Chapter One Introduction to Fiber Optics Communication System

Chapter One: Introduction to Fiber Optics Communication System prepared by : Maizatul Zalela bt Mohamed Sail

Fiber Optic Cable Fiber Optic lamp Profesional lamp – fiber optic

What is Fiber Optic? Fiber optics – • A means to carry information from one point to another or serves as transmission medium (optical fiber). • A technology that uses thin strand of glass (or plastic) threads (fibers) to transmit data. • A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves. prepared by : Maizatul Zalela bt Mohamed Sail

Introduction An optical fiber is essentially a waveguide for light It consists of a core and cladding that surrounds the core The index of refraction of the cladding is less than that of the core, causing rays of light leaving the core to be refracted back into the core A light-emitting diode (LED) or laser diode (LD) can be used for the source prepared by : Maizatul Zalela bt Mohamed Sail

Optical Fiber prepared by : Maizatul Zalela bt Mohamed Sail

Optical Fiber Optical fiber is made from thin strands of either glass or plastic It has little mechanical strength, so it must be enclosed in a protective jacket Often, two or more fibers are enclosed in the same cable for increased bandwidth and redundancy in case one of the fibers breaks It is also easier to build a full-duplex system using two fibers, one for transmission in each direction prepared by : Maizatul Zalela bt Mohamed Sail

History 1870’s John Tyndall showed a beam of light would follow a specific path by refraction 1880, William Wheeling received a patent doing same thing with mirrored pipe. 1950’s Alexander Graham Bell patented an optical telephone system, which he called the Photophone. However, his earlier invention, the telephone, was more practical and took tangible shape. saw development of the “fiberscope” prepared by : Maizatul Zalela bt Mohamed Sail

History 1957 Lasers first used as light source. Light has an information-carrying capacity 10, 000 times that of the highest radio frequencies being used. 1970 Drs. Robert Maurer, Donald Keck, and Peter Schultz of Corning succeeded in developing a glass fiber that exhibited attenuation at less than 20 d. B/km, the threshold for making fiber optics a viable technology. It was the purest glass ever made. the U. S. Navy fiber optic telephone link aboard the U. S. S. Little Rock. 1976 Air Force followed suit by developing its Airborne Light Optical Fiber Technology (ALOFT) prepared by : Maizatul Zalela bt Mohamed Sail

History 1977 both AT&T and GTE installed fiber optic telephone systems in Chicago and Boston respectively. 1980 broadcasters of the Winter Olympics, in Lake Placid, New York, requested a fiber optic video transmission system for backup video feeds. The fiber optic feed, because of its quality and reliability, soon became the primary video feed, making the 1980 Winter Olympics the first fiber optic television transmission. 1990 Bell Labs transmitted a 2. 5 Gb/s signal over 7, 500 km without regeneration. The system used a soliton laser and an erbium-doped fiber amplifier (EDFA) that allowed the light wave to maintain its shape and density. prepared by : Maizatul Zalela bt Mohamed Sail

History 1990 Bell Labs transmitted a 2. 5 Gb/s signal over 7, 500 km without regeneration. The system used a soliton laser and an erbium-doped fiber amplifier (EDFA) that allowed the light wave to maintain its shape and density. 1994 Winter Olympics in Lillehammer, Norway, fiber optics transmitted the first ever digital video signal, an application that continues to evolve today. . 1998 transmitted 100 simultaneous optical signals each at a data rate of 10 gigabits (giga = billion per second) distance of nearly 250 miles (400 km). prepared by : Maizatul Zalela bt Mohamed Sail

Advantages The advantages of fiber-optic systems warrant considerable attention. This new technology has clearly affected the telecommunications industry and will continue to thrive due to the numerous advantages it has over its copper counterpart. The major advantages include. • • Wide Bandwidth Low Loss Electromagnetic Immunity Light Weight Small Size Noise Immunity and Safety Security Economic Reliability

Wide Bandwidth Fiber optic communications can run at 10 Ghz and have the potential to go as high as 1 Thz (100, 000 GHz). A 10 Ghz capacity can transmit (per second): 1000 books 130, 000 voice channels 16 HTDV channels or 100 compressed HDTV channels. Separate Voice, data and video channels are transmitted on a single cable.

