented his photophone that year which transmitted a
vo...
Heinrich Lamm
It was a medical student Heinrich Lamm, who first assembled a
bundle of optic fibers in order to carry an im...
Abraham Van Heel and Harold.H.Hopkins
A theoretical description on single mode fibers was published in
1961 by Elias Snitz...
Robert Maurer, Donald Keck and Peter Schultz
problems with fiber optics that were spotted by Dr.C.K.Kao.
The application o...
The losses for light propagating in fibers are amazingly small: ≈ 
0.2 dB/km for modern single-mode silica fibers, so that...
The third telecom window, which is now very widely used, utilizes
wavelengths around 1.5 μm. The losses of silica fibers a...
light over some distance, and a receiver. The transmission fiber
may be equipped with additional components such as fiber
...
are constantly being developed, it is not clear so far which kind of
system will dominate the future of optical fiber comm...
can be several terabits per second, sufficient for transmitting
many millions of telephone channels simultaneously. Even t...
semiconductor and fiber amplifiers (mostly erbium-doped fiber
amplifiers, sometimes Raman amplifiers) for maintaining
suff...
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Fiber optical

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Fiber optical

  1. 1. Fiber Optics Communication System -- A Brief Overview Part I Fiber optic communication which was invented in the early 1970s paved way for the telecommunication systems. The phenomenon of transmitting images, data and voice through the passage of light via thin transparent fibers is known as the fiber optics communication. Compared with electrical cables, fiber-optic cables are very lightweight. Fiber-optic cables are immune to problems that arise with electrical cables, such as ground loops or electromagnetic interference (EMI). Such issues are important, for example, for data links in industrial environments. Mostly due to their very high data transmission capacity, fiberoptic transmission systems can achieve a much lower cost than systems based on coaxial copper cables, if high data rates are needed. For low data rates, where their full transmission capacity cannot be utilized, fiber-optic systems may have less of an economic advantage, or may even be more expensive (not due to the fibers, but the additional transceivers). The primary reason, however, for the still widespread use of copper cables for the “last mile” (the connection to the homes and offices) is simply that copper cables are already laid out, whereas new digging operations would be required to lay down additional fiber cables. Fiber communications are already extensively used within metropolitan areas (metro fiber links), and even fiber to the home (FTTH) spreads more and more – particularly in Japan,
  2. 2. where private Internet users can already obtain affordable Internet connections with data rates of 100 Mbit/s – well above the performance of current ADSL systems, which use electrical telephone lines. In other countries, one often tries to squeeze out higher transmission capacities from existing copper cables, e.g. with the technique of vectoring, in order to avoid the cost of laying down fiber cables to the premises. This, however, is more and more seen only as a temporary solution, which cannot satisfy further growth of bandwidth demand. Part II Fiber-based systems have largely replaced radio transmitter systems for long-haul optical data transmission. They are widely used for telephony, but also for Internet traffic, long highspeedlocal area networks (LANs), cable TV (CATV), and increasingly also for shorter distances within buildings. In most cases, silica fibers are used, except for very short distances, where plastic optical fibers can be advantageous. Now let us try to explore what is Fiber Optics Technology In earlier centuries, when someone wanted to convey some important news to another person who was miles away, it was not that easy. A lot of traditional methods were employed to deliver the message. But, in this contemporary period, much advancement like mobile communication, communication through mail, satellite, and even more has made exchange of information easier and quite simpler. John Tyndall in 1854 experimentally proved that the light rays could evenly pass through a curved stream of water. Thus, he tried and succeeded in proving that the light signal can be bent.
  3. 3. Further advancement was made in 1880 by Alexander Graham Bell. He invented his photophone that year which transmitted a voice signal on a single beam of light. The basic mechanism behind his invention was focusing solar energy over a mirror and he then talked over a mechanism that made the mirror to vibrate. A detector was placed at the receiving end that reproduced the same voice received by the receiver. Any bad weather like a cloudy day can easily interfere with the working of this invention. John Logie Baird It was in 1902 an English man, John Logie Baird, along with an American, Clarence.W.Hansell, patented their unique innovation. They worked on using sequences of rods that were transparent that could easily transmit images for televisions.
  4. 4. Heinrich Lamm It was a medical student Heinrich Lamm, who first assembled a bundle of optic fibers in order to carry an image; it was in the year 1930. He successfully reported transmitting the image of a light bulb. But then, the image he made was of a very low quality. His patent for this innovation was denied. Since there was no efficient communication, people were not able to hear about the research work of others in nearby countries. In 1954, two scientists wrote papers on imaging bundles individually. The two were a Dutch scientist, Abraham Van Heel and a British scientist, Harold.H.Hopkins. The only difference between their papers was that Hopkins reported on bundles of unclad fibers whereas Abraham reported on a bundle of clad fibers. He tried covering the fibers with a transparent lower refractive index material. This helped a lot in reducing the interference between the fibers by restricting the external distortion.
