Fiber Optics: The Fastest Communication Links Ever Built - Research Paper Example

 Fiber Optics: The Fastest Communication Links Ever Built Outline THESIS: Today we enjoy fast and efficient ways of transmitting information and data courtesy of fiber optics, since its invention and large-scale use in 1990s; it has been the key to all our information needs. 1. Introduction a. History and development of fiber optics since 1790 2. Body a. Fiber optics have wide applications in communication industry b. How fiber optics operate Fiber have high operation capability in transmitting large amounts of information The plastic cable The glass cable Plastic-clad silica (PCS) Fiber Cable. 3. Operational characteristics of Optic Fiber Cables includes interference, attenuation, dispersion, dispersion by polarization and optical Signal-to-Noise Ratio 4. There are five connectors used to link fiber cable 5. There are five types of fiber optics 6. Main component of fiber optics communication system are the transmitter and receiver 7. Splicing is done to connect fiber cable to attain certain lengths 8. conclusion Introduction History and development of Fiber Optics. Application of optic in communication dates back to the late 1790s with the invention of semaphore by Claude Chappe. Coming the year 1880, Alexander Graham invented the Photophone, which utilized reflective surfaces to transmit information. This invention was largely experimental and it never reached the height of public usage. In the mid-1950s, John Loggie and Clerance Hansell come up with the idea of using hollow reflective pipes for imaging in television broadcastings and facsimile1. Abraham Hell of Dutch Republic and Harold Hopkins of Britain in 1954 wrote independent paper on imaging bundles, Hopkins reported on unclad while Hell reported on clad fiber bundles. In Van Abraham’s experiment, he used a lower refractive index transparent material to cover the fiber in order to reduce external interference on the fiber’s reflective surface, this significantly reduced distortion and interference. By the year 1961, Elias Snitzer engineered an optical fiber so thin that it could carry light with only one waveguide mode. This fiber was fit for medical examination but not for communication purposes since it had higher losses to the degree 1decbel per meter along its length. For optical fiber to be efficiently used in communication, it requires that the fiber be able to have a maximum loss of 10decibels per kilometer. Improvement were made on the fiber in the year 1070 by a team of researcher who used fused silica to experiment the information transmission. The material was capable of attaining high levels of purity and had high melting point. Corning Glass researcher later the same year come up with a fiber-optic wire, which carried information by use of patterns of light. It was capable of transmitting 65,000 times more information than the original copper wire. This solved the decibel loss problem inherent in the first fiber. The fiber’s efficiency was reinforced with titanium. By June of 1972, Robert Maurer, Donald Keck, and Peter Schultz invented multimode germanium-doped fiber with a loss of 4 dB per kilometer and much greater strength than titanium-doped fiber. In 1973, John MacChesney developed a modified chemical vapor-deposition process for fiber manufacture at Bell Labs. This process spearheaded the commercial manufacture of fiber-optic cable1. Fiber optic was first availed for public use in April 1977 when General Telephone and Electronics tested and created the world’s first telephone traffic with a speed of 6megabites. In May the same year, Bell Company installed a 1.5 optic fiber connection in downtown Chicago. A single fiber carried traffic equivalent to 672 voices. Today we enjoy fast and efficient ways of transmitting information and data courtesy of fiber optics, since its invention and large-scale use in 1990s; it has been the key to all our information needs. Fiber Optics have wide applications in communication industry. The use of fiber optic has completely revolutionized communication. There are numerous applications of fiber optics with advancement from use within a few meters to hundreds of kilometers. The use of fiber optics has given telecommunication and global network a new dimension2. Fiber optics guarantees reliable, efficient and secure media for data and information. This includes transfer of financial data from one building to another or between two or more terminal computers. Another example is the application in telecast and telecast and high definition TV that require high bandwidth of media to transfer. Fiber optics offers more bandwidth hence reliable for transferring broadband signals. The application has been systemized to work with intelligent transportation systems