Electromagnetic Immunity Copper cables can act as an antennae picking up EMI from power lines, computers, machinery and other sources. Fiber is not susceptible to Electro-Magnetic Interference and thus no interference allowing error-free transmissions.

Light Weight and Volume Comparison: Fiber – 4 kg or 9 lb per 1000 ft. (due mainly to packaging). Coax – 36 kg or 80 lb per 1000 ft. Fiber optic cables are substantially lighter in weight and occupy much less volume than copper cables with the same information capacity. Fiber optic cables are being used to relieve congested underground ducts in metropolitan and suburban areas. For example, a 3 -in. diameter telephone cable consisting of 900 twisted-pair wires can be replaced with a single fiber strand 0. 005 inch. In diameter (approximately the diameter of a hair strand) and retain the same information carrying capacity.

Small Size Use where space is at a premium: Aircraft, submarines Underground conduit High density cable areas – Computer centers.

Noise Immunity and Safety No electricity thus no spark hazards so can be used through hazardous areas. Because fiber is constructed of dielectric materials, it is immune to inductive coupling or crosstalk from adjacent copper or fiber channels. In other words, it is not affected by electromagnetic interference (EMI) or electrostatic interference.

Security Since fiber does not carry electricity, it emits no EMI which could be used for eavesdropping. Difficult to 'tap' – cable must be cut and spiced. Because light does not radiate from a fiber optic cable, it is nearly impossible to secretly tap into it without detection. For this reason, several applications requiring communications security employ fiber-optic systems. Military information, for example, can be transmitted over fiber to prevent eavesdropping. In addition, metal detectors cannot detect fiber-optic cables unless they are manufactured with steel reinforcement for strength.

Economics Presently, since the cost of fiber is comparable to copper it is expected to drop as it becomes more widely used. Because transmission losses are considerably less than for coaxial cable, expensive repeaters can be spaced farther apart. Fewer repeaters mean a reduction in overall system costs and enhanced reliability.

Reliability Once installed, a longer life span is expected with fiber over its metallic counterparts, because it is more resistant to corrosion caused by environmental extremes such as temperatures, corrosive gases, and liquids.

Disadvantages of Fiber-Optic System In spite of the numerous advantages that fiber-optic systems have over conventional methods of transmission, there are some disadvantages, particularly because of its newness. Many of these disadvantages are being overcome with new and competitive technology. The disadvantages include: i. Interfacing Costs ii. Strength iii. Remote powering of devices iv. Inability to interconnected

Interfacing Costs Electronic facilities must be converted in order to interface to the fiber. Often these costs are initially overlooked. Fiber-optic transmitters, receivers, couplers, and connectors, for example, must be employed as part of the communication system. Test and repair equipment is costly. If the fiber-optic cable breaks, splicing can be costly and tedious task. Manufacturers in this related field however are continuously introducing new and improved field repair kits.

Strength Optical fiber , by itself has a significant lower tensile strength than coaxial cable. Surrounding the fiber with stranded Kevlar (A nonmetallic, difficult to-stretch, strengthening material) and a protective PVC jacket can help to increase the pulling strength. Installations requiring greater tensile strengths can be achieved with steel reinforcement.

Remote Powering Of Devices Occasionally, it is necessary to provide electrical power to a remote device. Because this cannot be achieved through the fiber, metallic conductors are often included in the cable assembly. Several manufacturers now offer a complete line of cable types, including cables manufactured with both copper wire and fiber.

Inability to interconnect easily requires that current communication hardware systems be somewhat retrofitted to the fiber-optic networks. Much of the speed that is gained through optical fiber transmission can be inhibited at the conversion points of a fiber-optic chain. When a portion of the chain experiences heavy use, information becomes jammed in a bottleneck at the points where conversion to, or from, electronic signals is taking place. Bottlenecks like this should become less frequent as microprocessors become more efficient and fiber-optics reach closer to a direct electronic hardware interface.

