Member Login

Membership Registration

Senior/KBTC Member

Executive Member

Free Member

for fees and registration »

 

Bangladesh Textile Today - A Comprehensive Publication for the Textile & Apparel Industry
Features of the Month

Optical fibre for smart communication

Prologue: In modern-day, optical communications is the most requested and preferred telecommunication technology, due to its large bandwidth and low propagation attenuation, when compared with the electric transmission lines. Besides these advantages, the use of optical fibers often represents for the telecom operators a low implementation and operation cost. Communication is an important part of our daily life. The communication process involves information generation, transmission, reception and interpretation. As needs for various types of communication such as voice, images, video and data communications increase demands for large transmission capacity also increase. This need for large capacity has driven the rapid development of light wave technology; a worldwide industry has developed. An optical or light wave communication system is a system that uses light waves as the carrier for transmission. An optical communication system mainly involves three parts: transmitter, receiver and channel. In optical communication transmitters are light sources, receivers are light detectors and the channels are optical fibers. In optical communication the channel i.e., optical fibers play an important role because it carries the data from transmitter to the receiver. Hence, here we shall discuss mainly about optical fibers. Key words- Communication, interpretation, light wave, optical fibre, reception transmission. Introduction Optical fibres are arguably one of the world’s most influential scientific developments from the latter half of the 20th century. Fiber optics are simple strands of flexible glass as thin as human hair that is used for communications. These strands carry digital signals in form of light rays. Even though these cables are made of glass, they are not stiff and fragile; they can bend kind like wires and are very tough. When hundreds and thousands of these strands are arranged in bundles, it is called an optical cable [1]. These glass cables are covered with a special protective layer called cladding. It is made from a material that reflects the light back into the core or centre of the cable. This cladding creates a mirror-lined wall. The final outer layer is a buffer coating to protect this special glass cable from physical damage and moisture. A typical optical fiber can be either made out of glass (otherwise known as silicon dioxide) or plastic (typically a polystyrene or polymethyl methacrylate), because of the fibre’s light weightiness and compact size and the ability to have greater information carrying capacities than metallic wires, they are more suitable for many different applications [2]. With so many beneficial factors in using an optical fiber it is no surprise that many companies have applied this technology in developing new installations and applications, in-turn making them commercially viable. There are two different verities based on its raw material usage for making the optical fiber (plastic and glass). In plastic core fibers, they are more flexible and inexpensive compared to glass fibers, they are easier to install and can withstand greater stresses with 60% less weight than glass fibers [3]. However, they transmit light less efficiently leading to high losses, giving them very limited use in communication applications, such plastic fibers are practical for short runs such as within buildings. Therefore, due to their restrictive nature glass core fibers are much more widely used because they are capable of transmitting light effectively over large distances. Optical fibres have a high bandwidth (data carrying capacity) of the order of GHz. Consequently, they carry 100 million times more information and 100 times faster than telephone lines. These optical fibres are very light weight, easily twistable and have a low attenuation (power loss and hence information loss) i.e. 0.5 decibels/kilometre (dB/km) which is approximate 10 times less than telephone cables. Since it is made up of cylindrical silica which is non conductive and non irradiative, there is no possibilities of cross talk. Fibers are resistive to high temperature as the melting point of silica is very high i.e 1900ºC. Besides, the transmitted signals are optical and problems associated with sparking at the ends of cable are not encountered in this case. [4] Principle of optical fibres: The fibre optic cable works by applying the principles of reflection and refraction. When light strikes a shiny or mirrored object it “bounces” off it, just like a ball bouncing off the ground. When light travels between two substances that are of different thickness or densities, it bends (refracts), depending on the angle at which it strikes the substance. At a certain angle, light no longer travels between the substances, but reflects back into the original substance completely. The boundary now acts like a mirror, keeping the light inside. This is called total internal reflection and is the basis of the fibre optic cable.         