such as use in modern telemedicine, traffic lights and messages sign, which are changeable. Other advanced technological application includes automation, military and space technology2. How Fiber –Optics Operates It consist of two concentric layers, the cladding and the core. They vary in refractive index. The hollow inner core is a vacuum since light travels faster in vacuum. Light propagates through the inner core through a series of reflection of light. Refraction and reflection may occur if the angle of incidence at the inner core false below the cladding. Refraction of the light beams results to attenuation and therefore repeaters are installed after some intervals to boost signal strength. The cladding and core are usually manufactured as a combination to reduce the difference in refractive indices. The outer protecting layer, which is the Ultraviolet (UV) light cured acrylate, provides protection against environmental degradation and physical strength. Optic cable sizes are usually mentioned with the core size as the first and cladding size as the second e.g. 45/145 is the dimension for 45 microns of diameter for core and 145 microns diameter for cladding 2. Fiber have high operation capability in transmitting large amounts of information Cable optics is more efficient when large amounts of light beams are passed through the core. The large amount of light leads to low bit error rate too. This implies more light reaches the destination and therefore attenuation is greatly reduced. The rate of data exchange too increases between the receiver and the sender. Fiber composition, size and mode of propagation affect the rate of data transmission. The common materials used for fiber optics includes plastic –clad silica (PCS), glass and plastic3. The Plastic Cable It is most probably has higher attenuation compared to glass and plastic-clad silica. The core is plastic mainly manufactured from polymethylmethacrylate that is coated with flour polymer. Though the plastic cable may be suitable under tight budget, it is highly frames and susceptible strenuous bends. It may not be suitable for some environments as well in addition to its high attenuation. Glass Cable However, the most the most expensive of the three types, it offers low attenuation and therefore the most efficient type to use in most cases. The inner core and the cladding are made of glass material. The glass used is fused quartz, silicon oxide, ultra-transparent or ultra-pure glass. Its perfection may be limited by residual impurities in the final glass product that results to attenuation due to absorption or catering of light. Plastic-clad silica (PCS) Fiber Cable. Its performance lies between that of glass and plastic cable. Though the inner core is made of glass, the cladding is made of plastic i.e. low refractive index silicon elamoster. The glass core usually consists of vitreous silica. It is mostly applicable in link installers though it is difficult to make connector and adhesive bonding with PCS 5. Generally, multi cable systems have been used to improve on the modern cable physical strength against crushing during pulling. Usually, the central core is made up of dielectric core and individual fibers positioned around it. Some cables consist of outer strength material members that provide extra protection to the entire enclosed fibers. Operational characteristics of Optic Fiber Cables Interference Fiber Optics is highly resistive to radioactive and electromagnet interferences. It is therefore best suited for areas where high voltage and noise is eminent. It also poses desirable characteristics that are most applicable in biometric and industrial networks. Attenuation It is generalized as either intrinsic or extrinsic attenuation. Attenuation is measured in decibels and usually expressed as in decibel per kilometer. Intrinsic - Substances found within the fiber material majorly cause this type of attenuation. Once light heats one of the impurities in the fiber material, it either is absorbed or scattered. Either Raleigh scattering or material absorption can characterize it. Material absorption occurs because of impurities and imperfection within the fiber material. Rayleigh scattering on the other hand is the results from elastic collusion between the silica molecule and light wave in the fiber material3. Extrinsic - This may result from external factors such as stretching and bending. The bending and stretching effect reduces optical power. Straining affects the refractive index and the critical angle. The fibers has a maximum bending radius that when exceeded, results in problems. Necessary precaution should be taken to avoid extreme bending while handling optic fiber cables. Minimal bending can be reversible4. Dispersion Dispersion results to the spread of light as it propagates