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Fiber Optics

Fiber optics cable transmits data through very small cores at the speed of light. Significantly different from copper cables, fiber optics cable offer high bandwidths and low losses, which allows high data transmission rates over long distances. Light propagates throughout the fiber cables according to the principle of total internal reflection. There are three types of fiber optics cable, viz. , single-mode, multi-mode and graded index. There are several designs of fiber optics cable, each made from different applications.

In addition, new fiber optic cables with different core and cladding designs have been emerging, which are faster and carry more modes. While fiber optics cable are used mostly in communication systems, they also have established their applications in various other fields ranging from bio-medical to military (Azzawi, 2007, p. 1). History of Fiber Optics Modern optical fiber sensors owe their development to two of the most important scientific advances made in the 1960s, i. e. , the laser (1960) and the modern low-loss optical fiber (1966).

Both equally had origins in work in the previous decades to the microwave predecessor of the laser (the maser) and the short-length low transparency fibers used in early endoscopes for medical and industrial applications. Thus, the early 1970s saw some of the first experiments on low-loss optical fibers being used, not for telecommunications, as had been the prime motivation for their development but for sensor purposes. This pioneering work quickly led to the growth of a number of research groups, which had a strong focus on the exploitation of this new technology in sensing and measurement.

The field has continued to progress and has developed enormously since that time (Grattan and Sun, 2000). Applications Optical fibers have advantages that make it attractive in a variety of applications. They have extremely high bandwidth. Their small diameter and high tensile strength result in smaller, lighter weight cables and connectors. They have promise for use in computer systems. It is attractive to replace parallel interconnects with serial fiber optic links. Cable and connector bulk is significantly reduced and reliability is improved.

Fiber optics high data rate, noise immunity, and low loss make it possible to extend high data rate channel links beyond the confines of the computer room. Fibers permit dramatic weight and bulk reduction and provide large bandwidth and high reliability. Fiber optics sonar links have been developed to transmit information from external sensors through the submarine hull to inboard signal processors. One of the original applications of fibers is image transmission. The flexible fiberscope has been widely used in medicines since the 1950s (Daly, p. 3).

Fiber optic sensor technology has come a long way in solving the needs of the industry. The products now available are installed in many scores of applications at hundreds of companies throughout the world. The advantages of fiber optics technology have been accepted for some years in the telecommunications industry. Sensing applications have been solved in the industrial factory environment by exploiting the dielectric properties of the fiber in hazardous environments and electrically noisy areas. Optical characteristics of the fiber allow interesting micro-movement detection.

These sensors offer amore cost-effective solution for solving challenging problems that have been plaguing us for years (Parro, 1989). Design Instruments designed to work with optical fiber sensors generally have five basic elements namely, i) A low pulsed radiation source in the form of incandescent lamps, light emitting diodes (LED) or collimated sources like laser, ii) narrow band filters to select the required wavelength, iii) a low powered detector, iv) miniature digital readout devices to display the data, and v) the optical fiber sensor system itself.

An important part of the design and construction of the optical fiber instruments is the coupling of the source, fiber and detector to attain maximum intensity of the light entering and leaving the fiber. This can be achieved by a direct contact with the source for example by focusing the pre-collimated beam from the source into the fiber. If the instrument has a double fiber, it is necessary to use two optical systems to obtain double coupling (Quevauviller et al. , 1995, p. 170). Advantages and benefits Fiber optics transmission systems have many advantages over more conventional transmission systems.

They are less affected by noise, do not conduct electricity and therefore provides electrical isolation, carry extremely high data transmission rates, and carry data over very long distances. The characteristics of non-conductivity of fibers make the cable immune to voltage surges. This eliminates interference that may be caused from ground loops, common mode voltages, as well as shifts and shorts in ground potential. A further advantage is that because optical fibers do not emit radiation and are not affected by interference, there is no cross talks between cables.

The raw materials used to fabricate glass fibers are sand, which is an abundant source (Bailey and Wright, 2003, p. 5). Disadvantages and limitations Intensity based fiber optic sensors have a series of limitations imposed by variable losses in the system that are not related to the environmental effect to be measured. Potential error sources include variable losses due to connections and splices, micro-bending loss, and mechanical creep and misalignment of light sources and detectors.

Yet another limitation of fiber optics sensor is that as the grating move from a totally transparent to a totally opaque position, the relative sensitivity of the sensor changes (Yin et al, 2008, p. 10). Future of Fiber Optics Technology Amazing progress has been made since the original development of low loss optical fibers. Attenuation levels of a few tenths of a decibel have been achieved as well as bandwidths of thousands of megahertz in graded index fibers. The major current challenge of the industry is to transfer these laboratory advances into practical cost effective hardware.

At the same time, trends towards longer wavelengths and multiple wavelength operation are quite evident. The next decade of optical fiber technology should see many of these trends brought to fruition with the common availability of high performance cost effective fibers (Gunderson, 1980). Some look forward to so-called ‘enhanced fibers. The basic fiber is being enhanced via novel doping and coatings, for example, to increase the sensitivity, spectral range and robustness to suit sensing requirements which cannot yet be met.

‘Smart materials’ are another key area for fibre and include embedded fiber Bragg gratings. Research topics, which have commercial promise, include diagnostics of the setting of concrete and the identification of failure modes in composites using embedded fiber optics. Glasses such as fiber optics are also used as a transmission medium for optical and electromagnetic diagnostics, which allows sensitive instrumentation to be located remotely. Thus fiber optics is being applied to temperature measurement, pollution monitoring, engine management or nuclear reactors.

A popular area, which may be low volume but is intrinsically high value, is use of fiber optics for well logging in the oil industry (Szweda, 2004). Conclusion Optical fiber current and voltage sensors have reached a high degree of maturity and fulfil the performance requirements for high-voltage substations. Commercial sensor products have been available already for a number of years and started to penetrate into the market. The benefits of optical sensors in comparison with their conventional counterparts are being recognized.

However, the numbers of installed sensors are still small, and more widespread use will require further build-up of confidence in the new technology. The signal format of optical sensors with digital electronics very much differs from the output of conventional instrument transformers. Hence, costly extra equipment for interface adaptation is often necessary. The full benefits of optical sensors can only be realized after also more modern solutions for the substation control equipment have been introduced. Bibliography

Azzawi, A. , and Abdul, A. , (2007) Fiber Optics, Principals and Practices, CRC Press, pp. 416 Bailey, D. , and Wright, E. , (2003) Practical Fiber Optics, Newnes Publishers, pp. 267 Daley, J. C. (1984) Fibre Optics, CRC Press, pp. 246 Gunderson, L. C. (1980) Future developments for fiber optics, Optics and Laser Technology, Vol. 12, issue 4, pp. 211-213 Grattan, K. T. V. and Sun, T. , (2000) Fiber optic sensor technology: an overview, Sensors and Actuators A.

Physical, vol. 82, issue1-3, pp. 40-61 Kersey, A. D. , (1996) A review of recent developments in fiber optics sensor technology, Optical Fiber Technology-2, pp291-317 Parro, T. J. (1989) Fiber optic sensors for industrial applications, ISA Transactions, Vol. 28, issue 2, pp. 31-34 Quevauviller, P. , Maier, E. A. , and Griepink, B. , (1995) Quality assurance for environmental analysis: Method evaluation within the measurements and testing programme (BCR), Elsevier, pp. 649 Szweda, R. , (2004) Enhancing fiber’s prospects, III-Vs review, Vol. 17, issue 6, pp. 47 Yin, S. , Ruffin, P. B. , and Yu, F. T. S. (2008) Fiber optic sensors, CRC Press, pp. 496

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