Fig.1- Total internal reflection When a light ray is sent into a fibre optic, it is sent at an angle towards the side of the fibre that will reflect. The light reflects and then strikes the opposite side of the fibre, again at an angle that will reflect. This light ray will reflect from side to side, travelling through the whole length of the fibre. The angle that the light will reflect at is called the critical angle. The diagram above shows what happens. An added bonus to the principle of total internal reflection is that light rays can pass through each other without causing any destruction or interference. The light signals will be unaffected, resulting in the ability of being able to send more than one signal through the fibre at the same time. Because of this, each fibre can carry many signals, such as phone calls, at the same time with great clarity to each caller.     Fig.2- Light traverse through optical fiber   Basic construction and structure of optical fibre: In fibers, there are three significant sections – the core, cladding and the buffer coating. The core is thin glass center of the fiber where the light travels and the cladding is an Outer optical material surrounding the core that reflects the light back into the core of slightly lower refractive index to cause total internal reflection. Usually both sections are fabricated from silica (glass). The light within the fiber is then continuously totally internally reflected along the waveguide. The Buffer coating is a plastic coating that protects the fiber from damage and moisture. Fig.3(a) and (b) Parts of Optical fibre Optical fibre system: A fibre optic system has four main components: Transmitter- converts a signal, for example sound, into a pattern of light. Optical Fibre- The cable that conducts the light patterns over large distances. Optical Regenerator- In transmittance, some light energy may be lost. This device boosts the light signal back up to continue its journey. This is used for signals sent over very large distances. Optical Receiver- converts the light patterns back to an understandable message, (i.e.sound). Classification of optical fibers: Optical fibers are classified into three types based on the material used, number of modes and refractive index. 1) Based on the materials used:-   Glass fibers: They have a glass core and glass cladding. The glass used in the fiber is ultra pure, ultra transparent silicon dioxide (SiO2) or fused quartz. Impurities are purposely added to pure glass to achieve the desired refractive index. Plastic clad silica: This fiber has a glass core and plastic cladding. This performance though not as good as all glass fibers, is quite respectable. Plastic fibers: They have a plastic core and plastic cladding. These fibers are attractive in applications where high bandwidth and low loss are not a concern. 2) Based on the number of modes:-  a. Single Mode fiber: When a fiber wave-guide can support only the HE11 mode, it is referred to as a single mode wave-guide. In a step index structure, this occurs when the wave-guide is operating at v<2.4 where v is dimensionless number which relates the propagating in the cladding. These single mode fibers have small size and low dopant level (typically 0.3% to 0.4% index elevation over the cladding index.) In high silica fibers the wave-guide and the material dispersion are often opposite signs. This fact can be used conveniently to achieve a single mode fiber of extremely large bandwidth. Reduced dopant level results in lower attenuation than multimode fibres. A single mode wave guide with its large and fully definable bandwidth characteristics is an obvious candidate for long distance, high capacity transmission applications. [7] Multimode fiber: It is a fiber in which more than one mode is propagating at the system operating wavelength. Multimode fiber system does not have the information carrying capacity of single mode fibers. However they offer several advantages for specific systems. The larger core diameters result in easier splicing of fibers. Given the larger cores, higher numerical apertures, and typically shorter link distances, multimode systems can use less expensive light sources such as LEDs. Multimode fibers have numerical apertures that typically range from 0.2 to 0.29 and have core size that ranges from 35 to100 micro-meter.                                            Fig 4: Different modes of wave propagation 3) Based on refractive index:- a. Step index fiber: The step index (SI) fiber consists of a central core whose refractive index is n1, surrounded by a cladding whose refractive index is n2, lower than that of core. Because of an abrupt index change at the core cladding interface such fibers are called step index fibers.