  5. 5. Abraham Van Heel and Harold.H.Hopkins A theoretical description on single mode fibers was published in 1961 by Elias Snitzer who belonged to the American optical. He tried proving that a small core fiber can carry only a single waveguide mode. His set up had a disadvantage that it had a light loss of about one decibel per kilometer. Part III The Breakthrough In the year of 1970, a good team of scientists started experimenting with the usage of silica. They chose silica as it had a high melting point with good purity and also a comparatively lower refractive index. Patent number #3,711,262 marks the invention of fiber optics wire by corning glass researchers, Robert Maurer, Donald Keck and Peter Schultz. These optical wave guide fibers were more advantageous. They carried 65,000 times more information than the randomly employed copper wire. Even miles apart, the information can be received with a very high rate of efficiency. The information was decoded with a particular pattern of light waves. This team concentrated more on solving the
  6. 6. Robert Maurer, Donald Keck and Peter Schultz problems with fiber optics that were spotted by Dr.C.K.Kao. The application of fiber optics extends to a wider range. In the year of 1975, the government of the United States of America planned of linking the computers that were present in the NORAD headquarters using fiber optics techniques. They also executed the plan hoping that will help in reducing the interference. Under the downtown of Chicago, fiber optic communication was laid for about 1.5 miles in the year of 1977. Here, every single optical fiber carried the equivalent of about 672 voice channels. At present, fiber optic communication is used across the world in every nook and corner. As much as about eighty percentage of the long distance traffic is being carried out with the optical fibers that were designed by the three people, Maurer, Keck and Schultz. The capacity of fibers for data transmission is huge: a single silica fiber can carry hundreds of thousands of telephone channels, utilizing only a small part of the theoretical capacity. In the last 30 years, the progress concerning transmission capacities of fiber links has been significantly faster than e.g. the progress in the speed or storage capacity of computers.
  7. 7. The losses for light propagating in fibers are amazingly small: ≈  0.2 dB/km for modern single-mode silica fibers, so that many tens of kilometers can be bridged without amplifying the signals. A large number of channels can be reamplified in a single fiber amplifier, if required for very large transmission distances. Due to the huge transmission rate achievable, the cost per transported bit can be extremely low. − Telecom Windows Optical fiber communications typically operate in a wavelength region corresponding to one of the following “telecom windows”: The first window at 800–900 nm was originally used. GaAs/AlGaAs-based laser diodes and light-emitting diodes (LEDs) served as transmitters, and silicon photodiodes were suitable for the receivers. However, the fiber losses are relatively high in this region, and fiber amplifiers are not well developed for this spectral region. Therefore, the first telecom window is suitable only for shortdistance transmission. The second telecom window utilizes wavelengths around 1.3 μm, where the loss of silica fibers is much lower and the fibers' chromatic dispersion is very weak, so that dispersive broadening is minimized. This window was originally used for long-haul transmission. However, fiber amplifiers for 1.3 μm (based on, e.g. on praseodymium-doped glass) are not as good as their 1.5-μm counterparts based on erbium. Also, low dispersion is not necessarily ideal for long-haul transmission, as it can increase the effect of optical nonlinearities.
