Fundamentals of Optical Fibre Communication - Essay Example

? Fibre Optics Table of Contents Theory of light relevant to fibre optics Construction of fibre optic cables.  Basic fibre optic theory.  Types of fibre optic cable.  Sources and detectors used in fibre optic communication.  Attenuation in fibre optics systems.  Advantage of fibre optics compared to copper wire.  Use of fibre optics in aircraft systems.  Fibre Optics Technology over the past century has advanced greatly. Fibre optics however is being utilized since more than a hundred years. Optical fibre is a model that has evolved greatly over time. From guided transmission lights experiments to lasers and light emitting diodes (LED), and to dense wavelength-division multiplexing (DWDM), the area under which optical fibre can be used has expanded. One of the modern and commonly used applications of fibre optics is high resolution visuals (HDTV) which has enabled us to view broadcasts at 1080p screen resolution which is a result of FTTc and FTTh (fibre to the curb) network. Satellites making use of fibre optics do not have to undergo lessening (fibreopticsinfo). There are generally six theories of light from which the theory of optical fibre has evolved. The relevant theories to optical fibre are emission theory, corpuscular theory, wav theory, electromagnetic theory and quantum theory. Reflection and refraction of light are vital elements in optical fibre. These two properties have been explained by Newton in his laws. Another very important property relative to fibre optics is the critical angle of light. Critical angle is defined as the minimum angle which can allow total internal reflection to take place. This is governed by Snell’s law. There are two theories which explain the propagation of light through optical fibres. The first theory is the ‘Ray Theory’ under which light is considered to be a simple ray of light and the propagation properties are relevant to that. This theory explains the accepting and guiding behavior of light inside a fibre (Sathish Kumar). The second theory is the ‘Mode Theory’ or the ‘Wave Representation’ approach. According to the Mode Theory, light is an electromagnetic wave and acts like an electromagnetic wave inside a fibre. This theory explains the phenomenon of absorption and dispersion of light inside a fibre as well as its attenuation (The Theory of Optical Fibres). Fibre optic cables are the source of transmission of light using the fibre optics technology. Fibre optic cables enable light to be transmitted along them from one point to another and there is no significant loss in the intensity of light which passes through fibre optical cables. The construction of a fibre optic cable has three main parts: A central core, cladding and a Plastic Jacket surrounding both the core is present at the centre of the cable which acts as a buffer. It is composed of fine quality thin transparent glass polymer or a dielectric. The refractive index of the core is ?1 and the diameter of the central core ranges from 10 ? to 100 ?. surrounding the central core is a jacket layer of plastic or glass called Cladding. The refractive index (?2) of the cladding has to be smaller than that of the central core so that the light stays inside the core due to total internal reflection (?1 > ?2). Safety and strength are provided to cable by surrounding the cladding and the central core with a plastic jacket or the buffer (Loremate). The transmission of light by fibre optics has the same basic components as the normal wiring transmitting devices. The system comprises of a transmitter, a medium through which the signals are propagated and a receiver. The propagating medium is a cable in case of fibre optics. The transmitter has an ability to emit light with the help of either a light emitting diode or a laser. The user inputs data into the transmitter in the form of audio, video or other data. The encoder or modulator used in the transmitter to convert electrical signals to optical signals is AM, FM or digital. The user inputs data which gets modulated and then transmitted through the fibre optic cable to the receiver where it converts from optical back to electrical and gives output in the form of audio or video or data. AM, FM or digital demodulators are present in the receiver which convert the signals and the light detectors inside the receiver are PIN diode or APD made of Silicon, Germanium or Indium (fiber-optics.info). Fibre optic cables are used for the transmission of light using fibre optics. There are two types of fibres: Step Index Fibre (can be multimode or single mode), and Graded Index Fibre (only multimode). The step index fibre is named so because it steps up as we move from the cladding to the central core i.e. the refractive index of the central core is constant and the refractive index of the cladding is constant as well but the refractive index of the central core is greater than that of the cladding. Single mode step index fibres have a very narrow core. Due to this no core there is space enough only for one mode, hence the term Single Mode. This single mode is called the Lowest Order Mode (The Theory of Optical Fibres). Figure: Single mode step index fibre. Particular directions of rays of light which can travel along the length of the fibre are called Fibre Mode. In Multimode Step Index Fibres, the fibre can support a number of different Modes (The Theory of Optical Fibres). Figure: Multimode Step Index Fibres In the second type of optical cables, the Graded Index Fibres, the structure of the central core differs from the step index fibres. In the step index fibres the value of the refractive index is constant in the core. On the other hand, the refractive index of the central core of graded index fibres changes constantly