[4] b. Graded index fibers: The refractive index of the core in graded index fiber is not constant, they decrease gradually from, its maximum value n1 to its minimum value n2 at the core-cladding interface. The ray velocity changes along the path because of variations in the refractive index. The ray propagating along the fiber axis takes the shortest path but travels most slowly, as the index is the largest along this path in medium of lower refractive index, they travel faster. It is therefore possible for all rays to arrive together at the fiber output by a suitable choice of refractive index profile. [2]                                                                    Manufacturing process of optical fibre: Making optical fibers requires the following steps: Making a preform glass cylinder Drawing the fibers from the preform Testing the fibers Making a preform glass cylinder - The glass for the preform is made by modified chemical vapor deposition (MCVD). In MCVD, oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and/or other chemicals. The precise mixture governs the various physical and optical properties (index of refraction, coefficient of expansion, melting point, etc.) of the cylinder. The gas vapors are then conducted to the inside of a synthetic silica or quartz tube (cladding) in a special lathe. As the lathe turns, a torch is moved up and down the outside of the tube. The extreme heat from the torch causes 1. The silicon and germanium react with oxygen, forming silicon dioxide (SiO2) and germanium dioxide (GeO2). 2. The silicon dioxide and germanium dioxide deposit on the inside of the tube and fuse together to form glass . The lathe turns continuously to make an even coating and consistent blank. The purity of the glass is maintained by using corrosion-resistant plastic in the gas delivery system (valve blocks, pipes, seals) and by precisely controlling the flow and composition of the mixture. The process of making the preform blank is highly automated and takes several hours. After the preform blank cools, it is tested for quality control. [3] Fig 5(a) synthesis of fiber and processing in lathe      Fig.no.5(b)- Drawing of optical fiber   Drawing Fibers from the Preform Blank: Once the preform blank has been tested, it gets loaded into a fiber drawing tower. Fiber drawing tower is used to draw optical glass fibers from a preform blank. The blank gets lowered into a graphite furnace (3,452 to 3,992 degrees Fahrenheit or 1,900 to 2,200 degrees Celsius) and the tip gets melted until a molten glob falls down by gravity. As it drops, it cools and forms a thread. The operator threads the strand through a series of coating cups (buffer coatings) and ultraviolet light curing ovens onto a tractor-controlled spool. The tractor mechanism slowly pulls the fiber from the heated preform blank and is precisely controlled by using a laser micrometer to measure the diameter of the fiber and feed the information back to the tractor mechanism. Fibers are pulled from the blank at a rate of 33 to 66 ft/s (10 to 20 m/s) and the finished product is wound onto the spool. It is not uncommon for spools to contain more than 1.4 miles (2.2 km) of optical fiber. Testing the Finished Optical Fiber: The finished optical fiber is tested for the following: Tensile strength Refractive index profile Fiber geometry Attenuation Information carrying capacity (bandwidth) Chromatic dispersion ) Operating temperature/humidity range Temperature dependence of attenuation Ability to conduct light underwater Essential features of an optical fiber: Good stable transmission characteristics in long lengths at a minimum cost and with maximum reproducibility. The fibers and fiber cables may be terminated and connected together without excessive practical difficulties and in ways which limit the effect of this process on the fiber transmission characteristics to keep them within acceptable operating levels. It is important that these jointing techniques may be applied with ease in the field location where cable connection takes place. The bandwidth of the fiber and light beam is extremely wide. It should be possible to handle signals which turn on and off at gigabit per second rates (1 gigabit, gbit =1000 Mbitts). The electric fields of the noise source should not affect the light beam in the fiber. No light escapes to the outside where loss or tampering of data should be done. Since there is no electricity or electrical energy in the fiber, it can be run in hazardous atmospheres where the danger of explosion from spark may exist. Also, the fiber itself is immune to many types of poisonous gases, chemicals, and water.[7] Application of optical fiber: Fiber optics has lots of uses. It is a perfect application because it is digital information and the fiber optic cables send digitally. Telephones were one of the first uses for fiber optics. Many times internet and telephone signals travel over the same cables. Digital television (cable TV) is often transmitted by fiber optic cables. Other uses are medical imaging, Textile smart fabric, and mechanical inspection. Textile Application: Optical fibers are attractive supports for biosensors integrated into textiles, and consist of an optical fiber with a sensing layer comprising the chemical or biological sensing element, a light source, and a detector. Multiple reflections of the light propagating in the optical fiber allow sensing of optical changes in the vicinity of the fiber core - within the evanescent field. Transmitted light is collected with a spectrometer or photodiode, which allows detection of changes in the colour of the sensing layer.