Optical Fibres Are the Most Advanced Form of Cables - Essay Example

PART A INTRODUCTION Optical fibres are the modern and most advanced form of cables that are used in the digital communication. They make use of the light signals for transmitting the data traffic. Another type is the Plastic optical fibre which differs from the other commonly used optical fibre. The overall mechanism of optical fibre includes polymethylmethacrylate (PMMA). The cost consideration are making them more desired in their working. Internal structure of optical fibre constitute cylindrical strand coated with plastic. It is where the light passes through. The cladding provides the outer covering to it followed by the buffer coating which serves as the outer most covering. These layers make them resistant to electrical and mechanical interferences. A pictorial representation of the components that makeup an optical fibre is shown in figure 1 of appendix A Types of plastic fibres The refractive index feature makes plastic optics fibre multimode. The predecessor glass fibre come in single mode of step index or graded index profile. An illustrated diagram on how the two types guide the light is shown in appendix A figure 2. Step index fibre Step index fiber consists core with one index of refraction, and the refractive index may drop down to a smaller index of refraction. Three different light waves travel through the fiber. While the first one passes straight through the center of the core, the second mode passes at a steep angle and bounces back through the concept of total internal reflection. The third mode surpasses the critical angle, refracting into the cladding (www.fiberoptics4sale.com). The second mode is able to cover more distance than the first mode. These rays travel through a different paths, they thereby have different modes taking different time to reach. The variation so visible is termed as the dispersion, ultimately giving muddied signal at the receiving node. The output pulse varied against the input pulse. Graded index fibre (continuous-index) In case of the graded index fiber, the refractive index gradually dips down from the core, resulting in the indistinct separation between cladding and core. Increased index of refraction in the centre of the core leads to slowing down of the speed of some light rays, resulting in the rays to reach the receiving end at nearly about the same time, ultimately minimizing the dispersion and increase in the bandwidth (www.fiberoptics4sale.com).. How fibre optics work Fibres work on concept of propagation of light, the light in a fiber-optic cable passes through the core of the fibre. At that time, if there are bends, it will result in reflection across the cladding .This concept is termed as total internal reflection. Reflection and refraction When a light passes through a transparent material like plastic, part of the light is reflected through surface and part of it is transmitted away from the transparent material. The part of light that skips through changes the direction on entering the outer layer due to refraction. Refraction occurs due to varying speeds and varying different refractive index (Wiley J,Ungear S (1990). Refractive index The refractive index is defined as the ratio of the velocity of the speed of light in an optical fibre to the speed of light through the vacuum Tricker R (2002). Refractive index= Total internal reflection Total internal reflection occurs (see appendix A figure 4 )when light passing through one material gets intact with a different material resulting in the reflection to the original material Sibley M J N (1995). In case of fibre optics, light is processed through the fibre, passing into the core further to the cladding leading to the reflection and back into the core, either leading to total internal reflection or the angle at which the light enters the core through the critical angle. Larger the angle and part of light is lost and this does so due to angle of acceptance is greater than the critical angle. Critical angle If θ < θc, the ray splits. Part of it reflects off the boundary, the rest refracts as it passes through. This is not total internal reflection. In contrast, when θ > θc, the whole of ray reflects through the boundary. This is known as total internal reflection. Angle of incidence is one that gives an angle of refraction of 90˚. It is called the critical angle an example of critical angle is given in appendix A figure 4 Acceptance angle and numerical aperture The numerical aperture is the determination of the light capacity in the fibre. The numerical aperture helps knowing the amount of light that can be collected through the optical fiber. The numerical aperture deals with the acceptance angle. , giving the size of a cone of light that is acceptable by the fiber. The numerical aperture (NA) of the fiber is the sine of the maximum angle of an incident ray against the fibre axis. The NA is calculated via refractive index variation between core and cladding. The critical angle can be calculated from Snells law by setting the refraction angle equal to 90° NA= or Attenuation It is the loss of signal strength or light power when the light pulses propagate through a fibre. They are measured in decibels or dB/km and decibels. Attenuation in an optical fibre results from absorption, scattering, and bending. Figure six in appendix A provides the attenuation of plastic optical fibres and that ofpolymethyl metrhacrylate(PMMA) Bandwidth It is the rate at which the data is transmitted through the two points. Optical fibers make use of light to provide information, resulting in large quantity of data at a higher rate