through the fiber cable. When the light spread, they tend to overlap and therefore become more difficult to distinguish at the receding end. For instance, light from laser and LED travels at varying speeds and wavelengths. Due to distance, the wavelength vary in time .The wavelength continue to be dispersed as light propagates the fiber cable resulting to errors in wavelength received at the terminal4. Dispersion by Polarization Mechanical strains impacted on the fiber cables results to bends and stress. This causes distortion to the cylindrical perfect geometry of the fiber cable and interferes with the cylindrical wavelength guide, which in turn introduces small refractive index. The result is a phenomenon known as birefringence, which causes light to travel at varying speeds leading to difference in propagation time of data in the fiber cable4. Optical Signal-to-Noise Ratio The ratio is a parameter used to measure the signal power to the net noise. Signal amplifiers are used to boost the signal at intervals. Regeneration of the signal helps reduce some aspects of the signal-to-noise ratio and therefore boost the quality of signal received at the terminal. There are five connectors used to link fiber cables Connectors are devices mounted at the ends of fiber cable to link it with the next; it can be a mechanical device connected to the end of fiber cable, housing or the receiver. This allows the devices to be mated to another one of a similar kind. For a device to be used as a connector, it must be able to collect light, transmit it effectively and be easy to detach and attach to the structure. Repeatability and vibration resistance are some of the factors that are considered in choosing the right connector. Some of the connectors in market are discussed in this section. 1. FC Connectors- They are used both in multimode and single mode connections. They allow for accurate positioning of the optic cable in relation to the transmitter and the receiver. FC connectors are constructed with a metal housing and are nickel-plated. They have ceramic ferrules and are rated for 500 mating cycles. The insertion loss for matched FC connectors is 0.25 dB. From a design perspective, it is recommended to use a loss margin of 0.5 dB or the vendor recommendation for FC connectors5. 2. SC connectors - are used with single-mode and multimode fiber-optic cables. They offer low cost, simplicity, and durability. SC connectors provide for accurate alignment via their ceramic ferrules. An SC connector is a push-on, pull-off connector with a locking tab5. 3. ST connector - are keyed bayonet connector and is used for both multimode and single mode fiber-optic cables. It can be inserted into and removed from a fiber-optic cable both quickly and easily. Method of location is also easy. ST connectors come in two versions: ST and ST-II. These are keyed and spring-loaded. They are push-in and twist types. ST connectors are constructed with a metal housing and are nickel-plated. They have ceramic ferrules and are rated for 500 mating cycles5. 4. LC connectors - are used with single-mode and multimode fiber-optic cables. The LC connectors are constructed with a plastic housing and provide for accurate alignment via their ceramic ferrules. LC connectors have a locking tab. LC connectors are rated for 500 mating cycles. The typical insertion loss for matched LC connectors is 0.25 dB. From a design perspective, it is recommended to use a loss margin of 0.5 dB or the vendor recommendation for LC connectors5. 5. MT-RJ connectors - are used with single-mode and multimode fiber-optic cables. The MT-RJ connectors are constructed with a plastic housing and provide for accurate alignment via their metal guide pins and plastic ferrules. MT-RJ connectors are rated for 1000 mating cycles. From a design perspective, it is recommended to use a loss margin of 0.5 dB or the vendor recommendation for MT-RJ connectors5. Splicing is done to connect fiber cable to attain certain lengths Fiber manufacturing companies offers fibers of limited lengths hence the need for splicing; this is done to connect the cables to reach a certain length. In some case, splicing is done at building entrances or any other point that causes intermittency before the signal reaches the receiver. Two principle methods of splicing includes the fusion and mechanical method. In fusion method, the two ends are fused together by arc welding; the accuracy of such a connection is inspected by microscope examination. In mechanical method, the ends are joined by pressure or bindings. There are five types of fiber optics. This section discusses various type of MMF (multimode fiber) and SMF (single-mode fiber) that are recently used in premise, aerial, submarine, metro and long-haul applications. Global standardization body for telecommunication systems and vendors, the International Telecommunication Union (ITU-T), has standardized various fiber types listed below. 