[9] Smart Shirt: In October 1996, A project called “Georgia Tech Wearable Motherboard” (Smart Shirt) was initially funded by the U.S. Navy and in 2000, The Georgia Tech Research Corporation licensed the technology to New York-based SensaTex Inc. to manufacture and market the Smart Shirt. Dr. Sundaresan Jayaraman, who is a professor at the School of Textile & Fiber Engineering Georgia Institute of Technology, is also the principal investigator at this project. According to Jayaraman, Smart Shirt is a computer tshirt woven with fiber optics and electrically conductive thread that can monitor the health of soldiers, rescuers, the elderly and others who are medically vulnerable. The main advantage of Smart Shirt is that it provides a very systematic way of monitoring the vital signs of humans in an undisturbing manner. To use this new technology; first sensors are attached to the body, then the shirt.[9]    Fig 6: Smart shirt collects data from the wearer and transmits to the receiver end for analysis   The Smart Shirt is “armed” and ready to detect what is going on in an athlete’s body during workout. Shirt itself is so customizable that sensors to detect any required information, such as wounds, temperature, heart rate and respiration rate, oxygen levels or hazardous gas levels (which indicates that Smart Shirt can also be used by internal department when necessary. This flexible data bus integrated into the structure, transmits the signals to the tracker giving information about the health status of the person who wears it. Wearable Motherboard: Georgia Tech Wearable Motherboard can also be used on patients that are continuously need to be monitored (e.g., patients discharged after major surgeries, patients those are suffering from manic depression) and this reveals the possibility of telemedicine. Likewise, continuous monitoring of astronauts in space, of athletes during practice sessions and in competition are all extremely important.[10]                                                 Figure 7: Clothing with a flexible fiber-optics screen and remote-control Flexiable screen: France Telecom R&D, announced in the press release May 03, 2002 that, it has designed a prototype for a flexible screen made of woven optical fibers capable of downloading and displaying static or animated graphics such as; logos, texts, patterns, scanned images etc. Graphical communication interface, displaying visual information in real time and offering access to all telecom services (internet, video, e-commerce and 3G mobiles). This unique display technology is based on the association of fabric containing optical fibers and an electronic control system that controls lighting based on luminous diodes. A special abrasion process for the fibers at the surface of the fabric associated to a specific fabric weave developed by the France Telecom laboratories made it possible to create the first bitmap screen matrix on a flexible textile base.[9]                                                      Figure 8: Flexible Screen on clothing Wearable sensor:  Optical fiber sensing textiles are interesting for direct measurement in body fluids like sweat, urine or wound exudates. A first application was designed for performing pH measurement of sweat. Following chemical removal of the cladding of a commercial glass fiber, a pH sensitive sol-gel layer was deposited on the fiber core using dip coating technology. Sr.No Field Working Area Quality 2. Communication Links Short and Long distance communication, utilized to connect closely spaced items of electronics equipment. 50 bauds and 4.8 kbits-1, 7 MHz video links operating over distances of up to 10 m Trunk Network Transmit system at a high capacity in order to minimize costs per circuit enormously from under 20 km to over 300 km, and occasionally to as much as 1000 km Mobiles The small size and weight of optical fibers provide and attractive solution to space problems in these mobiles optical fiber transmission will allow the multiplexing of a number of signals on to a common bus Junction Network switching centers, telephone exchanges or offices in the junction network of large urban areas over distances of typically 5 to 20 km 3. Military application Communicate data without any data attenuation For very long range and confidential informations 4 Civil application stimulated investigation and application of these transmission techniques by public utility organizations low cost solution, also give enhanced protection in harsh environment, especially in relation to EMI and EMP, British Rail has successfully demonstrated a 2 Mbits-1 system suspended between