compared to the electrical method therefore they have a high bandwidth .Bandwidth of a fibre is subject to process known as dispersion. Dispersion It is the manner by which the light pulses scatter through. As the pulses scatter further across the fibre, it results in spreading across another. Dispersion for multimode fibre can be in two ways, the first is the modal and material dispersion and is stated and clarified as given. The single mode fibre does not come with the modal dispersion due to the only mode feature and it is characteristic from the name itself. Modal dispersion happens when different modes of light travels trough a fiber and they take different paths as a result some they are slower than others. Another factor is the different velocity of each mode in the fibre. Material dispersion is the result of the velocity of light (refractive index) which serves as the feature of wavelength. The wavelength takes different amount of time to passing through the same line. Maximum bit rate: It is the amount of data that is to be transmitted each second across the fibre communication link.(Senior J M).Plastic fibre have a higher bit rate against the silica based optical fibre Cut-off wavelength Cutoff wavelength in an optical fiber is the wavelength through which the the mode is dissipated (ni.com). The cut-off wavelength of a single mode fibre is the wavelength where the fibre dissipates through fundamental mode. Below the cut-off value, the fibre transmits multiple modes. Optical fibre that is single-mode at a particular wavelength can be with two or more than two modes at wavelengths at a point which is lower than the wavelength which is called the cut off wavelength. Mode field diameter The mode field diameter (MFD) helps knowing the transverse extent of the fundamental modal field Step index which is a step-like variation of the refractive index profile on the core-cladding interface. It is necessary to determine that the mode-field diameter relies on the larger wavelength against the smaller wavelength, which is called the Mode field diameter (MFD). Application of plastic optical fibre Plastic Optical fibres (POF) find their usage at the telecommunication industry for LAN equipment since they are capable to transmit greater amount of data. Across the optical interconnections in telecoms and LAN equipment. Other usages include-LANs (local area networks), building horizontal and vertical network cabling. Other uses include Industrial applications, Automotive and aeronautics industries, Residential network cabling for local offices and home established offices. Closed Circuit Television (CCTV) security systems. Plastic fibre compared to glass fibre and copper wire. The table below shows some differences of plastic fibre when compared to glass fibres. Plastic Glass Wavelength range Visible - therefore they are safer Infrared Numerical aperture High 0.4 Low 0.1-0.2 Cost Tends to be low More expensive Bandwidth Lower Higher Installation and handling Easy –less training Special tool and training Dispersion Smaller than glass High Attenuation Higher than glass Advantages of plastic fibres a) Plastic optical fibres are finding more use due to the cost effective factor. Their other uses include light transmission, imaging. b) The plastic optical fiber provides portability function since it is very small compared to the other types of wires. Small plastic optical fiber wires can be bundled together providing more channel features. c) Flexibility of fiber optics increases transmission of light. d)The plastic optical fiber does not catch fire. e) Signals in the POF are independent. Signals do not interfere with the clustered fibers providing clear signals in reception. Disadvantages of plastic fibres High losses in transmission as a result not suitable for long distance coverage. Graded index optical fibre results in the dispersion. Future of plastic fibres In the future plastic fibre are seen for a key player in the given domains of technology and communications. Medical industry has already made use of it for advanced researches and speedy processes. Ethernet gigabit network across plastic optical fibre for all kinds of enterprises. Data communication for the residential cabling: Home networking. Leisure/residential: High-speed ‘Fire wire’ connections used in the modern digital cameras and other digital devices. High quality video: High-speed DVI connections on Digital cameras and multimedia devices. (Senior J M (2009). Conclusion and reflection The article provides an insight into the plastic optical fibres as the potential substitute against the glass fibres. The advancement of ultra-high capacity local- and wide-area computer networks exponential growth of Internet traffic. The development of high-speed multimedia makes the demand further increased and fulfilling them require more usage of the use of optical fibre. Hence optical fibre is termed as the future technology backbone. Finally, plastic optical fibres are gaining more popularity due to number of features. The first is that of the cost, the second is that of the performance, and the third is that of the customer friendly and safer service options providing which are not provided by the previous technologies against this one. Providing high speed data and at reduced cost, and at a lower time period consumption also makes up for the feature and salient function of the optical fibre concept and technology. The POF progress and the improvement seen in the various areas is also a hint of how productive this technology can prove in the longer run towards improved services and better utilization of the digital technology as a whole. Read More