from the centre of the core to its periphery. It displays a Quadratic Profile which means if the squared distance from the centre of the core increases, the refractive index will increase as well (The Theory of Optical Fibres). Figure: The Graded Index Fibre (The Theory of Optical Fibres). The sources of light in an optical system may be a Light Emitting Diode (LED) or Injection LASER diode (ILD). A LED is a basic p-n junction diode made of semi conductors like aluminum gallium arsenide (Airgas) or gallium arsenide phosphate (Gasp). It impulsively radiates light when electrons and holes combine. LEDs are characterized by their brightness, response time and quantum efficiency. The high intensity of their radiance enables high optical power levels to couple into a fibre. The Injection LASER diode (ILD) resembles LED in a lot of ways and in some cases may also act like one. ILDs have highly polished ends which trap photons which produce movement causing the electrons to combine with holes. The main changes occurring in ILDs are absorption of photon, and spontaneous and stimulated emission of photons (fibre optical sources & detectors). The detectors of light in an optical system are PIN (positive-intrinsic-negative) diode and Avalanche Photo Diodes (APD). It is the detector which is usually used in optical devices. The operation PIN diode is reciprocal to that of an LED. Light is allowed to enter the device through a small space where it gets absorbed. Its sensitivity is very poor. An APD is positive-intrinsic-positive-negative in construction. It is a lot more sensitive than PIN diode and does not require a lot of additional amplification (fibre optical sources & detectors). Attenuation is the loss of light on the pathway between the input and the output. A sum of all attenuations is called Total Attenuation. Losses may take place through absorption, scattering, microbending, macrobending, and interface inhomogenities (Maurice Stephen O'Sullivan, page 382). Fiber optics is better than copper wires and the conventional methods in a lot of ways. Transmission from fibre optic cables is much faster than that from copper wires. Fibre optic cables can carry data at a rate of more than one gigabit/second. Due to this high amount of data transfer, the quality of telecommunication has increased significantly. Fibre opts are more reliable than copper wires. Recent researches will enable it to carry data at a rate of 10 gigabits/second. Atmospherically changes like weather, humidity, temperature, rain etc have no effect on the transmission of data whatsoever. Fibre optics is very cost effective and is cheaper than the copper wires. A repeater is needed after every mile while transmitting data through copper wires, but fibre optics can transmit data effectively without a repeater in miles. Fibre optics is very safe and has minimal energy losses and there are no unwanted radiations involved. Loss in signal can be detected immediately provided that it is being monitored. Fibre optic cables are very light in weight and are easier to transport overseas. They are highly sustainable. Copper is getting lesser everyday in nature and optical fire will soon replace copper wiring. Owing to its cheapness and effectiveness, fibre optics will be applied in a number of other fields as well (Mike Holt). Fibre optic sensors have an advantage that they can reach place where normally things cannot. Extrinsic sensors are used in aircraft jet engines. An optic sensor radiates transmission from inside the engine into a pyrometer outside and measures the temperature. Extrinsic sensors also detect and measure vibration, movement, rotation, speed, acceleration and torque (Mike Holt). Fibre optics’ role in our era is constantly increasing. Telecommunications have advanced greatly in a short period of time owing to fibre optics. Better and high definition quality of audio and video are being availed for interactive communication. High rates of transmission of data are made possible by fibre optics. Fibre optics has enabled us to have video conferences with up to 10 people in different corners of the world, simultaneously. Military is also making use of fibre optics as well as banking and industries. The designer can mould the application of fibre optics according to his imagination (Mike Holt). References: Chapter 4 - Fiber Optics | Engineering Physics. 2013. Chapter 4 - Fiber Optics | Engineering Physics. [ONLINE] Available at: http://ptuas.loremate.com/phy/node/4. [Accessed 02 January 2013]. Fiber-Optics.info | Optical Fiber Transmission using Light Signals for Video, Audio, Data in Analog and Digital wavelengths for fiber optics applications. 2013. Fiber-Optics.info | Optical Fiber Transmission using Light Signals for Video, Audio, Data in Analog and Digital wavelengths for fiber optics applications. [ONLINE] Available at: http://www.fiber-optics.info/. [Accessed 02 January 2013]. fibre optical sources & detectors. 2013. fibre optical sources & detectors. [ONLINE] Available at: http://www.scribd.com/doc/7314300/fibre-optical-sources-detectors. [Accessed 02 January 2013]. Maurice Stephen O'Sullivan, Rongqing Hui, 2009. Fiber Optic Measurement Techniques. 1st ed. Academic Press: Academic Press. Mike Holt Mike Holt Code Resources. 2013. Mike Holt Mike Holt Code Resources. [ONLINE] Available at: http://www.mikeholt.com/technical.php?id=lowvoltage/unformatted/fiberoptics&type=u&title=Low%20Voltage. [Accessed 02 January 2013]. Sathish Kumar , M., 2005. Fundamentals Of Optical Fibre Communication. 3rd ed. PHI Learning Pvt. Ltd: PHI Learning Pvt. Ltd. The Theory of Optical Fibres. 2013. The Theory of Optical Fibres. [ONLINE] Available at: http://library.thinkquest.org/C006694F/Optical%20Fibres/Physics%20Cover.htm#. [Accessed 02 January 2013]. Read More