the electrical power line gantries over a 6 km route in Cheshire 5 Medical Application Bronchoscopes, Endoscopes, Laparoscopes To examine the inside of the respiratory tract (detect or rule out tumors of the lungs or airways and to get tissue samples for analysis), the interior surfaces of an organ, growths within the abdomen or pelvic areas, to examine the female organs, stomach, liver, appendix, or gallbladder, and remove the appendix or gallbladder                         Fig 9: Drop cable - increase network efficiency & Fiber optic cable used for endoscopy Advantage of optical fibre: Digital signals: Optical fibers are ideally suited for carrying digital information without attenuation, which is especially useful in computer networks. Higher carrying capacity: Because optical fibers are thinner than copper wires, more fibers can be bundled to a given-diameter cable than copper wires. This allows multi-signal to go over the same cable or more channels to come through the cable into your business or home. Less signal degradation: The loss of signal in optical fiber is very less than in copper wire. Less expensive: Several miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider and you money. Thinner: Optical fibers can be drawn to smaller diameters than copper wire. Light signals: Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable. This means clearer phone conversations or TV reception. Low power: Because signals in optical fibers degrade less, lower-power transmitters can be used instead of the high-voltage electrical transmitters needed for copper wires. Again, this saves your provider and you money. Non-flammable: Because no electricity is passed through optical fibers, there is no fire hazard. Lightweight: An optical cable weighs less than a comparable copper wire cable. Fiber-optic cables take up less space in the ground. Flexible: Because fiber optics are so flexible and can transmit and receive light, they are used in many flexible digital cameras for medical imaging in bronchoscopes, endoscopes, laparoscopes; for mechanical imaging used in inspecting mechanical welds in pipes.[6]   Limitations of optical fibres: The use of fibers for optical communication does have some drawbacks in practice. Hence to provide a balance picture these disadvantages must be considered. They are Cost - Cables are expensive to install but last longer than copper cables.  Transmission - transmission on optical fibre requires repeating at distance intervals.  Fragile - Fibres can be broken or have transmission loses when wrapped around curves of only a few centimetres radius.  However by encasing fibres in a plastic sheath, it is difficult to bend the cable into a small enough radius to break the fibre.  Protection - Optical fibres require more protection around the cable compared to copper.[5] Conclusions: We are currently in the middle of a rapid increase in the demand for data bandwidth across the Earth. For most applications optical fibers are the primary solution to this problem. They have potentially a very high bandwidth, with many of the bandwidth limitations now being at the transceivers rather than being an intrinsic property of the fiber allowing easy upgrading of systems without relaying cable. This is creating a surge in the deployment of fiber both in backbones of networks and in topologically horizontal cabling, which in turn is supporting and propelling the industry into further research. With the adoption of new techniques such as DWDM, soliton transmission and ultimately the purely optical network, we have a medium that will satisfy our communication needs for the foreseeable future. Bibliography: Hecht, Jeff , Understanding fibre optics, 3rd edition,New Jersey, Prentice-Hall Inc, 1999. 2-Harlin, Ali, Mäikinen, Mailis & Vuorivirta, Ann “Development of   polymeric     optical fibre fabrics as illumination elements and textile displays”  Autex   Research Journal, march 2003 Vol.3, No 1.pg.no.1-8 3-Linda Oscarsson1“Flat knitting of a light emitting textile with optical fibre” Autex Research Journal, June 2009 Vol. 9, No2 pg.no-62-65. 4- Simon Kwan “Principles of Optical Fibers” In partial fulfillment of course requirement for MatE 115, Fall 2002 San Jose State University. 5- http://www.www-fibreoptics.com. 6-Savci. S, Curiskis J.I & Pailthorpe. “ Knittability of glass fibre weft-knitted preforms for composites” Textile Research, January 2001 vol 71(1), p. 15-21. 7- Bahaa E. A. Saleh, Malvin Carl Teich “Fundamentals of Photonics” Copyright © 1991 John Wiley & Sons, Inc. 8-Dina Meoli and Traci May-Plumlee “ Intractive electronics textile development” JTATM vol 2, Issue2, Spring 2002. 9-A. Schwarz et al “Integration of technology in textiles”Textile Progress2010 . 10-John Crisp, Introduction to Fiber Optics, 2nd Edition Newnes 2001.

 

February 2014
Weekly Analysis Event Preview
Newsletter Subscription
Name:            

Organization: 

Email:            

We respect your email privacy

Get full featured BTT weekly Newsletter via email

Find Articles by Interest Group




Supporting Events