Unit – V FIBRE OPTIC Dr. Ritesh S. Palaspagar PRMIT&R

HISTORY REPEATS ITSELF 21ST CENTURY TO FROM ANCIENT GREEKS

Transmission medium and physical layer

Classes of transmission media

Topics discussed in this section: GUIDED MEDIA Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. Topics discussed in this section: Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable

Evolution of Fiber 1880 – Alexander Graham Bell 1930 – Patents on tubing 1950 – Patent for two-layer glass wave-guide 1960 – Laser first used as light source 1965 – High loss of light discovered 1970s – Refining of manufacturing process 1980s – OF technology becomes backbone of long distance telephone networks in NA.

Why Optical Fibers ? As mans need and hunger for communication increased, the amount of bandwidth required increased exponentially. Initially we used smoke signals, then horse riders for communicating. But these ways were way to slow and had very little bandwidth or data caring capacity. Then came the telephone and telegraph that used copper wires for communication. But soon demand outstripped (included) the capacity and capability of copper wires and data transport got added to voice communication. Then came Coaxial copper cables, VHF and UHF Radios, Satellite but demand still outstripped the supply. It was not until Optical Fibers came on the scene that large amount of communication bandwidth became economically and easily available to everyone. As an example 50,000 voice / data circuit copper cable is massive in size and very expensive, while a single Optical Fiber, the diameter of human hair, can carry 5,00,000 circuits of voice and data. This capacity is increasing day by day as supporting electronics is developing. In itself the capacity of Optical Fibers is limitless.

INTRODUCTION Traditionally the communication was done with the help of copper wires. now a days it has been replaced by fibre optic cable. The difference between two system is that the fibre optics system uses light pulses to transmit information instead of using electronic pulses as used in copper wire system. Here a LED or ILD is used for generating the light pulses. Using lense the light pulses are transmitted into fibre optics system.

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

Wavelength of Transmitted Light

PRINCIPLE Light pulses move easily in fibre optic cable because of the principle known as total internal reflection (T.I.R). CONDITION FOR T.I.R Light should travel from denser medium to rarer medium. Angle of incidence is greater than the critical angle. Transparent glass or plastic fibre which allow light to be transmitted from transmitter to receiver with minimal loss.

Fiber optics: Bending of light ray

TOTAL INTERNAL REFLECTION

CONSTRUCTION

CONSTRUCTION… Core Cladding Buffer Jacket Glass or plastic with a higher index of refraction than the cladding 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 CONSTRUCTION…

Fiber CONSTRUCTION…

Propagation modes

Modes

DESCRIPTION STEP INDEX FIBRE IT IS AN OPTICAL FIBRE WHOSE CORE HAS A REFRACTIVE INDEX WHICH IS SLIGHTLY GREATER THAN THAT OF CLADDING. BECAUSE OF REFRACTIVE INDEX OF THIS TYPE THE FIBRE MAKES A STEP CHANGE A CORE CLADDING INTERFACE.

SINGLE MODE STEP INDEX DIAMETER VARIES FROM 8.3 - 10 MICRON. BANDWIDTH IS HIGHER THAN MULTIMODE. IT GIVES HIGHER TRANSMISSION RATE. NO OVERLAPPING,DISTORTION OF LIGHT PULSES OCCUR WITH LEASTY ATTENUATION.

MULTIMODE STEP INDEX DIAMETER VARIES FRM 50 - 100 MICRON. MUCH LARGER PORT DIAMETER. EASY TO SPLICE AND COUPLE SERGMENTS TOGETHER WITH MINIMAL LOSS. MULTIPATH DISPERSSION IS PRESENT. RAYS WITH SMALL ANGLE OF INCIDENCE REACH THE RECIEVER AFTER THOSE RAYS WHICH ARE LARGER ANGLE OF INCIDENCE.

MULTI MODE (CONT.)

