Jyoti
Jyoti
Jyoti
SHRI RAM MURTI SMARAK COLLEGE OF ENGINEERING AND TECHNOLOGY, BAREILLY 2011-12
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OPTICAL FIBERS.
AKNOWLEDGMENT
I take immense pleasure in thanking MR. VIRAT BHAMBHE, Department of Electrical and Electronics Engineering, SRMSCET for providing us the right ambience for carrying out this work. I wish to express my deep sense of gratitude to him who helped me in completing the project work, in time. Last but not the least, I thank all others, my beloved parents for their blessings and especially my classmates who in one way or another helped me in the successful completion of this work.
JYOTI GANGWAR
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OPTICAL FIBERS.
Contents
1) Preface 2) Acknowledgement 3) Introduction 4) Principles 5) Light propagation in Fiber optics 6) Some relevant definitions. 7) Classification. 8) Difference among fibers. 9) Attenuation. 10) Construction. 11) Advantages 12) Disadvantages 13) Applications 14) Conclusion 15) References
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OPTICAL FIBERS.
INTRODUCTION
The optical frequency range is extremely large when compared with radiofrequency range. As such a light beam can be used for communication purposes .A light beam can carry a more information to far off places. Optical fiber is a long thin transparent dielectric material made up of glass (or) plastic, which curries electromagnetic waves from one end of the fiber to other end of the fiber by means of multiple total internal reflections . Thus optical fibers works as wave guides in optical communication systems. An optical fiber consists of inner cylinder made of glass (or) plastic. It is called the core. The core carries light and it is surrounded by a second cylindrical shell of glass (or) plastic. It is called
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OPTICAL FIBERS.
the cladding. The reference index of core (n1) is slightly larger than the Refractive index of cladding (n2) the typical refractive index values are
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OPTICAL FIBERS.
FIBRE OPTICS
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OPTICAL FIBERS.
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OPTICAL FIBERS.
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OPTICAL FIBERS.
RELEVENT DEFINATIONS
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OPTICAL FIBERS.
ACCEPTANCE ANGLE
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OPTICAL FIBERS.
Again based on the mode of propagation all these fiber are divide into sin gle mode n multi mode fib er. In all optical fibers, the refractive index of cladding material is uniform.
OPTICAL FIBERS.
The number of paths available for light propagation in a fiber is known as mode
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Single mode step index fiber: In this type of fiber, the core diameter is about 8 to 10m and outer diameter of cladding is 60 to 70m. There is only one path for my propagation so it is called single mode fiber. In this fiber, the transmission of light is by total internal reflection. It is reflective type fiber. Nearly 801 of the fiber m anufacture in the world are single modefiber .Laser are used as light source in these fibers. These fibers are mainly used in submarine cable system.
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OPTICAL FIBERS.
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imposes limitation on the separation between pulses and reduces the transmission rate and capacity (2) Graded index fiber: In this fiber the refractive index decreases continuously from centre radically to the surface of the core. The refractive index is maximum at the centre and minimum of the surface of core. Fig shows cross sectional view and ray propagation of multimode graded index fiber. The diameter of core varies from 50 to 200m and outer diameter of cladding varies from 100 to 250m. In graded index fiber light rays travel at different speeds in different parts of the fiber. Near the surface of core, the refractive index is lower so rays near the outer surface travel faster than the rays travel of the centre. Because of all the rays arrive at the receiving end of the fiber approximately at the same time.
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OPTICAL FIBERS.
Transmission of signal in graded index fiber: Index multimode graded index fiber large number of paths is available for light ray propagation. To discuss about inter model dispersion we consider ray path 1 and ray path 2 Along the axis of fiber the refractive index of core is maximum so the speed of ray along path 1 is less path 2 is sinusoidal and it is longer. Along
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OPTICAL FIBERS.
the path the refractive index region, so the ray 2 move slight faster. Hence the pulses of signals that travel along path 1 and path 2 reaches other end of fiber simultaneously. Thus the problem of inter model dispersion can be reduced to large extent by using graded index fibers.
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OPTICAL FIBERS.
WHAT IS THE DIFFERENCE BETWEEN SINGLE MODE AND MULTI MODE FIBER
Multimode fiber has a relatively large light carrying core, usually 62.5 microns or larger in diameter. It is usually used for short distance transmissions with LED based fiber optic equipment. Single-mode fiber has a small light carrying core of 8 to 10 microns in diameter. It is normally used for long distance transmissions with laser diode based fiber optic transmission equipment.
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structure, material compositions, material dispersion, micro bending losses, and mode coupling radiation
losses, etc., the attenuation is function of wave length and material. Optical communication wave lengths are 0.8, 1.3 and 1.55 m. The attenuation is mainly due to (i) (ii) Absorption and Scattering.
