Fiber-optic CableMany extremely thin strands of glass or plastic boundtogether in a sheathing which transmits signals with lightbeamsCan be used for voice, data, and video
Introduction to Optical Fibers. Fibers of glass Usually 120 micrometers in diameter Used to carry signals in the form of light over distances up to50 km. No repeaters needed.
Fiber v. Copper Optical fiber transmits light pulses Can be used for analog or digital transmission Voice, computer data, video, etc. Copper wires (or other metals) can carry the same types ofsignals with electrical pulses
FREQUENCIES Frequency refers to the modulating message signalFrequency. The rapid exchange of energy from the beam to the dotexcites the phosphor into the radiating photon of energywhich agitate at 4.2857×10^64 times/sec.
Fiber Optics are cables that are made of optical fibers thatcan transmit large amounts of information at the speed oflight.
Optical Fiber Core Glass or plastic with a higher index of refraction than thecladding Carries the signal Cladding Glass or plastic with a lower index of refraction than the core Buffer Protects the fiber from damage and moisture Jacket Holds one or more fibers in a cable
Total Internal Reflection Optical fibers work on the principle of total internalreflection With light, the refractive index is listed The angle of refraction at the interface between twomedia is governed by Snell’s law:n1 sin1 n2 sin2
Total Internal Reflection Optical fibers work on the principle of total internalreflection The angle of refraction at the interface between twomedia is governed by Snell’s law:n1 sin1 n2 sin2
Numerical Aperture The numerical aperture of the fiberis closely related to the critical angle andis often used in the specification foroptical fiber and the components thatwork with it The numerical aperture is given by theformula: The angle of acceptance is twice thatgiven by the numerical aperture2221.. nnAN
7.23Figure 7.12 Propagation modesFigure 7.13 Modes1. Single-mode fiberCarries light pulsesalong single path.2. Multimode fiberMany pulses of lighttravel at differentangles
Singlemode Fiber Singlemode fiber has a core diameter of 8 to 9 microns, whichonly allows one light path or mode Images from arcelect.com (Link Ch 2a)Index ofrefraction
Singlemode FIber Best for high speeds and long distances Used by telephone companies and CATV
Multimode Step-Index Fiber Multimode fiber has a core diameter of 50 or 62.5 microns(sometimes even larger) Allows several light paths or modes This causes modal dispersion – some modes take longer to passthrough the fiber than others because they travel a longer distance See animation at link Ch 2fIndex of
Step-index Multimode Large core size, so source power can be efficiently coupled tothe fiber High attenuation (4-6 dB / km) Low bandwidth (50 MHz-km) Used in short, low-speed datalinks Also useful in high-radiation environments, because it can bemade with pure silica core
Multimode Graded-Index Fiber The index of refraction gradually changes across the core Modes that travel further also move faster This reduces modal dispersion so the bandwidth is greatly increasedIndex of
Graded-index Multimode Useful for “premises networks” like LANs, security systems,etc. 62.5/125 micron has been most widely used Works well with LEDs, but cannot be used for Gigabit Ethernet 50/125 micron fiber andVSELS are used for faster networks
7.31Table 7.3 Fiber typesIn multimode step-index fiber, the density of the core remains constant from thecenter to the edges. A beam of light moves through this constant density in a straightline until it reaches the interface of the core and the cladding. At the interface, there isan abrupt change due to a lower density; this alters the angle of the beams motion. Theterm step index refers to the suddenness of this change, which contributes to thedistortion of the signal as it passes through the fiber.In multimode graded-index fiber, decreases this distortion of the signal through thecable. The word index here refers to the index of refraction. As we saw above, the indexof refraction is related to density. A graded-index fiber, therefore, is one with varyingdensities. Density is highest at the center of the core and decreases gradually to itslowest at the edge. Figure 7.13 shows the impact of this variable density on thepropagation of light beams.
Fiber and Acrylate Coating Optical fiber is covered by an acrylatecoating during manufacture Coating protects the fiber from moisture andmechanical damage
Advantages of Optical Fibre Thinner Less Expensive Higher Carrying Capacity Less Signal Degradation& Digital Signals Light Signals Non-Flammable LightWeight
Areas of Application Telecommunications LocalArea Networks CableTV CCTV Optical Fiber Sensors
Type of FibersOptical fibers come in two types: Single-mode fibers – used to transmit one signal per fiber(used in telephone and cableTV).They have small cores(9microns in diameter) and transmit infra-red light from laser. Multi-mode fibers – used to transmit many signals per fiber(used in computer networks).They have larger cores(62.5microns in diameter) and transmit infra-red light from LED.
Splices and Connectors In fiber-optic systems, the losses from splices and connections can bemore than in the cable itself Losses result from: Axial or angular misalignment Air gaps between the fibers Rough surfaces at the ends of the fibers
How are Optical Fibre’s made?? Three Steps are Involved-Making a Preform Glass Cylinder-Drawing the Fibre’s from the preform-Testing the Fibre
Testing of Optical Fiber Tensile Strength Refractive Index Profile Fiber Geometry Information Carrying Capacity Operating temperature/humidity range Ability to conduct light under water Attenuation
Optical Fiber Laying Mechanical Linking Includes coupling of two connectors end to end Optical distribution frames allow cross connect fibers from by means ofconnection leads and optical connectors Soldering: This operation is done with automatic soldering machine that ensures: Alignment of fiber’s core along the 3 axis Visual display in real-time of the fibers soldering Traction test after soldering (50 g to 500 g)
Optical Fiber Laying (Cont…) Blowing Used in laying optical cables in roadways. Cables can be blown in a tube high density Poly Ethylene Optical fiber is then blown in the tube using an air compressorwhich can propel it up to 2 kilometers away.
Tools of Trade Cleaning fluid and rags Buffer tube cutter Reagent-grade isopropyl alcohol Canned air Tape (masking or scotch) Coating strip Microscope or cleaver checker Splicer Connector supplies
Fiber Optics Test Kit Features Includes Smart FO Power Meter and Mini LED or laser source FO test lite software for data logging Tests all networks and cable plants New versions of Gigabit Ethernet Low Cost Applications Measure optical power or loss Trouble shooting networks
Protecting Fibers Tougher than copper wires Designed in three concentric layers Core – Cladding – Buffer Two basic buffer types Tight buffer Loose tubes
Implementation of Different LANs IEEE 802.3 FOIRL Fiber optic inter repeater link Defines remote repeaters using fiber optics Maximum length – 1000 meters between any two repeaters.
IEEE 802.3 (Cont…) 10BASEF Star topology with hub in the center Passive hub: Short cables No cascading Reliable Active hum: Synchronous May be cascaded Do not count as one repeater Any 10BASEF active hub must have at least two FOIRL ports
Token Ring Advantages Long range Immunity to EMI/RFI Reliability Security Suitability to outdoor applications Small size Compatible with future bandwidth requirements and futureLAN standards
Token Ring (Cont…) Disadvantages Relatively expensive cable cost and installation cost Requires specialist knowledge and test equipment No IEEE 802.5 standard published yet Relatively small installed base.
Fiber Distributed Data Interface Stations are connected in a dual ring Transmission rate is 100 mbps Total ring length up to 100s of kms.
ConclusionThis concludes our study of Fiber Optics. We havelooked at how they work and how they are made. We haveexamined the properties of fibers, and how fibers arejoined together. Although this presentation does notcover all the aspects of optical fiber work it will haveequipped you knowledge and skills essential to the fiberoptic industry.