Advantage Bandwidth · High bandwidth and capacity · Lower signal attenuation (loss) Immunity to Electrical Noise, Electromagnetic Immunity · Immune to noise (electromagnetic interference [EMI] · No crosstalk · Lower bit error rates Signal Security · Difficult to tap · Nonconductive (does not radiate signals) Size and Weight · Reduced size and weight cables Overall System Economy · Low overall system cost · Lower installation cost Reliability · Less restrictive in harsh environments

Disadvantage Interfacing Costs • High planning, installation, and maintenance cost Strength • lower tensile strength than coaxial cable Remote Powering of Devices • necessary to provide electrical power to a remote device. • Cannot be achieved through the fiber, metallic conductors are often included in the cable assembly. Inability to interconnect • incompatibility with the electronic hardware systems that make up today's world.

Fiber Optic Block Diagram Fiber optics is a medium for carrying information from one point to another in the form of light. Unlike the copper form of transmission, fiber optics is not electrical in nature. A basic fiber optic system consists of: i) transmitting device that converts an electrical signal into a light signal, ii) optical fiber cable that carries the light, iii) receiver that accepts the light signal and converts it back into an electrical signal. prepared by : Maizatul Zalela bt Mohamed Sail

Block Diagram prepared by : Maizatul Zalela bt Mohamed Sail

Transmitter Its main function is to transmit the information signals like voice, video or computer in the form of light signals. As shown above, the information at input is converted into digital signals by coder or converter circuit. This circuit is actually ADC (analog to digital converter). Thus, it converts analog signals into proportional digital signals. If the input signals are computer signals, they are directly connected to light source transmitter circuit prepared by : Maizatul Zalela bt Mohamed Sail

Con’t The light source block is a powerful light source. It is generally a FOCUS type LED or low intensity laser beam source or in some cases infrared beam of light is also used. The rate, at which light source turns ON/OFF, depends on frequency of digital pulses. Thus, its flashing is proportional to digital input. In this way, digital signals are converted into equivalent light pulses and focused at one end of fiber-optic cable. They are then received at its other end. prepared by : Maizatul Zalela bt Mohamed Sail

Fiber Optic Cable When light pulses are fed to one end of fiber-optic cable, they are passed on to other end. The cable has VERY LESS attenuation (loss due to absorption of light waves) over a long distance. Its bandwidth is large; hence, its information carrying capacity is high. prepared by : Maizatul Zalela bt Mohamed Sail

Receiver At receiving end, a light detector or photocell is used to detect light pulses. It is a transducer, which converts light signals into proportional electrical signals. These signals are amplified and reshaped into original digital pulses, (while reshaping, distortion & noise are filtered out) with the help of shaper circuit. Then the signals are connected to decoder. It is actually ADC circuit (Analog to Digital Converter), which converts digital signals into proportional analog signals like voice, video or computer data. Digital signals for computer can be directly taken from output of shaper circuit prepared by : Maizatul Zalela bt Mohamed Sail

Con’t Thus, this total unit is used fiber optic communication system. However if the distance between transmitter and receiver is very large, then REPEATER UNITS are used. Due to repeaters signals attenuation is compensated. For this, light signals at far end are converted into electrical signals, amplified and retransmitted. Such repeater unit is also called RELAY STATION prepared by : Maizatul Zalela bt Mohamed Sail

Application Analog system Digital system Undersea cable High Definition Television (HDTV) Triple Play Technology ( voice, video , data ) prepared by : Maizatul Zalela bt Mohamed Sail

Quick Test Define fiber optic? 2. The advantages of fiber optic, overcome its disadvantages. Explain the advantages and disadvantages of fiber optic. 3. Draw the block diagram of fiber optic communication system. 4. State the function of each block in the diagram. 1.

Quick Test Which of the following answer, describe the application of fiber optic in communication system. i. iii. iv. Triple Play System Undersea Communication Cable Digital Transmission System Weather forecast System