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1Absorption losses:
In glass fibres there different absorptions takes plac e. They are ultraviolet absorption, infrared absorptio n and ionr e s o n a n c e a b s o r p t i o n .
Absorption losses in pure fused silica are shown in fig. Absorption of UV radiation around 0.14 m results in ionization of valence electrons. Absorption of IR photon by atoms with in t h e glass molecules causes heating .This gives absorption n peak at 8 m, also minor peaks at 3.2, and 3.8and 4 . 4 m . t h e O H i o n s o f w a t e r t r a p d u r i n g m a nufacturing causes absorption.
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2)Scattering losses:
The molten glass, when drawn into very thin fiber under proper tension causes submicroscopic variation in the density of glass in the fibre takes place. The do pants added to glass to vary ther e f r a c t i v e i n d e x a l s o l e a d s t o i n h o m o g e n i t i e s i n t h e f i b e r t h e microscopic variation of density and in homogeneities act as reflection gl a n d r e f r a c t i n g f a c e t s , t h e s e scatter a small portion of light p a s s i n g t h r o u g h t h e g l a s s . Thus the scattering losses. If the size of density fluctuating regions is of order of D/10 .On t h e s e b a s e s t h e s c a t t e r i n g losses at a wave length of 1.3m is about 0.3dB/Km whereas at a wave length of 0.7 m .it is about 5dB/Km.
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Fiber is either single mode or multimode. Fiber sizes are expressed by using two numbers: 8/125. The first number refers to the core size in microns. The second number refers to the core size plus the cladding size combined.
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Fiber Connectors
Several layers of buffer coatings protect the core and the cladding. The Layers act as a shock absorber to protect the core and cladding from Damage. A strength member, usually Aramid, is around the buffer layers. To prevent pulling damage during installation the strength member is Added to give critical tensile (pulling) strength to the cable. The outer Jacket protects against environmental factors. The most widely used fiber connector is the SC connector. The SC Connectors square cross section facilitates high packing density in Connector panels. Network administrators need to take into consideration low loss, footprint size, and locking capabilities when selecting a fiber connector.
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OPTICAL FIBERS.
Advantages
* High bandwidth for voice, video and data applications * Optical fiber can carry thousands of times more information than Copper wire. For example, a single-strand fiber strand could carry all the telephone conversations in the United States at peak hour * Fiber is more lightweight than copper. Copper cable equals Approximately 80 lbs./1000 feet while fiber weighs about 9 lbs./1000 feet * Low loss:- The higher frequency, the greater the signal loss using Copper cabling. With fiber, the signal loss is the same across frequencies, except at the very highest frequencies * Reliability:- Fiber is more reliable than copper and has a longer life span * Secure:- Fiber does not emit electromagnetic interference and is difficult to tap
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OPTICAL FIBERS.
DISADVANTAGES
Price - Even though the raw material for making optical fibres, sand, is abundant and cheap, optical fibres are still more expensive per metre than copper. Although, one fibre can carry many more signals than a single copper cable and the large transmission distances mean that fewer expensive repeaters are required. Fragility - Optical fibres are more fragile than electrical wires. Affected by chemicals - The glass can be affected by various chemicals including hydrogen gas (a problem in underwater cables.) Opaqueness - Despite extensive military use it is known that most fibres become opaque when exposed to radiation. Requires special skills - Optical fibres cannot be joined together as a easily as copper cable and requires additional training of personnel and expensive precision splicing and measurement equipment.
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OPTICAL FIBERS.
APPLICATIONS.
Fibres are widely used in illumination applications. They are used as light guides in medical and other applications where bright light needs to be shone on a target without a clear line-ofsight path. In some buildings, optical fibres route sunlight from the roof to other parts of the building. Optical fiber is also used in imaging optics. A coherent bundle of fibers is used, sometimes along with lenses, for a long, thin imaging device called an endoscope, which is used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures.. In spectroscopy, optical fiber bundles transmit light from a spectrometer to a substance that cannot be placed inside the spectrometer itself, in order to analyze its composition. A spectrometer analyzes substances by bouncing light off of and through them. An optical fiber doped with certain rare earth elements such as erbium can be used as the gain medium of a laser or optical amplifier. Rare-earth doped optical fibres can be used to provide signal amplification by splicing a short section of doped fiber into a regular (undoped) optical fiber line.
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CONCLUSION
Although the widespread use of fiber began with the push from the telecommunications industry, today it is commonplace. Many enterprises take advantage of fiber to increase the capacity and functionality of their local area networks (LANs) and now metropolitan area networks (MANs). One issue faced by some enterprises is how to connect legacy equipment and infrastructure without expensive "forklift" upgrades. By using copper to fiber media converters or multimode to single mode media converters, fiber can be connected in almost any legacy environment. Transition Networks comprehensive line of media conversion products are designed to ease the migration to fiber, while minimizing cost and installation issues.
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REFRENCES
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