1. Multimode fiber with a 50-Micron core (ITU-T G.651) It’s an MMF which has a nominal diameter core of 50- µm, a 125- µm nominal cladding diameter with a graded refractive index and attenuation parameter of 0.8 dB/km at 1310nm. It’s mainly used for short-reach optical transmission systems and optimized for use in the 1300-nm band but can operate also in the 850-nm band6. 2. Nondispersion-Shifted Fiber (ITU-T G.652) This is the mostly used fiber and is also called standard SMF. It is optimized for use in the 1310-nm band but can also fit in the 1550-nm band. Its attenuation parameter are is 0.2 dB/km at 1550 nm, and the PMD parameter is less than 0.1 ps/√km. Coming SMF-28 is a good example of standard SMF6. 3. Low Water Peak Nondispersion-Shifted Fiber (ITU-T G.652.C) It is optimized for networks where transmission occurs across a broad range of wavelengths from 1285nm to 1625nm. This fiber has excellent capabilities for shorter, unamplified metro and access networks but they cannot fully address the needs for 1550-nm transmission. It has attenuation parameter of typically 0.2 dB/km at 1550 nm and the PMD parameter is less than 0.1ps/√km. An example is Coming SMF-28e6. 4. Dispersion-Shifter Fiber (ITU-T G.653) It shows high dispersion values over the range between 1500 nm and 1600 nm but almost zero-dispersion wavelength near the 1310-nm window band. The trend for shifting the operating transmission from 1310 nm to 1500 nm lead to the introduction of a fiber type known as dispersion-shifted fiber(DSF)6. 5. Nonzero Dispersion Shifted Fiber (ITU-T G.655) Nonzero Dispersion Shifted Fiber (NZDSF) mitigates nonlinear characteristics. NZDSF fiber moves the zero-dispersion wavelength outside the 1550-nm operating window thus overcoming these effects of nonlinear characteristics. The practical effect of this is to have a small but finite amount of chromatic dispersion at 1550 nm, which minimizes nonlinear effects, such as FWM, SPM, and XPM, which are seen in the dense wavelength-division multiplexed (DWDM) systems without the need for costly dispersion compensation6. There are two fiber families called nonzero dispersion (NZD+ and NZD–), in which the zero-dispersion value falls before and after the 1550-nm wavelength, respectively. Its attenuation parameter is 0.2dB/km at 1550-nm, and PDM parameter less than 0.1 ps/√km1. An example is the Coming LEAF fiber. The dispersion slope of NZDSF with respect to SMF and DSF is shown in the diagram above­­­­­­­­­­­­­­­­­­­­­­­­­­­6. Main component of fiber optics communication system are the transmitter and the receiver Information in the form of voice, data and video from the source is encoded into electrical signals that can drives the transmitter. The photons travel through the fiber down the optical path toward the receiver. The decoder convert the signals from optical to electrical and then sent to their destination3. The system consists mainly of: Transmitter This transmitter has two functions. 1. Source of light launched into the fiber-optic cable. 2. Modulating this light to represent the binary data that has been received from the source. The transmitter’s physical dimension must match the size of the optical fiber cable being used this meaning that it must emit light in a cone with a cross-sectional diameter of 8 to 100 microns; otherwise, it cannot be coupled into the fiber-optic cable7. Receiver The receiver performs two main functions. 1. Detects the light emanating from the fiber optic cable and convert it into an electrical signal. 2. Demodulate the light to determine the identity of the binary data that it represents To detect light it applies photodiode, which sense and convert it into an electrical current. The optical signal from the fiber optic cable and the resulting electrical current have a small amplitude and thus photodiode circuitry is followed by one or more amplification stages. There are also filters and equalizers that shape and improve the information bearing electrical signal. Conclusion Optical communication ranging in scales from worldwide connections desktop connections within an organization. Analog phone services can be transmitted by optical fibers by use of carriers. Digital video have for a long a time been transmitted by use of fibers, most of television companies have migrated from the use of analog transmission since the invention of optic fiber. Intelligent transportation systems and biomedical systems also use fiber-optic transmission systems. Optical cable is also the industry standard for subterranean and submarine transmission systems7. Fiber optic utilizes the principle of total internal reflection to transmit light signals. Different