GRADED INDEX CONTAINS A CORE IN WHICH R.I GRADUALLY DECREASES FROM CORE TO CLADDING. THE HIGHER R.I AT THE CORE MAKES THE LIGHT RAY MOVING DOWN THE AXIS ADVANCE MORE SLOWLY THAN THOSE NEAR CLADDING. HERE LIGHT RAYS MOVE IN HELICAL PATH INSTEAD OF ZIGZAGGING DUE TO GRADED INDEX , HENCE REDUCING TRAVELLING TIME.

Fiber Optic Specifications Attenuation Loss of signal, measured in dB Dispersion Blurring of a signal, affects bandwidth Bandwidth The number of bits per second that can be sent through a data link Numerical Aperture Measures the largest angle of light that can be accepted into the core

Attenuation Modern fiber material is very pure, but there is still some attenuation The wavelengths used are chosen to avoid absorption bands 850 nm, 1300 nm, and 1550 nm Plastic fiber uses 660 nm LEDs

Optical fiber performance

Three Types of Dispersion Dispersion is the spreading out of a light pulse as it travels through the fiber Three types: Modal Dispersion Chromatic Dispersion Polarization Mode Dispersion (PMD)

Modal Dispersion Modal Dispersion Spreading of a pulse because different modes (paths) through the fiber take different times Only happens in multimode fiber Reduced, but not eliminated, with graded-index fiber

Chromatic Dispersion Different wavelengths travel at different speeds through the fiber This spreads a pulse in an effect named chromatic dispersion Chromatic dispersion occurs in both singlemode and multimode fiber Larger effect with LEDs than with lasers A far smaller effect than modal dispersion

Polarization Mode Dispersion Light with different polarization can travel at different speeds, if the fiber is not perfectly symmetric at the atomic level This could come from imperfect circular geometry or stress on the cable, and there is no easy way to correct it It can affect both singlemode and multimode fiber.

Numerical Aperture If the core and cladding have almost the same index of refraction, the numerical aperture will be small This means that light must be shooting right down the center of the fiber to stay in the core

MERITS SPEED : FIBRE OPTIC NETWORK OPERATE AT HIGH SPEED UPTO GIGABYTES. DISTANCE : FIBRE OPTIC CABLE CAN COMMUNICATE OVER A LONG DISTANCE. COST : MUCH LESS AS COMPARED TO OTHER TRANSMITTING MEDIA.

MERITS(CONT.) BAND WIDTH : FIBRE OPTIC CABLES HAVE MUCH GREATER BANDWIDTH THAN METAL CABLES. LESS WEIGHT :IT IS LESS WEIGHER THAN COPPER WIRE. SECURITY :IMPOSSIBLE TO TAP INTO A FIBRE OPTICS CABLE, MAKING IT MORE SECURE. BECAUSE OF NO ELECTRICITY THROUGH OPTICAL FIBRE IT IS NON FLAMABLE. DATA CAN BE TRANSMITTED DIGITALLY.

DEMERIT FIBRE OPTIC CABLE ARE EXPENSIVE TO INSTALL. THE TERMINATION OF FIBRE OPTIC CABLE IS COMPLEX. THEY ARE MORE FRAGILE THAN COAXIAL CABLE

APPLICATION TELE COMMUNICATION CABLE TV IT INDUSTRY (HIGH SPEED LAN WIRES) INTERNET INDUSTRIAL PLANT

CONCLUSION THE AGE OF OPTICAL COMMUNICATION IS A NEW ERA. IN SEVERAL ASPECTS FIBREOPTICS COMMUNICATION IS BETTER THAN ELECTRIC COMMUNICATION. WITH A BANDWIDTH AND INFORMATION CAPACITY A THOSAND TIMES GREATER THAN COPPER WIRES, FIBRE OPTICS WILL SOON PROVIDE US WITH ALL COMMUNICATION TECHNOLOGY AT A COST EFFICIENT PRICE.

Thank You