  8. 8. The third telecom window, which is now very widely used, utilizes wavelengths around 1.5 μm. The losses of silica fibers are lowest in this region, and erbium-doped fiber amplifiers are available which offer very high performance. Fiber dispersion is usually anomalous but can be tailored with great flexibility (→ dispersionshifted fibers). The second and third telecom windows are further subdivided into the following wavelength bands: Band Description Wavelength range O band original 1260–1360 nm E band extended 1360–1460 nm S band short wavelengths 1460–1530 nm C band conventional (“erbium window”) 1530–1565 nm L band long wavelengths 1565–1625 nm U band ultralong wavelengths 1625–1675 nm The second and third telecom windows were originally separated by a pronounced loss peak around 1.4 μm, but they can effectively be joined with advanced fibers with low OH content which do not exhibit this peak. Part IV -- Fiber Optics System Design The simplest type of fiber-optic communication system is a fiberoptic link providing a point-to-point connection with a single data channel. Such a link essentially contains a transmitter for sending the information optically, a transmission fiber for transmitting the
  9. 9. light over some distance, and a receiver. The transmission fiber may be equipped with additional components such as fiber amplifiers for regenerating the optical power ordispersion compensators for counteracting the effects of chromatic dispersion. The article on fiber-optic links gives more details. A typical channel capacity for long-haul transmission is nowadays 2.5 or 10 Gbit/s; 40, 100 or even 160 Gbit/s may be used in the future. More advanced systems increase the transmission capacity by simultaneously using several, dozens or even hundreds of different wavelength channels (coarse or dense wavelength division multiplexing). The main challenges are to suppress channel cross-talk via nonlinearities, to balance the channel powers (e.g. with gain-flattened fiber amplifiers), and to simplify the systems. Another approach is time division multiplexing, where several input channels are combined by nesting in the time domain, and solitons are often used to ensure that the sent ultrashort pulses stay cleanly separated even at small pulseto-pulse spacings. Another important development is that of systems which link many different stations with a sophisticated fiber-optic network. This approach can be very flexible and powerful, but also raises a number of non-trivial technical issues, such as the need for adding or dropping wavelength channels, ideally in a fully reconfigurable manner, or to constantly readjust the connection topology so as to obtain optimum performance, or to properly handle faults so as to minimize their impact on the overall system performance. As many different concepts (e.g. concerning topologies, modulation formats, dispersion management, nonlinear management, and software) and new types of devices (senders, receivers, fibers, fiber components, electronic circuits)
  10. 10. are constantly being developed, it is not clear so far which kind of system will dominate the future of optical fiber communications. For a discussion of aspects such as bit error rates and power penalties, see the article on optical data transmission. − Transmission Capacity of Optical Fibers Within the last 30 years, the transmission capacity of optical fibers has been increased enormously. The rise in available transmission bandwidthper fiber is even significantly faster than e.g. the increase in storage capacity of electronic memory chips, or in the increase in computation power of microprocessors. The transmission capacity of a fiber depends on the fiber length. The longer a fiber is, the more detrimental certain effects such intermodal orchromatic dispersion are, and the lower is the achievable transmission rate. For short distances of a few hundred meters or less (e.g. within storage area networks), it is often more convenient to utilize multimode fibers, as these are cheaper to install (for example, due to their large core areas, they are easier to splice). Depending on the transmitter technology and fiber length, they achieve data rates between a few hundred Mbit/s and ≈ 10 Gbit/s. Single-mode fibers are typically used for longer distances of a few kilometers or more. Current commercial telecom systems typically transmit 2.5 or 10 Gbit/s per data channel over distances of ten kilometers or more. Future systems may use higher data rates per channel of 40 or even 160 Gbit/s, but currently the required total capacity is usually obtained by transmitting many channels with slightly different wavelengths through fibers; this is called wavelength division multiplexing (WDM). Total data rates
  11. 11. can be several terabits per second, sufficient for transmitting many millions of telephone channels simultaneously. Even this capacity does not reach by far the physical limit of an optical fiber. In addition, note that a fiber-optic cable can contain multiple fibers. In conclusion, there should be no concern that technical limitations to fiber-optic data transmission could become severe in the foreseeable future. On the contrary, the fact that data transmission capacities can evolve faster than e.g. data storage and computational power, has inspired some people to predict that any transmission limitations will soon become obsolete, and large computation and storage facilities within high-capacity data networks will be extensively used, in a similar way as it has become common to use electrical power from many power stations within a large power grid. Such developments may be more severely limited by software and security issues than by the limitations of data transmission. − Key Components for Optical Fiber Communications Optical fiber communication systems rely on a number of key components: optical transmitters, based mostly on semiconductor lasers (often VCSELs), fiber lasers, and optical modulators optical receivers, mostly based on photodiodes (often avalanche photodiodes) optical fibers with optimized properties concerning losses, guiding properties, dispersion, and nonlinearities dispersion-compensating modules
  12. 12. semiconductor and fiber amplifiers (mostly erbium-doped fiber amplifiers, sometimes Raman amplifiers) for maintaining sufficient signal powers over long lengths of fibers, or as preamplifiers before signal detection optical filters (e.g. based on fiber Bragg gratings) and couplers optical switches and multiplexers (e.g. based on arrayed waveguide gratings); for example, optical add/drop multiplexers (OADMs) allow wavelength channels to be added or dropped in a WDM system electrically controlled optical switches devices for signal regeneration (electronic or optical regenerators), clock recovery and the like various kinds of electronics e.g. for signal processing and monitoring computers and software to control the system operation In many cases, optical and electronic components for fiber communications are combined on photonic integrated circuits. Further progress in this technological area will help optical fiber communications to be extended to private households (→ fiber to the home) and small offices.

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