wavelengths of light are guide through the core of and are extracted for interpretation by the receptors at desired points. Fiber optic uses two method of propagation, the single mode and the multi-mode. The performance of these two modes differ in relation to attenuation and time dispersion. SMF cable provides better performance than MMF cable. The three primary propagation modes include multimode step index, single-mode step index, and multimode graded index propagation7. Optical transmission are less prone to tapping and any interference can be detected with much ease than other methods of transmission. The small size of the optic cable gives room to accommodate more fibers in a small space as compared to the case of metallic-wire transmission. They are also much faster than wireless transmission. Attenuation behaviors of optic are classified as either intrinsic or extrinsic. Intrinsic attenuation occurs because of substances inherently present in the fiber, whereas extrinsic attenuation occurs because of external influences such as bending, decibel loss at the connector interface and rigidity of the connector. The choice of connector depends mainly on the equipment and the mode of application. Whether the connectors are permanent or semi-permanent, the connections must be spliced. Splicing is done to realize a certain length of connection. In splicing, the sections needs to be aligned precisely at the mated point to ensure that all the light is transferred to the next chord. Splicing can be done either mechanically or by using fusion technique. The total losses between the point at which the signal if fed into the fiber (transmitter) and the exit point (receiver) account for the total loss in transmission. Loss-budget analysis is the calculation and verification of a fiber-optic system’s operating characteristics. This encompasses items such as fiber routing, electronics, wavelengths, fiber type, and circuit length. Attenuation and nonlinear fiber characteristics are the key parameters for fiber span analysis. Transmitter launch power, receiver sensitivity, and the dynamic range of the receiver are crucial numbers used in span analysis5. Without a single doubt, the efficient communication system that we enjoy today are based on fiber optics. Reference 1. D. J. Morris, 2003. Pulse Code Formats for Fiber Optical Data Communication: Basic Principles and Applications, Marcel Dekker, New York. 2. Y. Suematsu and K. Iga, 2002. Introduction to Optical Fiber Communications, Wiley, New York. 3. C. P. Sandbank, 2000. Optical Fiber Communication Systems, Wiley, New York. 4. J. E. Midwinter, 2009. Optical Fibers for Transmission, Wiley, New York, 5. S. E. Miller and A. G. Chynoweth, 2007.Optical Fiber Telecommunications, Academic Press, New York. 6. G. R. Elion and H. A. Elion, 2008. Fiber Optics in Communication Systems, Marcel Dekker, New York. A. B. Sharma, S. J. Halme, and M. M. Butusov, 2006. Optical Fiber Systems and Their Components, Springer-Verlag, Berlin. 7. M. K. Barnoski, 2001. Fundamentals of Optical Fiber Communications, Academic Press, New York, 2nd Ed. Annotated Bibliography D. J. Morris, 2003. Pulse Code Formats for Fiber Optical Data Communication: Basic Principles and Applications, Marcel Dekker, New York. The author give historical accounts of how fiber optic developed, he dates its application back to the late 1790s with the invention of semaphore by Claude Chappe. Coming the year 1880, Alexander Graham invested the Photophone, which utilized reflective surfaces to transmit information. He says that this invention was largely experimental and never reached the height of public usage. According to Morris, it was used in the year 1977 when General Telephone and Electronics tested and created the world’s first telephone traffic with a speed of 6megabites Y. Suematsu and K. Iga, 2002. Introduction to Optical Fiber Communications, Wiley, New York. The author discusses the needs for connectors and different types of connectors; he says that connectors allows the devices to be mated to another device of a similar kind. For a device to be used as a connector, it must be able to collect light, transmit it effectively and be easy to detach and attach to the structure. Repeatability and vibration resistance are some of the factors that are considered in choosing the right connector. Some of the connectors in market are discussed in this section. C. P. Sandbank, 2000. Optical Fiber Communication Systems, Wiley, New York, In this section, the book explicitly described the component of the fiber optic cable. A fiber-optic cable is composed of two concentric layers, called the core and the cladding. The core and cladding have different refractive indices, with the core having a refractive index of n1, and the cladding having a refractive index of n2. The author further explains that the index of refraction is a way of measuring the speed of light in a material. Light travels fastest in a vacuum. The actual speed of light in a vacuum is 300,000 kilometers per second, or 186,000 miles per second J. E. Midwinter, 2009. Optical Fibers for Transmission, Wiley, New York, The author describes the principle operation of the optic fiber cable. The greater the amount of light that can be coupled into the core, the lower the bit error rate (BER), because more light reaches the receiver. The book illustrates that attenuation of light ray experiences in propagating down the core is inversely proportional to the efficiency of the optical cable because the lower the attenuation in propagating down the core, the lower the BER. This is because more light reaches the receiver. In addition, the less chromatic dispersion realized in propagating down the core, the faster the signaling rate and the higher the end-to-end data rate from source to destination. The major factors that affect performance considerations described in this paragraph are the size of the fiber, the composition of the fiber, and the mode of propagation S. E. Miller and A. G. Chynoweth, 2007.Optical Fiber Telecommunications, Academic Press, New York. In the section, the author describes the dimension and components of the Plastic-clad silica cable. The diameter of the cladding surrounding each of these cores is 125 µm. Core sizes of 85 µm and 100 µm were used in early applications, but are not typically used today has mentioned by the author. The core and cladding are manufactured together as a single solid component of glass with slightly different compositions and refractive indices. The third section of an optical fiber is the outer protective coating known as the coating. The coating is typically an ultraviolet (UV) light-cured acrylate applied during the manufacturing process to provide physical and environmental protection for the fiber G. R. Elion and H. A. Elion, 2008. Fiber Optics in Communication Systems, Marcel Dekker, New York. In this book, it author states the different types of fibers. NZDSF fiber overcomes the defect of nonlinear characteristics by moving the zero-dispersion wavelength outside the 1550-nm operating window. The practical effect of this is to have a small but finite amount of chromatic dispersion at 1550 nm, which minimizes nonlinear effects, such as FWM, SPM, and XPM, which are seen in the dense wavelength-division multiplexed (DWDM) systems without the need for costly dispersion compensation. There are two fiber families called nonzero dispersion (NZD+ and NZD–), in which the zero-dispersion value falls before and after the 1550-nm A. B. Sharma, S. J. Halme, and M. M. Butusov, 2006. Optical Fiber Systems and Their Components, Springer-Verlag, Berlin. The author of this book explains how communication in fiber optic fiber works. First, it must be a source of the light launched into the fiber-optic cable. Second, it must modulate this light to represent the binary data that it receives from the source. A transmitter’s physical dimensions must be compatible with the size of the fiber-optic cable being used. This means that the transmitter must emit light in a cone with a cross-sectional diameter of 8 to 100 microns; otherwise, it cannot be coupled into the fiber-optic cable. The optical source must be able to generate enough optical power so that the desired BER can be met over the optical path. S. D. Personick, 2001. Optical Fiber Transmission Systems, Plenum Press, New York. Personick discusses Loss-budget analysis as the calculation and verification of a fiber-optic system’s operating characteristics. It encompasses items such as fiber routing, electronics, wavelengths, fiber type, and circuit length. Attenuation and nonlinear fiber characteristics are the key parameters for fiber span analysis. He says that transmitter launch power, receiver sensitivity, and the dynamic range of the receiver are crucial numbers used in span analysis. M. K. Barnoski, 2001. Fundamentals of Optical Fiber Communications, Academic Press, New York, 2nd Ed. Barnoski explains the principles under which fiber optics work; he says that it utilizes the principle of total internal reflection to transmit light signals. Different wavelengths of light are guided through the core and are extracted for interpretation by the receptors at desired points. He goes ahead and explains the modes of propagation as the single mode and the multi-mode. The performance of these two modes differ in relation to attenuation and time dispersion. SMF cable provides better performance than MMF cable. He summarizes the three primary propagation modes as the multimode step index, single-mode step index, and multimode graded index propagation. Read More